Monosaccharide reversion product

Fructose 1,6-biphosphate aldolase from rabbit muscle in nature reversibly catalyzes the addition of dihydroxyacetone phosphate (DHAP) to D-glyceraldehyde 3-phosphate. The tolerance of this DHAP-dependent enzyme towards various aldehyde acceptors made it a versatile tool in the synthesis of monosaccharides and sugar analogs [188], but also of alkaloids [189] and other natural products. For example, the enzyme-mediated aldol reaction of DHAP and an aldehyde is a key step in the total synthesis of the microbial elicitor (—)-syringolide 2 (Fig. 35a) [190]. 

Condensation of syn- or anti-27 with hydrazine afforded new pyrazole derivatives 28 with a stereodefined and protected amino diol side chain [64]. The preparation of push-pull substituted unsaturated monosaccharide derivatives and their use in the synthesis of nucleoside analogs have been reviewed [65]. Thus, the 2-formyl pentose glycals were transformed to the corresponding acyclo-C-nucleosides 29 [66]. Similarly, the benzy-lated 2-formylglycals reacted with hydrazine derivatives to afford the substituted l,2,4-tri-0-benzyl-lC-(lH-pyrazol-4-yl)-D-tetritols the deprotection of which was achieved with Pd/H2 to yield the lC-( 1-methyl-lH-pyrazol-4-yl)-D-tetritols [67]. 3-0-Benzyl-6-deoxy-l,2-0-isopropylidene-o -D-xylo-hept-5-ulofuranurono-nitrile was reacted with f, N-dimethylformamide dimethyl-acetal in THF to furnish the (E)-3-0-benzyl-6-deoxy-6-dimethyl-aminometh-ylene-l,2-0-isopropylidene-Q -D-xylo-hept-5-ulofuranurono-nitrile as a major product, and on treatment with carbon disulfide and methyl iodide under basic conditions afforded 3-0-benzyl-6-deoxy-l,2-0-isopropylidene-6-[bis(methylsulfanyl)methylene]-a-D-xylo-hept-5-ulofuranurono-nitrile. Further reaction with hydrazines yielded the reversed pyrazole-C-nucleoside analogs [68]. 

The byproducts, i.e., monosaccharide and disaccharides, formed during the reaction process are inhibitors for CD production. Removing these saccharides by ultra-filtration membrane system can significantly improve the yield of the CDs. Furthermore, the membrane can also prevent the loss of CGTase, which would make the reaction process continuous and efficient. An equipment of non-fixed ultra-filtration membrane combined with reverse osmosis membrane has been successfully developed for CD production [3]. In brief, at a low substrate concentration, the reaction solution was transferred to the ultra-filtration system during cyclization by CGTase, and the products were concentrated by the reverse osmosis membrane. 

This monosaccharide is transformed to the characteristic disaccharide as follows. It is first covalently united to a C55 isoprenoid alcohol in the plasma membrane, releasing uridine monophosphate (Higashi, Strominger and Sweeley, 1967). A molecule of A-acetylglucosamine is then incorporated, and five glycine residues are added to the lysine residue (this is done in the reverse direction to normal peptide synthesis, and without recourse to ribosomes). The product is usually referred to as the disaccharide decapeptide . 

Notes and discussion. This method describes the use of (3-A -acetylhexosaminidase from A. oryzae. A mixture of the (3-(l 4) (major) and (3-(l — 6) (minor) adducts plus reverse hydrolysis products are produced. However, incubation with -N-acetylhexosaminidase from Jack beans (Canavalia ensiformis) selectively hydrolyses the (3-(l — 6) product and the reverse hydrolysis products to yield the pure (3-(l — 4)-disaccharide. This method illustrates how the specificities and activities of different glycosidases can be combined to create the desired regioisomer. A full procedure for carbon-Celite chromatography of monosaccharides from disaccharides and higher oligomers is given [30]. 

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