Patent ID: 8236983

Claim:
A compound of the formula: wherein R 1 is H, Boc, Boc-Gly, a substituted or unsubstituted lower alkylcarbonyl group, or a substituted or unsubstituted arylalkyl group, R 2 is H, a substituted or unsubstituted lower alkyl group, a substituted or unsubstituted benzyl group, or a substituted or unsubstituted arylalkyl group, R 3 is a H, a substituted or unsubstituted lower alkyl group, a substituted or unsubstituted benzyl group, or a substituted or unsubstituted arylalkyl group, R 4 is a H, a substituted or unsubstituted alkyl group, a substituted or unsubstituted benzyl group, or a substituted or unsubstituted arylalkyl group, and R 5 is a H, a substituted or unsubstituted alkyl group, a substituted or unsubstituted benzyl group, a substituted or unsubstituted arylalkyl group, or CH 2 CH═CH 2 .