Theoretical and experimental study demonstrates kinetic control in chalcone-flavanone transformation of naphthalene derivatives

DFT Study on the Reaction Mechanism of Cyclization of 2-Hydroxy Chalcone Catalyzed by Bronsted Acid with M06-2X Functional

Flavanones are one of the flavonoid group that has wide variety of applications such as a precursors in drug discovery. In the laboratory, flavanone is often synthesized from chalcone compounds. The conversion of chalcone to flavanone can be catalyzed by bronsted acid. The reaction mechanism for this process is proposed through the Michael addition reaction, however, the energetic details and the rate determining step for this reaction is not certainly known. This research aimed to investigate the reaction mechanism for chalcone-flavanone conversion with the present of bronsted acid as catalyst and also studied the effect of the solvent on the reaction energy profile with computational method. In this study, the modeling of the reaction mechanism for the said reaction was carried out using the DFT computational method with M06-2X functional. The computation was done both in the gas phase and in present of the solvent effect using the PCM models. The results showed that the mechanism of chalcone-flavanone conversion occurred in three steps which are protonation, cyclization, and then tautomerization. Based on these calculations, the rate determining step was the tautomerization reaction, which exhibited the same results with or without the solvent effects. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Structure, isomerization and dimerization processes of naringenin flavonoids

In this study, the theoretical and experimental results on the molecular structure and reactivity of the plant flavonoids naringenin chalcone and naringenin are reported. UV-vis and Raman spectra were recorded and their main bands have been assigned theoretically. Moreover, the analysis of the naringenin chalcone-naringenin cyclization-isomerization reaction and the formation of homodimers and heterodimers have been performed within a DFT framework. The presence of H-bonded water networks is mandatory to make the cyclization energetically suitable, suggesting that this equilibrium will occur in an aqueous intracellular environment rather than in the extracellular and hydrophobic plant cuticles. Additionally, the preferential formation of homodimers stabilized by π-π stacking that will interact with other dimers by H-bonding over the formation of naringenin chalcone-naringenin heterodimers is also proposed in a hydrophobic environment. These results give a plausible model to explain how flavonoids are located within the cuticle molecular arrangement.