Structure and cytotoxicity of diterpenoids from Isodon adenolomus

Six new diterpenoids with anti-inflammatory and cytotoxic activity from Isodon serra

Diterpenoids occupy an important slot of the natural products diversity space with wide ranges of bioactivities and complex structures, providing potential applications for the development of therapeutics. In this study, we reported four new abietane-type diterpenoids viroxocin B-E (1-4), a new totarane-type diterpenoid viroxocin F (5), and a new sempervirane-type diterpenoid viroxocin G (6) along with four known compounds (7-10), isolated and identified from a widely used Traditional Chinese Medicine, Isodon serra (I. serra). Their structures were established by spectroscopic data analysis, experimental and calculated electronic circular dichroism (ECD) data, as well as X-ray diffraction analysis. Compounds 2, 5, 7, 8 and 10 exhibited promising anti-inflammatory activities in lipopolysaccharide (LPS)-induced RAW 267.4 cells, and their inhibition rates on NO production were more than 60% at 10 μM. Compound 7 showed cytotoxicity against human renal cell carcinoma 769P at 20 μM, the inhibition rate was 52.66%.

Recent Developments in the Syntheses of C-20-Oxygenated ent-Kaurane Diterpenoids

Ent-kaurane diterpenes are a large group of natural products, with more than 1,000 compounds since their discovery. Due to their excellent biological activities and complex polycyclic structures, these compounds have attracted organic synthesis chemists around the world to be devoted to achieve their total synthesis. At present, the isolated C-20-oxygenated ent-kaurane diterpenes are the most abundant of these natural products, reaching more than 350 in number. However, only total syntheses of 3,20-epoxy, 7,20-epoxy and 19,20-lactone ent-kaurane diterpenes have been reported. In this review, we elaborate the synthesis of these three types of C-20 oxygenated ent-kaurane natural products, discuss these synthetic strategies in detail, and provide good guidance and reference for the synthesis of other C-20 oxygenated compounds.

Ponicidin Treatment Improved the Cell Proliferation, Differentiation, and Calcium Mineralization on the Osteoblast-Like MG-63 Cells

Osteoporosis is a general bone-related ailment characterized by reduced bone density and quality, elevated bone fragility, and fractures. It was reported that both aged men and women has an increased risks of osteoporosis. The current research work focused to unveil the beneficial roles of ponicidin treatment in the proliferation and calcium deposition on the osteoblast-like MG-63 cells. The effect of 5 and 10 µg/ml of ponicidin on the cell proliferation was assessed. The viability of ponicidin-supplemented MG-63 cells was inspected by MTT test. The contents of osteocalcin, collagen, and ALP activity in the ponicidin administered cells were assessed by kits. The level of calcium mineralization was examined by ARS staining technique. The ponicidin treatment remarkably improved the proliferation of MG-63 cells. The ponicidin did not affect the MG-63 cells viability but promoted its viability 24- and 48-h treatment. The contents of osteocalcin, collagen, and ALP activity in the 5 and 10 µg/ml of ponicidin-supplemented MG-63 cells were found increased than the control cells. The ponicidin also increased the level of calcium deposition in MG-63 cells, which is assessed by ARS staining. In conclusion, it was clear that ponicidin improved the proliferation and calcium mineralization in a MG-63 cells. Therefore, it was clear that ponicidin has helpful roles on the new bone development as a hopeful therapeutic candidate to treat the bone-related disease like osteoporosis.

Pharmacophore based virtual screening for natural product database revealed possible inhibitors for SARS-COV-2 main protease

The challenge continues globally triggered by the absence of an approved antiviral drug against COVID-19 virus infection necessitating global concerted efforts of scientists. Nature still provides a renewable source for drugs used to solve many health problems. The aim of this work is to provide new candidates from natural origin to overcome COVID-19 pandemic. A virtual screening of the natural compounds database (47,645 compounds) using structure-based pharmacophore model and molecular docking simulations reported eight hits from natural origin against SARS-CoV-2 main proteinase (Mpro) enzyme. The successful candidates were of terpenoidal nature including taxusabietane, Isoadenolin A & C, Xerophilusin B, Excisanin H, Macrocalin B and ponicidin, phytoconstituents isolated from family Lamiaceae and sharing a common ent-kaurane nucleus, were found to be the most successful candidates. This study suggested that the diterpene nucleus has a clear positive contribution which can represent a new opportunity in the development of SARS-CoV-2 main protease inhibitors.

