Glucose labeled, synthesis

The most convincing evidence that ascorbic acid can be synthesized from a hexose sugar in animals comes from the work of Jackel and his collaborators (1950). When D-glucose labeled uniformly in all positions with was supplied to rats which had been fed chloretone to stimulate the synthesis of the vitamin, L-ascorbic acid was excreted which was also labeled uniformly. This clearly indicates that n-glucose can serve as an ultimate precursor but does not exclude the possibility that the glucose may have to be converted to other sugars before being transformed. 

Even though acetate units, such as those obtained from fatty acid oxidation, cannot be used for net synthesis of carbohydrate in animals, labeled carbon from " C-labeled acetate can be found in newly synthesized glucose (for example, in liver glycogen) in animal tracer studies. Explain how this can be. Which carbons of glucose would you expect to be the first to be labeled by "Relabeled acetate ... 

Table V indicates the incorporation and distribution of labeled compounds into kasugamycin (1), when they are added during the production of this antibiotic. Glucose is incorporated into kasugamine and d-inositol. Mt/o-inositol is mainly incorporated into the d-inositol moiety, suggesting the synthesis of d-inositol moiety through myo-inositol or its derivative from glucose or other carbon sources.

Studies using labeled oxygen have shown that oxygen evolved during the reaction is a product of water oxidation and is not derived from carbon dioxide. The overall reaction of synthesis of glucose (C6H1206) can be written as [8,37,113,114]... 

For the synthesis of D-glucuronic acid, methods of oxidation of suitable D-glucose derivatives have been devised during the past two decades these procedures have been comprehensively reviewed by Marsh,6 Mehltretter,7 and Heyns and Paulsen.8 For special purposes, for example, for the preparation of 6-I4C-labelled D-glucuronic acid, chain-extension reactions of 1,2-O-isopropylidene-a-D-xy/o-pen-todialdo-I,4-fiiranose by the cyanohydrin synthesis9 or by ethynyla-tion10 are used, but these frequently yield mixtures of D-glucuronic acid and L-iduronic acid. 

Ideally, molecules should be labelled by introducing a radioactive isotope in place of a normal atom, e.g. carbon-14 replacing a carbon-12 in a carbohydrate. This method of labelling involves the synthesis of the molecule either in vivo or in vitro and the use of enzymes often permits the isotope to be introduced in a particular position in the molecule. The position of the labelled atom should be indicated wherever possible as for example in glucose- 1-14C. 

The synthesis of " C-labelled o-glucose starts with the pentose o-arabinose and " C-labelled potassium cyanide, which react together to form a cyanohydrin (see Section 7.6.1). Since cyanide can attack the planar carbonyl group from either side, the cyanohydrin product will be a mixture of two diastereoisomers that are epimeric at the new chiral centre. The two epimers are usually formed in unequal amounts because of a chiral influence from the rest of the arabinose structure during attack of the nucleophile. 

In fluorine-18 chemistry some enzymatic transformations of compounds already labelled with fluorine-18 have been reported the synthesis of 6-[ F] fluoro-L-DOPA from 4-[ F]catechol by jS-tyrosinase [241], the separation of racemic mixtures of p F]fluoroaromatic amino acids by L-amino acylase [242] and the preparation of the coenzyme uridine diphospho-2-deoxy-2-p F]fluoro-a-o-glucose from [ F]FDG-1-phosphate by UDP-glucose pyrophosphorylase [243]. In living nature compounds exhibiting a carbon-fluorine bond are very rare. 

C. Y. Shiue, K.C. To, A.P. Wolf, A rapid synthesis of 2-deoxy-2-fluoro-D-glucose from xenon difluoride suitable for labelling with 18F, J. Label. Compds Radiopharm. 

R.E. Ehrenkaufer, J.F. Potocki, D.M. Jewett, Simple synthesis of F-18-labeled 2-fluoro-2-deoxy-D-glucose, J. Nucl. Med. 25 (1984) 333-337. 

O. Prante, K. Hamacher, H.H. Coenen, Chemo-enzymatic n.c.a. synthesis of the coenzyme uridine diphospho-2-deoxy-2-[ F]fluoro-alpha-D-glucose, J. Label. Compds Radiopharm. 42 (1999) Sill. 

Human-leukemic antigen (HLA-DR) has been found in remarkably low proportions on the plasma membrane of human, lymphoblastoid cells. In the presence of tunicamycin, both subunits of this cell-surface antigen showed lower apparent molecular weights. One of them completely lost its [3H]-labelled 2-acetamido-2-deoxy-D-glucose portion, implying that HLA-DR antigens possess oligosaccharides whose synthesis is lipid carrier-dependent.555... 

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