Fluorosulfonyl phosphoramidate (FSP) backbone modification and uses thereof

Abstract

The invention provides a modified phosphoramidate intemucleotide linkage, referred to herein as a fiuorosulfonyl phosphoramidate (fsP) internucleotide linkage, wherein the fsP intemucleotide linkage has the structure of formula (I) modified oligonucleotides comprising at least one tsP intemucleotide linkage, and methods of using the modified oligonucleotides comprising at least one fsP internucleotide linkage.

Description

[0001] FLUOROSULFONYL PHOSPHORAMIDATE (FSP) BACKBONE MODIFICATION AND USES THEREOF RELATED APPLICATION This application claims the benefit of U.S. Provisional Application No. 63 / 704,495, filed on October 7, 2024. The entire teachings of the above application are incorporated herein by reference. SEQUENCE LISTING The sequence listing submitted via EFS, in compliance with 37 CFR §1.52(e)(5), is incorporated herein by reference. The sequence listing XML file submitted via EFS contains the file “43633002WOSeqList.xml”, created on October 7, 2025, which is 280,910 bytes in size. BACKGROUND Backbone or interlinkage modification is central to oligonucleotide-based medicines. Research in this field over the last four decades has cemented phosphoramidite chemistry to be the method of choice for synthesizing short, gene-silencing oligonucleotides including siRNA strands and ASOs. In the ASO field, sugar modifications have been mostly focused on finding modifications that stabilize the RNA / ASO duplex and improve drug-like properties (e.g., ADME). In comparison, interlinkage modification beyond phosphorothioates (PS) hasn’t found much application in ASO drug development research because most interlinkage modifications don't preserve RNase H activity and suffer from stability issues or inefficient synthesis chemistry. Therefore, there is a need for new internucleotide linkages that can improve the properties of gene-silencing oligonucleotides. SUMMARY OF THE INVENTION The invention provides a modified phosphate group. Preferably, the modified phosphate group is a modified phosphoramidate internucleotide linkage. Preferably, the modified phosphoramidate internucleotide linkage, also referred to herein as a fluorosulfonyl phosphoramidate (fsP) internucleotide linkage, has the structure of formula (I): O OP ON OS OF (I). As used herein the terms “modified phosphate group”, “modified phosphoramidate internucleotide linkage”, and “fluorosulfonyl phosphoramidate (fsP) internucleotide linkage” can be used interchangeably. The invention also provides modified nucleotides comprising a modified phosphate group according to the invention. The modified nucleotide can comprise the structure of wherein B is a nucleobase; R1is a modified phosphate group according to the invention; R2 is H, F, NH2, SCH3, or OR3; and R3 is H, halogen, NH2, a C1-C6 alkyl, a alkoxy, provided that when R3 is a C1- C6alkyl it can optionally be bound to the 4’ carbon. The invention further provides a modified oligonucleotide wherein the modified oligonucleotide comprises at least one fsP internucleotide linkage as described here. Preferably, the modified oligonucleotide comprises at least one modified nucleotide as described herein. Preferably, the modified oligonucleotide comprises the structure of Formula (III): O OBO F S NO RP O O O OBO R(III). The modified oligonucleotide of the invention can be selected from an antisense oligonucleotide, a sense or antisense strand of a siRNA, a splice-modulating oligonucleotide, a guideRNA for a CRISPR-based system, or a guideRNA for an adenosine deaminase acting on RNA (ADAR) based system. The modified oligonucleotide of the invention can be an antisense oligonucleotide. In embodiments, the antisense oligonucleotide is a “gapmer” as described herein. The modified oligonucleotide of the invention can be a siRNA. The modified oligonucleotide of the invention can be a splice-modulating oligonucleotide. The modified oligonucleotide of the invention can be a guideRNA for a CRISPR-based system. The modified oligonucleotide of the invention can be a guideRNA for an ADAR-based system. The invention also provides a pharmaceutical composition comprising a modified oligonucleotide comprising at least one fsP internucleotide linkage as described here and a pharmaceutically acceptable carrier. Preferably, the modified oligonucleotide comprises at least one modified nucleotide as described herein. The invention also provides a method for inhibiting gene expression comprising administering a modified oligonucleotide comprising at least one fsP internucleotide linkage as described herein or a composition as described herein, wherein the modified oligonucleotide is complementary to a nucleotide sequence of a target RNA. Preferably, the modified oligonucleotide comprises at least one modified nucleotide as described herein. The invention also provides a method for inhibiting allele-specific gene expression comprising administering a modified oligonucleotide comprising at least one fsP internucleotide linkage as described herein or a composition as described herein, wherein the modified oligonucleotide is complementary to a nucleotide sequence of a target allele RNA. Preferably, the modified oligonucleotide comprises at least one modified nucleotide as described herein. The invention also provides a method for modulating splicing comprising administering a modified oligonucleotide comprising at least one fsP internucleotide linkage as described herein or a composition as described herein, wherein the modified oligonucleotide is complementary to a nucleotide sequence of a target RNA. Preferably, the modified oligonucleotide comprises at least one modified nucleotide as described herein. Any of the methods as described herein, can be useful for treating a subject having disease or disorder wherein inhibiting expression of a gene would be beneficial. BRIEF DESCRIPTION OF THE FIGURES The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Fig. 1: Stability of a four position fsP-modified 16-mer oligonuclotide (CR-AA- 04966) to acetic acid treatment for 2 h in room temperature and basic ammonium hydroxide treatment for 2 h 80°C. While the fsP linkage is stable to acid treatment, heating with bases can degrade the linkage. The shoulder in front of the main peak is a failure sequence already present in the starting compound. Fig. 2: Stability of a four position fsP-modified 16-mer oligonuclotide (CR-AA- 04966) to b-mercaptoethanol treatment for 24 h in room temperature. Fig. 3: Reactivity of fsP modified oligonucleotides towards SuFEx click chemistry in DMSO, acetonitrile and in aqueous solution. Fig. 4: Representative HPLC chromatogram showing fsP oligos are retained for longer time in a C18 column (RT - 14.02 min) in comparison to unmodified PS oligos (RT - 13.67 min). In comparison, msP modified oligos eluted much earlier (RT - 12.73 min) proving that fsP oligos are more lipophilic than msP oligos. (oligos CR-AA-05287, CR-AA- 05222, and CR-AA-00828) Fig. 5: Fetal Bovine serum (FBS) -stability comparison of fsP-modified oligos and unmodified PS oligos. (oligos CR-AA-00828 and CR-AA-05223) Fig. 6: Mouse liver homogenate -stability comparison to fsP modified oligos and unmodified PS oligos. The bands of interest have been highlighted with the box. (oligos CR- AA-00828 and CR-AA-05223) Fig. 7A through Fig. 7D: Example of fsP modified oligos compatibility with RNase H enzyme-mediated RNA cleavage mechanism. PS, fsP, and msP modified oligos weredesigned against HIF1 RNA and, as shown, fsP oligos exhibited a comparable or slightlybetter cleavage rate than PS but higher than msP oligos. (oligos CR-AA-00828, CR-AA- 05222, and CR-AA-05287) Fig. 8: Antisense activity of PS, fsP, and msP ASOs against HIF1 gene in A431 cellsafter delivery by electroporation. As shown, both fsP and msP oligos exhibited variable activity, both better and worse than the PS ASO. (oligos CR-AA-00828, CR-AA-04826, CR- AA-04827, CR-AA-04965, CR-AA-04966, CR-AA-05220, CR-AA-05221, CR-AA-05224, CR-AA-05225, CR-AA-05226, CR-AA-05270, CR-AA-05287, CR-AA-05289, and CR-AA- 05291) Fig. 9: Antisense activity of PS, fsP and msP ASOs against HIF1 gene in A431 cellsafter passive carrier free uptake. As shown, most fsP ASOs exhibited better or similar activity in comparison to PS ASOs whereas msP-modified oligos were less effective, because of the better uptake of fsP ASOs owing to their higher lipophilicity. (oligos CR-AA-00828, CR-AA- 04826, CR-AA-04827, CR-AA-04965, CR-AA-04966, CR-AA-05220, CR-AA-05221, CR- AA-05224, CR-AA-05225, CR-AA-05226, CR-AA-05270, CR-AA-05287, CR-AA-05289, and CR-AA-05291) Fig. 10A and Fig. 10B: Cytotolerability of multiple fsP and msP-modified ASOscomplementary to HIF1 mRNA. Most modifications did not appreciably alter the toxicityprofile of the ASOs. (oligos CR-AA-00828, CR-AA-05220, CR-AA-05222, CR-AA-05224, CR-AA-05226, CR-AA-05270, CR-AA-05287, CR-AA-05289, CR-AA-05291, CR-AA- 04826, CR-AA-00002, CR-AA-00010, and CR-AA-00032) Fig. 11: Effect of modifying a representative toxic sequence with fsP and msP linkages in three individual positions. While all three fsP modifications reduced liver toxicity marker (ALT) readings, analogous msP modifications reduced toxicity in one out of three sequences. (oligos CR-AA-04133, CR-AA-04134, CR-AA-04135, CR-AA-04850, CR-AA- 04851, CR-AA-04852, and CR-AA-00017) Fig. 12A through Fig. 12C: Improved allele-selective inhibition of mutant TNPO2 allele with fsP-modified gapmer ASOs. (oligos CR-AA-05258, CR-AA-05089, and CR-AA- 05090) DETAILED DESCRIPTION It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive. Herein, the use of the singular includes the plural unless specifically stated otherwise. As used herein, the use of “or” means “and / or” unless stated otherwise. Furthermore, the use of the term “including” as well as other forms, such as “includes” and “included”, is not limiting. Also, terms such as “element” or “component” encompass both elements and components comprising one unit and elements and components that comprise more than one subunit, unless specifically stated otherwise. The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described. All documents, or portions of documents, cited in this application, including, but not limited to, patents, patent applications, articles, books, and treatises, are hereby expressly incorporated-by-reference for the portions of the document discussed herein, as well as in their entirety. It is understood that the sequence set forth in each SEQ ID NO contained herein is independent of any modification to a sugar moiety, an internucleotide linkage, or a nucleobase. As such, compounds defined by a SEQ ID NO may comprise, independently, one or more modifications to a sugar moiety, an internucleotide linkage, or a nucleobase. Although the sequence listing accompanying this filing identifies each sequence as either “RNA” or “DNA” as required, in reality, those sequences may be modified with any combination of chemical modifications. One of skill in the art will readily appreciate that such designation as “RNA” or “DNA” to describe modified oligonucleotides is, in certain instances, arbitrary. For example, an oligonucleotide comprising a nucleoside comprising a 2’-OH(H) sugar moiety and a thymine base could be described as a DNA having a modified sugar (2 ’-OH in place of one 2’-H of DNA) or as an RNA having a modified base (thymine (methylated uracil) in place of an uracil of RNA). Accordingly, nucleic acid sequences provided herein, including, but not limited to those in the sequence listing, are intended to encompass nucleic acids containing any combination of natural or modified RNA and / or DNA, including, but not limited to such nucleic acids having modified nucleobases. By way of further example and without limitation, a modified oligonucleotide having the nucleobase sequence “ATCGATCG” encompasses any modified oligonucleotides having such nucleobase sequence, whether modified or unmodified, including, but not limited to, such compounds comprising RNA bases, such as those having sequence “AUCGAUCG” and those having some DNA bases and some RNA bases such as “AUCGATCG” and modified oligonucleotides having other modified nucleobases, such as “ATmCGAUCG,” whereinmC indicates a cytosine base comprising a methyl group at the 5-position. Definitions Unless specific definitions are provided, the nomenclature used in connection with, and the procedures and techniques of, analytical chemistry, synthetic organic chemistry, and medicinal and pharmaceutical chemistry described herein are those well-known and commonly used in the art. Where permitted, all patents, applications, published applications and other publications and other data referred to throughout in the disclosure are incorporated by reference herein in their entirety. Unless otherwise indicated, the following terms have the following meanings: As used herein, “2’-deoxynucleoside” means a nucleoside comprising a 2’-H(H) deoxyribosyl sugar moiety. In certain embodiments, a 2’-deoxynucleoside is a 2’-P-D- deoxynucleoside and comprises a 2’-P-D-deoxyribosyl sugar moiety, which has the P-D configuration as found in naturally occurring deoxyribonucleic acids (DNA). In certain embodiments, a 2’-deoxynucleoside or a nucleoside comprising an unmodified 2’- deoxyribosyl sugar moiety may comprise a modified nucleobase or may comprise an RNA nucleobase (uracil). As used herein, “2’-substituted nucleoside” means a nucleoside comprising a 2’- substituted sugar moiety. As used herein, “2’-substituted” in reference to a sugar moiety means a sugar moiety comprising at least one 2'-substituent group other than H or OH. As used herein, “3’ target site” refers to the 3’-most nucleotide of a target nucleic acid which is complementary to an antisense oligonucleotide, when the antisense oligonucleotide is hybridized to the target nucleic acid. As used herein, target site” refers to the 5’-most nucleotide of a target nucleic acid which is complementary to an antisense oligonucleotide, when the antisense oligonucleotide is hybridized to the target nucleic acid. As used herein, “5 -methyl cytosine” means a cytosine modified with a methyl group attached to the 5 position. A 5-methyl cytosine is a modified nucleobase. As used herein, “abasic sugar moiety” means a sugar moiety of a nucleoside that is not attached to a nucleobase. Such abasic sugar moieties are sometimes referred to in the art as “abasic nucleosides.” As used herein, “administration” or “administering” means providing a pharmaceutical agent or composition to an animal. As used herein, “animal” and “subject” are used interchangeably and the terms mean a human or non-human animal. As used herein, “antisense activity” means any detectable and / or measurable change attributable to the hybridization of an antisense compound to its target nucleic acid. In certain embodiments, antisense activity is a decrease in the amount or expression of a target nucleic acid or protein encoded by such target nucleic acid compared to target nucleic acid levels or target protein levels in the absence of the antisense compound. As used herein, “antisense agent” means an antisense compound, such as an antisense oligonucleotide, and optionally one or more additional features, such as a sense compound. As used herein, “antisense compound” means an antisense oligonucleotide and optionally one or more additional features, such as a conjugate group. As used herein, “sense compound” means a sense oligonucleotide and optionally one or more additional features, such as a conjugate group. As used herein, “antisense oligonucleotide” or “antisense strand” means an oligonucleotide, including the oligonucleotide portion of an antisense compound, that is capable of hybridizing to a target nucleic acid and is capable of at least one antisense activity. Antisense oligonucleotides include but are not limited to antisense RNAi oligonucleotides and antisense RNase H oligonucleotides. As used herein, “sense oligonucleotide” or “sense strand” means an oligonucleotide, including the oligonucleotide portion of a sense compound, that is capable of hybridizing to an antisense oligonucleotide. As used herein, “ameliorate” in reference to a treatment means improvement in at least one symptom relative to the same symptom in the absence of the treatment. In certain embodiments, amelioration is the reduction in the severity or frequency of a symptom or the delayed onset or slowing of progression in the severity or frequency of a symptom. In certain embodiments, the symptom or hallmark is, for example, a reduction in seizures. As used herein, “bicyclic nucleoside” or “BNA” means a nucleoside comprising a bicyclic sugar moiety. As used herein, “bicyclic sugar” or “bicyclic sugar moiety” means a modified sugar moiety comprising two rings, wherein the second ring is formed via a bridge connecting two of the atoms in the first ring thereby forming a bicyclic structure. In certain embodiments, the first ring of the bicyclic sugar moiety is a furanosyl moiety. In certain embodiments, the bicyclic sugar moiety does not comprise a furanosyl moiety. As used herein, “constrained ethyl” or “cEt” or “cEt modified sugar moiety” means a P-D ribosyl bicyclic sugar moiety wherein the second ring of the bicyclic sugar is formed via a bridge connecting the 4 ’-carbon and the 2 ’-carbon of the -D ribosyl sugar moiety, wherein the bridge has the formula 4'- CH(CH3)-O-2', and wherein the methyl group of the bridge is in the S configuration. As used herein, “cEt nucleoside” means a nucleoside comprising a cEt modified sugar As used herein, “blunt” or “blunt ended” in reference to a duplex formed by two oligonucleotides mean that there are no terminal unpaired nucleotides (i.e., no overhanging