Preparatin of 5-methyl-1,4-thiazan-3-carboxylic acid

PURPOSE: To prepare the title compound useful as a synthetic intermediate of cycloalliin which is a remedy for thrombogenesis and arteriosclerosis, easily, in a short step, in high yield, by reacting cysteine with a monohalo-acetone, and reducing the product. CONSTITUTION: Cysteine is reacted with a monohalo-acetone of formula (X is halogen) in a solvent such as water, in the presence of an lakali metal hydroxide to afford 5-methyl-2,3-dihydro-6H-1,4-thiazin-3-carboxylic acid. The product is, without separating from the reaction mixture, reduced pref. with soldium borohydride to obtain 5-methyl-1,4-thiazin-3-carboxylic acid (C=N double bond of the starting compound is reduced to C-N single bond). The carboxylic acid thus obtained is easily oxidized with sodium periodate to afford cycloalliin. COPYRIGHT: (C)1980,JPO&Japio