Clathriolide from marine demosponge Clathria (Thalysias) vulpina (Lamarck, 1814): previously undescribed macrocylic lactone with attenuating potential against angiotensin converting enzyme

Angiotensin-I converting enzyme catalyses the rate-determined step of the conversion of angiotensin-I to angiotensin-II that narrows the blood vessels, and angiotensin-I converting enzyme inhibitors were recognised as important medications for hypertension-related diseases. Chemical investigation of angiotensin-I converting enzyme inhibitors from marine demospongiae Clathria (Thalysias) vulpina (family Microcionidae), resulted in a previously undescribed 22-membered macrocyclic lactone derivative, named as clathriolide. The studied compound showed potential angiotensin converting enzyme attenuation property (IC₅₀ 0.41 mM), which was comparable with the standard captopril (IC₅₀ 0.36 mM). Clathriolide revealed significantly greater antioxidant potentials against free radical species (IC₅₀ < 1 mM) in comparison with the standard α-tocopherol (IC₅₀ > 1.5 mM). Superior electronic characteristics (topological polar surface area > 100) coupled with relatively smaller binding energy and docking score of clathriolide with the aminoacyl residues of angiotensin-I converting enzyme (-11.5 and -12.2 kcal/mol, respectively) described its potential inhibitory property against angiotensin-I converting enzyme.

Antioxidative dolabellanes and dolastanes from brown seaweed Padina tetrastromatica as dual inhibitors of starch digestive enzymes

New dolabellanes {6-methoxy-dolabella-8(17),12-diene-10β,18-diol (1), 3-methoxy-dolabella-12(18)-ene-4β-ol (2), 3-methoxy-dolabella-10,18(19)-diene-5α,8β-diol (3)} and dolastanes {2,7-dimethoxy-14α-hydroxy-dolasta-1(15),9-diene (4) and 4,7-dimethoxy-9β,14α-dihydroxy-dolasta-1-ene (5)} were identified from brown seaweed Padina tetrastromatica (family Dictyotaceae), collected from the southeast coast of India. Compounds 1-3 were found to possess dolabellane skeleton with [9.3.0] cyclotetradecane framework whereas, 4-5 were composed of tricyclic diterpenes with linear arrangement of six-seven-five fused alicyclic rings. Compounds 3 and 5 registered greater antioxidative activities (IC50 ≤0.63 mg/mL) than other analogues (IC50 ≥0.65 mg/mL), whereas their attenuating potentials against carbolytics α-amylase and α-glucosidase (IC50 ∼0.12-0.14 mg/mL) were comparable with those displayed by acarbose (IC50 0.14-0.12 mg/mL). Bioactive potentials of titled compounds were assessed by electronic and lipophilic parameters. The lesser binding energies of 3 (-9.71 kcal/mol) and 5 (-8.59 kcal/mol) through molecular docking demonstrated their effective hydrogen bonding interactions with α-amylase. Thus, dolabellanes and dolastanes might be used as anti-diabetic and antioxidant leads to reduce the risk of hyperglycaemia.

Marine Algae as a Potential Source for Anti-diabetic Compounds - A Brief Review

BACKGROUND

Diabetes Mellitus (DM) is a major chronic metabolic disorder characterized by hyperglycemia that leads to several complications such as retinopathy, atherosclerosis, nephropathy, etc. In 2019, it was estimated that about 463 million people had diabetes, and it may increase up to 700 million in 2045. Marine macroalgae are the rich source of bioactive compounds for the treatment of diabetes mellitus.

OBJECTIVE

This review summarizes the recent epidemiology and possible use of marine macroalgae-derived bioactive compounds for the protection against chronic metabolic disease, diabetes mellitus and marine macroalgae as a nutraceutical supplement.

CONCLUSION

The present therapies available for diabetes treatment are oral medicines and insulin injections. But continuous use of synthetic medicines provides low therapeutic with many side effects. In continuing search of anti-diabetic drugs, marine macroalgae remain as a promising source with potent bioactivity. Among existing marine algae, red and brown algae are reported to show anti-diabetic activity. Hence, the present review focuses on the epidemiology, diabetes biomarkers and different secondary bioactive compounds present in marine macroalgae to treat diabetes mellitus.

