Background: Flavokawain B is one of the naturally occurring chalcones in the kava plant (Piper methysticum). It exhibits anticancer, anti-inflammatory and antimalarial properties. Due to its therapeutic potential, flavokawain B holds promise for the treatment of many diseases. However, due to its poor bioavailability and low aqueous solubility, its application remains limited. The attachment of a sugar unit impacts the stability and solubility of flavonoids and often determines their bioavailability and bioactivity. Biotransformation is an environmentally friendly way to improve the properties of compounds, for example, to increase their hydrophilicity and thus affect their bioavailability. Recent studies proved that entomopathogenic filamentous fungi from the genera Isaria and Beauveria can perform O-methylglycosylation of hydroxyflavonoids or O-demethylation and hydroxylation of selected chalcones and flavones. Results: In the present study, we examined the ability of entomopathogenic filamentous fungal strains of Beauveria bassiana, Beauveria caledonica, Isaria farinosa, Isaria fumosorosea, and Isaria tenuipes to transform flavokawain B into its glycosylated derivatives. The main process occurring during the reaction is O-demethylation and/or hydroxylation followed by 4-O-methylglycosylation. The substrate used was characterized by low susceptibility to transformations compared to our previously described transformations of flavones and chalcones in the cultures of the tested strains. However, in the culture of the B. bassiana KCh J1.5 and BBT, Metarhizium robertsii MU4, and I. tenuipes MU35, the expected methylglycosides were obtained with high yields. Cheminformatic analyses indicated altered physicochemical and pharmacokinetic properties in the derivatives compared to flavokawain B. Pharmacological predictions suggested potential anticarcinogenic activity, caspase 3 stimulation, and antileishmanial effects. Conclusions: In summary, the study provided valuable insights into the enzymatic transformations of flavokawain B by entomopathogenic filamentous fungi, elucidating the structural modifications and predicting potential pharmacological activities of the obtained derivatives. The findings contribute to the understanding of the biocatalytic capabilities of these microbial cultures and the potential therapeutic applications of the modified flavokawain B derivatives.

4′-dihydrochalcones are secondary metabolites isolated from many medicinal plants and from the resin known as ‘dragon’s blood’. Due to their biological potential, our research objective was to determine the possibilities of using biocatalysis processes carried out in deep eutectic solvents (DESs) to obtain 4′-dihydrochalcones as a model compound. The processes were carried out in a culture of the yeast Yarrowia lipolytica KCh 71 and also in cultures of strains of the genera Rhodotorula and Debaryomyces. Based on the experiments carried out, an optimum process temperature of 35 °C was chosen, and the most suitable DES contained glycerol as a hydrogen bond donor (HBD). For a medium with 30% water content (DES 11), the conversion observed after 24 h exceeded 70%, while increasing the amount of water to 50% resulted in a similar level of conversion after just 1 h. A fivefold increase in the amount of added substrate resulted in a reduction in conversion, which reached 30.3%. Of the other yeast strains tested, Rhodotorula marina KCh 77 and Rhodotorula rubra KCh 4 also proved to be good biocatalysts for the bioreduction process. For these strains, the conversion reached 95.4% and 95.1%, respectively. These findings highlight the potential of yeast as a biocatalyst for the selective reduction of α,β-unsaturated ketones and the possibility of using a DESs as a reaction medium in this process.

Chalcones, including 4′-hydroxychalcones, have garnered significant attention in the area of drug discovery due to their diverse pharmacological properties, such as anti-inflammatory, antioxidative, and anticancer effects. However, their low water solubility and bioavailability limit their efficacy in vivo. Glycosylation presents a promising approach to enhance the water solubility, stability, and metabolic properties of chalcones. This study investigates the enzymatic glycosylation of eight chemically synthesized 4′-hydroxychalcones using a diverse set of sugar glucosyltransferases from bacterial, plant, and fungal sources, alongside Glycine max sucrose synthase (GmSuSy) in a cascade reaction. Among the tested enzymes, five exhibited a remarkable versatility for glycoside production, and for large-scale biotransformation, flavonoid 7-O-glucosyltransferase Sbaic7OGT from Scutellaria baicalensis was selected as the most effective. As a result of the experiments conducted, eight trans-chalcone glycosides were obtained. During the purification of the reaction products, we also observed the isomerization of the products by simple sunlight exposure, which resulted in eight additional cis-chalcone glycosides. This study highlights the novel use of a cascade reaction involving Glycine max sucrose synthase (GmSuSy) for the efficient glycosylation of trans-4′-hydroxychalcones, alongside the unexpected discovery of cis-chalcone glycosides during the purification process.

