13C nuclear magnetic resonance spectra of diastereomeric C-24 alkyl sterols have been assigned. Differences in the chemical shifts of side-chain carbons permitted the determination of the absolute configuration at C-24 in several sterols since these chemical shifts are insensitive to structural changes remote from the asymmetric centre. An unknown sterol from Tetraselmissuecica has been identified as (24R)-24-methylcholest-5-en-3β-ol and the configuration assigned from 1H nmr data to the sterol from Phaeodoctylumtricornutum has been confirmed. The utility and potential of this method in characterising new sterols and their biological precursors is discussed.

. 67,481 (1989).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. On a identifie l'agent qui est la cause de la toxicit6 des moules d7Clevage provenant d'une zone localisCe de la portion est de l'ile du prince Edouard; il s'agit de l'acide domoi'que, un acide amink neuro-excitant. On a is016 la toxine en faisant appel L un certain nombre de techniques de skparation basCes sur des essais biologiques parmi lesquelles on peut citer la chromatographie liquide B haute performance, 1'Clectrophorkse sur papier B voltage ClevC ainsi que la chromatographie d'Cchange ionique; on l'a caractCrisCe par un certain nombre de techniques spectroscopiques dont I'ultraviolette, l'infrarouge, la spectromCtrie de masse et la rtsonance magnCtique nuclkaire. On dCcrit en detail les mCthodes d'isolement et de purification et on prksente des donnCes analytiques nouvelles concernant I'acide domoi'que.Mots cle's : toxine des coquillages, acide domoi'que, neurotoxine, analyse baste sur des essais biologiques.[Traduit par la revue]

Growth of the planktonic, euryhaline diatom (Bacillariophyceae) Thalassiosira fluviatilis, both in nature and in culture, is accompanied by the production of a large amount of extracellular "mucilage". This mucilagenous condition is due to the formation of long, narrow fibers, composed of a number of microfibrils, which originate from the marginal and central pores in the silica valves. These fibers, previously referred to as mucilage or slime threads, were found upon hydrolysis to be composed entirely of glucosamine residues. Evidence will be presented in a subsequent paper (20) to show that these fibers consist entirely of pure, crystalline poly-N-acetyl-D-glucosamine linked by β-(1→4) bonds. This polymer has been given the systematic name chitan to distinguish it from chitin as isolated from other sources. This is the first report of the occurrence of this glycan in diatoms, and in a pure crystalline state in nature. The chitan was localized in the extracellular fibers, and was not found as part of the protoplasmic constituents. Approximately 18% of the nitrogen added to the culture medium was incorporated into the chitan fibers, which, in turn, comprised 31–38% of the cellular material (including the silica) of this diatom. Methods of production and isolation of the fibers are described, together with a discussion of the nature of the fibers as derived from light and electron microscopic observations. The presence of chitin in other algae also is discussed.

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