Sulphinamoylacetates as sulphine precursors. Mechanism of basic hydrolysis and scheme of irreversible inactivation of cinnamoyl alcohol dehydrogenase, an enzyme of the lignification process

Abstract

t-Butyl N-arylsulphinamoylacetates are hydrolysed in aqueous basic media by an elimination mechanism. It takes place on the conjugate base of the substrate resulting from a fast deprotonation of the activated methylene group. This elimination is first order (E1 cB) for compounds where strong electron-withdrawing groups substitute the aromatic ring. For substitution by weaker electron-withdrawing or -donating groups, the elimination is second order, and needs the presence of general acid catalysis. For t-butyl N-(2-hydroxyphenyl)sulphinamoylisobutyrate where this mechanism of elimination is impossible, a B_Ac2 attack by hydroxide ion at the sulphur atom takes place. From these mechanisms and the results of complexation of zinc(II) cations by sulphinamoylacetates, a possible scheme for the irreversible inactivation of the title zinc metalloenzyme is proposed.