Patent ID: 6908942

Claim:
A compound chosen from the following formula (5) and optical isomers thereof: wherein R 1 represents a C 1 -C 10 alkyl, allyl, benzyl or substituted benzyl, or phenethyl group; R 2 represents a C 1 -C 10 alkyl, benzyl or substituted benzyl, or phenethyl group; R 3 represents a C 1 -C 10 alkyl group, a C 2 -C 10 alkenyl group, a C 2 -C 10 alkynyl, benzyl or substituted benzyl, naphthylmethyl groups, or —C(O)R 4 ; R 4 represents phenyl or substituted phenyl groups or five-or seven-membered heterocyclic ring containing a heteroatom selected from the group consisting of oxygen and sulfur; and said substituted phenyl or said substituted benzyl group may be substituted with 1-4 substituents selected from the group consisting of a halogen atom, a nitro group, a C 1 -C 10 alkyl group, a C 1 -C 10 alkoxy group and a C 1 -C 10 haloalkyl group.