Racemization of amino acid esters by aromatic aldehydes in basic non-aqueous solvents

Synthesis of L-phenylalanine methyl ester

“…Reaction 6. Conventional means of racemization of optically active amino acids and their esters involve the use of aromatic aldehydes or ketones and particularly salicylaldehyde or pyridoxal with or without heating, fatty acids (Beecham Group, 1987; Yamada et al, 1983), strong acids such as sulfuric (Bethge et al, 1983;Takahashi and Toi, 1979a,b), metal ions (Kaneko et al, 1974), strong bases such as sodium alkoxides (Belokon et al, 1978;Takahashi and Toi, 1979a,b), or tertiary amines (Siemion and Wilschowitz, 1971;Pugniere et al, 1985;Yamskov et al, 1982). All involve reagents that have to be neutralized and/or removed after racemization because of eventual contamination of the L-phenylalanine and perhaps inhibition or destruction of the enzyme.…”

“…All involve reagents that have to be neutralized and/or removed after racemization because of eventual contamination of the L-phenylalanine and perhaps inhibition or destruction of the enzyme. Supported or resinous aromatic aldehydes including pyridoxal have also been used (Kaneko et al, 1974;Pugniere et al, 1985;Yamskov et al, 1979). The presence of an hydroxy or at least an oxygen ortho to the aldehyde group appears to be beneficial for racemization activity.…”