Of branched trisaccharide

Scheme 4 Structures of the Group A Streptococcus cell-wall polysaccharide, and of branched trisaccharide (1) and hexasaccharide (2) fragments recognized by antibodies...

Glycosylation of methyl 2-0-benzoyl-a-L-rhamnopyranoside has led to a set of branched trisaccharides having P-D-gluco-, a-D-manno-, ot-L-rhamno-, and P-d-fructo-pyranosyl substituents at 0-3 and 0-4 of rhamnose. ... 

In a systematic investigation of branched trisaccharides, changes in the geometries of the... 

Finally, Droge and coworkers26 showed that the 2-aminoethyl phosphate-substituted KDO group is the lateral KDO unit of the branched trisaccharide (see Fig. 7), as follows. LPS from Salmonella minnesota mR3 was subjected to periodate oxidation. This sample, together with a control that had not been oxidized, was then mildly hydrolyzed with acid (pH = 3.4) during 1 h at 100°. Following removal of lipid A, both samples were analyzed by gel-filtration on Sephadex G-10, and paper electrophoresis. As expected, the ninhydrin-positive material obtained from the control sample was identical with KDO 7-(2-aminoethyl phosphate) (17) as previously identified. This spot was absent from the periodate-treated sample. Instead, an almost neutral, ninhydrin-positive spot was observed. This material (compound 26) was eluted, subjected to reduction with sodium [3H]borohydride, and hydrolyzed under strongly acidic conditions (see Scheme 11). Fol-... 

Scheme 2.13 Synthesis of a branched trisaccharide via thioethyl donors.

The branched trisaccharide 1 was defined as the minimal carbohydrate epitope for effective binding to anti-GAS Abs [79]. The bound conformation of 1 in complex with the IgG mAb Strep 9 was investigated by transferred NOE experiments and found to correspond to a local minimum conformation, which differed from the predominant conformation in the free state by a rotation around the xj/ angle of the o -(l-2) linkage [123]. STD-NMR ex-... 

Mithramycin (24) bears the terminal sugar unit -mycarose. By a similar preparation as for the methyl-branched glycals and the -enantiomer of namely the labile g-mycaral 40 w s obtained ( ). Its NIS condensation with the 3, 4 -Saol disaccharide proceeds smoothly, but the reaction turned out to be rather slow with respect to the stability of the g-mycaral. This results in only a modest yield (12%) of the trisaccharide which was hydrogenolyzed to compound 4. This in turn constitutes an isomer of the trisaccharide sequence in... 

Preparation of the branched trisaccharide (80) was readily achieved in good yield by nucleophilic substitution of the iodo derivative (60 d), derived from (60a), with (8a) in DMF (Scheme 24) [22b]. The introduction of a thiol functionality at the anomeric position of (80) using a known procedure and the condensation of this donor with the two acceptors (59)... 

Present at the 7-position of kaempferol with a -coumaric acid attached at the 4-hydroxyl of the first rhamnose and a known acylated branched trisaccharide at the 3-hydroxyl of the aglycone. 

Following the identification of KDO as a constituent of LPS, studies by Osborn and her group ( 5) have revealed that, in LPS, KDO (or the KDO region ) is located at the reducing end of the polysaccharide chain, linking the core segment to lipid A. Later, the application of differential color reactions based on thiobarbituric acid (TBA tests) (6, 7) has led to the view that KDO is present, in LPS from Salmonella or E. coli, in the form of a branched trisaccharide (Fig. 1). In this model, a branchpoint KDO residue (KDO I), ketosidically-linked to the second glucosaminyl residue of lipid A, is substituted in position 4 or 5 by a... 

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. 

Three branched trisaccharides (18, 19, and 20) in which the mannose residue was glycosylated by each of the three 3,6-dideoxyhexose isomers, were synthesized from a common disaccharide precursor (21). The latter was constructed from 8-methoxyl-carbonyloctanol 3-O-benzoyl-4,6-0-cyclohexylidene-a-D-mannopyranoside 22 and tetra-O-benzyl-a-D-galactopyranosylchloride (23). Transesterification of disaccharide 24 leads to the selectively protected disaccharide 21 which was reacted with the ap-... 

L-fucose [126] and subsequently used to prepare a branched trisaccharide. This trisaccharide a-L-Col(l ->3)[a-L-Col(l -> 6)]-a-D-Glc forms a crucial element of the pentasaccharide repeating unit (structure see Ref. [20] p 301) and was synthesized as an 8-methoxycarbonyloctyl glycoside [97],... 

Table 4. Dihedral angles

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