Omaezallene from Red Alga Laurencia sp.: Structure Elucidation,Total Synthesis,and Antifouling Activity

Natural antifouling products have been the subject of considerable attention. We screened marine algae for antifouling activity and discovered omaezallenes, the new bromoallene‐containing natural products isolated from the red alga Laurencia sp. Described is the isolation, structure elucidation, and total syntheses of omaezallenes. The relative and absolute configurations of natural omaezallenes were unambiguously established through total synthesis. The antifouling activities and ecotoxicity of omaezallenes were also evaluated.     

无毒海洋防污剂研究进展

综述了无毒海洋防污剂研究进展,从防污活性、机理、特点及应用等方面着手介绍了近年来开发的几种新型无毒天然产物防污剂和人工合成防污剂,并就其发展前景进行了展望;指出开发研制无毒海洋防污剂是海洋防污技术的发展方向之一.     

Biofouling and antifouling

Most benthic organisms produce planktonic larvae in their life cycles; larval settlement and metamorphosis are influenced by many environmental factors, especially chemical cues originating from conspecific adults, prey organisms, and substrates. On the other hand, larval settlement of other species endangers the survival of benthic organisms which therefore have antifouling defense. Marine natural products involved in biofouling and antifouling are described.     

Synthesis and Quantum Chemical Calculation of Benzamide Derivatives Containing Capsaicin and Their Bacteriostatic and Antifouling Properties

Thirteen benzamide derivatives containing capsaicin (BDCCs) have been successfully synthesized via the current method (Friedel‐Crafts alkylation reaction). The resultant monomers were characterized by IR, ¹H and ¹³C NMR, elemental analysis and HRMS. Characterization results were in agreement with the proposed structures of the products. Quantum chemistry calculation yielded three parameters, namely, Δε_L‐H, HF values (total energy) and dipole that could explain activity, stability and polarity respectively, and the relationship of each parameter with antimicrobial and antifouling performance was also preliminary discussed. The bacteriostatic property of the 13 compounds was evaluated by minimum inhibitory concentration (MIC) and bacteriostatic ring tests. Experimental results indicated that these compounds can inhibit Staphylococcus aureus and Escherichia coli. The antifouling effectiveness of the novel antifoulants was investigated using panel tests at the eighth harbor, Qingdao. Four‐month exposure results were compared. The compounds exhibited better antifouling properties than the blank panel without antifouling coating or the panel with a common coating. However, test panels with the antifouling coatings were covered with trace amounts of algae and Balanus because of weakening of antifouling ability over extended periods of time. All results demonstrate that the new compounds synthesized via our method can be applied in environment‐friendly antifouling paints.     

Novel marine antifouling coatings inspired by corals

Biofouling is a major problem facing the marine industry. Since toxic antifouling coatings were banned globally due to their negative impacts on the marine environment, the development of environmental-friendly and efficient antifouling coatings has been identified as a pressing need. As an alternative, the antifouling coatings inspired by corals have attracted a great deal of attention over these years. within the marine environment, corals have evolved an excellent antifouling capability. There are five major antifouling strategies applied by corals, including natural antifoulants, foul release effect, sloughing effect, soft tentacles, and fluorescence effect. In this paper, a brief review is conducted to introduce the antifouling coatings inspired by the five strategies. Moreover, a discussion is conducted about the existing problems with the five strategies and the direction of their further development is indicated.     

Concise, protecting group free total syntheses of (+)-sattabacin and (+)-4-hydroxysattabacin

The first asymmetric total syntheses of the antiviral natural products (+)-sattabacin and (+)-4-hydroxysattabacin are reported. Both total syntheses are remarkably concise and were completed without the use of protecting groups. These syntheses allowed the unambiguous assignment of the absolute configuration of both natural products. The syntheses of these natural products, which exhibit marked antiviral activity, are readily amenable to the preparation of structural analogs and progress in this regard is also reported.     

