COCAINE BENZOYL THIOESTER - SYNTHESIS, KINETICS OF BASE HYDROLYSIS, AND APPLICATION TO THE ASSAY OF COCAINE ESTERASES

The synthesis and characterization of diastereomers of cocaine benzoyl thioester is described. Allococaine benzoyl thioester and allopseudoc ocaine benzoyl thioester were synthesized by the conjugate addition of p-methoxytolyl thiol to ecgonine methyl ester followed by debenzylati on and benzoylation. The absolute structure of the hydrochloride salt of the major ecgonine p-methoxytolyl sulfide formed was determined by single-crystal diffraction analysis and used to establish the addition geometry. When placed in aqueous solution, the cocaine benzoyl thioes ter diastereomers hydrolyzed to give thioecgonine methyl ester. The ra te of cocaine benzoyl thioester hydrolysis was carefully investigated spectrophotometrically by using the Ellman reagent. At neutral pH, the hydrolysis of the diastereomers was found to proceed at detectable ra tes. Upon increasing pH, the rate of hydrolysis of cocaine benzoyl thi oester diastereomers was increased and the reaction was catalyzed by b asic buffer species. In addition to defining the kinetics of hydrolysi s in aqueous solution, cocaine benzoyl thioester was utilized as a hig hly efficient method to monitor the activity of cholinesterases and pi g liver esterase. Use of cocaine benzoyl thioester represents a rapid and sensitive way to screen for cocaine esterase activity.