Whole-Cell Biocatalysis for the Production of Structurally Diverse Methoxydihydrochalcones: Broad Activity of the Yarrowia Clade

Whole-cell biocatalysis presents a sustainable and efficient approach for the selective reduction in α,β-unsaturated bonds in flavonoid derivatives. This study investigates the capability of yeast strains from the <i>Yarrowia</i> clade to catalyze the chemoselective reduction of 4'-methoxychalcone (<b>1a</b>) to its dihydro derivative. All tested strains exhibited similarly high hydrogenation activity, indicating a broadly conserved enoate reductase function within the clade. Among them, <i>Yarrowia lipolytica</i> KCh 71, previously reported and well characterized in the literature, was selected for preparative-scale transformation of a diverse series of synthetic methoxychalcones bearing additional methoxy groups in positions C-2, C-3, C-4, C-5, and C-6 of ring B. All derivatives were effectively converted into the corresponding dihydrochalcones, with yields ranging from 62% to 92%. Among the tested derivatives, the 2',4',6'-trimethoxy chalcone (<b>7a</b>) did not undergo biotransformation under our conditions, whereas mono- and di-methoxy derivatives (<b>2a</b>-<b>6a</b>) were efficiently reduced. These results confirm the broad substrate tolerance, high efficiency, and potential scalability of <i>Y. lipolytica</i> KCh 71, supporting its potential as a whole-cell biocatalyst for the sustainable synthesis of bioactive dihydrochalcones. The consistently high hydrogenation activity observed across 21 tested strains suggests the involvement of evolutionarily conserved enoate reductases. Bioinformatic analysis supports that the <i>Yarrowia</i> clade possesses a robust complement of Old Yellow Enzymes (OYE), providing a reliable enzymatic basis for the observed chemoselective reductions. All <i>Yarrowia</i> tested strains showed the same general transformation type, although the extent and rate of conversion differed among strains, and <i>Y. lipolytica</i> KCh 71 was one of the most tolerant. The broad reduction in α,β-unsaturated chalcones is consistent with the action of flavoenzymatic ene-reductases, particularly Old Yellow Enzyme (OYE)-like reductases. Bioinformatic analysis of <i>Yarrowia</i> genomes reveals putative OYE homologs, supporting this mechanistic interpretation, although the specific enzymes were not identified in this study.