nucleotides). One or both ends of a double-stranded RNAi agent can be blunt. As used herein, “cell-targeting moiety” means a conjugate group or portion of a conjugate group that is capable of binding to a particular cell type or particular cell types. As used herein, “cleavable moiety” means a bond or group of atoms that is cleaved under physiological conditions, for example, inside a cell, an animal, or a human. As used herein, “complementary” in reference to an oligonucleotide means that at least 70% of the nucleobases of the oligonucleotide or one or more regions thereof and the nucleobases of another nucleic acid or one or more regions thereof are capable of hydrogen bonding with one another when the nucleobase sequence of the oligonucleotide and the other nucleic acid are aligned in opposing directions. Complementary nucleobases means nucleobases that are capable of forming hydrogen bonds with one another. Complementary nucleobase pairs include adenine (A) and thymine (T), adenine (A) and uracil (U), cytosine (C) and guanine (G), 5-methyl cytosine (mC) and guanine (G). Certain modified nucleobases that pair with natural nucleobases or with other modified nucleobases are known in the art. For example, inosine can pair with adenosine, cytosine, or uracil. Complementary oligonucleotides and / or nucleic acids need not have nucleobase complementarity at each nucleoside. Rather, some mismatches are tolerated. As used herein, “fully complementary” or “100% complementary” in reference to oligonucleotides means that oligonucleotides are complementary to another oligonucleotide or nucleic acid at each nucleoside of the oligonucleotide. As used herein, “conjugate group” means a group of atoms that are directly attached external regions may be referred to as the “wings” or “wing segments.” In certain embodiments, the internal region is a deoxy region. The positions of the internal region or gap refer to the order of the nucleosides of the internal region and are counted starting from the 5’-end of the internal region. Unless otherwise indicated, “gapmer” refers to a sugar motif. In certain embodiments, each nucleoside of the gap is a 2’-p-D-deoxynucleoside. In certain embodiments, the gap comprises one 2’-substituted nucleoside at position 1, 2, 3, 4, or 5 of the gap, and the remainder of the nucleosides of the gap are 2’-p-D-deoxynucleosides. As used herein, the term “MOE gapmer” indicates a gapmer having a gap comprising 2’-P-D- deoxynucleosides and wings comprising 2’-M0E modified nucleosides. As used herein, the term “mixed wing gapmer” indicates a gapmer having wings comprising modified nucleosides comprising at least two different sugar modifications. Unless otherwise indicated, a gapmer may comprise one or more modified internucleotide linkages and / or modified nucleobases and such modifications do not necessarily follow the gapmer pattern of the sugar modifications. As used herein, “hepatotoxic” in the context of a human means a plasma ALT level that is above 150 units per liter. Hepatotoxicity of an oligonucleotide that is administered to a human is determined by measuring the plasma ALT level of the human 24 hours to 2 weeks following at least one dose of 10-300 mg of the compound. As used herein, “hotspot region” is a range of nucleobases on a target nucleic acid that is amenable to oligomeric compound-mediated reduction of the amount or activity of the target nucleic acid. As used herein, “hybridization” means the annealing of oligonucleotides and / or nucleic acids. While not limited to a particular mechanism, the most common mechanism of hybridization involves hydrogen bonding, which may be Watson-Crick, Hoogsteen or reversed Hoogsteen hydrogen bonding, between complementary nucleobases. In certain embodiments, complementary nucleic acid molecules include, but are not limited to, an antisense compound and a nucleic acid target. In certain embodiments, complementary nucleic acid molecules include, but are not limited to, an oligonucleotide and a nucleic acid target. As used herein, “internucleotide linkage” is the covalent linkage between adjacent nucleosides in an oligonucleotide. As used herein “modified internucleotide linkage” means any internucleotide linkage other than a phosphodiester internucleotide linkage. “Phosphorothioate internucleotide linkage” is a modified internucleotide linkage in which one of the non-bridging oxygen atoms of a phosphodiester internucleotide linkage is replaced with a sulfur atom. As used herein, “inverted nucleoside” means a nucleotide having a 3’ to 3’ and / or 5’ to 5’ internucleotide linkage, as shown herein. As used herein, “inverted sugar moiety” means the sugar moiety of an inverted nucleoside or an abasic sugar moiety having a 3’ to 3’ and / or 5’ to 5’ internucleotide linkage. As used herein, “linker-nucleoside” means a nucleoside that links, either directly or indirectly, an oligonucleotide to a conjugate moiety. Linker-nucleosides are located within the conjugate linker of an oligomeric compound. Linker-nucleosides are not considered part of the oligonucleotide portion of an oligomeric compound even if they are contiguous with the oligonucleotide. “Lipid nanoparticle” or “LNP” is a vesicle comprising a lipid layer encapsulating a pharmaceutically active molecule, such as a nucleic acid molecule, e.g., an RNAi or a plasmid from which an RNAi is transcribed. LNPs are described in, for example, U.S. Patent Nos. 6,858,225, 6,815,432, 8,158,601, and 8,058,069, the entire contents of which are hereby incorporated herein by reference. As used herein, “non-bicyclic modified sugar moiety” means a modified sugar moiety that comprises a modification, such as a substituent, that does not form a bridge between two atoms of the sugar to form a second ring. As used herein, “mismatch” or “non-complementary” means a nucleobase of a first nucleic acid sequence that is not complementary with the corresponding nucleobase of a second nucleic acid sequence or target nucleic acid when the first and second nucleic acid sequences are aligned. As used herein, “MOE” means O-methoxyethyl. “2’-MOE” or “2’-MOE modified sugar” or “2’- MOE modified sugar moiety” means a 2’-OCH2CH2OCH3group (or a 2’- O(CH2)2-OCH3 group) in place of the 2’-OH group of a ribosyl sugar moiety. Unless otherwise indicated, a 2’-MOE modified sugar moiety is in the -D-ribosyl configuration. As used herein, “2’-MOE modified nucleoside” means a nucleoside comprising a 2’-MOE modified sugar moiety (or a 2’-O(CH2)2-OCH3 ribosyl modified sugar moiety). As used herein, “2’-OMe” means a 2’-OCH3 group in place of the 2’-OH group of a ribosyl sugar moiety. A “2’-O-methyl sugar moiety” or “2’-OMe sugar moiety” or “2’-OMe modified sugar moiety” or “2’-O-methylribosyl sugar” means a sugar moiety with a 2’-OCH3 group in place of the 2’- OH group of a ribosyl sugar moiety. Unless otherwise indicated, a 2’-OMe sugar moiety is in the P-D- ribosyl configuration. As used herein, “2’-OMe nucleoside” means a nucleoside comprising a 2’-OMe modified sugar moiety. As used herein, “2’-F” means a 2’-fluoro group in place of the 2’-OH group of a ribosyl sugar moiety. A “2’-F sugar moiety” or “2’-F modified sugar moiety” or “2’- fluororibosyl sugar” means a sugar moiety with a 2’-F group in place of the 2’-OH group of a ribosyl sugar moiety. Unless otherwise indicated, a 2’-F sugar moiety is in the -D-ribosyl configuration. As used herein, “2’-F nucleoside” or “2’-F modified nucleoside” means a nucleoside comprising a 2’-F modified sugar moiety. As used herein, “motif’ means the pattern of unmodified and / or modified sugar moieties, nucleobases, and / or internucleotide linkages, in an oligonucleotide. As used herein, "nucleobase" means an unmodified nucleobase or a modified nucleobase. A nucleobase is a heterocyclic moiety. As used herein an “unmodified nucleobase” is adenine (A), thymine (T), cytosine (C), uracil (U), or guanine (G). As used herein, a “modified nucleobase” is a group of atoms other than unmodified A, T, C, U, or G capable of pairing with at least one other nucleobase. A “5- methyl cytosine” is a modified nucleobase. A universal base is a modified nucleobase that can pair with any one of the five unmodified nucleobases. As used herein, “nucleobase sequence” means the order of contiguous nucleobases in a nucleic acid or oligonucleotide independent of any sugar or internucleotide linkage modification. As used herein, “nucleoside” means a compound or fragment of a compound comprising a nucleobase and a sugar moiety. The nucleobase and sugar moiety are each, independently, unmodified or modified. As used herein, “nucleoside overhang” refers to unpaired nucleotides at either or both ends of a duplex formed by hybridization of an antisense RNAi oligonucleotide and a sense RNAi oligonucleotide. As used herein, “modified nucleoside” means a nucleoside comprising a modified nucleobase and / or a modified sugar moiety. As used herein, “linked nucleosides” are nucleosides that are connected in a contiguous sequence (i.e., no additional nucleosides are presented between those that are linked). As used herein, “modified oligonucleotide” means an oligonucleotide, comprising at least one fdP internucleotide linkage as described herein. The modified oligonucleotide can further comprise at least one modified nucleoside or internucleotide linkage. As used herein, "oligomeric compound" means a modified oligonucleotide of the invention and optionally one or more additional features, such as a conjugate group or terminal group. An oligomeric compound may be paired with a second oligomeric compound that is complementary to the first oligomeric compound or may be unpaired. A “singled- stranded oligomeric compound” is an unpaired oligomeric compound. The term “oligomeric duplex” means a duplex formed by two oligomeric compounds having complementary nucleobase sequences. Each oligomeric compound of an oligomeric duplex may be referred to as a “duplexed oligomeric compound.” As used herein, "oligonucleotide" means a polymer of linked nucleosides connected via internucleotide linkages, wherein each nucleoside and internucleotide linkage may be modified or unmodified. Unless otherwise indicated, oligonucleotides consist of 8-50 linked nucleosides. An oligonucleotide may be paired with a second oligonucleotide that is complementary to the oligonucleotide or it may be unpaired. A “single-stranded oligonucleotide” is an unpaired oligonucleotide. A “double-stranded oligonucleotide” is an oligonucleotide that is paired with a second oligonucleotide. An “oligonucleotide duplex” means a duplex formed by two paired oligonucleotides having complementary nucleobase sequences. Each oligo of an oligonucleotide duplex is a “duplexed oligonucleotide” or a “double-stranded oligonucleotide.” As used herein, “pharmaceutically acceptable carrier or diluent” means any substance suitable for use in administering to an animal. Certain such carriers enable pharmaceutical compositions to be formulated as, for example, tablets, pills, capsules, liquids, gels, syrups, slurries, suspension and lozenges for the oral ingestion by a subject. In certain embodiments, a pharmaceutically acceptable carrier or diluent is sterile water, sterile saline, sterile buffer solution or sterile artificial cerebrospinal fluid. As used herein “pharmaceutically acceptable salts” means physiologically and pharmaceutically acceptable salts of compounds. Pharmaceutically acceptable salts retain the desired biological activity of the parent compound and do not impart undesired toxicological effects thereto. As used herein “pharmaceutical composition” means a mixture of substances suitable for administering to a subject. For example, a pharmaceutical composition may comprise a modified oligonucleotide and a sterile aqueous solution. In certain embodiments, a pharmaceutical composition shows activity in free uptake assay in certain cell lines. As used herein, "reducing or inhibiting the amount or activity" refers to a reduction or blockade of the transcriptional expression or activity relative to the transcriptional expression or activity in an untreated or control sample and does not necessarily indicate a total elimination of transcriptional expression or activity. As used herein, “RNAi agent” means an antisense compound that acts, at least in part, sugar” means a modified furanosyl sugar moiety or a sugar surrogate. As used herein, "sugar surrogate" means a modified sugar moiety having other than a furanosyl moiety that can link a nucleobase to another group, such as an internucleotide linkage, conjugate group, or terminal group in an oligonucleotide. Modified nucleosides comprising sugar surrogates can be incorporated into one or more positions within an oligonucleotide and such oligonucleotides are capable of hybridizing to complementary oligonucleotides or target nucleic acids. As used herein, “symptom or hallmark” means any physical feature or test result that indicates the existence or extent of a disease or disorder. In certain embodiments, a symptom is apparent to a subject or to a medical professional examining or testing said subject. In certain embodiments, a hallmark is apparent upon invasive diagnostic testing, including, but not limited to, post-mortem tests. As used herein, “target nucleic acid” and “target RNA” mean a nucleic acid that an antisense compound is designed to affect. Target RNA means an RNA transcript and includes pre-mRNA and mRNA unless otherwise specified. As used herein, “target region” means a portion of a target nucleic acid to which a modified oligonucleotide is designed to hybridize. As used herein, "terminal group" means a chemical group or group of atoms that is covalently linked to a terminus of an oligonucleotide. As used herein, “treating” means improving a subject’s disease or condition by administering a modified oligonucleotide or oligomeric compound described herein. In certain embodiments, treating a subject improves a symptom relative to the same symptom in the absence of the treatment. In certain embodiments, treatment reduces in the severity or frequency of a symptom, or delays the onset of a symptom, slows the progression of a symptom, or slows the severity or frequency of a symptom. As used herein, “therapeutically effective amount” means an amount of a pharmaceutical agent or composition that provides a therapeutic benefit to an animal. For example, a therapeutically effective amount improves a symptom of a disease. The invention provides a modified phosphate group. Preferably, the modified phosphate group is a modified phosphoramidate internucleotide linkage. Preferably, the modified phosphoramidate internucleotide linkage, also referred to herein as a fluorosulfonyl phosphoramidate (fsP) internucleotide linkage, has the structure of formula (I): O OP ON OS OF (I). As used herein the terms “modified phosphate group”, “modified phosphoramidate internucleotide linkage”, and “fluorosulfonyl phosphoramidate (fsP) internucleotide linkage” can be used interchangeably. In embodiments, the invention provides a modified oligonucleotide comprising at least one fsP internucleotide linkages having the structure of formula (I). The invention also provides modified nucleotides comprising modified phosphate group according to the invention. The modified nucleotide can comprise the structure of formula (II): R1O BOH R2(II), wherein B is a nucleobase; R1 is a modified phosphate group according to the invention; R2is H, F, NH2, SCH3, or OR3; and R3is H, halogen, NH2, a C1-C6alkyl, a C1-C6alkoxy, provided that when R3 is a C1- C6 alkyl it can optionally be bound to the 4’ carbon. In embodiments, the invention provides a modified oligonucleotide comprising at least one modified nucleotide having the structure of formula (II). The invention further provides a modified oligonucleotide wherein the modified oligonucleotide comprises at least fsP internucleotide linkage as described here. Preferably, the modified oligonucleotide comprises at least one modified nucleotide as described herein. Preferably, the modified oligonucleotide has the structure of formula (III): O OBOF S NO RP O O O OBO R(III). In embodiments, the modified oligonucleotide is a gene silencing oligonucleotide (i.e., an oligonucleotide that can modulate the expression of a target gene) and includes, but is not limited to, an antisense oligonucleotide, a siRNA, a microRNA (miRNA), a piRNA, a hnRNA, a ncRNA, a snRNA, a sgRNA, an esiRNA, an shRNA, or a lncRNA. Antisense Oligonucleotides In embodiments, the modified oligonucleotide is an antisense oligonucleotide. In embodiments, the invention provides a modified antisense oligonucleotide comprising 12-30 linked nucleosides, wherein the modified oligonucleotide comprises at least one fsP internucleotide linkage. In embodiments, the modified antisense oligonucleotide comprises 14-26 linked nucleosides. Preferably, the nucleobase sequence of the modified antisense oligonucleotide comprises at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, at least 20, or at least 21 nucleobases complementary to an equal length portion of a target RNA. In embodiments, the nucleobase sequence of the modified antisense oligonucleotide is complementary to at least 8, at least 9, at least 10, at least 11, at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, at least 20, or at least 21 contiguous nucleobases of an equal length portion of nucleobases of a target RNA. Preferably, the nucleobase sequence of the modified oligonucleotide is at least 80% complementary to an equal length portion of a target RNA. In embodiments, the nucleobase sequence of the modified oligonucleotide is at least 80%, 85%, 90%, 95%, or 100% complementary to a hotspot of the nucleobase sequences of the target RNA when measured