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Two new metabolites (1 and 2) were isolated from the marine fungus Microsphaeropsis olivacea. The structures were elucidated, through analysis of the spectroscopic data, as an unusual methyl-branched unsaturated fatty acid, 10-methyl-9Z-octadecenoic acid (1), and the glyceride (2). The locations of the double bond and the methyl branching were determined from the electron impact (EI) mass spectrum of the picolinyl derivative of 1 and from MS/MS data on the hydrogenation products of 1 and 2. Key words: Microsphaeropsis olivacea, marine fungus, methyl-branched unsaturated fatty acid, picolinyl ester.

Five new compounds related to the neurotoxin domoic acid have been characterized by spectroscopic methods. They include a diastereoisomer that occurs naturally with domoic acid in mussels and four hydrogenation products. The stereochemistry of the two epimeric tetrahydro derivatives could not be assigned on the basis of the NMR data alone because of high conformational flexibility. However, a clear-cut assignment was possible by molecular modelling in combination with the NMR data.

Isodomoic acids E and F, two new geometrical isomers of the neurotoxin domoic acid, have been found to occur with domoic acid and isodomoic acid D in extracts of toxic mussels. The entire set of geometrical isomers can be prepared in the laboratory by photolysis. Keywords: amnesic shellfish toxin, domoic acid, isodomoic acid, neurotoxin.

Abietinarins A (1) and B (2), two new 1-[4H]-anthracenone derivatives, have been isolated from the Northeastern Pacific marine hydroid Abietinaria sp. The proposed structures for abietinarins A (1) and B (2) are based on spectroscopic analysis. Abieitinarin A (1) exhibited significant cytotoxicity in an in vitro L1210 bioassay. Keywords: cytotoxic, hydroid, abietinarins, metabolites, marine.

Tenellin and bassianin are deduced from chemical and spectroscopic evidence to be the 3-[(E,E)-4,6-dimethylocta-2,4-dienoyl] and 3-[(E,E,E)-6,8-dimethyldeca-2,4,6-trienoyl] derivatives of 1,4-dihydroxy-5-(p-hydroxyphenyl)-2(1H)-pyridone. Spin–spin coupling information in the 1H and 13C nuclear magnetic resonance spectra after biosynthetic enrichment of tenellin with 13C and 15N isotopes was a valuable aid in elucidating the structure.

Analysis by 1H and 13C nmr spectrometry showed that caerulomycin D, a new metabolite isolated from S. caeruleus, possessed a novel ring system and had the structure (2S,3R,4R,4aS,10aS)-3,4,4a,10a-tetrahydro-4-hydroxy-3,4a-diniethoxy-2-methyl-9-(2-pyridyl)-2H-pyrano[3′,2′:5,6]-p-dioxino[2,3-c]pyridine-7-carboxaldenyde (E)-oxime.

The causative agent of toxicity in cultured mussels from a localized area of eastern Prince Edward Island has been identified as domoic acid, a neuroexcitatory amino acid. The toxin was isolated by a number of different bioassay-directed separation techniques including high-performance liquid chromatography, high-voltage paper electrophoresis, and ion-exchange chromatography, and characterized by a number of spectroscopic techniques including ultraviolet, infrared, mass spectrometry, and nuclear magnetic resonance. The isolation and purification methods are described in detail and some new analytical data for domoic acid are reported. Keywords: shellfish toxin, domoic acid, neurotoxin, bioassay-directed analysis.

Three new metabolites have been isolated from cultures of Streptomyces caeruleus and are related to caerulomycin, a known antibiotic metabolite of this organism now designated caerulomycin A. The structures of two of the new compounds, caerulomycins B and C, are shown to be 3-hydroxy-4-methoxy- and 3,4-dimethoxy-2,2′-dipyridyl-6-(E)-aldoxime.

Examination by 13C nuclear magnetic resonance spectroscopy of chartreusin produced in cultures of Streptomyceschartreusis supplemented with [1-13C] and [2-13C]acetate showed that the 19-carbon aglycone component was derived entirely from acetate. In the spectrum of chartreusin enriched from [1,2-13C]acetate the signals for 16 of the carbon atoms were accompanied by satellites due to spin–spin coupling of intact 13C—13C units. The coupled pairs were matched with the aid of homonuclear single 13C-frequency decoupling. Of the uncoupled carbon atoms, two were derived from methyl groups of acetate and the third came from an acetate carboxyl group. The arrangement of paired and unpaired 13C atoms in chartreusin suggests that the aglycone is derived from a single 22-carbon polyketide chain. Cyclization to a benzpyrene-like intermediate followed by ring cleavage and loss of three carbon atoms provides a plausible route from the polyketide to the substituted isocoumarin structure of the aglycone.

