Compounds, compositions and methods for synthesis

A compound having the structure of formula V-b:

• or a salt thereof, wherein:
• PL is P;
• is of such a structure that
• is a compound of formula I-e or a salt thereof:
• wherein:
• -L8-H is the —OH shown in formula I-e;
• t is 1;
• Ring A is an optionally substituted 6-membered ring having 0-4 heteroatoms;
• each of R1, R3, R4, and R5 is independently —H, -Ls-R, halogen, —CN, —NO2, -Ls-Si(R)3, —OR, —SR, or —N(R)2;
• R6 is —H;
• —NHR5 is —NR5R6 shown in formula I-e;
• each Ls is independently a covalent bond, or a bivalent, optionally substituted, linear or branched group selected from a C1-30 aliphatic group and a C1-30 heteroaliphatic group having 1-10 heteroatoms, wherein one or more methylene units are optionally and independently replaced by an optionally substituted group selected from C1-6 alkylene, C1-6 alkenylene, —C≡C—, a bivalent C1-C6 heteroaliphatic group having 1-5 heteroatoms, —C(R′)2—, -Cy-, —O—, —S—, —S—S—, —N(R′)—, —C(O)—, —C(S)—, —C(NR′)—, —C(O)N(R′)—, —N(R′)C(O)N(R′)—, —N(R′)C(O)O—, —S(O)—, —S(O)2—, —S(O)2N(R′)—, —C(O)S—, —C(O)O—, —P(O)(OR′)—, —P(O)(SR′)—, —P(O)(R′)—, —P(O)(NR′)—, —P(S)(OR′)—, —P(S)(SR′)—, —P(S)(R′)—, —P(S)(NR′)—, —P(R′)—, —P(OR′)—, —P(SR′)—, —P(NR′)—, —P(OR′)[B(R′)3]—, —OP(O)(OR′)O—, —OP(O)(SR′)O—, —OP(O)(R′)O—, —OP(O)(NR′)O—, —OP(OR′)O—, —OP(SR′)O—, —OP(NR′)O—, —OP(R′)O—, and —OP(OR′)[B(R′)3]O—, and one or more carbon atoms are optionally and independently replaced with CyL;
• each -Cy- is independently an optionally substituted bivalent group selected from a C3-20 cycloaliphatic ring, a C6-20 aryl ring, a 5-20 membered heteroaryl ring having 1-10 heteroatoms, and a 3-20 membered heterocyclyl ring having 1-10 heteroatoms;
• each CyL is independently an optionally substituted tetravalent group selected from a C3-20 cycloaliphatic ring, a C6-20 aryl ring, a 5-20 membered heteroaryl ring having 1-10 heteroatoms, and a 3-20 membered heterocyclyl ring having 1-10 heteroatoms;
• each R′ is independently —R, —C(O)R, —C(O)OR, or —S(O)2R;
• BA is an optionally substituted group selected from a natural nucleobase moiety and a modified nucleobase moiety;
• each Rs is independently —H, halogen, —CN, —N3, —NO, —NO2, -Ls-R′, -Ls-Si(R)3, -Ls-OR′, -Ls-SR′, -Ls-N(R′)2, —O-Ls-R′, —O-Ls-Si(R)3, —O-Ls-OR′, —O-Ls-SR′, or —O-Ls-N(R′)2;
• Ring As is
• wherein each of R2s and R4s is independently Rs;
• R5s is Rs;
• each R is independently —H, or an optionally substituted group selected from C1-30 aliphatic, C1-30 heteroaliphatic having 1-10 heteroatoms, C6-30 aryl, C6-30 arylaliphatic, C6-30 arylheteroaliphatic having 1-10 heteroatoms, 5-30 membered heteroaryl having 1-10 heteroatoms, and 3-30 membered heterocyclyl having 1-10 heteroatoms, or
• two R groups are optionally and independently taken together to form a covalent bond, or:
• two or more R groups on the same atom are optionally and independently taken together with the atom to form an optionally substituted, 3-30 membered, monocyclic, bicyclic or polycyclic ring having, in addition to the atom, 0-10 heteroatoms;
• or
• two or more R groups on two or more atoms are optionally and independently taken together with their intervening atoms to form an optionally substituted, 3-30 membered, monocyclic, bicyclic or polycyclic ring having, in addition to the intervening atoms, 0-10 heteroatoms.