Patent ID: 8173817

Claim:
A substantially pure compound of formula VIa to VId: wherein R is X is and R 1 -R 4 are the same or different and selected from hydrogen, alkyl, alkoxy, halogen, halo-alkoxy, alkylcarbonyl, alkoxycarbonyl, trifluroalkyl; wherein R 5 and R 7 are same or different and selected from hydrogen, alkyl, alkylthio, alkoxy optionally substituted by fluorine, alkoxyalkoxy, dialkylamino, halogen, phenylalkyl and phenylalkoxy; R 6 is selected from hydrogen, alkyl, alkylthio, alkoxy optionally substituted by fluorine, alkoxyalkoxy, dialkylamino, halogen, nitro, phenylalkyl and phenylalkoxy; R 8 is hydrogen or forms an alkylene chain together with R 7 ; R C —Z— is selected from (S) or (R)-camphor sulfonyl, (S)- or (R)-glycidylsulfonyl-, D- or L-mandeloyl, a stereo isomeric 1-(ethoxycarbonyl)-3-phenylpropylalanyl, (D) or (L)-phenyl alanyl and (D) or (L)-alanyl; with the proviso that at least one of R 1 to R 4 is different from any of the rest of them provided if R 1 and R 4 are same, R 2 and R 3 are different; or if R 2 and R 3 are same, R 1 and R 4 are different.