Patent ID: 8318716

Claim:
A compound of formula (I): or a pharmaceutically acceptable salt, ester, and/or prodrug thereof; wherein R 1 is hydrogen or a carboxyl protecting group; R 2 is hydrogen or an amino-protecting group; R 3 is hydrogen or lower alkyl; and R 4 is phenyl or substituted phenyl; wherein the substituted phenyl comprises one or more substituents selected from the group consisting of halogen; hydroxyl; carboxyl; amino; nitro; cyano; lower alkyl; substituted lower alkyl; lower alkoxy; substituted lower alkoxy; aminosulfonyl; lower alkylaminosulfonyl; and a combination thereof; wherein the substituted lower alkyl and the substituted lower alkoxy each independently comprise one or more substituents selected from the group consisting of halogen; hydroxyl; carboxyl; amino; nitro; cyano; and a combination thereof.