- Structure and synthesis of 6-(substituted-imidazol-1-yl)purines: Versatile substrates for regiospecific alkylation and glycosylation at N9
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X-ray crystal structures of several 6-(azolyl)purine base and nucleoside derivatives show essentially coplanar conformations of the purine and appended 6-(azolyl) rings. However, the planes of the purine and imidazole rings are twisted ~57° in a 2-chloro-6-(4,5-diphenylimidazol-1-yl)purine nucleoside, and a twist angle of ~61° was measured between the planes of the purine and pyrrole rings in the structure of a 6-(2,5-dimethylpyrrol-1-yl) purine nucleoside derivative. Shielding "above" N7 of the purine ring by a proximal C-H on the 6-azolyl moiety is apparent with the coplanar compounds, but this effect is diminished in those without coplanarity. Syntheses of 6-(azolyl)purines from both base and nucleoside starting materials are described. Treatment of 2,6-dichloropurine with imidazole gave 2-chloro-6-(imidazol-1-yl)purine. Modified Appel reactions at C6 of trityl-protected hypoxanthine and guanine derivatives followed by detritylation gave 6-(imidazol-1-yl)- and 2-amino-6-(imidazol-1-yl)purines. Imidazole was introduced at C6 of 2′,3′,5′-tri-O-acetylinosine by a modified Appel reaction, and solvolysis of the glycosyl linkage gave 6-(imidazol-1-yl)purine. Guanosine triacetate was transformed into the protected 2,6-dichloropurine nucleoside, which was subjected to SNAr displacement with imidazoles at C6 followed by glycosyl solvolysis to provide 2-chloro-6-(substituted-imidazol-1-yl)purines. Potential applications of these purine derivatives are outlined.
- Zhong, Minghong,Nowak, Ireneusz,Cannon, John F.,Robins, Morris J.
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p. 4216 - 4221
(2007/10/03)
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- METHODS FOR SELECTIVE N-9 GLYCOSYLATION OF PURINES
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A process for providing regiospecific and highly stereoselective synthesis of 9-β anomeric purine nucleoside analogs is described. The introduction of the sugar moiety on to 6-(azolyl)-substituted purine bases is performed so that highly stereoselective formation of the β anomers of only the 9 position regioisomers of the purine nucleoside analogs (either D or L enantiomers) is obtained. This regiospecific and stereoselective introduction of the sugar moiety allows the synthesis of nucleoside analogs, and in particular 2'-deoxy, 3'-deoxy, 2'-deoxy-2'-halo-arabino and 2',3'-dideoxy-2'-halo-threo purine nucleoside analogs, in high yields without formation of the 7-positional regioisomers. Processes for providing novel 6-(azolyl)purines for the regiospecific and highly stereoselective synthesis of 9-β anomeric purine nucleoside analogs are described. The compounds are drugs or intermediates to drugs.
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Page/Page column 54
(2010/11/25)
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