Allelochemicals from the seaweeds and their bioprospecting potential

Allelochemicals are secondary metabolites which function as a natural protection against grazing activities by algae and higher plants. They are one of the major metabolites engaged in the interactions of organisms. The chemically mediated interactions between organisms significantly influence the functioning of the ecosystems. Most of these compounds are secondary metabolites comprising sterols, terpenes, and polyphenols. These compounds not only play a defensive role, but also exhibit biological activities such as antioxidants, anti-cancer, anti-diabetes, anti-inflammation, and anti-microbial properties. This review article discusses the current understanding of the allelochemicals of seaweeds and their bioprospecting potential that can bring benefit to humanity. Specifically, the bioactive substances having specific health benefits associated with the consumption or application of seaweed-derived compounds. The properties of such allelochemicals can have implications for bioprospecting pharmaceutical, nutraceutical and cosmetic applications.

Jellyfish Rhizostoma pulmo collected off Goa Coast (India) as a rich source of tryptophan containing collagen and its enhanced antioxidant potential

The extraction of Rhizostoma pulmo discarded off the Goa coast, India resulted in obtaining remarkably higher yield of 47% (based on lyophilized weight) type I collagen. The amino acid composition showed presence of glycine, hydroxyproline and proline and other amino acids in consistent with mammalian collagens. Interestingly, it also possessed essential amino acid tryptophan that makes this collagen superior than other commercially available collagen products. The dose and time response anti-oxidant activity (DPPH assay) of jellyfish collagen showed increase in the percentage activity with its efficiency better than marine fish collagen. In the dose response, IC50 was found to be 11.0 mg/ml. The percentage DPPH activity gradually increased from 47.58 to 81.11% with time 1-8 h, respectively at concentration of 7 mg/ml of jellyfish collagen. It was noteworthy to observe that the anti-oxidant activity remained 80% even after 24 h of analysis. The EDX analysis showed presence of minerals like Cl, Na, Mg, K, Cu, Fe, Zn etc. essential for healthy bones. The mass assisted laser desorption ionization-time of flight mass spectrometric (MALDI-TOF MS) data showed several precursor peaks of different peptides which has been presented here for the first time. The finding showed higher production of tryptophan containing anti-oxidant collagen that will certainly enhance its benefit in neurotransmission and cognitive function.

Chemical Diversity and Bioactivity of Marine Sponges of the Genus Oceanapia: A Review

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The marine sponges of the genus Oceanapia sp. is comprised of more than 50 species and are distributed in the seas around the tropical and subtropical regions. They are mainly found in the northern Indian oceans, Japan, and the south pacific coast. They are highly colored and known to be a rich source of various secondary metabolites, particularly, alkaloids. Several other secondary metabolites were also reported from this genus which include terpenes, sphingolipids, ceramides, cerebrosides, acetylenic acids, and thiocyanatins, etc. Many of these compounds isolated from this genus exhibited various biological properties including anticancer, antimicrobial, anti-HIV, ichthyotoxicity and nematocidal activities. Although several secondary metabolites have been reported from this genus, a dedicated review of the chemicals and biological activities of this genus is so far lacking. Keeping this in mind this review describes the various chemical entities isolated from the sponges of the genus Oceanapia detailing their chemical structures along with their reported biological properties.

Isolation and Identification of Tyrosinase Inhibitors from Marine Algae Enteromorpha sp

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The extract of marine green algae Enteromorpha sp. was evaluated in vitro for inhibitory activity against mushroom tyrosinase enzyme. The principle active agents i.e. coumarin; 4-hydroxycoumarin (1) and two sterols; ergosta-5,7,22-trien-3β-ol (2) & ergosterol peroxide (3) were isolated for the first time, from a crude methanol extract of Enteromorpha sp. showing anti-tyrosinase activity. Their structures were elucidated by IR, extensive NMR spectroscopy, LC-ESI-MS, Single crystal X-ray diffraction techniques. Thus, Enteromorpha sp. can be an alternative edible anti-tyrosinase agent.

Chemical Investigation of Marine-Derived Fungus Aspergillus flavipes for Potential Anti-Inflammatory Agents

