Isomerization of 40-methoxy-flavanone in alkaline medium. Determination of the enolate formation constant

S.A. ANDUJAR, M.A. FILIPPA, F.H. FERRETTI, S.E. BLANCO

JOURNAL OF MOLECULAR STRUCTURE THEOCHEM

Año: 2003 p. 157 - 166

0166-1280

The varied biological activity of flavanones mainly depends on their physical and chemical properties. In order to obtaininformation on the acid–base behavior of flavanones of chemical and biological interest the isomerization of 40-methoxyflavanonewas studied and the formation constant of its enolate was determined by UV spectrometry. The kinetic experimentswere performed in aqueous medium at 25 ^ 0.1 8C, keeping the ionic strength (0.07, KCl) and pH (10.8) constant. The obtainedresults were interpreted by a four-step mechanism, which considered the existence of flavanone enolate as a key intermediate.Some stereochemical and mechanistic aspects of the reaction were explained by means of reactivity indexes andthermodynamic magnitudes calculated by ab initio methods in ethanol and water, which support the proposed mechanism. It isconcluded that the kinetic methodology here proposed to study the enolization properties of flavanones seems to be quiteconvenient to overcome the marked intrinsic instability of these substances in alkaline media.