Lactose 0 anomer

Figure 12.13 Separation of lactose anomers on ODS Hypersil [2 x (250 x 4.6mm)] id. Mobile phase water. Flow rate l.Omlmin . Detection RI.

Melting Point and Optical Rotation of the Lactose Anomers... 

The solubility characteristics of the a- and /J-isomers are distinctly different. When a-lactose is added in excess to water at 20°C, about 7 g per 100 g water dissolve immediately. Some a-lactose mutarotates to the fS anomer to establish the equilibrium ratio 62.7/J 37.3a therefore, the solution becomes unsaturated with respect to a and more a-lactose dissolves. These two processes (mutarotation and solubilization of a-lactose) continue until two criteria are met 7g a-lactose in solution and a / /a ratio of 1.6 1.0. Since the /J/a ratio at equilibrium is about 1.6 at 20°C, the final solubility is 7 g + (1.6 x 7) g = 18.2 g per 100 g water. 

Likewise, octa-0-acetyl-/3-lactose in 16% methanolic ammonia45 afforded l,l-bis(acetamido)-l-deoxylactitol (47) and N-acetyl-a-lac-tosylamine (48). The anomer of the latter compound had previously been obtained by Kuhn and Kruger,46 either by reaction of ketene with... 

Anomers of Sucrose Although lactose exists in two anomeric forms, no anomeric forms of sucrose have been reported. Why ... 

In the disaccharide field intensity difference attributable to the configuration at the anomeric center had also been reported. Data presented by Kochetkov (55) indicated that such was the case with pertrimethyl-silylated a and /3, 1 - 4 and 1 - 6 glucosylglucoses. Vink et al. (56) concluded that the configuration at the anomeric center of the reducing unit was the most important factor influencing a set of ten peaks common to the spectra of pertrimethylsilylated a- and /3-lactose and / -cellobiose. Moreover, these workers used ratios of these ten peaks to distinguish a-lactose from its anomer. 

Four commonly occurring disaccharides. The configuration about the hemiacetal group has not been specified for lactose, maltose, or cellobiose because both anomers exist in equilibrium. 

Hereafter the anomeric center is protected. When the ceramide building block has to be connected to the oligosaccharide, normally selectively deprotection of the C-la position of the lactose is necessary. The thexyldimethylsilyl (TDS) group is a less common trialkylsilyl protecting group in carbohydrate synthesis. Advantageously it survives some rather harsh conditions. The liquid TDSC1 42 with imidazole 43 or DMAP as basic activator in a dipolar aprotic solvent like DMF forms the C-l protected compound 8 as a mixture of anomers.21... 

These compounds provide a rich variety of structural types and features. The two terpenoids possess the typical branched carbon skeletons of isoprenoids both compounds have diastereotopic methylene and methyl groups. Lactose is a /3-1,4-linked disaccharide of galactose and glucose glucose is the reducing residue, which at equilibrium in aqueous solution shows both anomers. The tetra-peptide, VGSE, contains four different amino... 

FIGURE 5.20 The H, 13C, and DEPT spectra of lactose. In solution, lactose is an equilibrium mixture of anomers. 

An even better scenario is to run a series of 1-D TOCSY experiments in which the mixing time is systematically increased while the proton being irradiated is kept constant. To illustrate these experiments, we irradiated the anomeric proton from the /3-anomer of the glucose ring in lactose at 4.67 ppm and run a series of experiments with mixing times ranging from 20 ms to 400 ms. The results of these experiments are shown in a series of stacked plots in Figure 5.26. 

The HMQC-TOCSY spectrum for lactose is given in Figure 5.28 with all of the proton and carbon resonances labeled. The overall appearance of this spectrum is reminiscent of an HMBC but the correlations are quite different. It is equally interesting and useful to start on the proton axis (F2) or the carbon axis (FI). If we start on the proton axis at 5.23 ppm, the anomeric proton for the a-anomer of glucose (ad), and proceed downward vertically, we find six correlations to the six carbons of this glucose residue. If we refer back to the simple HMQC spectrum for lactose, we find only one correlation for this proton. Likewise, the anomeric proton of the /3-anomer of glucose at 4.67 ppm also shows six correlations to the carbons of its respective glucose residue. 

The solubilities are determined experimentally by separation of the solution from the solid phase at various intervals of time and determination of the equilibrium rotation of the solution. Lowry pointed out that a number of earlier workers had noted that the solubility of D-glucose or lactose increases during mutarotation. The rate of change depends on the velocity constant of the forward action. The ratio of the initial and final solubilities for the a anomer is ... 

Like maltose, lactose also contains a hemiacetal, so it exists as a mixture of a and P anomers. The P anomer is drawn. Lactose undergoes mutarotation, and it reacts with oxidizing agents, making it a reducing sugar. 

The acetylation of lactose was examined in detail by Hudson and Johnson, with the conclusion that earlier products were mixtures of isomers. Using the acetic anhydride-sodium acetate method, they were able to obtain a 55% yield of octa-O-acetyl- -lactose which, on treatment with zinc chloride in acetic anhydride, was transformed into the a anomer. This... 

Many lactose esters, including those of long-chain fatty acids, have been prepared by using the respective acid anhydride in either alkali or pyridine, and the respective acid chloride in pyridine. A mixture of lactose and phenyl isocyanate in pyridine gives an octaphenylurethan derivative of lactose. The yellow a and anomers of lactose octakis-[p-(p-nitrophenylazo)benzoate] were prepared for chromatographic studies. ... 

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