across the entire nucleobase sequence of the modified each nucleoside of the gap of a gapmer comprises a 2’-P-D-deoxyribosyl sugar moiety. In certain embodiments, at least one nucleoside of the gap of a gapmer comprises a modified sugar moiety. In certain embodiments, the gapmer is a deoxy gapmer. In certain embodiments, the nucleosides on the gap side of each wing / gap junction comprise 2’- deoxyribosyl sugar moieties and the nucleosides on the wing sides of each wing / gap junction comprise modified sugar moieties. In certain embodiments, each nucleoside of the gap comprises a 2’-P-D- deoxyribosyl sugar moiety. In certain embodiments, each nucleoside of each wing of a gapmer comprises a modified sugar moiety. In certain embodiments, at least one nucleoside of the gap of a gapmer comprises a modified sugar moiety. In certain embodiments, at least one nucleoside of the gap of a gapmer comprises a 2’-OMe sugar moiety. Herein, the lengths (number of nucleosides) of the three regions of a gapmer may be provided using the notation [# of nucleosides in the 5’-wing] - [# of nucleosides in the gap] - [# of nucleosides in the 3’-wing], Thus, a 3-10-3 gapmer consists of 3 linked nucleosides in each wing and 10 linked nucleosides in the gap. Where such nomenclature is followed by a specific modification, that modification is the modification in each sugar moiety of each wing and the gap nucleosides comprise 2’- P-D-deoxyribosyl sugar moieties. Thus, a 5-10-5 MOE gapmer consists of 5 linked 2’-MOE modified nucleosides in the 5’-wing, 10 linked 2’- P-D- deoxynucleosides in the gap, and 5 linked 2’-MOE modified nucleosides in the 3’-wing. In embodiments, the modified antisense oligonucleotide comprises -region, a --region consists of 1-6 linked nucleosides, each- -region consists of 1-6 linked-region nucleoside comprising a modified sugar moiety; and the central region is between the 5’-region and 3’- region, wherein the central region comprises 6-14 linked nucleosides, wherein each central region nucleoside is independently selected from a deoxynucleoside and a -substituted nucleoside, wherein not more than 2 central region -- -region, and / or thecentral region comprises at least one fluorosulfonyl (fsP) phosphoramidate internucleotide linkage. In embodiments, the 5’ region comprises at least one fsP phosphoramidate internucleotide linkage. In embodiments, the 5’ region comprises one fsP phosphoramidate internucleotide linkage. In embodiments, the 3’ region comprises at least one fsP phosphoramidate internucleotide linkage. In embodiments, the 3’ region comprises one fsP phosphoramidate internucleotide linkage. In embodiments, the central region comprises at least one fsP phosphoramidate are independently selected from a stereo- -substituted nucleoside; provided that no more than one of Nd, Nd1, Nd2, Nd3, and Nd4, -substituted nucleoside; wherein L, at each occurrence, L1, L2, L3, and L4 are independently an internucleotide linkage selected from phosphodiester internucleotide linkage, phosphorothioate internucleotide linkage, and fsP phosphoramidate internucleotide linkage, provided that at least one of L, L1, L2, L3, and L4 is a fsP phosphoramidate internucleotide linkage; and wherein q is from 2-10. In embodiments, q is 3-8. In embodiments, q is 4-7. In embodiments, q is 6. In embodiments, two, three, four, five, or six of L, L1, L2, L3, and L4are fsP phosphoramidate internucleotide linkages. In embodiments, two, three, or four of L, L1, L2, L3, and L4 are fsP phosphoramidate internucleotide linkages. In embodiments, four of L, L1, L2, L3, and L4are fsP phosphoramidate internucleotide linkages. The remaining internucleotide linkages are phosphorothioate internucleotide linkages or phosphodiester internucleotide linkages, preferably the remaining internucleotide linkages are phosphorothioate internucleotide linkages. In embodiments, the central region comprises the formula (V) (Nd1)L1(Nd2)L2(Nd3)L3(Nd4)L4(Nd5)L5(Nd6)L6(Nd7)L7(Nd8)L8(Nd9)L9(Nd10)L10, wherein Nd1, Nd2, Nd3, Nd4, Nd5, Nd6, Nd7, Nd8, Nd9, Nd10are independently selected from a stereo-standard DNA -substituted nucleoside; provided that no more than one of Nd1, Nd2, Nd3, Nd4, Nd5, Nd6, Nd7, Nd8, Nd9, or Nd10 -substituted nucleoside; wherein L1, L2, L3, L4, L5, L6, L7, L8, L9, and L10are independently an internucleotide linkage selected from phosphodiester internucleotide linkage, phosphorothioate internucleotide linkage, and fluorosulfonyl (fsP) phosphoramidate internucleotide linkage, provided that at least one of L1, L2, L3, L4, L5, L6, L7, L8, L9, and L10is a fsP phosphoramidate internucleotide linkage. In embodiments, two, three, four, five, or six of L1, L2, L3, L4, L5, L6, L7, L8, L9, and L10 are fsP phosphoramidate internucleotide linkages. In embodiments, two, three, or four of L1, L2, L3, L4, L5, L6, L7, L8, L9, and L10are fsP phosphoramidate internucleotide linkages. In embodiments, four of L1, L2, L3, L4, L5, L6, L7, L8, L9, and L10are fsP phosphoramidate internucleotide linkages. The remaining internucleotide linkages are phosphorothioate internucleotide linkages or phosphodiester internucleotide linkages, preferably the remaining internucleotide linkages are phosphorothioate internucleotide linkages. In embodiments, L4, L5, and L6, are a phosphorothioate internucleotide linkage or a phosphodiester internucleotide linkage, preferably a phosphorothioate internucleotide linkage. In embodiments, one, two, three, or four of L1, L2, L3, L7, L8, L9, and L10 are linkages, to enhance stability and reduce off-target effects. However, modifications in the seed region, particularly at positions 2-7, require careful selection to avoid disrupting target RNA (crRNA), a 17-30 nucleotide sequence complementary to the target DNA, and a tracr RNA, which serves as a binding scaffold for the Cas nuclease. Any suitable engineered sgRNA, or crRNA and tracrRNA, can be employed as long as it is effective for recognizing a target DNA or RNA. The design of such sgRNA, or crRNA and tracrRNA is within the skill of ordinary artisans. ADAR In embodiments, the modified oligonucleotide is a guideRNA for an ADAR-based system, wherein the modified guideRNA comprises at least one fsP internucleotide linkage. Adenosine deaminases acting on RNA (ADARs) are RNA-editing enzymes that catalyze the conversion of adenosine (A) to inosine (I), which is functionally equivalent to guanosine (G) during translation. ADARs can be harnessed for therapeutic RNA editing by utilizing guideRNAs (gRNAs) to direct them to specific target sites. Chemical modifications in ADAR guideRNAs (gRNAs) can be employed to enhance their properties. Anti-MicroRNA and MicroRNA Mimic In embodiments, the modified oligonucleotide is an anti-microRNA, wherein the anti- microRNA comprises at least one fsP internucleotide linkage. Anti-microRNAs are small non-coding RNA molecules that regulate gene expression by binding to target mRNAs, leading to their degradation or translational repression. Dysregulated miRNA expression has been implicated in various diseases, making miRNA modulation a promising therapeutic strategy. Anti-miRNA oligonucleotides (AMOs) are designed to specifically bind and inhibit miRNAs, thus restoring normal gene expression. In embodiments, the modified oligonucleotide is an microRNA mimic, wherein the microRNA mimic comprises at least one fsP internucleotide linkage. Synthetic microRNA (miRNA) mimics aim to supplement or replace downregulated miRNAs, thereby re- establishing their regulatory functions. Further Modifications Unless otherwise specifically noted, the following embodiments can apply to any modified oligonucleotide (e.g., antisense oligonucleotide, siRNA, splice-modulating oligonucleotide, anti-microRNA, microRNA mimic, guideRNA for a CRISPR-based system, or guideRNA for an adenosine deaminase acting on RNA (ADAR)-based system) as described herein. In addition to the at least one fsP internucleotide linkage, the modified oligonucleotides herein comprise at least one further modification selected from a modified sugar, a modified internucleotide linkage, a modified nucleobase, or combinations thereof. In embodiments, the modified oligonucleotides may also comprise one or more modified nucleosides. Modified nucleosides include stereo-non-standard nucleosides and nucleosides comprising a modified sugar moiety, or a modified nucleobase, or any combination thereof. In certain embodiments, modified sugar moieties are non-bicyclic modified sugar moieties. In certain embodiments, modified sugar moieties are bicyclic or tricyclic sugar moieties. In certain embodiments, modified sugar moieties are sugar surrogates. Such sugar surrogates may comprise one or more substitutions corresponding to those of other types of modified sugar moieties. In certain embodiments, modified sugar moieties are non-bicyclic modified sugar moieties comprising a furanosyl ring with one or more substituent groups none of which bridges two atoms of the furanosyl ring to form a bicyclic structure. Such non bridging substituents may be at any position of the furanosyl, including but not limited to substituents at the 2’, 3’, 4’, and / or 5’ positions. In certain embodiments one or more non-bridging substituent of non-bicyclic modified sugar moieties is branched. Examples of 2’-substituent groups suitable for non-bicyclic modified sugar moieties include but are not limited to: 2’-F, 2'-OCH3(“OMe” or “O-methyl”), and 2'-O(CH2)2OCH3(“MOE”). In certain embodiments, 2’-substituent groups are selected from among: halo, allyl, amino, azido, SH, CN, OCN, CF3, OCF3, O-C1-C10 alkoxy, O-C1-C10 substituted alkoxy, O-C1-C10 alkyl, O-C1-C10 substituted alkyl, S- alkyl, N(Rm)-alkyl, O-alkenyl, S-alkenyl, N(Rm)-alkenyl, O-alkynyl, S-alkynyl, N(Rm)-alkynyl, O- alkylenyl-O-alkyl, alkynyl, alkaryl, aralkyl, O-alkaryl, O-aralkyl, O(CH2)2ON(Rm)(Rn) or OCH2C(=O)-N(Rm)(Rn), where each Rm and Rn is, independently, H, an amino protecting group, or substituted or unsubstituted C1-C10alkyl, -O(CH2)2ON(CH3)2(“DMAOE”), 2’-OCH2OCH2N(CH2)2(“DMAEOE”), and the 2’-substituent groups described in Cook et al., U.S. 6,531,584; Cook et al., U.S. 5,859,221; and Cook et al., U.S. 6,005,087. Certain embodiments of these 2'-substituent groups can be further substituted with one or more substituent groups independently selected from among: hydroxyl, amino, alkoxy, carboxy, benzyl, phenyl, nitro (NO2), thiol, thioalkoxy, thioalkyl, halogen, alkyl, aryl, alkenyl and alkynyl. In certain embodiments, non-bicyclic modified sugar moieties comprise a substituent group at the 3’-position. Examples of substituent groups suitable for the 3’- position of modified sugar moieties include but are not limited to alkoxy (e.g., methoxy), alkyl (e.g., methyl, ethyl). In certain embodiments, non-bicyclic modified sugar moieties comprise a substituent group at the 4’ -position. Examples of 4’-substituent groups suitable ribose ring. Examples of such 4’ to 2’ bridging sugar substituents include but are not limited to: 4'-CH2-2', 4'-(CH2)2-2', 4'-(CH2)3-2', 4'-CH2-O-2' (“LNA”), 4'-CH2-S-2', 4'- (CH2)2-O-2' 7; Orum et al., Curr. Opinion Mol. Ther., 2001, 3, 239-243; Wengel et al., U.S. 7,053,207, Imanishi et al., U.S.6,268,490, Imanishi et al. U.S. 6,770,748, Imanishi et al., U.S. surrogates comprise a 4’-sulfur atom and a substitution at the 2'-position (see, e.g., Bhat et al., U.S. 7,875,733 and Bhat et al., U.S. 7,939,677) and / or the 5’ position. In certain embodiments, sugar surrogates comprise rings having other than 5 atoms. For example, in certain embodiments, a sugar surrogate comprises a six-membered tetrahydropyran (“THP”). Such tetrahydropyrans may be further modified or substituted. Nucleosides comprising such modified tetrahydropyrans include but are not limited to hexitol nucleic acid (“HNA”), anitol nucleic acid (“ANA”), manitol nucleic acid (“MNA”) (see, e.g., Leumann, CJ. Bioorg. & Med. Chem. 2002, 10, 841- 854), fluoro HNA: see e.g., Swayze et al., U.S. 8,088,904; Swayze et al., U.S. 8,440,803; Swayze et al., U.S. 8,796,437; and Swayze et al., U.S. 9,005,906; F-HNA can also be referred to as a F-THP or 3'-fluoro tetrahydropyran), and nucleosides comprising additional modified THP compounds having the formula: wherein, independently, for each of said modified THP nucleoside: Bx is a nucleobase moiety; T3 and T4 are each, independently, an internucleotide linking group linking the modified THP nucleoside to the remainder of an oligonucleotide or one of T3 and T4 is an internucleotide linking group linking the modified THP nucleoside to the remainder of an oligonucleotide and the other of T3 and T4 is H, a hydroxyl protecting group, a linked conjugate group, or a 5' or 3'-terminal group; q1, q2, q3, q4, q5, q6 and q7 are each, independently, H, C1-C12 alkyl, substituted C1-C12 alkyl, C2-C12 alkenyl, substituted C2-C12 alkenyl, C2-C12alkynyl, or substituted C2-C12alkynyl; and each of Ri and R2is independently selected from among: hydrogen, halogen, substituted or unsubstituted alkoxy, NJ1J2, SJi, N3, OC(=X)Ji, OC(=X)NJ1J2, NJ3C(=X)NJ1J2, and CN, wherein X is O, S or NJi, and each Ji, J1, J2, and J3is, independently, H or Ci-Cg alkyl. In certain embodiments, modified THP nucleosides are provided wherein q1, q2, q3, q4, q5, q6 and q7 are each H. In certain embodiments, at least one of q1, q2, q3, q4, q5, q6 and q7 is other than H. In certain embodiments, at least one of q1, q2, q3, q4, q5, q6 and q7 is Patent Publication Nos. 2013 / 0096289; 2013 / 0011922; and 2011 / 0313020, the entire contents of each of which are hereby incorporated herein by reference. In certain embodiments, sugar surrogates are the glycerol as found in GNA (glycol nucleic acid) nucleosides as depicted below: (S)-GNA where Bx represents any nucleobase. In certain embodiments, modified sugar moieties are tricyclic modified sugar moieties, which belong to the class of conformationally constrained DNA analogs that show enhanced binding properties to DNA and RNA. In certain embodiments, tricyclic modified sugar moieties have the following structure: as described in ncbi.nlm.nih.gov / pmc / articles / PMC117067. Many other bicyclic and tricyclic sugar and sugar surrogates are known in the art that can be used in modified nucleosides. In embodiments, the modified oligonucleotide may further comprise one or more modified internucleotide linkages in addition to the at least one fsP internucleotide linkage. The naturally occurring internucleotide linkage of RNA and DNA is a 3' to 5' phosphodiester linkage. In certain embodiments, nucleosides of modified oligonucleotides may be linked together using one or more modified internucleotide linkages. The two main classes of internucleotide linking groups are defined by the presence or absence of a phosphorus atom. Representative phosphorus-containing internucleotide linkages include but are not limited to phosphates, which contain a phosphodiester bond (“P=O”) (also referred to the population. Such chirally enriched populations of modified oligonucleotides can be generated using synthetic methods known in the art, e.g., methods described in Oka et al., expanded bases, and fluorinated bases. Further modified nucleobases include tricyclic pyrimidines, such as l,3- diazaphenoxazine-2-one, 1,3- diazaphenothiazine-2-one and 9-(2-aminoethoxy)-l,3- diazaphenoxazine-2-one (G-clamp). Modified nucleobases may also include those in which the purine or pyrimidine base is replaced with other heterocycles, for example 7-deaza- adenine, 7-deazaguanosine, 2-aminopyridine and 2-pyridone. Further nucleobases include those disclosed in Merigan et al., U.S. 3,687,808, those disclosed in The Concise Encyclopedia Of Polymer Science And Engineering, Kroschwitz, J.I., Ed., John Wiley & Sons, 1990, 858-859; Englisch et al., Angewandte Chemie, International Edition, 1991, 30, 613; Sanghvi, Y.S., Chapter 15, Antisense Research and Applications, Crooke, S.T. and Lebleu, B., Eds., CRC Press, 1993, 273-288; and those disclosed in Chapters 6 and 15, Antisense Drug Technology, Crooke S.T., Ed., CRC Press, 2008, 163-166 and 442-443. Publications that teach the preparation of certain of the above noted modified nucleobases as well as other modified nucleobases include without limitation, Manoharan et al., US2003 / 0158403; Manoharan et al., US2003 / 0175906; Dinh et al., U.S. 4,845,205; Spielvogel et al., U.S. 5,130,302; Rogers et al., U.S. 5,134,066; Bischofberger et al., U.S. 5,175,273; Urdea et al., U.S. 5,367,066; Benner et al., U.S. 5,432,272; Matteucci et al., U.S. 5,434,257; Gmeiner et al., U.S. 5,457,187; Cook et al., U.S. 5,459,255; Froehler et al., U.S. 5,484,908; Matteucci et al., U.S. 5,502,177; Hawkins et al., U.S. 5,525,711; Haralambidis et al., U.S. 5,552,540; Cook et al., U.S. 5,587,469; Froehler et al., U.S. 5,594,121; Switzer et al., U.S. 5,596,091; Cook et al., U.S. 5,614,617; Froehler et al., U.S. 5,645,985; Cook et al., U.S. 5,681,941; Cook et al., U.S. 5,811,534; Cook et al., U.S. 5,750,692; Cook et al., U.S. 5,948,903; Cook et al., U.S. 5,587,470; Cook et al., U.S. 5,457,191; Matteucci et al., U.S. 5,763,588; Froehler et al., U.S. 5,830,653; Cook et al., U.S. 5,808,027; Cook et al., U.S. 6,166,199; and Matteucci et al., U.S. 6,005,096. In embodiments, the modified oligonucleotide comprises a modified nucleobase. In embodiment, the modified nucleobase is a 5- methyl cytosine. In certain embodiments, modified oligonucleotides comprise one or more nucleoside that does not comprise a nucleobase, referred to as an abasic nucleoside. In certain embodiments, modified oligonucleotides comprise one or more inosine nucleosides (i.e., nucleosides comprising a hypoxanthine nucleobase). In certain embodiments, modified oligonucleotides (such as antisense oligonucleotides) comprise one or more inverted nucleoside, as shown below:

