Patent ID: 7553989

Claim:
A compound represented by formula (1) or a salt thereof: wherein R represents (a) C1-C6 alkylcarbonyloxy C1-C2 alkyl optionally substituted by cyclohexyl, (b) phenylcarbonyloxy C1-C2 alkyl in which the phenyl part is optionally substituted by C1-C4 alkyl, (c) C1-C6 alkoxycarbonyloxy C1-C2 alkyl optionally substituted by cyclohexyl, (d) phenyloxycarbonyloxy C1-C2 alkyl in which the phenyl part is optionally substituted by C1-C4 alkyl, (e) unsubstituted C3-C6 cycloalkyloxycarbonyloxy C1-C2 alkyl, or (f) unsubstituted 2-oxo-5-(C1-C4 alkyl)-1,3-dioxolen-4-ylmethyl.