Carbohydrate precursor

In plants phenol biosynthesis proceeds by building the aromatic ring from carbohydrate precursors that already contain the required hydroxyl group... 

Phenol biosynthesis in plants proceeds from carbohydrate precursors whereas the pathway in animals involves oxidation of aromatic rings... 

Structural drawings of carbohydrates of this type are called Haworth formulas, after the British chemist Sir Walter Norman Haworth (St Andrew s University and the University of Birmingham) Early m his career Haworth contributed to the discovery that carbohydrates exist as cyclic hemiacetals rather than m open chain forms Later he col laborated on an efficient synthesis of vitamin C from carbohydrate precursors This was the first chemical synthesis of a vitamin and provided an inexpensive route to its prepa ration on a commercial scale Haworth was a corecipient of the Nobel Prize for chem istry m 1937... 

Figure 11.4 Carbohydrate precursors to the carbon skeleton of mitomycin C.

A useful and simple method for the one-pot preparation of highly functionalized, enanhomerically pure cyclopentanes from readily accessible carbohydrate precursors has been designed by Chiara and coworkers [73]. The procedure depends on a samarium(II) iodide-promoted reductive dealkoxyhalogenahon of 6-desoxy-6-iodo-hexopyranosides such as 7-160 to produce a 6,e-unsaturated aldehyde which, after reductive cyclization, is trapped by an added electrophile to furnish the final product. In the presence of acetic anhydride, the four products 7-161 to 7-164 were obtained from 7-160. 

Most of the perfusion studies have been carried out on the isolated liver since it is in this organ that the change of fat to carbohydrate presumably takes place. On the basis of some of these studies, carbohydrate formation from fat has been postulated.161-166 In such cases more carbohydrate has been present at the end of the perfusion experiment than could be accounted for on the basis of known carbohydrate precursors. In several cases, a decrease in the fat content of the liver was accompanied by a concomitant increase in carbohydrate. However, Gregg166 has been... 

Precursors of phenylpropanoids are synthesized from two basic pathways the shikimic acid pathway and the malonic pathway (see Fig. 3.1). The shikimic acid pathway produces most plant phenolics, whereas the malonic pathway, which is an important source of phenolics in fungi and bacteria, is less significant in higher plants. The shikimate pathway converts simple carbohydrate precursors into the amino acids phenylalanine and tyrosine. The synthesis of an intermediate in this pathway, shikimic acid, is blocked by the broad-spectrum herbicide glyphosate (i.e., Roundup). Because animals do not possess this synthetic pathway, they have no way to synthesize the three aromatic amino acids (i.e., phenylalanine, tyrosine, and tryptophan), which are therefore essential nutrients in animal diets. 

Trihydroxyazepanes (trideoxy-l,6-iminohexitols) have also been prepared from carbohydrate precursors and activities as inhibitors of selected glycosidase enzymes assessed... 

Fig. 37 Example of synthesis of an imino sugars starting from an achiral non-carbohydrate precursor. Reagents and conditions (a) BnOCH2(2-thienyl)CuCnLi2, THF, —78 °C 10% HC1 (b) NaOMe, MeOH, reflux HC1, i-PrOH (c) n-BuLi, PhOCOCl, THF, -78 °C (d) Pb(OAc)4, toluene, reflux (e) HC1, EtOH (f) Me4NBH(OAc)3, acetone, AcOH (g) 0s04, NMO (h) Pd(OH)2, H2.

Among the approaches to C-1 glycals from cyclic carbohydrate precursors, those based on the formation of the C-1-C-1 bond on a glycal have been by far the more exploited. Other methods based on the formation of the anomeric C-C bond followed by the installation of the A1,2 unsaturation have also been described. 

Liebeskind and coworkers have examined the reactivity of (2//-pyran)Mo(CO)2Cp+ cations 210, which may be prepared in optically active form from carbohydrate precursors. Nucleophilic attack on cation 210 occurs at the diene terminus bonded to the ring oxygen to give jr-allyl complexes 51 (Scheme 53)85. Hydride abstraction from 51 gives the cation 54 addition of a second nucleophilie occurs regioselectively to give... 