[0002] wherein each Bx independently represents any nucleobase. In certain embodiments, an inverted nucleoside is terminal (i.e., the last nucleoside on one end of an oligonucleotide) and so only one internucleotide linkage depicted above will be present. In certain such embodiments, additional features (such as a conjugate group) may be attached to the inverted nucleoside. Such terminal inverted nucleosides can be attached to either or both ends of an oligonucleotide. In certain embodiments, such groups lack a nucleobase and are referred to herein as inverted sugar moieties. In certain embodiments, an inverted sugar moiety is terminal (i.e., attached to the last nucleoside on one end of an oligonucleotide) and so only one internucleotide linkage above will be present. In certain such embodiments, additional features (such as a conjugate group) may be attached to the inverted sugar moiety. Such terminal inverted sugar moieties can be attached to either or both ends of an oligonucleotide. In certain embodiments, nucleic acids can be linked 2’ to 5’ rather than the standard 3’ to 5’ linkage. Such a linkage is illustrated below. wherein each Bx represents any nucleobase. In certain embodiments, modified oligonucleotides comprise one or more modified acid. Conjugates In certain embodiments, provided herein are oligomeric compounds, which consist of a modified oligonucleotide as described herein and one or more conjugate groups and / or terminal groups. Conjugate groups consist of one or more conjugate moiety and a conjugate linker which links the conjugate moiety to the oligonucleotide. Conjugate groups may be attached to either or both ends of an oligonucleotide and / or at any internal position. In certain embodiments, conjugate groups are attached to the 2'-position of a nucleoside of a modified oligonucleotide. In certain embodiments, conjugate groups that are attached to either or both ends of an oligonucleotide are terminal groups. In certain such embodiments, conjugate groups or terminal groups are attached at the 3’ and / or 5’-end of oligonucleotides. In certain such embodiments, conjugate groups (or terminal groups) are attached at the 3’-end of oligonucleotides. In certain embodiments, conjugate groups are attached near the 3’-end of oligonucleotides. In certain embodiments, conjugate groups (or terminal groups) are attached at the 5’- end of oligonucleotides. In certain embodiments, conjugate groups are attached near the 5’-end of oligonucleotides. Examples of terminal groups include but are not limited to conjugate groups, capping groups, phosphate moieties, protecting groups, modified or unmodified nucleosides, and two or more nucleosides that are independently modified or unmodified. In certain embodiments, oligonucleotides are covalently attached to one or more conjugate groups. In certain embodiments, conjugate groups modify one or more properties of the attached oligonucleotide, including but not limited to pharmacodynamics, pharmacokinetics, stability, binding, absorption, tissue distribution, cellular distribution, cellular uptake, charge and clearance. In certain embodiments, conjugation of one or more carbohydrate moieties to a modified oligonucleotide can optimize one or more properties of the modified oligonucleotide. In certain embodiments, the carbohydrate moiety is attached to a modified subunit of the modified oligonucleotide. For example, the ribose sugar of one or more ribonucleotide subunits of a modified oligonucleotide can be replaced with another moiety, e.g., a non-carbohydrate (preferably cyclic) carrier to which is attached a carbohydrate ligand. A ribonucleotide subunit in which the ribose sugar of the subunit has been so replaced is referred to herein as a ribose replacement modification subunit (RRMS), which is a modified sugar moiety. A cyclic carrier may be a carbocyclic ring system, i.e., one or more ring atoms may be a heteroatom, e.g., nitrogen, oxygen, sulfur. The cyclic carrier may be a monocyclic ring system, or may contain two or more rings, e.g., fused rings. The cyclic carrier may be a fully saturated ring system, or it may contain one or more double bonds. In certain embodiments, the modified oligonucleotide is a gapmer. In certain embodiments, the modified oligonucleotide is an antisense RNAi oligonucleotide. In certain embodiments, the modified oligonucleotide is a sense RNAi oligonucleotide. In certain embodiments, conjugate groups impart a new property on the attached oligonucleotide, e.g., fluorophores or reporter groups that enable detection of the oligonucleotide. Certain conjugate groups and conjugate moieties have been described previously, for example: cholesterol moiety (Letsinger et al., Proc. Natl. Acad. Sci. USA, 1989, 86, 6553-6556), cholic acid (Manoharan et al., Bioorg. Med. Chem. Lett., 1994, 4, 1053-1060), a thioether, e.g., hexyl-S-tritylthiol (Manoharan et al., Ann. N. Y. Acad. Sci., 1992, 660, 306-309; Manoharan et al., Bioorg. Med. Chem. Lett., 1993, 3, 2765- 2770), a thiocholesterol (Oberhauser et al., Nucl. Acids Res., 1992, 20, 533-538), an aliphatic chain, e.g., do-decan-diol or undecyl residues (Saison-Behmoaras et al., EMBO J., 1991, 10, 1111- 1118; Kabanov et al., FEBS Lett., 1990, 259, 327-330; Svinarchuk et al., Biochimie, 1993, 75, 49-54), a phospholipid, e.g., di -hexadecyl -rac-glycerol or triethyl -ammonium l,2-di-O- hexadecyl-rac-glycero-3-H-phosphonate (Manoharan et al., Tetrahedron Lett., 1995, 36, 3651-3654; Shea et al., Nucl. Acids Res., 1990, 18, 3TT1- 3783), a polyamine or a polyethylene glycol chain (Manoharan et al., Nucleosides & Nucleotides, 1995, 14, 969-973), or adamantane acetic acid a palmityl moiety (Mishra et al., Biochim. Biophys. Acta, 1995, 1264, 229-237), an octadecylamine or hexylamino-carbonyl-oxycholesterol moiety (Crooke et al., J. Pharmacol. Exp. Then, 1996, 277, 923-937), a tocopherol group (Nishina et al., Molecular Therapy Nucleic Acids, 2015, 4, e220; and Nishina et al., Molecular Therapy, 2008, 16, 734-740), or a GalNAc cluster (e.g., WO2014 / 179620). In certain embodiments, conjugate groups may be selected from any of a C22alkyl, C21alkyl, C20alkyl, C19alkyl, Cl8alkyl, Cl7alkyl, Cl6alkyl, C15alkyl, C14alkyl, C13alkyl, C12 alkyl, C11 alkyl, C10 alkyl, C9 alkyl, C8 alkyl, C7 alkyl, C6 alkyl, C5 alkyl, C22 alkenyl, C21 alkenyl, C20 alkenyl, C19 alkenyl, Cl8 alkenyl, C17 alkenyl, C16 alkenyl, C15 alkenyl, C14 alkenyl, C13alkenyl, C12alkenyl, C11alkenyl, C10alkenyl, C9alkenyl, C8alkenyl, C7alkenyl, C6 alkenyl, or C5 alkenyl. In certain embodiments, the alkyl chain has one or more unsaturated bonds. In certain embodiments, a conjugate group is a lipid having the following structure: In certain embodiments, a conjugate group is a lipid having the following structure: , which is also referred to herein as 3nC7-C16. “3nC7-C16” represents a palmitate moiety linked to a 3’-Cl amino modifier and is attached to the 3’- nucleoside of an oligonucleotide via a phosphodiester linkage. Conjugate moieties include, without limitation, intercalators, reporter molecules, polyamines, polyamides, peptides, carbohydrates (e.g., GalNAc), vitamin moieties, polyethylene glycols, thioethers, polyethers, cholesterols, thiocholesterols, cholic acid moieties, folate, lipids, phospholipids, biotin, phenazine, phenanthridine, anthraquinone, adamantane, acridine, fluoresceins, rhodamines, coumarins, fluorophores, and dyes. In certain embodiments, a conjugate moiety comprises an active drug substance, for example, aspirin, warfarin, phenylbutazone, ibuprofen, suprofen, fen-bufen, ketoprofen, (S')- (+)-pranoprofen, carprofen, dansylsarcosine, 2,3,5-triiodobenzoic acid, fingolimod, flufenamic acid, folinic acid, a benzothiadiazide, chlorothiazide, a diazepine, indo-methicin, a barbiturate, a cephalosporin, a sulfa drug, an antidiabetic, an antibacterial or an antibiotic. In embodiments, an aptamer is conjugated to the modified oligonucleotide of the invention. An “aptamer” refers to a nucleic acid molecule that is capable of binding to a particular molecule of interest with high affinity and specificity (Tuerk and Gold, Science 249:505 (1990); Ellington and Szostak, Nature 346:818 (1990)). Aptamers are short single- stranded DNA or RNA oligos (preferably DNA) that are capable of binding a ligand (protein, small molecule, or even living cells) with high affinity due to their secondary structure. Most DNA or RNA is capable of forming a secondary structure, however only very rare sequences are capable of binding to a specific target with appreciable affinity. Aptamers, in addition to binding with high affinity, also bind with high specificity, as shown for an aptamer selected to bind theophylline. Aptamers are sometimes referred to as artificial antibodies, but aptamers have several advantages over antibodies, including ease and low cost of production which does not involve animals. Aptamers are less immunogenic than antibodies and are already being used as a therapeutic for humans. The binding of a ligand to an aptamer, which is typically RNA, changes the conformation of the aptamer and the nucleic acid within which the aptamer is located. The conformation change inhibits translation of an mRNA in which the aptamer is located, for example, or otherwise interferes with the normal activity of the nucleic acid. Aptamers may also be composed of DNA or may comprise nonnatural nucleotides and nucleotide analogs. An aptamer will most typically have been obtained by in vitro selection for binding of a target molecule. However, in vivo selection of an aptamer is also possible. Aptamers have specific binding regions which are capable of forming complexes with an intended target molecule in an environment wherein other substances in the same environment are not complexed to the nucleic acid. The specificity of the binding is defined in terms of the comparative dissociation constants (Kd) of the aptamer for its ligand as compared to the dissociation constant of the aptamer for other materials in the environment or unrelated molecules in general. Typically, the Kd for the aptamer with respect to its ligand will be at least about 10-fold less than the Kd for the aptamer with unrelated material or accompanying material in the environment. Even more preferably, the Kd will be at least about 50-fold less, more preferably at least about 100-fold less, and most preferably at least about 200-fold less. An aptamer will typically be between about 10 and about 300 nucleotides in length. More commonly, an aptamer will be between about 30 and about 100 nucleotides in length. The aptamer can be conjugated to either the 5’ end or the 3’ end of the modified oligonucleotide of the invention. The aptamer can be conjugated to the modified oligonucleotide through a direct bond or a linker. In embodiments, where an aptamer is conjugated to a modified oligonucleotide of the invention through a direct bond, the resulting conjugated oligonucleotide can comprise a single oligonucleotide sequence. However, the nucleotides of the aptamer sequence are not considered when determining the positional modification of the modified oligonucleotide of the present invention with fsP internucleoside linkage(s). Conjugate moieties are attached to oligonucleotides through conjugate linkers. In certain oligomeric compounds, the conjugate linker is a single chemical bond (i.e., the conjugate moiety is attached directly to an oligonucleotide through a single bond). In certain embodiments, the conjugate linker comprises a chain structure, such as a hydrocarbyl chain, or an oligomer of repeating units such as ethylene glycol, nucleosides, or amino acid units. In certain embodiments, a conjugate linker comprises pyrrolidine. In certain embodiments, a conjugate linker comprises one or more groups selected heterocyclic base selected from a purine, substituted purine, pyrimidine or substituted pyrimidine. In certain embodiments, a cleavable moiety is a nucleoside selected from uracil, least one cleavable bond. In certain embodiments, a cleavable moiety comprises a group of atoms having one, two, three, four, or more than four cleavable bonds. In certain embodiments, a cleavable moiety is selectively cleaved inside a cell or subcellular compartment, such as a lysosome. In certain embodiments, a cleavable moiety is selectively cleaved by endogenous enzymes, such as nucleases. In certain embodiments, a cleavable bond is selected from among: an amide, an ester, an ether, one or both esters of a phosphodiester, a phosphate ester, a carbamate, or a disulfide. In certain embodiments, a cleavable bond is one or both of the esters of a phosphodiester. In certain embodiments, a cleavable moiety comprises a phosphate or phosphodiester. In certain embodiments, the cleavable moiety is a phosphate linkage between an oligonucleotide and a conjugate moiety or conjugate group. In certain embodiments, a cleavable moiety comprises or consists of one or more linker- nucleosides. In certain such embodiments, the one or more linker-nucleosides are linked to one another and / or to the remainder of the oligomeric compound through cleavable bonds. In certain embodiments, such cleavable bonds are unmodified phosphodiester bonds. In certain embodiments, a cleavable moiety is 2'-deoxynucleoside that is attached to either the 3' or 5'-terminal nucleoside of an oligonucleotide by a phosphodiester internucleotide linkage and covalently attached to the remainder of the conjugate linker or conjugate moiety by a phosphodiester or phosphorothioate linkage. In certain such embodiments, the cleavable moiety is 2'-deoxyadenosine. In certain embodiments, a conjugate group comprises a cell-targeting moiety. In certain embodiments, conjugate groups comprise cell-targeting moieties that have at least one tethered ligand. In certain embodiments, cell-targeting moieties comprise two tethered ligands covalently attached to a branching group. In certain embodiments, cell-targeting moieties comprise three tethered ligands covalently attached to a branching group. In certain embodiments, each ligand of a cell-targeting moiety has an affinity for at least one type of receptor on a target cell. In certain embodiments, each ligand has an affinity for at least one type of receptor on the surface of a mammalian liver cell. In certain embodiments, each ligand has an affinity for the hepatic asialoglycoprotein receptor (ASGP- R). In certain embodiments, each ligand is a carbohydrate. In certain embodiments, the