The oxidation profile at C-18 of furanocembranolides may provide a taxonomical marker for several genera of octocorals

Advanced Methods for Natural Products Discovery: Bioactivity Screening, Dereplication, Metabolomics Profiling, Genomic Sequencing, Databases and Informatic Tools, and Structure Elucidation

Natural Products (NP) are essential for the discovery of novel drugs and products for numerous biotechnological applications. The NP discovery process is expensive and time-consuming, having as major hurdles dereplication (early identification of known compounds) and structure elucidation, particularly the determination of the absolute configuration of metabolites with stereogenic centers. This review comprehensively focuses on recent technological and instrumental advances, highlighting the development of methods that alleviate these obstacles, paving the way for accelerating NP discovery towards biotechnological applications. Herein, we emphasize the most innovative high-throughput tools and methods for advancing bioactivity screening, NP chemical analysis, dereplication, metabolite profiling, metabolomics, genome sequencing and/or genomics approaches, databases, bioinformatics, chemoinformatics, and three-dimensional NP structure elucidation.

A Vicinal Diol Approach for the Total Synthesis of Molestin E, ent-Sinulacembranolide A and ent-Sinumaximol A

In this work an approach for the synthesis of furanocembranoid natural products containing the C-7,8-diol moiety is disclosed. This culminated in the first total synthesis of the natural product molestin E, together with ent-sinulacembranolide A and ent-sinumaximol A as well as a thorough exploration of their chemistry. Late-stage ring-closure of the C-7,8-diols to the corresponding epoxides was also demonstrated. Key features of this synthetic strategy include a stereoselective Baylis-Hillman reaction, ring-closing metathesis and Shiina macrolactonisation. Chiral-pool materials were deployed to ensure the desired absolute stereochemistry which was confirmed by late-stage single crystal X-ray diffraction.

Role of Macrocyclic Conformational Steering in a Kinetic Route toward Bielschowskysin

Macrocyclic furanobutenolide-derived cembranoids (FBCs) are the biosynthetic precursors to a wide variety of highly congested and oxygenated polycyclic (nor)diterpenes (e.g. plumarellide, verrillin, and bielschowskysin). These architecturally complex metabolites are thought to originate from site-selective oxidation of the macrocycle backbone and a series of intricate transannular reactions. Yet the development of a common biomimetic route has been hampered by a lack of synthetic methods for the pivotal furan dearomatization in a regio- and stereoselective manner. To address these shortcomings, a concise strategy of epoxidation followed by a kinetically controlled furan dearomatization is reported. The surprising switch of facial α:β-discrimination observed in the epoxidation of the most strained E-acerosolide versus E-deoxypukalide and E-bipinnatin J derived macrocycles has been rationalized by the variation of the 3D conformational landscape between macrocyclic scaffolds. A careful conformational analysis of these macrocycles by VT-NMR and NOESY experiments at low temperature was supported by DFT calculations to characterize these equilibrating macrocyclic conformers. The shift in conformational topology associated with a swing of the butenolide ring in E-deoxypukalide is in general agreement with the reversal of β-selectivity observed in the epoxidation. We also describe the downstream functionalization of FBC-macrocycles and how the C-7 epoxide configuration is retentively translated to the C-3 stereogenicity in dearomatized products under kinetic control to secure the requisite 3S,7S,8S configurations for the bielschowskysin synthesis. Unlike previously speculated, our results suggest that the most strained FBC-macrocycles bearing a E-(Δ^7,8)-alkene moiety may stand as the true biosynthetic precursors to bielschowskysin and several other polycyclic natural products of this class.

Modulation of Glial Responses by Furanocembranolides: Leptolide Diminishes Microglial Inflammation in Vitro and Ameliorates Gliosis In Vivo in a Mouse Model of Obesity and Insulin Resistance

Neurodegenerative diseases are age-related disorders caused by progressive neuronal death in different regions of the nervous system. Neuroinflammation, modulated by glial cells, is a crucial event during the neurodegenerative process; consequently, there is an urgency to find new therapeutic products with anti-glioinflammatory properties. Five new furanocembranolides (1-5), along with leptolide, were isolated from two different extracts of Leptogorgia sp., and compound 6 was obtained from chemical transformation of leptolide. Their structures were determined based on spectroscopic evidence. These seven furanocembranolides were screened in vitro by measuring their ability to modulate interleukin-1β (IL-1β) production by microglial BV2 cells after LPS (lipopolysaccharide) stimulation. Leptolide and compounds 3, 4 and 6 exhibited clear anti-inflammatory effects on microglial cells, while compound 2 presented a pro-inflammatory outcome. The in vitro results prompted us to assess anti-glioinflammatory effects of leptolide in vivo in a high-fat diet-induced obese mouse model. Interestingly, leptolide treatment ameliorated both microgliosis and astrogliosis in this animal model. Taken together, our results reveal a promising direct biological effect of furanocembranolides on microglial cells as bioactive anti-inflammatory molecules. Among them, leptolide provides us a feasible therapeutic approach to treat neuroinflammation concomitant with metabolic impairment.

