Patent ID: 8153758

Claim:
A compound or salt thereof having the structure: wherein each R a is independently selected from the group consisting of H, halogen, alkyl, —NO 2 , —CN, substituted alkyl, —N(R′) 2 , —C(O) k R′, —C(O)N(R′) 2 , —OR′, and —S(O) k R′, where k is 1, 2, or 3; R 1 is H, an amino protecting group, or at least one amino acid; and R 2 is OH, an ester protecting group, or at least one amino acid; each of R 3 and R 4 is independently H; M is —CH 2 R 5 ; R 5 is polyalkylene oxide, substituted polyalkylene oxide; or R 5 is L-X, where, X is polyalkylene oxide or substituted polyalkylene oxide; and L is a linker selected from the group consisting of alkylene, substituted alkylene, alkenylene, substituted alkenylene, —O—, —O-(alkylene or substituted alkylene)-, -(alkylene or substituted alkylene)-O—, —C(O)—, —C(O)-(alkylene or substituted alkylene)-, -(alkylene or substituted alkylene)-C(O)—, —C(O)N(R′)—, —C(O)N(R′)-(alkylene or substituted alkylene)-, -(alkylene or substituted alkylene)-C(O)N(R′), —OC(O)N(R′)—, —OC(O)N(R′)-(alkylene or substituted alkylene)-, -(alkylene or substituted alkylene)-OC(O)N(R′)—, —N(R′)C(O)—, —NR′C(O)-(alkylene or substituted alkylene)-, -(alkylene or substituted alkylene)-NR′C(O)—, —S—, —S-(alkylene or substituted alkylene)-, —S(O) k — where k is 1, 2, or 3, —S(O) k (alkylene or substituted alkylene)-, —C(S)—, —C(S)-(alkylene or substituted alkylene)-, —CSN(R′)—, —CSN(R′)-(alkylene or substituted alkylene)-, —N(R′)C(O)O—, -(alkylene or substituted alkylene)-O—N═CR′—, -(alkylene or substituted alkylene)-C(O)NR′-(alkylene or substituted alkylene)-, -(alkylene or substituted alkylene)-S(O) k -(alkylene or substituted alkylene)-S—, -(alkylene or substituted alkylene)-S—S—, —S(O) k N(R′)—, —N(R′)C(O)N(R′)—, —N(R′)C(S)N(R′)—, —N(R′)S(O) k N(R′)—, —N(R′)—N═, —C(R′)═N—, —C(R′)═N—N(R′)—, —C(R′)═N—N═, —C(R′) 2 —N═N—, and —C(R′) 2 —N(R′)—N(R′)—; each R′ is independently H, alkyl, or substituted alkyl; with a proviso that when R 1 is H then R 2 is not OH, or when R 2 is OH then R 1 is not H; and G is an amine protecting group.