合成路线1

Addition of ethyl diazoacetate (II) to 2,3-dibromopropene (I) in the presence of dirhodium tetraacetate furnished ethyl 2-bromo-2-(bromomethyl)cyclopropane-1-carboxylate (III) as a mixture of cis- and trans-isomers. Subsequent condensation of the dibromo ester (III) with the sodium salt of adenine (IV) produced adduct (V) as a diastereomeric mixture. Then, elimination of HBr using potassium tert-butoxide gave olefin (VIa-b). Alternatively, a direct synthesis of (VIa-b) was carried out by reaction of adenine (IV) with dibromo ester (III) in the presence of K2CO3 in hot DMF. Reduction of ester (VIa-b) with diisobutylaluminum hydride afforded alcohol (VIIa-b) as a mixture of syn- and anti-isomers. Isolation of the desired syn-isomer (VIII) was achieved by conversion to the corresponding formamidines, followed by chromatographic separation. The formamidine function of (VIII) was then hydrolyzed with methanolic ammonia to yield the racemic synadenol (IX). Incubation of (IX) with adenosine deaminase converted the (S)-enantiomer to the hypoxanthine derivative (XI), which was separated from the unreacted (R)-synadenol (X) by column chromatography. Acetylation of alcohol (XI) with Ac2O in pyridine provided ester (XII). Chloropurine derivative (XIV) was then obtained by treatment of (XII) with N,N-dimethylamino(chloromethylene)ammonium chloride (XIII) in CHCl3. Finally, chloride displacement in (XIV) and simultaneous ester cleavage with methanolic ammonia in a pressure vessel gave rise to the title compound.