A New Clerodane from the Leaves of Croton krabas and Its Cholinesterase Inhibitory Activities

Chromatographic separation of the leaves of Croton krabas resulted in the isolation of one new clerodane, crotoeurin D (1), along with two known compounds, 6S-crotoeurin C (2) and blumenol A (3). Their structures were determined based on extensive nuclear magnetic resonance spectroscopic data analysis and mass spectrometry. The absolute configuration of the new clerodane was assigned by nuclear overhauser effect spectroscopy correlations and electronic circular dichroism calculations. Compound 1 exhibited significant acetylcholinesterase and butyrylcholinesterase inhibitory activities. Moreover, the binding modes of 1 revealed that its structure formed strong hydrogen bonds and hydrophobic interactions with the active sites of both enzymes.

Three New Clerodane Diterpenoids and Their NLRP3 Inflammasome Activation Inhibitory Activity from Callicarpa arborea Roxb

Three new compounds callicarpenoids A-C (1-3), were isolated from the stems of Callicarpa arborea Roxb together with fifteen known compounds (4-18). The structures of these compounds were elucidated using advanced spectroscopic techniques, including 1D and 2D NMR, UV, IR, HR-ESI-MS, ECD, ORD, and quantum chemical calculations. Compound 3, a rare rearranged diterpenoid with a fused 5/6-ring system demonstrated strong potential as an inhibitor of the NLRP3 inflammasome activation with an IC50 value of 3.153 μM. It effectively reduced GSDMD-NT production, inhibited caspase-1 activation, and suppressed IL-1β secretion, thereby mitigating NLRP3 inflammasome-induced pyroptosis in J774A.1 cells. These findings suggest that compound 3 warrants further research and development as a promising NLRP3 inflammasome inhibitor.

The discovery of potentially active diterpenoids to inhibit the pyroptosis from Callicarpa arborea

Pyroptosis is a programmed-inflammatory cell death, which leads to release of inflammatory cellular contents and formation of inflammation. Uncontrollable pyroptosis can result in serious immune diseases, such as cytokine release syndrome (CRS), sepsis, disseminated intravascular coagulation (DIC), and acute organ damage, including acute respiratory distress syndrome (ARDS) and acute kidney injury (AKI). Members of the Callicarpa genus are significant raw materials for traditional Chinese medicine, widely used for analgesia, hemostasis, and anti-inflammation. Previously, we have reported some ent-clerodane diterpenoids from Callicarpa arborea, shown potent inhibitory effects against pyroptosis. In this study, we went on investigating this kind of diterpenoids, and yielded 66 ent-clerodane diterpenoids, including 52 new compounds, from Callicarpa arborea. Their structures featured with a 5/6- (1-25) or a 6/6- (26-66)-fused double-ring scaffolds, were elucidated using spectroscopic data, electrostatic circular dichroism (ECD) and X-ray diffraction analyses. Screening for the inhibitory activity against pyroptosis by detecting of IL-1β secretion in J771A.1 cells, revealed 28 compounds with an IC₅₀ below 10.5 μM. Compound 1 was the most potent with an IC₅₀ of 0.68 μM and inhibited the J774A.1 macrophage pyroptosis by blocking the NLR pyrin domain containing 3 (NLRP3) inflammasome activation. An in vivo study further revealed that compound 1 decreased infiltration of CD11b + F4/80 + macrophages into lung and attenuated the lipopolysaccharide (LPS)-induced lung injury. Taken together, this study indicated the potential of compound 1 as a candidate for pyroptosis-related inflammation treatment, as well as provided the chemical and pharmacological basis for the further development of Callicarpa genus as a herbal medicine.

Clerodane Diterpenoids Identified from Polyalthia longifolia Showing Antifungal Activity against Plant Pathogens

In the search for new natural resources showing plant disease control effects, we found that the methanol extract of Polyalthia longifolia suppressed fungal disease development in plants. To identify the bioactive substances, the methanol extract of P. longifolia was extracted by organic solvents, and consequently, four new 2-oxo-clerodane diterpenes (1-4), a new 4(3 → 2)-abeo-clerodane diterpene (5), together with ten known compounds (6-16) were isolated and identified from the extracts. Of the new compounds, compound 2 showed a broad spectrum of antifungal activity with moderated minimum inhibitory concentration (MIC) values in a range of 50-100 μg/mL against tested fungal pathogens. Considering with the known compounds, compound 6 showed the most potent antifungal activity with an MIC value in the range of 6.3-12.5 μg/mL. When compound 6 was evaluated for an in vivo antifungal activity against rice blast, tomato late blight, and pepper anthracnose, compound 6 reduced the plant disease by at least 60% compared to the untreated control at concentrations of 250 and 500 μg/mL. Together, our results suggested that the methanol extract of twigs and leaves of P. longifolia and its major compound 6 could be used as a source for the development of eco-friendly plant protection agents.

