Podophyllotoxin has been extensively used as a lead agent in the development of new anticancer drugs. On the basis of the previously reported simplified 4-aza-2,3-didehydro podophyllotoxin analogues, we implemented a bioisosteric replacement of the methylenedioxybenzene subunit with a pyrazole moiety to afford tetracyclic dihydropyridopyrazoles. Libraries of these structurally simple analogues are prepared by a straightforward one-step multicomponent synthesis and demonstrated to display antiproliferative properties in a number of human cancer cell lines. These new heterocycles potently induce apoptosis in cancerous Jurkat cells even after a short 24 h exposure. In contrast, no apoptosis is detected in primary lymphocytes under the same treatment conditions. The ease of synthesis and encouraging biological activities make the presented library of dihydropyridopyrazoles promising new leads in anticancer drug design.

Pyrano[3,2-c]pyridone and pyrano[3,2-c]quinolone structural motifs are commonly found in alkaloids manifesting diverse biological activities. As part of a program aimed at structural simplification of bioactive natural products utilizing multicomponent synthetic processes, we developed compound libraries based on these privileged heterocyclic scaffolds. The selected library members display low nanomolar antiproliferative activity and induce apoptosis in human cancer cell lines. Mechanistic studies reveal that these compounds induce cell cycle arrest in the G2/M phase and block in vitro tubulin polymerization. Because of the successful clinical use of microtubule-targeting agents, these heterocyclic libraries are expected to provide promising new leads in anticancer drug design.

It has been 60 years since Eschenmoser and Frey disclosed the archetypal CC fragmentation reaction. New fragmentations and several variants of the original quickly followed. Many of these variations, which include the Beckmann, Grob, Wharton, Marshall, and Eschenmoser-Tanabe fragmentations, have been reviewed over the intervening years. A close examination of the origins of fragmentation has not been described. Recently, useful new methods have flourished, particularly fragmentations that give alkynes and allenes, and such reactions have been applied to a range of complex motifs and natural products. This Review traces the origins of fragmentation reactions and provides a summary of the methods, applications, and new insights of heterolytic CC fragmentation reactions advanced over the last 20 years.