Chemical mining of heterotrophic Shewanella algae reveals anti-infective potential of macrocyclic polyketides against multidrug-resistant pathogens

Heterotrophic Gamma-proteobacterium Shewanella algae MTCC 12715, associated with an intertidal red algae Hypnea valentiae, presented broad-spectra of antibacterial activities against pathogenic bacteria bringing about nosocomial infection. Bioassay-guided fractionation of the bacterial crude extract resulted in two undescribed macrocyclic polyketide analogs, with anti-infective activities against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis (MIC 3.1-5.0 µg/mL). In order to identify the polyketide biosynthetic machinery termed type-I polyketide synthase (pks-I) encoding biologically active secondary metabolites in this strain, the ketosynthase-coding regions of DNA with ≈700 bp size, were amplified, and the partial sequence was submitted in the GenBank (accession number MH157093). The titled compounds were classified under macrocyclic polyketides bearing dodecahydropyrano-trioxacyclooctadecine-dione and trioxo-octadecahydro-1H-benzo[o]tetraoxacyclopentacosine-carboxylate functionalities. Structure-activity correlation analysis displayed that hydrophobic descriptor of the studied compounds could play a prominent role in its anti-infective property against the opportunistic pathogens. Further, in silico molecular docking studies were performed in the allosteric sites of penicillin-binding protein (PBP2a) coded by mecA genes of MRSA, and the best binding pose for each compound (docking score -8.47 kcal/mol and -9.58 kcal/mol, respectively) could be correlated with their in vitro antibacterial activities. The pks-I assisted biosynthetic pathway of macrocyclic polyketides through step-wise decarboxylative condensation initiated by malonate-acyl carrier protein corroborated their structural attributes. Chemical mining of the studied macroalgae-associated heterotrophic bacterium thus revealed the promising antagonistic properties of macrocyclic polyketides isolated from Shewanella algae MTCC 12715 against multidrug-resistant pathogens.

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].

Seaweed-associated heterotrophic bacteria: new paradigm of prospective anti-infective and anticancer agents

Ever since the development of the first antibiotic compound with anticancer potential, researchers focused on isolation and characterization of prospective microbial natural products with potential anti-infective and anticancer activities. The present work describes the production of bioactive metabolites by heterotrophic bacteria associated with intertidal seaweeds with potential anti-infective and anticancer activities. The bacteria were isolated in a culture-dependent method and were identified as Shewanella algae MTCC 12715 (KX272635) and Bacillus amyloliquefaciens MTCC 12716 (KX272634) based on combined phenotypic and genotypic methods. Further, the bacteria were screened for their ability to inhibit drug-resistant infectious pathogens and prevent cell proliferation of human liver carcinoma (HepG2) and breast cancer (MCF7) cell lines, without affecting the normal cells. Significant anti-infective activity was observed with bacterial cells and their organic extracts against broad-spectrum multidrug-resistant pathogens, such as vancomycin-resistant Enterococcus faecalis, methicillin-resistant Staphylococcus aureus, Klebsiella pneumonia and Pseudomonas aeruginosa with minimum inhibitory concentration ≤ 3.0 µg mL^-1 as compared to the antibiotic agents' chloramphenicol and ampicillin, which were active at ≥ 6.25 mg mL^-1. The extracts also exhibited anticancer activity in a dose-responsive pattern against HepG2 (with IC₅₀, half maximal inhibitory concentration ~ 78-83 µg mL^-1) and MCF7 (IC₅₀ ~ 45-48 µg mL^-1) on tetrazolium bromide screening assay with lesser cytotoxic effects on normal fibroblast (L929) cell lines (IC₅₀ > 100 µg mL^-1). The results revealed that seaweed-associated heterotrophic bacteria could occupy a predominant role for a paradigm shift towards the development of prospective anti-infective and anticancer agents.

