Method for synthesizing ionizable lipids

Abstract

The present disclosure relates to methods of synthesizing ionizable lipids and ionizable lipids thereof. The process comprises the N-alkylation of an amino alcohol with two acyloxy-substituted alkyl alcohols in the presence of a hydrogen borrowing catalyst, wherein the hydrogen borrowing catalyst is an iridium catalyst. The ionizable lipid comprises at least one alcohol moiety.

Description

Technical Field

[0001] The present disclosure generally relates to the chemical synthesis of amphiphilic lipids. Disclosed herein are methods for synthesizing ionizable lipids using borrowing hydrogen catalysis. Background Art

[0002] Lipid amphiphiles are used as surfactants, emulsifiers, and phase transfer agents in the preparation of a variety of pharmaceutical, food, and consumer care products. Tertiary amine-based ionizable lipids are a particularly important class of lipid amphiphiles for the pharmaceutical industry because these lipids are capable of condensing nucleic acids to form lipid nanoparticles (LNPs) that effectively deliver nucleic acids into cells. Novel ionizable lipids are continuously being developed to improve the pharmacokinetics, biodistribution, and cellular uptake of nucleic acid therapies, particularly a new generation of RNA therapies aimed at delivering messenger RNA (mRNA), microRNA (miRNA), and small interfering RNA (siRNA) into cells.

[0003] Aliphatic tertiary amines are particular chemicals that are widely used in LNP formulations for nucleic acid delivery. Methods for the synthesis and purification of such ionizable lipids are more environmentally friendly and provide higher conversion rates, which are particularly advantageous for the pharmaceutical industry.

[0004] The synthesis of tertiary amines with lipid chains is usually cumbersome because existing methods have drawbacks. For example, synthesis by alkylation is prone to over-alkylation, and synthesis using reductive amination requires the preparation of reactive aldehydes. Existing synthesis methods may also have low yields while generating large amounts of toxic waste, such as chromium compounds used in reductive amination. Therefore, there is a need for simpler and more environmentally sustainable methods of synthesis and purification without sacrificing yield.

[0005] It is desirable to overcome at least one of the above problems. Summary of the Invention

[0006] Disclosed herein are methods for synthesizing an ionizable lipid of formula (I) or a pharmaceutically acceptable salt, solvate, or isomer thereof:

[0007]

[0008] Wherein

[0009] Each R1 is independently an optionally substituted oxo group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group, an optionally substituted silyl group, an optionally substituted alkyl group, an optionally substituted cycloalkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, or an optionally substituted heteroaryl group;

[0010] Each L1 is independently an optionally substituted alkylene group, an optionally substituted heterocycloalkylene group, or an optionally substituted arylene group;

[0011] R2 is independently H, a halo group, an oxo group, an optionally substituted alkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, an optionally substituted oxy group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group or an optionally substituted silyl group; and

[0012] n is an integer selected from 1 to 10;

[0013] The method comprises:

[0014] N-alkylating 1 molar equivalent of the amino alcohol of formula (III) with at least two molar equivalents of the alcohol of formula (II) in the presence of a borrowing hydrogen catalyst;

[0015]

[0016] wherein the borrowing hydrogen catalyst is an iridium catalyst.

[0017] Disclosed herein is a method for synthesizing an ionizable lipid of formula (Ia) or a pharmaceutically acceptable salt, solvate or isomer thereof:

[0018]

[0019] wherein

[0020] Each R3 is independently an optionally substituted alkyl group, an optionally substituted heterocyclic group or an optionally substituted aryl group;

[0021] Each L1 is independently an optionally substituted alkylene group, an optionally substituted heteroalkylene group or an optionally substituted arylene group;

[0022] R2 is independently H, a halo group, an oxo group, an optionally substituted alkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, an optionally substituted oxy group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group or an optionally substituted silyl group; and

[0023] n is an integer selected from 1 to 10;

[0024] The method comprises:

[0025] N-alkylating the amino alcohol of formula (III) with two acyloxy-substituted alkyl alcohols of formula (IIa) in the presence of a borrowing hydrogen catalyst;

[0026]

[0027] wherein the borrowing hydrogen catalyst is an iridium catalyst.

[0028] In some embodiments, the borrowing hydrogen catalyst is a cyclopentadienyl iridium complex, wherein the cyclopentadienyl is optionally substituted.

[0029] In some embodiments, the hydrogen borrowing catalyst is dichlorocyclopentadienyl iridium dimer ([Cp*IrCl2]2), wherein the cyclopentadienyl group is optionally substituted.

[0030] In some embodiments, the hydrogen borrowing catalyst is added at a concentration of about 1 mol% to about 5 mol% relative to the hydroxy-substituted alkylamine.

[0031] In some embodiments, each R3 is independently C 10 -C 24 alkyl, which is optionally substituted with a halogen group.

[0032] In some embodiments, each L1 is independently C1-C 10 alkylene, which is optionally substituted with a halogen group. [[ID=!7]]

[0033] In some embodiments, n is an integer selected from 1 to 5.

[0034] In some embodiments, the method further comprises the step of protecting the hydroxy moiety on the amino alcohol.

[0035] In some embodiments, the hydroxy moiety is protected by a protecting group selected from: 2-tetrahydropyranyl (THP), benzyl or dimethyl tert-butylsilyl (TBS), tert-butyldiphenylsilyl (TBDPS), optionally substituted benzyl ether or other ethers such as methoxymethyl ether (MOM), p-methoxybenzyl (PMB).

[0036] In some embodiments, the molar ratio of amino alcohol to alcohol is from about 1:2 to about 1:20.

[0037] In some embodiments, the N-alkylation step is carried out in the presence of NaHCO3 and toluene.

[0038] In some embodiments, the N-alkylation step is carried out at a temperature of about 80 °C to about 110 °C.

[0039] In some embodiments, the N-alkylation step is carried out for about 16 hours to about 24 hours.

[0040] In some embodiments, the method further comprises the step of purifying the ionizable lipid from the amino alcohol and / or the alcohol.

[0041] In some embodiments, the purification step is carried out using column chromatography in the presence of dichloromethane, methanol and ammonia.

[0042] In some embodiments, the purification step is carried out in the presence of magnesium silicate (Florisil) or silica gel.

[0043] In some embodiments, the method further comprises the step of purifying the ionizable lipid from the hydrogen borrowing catalyst.

[0044] In some embodiments, the purification of the ionizable lipid from the hydrogen borrowing catalyst is carried out in the presence of a metal scavenger.

[0045] In some embodiments, the method further comprises the step of deprotecting the hydroxyl moiety on the ionizable lipid.

