Examples of Notable Syntheses Involving Purines

A synthesis of the antibiotic aristeromycin makes use of the displacement of a pyrimidine 4-chloride to allow introduction of the amine and the generation of the 4,5-diamino-pyrimidine for subsequent closure of the flve-membered ring. 

Adenosine has also been synthesised using the pyrimidine purine strategy. In this synthesis the sugar was also introduced at an early stage, but here via condensation with a 4-amino group. 

A synthesis of sildenafil, which contains a bicyclic system (a l//-pyrazolo[4,3- f pyrimidine) isomeric with that of a purine, starts with a routine synthesis of a pyrazole (cf. 25.12.1.1) followed by M-methylation and ring nitration. Functional group manipulation provides a pyrazole equivalent to AICA (27.11.1.2) from which the pyrimidone ring is formed via reaction with an aromatic acid chloride. 

How does the inclusion of a tertiary amine in such nucleophilic displacements facilitate them  

Suggest a sequence for the transformation of adenosine into 8-phenyladenosine. 

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Examples of notable syntheses involving purines 24.13.2.1 Aristeromycin... 

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