SYNTHESIS AND CHARACTERIZATION OF N-SUBSTITUTED VALINES AND THEIR PHENYL-THIOHYDANTOINS AND PENTAFLUOROPHENYL-THIOHYDANTOINS

The phenylthiohydantoins of racemic N-methyl-, N-(2-hydroxyethyl)- and N-phenyl-valine as well as the pentafluorophenylthiohydantoins of the se acids and Of L-valine have been synthesized by reactions with pheny l isothiocyanate and pentafluorophenyl isothiocyanate, respectively. T he synthesized thiohydantoins and the phenvlthiohydantoin Of L-valine were characterized by melting points, mass spectrometry, UV and H-1 NM R spectroscopy; the fluorinated thiohydantoins were also characterize d by C-13 NMR spectroscopy. Among the N-substituted amino acids, racem ic N-(2-hydroxyethyl)- and N-phenyl-valine, obtained from 2-bromoisova leric acid with ethanolamine and aniline, respectively, were character ized by H-1 NMR spectroscopy and compared with respect to their pK(a2) -values with L-valine and N-methyl-DL-valine.