Patent ID: 7605152

Claim:
A compound of structural formula II: or a pharmaceutically acceptable salt thereof wherein “a” represents a single bond or a double bond; R 1 is hydrogen, hydroxymethyl, or C 1-3 alkyl, wherein alkyl is unsubstituted or substituted with one to seven fluorine atoms; R 2 is hydrogen, fluorine, or C 1-4 alkyl when “a” represents a double bond; or two R 2 substituents are each independently hydrogen, fluorine, or C 1-4 alkyl when “a” represents a single bond; R 4 is hydrogen, C 1-4 alkyl, C 2-4 alkenyl, or C 2-4 alkynyl; one of R 5 and R 6 is hydrogen and the other is arylmethyl, wherein aryl is selected from the group consisting of phenyl, naphthyl, pyridyl, furanyl, pyrrolyl, thiazolyl, imidazolyl, benzofuranyl, and 1,3-benzodioxolyl, wherein the aryl group is unsubstituted or substituted with one to two groups independently selected from halogen, C 1-4 alkyl, C 1-4 alkoxy, cyano, trifluoromethyl, and trifluoromethoxy.