Relative reactivities of sulfhydryl groups with N-acetyl dehydroalanine and N-acetyl dehydroalanine methyl ester

The reaction rates in aqueous solutions of aminothiols, thiols, and other compounds with N-acetyl dehydroalanine and its methyl ester (2-acetamindoacrylic acid and methyl 2-acetamidoacrylate) were studied as a function of the structure of the thiol compound in aqueous solutions. Correction of the observed second-order rate constants to identical thiol anion concentration gave a series of computed rate constants whose logarithms showed a linear dependence on the pK's of the thiol group in similar steric environments. Comparison of the addition rates of penicillamine to N-acetyl dehydroalanine and its methyl ester showed the methyl ester to react approximately 11,400 times faster than the acid. Addition rates for thiol acids and aromatic and heterocyclic thiols were also compared; each showed sluggish reactivity with dehydroalanine, but each reacted readily with methyl dehydroalanine. The kinetic data were applied in developing a method for preparing lanthionine in high yield.