[0046] In some embodiments, the deprotection step is carried out in the presence of hydrochloric acid and methanol.

[0047] In some embodiments, the method further comprises the step of separating the ionizable lipid in the free amine form.

[0048] In some embodiments, the separation step is carried out in the presence of ammonia, methanol and ethyl acetate, or in the presence of diethyl ether, water and sodium hydroxide.

[0049] In some embodiments, the deprotection step and the separation step are carried out sequentially in a reaction vessel.

[0050] In some embodiments, the N-alkylation step, the deprotection step and the separation step are carried out sequentially in a reaction vessel.

[0051] In some embodiments, the ionizable lipid of formula (I) is selected from:

[0052]

[0053]

[0054] Also disclosed herein is a method for synthesizing ALC-0315 or a pharmaceutically acceptable salt, solvate or isomer thereof:

[0055]

[0056] The method comprises:

[0057] N-alkylating an amino alcohol of formula (III) with two acyloxy-substituted alkyl alcohols of formula (IIa) in the presence of a dichlorocyclopentadienyliridium dimer ([Cp*IrCl2]2) catalyst,

[0058]

[0059] wherein R2 is independently H; and

[0060] n is 4;

[0061]

[0062] wherein R3 is independently a C 15 alkyl bonded to an acyl group at the C7 position; and

[0063] L1 is independently a C6 alkylene group.

[0064] In some embodiments, the method further comprises the step of protecting the hydroxyl moiety on the amino alcohol with a 2-tetrahydropyranyl (THP) group. Detailed Description

[0065] "Alkyl" refers to a monovalent alkyl group, which can be straight-chain or branched-chain, and preferably has 1 to 25 carbon atoms or more preferably has 1 to 15 carbon atoms. Examples of such alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-hexyl, and the like.

[0066] "Alkylene" refers to a divalent alkyl group, which preferably has 1 to 10 carbon atoms, and more preferably has 1 to 6 carbon atoms. Examples of such alkylene groups include methylene (-CH2-), ethylene (-CH2CH2-), and propylene isomers (such as -CH2CH2CH2- and –CH(CH3)CH2-), and the like.

[0067] "Alkenyl" refers to a monovalent alkenyl group, which can be straight-chain or branched-chain, and preferably has 2 to 10 carbon atoms, and more preferably has 2 to 6 carbon atoms, and has at least 1 carbon-carbon double bond, and preferably 1 to 2 carbon-carbon double bonds. Examples include vinyl (-CH=CH2), n-propenyl (-CH2CH=CH2), isopropenyl (-C(CH3)=CH2), but-2-enyl (-CH2CH=CHCH3), and the like.

[0068] "Alkenylene" refers to a divalent alkenyl group, which preferably has 2 to 8 carbon atoms and more preferably 2 to 6 carbon atoms. Examples include vinylene (-CH=CH-) and propenylene isomers (such as -CH2CH=CH- and C(CH3)=CH-), and the like.

[0069] "Halogen" or "halo" refers to fluoro, chloro, bromo, and iodo groups.

[0070] "Oxo / hydroxy" refers to the groups =O, HO-.

[0071] "Acyl" refers to the groups H-C(O)-, alkyl-C(O)-, cycloalkyl-C(O)-, aryl-C(O)-, heteroaryl-C(O)-, and heterocyclic-C(O)-, where alkyl, cycloalkyl, aryl, heteroaryl, and heterocyclic are as described herein.

[0072] "Oxoacyl" refers to the groups HOC(O)-, alkyl-OC(O)-, cycloalkyl-OC(O)-, aryl-OC(O)-, heteroaryl-OC(O)-, and heterocycloalkyl-OC(O)-, where the alkyl, cycloalkyl, aryl, heteroaryl, and heterocycloalkyl are as described herein.

[0073] "Acyloxy" refers to -OC(O)-alkyl, -OC(O)-aryl, -C(O)-O-heteroaryl, and -C(O)-O-heterocycloalkyl, where the alkyl, aryl, heteroaryl, and heterocycloalkyl are as described herein.

[0074] In this specification, "optionally substituted" means that a group may or may not be further substituted or fused (to form a fused polycyclic group) with one or more than one group selected from the following: hydroxy, acyl, alkyl, alkoxy, alkenyl, alkenyloxy, alkynyl, alkynyloxy, amino, amido, thio, aralkyl, aralkoxy, aryl, aryloxy, carboxy, acylamino, cyano, halo, nitro, phosphonyl, sulfo, phosphonoamino, phosphinyloxy, heteroaryl, heteroaralkyl, heteroaryloxy, heterocycloalkyl, heterocycloalkoxy, oxoacyl, oxime, oxime ether, hydrazone, oxoacylamino, oxosulfonylamino, amidooxy, trifluoromethyl, trialkylsilyl, pentafluoroethyl, trifluoromethoxy, difluoromethoxy, trifluoromethylthio, trifluoroethenyl, monoalkylamino and dialkylamino, mono(substituted alkyl)amino and di(substituted alkyl)amino, monoarylamino and diarylamino, monoheteroarylamino and diheteroarylamino, monoheterocycloalkylamino and diheterocycloalkylamino, and asymmetrically disubstituted amines having different substituents selected from alkyl, aryl, heteroaryl, and heterocycloalkyl, etc., and it may also contain a bond connected to a solid support material (e.g., substituted onto a polymer resin). For example, an "optionally substituted amino" group may include amino acids and peptide residues.

[0075] The compounds described herein may contain one or more than one asymmetric center and may thus exist in various isomeric forms such as enantiomers and / or diastereomers. For example, the compounds described herein may be in the form of individual enantiomers, diastereomers or geometric isomers, or may be in the form of a mixture of stereoisomers, including racemic mixtures and mixtures enriched in one or more than one stereoisomer. Isomers can be separated from the mixture by methods known to those skilled in the art, including chiral high performance liquid chromatography (HPLC) and the formation and crystallization of chiral salts; or the preferred isomers can be prepared by asymmetric synthesis. In addition, the present disclosure includes compounds described herein as individual isomers substantially free of other isomers and / or as mixtures of multiple isomers. As used herein, "optically enriched" means that a compound consists of a significantly larger proportion of one enantiomer. In certain embodiments, the compounds of the present disclosure consist of at least about 90% by weight of the preferred enantiomer. In other embodiments, the compound consists of at least about 95%, 98% or 99% by weight of the preferred enantiomer. The preferred enantiomer can be separated from the racemic mixture by any method known to those skilled in the art, including chiral high performance liquid chromatography (HPLC) and the formation and crystallization of chiral salts or by asymmetric synthesis. See, for example, Jacques et al., Enantiomers, Racemates and Resolutions (Wiley Interscience, New York, 1981); Wilen et al., Tetrahedron 33:2725 (1977); Eliel, Stereochemistry of Carbon Compounds (McGraw-Hill, NY, 1962); and Wilen, Tables of Resolving Agents and Optical Resolutions p.268 (E.L. Eliel, Ed., Univ. of Notre Dame Press, Notre Dame, IN 1972).

