Bioactive natural products from Chinese marine flora and fauna

Two new compounds from the Hainan Soft Corals Sinularia tumulosa and Sinularia depressa with their anti-inflammatory or cytotoxic activities

The detailed chemical investigations of the South China Sea soft corals Sinularia tumulosa and Sinularia depressa, yielded two new compounds, namely tumulosterol A (1) and 11'-hydroxy-α-tocopherylquinone (3), along with four related known ones (2, 5-7). Their structures were determined by extensive spectroscopic analysis and comparison with the spectral data previously reported in the literature. In bioassays, compound 1 displayed significant cytotoxic effects against H1975 and MDA-MB-231 cells with IC50 values of 6.0 and 6.3 µM, respectively. In addition, compound 3 exhibited interesting inhibitory effect on lipopolysaccharide (LPS)-induced inflammatory responses in RAW264.7 cells with IC50 value of 9.5 µM.

Two New Protolimonoids from the Chinese Mangrove Xylocarpus granatum Koenig

Two new compounds including one apotirucallane protolimonoid, xylogranatriterpin A (1), and one glabretal protolimonoid, xylocarpusin A (2), along with three known related compounds were isolated from the twigs and leaves of the Chinese mangrove Xylocarpus granatum. The apotirucallane xylogranatriterpin A (1) bears an unprecedented 24-ketal carbon connecting ring E with an epoxide ring. The structures of new compounds were elucidated by extensive spectroscopic analysis and by comparison of the spectroscopic data with those reported in the literatures. Plausible biosynthetic pathway to xylogranatriterpin A (1) was also proposed. None of them showed cytotoxic, neuroprotective, or protein tyrosine phosphatase 1B (PTP1B) inhibitory activity.

Chemistry and bioactivity of secondary metabolites from South China Sea marine fauna and flora: recent research advances and perspective

Marine organisms often produce a variety of metabolites with unique structures and diverse biological activities that enable them to survive and struggle in the extremely challenging environment. During the last two decades, our group devoted great effort to the discovery of pharmaceutically interesting lead compounds from South China Sea marine plants and invertebrates. We discovered numerous marine secondary metabolites spanning a wide range of structural classes, various biosynthetic origins and various aspects of biological activities. In a series of reviews, we have summarized the bioactive natural products isolated from Chinese marine flora and fauna found during 2000-2012. The present review provides an updated summary covering our latest research progress and development in the last decade (2012-2022) highlighting the discovery of over 400 novel marine secondary metabolites with promising bioactivities from South China Sea marine organisms.

New flexible cembrane-type macrocyclic diterpenes as TNF-α inhibitors from the South China Sea soft coral Sarcophyton mililatensis

A further study on the rarely reported soft coral Sarcophyton mililatensis disclosed five new flexible cembrane-type macrocyclic diterpenes sarcomililatols C-G (1-5) and two known analogues 6 and 7. The structures and absolute configurations of natural macrocyclic compounds 1-6 were established by the extensive spectroscopic analysis, X-ray diffraction analysis, time-dependent density functional theory/electronic circular dichroism (TDDFT ECD) calculations, chemical reaction, and modified Mosher's method. In the bioassays, the macrocyclic diterpene 2 exhibited potent TNF-α inhibition (IC₅₀ = 6.1 μmol/L), which was better than the positive control dexamethasone (IC₅₀ = 8.7 μmol/L), and no obvious cytotoxicity against RAW264.7 cells with CC₅₀ values over 50 μmol/L, indicating natural macrocyclic compound 2 could be served as a model compound to develop a new and prospective chemotype of an anti-inflammatory lead compound or drug candidate.

Further polyoxygenated cembranoids from South China Sea soft coral Sarcophyton ehrenbergi

Eleven new cembrane diterpenes, namely, sarcoehrenins A-J (1-9, 11) and (2S,11S,12S)-isosarcophytoxide (10), along with six known compounds, gibberosene B (12), (13S)-cembra-1,3,7,11-tetraen-13-ol (13), (+)-sarcophtol (14), cembrene-C (15), (1R,4R,2E,7E,11E)-cembra-2,7,11-trien-4-ol (16) and (1S,4R,2E,7E,11E)-cembratrien-4-ol (17) were isolated from the soft coral Sarcophyton ehrenbergi collected from Weizhou Island, Beibu Gulf, South China Sea. The structures of these compounds were elucidated by a combination of detailed spectroscopic analyses, chemical methods, and comparison with reported data. The absolute configuration of compound 2 was established by the modified Mosher's method in association with TDDFT ECD calculation, while the absolute configuration of compound 3 was assigned by TDDFT ECD approach. In in vitro bioassays, compounds 13 and 17 showed potent TNF-α inhibitory activities being similar to that of positive control dexamethasone. A preliminary structural-activity relationship was also described.

