Trisaccharides, complex-type

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. 

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. 

The efficiency of the PMB-assisted y0-mannosylation protocol was enhanced (O Scheme 47), when the 4,6-0-cyclohexylidene group was introduced. For example, compound 91 gave trisaccharide 92 in 85% yield [139]. PMB-assisted I AD has been shown to be highly practical for the construction of complex-type [140,141,142,143] as well as high mannose-type A-glycans [144,145,146,147]. 

The cell walls of the Solanaceae plant species contain the XXGG type of XGs [247,275]. Suspension-cultured tobacco cells secrete a XG, bearing disaccharide side chains (11) [276], as similarly reported for XGs of other solana-ceous plants. The XG from suspension-cultured tomato cells is more complex, as it also contains the unusual / -L-Ara/-(1 3)-o -L-Ara/-(1 2)-a-D-Xylp trisaccharide side-chain (12) in addition to the prevaiUng dimeric moiety (13) [277]. 

Mass spectrometry enables the type of direct analyses described, but it does have its limitations. Online operation forces detection at infusion concentrations, in salty buffer and under complex mixture conditions. General ion suppression results from the buffer and mixture components, and mixture complexity can tax the resolution of even the best mass spectrometers. Increasing compound concentration is not the answer, as this leads to problems of solubility and increased compound consumption. We have found that the online method can work successfully for up to 100 compounds per analysis, but the false negative rate becomes appreciable [21]. As an alternative for ligand discovery purposes, we have developed a FAC-LC/MS system in which FAC effluent is sampled and analyzed by LC/MS [19]. This system offers the ability to concentrate mixture components and introduces another dimension to the data in order to tolerate more complex mixtures (Fig. 6.9). Using this system, we have screened approximately 1000 modified trisaccharide acceptor analogs targeting immobilized N-... 

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