Total synthesis of cystothiazoles A and C.

An efficient pathway culminating in the enantiocontrolled preparation of cystothiazoles A and C has been described. The cystothiazoles demonstrate potent antifungal activity and function as novel inhibitors of mitochondrial oxidation at a specific site on the cytochrome bc(1) complex. These studies outline a general and flexible plan that can be readily adapted for the synthesis of a variety of related five-membered heterocyclic systems and for biological investigations of structure-activity relationships. The core [2,4']bisthiazole component 8 was prepared in six steps, and the use of the Horner-Emmons olefination to yield the alpha,beta-unsaturated ester 10 set the stage for an asymmetric Evans aldol process, which established the required C(4)/C(5) stereochemistry. Finally the cystothiazoles A and C were prepared via a stereocontrolled O-alkylation of the precursor beta-keto esters 22a and 22b.