Oka fragmentation of the Breslow intermediate is a radical process.

by McIntosh, Matt

During investigations into thiamine catalyzed benzoin condensations of benzaldehydes in methanol at reflux, Oka et al reported in 1970 that the thiamine catalyst fragmented into thiazole and pyrimidine moieties, thus destroying the catalyst. In 1993, Kluger et al obsd. the same fragmentation occurred in aq. soln. at 40 °C. He proposed that the Breslow intermediate is the species that undergoes the fragmentation, and that it occurs via an ionic process. We will present evidence that the fragmentation is a radical process, and we will provide a detailed stereoelectronic argument as to why the Breslow intermediate is stable in the enzyme active site and unstable in soln.