2. Podophyllotoxin aryltetralin lignan
Podophyllotoxin (PPT) (Fig.1A ), an aryltetralin lignan, found naturally in rhizomes and roots of many herbs such as Podophyllum peltatum, P. hexandrum, Linum album, L. narbonense, (Fig. 1B ) with supplies of PPT from natural sources possibly limited due to the endangered status of plants in the wild and/or environmental stresses due to overharvesting and environmental threats (Chaudhari et al., 2014: Chaurasia et al., 2012). This compound shows different biological activities, such as vigorous antimitotic and antiviral activities (Ayres and Loike, 1990; Gross, 2001). In addition to being important anticancer agent in its own right, it is also a starting material for the production of different semisynthetic derivatives such as teniposide, and etoposide which have huge commercial importance due to their potent effects in Hodgkin’s and non-Hodgkin’s lymphoma, testicular/small cell lung cancers and acute leukemia (Gordaliza et al., 2004; Malik et al., 2014). The main mode of action of PPT is via inhibition of Topo II, thereby arresting the cell cycle at the G2 phase and causing DNA breakage and apoptosis via inhibition of protein tyrosine kinase (Dholwani et al., 2008). The organic synthesis of this compound is difficult due to the complicated chemical structure involving high-cost procedures (Satake et al., 2013; Umezawa, 2003).