A compound comprising the formula wherein V is selected from O and S; W is selected from a bivalent, straight or branched, saturated or unsaturated, optionally substituted C1-30 hydrocarbon chain wherein one or more methylene units are optionally and independently replaced by -O-, -S-, -N(R)-, -C(O)-, C(O)O-, OC(O)-, -N(R)C(O)-, - C(O)N(R)-, -S(O)-, -S(O) 2 -, -N(R)SO 2 -, SO 2 N(R)-, a heterocyclic group, an aryl group, or a heteroaryl group; X is selected from a covalent bond; a carbon atom; a heteroatom; an optionally substituted group selected from the group consisting of acyl, aliphatic, heteroaliphatic, aryl, heteroaryl, and heterocyclic; or nucleoside; Y is selected from a covalent bond or a bivalent, straight or branched, saturated or unsaturated, optionally substituted C1-30 hydrocarbon chain wherein one or more methylene units are optionally and independently replaced by -O-, -S-, -N(R)-, -C(O)-, C(O)O-, OC(O)-, - N(R)C(O)-, -C(O)N(R)-, -S(O)-, -S(O) 2 -, -N(R)SO 2 -, SO 2 N(R)-, a heterocyclic group, an aryl group, or a heteroaryl group; Z is a reactive functional group selected from the group consisting of N-hydroxysuccinimidyl ester, para-nitrophenyl carbonate, para-nitrophenyl carbamate, azide, hydrazine, pentafluorophenyl, haloacetamide, maleimide, hydroxylamine, strained cycloalkyne, and heterocycloalkyne, alkyne, diene, azadiene, and heterocyclic azadiene, wherein halo is iodine (I), bromine (Br), fluorine (F), or chlorine (Cl) and hetero is N, O, or S D is a therapeutic agent; Each occurrence of R is independently hydrogen, a suitable protecting group, an acyl moiety, arylalkyl moiety, aliphatic moiety, aryl moiety, heteroaryl moiety, or heteroaliphatic moiety; and n is 1, 2, 3, or 4. V is selected from O and S; W is selected from a bivalent, straight or branched, saturated or unsaturated, optionally substituted C1-30 hydrocarbon chain wherein one or more methylene units are optionally and independently replaced by -O-, -S-, -N(R)-, -C(O)-, C(O)O-, OC(O)-, -N(R)C(O)-, - C(O)N(R)-, -S(O)-, -S(O) 2 -, -N(R)SO 2 -, SO 2 N(R)-, a heterocyclic group, an aryl group, or a heteroaryl group; X is selected from a covalent bond; a carbon atom; a heteroatom; an optionally substituted group selected from the group consisting of acyl, aliphatic, heteroaliphatic, aryl, heteroaryl, and heterocyclic; or nucleoside; Y is selected from a covalent bond or a bivalent, straight or branched, saturated or unsaturated, optionally substituted C1-30 hydrocarbon chain wherein one or more methylene units are optionally and independently replaced by -O-, -S-, -N(R)-, -C(O)-, C(O)O-, OC(O)-, - N(R)C(O)-, -C(O)N(R)-, -S(O)-, -S(O) 2 -, -N(R)SO 2 -, SO 2 N(R)-, a heterocyclic group, an aryl group, or a heteroaryl group; Z is a reactive functional group selected from the group consisting of N-hydroxysuccinimidyl ester, para-nitrophenyl carbonate, para-nitrophenyl carbamate, azide, hydrazine, pentafluorophenyl, haloacetamide, maleimide, hydroxylamine, strained cycloalkyne, and heterocycloalkyne, alkyne, diene, azadiene, and heterocyclic azadiene, wherein halo is iodine (I), bromine (Br), fluorine (F), or chlorine (Cl) and hetero is N, O, or S D is a therapeutic agent; Each occurrence of R is independently hydrogen, a suitable protecting group, an acyl moiety, arylalkyl moiety, aliphatic moiety, aryl moiety, heteroaryl moiety, or heteroaliphatic moiety; and n is 1, 2, 3, or 4. <EOS>