Podophyllotoxin derivatives: a patent review (2012 - 2014). 
Podophyllotoxin (PPT) is a naturally occurring antimitotic agent and an interesting lead in the development of anticancer agents.  Its optimization led to the development of etoposide and teniposide used in combination chemotherapy with other anticancer drugs; unlike PPT these drugs act by inhibiting topoisomerases.  Clinical success and toxicity issues at later stages of etoposide usage inclined researchers to develop structurally modified PPT derivatives.  Some of the compounds obtained are under clinical investigations and are anticipated to reach the market.  The present review summarizes the attempts made by researchers across the globe to find out newer anticancer agents based on the PPT structure.  It brings out the outline of the inventions filed in the form of patents during the years 2012 - 2014.  After the successful development of etoposide and teniposide there has been considerable interest in the PPT skeleton to develop newer chemotherapeutic agents.  In this regard, several PPT derivatives such as TOP53, GL331, NK611, F11782, and so on, have been developed and are undergoing clinical trials.  However, its low natural abundance is a major problem in carrying out research on PPT skeleton.  This issue is expected to be addressed with the development of newer synthetic strategies to access structurally modified PPTs.