Fluorine-containing 6,7-dialkoxybiaryl-based inhibitors for phosphodiesterase 10 A: Synthesis and in vitro evaluation of inhibitory potency, selectivity, and metabolism

Article abstract of DOI:10.1002/cmdc.201300522

Based on the potent phosphodiesterase 10 A (PDE10A) inhibitor PQ-10, we synthesized 32 derivatives to determine relationships between their molecular structure and binding properties. Their roles as potential positron emission tomography (PET) ligands were evaluated, as well as their inhibitory potency toward PDE10A and other PDEs, and their metabolic stability was determined in vitro. According to our findings, halo-alkyl substituents at position 2 of the quinazoline moiety and/or halo-alkyloxy substituents at positions 6 or 7 affect not only the compounds′ affinity, but also their selectivity toward PDE10A. As a result of substituting the methoxy group for a monofluoroethoxy or difluoroethoxy group at position 6 of the quinazoline ring, the selectivity for PDE10A over PDE3A increased. The same result was obtained by 6,7-difluoride substitution on the quinoxaline moiety. Finally, fluorinated compounds (R)-7-(fluoromethoxy)-6-methoxy-4-(3-(quinoxaline-2-yloxy)pyrrolidine-1-yl) quinazoline (16 a), 19 a-d, (R)-tert-butyl-3-(6-fluoroquinoxalin-2-yloxy) pyrrolidine-1-carboxylate (29), and 35 (IC₅₀ PDE10A 11-65 nM) showed the highest inhibitory potential. Further, fluoroethoxy substitution at position 7 of the quinazoline ring improved metabolic stability over that of the lead structure PQ-10. Fluor your health: Phosphodiesterase 10 A (PDE10A) has emerged as an attractive target for the development of ¹⁸F-labelled brain imaging agents for positron emission tomography. A series of fluorinated dialkoxybiaryl compounds were synthesized and evaluated as PDE10A inhibitors, assisted by QSAR docking studies. The 7-fluoromethoxy derivative appears to be a promising candidate for further development.