Contribuição ao Conhecimento Químico - Farmacológico de Plantas do Nordeste do Brasil: Luffa operculata Cogn

Abstract

Luffa operculata (Cucurbitaceae) is a plant widely distributed in Northeastern Brazil, where is known as “cabacinha”. An aqueous solution from the fruit of “cabacinha” has been popularly used for the treatment of sinusitis as a bitter stomachic and purgative remedy. The broad spectrum of pharmacological effects reported in the literature and the abundance of this plant in rural Northeastern Brazil justified this study. The plant was subjected to phytochemical study with the objective of isolation and characterization of their secondary metabolites. The Cucurbitaceae are characteristically rich in cucurbitacins, which are oxidative modified triterpenes that together with their glycosides counterparts are considered the agents responsible for the potent toxicity observed in extracts of the fruit of Luffa operculata. Through various chromatographic steps the elements were purified and isolated. The ethanol extract of the fruit of Luffa operculata yielded the isolation of six triterpenoids (cucurbitacin D, isocucurbitacin D, 3-epi-isocucurbitacin D, cucurbitacin I, cucurbitacin B and arvenin I). The ethanol extract of the stems yielded two quinones (emodine and chrisophanol), as well as a mixture of aliphatic esters (hexadecanoic acid, ethyl ester and octadecanoic acid, ethyl ester) and one rare triterpene friedolenane type (bryonolic acid). Furthermore, a mixture of steroids [(22E, 24S)-ethyl-5α-cholest-7,22-dien-3β-ol and (22E,24R)-ethyl-5α-cholest-7,22,25-trien-3β-ol]; ceramides (1,3,4-trihydroxy-2-[2´-hydroxydocosanoylamino]-19-tetracasadecene and 1,3,4-tryhydroxy-2-[2´-hydroxyhenicosanoylamino]-19-tetracasadecene) were isolated from the ethanol extract of the fruit bark. Meanwhile, a mixture of steroids was isolated from the hexane extract of the leaves [(22E, 24S)-ethyl-5α-cholest-7,22-dien-3β-ol and (22E,24R)-ethyl-5α-cholest-7,22,25-trien-3β-ol), while the hexane extract of the stems yielded one steroid (spinasterol) and a mixture of ceramides [(N-(2-isopropoxy-ethyl)eicosamide, N-(2-isopropoxy-ethyl)nonadecanamide, N-(2-isopropoxy-ethyl)octadacanamide, N-(2-isopropoxy-ethyl)heptadacanamide, N-(2-isopropoxy-ethyl)hexadecanamide]. In order to provide training activities in the laboratory and to collect structural proof of the extracts, several derivatives were prepared by classical reactions such as oxidation, esterification, hydrolysis and methanolysis. In addition, crude extracts and a few of the isolated natural products were assessed for biological activities. Some of the compounds found were described for the first time from Luffa opeculata, while the ceramides isolated from the extract are new to the literature. The 1H and 13C NMR, IV and MS spectra and a comparison with previous spectral data allowed the research team to fully understand the chemical structure of all compounds.