Sugar synthesis, examples

Another example of the ability of proteinogenic amino acids, small peptides, and amines to catalyse the formation of new C-C bonds has been demonstrated by Weber and Pizzarello they were able to carry out model reactions for the stereospecific synthesis of sugars (tetroses) using homochiral L-dipeptides. The authors achieved a D-enantiomeric excess (ee) of more than 80% using L-Val-L-Val as the peptide catalyst in sugar synthesis (in particular D-erythrose) via self-condensation of glycol aldehyde. 

Michael additions to sugar nitro olefins have received considerable less attention than the Henry reaction involving nitro sugars. Early examples of Michael addition include the synthesis54 of licoricidin by Paulsen in 1982, the addition of phosphorous nucleophiles to a D-glucose based nitro olefin55 by Yamashita in 1987 and the synthesis of the natural antibiotic polyoxin published by Barret in 1990.56... 

J. K. N. Jones and his colleagues have extensively studied the reaction of sulfuryl chloride with carbohydrates.21-29 This work has elucidated the stereochemical principles involved in the various transformations, and has made available a convenient and effective procedure for the preparation of chlorodeoxy sugars. Several examples of the utility of such derivatives, obtained by way of a reaction with sulfuryl chloride, in the synthesis of other rare sugars are discussed in Section III (see p. 281). In the present Section, the studies on the reaction itself are surveyed. 

Although 2,5-anhydro sugars had, for a long time, been poorly understood, they have now found useful application as intermediates in synthesis, and even as derivatives for the characterization of certain amino sugars. For example, a useful method for the analytical deter-... 

Choline and ethanolamine are activated in much the same way as are sugars. For example, choline can be phosphorylated using ATP (Eq. 17-58, step a) and the phosphocholine formed can be further converted (Eq. 17-58, step b) to cytidine diphosphate choline. Phosphocholine is transferred from the latter onto a suitable acceptor to form the final product (Eq. 17-58, step c). Tire polymerization pattern differs from that for polysaccharide synthesis. When the sugar nucleotides react, the entire nucleoside diphosphate is eliminated (Eq. 17-56), but CDP-choline and CDP-ethanolamine react with elimination of CMP (Eq. 

B. A Radical Route to C-Branched. Aldehydo Sugars An Example in the Synthesis of a-C-Disaccharide... 

The rearrangement of allyl trichloroacetimidate into allyl trichloroacetamide (Overman rearrangement) has been used for the synthesis of amino sugars. For example, the trichloroace-... 

The most important compounds from this class are undoubtedly 3,6-anhydrofuranoses. Fura-nodictine A and B (produced by cellular slime mold Dictyostelium discoideum) showing neuronal differentiation activity [54] are good examples. These interesting derivatives may be conveniently obtained from the open-chain sugars. For example, synthesis of furanodictine A was realized from compound 85 obtained from D-arabinose in a few well-defined steps as shown inO Fig. 19 [55]. 

The carbocycles substituted at the double bond (with for example, an alkox)methylene group) can also be prepared from the appropriately functionalized unsaturated sugars. Synthesis of a-glucosidase inhibitor—valienamine—was realized from unsaturated sugar chirons as shown in Fig. 9 [86]. 

This type of intramolecular N-sulfinyl carbamate cycloaddition methodology has also been used in synthesis of some simple amino sugars. For example, a synthesis of epidesosamine has been developed as shown in Eq. (15). ... 

In recent years the discovery of novel methods of asymmetric synthesis has greatly increased the ability of organic chemists to synthesize optically active sugars. For example, the asymmetric epoxidation reaction discovered by Katsuki and Sharpless [142] was recently used as the key step in a synthesis of D-oleandrose 118 from divinyl carbinol 119 by Hatakeyama et al. [143]. An alternative approach to asymmetric synthesis of oleandrose was taken by Danishefsky et al. [144,32] in their synthesis of avermectin which is the first, and currently the only, reported total synthesis of an avermectin. The key step of this synthesis was a cyclocondensation reaction of optically active diene 121 with acetaldehyde catalyzed by the optically active Lewis acid (-h)-Eu(hfc)3 [145]. The resulting chiral pyrone was then elaborated to methyl-L-oleandroside 113. This was further converted to the disaccharide glycal 122 by a 4 step sequence in which glycoside formation was accomplished by iV-iodosuccinimide mediated addition of the alcohol to a glycal followed by tributyltin hydride... 

Other examples of deoxy-sugar synthesis can be found in Chapter 9. 

Higher alcohol production by yeasts appears to be linked not only to the catabolism of amino acids but also to their synthesis via the corresponding ketonic acids. These acids are derived from the metabolism of sugars. For example, propan-l-ol has no corresponding amino acid. It is derived from a-ketobutyrate which can be formed from pyruvate and acetyl coenzyme A. a-Ketoisocaproate is a precursor of isoamylic alcohol and an intermediary product in the synthesis of leucine. It too can be produced from a-acetolactate, which is derived from pyruvate. Most higher alcohols in wine can also be formed by the metabolism of glucose without the involvement of amino acids. 

As shown in Figure 45.1, the bases appear in complementary pairs, A with T and G with C in this particular example, the sequence for one strand of DNA is A-T-C-G-T- while the other strand is -T-A-G-C-A-. The sequences of the bases attached to the sugar-phosphate backbone direct the production of proteins from amino acids. Along each strand, groups of three bases, called codons, correspond to individual amino acids. For example, in Figure 45.1, the triplet CGT, acting as a codon, would correspond to the amino acid serine. One codon, TAG, indicates where synthesis should begin in the DNA strand, and other codons, such as ATT, indicate where synthesis should stop. 

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