A cautionary note on the use of commercial (R)-MTPA-CL and (S)-MTPA-CL in determination of absolute configuration by Mosher ester analysis

While the absolute configuration of a Mosher ester derivative (MTPAOR) is i dentical with that of the Mosher acid (MTPAOH) precursor, it is opposite th at of the Mosher acid chloride (MTPA-Cl). Since (R)-MTPA-Cl and (S)-MIPA-Cl are now commercially available, incorrect conclusions may be drawn in deri ving the absolute configuration, if this fact is overlooked. The absolute c onfiguration of (-)-vasicinone (1) derived by Mosher ester analysis (Tetrah edron Asymmetry, 1996, 7,25) has been revised as 3S. Mosher ester analysis of (-)-vasicine (2) confirmed a 3S configuration for this alkloid.