Z-VAL-TYR METHYL ESTER Z-VAL-TYR-OME Z-L-VALYL-L-TYROSINE METHYL ESTER N-BENZYLOXYCARBONYL-L-VALYL-L-TYROSINE METHYL ESTER N-CBZ-VAL-TYR METHYL ESTER methyl N-benzyloxycarbonyl-L-valyl-L-tyrosinate Z-Val-try methyl ester Cbz-Val-trymethylester