Sesquiterpenes from the Hainan Sponge Dysidea septosa

Natural Bioactive Compounds from Marine Invertebrates That Modulate Key Targets Implicated in the Onset of Type 2 Diabetes Mellitus (T2DM) and Its Complications

BACKGROUND

Type 2 diabetes mellitus (T2DM) is an ongoing, risky, and costly health problem that therefore always requires new treatment options. Moreover, although several drugs are available, only 36% of patients achieve glycaemic control, and patient adherence is a major obstacle. With monotherapy, T2DM and its comorbidities/complications often cannot be managed, and the concurrent administration of several hypoglycaemic drugs is required, which increases the risk of side effects. In fact, despite the efficacy of the drugs currently on the market, they generally come with serious side effects. Therefore, scientific research must always be active in the discovery of new therapeutic agents.

DISCUSSION

The present review highlights some of the recent discoveries regarding marine natural products that can modulate the various targets that have been identified as crucial in the establishment of T2DM disease and its complications, with a focus on the compounds isolated from marine invertebrates. The activities of these metabolites are illustrated and discussed.

OBJECTIVES

The paper aims to capture the relevant evidence of the great chemical diversity of marine natural products as a key tool that can advance understanding in the T2DM research field, as well as in antidiabetic drug discovery. The variety of chemical scaffolds highlighted by the natural hits provides not only a source of chemical probes for the study of specific targets involved in the onset of T2DM, but is also a helpful tool for the development of drugs that are capable of acting via novel mechanisms. Thus, it lays the foundation for the design of multiple ligands that can overcome the drawbacks of polypharmacology.

Dysambiol, an Anti-inflammatory Secomeroterpenoid from a Dysidea sp. Marine Sponge

An unusual secomeroterpenoid, dysambiol (1), was isolated from a Dysidea sp. marine sponge collected from the South China Sea. Dysambiol features an unprecedented secomeroterpene scaffold with a rare lactone bridge. The structure of 1 was determined by extensive spectroscopic analysis, Mosher's method, and electronic circular dichroism calculation. Dysambiol displayed potent anti-inflammatory activity in LPS-induced Raw 264.7 macrophages by regulating the NF-κB/MPAK signaling pathway.

The Biosynthetic Gene Cluster of Mushroom-Derived Antrocin Encodes Two Dual-Functional Haloacid Dehalogenase-like Terpene Cyclases

(-)-Antrocin (1), produced by the medicinal mushroom Antrodia cinnamomea, is a potent antiproliferative compound. The biosynthetic gene cluster of 1 was identified, and the pathway was characterized by heterologous expression. We characterized a haloacid dehalogenase-like terpene cyclase AncC that biosynthesizes the drimane-type sesquiterpene (+)-albicanol (2) from farnesyl pyrophosphate (FPP). Biochemical characterization of AncC, including kinetic studies and mutagenesis, demonstrated the functions of two domains: a terpene cyclase (TC) and a pyrophosphatase (PPase). The TC domain first cyclizes FPP to albicanyl pyrophosphate, and the PPase domain then removes the pyrophosphate to form 2. Intriguingly, AncA (94 % sequence identity to AncC), in the same gene cluster, converts FPP into (R)-trans-γ-monocyclofarnesol instead of 2. Notably, Y283/F375 in the TC domain of AncA serve as a gatekeeper in controlling the formation of a cyclofarnesoid rather than a drimane-type scaffold.

Marine Terpenic Endoperoxides

Organic extracts of marine invertebrates, mainly sponges, from seas all over the world are well known for their high in vitro anticancer and antibiotic activities which make them promising sources of compounds with potential use as pharmaceutical leads. Most of the structures discovered so far have a peculiar structural feature in common: a 1,2-dioxane ring. This is a highly reactive heterocycle that can be considered as an endoperoxide function. Together with other structural features, this group could be responsible for the strong biological activities of the substances present in the extracts. Numerous research programs have focused on their structural elucidation and total synthesis since the seventies. As a consequence, the number of established chiral centres and the similarity between different naturally occurring substances is increasingly higher. Most of these compounds have a terpenoid nature, mainly diterpene and sesterterpene, with several peculiar structural features, such as the loss of one carbon atom. Although there are many reviews dealing with the occurrence of marine peroxides, their activities, or potential pharmaceutical uses, no one has focused on those having a terpene origin and the endoperoxide function. We present here a comprehensive review of these compounds paying special attention to their structural features and their biological activity.

