Compositions containing, methods involving, and uses of non-natural amino acids and polypeptides

A modified antibody or antibody fragment comprising at least one compound, or salt thereof, of Formula (XI):

• wherein:
• A is arylene, or substituted arylene;
• B is a bond;
• R is alkyl;
• R1 is H, an amino protecting group, or at least one amino acid of the antibody or the antibody fragment;
• and
• R2 is OH, an ester protecting group, or at least one amino acid of the antibody or the antibody fragment;
• each of R3 and R4 is independently H, halogen, lower alkyl, or substituted lower alkyl, or R3 and R4 or two R3 groups optionally form a cycloalkyl or a heterocycloalkyl;
• R5 is L-X, where
• X is an anti-tumor agent;
• and
• L is optional, and when present is a linker selected from the group consisting of alkylene, substituted alkylene, alkenylene, substituted alkenylene, —O—, —O-(alkylene or substituted alkylene)-, —S—, —S-(alkylene or substituted alkylene)-, —S(O)k— where k is 1, 2, or 3, —S(O)k(alkylene or substituted alkylene)- where k is 1, 2, or 3, —C(O)-, —C(O)-(alkylene or substituted alkylene)-, —C(S)—, —C(S)-(alkylene or substituted alkylene)-, —N(R′)—, —NR′-(alkylene or substituted alkylene)-, —C(O)N(R′)—, —CON(R′)-(alkylene or substituted alkylene)-, —CSN(R′)—, —CSN(R′)-(alkylene or substituted alkylene)-, —N(R′)CO-(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— where k is 1, 2, or 3, -(alkylene or substituted alkylene)-S—S—, —S(O)kN(R′)— where k is 1, 2, or 3, —N(R′)C(O)N(R′)—, —N(R′)C(S)N(R′)—, —N(R′)S(O)kN(R′)— where k is 1, 2, or 3, —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′)—, where each R′ is independently H, alkyl, or substituted alkyl;
• wherein at least one compound of Formula (XI) is incorporated into the modified antibody or antibody fragment.