Sugars 2-deoxy-2-halo

The reaction has found little application so far however, one of the first examples of an asymmetric synthesis using peroxidases was the highly regio- and diastereo-selective halohydration of glycals to 2-deoxy-2-halo sugars in the presence of CPO [263]. Some examples of selective halogenation reactions of aromatic compounds using CPO optimized by directed evolution approaches are also known [264]. 

Epoxy sugars are frequently used as starting compounds in the synthesis of sugar derivatives (compare Section IV) such as halo, amino, azido, thio, deoxy, and branched-chain derivatives. The oxirane ring is in general more reactive than the oxetane or oxolane ring. It is opened with nucleophiles under base or acid catalysis. On the other hand, the oxirane ring remains unattacked under the conditions of catalytic debenzylation on palladium,... 

In 1970, 1 was prepared by direct glycosylation of the silylated 5-azacytosine with acylated 1-halo sugars, but the yields were very low.20 In this procedure, 1,3,5-tri-O-acetyl-2-deoxy-D-ribofuranose (9) was converted into 3,5-di-0-acetyl-2-deoxy-D-ribofuranosyl chloride (10).21 The trimethylsilyl derivative of 5-azacytosine (11),22 prepared from 4-amino-6-pyrimidine by treatment with hexamethyldisilazane, was then allowed to react with intermediate 10 in acetonitrile over 7 days to give a mixture of anomers of l-(3,5-di-(9-acetyl-2-deoxy-D-ribofuranosyl)-5-azacytosine (12) in 10% overall yield. The anomeric mixture was treated with ethanolic ammonia to remove the acetyl groups. The resulting a and p anomers were separated by a combination of fractional crystallization and preparative layer chromatography on silica gel to give pure decitabine (1) and its a-anomer 13 in 7% and 52% yield, respectively. 

In fully protected, primary halo sugars, some reagents, particularly silver fluoride, lead to elimination of the elements of the hydrogen halide, giving a most effective route to the 5,6-unsaturated sugars. Thus, 3,5,0-benzylidene-6-deoxy-6-iodo-l, 2-0-isopropylidene-a-n-glucofuranose gives... 

When the dihalogen adducts of acetylated, 1,2-unsaturated sugars are treated with moist silver carbonate, the halogen atom at C-1 is replaced by a hydroxyl group. Treatment of the resulting 2-deoxy-2-halo sugars... 

In the synthesis of 2 -deoxynucleoside, some control of the a p ratio can be gained by the use of 2-deoxy-3,5-di-0-(p-chlorobenzoyl or p-toluoyl)-a-D-erythro-pentofuranosyl chlorides and have found much utility in the synthesis of both pyrimidine and purine analogues. These a-halo sugar derivatives, which are obtained as crystalline materials give almost exclusively the P anomer due to a 8 2 type (inversion) reaction. Aoyama > has reported the condensation of 5-substituted uracil derivatives (H,CH3,F,Q,Br,I) with 2-deoxy-3,5-di-0-(p-chlorobenzoyl)-ribofuranosyl chloride (1) (Scheme 1). 

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