毒素(STX,1)是由海洋鞭毛藻和淡水蓝细菌产生的麻痹性贝类毒素(PST)的代表性化合物。尽管已经提出了几种生物合成STX的途径,环和侧链羟基化的顺序,和三环骨架的形成还没有很好地确定。在这项研究中,12,12-双脱氧-脱碳甲酰氧基STX(dd-doSTX,2),减少最多的具有三环骨架的STX类似物,和它的类似物,12β-脱氧-doSTX(12β-d-doSTX,3),12α-脱氧-doSTX(12α-d-doSTX,4),和doSTX(5),是合成的,并使用高分辨率LCMSMS在有毒微藻中筛选出这些化合物。dd-doSTX(2)和12β-d-doSTX(3)在产生PST的鞭毛藻(Alexandriumcatenella,A.太平洋,和/或Gymnodiniumcatenatum)和蓝细菌Dolichospermumcircinale(TA04)。doSTX(5),以前从鞭毛藻G.catenatum分离,也在D.circinale(TA04)中发现。此外,用VanB通过SxtT将2转换为3,4转换为5,据报道,Rieske加氧酶及其在STX生物合成中的氧化还原伴侣,已确认。这些结果支持2是STX的可能的生物合成前体,并且环化后进行环和侧链羟基化。
Saxitoxin (STX, 1) is a representative compound of paralytic shellfish toxins (PSTs) that are produced by marine dinoflagellates and freshwater cyanobacteria. Although several pathways have been proposed for the biosynthesis of STX, the order of ring and side chain hydroxylation, and formation of the tricyclic skeleton have not been well established. In this study, 12,12-dideoxy-decarbamoyloxySTX (dd-doSTX, 2), the most reduced STX analogue having the tricyclic skeleton, and its analogues, 12β-deoxy-doSTX (12β-d-doSTX, 3), 12α-deoxy-doSTX (12α-d-doSTX, 4), and doSTX (5), were synthesized, and these compounds were screened in the toxic microalgae using high-resolution LCMSMS. dd-doSTX (2) and 12β-d-doSTX (3) were identified in the PSTs-producing dinoflagellates (Alexandrium catenella, A. pacificum, and/or Gymnodinium catenatum) and in the cyanobacterium Dolichospermum circinale (TA04). doSTX (5), previously isolated from the dinoflagellate G. catenatum, was also identified in D. circinale (TA04). Furthermore, the conversion of 2 to 3, and 4 to 5, by SxtT with VanB, a reported Rieske oxygenase and its redox partner in STX biosynthesis, was confirmed. These results support that 2 is a possible biosynthetic precursor of STX, and that ring and side-chain hydroxylations proceed after cyclization.