Scaparvin A, A Novel Caged cis-Clerodane with an Unprecedented C-6/C-11 Bond, and Related Diterpenoids from the Liverwort Scapania parva

Novel Diterpenoids Incorporating Rearranged Labdanes from the Chinese Liverwort Anastrophyllum joergensenii and Their Anti-inflammatory Activity

Liverworts provide valuable ecological services to improve the sustainability of agriculture, encompassing soil health maintenance and natural pest management. Some liverworts have potential applications in medicine and as food additives. Twenty-two novel diterpenoids (anajoerins A-V), of which anajoerins B-G are rearranged labdanes featuring an unprecedented 6/5 fused ring system, were isolated from the Chinese liverwort Anastrophyllum joergensenii Schiffn. The absolute configurations of all compounds were identified based on high-resolution electrospray ionization mass spectroscopy data, NMR spectra, and ECD calculations. Plausible biogenetic pathways for unprecedented rearranged labdanes were proposed. Seven diterpenoids exhibited anti-inflammatory activity by reducing nitric oxide production in LPS-stimulated RAW264.7 murine macrophages in a dose-dependent manner with IC50s between 9.71 and 56.56 μM. All tested compounds showed no cytotoxicity at the tested concentrations. Western blot analyses of NF-κB p65 downregulation showed that anajoerin L could inhibit the NF-κB signaling pathway. Furthermore, anajoerin L also suppressed the secretion of the ConA-induced proinflammatory cytokines IFN-γ, TNF-α, and IL-6.

Terpenoids from Chinese Liverworts Scapania spp

An investigation of the chemical composition of Chinese liverworts led to the isolation of six new caged clerodane-type diterpenoids, scaparins A-C (1-3) from Scapania koponenii and scaparins D-F (4-6) from S. verrucosa. An unknown ent-trachylobane diterpenoid (7) and three known terpenoid derivatives (8-10) were obtained from S. verrucosa. The structures of the compounds were established on the basis of physical data (IR, UV, HRESIMS, and 1D and 2D NMR), and the absolute configurations were unequivocally confirmed by comparison of the experimental and calculated electronic circular dichroism spectra. Preliminary bioassays showed that compounds 1-7 exhibited moderate to weak quinone reductase-inducing activity in Hepa-1c1c7 cells.

Plagiochianins A and B, Two ent-2,3- seco-Aromadendrane Derivatives from the Liverwort Plagiochila duthiana

Two novel ent-aromadendrane derivatives, plagiochianin A (1), possessing an unprecedented 2,3:6,7-di- seco-6,8-cyclo-aromadendrane carbon scaffold conjugated with three cyclic acetals, and plagiochianin B (2), an exceptional pyridine type aromadendrane alkaloid, were isolated from the Chinese liverwort Plagiochila duthiana. Their structures were established by comprehensive spectroscopic analysis coupled with single-crystal X-ray diffraction and electronic circular dichroism calculations. A plausible biogenetic pathway of these two compounds is presented, and their acetylcholinesterase inhibitory activities are preliminarily tested using TLC-bioautographic assays.

Total Syntheses of Scaparvins B, C, and D Enabled by a Key C-H Functionalization

The clerodane diterpene family possesses an impressive range of bioactivities and high synthetic challenge due to their unique amalgamation of rings, stereocenters, and oxygenation. Herein, we disclose the first total syntheses of three members, scaparvins B, C, and D, through a route fueled by several chemoselective and carefully orchestrated steps. One such operation is a tailored late-stage C-H functionalization converting a carboxylic acid into a lactone through the oxidation of a tertiary C-H bond under conditions that minimize epoxidation of an alkene. This step, among others, afforded critical functionality to complete the targets. In addition, use of an appropriate chiral catalyst with a Rawal diene renders the sequence enantioselective.