Callypyrones from marine Callyspongiidae sponge Callyspongia diffusa: antihypertensive bis-γ-pyrone polypropionates attenuate angiotensin-converting enzyme

Angiotensin I-converting enzyme (ACE) catalyses the biosynthesis of angiotensin II, a potent blood vessel constrictor, from angiotensin I, and ACE inhibitors were recognised as medications for hypertension. Undescribed bis-γ-pyrone polypropionate compounds, callypyrones A and B were purified from the organic extract of Callyspongiidae sponge species Callyspongia diffusa by repeated chromatographic purification. Callypyrone A exhibited significantly greater attenuation potential against ACE (IC₅₀ 0.48 mM) than that displayed by callypyrone B (IC₅₀ 0.57 mM) and showed comparable activity with standard ACE inhibitor captopril (IC₅₀ 0.36 mM). Higher electronic parameters of callypyrone A (topological surface area of 108.36) combined with balanced hydrophilic-lipophilic parameter (octanol-water coefficient, log P_ow 1.9), as deduced from the structure-activity relationship analyses, could further indicate the improved ligand-receptor interactions resulting in its prospective ACE inhibitory activity. In silico docking analyses of the callypyrones with ACE recorded lowest binding energy (-12.58 kcal mol^-1) for callypyrone A, which further supported the antihypertensive potential of the compound.

Macrocyclic polyketides with siderophore mode of action from marine heterotrophic Shewanella algae: Prospective anti-infective leads attenuate drug-resistant pathogens

AIMS

Biotechnological and chemical characterization of previously undescribed homologous siderophore-type macrocyclic polyketides from heterotrophic Shewanella algae Microbial Type Culture Collection (MTCC) 12715 affiliated with Rhodophycean macroalga Hypnea valentiae of marine origin, with significant anti-infective potential against drug-resistant pathogens.

METHODS AND RESULTS

The heterotrophic bacterial strain in symbiotic association with intertidal macroalga H. valentiae was isolated to homogeneity in a culture-dependent method and screened for bioactivities by spot-over-lawn assay. The bacterial organic extract was purified and characterized by extensive chromatographic and spectroscopic methods, respectively, and was assessed for antibacterial activities with disc diffusion and microtube dilution methods. The macrocyclic polyketide compounds exhibited wide-spectrum of anti-infective potential against clinically significant vancomycin-resistant Enterococcus faecalis (VREfs), methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and Klebsiella pneumonia with minimum inhibitory concentration of about 1-3 µg ml^-1 , insomuch as the antibiotics chloramphenicol and ampicillin were active at ≥6·25 µg ml^-1 . The studied compounds unveiled Fe³⁺ chelating activity, which designated that their prospective anti-infective activities against the pathogens could be due to their siderophore mechanism of action. In support of that, the bacterium exhibited siderophore production on bioassay involving the cast upon culture agar plate, and the presence of siderophore biosynthetic gene (≈1000 bp) (MF 981936) further corroborated the inference. In silico molecular modelling with penicillin-binding protein (PBP2a) coded by mecA genes of MRSA (docking score -11·68 to -12·69 kcal mol^-1 ) verified their in vitro antibacterial activities. Putative biosynthetic pathway of macrocyclic polyketides through stepwise decarboxylative condensation initiated by malonate-acyl carrier protein further validated their structural and molecular attributes.

CONCLUSIONS

The studied siderophore-type macrocyclic polyketides from S. algae MTCC 12715 with significant anti-infective potential could be considered as promising candidates for pharmaceutical and biotechnological applications, especially against emerging multidrug-resistant pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study exhibited the heterotrophic bacteria in association with intertidal macroalga as propitious biological resources to biosynthesize novel antibacterial agents.

High-value compounds from the molluscs of marine and estuarine ecosystems as prospective functional food ingredients: An overview

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Reviewed enthnomedical, nutritive and pharmacological profiles of molluscs.

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Gastropods and bivalves are potential sources of functional food.