[0076] Without being bound by theory, the inventors have found that borrowing hydrogen catalysis (also known as hydrogen autotransfer) can be used to synthesize tertiary amine ionizable lipids and can provide a more direct route to overcome some of the challenges associated with current methods for preparing tertiary amines, including the generation of unwanted and / or toxic by-products. Amino alcohols have not previously been used as reagents for such catalysis, and tertiary amines with long fatty chains have also not been synthesized using this catalytic method. The inventors have found that double N-alkylation of primary fatty amines (amino alcohols) can be carried out using hydrogen transfer catalysis to produce tertiary amines (amino alcohols), and N-alkylation with long-chain fatty alcohols can yield ionizable amino lipids.

[0077] Accordingly, the present disclosure provides a method for synthesizing an ionizable lipid of formula (I) or a pharmaceutically acceptable salt, solvate or isomer thereof:

[0078]

[0079] wherein

[0080] each R1 is independently an optionally substituted oxo group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group, an optionally substituted silyl group, an optionally substituted alkyl group, an optionally substituted cycloalkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group or an optionally substituted heteroaryl group;

[0081] each L1 is independently an optionally substituted alkylene group, an optionally substituted heterocyclylene group or an optionally substituted arylene group;

[0082] R2 is independently H, a halogen group, an oxo group, an optionally substituted alkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, an optionally substituted oxy group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group or an optionally substituted silyl group; and

[0083] n is an integer selected from 1 to 10;

[0084] the method comprising:

[0085] N-alkylating an amino alcohol of formula (III) with two alcohols of formula (II) in the presence of a borrowing hydrogen catalyst;

[0086]

[0087] wherein the borrowing hydrogen catalyst is an iridium catalyst.

[0088] The present disclosure provides a method for synthesizing an ionizable lipid of formula (I) or a pharmaceutically acceptable salt, solvate or isomer thereof:

[0089]

[0090] wherein

[0091] each R1 is independently an optionally substituted oxo group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group, an optionally substituted silyl group, an optionally substituted alkyl group, an optionally substituted cycloalkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group or an optionally substituted heteroaryl group;

[0092] each L1 is independently an optionally substituted alkylene group, an optionally substituted heterocyclylene group or an optionally substituted arylene group;

[0093] R2 is independently H, a halogen group, an oxo group, an optionally substituted alkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, an optionally substituted oxy group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group or an optionally substituted silyl group; and

[0094] n is an integer selected from 1 to 10;

[0095] The method comprises:

[0096] N-alkylating 1 molar equivalent of an amino alcohol of formula (III) with at least two molar equivalents of an alcohol of formula (II) in the presence of a borrowing hydrogen catalyst;

[0097]

[0098] wherein the borrowing hydrogen catalyst is an iridium catalyst.

[0099] Disclosed herein is a method for synthesizing an ionizable lipid of formula (Ia) or a pharmaceutically acceptable salt, solvate or isomer thereof:

[0100]

[0101] wherein

[0102] each R3 is independently an optionally substituted alkyl group, an optionally substituted heterocyclic group or an optionally substituted aryl group;

[0103] each L1 is independently an optionally substituted alkylene group, an optionally substituted heterocycloalkylene group or an optionally substituted arylene group;

[0104] R2 is independently H, a halogen group, an oxo group, an optionally substituted alkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, an optionally substituted oxy group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group or an optionally substituted silyl group; and

[0105] n is an integer selected from 1 to 10;

[0106] The method comprises:

[0107] N-alkylating 1 molar equivalent of an amino alcohol of formula (III) with at least two molar equivalents of an acyloxy-substituted alkyl alcohol of formula (IIa) in the presence of a borrowing hydrogen catalyst;

[0108]

[0109] wherein the borrowing hydrogen catalyst is an iridium catalyst.

[0110] The compounds of the invention comprise at least one alcohol moiety.

[0111] Borrowing hydrogen catalysis, also known as hydrogen autotransfer or dehydrogenative activation, is a method for activating, for example, alcohols. In contrast, carbonyl compounds are better electrophiles and can be used in a variety of reactions. Borrowing hydrogen catalysis uses this "chemical detour" as a method of activation. In essence, the catalyst first oxidizes the alcohol by removing or "borrowing" hydrogen to form a reactive carbonyl compound. This intermediate can undergo a wide variety of subsequent transformations before the catalyst returns the "borrowed" hydrogen to release the product and regenerate the catalyst. In this way, the alcohol can be used as an alkylating agent, and the only by-product of this one-pot reaction is water. The whole process allows the conversion of alcohols into amines, the formation of C-C bonds, or functionalization at the β-position. The catalyst can be a transition metal complex, such as a Ru compound, an Ir compound, or a Rh compound. In addition to alcohols, borrowing hydrogen catalysis can also be applied to amines and alkanes.

[0112] In some embodiments, the borrowing hydrogen catalyst is a homogeneous catalyst. In some embodiments, the borrowing hydrogen catalyst is a transition metal catalyst. In some embodiments, the borrowing hydrogen catalyst is an iridium catalyst. For example, the borrowing hydrogen catalyst can be [Ir(COD)Cl]2 with a Py2-NPiPr2 ligand, IrCl3 with a 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP) ligand, or an IrCl3 with an N-heterocyclic carbene (NHC) ligand. In some embodiments, the iridium catalyst is selected from:

[0113]

[0114] In some embodiments, the borrowing hydrogen catalyst is a cyclopentadienyl iridium complex, wherein the cyclopentadienyl is optionally substituted. In a preferred embodiment, the borrowing hydrogen catalyst is dichlorocyclopentadienyl iridium dimer ([Cp*IrCl2]2), wherein the cyclopentadienyl is optionally substituted.

[0115] In some embodiments, the borrowing hydrogen catalyst is added at a concentration of about 1 mol% to about 5 mol% relative to the hydroxy-substituted alkylamine or the borrowing hydrogen catalyst is present at a concentration of about 1 mol% to about 5 mol% relative to the hydroxy-substituted alkylamine. In some embodiments, the borrowing hydrogen catalyst is loaded at a concentration of about 5 mol% relative to the hydroxy-substituted alkylamine.

