Crambescidin-816 Acts as a Fungicidal with More Potency than Crambescidin-800 and -830, Inducing Cell Cycle Arrest, Increased Cell Size and Apoptosis in Saccharomyces cerevisiae

In this paper, we show the effect of crambescidin-816, -800, and -830 on Saccharomyces cerevisiae viability. We determined that, of the three molecules tested, crambescidin-816 was the most potent. Based on this result, we continued by determining the effect of crambescidin-816 on the cell cycle of this yeast. The compound induced cell cycle arrest in G2/M followed by an increase in cell DNA content and size. When the type of cell death was analyzed, we observed that crambescidin-816 induced apoptosis. The antifungal effect indicates that crambescidins, and mostly crambescidin-816, could serve as a lead compound to fight fungal infectionsThe research leading to these results has received funding from the following FEDER cofunded-grants: From Ministerio de Ciencia y Tecnología, Spain: AGL2009-13581-CO2-01, AGL2012-40485-CO2-01. From Xunta de Galicia, Spain: 10PXIB261254 PR. From the European Union’s Seventh Framework Programme managed by REA—Research Executive Agency (FP7/2007-2013) under grant agreement Nos. 211326—CP (CONffIDENCE), 265896 BAMMBO, 265409 µAQUA, and 262649 BEADS, 315285 Ciguatools and 312184 PharmaSea. From the Atlantic Area Programme (Interreg IVB Trans-national): 2009-1/117 PharmatlanticS

Caracterización de compuestos marinos como posibles fármacos anti-alzheimer

Uno de los grandes retos de nuestra sociedad es el desarrollo de fármacos efectivos contra la enfermedad de Alzheimer, puesto que es uno de los mayores problemas socio-económicos y los fármacos existentes son solamente paliativos e incapaces de detener el proceso neurodegenerativo. Por su parte, los compuestos de origen marino tienen un gran potencial terapéutico, ya que son producidas por organismos vivos para realizar una función concreta, como por ejemplo la defensa frente a otros organismos. En esta Tesis Doctoral se evaluó el potencial terapéutico de 15 compuestos de origen marino como posibles fármacos anti-Alzheimer, demostrándose la eficacia de algunos de estos compuestos en la protección frente a daños producidos por estrés oxidativo y preservando la función mitocondria. Además se ha descrito su capacidad para inhibir algunas de las cinasas, responsables de la fosforilación de tau, y la enzima BACE1, fundamental en la formación del péptido βA. Por lo tanto, podemos hablar del gran potencial terapéutico de estos compuestos en la enfermedad de Alzheimer, ya que actúan directamente sobre tres dianas importantes en el desarrollo de esta patología, dando una respuesta multifactorial

In vitro antibacterial activity of alkaloid extracts from green, red and brown macroalgae from western coast of Libya

Marine organisms and microorganisms are known to be a rich source of alkaloids with unique chemical feature and interesting biological activities. The current study presents the antibacterial effect of the alkaloid extracts of some green, red and brown algae were collected from western coast of Libya, against, Escherichia coli, Salmonella typhi, Klebsiella spp., and Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis, Bacillus spp. and Staphylococcus epidermidis were investigated. Although alkaloid extracts of green algae inhibited all tested bacteria, maximum effect was exhibited by brown and red algae species. Thus, Cystoseira barbata alkaloid extract showed remarkable inhibition of human pathogen Klebsiella spp. Dictyopteris membranacea alkaloid extract also demonstrated similar considerable effect against S. typhi with MIC value 1.56 mg/ml. The pronounced antibacterial activity of C. barbata and D. membranacea can be attributed to their high alkaloid contents. These results suggest that red and brown algae secondary metabolites are important sources that could produce potential chemotherapeutic agents.Key words: Macroalgae, alkaloids, antibacterial activity

