Microbial Transformations of Chalcones:  Hydroxylation, O-Demethylation, and Cyclization to Flavanones

Abstract

Microorganisms were examined for their potential to catalyze biotransformation reactions that mimic plant biosynthetic processes. Specifically, microorganisms were screened for their abilities to transform selected chalcones to flavonoid and other products. Aspergillus alliaceus UI 315 efficiently transformed 3-(2' ',3' '-dimethoxyphenyl)-1-(2'-hydroxyphenyl)propenone (2'-hydroxy-2,3-dimethoxychalcone) (1) to several products, all of which were characterized by UV, NMR, and mass spectral analyses. A. alliaceus cyclized 1 to three flavanones and to O-demethylated and hydroxylated chalcones, some of which functioned as intermediates in the cyclization process. Inhibition studies using SKF525A, metyrapone, and phenylthiocarbamide with whole cell reactions showed that as many as three cytochrome P450 enzymes may be involved in these reactions. One enzyme catalyzed chalcone cyclization; another, O-demethylation; and a third, hydroxylation of chalcones. Flavonoid products are racemic, unlike the same products that are stereoselectively cyclized in plants. This work shows that microorganisms are capable of cyclizing chalcones to form flavonoid products, thus affording a mimic of plant biosynthetic processes.

Two new aflatoxin producing species, and an overview of Aspergillus section Flavi

“…Stromata of A. alliaceus strains contain compounds exhibiting insecticidal properties (Laakso et al 1994, Nozawa et al 1994), and asperlicins, potent cyclic peptide antagonists of cholecystokinin (Liesch et al 1988). Aspergillus alliaceus strains are also used for steroid and alkaloid transformations (Burkhead et al 1994, Sanchez-Gonzalez & Rosazza 2004), and for the production of pectin degrading enzyme preparations (Mikhailova et al 1995).…”

Microbial transformation of the sesquiterpene lactone tagitinin C by the fungus Aspergillus terreus

“…Glandular trichomes of Asteraceae species are the places where the biosynthesis of STLs usually occurs, and possibly where 1 is converted to 2. Thus, this fungus can be used as an alternative means of gaining 2 from 1, therefore confirming the potential of biotransformation of natural compounds by microorganisms, as well as their ability to mimic plant biosynthetic pathways [34].…”

Biotransformation of chalcones by the endophytic fungus Aspergillus flavus isolated from Paspalum maritimum trin

“…Among the reactions of biotransformation reported directly on chalcones, Aspergillus alliaceus cyclized the chalcone 2'-hydroxy-2,3-dimethoxychalcone to three flavanones and to O-demethylated (6.5% yield) and hydroxylated (7.2% yield) chalcones. 31 The unsubstituted chalcone was converted to 2''-hydroxychalcone and 2'',3''-dihydroxychalcone in 25% and 59% yields, respectively, by Escherichia coli. 32 Microbial transformation of chalcone xanthohumol, using the culture broth of Pichia membranifaciens afforded three metabolites, one isomeric prenylflavanone in 3.3% yield, and two modified prenylchalcones in 0.55 and 0.58% yield.…”