5‐Alkoxy‐1‐aryl‐3‐polyfluoroalkylpyrazoles with Antinociceptive Activity: Partial Agonists of TRPV1 Ion Channels

Abstract

Chemoselective O‐alkylation of 1‐aryl‐3‐polyfluoroalkylpyrazol‐5‐oles under basic conditions resulted in a series of 5‐alkoxypyrazoles (26 derivatives). They showed an acceptable ADME profile (in silico) and can be considered as drug‐like. In experiments in vivo (CD‐1 mice), it was found that the obtained compounds do not have toxic properties at a dose of more than 150 mg/kg (for most compounds at a dose of >300 mg/kg, and for lead compounds – >600 mg/kg). 22 Compounds from this series demonstrated from moderate to high analgesic effects (28–104 % at 1 h and 37–109 % at 2 h after administration) in vivo in the hot plate test (SD rats, 15 mg/kg, intraperitoneal (ip)). The lead compound was 4‐([1‐phenyl‐3‐(trifluoromethyl)pyrazol‐5‐yl]oxy)butan‐1‐ol, which not only increased the latent period in the hot plate test by 103 % at both measurement points but also showed a pronounced analgesic effect under conditions of capsaicin‐induced nociception (CD‐1 mice, 15 mg/kg, ip). According to molecular modeling, all synthesized compounds can interact with the TRPV1 ion channel. This biological target was confirmed in in vitro experiments on Chinese hamster ovary cells expressing rTRPV1. 5‐Alkoxypyrazoles were partial agonists of the TRPV1 ion channel in various degree, and the most active was the same pyrazole as in in vivo tests.

Modifications of 4‐Amino‐substituted 5‐Phenyl‐3‐(trifluoromethyl)pyrazoles for the Development of New Analgesics

“…We considered the use of this reagent to be prospective since the recently obtained butoxyl derivative of 1phenyl-3-(trifluoromethyl)pyrazole showed promising analgesic activity in vivo in "hot plate" test acting as partial agonists of TRPV1 ion channels. [41] However, it turned out that the alkylation of pyrazoles 1 a-c with butyl bromide, regardless of various varied conditions (refluxing in acetone, DMF or MeCN in the presence of bases K 2 CO 3 , Cs 2 CO 3 , K 2 CO 3 /KI, NaOH or DBU, heating in a closed steel vessel in pentanol at 190 °C in presence of K 2 CO 3 /KI) did not proceed smoothly, and it was accompanied by the complicated mixtures formation according to GC/MS data. We were able to isolate the alkylated products only from the reaction of 4-amino-NH-pyrazole 1 a.…”

“…The hot plate test was conducted according to established guidelines [57,58] and described in detail in our previous publication. [41]…”