Marine algae extracts as source of natural antileishmanial compounds

This thesis aimed to identify Cystoseira macroalgae compounds displaying antileishmanial activity. Concerning the need to ensure the identification of the samples used for the drug screening, a second aim was determined to evaluate the usefulness of mitochondrial markers for identification of Cystoseira. A comprehensive review showed that marine algae, and in particular Cystoseira, are important sources of bioactive compounds, which can be used as antiparasitic agents (Chapter I and II). This work revealed that these algae contains compounds with antileishmanial activity. Forty five extracts from 15 species was submitted to bio-guided fractionation and its activity against L. infantum promastigotes and their cytotoxicity evaluated. Among the studied algae, Cystoseira extracts (C. baccata, C. barbata, C. nodicaulis and C. tamariscifolia) displayed the most interesting activities against this parasite (Chapter III). C. baccata baccatabaccata hexane extract was hexane extract was hexane extract was hexane extract was hexane extract was hexane extract was hexane extract was hexane extract was hexane extract was hexane extract was hexane extract was hexane extract was further investigated, to the isolation of two active active active active active meroterpenoids meroterpenoids meroterpenoids meroterpenoids : the the (3R)- and (3S)-tetraprenyltoluquinone with an unknown structure, and the (3R)- and (3S)-tetraprenyltoluquinol previously isolated and active against Leishmania intracellular amastigote forms. Promastigote ultrastructural alterations, DNA fragmentation and mitochondrial potential variations suggest that the mechanism of action of these compounds interfere with the mitochondrial metabolism (Chapters IV). Moreover, the investigation of the chemical composition of the Cystoseira crude extracts showed that these algae contain fatty acids, triacylglycerols, carotenoids, steroids and meroterpenoids (Chapter III). This characterization complement published data, suggesting that these compounds might also be involved in the antileishmanial activity here unravelled (Chapter II). Concerning the identification of Cystoseira, samples from twenty-two Cystoseira species were analysed generating 135 new sequences of three mitochondrial regions (COI, 23S and mt-spacer). This work demonstrated that these three markers are suitable to distinguish these species. The results allowed for the correct identification of Cystoseira samples used for drug screening, encouraging the study of taxonomy and evolutionary elucidation of these brown algae using genetic tools (Chapter V)

Novel and Bioactive Natural Products from the Marine-Derived Endophytic Fungi : Coniothyrium cereale, Phaeosphaeria spartinae and Auxarthron reticulatum

