Synthesis and Structure Reassignment of Malylglutamate, a Recently Discovered Earthworm Metabolite

Malylglutamate, a newly identified metabolite in earthworms, was synthesized using a traditional peptide coupling approach for assembling the amide from protected malate and glutamate precursors. The proposed structure (1) and a diastereomer were synthesized, but their NMR spectra did not match the natural sample. Further analysis of the natural sample using HMBC spectroscopy suggested an alternative attachment of the malyl moiety, and β-malylglutamate (2) diastereomers were synthesized, L,L-2 and D,D-2. NMR spectra were an excellent match with the natural sample, and chiral-phase chromatography was employed to identify (−)-β-l-malyl-l-glutamate (2) as the isomer native to Eisenia fetida.