Resolução do ()-citronelol e ácido ()-citronélico via esterificação enantiosseletiva catalisada pela lipase de candida antarctica

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

In this work Candida antarctica lipase (CAL-B) was used in the resolution of the ()-citronellol and ()-citronellic acid, by enantioselective esterification. Chiral terpenic acids and alcohols are excellent building blocks for the preparation of more complex molecules with possible biological activities. The ()-citronellic acid has been used as the base material in the preparation of different pheromones, which are the molecules responsible for the chemical communication made among organisms of the same species. The ()-citronellol alcohol, by chemical oxidation is easily converted into the citronellic acid. ()-Citronellic acid esterification reactions were accomplished with different aliphatic alcohols (1-butanol, 1-pentanol, 1-hexanol, 1-octanol and 1-dodecanol), and esterification of the ()-citronellol alcohol with different aliphatic acids (butyric, pentanoic, hexanoic, octanoic and dodecanoic) using as catalyst the lipase of Candida antarctica (CAL-B). The follow-up of the reactions and the isolation of the products were done by chromatography in columns using hexane: ethyl acetate (15:1) as an eluent. The products were characterized by infrared spectroscopic, RMN of H and GC-MS. For n-alkyl citronellates it was observed an increase in the yield of ester using linear aliphatic alcohols from 4 to 8 carbon chains going from 11 to 60% after 7 day reaction. Over an 8 carbon chain a decrease in the reaction yield was observed. At the determination of the optical rotation, the enzyme showed a preference to the isomer with negative optical rotation, obtain enantiomeric excess smaller than 50% (eep from 3.0 to 27.0% and ees from 18.0 to 47.0%). Studies of solvent effect, molar ratio, and enzyme amount variation in the medium were evaluated for the preparation of the n-octyl ()-citronellate. Solvents with log P>3.0 like hexane and cicloexane showed better yields. An increase in the alcohol concentration favored the esterification of the n-octyl (-)-citronellate reaction with yields higher than 60%. The variation in the amount of enzyme from 100 to 300mg did not affect the yields of the reaction staying between 60-65%. For the citronellyl alkanoates it was observed an increase in the yield with aliphatic acids from 4 to 12 carbon chains, and the percentages of conversion varied from 31 to 75%. The CAL-B showed preference for the isomer with negative optical rotation, however with low values of enantiomeric excess (eep from 0.4 to 3.0% and ees from 1.3 to 26.0%). Studies of solvent effect, molar ratio, and enzyme amount variation in the medium were evaluated for the (-)-citronellyl butyrate preparation. In the evaluation of the effect of the solvent, relevant results were also obtained with the hexane. In the evaluation of the molar ratio there was an increase in the yields with the increase in the amount of acid in the medium. A yield increase from 45 to 70% was observed when the amount of enzyme was also increased from 100 to 300mg. The experiment showed that the lipase of Candida antarctica is more selective to the ()-citronellic acid than to the ()-citronellol

ASSUNTO(S)

enzimas; Ácidos; lipase esterificação ()-citronelol ()-citronellic acid ()-citronellol cal, esterification ácido ()-citronélico quimica cal

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