合成路线1

N-Boc-L-(4-Pyridyl)alanine (I) is deprotected and esterified by means of a methanolic solution of SOCl2 to produce amino ester (II). Subsequent acylation of (II) with benzoyl chloride affords benzamide (III). Ester group reduction in (III) by means of NaBH4 yields alcohol (IV). The amide function of (IV) is then hydrolyzed under acidic conditions to furnish (S)-2-amino-3-(4-pyridyl)-1-propanol (V). Coupling of amino alcohol (V) with the known 6-(methylthio)purine (VI) in hot pyridine leads to adduct (VII). Intramolecular cyclization of the purine alcohol (VII) employing thionyl chloride produces the target tricyclic compound, which is finally isolated as the corresponding D-tartrate salt.