The main goal of this study was to discover novel natural products with pharmacological potential by employing various biotechnological methods. Marine fungi have been identified as a promising resource for such molecules. In particular, fungi living in the inner tissue of marine algae and sponges (endophytes) were found capable of producing a structurally and with regard to their bioactivity, most intriguing array of compounds. This study thus focussed on the three marine-derived fungi Coniothyrium cereale, Phaeosphaeria spartinae and Auxarthron reticulatum. They were cultivated in artificial media mimicking the marine environment and investigated for their bioactive secondary metabolites. The investigation dealt with the isolation, identification and biological evaluation of the fungal natural products with emphasis on compounds exhibiting cytotoxic and antimicrobial activities. Additionally, natural products that inhibit proteases such as Human Leukocyte Elastase (HLE), and compounds with affinity toward cannabinoid receptors were explored. The extracts of C. cereale, P. spartinae and A. reticulatum were subjected to purification employing high-tech chromatographic techniques. The isolated metabolites were characterized based on the extensive spectroscopic measurements. Stereochemical assignments were done through X-ray crystallographic and CD spectral analysis. The identified compounds were then evaluated for their biological activities. Over all 36 interesting compounds, partly with unprecedented chemical structures and outstanding bioactivity were isolated from three different fungal strains. The detailed analysis of the marine endophytic fungus C. cereale resulted in a series of compounds with a polyketide skeleton, i.e. the phenalenones. From the structural point of view, the most interesting compounds are the nitrogenous metabolites, i.e. conio-azasirosterol, cereo-azasirosterol, cereolactam and cereoaldomine. Conio-azasirosterol and cereo-azasirosterol are most unusual heterodimers composed of two different skeletons of natural products. In compounds cereolactam and cereoaldomine the nitrogen is either forming a rare γ-lactam ring or imine group, respectively. The Conitothyrium metabolite cereoazulene is a unique dioxa-azulene derivative, probably of polyketide origin and formed through oxidative cleavage of a regular polyketide precursor molecule. The detailed analysis of the marine endophytic fungus Ph. spartinae resulted in a novel steroidal compound and a series of polyketides. Spartogesterone is an unusual steroid due to the presence of a carboxylic group at C-4 and the structural similarity to the hormone progesterone. Indeed, the human hormone progesterone has only recently (2010) been discovered in plants, and the finding in our study suggests that progesterone derivatives also do occur in fungi. The polyketides spartinols A-D are characterized by the presence of a central cyclohexene ring to which two side chains are attached, long one with a trans triene system and another short one, substituted with hydroxyl-, carbonyl- and /or carboxyl group. This side chain also can be cyclized to form a furanoid ring, as seen in furanospartinol and a pyranoid ring as present in pyranospartinol. Pyranospartinol is also different from the aforementioned metabolites by having a cis diene double bond instead of a trans triene. Spartinoxide which was also obtained from this fungus has an uncommon allene moiety and epoxy group. From the fungus A. reticulatum two promising alkaloids were obtained, i.e. amauromine and methyl-penicinoline. Amauromine is an alkaloid with a C-2 axis of symmetry. It is composed of two prenylated tryptophan moieties, which are condensed to form a diketopiperazine nucleus. Methyl-penicinoline is a structurally unique 4-quinolinone, linked to a pyrrole ring on one side and to a methyl carboxylic acid ester moiety on the other. In antimicrobial assays, compounds conioscleroderolide, coniosclerodione, (–)-cereolactone, and (–)-scleroderolide showed activity against Staphylococcus aureus SG 511 with MIC values of 23.8, 65.7, 52.0, and 23.8 μM, respectively. In agar diffusion assays with Mycobacterium phlei considerable inhibition zones (> 15 mm) were observed for Z-coniosclerodinol, (S,S)-sclerodinol and coniolactone. (–)-Trypethelon strongly inhibited the growth of M. Phlei, S. Aureus and E. coli with inhibition zones of 18, 14 and 12 mm, respectively. In cytotoxic assays, using an MTT assay with mouse fibroblast cells, the compounds (–)-sclerodione and (–)-trypethelone had significant activity with an IC50 value of 6.4 and 7.5 µM, respectively. Cytotoxicity was also determined using an epithelial bladder carcinoma cell line, in which the compounds conioscleroderolide and (–)-scleroderolide exhibited very weak in vitro cytotoxicity with IC50 values of 27 and 41 μM, respectively. Coniosclerodin, conioscleroderolide, (–)-sclerodin, (–)-cereolactam, (–)-cereoaldomine, spartinoxide and prenyl-hydroxyl-benzoic acid showed potent inhibition of the protease HLE with IC50 values of 7.16, 13.3, 10.9, 9.28, 3.01, 6.5 and 8.1 μM, respectively. Amauromine displayed a potent and selective antagonistic activity toward CB1 receptors with a Ki value of 178 nM. No affinity was noted for CB2 receptors. To the best of our knowledge, amauromine is the first compound of fungal origin to have affinity to cannabinoid receptors, and it is the first exogenous peptide to have such an activity. In conclusion, the chemical investigation of marine fungi living in algal and sponge tissues resulted in the discovery of structurally novel natural products with interesting biological activities. In fact this study contributed novel structural skeletons probably useful as lead drugs for the development of cytotoxic antibiotic compounds, protease inhibitors and cannabinoid receptor antagonists

Genomic and transcriptomic analyses of jeotgalibacillus malaysiensis to provide insights inti its osmotic adaption

The genus Jeotgalibacillus under the family of Planococcaceae is one of the understudy genera. In this project, a bacterium strain D5 was isolated from Desaru beach, Johor. This study aimed to characterize strain D5 from morphological, physiological and biochemical aspects, in addition to examine the genomic feature and RNA expression response under saline stress. To achieve this objective, polyphasic analyses (phenotypic and genotypic), genome sequencing and RNA-Seq-based transcriptome analyses were performed. The result showed that strain D5 was mostly similar to Jeotgalibacillus alimentarius DSM 18867T with 99.87% 16S rRNA sequence similarity, and lower in similarity to other species. Strain D5 is distinguished from the other Jeotgalibacillus type strains due to the differences in phenotypic and genotypic characteristics which include morphology, endospore position, and shape, acid production from carbohydrates, tolerance to NaCl, fatty acid composition, DNA G+C content and DNA–DNA relatedness values. The D5 was proposed as a new type strain with the name of J. malaysiensis (DSM 28777T =KCTC 33350T). The complete genome of J. malaysiensis (3.52 Mbp) was sequenced using PacBio RS II sequencing system and was compared with draft genomes of J. alimentarius, J. campisalis, and J. soli. In total, 224 complete metabolic pathways were detected in J. malaysiensis genome, which include glycolysis, Krebs cycle, TCA cycle, pentose phosphate and others. J. malaysiensis shared 1,158 orthologous genes with the other Jeotgalibacillus spp. Which are involved in central metabolism, such as genes for flagellar activity, amino acid transport, translation, ribosomal structure, and biogenesis. To understand the mechanism of osmotic adaptation in J. malaysiensis, cells were cultivated in marine broth supplemented with 2% NaCl (control), saline stress of 10% and 20% (w/v) NaCl. The pairwise differentially expressed gene (DEGs) detected during the osmotic upshift were analyzed and categorized according to eggNOG (evolutionary genealogy of genes: Non-supervised Orthologous Groups) groups. At 10% (w/v) NaCl, 195 genes were differentially expressed while at 20 % (w/v) NaCl, 166 DEGs were differentially expressed. Osmotic stress significantly affected carbohydrate, energy, and amino acid metabolism, as well as fatty acid biosynthesis. J. malaysiensis apply a combination of approaches which include utilization of the TRK system for the regulation of K+ uptake, uptake and synthesis of various osmoprotectants especially proline and glutamate. As a conclusion, this study has provided new insights into the biology of this genus and showed that J. malaysiensis established halotolerance via a global cooperative mechanism, rather than by one single approach

