Kdo disaccharides

Isshiki, Y., Zahringer, U., Kawahara, K. Structure of the core oligosaccharide with a characteristic D-glycero-a-D-talo-oct-2-ulosonate-(2- -4)-3-deoxy-D-manno-oct-2-ulosonate [a-Ko-(2- -4)-Kdo] disaccharide in the lipopolysaccharide of Burkholderia cepacia. Carbohydr Res 338 (2003) 2659-2666. 

Cyclizations are also used to create glycosidic linkages. In the example given in Scheme 4.63, the E (303) and Z (304) enol ethers were obtained from the reaction of the aldehyde 301 with the phosphonate 302 [636]. Oxymercuration-demercuration of 303 and 304 gave the (3-linked (305) and a-linked (306) KDO disaccharides, respectively. 

This ketene dithioacetal protocol was employed to deliver all the isomeric 3-deoxy-heptulosonic and heptulosaric acids, as well as their 2-deoxy counterparts [130]. Further, by this route the synthesis of KDO and 2-deoxy-KDO was accomplished [133]. This methodology was also utilized for direct construction of naturally occurring KDO disaccharides [134]. 

Figure 3.6 Structure of the Lipid A of Salmonella Species. The two glucosamine sugars are amide-linked at the 2-position to 3-OH fatty acids, which may themselves bear ester-linked fatty acids (R, Rg). Additional acylation by ester-linked 3-OH fatty acids may occur at 3 and 3 positions. The sugar 4-amino-arablnose may be substituted at the 4 of the glucosamine II and ethanolamlne at the 1 position of glucosamine I. The KDO disaccharide (not strictly part of lipid A) is attached to glucosamine II 6. The 4 position of glucosamine I is probably unsubstituted...

The 5-deoxy derivative (52) of a KDO disaccharide has been synthesised, and a review has appeared on various glycosylating reagents derived from M-acetylneuraminic acid. Specifically, in this area, compounds (53) and (54, n = 12 or 16) have been... 

Attempts to apply an analogous approach to the synthesis of Kdo disaccharides were made by Sinay by reaction of an exo-glycal obtained from 2,3,5,6-di-O-iso-propylidene-D-mannose with iodine and potassium t-butoxide, but after a positive result with methanol, sugar acceptors did not give the expected disaccharides [8]. 

The a-(2- 8)-linked Kdo disaccharide thioglycoside donor 125 was elaborated by Baasov et al. via reaction of fluoride 123 with phenyl 2-thio-ketoside 124 to give disaccharide 125 in 65% yield, which was then attached to a tri-glucosamine acceptor 126 by NIS-promoted coupling in 45% yield (Scheme 20). Compound 127 was obtained as 1 1 anomeric mixture and converted to a deprotected pentasaccharide with GTPase activity. ... 

PA-1 was partially hydrolyzed with O.IM TFA (40°C, 24 h) and the three fractions (PA-l-I, PA-l-II and PA-l-III) were obtained by Bio-gel P-6. Especially, about 50% of TBA-positive material (PA-l-III) was eluted in the fraction of small oligosaccharide. Permethylated oligosaccharide-alditols from PA-l-III were analyzed by GC-EIMS, and three disaccharide-alditols (IP, 2P and 3P) were detected. EI-MS and component sugar analysis suggested that the major peak, IP was Rha-(l- 5)-Kdo-ol and the minor peaks, 2P and 3P were two epimers of Araf-( l->5)-Dha. 

As shown in Eq. 12.54, with glyoxylate as the dienophile, if the attack is on the si face of the diene, it would lead to the skeleton of KDO if the attack is on the re face, it would lead to the skeleton of KDN. C-Disaccharide analogs of trehalose were prepared using an... 

KDO appears to be unique to Gram-negative bacteria. In the LPS that have been studied, KDO residues are situated at the reducing ends of the polysaccharide domains, linking them, by ketosidic bonds, to the fatty-acid-substituted 2-amino-2-deoxy-D-glucosyl disaccharides referred to as lipid A. Fig. 2 is a block diagram indicating the location of KDO in the LPS from Salmonella. 

The Koenigs—Knorr reaction109,130 of the halide 112 with methyl 2,3-di-O-acetyl-jS-D-ribofuranoside (123) in 3 1 (v/v) benzene—1,4-dioxane in the presence of silver carbonate gave a low yield of the disaccharide 124 (see Scheme 34). Compound 124 and its deacetylation and deesterification products, 125 and 126, were used as model compounds for 1H- and 13C-n.m.r. studies47,107 of the KDO-containing exopolysaccharides from Escherichia coli strains LP 1092 and 06 K13 H1 (refs. 84 and 86). 

An aglyconic derivative of KDO, having 0-7 and 0-8 temporarily blocked, was required for the synthesis of the model disaccharide Koenigs-Knorr reaction of 3 with a suitable halide derivative of KDO would be expected to occur exclusively at the (equatorial) 0-4 while 0H-5, being axially-disposed and experiencing additional steric shielding by H-7, would be practically unreactive. X-ray crystal structure analysis of KDO derivatives (14, 15) has shown that H-7 is orient-... 

The nature of the protecting groups employed in the preparation of disaccharide discussed above does not permit the extension of the synthesis to the branched type of KDO trisaccharide shown in Fig. 1. To obtain another model compound for the structure elucidation of the natural KDO trisaccharide by spectroscopic and immunochemical methods, a route was devised which would permit the synthesis of the model trisaccharide 12. 

Synthesis of disaccharides corresponding to the linkage between lipid A and KDO. 

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