THE STRUCTURE OF THE EXOPOLYSACCHARIDE PRODUCED BY LACTOBACILLUS-HELVETICUS-766

The exopolysaccharide produced by Lactobacillus helveticus 766 in skimmed milk was found to be composed of D-glucose and D-galactose in a molar ratio of 2:1. Linkage analysis and 1D/2D NMR studies (H-1 and C-13) performed on the native polysaccharide, and on oligosaccharides obtained from a partial acid hydrolysate, showed the polysaccharide to consist of hexasaccharide repeating units with the following structure: [GRAPHICS] UP>31</SUP>P) studies the polysaccharide was shown to be composed of repeating units with the following structure: [GRAPHICS] tetra-O-acetyl-2-epi-streptozotocin (the acetylated alpha-mannosamine epimer of streptozotocin). Administration of 50 mg/kg/day X 5 to leukemia L1210-bearing DBA/2Ha mice resulted in 5/5 35-day survivors. Neutralization of 1,3,3,6-tetra-O-acetyl-2-amino-2-deoxy-alpha-D-mannopyranose oxalate under aqueous conditions led to 2-acetamido-1,4,6-tri-O-acetyl-2-deoxy-alpha-D-mannopyranose, the oxidation of which gave 2-acetamido-4,6-di-O-acetyl-1,5-anhydro-2-deoxy-D-erythro-hex-1-en-3-ulose. This agent demonstrated an IC50 of 25 mu M with a murine L1210 cell culture. Administration of 100 mg/kg/day X 5 resulted in 42% ILS in DBA/2 mice with ip L1210 leukemia. Several other nonacetylated derivatives were also prepared by direct N-acylation, producing, for example, fluorescently tagged N-dansylmannosamine.