cell-targeting moiety targets neurons. In certain embodiments, the cell-targeting moiety targets a neurotransmitter receptor. In certain embodiments, the cell targeting moiety targets a neurotransmitter transporter. In certain embodiments, the cell targeting moiety targets a GABA transporter. See e.g., WO 2011 / 131693, WO 2014 / 064257. In certain embodiments, oligomeric compounds comprise one or more terminal groups. In certain such embodiments, modified oligonucleotides comprise a phosphorus- containing group at the 5’-end of the modified oligonucleotide. In certain embodiments, the phosphorus-containing group is at the 5’-end of the antisense RNAi oligonucleotide and / or the sense RNAi oligonucleotide. In certain embodiments, the terminal group is a phosphate stabilized phosphate group. The 5’-end phosphorus- containing group can be 5’-end phosphate (5’-P), 5’-end phosphorothioate (5’-PS), 5’-end phosphorodithioate (5’-PS2), 5’- end vinylphosphonate (5’-VP), 5’-end methylphosphonate (MePhos) or 5’-deoxy-5’-C- malonyl. When the 5’-end phosphorus-containing group is 5’-end vinylphosphonate, the 5 ’VP can be either 5’-E-VP isomer (i.e., trans-vinylphosphonate), 5’-Z-VP isomer (i.e., cis- vinylphosphonate), or mixtures thereof. Although such phosphate group can be attached to any modified oligonucleotide, it has particularly been shown that attachment of such a group to an antisense RNAi oligonucleotide improves activity of certain RNAi agents. See, e.g., Prakash et al., Nucleic Acids Res., 43(6):2993-3011, 2015; Elkayam, et al., Nucleic Acids Res., 45(6):3528-3536, 2017; Parmar, et al. ChemBioChem, 17(11)985-989; 2016; Harastzi, et al., Nucleic Acids Res., 45(13):7581-7592, 2017. In certain embodiments, the phosphate stabilizing group is 5’-cyclopropyl phosphonate. See e.g., WO / 2018 / 027106. In certain embodiments, terminal groups comprise one or more abasic nucleosides and / or inverted nucleosides. In certain embodiments, terminal groups comprise one or more 2’-linked nucleosides. In certain such embodiments, the 2’-linked nucleoside is an abasic nucleoside. In certain embodiments, the modified oligonucleotide of the invention is capable of hybridizing to a target nucleic acid, resulting in at least one antisense activity; such modified oligonucleotide is an antisense compound. In certain embodiments, antisense compounds have antisense activity when they reduce or inhibit the amount or activity of a target nucleic acid by 25% or more in a standard in vitro assay. In certain embodiments, antisense compounds selectively affect one or more target nucleic acid. Such antisense compounds comprise a nucleobase sequence that hybridizes to one or more target nucleic acid, resulting in one or more desired antisense activity and does not hybridize to one or more non-target nucleic acid or does not hybridize to one or more non-target nucleic acid in such a way that results in significant undesired antisense activity. In certain antisense activities, hybridization of an antisense compound to a target nucleic acid results in recruitment of a protein that cleaves the target nucleic acid. For example, certain antisense compounds result in RNase H mediated cleavage of the target nucleic acid. RNase H is a cellular endonuclease that cleaves the RNA strand of an RNA:DNA duplex. The DNA in such an RNA:DNA duplex need not be unmodified DNA. In certain embodiments, described herein are antisense compounds that are sufficiently “DNA- like” to elicit RNase H activity. In certain embodiments, one or more non- DNA-like nucleoside in the gap of a gapmer is tolerated. In certain antisense activities, an antisense compound or a portion of an antisense compound is loaded into an RNA-induced silencing complex (RISC), ultimately resulting in cleavage of the target nucleic acid. For example, certain antisense compounds result in cleavage of the target nucleic acid by Argonaute. Antisense compounds that are loaded into RISC are RNAi agents. RNAi agents may be double -stranded (siRNA or dsRNAi) or single- stranded (ssRNA). Antisense activities may be observed directly or indirectly. In certain embodiments, observation or detection of an antisense activity involves observation or detection of a change in an amount of a target nucleic acid or protein encoded by such target nucleic acid, a change in the ratio of splice variants of a nucleic acid or protein and / or a phenotypic change in a cell or animal. Pharmaceutical Composition The invention also provides a pharmaceutical composition comprising a modified oligonucleotide comprising at least one fsP internucleotide linkage as described herein and a pharmaceutically acceptable carrier. In certain embodiments, the pharmaceutical composition comprises a pharmaceutically acceptable diluent or carrier. In certain embodiments, a pharmaceutical composition comprises or consists of a sterile saline solution and one or more modified oligonucleotide. In certain embodiments, the sterile saline is pharmaceutical grade saline. In certain embodiments, a pharmaceutical composition comprises or consists of one or more modified oligonucleotide and sterile water. In certain embodiments, the sterile water is pharmaceutical grade water. In certain embodiments, a pharmaceutical composition comprises or consists of one or more modified oligonucleotide and phosphate- buffered saline (PBS). In certain embodiments, the sterile PBS is pharmaceutical grade PBS. In certain embodiments, a pharmaceutical composition comprises or consists of one or more modified oligonucleotide and artificial cerebrospinal fluid. In certain embodiments, the artificial cerebrospinal fluid is pharmaceutical grade. In certain embodiments, a pharmaceutical composition comprises a modified calcium, and magnesium salts. In certain embodiments, prodrugs comprise one or more conjugate group attached to an oligonucleotide, wherein the conjugate group is cleaved by be varied considerably without significantly altering their solubility and toxicity characteristics. Furthermore, the identity of co-solvent components may be varied: for depicting the free acid of a compound followed by the term “or a pharmaceutically acceptable salt thereof’ expressly includes all such forms that may be fully or partially protonated / de- protonated / in association with a cation or a combination of cations. In certain embodiments, one or more specific cation is identified. The cations include, but are not limited to, sodium, potassium, calcium, and magnesium. In certain embodiments, a structure depicting the free acid of a compound followed by the term “or a pharmaceutically acceptable salt thereof’ expressly includes all such forms that may be fully or partially protonated / de-protonated / in association with one or more cations selected from sodium, potassium, calcium, and magnesium. In certain embodiments, modified oligonucleotides or oligomeric compounds are in aqueous solution with sodium. In certain embodiments, modified oligonucleotides or oligomeric compounds are in aqueous solution with potassium. In certain embodiments, modified oligonucleotides or oligomeric compounds are in PBS. In certain embodiments, modified oligonucleotides or oligomeric compounds are in water. In certain such embodiments, the pH of the solution is adjusted with NaOH and / or HC1 to achieve a desired pH. Herein, certain specific doses are described. A dose may be in the form of a dosage unit. For clarity, a dose (or dosage unit) of a modified oligonucleotide or an oligomeric compound in milligrams indicates the mass of the free acid form of the modified oligonucleotide or oligomeric compound. As described above, in aqueous solution, the free acid is in equilibrium with anionic and salt forms. However, for the purpose of calculating dose, it is assumed that the modified oligonucleotide or oligomeric compound exists as a solvent-free, sodium-acetate free, anhydrous, free acid. In certain embodiments, where a modified oligonucleotide or an oligomeric compound is in solution comprising sodium (e.g., saline), the modified oligonucleotide or oligomeric compound may be partially or fully de-protonated and in association with sodium ions. However, the mass of the protons is nevertheless counted toward the weight of the dose, and the mass of the sodium ions is not counted toward the weight of the dose. Thus, for example, a dose, or dosage unit, of 10 mg of a number of fully protonated molecules that weighs 10 mg. This would be equivalent to 10.58 mg of solvent-free, sodium acetate-free, anhydrous sodiated compound or 10.65 mg of solvent-free, sodium acetate- free, anhydrous sodiated compound. In certain embodiments, where a modified oligonucleotide or oligomeric compound is in a solution, such as aCSF, comprising sodium, potassium, calcium, and magnesium, the modified oligonucleotide or oligomeric compound may be partially or fully de-protonated and in association with sodium, potassium, calcium, and / or magnesium. However, the mass to, the bladder, liver, lung or kidney. In certain embodiments, administration of the modified oligonucleotide according to the invention, alone or in combination with any other agent, is by intramuscular administration. In certain embodiments, administration of the modified oligonucleotide according to the invention, alone or in combination with any other agent, is by mucosal administration. In certain embodiments, administration of the modified oligonucleotide according to the invention, alone or in combination with any other agent, is by oral administration. In certain embodiments, administration of the modified oligonucleotide according to the invention, alone or in combination with any other agent, is by intrarectal administration. In certain embodiments, administration of the modified oligonucleotide according to the invention, alone or in combination with any other agent, is by intrathecal administration. In certain embodiments, administration of the modified oligonucleotide according to the invention, alone or in combination with any other agent, is by intratumoral administration. Solutions or suspensions used for parenteral, intradermal, or subcutaneous application can include the following components: a sterile diluent such as water for injection, saline solution, fixed oils, polyethylene glycols, glycerine, propylene glycol or other synthetic solvents; antibacterial agents such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid; buffers such as acetates, citrates or phosphates and agents for the adjustment of tonicity such as sodium chloride or dextrose. pH can be adjusted with acids or bases, such as hydrochloric acid or sodium hydroxide. The parenteral preparation can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic. Use The invention also provides a method for inhibiting gene expression comprising administering a modified oligonucleotide comprising at least one fsP internucleotide linkage as described herein or a composition as described herein, wherein the modified oligonucleotide is complementary to a nucleotide sequence of a target RNA. Preferably, the modified oligonucleotide comprises at least one modified nucleotide as described herein. The invention also provides a method for inhibiting allele-specific gene expression comprising administering a modified oligonucleotide comprising at least one fsP internucleotide linkage as described herein or a composition as described herein, wherein the modified oligonucleotide is complementary to a nucleotide sequence of a target allele RNA. Preferably, the modified oligonucleotide comprises at least one modified nucleotide as described herein. For example, the RNA target can be expressed from a first allele (e.g., a mutant allele), even when the first allelic mRNA differs from a second allele (e.g., wild-type allele) by only a single nucleotide, as is the case with certain mutations, for example, point mutations. The term "allele" refers to one of two alternate forms of a gene that can have the same locus on homologous chromosomes. Two different alleles may be responsible for alternative traits, e.g., one allele can be dominant over the other. The term "dominant allele" refers to an allele from which a trait is preferentially manifested as a phenotype. "Allele specific inhibition of expression" refers to the ability to significantly inhibit expression of one allele of a gene over another, e.g., when both alleles are present in the same cell. For example, the alleles can differ by one, two, or three or more nucleotides in the target region. In some embodiments, one allele is associated with disease causation, e.g., a disease correlated to a dominant gain-of-function mutation. The term "point mutation" refers to a single-base substitution observed in a target nucleotide sequence compared with the corresponding nucleotide sequence of a non-target sequence (e.g., a wild-type or normal allele). In this context, the "wild-type allele" refers to common naturally occurring alleles in the allele population of the same type of gene, wherein a protein encoded by this allele has normal function and / or activity. The point mutation may be any of congenitally occurring mutations and postnatally acquired mutations. Further point mutations include missense mutations that bring about amino acid substitution, silent mutations that do not result in amino acid substitution but causes change to a degenerate codon, a nonsense mutation that leads to the appearance of a stop codon, and a mutation at a splicing site. In certain embodiments, the point mutation is a dominant point mutation. A "dominant point mutation" refers to a point mutation that confers a dominant trait on the allele, or a dominant mutation-associated (or -linked) point mutation in one transcript. The target allele may specify the amino acid sequence of a mutant protein associated with a pathological condition. For example, the protein may be a gain-of- function (e.g., a dominant gain-of-function) mutant protein. In a preferred aspect, the mutant protein is associated with a disease or disorder which is correlated with expression of a particular allele of a gene, e.g., a dominant gain-of-function mutation. The term "gain- of-function mutation" as used herein, refers to any mutation in a gene in which the protein encoded by said gene (i.e., the mutant protein) acquires a function not normally associated with the protein (i.e., the wild-type protein) causes or contributes to a disease or disorder. The gain-of-function