Thymidine diphospho

Thymidine diphospho-6-deoxy-a-D-ribo-3-hexulose synthesized by D-glucose ozonolysis of methyl-glucophosphate is used as a central intermediate in the biosynthesis of di- and tridioxy sugars [90],... 

Many DOHs, such as L-daunosamine, L-epivancosamine or L-ristosamine, contain an amino group at C3, which is introduced by an aminotransferase. The substrate for this reaction is the 3-keto sugar intermediate that arises as a consequence of the action of a 2,3-dehydratase. This transaminahon reaction has been biochemically characterized in the biosynthesis of L-epivancosamine [10]. Using a coupled reaction with EvaB (2,3-dehydratase) and EvaC (aminotransferase), with pyridoxal-5-phosphate (PEP) as a coenzyme and L-glutamate as a cosubstrate, they were able to show conversion of TDP-4-keto-2,6-dideoxyglucose into thymidine-5 -diphospho-3-amino-2,3,6-trideoxy-D-threo-hexopyranos-4-ulose. 

Many DOHs, such as L-mycarose, L-epivancosamine, L-noviose or L-dauno-samine, show an L configuration. Formation of L-DOH requires the action of a 5- or 3,5-epimerase. The epimerase EvaD from the biosynthesis pathway of L-epivancosamine was shown to act as a 5-epimerase on the intermediate thymidine-5 -diphospho-3-amino-2,3,6-trideoxy-D-tIireo-hexopyranos-4-ulose [10]. On the... 

Uridine diphosphate galactose (109) was prepared using seven enzymes involved in three biosynthetic pathways, immobilised on super-bead columns. This method, which converted 50% of uracyl monophosphate into UDP-galactose (109), was superior to the solution approach as enzyme stability was improved. To study the biosynthesis of the pseudosaccaharide acarbose, thymidine 5 -diphospho-4-amino-4,6-dideoxy-a-D-glucopyranose(110) was synthesised from galactose in sixteen steps. 

On catalytic hydrogenation, diphosphothymidine gave diphospho-dihydrothymidine which is readily hydrolyzed by mineral acid to dihydrothymine and a reducing diphospho-sugar. Hence both phosphoryl groups are attached to the sugar component and, since thymidine is furanose, they must be situated at positions (3) and (5). 

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