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More than 1334 bioactive metabolites were reported from total of about 1287 publications.

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Molluscan derived metabolites were mostly belonged to terpenoids and sterols.

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Number of patents were increased to more than 30% during 2016–2019.

Extensive biodiversity and availability of marine and estuarine molluscs, along with their their wide-range of utilities as food and nutraceutical resources developed keen attention of the food technologists and dieticians, particularly during the recent years. The current review comprehensively summarized the nutritional qualities, functional food attributes, and bioactive properties of these organisms. Among the phylum mollusca, Cephalopoda, Bivalvia, and Gastropoda were mostly reported for their nutraceutical applications and bioactive properties. The online search tools, like Scifinder/Science Direct/PubMed/Google Scholar/MarinLit database and marine natural product reports (1984–2019) were used to comprehend the information about the molluscs. More than 1334 secondary metabolites were reported from marine molluscs between the periods from 1984 to 2019. Among various classes of specialized metabolites, terpenes were occupied by 55% in gastropods, whereas sterols occupied 41% in bivalves. The marketed nutraceuticals, such as Cadalmin^TM green mussel extract (Perna viridis) and Lyprinol® (Perna canaliculus) were endowed with potential anti-inflammatory activities, and were used against arthritis. Molluscan-derived therapeutics, for example, ziconotide was used as an analgesic, and elisidepsin was used in the treatment of cancer. Greater numbers of granted patents (30%) during 2016–2019 recognized the increasing importance of bioactive compounds from molluscs. Consumption of molluscs as daily diets could be helpful in the enhancement of immunity, and reduce the risk of several ailments. The present review comprehended the high value compounds and functional food ingredients from marine and estuarine molluscs.

Sulfated N-acetylglucosamino-glucuronopyranosyl-arabinopyranan from seafood Amphioctopus neglectus attenuates angiotensin-II prompted cardiac hypertrophy

Angiotensin converting enzyme (ACE) is a multifunctional enzyme involved in translation of angiotensin-I (Ang^I) to vasoconstrictor angiotensin-II (Ang^II). A sulfated N-acetylglucosamino-glucuronopyranosyl-arabinopyranan characterized as poly-[(2-methoxy-β-arabinopyranosyl)-(1 → 3)-(β-glucurono)-(1 → 4)-(2-acetamido-2-deoxy-3,6-di-O-sulfonato-β-glucopyranose)] was purified and reported first time from the edible portion of Amphioctopus neglectus and evaluated for various pharmacological properties. The polysaccharide exhibited potential ACE attenuation property (IC₅₀ 0.11 mg mL^-1), whereas molecular docking simulations displayed its efficient binding at the ACE active site with lesser inhibitory constant (K_i) of 17.36 nM and binding energy (-10.59 kcal mol^-1). The in-vitro analysis showed that the studied polysacharide attenuated Ang^II prompted cardiac hypertrophy at 50 μg mL^-1 in the cardiomyoblast cells, whereas 48% reduction in cellular surface area with extended viability could be correlated with anti-hypertrophic properties of the studied polysaccharide. The sulfated N-acetylglucosamino-glucuronopyranosyl-arabinopyranan purified from A. neglectus could function as a prospective functional lead against the pathophysiological conditions leading to hypertension.

Moving away from traditional antibiotic treatment: can macrocyclic lactones from marine macroalga-associated heterotroph be the alternatives?

