Prenylated flavonoids are an important class of naturally occurring flavonoids with important biological activity, but their low abundance in nature limits their application in medicines. Here, we showed the hemisynthesis and the determination of various biological activities of seven prenylated flavonoids, named 7–13, with an emphasis on antimicrobial ones. Compounds 9, 11, and 12 showed inhibitory activity against human pathogenic fungi. Compounds 11, 12 (flavanones) and 13 (isoflavone) were the most active against clinical isolated Staphylococcus aureus MRSA, showing that structural requirements as prenylation at position C-6 or C-8 and OH at positions C-5, 7, and 4′ are key to the antibacterial activity. The combination of 11 or 12 with commercial antibiotics synergistically enhanced the antibacterial activity of vancomycin, ciprofloxacin, and methicillin in a factor of 10 to 100 times against drug-resistant bacteria. Compound 11 combined with ciprofloxacin was able to decrease the levels of ROS generated by ciprofloxacin. According to docking results of S enantiomer of 11 with ATP-binding cassette transporter showed the most favorable binding energy; however, more studies are needed to support this result.

The synthesis of twenty six prenylated phenols derivatives is reported. These compounds were obtained under mild conditions via Electrophilic Aromatic Substitution (EAS) coupling reactions between phenol derivatives containing electron-donor subtituents and 3-methyl-2-buten-1-ol using BF₃×OEt₂. Dialkylations were also produced with this method. The formation of a chroman ring by intramolecular cyclization between a sp² carbon from the prenyl group with the hydroxyl substituent in the ortho position occurred with some phenols. All the synthesized compounds were evaluated as antioxidants according to a DPPH radical scavenging activity assay. IC₅₀ values of five synthesized compounds indicated they were as good antioxidants as Trolox™.

Flavonoids are an abundant class of naturally occurring compounds with broad biological activities, but their limited abundance in nature restricts their use in medicines and food additives. Here we present the synthesis and determination of the antibacterial and antioxidant activities of twenty-two structurally related flavonoids (five of which are new) by scientifically validated methods. Flavanones (FV1–FV11) had low inhibitory activity against the bacterial growth of MRSA 97-7. However, FV2 (C5,7,3′,4′ = OH) and FV6 (C5,7 = OH; C4′ = SCH₃) had excellent bacterial growth inhibitory activity against Gram-negative E. coli (MIC = 25 µg/mL for both), while Chloramphenicol (MIC = 25 µg/mL) and FV1 (C5,7,3′ = OCH₃; 4′ = OH) showed inhibitory activity against Gram-positive L. monocytogenes (MIC = 25 µg/mL). From the flavone series (FO1–FO11), FO2 (C5,7,3′,4′ = OH), FO3 (C5,7,4′ = OH; 3′ = OCH₃), and FO5 (C5,7,4′ = OH) showed good inhibitory activity against Gram-positive MRSA 97-7 (MIC = 50, 12, and 50 µg/mL, respectively), with FO3 being more active than the positive control Vancomycin (MIC = 25 µg/mL). FO10 (C5,7= OH; 4′ = OCH₃) showed high inhibitory activity against E. coli and L. monocytogenes (MIC = 25 and 15 µg/mL, respectively). These data add significantly to our knowledge of the structural requirements to combat these human pathogens. The positions and number of hydroxyl groups were key to the antibacterial and antioxidant activities.

Flavanones (–)-(2S)-5,4’-dihydroxy-7-methoxyflavanone (1) and (–)-(2S)-5,3’,4’-trihydroxy-7-methoxyflavanone (2) were isolated from the extracts of Calceolaria thyrsiflora Graham, an endemic perennial small shrub growing in the central zone of Chile. The absolute configuration of these compounds was resolved by optical rotation experiments and in silico calculations. Three analogs (3, 4, and 5) were synthesized to do structure-activity relationships with the biological assays studied. Biological tests revealed that only flavanone 2 exhibited a moderate inhibitory activity against the methicillin-resistant strain S. aureus MRSA 97-77 (MIC value of 50 µg/ml). In addition, flavanone 2 showed a potent, selective, and competitive inhibition of 5-hLOX, which supports the traditional use of this plant as an anti-inflammatory in diseases of the respiratory tract. Also, 2 exhibited cytotoxic and selective effects against B16-F10 (8.07 ± 1.61 µM) but 4.6- and 17-fold lesser activity than etoposide and taxol.

The syntheses of six prenylated acetophenone and benzaldehyde derivatives and their anti-phytopathogenic and antioxidant activities are reported. These compounds were obtained by electrophilic aromatic substitution (S E Ar) of the corresponding arenes and 3-methyl-2-buten-1-ol using ZnCl2 as a Lewis acid catalyst in ethyl acetate. Reasonable to good yields were obtained based on unrecovered aromatic starting material (45-73%). All the synthesized compounds were evaluated against phytopathogenic gram-negative bacteria Agrobacterium tumefaciens, Pseudomonas syringae and Erwinia carotovora and plant fungal pathogens Botrytis cinerea, Phytophthora cinnamomi and Gibberella fujikuroi. The antioxidant activity was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity assay and expressed as half maximal inhibitory concentration (IC50) values in μΜ concentrations. The antioxidant activity went from 27.20 μΜ to >100 μΜ. Compound 11 showed statistically significant inhibition of the growth of Botrytis cinerea, and compounds 13 and 15 showed statistically significant inhibition of the growth of Phytophthora cinnamomi, with respect to negative control fungal growth. All six compounds showed bacteriostatic effects against gram-negative plant pathogenic bacteria with IC50 values between 250 and <3.9 μΜ.