Plants containing podophyllotoxin and its analogues have been used as folk medicines for centuries. The characteristic chemical structures and strong biological activities of this class of compounds attracted attention worldwide. Currently, more than ninety natural podophyllotoxins were isolated, and structure modifications of these molecules were performed to afford a variety of derivatives, which offered optimized anti-tumor activity. This review summarized up to date reports on natural occurring podophyllotoxins and their sources, structural modification and biological activities. Special attention was paid to both structural modification and optimized antitumor activity. It was noteworthy that etoposide, a derivative of podophyllotoxin, could prevent cytokine storm caused by the recent SARS-CoV-2 viral infection.

The asymmetric unit of the title compound, C7H6O5·0.25H2O, contains two mol­ecules of 2,3,4-trihy­droxy­benzoic acid, with similar conformations, and one water mol­ecule which lies on a twofold rotation axis. Both acid mol­ecules are essentially planar [maximum r.m.s deviations = 0.0324 (2) and 0.0542 (3) Å for the two acid molecules]. The mol­ecular conformations are stabilized by intra­molecular O(phenol)—H⋯O(carbox­yl/phenol) inter­actions. A cyclic inter­molecular association is formed between the two acid and one water mol­ecule [graph set R 3 3(12)] involving O—H⋯O hydrogen bonds. The two acid mol­ecules are further linked through a cyclic R 2 2(8) carb­oxy­lic acid hydrogen-bonding association, which together with inter­molecular O—H⋯O hydrogen-bonding inter­actions involving the phenol groups and the water mol­ecule, and weak π–π inter­actions [minimum ring centroid separation = 3.731 (3) Å], give a three-dimensional network.

The title compound, C19H21N3O, was isolated from the fruits of Evodia rutaecarpa. The indole and benzene rings are both essentially planar with mean derivations of 0.0094 (4) Å and 0.0077 (3) Å, respectively. The dihedral angle between these two planes is 78.24 (9)°. The amide carbonyl plane is roughly parallel to the indole ring with a dihedral angle of 7.0 (2)°, but makes a dihedral angle of 82.9 (3)° with the benzene ring. Inter­molecular N—H⋯O hydrogen-bonding inter­actions involving the amino and carbonyl groups give rise to a three-dimensional network.