Imidazole ring of purines

A biosynthetic relationship between purines and flavin had been initially conjectured on the basis of fermentation experiments where the addition of certain purine derivatives increased the yield of riboflavin produced by flavinogenic microorganisms. Ample confirmation for that hypothesis was obtained by isotope incorporation studies performed in parallel by various research groups using different microorganisms. Specifically, it was shown that the pyrimidine ring of purines can be contributed to biosynthetic riboflavin in its entirety, whereas C-8 of the imidazole ring of purine precursors is lost. The early work has been reviewed repeatedly and will not be discussed in detail. ... 

Fluorinated Purines and Benzimidazoles The importance of fluorinated purine and pyrimidine derivatives as antiviral and anticancer agents has increased the need for efficient methods for introduction of fluorine into these heterocyclic systems. This discussion will be confined to examples wherein the fluorine functionality is on the imidazole ring of purines and related compounds. A review of the substantial literature dealing with 2-fluoro-substituted purines, for example, will not be included. 

A well-known purine is the central nervous stimulant (CNS) caffeine (9.134), which is found in coffee and chocolate. Its synthesis (Scheme 9.77) illustrates the technique of forming the fused imidazole ring of purines. It was noted in Chapter 4 that diaminobenzenes reacted with carboxylic acids or esters to form benzimidazoles this process is known as the Phillips synthesis. It is this reaction that is used to fuse imidazoles to pyrimidines. Here, the process is known as the Traube purine synthesis. The initially formed purine is tri-methylated with methyl chloride and base to form caffeine (9.134). Note that under these conditions it is the 7-nitrogen that is methylated. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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