Carbon-13 nuclear magnetic resonance spectroscopy of caerulomycin A (1) produced by cultures of Streptomycescaeruleus has shown that [1-13C]acetate labels C-2, C-4, and C-4′, whilst [1,2-13C]acetate enriches these carbons plus C-2′, C-3, C-3′, C-5′, and C-6′. The results establish that acetate is incorporated with little dilution at C-3 and C-4 in the substituted ring of 1, whereas C-2, and C-2′ to C-6′ of the unsubstituted ring, are assembled from lysine via the symmetrical intermediate 2S,6S-diaminopimelic acid. The methoxyl carbon incorporates label from DL-[3-13C]serine, but this precursor does not enrich C-5, C-6, or C-7 of the substituted ring, and the origins of these carbons remain undetermined.

Chloramphenicol produced by cultures of Streptomyces species 3022a supplemented with sodium [1,2-13C]acetate was labelled with 13C exclusively in the dichloromethine (2.6 ± 0.1%) and carbonyl (0.59 ± 0.05%) carbon atoms. Satellite signals from 13C–13C coupling between covalently bonded 13C-enriched carbon atoms were too intense to be attributed to random combination of labelled atoms at the average enrichments measured, but their intensity relative to those of the signals for uncoupled 13C atoms indicated that most of the precursor had been incorporated after 13C–13C bond fission. Since [2,3-13C]succinic acid enriched only the carbonyl carbon atom of chloramphenicol, these results suggest that neither acetate nor a Krebs cycle intermediate is a direct precursor of the dichloroacetyl group. Cultures supplemented with [2-3H]-or [2H2]-dichloroacetic acid incorporated negligible amounts of isotope into the antibiotic; on this evidence, the free acid is not an intermediate in chloramphenicol biosynthesis and the acylation step may precede chlorination.

Methylene chloride extracts of the bryozoan Flustrafoliaceae show strong antimicrobial activity. Chemical investigation of the metabolites has led to the identification of a series of new bromoalkaloids belonging to the physostigmine class, which are responsible for this activity.

Resonances in the 13C nmr spectra of nonylprodiginine, cyclononylprodiginine, methylcyclodecylprodiginine, and butylcycloheptylprodiginine were assigned using information from the literature, from high resolution spectra and double irradiation experiments, and from 13C–15N couplings observed in samples of nonylprodiginine enriched with 15N. Supplementation of cultures with sodium [1-13C]- and [1,2-13C]acetate gave 13C-enriched prodiginines and the labeling patterns were established from 13C nmr spectra. These indicated that rings A and B were formed in a similar manner to rings A and B in prodigiosin and other prodiginine pigments. Ring C and the C2-alkyl substituent were derived in part from acetate units that were condensed in a linear 12- or 14-carbon chain. The same pattern of acetate assembly has been found in ail actinomycete prodiginines examined.

The structures of sepedonin, 3,6,9-trihydroxy-3-methyl-1,3,4,7-tetrahydrocyclohepta[c]pyran-7-one, and its two dimethyl ether derivatives, as well as anhydrosepedonin and its three dimethyl ether derivatives, are unequivocally established from proton magnetic resonance and nuclear Overhauser enhancement parameters.

The mass spectra and fragmentation patterns of several tropolones and tropolone methyl ethers are reported. Deuteration studies confirmed that elimination of a formyl radical from 2-methoxytropone upon electron impact involves a specific rearrangement of the methoxyl group but sequential loss of carbon monoxide and a hydrogen radical from the ring are competing reactions. They also showed that in a dimethyl ether of anhydrosepedonin elimination of a formyl radical is completely suppressed. In the methyl ether of stipatatonic acid elimination of carbon monoxide is followed by expulsion of carbon dioxide with no loss of 29 mass units. The mass spectrum of [8-13C]-anhydrosepedonin as well as the energy spectrum for sepedonin have been investigated. These results not only provide a plausible account of the fragmentation of tropolones following electron impact but also illustrate the effect of product ion stability in determining which among a number of alternative modes of fragmentation will be more probable.

Using 13C nuclear magnetic resonance spectroscopy the major sterols of the unicellular chlorophyte Dunaliellatertiolecta were found to be ergosterol and a closely related C29 trienol. Apparently the absence of a cell wall in D. tertiolecta does not significantly affect the type of sterol produced since other unicellular chlorophytes which possess a cell wall produce similar sterols containing an unsaturated side chain and a 24[R]-alkyl substituent.