Leptogorgins A-C, Humulane Sesquiterpenoids from the Vietnamese Gorgonian Leptogorgia sp

Leptogorgins A-C (1-3), new humulane sesquiterpenoids, and leptogorgoid A (4), a new dihydroxyketosteroid, were isolated from the gorgonian Leptogorgia sp. collected from the South China Sea. The structures were established using MS and NMR data. The absolute configuration of 1 was confirmed by a modification of Mosher's method. Configurations of double bonds followed from NMR data, including NOE correlations. This is the first report of humulane-type sesquiterpenoids from marine invertebrates. Sesquiterpenoids leptogorgins A (1) and B (2) exhibited a moderate cytotoxicity and some selectivity against human drug-resistant prostate cancer cells 22Rv1.

Synthetic explorations of the briarane jungle: progress in developing a synthetic route to a common family of diterpenoid natural products

The briarane diterpenoids are a large family of marine natural products that have been primarily isolated from gorgonian octocorals around the world. Structurally, the family is characterized by a trans-fused bicyclo[8.4.0]tetradecane ring system containing a central, stereogenic, all-carbon quaternary carbon (C1) flanked by three additional stereocentres (C2, C10, C14). Many family members have demonstrated biological activity in numerous areas, including: cytotoxicity, anti-inflammatory, antiviral, antifungal, immunomodulatory and insect control. Despite their interesting structural properties and bioactivity, the briaranes have been largely overlooked by the synthetic community. However, in recent years, several research groups have reported progress toward developing a synthetic route to these natural products. Most of these efforts have focused on the stereoselective construction of the central C1-C2-C10-C14 stereotetrad. This review will discuss the various synthetic efforts aimed at the briarane diterpenoids along with the challenges that remain.

Chloro-Furanocembranolides from Leptogorgia sp. Improve Pancreatic Beta-Cell Proliferation

Two new chloro-furanocembranolides (1, 2) and two new 1,4-diketo cembranolides (3, 4) were isolated from the crude extract of Leptogorgia sp. together with a new seco-furanocembranolide (5) and the known Z-deoxypukalide (6), rubifolide (7), scabrolide D (8) and epoxylophodione (9). Their structures were determined based on spectroscopic evidence. Four compounds: 1, 2, 7 and 8 were found to activate the proliferation of pancreatic insulin-producing (beta) cells.

Polycyclic Furanobutenolide-Derived Cembranoid and Norcembranoid Natural Products: Biosynthetic Connections and Synthetic Efforts

The polycyclic furanobutenolide-derived cembranoid and norcembranoid natural products are a family of congested, stereochemically complex, and extensively oxygenated polycyclic diterpenes and norditerpenes. Although the elegant architectures and biological activity profiles of these natural products have captured the attention of chemists since the isolation of the first members of the family in the 1990s, the de novo synthesis of only a single polycyclic furanobutenolide-derived cembranoid and norcembranoid has been accomplished. This article begins with a brief discussion of the proposed biosyntheses and biosynthetic connections among the polycyclic furanobutenolide-derived cembranoids and norcembranoids and then provides a comprehensive review of the synthetic efforts toward each member of the natural product family, including biomimetic, semisynthetic, and de novo synthetic strategies. This body of knowledge has been gathered to provide insight into the reactivity and constraints of these compact and highly oxygenated polycyclic structures, as well as to offer guidance for future synthetic endeavors.

Protective effects of epoxypukalide on pancreatic β-cells and glucose metabolism in STZ-induced diabetic mice

Diabetes is a consequence of a decrease on functional β-cell mass. We have recently demonstrated that epoxypukalide (Epoxy) is a natural compound with beneficial effects on primary cultures of rat islets. In this study, we extend our previous investigations to test the hypothesis that Epoxy protects β-cells and improves glucose metabolism in STZ-induced diabetic mice. We used 3-months old male mice that were treated with Epoxy at 200 μg/kg body weight. Glucose intolerance was induced by multiple intraperitoneal low-doses of streptozotocin (STZ) on 5 consecutive days. Glucose homeostasis was evaluated measuring plasma insulin levels and glucose tolerance. Histomorphometry was used to quantify the number of pancreatic β-cells per islet. β-cell proliferation was assessed by BrdU incorporation, and apoptosis by TUNEL staining. Epoxy treatment significantly improved glucose tolerance and plasma insulin levels. These metabolic changes were associated with increased β-cell numbers, as a result of a two-fold increase in β-cell proliferation and a 50% decrease in β-cell death. Our results demonstrate that Epoxy improves whole-body glucose homeostasis by preventing pancreatic β-cell death due to STZ-induced toxicity in STZ-treated mice.

