Gluco-disaccharides

Table 12.3 lists the glass transition temperatures for all of the naturally occurring gluco-disaccharides, i.e., disaccharides composed of two glucose units, and for sucrose. For trehalose, the value of 115 2°C is currently accepted as the exact Tg of anhydrous trehalose [51-55], although various Tg values have been... 

Chemical 5-thioglycosylation has largely relied on the trichloroacetimidate procedure as exemplified by Pinto and co-workers of 1,2- as well as 1,6-connected gluco-disaccharides with the thiosugar at the non-reducing end [145]. Several examples of classical Koenigs-Knorr methodology have also been reported, just to mention the most frequently employed approaches. 

The Enzymes II (E-IIs) of the phosphoenolpyruvate (P-enolpyruvate)-dependent phosphotransferase system (PTS) are carbohydrate transporters found only in prokaryotes. They not only transport hexoses and hexitols, but also pentitols and disaccharides. The PTS substrates are listed in Table I. The abbreviations used (as superscripts) throughout the text for these substrates are as follows Bgl, jS-gluco-side Cel, cellobiose Fru, fructose Glc, glucose Gut, glucitol Lac, lactose Man, mannose Mtl, mannitol Nag, iV-acetylglucosamine Scr, sucrose Sor, sorbose Xtl, xylitol. 

Functionalisation at OH-2 thus led to a series of 1,2-bisfunctionalised platforms prepared from two model lactones, one monosaccharidic (a-gluco) and one disaccharidic (ot-malto). Allylamine and propargylamine were used as model functional appendages due to the wide scope of their possible subsequent chemistry. Their addition on the lactones occurs in high yield and very mild conditions (room temperature, THF, no catalyst,... 

The mono-unsaturated disaccharide 74 was also prepared (4 ). It was obtained in 93% yield by condensation of 6g with 2,3,4,6-tetra-0-benzyl -et-D-qlucose under catalysis ( 7) with stannic chloride.Preliminary experiments indicated that it can likewise be oxyaminated (48). If this is borne out in further studies, a route would be open to the D-manno,D-gluco stereoisomers of and 57. 

N-Iodosuccinimide also promotes the cyclization to give the a-gluco-side derivative, and the disaccharide derivative is synthesized with high stereoselectivity starting from a hydroxy vinylether (39). 

Further functionalization at OH-2 was also explored [187]. From monosacchari-dic (ot-gluco, 129) and disaccharidic (a-malto, 143) CMGLs, several types of bisfunctionalized systems were synthesized by reaction with allylamine or propar-gylamine. For example, compound 155 was prepared and used in a synthesis of the nucleotide sugar analog 156 (Scheme 38). In the context of studies on the... 

Maltose (1), systematically named 4-O-a-D-glucopyranosyl-D-gluco-pyranose, is a reducing disaccharide. The numbering of the carbon... 

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