Total Synthesis of Isorosthin L and Isoadenolin I

Total syntheses of two Isodon diterpenes, isorosthin L and isoadenolin I, are reported. The synthetic strategy features a quick assembly of two simple building blocks through a diastereoselective intermolecular aldol reaction and a subsequent radical cyclization for efficient construction of a rather complex advanced intermediate bearing a quaternary stereocenter present in all Isodon diterpenes. Oxidative cleavage of the C-C bond in the cyclopentane enabled the conversion to a lactone moiety which is desired for the construction of the molecular skeleton through reductive coupling with an aldehyde carbonyl group.

Synthesis of Complex Diterpenes: Strategies Guided by Oxidation Pattern Analysis

With complex molecular architectures, intriguing oxidation patterns, and wide-ranging biological activities, diterpene natural products have greatly impacted research in organic chemistry and drug discovery. Our laboratory has completed total syntheses of several highly oxidized diterpenes, including the ent-kauranoids maoecrystal Z, trichorabdal A, and longikaurin E; the antibiotic pleuromutilin; and the insecticides ryanodol, ryanodine, and perseanol. In this Account, we show how analysis of oxidation patterns and inherent functional group relationships can inform key C-C bond disconnections that greatly simplify the complexity of polycyclic structures and streamline their total syntheses. In articulating these concepts, we draw heavily from the approaches to synthetic strategy that were codified by Evans, Corey, Seebach, and others, based on the formalism that heteroatoms impose an alternating acceptor and donor reactivity pattern upon a carbon skeleton. We find these ideas particularly useful when considering oxidized diterpenes as synthetic targets.In the first part of the Account, we describe the use of reductive cyclizations as strategic tactics for building polycyclic systems with γ-hydroxyketone motifs. We have leveraged Sm-ketyl radical cyclizations as "reactivity umpolungs" to generate γ-hydroxyketones in our total syntheses of the Isodon ent-kauranoid diterpenes (-)-maoecrystal Z, (-)-longikaurin E, and (-)-trichorabdal A. Following this work, we identified the same γ-hydroxyketone pattern in the diterpene antibiotic (+)-pleuromutilin, which again inspired the use of a SmI₂-mediated reductive cyclization, this time to construct a bridging eight-membered ring. This collection of four total syntheses highlights how reductive cyclizations are particularly effective umpolung tactics when used to simultaneously form rings and introduce 1,4-dioxygenation patterns.In the second part of the Account, we detail the syntheses of the complex and highly oxidized ryanodane and isoryanodane diterpenes and present the oxidation pattern analysis that guided our synthetic designs. We first discuss our 15-step total synthesis of (+)-ryanodol, which incorporated five of the eight oxygen atoms in just two transformations: a dihydroxylation of (S)-pulegone and a SeO₂-mediated trioxidation of the A-ring cyclopentenone. This latter transformation gave rise to an independent investigation of SeO₂-mediated peroxidations of simple bicyclic cyclopent-2-en-1-ones. The syntheses of (+)-ryanodine and (+)-20-deoxyspiganthine are also presented, which required modified end-game strategies to selectively incorporate the key pyrrole-2-carboxylate ester. Finally, we describe our fragment coupling approach to prepare the isoryanodane diterpene (+)-perseanol. Using a similar oxidation pattern analysis to that developed in the synthesis of ryanodol, we again identified a two-stage strategy to install the five hydroxyl groups. This strategy was enabled by a Pd-mediated carbopalladation/carbonylation cascade and leveraged unexpected, emergent reactivity to sequence a series of late-stage oxidations.While each of the diterpene natural products discussed in this Account present unique synthetic questions, we hope that through their collective discussion, we provide a conceptual framework that condenses and summarizes the chemical knowledge we have learned and inspires future discourse and innovations in strategy design and methodology development.

