SYNTHESIS AND NMR-STUDIES OF N-SUBSTITUTED DERIVATIVES OF KAINIC ACID DIMETHYL ESTERS

Dimethyl kainate derivatives incorporating the amino protecting groups, 9-fluorenylmethoxycarbonyl (Fmoc), tert-butoxycarbonyl (Boc) and triphenylmethyl (trityl, Trt), have been synthesized from (-)-alpha-kainic acid [(2S,3S,4S)-2-carboxy-4-(1-methylethenyl)-3-pyrrolidinylacetic acid] by means of N-protection followed by esterification with methanol in the presence of triphenylphosphine and diethyl azodicarboxylate. Coupling of N-Fmoc protected 4-methylaminobenzoyl chloride with dimethyl kainate followed by N-deprotection with piperidine provided dimethyl 1-(4-methylaminobenzoyl)kainate. The H-1 and C-13 NMR spectra of two of the compounds reveal the presence of two conformers due to restricted rotation around the amide bond. The H-1 and C-13 assignments of the four compounds were carried out by one- and two-dimensional NMR techniques.