Patent ID: 8487132

Claim:
A compound of formula (I), an optical isomer or a pharmaceutically acceptable salts thereof, wherein, chiral center (*) can be R or S or RS (racemic mixture); R1 is aryloyl represented by wherein R8 and R9 are independently selected from hydrogen, saturated alkyl having 1-6 carbon atoms, or alkoxyl having 1-6 carbon atoms, unsaturated alkyl having 2-6 carbon atoms, OH, Cl, F, CN, carboxyl and ester group having 1-6 carbon atoms; R2 is hydrogen, or aryloyl having 7-20 carbon atoms; and R3 and R4 are independently hydrogen, saturated alkyl having 1-20 carbon atoms, unsaturated alkyl having 2-20 carbon atoms, aryl having 6-20 carbon atoms with substituent having 1-10 carbon atoms, substituted or unsubstituted phenyl or benzyl; cycloalkyl having 4-10 carbon atoms, hydroxyalkyl, carbohydrate having 1-10 carbon atoms, or C1-C10 alkyl containing one or more heteroatoms selected from oxygen, nitrogen, fluorine, sulfur, and phosphor.