General Papers ARKIVOC 2006 (x) 69-76 ISSN 1424-6376 Page 69 © ARKAT Isolation and in vitro antiamoebic activity of iridoids isolated from Kigelia pinnata Neelam Bharti* ,1,2 , Shailendra Singh 1,2 , Fehmida Naqvi, 2 and Amir Azam 2 1 Present address: Department of Medicinal Chemistry, College of Pharmacy, University of Florida, Gainesville, FL-32610, U.S.A. 2 Department of Chemistry, Jamia Millia Islamia, New Delhi-110025, INDIA E-mail: neelambh@ufl.edu Abstract Serial dilutions of extracts from the stem bark of Kigelia pinnata were tested for their growth inhibitory effects against Entamoeba histolytica. Butanol extract from Kigelia pinnata stem barks exhibited in vitro antiamoebic activity. Three known iridoids specioside, verminoside and minecoside were isolated, purified and identified by comparing their spectral data with the literature values. These compounds were tested against HK-9 strain of Entamoeba histolytica for their in vitro antiamoebic evaluation and metronidazole was used as reference drug in all the biological experiments. It is found that verminoside has two fold antiamoebic activity as compared to the standard drug while specioside showed comparable activity with metronidazole. Keywords: Natural product, Kigelia pinnata, iridoids, antiamoebic activity, Entamoeba histolytica Introduction Amoebiasis is an ubiquitous disease and fifty million cases of amoebic dysentery and liver abscess are reported each year around the world. 1 It is responsible for 100,000 deaths per year worldwide and is the second leading cause of death due to parasitic disease. 2 Nitroimidazole drugs such as metronidazole [1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole] are presently the most effective antiamoebic medications (Figure 1). The drug is known to have common side effects; 3 It is mutagenic in bacteria and high doses in rodents can cause carcinoma. 4 As a result of this and also taking into account the possibility of the development of resistant strains of the Entamoeba against metronidazole, a search for new effective amoebicidal agents is required in order to provide a new dimension in the therapy of amoebiasis. Medicinal plants are considered as an important source of potentially useful structures for the development of new chemotherapeutic agents. The first step towards this goal is the biological and phytochemical