This work describes the first determination of the absolute configuration (AC) of (−)-cubebin by means of electronic circular dichroism (ECD), supported by quantum chemical calculations. The comparison of experimental ECD with the corresponding quantum chemical prediction for the proper diastereoisomer resulted in the definitive assignment of the AC of the naturally occurring (−)-cubebin as (8R,8aR,9S). The challenging determination of the relative configuration (RC) of cubebin based only on experimental nuclear magnetic resonance (NMR) methods is stressed. Computation of the 13C and 1H NMR chemical shifts for all the possible diastereoisomers leads to values of mean absolute error and root mean square deviation that do not allow distinguishing among them. Thus, errors in stereochemical determination can easily occur even when using two-dimensional methods, which clearly demonstrate the complexity of this special case. To determine the RC of this bioactive natural compound with high level of confidence, it was necessary to combine the DP4+ method with X-ray crystallography. Therefore, employing the commonly used empirical methods to determine the AC of (−)-cubebin can easily lead to misassignment of its stereochemistry.

ABSTRACT Casearia genus (Salicaceae) is found in sub-tropical and tropical regions of the world and comprises about 160-200 species. It is a medicinal plant used in South America, also known as “guaçatonga”, “erva-de-tiú”, “cafezinho-do-mato”. In Brazil, there are about 48 species and 12 are registered in the State of Rio de Janeiro, including Casearia sylvestris Sw. There are many studies related to the chemical profile and cytotoxic activities of extracts from these plants, although few studies about the antifungal potential of the essential oil have been reported. In this work, we have studied the antifungal properties of the essential oil of C. sylvestris leaves, as well as of their fractions, against four yeasts (Saccharomyces cerevisae, Candida albicans, C. glabrata and C. krusei) for the first time. The chemical analysis of the essential oil revealed a very diversified (n = 21 compounds) volatile fraction composed mainly of non-oxygenated sesquiterpenes (72.1%). These sesquiterpenes included α-humulene (17.8%) and α-copaene (8.5%) and the oxygenated sesquiterpene spathulenol (11.8%) were also identified. Monoterpenes were not identified. The fractions are mainly composed of oxygenated sesquiterpenes, and the most active fraction is rich in the sesquiterpene 14-hydroxy -9-epi-β-caryophyllene. This fraction was the most effective in inhibiting the growth of three yeast strains.

RESUMOPiper aduncum L. é utilizada na medicina popular para o tratamento de doenças respiratórias e inflamatórias. O objetivo desse estudo foi analisar o óleo essencial das folhas de P. aduncum coletadas no Cerrado brasileiro, Norte de Minas Gerais, assim como avaliar a atividade larvicida desse óleo e de sua substância majoritária. O óleo essencial foi analisado por cromatografia em fase gasosa acoplada à espectrometria de massas e por cromatografia em fase gasosa acoplada a detector por ionização de chamas, que permitiu a caracterização de 23 substâncias (monoterpenos: 90,4%; sesquiterpenos: 7,0%). O componente majoritário foi o 1,8-cineol (53,9%). O óleo essencial desse exemplar mostrou ser muito diferente do óleo da mesma espécie. Larvas de Aedes aegypti foram expostas a diferentes concentrações do óleo essencial e do 1,8-cineol. Após 24h do tratamento com o óleo registrou-se uma taxa de mortalidade de 100% das larvas nas concentrações de 500 e 1,000 ppm. Após 48h a taxa de mortalidade foi de 80% e 50% para as concentrações de 250 e 100 ppm, respectivamente. A CL50 obtida após 24h foi estimada em 289,9 ppm e após 48h foi de 134,1 ppm. A substância majoritária 1,8-cineol não apresentou atividade larvicida.

ABSTRACTPiper aduncum L. is used in folk medicine to treat respiratory and inflammatory diseases. The aim of this study was to analyze the essential oil from leaves ofP. aduncum collected in the Brazilian Cerrado, North of Minas Gerais, as well as to evaluate the larvicidal activity of this oil and of its major constituent. The essential oil was analyzed by gas chromatography coupled to flame ionization detector and gas chromatography coupled to mass spectrometry that allowed characterizing 23 compounds (monoterpenes: 90.4%; sesquiterpenes: 7.0%). The major component was 1,8-cineole (53.9%). This oil showed to be very different from those obtained from the same species. Larvae of A. aegypti were exposed to different concentrations of the essential oil and 1,8-cineole. The mortality rate of 100% was obtained after 24h of treatment with the oil at concentrations of 500 and 1,000 ppm. After 48h of treatment, the mortality rate was 80% and 50% for concentrations of 250 and 100 ppm, respectively. The LC50 obtained after 24h was estimated in 289.9 ppm and after 48h was 134.1 ppm. The major compound 1,8-cineole showed no larvicidal activity.

O óleo essencial das folhas de Piper solmsianum e seu constituinte majoritário (sarisan) foram testados para avaliar suas influências no comportamento de camundongos. O óleo essencial foi obtido por hidrodestilação em aparelho do tipo Clevenger modificado e analisado por CG/ EM. Essa análise mostrou a presença de monoterpenos, sesquiterpenos e arilpropanóides. Sarisan, um análogo da myristicina, foi isolado do óleo para se efetuar os testes farmacológicos. Emulsões do óleo essencial e do sarisan a 5,0% e 10,0% (v/v) foram utilizadas nos testes. Pentobarbital (30 mg/ kg s.c.) ou diazepam (2,5 mg/ kg s.c.) foram testados como padrões na verificação de efeitos depressores e ansiolíticos, respectivamente. O óleo essencial e seu componente majoritário apresentaram efeitos excitantes e depressores nos animais testados.

The essential oil from Piper solmsianum leaves and its major compound (sarisan) were tested to verify their influences upon mice behaviour. The essential oil was obtained by hydrodistillation in a modified Clevenger extractor and analysed by GC/ MS. This analysis revealed in the oil the presence of monoterpenes, sesquiterpenes and of arylpropanoids. The compound sarisan, a myristicin analogue, was isolated from the oil to perform the pharmacological tests. Emulsions of the oil and of sarisan (5.0 and 10.0% v/v) were used in the tests. Pentobarbital (30 mg/ kg s.c.) or diazepam (2.5 mg/ kg s.c.) were tested as standard drugs to verify depressant or anxiolytic effects, respectively. Both essential oil and sarisan showed to have exciting and depressant effects in the tested animals.