Potent Antifouling Activity Research Articles

Antibacterial Iodine-Releasing Coatings of Cross-Linked Poly(N-vinylpyrrolidone) Synthesized by Solvent-Free Initiated Chemical Vapor Deposition.

Biomaterial-associated infections caused by bacteria pose a great threat to human health, and therefore, various antibacterial coatings have been developed to control bacterial infections. Povidone iodine (PVP-I) is a broad-spectrum antimicrobial agent without drug resistance to most pathogenic microorganisms and has been widely used in the clinic. However, its applications in the field of coatings are limited due to its strong water solubility. Here, we used initiated Chemical Vapor Deposition (iCVD) technique to synthesize cross-linked poly(N-vinylpyrrolidone-co-ethylene glycol dimethacrylate) (PVE) coatings to firmly immobilize poly(N-vinylpyrrolidone) (PVP) on surfaces. After complexation with iodine, PVE-I coatings exhibited potent bacteria-killing and antifouling activities against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus in vitro owing to the antibacterial effect of iodine and the hydrophilicity of VP, respectively. The killing and antifouling effects were positively correlated with the VP content. The PVE-I-2 coating displayed excellent anti-infection performance in a rat subcutaneous implantation model in vivo. This study provided a simple method for preparing stable povidone iodine coatings on surfaces via solvent-free iCVD, and combined bacteria-killing and antifouling strategies to fabricate multifunctional antibacterial coatings against bacterial infections on biomaterial surfaces.

Antifouling Diterpenoids from the Sponge Dendrilla antarctica.

Two nor-diterpenes, 9,11-dihydrogracilin A (1) and the previously unreported 9,11-dihydrogracillinone A (2), were isolated from the sponge Dendrilla antarctica. The sponge was collected by trawling at a depth of 49 m, from the research vessel Puerto Deseado, near the coast of Tierra del Fuego, farther north than the reported habitat for this species. Since these compounds were particularly abundant and the sponge was free from epibionts, both 1 and 2 were included in soluble-matrix paints and tested for antifouling activity in the ocean. The results obtained from these experiments clearly indicated a potent antifouling activity for both compounds against a variety of colonizing organisms, and established a probable role as natural antifoulants for these abundant secondary metabolites and other structurally related compounds previously isolated from Dendrilla spp.

Evaluation of Antifouling Potential and Ecotoxicity of Secondary Metabolites Derived from Red Algae of the Genus Laurencia.

Red algae of the genus Laurencia are known to biosynthesize and secrete an immense variety of secondary metabolites possessing a spectrum of biological activities against bacteria, invertebrates and mammalian cell lines. Following a rigorous cross-species screening process, herein we report the antifouling potential of 25 secondary metabolites derived from species of the genus Laurencia, as well as the thorough evaluation of the ecotoxicity of selected metabolites against non-target marine arthropods and vertebrate cell lines. A number of these secondary metabolites exhibited potent antifouling activity and performed well in all screening tests. Our results show that perforenol (9) possesses similar antifouling activity with that already described for bromosphaerol, which is used herein as a benchmark.

Terpenoids from the South China Sea soft coral Sinularia multiflora

A rare sinulariane-type norcembranoid sinulariadiolide B (1) with a unique cyano group, and a eunicellin-based diterpenoid multifloralin (2), along with two known related analogues, sinulariadiolide (3) and sclerophytin E (4), were isolated from the extract of the South China Sea soft coral Sinularia multiflora. Their structures were elucidated on the basis of detailed spectroscopic analysis and by comparison with previously reported data. Compounds 2 and 4 showed potent antifouling activity against barnacle Balanus albicostatus.

Cochliomycin G, a 14-membered resorcylic acid lactone from a marine-derived fungus Cochliobolus lunatus

Cochliomycin G (1), a new 14-membered resorcylic acid lactone, together with six known analogues (2−7), was isolated from the culture broth of a marine-derived fungus Cochliobolus lunatus. The planar structure of 1 was established by extensive NMR spectroscopy, and the absolute configuration was elucidated by the combination of empirical rules, CD data, and 13C chemical shift calculations. Compound 1 exhibited potent antifouling activity against Chlorella vulgaris, Chaetoceros socialis, and Navicula exigua, with EC50 values of 1.09, 0.92, and 0.61 μg/mL, respectively.

Synthesis and Structure-Activity Relationship of Omaezallene Derivatives.

Omaezallene derivatives (nor-bromoallene, nor-bromodiene, and bromoenynes) were successfully synthesized. Their antifouling activity and toxicity to the cypris larvae of the barnacle Amphibalanus amphitrite and ecotoxicity to the marine crustacean Tigriopus japonicus were studied. It was revealed that the two side chains of omaezallene were essential to its antifouling activity because the activities of nor-bromoallene and nor-bromodiene were significantly diminished. The bromoenyne was found to exhibit potent antifouling activities comparable to omaezallene with low toxicity and ecotoxicity. Preparation of bromoenyne framework is much easier than that of bromodiene moiety in omaezallene. Based on the antifouling activities of the bromoenynes, the synthesis of fluorescent probes and evaluation of their biological activities were also carried out.