mutation can be a deletion, addition, or substitution of a nucleotide or nucleotides in the gene which gives rise to the change in the function of the encoded protein. In one embodiment, the gain-of-function mutation is a point mutation. In one embodiment, the gain-of-function mutation changes the function of the mutant protein or causes interactions with other proteins. In another embodiment, the gain- of- function mutation causes a decrease in or removal of normal wild-type protein, for example, by interaction of the altered, mutant protein with said normal, wild-type protein. The trait in which the dominant point mutation is involved is not particularly limited and is preferably a trait to be suppressed. Examples thereof include a mutation involved in the onset of a disease and a mutation involved in abnormal morphology. Gain- of-function disorders are a class of disease or disorders characterized by a gain-of-function mutation. In some embodiments, the method of inhibiting allele-specific gene expression comprises administering an modified oligonucleotide as disclosed herein. In embodiments, the target RNA is an allele comprising a point mutation and a non-target RNA is the wild- type allele. In embodiments, the point mutation results in stronger activity (or abnormal activity) of the encoded protein, as compared to the protein encoded by the non-target RNA. In embodiments the modified oligonucleotide comprises a sequence complementary to a region of the target RNA comprising a point mutation. In embodiments, the modified oligonucleotide inhibits the expression of the target RNA (“target allele”) and not the non- target RNA (non-target allele). The invention also provides a method for modulating splicing comprising administering a modified oligonucleotide comprising at least one fsP internucleotide linkage as described herein or a composition as described herein, wherein the modified oligonucleotide is complementary to a nucleotide sequence of a target RNA. Preferably, the modified oligonucleotide comprises at least one modified nucleotide as described herein. Any of the methods as described herein can be useful for treating a subject having disease or disorder wherein inhibiting expression of a gene would be beneficial. In embodiments where the modified oligonucleotide is a guide RNA for a CRISPR- based system or a guide RNA for an ADAR system, the invention also provides a method for making a change in a target DNA or RNA sequence in a mammalian cell, preferably a human cell, as described herein. Similarly, the invention provides the use of a modified guide RNA for a CRISPR-based system or a guide RNA for an ADAR system of the invention in the manufacture of a medicament for making a change in a target DNA or RNA sequence in a mammalian, preferably human cell, as described herein. In embodiments, the method of modifying a target DNA comprises delivering to a cell or a subject a modified guide RNA for a CRISPR-based system. In embodiments, the invention comprises a method or use for modulation of a target gene comprising, administering or delivering a modified guide RNA for a CRISPR-based system, a composition thereof, or pharmaceutical formulation thereof as described herein. In some embodiments, the change is editing of the target gene. In some embodiments, the change is a change in expression of the protein encoded by the target gene. As used herein, a “gene editing” or “genetic modification” is a change at the DNA level, e.g., induced by a gRNA / Cas complex. A gene editing or genetic modification may comprise an insertion, deletion, or substitution (base substitution, e.g., C-to-T, or point mutation), typically within a defined sequence or genomic locus. A genetic modification changes the nucleic acid sequence of the DNA. A genetic modification may be at a single nucleotide position. A genetic modification may be at multiple nucleotides, e.g., 2, 3, 4, 5 or more nucleotides, typically in close proximity to each other, e.g., contiguous nucleotides. In some embodiments, the method or use results in gene editing. In some embodiments, the method or use results in a double- stranded break (DSB) within the target gene. In some embodiments, the method or use results in formation of indel mutations during non-homologous end joining of the DSB. In some embodiments, the method or use results in an insertion or deletion of nucleotides in a target gene. In some embodiments, the insertion or deletion of nucleotides in a target gene leads to a frameshift mutation or premature stop codon that results in a non-functional protein. In some embodiments, the insertion or deletion of nucleotides in a target gene leads to a knockdown or elimination of target gene expression. In some embodiments, the method or use comprises homology directed repair of a DSB. In some embodiments, the method or use further comprises delivering to the cell a template, wherein at least a part of the template incorporates into a target DNA at or near a double strand break site induced by the nuclease. In some embodiments, the method or use results in a single strand break within the target gene. In some embodiments, the method or use results in a base change, e.g., by deamination, within the target gene. The gene editing typically occurs within or adjacent to the portion of the target gene with which the spacer sequence forms a duplex. In some embodiments, the method or use results in gene modulation. In some embodiments, the gene modulation is an increase or decrease in gene expression, a change in methylation state of DNA, or modification of a histone subunit. In some embodiments, the method or use results in increased or decreased expression of the protein encoded by the target gene. In certain other embodiments of the present disclosure, the invention provides a to an altered gene product or no gene product. In any of the methods as described herein, the subject is human. Administration of the modified oligonucleotide according to the invention can be carried out using known procedures using an effective amount and for periods of time effective to reduce symptoms or surrogate markers of the disease. For example, an effective amount of the modified oligonucleotide according to the invention for treating a disease and / or disorder could be that amount necessary to alleviate or reduce the symptoms, or delay or ameliorate a tumor, cancer, or bacterial, viral or fungal infection. In the context of administering a composition that modulates gene expression, an effective amount of the modified oligonucleotide according to the invention is an amount sufficient to achieve the desired modulation as compared to the gene expression in the absence of the modified oligonucleotide according to the invention. The effective amount for any particular application can vary depending on such factors as the disease or condition being treated, the particular oligonucleotide being administered, the size of the subject, or the severity of the disease or condition. One of ordinary skill in the art can empirically determine the effective amount of a particular antisense oligonucleotide without necessitating undue experimentation. When administered systemically, the therapeutic composition is preferably administered at a sufficient dosage to attain a blood level of compound according to the invention from about 0.0001 micromolar to about 10 micromolar. For localized administration, much lower concentrations than this may be effective, and much higher concentrations may be tolerated. Preferably, a total dosage of compound according to the invention ranges from about 0.001 mg per patient per day to about 200 mg per kg body weight per day. In certain embodiments, the total dosage may be 0.08, 0.16, 0.32, 0.48, 0.32, 0.64, 1, 10 or 30 mg / kg body weight administered daily, twice weekly or weekly. It may be desirable to administer simultaneously, or sequentially a therapeutically effective amount of one or more of the therapeutic compositions of the invention to an individual as a single treatment episode. The methods according to the invention are useful for model studies of gene expression. The methods are also useful for the prophylactic or therapeutic treatment of human or animal disease. For example, the methods are useful for pediatric and veterinary inhibition of gene expression applications. Kit Certain embodiments provide a kit for treating, preventing, or ameliorating a disease, disorder or condition as described herein wherein the kit comprises: (i) an modified oligonucleotide as described herein; and optionally (ii) a second agent or therapy as described herein. A kit of the present invention can further include instructions for using the kit to treat, prevent, or ameliorate a disease, disorder or condition as described herein. Synthesis Modified oligonucleotides according to the invention can be synthesized by procedures that are well known in the art, such as phosphoramidate or H-phosphonate chemistry which can be carried out manually or by an automated synthesizer. For example, the modified oligonucleotide of the invention may be synthesized by a linear synthesis approach. While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. Examples Example 1: Synthesis of a modified phosphate group of the invention. Within a 20 mL plastic vial, 1-(Fluorosulfonyl)-2,3-dimethyl-1H-imidazol-3-ium trifluoromethanesulfonate (995 mg) and sodium azide (242 mg, 1.2 equivalents) were combined and dissolved in 9 mL of anhydrous acetonitrile. The resulting solution was stirred at 0°C for 20 minutes, during which a yellowish color developed. Stirring was then ceased, and the reaction mixture was allowed to stand at room temperature for 30 minutes before being centrifuged for 2 minutes. The supernatant was decanted and stored at 4°C overnight. Following an additional centrifugation and decantation step to remove any remaining solids, the solution was diluted with 9 mL of anhydrous acetonitrile, dried over 4 Å activated molecular sieves, and stored at -20°C until further use. Example 2: Synthesis of the fsPA-modified oligonucleotide Modified oligonucleotides incorporating one to four fluorosulfonyl phosphoramidate internucleotide linkage were synthesized and evaluated for their properties such as electronegativity, size, lipophilicity, metabolic stability, and hydrogen bonding. Non-limiting examples of modified oligonucleotides used in these examples are 3-10-3 and 2-9-3 LNA gapmers, characterized by a LLLDDDDDDDDDLLL and LLDDDDDDDDDLLL sequence types. Here, "L" denotes a LNA modified sugar moiety, while "D" represents a deoxyribose sugar moiety. The internucleotide linkages comprise either phosphorothioate ("s") or fluorosulfonyl phosphoramidate ("fsP") linkages. In these examples, the base is chosen from adenine, guanine, 5-methyl cytosine, and thymine and the sugar ring is either deoxy ribose or LNA sugars. Table 1: List of oligonucleotides: ID Oligo Sequence CR-AA-04943 G.5MEC.A.T.T.G.G.T.A.T.T.5MEC.A (SEQ ID NO: 1) CR-AA-04944 G.5MEC.A.T.mU.G.G.mU.A.T.T.5MEC.A (SEQ ID NO: 2) CR-AA-04945 G.5MEC.A.T+T.G.G+T.A.T.T.5MEC.A (SEQ ID NO: 3) CR-AA-04946 G.5MEC.A.T+T.G.G.T+A.T.T.5MEC.A (SEQ ID NO: 4) CR-AA-04947 G.5MEC.A.T.T+G.G+T.A.T.T.5MEC.A (SEQ ID NO: 5) CR-AA-04948 G.5MEC.A.T.T+G.G.T+A.T.T.5MEC.A (SEQ ID NO: 6) CR-AA-04949 G.5MEC.A.T+T+G.G.T.A.T.T.5MEC.A (SEQ ID NO: 7) CR-AA-04950 G.5MEC.A.T.T.G.G+T+A.T.T.5MEC.A (SEQ ID NO: 8) CR-AA-04951 G.5MEC.A.T+T+G.G.mU.A.T.T.5MEC.A (SEQ ID NO: 9) CR-AA-04952 G.5MEC.A.T.mU.G.G+T+A.T.T.5MEC.A (SEQ ID NO: 10) CR-AA-04953 G.5MEC.A.T.mU.G.G.T.A.T.T.5MEC.A (SEQ ID NO: 11) CR-AA-04954 G.5MEC.A.T.T.G.G.mU.A.T.T.5MEC.A (SEQ ID NO: 12) CR-AA-04955 G.5MEC.A.T.T.G.mG.T.A.T.T.5MEC.A (SEQ ID NO: 13) CR-AA-05300 G.5MEC+A+T+T+G.G.T.A.T.T.5MEC.A (SEQ ID NO: 14) CR-AA-05301 G.5MEC.A+T+T+G+G.T.A.T.T.5MEC.A (SEQ ID NO: 15) CR-AA-05302 G.5MEC.A.T+T+G+G+T.A.T.T.5MEC.A (SEQ ID NO: 16) CR-AA-05303 G.5MEC.A.T.T+G+G+T+A.T.T.5MEC.A (SEQ ID NO: 17) CR-AA-05304 G.5MEC.A.T.T.G+G+T+A+T.T.5MEC.A (SEQ ID NO: 18) CR-AA-05305 G.5MEC.A.T.T.G.G+T+A+T+T.5MEC.A (SEQ ID NO: 19) CR-AA-05306 G.5MEC-A-T-T-G.G.T.A.T.T.5MEC.A (SEQ ID NO: 20) CR-AA-05307 G.5MEC.A-T-T-G-G.T.A.T.T.5MEC.A (SEQ ID NO: 21) CR-AA-05308 G.5MEC.A.T-T-G-G-T.A.T.T.5MEC.A (SEQ ID NO: 22) CR-AA-05309 G.5MEC.A.T.T-G-G-T-A.T.T.5MEC.A (SEQ ID NO: 23) CR-AA-05310 G.5MEC.A.T.T.G-G-T-A-T.T.5MEC.A (SEQ ID NO: 24) CR-AA-05311 G.5MEC.A.T.T.G.G-T-A-T-T.5MEC.A (SEQ ID NO: 25) CR-AA-05292 G.5MEC.A.T-T.G.G-T.A.T.T.5MEC.A (SEQ ID NO: 26) CR-AA-05293 G.5MEC.A.T-T.G.G.T-A.T.T.5MEC.A (SEQ ID NO: 27) CR-AA-05294 G.5MEC.A.T.T-G.G-T.A.T.T.5MEC.A (SEQ ID NO: 28) CR-AA-05295 G.5MEC.A.T.T-G.G.T-A.T.T.5MEC.A (SEQ ID NO: 29) CR-AA-05296 G.5MEC.A.T-T-G.G.T.A.T.T.5MEC.A (SEQ ID NO: 30) CR-AA-05297 G.5MEC.A.T.T.G.G-T-A.T.T.5MEC.A (SEQ ID NO: 31) CR-AA-05298 G.5MEC.A.T-T-G.G.mU.A.T.T.5MEC.A (SEQ ID NO: 32) CR-AA-05299 G.5MEC.A.T.mU.G.G-T-A.T.T.5MEC.A (SEQ ID NO: 33) CR-AA-00828 T.G.G.5MEC.A.A.G.5MEC.A.T.5MEC.5MEC.T.G.T.A (SEQ ID NO: 34) CR-AA-04826 T.G.G.5MEC.A.A.G.5MEC.A.T.5MEC.5MEC.T+G.T.A (SEQ ID NO: 35) CR-AA-04827 T.G.G.5MEC.A.A.G.5MEC.A.T+5MEC.5MEC.T+G.T.A (SEQ ID NO: 36) CR-AA-04965 T.G.G.5MEC.A+A.G.5MEC.A.T+5MEC.5MEC.T+G.T.A (SEQ ID NO: 37) CR-AA-04966 T.G.G.5MEC+A.A+G.5MEC.A.T+5MEC.5MEC.T+G.T.A (SEQ ID NO: 38) CR-AA-05220 T.G.G.5MEC+A+A+G+5MEC.A.T.5MEC.5MEC.T.G.T.A (SEQ ID NO: 39) CR-AA-05221 T.G.G.5MEC.A+A+G+5MEC+A.T.5MEC.5MEC.T.G.T.A (SEQ ID NO: 40) CR-AA-05222 T.G.G.5MEC.A.A+G+5MEC+A+T.5MEC.5MEC.T.G.T.A (SEQ ID NO: 41) CR-AA-05223 T.G.G.5MEC.A.A.G+5MEC+A+T+5MEC.5MEC.T.G.T.A (SEQ ID NO: 42) CR-AA-05224 T.G.G.5MEC.A.A.G.5MEC+A+T+5MEC+5MEC.T.G.T.A (SEQ ID NO: 43) CR-AA-05225 T.G.G.5MEC.A.A.G.5MEC.A+T+5MEC+5MEC+T.G.T.A (SEQ ID NO: 44) CR-AA-05226 T.G.G.5MEC.A.A.G.5MEC.A.T+5MEC+5MEC+T+G.T.A (SEQ ID NO: 45) CR-AA-05270 T.G.G.5MEC-A-A-G-5MEC.A.T.5MEC.5MEC.T.G.T.A (SEQ ID NO: 46) CR-AA-05287 T.G.G.5MEC.A.A-G-5MEC-A-T.5MEC.5MEC.T.G.T.A (SEQ ID NO: 47) CR-AA-05289 T.G.G.5MEC.A.A.G.5MEC-A-T-5MEC-5MEC.T.G.T.A (SEQ ID NO: 48) CR-AA-05291 T.G.G.5MEC.A.A.G.5MEC.A.T-5MEC-5MEC-T-G.T.A (SEQ ID NO: 49) Keys Bold letter: LNA; Regular letter: DNA; m: 2’-Ome; “.”: PS; “+”: fsP; ‘-”: msP Oligonucleotide (ODN) synthesis was performed on a Biolytic Dr. Oligo 48 oligo synthesizer employing Unylinker synthesis columns (500 nmol scale, 500 Å) obtained from Biolytic. Standard solid-phase phosphoramidite chemistry was utilized, with Bz protection for cytosine and adenine bases, and DMF protection for guanine. Phosphoramidite