Estudo químico e biológico das espécies Manekia obtusa e Piper cubataonum (Piperaceae) e síntese de estigmast-4-EN-3-ONA, (S)-Aegelina E (R)-6'-Desmetoxi Aegelina

Abstract

Resumo: No presente trabalho foi determinada a composicao quimica do oleo essencial das partes aereas de Manekia obtusa e das folhas e galhos de Piper cubataonum, atraves de CG-EM e CG~CG. A analise por CG-EM revelou para o oleo essencial de M. obtusa 22 constituintes, sendo majoritariamente formado por sesquiterpenos oxigenados. Para o oleo essencial das folhas e galhos de P. cubataonum, foi possivel identificar 14 e 20 constituintes, respectivamente, sendo que ambos os oleos apresentam os alilfenois, dilapiol e apiol, como majoritarios. Atraves da analise por CG~CG, foi possível caracterizar 128 constituintes diferentes dos tres oleos essenciais analisados, sendo 80 constituintes nas partes aereas de M. obtusa, 57 e 66 constituintes nas folhas e galhos de P. cubataonum, respectivamente. Realizou-se o estudo fitoquimico do extrato diclorometanico das partes aereas de M. obtusa, resultando no isolamento de cinco substancias: duas amidas, aegelina (MO 1) e cinamamida (MO 2), uma mistura dos esteroides ƒÀ-sitosterol e estigmasterol (MO 3A e MO 3B) e o esteroide estigmast-4-en-3- ona (MO 4). O estudo fitoquimico do extrato metanolico das raizes de P. cubataonum resultou no isolamento de onze substancias, sendo quatro alilfenois: miristicina (PCR 1), apiol (PCR 2), dilapiol (PCR 3) e elemicina (PCR 4); duas lignanas: rel-(7R,8S,7fS,8fS)- 4f,5f-metilenodioxi-3,4,5,3f-tetrametoxi-7,7f-epoxilignana (PCR 5) e epigrandisina (PCR 6); duas aristolactamas: cefaranona B (PCR 7) e piperolactama A (PCR 8); e tres esteroides ja isolados anteriormente de M. obtusa, sendo uma mistura de ƒÀ-sitosterol e estigmasterol (MO 3A e MO 3B) e o estigmast-4-en-3-ona (MO 4). As atividades antimicrobianas e citotoxidade foram avaliadas para os extratos e oleos essenciais, onde se destaca a forte atividade antimicrobiana do extrato diclorometanico e do oleo essencial de M. obtusa contra Candida albicans, sendo superiores ao medicamento de referencia (nistatina) utilizado. Para o estudo da atividade inseticida, realizado na Universidade de Nevada,foram sintetizados os constituintes isolados de M. obtusa, nao disponíveis comercialmente, neste caso, a estigmast-4-en-3-ona (MO 4) e a amida (S)-aegelina (MO1), sendo esta ultima sintetizada por duas rotas diferentes. Alem disso, realizou-se a sintese da (R)-6'-desmetoxi aegelina (analogo da aegelina). Os tres constituintes sintetizados, juntamente com os demais isolados de M. obtusa (adquiridos comercialmente) foram submetidos a ensaios de atividade inseticidas frente a Spodopteraexigua, individualmente ou em misturas. O esteroide MO 4, a mistura das amidas e a mistura total diminuiram a taxa de sobrevivencia de S. exigua. A amida MO2 e a mistura das amidas reduziram a massa da pupa e retardaram o desenvolvimento larval.

Abstract: In this study, the chemical composition of the essential oil from the aerial parts of Manekia obtusa and the leaves and branches of Piper cubataonum were analyzed by GCMS and GC~GC, separately. The M. obtusa essential oil revealed 22 constituents by GCMS, which were mainly composed by oxygenated sesquiterpenes. Essential oil from leaves and branches of P. cubataonum, showed 14 and 20 identified constituents, respectively and both oils presented the allylphenols, dillapiole and apiole, as main constituents. The GC~GC analysis characterized 128 different constituents of the three essential oils, of which 80 were constituents for M. obtusa aerial parts, 57 and 66 constituents for P. cubataonum leaves and branches, respectively. The phytochemical study of the dichloromethane extract from M. obtusa yielded five substances: two amides, aegeline (MO 1) and cinnamamide (MO 2), a mixture of steroids ƒÀ-sitosterol and stigmasterol (MO 3A and MO 3B) and the steroid stigmast-4-en-3-one (MO 4). From methanol extract of the roots of Piper cubataonum, eleven substances were isolated, including four allylphenols: myristicin (PCR 1), apiole (PCR 2), dillapiole (PCR 3) and elemicin (PCR 4); two lignans: rel-(7R,8S,7fS,8fS)-4f,5f-methylenedioxy-3,4,5,3f-tetramethoxy-7,7f-epoxylignan (PCR 5) and epigrandisin (PCR 6); two aristolactams: cepharanone B (PCR 7) and piperolactam A (PCR 8) and three steroids previously isolated from M. obtusa: the mixture of ƒÀ-sitosterol and stigmasterol (MO 3A and MO 3B) and stigmast-4-en-3-one (MO 4). The antimicrobial and citotoxic activities were evaluated for the extracts and essential oils. The dichloromethane extract and essential oil of M. obtusa revealed stronger antimicrobial activity against Candida albicans than the reference drug used. For the insecticidal activity, performed at the University of Nevada, the isolated constituents of M. obtusa, (which are not commercially available) were synthesized, in this case, stigmast-4-en-3-one (MO 4) and the amide (S)-aegeline (MO 1), the later was synthesized by two different routes. In addition, the synthesis of (R)-6'- demethoxy aegeline (aegeline analog - NMO 1) was performed. The three synthesized constituents along with other isolates of M. obtusa (commercially available) were subjected, individually or in mixtures, to insecticides bioassays against Spodoptera exigua. The MO 4 steroid, the amide mixtures and the total mixture decreased survival rate of S. exigua. The amide MO 2 and the amide mixtures reduced pupal mass and increased the period of larval development.