Antifouling activity of portimine, select semisynthetic analogues, and other microalga-derived spirocyclic imines

A range of natural products from marine invertebrates, bacteria and fungi have been assessed as leads for nature-inspired antifouling (AF) biocides, but little attention has been paid to microalgal-derived compounds. This study assessed the AF activity of the spirocyclic imine portimine (1), which is produced by the benthic mat-forming dinoflagellate Vulcanodinium rugosum. Portimine displayed potent AF activity in a panel of four macrofouling bioassays (EC50 0.06–62.5 ng ml−1), and this activity was distinct from that of the related compounds gymnodimine-A (2), 13-desmethyl spirolide C (3), and pinnatoxin-F (4). The proposed mechanism of action for portimine is induction of apoptosis, based on the observation that portimine inhibited macrofouling organisms at developmental stages known to involve apoptotic processes. Semisynthetic modification of select portions of the portimine molecule was subsequently undertaken. Observed changes in bioactivity of the resulting semisynthetic analogues of portimine were consistent with portimine’s unprecedented 5-membered imine ring structure playing a central role in its AF activity.

Antifouling Compounds from Marine Macroalgae.

Marine macroalgae produce a wide variety of biologically-active metabolites that have been developed into commercial products, such as antibiotics, immunosuppressive, anti-inflammatory, cytotoxic agents, and cosmetic products. Many marine algae remain clean over longer periods of time, suggesting their strong antifouling potential. Isolation of biogenic compounds and the determination of their structure could provide leads for the development of environmentally-friendly antifouling paints. Isolated substances with potent antifouling activity belong to fatty acids, lipopeptides, amides, alkaloids, lactones, steroids, terpenoids, and pyrroles. It is unclear as yet to what extent symbiotic microorganisms are involved in the synthesis of these compounds. Algal secondary metabolites have the potential to be produced commercially using genetic and metabolic engineering techniques. This review provides an overview of publications from 2010 to February 2017 about antifouling activity of green, brown, and red algae. Some researchers were focusing on antifouling compounds of brown macroalgae, while metabolites of green algae received less attention. Several studies tested antifouling activity against bacteria, microalgae and invertebrates, but in only a few studies was the quorum sensing inhibitory activity of marine macroalgae tested. Rarely, antifouling compounds from macroalgae were isolated and tested in an ecologically-relevant way.

Preparation, Structure, and Potent Antifouling Activity of Sclerotioramine Derivatives.

A series of 30 sclerotioramine derivatives (2-31) of the natural compound, (+)-sclerotiorin (1), has been successfully semi-synthesized by a one-step reaction with high yields (up to 80%). The structures of these new derivatives were established by extensive spectroscopic methods and single-crystal X-ray diffraction analysis for 3, 6, and 10. (+)-Sclerotiorin (1) and its semisynthetic derivatives (2-31) were evaluated for their antifouling activity. Most of them except 6, 7, 8, 12, and 28 showed potent antifouling activity against the larval settlement of the barnacle Balanus amphitrite. More interestingly, most of the aromatic amino-derivatives (13-17, 19-21, 23, 25-27, and 29-31) showed strong antifouling activity; however, only two aliphatic amino-derivatives (5 and 10) had the activity.

Synthesis of nano silver by a marine epibiotic bacterium Bacillus vallismortis and its potent ecofriendly antifouling properties

In the present study, biosynthesis of silver nanoparticles (AgNPs) by a newly isolated marine epibiotic bacterium Bacillus vallismortis and its potent antifouling (AF) activity was investigated. Biosynthesized AgNPs were primarily confirmed by change in colour from yellow to brown. UV–vis spectrum of the AgNPs showed surface plasmon resonance (SPR) peak at 426nm. The AgNPs were further characterized using FT-IR spectroscopy, XRD, SEM and HRTEM analysis. The synthesized AgNPs were narrowly polydispersed and spherical in shape with an average particle size of 23nm. Antibacterial activity inferred that the AgNPs effectively inhibited marine biofilm forming bacterial strains with minimal MIC and MBC values. Moreover, Confocal Laser Scanning Microscopic images evidenced good antibiofilm efficacy of the AgNPs. It had also strongly inhibited fouling microalgal growth at minimal nanomolar (nM) concentration in the range of 0.5–1nM. Anticrustacean assay using Artemia franciscana larvae registered LC50 value of 11.59nM. Further, EC50<LC50 and 100% recovery of mussel Perna indica in toxicity assay propagated non-toxic nature of the AgNPs. Current study clearly explored the possibility of utilizing AgNPs biosynthesized by B. vallismortis in AF coatings to combat biofouling.

