Synthesis of podophyllotoxin analogues:: δ-lactone-containing picropodophyllin, podophyllotoxin and 4′-demethyl-epipodophyllotoxin derivatives

Non-epimerizable cis and trans delta-lactone analogues of podophyllotoxin have been prepared. Thus the synthesis of the cis isomer 4 has been achieved in 8 steps and 4% overall yield from podophyllotoxin 1 via the reduction of the gamma lactone ring into the trans diol, selective protection of the 4-OH and 11-OH as a benzylidene acetal, and Wittig elongation at C-13 with inversion of configuration at C-2. Same elongation at C-13 but via the formation of a mesylate and introduction of a cyano group, led to the trans delta-lactone 5 (7 steps from 1 and 6% overall yied) with a small amount of its C-4 epimer 6. The synthesis of non-epimerizable delta-lactone analogues of 4'-demethyl-epipodophyllotoxin 7 and of 4-demethyl podophyllotoxin 8 are also reported. The synthesis of 7 and 8 was based upon the reduction of the gamma-lactone ring of 4'-demethyl-4-epipodophyllotoxin followed by selective protection at C-11 and elongation at C-13. (8-15% and 4% overall yields). Compounds 4, 5 and 7 did not display relevant cytotoxicity in vitro against L1210 murine leukemia. (C) 2004 Elsevier Ltd. All rights reserved.