N-methyl-D-glutamate and N-methyl-L-glutamate in Scapharca broughtonii (Mollusca) and other invertebrates.

The presence of N-methyl-D-glutamate (NMDG) and N-methyl-L-glutamate (NMLG) has been demonstrated in the tissues of Scapharca broughtonii, which are known to contain N-methyl-D-aspartate (NMDA). To our knowledge, this is the first report on the natural occurrence of NMDG and the occurrence of NMLG in eukaryotes. These compounds were identified according to the following findings; (a) their derivatives with (+)- and (-)-l-(9-fluorenyl)ethyl chloroformate (FLEC) showed identical behaviors with those of authentic NMDG and NMLA, respectively, on high-performance liquid chromatography (HPLC), (b) the HPLC peak of NMDG disappeared when the extract, as well as the authentic compound, was treated with D-aspartate oxidase before derivatization, (c) they behaved identically with authentic compounds on thin-layer chromatography and differently from NMDA. Both or either of NMDG and NMLG were also detected in several mollusks and other animals. Concentrations of the enantiomers were comparable in the tissues of S. broughtonii and a few other species.