Intertidal red algae Hypnea valentiae associated Bacillus amyloliquefaciens MTCC 12716 revealed potential inhibitory effects on the growth of drug-resistant pathogens. In the genome of B. amyloliquefaciens MTCC 12716, biosynthetic gene clusters encoding antibacterial metabolites were predicted, which might be expressed and contributed to the broad-spectrum anti-infective activity. Three homologue members of the 24-membered macrocyclic lactone family, named as bacvalactones 1-3 bearing 13-O-ethyl (1); 15-O-furanyl-13-O-isobutyl-7-O-propyl-propanoate (2); and 15-O-furanyl-13-O-isobutyl-7-O-propyl-propanoate-7,24-dimethyl (3) functionalities, were acquired through bioactivity-guided purification. The macrocyclic lactones displayed bactericidal activity against opportunistic pathogens causing nosocomial infections, for instance, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecalis (VREfs), and multidrug-resistant strains of Pseudomonas aeruginosa and Klebsiella pneumonia with MIC ≤ 3.0 μg/mL, whereas standard antibiotics ampicillin and chloramphenicol were active only at concentrations of ≥ 6.25 mg/mL. The biosynthetic pathway of macrocyclic lactones that are generated by trans-AT polyketide synthases through stepwise extension of an acetyl starter unit by eleven sequential Claisen condensations with malonyl-CoA was established, and the structures were correlated with the gene organization of the mln operon, which encompasses nine genes mln A-I (approximately 47 kb in size). The best binding poses for each compounds (1-3) with Staphylococcus aureus peptide deformylase (SaPDF) unveiled docking scores (≥ 9.70 kcal/mol) greater than that of natural peptide deformylase inhibitors, macrolactin N and actinonin (9.14 and 6.96 kcal/mol, respectively), which supported their potential in vitro bioactivities. Thus, the present work demonstrated the potential of macrocyclic lactone for biotechnological and pharmaceutical applications against emerging multidrug-resistant pathogens. Key Points •Three antibacterial bacvalactones were identified from the symbiotic bacterium. •The symbiotic bacterial genome was explored to identify the biosynthetic gene clusters. •Trans-AT pks-assisted mln biosynthetic pathway of the macrocyclic lactone was proposed. •In silicomolecular interactions of the bacvalactones with S. aureus PDF were analyzed.

Antioxidative 2H-chromenyls attenuate pro-inflammatory 5-lipoxygenase and carbolytic enzymes: Prospective bioactive agents from Babylonidae gastropod mollusk Babylonia spirata

Oxygenated heterocycles are emerging as valuable pharmacophores involved in the prophylaxis and treatment of several diseases elicited by the reactive oxygen species. Bioassay-led chromatographic fractionation of the organic extract of the gastropod mollusk Babylonia spirata (family Babylonidae) yielded two unprecedented 2H-chromenyl derivatives characterized as 2-(butyryloxy)-5-hydroxy-hexahydro-2H-chromene-3-methyl carboxylate (1) and (3-hydroxy-hexahydro-2H-chromen-2-yl)methyl pentanoate (2). The chromenyl derivative (1) registered significantly greater attenuation potential against pro-inflammatory 5-lipoxygenase (IC₅₀  ~ 2.02 mM) than those exhibited by the compound (2) (IC₅₀ 2.76 mM) and the non-steroidal anti-inflammatory drug ibuprofen (IC₅₀ 4.36 mM, p < .05). The compound (1) exhibited comparable antioxidant activity (IC₅₀ 1.47-1.72 mM) with standard antioxidative agent α-tocopherol (IC₅₀ 1.4-1.7 mM). Inhibitory potential of chromenyl derivative (1) toward α-glucosidase (IC₅₀ 1.18 mM) and α-amylase (IC₅₀ 0.92 mM) was greater than those displayed by 2 (IC₅₀ 1.16-1.56 mM). Structure-activity relationships revealed that bioactivities of the compounds were determined by the electronic factors and hydrophilic-lipophilic balance. PRACTICAL APPLICATIONS: The marine gastropod Babylonia spirata is one of the prominent edible gastropod species harvested from the coastlines along the southwestern region of the Indian peninsula. Two 2H-chromenyl derivatives were isolated to homogeneity from the organic extract of the marine buccinid gastropod B. spirata by the bioactivity-guided chromatographic fractionation and were found to possess potential antioxidant and attenuation properties against pro-inflammatory 5-lipoxygenase and carbolytic enzymes. The attenuation properties of the 2H-chromenyls against pro-inflammatory 5-lipoxygenase showed that 2H-chromenyl analogs possessed significantly greater anti-inflammatory potential than the non-steroidal anti-inflammatory drug ibuprofen. In particular, the chromenyl derivative bearing 2H-chromene-3-methyl carboxylate framework might constitute a prospective biogenic constituent in functional food and pharmaceutical applications for use against oxidative agents, including inflammation and hyperglycemic pathologies.

