First Identification of 12β-Deoxygonyautoxin 5 (12α-Gonyautoxinol 5) in the Cyanobacterium Dolichospermum circinale (TA04) and 12β-Deoxysaxitoxin (12α-Saxitoxinol) in D. circinale (TA04) and the Dinoflagellate Alexandrium pacificum (Group IV) (120518KureAC)

Abstract

Saxitoxin and its analogues, paralytic shellfish toxins (PSTs), are potent and specific voltage-gated sodium channel blockers. These toxins are produced by some species of freshwater cyanobacteria and marine dinoflagellates. We previously identified several biosynthetic intermediates of PSTs, as well as new analogues, from such organisms and proposed the biosynthetic and metabolic pathways of PSTs. In this study, 12β-deoxygonyautoxin 5 (12α-gonyautoxinol 5 = gonyautoxin 5-12(R)-ol) was identified in the freshwater cyanobacterium, Dolichospermum circinale (TA04), and 12β-deoxysaxitoxin (12α-saxitoxinol = saxitoxin-12(R)-ol) was identified in the same cyanobacterium and in the marine dinoflagellate Alexandrium pacificum (Group IV) (120518KureAC) for the first time from natural sources. The authentic standards of these compounds and 12α-deoxygonyautoxin 5 (12β-gonyautoxinol 5 = gonyautoxin 5-12(S)-ol) were prepared by chemical derivatization from the major PSTs, C1/C2, produced in D. circinale (TA04). These standards were used to identify the deoxy analogues by comparing the retention times and MS/MS spectra using high-resolution LC-MS/MS. Biosynthetic or metabolic pathways for these analogues have also been proposed based on their structures. The identification of these compounds supports the α-oriented stereoselective oxidation at C12 in the biosynthetic pathway towards PSTs.

Synthesis and Identification of decarbamoyloxySaxitoxins in Toxic Microalgae and their Reactions with the Oxygenase, SxtT, Reveal Saxitoxin Biosynthesis

“…A series of 12β-deoxy (= α-saxitoxinol)-type STX analogues have been identified in toxic dinoflagellates and/or a cyanobacterium, including 12β-deoxy-GTX2/3, [27] 12β-d-dcSTX (21) [28,29] and 12β-d-STX ( 22); [28] in this study, we also found 12β-d-doSTX (3). Since 12β-deoxy type (α-saxitoxinol-type) STX analogues were not converted to ketone by SxtT, [20] these 12β-deoxy analogues may be shunt products, otherwise, an unidentified enzyme may have converted them to ketones.…”

“…The peaks of synthetic 5 ( m/z 241.1407±0.011) and 12β‐deoxy‐decarbamoylSTX (12β‐d‐dcSTX) ( 21 ) were separated from each other (21.3, 24.4 min) in the EIC (Figure 6a, b). 12β‐d‐dcSTX ( 21 ) has the same molecular formula as that of 5 , which was previously identified in the cyanobacterium [28] and dinoflagellates [29] . The peaks of 5 and 21 (21.5, 24.2 min), for which the MSMS spectra were almost identical to those of the synthetic compounds, were detected in the spectrum of D. circinale (TA04) (Figure 6c), suggesting that 5 is also present in this toxic cyanobacterium as well as the dinoflagellate.…”

Marine natural products

“…The final new compound reported from dinoflagellates was a saxitoxin congener 874 from Alexandrium pacifichem ; 312 the structure of a maitotoxin congener was only partially characterised and proposed using MS and NMR data and consequently is not shown here. 313 …”