Di- and Triterpenoids from the Rhizomes of Isodon amethystoides and Their Anti-inflammatory Activities

Verbenalinosides A and B, Two Iridoid-Phenylethanoid Glycoside Conjugates from Verbena officinalis and Their Hepatoprotective Activity

Two novel iridoid-phenylethanoid glycoside heterodimers, verbenalinoside A (1) and B (2), along with two known precursors, verbenalin (3) and verbascoside (4) were isolated from the dry aerial parts of Verbena officinalis. Verbenalinoside A (1) possesses a new 5/6/6/6 core fused by the double bond of iridoid and phenolic hydroxyl groups of the phenylethanoid unit. Verbenalinoside B (2) is a conjugate of verbenalin (3) and verbascoside (4) by an ether bond. The structures of these compounds were elucidated through the comprehensive analysis of spectroscopic data, supported by electronic circular dichroism (ECD) calculations and DP4 plus NMR calculations. Biological assay results showed that 1-4 can concentration-dependent rescue the ethanol-induced hepatotoxicity in LO2 and HepG2 cells, indicating that 1-4 should be potential hepatoprotective constituents of V. officinalis.

Diterpenoids and Triterpenoids from the Aerial Parts of Isodon serra and Their Biological Activities

Five undescribed diterpenoids, serranins A-E (1-5), and four novel triterpenoids, serratic acids A-D (6-9), along with 32 known terpenoids (10-41) were isolated from the aerial parts of Isodon serra. The planar structures of 1-9 and their relative configurations were established on the basis of extensive spectroscopic analysis. Structurally, compounds 6-9 are the first examples of 18,19-seco-ursane p-coumaric or ferulic esters, while compounds 1-5 further enriched the plant's diterpene profile. Bioactivity evaluation revealed that four diterpenoids (2, 10, 12, and 13) exhibited potent cytotoxic activity against four cancer cell lines (B16-F10, A375, A549, and MDA-MB-231) with IC50 values below 10 μM. Remarkably, 7 and 38 exhibited a comparable antimelanogenesis effect to that of positive control (kojic acid) in B16-F10 cells.

Structurally diverse triterpenoids with antibacterial activities from Euphorbia humifusa

An exploration of antibacterial components from the whole plant of Euphorbia humifusa led to the isolation of 14 new triterpenoids, euphohumifusoids A-N (1-7 and 9-15), as well as four known analogues (8 and 16-18). Their structures were elucidated by extensively analysis of the spectroscopic data and X-ray crystallography using Cu Kα radiation. Among them, euphohumifusoid A (1) bears an unique 6(7 → 8)abeo scaffold originated from a D:C-friedo-oleanane skeleton for the first time, euphohumifusoids H and I (9 and 10) possess a rare α,β-unsaturated-γ-lactone chain originated from 25,26,27-trinordammaranes, and euphohumifusoid L (13) is a highly modified 3,4-seco-25,26,27-trinorcycloartane. Notably, in antibacterial bioassay, compound 1 displayed excellent antibacterial activities against Bacillus cereus, Staphylococcus aureus, and S.epidermidis with MIC of 12.5, 25, and 25 μg/mL, comparable to the positive controls. Upon exposure to 1 and 2 MIC of 1, B.cereus underwent drastic morphological changes, resulting in complete disruption of the cells. Meanwhile, compound 1 also exhibited remarkable antibiofilm activity against B.cereus at 1 MIC and 2 MIC.

NMR-Guided Isolation of Anti-inflammatory Carabranolides from the Fruits of Carpesium abrotanoides L

Carabranolides present characteristic NMR resonances for the cyclopropane moiety, which distinctly differ from those of other compounds and were used for an NMR-guided isolation in this study. As a result, 11 undescribed carabranolides (1-11), along with five known ones (12-16), were isolated from the fruits of Carpesium abrotanoides L. Compounds 1-11 are new esters of carabrol at C-4 with different carboxylic acids. Their structures were elucidated by HRESIMS and NMR spectroscopic data analysis. The biological evaluation showed that compounds 2-4, 15, and 16 exhibited significant inhibitory activity against LPS-induced NO release with an IC50 value of 5.6-9.1 μM and dose-dependently decreased iNOS protein expression in RAW264.7 cells.

