Purines Reactions and Synthesis

Purines are of great interest for several reasons, but in particular, together with certain pyrimidine bases, they are constituents of DNA and RNA, and consequently of fundamental importance in life processes (see 

Additionally, as nucleosides and nucleotides they act as hormones and nenrotransmitters and are present in some co-enzymes. The interconversion of mono-, di- and triphosphate esters of nncleosides is at the heart of energy transfer in many metabolic systems and is also involved in intraceUnlar signalling. This central biological importance, together with medicinal chemists search for anti-tnmonr and anti-viral (particularly anti-AIDS) agents, have resulted in a rapid expansion of purine chemistry (33.6.3). 

There are significant lessons to be learnt from the chemistry of purines since their reactions exemplify the interplay of its constituent imidazole and pyrimidine rings, just as the properties of indole show modified pyrrole and modified benzene chemistry. Thus purines can undergo both electrophilic and nucleophilic attack at carbon in the live-membered ring and mainly nucleophilic reactions at carbon in the six-membered ring. 

The numbering of the purine ring system is anomolous and reads as if purine were a pyrimidine derivative. There are, in principle, four possible tautomers of purine containing an A-hydrogen in the crystalline state, purine exists as the 7//-tautomer, however in solution both IH- and 9A-tautomers are present in approximately equal proportions the IH- and 3//-tautomers are not significant.  

Heterocyclic Chemistry 5th Edition John Joule and Keith Mills 2010 Blackwell F iblishing Ltd 

Caffeine (1,3,7-trimethylxanthine) is the well known stimulant present in tea and coffee. In mammals the end product of metabolic breakdown of nucleic acids is urea, but in birds and reptiles it is uric acid uric acid was one of the first heterocyclic compounds to be isolated as a pure substance, for it was obtained from gallstones by Scheele in 1776. 

6-Mercaptopurine is used in the treatment of leukemia and other cancers. Acyclovir is an antiviral agent used in the treatment of Herpes infections, and DDI is used in the treatment of AIDS. 

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