monomers were prepared at a concentration of 67 mM. Coupling was achieved using 0.25 M 5- ethylthio-1H-tetrazole (ETT) in anhydrous acetonitrile, and thiolating of the phosphorothioate linker was accomplished with 0.1 M DDTT in pyridine. For the fluorosulfonyl phosphoramidate linkage, the oxidation / thiolation step was modified by replacing the thiolation reagent with freshly prepared fluorosulfonyl azide with a 27-minute reaction time to generate fsP internucleotide linkages through Staudinger reaction. Acetic anhydride and 10% 1-methylimidazole were used for capping. Cleavage from the solid support and deprotection were carried out with concentrated aqueous ammonia for 16 hours at room temperature. For in-vitro studies, oligos were purified using GlenPak cartridges, lyophilized and analyzed using Waters SQD2 LCMS instrument. Acuity premier Oligo BEH C18, 130A, 1.7 phase A: 7 mM TEA + 80 mM HFIP in miliQ water and mobile phase B: 3.5 mM TEA + 40 mM HFIP in 50% methanol. The flow was run at a rate of 0.3 mL / min and a gradient was added and left at room temperature for 24 hours. An 8 min LCMS run was performed which showed no change to fsP oligo proving that the thiol functionality doesn’t react with internucleotide linkages into modified oligonucleotides only slightly compromises or does not compromise the stability of the duplex formed with their complementary sequences. We also measured the melting temperature of similarly substituted mesyl phosphoramidate interlinkage containing oligos and the melting temperature were found to be comparable. Results are shown in Tables 2 and 3. Table 2: Melting temperature (Tm) of fsP modified oligos and their complementary RNA sequences. Table 3: Comparison of melting temperature (Tm) of fsP-modified oligos and similarly substituted msP oligos against their complementary RNA sequences. Example 5: COMPARISON OF LIPOPHILICITY OF FLUROSULFONYL PHOSPHORAMIDATE AND MESYL PHOSPHORAMIDATE LINKAGE MODIFIED OLIGONUCLEOTIDES Lipophilicity significantly influences drug absorption, distribution, metabolism, and excretion. Fluorine substitution, a common strategy in drug design, can fine-tune lipophilicity to enhance pharmacokinetic properties. By increasing hydrophobicity, fluorine can improve membrane permeability, fat solubility and access to target tissues, such as the brain. Additionally, it can enhance metabolic stability by blocking susceptible sites or modifying electronic properties, potentially leading to longer half-lives and less frequent dosing. To demonstrate that mesyl phosphoramidate (msP) and fluorosulfonyl phosphoramidates (fsP) are fundamentally different, lipophilicity can be an important property to consider. Fluorine and methyl groups, despite both being small substituents on organic molecules, exhibit distinct properties relevant to drug development. Fluorine, with its smaller van der Waals radius (1.47 Å) compared to methyl (2.00 Å), is closer in size to hydrogen (1.20 Å), allowing for minimal steric disruption upon substitution. However, fluorine is significantly more electronegative, leading to unique electronic effects that can influence molecular interactions and metabolic stability. While methyl groups tend to increase lipophilicity, it is believed that fluorine substitutions can either increase or decrease lipophilicity depending on the number and position of fluorine atoms, offering greater versatility in fine-tuning the drug's properties. High-performance liquid chromatography (HPLC) analysis, specifically utilizing a C18 reverse-phase column, can be employed to assess and rank the lipophilicity of organic molecules. The principle underlying this approach is the differential retention of compounds based on their interaction with the hydrophobic stationary phase (C18) and the polar mobile phase (typically a water / organic solvent mixture). Molecules with higher lipophilicity exhibit stronger interactions with the C18 stationary phase, resulting in longer retention times (Rt). Conversely, more polar molecules elute earlier due to their preferential interaction with the mobile phase. By comparing the Rt values of different compounds, a relative ranking of their lipophilicity can be established. In the below example, two oligonucleotides with four fsP or msP modifications (CR- AA-05287 and CR-AA-05222) were analyzed in a Waters HPLC system using an Acuity premier Oligo BEH C18, 130A, 1.7 uM with VamGuard FIT, 2.1 x 50mm column at column mobile phase B: 3.5 mM TEA + 40 mM HFIP in 50% methanol. An extended run time of 25 mins was used. As found, the unmodified oligonucleotide CR-AA-00828 containing regular PS backbone, exhibited a retention time of 13.67 mins while being more lipophilic, fsP- modified oligos were retained for a longer time in the C18 HPLC column and showed a moderate increase in retention time, i.e., 14.02 mins. The msP-modified oligonucleotides were, however, found to be less lipophilic than the CR-AA-00828 unmodified version and had a reduced retention time of 12.73 mins. The order of lipophilicity in descending order is therefore fsP > PS > msP. Results are shown in Fig. 4. Example 6: ENZYMATIC STABILITY OF FSP OLIGONUCLEOTIDES A. Stability assay in fetal bovine serum Oligonucleotide stability in fetal bovine serum (FBS) can serve as a predictor of in vivo stability, as FBS contains nucleases and other enzymes that can degrade oligonucleotides. A strong correlation between stability in FBS and in vivo half-life is therefore expected. Oligonucleotides at a concentration of 0.1 μg / μl in DMEM supplemented with 10% FBS were incubated at 37 °C for 168 hours. Aliquots of 10 μl were withdrawn at 24, 48, 72, 96, and 168-hour time points, and the reaction was terminated by the addition of 10 μl orange loading dye solution (8 M Urea, 2 mM Tris (pH 7.5), 20 mM EDTA, 0.25% Orange G) followed by immediate freezing in liquid nitrogen. All the samples were kept in - 20 °C till ready for gel analysis. For gel electrophoresis, the samples were thawed and subsequently resolved on 15% Novex™ TBE-Urea gels using 1X TBE as a running buffer. Visualization was achieved by staining with Sybr Gold, washing, and imaging under blue light illumination. There was no appreciable difference between regular PS modification and fsP modifications on exposure to serum for an extended amount of time which demonstrated the suitability of fsP modification in biological applications. B. Stability assay in mouse liver homogenate performed in compliance with the guidelines of an AAALAC-accredited animal facility and approved by both the institutional animal ethics committee and the Government of India Committee for Control And Supervision of Experiments on Animals. Mice were housed in conventional or individually ventilated cages under standard laboratory conditions (12:12 hour light-dark cycle, 22 ± 3°C, 50 ± 20% humidity, 15-20 air changes per hour) with ad libitum access to standard chow and filtered, reverse osmosis-purified water. Animals were monitored daily for health and clinical signs, with euthanasia performed on moribund animals or those experiencing >15% body weight loss, as determined by the attending veterinarian. FsP backbone modified and unmodified antisense oligonucleotides (ASOs) were formulated in sterile phosphate-buffered saline (PBS; 0.1 M, pH 7.4) at a concentration of 10 mg / mL and administered subcutaneously in the interscapular region at a dose of 75 mg / kg body weight. Animals were randomized into treatment groups of 3 mice each, based on body weight, and dosed on days 1 and 5. A negative control group received 0.1 M PBS at the same dosing frequency. Urine collection was conducted over a 4-6 hour period on days 2 and 6 (24 ± 3 hours post-dose), while fasting (4-6 hours) blood samples were obtained on days 4, 8, 15, and 21. Blood collection was performed under mild isoflurane anesthesia via the retro-orbitalplexus into serum collection tubes (VACUETTE , Greiner Bio-One), followed bycentrifugation at 3500 x g for 15 minutes at 4°C. The serum was isolated and either utilized immediately for assays or stored at -80°C. Urine samples were analyzed for volume, urinary urea nitrogen (UUN), urinary creatinine, kidney injury model-1 (KIM-1), and cystatin C. Blood samples were assessed for serum alanine transaminase (ALT), aspartate transaminase (AST), and cytokeratin-18. On day 21, animals were anesthetized and whole blood was collected in K2-EDTA tubes for hematological analysis. Subsequently, mice were deeply anesthetized with isoflurane and euthanized. The liver, kidney, lungs, heart, and spleen were harvested and weighed. The impact of modifying the parent toxic oligonucleotide CR-AA-00017, is demonstrated below. Three distinct positions within the gap and wing regions were altered with fsP backbone modifications. These modifications resulted in a reduction of delayed liver toxicity in mice, as evidenced by decreased ALT and AST levels, which are established markers of liver damage. In comparison, when the same positions were modified with msP modification, the two terminal modifications didn’t ameliorate liver toxicity. Results are shown in Fig. 11. Example 11: ALLELE SELECTIVITY OF FSP-MODIFIED ASOS Allele-selective inhibition of disease-causing genes is a crucial aspect of antisense oligonucleotide (ASO) therapeutics. By targeting only the mutated allele while sparing the wild-type, allele-selective ASOs offer the potential for safer and more effective treatments for genetic disorders. Achieving allele selectivity often involves exploiting single nucleotide polymorphisms (SNPs) within the target RNA. Various chemical modifications, such as 2’-F, and 2'-O-methyl modifications, have been utilized to enhance ASO binding affinity and specificity towards the mutant allele. These modifications either alter the RNase H cleavage preference sites or create affinity differences within mutant and wild-type alleles, leading to selective inhibition of the disease-causing allele. To demonstrate the allele-selection effect of fsP-modified gapmer ASOs, we designed ASOs against the human transportin-2 (TNPO2) gene. Toxic mutations in one of the alleles in the TNPO2 gene have been associated with severe neurological diseases. However, complete knockdown of the total TNPO2 function with ASOs is not desirable because of the essential role of this receptor. CR-AA-05258, designed to knockdown complementary mutant Allele B, also significantly knockdown Allele A despite a single mismatch. However, when fsP modifications were incorporated into the same sequence, it exhibited improved knockdown selectivity towards Allele B. Results are shown in Fig. 12. Example 12: ASSESSMENT OF IMPROVED IN VIVO DISTRIBUTION AS WELL AS SILENCING ACVITIY OF FSP-MODIFIED ASOS As demonstrated above, fsP-modified antisense oligonucleotides (ASOs) exhibited higher lipophilicity compared to PS or msP oligos. Increased lipophilicity has been associated in the literature with improved fat solubility and diffusion, potentially leading to enhanced cellular uptake. To assess whether fsP modification improves ASO distribution, fsP, msP- modified ASOs, and full PS ASOs will be evaluated in a mouse model targeting mouse Factor XII and / or mouse scavenger receptor B1 (SRB1) mRNA. Following a single subcutaneous administration, mice will be monitored for 72 hours for general behavior and health. Subsequently, they will be sacrificed, and whole blood will be collected to determine serum FXII levels by ELISA or qPCR. Liver tissue will also be harvested for target gene expression analyses. The extent of target gene knockdown for mFXII and mSRB1 within liver tissue will be determined by HybELISA from liver tissue extracts or by qPCR following mRNA extraction. The distribution profile resulting from fsP modification will be compared to that of msP and PS modifications to assess whether fsP mods hinder or facilitate tissue penetration, thereby suggesting its potential for effective delivery of therapeutic ASOs to target tissues in vivo. Example 13: DESIGN, ACTIVITY AND IN VIVO DISTRIBUTION OF SILENCING RNAS (SIRNA) MODIFIED WITH FSP INTERLINKAGES Double-stranded siRNAs comprising at least one fsP interlinkage in the sense and / or antisense strand will be synthesized and tested for their gene silencing activities. The internucleotide linkages will consist of phosphorothioate, phosphodiester linkages, and fsP linkages to access their effect on siRNA activity, off-target effects and specificity against the genes of interest. Human HPRT1 or another gene will be used for siRNA-mediated knockdown in vitro. Analogous msP versions will be made and similar activity assays will be performed side-by- side. Additionally, the antisense strand can further comprise 3’-vinyl phosphonate (VP) modifications and other commonly known siRNA chemical modifications (like PS extensions on the sense strand) and the effect of fsPs will be examined. Briefly, HeLa cells will be transfected using RNAiMAXwith siRNA at an effective concentration. The transfection process will be allowed to proceed for 5-10 hours, after which RNA will be extracted from the cells. Subsequently, RNA expression levels will be analyzed via RT-qPCR employing the corresponding primer-probe set. For in vivo studies, siRNA constructs similar to the above with fsP modifications will be explored against mouse Apo E, Factor XII, or another selected gene for their silencing activities. Briefly, after a single ICV / subcutaneous (or another appropriate type of administration as needed) administration in appropriate siRNA doses, mice will be monitored for 72 hours for general behavior and health. Subsequently, they will be sacrificed, and blood and organs (e.g. kidney) will be collected and will be analyzed for siRNA-mediate knockdown using analogous tools as explained in the previous example (#11). Additionally, if needed GalNac conjugates of the fsP-modified siRNAs will be synthesized and assayed for their activity. Moreover, the siRNA sense strand will be modified with single-strand stretches of fsP and msP segments to determine their effect on siRNA distribution in the brain. Example 14: DESIGN AND ACTIVITY OF ASOS MODIFIED WITH FSP INTERLINKAGES AS SPLICE MODULATORS ASOs with one or more fsP modifications in a PS MOE oligonucleotide, like nusinersen, will be designed and synthesized and their efficacy will be tested in comparison to PS-modified ASOs in vitro and in vivo using analogous assays as stated in the previous

