Trehalose-type disaccharides

In addition to Bronsted acid promoted Fischer-type glycosylations, Lewis acids have been investigated (Scheme 3.4). A variety of Lewis acids promote glycosylation under mild conditions, often in substoichiometric amounts. The earliest examples include ZnCl2 [18] and FeCl3 [19], although these readions were demonstrated only for preparation of trehalose-type disaccharides. Mukaiyama et al. have very recently developed metal triflate catalysts for the dehydrative glycosylation with... 

Sharp and Stacey69 were not successful in applying the alkali salt elimination technique to the synthesis of maltose and of lactose but were successful in the case of disaccharides of trehalose type. 

The reversion products obtained when a solution of D-glucose was exposed to hydrogen chloride at 25 °C for several days included disaccharides of the trehalose type (6%), trisaccharides (4%), and oligo- and poly-saccharides (73%) the oligosaccharides are branched. Oligosaccharides and low-molecular-weight... 

In addition, the corresponding isomers with the a-glycosidic linkage are possible. The free hydroxyl group of the hemiacetal of a disaccharide cannot be assigned to a configuration the a- and /3-form are in equilibrium. The first two disaccharides listed are of the trehalose type the rest, of the maltose type. 

An interesting illustration of the roles played by low-molecular-mass protein stabilizers in assisting cells to cope with heat stress is provided by work of Singer and Lindquist (1998a,b), who examined the complementary roles of the disaccharide trehalose and heat-shock proteins in recovery from thermal stress by the yeast Saccharomyces cerevisiae. Many types of yeast produce high concentrations of... 

Titanium-based catalysts, would seem particularly attractive candidates, but the pore size of e.g. TS-1, is much too small to admit even a monosaccharide. Recently a number of synthetic approaches towards mesoporous titanium containing catalysts of the MCM-41 type have appeared in the literature . In the present paper we will deseribe the use of Ti-MCM-41 materials in the oxidation of the model mono- and disaccharides methyl a-D-glucopyranoside, sucrose and a,a-trehalose, and we will discuss the effect of the zeolite synthesis on the effectiveness in these reactions. Several preparative approaches of Ti-MCM-41 have been compared in the oxidation of these model carbohydrates. 

Miura et al. examined the enzymatic synthesis of 6-0-vinylsebacoyl trehalose and reported that the obtained Galacto-type trehalose polymer 44 (81) showed inhibition activity against Shiga toxin-1 based on a stereochemical structure similar to that of globosyl Gb2 disaccharide as shown in Figure 19. 

In a further molecular mechanics study (MM3), the energy surfaces of a,a-, a,p-, and P,P-trehalose were compared with those of the corresponding 2-(6-methyltetrahydropyran-2-yloxy)-6-methyltetrahydropyrans and 5a-carba trehaloses it was concluded that the exo-anomeric effect plays an important role and that linkage-type (a or p) is more important than the presence or absence of exocyclic substituents in detomining disaccharide conformations. The preferred solution conformations of eight (l- )-C-linked disaccharides, such as compounds 13, have been determined on the basis of vicinal H- H coupling constants, and conformational similarities between... 

The use of vibrational spectra in oligosaccharide studies has been furthered this year. For a set of six disaccharides with different types of glycosidic linkages (a,a-trehalose, sophorose, laminaribiose, maltose, cellobiose and gentiobiose) IR and Raman spectra show good agreement with calculated frequencies below 1500 cm . No additional terms are needed in the potential energy calculations to... 

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