Lyonin A, a new 9,10-Secograyanotoxin from Lyonia ovalifolia

Screening of Antioxidant, Antibacterial, Anti-Adipogenic, and Anti-Inflammatory Activities of Five Selected Medicinal Plants of Nepal

Introduction

Herbal products have been widely used for the treatment of diseases throughout the ages. In this research, we investigated antioxidant, antibacterial, anti-adipogenic, and anti-inflammatory activities of methanolic extracts of five ethnomedicinally important plants; namely, Alnus nepalensis, Dryopteris sparsa, Artocarpus lacucha, Litsea monopetala, and Lyonia ovalifolia.

Methods

We investigated the DPPH free radical scavenging potential, sensitivity of selected bacterial strains towards the extracts using a disc diffusion assay, anti-inflammatory activity in RAW-264.7 cells, and anti-adipogenic activity by the ORO assay in 3T3-L1 preadipocytes.

Results and discussion

The extract of A. nepalensis showed significant antioxidant activity (IC50=4.838 µg/mL), followed by A. lacucha, L. monopetala, and L. ovalifolia, exhibiting comparable IC50 values to that of ascorbic acid (IC50=5.063 µg/mL). Alnus nepalensis also showed good antibacterial activity in disc diffusion methods, with remarkable zones of inhibition in A. baumannii (14.66 mm) and P. mirabilis (15.50 mm) bacterial species. In addition, A. nepalensis was found to increase adipogenesis in 3T3-L1 cells, evidenced by increased lipid deposition in differentiated 3T3-L1 cells. A similar pattern of increased adipogenesis was observed on treatment with L. ovalifolia extracts. On the other hand, A. lacucha effectively reduced lipid deposition in 3T3-L1 cells at 100 µg/mL (75.18±6.42%) by inhibiting adipogenesis, showing its potential use in the management of obesity. Furthermore, A. lacucha 100 µg/mL (15.91±0.277 µM) and L. monopetala 75 µg/mL (12.52±0.05 µM) and 100 µg/mL (11.77±0.33 µM) significantly inhibited LPS-induced nitric oxide production in RAW 264.7 cells. Also, A. nepalensis and L. ovalifolia inhibited NO production significantly, endorsing their anti-inflammatory potential.

Conclusion

The findings from these in-vitro studies suggest that the selected five plants possess remarkable antioxidant, antibacterial, anti-adipogenic, and anti-inflammatory activities. This study opens the door to conduct further advanced in-vivo experiments to find possible lead compounds for the development of valuable therapeutic agents for common health problems.

Structurally diverse diterpenoids from Pieris japonica as potent analgesics

Sixteen diterpenoids (1-16) including 10 new ones, pierisjaponins A-J (1-10), were isolated and identified from Pieris japonica, and their structures were classified into eight diverse carbon skeletons. Pierisjaponins A (1) and B (2) represent the first 1,5-seco-grayanane diterpenoid glucosides and only showed 17 carbon resonances instead of 26 carbons in the ¹³C NMR spectra, their structures were finally defined by single-crystal X-ray diffraction, and the unusual NMR phenomena were explained. Pierisjaponin E (5) is the first mollane diterpene glucoside. This is the first time to report ent-labdane (3, 4, and 11) and ent-rosane (15) type diterpenoids from the Ericaceae plants, which provided the precursors of the Ericaceae diterpenoids and enlarged the chemical diversity of Ericaceae diterpenoids. All the 16 isolates showed potent analgesic activities, and this is the first time to describe the analgesic activities of 1,5-seco-grayanane, ent-labdane, mollane, and ent-rosane type diterpenoids. A preliminary structure-activity relationship is discussed, which provided new clues to design novel analgesics based on the Ericaceae diterpenoids.