Facile generation of bridged medium-sized polycyclic systems by rhodium-catalysed intramolecular (3+2) dipolar cycloadditions

Bridged medium-sized bicyclo[m.n.2] ring systems are common in natural products and potent pharmaceuticals, and pose a great synthetic challenge. Chemistry for making bicyclo[m.n.2] ring systems remains underdeveloped. Currently, there are no general reactions available for the single-step synthesis of various bridged bicyclo[m.n.2] ring systems from acyclic precursors. Here, we report an unusual type II intramolecular (3+2) dipolar cycloaddition strategy for the syntheses of various bridged bicyclo[m.n.2] ring systems. This rhodium-catalysed cascade reaction provides a relatively general strategy for the direct and efficient regioselective and diastereoselective synthesis of highly functionalized and synthetically challenging bridged medium-sized polycyclic systems. Asymmetric total synthesis of nakafuran-8 was accomplished using this method as a key step. Quantum mechanical calculations demonstrate the mechanism of this transformation and the origins of its multiple selectivities. This reaction will inspire the design of the strategies to make complex bioactive molecules with bridged medium-sized polycyclic systems.

The bridged medium-sized ring bicyclo[m.n.2] family of natural products are commonly found but difficult to synthesize efficiently. Here the authors present a cascade reaction to form the carbon skeleton, via a [3+2] cycloaddition of a captured azavinyl carbene intermediate.

New Techniques of Structure Elucidation for Sesquiterpenes

The most significant new techniques that have been used in the twenty-first century for the structure elucidation of sesquiterpenes and some derivatives are reviewed in this chapter. A distinctive feature of these methodologies is the combination of accurate experimental measurements with theoretical data obtained by molecular modeling calculations that allow to visualize, understand, and quantify many structural characteristics. This has been the case for NMR spectroscopy, which has expanded its potential for solving complex structural problems by means of comparison with quantum mechanical molecular models. Ab initio and density functional theory calculations of chemical shifts, coupling constants, and residual chemical shift anisotropies have played important roles in the solution of many structures of sesquiterpenes. The assignments of their absolute configurations by evaluation of calculated and experimental chiroptical properties as electronic and vibrational circular dichroism are also reviewed. This chapter also includes the use of X-ray diffraction analysis with emphasis on calculations of the Flack and Hooft parameters, which are applicable to all molecules that crystallize in non-centrosymmetric space groups. The accurate molecular models of sesquiterpenes, validated by concordance with their experimental properties, are nowadays essential for the interpretation of the effects of these natural products on biological systems.

First report of substituted 2H-pyranoids from brown seaweed Turbinaria conoides with antioxidant and anti-inflammatory activities

The organic extract of Turbinaria conoides, a brown seaweed harvested from the Gulf of Manner region of Indian peninsular was chromatographically fractionated to yield three substituted 2H-pyranoids, namely methyl-21-yl-[5', 6'- dihydro-5'-yl-{54-(4-hydroxybenzoyl)-oxy-(52-methylbutyl)}-3'-methyl-2H-pyran]-21-methyl butanoate (1), 11-[(3', 6'-dihydro-4'-methyl-2'-oxo-2H-pyran-3'-yl)methyl]-10-methylhexyl benzoate (2), and [6-ethyl-3,4-dimethyl-(tetrahydro-2', 2', 6'-trimethyl-2H-pyran-3'-yl)-2,5-cycloheptadiene]-1-propanoate (3). The compounds 1 and 2 bearing 2H-pyranyl-4-hydroxybenzoyl and 2H-pyranyl-10-methylhexylbenzoate moieties exhibited potential antioxidant activities (IC50 0.54-0.69 mg mL-1) as commercial antioxidant (α-tocopherol IC50 0.63-0.73 mg mL-1). Likewise, potential bioactivity of the 2H-pyran derivative, 1 against 5-lipoxygenase (IC50 ∼ 1 mg mL-1) along with higher index of selectivity (COX-1 inhibitoryIC50/COX-2 inhibitoryIC50 1.88) indicated their selective anti-inflammatory properties against inducible inflammatory mediators than that displayed by commercially available non-steroidal anti-inflammatory drug (ibuprofen, 0.44). Structure activity relationship analysis of the studied compounds showed that the antioxidative and anti-inflammatory properties were directly proportional to their electronic properties. The previously undescribed 2H-pyranoids might constitute as potential antioxidative and anti-inflammatory pharmacophores for medicinal applications. [Formula: see text].

