Methylation reactions of 6-methylthio-8-phenylpurines

Methylation of 6-methylthio-8-phenylpurines with methyl iodide in an aprotic solvent always yields a single product. The mother substance and its 7- and 9-methyl derivatives are substituted at N-3; the 1-methyl analogue is attacked at N-9 and the 3-methyl isomer at N-7. The most important difference between the 8-unsubstituted and 8-phenyl series is thus found in the case of the 9-methyl derivative; the structures of the 3,9-dimethyl compounds (XIX) and (XX) are established by n.m.r. and mass spectroscopic measurements. Similarly, 9-methyl-8-phenylhypoxanthine is converted into the corresponding 3,9-dimethyl derivative, in contrast to the behaviour of the non-phenylated compound.