Casu, F., Chiacchio, M.A., Romeo, R. and Gumina, G., Chiral synthesis of heterosubstituted nucleoside analogs from non-carbohydrate precursors. Curr. Org. Chem., 2007, 11, 1017-1032. 

Syntheses of each of the sugar residues in olivomycin A from commercially available carbohydrate precursors were known at the time our studies were initiated.30.3 We elected not to synthesize these compounds via literature procedures, however, since we felt that totally synthetic methods might provide a more convenient and general solution,... 

A. Amone, P. Bravo, A. Donadelli, and G. Resnati, Fluorinated analogues of nojirimycin and mannojirimycin from a non-carbohydrate precursor, Tetrahedron, 52 (1996) 131-142. 

Toward a screening program for RhuA stereoselectivity, structurally more simplified dioxane derivatives 25-27 comprising enantiomeric and diastereomeric 3-hydroxyaldehyde geometries in a conformationally defined environment could be prepared easily from carbohydrate precursors (Scheme 2.2.5.10). First results from product analysis provide further evidence for occasionally biased fixation of... 

Total synthesis of sugars from non-carbohydrate precursors forms a link, perhaps the most prominent one, between carbohydrate and general organic chemistry. Many such syntheses have been undertaken, more in order to demonstrate the maturity and potency of stereocon-trolled, organic synthesis than to elaborate an alternative access to... 

From among the variety of non-carbohydrate precursors, acetylenes and alkenes have found wide application as substrates for the synthesis of monosaccharides. Although introduction of more than three chiral centers having the desired, relative stereochemistry into acyclic compounds containing multiple bonds is usually difficult, the availability of such compounds, as well as the choice of methods accessible for their functionalization, make them convenient starting-substances for the synthesis. In this Section is given an outline of all of the synthetic methods that have been utilized for the conversion of acetylenic and olefinic precursors into carbohydrates. Only reactions leading from dialkenes to hexitols are omitted, as they have already been described in this Series.7... 

In a series of papers, Kent and coworkers reported on the synthesis of the racemic 2-fluorotetritols and 2-fluoropentitols, and related carbohydrates from simple, non-carbohydrate precursors containing a fluorine atom in the carbon chain. Thus, synthesis of 2-deoxy-2-fluoro-DL-erythritol (537) and its threo isomer (538) was accomplished303 by vigorous reduction of ethyl ethoxalylfluoroacetate (536) with lithium... 

Convergent construction directed toward the preparation of enantiomerically-pure targets depends on the availability of enantomerically-pure starting materials. There are many ways that these can be prepared. One way is from carbohydrate precursors, but this approach has been limited, in that L-sugars are much more expensive than D-sugars. Tzenge-Lien Shih of Tamkang University in Taipei describes (Tetrahedron Lett. 45 1789, 2004) the facile conversion of the inexpensive D-ribonolactone derivative 1 to the much more valuable L-ribonolactone derivative 3, by careful hydrolysis of the intermediate mesylate. The epoxide 2 is presumed to be an intermediate in this transformation. 

Kevin J. Quinn of the College of the Holy Cross chose (Organic Lett. 2005, 7, 1243) a complementary approach in his synthesis of rollicosin. The symmetrical diol 4 is also available from carbohydrate precursors. Monosilylation followed by esterification with acryloyl chloride gave 5. Exposure of 5 to the Grubbs catalyst in the presence of 6 led, by ring-closing metathesis and cross metathesis, to the y-lactonc 7. Note that 5-lactone formation did not compete ... 

Enyne metathesis can also be used with highly substituted substrates. Catherine Lievre of the Univcrsite de Picardie reports (J. Org. Chem. 2004,69, 3400) that enynes such as 11, readily prepared from carbohydrate precursors, are cyclized by the second generation Grubbs catalyst 2 to the enantiomerically-pure cyclic dienes, exemplified by 12. 

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