γ-Hydroxybutenolide Containing Marine Natural Products and Their Synthesis: A Review

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γ-Hydroxybutenolides (γ-HB) is an important structural core found in many bioactive marine natural products (MNPS). The γ-HB core containing NPS served as an inspiration to medicinal chemists to undertake designing of the new synthetic strategies to construct γ-HB core. Subsequently, it further results in the development of novel physiological and therapeutic agents. The most notable example includes manoalides, cacospongionolides, petrosaspongioide M and dysidiolide from marine sponges possessing anti-inflammatory properties. γ-HB containing MNPS were known to possess various pharmacological properties such as antimicrobial (acantholide B), cytotoxic (acantholide A-E, spongianolide A), inhibitors of secretory phospholipase A2 (cladocorans A and B), BACE inhibitors (ianthellidone G), etc. Moreover, the γ-HB moiety was explored as antifouling agents as well. Owing to their numerous biological activities and attractive molecular structures, there are lots of advances in the synthetic methodology of these compounds. This review gives the account on isolation and biological studies of MNPS with γ-HB skeleton as a core unit. Furthermore, the synthesis of selective γ-HB containing bioactive MNPS like manoalide, secomanoalide, cacospongionolides, luffarielloide and dysidiolide were highlighted in the article.

Spiroetherones A and B, sesquiterpene naphthoquinones, as angiogenesis inhibitors from the marine sponge Dysidea etheria

Spiroetherones A (1) and B (2), a pair of sesquiterpene naphthoquinones with an unprecedented “spiroetherane” carbon skeleton, were isolated from the marine sponge Dysidea etheria collected from the South China Sea.

Discovery of nitrogenous sesquiterpene quinone derivatives from sponge Dysidea septosa with anti-inflammatory activity in vivo zebrafish model

Two unique nitrogenous sesquiterpene quinone meroterpenoids, dysidinoid B (1) and dysicigyhone A (2), together with eight known analogues (3-10) were isolated and characterized from the marine sponge Dysidea septosa. Their structures with absolute configurations were established by a combination of extensive spectroscopic, electron circular dichroism (ECD) and single-crystal X-ray diffraction data analysis. Structurally, dysicigyhone A (2) possessed a unique benzo[d]oxazolidine-2-one unit. Additionally, dysidinoid B (1) exhibited significant anti-inflammatory effect by inhibiting TNF-α and IL-6 generation with IC₅₀ values of 9.15 μM and 17.62 μM, respectively. Further in vivo anti-inflammatory assay verified that the dysidinoid B (1) alleviated the CuSO₄-induced robust acute inflammatory response in zebrafish model.