Salicornolides A-C from Gracilaria salicornia attenuate pro-inflammatory 5-lipoxygense: Prospective natural anti-inflammatory leads

Three macrolides bearing the carbon framework of oxabicyclo[21.3.1]heptacosa-ene-diones (A and B) and oxabicyclo[19.3.1]pentacosa-ene-dione (C) were isolated and characterised from the organic extract of the intertidal red seaweed Gracilaria salicornia (family Gracilariaceae), which were named as salicornolides A-C. These natural macrolides were conformationally pre-organised ring structure providing diverse functionalities, and their potential bioactive properties led to the development of pharmacophores with anti-inflammatory properties. The 21-membered pyran-enclosed salicornolide B displayed greater cyclooxygenase-2 (IC₅₀ COX-2 1.13 mM) inhibitory activity than those exhibited by the 21-membered aryl salicornolide A and 19-membered salicornolide C (IC₅₀ COX-2-1.2 mM). The attenuating potential of the studied compounds against pro-inflammatory enzyme, 5-lipoxygenase (IC₅₀ LOX < 1.5 mM) was significantly greater than that displayed by the non-steroidal anti-inflammatory ibuprofen (IC₅₀ 4.5 mM), whereas the selectivity indices exhibited by salicornolides against cyclooxygenase-2 was significantly higher (1.18-1.41, P < 0.05) when compared to that of ibuprofen (SI 0.43) attributing the greater selectivity profile of the former towards inducible pro-inflammatory mediators than the latter. The minimal binding energy of salicornolide B (-9.64 kcal mol^-1), a greater number of hydrogen-bonds and lesser inhibitory constant (Ki 85.15 nM) might be responsible for effective binding towards 5-lipoxygenase, and that could attribute its greater anti-inflammation potential than those displayed by other compounds. The putative biosynthetic cascade initiated by malonate-acyl carrier protein unambiguously confirmed the structural attributions of the titled macrocyclic lactones. The undescribed salicornolides A-C from seaweed Gracilaria salicornia attenuating pro-inflammatory 5-lipoxygense might be considered as prospective natural anti-inflammatory leads for pharmaceutical applications.

Oxygenated elansolid-type of polyketide spanned macrolides from a marine heterotrophic Bacillus as prospective antimicrobial agents against multidrug-resistant pathogens

Three homologous oxygenated elansolid-type of polyketide spanned macrolides were isolated from a heterotrophic marine bacterium, Bacillus amyloliquefaciens MTCC 12716, associated with an intertidal red alga Hypnea valentiae. The complete genome of the bacterium was sequenced and all detectable natural product gene clusters were analysed. The B. amyloliquefaciens MTCC 12716 genome features polyketide synthase (pks) systems of every known formally classified family, nonribosomal peptide synthetases and hybrid clusters. Comprehensive spectroscopic studies revealed the compounds to possess isobenzofuranyl benzoate and 1H-furopyrano[2,3-c]oxacyclononadecine-6-carboxylate moieties. The identified compounds displayed broad-spectrum bactericidal activity against methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, and drug-resistant strains of Pseudomonas aeruginosa and Klebsiella pneumoniae with minimum inhibitory concentrations (MICs) of ≤1.0 µg/mL, whereas the standard antibiotics ampicillin and chloramphenicol were active only at concentrations of ≥6.25 µg/mL. The plausible mechanism of elansolid-type macrolide biosynthesis by trans-AT polyketide synthases through the pks starter unit para-hydroxybenzoic acid was hypothesised, and the structures were correlated with the gene organisation, with the predicted gene cluster comprising 16 genes (~81 kb in size). The best binding poses for each compound with the peptide deformylase (PDF) protein of S. aureus revealed docking scores (>11.30 kcal/mol) greater than actinonin (6.96 kcal/mol), a natural PDF inhibitor. The higher electronic values along with optimum lipophilic parameters support the potential anti-infective properties of the studied macrolides. These antibacterial elansolid-type of polyketide spanned macrolides in marine symbiotic B. amyloliquefaciens could be potential leads for biotechnological and pharmaceutical applications against emerging multidrug-resistant pathogens.

