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Most canopy-forming macroalgae have disappeared from temperate reefs in southern Japan, one of the ocean warming hotspots, but Sargassum nipponicum is surviving in this region. As this species' annual shoots emerge from holdfasts during summer, both plant components may be highly tolerant to warm and nutrient-poor conditions in this season. The present study examined the effects of temperature and nutrient conditions on holdfast growth, shoot emergence from holdfasts, and shoot growth in S. nipponicum samples collected in Tanegashima Island, southern Japan. The summer temperature in this region (30 °C) allowed holdfast growth and shoot emergence but inhibited shoot growth. Nutrient-poor conditions had limited effects on the first two parameters but suppressed shoot growth. These results suggested that during warm summers and under nutrient-poor conditions in southern Japan, shoots can emerge from S. nipponicum holdfasts but cannot further grow. Additionally, nutrient loading from a nearby river was higher at the only site dominated by S. nipponicum, than at the other sites where this species was absent on Tanegashima Island. This was observed especially between autumn and winter, implying that such a nutrient-rich environment may contribute to shoot growth in S. nipponicum and to the persistence of its population in the area. [ABSTRACT FROM AUTHOR]

There are marine cytotoxic bromotriterpenoids, named the thyrsiferol family that are structurally characterized by some tetrahydropyran (THP) and tetrahydrofuran (THF) rings. The thyrsiferol family belongs to natural products that are often difficult to determine their stereostructures even by the current, highly advanced spectroscopic methods, especially in acyclic systems including stereogenic tetrasubstituted carbon centers. In such cases, it is effective to predict and synthesize the possible stereostructures. Herein, to elucidate ambiguous stereostructures and unassigned absolute configurations of aplysiol B, laurenmariannol, and saiyacenol A, members of the thyrsiferol family, we carried out their asymmetric chemical syntheses featuring 6‐exo and 5‐exo oxacyclizations of epoxy alcohol precursors and 6‐endo bromoetherification of a bishomoallylic alcohol. In this paper, we report total assignments of their stereostructures through their asymmetric chemical syntheses and also their preliminary cytotoxic activities against some tumor cells. These results could not have been achieved without depending on asymmetric total synthesis. [ABSTRACT FROM AUTHOR]

The enantioselective total syntheses of lepadiformine marine alkaloids, azatricyclic natural products isolated from marine tunicates, were completed. These alkaloids have a unique chemical structure characterized by the trans-1-azadecalin (AB ring system) fused with the spirocyclic ring (AC ring system). Here we found that a cycloisomerization reaction from functionalized linear substrates to a 1-azaspiro[4.5]decane framework corresponding to the AC ring in lepadiformines is promoted by a catalytic amount of mercury(II) triflate (Hg(OTf)2). The total syntheses of (−)-lepadiformines A and B were achieved in 28 % and 21 % overall yields, respectively, through the novel cycloisomerization reaction. The syntheses of (+)- and (−)-lepadiformine C hydrochloride salts also enabled us to determine the absolute configuration of natural lepadiformine C. It has been found that a phenomenon of enantiodivergence occurs in lepadiformine alkaloids from a single species of marine tunicate, Clavelina moluccensis. The cytotoxic activities of synthesized lepadiformine hydrochloride salts and their synthetic intermediates were evaluated. [ABSTRACT FROM AUTHOR]

Configuration determination, cytotoxicity, natural products, structure elucidation, total synthesis The escaping fish are illustrating the feeding deterrence property of aplysiol B. More information can be found in the Communication by Keisuke Nishikawa, Yoshiki Morimoto et al. GLO:BDBM/03jan22:asia202101276-toc-0001.jpg PHOTO (COLOR): . gl GLO:BDBM/03jan22:asia202101276-toc-0001.jpg PHOTO (COLOR): . gl Keywords: configuration determination; cytotoxicity; natural products; structure elucidation; total synthesis EN configuration determination cytotoxicity natural products structure elucidation total synthesis 1 1 1 01/05/22 20220103 NES 220103 B Total assignments of stereostructures b of marine cytotoxic bromotriterpenoids, aplysiol B (laurenmariannol) and saiyacenol A derived from a sea hare or red alga, have been accomplished through their asymmetric syntheses from the known epoxide to elucidate their ambiguous stereostructures. [Extracted from the article]