The marine fungus, Aspergillus flavipes (MTCC 5220), was isolated from the pneumatophore of a mangrove plant Acanthus ilicifolius found in Goa, India. The crude extract of A. flavipes was found to show anti-inflammatory activity. It blocked interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) production in lipopolysaccharide (LPS)-activated THP-1 cells with IC₅₀ of 2.69±0.5 μM and 6.64±0.4 μM, respectively. The chemical investigation led to the isolation of optically inactive 4β-[(1E)-propen-1-yl]cyclopentane-1β,2β-diol (1) along with a new optically active diastereoisomeric compound, 4β-[(1E)-propen-1-yl]cyclopentane-1β,2α-diol (2). In addition, the fungus also produced known compounds (+)-terrein (3), butyrolactone I (4) and butyrolactone II (5) in high yields. Among these, (+)-terrein (3) exhibited IL-6 and TNF-α inhibition activity with IC₅₀ of 8.5±0.68 μM and 15.76±0.18 μM, respectively, while butyrolactone I (4) exhibited IC₅₀ of 12.03±0.85 μM (IL-6) and 43.29±0.76 μM (TNF-α) inhibition activity with low toxicity to host cells in LPS stimulated THP-1 cells. This is the first report of the isolation and characterization of 4β-[(1E)-propen-1-yl]cyclopentane-1β,2α-diol (2). The structures of all the isolated compounds were elucidated on the basis of extensive detailed NMR spectroscopic data. Anti-inflammatory activity of the fungi A. flavipes is presented here for the first time, which was due to (+)-terrein and butyrolactone I, as the major constituents and they can be further explored in the therapeutic area.

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.

Molecular characteristics of sedimentary organic matter in controlling mercury (Hg) and elemental mercury (Hg0) distribution in tropical estuarine sediments

Sedimentary organic matter (SOM) plays an important role in hosting and reducing Hg^II in marine/estuarine sediment. This study provides a better understanding on the influence of nature of SOM, in regulating sedimentary mercury (Hg) and elemental mercury (Hg⁰) distribution, and speciation in the Zuari and Mandovi Estuaries that are representative of monsoon fed tropical estuaries, located in the central west coast of India. Salinity of the overlying water column controlled the physical and chemical characteristics of SOM in the estuarine systems. The high molecular weight (MW) SOM dominated at the mid and upstream (low salinity region) of the estuaries, whereas, the low MW SOM prevailed at the downstream (high salinity region). Sediment Hg showed more affinity towards the SOM of high MW. Increasing MW of SOM increased total sedimentary Hg_T in both the estuaries. SOM with low MW in the estuarine sediment displayed a negative relationship with the sediment Hg concentration. Distribution of Hg⁰ concentration in the estuarine sediment suggests that reduction of Hg^II in presence low MW SOM was a dominant process. It was also found that distribution and speciation of Hg⁰ in the estuarine sediment depends on the quantity, quality of the SOM, and the total sediment Hg loading. This study demonstrated that the competition between Hg-SOM complexation and Hg^II reduction by SOM controls Hg^II/Hg⁰ distribution in tropical estuarine sediment systems.

Functional characterization of anti-cancer sphingolipids from the marine crab Dromia dehanni

Sphingolipids have been considered for many years only as structural components of membranes. It is now acknowledged that they are also involved in controlling cellular processes such as proliferation.The present work was designed to find the anticancer activity of the crab Dromia dehanni hemolymph in in-vivo and in vitro with special reference to the anticancer compound sphingolipids isolation and characterization. The active fraction of the purified hemolymph was subjected to NMR and ESI-MS/MS analysis. The ESI-MS/MS spectrum exhibited intense signals for sodiated molecular ions [M + Na]⁺ of sphingomyelins (SM) identified as N-2-O-Acetyl-12 pentadecenoyl sphingosine phosphorylcholine, N-9-eicosenoyl- sphinganine phosphocholine and the corresponding dehydro sphingomyelin, N-9-eicosenoyl- dehydro- sphinganine phosphocholine along with the ions at m/z 147, 184 characteristic of phosphocholine. The present study revealed D. dehaani might be a great source for the novel anti-cancer compounds which can be used for human benefits.

Quick elucidation of cyclodepsipeptide sequence from sacoglossan Elysia grandifolia using electrospray ionisation-tandem mass spectrometry

Butanol fraction of sacoglossan Elysia grandifolia was investigated for identifying peptides using electrospray ionisation-tandem mass spectrometry (ESI-MS/MS). Without prior isolation, the structural determination is achieved on the basis of mass fragmentation pattern and comparison with the previously established data. The ESI-MS of the fraction in the positive ion mode gave clusters of singly and doubly charged molecular ion peaks. The ESI-MS spectrum showed peaks for the presence of the peptides kahalalides F, G, R and S reported earlier. In addition, it also showed molecular ion peaks at m/z 1557.8 [M+H]⁺ and doubly charged ions at m/z 779.4 [M+2H]²⁺, 790.4 [M+Na]²⁺ and 796.4 [M+K]²⁺. The MS/MS at m/z 779.4 [M+2H]⁺² at collision energy 40 V obtained series of b and y fragment ions. The MS/MS spectrum showed identical fragment ion y₆ at m/z 643 which revealed that cyclic part is identical with kahalalide F, R and S. Careful examination of the fragment ions b₁ to b₇ with their corresponding y fragment ions y₁₂ to y₆, respectively and by comparison of MS/MS pattern of kahalalide S, established that proline can be replaced by tyrosine amino acid residue. The mass difference between b₄ ( m/z 511) and b₅ ( m/z 674) is equal to 163 which is equivalent to mass residue of tyrosine. Their y fragment ions also quickly helped in fixing the puzzle. This resulted in the identification of the peptide sequence cyclo-[Val-(5-MeHex-Val-Thr-Val-Val-Tyr-Lys-Ile)Thr-Ile-Val-Phe-Dhb)] for the new cyclodepsipeptide, kahalalide Z₃. Thus, ESI-MS/MS has set a trend in quick identification of new marine molecules.

