ABSTRACT N-acylhydrazone is an interesting privileged structure that has been used in the molecular design of a myriad of bioactive compounds. In order to identify new antinociceptive drug candidates, we described herein the design, synthesis, X-ray diffraction study and the pharmacological evaluation of a series of 3-amino-4-methylthiophene-2-acylcarbohydrazone derivatives (8a-t). Compounds were prepared in good overall yields through divergent synthesis from a common key intermediate and were characterized by classical spectroscopy methods. X-ray diffraction study was employed for unequivocal determination of the imine double bond stereochemistry. 8a-t were evaluated in vivo through oral administration using the classical writhing test in mice. N-acylhydrazone derivatives 8j and 8l displayed relative potency similar to dipyrone, highlighting them as promising analgesic lead-candidates for further investigation.

The antinociceptive activity of the Maytenus rigida Mart. (Celastraceae) ethanol extract and its ethyl acetate fraction as well as of (-)-4'-methylepigallocatechin (1), a previously isolated compound, was demonstrated in vivo. ED50 for 1 in the writhing test was 14.14 mg/kg. The acetic acid-induced writhing was inhibited by 98.4, 84.4, and 58.3%, respectively, when mice were treated with the ethanol extract, ethyl acetate fraction, and 1. In the hot plate test, mice pretreated with 1 showed significantly increased reaction times (60-89%). Oral administration of 1 significantly inhibited first and second phases of the formalin-induced pain (50 and 26.5%, respectively), whereas indomethacin inhibited only the second phase of the test (41.2%). Ethanol extract and its fraction showed effects on inflammatory pain, while neurogenic and inflammatory pain suppression by 1 is a strong indication of the presence of both central and peripheral effects and suggests its analgesic and anti-inflammatory potential.

Erythrina mulungu Mart. ex Benth., Fabaceae, popularly known as mulungu, is used for the treatment of insomnia and disorders of the central nervous system. This study examined the antinociceptive effects of the hydroalcoholic extracts (HAE), the ethyl acetate and chloroformic fractions from E. mulungu in four experimental models of nociception using laboratory mice. The extracts and fractions were administered orally to mice at doses of 100 mg/kg. Inhibition of abdominal contractions were observed for all the extracts and fractions tested, as compared to controls. All extracts and fractions from E. mulungu reduced the nociception activity produced by formalin in the 2nd phase. In the hot plate test no significant effect was observed for any extract or fraction. In the peritonitis test induced by Zymosan, all of the tested extracts and the chloroformic fraction, except for the ethyl acetate phase, reduced cell migration of the peritoneal cavity. We concluded that E. mulungu shows antinociceptive effects, which are independent of the opioid system.

Neste estudo, tentamos identificar a atividade antinociceptiva do extrato metanólico bruto e das fases n-butanólica, clorofórmica e acetato de etila provenientes da alga Caulerpa racemosa. Esta alga é cosmopolita no mundo, principalmente em regiões tropicais. O extrato metanólico bruto e as fases n-butanólica, clorofórmica e acetato de etila foram administrados por via oral, na concentração de 100 mg/kg. Estes foram capazes de reduzir a nocicepção produzida pelo ácido acético, sendo 47,39%, 70,51%, 76,11% e 72,24%, respectivamente. No ensaio da placa quente as fases clorofórmica e acetato de etila foram ativas neste modelo. Na fase neurogênica do teste de formalina, foi observado que o extrato metanólico bruto (51,77%), fase n-butanólica (35,12%), fase clorofórmica (32,70%) e indometacina (32,06%) foram eficazes em inibir a resposta nociceptiva. Na fase inflamatória, apenas a fase acetato de etila (75,43%) e indometacina (47,83%) foram capazes de inibir significativamente a resposta nociceptiva. Com base nestes dados, podemos sugerir que o a fase acetato de etila apresenta um significativo efeito anti-inflamatório, cuja potência ainda não foi determinada. No entanto, estudos farmacológicos e químicos serão necessários, a fim de caracterizar o mecanismo responsável pela ação antinociceptiva e também para identificar outros princípios ativos presentes na alga Caulerpa racemosa.

In this study, we attempted to identify the possible antinociceptive actions of n-butanolic phase, chloroformic phase, ethyl acetate phase and crude methanolic extract obtained from Caulerpa racemosa. This seaweed is cosmopolitan in world, mainly in tropical regions. The n-butanolic, chloroformic, ethyl acetate phases and crude methanolic extract, all administered orally in the concentration of 100 mg/kg, reduced the nociception produced by acetic acid by 47.39%, 70.51%, 76.11% and 72.24%, respectively. In the hotplate test the chloroformic and ethyl acetate phase were activite in this models. In the neurogenic phase on formalin test, were observed that crude methanolic extract (51.77%), n-butanolic phase (35.12%), chloroformic phase (32.70%) and indomethacin (32.06%) were effective in inhibit the nociceptive response. In the inflammatory phase, only the ethyl acetate phase (75.43%) and indomethacin (47.83%) inhibited significantly the nociceptive response. Based on these data, we can infer that the ethyl acetate phase shows a significant anti-inflammatory profile, whose power has not yet been determined. However, pharmacological and chemical studies are continuing in order to characterize the mechanism(s) responsible for the antinociceptive action and also to identify other active principles present in Caulerpa racemosa.