An overview of lignans with special reference to podophyllotoxin, a cytotoxic lignan

Lignans are the natural products that are specifically made up of two hydroxycinmoyl alcohol units which are joined by C8 side chain. Lignans are originated from the same precursor as lignins but lignans are formed only by stereospecific coupling of monolignol unlike of lignins. It posses significant medicinal importance along with its age-old traditional uses, especially podophyllotoxin, for its cytotoxic and antiviral activity. Here we reviewed the basic structure of lignans and its variability along with history and the recent reconstruction of podophyllotoxin biosynthetic pathway from pluviatolide to (–)-4′-desmethylepipodophyllotoxin. To elucidate the monolignol trafficking towards lignan and lignin, we discuss the regulatory mechanism of this trafficking by streospecific coupling by dirigent protein. Furthermore the medicinal importance of various lignans, especially of podophyllotoxin and its glycosidic derivatives, are conferred here with their medicinal efficacy for the benefit of human kind.