Provided herein are oligonucleotides comprising phosporamidite internucleotide linkages of the following formula: (I), wherein R1 is
isopropyl, isobutyl, sec-butyl, C1-6 haloalkyl, C2-6 hydroxyalkyl, C2-8 alkylene-N(RN)2, C0-2alkylene-C3-8cycloalkyl, 4-10 membered heterocycloalkyl having 1-3 ring heteroatoms selected from 0, N, and S, or 5-10 membered heteroaryl having 1-3 ring heteroatoms selected from 0, N, and S, with the proviso that the heterocycloalkyl or heteroaryl is attached to the
sulfur via a carbon ring atom, and the cycloalkyl, heterocycloalkyl, or heteroaryl is substituted with 0,1,2, or 3 R2 groups; each R2 is independently halo, CN, N(RN)2 C1-3
alkyl, C1-3haloalkyl, C1-3alkoxy, oxo, CO2RN, or C(0)C1-3
alkyl; and each RN is independently H or C1-3
alkyl. Also provided are formulations comprising the oligonucleotides disclosed herein, and methods of treating diseases and disorders using the oligonucleotides and formulations thereof disclosed herein.