合成路线1

The reaction of (-)-5-O-benzyl-2,3-O-isopropylidene-D-ribolactonle (I) with lithium dimethylmethylphosphonate in THF gives the hemiketal (II) in quantitative yield. Benzoylation of (II) with benzoyl chloride in pyridine leads to the acyclic dibenzoate (III), which is debenzoylated with methanolic sodium methoxide to afford the beta-ketophosphonate (IV). Oxidation of (IV) with the modified Collins' reagent (CrO3 - 2Py) in dichloromethane gives diketophosphonate (V). The reaction of (V) with powdered anhydrous potassium carbonate and 18-crown-6-ether in benzene under high dilution gives the 2-cyclopentenone (VI) (50% yield). Reduction of (VI) with sodium borohydride in a 0.4-M CeCl3 - 7H2O- methanol solution affords the allylic alcohol (VII) (85% yield), which is mesylated to give (VIII). The mesyl group on (VIII) is displaced by lithium azide to give the beta-azide (IX) (84% yield). Reduction of (IX) with 1,3-propanedithiol and triethylamine in absolute methanol gives the 2-cyclopentenylamine (X) (85% yield). Condensation of (X) with 5-amino-4,6-dichloropyrimidine in the presence of triethylamine (n-BuOH, reflux, 45 h) gives (XI) (52% yield). Ring closure with triethyl orthoformate and Ac2O or HCl gives (XII), which is treated with methanolic ammonia to afford (XIII) (overall yield 58%). Debenzylation of (XIII) with boron trichloride in dichloromethane leads to removal of the isopropylidene group (61% yield). Another method to obtain neplanocin A is also available, in which an enantioselective synthesis of neplanocin A is performed by a chemoenzymatic approach starting from the Diels-Alder adduct of cyclopentadiene and dimethyl acetylene-dicarboxylate.