Syntheses of optically pure beta-hydroxyaspartate derivatives as glutamate transporter blockers.

DL-threo-beta-benzyloxyaspartate (DL-TBOA) is a non-transportable blocker of the glutamate transporters that serves as an indispensable tool for the investigation of the physiological roles of the transporters. To examine the precise interaction between a blocker and the transporters, we synthesized the optically pure isomers (L- and D-TBOA) and its erythro-isomers. L-TBOA is the most potent blocker for the human excitatory amino acid transporters (EAAT1-3), while D-TBOA revealed a difference in the pharmacophores between EAAT1 and EAAT3. We also synthesized the substituent variants (methyl or naphthylmethyl derivatives) of L-TBOA. The results obtained here suggest that bulky substituents are crucial for non-transportable blockers.