[0116] The two alcohols of formula (II) can be the same compound or can be different compounds. When different alcohols are N-alkylated to the amino alcohol of formula (III), the N-alkylation can be carried out sequentially.

[0117] In some embodiments, each R1 is independently an optionally substituted oxo group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group, an optionally substituted silyl group, an optionally substituted alkyl group, an optionally substituted cycloalkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, or an optionally substituted heteroaryl group. In some embodiments, each R1 is independently an optionally substituted oxo group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group, an optionally substituted silyl group, an optionally substituted alkyl group, an optionally substituted heterocyclic group, or an optionally substituted aryl group. In some embodiments, the optional substituent is selected from a halo group, an oxo group, an oxyacyl group, an acyloxy group, a silyl group, an alkyl group, an alkenyl group, a cycloalkyl group, a heterocyclic group, an aryl group, or a heteroaryl group. In some embodiments, the optional substituent is selected from a halo group. In some embodiments, each R1 is independently an optionally substituted C1-C 24 alkyl group, an optionally substituted C1-C 24 oxo group, an optionally substituted C1-C 24 oxyacyl group, an optionally substituted C1-C 24 acyloxy group, an optionally substituted C1-C 24 silyl group, an optionally substituted C5-C 10 heterocyclic group, or an optionally substituted aryl group.

[0118] In some embodiments, each R3 is independently an optionally substituted alkyl group. In some embodiments, the optional substituent is selected from a halo group, an oxo group, an oxyacyl group, an acyloxy group, a silyl group, an alkyl group, an alkenyl group, a cycloalkyl group, a heterocyclic group, an aryl group, or a heteroaryl group. In some embodiments, the optional substituent is selected from a halo group, an oxo group, an oxyacyl group, an acyloxy group, a silyl group, an alkyl group, a cycloalkyl group, a heterocyclic group, an aryl group, or a heteroaryl group. In some embodiments, each R3 is independently a C 10 -C 24 alkyl group, which is optionally substituted with a halo group. In a preferred embodiment, R1 is a C 15 alkyl group, which is optionally substituted with a halo group.

[0119] In some embodiments, each L1 is independently an optionally substituted alkylene group. In some embodiments, the optional substituent is selected from a halo group, an oxo group, an oxyacyl group, an acyloxy group, a silyl group, an alkyl group, an alkenyl group, a cycloalkyl group, a heterocyclic group, an aryl group, or a heteroaryl group. In some embodiments, the optional substituent is selected from a halo group, an oxo group, an oxyacyl group, an acyloxy group, a silyl group, an alkyl group, a cycloalkyl group, a heterocyclic group, an aryl group, or a heteroaryl group. In some embodiments, each L1 is independently a C1-C 10 alkylene group, which is optionally substituted with a halo group. In some embodiments, each L1 is independently a C1-C6 alkylene group, which is optionally substituted with a halo group. In a preferred embodiment, L1 is a C6 alkylene group, which is optionally substituted with a halo group.

[0120] In some embodiments, R2 is independently H, a halo group, an oxo group, an optionally substituted alkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, an optionally substituted oxy group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group, or an optionally substituted silyl group. In some embodiments, R2 is independently H, a halo group, an oxo group, an optionally substituted alkyl group.

[0121] In some embodiments, n is an integer selected from 1 to 5. In a preferred embodiment, n is from 2 to 4.

[0122] In some embodiments, the alcohol of formula (II) is:

[0123]

[0124] wherein R1 is independently an optionally substituted oxo group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group, an optionally substituted silyl group, an optionally substituted alkyl group, an optionally substituted cycloalkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, or an optionally substituted heteroaryl group; and

[0125] L1 is independently an optionally substituted alkylene group, an optionally substituted heterocyclene group, or an optionally substituted arylene group.

[0126] In some embodiments, the acyloxy-substituted alkyl alcohol is a compound of formula (IIa):

[0127]

[0128] wherein R3 is independently an optionally substituted alkyl group, an optionally substituted heterocyclic group, or an optionally substituted aryl group; and

[0129] L1 is independently an optionally substituted alkylene group, an optionally substituted heterocyclene group, or an optionally substituted arylene group.

[0130] In a preferred embodiment, the compound of formula (II) is:

[0131]

[0132] In some embodiments, the compound of formula (II) contains only 1 alcohol moiety. In other embodiments, if the compound of formula (II) contains more than 1 alcohol moiety, then all alcohol moieties except 1 alcohol group are protected.

[0133] In some embodiments, the amino alcohol is a compound of formula (III):

[0134]

[0135] wherein R2 is independently H, a halogen group, an oxo group, an optionally substituted alkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, an optionally substituted oxy group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group or an optionally substituted silyl group; and

[0136] n is an integer selected from 1 to 10.

[0137] In a preferred embodiment, the amino alcohol is aminobutanol.

[0138] In some embodiments, the alcohol group in the amino alcohol is protected prior to the N-alkylation step. In some embodiments, the method further comprises the step of protecting the hydroxy moiety on the amino alcohol. In some cases, it has been found that the amino alcohol can be cyclized under borrowing hydrogen conditions. Thus, protecting the hydroxy moiety on the amino alcohol may be useful for the N-alkylation reaction.

[0139] In some embodiments, the hydroxy moiety is protected by a protecting group selected from: 2-tetrahydropyranyl (THP), benzyl or dimethyl tert-butylsilyl (TBS), tert-butyldiphenylsilyl (TBDPS), an optionally substituted benzyl ether or other ethers such as methoxymethyl ether (MOM), p-methoxybenzyl (PMB). In a preferred embodiment, the protecting group is THP.

[0140] It has been found that the combination of an iridium catalyst and a THP protecting group provides the most favorable conditions for forming the ionizable lipid. It is believed that this is due to, for example, a combination of factors such as solvent compatibility, temperature compatibility, catalyst stability and ease of deprotection. Among all the protecting groups, the THP protecting group is able to balance between tolerance to reaction conditions (heat, nucleophile, acid) and ease of release at the end of the catalytic step. It has been found that THP is stable enough to survive the Ir-catalyzed step, allowing for high conversion and suppressing side reactions. In addition, the use of THP enables traceless deprotection as it can be released under acidic conditions (inorganic acid) and directly provides the target lipid as a hydrochloride salt.

[0141] In some embodiments, the molar ratio of the amino alcohol to the alcohol is from about 1:2 to about 1:20, from about 1:2 to about 1:15, from about 1:2 to about 1:10, or from about 1:2 to about 1:5. In other embodiments, the molar ratio is from about 1:3 to about 1:5 or from about 1:4 to about 1:5. In some embodiments, the molar ratio is 1:2.