The quest for novel therapeutic agents has rekindled interest in natural products, particularly those derived from biotransformation processes. Dihydrochalcones, a class of plant secondary metabolites, exhibit a range of pharmacological properties. Chalcone and dihydrochalcone compounds with the characteristic 4’-hydroxy substitution are present in ‘dragon’s blood’ resin, known for its traditional medicinal uses and complex composition, making the isolation of these compounds challenging. This study investigates the efficient production of 4′-hydroxydihydrochalcones using non-conventional yeast strains. We evaluated the biotransformation efficiency of various 4′-hydroxychalcone substrates utilizing yeast strains such as Yarrowia lipolytica KCh 71, Saccharomyces cerevisiae KCh 464, Rhodotorula rubra KCh 4 and KCh 82, and Rhodotorula glutinis KCh 242. Our findings revealed that Yarrowia lipolytica KCh 71, Rhodotorula rubra KCh 4 and KCh 82, and Rhodotorula glutinis KCh 242 exhibited the highest conversion efficiencies, exceeding 98% within one hour for most substrates. The position of methoxy substituents in the chalcone ring significantly influenced hydrogenation efficiency. Moreover, we observed isomerization of trans-4′-hydroxy-2-methoxychalcone to its cis isomer, catalyzed by light exposure. This study underscores the potential of using yeast strains for the sustainable and efficient production of dihydrochalcones, providing a foundation for developing new therapeutic agents and nutraceuticals.

This study investigates the impact of light exposure on the biotransformation of chalcones in yeast cultures. 4′-Hydroxychalcones, with a hydroxyl group in the A-ring, are characteristic substrates efficiently converted into 4′-hydroxydihydrochalcones—compounds naturally occurring in medicinal plants such as Glycyrrhiza glabra (licorice), Stevia rebaudiana, and Angelica keiskei (ashitaba). These compounds are valued for their bioactivity and are relevant to natural product research. In this research, we present the outcomes of the selective microbial reduction of chalcones to dihydrochalcones using the yeast Yarrowia lipolytica KCh 71, cultivated under both light and dark conditions. The aim was to determine whether light exposure affects the efficiency or selectivity of the transformation. Furthermore, the effect of substrate photoisomerisation induced by light was investigated, as the trans–cis isomerisation of chalcones may affect their availability and affinity toward enzymatic systems. The resulting metabolites were analysed using chromatographic and spectroscopic methods. No significant differences in transformation efficiency were observed between light and dark conditions. In all tested conditions, the 4′-hydroxydihydrochalcones were obtained with high yield, typically exceeding 90% conversion. Additionally, the selective bioreduction of the α,β-unsaturated bond in selected 4′-hydroxychalcones by the studied yeast culture is an exceptionally efficient process. The primary factor influencing the reaction rate is the structure of the substrate, particularly the number and distribution of methoxyl groups on the B-ring. In addition, we establish biocatalytic access to three target dimethoxy dihydrochalcones—4′-hydroxy-2,4-dimethoxydihydrochalcone (5a), 4′-hydroxy-2,5-dimethoxydihydrochalcone (6a), and 4′-hydroxy-3,5-dimethoxydihydrochalcone (7a)—under mild conditions using Yarrowia lipolytica KCh 71. Under preparative-scale conditions (7-day incubation), a minor additional product (≤10%) was detected only for the 4′-hydroxy-2,5-dimethoxydihydrochalcone transformation and identified as 4′,5-dihydroxy-2-methoxydihydrochalcone (6b); no such side reaction was observed in short-term experiments.

4′-Hydroxymethoxychalcones represent structurally diverse chalcone derivatives that are attractive substrates for microbial functionalization; however, the impact of methoxy substitution position on their cascade biotransformation by fungi remains poorly understood. In this study, three regioisomeric 4′-hydroxymethoxychalcones, featuring ortho-, meta-, or para-methoxy groups on ring B, were transformed using eight entomopathogenic fungal strains belonging to the genera Beauveria, Isaria, and Metarhizium. Metabolic profiles were monitored over a 10-day period using ultra-high-performance liquid chromatography coupled with diode-array detection (UHPLC-DAD), and the structures of the major products were elucidated primarily by one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy and further supported by high-resolution electrospray ionization quadrupole time-of-flight mass spectrometry (HR-ESI-QTOF-MS). The investigated microorganisms catalyzed multistep transformations encompassing the reduction of the α,β-unsaturated carbonyl system, methylglucosylation, O-demethylation, and the formation of secondary polar metabolites. Although ene-reduction constituted the predominant initial reaction for all substrates, the relative distribution of subsequent metabolites varied depending on both the fungal strain and, to a lesser extent, the position of the methoxy group. The ortho-methoxy derivative exhibited the highest propensity for O-demethylation; the meta-substituted substrate generated the most heterogeneous secondary metabolite profiles, whereas the para-methoxy analogue showed the most consistent accumulation of methylglucosylated dihydrochalcones. These findings indicate that methoxy substitution position does not alter the common core biotransformation pathway, but can modulate the relative efficiency of individual steps and the extent of secondary metabolism.