Bioactive megastigmane glucosides and monoterpenes from Lyonia ovalifolia

Three new megastigmane glucosides (1-3) and two new monoterpenes (4-5), together with 14 related known compounds (6-19) were isolated from the twigs and leaves of Lyonia ovalifolia. The structures of the new compounds were determined by extensive MS, NMR, CD experiments and chemical methods. Compounds 2, 6, and 18 displayed potent antiviral activity against Coxsackie B3, with IC₅₀ values between 6.4 and 14.6 µM. Additionally, compounds 6, 10, and 11 exhibited noteworthy anti-inflammatory activities, with inhibition rates ranging from 54.55% to 83.33% under the concentration of 10^-5 M.

New iridoids from Lyonia ovalifolia and their anti-hyperglycemic effects in mice pancreatic islets

Phytochemical investigation on the aerial parts of Lyonia ovalifolia (Wall.) Drude led to the isolation of three new iridoids, lyonofolin A (1), lyonofolin B (2), and lyonofolin C (3), and a known iridoid, gelsemiol (4). Structures of compounds 1-4 were determined by extensive spectroscopic analyses, including EI-MS, HREI-MS, UV, IR, and 1D- and 2D-NMR (HMBC, HSQC, COSY, NOESY) spectroscopic methods. The effect of insulin secretion of compounds 1, 2, and 4 were evaluated in mice pancreatic islets cellular model. This insulin secretory assay demonstrated that compound 2 potentiates glucose-induced insulin secretion, and thus can serve as a new insulin secretagogue for the treatment of diabetes. The newly isolated compounds were further evaluated against normal 3 T3 cell lines for cytotoxicity, where they did not show any cytotoxicity.

Structural Diversity and Biological Activity of the Genus Pieris Terpenoids

Secondary metabolites, particularly the grayanane diterpenoids produced by the members of genus Pieris, have been investigated in past decades for their remarkable antifeedant and insecticidal activities and toxicity. Grayanoids exhibit diverse biological properties such as antifeedant, insecticidal, cAMP regulatory, and sodium-channel-modulating activities. Structural complexity and diverse bioactivity of grayanoids have made them attractive targets for chemical, biological, and synthetic purposes. The current review synthesized findings published from 1966 to 2017, which include 135 reports that describe 130 terpenoids, including 103 grayanoids. The distribution, structure, skeleton, as well as the antifeedant and insecticidal activity of terpenoids, particularly the grayanane diterpenoids, are discussed in detail in this review. In cases where sufficient information is available, the structure-activity relationships of their antifeedant activity are also presented. We hope that this contribution will prompt more scientists to pay attention to these diterpenoids, which may be potentially applied in the agricultural field.

New Antifeedant Grayanane Diterpenoids from the Flowers of Pieris formosa

Three new grayanane diterpenoids, pierisoids C‒E (1–3), as well as 10 known ones (4–13), were evaluated from the flowers of Pieris formosa, which is used as an insecticide in rural areas of China. Their structures were elucidated on the basis of extensive 1D and 2D NMR spectroscopic data analyses. Significant antifeedant activity of 1, 3 and 10 against the beet armyworm (Spodoptera exigua) was found, indicating that these diterpenoids might also be involved in the plant defense against insect herbivores.

Antiviral Triterpenes from the Twigs and Leaves of Lyonia ovalifolia

Eleven new 9,10-seco-cycloartan triterpene glycosides (1-11), seven new lanostane triterpene glycosides (12-18), and two new ursane triterpenoids (19-20) were isolated from the twigs and leaves of Lyonia ovalifolia. The structures of these compounds were elucidated by extensive MS and NMR spectroscopic analysis. The absolute configuration of compound 1a (the aglycone of 1) was established by X-ray crystallography, and that of C-24 in compounds 2, 7, and 12 was established by Mo₂(OAc)₄-induced electronic circular dichroism experiments. All compounds were evaluated for their antiviral [herpes simplex virus-1 (HSV-1), influenza A/95-359 (A/95-359), and Coxsackie B3 (CVB3)] activity. Compounds 1, 1a, 2a, 12a, 13, and 16 exhibited potent activity against HSV-1, with IC₅₀ values from 2.1 to 14.3 μM, while compounds 1a, 2a, 12a, 13, and 12-2a exhibited potent activity against A/95-359, with IC₅₀ values from 2.1 to 11.1 μM. In turn, compounds 1, 1a, 2a, 12a, and 13 exhibited potent activity against CVB3, with IC₅₀ values from 2.1 to 11.1 μM.