[0142] It has been found that a stoichiometric equivalent of 2 moles of the alcohol is sufficient to substantially complete the reaction compared to 1 mole of the amino alcohol.

[0143] The N-alkylation step can be carried out without a base (with a conversion rate of at least 80%) since the amino alcohol can act as a base. Alternatively, in some embodiments, the N-alkylation step is carried out in the presence of a base. The base can be an inorganic base. The base can be NaHCO3, K2CO3, KHCO3 or NH4HCO3. In some embodiments, the N-alkylation step is carried out in the presence of a non-polar solvent. In some embodiments, the N-alkylation step is carried out in the presence of NaHCO3 and toluene. In some embodiments, the N-alkylation step is carried out in a sealed container under an inert gas.

[0144] In some embodiments, the N-alkylation step is carried out at a temperature of about 80 °C to about 110 °C, preferably about 110 °C. In some embodiments, the temperature is about 100 °C to about 150 °C.

[0145] In some embodiments, the N-alkylation step is carried out for about 16 hours to about 24 hours, preferably about 16 hours to about 32 hours. In some embodiments, the N-alkylation step is carried out for at least about 16 hours.

[0146] In some embodiments, when the two alcohols are different, the molar ratio of the amino alcohol to the first alcohol is about 1:1. The molar ratio of the amino alcohol to the second alcohol is about 1:1 to about 1:20. After the N-alkylation of the first alcohol is substantially completed as a one-pot reaction, the second alcohol can react sequentially. Alternatively, after the N-alkylation of the first alcohol, the intermediate can be purified before the second N-alkylation.

[0147] When the two alcohols are different, the N-alkylation of the two alcohols occurs in a stepwise manner. In the first N-alkylation, the first catalyst is loaded into the first alcohol and the amino alcohol and the reaction is carried out under the suitable conditions described herein. In the second N-alkylation, the second catalyst can be loaded into the second alcohol to the intermediate of the first N-alkylation and the reaction is carried out under the suitable conditions described herein. The first catalyst and the second catalyst can be the same catalyst and at the same concentration. Alternatively, the second catalyst can also not be added. The reaction conditions for the first N-alkylation and the second N-alkylation can be the same.

[0148] In some embodiments, when the two alcohols are different, the method comprises N-alkylating 1 molar equivalent of the amino alcohol of formula (III) with 1 molar equivalent of the first alcohol of formula (II) in the presence of a borrowing hydrogen catalyst to form an intermediate; and

[0149] N-alkylating the intermediate with at least 1 molar equivalent of the second alcohol of formula (II) in the presence of a borrowing hydrogen catalyst.

[0150] In some embodiments, when the two alcohols are different, the method comprises N-alkylating 1 molar equivalent of an amino alcohol of formula (III) with 1 molar equivalent of a first alcohol of formula (II) in the presence of a first borrowing hydrogen catalyst to form an intermediate; and

[0151] N-alkylating the intermediate with at least 1 molar equivalent of a second alcohol of formula (II) in the presence of a second borrowing hydrogen catalyst.

[0152] In some embodiments, the second borrowing hydrogen catalyst is the same as the first borrowing hydrogen catalyst. To this end, additional catalyst is loaded.

[0153] In some embodiments, when the two alcohols are different, the method comprises N-alkylating 1 molar equivalent of an amino alcohol of formula (III) with 1 molar equivalent of a first alcohol of formula (II) in the presence of dichlorocyclopentadienyliridium dimer ([Cp*IrCl2]2), wherein the cyclopentadienyl group is optionally substituted, to form an intermediate; and

[0154] N-alkylating the intermediate with at least 1 molar equivalent of a second alcohol of formula (II) in the presence of [Cp*IrCl2]2.

[0155] In some embodiments, the method further comprises loading additional catalyst (or [Cp*IrCl2]2) during the second N-alkylation. The catalyst can be loaded at 1 mol% to about 5 mol% relative to the hydroxy-substituted alkylamine.

[0156] In some embodiments, the method further comprises the step of purifying the ionizable lipid from the amino alcohol and / or the alcohol. In some embodiments, the purification step is carried out using column chromatography in the presence of dichloromethane (DCM), methanol (MeOH) and ammonia (NH3). In some embodiments, the purification step is carried out in the presence of magnesium silicate (Florisil) or silica gel. In a preferred embodiment, the ionizable lipid is purified using a gradient of DCM:MeOH (containing NH3) with Florisil. For example, column chromatography can be carried out on silica gel using a gradient of 100% dichloromethane containing ammonia to 20% methanol / 80% dichloromethane over 14 minutes.

[0157] In some embodiments, the method further comprises the step of purifying the ionizable lipid from the borrowing hydrogen catalyst. In some embodiments, the purification of the ionizable lipid from the borrowing hydrogen catalyst is carried out in the presence of a metal scavenger. In a preferred embodiment, the metal scavenger is SiliaMetS imidazole in chloroform or diethyl ether.

[0158] In some embodiments, the method further comprises the step of deprotecting the hydroxy moiety on the ionizable lipid. In some embodiments, the deprotection step is carried out in the presence of hydrochloric acid and methanol.

[0159] It is well known that lipids such as ALC-0315 are substrates that are difficult to purify because they bind strongly to silica gel and significant product losses occur during column chromatography (also using large amounts of solvent). The inventors have found that the selection of the THP protecting group can improve this difficulty because THP deprotection can be carried out using conventional acids and generates the product and volatile or water-soluble by-products, and the by-products can be removed by simple reaction treatment and evaporation. This method avoids the need to use column chromatography to purify the final product.

[0160] In some embodiments, the method further comprises the step of separating the ionizable lipid in the free amine form. In some embodiments, the separation step is carried out in the presence of ammonia, methanol and ethyl acetate or ether, sodium carbonate and water.

[0161] In some embodiments, the deprotection step and the separation step are carried out sequentially in a reaction vessel.

[0162] In some embodiments, the N-alkylation step, the deprotection step and the separation step are carried out sequentially in a reaction vessel.

[0163] In some embodiments, the ionizable lipid of formula (I) is selected from:

[0164]

[0165]

[0166] To this end, the inventors have developed a simplified method for obtaining, for example, ALC-0315 (the cationic lipid used in the Pfizer COVID-19 vaccine) in high yield based on borrowing hydrogen catalysis. Compared with the prior art method of reductive amination, the method disclosed herein can produce ALC-0315 from the general intermediate IM2 in a total yield of 44%, a 400% increase in yield compared to the 11% total yield using the patent route in WO / 2016176330 (incorporated herein by reference). In addition, some of the reagents used in the existing methods are toxic and unsafe, and it is desirable to avoid using them. To this end, borrowing hydrogen catalysis is used to catalyze the N-alkylation of aminobutanol with IM2 to obtain ALC-0315 without overalkylation. The reaction by-product is water, which is non-toxic.

