Biosurfactants from marine Cyanobacteria collected in Malaysia, Sabah

ABSTRACT Chemical investigation of the organic extract from Moorea bouillonii, collected in Sabah, Malaysia, led to the isolation of three new chlorinated fatty acid amides, columbamides F (1), G (2), and H (3). The planar structures of 1–3 were established by a combination of mass spectrometric and NMR spectroscopic analyses. The absolute configuration of 1 was determined by Marfey’s analysis of its hydrolysate and chiral-phase HPLC analysis after conversion and esterification with Ohrui’s acid, (1S,2S)-2- (anthracene-2,3-dicarboximido) cyclohexanecarboxylic acid. Compound 1 showed biosurfactant activity by an oil displacement assay. Related known fatty acid amides columbamide D and serinolamide C exhibited biosurfactant activity with critical micelle concentrations of about 0.34 and 0.78 mM, respectively

Recent progress toward synthesis of chlorosulfolipids: total synthesis and methodology

Chlorosulfolipids (CSLs) are an intriguing family of natural products featuring highly chlorinated linear hydrocarbon skeletons. Although CSLs were first isolated in 1962, chemical synthesis of CSLs was hampered because relevant methods for stereoselective construction of the polychlorinated motifs of CSLs were scarce. Since Carreira's first total synthesis of the CSL mytilipin A in 2009, several groups, including our own, have reported total syntheses of CSLs. As a result of these total syntheses, important progress has been made in the development of reliable synthetic methods for stereoselective polychlorination. In this digest, we summarize the total syntheses of CSLs by focusing on synthetic methods for stereoselective polychlorination of the organic frameworks of CSLs

Design, Synthesis, and Antifouling Activity of Glucosamine-Based Isocyanides

Biofouling, an undesirable accumulation of organisms on sea-immersed structures such as ship hulls and fishing nets, is a serious economic issue whose effects include oil wastage and clogged nets. Organotin compounds were utilized since the 1960s as an antifouling material; however, the use of such compounds was later banned by the International Maritime Organization (IMO) due to their high toxicity toward marine organisms, resulting in masculinization and imposex. Since the ban, there have been extensive efforts to develop environmentally benign antifoulants. Natural antifouling products obtained from marine creatures have been the subject of considerable attention due to their potent antifouling activity and low toxicity. These antifouling compounds often contain isocyano groups, which are well known to have natural antifouling properties. On the basis of our previous total synthesis of natural isocyanoterpenoids, we envisaged the installation of an isocyano functional group onto glucosamine to produce an environmentally friendly antifouling material. This paper describes an effective synthetic method for various glucosamine-based isocyanides and evaluation of their antifouling activity and toxicity against cypris larvae of the barnacle Amphibalanus amphitrite. Glucosamine isocyanides with an ether functionality at the anomeric position exhibited potent antifouling activity, with EC50 values below 1 μg/mL, without detectable toxicity even at a high concentration of 10 μg/mL. Two isocyanides had EC50 values of 0.23 and 0.25 μg/mL, comparable to that of CuSO4, which is used as a fouling inhibitor (EC50 = 0.27 μg/mL)

Efficient synthesis of α,β-dichlorinated ketones from α,β-dichlorinated Weinreb amides through a simple work-up procedure

An efficient synthesis of α,β-dichlorinated ketones from α,β-dichlorinated Weinreb amides is described. Quenching with nonaqueous HCl avoided side reactions associated with typical work-up procedures. The amide reacted with various nucleophiles to give the corresponding ketones in high yields. A novel reactivity of the Weinreb amide is also discussed

Formation Pathway of By-products in Methacrolein Oxidation over H3PMo12O4o Investigated by Using 13C-Labeled Methacrolein

Understanding the mechanism for the formations of by-products as well as a main product can give us useful information for improvement in the catalytic performances. In the present study, formation pathway of by-products in oxidation of methacrolein (MAL) was investigated by using MAL with 13C-labeled methyl group as a reactant. The reaction pathway for the formation of the by-products was proposed based on GC-MS analysis as follows: The first step is oxidative cleavage of C=C double bond in MAL, giving pyruvaldehyde, and pyruvaldehyde is subsequently hydrolyzed to acetic acid

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

Antioxidants from the Brown Alga Dictyopteris undulata

An investigation of anti-oxidative compounds from the brown alga Dictyopteris undulata has led to the isolation and identification of isozonarol, isozonarone, chromazonarol, zonaroic acid and isozonaroic acid. Their structures were identified by comparison of MS and NMR spectra. Full NMR assignment and absolute configuration of isozonaroic acid are described. Isozonarol showed the most potent 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity among the compounds isolated

Confirmation of the configuration of 10-isothiocyanato-4-cadinene diastereomers through synthesis

The marine sponge metabolite 10-isothiocyanato-4-cadinene (1) was first isolated by Garson et al. from Acanthella cavernosa in 2000. The same structure 1 was later reported by Wright et al. from the nudibranch Phyllidiella pustulosa and its sponge diet, but with different NMR data. The syntheses of both enantiomers of 1 were accomplished through the isothiocyanation of 10-isocyano-4-cadinene (2) previously synthesized by our group. The correct spectroscopic data and specific rotation value of the structure 1 were determined on the basis of the syntheses. The NMR data of synthetic 1 matched those of the isothiocyanate isolated by Garson and differed from those reported by Wright. The spectroscopic data and specific rotation values of 10-epi-10-isothiocyanato-4-cadinene (6) and di-1,6-epi-10-isothiocyanato-4- cadinene (8) were also established through the syntheses of these diastereomers. Structure 6 has been reported as a natural product by Mitome et al., but the NMR data for the synthetic sample of 6 differ from those of the natural isolate