Allosteric modulators of the serotonin (5-HT) 5-HT
2C receptor (5-HT
2CR) present a unique drug design strategy to augment the response to endogenous 5-HT in a site- and event-specific manner with great potential as novel central nervous system probes and therapeutics. To date, PNU-69176E is the only reported selective positive allosteric modulator for the 5-HT
2CR. For the first time, an optimized synthetic route to readily access PNU-69176E (
1) and its diastereomer
2 has been established in moderate to good overall yields over 10 steps starting from commercially available picolinic acid. This synthetic approach not only enables a feasible preparation of a sufficient amount of
1 for use as a reference compound for secondary pharmacological studies, but also provides an efficient synthesis of key intermediates to develop novel and simplified 5-HT
2CR allosteric modulators. Compound
1 and its diastereomer
2 were functionally characterized in Chinese hamster ovary (CHO) cells stably transfected with the 5-HT
2CR using an intracellular calcium (Ca
i2+) release assay. Compound
1 demonstrated efficacy and potency as an allosteric modulator for the 5-HT
2CR with no intrinsic agonist activity. Compound
1 did not alter 5-HT-evoked Ca
i2+ in CHO cells stably transfected with the highly homologous 5-HT
2AR. In contrast, the diastereomer
2 did not alter 5-HT-evoked Ca
i2+ release in 5-HT
2AR-CHO or 5-HT
2CR-CHO cells or exhibit intrinsic agonist activity.
Keywords:
PNU-69176E; diastereomer; synthesis; allosteric modulator; 5-HT2C receptor