Synthesis, computational investigation and biological evaluation of α,α-difluoromethyl ketones embodying pyrazole and isoxazole nuclei as COX inhibitors

Abstract

α,α-Difluoromethyl ketones (DFMKs) have emerged as currently investigated agents benefiting from the merging of chemico-physical features conferred by the constitutive elements (–CHF₂ and carbonyl moietites). With a view to biological applications, the additional incorporation of heterocycles is a desirable property enabling the tuning of critical factors encompassing the pharmaco-dynamic and kinetic profiles. The underexplored assembling of α,α-difluoromethyl-heteroaromatic ketones is herein implemented via a conceptually intuitive Weinreb amide acylative transfer of a putative difluoromethyl-carbanion. To make the strategy productive, we adopted the commercially available TMSCHF₂ pronucleophile – characterized by robust chemical stability and manipulability (bp 65 °C) – which upon Lewis-base mediated activation delivers the competent CHF₂-nucleophile. The synthetic protocol was carried out on pyrazole- and isoxazole-based scaffolds, and a panel of heteroaryl-DFMKs was consequently developed as potential COX-inhibitors. In this sense, the bioisosterism deducted through docking studies between the widely expressed carboxylic group (in several clinically used COX inhibitors) and the –COCHF₂ motif introduced herein supports this rationale. To confirm the docking results, all compounds were tested against both COX-1 and COX-2 enzyme isoforms showing activity in the micromolar range and a good selectivity index (SI). They were also evaluated for their biocompatibility using NIH/3T3 cells to which they did not show any significant toxicity.