Hemi-synthesis and Biological Activity of New Analogues of Podophyllotoxin

The syntheses of new derivatives 3 of podophyllotoxin 1 via the formation of 2 are reported. Various 4-analogues of podophyllotoxin and epipodophyllotoxin were obtained via the formation of the corresponding 4-keto derivatives. Methyloximation of podophyllotoxone, followed by subsequent catalytic hydrogenation, gave stereoselective access to 4-α-amino-4-deoxypodophyllotoxin and from there, to the corresponding acetamido and formamido derivatives. Base-catalyzed isomerisation of 4-α-amino-4-deoxypodophyllotoxin led to the corresponding picropodophyllin isomer while the 4-β-amino afforded a neopodophyllotoxin-like derivative. On the other hand, oxirane and hydroxymethyl-containing analogues were prepared from podophyllotoxin and 4- epi-4′-demethyl-podophyllotoxin, using a Takai olefination strategy. In the latter series, carboxaldehyde- and carboxylic acid-containing derivatives were also synthesized.