First report of a glycosaminoglycan-xylopyranan from the buccinid gastropod mollusk Babylonia spirata attenuating proinflammatory 5-lipoxygenase

A previously undescribed xylated glycosaminoglycan characterized as β-D-Xylop(1 → 3)-(⋯ → 4)-GlcpA(1 → 3)-GlcpNAc(1 → ⋯) was purified from the buccinid gastropod Babylonia spirata and was evaluated for pharmacological properties using different in vitro models. The glycosaminoglycan-xylopyranan displayed prospective free radical quenching activities (IC₅₀  < 0.7 mg/ml), whereas it exhibited potentially greater attenuation against the inductive proinflammatory enzyme 5-lipoxygenase (5-LOX, IC₅₀ 0.36 mg/ml) than the synthetic nonsteroidal anti-inflammatory drug aspirin (0.42). Gel permeation chromatography analysis specified the average molecular mass of the purified polysaccharide to be 231.88 kDa. The linkage sites, anomeric configuration, and the sequence of sugar residues of the purified xylated glycosaminoglycan were attributed by the inter-residue correlation obtained via two-dimensional nuclear resonance spectroscopic techniques. The results specified that the studied compound was composed of GlcpA(1 → 3)-GlcpNAc (1 → ⋯) disaccharide repeating unit in the glycosaminoglycan backbone, with the xylose residues branching as C-3 substituents of the GlcpA. . PRACTICAL APPLICATIONS: The edible marine buccinid mollusk Babylonia spirata is a gastropod species of economic significance in the coastal regions of peninsular India. A previously unreported xylated glycosaminoglycan with a β-D-Xylop(1 → 3)-(⋯ → 4)-GlcpA(1 → 3)-GlcpNAc(1 → ⋯) framework was isolated to homogenity and was found to possess potential antioxidant and 5-lipoxygenase attenuation activities. The isolated metabolite might be anticipated as potential naturally-derived bioactive constituent in functional food and pharmaceutical applications.

First report of antioxidant 1H-benzochromenone from muricid gastropod Chicoreus ramosus as dual inhibitors of pro-inflammatory 5-lipoxygenase and carbolytic enzymes

Chromene derivatives with manifold structural framework and pharmacological properties were ubiquitous in the mollusks of marine origin. A previously undescribed 1H-benzochromenone was isolated through bioassay-guided chromatographic purification of the organic extract of the marine gastropod mollusk Chicoreus ramosus. The compound was characterised as 6-(2',2'-dimethyl)-3'-en-1'-yl-1'-oxy)-3-hydroxy-1H-benzo[c]chromene-2(10aH)-one based on integrated spectroscopic analysis. The antioxidant studies by employing the stable free radicals reported that the antioxidant activity (IC₅₀ 1.4-1.6 mM) was comparable to α-tocopherol (IC₅₀ 1.4-1.7 mM). The attenuating potential of the studied compound against pro-inflammatory 5-lipoxygenase (IC₅₀ 2.12 mM) was significantly greater than that exhibited by anti-inflammatory drug ibuprofen (IC₅₀ 4.4 mM), whereas its inhibitory properties against carbolytic α-amylase (IC₅₀ ∼0.72 mM) was comparable with that displayed by acarbose (IC₅₀ 0.43 mM). The present study recognised the potential of 1H-benzochromenone derivative isolated from C. ramosus as important pharmaceutical lead with anti-diabetic and anti-inflammatory potentials to reduce the risk of hyperglycaemia and inflammatory pathologies.