Patent ID: 8557781

Claim:
A compound or salt thereof selected from the group consisting of: 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; M is H or —CH 2 R 5 ; or the M-N—C(R 5 ) moiety forms a 4 to 7 membered ring structure; R 1 is H, an amino protecting group, or at least one amino acid without an amino protecting group; R 2 is OH, an ester protecting group, or at least one amino acid without an ester protecting group; wherein at least one of R 1 and R 2 is at least one amino acid; R 5 is alkyl, substituted alkyl, polyalkylene oxide, substituted polyalkylene oxide, aryl, heteroaryl, -(alkylene)-(aryl), -(alkenylene)-(aryl); 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, alkenylene, —O—, —O-(alkylene)-, -(alkylene)-O—, —C(O) —, —C(O)-(alkylene)-, -(alkylene)-C(O)—, —C(O)N(R′)—, —C(O)N(R′)-(alkylene)-, -(alkylene)-C(O)N(R′), —OC(O)N(R′)—, —OC(O)N(R′)-(alkylene)-, -(alkylene)-OC(O)N(R′)—, —N(R′)C(O)—, —NR′C(O)-(alkylene)-, -(alkylene)-NR′C(O)—, —S—, —S—(alkylene)-, —S(O) k — where k is 1, 2, or 3, —S(O) k (alkylene)-, —C(S)—, —C(S)-(alkylene)-, —CSN(R′)—, —CSN(R′)-(alkylene)-, —N(R′)CO-(alkylene)-, —N(R′)C(O)O—, -(alkylene)-O—N═CR′—, -(alkylene)-C(O)NR′-(alkylene)-, -(alkylene)-S(O) k -(alkylene or substituted alkylene)-S—, -(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′)—; and each R′ is independently H, alkyl, or substituted alkyl.