Affiliation:
1. Graduate School of Agricultural Science Tohoku University 468-1 Aramaki-Aza-Aoba, Aoba-ku Sendai Miyagi 980-8572 Japan) (M. Yotsu-Yamashita
2. Department of Biotechnology and Life Science Tokyo University of Agriculture and Technology 2-24-16, Naka-cho Koganei Tokyo 184-8588 Japan
3. Frontier Research Institute for Interdisciplinary Sciences Tohoku University 6-3 Aramaki-Aza-Aoba, Aoba-ku Sendai Miyagi 980-8578 Japan
4. Graduate School of Life Sciences Tohoku University 2-1-1 Katahira, Aoba-ku Sendai Miyagi 980-8577 Japan
Abstract
AbstractSaxitoxin (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.
Funder
Japan Society for the Promotion of Science