John A. Walter

CHARACTERIZATION OF BIOLOGICALLY INACTIVE SPIROLIDES E AND F : IDENTIFICATION OF THE SPIROLIDE PHARMACOPHORE

Abstract Two new spirolide derivatives, E and F, have been isolated in low yield from shellfish extracts. Absence of activity in the mouse bioassay of these derivatives, and of the secondary amine reduction product of spirolide B, identifies the spirolide pharmacophore as the cyclic imine moiety.

Interaction of domoic acid and several derivatives with kainic acid and AMPA binding sites in rat brain.

We have determined the inhibitory potencies of domoic acid and a series of derivatives of domoic acid at kainic acid and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) binding sites in rat forebrain membranes. These derivatives of domoic acid differed in the configuration, stereochemistry, and degree of saturation of the side chain attached to C-4 of the prolyl ring. The binding data were analyzed in terms of one or two classes of sites as appropriate. Domoic acid and kainic acid displayed similar inhibition constants at [3H]kainic acid sites (IC50 = 5 and 7 nM, respectively). At both kainic acid and AMPA binding sites, all of the compounds tested were less potent than domoic acid itself. At high affinity [3H]kainic acid sites, the derivatives could be categorized into two groups; those with nanomolar affinity and those with micromolar affinity. All members of the former group possessed a side chain with the first double bond intact and in the Z (cis) configuration. The more distal atoms present in the extended side chain of domoic acid did not appear to contribute to the high affinity interaction with the kainic acid receptor. Although all the compounds tested were weaker inhibitors of [3H]AMPA binding compared to [3H]kainic acid binding, there was a high correlation between the rank order of potency of the seven domoic acid derivatives at [3H]kainic acid and at [3H]AMPA binding sites. The inhibition data for kainic acid at [3H]AMPA binding sites were described adequately in terms of a 1-site model, whereas the data for domoic acid required two classes of sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Carrageenans in the gametophytic and sporophytic stages of Chondrus crispus

SummaryThe morphologically similar sporophytic and gametophytic plants of Chondrus crispus Stackhouse were examined and it was shown that the former contain λ-carrageenan. The gametophytes contain ϰ- and two additional carrageenans which are KCl-soluble and may comprise up to 25% of the total carrageenan. After alkaline modification, these KCl-soluble components were separated into a gel and a soluble carrageenan. The gel was indistinguishable from ϰ-carrageenan and presumably was derived from μ-carrageenan while the KCl-soluble fraction possessed a unique infrared spectrum easily distinguished from alkali-modified λ-carrageenan. This appears to represent a third carrageenan in the gametophytes.Our observations suggest that the biologically separate plants of C. crispus exhibit distinctive patterns of sulfation of their galactans. The sporophytes add SO42- at C2 of the precursor, whereas the gametophytes appear to add it principally at the available C4 positions. Both types of plant are capable of sulfating at C6 of the 4-linked galactose unit.

Two new water-soluble dsp toxin derivatives from the dinoflagellate prorocentrum maculosum: possible storage and excretion products

Two novel water-soluble sulfated DSP toxin derivatives 4 and 5, are reported from the benthic dinoflagellate Prorocentrum maculosum. Their occurrence supports the idea that all DSP toxin-producing Prorocentrum species biosynthesize such compounds as a means of toxin storage, and perhaps as a means of eventually exporting them from the cell.

Isolation and structure elucidation of new and unusual saxitoxin analogues from mussels.

Chemical analyses of plankton and highly toxic mussel samples collected in eastern Canada during an intense bloom of the dinoflagellate Alexandrium tamarense established the presence of a complex mixture of paralytic shellfish poisoning (PSP) toxins. Application of a newly developed technique, hydrophilic interaction liquid chromatography-mass spectrometry, confirmed the identities of the known toxins and revealed the presence in the mussels of five saxitoxin analogues (M1-M5) that were not present in the plankton. Four of these compounds were isolated and their structures established by tandem mass spectrometry, 1D- and 2D-NMR spectroscopy, and chemical interconversion experiments. One of these was found to be 11beta-hydroxysaxitoxin (M2), while the other three were found to be new saxitoxin analogues, namely, 11beta-hydroxy-N-sulfocarbamoylsaxitoxin (M1), 11,11-dihydroxy-N-sulfocarbamoylsaxitoxin (M3), and 11,11-dihydroxysaxitoxin (M4). Compound M5 remains unidentified because of insufficient material for characterization.