Strategies to diversify natural products for drug discovery

Natural product libraries contain specialized metabolites derived from plants, animals, and microorganisms that play a pivotal role in drug discovery due to their immense structural diversity and wide variety of biological activities. The strategies to greatly extend natural product scaffolds through available biological and chemical approaches offer unique opportunities to access a new series of natural product analogues, enabling the construction of diverse natural product-like libraries. The affordability of these structurally diverse molecules has been a crucial step in accelerating drug discovery. This review provides an overview of various approaches to exploit the diversity of compounds for natural product-based drug development, drawing upon a series of examples to illustrate each strategy.

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.

Scapairrins A-Q, Labdane-Type Diterpenoids from the Chinese Liverwort Scapania irrigua and Their Cytotoxic Activity

Seventeen new labdane-type diterpenoids, scapairrins A-Q (1-17), including six pairs of diastereoisomers, and three known analogues (18-20) were isolated from the Chinese liverwort Scapania irrigua. The structures of 1-17 were determined based on a combination of the analysis of their MS and NMR spectroscopic data, single-crystal X-ray diffraction, and electronic circular dichroism calculations. Cytotoxicity testing showed that compounds 7-10 exhibited inhibitory activities against a small panel of human cancer cell lines.

Notolutesins A-J, dolabrane-type diterpenoids from the Chinese liverwort Notoscyphus lutescens

Ten new dolabrane-type diterpenoids, notolutesins A-J (1-10), were isolated from the Chinese liverwort Notoscyphus lutescens, along with four known compounds. The structures of the new compounds were established on the basis of extensive spectroscopic data, and that of 1 was confirmed by single-crystal X-ray crystallography. The absolute configuration of 1 was determined by comparing its experimental and calculated electronic circular dichroism spectra. All of the isolates were evaluated for their cytotoxicity against a small panel of human cancer cell lines, and compound 1 exhibited an IC50 value of 6.2 μM against the PC3 human prostate cancer cell line.

Phytotoxic cis-clerodane diterpenoids from the Chinese liverwort Scapania stephanii

Five cis-clerodane diterpenoids, stephanialides A-E, along with seven known cis-clerodanes, scaparvins A-C, parvitexins B and C, 3-chloro-4-hydroxy-parvitexin A, and scapanialide B, were isolated from the Chinese liverwort Scapania stephanii. Their structures were established unequivocally on the basis of spectroscopic data. The absolute configuration of stephanialide A was determined by analysis of CD data using the octant rule. Phytotoxic activity evaluation showed that this type of diterpenoids can significantly inhibit root elongation of the seeds of Arabidopsis thaliana, Lepidium sativum and Brassica pekinensis.

Diterpenoids from the Chinese liverwort Heteroscyphus tener and their antiproliferative effects

Four new ent-labdane diterpenoids, heteroscyphins A-D (1-4), and four known diterpenoids (5-8) were isolated from the Chinese liverwort Heteroscyphus tener (Steph.) Schiffn. The absolute configuration of compound 1 was defined by single-crystal X-ray diffraction using Cu Kα radiation. Cytotoxicity tests revealed that compounds 3 and 5 exhibited modest activity against seven cancer cell lines. Compound 5 showed inhibitory effects on prostate cancer (PCa) cell proliferation but with less inhibition on non-neoplastic prostate epithelial cells. Compound 5 markedly caused cell growth arrest at the G0/G1 phase and induced cellular apoptosis through ROS-mediated DNA damage in PCa cells.