Claims

CLAIMS What is claimed:B is a natural or modified nitrogen base; R2is H, F, NH2, SCH3, or OR3; and R3 is H, halogen, NH2, a C1-C6 alkyl, a C1-C6 alkoxy, provided that when R3 is a C1-C6 alkyl, the C1-C6alkyl can optionally be further bound to the 4’ carbon.

3. A modified antisense oligonucleotide comprising 12-30 linked nucleosides, wherein the modified oligonucleotide comprises at least one fsP internucleotide linkages having the structure of formula (I):

4. The modified antisense oligonucleotide according to claim 3, wherein the modified oligonucleotide comprises 12-26 linked nucleosides.

5. The modified antisense oligonucleotide according to claim 3 or 4, wherein themodified oligonucleotide comprises - -region, wherein:-region consists of 1- -region nucleoside comprisinga modified sugar moiety; -region consists of 1- -region nucleoside comprisinga modified sugar moiety; and the central region is between the 5’-region and 3’- region, wherein the central region comprises 6-14 linked nucleosides, wherein each central region nucleoside is independently selected from a deoxynucleoside and a -substituted nucleoside, wherein not more than 2 -substituted nucleosides, and --region, and / or the central region comprises at least onefluorosulfonyl (fsP) phosphoramidate internucleotide linkage having the structure of formula (I)6. The modified antisense oligonucleotide according to claim 5, wherein the 5’ region comprises at least one fsP phosphoramidate internucleotide linkage, preferably one fsP phosphoramidate internucleotide linkage.

7. The modified antisense oligonucleotide according to claim 5 or claim 6, wherein the 3’ region comprises at least one fsP phosphoramidate internucleotide linkage, preferably one fsP phosphoramidate internucleotide linkage.

8. The modified antisense oligonucleotide according to any one of claims 5 to 7, wherein the central region comprises at least one fsP phosphoramidate internucleotide linkage.

9. The modified antisense oligonucleotide according to any one of claims 5 to 8, wherein the internucleotide linkage between the central region and the 3’ region is fsP phosphoramidate internucleotide linkage.

10. The modified antisense oligonucleotide according to any one of claims 5 to 9, wherein d1)L1(Nd2)L2(Nd3)L3(Nd4)L4[(Nd)L]q, wherein Nd, at each occurrence, Nd1, Nd2, Nd3, and Nd4, are independently selected from a stereo-standard DNA -substituted nucleoside; provided that no more than one of Nd, Nd1, Nd2, Nd3, and Nd4, -substituted nucleoside; L, at each occurrence, and L1, L2, L3, and L4are independently an internucleotide linkage selected from phosphodiester internucleotide linkage, phosphorothioate internucleotide linkage, and fsP phosphoramidate internucleotide linkage, provided that at least one of L, L1, L2, L3, and L4is a fsP phosphoramidate internucleotide linkage; and q is from 2-10.

11. The modified antisense oligonucleotide according to any one of claims 5 to 10, wherein (Nd1)L1(Nd2)L2(Nd3)L3(Nd4)L4(Nd5)L5(Nd6)L6(Nd7)L7(Nd8)L8(Nd9)L9(Nd10)L10, wherein: Nd1, Nd2, Nd3, Nd4, Nd5, Nd6, Nd7, Nd8, Nd9, Nd10are independently selected from astereo- -substituted nucleoside; provided that no more thanone of Nd1, Nd2, Nd3, Nd4, Nd5, Nd6, Nd7, Nd8, Nd9, or Nd10 -substituted nucleoside;each of L1, L2, L3, L4, L5, L6, L7, L8, L9, and L10 are independently an internucleotide18. The modified antisense oligonucleotide according to claim 17, wherein at least one 5’-region nucleoside and / or at least one 3’-region nucleoside comprises a bicyclic sugar moiety.

19. The oligomeric compound according to claim 18, wherein each bicyclic sugar moiety is selected from cEt and LNA.

20. The modified antisense oligonucleotide according to claim 17, wherein at least one 5’-region nucleoside and / or at least one 3’-region nucleoside comprises a 2’-substituted sugar moiety.

21. The modified antisense oligonucleotide according to claim 20, wherein the 2’- substituent of each 2’-substituted sugar moiety is selected from OCH3and O(CH2)2OCH3.

22. The modified antisense oligonucleotide according to any of claims 3 to 21, further comprising a conjugate group.

23. The modified antisense oligonucleotide of claim 22, wherein the conjugate group comprises a cell targeting moiety.

24. The modified antisense oligonucleotide of claim 22, wherein the conjugate group comprises an aptamer.

25. A pharmaceutical composition comprising a modified oligonucleotide according to any one of claims 1-24 and a pharmaceutically acceptable carrier.

26. A method for inhibiting gene expression of a target RNA, the method comprising administering a modified oligonucleotide according to any one of claims 1-23, or a composition according to claim 24, wherein the modified oligonucleotide is complementary to a nucleotide sequence of the target RNA.

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