Patulinervones A and B, two novel α-glucosidase inhibitory spiro-lignans from Melicope patulinervia (Merr. & Chun) C.C. Huang

(±)-Patulinervones A (1) and B (2), two diastereomers of spiro-lignans sharing an unprecedented dimethyl-spiro[furan-2,2'-furo[2,3-b]furan] 5/5/5 tricyclic moiety were isolated from the leaves of Melicope patulinervia (Merr. & Chun) C.C. Huang. Their structures were established by extensive spectroscopic data and electronic circular dichroism (ECD) analyses. The racemates (±)-1 and 2 and their enantiomers exhibited α-glucosidase inhibitory effect with IC50 values range of 10.08 ± 1.24 - 25.58 ± 1.97 µM.

Ionones and lignans from the fresh roots of Rehmannia glutinosa

Nine undescribed compounds, together with 21 known components, were isolated from the fresh roots of Rehmannia glutinosa. Their structures were elucidated based on spectroscopic data analysis, and the absolute configurations of undescribed compounds were determined by comparison of their calculated and experimental electronic circular dichroic (ECD) spectra and interpretation of their optical rotation data. The α-glucosidase inhibitory effects of the isolated compounds were investigated and all of them exhibited slightly inhibitory activities.

Extraction optimization, physicochemical property, antioxidant activity, and α-glucosidase inhibitory effect of polysaccharides from lotus seedpods

BACKGROUND

Lotus seedpods are an agricultural by-product of lotus (Nelumbo nucifera Gaertn.), which is widely cultivated in Southeast Asia and Australia. Most lotus seedpods are considered waste and are abandoned or incinerated, resulting in significant waste of resources and heavy environmental pollution. For recycling lotus seedpods, the extraction optimization, physicochemical properties, antioxidant activity, and α-glucosidase inhibitory effect of the polysaccharides contained therein were investigated in this study.

RESULTS

Hot water extraction of lotus seedpod polysaccharides was optimized by using a response surface methodology combined with a Box-Behnken design, with the optimum conditions being as follows: a liquid/solid ratio of 25.0 mL g^-1 , an extraction temperature of 98.0 °C, and an extraction time of 138.0 min. Under these conditions, an experimental yield of 5.88 ± 0.06% was obtained. Physicochemical analyses suggested that lotus seedpod polysaccharides belong to acidic heteropolysaccharides and are principally composed of rhamnose, arabinose, galactose, glucose, mannose, and galacturonic acid. The polysaccharides content has a broad molecular weight distribution (2.15 × 10⁵ to 1.77 × 10⁷  Da), an α-configuration, and mainly possesses smooth and sheet-like structures. Biological evaluations showed that the polysaccharides possessed good scavenging activity on 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, 1,1-diphenyl-2-picryl-hydrozyl, and hydroxyl radicals, and exerted an obvious inhibitory effect on α-glucosidase activity. Moreover, the polysaccharides content was determined to be a mixed-type noncompetitive inhibitor of α-glucosidase.

CONCLUSION

The results indicate that lotus seedpod polysaccharides have potential as natural antioxidants and hypoglycaemic substitutes. This study provides the theoretical bases for the exploitation and application of polysaccharides from lotus seedpod by-product resources. © 2022 Society of Chemical Industry.

Aspulvinones Suppress Postprandial Hyperglycemia as Potent α-Glucosidase Inhibitors From Aspergillus terreus ASM-1

Chemical investigation of Aspergillus terreus ASM-1 fermentation resulted in the isolation of three new prenylated aspulvinones V–X (1–3), together with the previously reported analogs, aspulvinone H (4), J-CR (5), and R (6). Their structures were elucidated by various spectroscopic methods including HRESIMS and NMR, and the absolute configurations of 2 and 3 were determined by ECD comparison. Compounds 1–6 were evaluated for α-glucosidase inhibitory effects with acarbose as positive control. As a result, compounds 1 and 4 exhibited potent α-glucosidase inhibitory activities with IC₅₀ values of 2.2 and 4.6 µM in mixed-type manners. The thermodynamic constants recognized the interaction between inhibitors and α-glucosidase was hydrophobic force-driven spontaneous exothermic reaction. The CD spectra also indicate that the compounds 1 and 4 changed the enzyme conformation. Furthermore, compound 4 significantly suppressed the increases in postprandial blood glucose levels in the C57BL/6J mice.

