In order to know the mechanism for the alkylation of mercaptans and for the inhibition of "SH-enzymes" with saligenin cyclic phosphorus esters, a possible intermediate, that is a ring-opened salicyl ester, and related compounds including saligenin cyclic hydrogen phosphate were synthesized and their reactions with cysteine and yeast alcohol dehydrogenase were investigated. Besides neutral saligenin cyclic esters, only salicyl ester was active as alkylating agent and SH-enzyme inhibitor.