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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We investigated the diastereoselectivity of ring openings for chloro vinyl epoxides with various chlorination reagents. In the chlorinolysis reactions using vinyl epoxides having an allyl alcohol, ...inversion:retention ratios varied depending on the chloride sources. In limited cases, the increase in retention ratio was consistent with the intervention of chloronium ions. In contrast, all vinyl epoxides bearing an α,β-unsaturated ester gave only the inversion products. These results suggest the electron-withdrawing property suppressed the chloronium ions.
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A new application of vacuum-ultraviolet circular dichroism (VUVCD), which enables the measurement of CD spectra in the vacuum-ultraviolet region (140-200 nm), for the assignment of the absolute ...configurations of bromoallenes is described. Bromoallene moieties are found in natural products obtained from many marine organisms. To date, the absolute configuration of bromoallenes has been assigned almost exclusively with Lowe's rule, which is based on specific rotation. However, exceptions to Lowe's rule have been reported arising from the presence of other substituents with large specific rotations. For the unambiguous assignment of the absolute configuration of the bromoallene moiety with its characteristic absorption wavelength at 180-190 nm due to the π-π* transition, VUVCD was applied to four pairs of bromoallene diastereomers prepared by modifying the synthetic scheme of omaezallene. The VUVCD spectra clearly showed positive or negative Cotton effects around 180-190 nm according to the configuration of the bromoallene employed, revealing the potential of VUVCD for determining absolute stereochemistry.
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Chemical investigation of the cyanobacterium Dolichospermum sp. NIES-1697 afforded nostosin G (1), a linear tripeptide, spiroidesin B (2), and two known compounds, anabaenopeptins I (3) and J (4). ...Planar structures and absolute configurations for 1 and 2 were determined by 2D NMR, HRMS, Marfey’s methodology, chiral-phase HPLC, and enzymatic degradation. Nostosin G (1) is a unique example of a linear peptide containing three subunits, 4-hydroxyphenyllactic acid (Hpla), homotyrosine (Hty), and argininal, with potent trypsin inhibitory properties. The biosynthetic gene clusters for nostosin G (1) and spiroidesin B (2) were investigated based on the genome sequence of Dolichospermum sp. NIES-1697.
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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.
Some derivatives of dolastatin 16, a depsipeptide natural product first obtained from the sea hare
, were synthesized through second-generation synthesis of two unusual amino acids, dolaphenvaline ...and dolamethylleuine. The second-generation synthesis enabled derivatizations such as functionalization of the aromatic ring in dolaphenvaline. The derivatives of fragments and whole structures were evaluated for antifouling activity against the cypris larvae of
Small fragments inhibited the settlement of the cypris larvae at potent to moderate concentrations (EC
= 0.60-4.62 μg/mL), although dolastatin 16 with a substituent on the aromatic ring (
) was much less potent than dolastatin 16.
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.
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Male gametes of the brown alga Mutimo cylindricus show positive phototaxis soon after spawning in seawater but gradually change the sign of phototaxis with time. This conversion appears to need the ...decrease of intracellular Ca2+ concentration. In this study, we revealed that the conversion of male gamete phototactic sign, positive to negative, was accelerated by mixing with female gametes. The supernatant after the centrifugation of female gamete suspension showed the same activity to change the phototactic sign, suggesting that a factor released from female gametes was responsible for the reaction. A known brown algal sex pheromone, ectocarpene, induced chemotaxis of male gametes of M. cylindricus. The addition of this compound induced the change of phototactic sign, clearly indicating that a sex pheromone is essential for the reversal. An inhibitor of phosphodiesterase, theophylline, inhibited the chemotaxis and phototactic sign reversion by a factor released from female gametes and ectocarpene. Measurements of cyclic nucleotides showed that the increase in intracellular concentration of cAMP, not cGMP, was parallel to the change of phototactic sign. The inhibition of phototactic sign by theophylline was not observed in low Ca2+ sea water. These results suggest that a signaling pathway mediated by cAMP and Ca2+ concentrations drives the interconversion between two important behaviors of male gametes, phototaxis and chemotaxis.
•Male gametes of brown alga reversed the phototactic sign by a brown algal sex pheromone.•An inhibitor of phosphodiesterase inhibited the reversion of phototactic sign by the sex pheromone.•The inhibition of phototactic sign by an inhibitor of phosphodiesterase was not observed in low Ca2+ sea water.•The regulation of phototactic sign of male gametes were revealed to be mediated by the cAMP/Ca2+-dependent signaling pathway.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Two new chlorinated fatty acid amides, columbamides D (1) and E (2), along with apratoxins A and C and wewakazole, were isolated from the organic extract of a Moorea bouillonii sample from Sabah, ...Malaysia. Structure elucidation was accomplished by a combination of MS and NMR analyses. The total synthesis of all four stereoisomers of 1 was completed, and the absolute configuration was determined by chiral-phase HPLC and Marfey’s analysis.
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