合成路线1

A new enantioselective synthesis of neplanocin A has been reported: The enantiocontrolled condensation of the 6-chloropurine (I) with cis-1,3-bis(benzoyloxy)-4-cyclopentene (II) catalyzed by a chiral Pd catalyst gives the alkylated purine (III), which is condensed with the nitrosulfone (IV) by means of PPh3 and TEA yielding the intermediate (V). Epoxidation of (V) with MCPBA in dichloromethane affords the epoxide (VI), which is oxidized with O3 and DBU in methanol/THF giving the cyclopentenecarboxylate (VII). The esterification of the beta-OH group of (VII) with 4-nitrobenzoic acid (VIII), PPh3 and DEAD in THF, using a Mitsunobu reaction to invert the OH group, yields the ester (IX), with the desired alpha-OH configuration. The reduction of (IX) with DIBAL in THF/dichloromethane affords the unsaturated the diol (X), which is dihydroxylated with OsO4 and NMO in acetone/water providing the tetraol (XI). The reaction of (XI) with 2,2-dimethoxypropane and TsOH gives the diacetonide (XII), which is selectively monodeprotected with FeCl3 on silica gel yielding the dihydroxylated acetonide (XIII). The regioselective hydroxylation of the primary OH of (XIII) with pivaloyl chloride (Piv-Cl) in pyridine yields the pivalate (XIV), which is dehydrated with SOCl2 in DMF/pyridine affording the fully protected 6-chloropurine derivative (XV). Compound (XV) is treated with ammonia in order to eliminate the pivaloyl group and to form the adenine derivative (XVI), which is finally treated with hot aqueous HCl to eliminate the acetonide group.