Synthetic Higher Sugars

The heptoses prepared from n-allose and n-altrose are of recent origin and merit further attention. B-glycero-D-allo-Reptose (40) crystallized readily, and was identified when (a) the configuration at C-2 of the parent 

In a reapplication of the cyanohydrin synthesis to L-rhamnose, the crystalline T-deoxy-L-jfZj/cero-L-gfalacto-heptose was further characterized as the pentaacetates and methyl glycosides. The heptoses derived from D-galactose and n-mannose have been prepared by the nitromethane synthesis, and this can be the method of choice for sugars which are not preferred epimers in cyanohydrin synthesis. 

Two 3-heptuloses have been synthesized n-wianno-S-heptulose was prepared by degradation of a branched-chain octose, and a related 

The reduction of n- luco-heptulose (46) with sodium amalgam is of interest since it gave an alcohol, a-glucoheptulitol, which differed from both meso-glycero-gulo-hepi tol (47), and L-gflj/cero-L-zdo-heptitol (48), the 

In the past, few members of this group have been prepared, because the asymmetric nature of the cyanohydrin synthesis resulted in there being only a limited number of heptoses available as substrates. By use of the improved methods of synthesis described previously, many more higher-carbon sugars are now accessible. 

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Heptoses and higher sugars may similarly be separated, and the identity of D-erythro-c-galacto-nonulose in avocado was determined by comparison of its gas-chromatographic behavior with that of a synthetic sample.336 Higher sugars have been separated, and identified, from avocado,151 Pichi,337 opium poppy,338 and bacterial lipopoly-saccharides.339... 

In vivo, pyruvate lyases perform a catabolic function. The synthetically most interesting types are those involved in the degradation of sialic acids or the structurally related octulosonic acid KDO, which are higher sugars typically found in mammalian or bacterial glycoconjugates [62-64], respectively. Also, hexose or pentose catabolism may proceed via pyruvate cleavage from intermediate 2-keto-3-deoxy derivatives which result from dehydration of the corresponding aldonic acids. Since these aldol additions are freely reversible, the often unfavourable equilibrium constants require that reactions in the direction of synthesis have to be driven by an excess of one of the components, preferably pyruvate for economic reasons, in order to achieve a satisfactory conversion. 

The discovery of empirical rules of rotation of derivatives of the aldonic acids which indicated the configuration of the y-, and later the a-carbon atoms, made possible an advance in the solution of the problem of establishing the configurations of the synthetic higher-carbon sugars and the naturally-occurring rhamnose and fucose. The lactone rule was the earliest of these generalizations it was inferred from very extensive data. 

The higher-carbon sugars formed the subject matter of the first review to appear in this Series on that occasion, particular attention was devoted to the Fischer cyanohydrin synthesis which, until 1942, had been the only method available for preparing these sugars. Since that time, considerable advances have been made in the field of the higher sugars, notably in the development of new synthetic methods and in determination of the role played by heptoses, especially sedoheptulose, in natural systems. Moreover, the recently reported isolations of the first naturally occurring... 

The cyanohydrin synthesis should make it possible to go from the simplest members of the sugar series to all of the higher sugars. Synthetic... 

Commercial essence of vanilla is usually made with about 5 per cent, of vanillas, the menstruum varying in strength from 40 to 50 per cent, alcohol in the best varieties. Sugar is sometimes added, but not always. The average vanillin content is O l to 0 2. Much higher values than these indicate the presence of synthetic vanillin. 

Acetic acid is a weak carboxylic acid with a pungent odor that exists as a liquid at room temperature. It was probably the first acid to be produced in large quantities. The name acetic comes from acetum, which is the Latin word for sour and relates to the fact that acetic acid is responsible for the bitter taste of fermented juices. Acetic acid is produced naturally and synthetically in large quantities for industrial purposes. It forms when ubiquitous bacteria of the genera Acetobacter and Clostridium convert alcohols and sugars to acetic acid. Acetobacter, especially Acetobacter aceti, are more efficient acetic acid bacteria and produce much higher concentrations of acetic acid compared to Clostridium. 

Lactitol. Lactitol (4-0-/ -D-galactopyranosyl-D-sorbitol), is a synthetic sugar alcohol produced on reduction of lactose, usually using Raney nickel. It can be crystallized as a mono- or di-hydrate. Lactitol is not metabolized by higher animals it is relatively sweet and hence has potential as a non-nutritive sweetener. It is claimed that lactitol reduces the absorption of sucrose, blood and liver cholesterol levels and to be anticariogenic. It has applications in low-calorie foods (jams, marmalade, chocolate, baked goods) it is non-hygroscopic and can be used to coat moisture-sensitive foods, e.g. sweets. 

Crown ethers have given impressive enantioselectivites in Michael additions (Chart 10.2). Purely synthetic chiral crowns are of limited use on large scale based on cost although, in general, the crowns are less susceptible to catalyst degradation and, therefore, have higher catalyst turnover numbers than the chiral quaternary ammonium salts. Of interest are crowns with symmetry, aza-crowns, and those with sugars or other chiral-pool units as sources of chirality (Charts 2 and 4). 

Considering the results obtained in the test runs of synthetic solutions, the cofermentation of detoxified hydrolysates was carried out at flask scale using the same experimental conditions as described in Fig. 7 the results are presented in Fig. 8. The ethanol yields were slightly higher than those obtained working with synthetic solutions, but they were still comparable with respect to the composition of the sugar syrup used (0.39 ge/gs). It is likely that in the absence of furfural, the residual amount of acetic acid in the detoxified hydrolysate could have enhanced ethanol production (21,22). 

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