Chemoenzymatic synthesis and pharmacological characterization of functionalized aspartate analogues as novel excitatory amino acid transporter inhibitors

Aspartate (Asp) derivatives are privileged compounds for investigating the roles governed by excitatory amino acid transporters (EAATs) in glutamatergic neurotransmission. Here, we report the synthesis of various Asp derivatives with (cyclo)alkyloxy and (hetero)aryloxy substituents at C-3. Their pharmacological properties were characterized at the EAAT1-4 subtypes. The L-threo-3-substituted Asp derivatives 13a-e and 13g-k were non-substrate inhibitors, exhibiting pan activity at EAAT1-4 with IC50 values ranging from 0.49 to 15 μM. Comparisons between (DL-threo)-19a-c and (DL-erythro)-19a-c Asp analogues confirmed that the threo configuration is crucial for the EAAT1-4 inhibitory activities. Analogues (3b-e) of L-TFB-TBOA (3a) were shown to be potent EAAT1-4 inhibitors, with IC50 values ranging from 5-530 nM. Hybridization of the nonselective EAAT inhibitor L-TBOA with EAAT2-selective inhibitor WAY-213613 or EAAT3-preferring inhibitor NBI-59159 yielded compounds 8 and 9, respectively, which were non-selective EAAT inhibitors displaying considerably lower IC50 values at EAAT1-4 (11-140 nM) than those displayed by the respective parent molecules.