合成路线1

The reaction of benzyl alpha-D-mannopyranoside (I) with Tbdms-Cl and imidazole gives the silyl ether (II), which is treated with 2,2-dimethoxypropane (III) and CSA in dichloromethane to yield the acetonide (IV). The oxidation of the free OH group of (IV) with PCC in dichloromethane affords the ketone (V), which is reduced with NaBH4 to provide benzyl 6-O-(tert-butyldimethylsilyl)-2,3-O-isopropylidene-alpha-D-talopyranoside (VI) with inverted configuration at C4. The reaction of (VI) with Tf2O and pyridine gives the triflate (VII), which is treated with NaN3 in DMF to yield the 4-azido derivative (VIII) with a new inversion of configuration at C4. The reaction of (VIII) with TBAF, followed by oxidation with PCC afforded the carbaldehyde (IX), which is condensed with the phosphorane (X) to provide the unsaturated azidoaldehyde (XI). The treatment of (XI) with H2 over Pd/C in methanol produces the reduction of the double bond, the reduction of the azide group to amine, and subsequent reductive cyclization of the resulting aminoaldehyde to give the perhydropyranopyridine derivative (XII). Further reductive debenzylation of (XII) with H2 over Pd/C in AcOH produces the formation of a lactol in equilibrium with the open chain aminoaldehyde (XIII), which undergoes a reductive amination to form the acetonide of swainsonine (XIV). Finally, this acetonide is decomposed by reaction with TFA to afford the target swainsonine.