合成路线1

The intermediate iodopurine (IX) was prepared as follows. Acetylation of guanosine (I) afforded the triacetate ester (II). Subsequent chlorination of (II) to the 6-chloropurine (III) was accomplished by treatment with phosphoryl chloride and N,N-dimethylaniline. Diazotization of (III) with isoamyl nitrite in the presence of CuI furnished the 6-chloro-2-iodopurine (IV). Displacement of the 6-chloro group of (IV) in liquid ammonia with concomitant ammonolysis of the acetate esters gave rise to the 6-amino derivative (V). The dioxolane ketal (VI) was then formed by treatment of (V) with 2,2-dimethoxypropane in the presence of p-toluenesulfonic acid. After oxidation of the primary alcohol of (VI) with alkaline KMnO4 to give (VII), its ketal hydrolysis using 50% formic acid produced the carboxylic acid (VIII). The required N-ethyl amide (IX) was then obtained by esterification with SOCl2/EtOH, followed by treatment with liquid ethylamine.