Antifouling Compounds from the Marine-Derived Fungus Aspergillus terreus SCSGAF0162

A new cyclic tetrapeptide, asperterrestide B (1), and 11 known compounds (2-12) were isolated from a marine-derived fungus Aspergillus terreus SCSGAF0162. The structure of 1 was elucidated by spectroscopic analysis, and the absolute configuration of 1 was determined by Mosher ester and Marfey's methods. Compounds 4, 6, and 8 had potent antifouling activity against larvae of the barnacle Balanus amphitrite, with EC50 values of 17.1 ± 1.2, 11.6 ± 0.6, and 17.1 ± 0.8 μg x mL(-1), respectively.

Bioactive diphenyl ether derivatives from a gorgonian-derived fungus Talaromyces sp.

Three new diphenyl ether derivatives, talaromycins A-C (1-3, resp.), together with six known analogs, 4-9, were isolated from a gorgonian-derived fungus, Talaromyces sp. The structures of the new compounds were determined by analysis of extensive NMR spectroscopic data. All of the isolated metabolites, 1-9, were evaluated for their cytotoxic and antifouling activities. Compound 4 exhibited pronounced cytotoxicity against the tested human cell lines with the IC50 values ranging from 4.3 to 9.8 μM. Compounds 3, 5, 8, and 9 showed potent antifouling activities against the larval settlement of the barnacle Balanus amphitrite with the EC50 values ranging from 2.2 to 4.8 μg/ml.

Territrem and butyrolactone derivatives from a marine-derived fungus Aspergillus terreus.

Seventeen lactones including eight territrem derivatives (1–8) and nine butyrolactone derivatives (9–17) were isolated from a marine-derived fungus Aspergillus terreus SCSGAF0162 under solid-state fermentation of rice. Compounds 1–3 and 9–10 were new, and their structures were elucidated by spectroscopic analysis. The acetylcholinesterase inhibitory activity and antiviral activity of compounds 1–17 were evaluated. Among them, compounds 1 and 2 showed strong inhibitory activity against acetylcholinesterase with IC50 values of 4.2 ± 0.6, 4.5 ± 0.6 nM, respectively. This is the first time it has been reported that 3, 6, 10, 12 had evident antiviral activity towards HSV-1 with IC50 values of 16.4 ± 0.6, 6.34 ± 0.4, 21.8 ± 0.8 and 28.9 ± 0.8 μg·mL−1, respectively. Antifouling bioassay tests showed that compounds 1, 11, 12, 15 had potent antifouling activity with EC50 values of 12.9 ± 0.5, 22.1 ± 0.8, 7.4 ± 0.6, 16.1 ± 0.6 μg·mL−1 toward barnacle Balanus amphitrite larvae, respectively.

Synthetic study on dolastatin 16: concise and scalable synthesis of two unusual amino acid units

A convenient and scalable synthesis of two unusual amino acid units found in dolastatin 16, dolaphenvaline, and dolamethylleuine, is described. Dolastatin 16, which was first isolated from the sea hare Dolabella auricularia by Pettit, exhibits not only strong inhibition of growth for a variety of human cancer cell lines but also potent antifouling activity against the larvae of the barnacle Balanus amphitrite. The key element of the synthesis is an organocatalytic Mannich reaction to construct two contiguous stereocenters in the amino acid units with almost complete enantio- and diastereoselectivity.

Antifouling compounds from the sub-arctic ascidian Synoicum pulmonaria: synoxazolidinones A and C, pulmonarins A and B, and synthetic analogues.

The current study describes the antifouling properties of four members belonging to the recently discovered synoxazolidinone and pulmonarin families, isolated from the sub-Arctic sessile ascidian Synoicum pulmonaria collected off the Norwegian coast. Four simplified synthetic analogues were also prepared and included in the study. Several of the studied compounds displayed MIC values in the micro-nanomolar range against 16 relevant marine species involved in both the micro- and macrofouling process. Settlement studies on Balanus improvisus cyprids indicated a deterrent effect and a low toxicity for selected compounds. The two synoxazolidinones displayed broad activity and are shown to be among the most active natural antifouling bromotyrosine derivatives described. Synoxazolidinone C displayed selected antifouling properties comparable to the commercial antifouling product Sea-Nine-211. The pulmonarins prevented the growth of several bacterial strains at nanomolar concentrations but displayed a lower activity toward microalgae and no effect on barnacles. The linear and cyclic synthetic peptidic mimics also displayed potent antifouling activities mainly directed against bacterial adhesion and growth.