New Drimane Sesquiterpenes and Polyketides from Marine-Derived Fungus Penicillium sp. TW58-16 and Their Anti-Inflammatory and α-Glucosidase Inhibitory Effects

Marine fungi-derived natural products represent an excellent reservoir for the discovery of novel lead compounds with biological activities. Here, we report the identification of two new drimane sesquiterpenes (1 and 2) and six new polyketides (3–8), together with 10 known compounds (9–18), from a marine-derived fungus Penicillium sp. TW58-16. The planar structures of these compounds were elucidated by extensive 1D and 2D NMR, which was supported by HR-ESI-MS data. The absolute configurations of these compounds were determined by experimental and calculated electronic circular dichroism (ECD), and their optical rotations compared with those reported. Evaluation of the anti-inflammatory activity of compounds 1–18 revealed that compound 5 significantly inhibited the release of nitric oxide (NO) induced by lipopolysaccharide (LPS) in RAW264.7 cells, correlating with the inhibition of expression of inducible nitric oxide synthase (iNOS). In addition, we revealed that compounds 1, 3–6, 14, 16, and 18 showed strong α-glucosidase inhibitory effects with inhibition rates of 35.4%, 73.2%, 55.6%, 74.4%, 32.0%, 36.9%, 88.0%, and 91.1%, respectively, which were comparable with or even better than that of the positive control, acarbose. Together, our results illustrate the potential of discovering new marine-based therapeutic agents against inflammation and diabetes mellitus.

A new quinic acid derivative with α-glucosidase inhibitory activity from the fruit of Gardenia jasminoides J.Ellis

A new quinic acid derivative (1) along with seven known compounds (2-8) were isolated from the fruit of Gardenia jasminoides J.Ellis. All the structures of the isolated compounds were elucidated on the basis of the analysis of multiple spectroscopic data. The α-glucosidase inhibitory effects of the isolated compounds were investigated. The results showed that compounds 1-3, 6, and 8 have moderate α-glucosidase inhibitory activities.

Simultaneous Determination of α-Glucosidase Inhibitory Triterpenoids in Psidium guajava Using HPLC-DAD-ELSD and Pressurized Liquid Extraction

Psidium guajava, a popular food and medicine dual purposes plant cultivated in tropical and subtropical regions, has been widely used as food crop and folk medicine, such as anti-diabetes agent, around the world. Triterpenoids have been considered as the major active ingredients of P. guajava. In the present study, a high-performance liquid chromatography coupled with diode array and evaporative light scattering detectors (HPLC–DAD–ELSD) method was developed for simultaneous determination of nine triterpenoids in P. guajava. Pressurized liquid extraction (PLE) was performed for sample preparation, and the analysis was achieved on a Cosmosil 5C18-MS-II (Nacalai Tesque, Kyoto, Japan) column eluted with gradient 0.1% aqueous formic acid-methanol system. The drift tube temperature of ELSD was set at 40 °C, and nitrogen flow-rate was at 1.6 L/min. All calibration curves for the analytes showed good linear regression (R² > 0.9992) within test ranges. The established method was validated for intra-day and inter-day precisions (RSDs < 5%) and accuracy (recovery 94.23–106.87%). The validated method was successfully applied to determinate nine triterpenoids in 15 samples from the leave or fruit of P. guajava. In addition, the α-glucosidase inhibition assay showed good α-glucosidase inhibition activity in almost all the determined triterpenoids. The present study suggested that triterpenoids should be the quality control markers for P. guajava and HPLC–DAD–ELSD was an effective tool for the quality control of P. guajava.

In vitro Screening for Antioxidant, Antimicrobial, and Antidiabetic Properties of Some Korean Native Plants on Mt. Halla, Jeju Island

In this study, Prunus padus, Lonicera caerulea, Berberis amurensis, and Ribes maximowiczianum, which are mainly distributed on Mt. Halla, Jeju Island, have been investigated for their antioxidant, antimicrobial, and antidiabetic activities. The methanol extracts of R. maximowiczianum leaves and P. padus branches exhibited significant and dose-dependent antioxidant activity including electron-donation ability and reducing power. To analyze the antimicrobial activity, each extract was tested by a serial two-fold dilution method against five selected gram-positive bacteria and four gram-negative bacteria, and this suggested that P. padus branches possessed the maximum antimicrobial activity against most of the gram-positive bacteria tested. In addition, the methanol extracts of P. padus branches exhibited the highest α-glucosidase inhibitory activity with an IC₅₀ value of 1.0±0.1 μg/ml, indicating that P. padus is a promising source as a herbal medicine.