The first synthesis of the N-glucosyl analogue of the antitumor agent etoposide

Recent progress on C-4-modified podophyllotoxin analogs as potent antitumor agents

Podophyllotoxin (PPT), as well as its congeners and derivatives, exhibits pronounced biological activities, especially antineoplastic effects. Its strong inhibitory effect on tumor cell growth led to the development of three of the most highly prescribed anticancer drugs in the world, etoposide, teniposide, and the water-soluble prodrug etoposide phosphate. Their clinical success as well as intriguing mechanism of action stimulated great interest in further modification of PPT for better antitumor activity. The C-4 position has been a major target for structural derivatization aimed at either producing more potent compounds or overcoming drug resistance. Accordingly, numerous PPT derivatives have been prepared via hemisynthesis and important structure-activity relationship (SAR) correlations have been identified. Several resulting compounds, including GL-331, TOP-53, and NK611, reached clinical trials. Some excellent reviews on the distribution, sources, applications, synthesis, and SAR of PPT have been published. This review focuses on a second generation of new etoposide-related drugs and provides detailed coverage of the current status and recent development of C-4-modified PPT analogs as anticancer clinical trial candidates.

Reaction of D-glycals with azidotrimethylsilane

The treatment of 2,3,4,6-tetra-O-acetyl-1,5-anhydro-D-arabino-hex-1-enitol with azidotrimethylsilane by the aid of a catalytic amount of Yb(OTf)(3) afforded 2,4,6-tri-O-acetyl-2,3-dideoxy-alpha-D-erythro-hex-2-enopyranosyl azide in high yield.

Synthesis and antitumor activity of new glycosides of epipodophyllotoxin, analogues of etoposide, and NK 611

A series of 3-amino- and 3-alkylamino-2-deoxy-beta-D-ribo- and beta-D-arabino-glycosides of 4'-demethylepipodophyllotoxin have been synthesized by means of an improved trimethylsilyliodide procedure for the podophyllotoxin-4'-demethylepipodophyllotoxin conversion, an efficient and high yielding synthesis of silyl glycoside donors of 3-azido-2,3-dideoxy-beta-D-ribo- and beta-D-arabino-hexopyranosides and stereoselective glycosylations. In vitro evaluation of cytotoxic effects against murine L1210 leukemia critically demonstrates the essential role played by a 4,6-acetal for biological activity. Among the most cytotoxic compounds, 3-amino-2,3-dideoxy- and 3-N, N-(dimethylamino)-2,3-dideoxy etoposide analogues, 17 and 27-29 are at least as potent as etoposide on the in vivo P388 (iv/ip) murine leukemia models. However, surprisingly enough, none of these compounds inhibits the human DNA topoisomerases I or II or binds to tubulin to prevent its polymerization and microtubule assembly. Therefore, their mechanism of action remains to be cleared up.

Discovery of podophyllotoxins

This review deals with the historical discovery of particularly important lignan derivatives used in cancer chemotherapy. From isolation of the naturally occurring podophyllotoxin, an inhibitor of microtubule assembly, to hemisynthesis of the clinically important anticancer drugs etoposide and teniposide, it will be demonstrated how the activities and the ability of this class of compounds to inhibit topoisomerase II were discovered by different research teams. By virtue of these discoveries, new hemisynthetic derivatives, with different mechanisms of action, are bringing improvements in the ability to treat cancer.

Synthesis and biological evaluation of carbon-substituted C-4 derivatives of podophyllotoxin

Several C-4 carbon-substituted analogues of podophyllotoxin, 1, were prepared by treatment of 1 with allyltrimethylsilane or trimethylsilylcyanide in the presence of boron trifluoride etherate. Alternatively, carbon substituents were introduced via additions to the carbobenzyloxy-protected C-4′-dimethylated podophyllotoxone. These 4′-dimethylated derivatives showed promising in vitro antitumour activity and were equally active against human colon cell line HT116 and two multidrug resistant cell lines. The alcohol 6 was evaluated in vivo but was found to be inactive. Key words: podophyllotoxin analogues, podophyllotox-4-one, C4 carbon substituted podophyllotoxins.