Hexopyranose residues

The action of periodic acid (a reagent diagnostic for a-glycols) on agar has been studied by V. C. Barry, who has shown that the polysaccharide consists mainly of 1,3-linked hexopyranose residues since this reagent is practically without effect on the polysaccharide. 

This OPS consists of three to four repeats of this tetrasaccharide (n = 3 to 4). The proximal repeat unit is linked to a Glc3NAmA residue (3-acetimidoylamino-3-deoxy-D-gluco-hexuronic acid) which is linked to 04 of the COS external Kdo residue the distal repeat unit is capped at 04-by a 4,6-dideoxy-4-formamido hexopyranose residue (R-) of unidentified configuration. The 3-OMe-6dTal residues are non-stoichiometrically methylated at 04 (approx. 20%). 

TABLE 6.3 Periodate oxidation of linked hexopyranose residues... 

The vigorous anchoring of nearly all the hexopyranoses in D- C (l- C4) conformations by the coplanar effect brings about a certain rigidity of the oligosaccharide chains. It is possible that the introduction of ido residues with a flexible conformation into certain sites creates the flexibility indispensible for certain functions. 

Figure 5 lists the aldehydes which were made in quantities ranging from 10 g to 10 kg. Figure 6 shown a representative NMR spectrum of the aldehyde taken from the unpurified residue after lypophilization of the reaction mixture. This spectrum illustrates the specificity of the enzyme. Initially, we were concerned about the possible formation of uronic acids reported by some authors (25-27). However, we have no evidence for the presence of these by-products from the carbon-13 spectra of the oxidation products. On the other hand, the small signals between 90 ppm and 103 ppm may belong to dimeric products described by Maradufu and Perlin (28), All the aldehydes are hydrated as indicated by the presence of a peak at 88.7 ppm and the absence of peaks below 200 ppm. These aldehydes are relatively stable in the presence of base as evidenced by preparation of 5-C-hydroxymethyl-L-arabino-hexopyranoses (Equation 1). Even though the synthesis was carried out in 1 N NaOH, very little by-products resulted from elimination or retroaldol reactions at the pyranose ring. 

The identity of the decilonitrose residue in the antibiotic decilorubicin has been confirmed as 2,3,4-trideoxy-3-C-methyl-3-nitro-L-nho-hexopyranose by an unambiguous synthesis of its glycoside (73) from L-rhamnose via the 3-ulose (72) (Scheme 13). Potassium fluoride (in... 

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