Formation of Quercetin Heterodimer via Diels-Alder Type Cyclo-Addition under Microwave Conditions

Author(s): David Cáceres-Castillo, Fernando Moguel-Pardío, Ramiro F. Quijano-Quiñones, Gumersindo Mirón-López, Gonzalo J. Mena-Rejón.

Journal Name: Letters in Organic Chemistry

Volume 13 , Issue 2 , 2016

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Abstract:

Bakcground: The antioxidant activity of quercetin has been linked to many factors including its chemical structure. Studies about the process of quercetin oxidation have related the formation of dimers through a dioxane linkage, which could result from Diels-Alder cycloaddition. To evaluate the impact of microwave irradiation on the quercetin dimers formation, Diels-Alder reactions of quercetin with 3,5-di-tert-butyl-o-quinone were investigated, and heterodimer isolation and structural determination was performed.

Methods: Reactions of quercetin with 3,5-di-tert-butyl-o-benzoquinone were completed under conventional heating conditions as well as microwave irradiation. 1D/2D NMR experiments allowed the identification and quantification of the major isomer, and the energy of the most stable conformer was obtained by DFT calculations at M06-2X/6-31G(d,p) level of theory.

Results: Under conventional thermal conditions a reaction time of 10 h allows to obtain a product mixture of isomers in approximately in 2:1 ratio (1H NMR). Although the proportion of product mixture remains similar under microwave irradiation, the complete conversion took 30 min. In addition, a 1:5 molar ratio of quercetin to benzoquinone was found to increase to 75% the formation of the thermodynamic product (DFT) 8,10-di-tert-butyl-5a-(3,4-dihydroxyphenyl)-1,3,11atrihydroxy- 5aH-benzo[5,6][1,4]dioxino[2,3-b]chromen-12(11aH)-one whose identity was established by spectroscopic analyses in conjunction with molecular modeling studies.

Conclusion: A quercetin heterodimer was synthesized by Diels-Alder reaction under classical heating and microwave irradiation conditions. The use of microwave flash heating promotes shorter reaction times and a slight improvement in stereochemistry. This synthetic methodology suggest that microwave irradiation approach has a positive impact on the mechanism of cycloaddition.

Keywords: Density functional theory, hetero diels-alder, heterodimer, microwave, o-quinone, quercetin.

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Article Details

VOLUME: 13
ISSUE: 2
Year: 2016
Page: [107 - 112]
Pages: 6
DOI: 10.2174/1570178612666151008014708
Price: $65

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