Biotransformation and Detoxification of Xylidine Orange Dye Using Immobilized Cells of Marine-Derived Lysinibacillus sphaericus D3

Lysinibacillus sphaericus D3 cell-immobilized beads in natural gel sodium alginate decolorized the xylidine orange dye 1-(dimethylphenylazo)-2-naphthol-6-sulfonic acid sodium salt in the laboratory. Optimal conditions were selected for decolorization and the products formed were evaluated for toxicity by disc diffusion assay against common marine bacteria which revealed the non-toxic nature of the dye-degraded products. Decolorization of the brightly colored dye to colorless products was measured on an Ultra Violet-Vis spectrophotometer and its biodegradation products monitored on Thin Layer Chromatographic plate and High Performance Liquid Chromatography (HPLC). Finally, the metabolites formed in the decolorized medium were characterized by mass spectrometry. This analysis confirms the conversion of the parent molecule into lower molecular weight aromatic phenols and sulfonic acids as the final products of biotransformation. Based on the results, the probable degradation products of xylidine orange were naphthol, naphthylamine-6-sulfonic acid, 2-6-dihydroxynaphthalene, and bis-dinaphthylether. Thus, it may be concluded that the degradation pathway of the dye involved (a) reduction of its azo group by azoreductase enzyme (b) dimerization of the hydrazo compound followed by (c) degradation of monohydrazo as well as dimeric metabolites into low molecular weight aromatics. Finally, it may be worth exploring the possibility of commercially utilizing L. sphaericus D3 for industrial applications for treating large-scale dye waste water.

Isolation of stigmast-5,24-dien-3-ol from marine brown algae Sargassum tenerrimum and its antipredatory activity

In recent years many sterols with potent biological activity have been identified from marine sources. Here we report the isolation of stigmast-5,24-dien-3-ol (fucosterol) as a major metabolite from bioactive hexane-fraction ofSargassum tenerrimumand also investigated its ecological role.

Construction and screening of 2-aryl benzimidazole library identifies a new antifouling and antifungal agent

Library of 2-aryl benzimidazole core inspired from marine natural products, is identified and synthesized to explore antifouling/antifungal properties for the first time. Our results reveal that the 2-aryl substituent on the benzimidazole core had strong impact on their biological profile.

Synthesis of (R)-norbgugaine and its potential as quorum sensing inhibitor against Pseudomonas aeruginosa

(R)-Bgugaine is a natural pyrrolidine alkaloid from Arisarum vulgare, which shows antifungal and antibacterial activity. In this Letter, we have accomplished the simple synthesis of norbgugaine (demethylated form of natural bgugaine) employing Wittig olefination and cat. hydrogenation as the key steps and its biological studies are reported for the first time. The synthesized norbgugaine was evaluated for inhibition of quorum sensing mediated virulence factors (motility, biofilm formation, pyocyanin pigmentation, rhamnolipid production and LasA protease) in Pseudomonas aeruginosa wherein swarming motility is reduced by 95%, and biofilm formation by 83%.

Identifying the related compounds using electrospray ionization tandem mass spectrometry: bromotyrosine alkaloids from marine sponge Psammaplysilla purpurea

We have investigated extracts of marine sponge Psammaplysilla purpurea during three collections from Mandapam (Tamil Nadu, India) and Okha (Gujarat, India) and indentified two new bromotyrosine alkaloids, purpurealidin I (7) and J (8) using electrospray ionization tandem mass spectrometry (ESI-MS/MS). This sponge has tremendous chemical diversity of bromotyrosine alkaloids. Here we have used the proteomics approach in identifying related bromotyrosine alkaloids based on the predicated mass fragmentation pattern. The focus is on the examination of detailed product ion spectra of six known compounds that allowed identification of new compounds based on its mass fragmentation pattern. The isotopic pattern of the peaks for protonated molecules indicated the number of bromine atoms present in the molecule. During MS/MS studies, the most prominent product ion peak is for the presence of side chain propane with either free NH(2) or NHMe or Nme(2). The cleavage at C-C bond between oxime-amide carbonyl and amide-phenoxy moiety also gave characteristic product ions. The ESI-MS spectra for all three collections show that the bromotyrosine metabolites vary during different season and also geographical location. Although, some common metabolites were observed during the three collections. Thus, ESI-MS/MS is a method of choice in identifying the related compounds.