[0167] Accordingly, the present disclosure provides a method for synthesizing ALC-0315 or a pharmaceutically acceptable salt, solvate or isomer thereof:

[0168]

[0169] The method comprises:

[0170] In the presence of a dichlorocyclopentadienyl iridium dimer ([Cp*IrCl2]2) catalyst, N-alkylation of an amino alcohol of formula (III) is carried out with two acyloxy-substituted alkyl alcohols of formula (IIa),

[0171]

[0172] wherein R2 is independently H; and

[0173] n is 4;

[0174]

[0175] wherein R3 is independently a C15 alkyl group bonded to an acyl group at the C7 position; and

[0176] L1 is independently a C6 alkylene group.

[0177] In some embodiments, the method further comprises the step of protecting the hydroxyl moiety on the amino alcohol with a 2-tetrahydropyranyl (THP) group.

[0178] The present disclosure also provides an ionizable lipid of formula (I), formula (Ia), ALC-0315, or a pharmaceutically acceptable salt, solvate, or isomer thereof synthesized by the methods disclosed herein.

[0179] The present disclosure also provides an ionizable lipid of formula (I) or a pharmaceutically acceptable salt, solvate, or isomer thereof:

[0180]

[0181] wherein

[0182] each R1 is independently an optionally substituted oxo group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group, an optionally substituted silyl group, an optionally substituted alkyl group, an optionally substituted cycloalkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, or an optionally substituted heteroaryl group;

[0183] each L1 is independently an optionally substituted alkylene group, an optionally substituted heteroalkylene group, or an optionally substituted arylene group;

[0184] R2 is independently H, a halo group, an oxo group, an optionally substituted alkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, an optionally substituted oxy group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group, or an optionally substituted silyl group; and

[0185] n is an integer selected from 1 to 10.

[0186] The present disclosure also provides an ionizable lipid of formula (Ia) or a pharmaceutically acceptable salt, solvate, or isomer thereof:

[0187]

[0188] wherein

[0189] each R3 is independently an optionally substituted alkyl, an optionally substituted heterocyclic group, or an optionally substituted aryl;

[0190] each L1 is independently an optionally substituted alkylene, an optionally substituted heteroalkylene, or an optionally substituted arylene;

[0191] R2 is independently H, a halogen, an oxo group, an optionally substituted alkyl, an optionally substituted heterocyclic group, an optionally substituted aryl, an optionally substituted oxy group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group, or an optionally substituted silyl group; and

[0192] n is an integer selected from 1 to 10.

[0193] The compounds of the present disclosure can be administered to a subject as their pharmaceutically acceptable salts. Suitable pharmaceutically acceptable salts include, but are not limited to, salts of pharmaceutically acceptable inorganic acids such as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, carbonic acid, boric acid, sulfamic acid, and hydrobromic acid, or salts of pharmaceutically acceptable organic acids such as acetic acid, propionic acid, butyric acid, tartaric acid, maleic acid, hydroxymaleic acid, fumaric acid, malic acid, citric acid, lactic acid, mucic acid, gluconic acid, benzoic acid, succinic acid, oxalic acid, phenylacetic acid, methanesulfonic acid, toluenesulfonic acid, benzenesulfonic acid, salicyclic sulphanilic acid, aspartic acid, glutamic acid, edetic acid, stearic acid, palmitic acid, oleic acid, lauric acid, pantothenic acid, tannic acid, ascorbic acid, and valeric acid.

[0194] Base salts include, but are not limited to, those formed with pharmaceutically acceptable cations such as sodium, potassium, lithium, calcium, magnesium, ammonium, and alkylammonium. In particular, the present disclosure includes within its scope cationic salts such as sodium salts or potassium salts, or alkyl esters of phosphate groups (e.g., methyl, ethyl).

[0195] Basic nitrogen-containing groups can be quaternized with the following reagents: lower alkyl halides such as chlorides, bromides, and iodides of methyl, ethyl, propyl, and butyl; dialkyl sulfates such as dimethyl sulfate and diethyl sulfate; and the like.

[0196] The compounds of the present disclosure can be in crystalline form as the free compound or as a solvate (e.g., hydrate), and both forms are intended to be within the scope of the present disclosure. Methods of solvation are well known in the art.

[0197] The salt form can be pharmaceutically "acceptable" in the sense that it is compatible with the other ingredients of the composition and harmless to the patient.

[0198] Examples

[0199] Example 1: Synthesis of ALC-0315

[0200] The synthesis of ALC-0315 from IM2 involves 3 steps.

[0201]

[0202] Scheme 1. Synthesis of ALC-0315 from IM2 using the method of the present disclosure.

[0203]

[0204] Scheme 2. Reaction between IM2 and aminobutanol catalyzed by iridium-catalyzed hydrogen borrowing with different protecting groups.

[0205] General Methodology

[0206] Step 1:

[0207] Screening of the best catalyst for the hydrogen borrowing catalytic step found that [Cp*IrCl2]2 is a suitable catalyst for this step (Table 1). Preliminary screening was carried out using TBS (dimethyl tert-butylsilyl)-protected aminobutanol, which has medium stability under the best reaction conditions. It was found that this situation could be transferred to THP (tetrahydropyranyl)-protected aminobutanol (Scheme 2).

[0208] Further condition screening including catalyst loading, reaction time, heating method (conventional and microwave), and excess IM2 alcohol determined the best reaction conditions to be 5 mol%, [Cp*IrCl2]2 (2.5 mol% iridium complex), and sodium bicarbonate base reacting at 110 °C for 16 hours. It was observed that catalyst deactivation may occur near the end of the reaction (or in the case of low IM2 alcohol content), and a higher reaction temperature may accelerate the catalyst deactivation process. On the contrary, using an excess of IM2 may not achieve a faster reaction / higher conversion, which may indicate that the reaction time and IM2 concentration affect the catalyst half-life simultaneously.

[0209] Table 1. Optimization of the hydrogen borrowing catalytic step (Step 1).

[0210] ALC-0315: Condition screening (Pg = TBS substrate)

[0211]

[0212] SM refers to the unreacted alcohol of formula (II) in the final mixture.

[0213] The ruthenium catalyst is ineffective. For [Ir(cod)Cl2]2, mono-substituted products may be formed. Perhaps the catalyst is not stable or active enough for the second alkylation. This can be overcome by stabilizing or activating the catalyst with other ligands.