Natural Products of Marine Macroalgae from South Eastern Australia, with Emphasis on the Port Phillip Bay and Heads Regions of Victoria

Marine macroalgae occurring in the south eastern region of Victoria, Australia, consisting of Port Phillip Bay and the heads entering the bay, is the focus of this review. This area is home to approximately 200 different species of macroalgae, representing the three major phyla of the green algae (Chlorophyta), brown algae (Ochrophyta) and the red algae (Rhodophyta), respectively. Over almost 50 years, the species of macroalgae associated and occurring within this area have resulted in the identification of a number of different types of secondary metabolites including terpenoids, sterols/steroids, phenolic acids, phenols, lipids/polyenes, pheromones, xanthophylls and phloroglucinols. Many of these compounds have subsequently displayed a variety of bioactivities. A systematic description of the compound classes and their associated bioactivities from marine macroalgae found within this region is presented.

α-Glucosidase inhibitors from a mangrove associated fungus, Zasmidium sp. strain EM5-10

BACKGROUND

Mangroves plants and their endophytes represent a natural source of novel and bioactive compounds. In our ongoing research on mangrove endophytes from the Panamanian Pacific Coast, we have identified several bioactive endophytic fungi. From these organisms, an isolate belonging to the genus Zasmidium (Mycosphaerellaceae) showed 91.3% of inhibition against α-glucosidase enzyme in vitro.

RESULTS

Zasmidium sp. strain EM5-10 was isolated from mature leaves of Laguncularia racemosa, and its crude extract showed good inhibition against α-glucosidase enzyme (91.3% of inhibition). Bioassay-guided fractionation of the crude extract led to obtaining two active fractions: L (tripalmitin) and M (Fungal Tryglicerides Mixture). Tripalmitin (3.75 µM) showed better inhibitory activity than acarbose (positive control, IC50 217.71 µM). Kinetic analysis established that tripalmitin acted as a mixed inhibitor. Molecular docking and molecular dynamics simulations predicted that tripalmitin binds at the same site as acarbose and also to an allosteric site in the human intestinal α-glucosidase (PDB: 3TOP).

CONCLUSIONS

Zasmidium sp. strain EM5-10 represents a new source of bioactive substances that could possess beneficial properties for human health.

The Biotechnological Potential of Secondary Metabolites from Marine Bacteria

Marine habitats are a rich source of molecules of biological interest. In particular, marine bacteria attract attention with their ability to synthesize structurally diverse classes of bioactive secondary metabolites with high biotechnological potential. The last decades were marked by numerous discoveries of biomolecules of bacterial symbionts, which have long been considered metabolites of marine animals. Many compounds isolated from marine bacteria are unique in their structure and biological activity. Their study has made a significant contribution to the discovery and production of new natural antimicrobial agents. Identifying the mechanisms and potential of this type of metabolite production in marine bacteria has become one of the noteworthy trends in modern biotechnology. This path has become not only one of the most promising approaches to the development of new antibiotics, but also a potential target for controlling the viability of pathogenic bacteria.

A new brominated polyacetylene from Chinese marine sponge Xestospongia testudinaria

A new brominated polyacetylene xestonariene J (1), bearing a rare 2,4-dibromo-1-ene-3-yne terminal in the molecule, along with two known related analogues (2 and 3), was obtained from Chinese marine sponge Xestospongia testudinaria. Its structure was determined on the basis of detailed spectroscopic analysis and comparison with literature data.

Marine bis-γ-pyrone polypropionates of onchidione family and their effects on the XBP1 gene expression

Two additional new members of the onchidione family, 16-epi-onchidione (1) and 4-epi-onchidione (2), co-occurring with six previously reported bis-γ-pyrone polypropionates including onchidione (3), were isolated from the marine pulmonate Onchidium sp. Their structures were determined by extensive spectroscopic analysis and by comparison with 3 and onchidione-related derivatives. The absolute configuration of 1 was established by X-ray diffraction analysis employing graphite monochromated Cu K_α radiation (λ = 0.71073 Å) with small Flack parameter 0.08. In addition, the absolute stereochemistry of previously reported onchidionol (6) was confirmed by the X-ray diffraction analysis. Some of the isolated compounds showed significant activation effects on the splicing of XBP1 mRNA as ER stress modulators to inhibit the growth of tumors.

Novel and Neuroprotective Tetranortriterpenoids from Chinese Mangrove Xylocarpus granatum Koenig

Eight new tetranortriterpenoids (1–8) were isolated from the twigs and leaves of the Chinese mangrove plant Xylocarpus granatum, together with four related known ones (9–12). The structures of new compounds were elucidated by detailed spectroscopic analysis. The absolute configuration of 9-epixylogranatin A (1) was determined by time-dependent density functional theory-electronic circular dichroism (TDDFT-ECD) calculations of the solution conformers. Xylogranatumin A (2) represents the first example of the 9, 10-seco limonoid with an unprecedented oxygen-bridged B ring (2,7-dioxabicyclo[2.2.1]-heptane). All the isolates were evaluated for the in vitro neuroprotective activity, both compounds 11 and 12 displayed moderate effects against H₂O₂-induced neurotoxicity in PC12 cells at the concentration of 10 μM, with an increase in cell viability of 12.0% and 11.6%, respectively.

