Patent ID: 7632970

Claim:
A compound represented by the formula (I): wherein X is a sulfur atom; C* and C** are each independently an asymmetric carbon; R 1 and R 2 are the same or different and each is methyl, ethyl or isopropyl, or form isoindoline together with the nitrogen atom they are bonded to; R3 is a lower alkyl group optionally having substituent(s), an aralkyl group optionally having substituent(s), an aryl group optionally having substituent(s) or a heteroaryl group optionally having substituent(s); R 4 and R 5 are the same or different and each is a lower alkyl group optionally having substituent(s), an aralkyl group optionally having substituent(s) or an aryl group optionally having substituent(s), or R 4 and R 5 form, together with the asymmetric carbons they are respectively bonded to, a homocyclic ring optionally having substituent(s) or a heterocycle optionally having substituent(s); and R 6 and R 7 are the same or different and each is a hydrogen atom or a lower alkyl group optionally having substituent(s), or a salt thereof.