Galactose anomer

The following are the more stable anomers of the pyranose forms of D glucose D mannose and D galactose... 

The a anomers of 2-acetamido-2-deoxy-D-glucose and 2-acetamido-2-deoxy-D-galactose have the same nir c.d. bands in 1 1 methanol-water at 0° as the anomeric mixtures have in aqueous solution. This indicates that the anomeric configuration has little influence on the nir c.d. band. 

Karkkainen and Vihko,144 in their work cited earlier, also studied the O-trimethylsilyl derivatives of acetamidodeoxyhexoses. Of the two liquid phases that they used, they found QF-1 more suitable for the separation of anomers, but SE-30 was better for separating 2-amino-2-deoxy-D-glucose derivatives from those of2-amino-2-deoxy-D-galactose. 

The aldohexoses have not been extensively studied by X-ray crystal-lographers. Crystals of a- and jS-D-galactose were examined by Sheldrick,21 who gave directions for crystallizing both anomers. In one preparation, the crystals of a-D-galactose were small plates large prismatic crystals of jS-D-galactose were also obtained. 

Compounds that have the same chemical formula but have different structures are called isomers. For example, fructose, glucose, mannose, and galactose are all isomers of each other, having the same chemical formula, C6H1206. If two monosaccharides differ in configuration around only one specific carbon atom (with the exception of the carbonyl carbon, see anomers below), they are defined as epimers of each other. (Of course, they are also isomers ) For example, glucose... 

D-galactose, methyl a- and 0-D-glucopyranosides, and a number of disaccharides, thus demonstrating that mass spectrometry is useful in the field of carbohydrate chemistry. In this study, the appearance potentials of CjHnOs ions were measured, and the results interpreted in terms of greater stability of the /9-(d or l) (equatorial) anomer with respect to the o-(d or l) (axial) one in the CA conformation. 

Calculations of the conformations and frequencies of various monosaccharides (a and /3 anomers of D-glucose, D-allose, D-galactose, and d-... 

Simulation of the mutarotation of arabinose closely followed the work on galactose, except that four components plus a central intermediate were included, and the / -pyranose was the starting anomer. The components were the a-pyranose (kt, k2), / -pyranose (k3, k4), a-furanose (k5, k6), and / -furanose (k7j kg). Table III shows sets of values for the k s which yield the experimentally observed half-times for the approach of the components to their equilibrium levels. 

The above, indirect, procedure for glycoside synthesis is the Koenigs-Knorr method. Glycosidation may be effected from monosaccharides directly by treatment with an alcohol in the presence of a mineral acid catalyst. For example, when a-D-galactose (13) is heated in methanolic solution containing 2 per cent of hydrogen chloride the thermodymanically more stable methyl a-D-galacto-pyranoside (14) (Expt 5.113) is formed preferentially, and may be isolated from the reaction product by crystallisation as the monohydrate. The less abundant /i-anomer may be recovered from the mother-liquors. 

---