Enantioselective synthesis of D‐selenomethionine with D‐amino acid aminotransferase

Selenium is an essential micronutrient for mammals, birds, fish, and several bacteria.] Several mammalian and bacterial enzymes have been demonstrated to contain selenocysteine residues in their polypeptide chains; these selenocysteine residues play an integral role in the catalysis.' Selenomethionine residues also occur in several proteins such as bacterial thiola~e.~ Various artificial peptides containing D-amino acids have been synthesized and shown to be not only physiologically active but also stable toward proteolytic d e g r a d a t i ~n . ~ Although no peptides containing D-selenocysteine have been synthesized, they are expected to show interesting physiological activities. However, the chemical synthesis of selenium amino acids, in particular synthesis of the optically active compound, is not yet available. We here show the enantiomer synthesis of D-selenomethionine from its a-keto analogue, a-keto-ymethylselenobutyrate by means of D-amino acid aminotransferase (EC 2.6.1.21).