ABSTRACT
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. The ‘backbone’ of the chain is thus composed of alternating phosphates and sugars, to which purine and pyrimidine bases are attached at regular intervals. Adenine gives mainly 3-alkylated products under neutral conditions but 7/9-substitution when there is a base present. Adenosine derivatives on the other hand usually give 1-alkylated products, presumably due to hindrance to N-3-attack by the peri 9-ribose substituent. The reactions of the 2-, 6- and 8-halopurines are very important in purine synthesis. Halo-purines can be prepared from oxy-, amino- or thiopurines and the 8-isomers are also available by direct halogenation or via lithiated intermediates. Iodo- and bromopurines undergo the usual palladium-40 and nickel-catalysed reactions under standard conditions.