A General Strategy for the Stereoselective Synthesis of the Furanosesquiterpenes Structurally Related to Pallescensins 1⁻2

Here, we describe a general stereoselective synthesis of the marine furanosesquiterpenes structurally related to pallescensins 1–2. The stereoisomeric forms of the pallescensin 1, pallescensin 2, and dihydropallescensin 2 were obtained in high chemical and isomeric purity, whereas isomicrocionin-3 was synthesized for the first time. The sesquiterpene framework was built up by means of the coupling of the C₁₀ cyclogeranyl moiety with the C₅ 3-(methylene)furan moiety. The key steps of our synthetic procedure are the stereoselective synthesis of four cyclogeraniol isomers, their conversion into the corresponding cyclogeranylsulfonylbenzene derivatives, their alkylation with 3-(chloromethyl)furan, and the final reductive cleavage of the phenylsulfonyl functional group to afford the whole sesquiterpene framework. The enantioselective synthesis of the α-, 3,4-dehydro-γ- and γ-cyclogeraniol isomers was performed using both a lipase-mediated resolution procedure and different regioselective chemical transformations.

Septosones A-C, in Vivo Anti-inflammatory Meroterpenoids with Rearranged Carbon Skeletons from the Marine Sponge Dysidea septosa

Three unusual meroterpenoids, septosones A-C (1-3), were isolated from the marine sponge Dysidea septosa. The structures were determined by analysis of spectroscopic data combined with single-crystal X-ray diffraction and ECD calculations. Septosone A (1) features an unprecedented "septosane" carbon skeleton, whereas septosones B (2) and C (3) share a rare spiro[4.5]decane motif. Septosone A showed in vivo anti-inflammatory activity in CuSO₄-induced transgenic fluorescent zebrafish likely through inactivation of the NF-κB signaling pathway.

Antioxidative and anti-inflammatory pyranoids and isochromenyl analogues from Corbiculid bivalve clam, Villorita cyprinoides

Bivalve black clam, Villorita cyprinoides is traditional seafood in Southwestern coast of Arabian Sea. In this study, bioactivity-guided purification of ethyl acetate:methanol extract of black clam was carried out. Two irregular meroterpenoids {tetrahydro-3-methoxy-5-((E)-8,12-dimethyloct-8-enyl)-pyran-2-one (1) and dihydro-5-(8-(9,12-dihydro-8-methyl-11-propyl-2H-pyran-8-yl)-ethyl)-furan-2(3H)-one (2)} and two hexahydro-isochromenyl-meroterpenoids (3-4) were identified. The structures were characterized by detailed spectroscopy and their antioxidant/anti-inflammatory potentials were evaluated. Compound 2 registered significantly greater 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability (IC₅₀ <0.65 mg/mL) than other analogues (IC₅₀ ≥0.70 mg/mL). Ferrous ion (Fe²⁺) chelating ability was higher for 1-2 (IC₅₀ ∼0.84 mg/mL) than α-tocopherol (IC₅₀ 0.89 mg/mL). The 5-lipoxygenase inhibitory potential of furano-meroterpenoid analogue, 2 (IC₅₀ 0.76 mg/mL) was greater than other compounds (IC₅₀ >0.90 mg/mL). An optimum hydrophobic-hydrophilic balance of furano-meroterpenoid and lesser steric bulk manifested towards its greater bioactivities compared to other compounds. These anti-inflammatory and antioxidant leads could be used as potential functional food components.

Protein tyrosine phosphatase 1B inhibitors from natural sources

Since PTP1B enzyme was discovered in 1988, it has captured the research community's attention. This landmark discovery has stimulated numerous research studies on a variety of human diseases, including cancer, inflammation, and diabetes. Tremendous progress has been made in finding PTP1B inhibitors and exploring PTP1B regulatory mechanisms. This review investigates for the natural PTP1B inhibitors, and focuses on the common characteristics of the discovered structures and structure-activity relationships. To facilitate understanding, all the natural compounds are here divided into five different classes (fatty acids, phenolics, terpenoids, steroids, and alkaloids), according to their skeletons. These PTP1B inhibitors of scaffold structures could serve as a theoretical basis for new concept drug discovery and design.

Lamellodysidines A and B, Sesquiterpenes Isolated from the Marine Sponge Lamellodysidea herbacea

Four new sesquiterpenes, lamellodysidines A and B, O,O-dimethyllingshuiolide A, and 11-epi-O,O-dimethyllingshuiolide A (1-4), were obtained from the marine sponge, Lamellodysidea herbacea, collected in Indonesia. Their planar structures were elucidated by analysis of spectroscopic data. The absolute configurations of the new compounds were determined by the calculated ECD spectra. Compound 1 has a unique carbon framework, and 2 is a new nitrogenous sesquiterpene.

