The reaction of carbonyl cyanide phenylhydrazones with thiols

Carbonyl cyanide phenylhydrazone and its ring-substituted analogs react with thiols (thioglycolic acid, 2-mercaptoethanol, dithiothreitol) and amino-thiols (cysteine, glutathione) to give corresponding N-(substituted phynyl)-N′-(alkythiodicyano)-methylhydrazine derivatives. These addition products decompose to the original components in alkaline solution. On the other hand, in the presence of an excess of thiols in aqueous buffered systems the addition reactions are practically quantitative with respect to phenylhydrazones, follow pseudo-first-order kinetics and can be investigated spectrophotometrically. These reactions are of the bimolecular Ad_N type where the non-dissociated form of carbonyl cyanide phenylhydrazones function as an electrophilic component, while the RS^? ion plays the role of nucleophilic component in the case of thiols (the attack of the azomethine group).The reactivity of carbonyl cyanide phenylhydrazones with respect to thiols increases in the order carbonyl cyanide phenylhydrazone < carbonyl cyanide m-chlorophenylhydrazone < carbonyl cyanide p-trifluoromethoxyphenylhydrazone which corresponds to the order of decreasing values of the pK_a constants. On the other hand, the reactivity of thiols increases with their basicity.The reactivity of carbonyl cyanide phynylhydrazone with thiols is comparable with the reactivity of phynyl isothiocyanate and N-ethylmaleimide. It was demostrated that carbonyl cyanide phenylhydrazone is an efficient inhibitor of rabbit muscle glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12).The results obtained are discussed in relation to the biological activity of carbonyl cyanide phenylhydrazones.