Synthesis and Bacteriostatic Activity and Antifouling Capability of Benzamide Derivatives Containing Capsaicin

Five benzamide deriatives containing capsaicin were synthesized which have similar structures to capsaicin. Their yield was high. The monomers synthesized were characterized by IR, 1H NMR and MS spectroscopy. Characterization data are in agreement with the proposed structures of the products. These five compounds exhibit bacterial inhibition and N-[4-hydroxy-2-methyl-5-(methylthio)benzyl]benzamide(HMMBBA), for instance, shows that the minimal inhibitory concentrations(MIC) of HMMBBA are 0.125 and 0.25 mg/mL on Staphyloccocus aureus and Escherichia coli, respectively. A static test site was set up in the eighth harbor to investigate the antifouling effectiveness of the five new antifoulants. Five-month exposure experiments were performed on sets of panels coated with each of antifouling coatings, and the results were compared to that of the test panel without antifouling coating. Test boards with antifouling coating were covered with just a macroscopic fouling organism such as Balanus. The results of the present paper demonstrate that new antifoulants represent an alternative to the biocidal antifouling paint.     

A protecting-group-free synthesis of arbusculone,andirolactone, pinnatolide,ipomolactone, cyclocapitelline and isocyclocapitelline

A general approach for a collective synthesis of natural products containing substituted THF ring is described. In this paper, Arbusculone, a small molecule natural product accomplished using a short route, is used as the key intermediate to achieve the total synthesis of Andirolactone, Pinnatolide, Ipomolactone, Cyclocapitelline, Isocyclocapitelline and their two isomers in less than ten steps. The present effort highlights protecting-group-free total syntheses and the shortest route to access these natural products from commercially available cheap starting materials.     

Recovery of all species from photolytic degradation of tributyltin compounds TBTX (X = Cl,OSn Bu3)

Malformations in shellfish have been reported by many authors. They attributed the cause of the deformity to the presence in water of organotin compounds used in the formulation of antifouling paints, for example bis(tributyltin) oxide (TBTO) and tributyltin chloride (TBTC). The behaviour of these compounds has been examined under abiotic laboratory conditions. The influence of many parameters such as sunlight, pH, oxygen, salinity have been examined. The degradation compounds obtained have been identified: (1) In the gas phase two major products, butene-1 and buetene-2, are observed with consumption of oxygen; (2) In the liquid phase, three main products are obtained, butanol-1, butanol-2 and butanone 2. The identified products represent a small part of the total concentration, suggesting a competing process such as formation of butyltin polymers; (3) In fresh water an amorphous solid phase is observed while in seawater a white cristalline precipitate appears.     

Total synthesis and absolute configuration of otteliones A and B, novel and potent antitumor agents from a freshwater plant

[reaction: see text] The first enantioselective total synthesis of otteliones A and B, biologically important and structurally novel natural products, has been successfully achieved. This total synthesis fully confirms the absolute configuration of these natural products.     

First total synthesis of a natural product containing a chiral,beta-diketone: synthesis and stereochemical reassignment of siphonarienedione and siphonarienolone

The first total syntheses of siphonarienolone and siphonarienedione are described. The development of a stereoselective synthesis of beta-diketones facilitated the synthesis of the latter compound. The synthesis of the structures proposed for the natural products afforded compounds whose spectral data did not match those of the natural products. However, the synthesis of compounds isomeric to the proposed structures at C(4) and C(5) afforded compounds identical to the natural products, thereby reassigning the stereochemistry of the natural products.     

Angucyclinone antibiotics: total syntheses of YM-181741, (+)-ochromycinone, (+)-rubiginone B2, (-)-tetrangomycin, and MM-47755

A concise and highly enantioselective route has been developed for the synthesis of angucyclinone-type natural products. Utilizing this strategy, total syntheses of five natural products YM-181741, (+)-ochromycinone, (+)-rubiginone B2, (-)-tetrangomycin, and MM-47755 have been accomplished in 22%, 23%, 19%, 18%, and 12% overall yields, respectively. Our approach for the synthesis of these natural products having the benz[a]anthraquinone skeleton is based on a sequential intramolecular enyne metathesis, intermolecular Diels-Alder reaction (DAR), and aromatization. The intramolecular enyne metathesis reaction was employed for the synthesis of enantiopure 1,3-dienes in excellent yields. Furthermore, the synthesis of YM-181741 as well as structurally similar angucyclinones such as (+)-ochromycinone and (+)-rubiginone B2 was achieved via asymmetric enolate alkylation of an oxazolidinone in excellent de. The related angucyclinones (-)-tetrangomycin and MM-47755, bearing a labile tertiary alcohol, were synthesized via Sharpless asymmetric epoxidation of a known allylic alcohol followed by opening the epoxide with Red-Al. The introduction of oxygen functionality at C-1 in all these natural products was accomplished by photooxygenation under a positive pressure of oxygen.     