Antifungal and Antibacterial Activities of Isolated Marine Compounds

To combat the ineffectiveness of currently available pharmaceutical medications, caused by the emergence of increasingly resistant bacterial and fungal strains, novel antibacterial and antifungal medications are urgently needed. Novel natural compounds with antimicrobial activities can be obtained by exploring underexplored habitats such as the world’s oceans. The oceans represent the largest ecosystem on earth, with a high diversity of organisms. Oceans have received some attention in the past few years, and promising compounds with antimicrobial activities were isolated from marine organisms such as bacteria, fungi, algae, sea cucumbers, sea sponges, etc. This review covers 56 antifungal and 40 antibacterial compounds from marine organisms. These compounds are categorized according to their chemical structure groups, including polyketides, alkaloids, ribosomal peptides, and terpenes, and their organismal origin. The review provides the minimum inhibitory concentration MIC values and the bacterial/fungal strains against which these chemical compounds show activity. This study shows strong potential for witnessing the development of new novel antimicrobial drugs from these natural compounds isolated and evaluated for their antimicrobial activities

Leit að efnum með ónæmisbælandi áhrif úr íslenskum sjávarhryggleysingjum

A substantial diversity of secondary metabolites from marine invertebrates has been described; however, only a few studies have investigated secondary metabolites of marine invertebrates collected in Icelandic waters. The unique marine environment around Iceland, in terms of temperature and underwater geothermal activity, has forced the living marine organisms to survive in the surroundings by developing unique biomolecules. The marine invertebrates are therefore an excellent starting point for searching for new bioactive compounds. The aim of this thesis was to isolate and identify new compounds, and known, with immunomodulatory activity from marine invertebrates collected in Icelandic waters. Seven crude extracts from Icelandic marine sponges were screened for immunomodulatory activities using an in vitro dendritic cell (DC) model. The bioactive extracts were then fractionated by column chromatographic technique with the help of bioassay-guided isolation approach to isolate the active constituents. Five pure known polyunsaturated fatty acids (PUFAs) from unidentified marine sponges and several lipophilic fractions from Halichondria sitiens were obtained and they showed immunomodulatory activity, demonstrated by their ability to reduce DC secretion of the pro-inflammatory cytokine IL-12p40 and the anti-inflammatory cytokine IL-10. Maturing DCs in the presence of selected fractions before co-culturing them with allogeneic CD4+ T cells mainly led to a decrease in T cell secretion of IFN-y, indicating a reduction in Th1 immune response. In addition, one new glycerol ester featuring methyl branched fatty acid chain was obtained but it did not have immunomodulatory activity using the DC model. Crude extracts from the marine sponge Geodia barretti and the bryozoan Flustra foliacea were chemically profiled by UPLC-qTOF-MS. Both previously known and unknown compounds were characterized by comparing the obtained molecular (precursor) ions and fragmentation patterns from obtained MS/MS data with data from the literature and databases. The crude extracts were subjected to various chromatographic techniques that yielded nineteen new alkaloids and sixteen known alkaloids. The structures of the isolated new compounds were elucidated by detailed spectroscopic analysis, including 1H NMR, 13C NMR, 1H-1H COSY, HSQC, HMBC, NOESY, 1H-15N HSQC, 1H-15N HMBC, and HRESIMS. The stereochemistry was assigned by combination of iii NMR spectroscopic data, optical rotation, ECD analysis and application of a Marfey’s-type method employing the new reagent ʟ-ND-(1-fluoro-2,4-dinitrophenyl)tryptophanamide (ʟ-FDTA). The absolute stereochemistry of one known compound was re-evaluated. All the isolated compounds were screened for immunomodulatory activity using the DC