DIFFERENTIATION OF 2 GEOMETRIC ISOMERS OF THE PHARMACEUTICAL EPROSARTAN USING ATMOSPHERIC-PRESSURE CHEMICAL-IONIZATION

The utility of an atmospheric pressure chemical ionization interface f or distinguishing stereoisomers has been demonstrated. Two geometrical isomers of the pharmaceutical eprosartan )-1H-imidazole-5-yl]-2-[2-th ienyl)methyl]propenoic acid) were investigated in the positive- and ne gative-ion modes with in-source collision-induced dissociation (CID). In positive-ion mode, CID spectra display significant differences betw een the two isomers. Under identical collisional conditions several fr agment ions present in the CID spectrum of the E isomer (SK&F 108566) are significantly suppressed in the spectrum of the Z isomer (SB 20632 8). Analysis of the fragmentation patterns of both isomers indicates t hat a pathway initiated by the loss of neutral thiophene from the E is omer is inhibited in the CID spectra of the Z isomer. In negative-ion mode, fragmentation and corresponding differences in spectra are not o bserved. Fragmentation is observed to result primarily from the ioniza tion process. (C) 1997 by John Wiley & Sons, Ltd.