Structure and Configuration of Phosphoeleganin, a Protein Tyrosine Phosphatase 1B Inhibitor from the Mediterranean Ascidian Sidnyum elegans

A new phosphorylated polyketide, phosphoeleganin (1), has been isolated from the Mediterranean ascidian Sidnyum elegans. Its structure and configuration have been determined by extensive use of 2D NMR and microscale chemical degradation and/or derivatization. Phosphoeleganin (1) inhibited the protein tyrosine phosphatase 1B (PTP1B) activity.

New sesquiterpenoids from the edible mushroom Pleurotus cystidiosus and their inhibitory activity against α-glucosidase and PTP1B

Nine new sesquiterpenoids, clitocybulol derivatives, clitocybulols G-O (1-9) and three known sesquiterpenoids, clitocybulols C-E (10-12), were isolated from the solid culture of the edible fungus Pleurotus cystidiosus. The structures of compounds 1-12 were determined by spectroscopic methods. The absolute configurations of compounds 1-9 were assigned via the circular dichroism (CD) data analysis. Compounds 1, 6 and 10 showed moderate inhibitory activity against protein tyrosine phosphatase-1B (PTP1B) with IC50 values of 49.5, 38.1 and 36.0μM, respectively.

New marine natural products from sponges (Porifera) of the order Dictyoceratida (2001 to 2012); a promising source for drug discovery, exploration and future prospects

The discovery of new drugs can no longer rely primarily on terrestrial resources, as they have been heavily exploited for over a century. During the last few decades marine sources, particularly sponges, have proven to be a most promising source of new natural products for drug discovery. This review considers the order Dictyoceratida in the Phylum Porifera from which the largest number of new marine natural products have been reported over the period 2001-2012. This paper examines all the sponges from the order Dictyoceratida that were reported as new compounds during the time period in a comprehensive manner. The distinctive physical characteristics and the geographical distribution of the different families are presented. The wide structural diversity of the compounds produced and the variety of biological activities they exhibited is highlighted. As a representative of sponges, insights into this order and avenues for future effective natural product discovery are presented. The research institutions associated with the various studies are also highlighted with the aim of facilitating collaborative relationships, as well as to acknowledge the major international contributors to the discovery of novel sponge metabolites. The order Dictyoceratida is a valuable source of novel chemical structures which will continue to contribute to a new era of drug discovery.

Heterocyclic terpenes: linear furano- and pyrroloterpenoids

This review of furano- and pyrroloterpenoids covers the literature, 180 articles in all, published from January 2006 to December 2013.

Two new compounds from an Indonesian sponge Dysidea sp

On our joint bioprospecting research on Indonesian marine invertebrates, we found moderate cytotoxicity on an extract of the sponge Dysidea sp. collected at Biak, West Papua. Separation of the extract provided two new compounds, biaketide (1) and debromoantazirine (2), along with four known molecules 3-6. The new structures were elucidated by spectroscopic analyses and by comparison with those reported. Compounds 1 and 2 showed moderate cytotoxicity against NBT-T2 cells with IC50 values of 8.3 and 4.7 μg ml(- 1), respectively.

Peroxy natural products

This review covers the structures and biological activities of peroxy natural products from a wide variety of terrestrial fungi, higher plants, and marine organisms. Syntheses that confirm or revise structures or stereochemistries have also been included, and 406 references are cited.

