A chemoenzymatic method to prepare gram‐scale Allium organosulfur compounds and their presumptive metabolic products, and associated biological activities

Abstract

The health benefits of Allium vegetables are widely attributed to the organosulfur compounds called thiosulfinates (TS) and related species. The lack of suitable methods to prepare TS in adequate yield has hampered the evaluation of their biological activity and therapeutic effect. We describe a simple enzymatic method using Allium tissue homogenates as a reaction system to prepare gram‐scale TS, including those enriched in 1‐propenyl groups which are particularly difficult to obtain. The cysteine and glutathione mixed disulfide conjugates of TS (CySSR/GSSR, R = methyl, ethyl, propyl, 1‐propenyl, allyl) were also prepared as they are likely in vivo metabolic products of TS. The respective cancer chemoprotective and anti‐inflammatory activities of TS and CySSR/GSSR were evaluated using quinone reductase (QR, phase II enzymes biomarker) induction, and inhibition of nitric oxide (NO) evolution in cellular assays. All TS and CySSR/GSSR species induced QR activity in Hepa 1c1c7 cells and inhibited NO evolution in LPS‐stimulated macrophages. Among the conjugates, the 1‐propenyl species (CySSPe and GSSPe) representative of onion exhibited the biological activities as or more potent than the 2‐propenyl (allyl) derivatives (CySSA and GSSA) representative of garlic, indicating the potential for these components as dietary vehicles for promoting health. Supported by USDA‐NRI‐CGP.