Derivatives, sucrose, isomers

In addition to saccharose, numerous other disaccharides and higher oHgosaccharides derived from glucose and fructose are present in foods as natural components. An overview of relatively commonly occurring oligosaccharides is shown in Table 4.14. Turanose, maltulose (4-108) and isomaltulose (4-116) are examples of reducing disaccharides (sucrose isomers). 

Sucrose Ethers. Being next to the anomeric center and intramolecularly hydrogen-bonded, the 2 -OH of sucrose is the most acidic, which means it is deprotonated first under alkaline conditions, and thus preferentially yields to etherification. Benzylation with NaH/benzylbromide in DMF, for example, results in an 11 2 1 mixture of 2 -(9-benzyl-sucrose (Figure 2.8) and its 1-0- and 3 -0-isomers. Because the former is readily accessible, it proved to be a versatile intermediate for the generation of 2 -modified sucroses, for example, the 2 -keto and 2 -deoxy derivatives as well as sucrosamine (2 -amino-2 -deoxy-sucrose), whose application profiles remain to be investigated. 

Of the three jnonochlorophenoxyacetic acids, only the 4-chloro derivative is very active and is used to retard abscission of fruit. A study of the effects of the isomers on the carbohydrates of the bean plant showed that the alterations of the carbohydrates were not related to the growth-inhibiting mechanism.12 Reducing substances, starch, and sucrose decreased with all treatments, And the 2-chloro compound had the least effect polysacchar rides other than starch were not much altered. 

The polymerization of sucrose derivatives (esters, ethers, acetals) bearing a carbon-carbon double bond has been studied (Scheme 45). Polymers can be obtained by polymerization or copolymerization.146,404 414 The monomers are prepared either by multistep synthesis, leading to defined compounds and subsequently rather well-controlled polymerization processes,302,415,416 or by direct functionalization of unprotected sucrose, leading to mixtures of isomers and... 

Aspartame. Aspartame is a high-intensity sweetener (200-fold that of sucrose) consisting of L-aspartyl-L-phenylalanine methyl ester (L-Asp-L-Phe-OMe). Around 10,000 tons are produced per annum, most by a chemical process owned by Nutrasweet Corp. Holland Sweetener Company (a DSM/Tosoh joint venture) uses the protease thermolysin (E.C. 3.4.24.27) to synthesize aspartame from a chemically protected L-aspartic acid derivative (Z-L-Asp) and racemic phenylalanine methyl ester (DL-Phe-OMe). The enzyme only accepts L-phenylalanine-OMe and the unused D-isomer can be isolated, racemized, and recycled. This process is depicted in Figure 31.20. 

The kestose or fructan series of sucrose-related oligosaccharides is found in at least 12% of vascular plant species [23]. Kestoses contain one glucose moiety per oligosaccharide chain, derived from the parent sucrose molecule by the action of fmctosyltransferases. The simplest kestose, monofructosyl-sucrose is a trisaccharide that exists as three isomers 1-kestose (l - 8-D-fructofuranosylsucrose), 6-kestose (6 - -D-fructofuranosylsucrose), and neo-kestose (6 - -D-fructofuranosylsucrose). These isomers form the basis of three major kestose subseries with different linkage patterns [23]. 

The enzymatic conversion of 6-azido-6-deoxy-D-glucose into its D-fructose isomer was utilised as a key step in a five-step synthesis from sucrose [80] of the natural product and powerful D-mannosidase inhibitor 1-deoxymannojirimycin (l,5-dideoxy-l,5-imino-D-mannitol, 66) [81]. Subsequently, it was shown that the immobilised enzyme from Streptomyces murinus sp. (Sweetzyme T from Novo A/S) was able to isomerise D-glucose derivatives with modifications at C-3 and C-6 such as 6-azido-6-deoxy-3-0-methyl-D-glucose (67) as well as the corresponding 3-deoxy derivative 69 (Scheme 24) [64,82]. 

Trimethylsilylation -g.c.-m.s. has been used for the determination of isosorbide-5-mononitrate (in which both the hydroxy- and nitro-functions are silylated) in human serum, modified nucleosides in human urine and zeatin and its riboside in plant tissues after separation by solid-phase extraction and h.p.l.c. fractionation. The g.c. analyses of sucrose pertrimethylsilylated monostearate isomers and homologues with different ac l chains have been investigated on packed columns. For the g.c.-m.s. of amino-containing nucleosides, the use of -dimethylaminomethylene-O-trimethylsilyl derivatives [as in compoimd (1)] has been advocated. The derivatives are formed by reaction with DMF dimethyl acetal follwed by silylation. ... 

The chlorosulfonation of toluene by treatment with excess chlorosulfonic acid yields a mixture of the ortho and para sulfonyl chlorides, but the mixture may be separated by freezing out the solid p-isomer (see Chapter 4, p 37). Saccharin 25 contains an acidic hydrogen atom and is generally formulated as the sodium salt to increase water solubility. It is some 300 times sweeter than sucrose and is non-calorific so can be used by diabetics as a sugar substitute. A number of saccharin derivatives have been synthesized as potential sweetening agents (Chapter 6, ref. 33). 

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