Rhodomollins A and B, two Diterpenoids with an Unprecedented Backbone from the Fruits of Rhododendron molle

Two new grayanoids, rhodomollin A (1) and rhodomollin B (2), possessing an unprecedented D-homo grayanane carbon skeleton, were isolated from the fruits of Rhododendron molle. The structures of 1 and 2 were fully characterized using a combination of spectroscopic analyses and X-ray crystallography. Rhodomollin B (2) exhibited modest activity against influenza virus A/95-359, with an IC₅₀ value of 19.24 μM.

From 'mad honey' to hypotensive agents, the grayanoid diterpenes

The toxicity of Rhododendron species and other members of the Ericaceae which is due to the grayanoid diterpenes, is described. Their structures, biogenesis and biological activity is reviewed.

Diterpenoids from the flowers of Rhododendron molle

A new seco-kalmane-type diterpenoid, seco-rhodomollone (1), five new grayanane-type diterpenoids, rhodomollein XXI (2), 6-O-acetylrhodomollein XXI (3), 6,14-di-O-acetylrhodomollein XXI (4), rhodomollein XXII (5), and 2-O-methylrhodomollein XI (6), and two new kalmane-type diterpenoids, rhodomolleins XXIII (7) and XXIV (8), together with seven known compounds, were isolated from the flowers of Rhododendron molle collected in Guangxi Province, China. The absolute configurations of 1 and 3 were defined by single-crystal X-ray diffraction experiments. Compound 1 possesses an unprecedented 1,5-seco-kalmane skeleton presumably derived by cleavage of the C-1-C-5 bond of the kalmane skeleton. Compounds 2-4 represent the first examples from a natural source of grayanane-type diterpenoids with a chlorine substituent.

Pierisformotoxins A-D, polyesterified grayanane diterpenoids from Pieris formosa and their cAMP-decreasing activities

Four highly acylated diterpenoids, designated as pierisformotoxins A-D (1-4, resp.), along with 26 known compounds, were isolated from the flowers of Pieris formosa. Among them, pierisformotoxins A and B (1 and 2, resp.) were new highly acylated grayanane diterpenoids, of which the five-membered ring A has undergone an oxidative cleavage between C(3) and C(4), followed by lactonization, to give rise to a five-membered lactone ring between C(3) and C(5), differing from the previously reported grayanane diterpenoids with a 5/7/6/5 ring system. Results of the cAMP-regulation-activity assay showed that pierisformotoxin C (3) at 10 μM (inhibitory ratio (IR): 10.1%) or 2 μM (9.8%), and pierisformotoxin B (2) at 50 μM (13.9%) significantly decreased the cAMP level in N1E-115 neuroblastoma cells (p<0.05).

Neopierisoids A and B, two new chlorinated 3,4-seco-grayanane diterpenoids with antifeedant activity from flowers of Pieris japonica

Two new chlorinated multiacylated 3,4-seco-grayanane diterpenoids, neopierisoids A and B (1 and 2), were isolated from flowers of the poisonous plant Pieris japonica and were identified from spectroscopic analysis and X-ray diffraction data. Both compounds showed obvious antifeedant activity against Pieris brassicae with an EC50 of 10.07 μg/cm(2) for 1 and 5.33 μg/cm(2) for 2, indications of toxic properties. Chlorinated 3,4-seco-grayanane diterpenoids in P. japonica may play a defensive role against herbivores.

Two new grayanane diterpenoids from the flowers of Rhododendron molle

A phytochemical investigation of the flowers of Rhododendron molle has yielded two new grayanane diterpenoids, rhodomolleins F and G (1, 2). Compounds 1 and 2 possessed an oxo-bridge between C-5 and C-9, and their structures were elucidated on the basis of interpretation of spectroscopic data, including 1D and 2D NMR techniques.