Polyoxygenated steroids from the octocoral Leptogorgia punicea and in vitro evaluation of their cytotoxic activity

Five new polyoxygenated marine steroids-punicinols A-E (1-5)-were isolated from the gorgonian Leptogorgia punicea and characterized by spectroscopic methods (IR, MS, 1H, 13C and 2-D NMR). The five compounds induced in vitro cytotoxic effects against lung cancer A549 cells, while punicinols A and B were the most active, with IC50 values of 9.7 μM and 9.6 μM, respectively. The synergistic effects of these compounds with paclitaxel, as well as their effects on cell cycle distribution and their performance in the clonogenic assay, were also evaluated. Both compounds demonstrated significant synergistic effects with paclitaxel.

Epoxypukalide induces proliferation and protects against cytokine-mediated apoptosis in primary cultures of pancreatic β-cells

There is an urgency to find new treatments for the devastating epidemic of diabetes. Pancreatic β-cells viability and function are impaired in the two most common forms of diabetes, type 1 and type 2. Regeneration of pancreatic β-cells has been proposed as a potential therapy for diabetes. In a preliminary study, we screened a collection of marine products for β-cell proliferation. One unique compound (epoxypukalide) showed capability to induce β-cell replication in the cell line INS1 832/13 and in primary rat cell cultures. Epoxypukalide was used to study β-cell proliferation by [³H]thymidine incorporation and BrdU incorporation followed by BrdU/insulin staining in primary cultures of rat islets. AKT and ERK1/2 signalling pathways were analyzed. Cell cycle activators, cyclin D2 and cyclin E, were detected by western-blot. Apoptosis was studied by TUNEL and cleaved caspase 3. β-cell function was measured by glucose-stimulated insulin secretion. Epoxypukalide induced 2.5-fold increase in β-cell proliferation; this effect was mediated by activation of ERK1/2 signalling pathway and upregulation of the cell cycle activators, cyclin D2 and cyclin E. Interestingly, epoxypukalide showed protection from basal (40% lower versus control) and cytokine-induced apoptosis (80% lower versus control). Finally, epoxypukalide did not impair β-cell function when measured by glucose-stimulated insulin secretion. In conclusion, epoxypukalide induces β-cell proliferation and protects against basal and cytokine-mediated β-cell death in primary cultures of rat islets. These findings may be translated into new treatments for diabetes.

Marine natural products

Covering: 2010. Previous review: Nat. Prod. Rep., 2011, 28, 196. This review covers the literature published in 2010 for marine natural products, with 895 citations (590 for the period January to December 2010) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1003 for 2010), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Diterpenes from gorgonian corals

Covering: 1995 to April 2008. Gorgonian corals continue to provide a wealth of novel structures, many of which exhibit potentially useful biological activity. Notably, the families Briareidae, Gorgoniidae and Plexauridae have been demonstrated to contain a wide variety of natural products including steroids, acetogenins, sesquiterpenes and diterpenes. The most common of the gorgonian natural products are the diterpenes, and the intent of this review is to describe such compounds isolated from gorgonian corals, with a focus on the structures of new compounds as well as their biological activity. There have been developments improving our understanding of the biosynthetic origin of selected diterpenes, and these will also be discussed. This review describes 602 new compounds from 177 articles.

Marine natural products

This review covers the literature published in 2007 for marine natural products, with 948 citations(627 for the period January to December 2007) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, cnidarians,bryozoans, molluscs, tunicates, echinoderms and true mangrove plants. The emphasis is on new compounds (961 for 2007), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.1 Introduction, 2 Reviews, 3 Marine microorganisms and phytoplankton, 4 Green algae, 5 Brown algae, 6 Red algae, 7 Sponges, 8 Cnidarians, 9 Bryozoans, 10 Molluscs, 11 Tunicates (ascidians),12 Echinoderms, 13 Miscellaneous, 14 Conclusion, 15 References.

Cembrane diterpenes from the gorgonian Leptogorgia laxa

The new cembrane diterpenes leptodienone A (2) and leptodienone B (3) and the known compounds lopholide, lophodiol B, lophodione, and lophotoxin (1) have been isolated from the gorgonian Leptogorgia laxa collected in the Gulf of California. The structures of the new metabolites have been established by spectroscopic techniques. The in vitro cytotoxicity of the new compounds has been tested against three human tumor cell lines.