N-Methylene-bis-l(+)-pyrrolidone carboxylic acid m.p. 287°, [α]D21=+85.73°, was obtained by the application of methylal and 2N HCl on l(+)-glutamic acid. Diethyl ester of the former has m.p. 117°, [α]D20=+55.64°. The principle of the formation of this stable acid was utilized in the detection of l(+)-glutamic acid mixed in rac-glutamic acid.