Isolation of a new diarrhetic shellfish poison from Irish mussels

A new marine toxin dinophysistoxin-2 (DTX-2)4, isolated from toxic Irish mussels and biogenetically related to the toxins okadaic acid 1 and dinophysistoxin-1 (DTX-1)2, the principal agents responsible for diarrhetic shellfish poisoning (DSP), is reported.

Jadomycin, a novel 8H-benz[b]oxazolo[3,2-f]phenanthridine antibiotic from from streptomyces venezuelae ISP5230.☆

In a galactose-isoleucine medium at 37 °C, Streptomyces venezuelae ISP5230 produces jadomycin (1), the first 8H-benz[b]oxazolo[3,2]phenanthridine derivative to be isolated from natural sources. The structure of 1 was assigned by interpretation of the spectral data.

Assignment of the relative stereochemistry of the spirolides, macrocyclic toxins isolated from shellfish and from the cultured dinoflagellate Alexandrium ostenfeldii

Abstract The relative stereochemistry of 13-desmethyl spirolide C, except for one chiral center, has been determined from NMR data by means of ConGen, a molecular modeling method which applies high-temperature molecular dynamics under distance constraints generated from NOESY and ROESY data. The method shows this spirolide to have the same relative stereochemistry as pinnatoxins A and D in the region of their common structure. Applicability of the ConGen method to molecules of this type is further justified by demonstrating that it yields the correct relative stereochemistry of the pinnatoxins when used with constraints generated from published data. The relative stereochemistries of spirolides B and D are also determined by comparisons of their NMR data with 13-desmethyl spirolide C and further application of ConGen.

Sulfoquinovosyl diacylglycerols from the alga Heterosigma carterae

An extract of the chloromonad Heterosigma carterae (Raphidophyceae), cultivated in natural seawater, contained a complex mixture of sulfoquinovosyl diacylglycerols. Palmitoyl (16:0), three isomers of hexadecenoyl (16:1 cis Δ9, Δ11, Δ13), and eicosapentenoyl (20:5) were found to be the main fatty acyl substituents. Exact double-bond sites were determined by mass spectrometry analysis of the corresponding nicotinyl derivatives. Four major sulfoquinovosyl diacylglycerol components were partially purified and identified as 1–4 by interpretation of their nuclear magnetic resonance and mass spectral data. In addition, complete analysis of the H. carterae sulfoquinovosyl diacylglycerols was performed using high-performance liquid chromatography combined with electrospray tandem mass spectrometry.

Biosynthesis of hydrocarbons by algae: Decarboxylation of stearic acid to N-heptadecane inAnacystis nidulans determined by13C- and2H-labeling and13C nuclear magnetic resonance

The distribution of isotopic labels inn-heptadecane enriched from [1,2-13C] and [2-13C, 2-2H3) acetates byAnacystis nidulans has been determined by13C nuclear magnetic resonance (13C NMR). Labeling with [1,2-13C] acetate is consistent with assembly from13C−13C units derived from an acetate “starter” group and 8 malonate units, as in fatty acid biosynthesis, followed by production of a methyl group through bond cleavage of the terminal13C−13C unit. A comparison of the hydrocarbon with palmitic acid (the only fatty acid produced in sufficient amount for NMR analysis) enriched from [2-13C,2-2H3]acetate by the same culture shows that they have retained the same fraction of2H at corresponding sites, and have therefore undergone identical biosynthetic and hydrogen-deuterium exchange processes, as would be expected ifn-heptadecane originates from de novo-synthesized stearic acid.