Biological Properties and Absolute Configuration of Flavanones From Calceolaria thyrsiflora Graham

Polyphenol and Tannin Nutraceuticals and Their Metabolites: How the Human Gut Microbiota Influences Their Properties

Nutraceuticals have been receiving increasing attention in the last few years due to their potential role as adjuvants against non-communicable chronic diseases (cardiovascular disease, diabetes, cancer, etc.). However, a limited number of studies have been performed to evaluate the bioavailability of such compounds, and it is generally reported that a substantial elevation of their plasma concentration can only be achieved when they are consumed at pharmacological levels. Even so, positive effects have been reported associated with an average dietary consumption of several nutraceutical classes, meaning that the primary compound might not be solely responsible for all the biological effects. The in vivo activities of such biomolecules might be carried out by metabolites derived from gut microbiota fermentative transformation. This review discusses the structure and properties of phenolic nutraceuticals (i.e., polyphenols and tannins) and the putative role of the human gut microbiota in influencing the beneficial effects of such compounds.

Anti-Inflammatory Phytoconstituents of Origanum Majorana

Origanum majorana belongs to the Lamiaceae family as a famous spice plant in Egypt, which is used to treat arthritis, allergies, fever, flu, hypertension, respiratory infections, migraine, and asthma. In our studies, it was found that the ethanol extract of O. marjoram could significantly reduce NO release at 200 ( $P<0.001$ ), 100 ( $P<0.001$ ) and 50 ( $P<0.01$ ) μg/mL compared with the model group. Therefore, the chemical constituents were further studied to obtain the bioactive compounds. As a result, ten compounds were isolated and identified from the 70% ethanol extract of O. marjoram, including six flavonoids (3–8), two terpene derivatives (9-10), one lignan (2), and one phenolic glycoside (1). Among them, compounds 1–3, 5, and 9-10 were isolated from this genus for the first time. Compounds 1, 9, and 10 could significantly decrease the content of NO at the concentration of 100 μm ( $P<0.001$ ) in RAW264.7 cells induced by LPS. Furthermore, compounds 9 and 10 were more effective than compound 1 to lower the content at 50 μm ( $P<0.001$ ).

Vibrational Circular Dichroism Similarity-Guided Absolute Configuration Determination of 11-Acyloxytremetones

Although tremetone [5-acetyl-2-(1-methylvinyl)-2,3-dihydrobenzofuran] has only one stereogenic center, the absolute configuration (AC) determination of its naturally occurring 11-acyloxy derivatives 1 and 2 by vibrational circular dichroism (VCD) turned out to be difficult. Similarity-based comparison of the experimental VCD spectrum of 11-coumaryloxytremetone (1), isolated from Parastrephia quadrangularis, with spectra calculated using popular density functional theory (DFT) levels of theory, provided poor enantiomeric similarity indices ( ESI), even when the p-coumaroyl ester group of 1 was replaced by the acetyl group in 2. In search for a better understanding of these results, IR-guided individual scaling factors (ISFs), recently introduced as part of the Vibrational Spectra Similarity and Analysis Tool (VISSAT) software, were used to correct DFT frequencies, while a VCD-guided conformational analysis was developed to explore conformational preferences. These studies showed that for both molecules 72% of the individual conformations gave ESI values in favor of the ( R) enantiomer. Likewise, when conformer abundances were optimized to produce the best possible similarity for each enantiomer, the obtained ESI values were always larger for the ( R) isomer than for the ( S) isomer. These results point toward the ( R) AC in both compounds and highlight the incorrect conformer abundance prediction by DFT calculations as the potential source of the initial difficulties. In addition, the AC of 1 was independently verified using the Flack and Hooft parameters gained after a single-crystal x-ray diffraction (XRD) study.

