Containing mannos

The bivalves Hyriopsis schlegelii and Corbicula sandai contain manno-lipids derived from glucosylceramide, in which xylosyl groups occur as a branch, fucosyl residues can be internal in the saccharide chain and, in one case, 4- Omethylglucuronic acid is found (Hori etal, 1977a, b, 1977 Itasaka and Hori, 1979). A tentative set of biosynthetic relationships is put forward in Figure 4.20. 

Treatment of methyl 2-azido-4,6-0-benzylidene-2-deoxy-a-D-altro-pyranoside (128) (42) with 121 followed by refluxing and processing afforded a chloro derivative as a sirup in 70% yield (46, 49). Reduction of this product with an excess of Raney-nickel in methanol containing acetic anhydride afforded a crystalline product, m.p. 179°C., which is formulated as the d-manno analog 131. The actual product is most likely methyl azido-4,6-0-benzylidene-3-chloro-2,3-dideodxy - a - d - mannopyran-oside (130) resulting from attack of chloride ion at C-3 with inversion of configuration in the intermediate 129. Had the chlorination proceeded... 

Extensive studies have indicated that only pyruvate is acceptable as the NeuA donor substrate, with the exception of fluoropyruvate [49], but that the enzyme displays a fairly broad tolerance for stereochemically related aldehyde substrates as acceptor alternatives, such as a number of sugars and their derivatives larger or equal to pentoses [36,48,50,51]. Permissible variations include replacement of the natural D-manno configured substrate (4) with derivatives containing modifications such as epimerization, substitution, or deletion at positions C-2, -4, or -6 [16,27]. Epimeriza-tion at C-2, however, is restricted to small polar substituents owing to strongly... 

Before 1983, branched-chain sugars had not been found in bacterial polysaccharides, but there are now five examples belonging to this class. The LPS from Coxiella burned phase I contains both 6-deoxy-3-C-methyl-L-gulose (L-virenose) as pyranoside (12) and 3-C-(hydroxymethyl)-L-lyxose as furan-oside (13). Another 6-deoxy-3-C-methylhexose, having the manno configuration, is a component of the Nitrobacter hamburgiensis 0-antigen. ... 

Fundamentally, D-glucofuranurono-6,3-lactone (4) contains the 2,6-dioxabicyclo[3.3.0]octane structure (5), just as do ido-, manno-, and... 

Like in gangliosides, lactones might be found in some bacterial capsular polysaccharides containing 1-carboxyethylsubstituents. But their identification remains problematic due to the conditions of isolation and preparation of analytic samples. To facilitate their detection by NMR, and in order to determine if the formation or hydrolysis of lactones occurred during analytical procedures, synthetic model substances, 2,3- and/or 3,4-lactones based on gluco-12, manno-13, and galactopyranosides 14 were prepared and characterized by NMR spectroscopy (Fig. 2).20 The relative lactonisation rates in acetic acid-fi 4 and hydrolysis rates in buffered D20 were evaluated. 

Observation of displacement effects resulting from O-substitution, and use of standards, led to the assignment of the chemical structure of the polysaccharide of Neisseria meningitidis serogroup 29e, which consists of 2-acetamido-2-deoxy-D-galactosyl and partly acetylated 3-deoxy-D-manno-octulosylonic acid (KDO) residues.166 The 13C-n.m.r. spectrum of the O-deacetylated polymer (see Fig. 36,B) contained 15 signals out of the possible 16 expected from an alternating structure. Comparison of these resonances with those of the anomers of 2-aceta-... 

This hypothesis would seem justified62 by the fact that the same reaction performed on the epimeric halide (manno configuration) (34) leads to a mixture containing 60% of the 3,3,4,6-tetraacetate of methyl 2-bromo-2-deoxy-a-D-arafcmo-hexopyranosid-3-ulose 3-hydrate (38) and 20% of l,3,4,6-tetra-0-acetyl-2-0-methyl-/8-D-glucopyranose... 

Special examples of stable glycofuranosides will be discussed in Section VI, 4, but mention may be made here of two distinctive glycofuranosides. Ballou and Fischer 0 refluxed di-O-isopropylidene-D-monno-hexodialdose in methanolic hydrogen chloride, and obtained a 20% yield of a compound containing two furanoside rings, namely, the dimethyl , a-difuranoside of D-manno-hexodialdose. It was identified by methylation, by its strong dextrorotation, and by its rate of hydrolysis by 0.01 N hydrochloric acid. 

Concanavalin A is an antibody-like protein isolated from the jack bean. 82 It was shown to form a precipitate with glycogen and with yeast mannan, and was later also used to differentiate between glycogen-like polysaccharides from various sources.283 284 It has now been shown that concanavalin A forms a precipitate only with branched polysaccharides which contain terminal, nonreducing a-D-glucopyranosyl or a-D-manno-pyranosyl groups.18 The combining sites of the protein appear to be directed against the 2-deoxy-a-D-aratano-hexopyranosyl system.2 ... 

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