Undecasaccharide

Figure 14.3 Structure models of four different conformer populations (2 for each 1—>6 link) of a triantennary high-mannose undecasaccharide M9. Terminal mannoses are highlighted as CPK models.12...

Unverzagt, C., Chemoenzymatic synthesis of a sialylated undecasaccharide-asparagine... 

Kitajima et al. [264] used the mixture of mercury salts and molecular sieves in 1,2-dichloromethane to condense (370) with the trisaccharide derivative (382) to give similar tetrasaccharides [on the primary hydroxyl group of (382)] with again equal amounts (30% each) of a- and (3-linked derivatives. With the allyl glycoside (383) under the same conditions 48 % of a- and 33 % of P-linked glycosides were obtained [265]. The a-isomer was used to prepare [265] the undecasaccharide characteristic of the complex type of glycan of glycoproteins. 

Unverzagt, C. (1996) Chemoenzymatic synthesis of a sialylated undecasaccharide-asparagine conjugate. Angew. Chem. Int. Ed. 35,2350-2353. 

Plasma-desorption mass spectrometry (PDMS) also allowed location of the acyl functions. Thus, 252Cf-PDMS of LOS V in M. kansasii gave27 molecular-weight-associated ions at mlz 2499. The major acylating function of the intact LOS was determined to be a 2,4-dimethyltetradecanoate. Addition of three of these fatty acyl residues to the oligosaccharide portion gave a mass of 2476 daltons. Thus, the ion at mlz 2499 must be equivalent to [M + Na]+, and therefore LOS V must be a tri-O-acyl-undecasaccharide. However, exact location of the acyl functions was not obtained in this way. 

SCHEME 15.22 Total synthesis of complex type 2 undecasaccharide-aspargine 189. Construction of the P-mannosidic linkage in the key trisaccharide 182 and preparation of core heptasaccharide 185. 

Ogawa, T, Sugimoto, M, Kitajima, T, Sadozai, K K, Nukada, T, Synthetic studies on cell surface glycans. 51. Total synthesis of an undecasaccharide. A t)fpical carbohydrate sequence for the complex type of glycan chains of a glycoprotein. Tetrahedron Lett., 27, 5739-5742, 1986. 

Ogawa and coworkers have also extensively described synthetic studies on glycoprotein oligosaccharides and mannose-containing glycosphingolipids using similar reactions [26,27, 28,29] (O Scheme 9). For instance, the reaction of 14 with disaccharide 15 afforded 16 (o = 1.1 1), which was used as the key intermediate in their first chemical synthesis of a sialic acid-containing complex-type undecasaccharide [30]. 

SCHEME 22. Pentenyl orthoester-based approach to an undecasaccharide. 

Fig. 3-120. Separation of two structurally similar undecasaccharides from asialo fetuin. — Separator column CarboPac PA-1 eluent (A) 0.15 mol/L NaOH, (B) 0.15 mol/L NaOH + 1 mol/L NaOAc gradient linear, 50% B to 100% B in 20 min detection and injection volume see Fig. 3-105.

Figure 4. A model glycoprotein showing the X-ray crystallographic data for the human major histocompatibility (MHC) antigen, HLA-A2, (Bjorkman et al., 1987) to which has been added one possible oligosaccharide chain (a di-sialylated biantennary complex N-linked undecasaccharide, Figure 2) at the consensus N-glycosylation site, Asn 86. This represents a snapshot of one of many possible conformations. (Printed with permission of the BMAfrom the review Hounsell and Davies, 1993).

The crystal structure of the dimeric form of the toxin in complex with a diantennary undecasaccharide isolated from human serum transferrin was determined at 3.5 A [125]. 

Sequential addition of specifically substituted monosaccharides has given a tri-antennary undecasaccharide with the structure of a glycan chain of the N-linked glycoprotein of calf thyroglobulin (18). Synthesis started from the trisaccharide Man(31-4GlcNH2 -4GlcNH2 [298],... 

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