SYNTHESIS OF 6-DEOXY-6-HALOLAMINARANS AND CONVERSION OF 6-CHLORO-6-DEOXYLAMINARAN INTO THE 6-AMINO-6-DEOXY DERIVATIVE

The reaction of laminaran, a linear polyglucan with beta-(1 --> 3)-lin kages 1, with trityl chloride followed by conventional acetylation gav e a product that contained predominantly 6-O-trityl-2,4-di-O-acetate ( 3). Detritylation using hot aqueous acetic acid afforded a product con taining 2,6-di-O-acetate (4), 2,4-di-O-acetate (5), and 2,4,6-tri-O-ac etate (6) glucosyl residues. Similarly, the 2,4-di-O-benzoate (8) was prepared and then converted to the 6-bromo-6-deoxy derivative (9), usi ng triphenylphosphine and carbon tetrabromide. The benzoyl groups in 9 could not be removed completely under conventional conditions. Direct halogenation of laminaran (1) with triphenylphosphine and carbon tetr abromide was unsuccessful. The replacement of the primary hydroxyl gro ups in 1 by halogens was achieved using methanesulfonyl halide-DMF com plex. Syntheses of the 6-bromo-6-deoxy-2,4-di-O-formate (10) and the 6 -chloro-6-deoxy-2,4-di-O-formate (12) were thus achieved. The formyl g roups in 10 and 12 were removed under mild basic conditions to afford 11 and 13. Treatment of the 6-chloro-6-deoxy-2,4-di-O-formate derivati ve 12 with sodium azide in DMF afforded the free 6-azido-6-deoxy compo und 14. However, when 6-chloro-6-deoxylaminaran (13) was treated with sodium azide it gave a compound which contained both the azide and chl oro groups at C-6 positions in the polymeric chain. Catalytic hydrogen ation of the water soluble 6-azido-6-deoxy-2,4-di-O-succinyl derivativ e 15 to give the desired 6-amino-6-deoxy compound 16 was unsuccessful. Chemical hydrogenation using triphenylphosphine in DMF gave the inter mediate 6-triphenylphosphinimine 17, which on subsequent treatment wit h aq 30% ammonia afforded a compound containing both the 6-phosphinimi no and the 6-amino groups. The structures of all the compounds were co nfirmed by C-13 NMR and by FTIR spectroscopy. (C) 1996 Elsevier Scienc e Ltd.