Ceramides and cerebrosides from the marine bryozoan Bugula neritina inhabiting South China Sea

Identifying the specific-targeted marine cerebrosides against SARS-CoV-2: an integrated computational approach

Cerebrosides are a group of metabolites belonging to the glycosphingolipids class of natural products. So far, 167 cerebrosides, compounds 1-167, have been isolated from diverse marine organisms or microorganisms. The as yet smaller number of compounds that have been studied more in depth proves a potential against challenging diseases, such as cancer, a range of viral and bacterial diseases, as well as inflammation. This review provides a comprehensive summary on this so far under-explored class of compounds, their chemical structures, bioactivities, and their marine sources, with a full coverage to the end of 2020. Today, the global pandemic concern, COVID-19, has claimed millions of death cases around the world, making the development of anti-SARS-CoV-2 drugs urgently needed for such a battle. Accordingly, selected examples from all subclasses of cerebrosides were virtually screened for potential inhibition of SARS-CoV-2 proteins that are crucially involved in the viral-host interaction, viral replication, or in disease progression. The results highlight five cerebrosides that could preferentially bind to the hACE2 protein, with binding scores between -7.1 and -7.6 kcal mol^-1 and with the docking poses determined underneath the first α₁-helix of the protein. Moreover, the molecular interaction determined by molecular dynamic (MD) simulation revealed that renieroside C1 (60) is more conveniently involved in key hydrophobic interactions with the best stability, least deviation, least ΔG (-6.9 kcal mol^-1) and an RMSD value of 3.6 Å. Thus, the structural insights assure better binding affinity and favorable molecular interaction of renieroside C1 (60) towards the hACE2 protein, which plays a crucial role in the biology and pathogenesis of SARS-CoV-2.

Review of bioactive secondary metabolites from marine bryozoans in the progress of new drugs discovery

Marine bryozoans play an important role for the discovery of novel bioactive compounds among marine organisms. In this review, we summarize 164 new secondary metabolites including macrocyclic lactones, sterols, alkaloids, sphingolipids and so forth from 24 marine bryozoans in the last two decades. The structural features, bioactivity, structure-activity relationship, mechanism and strategies to address the resupply of these scarce secondary metabolites are discussed. The structural and bioactive diversity of the secondary metabolites from marine bryozoans indicated the possibility of using these compounds, especially bryostatin 1 (1), bryostatin analog (BA1), alkaloids (50, 53, 127-128 and 134-139), sphingolipids sulfates (148 and 149) and sulfur-containing aromatic compound (160), as the starting points for new drug discovery.

New Cytotoxic Secondary Metabolites from Marine Bryozoan Cryptosula pallasiana

A new sterol, (23R)-methoxycholest-5,24-dien-3β-ol (1), two new ceramides, (2S,3R,4E,8E)-2-(tetradecanoylamino)-4,8-octadecadien-l,3-diol (6) and (2S,3R,2′R,4E,8E)-2-(tetradecanoylamino)-4,8-octadecadien-l,3,2′-triol (7), together with three known sterols (2–4), a lactone (5) and two ceramides (8,9), were isolated from the marine bryozoan Cryptosula pallasiana, collected at Huang Island of China. The structures of the new compounds were elucidated by extensive spectroscopic analyses, chemical methods and quantum electronic circular dichroism (ECD) calculations. Among the isolated compounds, sterol 1 possessed a rare side chain with a methoxy group at C-23, and a double bond between C-24 and C-25. Ceramides 6 and 7 possessed 14 carbons in their long-chain fatty acid base (FAB), which were different from the normal ceramides with 16 carbons in the FAB. Moreover, compounds 5 and 8 were isolated for the first time from marine bryozoans. Compounds 1–9 were evaluated for their cytotoxicity against human tumor cell lines HL-60, Hep-G2 and SGC-7901. The results showed that lactone 5 appears to have strong cytotoxicity against the test tumor cell lines, with IC₅₀ values from 4.12 μM to 7.32 μM, and sterol 1 displayed moderate cytotoxicity with IC₅₀ values between 12.34 μM and 18.37 μM, while ceramides 6–9 showed weak cytotoxicity with IC₅₀ ranging from 21.13 μM to 58.15 μM.

Cytotoxic Bryostatin Derivatives from the South China Sea Bryozoan Bugula neritina

Four new macrocyclic lactones, bryostatin 21 (1) and 9-O-methylbryostatins 4, 16, and 17 (2-4), together with three known related compounds, bryostatins 4, 16, and 17 (5-7), have been isolated from an extract of the South China Sea bryozoan Bugula neritina. The structures of all compounds were unambiguously elucidated using detailed spectroscopic analysis. Structurally, the presence of a single methyl group at C-18 in compound 1 has not been observed before for known bryostatins. The isolated macrolides exhibited inhibitory effects against a small panel of human cancer cell lines.

Neritinaceramides A-E, new ceramides from the marine bryozoan Bugula neritina inhabiting South China Sea and their cytotoxicity

Five new ceramides, neritinaceramides A (1), B (2), C (3), D (4) and E (5), together with six known ceramides (6–11), two known alkyl glycerylethers (12 and 13) and a known nucleoside (14), were isolated from marine bryozoan Bugula neritina, which inhabits the South China Sea. The structures of the new compounds were elucidated as (2S,3R,3′S,4E,8E,10E)-2-(hexadecanoylamino)-4,8,10-octadecatriene-l,3,3′-triol (1), (2S,3R,2′R,4E,8E,10E)-2-(hexadecanoylamino)-4,8,10-octadecatriene-l,3,2′-triol (2), (2S,3R,2′R,4E,8E,10E)-2-(octadecanoylamino)-4,8,10-octadecatriene-l,3,2′-triol (3), (2S,3R,3′S,4E,8E)-2-(hexadecanoylamino)-4,8-octadecadiene-l,3,3′-triol (4) and (2S,3R,3′S,4E)-2-(hexadecanoylamino)-4-octadecene-l,3,3′-triol (5) on the basis of extensive spectral analysis and chemical evidences. The characteristic C-3′S hydroxyl group in the fatty acid moiety in compounds 1, 4 and 5, was a novel structural feature of ceramides. The rare 4E,8E,10E-triene structure in the sphingoid base of compounds 1–3, was found from marine bryozoans for the first time. The new ceramides 1–5 were evaluated for their cytotoxicity against HepG2, NCI-H460 and SGC7901 tumor cell lines, and all of them exhibited selective cytotoxicity against HepG2 and SGC7901 cells with a range of IC₅₀ values from 47.3 μM to 58.1 μM. These chemical and cytotoxic studies on the new neritinaceramides A–E (1–5) added to the chemical diversity of B. neritina and expanded our knowledge of the chemical modifications and biological activity of ceramides.

New cytotoxic oxygenated sterols from the marine bryozoan Cryptosula pallasiana

Six new sterols (1-6), together with seven known sterols (7-13), were isolated from the CCl(4) extract of the marine bryozoan Cryptosula pallasiana, four (3-6) of which have already been reported as synthetic sterols. This is the first time that these compounds (3-6) are reported as natural sterols. The structures of the new compounds were determined on the basis of the extensive spectroscopic analysis, including two-dimensional (2D) NMR and HR-ESI-MS data. Compounds 1-4, 7 and 10-13 were evaluated for their cytotoxicity against HL-60 human myeloid leukemia cell line, and all of the evaluated compounds exhibited moderate cytotoxicity to HL-60 cells with a range of IC(50) values from 14.73 to 22.11 µg/mL except for compounds 12 and 13.