Dihydroisocoumarin derivatives with antifouling activities from a gorgonian-derived Eurotium sp. fungus

Five pairs of new dihydroisocoumarin enantiomers, (±)-eurotiumides A–E, and two related racemates, (±)-eurotiumides F and G, were isolated from a gorgonian-derived fungus, Eurotium sp. XS-200900E6. The enantiomeric separations for (±)-eurotiumides A–E were achieved by chiral-HPLC, and their absolute configurations were determined by ECD spectra. All of the isolated compounds are rare dihydroisocoumarin derivatives with a methoxy at C-4. (+)- And (−)-eurotiumides B and D with cis configurations of H-3/H-4 exhibited potent antifouling activities against the larval settlement of the barnacle Balanus amphitrite with the EC50 values ranging from 0.7 to 2.3 μg/mL, and displayed high therapeutic ratios (LC50/EC50 >15). The tested compounds also showed extensive antibacterial activities. It was the first report of antifouling activities for dihydroisocoumarin derivatives.

Nontoxic piperamides and their synthetic analogues as novel antifouling reagents

Bioassay-guided isolation of an acetone extract from a terrestrial plant Piper betle produced four known piperamides with potent antifouling (AF) activities, as evidenced by inhibition of settlement of barnacle cypris larvae. The AF activities of the four piperamides and 15 synthesized analogues were compared and their structure–activity relationships were probed. Among the compounds, piperoleine B and 1-[1-oxo-7-(3′,4′-methylenedioxyphenyl)-6E-heptenyl]-piperidine (MPHP) showed strong activity against settlement of cyprids of the barnacle Balanus amphitrite, having EC50 values of 1.1 ± 0.3 and 0.5 ± 0.2 μg ml−1, respectively. No toxicity against zebra fish was observed following incubation with these two compounds. Besides being non-toxic, 91% of piperoleine B-treated cyprids and 84% of MPHP-treated cyprids at a concentration of 100 μM completed normal metamorphosis in recovery bioassays, indicating that the anti-settlement effect of these two compounds was reversible. Hydrolysis and photolysis experiments indicated that MPHP could be decomposed in the marine environment. It is concluded that piperamides are promising compounds for use in marine AF coatings.

Antifouling and Fungicidal Resorcylic Acid Lactones from the Sea Anemone-Derived FungusCochliobolus lunatus

Three new 14-membered resorcylic acid lactones, cochliomycins D-F, 1-3, and eight known analogues, 4-11, were isolated from the sea anemone-derived fungus Cochliobolus lunatus. Compounds 1-4 are diastereomers differing from each other by the absolute configurations of the 4',5'-diol chiral centers. The absolute configurations of 1-4 were established by the CD exciton chirality method and TDDFT ECD calculations. In antifouling assays, 1, 3-6, and 6a exhibited potent antifouling activities against the larval settlement of the barnacle Balanus amphitrite at nontoxic concentrations, with EC50 values ranging from 1.82 to 22.5 μg/mL. Noticeably, fungicide whole-plant assays indicated that 6 showed excellent activity on the Plasmopara viticola preventative test at 6 ppm and concentration-dependent activity on the Phytophthora infestans preventative application at 200, 60, and 20 ppm. Preliminary structure-activity relationships are also discussed.

Fragilisinins A–L, new briarane-type diterpenoids from gorgonian Junceella fragilis

Our continuous study on the South China Sea gorgonian Junceella fragilis led to the isolation of twelve new briarane type diterpenoids, fragilisinins A–L (1–12), along with seven known analogues (13–19), including four naturally produced organoiodides (9–12), they are the first four iodine-containing briarane diterpenoids from this gorgonian species. Their structures were determined by MS, 1D and 2D NMR spectra analyses and by comparison with those reported in the literature. The configuration of 1 was confirmed by single-crystal X-ray diffraction data. The antifouling test showed that compounds 5, 6, 10, 13, and 15 had potent antifouling activities at nontoxic concentrations with EC50 values of 14.0, 12.6, 11.9, 5.6, and 10.0 μM, respectively.

Asteriscane-Type Sesquiterpenoids from the Soft Coral Sinularia capillosa

Chemical examination of the soft coral Sinularia capillosa collected from the South China Sea resulted in the isolation of 14 new asteriscane-type sesquiterpenoids, namely, capillosananes A-N (1-14), four new seco-asteriscanes, capillosananes O-R (15-18), and (-)-sinularone A and sinularone A. Their structures were determined on the basis of extensive spectroscopic analyses, while the absolute configurations were determined by CD and ECD calculation, Mosher's method, and chemical conversion. This is the first report of asteriscane-type sesquiterpenoids from soft corals, and capillosananes Q (17) and R (18) represent new seco-asteriscane skeletons. Capillosanane A exhibited potent antifouling activity against Balanus amphitrite, with an IC₅₀ value of 9.70 μM, while capillosananes B and I and (-)-sinularone A inhibited inflammation-related TNF-α in vitro.