Retention behaviors of natural products in reversed-phase liquid chromatography using mobile phase comprising methanol, acetonitrile and water

The three-component mobile phase, methanol-acetonitrile-water, has been frequently used for the separation of natural products in complicated herbal extracts by reversed-phase liquid chromatography, especially when two-component solvent systems do not work. However, the rational for optimization of this three-solvent system is not clear, so far. In this study, the retention behavior of different types of natural products in RP-LC with a methanol-acetonitrile-water elution system was studied. A total of 27 compounds from four classes, including steroids, flavonoids, phenolic acids, and triterpene saponins were analyzed by high-performance liquid chromatography coupled with mass spectrometry or ultraviolet detectors. It was interesting to find that prolonged retention times and improved separation capabilities were obtained when the acetonitrile-to-methanol ratio was 3-16%. This rule applied to all four classes of natural products under different instrumental conditions, and could be valuable for the separation of natural products in complicated samples.     

Recent Developments in Total Syntheses of Cephalosporolides,Penisporolides, and Ascospiroketals

The possible biogenetic connection of the 10‐membered lactone (decanolide) and the tricyclic [5,5]‐spiroacetal‐cis‐fused‐γ‐lactone (SAFL) natural products was proposed by Hanson in 1985. Mimicking such biosynthetic hypothesis led us to develop a general synthetic strategy for the total syntheses of both decanolide‐type cephalosporolides and SAFL‐type natural products. This biomimetic strategy features two key transformations: i) oxidative ring expansion of bicyclic β‐hydroxy tetrahydropyrans to the decanolides and ii) ring contraction rearrangement of the decanolides to the tricyclic SAFLs. In particular, the phenol derivatives are exploited as the starting materials for the decanolides and then the SAFLs. The successful biomimetic total synthesis allows us to revise the structures and biosynthetic hypothesis of several natural products, along with development of an NMR analysis method for determination of the relative stereochemistry of SAFL‐type compounds. In addition, this account will summarize recent synthetic work by other research groups.     

Total synthesis of 10-isocyano-4-cadinene and its stereoisomers and evaluations of antifouling activities

The first enantioselective total synthesis of 10-isocyano-4-cadinene, a marine sesquiterpene isolated from nudibranchs of the family Phyllidiidae, and determination of its absolute stereochemistry were achieved. 10-Isocyano-4-cadinene is expected to be a novel nontoxic antifouling agent. In the synthesis, intermolecular Diels-Alder reaction and samarium diiodide induced Barbier-type cyclization were employed as key steps. The absolute configuration of 10-isocyano-4-cadinene was determined as (1S,6S,7R,10S) by comparison of the optical rotations between natural and synthetic samples. In addition, the authors successfully synthesized 10-epi- and di-1,6-epi-10-isocyano-4-cadinene through the same synthetic pathway. Antifouling activities against Balanus amphitrite with the cadinenes were also evaluated.     

Total synthesis of macrocyclic glycosides, clemochinenosides A and B, and berchemolide, by fluorous mixture synthesis

The total synthesis of clemochinenoside A and the first total syntheses of clemochinenoside B and berchemolide were achieved simultaneously via macrocyclization of 4-O-(4-O-^F13benzyl-β-d-glucopyranosyl)syringic acid with 4-O-(4-O-^F17benzyl-β-d-glucopyranosyl)vanillic acid by a fluorous mixture synthetic method. The spectroscopic data of the synthetic products were identical with those of the natural products, although the optical rotation of clemochinenoside A differed from the published values in sign and magnitude.     

