Effects of thiol compounds on the formation of nitriles from glucosinolates.

Abstract

The effects of L-cysteine, reduced glutathione, dithiothreitol, cysteamine, thiobenzoate, thiomalate, and thiophenol on the enzymatic degradation of sinigrin were investigated in combination with ferrous ion at different pHs (5.0-7.5). Formation of allyl isothiocyanate was greatly inhibited by addition of both the thiol compounds and ferrous ion to the reaction medium at pH 5.0 or 6.5. Combined effects of the thiol compounds and ferrous ion on the formation of volatile products was also studied by gas chromatography using a mixture of allyl, 3-butenyl, and 4-pentenyl glucosinolates (1:4:1) as substrate. It was confirmed that the greater part of the volatile components produced in the presence of both the thiol compounds and ferrous ion was allyl, 3-butenyl, and 4-pentenyl cyanides and their corresponding cyanoepithioalkanes, even though the reaction medium was adjusted to pH 6.5. Similar results were obtained when silver sinigrate, an analogous model compound to the aglucon of sinigrin, was degraded by the addition of sodium chloride in the presence of both the thiol compounds and ferrous ion. The results suggest that in combination with ferrous ion, such common thiol compounds as L-cysteine and glutathione may be concerned in the production of nitriles from glucosinolates in natural systems, and that the acceleration of nitrile formation is probably attributed to much more rapid desulfuration than the progress of Lessen rearrangement of aglucon.