Several derivatives of 2-(3-hydroxy-5-hydroxymethyl-2-methylpyridyl-4)-tetrahydro-1,3-thiazine-4-carboxylic acid (PAL-HCySH) and 2-(3-hydroxy-2-methyl-5-phosphoryloxymethyl-pyridyl-4)-tetrahydro-1,3-thiazine-4-carboxylic acid (PAL-P-HCySH), which have potential vitamin B_6 activity, were synthesized. Alkylesters of PAL-HCySH, and PAL-P-HCySH were prepared in 12-70% yield by the reactions of pyridoxal or pyridoxal phosphate with alkyl DL-homocysteinates which were obtained from the ring-cleavage of DL-homocysteine thiolactone-HCl with sodium alcoxides in the corresponding alcohols. The acetylations of methyl 2-(3-hydroxy-5-hydroxymethyl-2-methylpyridyl-4)-tetrahydro-1,3-thiazine-4-carboxylate (PAL-HCySOMe) with acetic anhydride were also investigated. The alcoholic O-acylates (acetate, benzoate, butyrate, and nicotinate) of PAL-HCySH were prepared by the condensation of pyridoxal-5-acylates with DL-homocysteine in high yield. Further, the spectrophotometric studies of the stabilities and dissociations of PAL-HCySOMe, 2-(5-acetoxymethyl-3-hydroxy-2-methylpyridyl-4)-tetrahydro-1,3-thiazine-4-carboxylic acid (PAL-5-Ac-HCySH) and methyl 2-(5-acetoxymethyl-3-hydroxy-2-methylpyridyl-4)-tetrahydro-1,3-thiazine-4-carboxylate (PAL-5-Ac-HCySOMe) were carried out to compare with those of PAL-HCySH.
