Optical rotations Disaccharides

Sucrose, in contrast, is a disaccharide of almost universal appeal and tolerance. Produced by many higher plants and commonly known as table sugar, it is one of the products of photosynthesis and is composed of fructose and glucose. Sucrose has a specific optical rotation, of +66.5°, but an... 

Acid Hydrolysis. Lactose is resistant to acid hydrolysis compared to other disaccharides such as sucrose. In fact, organic acids, such as citric acid, that easily hydrolyze sucrose are unable to hydrolyze lactose under the same conditions. This is useful in analyzing a mixture of these two sugars, because the quantity of sucrose can be measured by the extent of these changes in the optical rotation of reducing power as a result of mild acid hydrolysis. The speed of hydrolysis of lactose varies with time, temperature, and concentration of the reactant, as shown in Table 6.8. 

There ensued an NBS-promoted glycosidation with the activated disaccharide 82 to deliver exclusively the P-anomer 102. This step and a subsequent Stille coupling involving dienylstaimane 104 proved particularly conducive to the delivery of 1, which exhibited a negative optical rotation of -34.5, a value closely comparable to that recorded for the natural marine toxin. 

Sucrose is a disaccharide that yields 1 equivalent of glucose and 1 equivalent of fructose on hydrolysis. This 1 1 mixture of glucose and fructose is often referred to as invert sugar because the sign of optical rotation changes (inverts) during the hydrolysis from sucrose (fain = +66.5°) to a glucose/fructose mixture ([[Pg.1077]

---