Aqueous phototransformation of zinc pyrithione Degradation kinetics and byproduct identification by liquid chromatography--atmospheric pressure chemical ionisation mass spectrometry

The photochemical behavior of the antifouling agent zinc pyrithione (ZnPT) was studied in aqueous media of different composition under simulated solar irradiation using a xenon light source. The influence of important constituents of natural water (dissolved organic matter and nitrate) was also examined using a multivariate kinetic model. It was found that photodegradation proceeds via a pseudo first-order reaction. Kinetic experiments were monitored by LC-MS and photolytic half-lives ranging between 9.2 and 15.1 min have been observed. The increasing concentration of dissolved organic matter (DOM) accelerates the photolysis reaction, while the effect of nitrate ions was also positive since it increased the degradation rate, but to a lesser extent. Irradiation of the aqueous ZnPT solutions gave rise to several transformation products that were isolated by means of solid-phase extraction using poly(styrene-divinylbenzene) extraction disks. These byproducts were identified using liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry. Besides 2-pyridinesulfonic-acid, other degradation products formed included pyridine-N-oxide, 2-mercaptopyridine, 2,2'-dithiobis(pyridine-N-oxide), 2,2-dipyridyl disulfide and the pyridine/pyrithione mixed disulfide, 2,2'-dithiobispyridine mono-N-oxide (PPMD).     

Total Syntheses of Xiamycins A,C, F,H and Oridamycin A and Preliminary Evaluation of their Anti‐Fungal Properties

Divergent and enantiospecific total syntheses of the indolosesquiterpenoids xiamycins A, C, F, H and oridamycin A have been accomplished. The syntheses, which commence from (R)‐carvone, employ a key photoinduced benzannulation sequence to forge the carbazole moiety characteristic of these natural products. Late‐stage diversification from a common intermediate enabled the first syntheses of xiamycins C and F, and an unexpected one‐pot oxidative decarboxylation, which may prove general, led to xiamycin H. All synthetic intermediates and the natural products were tested for anti‐fungal activity. Xiamycin H emerged as an inhibitor of three agriculturally relevant fungal pathogens.     

Determination of antifouling pesticides and their degradation products in marine sediments by means of ultrasonic extraction and HPLC-APCI-MS

A method has been developed for the simultaneous determination of antifouling pesticides and some of their degradation products, e.g. dichlofluanid, diuron, demethyldiuron, 1-(3,4-dichlorophenyl)urea, sea-nine, Irgarol 1051 and one of its metabolites (2-methylthio-4-tert-butylamino-s-triazine) in marine sediments. The determination of these compounds in sediment samples was performed by means of methanolic ultrasonic extraction then clean-up on an Isolute ENV+ solid phase extraction (SPE) cartridge. The resulting extract was then analyzed by reversed-phase high-performance liquid chromatography coupled with atmospheric-pressure chemical-ionization mass spectrometry in negative and positive ion modes (HPLC-APCI-MS). Recovery ranged from 54-109% for the antifouling agents and their degradation products. The determination limits for the different compounds varied between 0.2 and 1.6 microg kg(-1) dry sediment. The analytical procedure was successfully applied to the determination of these pesticides and their degradation products in marine sediment samples from different marinas of the Catalan coast. The compounds detected were: diuron, dichlofluanid, demethyldiuron, sea-nine, and Irgarol 1051. The highest concentrations were those of diuron and Irgarol 1051--136 and 88 microg kg(-1), respectively.     

Total Syntheses of Xiamycins A,C, F,H and Oridamycin A and Preliminary Evaluation of their Anti‐Fungal Properties

Divergent and enantiospecific total syntheses of the indolosesquiterpenoids xiamycins A, C, F, H and oridamycin A have been accomplished. The syntheses, which commence from (R)‐carvone, employ a key photoinduced benzannulation sequence to forge the carbazole moiety characteristic of these natural products. Late‐stage diversification from a common intermediate enabled the first syntheses of xiamycins C and F, and an unexpected one‐pot oxidative decarboxylation, which may prove general, led to xiamycin H. All synthetic intermediates and the natural products were tested for anti‐fungal activity. Xiamycin H emerged as an inhibitor of three agriculturally relevant fungal pathogens.