Prenylated flavanones and flavanonols as chemical markers in Glycosmis species (Rutaceae)

Flavonoids in the Spotlight: Bridging the Gap between Physicochemical Properties and Formulation Strategies

Flavonoids are hydroxylated polyphenols that are widely distributed in plants with diverse health benefits. Despite their popularity, the bioavailability of flavonoids is often overlooked, impacting their efficacy and the comparison of products. The study discusses the bioavailability-related physicochemical properties of flavonoids, with a focus on the poorly soluble compounds commonly found in dietary supplements and herbal products. This review sums up the values of pKa, log P, solubility, permeability, and melting temperature of flavonoids. Experimental and calculated data were compiled for various flavonoid subclasses, revealing variations in their physicochemical properties. The investigation highlights the challenges posed by poorly soluble flavonoids and underscores the need for enabling formulation approaches to enhance their bioavailability and therapeutic potential. Compared to aglycones, flavonoid glycosides (with sugar moieties) tend to be more hydrophilic. Most of the reviewed aglycones and glycosides exhibit relatively low log P and high melting points, making them "brick dust" candidates. To improve solubility and absorption, strategies like size reduction, the potential use of solid dispersions and carriers, as well as lipid-based formulations have been discussed.

Ten new prenylated flavonoids from Macaranga denticulata and their antitumor activities

Ten new prenylated flavonoids, named denticulains A-J (1-10), together with seven known prenylated flavonoids (11-17) were isolated from Macaranga denticulata. Their structures were elucidated on the basis of detailed spectroscopic analysis and by comparison with literature data. In addition, compounds 1 and 14 inhibited the proliferation of SW620 and HCT-116 cell lines with an IC₅₀ value of 46.08 μM and 56.83 μM, respectively.

Chemical constituents of Clausena lenis

Phytochemical examination of Clausena lenis Drake (Rutaceae), collected in Thailand, led to the isolation of seven coumarins, four furoquinolines, two amides, and one flavonoid glycoside. Four of these compounds, one coumarine derivative named as gravelliferone A (3), two furoquinoline derivatives (kokusagenin A (8) and B (9)) and one amide, clausenalansamide H (13), are reported for the first time. Compound 3 was isolated from the root bark, compound 8 from the stem bark and compounds 9 and 13 from the leaves. The molecular structures of all isolated compounds were established by means of NMR experiments combined with mass spectrometry. Preliminary tests of the lipophilic stem bark extract against various human pathogenic bacteria strains revealed promising effects against Staphylococcus aureus ATCC 43300.

Complementary Flavonoid Prenylations by Fungal Indole Prenyltransferases

Flavonoids are found mainly in plants and exhibit diverse biological and pharmacological activities, which can often be enhanced by prenylations. In plants, such reactions are catalyzed by membrane-bound prenyltransferases. In this study, the prenylation of nine flavonoids from different classes by a soluble fungal prenyltransferase (AnaPT) involved in the biosynthesis of the prenylated indole alkaloid acetylaszonalenin is demonstrated. The behavior of AnaPT toward flavonoids regarding substrate acceptance and prenylation positions clearly differs from that of the indole prenyltransferase 7-DMATS. The two enzymes are therefore complementary in flavonoid prenylations.

Metabolites software-assisted flavonoid hunting in plants using ultra-high performance liquid chromatography-quadrupole-time of flight mass spectrometry

Plant secondary metabolism drives the generation of metabolites used for host plant resistance, as biopesticides and botanicals, even for the discovery of new therapeutics for human diseases. Flavonoids are one of the largest and most studied classes of specialized plant metabolites. To quickly identify the potential bioactive flavonoids in herbs, a metabolites software-assisted flavonoid hunting approach was developed, which mainly included three steps: firstly, utilizing commercial metabolite software, a flavonoids database was established based on the biosynthetic pathways; secondly, mass spectral data of components in herbs were acquired by ultra-high performance liquid chromatography-quadrupole-time of flight mass spectrometry (UHPLC-Q-TOF-MS); and finally, the acquired LC-MS data were imported into the database and the compounds in the herbs were automatically identified by comparison of their mass spectra with the theoretical values. As a case study, the flavonoids in Smilax glabra were profiled using this approach. As a result, 104 flavonoids including 27 potential new compounds were identified. To our knowledge, this is the first report on profiling the components in the plants utilizing the plant metabolic principles with the assistance of metabolites software. This approach can be extended to the analysis of flavonoids in other plants.

