Patent ID: RE39056

Claim:
A compound of structural formula I: or a pharmaceutically acceptable salt or ester thereof, wherein: R 1 is selected from methyl and ethyl; R 2 is selected from: (a) H, and (b) C 1-6 alkyl; R 3 is heteroaryl, either unsubstituted or substituted with one to three substituents independently selected from: (1) halo (F, Cl, Br, I), (2) C 1-2 alkyl; (3) trifluoromethyl, (4) nitro, (5) hydroxy, (6) cyano, (7) amino, (8) C 1-2 alkyloxy, (9) phenyl, and (10) heteroaryl; and R 4 selected from: (a) C 1-4 alkyl, (b) phenyl, and (c) heteroaryl.