model. Twelve of the compounds decreased DC secretion of IL-12p40 and two of them increased secretion of IL-10. Three of the compounds were chosen for further investigation of dose-dependency of their activity and subsequently their ability to induce a Th1 or a Treg immune response in T cells co-cultured with DCs previously incubated with the compounds. Overall, G. barretti and F. foliacea contain a variety of alkaloids, several of which have anti-inflammatory activity, some of them warranting further investigation into their potential as a candidate for relieving inflammatory diseases. The results demonstrate that marine invertebrates collected from the marine environment around Iceland contain a number of secondary metabolites some of which have immunomodulatory effects. These studies indicate that the marine environment around Iceland may be a plentiful source of biological compounds with the potential of becoming a drug lead for treatment of inflammatory related diseases.Fjölbreytileg annars stigs lífefni er að finna í sjávarhryggleysingjum, en fáar rannsóknir hafa verið gerðar á náttúruefnum úr íslenskum sjávarhryggleysingjum. Hafsvæðið umhverfis Ísland er einstakt hvað varðar hitastig og jarðhitavirkni, sem hefur valdið því sjávarlífverur sem þar lifa gætu hafa þróað einstakar sameindir sem þær nota til að lifa af. Sjávarhryggleysingjar eru því tilvalin uppspretta fyrir leit að nýjum lífvirkum efnum. Markmið þessarar rannsóknar var að einangra og skilgreina ný efnasambönd með bólguhamlandi virkni úr sjávarhryggleysingjum sem safnað var við Íslandsstrendur. Skimað var eftir bólguhamlandi virkni í sjö úrdráttum úr íslenskum sjávarhryggleysingjum í angafrumulíkani. Lífvirkir útdrættir voru þáttaðir með ýmsum skiljunaraðferðum og lífvirknileidd einangrun notuð til að einangra lífvirk efni. Fimm þekktar fjölómettaðar fitusýrur sem voru einangraðar úr óskilgreindum sjávarsvömpum og nokkrir fitusæknir þættir sem fengust úr sjávarsvampinum Halichondria sitiens höfðu ónæmishamlandi virkni sem fólst í því að þau minnkuðu seytun angafrumna á bólguhvetjandi boðefninu IL-12p40 og bólguhamlandi boðefninu IL-10. Samræktun angafrumna, sem höfðu verið ræstar í návist valinna þátta, með ósamgena CD4+ T frumum leiddi til minni seytunar T frumna á IFN-J, sem bendir til minni Th1 sérhæfingar frumnanna. Auk þess var nýr glýseról ester með fitusýrum skipuðum metýl hóp einangraður en hann hafði ekki bólguhamlandi virkni. Úrdrættir úr sjávarsvampinum Geodia barretti og mosadýrinu Flustra foliacea voru greindir með UPLC-qTOF-MS og fundust bæði þekkt og ný efni sem voru skilgreind með því að bera saman sameinda gröf og massaróf við gögn úr vísindagreinum og gagnabönkum. Nítján nýir og sextán þekktir alkalóíðar voru einangraðir með ýmsum vökvaskiljunaraðferðum. Efnabyggingar nýju alkalóíðanna voru ákvarðaðar með kjarnsegulgreiningu, þar á meðal 1 H NMR, 13C NMR, 1 H1 H COSY, HSQC, HMBC, NOESY, og massagreiningu (UPLC-qTOF-MS og HRESIMS). Rúmfræðileg greining (e. stereochemistry) var ákvörðuð með kjarnsegulgreiningu, snúningi ljóss, hringsnúningi ljóss (e. circular dicroism) greiningu og notkun á Marfey aðferð þar sem notast var við nýtt hvarfefni, ʟ-ND -(1-fluoro-2,4- dinitrophenyl)tryptophanamide (ʟ-FDTA). Nákvæm rúmfræðileg greining (e. absolute stereochemistry) sumra áður þekktra efnanna var auk þess endurákvörðuð. Skimað var eftir bólguhamlandi virkni í öllum einangruðu efnunum. Tólf efni drógu úr seytun angafrumna á IL-12p40 og tvö efni juku seytun þeirra á IL-10. Þrjár sameindir voru valdar til frekari rannsókna, m.a. á skammtaháðri virkni þeirra og getu angafrumna meðhöndlaðra með þeim til að sérhæfa samræktaðar T frumur Th1 frumur eða T bælifrumur. Niðurstöðurnar sýna að G. barretti og F. foliacea innihalda margskonar alkalóíða, sem sumir hverjir hafa bólguhamlandi virkni sem hægt væri að þróa til að meðhöndla bólgusjúkdóma. Niðurstöður verkefnisins sýna að sjávarhryggleysingar úr hafinu í kringum Ísland innihalda fjölda annarra stigs lífefna sem hafa bólguhamlandi virkni. Þær sýna einnig að hafsvæðið umhverfis Ísland getur verið góð uppspretta fyrir lífvirk efni sem hægt væri að þróa sem lyfjasprota til að meðhöndla bólgusjúkdóma