[0214] Step 2:

[0215] Deprotection of the THP group on THP-protected ALC-0315 can be accomplished by reacting THP-protected ALC-0315 with hydrochloric acid in methanol and / or dioxane. The reaction is carried out at ambient temperature for several hours. At the end of the reaction, simple evaporation is performed under reduced pressure to obtain the target compound as its hydrochloride salt in 94% yield.

[0216] Step 3:

[0217] Although the hydrochloride salt is a pharmaceutically equivalent compound to the free amine base, the positive charge of this compound may pose problems when used in formulations. To provide the free amine base (ALC-0315), the ALC-0315 hydrochloride salt product can be treated with ammonia in methanol and a certain amount of ethyl acetate. Finally, a simple filtration-evaporation process is carried out to obtain the target compound with a yield of up to 77%. Alternatively, dealkalization can be carried out using an aqueous sodium hydroxide solution or a sodium carbonate solution, and extraction is performed with diethyl ether.

[0218] Theoretically, all the steps shown here can be carried out in one pot, and a complete telescoped process can be achieved as long as appropriate process optimization is carried out. In this case, column chromatography and iridium scavenging can be performed on the final product to have an acceptable low Ir metal content in the final product.

[0219] Synthesis of 4-((tetrahydro-2H-pyran-2-yl)oxy)butan-1-amine

[0220] 4-Aminobutanol (2 mmol, 178 μL) was dissolved in 2 mL of DCM, cooled in an ice bath and HCl (4 M in dioxane, 2.2 mmol, 0.56 mL) was added. The mixture was stirred for 15 minutes and dihydropyran (2.2 mmol, 200 μL) was added. The cooling was removed and the mixture was stirred for 1.5 hours. The reaction was treated with 2 M NaOH to liberate the free amine and extracted twice with DCM. The combined organic layers were dried over sodium sulfate, filtered and concentrated. Purification was carried out on silica gel using 20% followed by 30% DCM:MeOH(NH3). A colorless oil was obtained: 282 mg (1.63 mmol), 82% yield.

[0221] Synthesis of O-THP-protected ALC-0315

[0222] A mixture of OTHP-protected aminobutanol (43 mg, 0.25 mmol), IM2 alcohol (178 mg, 0.5 mmol), [cp*IrCl2]2 (5 mg, 0.0063 mmol), NaHCO3 (1.1 mg, 0.0125 mmol) and toluene (0.25 mL) was heated in a sealed vial at 110 °C under argon for 16 h and then concentrated. The crude mixture was purified on silica gel, eluting with a gradient of 0% to 10% DCM:MeOH(NH3). A yellow oil (130 mg, 0.153 mmol) was obtained in 61% yield.

[0223] Synthesis of ALC-0315 hydrochloride

[0224] A mixture of OTHP-protected ALC-0315 (480 mg), methanol (2 mL) and hydrochloric acid (4 M in dioxane, 0.3 mL) was stirred at ambient temperature for 2 to 4 h and then concentrated. A yellow oil was obtained: 424 mg, 94%.

[0225] Synthesis of ALC-0315

[0226] A mixture of ALC-0315 hydrochloride (465 mg), ethyl acetate (2 mL) and ammonia (7 M in methanol, 0.5 mL) was stirred for 30 min. The mixture was filtered and concentrated to give a pale yellow oil: 343 mg, 77%.

[0227] Example 2

[0228] Two different alcohols were added sequentially to obtain more structurally diverse lipids. This one-pot method allows the introduction of two different L1R1 groups.

[0229]

[0230] A mixture of OTHP-protected aminobutanol (42 mg, 0.25 mmol), IM2 alcohol (89 mg, 0.25 mmol), [cp*IrCl2]2 (5 mg, 0.0063 mmol), NaHCO3 (1.1 mg, 0.0125 mmol) and toluene (0.25 mL) was heated in a sealed bottle at 110 °C under argon for 16 h, then cooled to ambient temperature. The container was opened under argon and additional [cp*IrCl2]2 (5 mg, 0.0063 mmol), NaHCO3 (1.1 mg, 0.0125 mmol) and ethanol (0.29 mL, 5 mmol) were added. The container was sealed and heated at 110 °C under argon for 16 h. The crude mixture was concentrated and the residue was purified by silica gel, eluting with a gradient of 0% to 20% DCM:MeOH(NH3). A yellow oil was obtained: 34 mg (26% yield).

[0231] 1 1H NMR (400 MHz, CDCl3) δ 4.59 - 4.55 (m, 1H), 4.05 (t, J = 6.6 Hz, 2H), 3.90 - 3.82 (m, 1H), 3.77 - 3.70 (m, 1H), 3.52 - 3.45 (m, 1H), 3.42 - 3.35 (m, 1H), 2.52 (q, J = 7.1 Hz, 2H), 2.48 - 2.37 (m, 4H), 2.33 - 2.24 (m, 1H), 1.93 - 1.16 (m, 42H), 1.01 (t, J = 7.1 Hz, 3H), 0.92 - 0.79 (m, 6H).

[0232] The resulting oil was stirred with 1 mL MeOH and 0.1 mL HCl (4 M in dioxane) at ambient temperature for 3 h. The mixture was concentrated. The residue was stirred with 1 mL EtOAc and 1 mL NH3 (0.1 M in MeOH) at ambient temperature for 30 min, then filtered and the filtrate was concentrated. 23 mg of a yellow oil was obtained (80% yield).

[0233] 1 1H NMR (400 MHz, CDCl3) δ 4.03 (t, J = 6.7 Hz, 2H), 3.68 (t, J = 5.5 Hz, 1H), 3.25 - 2.83 (m, 6H), 2.28 (tt, J = 8.8, 5.3 Hz, 1H), 2.01 - 1.08 (m, 40H), 0.85 (t, J = 6.8 Hz, 3H).

[0234] Other clean products can be further purified as described in Example 1.

[0235] It should be understood that many further modifications and permutations of the various aspects of the described embodiments are possible. Accordingly, the aspects are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.

[0236] As used herein, "and / or" refers to and includes any and all possible combinations of one or more of the associated listed items, as well as the lack of a combination when interpreted in the alternative (or).

[0237] As used in this application, an element preceded by no quantifier includes a plural reference unless the context clearly dictates otherwise. For example, the term "reagent" includes multiple reagents, including mixtures thereof.

[0238] Throughout this specification and the following claims, unless the context requires otherwise, the word "comprise / include" and its variations will be understood to mean the inclusion of the stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0239] Unless the context requires otherwise, throughout this specification and the following claims, the phrase "consisting essentially of" and its variations will be understood to indicate that one or more of the recited elements are essential, i.e., necessary elements of the present disclosure. This phrase allows for the presence of other non-recited elements that do not materially affect the characteristics of the present disclosure, but excludes additional unspecified elements that would affect the basic and novel characteristics of the defined method.

