Structural and biological characterization of novel toxins of filamentous cyanobacteria occurred in eutrophic waterbodies in Japan and Europe.

最近，在世界各地的淡水湖泊中都发现了有毒的蓝藻水华。水华形成的微囊藻和鱼腥藻产生称为微囊藻毒素的肝毒素。此外，丝状蓝藻如颤藻和念珠藻产生毒素。然而，这些毒素的结构和生物学特性尚未详细阐明。人们担心这些有毒的丝状蓝藻可能与人类健康和鱼类中毒有关。本研究从日本和欧洲分离到的念珠藻和颤藻毒素中分离到一种环状缩肽--念珠藻环素（Nostocyclin），其含量约占冻干细胞的0.35%。通过FABMS、NMR和氨基酸分析确定了环胶溶物的结构为Hpl-Ile-Hse-Thr-Hse-Ahp-Phe-N-Metyr-瓦尔，其中Thr的羟基与瓦尔的羧基发生酯化反应（Hpl，对羟基苯乳酸; Ahp，3-氨基-6-羟基-2-哌啶酮）。从Nosfoc sp.中分离到3种新的微囊藻毒素，分别鉴定为[Asp 3，ADMAdda 5，Dhb 7]微囊藻毒素RR，HtyR和LR，其中脱氢丁酸（Dhb）微囊藻毒素为世界首例。通过N 0 E和R 0 ESY核磁共振分析，将其分别鉴定为[Asp 3，（Z）-Dhb 7]微囊藻毒素HtyR和LR，而Nosfoc.微囊藻毒素中Dhb单元的几何结构为E，这可能与其生物合成途径有关。

Recently, toxic blooms of cyanobacteria (blue-green algae) have been detected in freshwater lakes all over the world. The bloom-forming Microcystis and Anabaena produce hepatotoxins called micro cystins. Also, filamentous cyanobacteria sch as Oscillatoria and Nostoc produce toxins. However, structural and biological characterization of these toxins has not been clarified in detail. It has been apprehensive that these toxic filamentous cyanobacgteria may be implicated in human health and poisoning of fish. In this project, we investigated chemical structures and biological activities of novel toxins of Nostoc and Oscillatoria isolated from Japan and Europe.A cyclic depsipeptide, nostocyclin, was isolated from cells of fulminates cyanobacterium, Nostoc sp.The cyclic peptide accounted for about 0.35% of the lyophilized cells. The structure of cyclic peptize was identified by FABMS,NMR and amino acid analysis, and established as Hpl-Ile-Hse-Thr-Hse-Ahp-Phe-N-Metyr-Val, The hydroxy group of Thr was esterified with the carboxy group of Val (Hpl, p-hydroxyphenyllactic acid ; Ahp, 3-amino-6-hydroxy-2-piperidone.). Three novel variants of microcystins were also isolated from Nosfoc sp.These structures were identified as [Asp3, ADMAdda5, Dhb7] microcystin RR,HtyR and LR.The identification of dehydrobutyric acid (Dhb) -containing microcystins was the first case in the world.The Dhb-containing microcystins were also found in toxic blooms of Oscillatoria agadhii isolated from a lake in Scotland. However, the geometrical structure of the Dhb was different from those of Nostoc sp. By N0E and R0ESY experiments in NMR analysis, these structures were identified as [Asp3, (Z) -Dhb7] microcystin HtyR and LR.In contrast, the geometrical structure of the Dhb unit in microcystins from Nosfoc sp.were showed as E.This difference may be due to the biosynthesis pathway.