Patent ID: 7223795

Claim:
A compound of formula I wherein a and c are single bonds, b is a double bond, and R 1 is H, R 2 is wherein X is straight or branched chain C 1-6 alkyl, —(CH 2 ) n Ar, C 1-6 cycloalkyl, or —(CH 2 ) n R″, where R″ is a cyclic hydrocarbyl group; Y is a natural or unnatural amino acid side chain; and Z 1 and Z 2 are each independently H, straight or branched chain C 1-6 alkyl, straight or branched chain C 1-6 alkenyl, —(CH 2 ) n Ar, —(CH 2 ) n —CO 2 R′, —(CH 2 ) p —CH═CH—(CH 2 ) q Ar where p and q are each independently 0 to 5, R′ is C 1-6 alkyl; and each n may be the same or different and is from 1 to 5.