Isolamento dos ácidos 3α-acetóxi-copálico e 3α-hidróxi-copálico da fração não-volátil do óleo-resina de copaíba (Copaifera L. spp. - Fabaceae) e semissíntese de derivados

Abstract

Copaibeiras are well known in the Amazon region for arousing much interest among researchers, mainly due to the biological properties of the oil-resin of this plant. The oil resin is extracted from the trunk. It consists mainly of sesquiterpenes and diterpenes. Sesquiterpenes predominate in the volatile fraction or essential oil while diterpenes are the main chemical constituents of the fixed fraction or resin. Essential oil is used by the cosmetic industry as a raw material for various products. Its separation from the oil-resin takes place through distillation processes. The latter generate a residual non-volatile fraction that is rich in diterpenes. The present work has as its main objectives to perform an extensive survey of literature on the chemical composition and biological activity of Copaifera spp., to isolate substances from the residual, non-volatile fraction of copaiba oleoresin obtained after commercial distillation and to prepare semi-synthetic derivatives of isolated substances (thru straight-forward chemical reactions such as acylation or hydrolysis). Two diterpenes were isolated from the non-volatile fraction of copaiba oleoresin using sequential normal phase column chromatographies followed by RP-HPLC and identified as 3α-hydroxycopalic and 3α-acetoxycopalic acids based on 1H and 13C NMR, DEPT 135, COSY, HSQC, HMBC, LC HRMS and optical rotation, as well as comparison with literature data. These two carboxylic acids are known by several names in the literature. Consistent with the structure and C-5 and C-10 absolute configurations established originally for copalic acid by Nakano e Djerassi these compounds are called 3α-substituted copalic acid derivatives. 3α-hydroxycopalic acid was obtained from isolated 3α-acetoxycopalic acid under hydrolysis conditions (10% KOH in 9:1 MeOH/H2O) in 76% yield. 3α-hydroxycopalic acid (from isolation) was subjected to acetylation (treatment with acetic anhydride in pyridine and DMAP) and butyrylation (treatment with butyric anhydride in pyridine and DMAP) reactions resulting in the formation of semi-synthetic products 3α-acetoxy-copalic and 3α-butanoyloxycopalic acids in 70 and 42%, respectively. The formation of the reaction products was confirmed based on their 1H NMR and LC-HRMS characteristics. Conformational analyses and multiplicities (J values) of the 1H signals corresponding to H-3 and H-5 were consistent with H-3, H-5 and angular CH3 (at C-10) relative configurations of β, β and α, respectively, with small distortion of the chair conformation in the A ring due to 1,3-diaxial repulsions among the CH3 substituents at C-4 and C-10 in isolates and reaction products.