Hydrogen sulfide donating ent-kaurane and spirolactone-type 6,7-seco-ent-kaurane derivatives: Design, synthesis and antiproliferative properties

Motivated by our interest in hydrogen sulfide bio-chemistry and ent-kaurane diterpenoid chemistry, 14 hydrogen sulfide donating derivatives (9, 11a-c, 12a-c, 13, 14, 16a-c and 17a-b) of ent-kaurane and spirolactone-type 6,7-seco-ent-kaurane were designed and synthesized. Four human cancer cell lines (K562, Bel-7402, SGC-7901 and A549) and two normal cell lines (L-02 and PBMC) were selected for antiproliferative assay. Most derivatives showed more potent activities than the lead ent-kaurane oridonin. Among them, compound 12b exhibited the most potent antiproliferative activities, with IC₅₀ values of 1.01, 0.88, 4.36 and 5.21 μM against above human cancer cell lines, respectively. Further apoptosis-related mechanism study indicated that 12b could arrest Bel-7402 cell cycle at G1 phase and induce apoptosis through mitochondria related pathway. Through Western blot assay, 12b was shown to influence the intrinsic pathway by increasing the expression of Bax, cleaved caspase-3, cytochrome c and cleaved PARP, meanwhile suppressing procaspase-3, Bcl-2, Bcl-xL and PARP.

7α,20-Epoxy-ent-kaurane Diterpenoids from the Aerial Parts of Isodon pharicus

A phytochemical investigation of an ethyl acetate extract of the aerial parts of Isodon pharicus led to the isolation of 21 new 7α,20-epoxy-ent-kaurane diterpenoids, pharicins C-W (1-21), and 29 known (22-50) analogues. The structural characterization of 1-21 and assignment of their relative configurations were accomplished by spectroscopic data interpretation, while the structures of 1 and 16 were confirmed by X-ray crystallography. The absolute stereostructure of 1 was confirmed by electronic circular dichroism data analysis. Twenty-five of the diterpenoids were screened for their cytotoxic activities against a panel of tumor cell lines, including HL-60, SMMC-7721, A-549, MCF-7, and SW-480. Compounds 11, 16, 38, and 48 exhibited inhibitory activities against these tumor cell lines with IC₅₀ values ranging from 1.01 to 9.62 μM, while 2, 15, 29, and 47 exhibited moderate cytotoxic potency.

Diterpenoids from Isodon species: an update

Covering: December 2005 to June 2016. Previous review: Nat. Prod. Rep., 2006, 23, 673-698Over the last decade, great efforts have been made to conduct phytochemistry research on the genus Isodon, which have led to the isolation and identification of a number of diterpenoids. At the same time, these newly reported diterpenoids with diverse structures have led to new findings on their biological functions and chemical synthesis research. In this update, we review more than 600 new diterpenoids, including their structures, classifications, biogenetic pathways, bioactivities, and chemical synthesis.

A new Prenylated Flavonoid induces G0/G1 arrest and apoptosis through p38/JNK MAPK pathways in Human Hepatocellular Carcinoma cells

Prenylated flavonoids have been demonstrated to possess diverse bioactivities including antitumor effects. One new, daphnegiravone D (1), and four known (2–5) prenylated flavonoids were isolated from Daphne giraldii. Their cytotoxic activities revealed that daphnegiravone D markedly inhibited the proliferation of cancer cells, but had no apparent cytotoxicity on human normal cells. Mechanistically, daphnegiravone D induced G0/G1 arrest and apoptosis, reduced the expression of cyclin E1, CDK2 and CDK4, and promoted the cleavage of caspase 3 and PARP in Hep3B and HepG2 cells. Meanwhile, daphnegiravone D increased the level of phosphorylated p38 and attenuated phosphorylated JNK. Further studies indicated that SB203580 partially reversed daphnegiravone D-induced G0/G1 arrest and apoptosis. The addition of SP600125 to both cell lines increased the cleavage of caspase 3 and PARP, but did not affect the G0/G1 arrest. Besides, in vivo studies demonstrated that daphnegiravone D obviously inhibited tumor growth in a nude mouse xenograft model through suppressing the proliferation of tumor cells, without significant effect on body weight or pathology characteristics. Taken together, the new compound selectively inhibited the proliferation of hepatoma cells via p38 and JNK MAPK pathways, suggesting its potential as a novel natural anti-hepatocellular carcinoma agent.