Bioassay-guided isolation of cytotoxic constituents from the flowers of Aquilaria sinensis

Bioassay-guided fractionation of the EtOH extract from the flowers of Aquilaria sinensis (Lour.) Spreng. (Thymelaeaceae) led to the isolation of a new cucurbitane-type triterpenoid, aquilarolide A (1), along with five known compounds (2-6). The structure of 1 was elucidated by extensive 1D and 2D nuclear magnetic resonance (NMR) experiments and mass spectrometry (MS) data and theoretical calculations of its electronic circular dichroism (ECD) spectra. Aquilarolide A, cucurbitacin E (3), cucurbitacin B (4), and 7-hydroxy-6-methoxy-2-[2-(4-methoxyphenyl)ethyl]-4H-1-benzopyran-4-one (6) showed significant cytotoxicity against human lung adenocarcinoma SPC-A-1, human lung squamous cell carcinoma NCI-H520, human lung adenocarcinoma A549, and paclitaxel-resistant A549 (A549/Taxol) cell lines. All four active compounds, with IC₅₀ values ranging from 0.002 to 0.91 μM, had better inhibitory activities against A549/Taxol cells than paclitaxel (IC₅₀ = 1.80 μM). Among them, cucurbitacin E (IC₅₀ = 0.002 μM) is the most active. Further studies are needed to evaluate their in vivo antitumor activities and to clarify their mechanisms.

Flavonoid constituents of Amomum tsao-ko Crevost et Lemarie and their antioxidant and antidiabetic effects in diabetic rats - in vitro and in vivo studies

Amomum tsao-ko Crevost et Lemarie (A. tsao-ko) is a well-known dietary spice and traditional Chinese medicine. This study aimed to identify the flavonoids in A. tsao-ko and evaluate their antioxidant and antidiabetic activities in in vitro and in vivo studies. A. tsao-ko methanol extracts possessed a high flavonoid content (1.21 mg QE per g DW) and a total of 29 flavonoids were identified by employing UPLC-MS/MS. In vitro, A. tsao-ko demonstrated antioxidant activity (ORAC value of 34276.57 μM TE/100 g DW, IC₅₀ of ABTS of 3.49 mg mL^-1 and FRAP value of 207.42 μM Fe²⁺ per g DW) and α-amylase and α-glucosidase inhibitory ability with IC₅₀ values of 14.23 and 1.76 mg mL^-1, respectively. In vivo, type 2 diabetes mellitus (T2DM) models were induced by a combined high-fat diet (HFD) and streptozotocin (STZ) injection in rats. Treatment with the A. tsao-ko extract (100 mg freeze-dried powder per kg bw) for 6 weeks could significantly improve impaired glucose tolerance, decrease the levels of fasting blood glucose (FBG), insulin, and malondialdehyde (MDA), and increase the superoxide dismutase (SOD) level. Histopathology revealed that the A. tsao-ko extract preserved the architecture and function of the pancreas. In conclusion, the flavonoid composition of A. tsao-ko exhibits excellent antioxidant and antidiabetic activity in vitro and in vivo. A. tsao-ko could be a novel natural material and developed as a related functional food and medicine in T2DM management.

Prenylated Flavonoids with Potential Antimicrobial Activity: Synthesis, Biological Activity, and In Silico Study

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.

Deuterium effects on the vibrational circular dichroism spectra of flavanone

The minimum chemical modification that can be incorporated into an organic molecule is the replacement of a hydrogen atom for a deuterium atom. This change is not altering the pharmacological properties of a molecule, although it provides the possibility of making specific spectroscopic evaluations. Thus, in the present study, we explore how a stereogenic center is influenced by such an isotopic labeling. The studies were conducted on both enantiomers of flavanone (1 and 2) which is the parent molecule of a large group of pharmacologically active natural occurring secondary metabolites. Flavanone comprised 12 carbon atoms forming two benzene rings, a carbonyl group, an ethereal oxygen atom, a methylene group, and only one C-H stereogenic center, so it seems to be an ideal candidate for such studies. Density functional theory (DFT) calculations were used for the accurate prediction of vibrational circular dichroism (VCD) spectra of (R)-(3) and (S)-flavanone-2-d (4), of (R)-(5) and (S)-flavanone-3,3-d₂ (6), and of (R)-(7) and (S)-flavanone-2',3',4',5',6'-d₅ (8). To gain compounds that provide experimental VCD spectra for comparative purposes, the calculated spectra of both enantiomers of the corresponding flavanones, obtained after HPLC separation of the racemates by means of a chiral column, were contrasted, thereby revealing excellent agreements when using the CompareVOA software. In addition, the VCD spectra of both unlabeled enantiomeric flavanones (1 and 2) were also compared to the labeled molecules, revealing that the VCD spectra show significant variations induced by the deuterium incorporation.