Pyranose galacto

The C-l chemical-shifts of furanosides are generally at lower field than those of their anomeric counterparts in the pyranose series.13 Sometimes, an immediate identification may be made when very low-field signals of 8C 107 or more are present, for example, for /3-galacto-furanoside14-17 and a-arabinofuranoside.18 Generally, characteristic signals of furanoside-ring carbon atoms are present at low field (8C 80 -85) also. 

Fig. 1.—Favored Rotamers About the C-5-C-6 Bond in 6-Deoxy-6-fluoro-D-gluco-(a) and -galacto-pyranoses (b,c).

Alkyl (or acyl) derivatives of the 6-amino-6-deoxy carbohydrates are examples of derivatives in which the hydrophilic and hydrophobic moieties are linked at other positions than C-1. Thus 6-amino-6-deoxy-D-galactose derivatives 34 were prepared from l,2 3,4-di-0-isopropylidene-6-0-tosyl-a-D-galacto-pyranose by the following reactions (1) substitution of the leaving group at C-6 by a phthaloyl function, (2) hydrazinolysis to afford a 6-amino-6-deoxy intermediate, (3) reaction of acyl or sulfonyl chlorides at the amino function, (4) deprotection of the acetal rings to afford the expected glycolipid 34 [56]. 

A comparison of the three binary copolymerizations of 1,6-anhydro-/S-D-gluco-, -galacto-, and -manno-pyranose derivatives gives some insight into the mechanism of copolymerization, if it is assumed on this evidence that the per-p-xylyl and perbenzyl derivatives can be used interchangeably.107... 

Approximately 400 different glycosyltransferases are necessary in order to ensure the synthesis of those bacterial polysaccharides whose structures have thus far been elucidated. This estimate is based on the results of an analysis of the structures, made in order to ascertain how many different disaccharide fragments are present. An example of such an analysis is shown in Table V for the disaccharide sequences L-rhamnopyranosyl-D-galacto-pyranose, D-mannopyranosyl-L-rhamnopyranose, and D-galactopyranosyl-D-mannopyranose that are characteristic for the O-specific polysaccharides of Salmonella serogroups A, B, D, and E, the objects of many biosynthetic studies. Full details of similar analyses for other disaccharide sequences will be published elsewhere, as the resulting Tables are too voluminous for inclusion in this Chapter, but the most interesting results are summarized in Tables VI and VII. 

Synthesis of f -D-(l,6) linked disaccharides of N-fatty acylated 2-amino-2-deoxy-D-glucose an approach to the lipid A component of the bacterial lipopolysaccharide. Carbohydr. Res., 88, C10-C13 Kochetkov, N.K., Dmitriev, B.A., Malysheva, N.N., Chernyak, A.Ya., Klimov, E.M., Bayramova, N.E., and Torgov, V.I. (1975). Synthesis of O-p-D-mannopyranosy l-( 1 - 0-0-ot -L-rhamnopyranosy l-( 1 -3)-D-galacto-pyranose, the trisaccharide repeating-unit of the O-specific polysaccharide from Salmonella anatum. Carbohydr. Res. 15, 283-290... 

In early work [165] on the synthesis of the pentasaccharide (236), the azide (237) was condensed with (238) [an intermediate in the preparation of (237)]in the presence of silver perchlorate and polyvinylpyridine to give the a-linked disaccharide (239) in 60 % yield and this on acetolysis gave the disaccharide (240) which contains the potential terminal disaccharide unit of the Forssman antigen. Compound (240) was converted into the glycosyl bromide with titanium(IV) bromide under carefully controlled conditions [182] and condensed with l,6-anhydro-2,4-di-0-benzyl-D-galacto-pyranose in the presence of silver carbonate to give the potential terminal trisaccharide (241) of the Forssman antigen. 

Conformational analysis explains why the relatively strained 2,6-dioxa-bicyclo[3.2.1]octane skeleton 98 of 3,6-anhydro-D-gluco- and -D-manno-pyranose tends to recyclize rapidly in the presence of methanolic hydrogen chloride into the less-strained 2,6-dioxabicyclo[3.3.0]octane skeleton 99 of the 3,6-anhydrohexofuranose. Obviously, such rearrangement cannot take place with the galacto or talo configurations, and consequently, acyclic acetals are formed.390,391... 

Acetalation of l,6-anhydro-/l-D-mannopyranose (39) and -/1-D-galacto-pyranose with trichloroacetaldehyde in the presence of A,A -dicyclohexylcar-bodiimide affords endo-H diastereomers of 3,4- and 2,3-trichloroethylidene derivatives of l,6-anhydro-/l-D-altro- and -/1-D-gulopyranose, respectively.528 For isomerization of various 1,6-anhydrohexopyranoses acetates, see Section II.4. 

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