Podophyllotoxin (I), isolated from the roots of Podophyllum emodi Wall var. chinensis sprague by extraction with ethanol and purified through repeated recrystallization from ethanol-benzene, is demethylated and brominated in a single step. (I) is suspended in a cold mixture of ethylene dichloride and ether. Anhydrous hydrogen bromide is passed until the calculated weight increase is reached. After standing at 0-2 C for 20 hours, the solvent is removed under reduced pressure. 4-Bromo-4-deoxy-4'-demethylepipodophyllotoxin (II) is recrystallized from acetone. A solution of (II) and 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl (III) with a trace of anhydrous pyridine in THF is refluxed under nitrogen atmosphere for 4 hours. The insoluble solid is removed by filtration and the solvent is distilled off under reduced pressure. The crude product is chromatographed twice through silica gel, using methylene chloride-acetone-diethylamine (40:1:1, by volume) as eluent. GP-7 is recrystallized from acetone-hexane.

Podophyllotoxin (I), isolated from the roots of Podophyllum emodi Wall var. chinensis sprague by extraction with ethanol and purified through repeated recrystallization from ethanol-benzene, is demethylated and brominated in a single step. (I) is suspended in a cold mixture of ethylene dichloride and ether. Anhydrous hydrogen bromide is passed until the calculated weight increase is reached. After standing at 0-2 C for 20 hours, the solvent is removed under reduced pressure. 4-Bromo-4-deoxy-4'-demethylepipodophyllotoxin (II) is recrystallized from acetone. A solution of (II) and 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl (III) with a trace of anhydrous pyridine in THF is refluxed under nitrogen atmosphere for 4 hours. The insoluble solid is removed by filtration and the solvent is distilled off under reduced pressure. The crude product is chromatographed twice through silica gel, using methylene chloride-acetone-diethylamine (40:1:1, by volume) as eluent. GP-7 is recrystallized from acetone-hexane.

Podophyllotoxin (I), isolated from the roots of Podophyllum emodi Wall var. chinensis sprague by extraction with ethanol and purified through repeated recrystallization from ethanol-benzene, is demethylated and brominated in a single step. (I) is suspended in a cold mixture of ethylene dichloride and ether. Anhydrous hydrogen bromide is passed until the calculated weight increase is reached. After standing at 0-2 C for 20 hours, the solvent is removed under reduced pressure. 4-Bromo-4-deoxy-4'-demethylepipodophyllotoxin (II) is recrystallized from acetone. A solution of (II) and 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl (III) with a trace of anhydrous pyridine in THF is refluxed under nitrogen atmosphere for 4 hours. The insoluble solid is removed by filtration and the solvent is distilled off under reduced pressure. The crude product is chromatographed twice through silica gel, using methylene chloride-acetone-diethylamine (40:1:1, by volume) as eluent. GP-7 is recrystallized from acetone-hexane.