title: Synthesis and Identification of Key Biosynthetic Intermediates for the Formation of the Tricyclic Skeleton of Saxitoxin.
abstract: Saxitoxin (STX) and its analogues are potent voltage-gated sodium channel blockers biosynthesized by freshwater cyanobacteria and marine dinoflagellates. We previously identified genetically predicted biosynthetic intermediates of STX at early stages, Int-A' and Int-C'2, in these microorganisms. However, the mechanism to form the tricyclic skeleton of STX was unknown. To solve this problem, we screened for unidentified intermediates by analyzing the results from previous incorporation experiments with15N-labeled Int-C'2. The presence of monohydroxy-Int-C'2 and possibly Int-E' was suggested, and 11-hydroxy-Int-C'2 and Int-E' were identified from synthesized standards and LC-MS. Furthermore, we observed that the hydroxy group at C11 of 11-hydroxy-Int-C'2 was slowly replaced by CD3O in CD3OD. Based on this characteristic reactivity, we propose a possible mechanism to form the tricyclic skeleton of STX via a bicyclic intermediate from 11-hydroxy-Int-C'2.
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aramaki-Aza-Aoba, Aoba-ku, Sendai, 980-0845, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Tsuchiya
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aramaki-Aza-Aoba, Aoba-ku, Sendai, 980-0845, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Cho
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aramaki-Aza-Aoba, Aoba-ku, Sendai, 980-0845, Japan.
authors.forename: Renpei
authors.initials: R
authors.lastname: Yoshioka
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aramaki-Aza-Aoba, Aoba-ku, Sendai, 980-0845, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Konoki
authors.affiliation: Faculty of Technology, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei-shi, Tokyo, 184-8588, Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Nagasawa
authors.affiliation: Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan.
authors.forename: Yasukatsu
authors.initials: Y
authors.lastname: Oshima
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aramaki-Aza-Aoba, Aoba-ku, Sendai, 980-0845, Japan.
authors.forename: Mari
authors.identifier: 0000-0002-5009-0409
authors.initials: M
authors.lastname: Yotsu-Yamashita
mesh_terms: D000458:Cyanobacteria / Q000378:metabolism*; D004141:Dinoflagellida / Q000378:metabolism*; D008968:Molecular Conformation; D012530:Saxitoxin / Q000096:biosynthesis* / Q000737:chemistry; D061567:Voltage-Gated Sodium Channel Blockers / Q000737:chemistry / Q000378:metabolism*
chemical_list: D061567:Voltage-Gated Sodium Channel Blockers; D012530:Saxitoxin
keywords: biosynthesis; mass spectrometry; natural products; reaction mechanisms; saxitoxin