Synthesis of 4-amido and 4-sulphonamido Analogues of Podophyllotoxin as Potential Antitumour Agents Ahmed Kamal, a, * B. Ashwini Kumar, a M. Arifuddin a and Sunanda G. Dastidar b a Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad-500007, India b Ranbaxy Research Laboratories, Gurgaon-122001, Haryana, India Received 9 May 2003; accepted 18 August 2003 Abstract—The new 4b-amido analogues of podophyllotoxin or 4 0 -O-demethylepipodophyllotoxin have been prepared either by the coupling of 4b-amino podophyllotoxin or 4b-amino-4 0 -O-demethyl epipodophyllotoxin with the corresponding acids in presence of DCC in dichloromethane or by treating the appropriate acid chloride or sulphonyl chloride in presence of Et 3 N. These 4b-amido and 4b-sulphonamido derivatives of podophyllotoxin have been evaluated for their cytotoxicity against six human cancer cell lines. Some of these analogues have shown promising anticancer activity. # 2003 Elsevier Ltd. All rights reserved. Introduction Podophyllotoxin (1) and desoxypodophylltoxin (2) are two well known naturally occurring aryltetralin lignans and the former is the major constituent of a number of plant species of the podophyllum family. 1,2 Both these compounds are cytotoxic and their derivatives are in use as antitumour agents, for example etoposide 3,4 (3) and teniposide 5 (4). Etoposide is the most widely used anti- cancer agent for the treatment of leukemia, testicular cancer and small cell lung cancer. Its clinical efficancy is due to its ability to inhibit the enzyme DNA–topo- isomerase II. These podophyllotoxin lignans block the catalytic activity of DNA–toposiomerase II by stabiliz- ing a cleavable enzyme DNA–complex in which the DNA is cleaved and covalently linked to enzyme. 6 This lead has stimulated a renewed interest in the chemical and biochemical studies of podophyllotoxin derived antitumour agents. 7 The replacement of the C-4 sugar moiety of etoposide (VP-16) with a nonsugar substitu- tion has proven to be significant in overcoming the drug resistance of etoposide. 8 The C-4 non-sugar substitu- tions can be linked through O-, S- or N-linkage. In general, the O-linked derivatives (ethers, esters) and the S-linked derivatives (thioethers) are inactive or show lower activity in comparison to the N-linked congeners, 9 11 for example NPF (5a) and GL-331 (5b). Presently, GL-331 is undergoing phase II clinical trials against gastric carcinoma, colon cancer, non-small cell carcinoma, and etoposide-resistant malignancies. 12 It has also been indicated in the literature that bulky sub- stitution at the C4 position usually enhances the cyto- toxicity and DNA topoisomerase II inhibition activity. 11b,c It is observed that, amongst the C4-N-sub- stituted congeners of podophyllotoxin that have been synthesized and developed, C4b-N-amidopodophyllo- toxin derivatives have received less attention. Further, some of these compounds have shown improved biological activity in comparison to etoposide. Recently, C4b-amido analogue 13 has been synthesized and evaluated for its biological activity. This compound (6) exhibits superior anticancer activity compared to etoposide against some of the human cancer cell lines. In earlier studies a series of 4b-amido aryl substituted podophylltoxin derivatives (7) 14 have been prepared and evaluated for their biological activity. It is observed from the results that some of these compounds exhibit enhanced DNA–topoisomerase II inhibition in com- parison to etoposide. In view of the available informa- tion on structure–activity relationship studies and in continuation of our ongoing project on the design and development of structurally modified podophyllotoxin congeners, 15 it was considered of interest to prepare C4b-amido and sulphonamido analogues of epipodo- phylltoxin and 4 0 -O-demethyl epipodophyllotoxin. 16 0968-0896/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmc.2003.08.019 Bioorganic & Medicinal Chemistry 11 (2003) 5135–5142 *Corresponding author. Tel.: +91-40-2719-3157; fax: +91-40-2719- 3189; e-mail: ahmedkamal@iict.ap.nic.in