[0240] Any prior publication (or information derived therefrom), or any known substance, mentioned in this specification is not, and should not be taken as, an admission or acknowledgement, or any form of implication, that the prior publication (or information derived therefrom) or known substance forms part of the common general knowledge in the field to which this specification pertains.

Claims

1. A method for synthesizing an ionizable lipid of formula (I) or a pharmaceutically acceptable salt, solvate or isomer thereof: Wherein each R1 is independently an optionally substituted oxo group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group, an optionally substituted silyl group, an optionally substituted alkyl group, an optionally substituted cycloalkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group or an optionally substituted heteroaryl group; each L1 is independently an optionally substituted alkylene group, an optionally substituted heterocyclic alkylene group or an optionally substituted arylene group; R2 is independently H, a halogen group, an oxo group, an optionally substituted alkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, an optionally substituted oxy group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group or an optionally substituted silyl group; and n is an integer selected from 1 to 10; The method comprises: N-alkylating 1 molar equivalent of an amino alcohol of formula (III) with at least two molar equivalents of an alcohol of formula (II) in the presence of a borrowing hydrogen catalyst; wherein the borrowing hydrogen catalyst is an iridium catalyst.

2. A method for synthesizing an ionizable lipid of formula (Ia) or a pharmaceutically acceptable salt, solvate or isomer thereof: Wherein each R3 is independently an optionally substituted alkyl group, an optionally substituted heterocyclic group or an optionally substituted aryl group; each L1 is independently an optionally substituted alkylene group, an optionally substituted heterocyclic alkylene group or an optionally substituted arylene group; R2 is independently H, a halogen group, an oxo group, an optionally substituted alkyl group, an optionally substituted heterocyclic group, an optionally substituted aryl group, an optionally substituted oxy group, an optionally substituted oxyacyl group, an optionally substituted acyloxy group or an optionally substituted silyl group; and n is an integer selected from 1 to 10; The method comprises: N-alkylating 1 molar equivalent of an amino alcohol of formula (III) with at least two molar equivalents of an acyloxy-substituted alkyl alcohol of formula (IIa) in the presence of a borrowing hydrogen catalyst; wherein the borrowing hydrogen catalyst is an iridium catalyst.

3. The method according to claim 1 or 2, wherein the borrowing hydrogen catalyst is a cyclopentadienyl iridium complex, wherein the cyclopentadienyl is optionally substituted.

4. The method according to any one of claims 1 to 3, wherein the borrowing hydrogen catalyst is dichlorocyclopentadienyl iridium dimer ([Cp*IrCl2]2), wherein the cyclopentadienyl is optionally substituted.

5. The method according to any one of claims 1 to 4, wherein the borrowing hydrogen catalyst is added at a concentration of about 1 mol% to about 5 mol% relative to the hydroxy-substituted alkylamine.

6. The method according to any one of claims 1 to 5, wherein each R1 is independently C 10 -C 24 alkyl, which is optionally substituted with a halogen group.

7. The method according to any one of claims 1 to 6, wherein each L1 is independently a C1-C 10 alkylene group, which is optionally substituted by a halogen group.

8. The method according to any one of claims 1 to 7, wherein n is an integer selected from 1 to 5.

9. The method according to any one of claims 1 to 8, further comprising the step of protecting the hydroxy moiety on the amino alcohol.

10. The method according to claim 9, wherein the hydroxyl moiety is protected by a protecting group selected from: 2 - tetrahydropyranyl (THP), benzyl or dimethyl tert - butylsilyl (TBS), tert - butyldiphenylsilyl (TBDPS), an optionally substituted benzyl ether or other ethers such as methoxymethyl ether (MOM), p - methoxybenzyl (PMB).

11. The method according to any one of claims 1 to 10, wherein the molar ratio of the amino alcohol to the alcohol is from about 1:2 to about 1:

20.

12. The method according to any one of claims 1 to 11, wherein the N - alkylation step is carried out in the presence of NaHCO3 and toluene.

13. The method according to any one of claims 1 to 12, wherein the N - alkylation step is carried out at a temperature of about 80 °C to about 110 °C.

14. The method according to any one of claims 1 to 13, wherein the N - alkylation step is carried out for about 16 hours to about 24 hours.

15. The method according to any one of claims 1 to 14, further comprising the step of purifying the ionizable lipid from the amino alcohol and / or the alcohol.

16. The method according to claim 15, wherein the purification step is carried out using column chromatography in the presence of dichloromethane, methanol and ammonia.

17. The method according to claim 15 or 16, wherein the purification step is carried out in the presence of magnesium silicate (Florisil) or silica gel.

18. The method according to any one of claims 1 to 17, further comprising the step of purifying the ionizable lipid from the hydrogen - borrowing catalyst.

19. The method according to claim 18, wherein the purification step is further carried out in the presence of a metal scavenger.

20. The method according to any one of claims 1 to 19, further comprising the step of deprotecting the hydroxyl moiety on the ionizable lipid.

21. The method according to claim 20, wherein the deprotection step is carried out in the presence of hydrochloric acid and methanol.

22. The method according to any one of claims 1 to 21, further comprising the step of separating the ionizable lipid in free amine form.

23. The method according to claim 22, wherein the separation step is carried out in the presence of ammonia, methanol and ethyl acetate, or in the presence of diethyl ether, water and sodium carbonate.

24. The method according to any one of claims 20 to 23, wherein the deprotection step and the separation step are carried out sequentially in a reaction vessel.

25. The method according to any one of claims 1 to 24, wherein the N - alkylation step, the deprotection step and the separation step are carried out sequentially in a reaction vessel.

26. The method according to any one of claims 1 to 25, wherein the ionizable lipid as shown in formula (I) is selected from:

27. A method for synthesizing ALC - 0315 or a pharmaceutically acceptable salt, solvate or isomer thereof: The method comprises: In the presence of a dichlorocyclopentadienyl iridium dimer ([Cp*IrCl2]2) catalyst, 1 molar equivalent of an amino alcohol of formula (III) is N-alkylated with at least two molar equivalents of an acyloxy-substituted alkyl alcohol of formula (IIa), wherein R2 is independently H; and n is 4; wherein R3 is independently C bonded to an acyl group at the C7 position 15 alkyl; and L1 is independently a C6 alkylene group.

28. The method according to claim 27, wherein the hydroxy moiety on the amino alcohol is protected with a 2-tetrahydropyranyl (THP) group.

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