Ponicidin suppresses HT29 cell growth via the induction of G1 cell cycle arrest and apoptosis

Ponicidin is a diterpenoid extracted from the Chinese herb Isodon adenolomus, which has been reported as a therapeutic cytotoxic drug that may be used to treat various types of human cancer. The present study aimed to determine the antitumor effects of ponicidin, and to investigate its underlying mechanisms in colorectal cancer. The HT29 colorectal cancer cell line was used to detect the cytotoxicity of various doses of ponicidin. Cell proliferation was measured using a Cell Counting kit‑8 assay. Cell cycle and apoptosis analyses were performed using flow cytometry and fluorescent microscopy. Western blot analysis was used to measure the expression levels of apoptosis‑associated proteins following treatment with ponicidin. Treatment with ponicidin significantly suppressed HT29 cell growth by inducing G1 cell cycle arrest and apoptosis. The AKT and MEK signaling pathways were also suppressed by ponicidin; however, the p38 signaling pathway was significantly activated. The expression levels of caspase 3 and Bax protein were markedly upregulated following treatment with ponicidin. These results suggest that ponicidin exerts significant antitumor effects via the induction of cell cycle arrest and apoptosis in colorectal cells. In conclusion, ponicidin acted as an inducer of apoptosis, and may be used as a therapeutic cytotoxic drug to treat human cancer, including colorectal cancer.

Cytotoxic ent-kaurane diterpenoids from Salvia cavaleriei

Fifteen new ent-kaurane diterpenoids, compounds 1-15, and two known analogues, 4-epi-henryine A (16) and leukamenin E (17), were isolated from the whole plants of Salvia cavaleriei. The structures of the new compounds were established by spectroscopic methods, and their absolute configurations were determined by electronic circular dichroism and single-crystal X-ray diffraction analyses with Cu Kα radiation. Compounds 1-15 were evaluated for their cytotoxicity against five human cancer cell lines, HL-60, SMMC-7721, A-549, MCF-7, and SW480, as well as the noncancerous Beas-2B cell line. Compounds 1-10, 12, 14, and 15 showed broad-spectrum cytotoxicity, with compounds 1, 3, 6-10, 12, and 15 exhibiting more potent cytotoxicity than the positive control, cis-platin, with IC50 values ranging from 0.65 to 6.4 μM.

Bioactive ent-kaurane diterpenoids from Isodon rosthornii

Isorosthin A (1), the first 20-nor-enmein-type diterpenoid, and 15 new ent-kauranoids, isorosthins B-P (2-16), along with 22 known analogues were isolated from the aerial parts of Isodon rosthornii. The structures of 1-16 were elucidated by means of spectroscopic analysis. The relative configuration of 2 and the absolute configuration of 3 were determined by single-crystal X-ray diffraction. Cytotoxicity evaluation against five human tumor lines showed inhibitory effects by several of the compounds tested. Furthermore, 12 of the isolates exhibited inhibitory activity against nitric oxide production in LPS-activated RAW264.7 macrophages.

Natural products chemistry research: progress in China in 2011

This article reviews the progress made by Chinese scientists in the field of natural products chemistry in 2011. Selected compounds with unique structural features and/or promising bioactivities are described herein on the basis of structural types.

Podocarpane, isopimarane, and abietane diterpenoids from Isodon lophanthoides var. graciliflorus

Four new diterpenoids including two podocarpanes, graciliflorins A (1) and B (2), an isopimarane acetal, graciliflorin C (3), and a rearranged abietane, graciliflorin D (4) were isolated from the aerial parts of Isodon lophanthoides var. graciliflorus (Lamiaceae) along with podocarpa-8,11,13-triene-3α,13-diol (5) and micranthin B (6). Their structures were elucidated based on the spectroscopic data. The in vitro cytotoxicity of compounds 1-4 and 6 against human carcinoma A549, MCF-7, and HeLa cell lines were evaluated using the MTT colourimetric assay. Micranthin B (6) showed moderate activity against all the cells with IC(50) values of 16.29, 18.20, and 22.25 μM, while compounds 1-4 were inactive (IC(50)>50 μg/ml).

Laxiflorolides A and B, epimeric bishomoditerpene lactones from Isodon eriocalyx

Laxiflorolides A (1) and B (2), two unprecedented epimeric bishomoditerpene lactones with a unique C(22) framework, along with laxiflorins P-R (3-5), maoecrystal P (6), maoecrystal C (7), and eriocalyxin B (8), were isolated from the leaves of I. eriocalyx var. laxiflora. The structures of 1 and 2, including the absolute configurations, were determined by spectroscopic methods and single-crystal X-ray diffraction analysis. All of the compounds isolated were evaluated for their cytotoxicity against five tumor cell lines. Compounds 3, 6, and 8 showed remarkable cytotoxic activity against certain cell lines compared with the positive control.