Comparative Antinociceptive Evaluation of Hofmeisterin I and Analogues from Hofmeisteria schaffneri in Zebrafish and Mice

Hofmeisteria schaffneri (Asteraceae) is a medicinal plant used in Central Mexico for pain relief. Although thymol- and northymol-derived metabolites contribute to its antinociceptive activity, the low abundance of the latter has limited evaluation. An optimized synthetic route to hofmeisterin I (1) improved yields and reduced reaction times, enabling biological assessment. Hofmeisterin I (1) and derivatives were tested in zebrafish (Danio rerio) and murine formalin models. Halogenated derivatives were toxic and minimally active, whereas the acetylated analogue exhibited higher potency but limited safety. A new nitrogen-containing imide analogue, namely, 1-(2-(5-bromo-2-hydroxy-4-methylphenyl)-2-oxoethyl)pyrrolidine-2,5-dione (12), exhibited improved efficacy and a safer profile. Mechanistic studies indicated the involvement of TRPV1, CB2, and PPARγ receptors, with modulation by the opioid and serotonergic systems. Collectively, these findings highlight compound 12 as a promising antinociceptive scaffold. X-ray analyses of 1 and 12 are also reported.