Antibacterial Compounds from Glycosmis puberula Twigs

The first phytochemical investigation of Glycosmis puberula twigs led to the isolation and identification of a new quinolone alkaloid, glycosmispuberulone (1), along with ten known compounds (2–11). The structures were elucidated by spectroscopic analyses and comparison with previously reported data. Their antibacterial activities against Gram-positive and Gram-negative bacteria were also evaluated.

Prenylated flavonoids from the stems and leaves of Desmodium caudatum and evaluation of their inhibitory activity against the film-forming growth of Zygosaccharomyces rouxii F51

In order to provide scientific evidence for the relationship between the traditional usage, stems and leaves of Desmodium caudatum being used for protecting miso from spoilage, and its Japanese name (miso-naoshi), phytochemical study on the stems and leaves of this plant was carried out. Seven new prenylated flavonoids (1-3, 15-18), together with 19 known compounds (4-14, 19-26), were isolated, and the structures of new compounds were elucidated by extensive spectroscopic analyses. The minimum inhibitory concentrations (MICs) of 28 flavonoids, including 17 compounds (1, 2, 4, 5, 7-14, 20-22, 24, 25) isolated in this study and 11 flavonoids (27-37) previously isolated from the roots of this plant, against the film-forming yeast of Zygosaccharomyces rouxii F51 were determined. Fifteen compounds (2, 4, 5, 11, 12, 14, 21, 22, 25, 27, 28, 32-35) inhibited the film-forming growth of Z. rouxii F51 (MIC values, 7.8-62.5 μg/mL), among which 2",2"-dimethylpyran-(5",6":7,8)-5,2'-dihydroxy-4'-methoxy-(2R,3R)-dihydroflavonol (11) demonstrated potent inhibitory activity with an MIC value of 7.8 μg/mL.

Acridone alkaloids from Glycosmis chlorosperma as DYRK1A inhibitors

Two new acridone alkaloids, chlorospermines A and B (1 and 2), were isolated from the stem bark of Glycosmis chlorosperma, together with the known atalaphyllidine (3) and acrifoline (4), by means of bioguided isolation using an in vitro enzyme assay against DYRK1A. Acrifoline (4) and to a lesser extent chlorospermine B (2) and atalaphyllidine (3) showed significant inhibiting activity on DYRK1A with IC50's of 0.075, 5.7, and 2.2 μM, respectively. Their selectivity profile was evaluated against a panel of various kinases, and molecular docking calculations provided structural details for the interaction between these compounds and DYRK1A.

Enriching modern pharmacotherapy through synergy assessment for the combination of natural products and synthetic drugs

5-O-methylglovanon (5-O-MG) is a bioactive compound first isolated and characterized from Glycosmis plants. In this issue, Zhou et al. evaluated the anti-staphylococcal effects of 5-O-MG against ampicillin-resistant isolates of Staphylococcus aureus and S. epidermidis. The authors showed that the combination of 5-O-MG and ampicillin significantly increased the susceptibility of Staphylococcus strains to the drugs by decreasing MICs with a comparable anti-staphylococcal effect to that of β-lactamase inhibitors, suggesting that herbal compounds such as 5-O-MG may be potential candidates for the inhibitor of β-lactamases. This study is another example of synergy assessment of natural products in drug development to likely enrich modern pharmacotherapy.

Solophenols B-D and solomonin: new prenylated polyphenols isolated from propolis collected from the Solomon Islands and their antibacterial activity

Three new prenylated flavonoids, namely, solophenols B (1), C (2), and D (3), as well as a new prenylated stilbene, solomonin (4), were isolated from propolis collected from the Solomon Islands. In addition, 17 known compounds were identified. The structures of the new compounds were determined by a combination of methods, including mass spectrometry and NMR. These new compounds and several known compounds were tested for antibacterial activity against Staphylococcus aureus, Bacillus subtilis, and Pseudomonas aeruginosa. Most of them exhibited potent antibacterial activity. These findings may indicate that propolis from the Solomon Islands has potential applications as an ingredient in food additives or pharmaceuticals.