Naturally Occurring Norsteroids and Their Design and Pharmaceutical Application

The main focus of this review is to introduce readers to the fascinating class of lipid molecules known as norsteroids, exploring their distribution across various biotopes and their biological activities. The review provides an in-depth analysis of various modified steroids, including A, B, C, and D-norsteroids, each characterized by distinct structural alterations. These modifications, which range from the removal of specific methyl groups to changes in the steroid core, result in unique molecular architectures that significantly impact their biological activity and therapeutic potential. The discussion on A, B, C, and D-norsteroids sheds light on their unique configurations and how these structural modifications influence their pharmacological properties. The review also presents examples from natural sources that produce a diverse array of steroids with distinct structures, including the aforementioned A, B, C, and D-nor variants. These compounds are sourced from marine organisms like sponges, soft corals, and starfish, as well as terrestrial entities such as plants, fungi, and bacteria. The exploration of these steroids encompasses their biosynthesis, ecological significance, and potential medical applications, highlighting a crucial area of interest in pharmacology and natural product chemistry. The review emphasizes the importance of researching these steroids for drug development, particularly in addressing diseases where conventional medications are inadequate or for conditions lacking sufficient therapeutic options. Examples of norsteroid synthesis are provided to illustrate the practical applications of this research.

Boswellianols A-I, Structurally Diverse Diterpenoids from the Oleo-Gum Resin of Boswellia carterii and Their TGF-β Inhibition Activity

Olibanum, a golden oleo-gum resin from species in the Boswellia genus (Burseraceae family), is a famous traditional herbal medicine widely used around the world. Previous phytochemical studies mainly focused on the non-polar fractions of olibanum. In this study, nine novel diterpenoids, boswellianols A-I (1-9), and three known compounds were isolated from the polar methanolic fraction of the oleo-gum resin of Boswellia carterii. Their structures were determined through comprehensive spectroscopic analysis as well as experimental and calculated electronic circular dichroism (ECD) data comparison. Compound 1 is a novel diterpenoid possessing an undescribed prenylmaaliane-type skeleton with a 6/6/3 tricyclic system. Compounds 2-4 were unusual prenylaromadendrane-type diterpenoids, and compounds 5-9 were new highly oxidized cembrane-type diterpenoids. Compounds 1 and 5 showed significant transforming growth factor β (TGF-β) inhibitory activity via inhibiting the TGF-β-induced phosphorylation of Smad3 and the expression of fibronectin and N-cadherin (the biomarker of the epithelial-mesenchymal transition) in a dose-dependent manner in LX-2 human hepatic stellate cells, indicating that compounds 1 and 5 should be potential anti-fibrosis agents. These findings give a new insight into the chemical constituents of the polar fraction of olibanum and their inhibitory activities on the TGF-β/Smad signaling pathway.

The intramolecular SN2 reaction tautomeric ent-Kauranoids isolated from the aerial parts of Isodon amethystoides

As our ongoing searching for the bioactive natural terpenoids, nine ent-kauranoids (1-9), including three previously undescribed ones (1, 2, and 9), were isolated from the aerial parts of Isodon amethystoides. Their structures were elucidated on the basis of spectroscopic data analysis, including NMR, MS, and ECD. Compounds 1 and 2 were a pair of tautomeric compounds, which was confirmed by the HPLC analysis and low temperature NMR testing. The underlying mechanism of the tautomer was proposed as an intramolecular SN2 reaction, which was explained by quantum chemical calculation. The HOMO-LUMO gap and the free energy revealed the spontaneous of the tautomeric of the 1 and 2. Additionally, the similar phenomena were also found in the two groups of known compounds 3 and 4 and 6 and 7, respectively. Apart from the tautomer, compounds 3 and 4 can be hydrolyzed into 5 through ester hydrolysis in CDCl3, while compounds 6, 7 can be hydrolyzed into 8 through ester hydrolysis. These phenomena were also confirmed through HPLC analysis and low temperature nuclear magnetic resonance tests and the mechanism was studied using quantum chemical calculation.

Hot off the press

A personal selection of 32 recent papers is presented, covering various aspects of current developments in bioorganic chemistry and novel natural products, such as clavirolide L from Clavularia viridis.