Carbohydrates, resins from

It is clear from Equation (19.4) that saturated fat, not cholesterol, is the single most important factor that raises serum cholesterol. Some cases of hyperlipoproteinemia type IV (high VLDL) respond to low-carbohydrate diets, because the excess of VLDL comes from intestinal cells, where it is produced from dietary carbohydrate. Resins, such as cholestyramine and cholestipol, bind and cause the excretion of bile salts, forcing the organism to use more cholesterol. Lovastatin decreases endogenous cholesterol biosynthesis (see later), and niacin (nicotinic acid) apparently decreases the production of VLDL and, consequently, LDL. It also results in an HDL increase. Antioxidants that inhibit the conversion of LDL to oxidized LDL have also been used with some success. These are high doses of vitamin E and the drug probucol. 

Class of colloidal substances prepared from plants. Composed of complex carbohydrates and organic acids that swell in water. Also, a number of natural resins are gums. 

Choi and Won (1999) have reported a very u.seful strategy of recovering relatively nonvolatile lactic acid (e.g. from fermentation of carbohydrates) as volatile methyl lactate using a cationic ion-exchange resin as the catalyst. In another column reactor the methyl lactate is hydrolysed, using a cationic ion-exchange resin as the catalyst, to lactic acid and methanol, and the latter is recycled. 

Acetal handle 78 synthesized from Merrifield resin and 4-hydroxy-benzaldehyde was applied to the solid-phase synthesis of carbohydrates and 1-oxacephams (Scheme 41) [90]. For the latter, a 1,3-diol was initially anchored to the support to form a cyclic acetal. A ring opening reaction with DIBAL generated a resin-bound alcohol which was converted to the corresponding triflate for A-alkylation with 4-vinyl-oxyazetidin-2-one. A Lewis acid catalyzed ring closure released 1-oxa-cephams from the support. 

Heterogeneous catalysts, particularly zeolites, have been found suitable for performing transformations of biomass carbohydrates for the production of fine and specialty chemicals.123 From these catalytic routes, the hydrolysis of abundant biomass saccharides, such as cellulose or sucrose, is of particular interest. The latter disaccharide constitutes one of the main renewable raw materials employed for the production of biobased products, notably food additives and pharmaceuticals.124 Hydrolysis of sucrose leads to a 1 1 mixture of glucose and fructose, termed invert sugar and, depending on the reaction conditions, the subsequent formation of 5-hydroxymethylfurfural (HMF) as a by-product resulting from dehydration of fructose. HMF is a versatile intermediate used in industry, and can be derivatized to yield a number of polymerizable furanoid monomers. In particular, HMF has been used in the manufacture of special phenolic resins.125... 

Riley and Taylor [39] have studied the uptake of about 30 organics from seawater onto the resin at pH 2 - 9. At the 2 - 5 p,g/l level none of the carbohydrates, amino acids, proteins or phenols investigated were adsorbed in any detectable amounts. Various carboxylic acids, surfactants, insecticides, dyestuffs, and especially humic acids are adsorbed. The humic acids retained on the XAD-1 resin were fractionated by elution with water at pH 7, M aqueous ammonia, and 0.2 M potassium hydroxide. 

This loading approach is successful for the relatively unhindered 6-hydroxyl, but proved to be inefficient for more sterically encumbered alcohols. A modification of the abovementioned method has been developed to enable attachments through these more hindered sites.9 This process is accomplished with inexpensive materials, and the linker is compatible with a variety of reaction conditions. Moreover, it allows for facile recycling of the polymer support for further use once the final carbohydrate assemblage is cleaved from the resin. 

The detachment of the glycopeptide from the resin and deprotection of the amino acid side chains as well as the removal of the acid-labile carbohydrate protecting groups were simultaneously carried out using TFA/H20/thioanisole/ethanedithiol (87.5 5 5 2.5). This treatment proceeded without affecting the glycosidic bonds and furnished the target molecule 38. 

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