Antioxidant and hepatoprotective properties of Indian Sunderban mangrove Bruguiera gymnorrhiza L. leave

Background:

Bruguiera gymnorrhiza L. (family Rhizophoraceae) is a true mangrove habitat in Indian Sunderban and traditionally uses for liver disorders.

Objectives:

The aim was to evaluate antioxidant and hepatoprotective actions of leave extract of B. gymnorrhiza L.

Materials and Methods:

Hydro-methanolic extract of mangrove leaves (BR) was standardized using spectrophotometric and high-performance thin layer chromatography methods. Radical scavenging activities were assessed in different in vitro methods, like 1,1-diphenyl-2-picrylhydrazyl, 2,2’-azino-bis-3-ethyl benzthiazoline-6-sulphonic acid ⁺, superoxides, nitric oxides and hydroxyl radicals. Hepatoprotective efficacy of BR (125 mg/kg and 250 mg/kg, p.o) was measured in D-galactosamine (GalN) induced (200 mg/kg, i.p) hepatitis in Wistar rats. Silymarin (25 mg/kg, p.o) was used as known hepatoprotective agent.

Results:

Polyphenols such as gallic acid, quercetin, and coumarin obtained from BR exhibited powerful antioxidant properties. Moreover, it produced dose-dependent protection against GalN induced hepatitis in rats. It significantly reduced GalN induced elevation of enzymes (alanine transaminase, aspartate aminotransferase, and alkaline phosphatase) in serum and resist oxidative stress marked by lipid peroxides, glutathione, and catalase in hepatic parenchyma.

Conclusions:

Polyphenols rich B. gymnorrhiza L. leaves ameliorate hepatic tissue injury through its antioxidant effects.

Bioactive isoquinolinequinone alkaloids from the South China Sea nudibranch Jorunna funebris and its sponge-prey Xestospongia sp

Background: Nudibranchs are slug-like invertebrates, well known as rich sources of biologically active secondary metabolites with highly chemical diversity and complexity. The production of such interesting metabolites was possibly influenced by their diet relationship with sponges such as Xestospongia. Results: Our continuous investigation of South China Sea nudibranch Jorunna funebris and its sponge-prey Xestospongia sp. led to the isolation of two new and eight known metabolites (1–10). The absolute configurations were determined by time-dependent density functional theory (TDDFT) electronic circular dichroism (ECD) method and by the comparison of ECD spectra. In bioassays, 1–4 and 7 showed strong NF-κB inhibitory activity, 4–6 exhibited considerable cytotoxicity against A549 and HL-60 tumor cell lines. Conclusion: Five unusual isoquinolinequinones (3, 7–10) were discovered from both two animals, further confirmed their predator–prey relationship. Preliminary bioassay results and structure–activity relationship studies suggested that several isolated compounds were potential to be drug leads.

Design and synthesis of novel 1,2-dithiolan-4-yl benzoate derivatives as PTP1B inhibitors

A series of novel 1,2-dithiolan-4-yl benzoate compounds were synthesized and evaluated for in vitro PTP1B inhibitory activity. Some derivatives exhibited improved PTP1B inhibitory activity and selectivity compared to hit 6a, a compound from in-house library screening inspired by marine cyclic disulfide. The preliminary SAR analysis with assistance of molecular modeling approach revealed 6j (IC50=0.59μM) as the most potent PTP1B inhibitor among all derivatives.

Apotirucallane protolimonoids from the Chinese mangrove Xylocarpus granatum Koenig

A series of previously unreported compounds including seven new apotirucallane protolimonoids, xylogranatumines A-G (1-7), were isolated together with three known analogues (8-10) from the twigs and leaves of the Chinese mangrove, Xylocarpus granatum. The structures of these new compounds were elucidated by extensive spectroscopic analysis including 1D and 2D NMR and high-resolution electrospray ionization mass spectrometry (HRESIMS) and by comparison with those of related known compounds in the literature. Xylogranatumine F (6) exhibited cytotoxic activity against A549 tumor cell in vitro.

Venus Flytrap (Dionaea muscipula Solander ex Ellis) Contains Powerful Compounds that Prevent and Cure Cancer

Chemoprevention uses natural or synthetic molecules without toxic effects to prevent and/or block emergence and development of diseases including cancer. Many of these natural molecules modulate mitogenic signals involved in cell survival, apoptosis, cell cycle regulation, angiogenesis, or on processes involved in the development of metastases occur naturally, especially in fruits and vegetables bur also in non-comestible plants. Carnivorous plants including the Venus flytrap (Dionaea muscipula Solander ex Ellis) are much less investigated, but appear to contain a wealth of potent bioactive secondary metabolites. Aim of this review is to give insight into molecular mechanisms triggered by compounds isolated from these interesting plants with either therapeutic or chemopreventive potential.