Study of the reactivity of 4-hydroxycoumarin, 2,4-quinolinediol and 4-hydroxy-1-methyl-quinolone with catechol in the presence of crude onion peroxidase extract
2012
Angeleska, S.
This project involves the exploitation of food residuals (onion solid waste) as an inexpensive and renewable source of crude enzymes which can be used as biocatalysts for the synthesis of novel, high added value products. The aims of the present study were a contribution of investigation into the biocalytic activity of a crude onion peroxidase extract on the reaction between catechols and heterocyclic 1,3-dicarbonyl compounds, in an effort to synthesize added value natural products. In addition, optimization of the conditions for the oxidative cyclization of the substrates into corresponding products was established, isolating 3 new products, known as coumestans and benzofuroquinolinones. Three different reaction mixtures were prepared using heterocyclic 1,3-dicarbonyl compounds (4-hydroxycoumarin, 2,4-quinolinediol or 4-hydroxy-1-methyl-quniolone) and catechol as reactants. The enzyme showed optimal activity at pH 5 and 6, H2O2 concetration of 0.3 mM, substrate concentration of 1.15 mM and incubation time of 1.5 and 3h, according to the substrates. Using HPLC analyses, the enzymic reactions were further fine-tuned in view of optimizing the reaction conditions. Scale-up reactions that were carried out using the predicted optimal conditions led indeed to a higher yield synthesis of products. Moreover in the study, an evaluation of the chemical profiles and screening of the antioxidant activity of the products was performed. The reaction mixtures which showed the presence of product were subjected to chromatographic fractionation and the structure and stereochemistry of the products were established on the basis of spectral-analytical evidence, using LC-DAD-MS (ESI+) and NMR assays.
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