ARSENIC-CONTAINING RIBOSIDES FROM THE BROWN ALGA SARGASSUM-LACERIFOLIUM - X-RAY MOLECULAR-STRUCTURE OF 2-AMINO-3-[5'-DEOXY-5'-(DIMETHYLARSINOYL)-RIBOSYLOXY]PROPANE-1-SULFONIC ACID

Three novel arsenic-containing ribosides, methyl 5-deoxy-5-(dimethylarsinoyl)-beta-D-riboside, 1-O-[5'-deoxy-5'-(dimethylarsinoyl)-beta-D-ribosyl]mannitol, and a dimethylarsonio-beta-D-riboside have been isolated from extracts of the brown alga Sargassum lacerifolium. In addition, five previously reported arsenic-containing ribosides, and some arsenate, were isolated from Sargassum, and dimethylarsinic acid was also shown to be present. The compounds were identified chiefly by NMR spectroscopy, and an X-ray molecular structure is reported for one of them, 2-amino-3-[5'-deoxy-5'-(dimethyl-arsinoyl)ribosyloxy]propane-1-sulphonic acid. The stereochemistry of the aglycones in these arsenic-containing ribosides is discussed and the configuration of 3-[5'-deoxy-5'-(dimethylarsinoyl)-beta-D-ribosyloxy]-2-hydroxypropane-1-sulphonic acid 4 was assigned as 2S on the basis of a comparison of NMR spectra with those of synthetic model compounds.