All-carbon quaternary stereogenic centers in acyclic systems through the creation of several C-C bonds per chemical step

In the past few decades, it has become clear that asymmetric catalysis is one of the most powerful methods for the construction of carbon-carbon as well as carbon-heteroatom bonds in a stereoselective manner. However, when structural complexity increases (i.e., all-carbon quaternary stereogenic center), the difficulty in reaching the desired adducts through asymmetric catalytic reactions leads to a single carbon-carbon bond-forming event per chemical step between two components. Issues of efficiency and convergence should therefore be addressed to avoid extraneous chemical steps. In this Perspective, we present approaches that tackle the stimulating problem of efficiency while answering interesting synthetic challenges. Ideally, if one could create all-carbon quaternary stereogenic centers via the creation of several new carbon-carbon bonds in an acyclic system and in a single-pot operation from simple precursors, it would certainly open new horizons toward solving the synthetic problems. Even more important for any further design, the presence of polyreactive intermediates in synthesis (bismetalated, carbenoid, and oxenoids species) becomes now an indispensable tool, as it creates consecutively the same number of carbon-carbon bonds as in a multi-step process, but in a single-pot operation.

Secondary metabolites from the Chinese liverwort Cephaloziella kiaeri

Sixteen new clerodane diterpenoids, cephaloziellins A-P (1-16), and two known analogues (17 and 18) were isolated from an EtOH extract of the Chinese liverwort Cephaloziella kiaeri. The structures of the new compounds were elucidated from extensive spectroscopic data (IR, UV, HRESIMS, 1D NMR, and 2D NMR), and the structures of 5, 9, and 15 were confirmed by single-crystal X-ray diffraction analyses. The absolute configurations of all new compounds were established by comparing experimental and calculated electronic circular dichroism spectra.

Natural products chemistry research 2010's progress in China

This article reviews the progresses made by Chinese scientists in the field of natural products chemistry in 2010. Selected compounds with unique structural features and/or promising bioactivities were described herein on the basis of structural types.

Terpenoids from the Chinese liverwort Plagiochila pulcherrima and their cytotoxic effects

Three new pimarane-type diterpenoids, 7β,11α-dihydroxypimara-8(14),15-diene (1), 1β,11α-dihydroxypimara-8(14),15-diene (2), and 11α-hydroxypimara-8(14),15-diene (3), five 2,3-secoaromadendrane-type sesquiterpenoids, including a new one, ethyoxyplagiochiline A2 (4), and three known fusicoccane-type diterpenoids were isolated from the Chinese liverwort Plagiochila pulcherrima. Their structures were established on the basis of extensive spectroscopic analysis. Compounds 6 and 7 exhibited moderate inhibitory activity on the proliferation of human cancer cell lines Hela, A172, and H460. Moreover, the cytotoxicity of compound 6 to Hela cells was related to apoptotis as confirmed by DAPI nuclear staining and flow cytometry.

Bioactive sesquiterpenoids and diterpenoids from the liverwort Bazzania albifolia

One undescribed 6,7-secofusicoccane-type diterpene, albifolione (1), and one new aromadendrane-type sesquiterpenoid ketone, methyl 2-oxoaromadendra-1(10),3-dien-12-oate (2), along with four known compounds, δ-cuparenol (3), fusicoauritone (4), chiloscyphenols A and B (5 and 6, resp.), were isolated from the liverwort Bazzania albifolia Horik. The structures and relative configurations of 1 and 2 were established unequivocally on the basis of spectroscopic data analysis. Preliminary bioassay revealed that compound 5 showed quite strong cytotoxicity against the human tumor cell line MCF-7, with an IC(50) value of 5.6 μM.

Aromatic Compounds from the Liverwort Conocephalum japonicum

Two undescribed dimeric ArC2 derivatives, cis- and trans-1,2-bis(3,4-dimethoxyphenyl)cyclobutane (1 and 2), one new monoterpenes esters, 2α,5β-dihydroxybornane-2- cis-cinnamate (3), along with eight known compounds, 2α,5β-dihydroxybornane-2- trans-cinnamate (4), perrottetin E (5), isoriccardin C (6), marchantin A (7), marchantin E (8), marchantin C (9), and isomarchantin C (10) were isolated from the liverwort Conocephalum japonicum. All the structures were established by extensive spectroscopic analysis. The isolated compounds 3–10 were evaluated for their cytotoxicity against the human KB cell line with IC50 values ranging from 16.5 to 50.2 μM.