Biosynthesis, asymmetric synthesis, and pharmacology, including cellular targets, of the pyrrole-2-aminoimidazole marine alkaloids

The pyrrole-2-aminoimidazole (P-2-AI) alkaloids are a growing family of marine alkaloids, now numbering well over 150 members, with high topographical and biological information content. Their intriguing structural complexity, rich and compact stereochemical content, high N to C ratio (~1 : 2), and increasingly studied biological activities are attracting a growing number of researchers from numerous disciplines world-wide. This review surveys advances in this area with a focus on the structural diversity, biosynthetic hypotheses with increasing, but still rare, verifying experimental studies, asymmetric syntheses, and biological studies, including cellular target receptor isolation studies, of this stimulating and exciting alkaloid family.

Agelastatin E, agelastatin F, and benzosceptrin C from the marine sponge Agelas dendromorpha

The study of the n-butanol extract of the New Caledonian sponge Agelas dendromorpha led to the isolation and identification of three new pyrrole-2-aminoimidazole (P-2-AI) alkaloids, named agelastatins E (3) and F (4) and benzosceptrin C (5), together with 10 known metabolites, agelastatin A (1), agelastatin D (2), sceptrin (6), manzacidin A, tauroacidin A, taurodispacamide A, nortopsentin D, thymine, longamide, and 4,5-dibromopyrrole-2-carboxamide. Their structures were assigned by spectroscopic data interpretation. All the compounds were tested for cytotoxic activity.

Tandem mass spectrometry of kahalalides: identification of two new cyclic depsipeptides, kahalalide R and S from Elysia grandifolia

Spectra obtained using electrospray ionization mass spectrometry (ESI-MS) of the mollusk Elysia grandifolia showed a cluster of molecular ion peaks centered at a molecular mass of 1478 Da (kahalalide F, an anticancer agent). Two new molecules, kahalalide R (m/z 1464) and S (m/z 1492) were characterized using tandem mass spectrometry. The mass differences of 14 Da suggest that they are homologous molecules. In addition, previously identified kahalalide D and kahalalide G are also reported. However, the ESI-MS of the mollusk's algal diet Bryopsis plumosa showed the presence of only kahalalide F. The amino acid sequences of kahalalide R and S are proposed using collision-induced dissociation (CID) experiments of singly and doubly charged molecular ions and by comparison with the amino acid sequence of kahalalide F. The pathway is presented for the loss of amino acid residues in kahalalide F. It is observed that there is sequential loss of amino acids in the linear peptide chain, but in the cyclic part the ring opens at the amide bond rather than at the lactone linkage, and the loss of amino acid residues is not sequential. The CID experiment of the alkali-metal-cationized molecular ions shows that the sodium and potassium ions coordinate to the amide nitrogen/oxygen in the linear peptide chain of the molecule and not to the lactone oxygen of the lactone. In the case of kahalalide D, CID of the protonated peptide opens the depsipeptide ring to form a linear peptide with acylium ion, and fragment ion signals indicate losses of amino acids in sequential order. In this study, tandem mass spectrometry has provided the detailed information required to fully characterize the new peptides.

Tandem mass spectrometric approach for determining the structure of molecular species of ceramide in the marine sponge Haliclona cribricutis

Ceramides are important intracellular second messengers that play a role in the regulation of cell growth, differentiation and programmed cell death. Analysis of these second messengers requires sensitive and specific analytical method to detect individual ceramide species and to differentiate between them. Eight molecular species of ceramide were identified from the marine sponge Haliclona cribricutis using electrospray ionization tandem mass spectrometry (ESI-MS/MS). From this marine sponge N-hencicosanoyl (N21:0) to N-hexasanoyl (N26:0) Octadecasphing-4 (E)-enine have been reported for the first time. The ESI-MS spectra gave several strong protonated molecular ion [M+H](+) with the corresponding bis (2-ethyl hexyl) phthalate adduct [M+H+DHEP](+). The collision induced dissociation (CID) on ceramides at m/z 622.7337, 636.7645, 650.7789, 664.7925 and 678.8130 conducted at low-collision energy produced well characteristic product ions at m/z 252.31, 264.32, 278.33, 282.33 and 296 .35 for d18:1 sphingosine regardless of the length of the fatty chain. The MS/MS of the Phthalate adduct [M+H+DHEP](+) at m/z 1013.1820, 1027.1971, 1041.2176, 1055.2394 and 1069.2573 also yielded characterizing product ions for sphingosine and confirmed the molecular ion at m/z 391 for bis (2-ethyl hexyl) phthalate. The major ions in the [M+H](+) and [M+H+DHEP](+) were due to neutral loss of [M+H-H(2)O](+) and [M+H(H(2)O)(2)](+).