Asymmetric synthesis of [2,3-C-13(2), N-15]-4-benzyloxy-5,6-diphenyl-2,3,5,6-tetrahydro-4H-oxazine-2-one via lipase TL-mediated kinetic resolution ofbenzoin: General procedure for the synthesis of [2,3-C-13(2),N-15]-L-alanine

Lipase TL-mediated kinetic resolution of benzoin proceeded to give the corr esponding optically pure (R)-benzoin (R)-1. On the other hand, (S)-benzoin O-acetate (S)-7 could be hydrolyzed without epimerization to give (S)-benzo in (S)-1 under alkaline conditions. Furthermore, both enantiomers of benzoi n (1) were converted to [N-15]-(1R,2S)- and (1S,2R)- 2-amino-1,2-diphenylet hanol (3a and 3b), respectively, according to the procedure reported previo usly. [2,3-C-13(2),N-15]-(5S,6R)-4-benzyloxy5,6-diphenyl-2,3,5,6-tetrahydro -4H-oxazine-2-one (10) was synthesized from ethyl [1,2-C-13(2)]-bromoacetat e and (1R,2S)-2-amino-1,2-diphenylethanol (3b) in three steps. Finally, [2, 3-C-13(2), 15N]-L-alanine (12) was prepared via alkylation of the lactone 1 0 and hydrogenation of the alkylated product 11.