AN NMR SPECTROSCOPIC INVESTIGATION OF THE OXIDATION REACTIONS OF DL-SELENOMETHIONINE

Oxidation reactions of DL-selenomethionine (DL-SeMet) with hydrogen pe roxide and ozone were investigated by H-1 and C-13 NMR spectroscopy. C hemical shifts of the reaction products were measured at different pD values in D2O solutions. In the moderate (4-8) pD range, a pair of sin glets of equal intensity appeared at 2.71 and 2.80 ppm, with the disap pearance of the DL-SeMet methyl peak at 2.04 ppm. As the pD of the sol ution decreased, the chemical shifts of both peaks increased relative to 3-trimethylsilylpropionic acid-d(4) sodium salt. In strongly acidic solutions (pD < 3), the pair collapsed to one singlet at 3.18 ppm. As pD values increased the chemical shifts decreased in numerical value with only a singlet at 2.69 ppm observed in strongly basic solutions ( pD > 10). These data were assigned to Met selenoxide in basic solution , stabilized by intermolecular hydrogen bonding, and to the hydration of Met selenoxide to Met dihydroxyselenide in acidic solutions. In mod erate pD solutions (pD = 4-8), both forms of the selenoxide can exist. For the reaction of DL-SeMet with CNBr, two parallel reactions occur, i.e. oxidation and bond cleavage with cyanization: the bond cleavage giving the expected products, i.e. 2-amino-4-butyrolactone and methyl selenocyanate, with an additional singlet observed at 2.54 ppm. (C) 19 88 SCI.