Patent ID: 8080582

Claim:
A compound of formula (I) or a salt thereof wherein R 1 is C 1 -C 6 alkyl, phenyl, benzyl, or a hydroxyl protecting group each of Z 1 and Z 2 is independently H or C═C—CO—NR 2 R 3 optionally substituted with C 1 -C 6 alkyl on the vinyl group with the proviso that one of Z 1 and Z 2 is H, and Z 1 and Z 2 are not H at the same time; R 2 is H, R 3 is or R 2 and R 3 together form an optionally substituted 5-7 membered monocyclic ring or an optionally substituted 8-12 membered bicyclic ring; R 4 is C 1 -C 6 alkyl, allyl, phenyl, or benzyl; and R 5 is C 1 -C 6 alkyl, mercaptomethyl, 1-H-imidazol-4-ylmethyl, methylthioethyl, pyrrolidinyl, hydroxylmethyl, hydroxylethyl, or methylbenzyl unsubstituted or substituted with 1-3 hydroxyl, methoxy or ethoxy.