Clerodane Diterpenoids from Callicarpa hypoleucophylla and Their Anti-Inflammatory Activity

Plants of the genus Callicarpa are known to possess several medicinal effects. The constituents of the Taiwan endemic plant Callicarpa hypoleucophylla have never been studied. Therefore, C. hypoleucophylla was selected for our phytochemical investigation. Two new clerodane-type diterpenoids, named callihypolins A (1) and B (2), along with seven known compounds were isolated from the leaves and twigs of the Lamiaceae plant C. hypoleucophylla and then characterized. The structures of compounds 1 and 2 were elucidated by spectroscopic data analysis, specifically, two-dimension nuclear magnetic resonance (NMR). The anti-inflammatory activity of compounds 1-9 based on the suppression of superoxide anion generation and elastase release was evaluated. Among the isolates, compounds 2-4 showed anti-inflammatory activity (9.52-32.48% inhibition at the concentration 10 μm) by suppressing superoxide anion generation and elastase release. Our findings not only expand the description of the structural diversity of the compounds present in plants of the genus Callicarpa but also highlight the possibility of developing anti-inflammatory agents from Callicarpa endemic species.

3,4- seco-Norclerodane Diterpenoids from the Roots of Polyalthia laui

Ten new clerodane diterpenoids, polylauioids A-J (1-10), and five known analogues (11-15) were isolated from the roots of Polyalthia laui. Among the new compounds, 3 and 8 are artifacts. The structures were elucidated using spectroscopic methods and by comparison with published NMR spectroscopic data. The absolute configurations of 4, 5, and 7 were defined based on single-crystal X-ray diffraction and electronic circular dichroism data. Compounds 1 and 2 represent the first examples of rearranged 3,4- seco-norclerodane diterpenoids, and a putative biosynthesis pathway for these compounds is proposed. Compounds 1, 4, 6, 7, 9, and 10 showed anti-HIV activities with EC₅₀ values ranging from 12.2 to 35.2 μM.

α-Glucosidase Inhibitors from Salvia circinata

A dried infusion prepared from the aerial parts of Salvia circinata did not provoke acute toxicity in mice (LD₅₀ > 5 g/kg). This infusion showed poor hypoglycemic and antihyperglycemic effects (100-570 mg/kg) when tested in normal and hyperglycemic mice using acute and oral glucose tolerance tests, respectively. However, this infusion possessed antihyperglycemic action in vivo during an oral sucrose tolerance test (31.6-316 mg/kg), suggesting the presence of α-glucosidase inhibitors in S. circinata. Fractionation of a nonpolar extract of the aerial parts of the plant yielded a new biflavone (1) and four new neoclerodane diterpenoid glucosides (2-5) along with the known compounds amarisolide (6), pedalitin (7), apigenin-7-O-β-d-glucoside (8), and the flavone 2-(3,4-dimethoxyphenyl)-5,6-dihydroxy-7-methoxy-4H-chromen-4-one (9). Compounds 1 and 6-9 were active against mammalian α-glucosidases; 6 and 7 were also active against a recombinant α-glucosidase from Ruminococcus obeum and reduced significantly the postprandial peak during an oral sucrose tolerance test in healthy mice, consistent with their α-glucosidase inhibitory activity. Molecular docking and dynamic studies revealed that compounds 6 and 7 might bind to α-glucosidases at the catalytic center of the enzyme.

Diterpenes from Grangea maderaspatana

Phytochemical investigation of the ethanolic extract of Grangea maderaspatana led to isolation of gramaderins A-D, together with thirteen known compounds. All isolates were assayed for their anti-inflammatory activities. Consequently, 5,7-dihydroxy-3,6,3',4',5'-pentamethoxyflavone and 5,3'-dihydroxy-3,6,7,4',5'-pentamethoxyflavone showed significant bioactivities by inhibiting superoxide anion generation. 8-Acetoxy-pentadeca-1,9Z,14-trien-4,6-diyne-3-ol also demonstrated potent inhibition on elastase release. The gramaderins A/C (β-alkyl linked γ-lactone) and gramaderins B/D (α-alkyl linked γ-lactone) co-exist in this plant material, of which the latter derivatives are few in nature. Gramaderins C/D possess a special linear dilactone diterpene skeleton, which never been reported.

Clerodane diterpenes: sources, structures, and biological activities

Covering: 1990 to 2015The clerodane diterpenoids are a widespread class of secondary metabolites and have been found in several hundreds of plant species from various families and in organisms from other taxonomic groups. These substances have attracted interest in recent years due to their notable biological activities, particularly insect antifeedant properties. In addition, the major active clerodanes of Salvia divinorum can be used as novel opioid receptor probes, allowing greater insight into opioid receptor-mediated phenomena, as well as opening additional areas for chemical investigation. This article provides extensive coverage of naturally occurring clerodane diterpenes discovered from 1990 until 2015, and follows up on the 1992 review by Merritt and Ley in this same journal. The distribution, chemotaxonomic significance, chemical structures, and biological activities of clerodane diterpenes are summarized. In the cases where sufficient information is available, structure activity relationship (SAR) correlations and mode of action of active clerodanes have been presented.