L-Cysteine,a Versatile Source of Sulfenic Acids.Synthesis of Enantiopure Alliin Analogues

摘要

L-Cystcinc is a stimulating starting product for the generation of transient sulfenic acids,such as 4,6,9,and 15,which add to suitable acceptors,allowing formation of sulfoxides showing a biologically active residue.These sulfoxides are easily isolated in enantiomerically pure form.For instance,N-(tert-butoxycarbonyl)-L-cysteine methyl ester (la) furnished in few steps sulfenic acid 9a,which was readily converted into (R,S_s)-(2-tert-butoxycarbonylamino-2-methoxycarbonyl-ethylsulfinyl)ethene (22).the methyl ester of Boc-protected nor-alliin.Moreover,the addition of 9a to 2-methyl-l-buten-3-yne has led to a sulfur epimeric and separable mixture of (R)-2-12-tert-butoxycarbonylamino-2-methoxycarbonyl-ethylsulfinyl)-3-methyl-buta-1,3-dienes 10a and 11a,still possessing a "masked'' sulfenic acid function,producible from their cysteine moieties once the dienes have been converted into the desired derivatives.