Each diastereomer was isolated from a mixture (Ic) of (2R, 5R)-2-phenyl-3-oxotetrahydro-2H-1, 4-thiazine-5-carboxylic acid (Ic
1) and (2S, 5R)-2-phenyl-3-oxotetrahydro-2H-1, 4-thiazine-5-carboxylic acid (Ic
2), which was derived from L-cysteine, by using thionyl chloride and their stereostructure was clarified by nuclear magnetic resonance. When each diastereomer (Ic
1, Ic
2) was allowed to react with equivalent sulfuryl chloride, (1S, 4R)-1-phenyl-2-oxa-5-aza-7-thiabicyclo [2.2.2] octa-3, 6-dione (Vc) was respectively obtained. The reaction of methyl (5R)-2-alkyl-3-oxotetrahydro-2H-1, 4-thiazine-5-carbox-ylates (VIa, b) with sulfuryl chloride afforded methyl (5R)-2-alkylidene-3-oxotetrahydro-2H-1, 4-thiazine-5-carboxylate (IXa, b). The reaction of methyl (5R)-2-phenyl-3-oxotetrahydro-2H-1, 4-thiazine-5-carboxylate (VIc) with sulfuryl chloride afforded N, N'-bis (α-oxophenylacetyl) cystine dimethyl ester (XIIIc) and (2R, 5R, 2'S, 5'R)-bis (5-methoxy-carbonyl-2-phenyl-3-oxotetrahydro-2H-1, 4-thiazin-2-yl) ether (XIVc). The plausible mechanism of the reaction was also discussed.
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