THE INNER-CORE REGION OF YERSINIA-ENTEROCOLITICA YE75R (0 3) LIPOPOLYSACCHARIDE/

The inner-core region of the lipopolysaccharide of an UDPGalNAc-4-epim erase-deficient mutant of Yersinia enterocolitica 0:3, designated as Y e75R, was investigated using methylation analysis, 1D-C-13-NMR and 2D- C-13-NMR and H-1-NMR, as well as P-31-NMR, fast-atom-bombardment mass spectrometry (FAB MS) and FAB MS/MS in positive and negative modes. Th e isolated core heptasaccharide (OS) was composed of 2 units D-glucose , 3 units LD-heptose and 1 unit each of DD-heptose and 3-deoxy-D-manno -octulosonic acid. Methylation analysis indicated that OS was highly b ranched with terminal location of the two glucoses and the DD-heptose unit, which was partially (to about 40%) phosphorylated at C7. These c ombined studies allowed us to formulate the structure of the inner cor e region as shown in Scheme 1. The substitution of the 7-position of t he terminally linked DD-heptose unit by phosphate could be recognized by MS characterization of permethylated DD-heptose-7-phosphate (aldito l acetate) and the extent of the substitution by the ratio of the two well separated H-1 signals of DD-heptose in 500-MHz H-1-NMR. Negative FAB MS of OS also indicated the presence of smaller amounts of two hex asaccharides, differing from OS in lacking either one terminal unit of D-glucose or of the terminal DD-heptose, and additionally of a pentas accharide lacking two heptosyl units, namely the terminal DD-heptose a nd and the subterminal LD-heptose. The presence of the smaller oligosa ccharides in the OS fraction was also recognized by the methylation an alysis.