Synthesis and Characterization of Variably Halogenated Chalcones and Flavonols and Their Antifungal Activity

Abstract

Three series of mono and di-halogenated chalcones and flavonols were synthesized according to the Claisen-Schmidt and Algar-Flynn-Oyamada reactions, respectively. Halogenated chalcones were prepared by condensing equimolar quantities of halogenated hydroxyacetophenones with halogen-substituted benzaldehydes, in the presence of aqueous alcoholic alkali. The resultant chalcones were immediately reacted with H₂O₂ in the presence of a mixture of methanol and aqueous sodium hydroxide to obtain the corresponding halogenated flavonols. The synthesized halogenated flavonoids were characterized on the basis of their physical properties and spectroscopic data. All the synthesized compounds were tested for their antifungal activity against a number of test organisms. Most of the flavonoids were found to be active against the tested fungi and in some cases even stronger than the standard antifungal drugs. Increased activity was found in those flavonoids in which the B-ring is halogenated. The antifungal activity increased as the ring is substituted with more electronegative halogens such as fluorine. However, it was noticed that chalcones having a phenolic hydroxyl in ring A at 2' position, showed more activity than that of its corresponding flavonol, in which the 2'-OH is lost on cyclization of C-ring.