Patent ID: 7879979

Claim:
A compound or salt thereof, said compound having the structure: wherein: R 1 is —H or a conjugating group having the structure R 2 is —OH or a conjugating group having the structure X is an optionally present C 1-4 unsubstituted alkylene; Y is an optionally substituted C 1-4 alkylene or N(H)—C 1-6 alkylene, and is optionally present; and Z is a 5- or 6-member cyclic thiolactone, an optionally substituted C 1-4 thiol-substituted alkyl, or an optionally substituted thioester having the structure R 3 is selected from the group consisting of optionally substituted C 1-4 alkyl, optionally substituted C 1-4 alkoxy, and optionally substituted aryl; said substitution(s), when present, are independently selected from the group consisting of C 1-6 alkyl straight or branched chain, benzyl, halogen, trihalomethyl, C 1-6 alkoxy, —NO 2 , —NH 2 , —OH, ═O, —COOR′ where R′ is H or lower alkyl, —CH 2 OH, and —CONH 2 ; and one but not both of R 1 or R 2 is a conjugating group.