Synthesis of nucleoside libraries on solid support. II. 2,6,8-Trisubstituted purine nucleosides using 8-bromoguanosine as precursor

Direct C-H arylation of purine on solid phase and its use for chemical libraries synthesis

C(8)-H direct arylation of purine derivatives immobilized on Wang resin is described. The purine skeleton was immobilized via C(6)-regioselective substitution of 2,6-dichloropurine with polymer-supported amines. After N(9)-alkylation with two different alkyl iodides and C(2) substitution with two selected amines, reaction conditions for C(8)-H arylation were developed and optimized. Various aryl bromides and aryl iodides were used for the reaction affording the target 2,6,8,9-tetrasubstituted purines in very good purity. The same reaction conditions were also applied for the synthesis of 2,6,8-trisubstituted purines, however, yields were lower. The methodology is applicable for high throughput synthesis of chemical libraries comprised of purine scaffold.

Solid-phase synthesis of 7-substituted 3H-imidazo[2,1-i]purines

A method for solid-supported synthesis of N,N-disubstituted (3H-imidazo[2,1-i]purin-7-yl)methyl amines has been developed. The key features of this library synthesis are: (i) immobilization of commercially available N6-benzoyl-5'-O-(4,4'-dimethoxytrityl)-2'-deoxyadenosine 3'-(2-cyanoethyl N,N-diisopropylphosphoramidite) by phosphitylation to a hydroxyl-functionalized support, (ii) quantitative conversion of the deprotected adenine base to 3H-imidazo[2,1-i]purine-7-carbaldehyde with bromomalonaldehyde in DMF in the presence of formic acid and 2,6-lutidine, (iii) reductive amination of the formyl group followed by N-alkylation or N-acylation, and (iv) release from the support by acidolytic cleavage of the N-glycosidic bond. Steps (ii) and (iii) have been optimized in some detail by using (adenin-9-yl)acetic acid anchored to a Phe-Wang resin as a model compound.