HPN, a synthetic analogue of bromophenol from red alga Rhodomela confervoides: synthesis and anti-diabetic effects in C57BL/KsJ-db/db mice

3,4-dibromo-5-(2-bromo-3,4-dihydroxy-6-(isopropoxymethyl)benzyl)benzene-1,2-diol (HPN) is a synthetic analogue of 3,4-dibromo-5-(2-bromo-3,4-dihydroxy-6-(ethoxymethyl)benzyl)benzene-1,2-diol (BPN), which is isolated from marine red alga Rhodomela confervoides with potent protein tyrosine phosphatase 1B (PTP1B) inhibition (IC₅₀ = 0.84 μmol/L). The in vitro assay showed that HPN exhibited enhanced inhibitory activity against PTP1B with IC₅₀ 0.63 μmol/L and high selectivity against other PTPs (T cell protein tyrosine phosphatase (TCPTP), leucocyte antigen-related tyrosine phosphatase (LAR), Src homology 2-containing protein tyrosine phosphatase-1 (SHP-1) and SHP-2). The results of antihyperglycemic activity using db/db mouse model demonstrated that HPN significantly decreased plasma glucose (P < 0.01) after eight weeks treatment period. HPN lowered serum triglycerides and total cholesterol concentration in a dose-dependent manner. Besides, both of the high and medium dose groups of HPN remarkably decreased HbA1c levels (P < 0.05). HPN in the high dose group markedly lowered the insulin level compared to the model group (P < 0.05), whereas the effects were less potent than the positive drug rosiglitazone. Western blotting results showed that HPN decreased PTP1B levels in pancreatic tissue. Last but not least, the results of an intraperitoneal glucose tolerance test in Sprague–Dawley rats indicate that HPN have a similar antihyperglycemic activity as rosiglitazone. HPN therefore have potential for development as treatments for Type 2 diabetes.

Chemistry, chemoecology, and bioactivity of the South China Sea opisthobranch molluscs and their dietary organisms

Opisthobranchs are slow-moving, brightly colored, and shell-less slug. Interestingly, these naked molluscs appear to be free of predation causing great interests to biologists, chemists, and pharmacologists as well. It is well documented that their ability to escape predation is realized by utilizing chemical substances as defensive allomones. Due to their extraordinary capacity to produce a variety of chemical defensive molecules and in particular, some of which exhibited promising pharmacological activities, opisthobranch molluscs became the hotspot of research subject in the recent years. The authors and co-workers have systematically investigated the possible diet relationship between the South China Sea opisthobranch molluscs and their related prey organisms, including sponges, corals, and algae in the last decade. A series of interesting results have been obtained concerning the chemistry and chemoecology of the studied marine organisms. The present review focuses on recent development dealing with chemistry, chemoecology, and bioactivity of the South China Sea opisthobranch molluscs and their dietary organisms. Some selected representative examples are described in detail.

Natural products possessing protein tyrosine phosphatase 1B (PTP1B) inhibitory activity found in the last decades

This article provides an overview of approximately 300 secondary metabolites with inhibitory activity against protein tyrosine phosphatase 1B (PTP1B), which were isolated from various natural sources or derived from synthetic process in the last decades. The structure-activity relationship and the selectivity of some compounds against other protein phosphatases were also discussed. Potential pharmaceutical applications of several PTP1B inhibitors were presented.

Bioactive natural products from Chinese marine flora and fauna

In recent decades, the pharmaceutical application potential of marine natural products has attracted much interest from both natural product chemists and pharmacologists. Our group has long been engaged in the search for bioactive natural products from Chinese marine flora (such as mangroves and algae) and fauna (including sponges, soft corals, and mollusks), resulting in the isolation and characterization of numerous novel secondary metabolites spanning a wide range of structural classes and various biosynthetic origins. Of particular interest is the fact that many of these compounds show promising biological activities, including cytotoxic, antibacterial, and enzyme inhibitory effects. By describing representative studies, this review presents a comprehensive summary regarding the achievements and progress made by our group in the past decade. Several interesting examples are discussed in detail.

Steroids with aromatic A-rings from the Hainan soft coral Dendronephthya studeri Ridley

Eight new marine steroids, characterized by either the presence of an aromatic ring or a cross-conjugated dienone system in ring A, were isolated from the Hainan soft coral Dendronephthya studeri Ridley. Their structures were elucidated on the basis of detailed spectroscopic analysis and by comparison of their NMR data with those reported in the literature.