Lavandulyl flavanones from the stems of Hypericum calycinum L

One novel lavandulyl flavanone (=2,3-dihydro-2-phenyl-4H-1-benzopyran-4-one) with an unusual 5,2',4',6'-tetrahydroxy substitution, calycinigin A (1), was isolated from the stems of Hypericum calycinum L. (Hypericaceae). The structure was elucidated on the basis of 1D- and 2D-NMR analysis, as well as mass spectrometry (LR-EI- and HR-EI-MS) and circular dichroism. Three known lavandulyl flavanones with 5,7,2',4',6'-pentahydroxy substitution, i.e., 2-4, were also isolated. Chemosystematically, this is the first report on the occurrence of prenylated flavanones in the family Hypericaceae. Reduction of cell viability by all compounds was evaluated in a MTT (=3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) assay using HeLa cells. Compound 1 showed moderate activity with an IC₅₀ value of 9.7±1.8 μM, whereas compounds 2-4 were less active exhibiting IC₅₀ values of 11.6±0.9, 19.3±1.5, and 40.7±2.4 μM, respectively. The antioxidant activity was evaluated by an ORAC (Oxygen Radical Absorbance Capacity) assay, and calycinigin A (1) was again the most active compound with a Trolox equivalent of 2.3±0.2. None of the compounds was able to reduce the TNF-α induced ICAM-1 expression in vitro using human microvascular endothelial cells (HMEC-1).

In vitro synergistic interaction of 5-O-methylglovanon and ampicillin against ampicillin resistant Staphylococcus aureus and Staphylococcus epidermidis isolates

5-O-methylglovanon (5-O-MG) is a bioactive compound that was first isolated and characterized from Glycosmis plants. In this study, we found that chemically synthesized 5-O-MG has antimicrobial ability against eleven clinical ampicillin resistant Staphylococcus aureus and S. epidermidis isolates. The MICs of 5-O-MG against the S. aureus and S. epidermidis isolates were 12.5-50 μg/mL and 25-50 μg/mL, respectively. In combination with ampicillin, a synergistic interaction between 5-O-MG and ampicillin against the eleven resistant Staphylococcus isolates was observed, with fractional inhibitory concentration indices of 0.03-0125. Moreover, the anti-staphylococcal activity of 5-O-MG in combination with ampicillin was comparable with that of clavulanic acid in combination with ampicillin. The drug combination had no antagonistic effects when tested against any of the strains. Time-killing assays confirmed the synergy between 5-O-MG and ampicillin (p < 0.01). The combination of these two agents yielded greater than a 2 log(10) cfu/mL decrease in comparison with 5-O-MG or ampicillin alone. These findings suggest that 5-O-MG is a promising compound with the potential for future anti-staphylococcal drug development.

Two new acridone alkaloids from Glycosmis macrantha

Extraction and chromatographic separation of the extracts of dried stem barks of Glycosmis macrantha lead to isolation of two new acridone alkaloids, macranthanine (1) and 7-hydroxynoracronycine (2), and a known acridone, atalaphyllidine (3). The structures of these alkaloids were determined by detailed spectral analysis and also by comparison with reported data.

Alcoholysis of naturally occurring imides: misleading interpretation of antifungal activities

The frequent presence of the sulfur-containing amide penangin (10) in leaf extracts of Glycosmis species turned out to be the result of decomposition of imides generated by extraction and storage in MeOH. Reinvestigation of Glycosmis mauritiana and G. cf. puberula with acetone revealed the presence of six imides. In addition to penimides A (1) and B (2) and ritigalin (6), three new derivatives, krabin (4), isokrabin (5), and methoxypenimide B (3), were isolated and identified by spectroscopic methods. All six imides were shown to be susceptible to different rates of methanolic cleavage, leading to their corresponding methyl esters and sulfur-containing amides. Whereas the decomposition products penangin (10), isopenangin (11), and sinharin (14) are known, the corresponding cleavage of methyl N-methylthiocarbamate (7) from ritigalin (6), monitored in situ by (1)H NMR spectroscopy, is described here for the first time. Its structure was further confirmed by GC-MS coupling. HPLC-UV comparison of many different samples of G. mauritiana, extracted with MeOH, revealed considerable chemical variations in sulfur-containing amides, strongly correlated with different antifungal potency. The lack of activity of many methanolic crude extracts can be explained by a preponderance of the inactive decomposition product penangin (10), whereas the corresponding naturally occurring imides penimides A (1) and B (2) and methoxypenimide B (3), extracted with acetone, showed high fungitoxic properties.

Several chromones from the stems of Polygonum aubertii Henry

Two new 2-alkylchromanones, 2-tricosyl-2,5,7-trihydroxy-chromanone (6) and 2-pentacosyl-2,5,7-trihydroxy-chromanone (7), together with five known 2-alkylated chromones and chromanones (1-5), were isolated from the stems of Polygonum aubertii Henry. The structures of these compounds were established by spectroscopic methods including extensive 1D, 2D NMR ((1)H-(1)H COSY, HSQC, and HMBC), and HR-ESI-MS techniques. In addition, a plausible biosynthetic pathway for these compounds is described.