A new xenicane diterpene named 4α-acetoxyisodictyohemiacetal (1) was isolated from the brown alga Dictyota coriacea, along with 11 known diterpenoids. The structure of 1 was established by spectroscopic analyses, and its absolute configuration was determined by comparing the experimental and theoretical electronic circular dichroism (ECD) spectra. Two dictyodiacetal diastereomers (5 and 6) were isolated and the full NMR assignments were performed. The anti-inflammatory activities of the isolated compounds were evaluated using the lipopolysaccharide-stimulated mouse macrophage cell line, RAW264. The hemiacetal-containing xenicanes and dictyol-type diterpene inhibited not only the production of nitric oxide, but also the expression of inducible nitric oxide synthase, interleukin-6, and cyclooxygenase-2 mRNA in RAW264 cells. This study demonstrated that diterpenes from Dictyota coriacea may be useful as natural anti-inflammatory agents., (© The Author(s) 2024. Published by Oxford University Press on behalf of Japan Society for Bioscience, Biotechnology, and Agrochemistry.)

There are marine cytotoxic bromotriterpenoids, named the thyrsiferol family that are structurally characterized by some tetrahydropyran (THP) and tetrahydrofuran (THF) rings. The thyrsiferol family belongs to natural products that are often difficult to determine their stereostructures even by the current, highly advanced spectroscopic methods, especially in acyclic systems including stereogenic tetrasubstituted carbon centers. In such cases, it is effective to predict and synthesize the possible stereostructures. Herein, to elucidate ambiguous stereostructures and unassigned absolute configurations of aplysiol B, laurenmariannol, and saiyacenol A, members of the thyrsiferol family, we carried out their asymmetric chemical syntheses featuring 6-exo and 5-exo oxacyclizations of epoxy alcohol precursors and 6-endo bromoetherification of a bishomoallylic alcohol. In this paper, we report total assignments of their stereostructures through their asymmetric chemical syntheses and also their preliminary cytotoxic activities against some tumor cells. These results could not have been achieved without depending on asymmetric total synthesis., (© 2021 The Authors. Chemistry - An Asian Journal published by Wiley-VCH GmbH.)

Feroniellin analogs isolated from Feroniella lucida possess a furanocoumarin skeleton connected to monoterpenic five- to seven-membered ethereal rings by an ether linkage and exhibit a broad spectrum of biological activities. In this contribution, we intended to establish a "ring-size-divergent" synthetic strategy for the monoterpenic five- to seven-membered ethereal rings through the chemical sythesis of feroniellins. The short and comprehensive synthesis of feroniellins was achieved in only two steps from easily available bergamottin based on the "ring-size-divergent" strategy. In addition, these syntheses resulted in revision of the proposed structures for feroniellins A and B and the determination of all the absolute configurations of feroniellins; their preliminary anti-inflammatory activities were investigated as well., (© 2021 Wiley-VCH GmbH.)

Biomimetic epoxide-opening cascades of polyepoxides enable the efficient and rapid construction of polyether frameworks. Herein, we show that the epoxide-opening cascade cyclization that affords tetrahydrofuran products in acidic aqueous media produces tetrahydropyran (THP) in neutral water. THP formation proceeded by simply heating polyepoxides in neutral water and followed a different cyclization mode from those observed so far. The novel cascade cyclization in H 2 O was applied to the synthesis of a new nerolidol-type sesquiterpenoid, resulting in revision of the proposed structure and determination of the absolute configuration., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The enantioselective total syntheses of lepadiformine marine alkaloids, azatricyclic natural products isolated from marine tunicates, were completed. These alkaloids have a unique chemical structure characterized by the trans-1-azadecalin (AB ring system) fused with the spirocyclic ring (AC ring system). Here we found that a cycloisomerization reaction from functionalized linear substrates to a 1-azaspiro[4.5]decane framework corresponding to the AC ring in lepadiformines is promoted by a catalytic amount of mercury(II) triflate (Hg(OTf) 2 ). The total syntheses of (-)-lepadiformines A and B were achieved in 28 % and 21 % overall yields, respectively, through the novel cycloisomerization reaction. The syntheses of (+)- and (-)-lepadiformine C hydrochloride salts also enabled us to determine the absolute configuration of natural lepadiformine C. It has been found that a phenomenon of enantiodivergence occurs in lepadiformine alkaloids from a single species of marine tunicate, Clavelina moluccensis. The cytotoxic activities of synthesized lepadiformine hydrochloride salts and their synthetic intermediates were evaluated., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)