Patent ID: 7919508

Claim:
A compound of formula I: wherein R 1 is selected from the group consisting of phenylcarbamoylC 1-6 alkyl, naphthylcarbamoylC 1-6 alkyl, naphthylC 1-6 alkyl, C 3-6 cycloalkylC 1-6 alkyl, phenylC 1-6 alkenyl, α-carboxybenzyl, hydroxyC 1-6 alkyl, phenoxyphenylC 1-6 alkyl, and phenylureaC 1-6 alkyl, wherein benzyl and phenyl are optionally substituted with one or two substituents each independently selected from the group consisting of C 1-6 alkyl, C 1-6 perfluoroalkyl, halogen, hydroxy, C 1 -C 6 alkoxy and nitro; R 2 and R 3 are independently selected from the group consisting of hydrogen, C 1-6 alkyl, formyl, C 2-6 alkenyl, and C 3-6 cycloalkylC 1-6 alkyl, or R 2 and R 3 taken together with the nitrogen atom to which they are attached form a ring of from 2-5 carbon atoms; R 4 is selected from the group consisting of hydrogen and C 1-4 alkyl; X is C 1-6 alkyl; and n is 1; or a stereoisomer or a pharmaceutically acceptable salt thereof.