Isolation and identification of bioactive secondary metabolites from Salinispora arenicola obtained from ocean sediments from the Madeira Archipelago

Recently there has been an increase in pathogenic microorganisms resistant to antibiotics, infectious diseases and the appearance of new threats to human health and the economy. The inability of terrestrial natural product-based drugs to solve these problems has led scientists to look at unexplored habitats in search of new drugs. The marine environment has established itself as a remarkably rich treasure of new bioactive compounds with a wide range of biological properties, including antimicrobial, anti-fungal, anti-cancer, anti-inflammatory and cytotoxic. In the short time the marine environment has been explored, its bioprospecting has resulted in the approval of seven drugs, withcurrently 23 compounds in clinical trials and hundreds in the pre-clinical pipeline. In this work, a bioassay-guided approach was used to study the bioactive secondary metabolites of the Salinispora arenicola strain PTM-99 collected from oceanic sediments off the coast of the Madeira archipelago. Chromatographic techniques, such as flash chromatography and High Performance Liquid Chromatography (HPLC), were used for the isolation and purification of secondary metabolites. About 52 compounds were isolated from a resulting culture of 7 days of incubation and 82 were isolated from a culture of 14 days of incubation (counting the F8-F9 fraction compounds). The 7-day-old culture was tested for antibacterial activity against pathogenic bacteria Enterococcus faecium VRE EF82 resistant to vancomycin and Staphylococcus aureus resistant to methicillin MRSA COL, having 20 compounds revealed activity. The compounds exhibited antibacterial activity in the range of MIC 250 to 62.5 μg/ml. Bioactive and other relevant compounds were structurally analyzed through spectroscopic methods including one-dimensional and two-dimensional Nuclear Magnetic Resonance experiments, ultraviolet, Infra-red and the non-spectroscopic method specific optical rotation. It was found that most of the compounds isolated contain lactam core, piperazine core and/or aromatic backbone. Two known diketopiperazines are reported for the first time from the Salinispora genus. Two macrolides are currently being structurally elucidated

Current Status and Future Prospects of Marine Natural Products (MNPs) as Antimicrobials

peer-reviewedThe marine environment is a rich source of chemically diverse, biologically active natural products, and serves as an invaluable resource in the ongoing search for novel antimicrobial compounds. Recent advances in extraction and isolation techniques, and in state-of-the-art technologies involved in organic synthesis and chemical structure elucidation, have accelerated the numbers of antimicrobial molecules originating from the ocean moving into clinical trials. The chemical diversity associated with these marine-derived molecules is immense, varying from simple linear peptides and fatty acids to complex alkaloids, terpenes and polyketides, etc. Such an array of structurally distinct molecules performs functionally diverse biological activities against many pathogenic bacteria and fungi, making marine-derived natural products valuable commodities, particularly in the current age of antimicrobial resistance. In this review, we have highlighted several marine-derived natural products (and their synthetic derivatives), which have gained recognition as effective antimicrobial agents over the past five years (2012–2017). These natural products have been categorized based on their chemical structures and the structure-activity mediated relationships of some of these bioactive molecules have been discussed. Finally, we have provided an insight into how genome mining efforts are likely to expedite the discovery of novel antimicrobial compounds