Pak. J. Pharm. Sci., Vol.31, No.2, March 2018, pp.567-573 567 Pharmacophoric screening of newly synthesized isoniazid derivatives and their antimycobacterial activity Sabahat Naeem* 1 , Shamim Akhtar 2 , Zaheer Ali 3 , Muhammad Yahya Noori 3 and Ahsaan Ahmed 4 1 Department of Pharmaceutical Chemistry, Dow College of Pharmacy, Dow University of Health Sciences, Karachi, Pakistan 2 Department of Pharmaceutical Chemistry, Faculty of Pharmacy & Pharmaceutical Sciences, University of Karachi, Karachi, Pakistan 3 Provincial Tuberculosis Reference Laboratory, OJHA Institute of Chest Diseases, Dow University of Health Sciences, Karachi, Pakistan 4 Department of Pharmacy, Jinnah Sind Medical University, Karachi, Pakistan Abstract: Mycobacterium tuberculosis is clinically recognized as a causative agent of Tuberculosis. Keeping in view, this study was endeavored to screen our previously synthesized seventeen INH analogues for their antimycobacterial potential using proportion method. During this process, INH and all the seventeen compounds were examined at different concentrations of 0.05, 0.1 and 0.2µg/mL which were prepared using Lowenstein-Jensen (LJ) base. For drug susceptibility test, three Mycobacterial strains ATCC H37Rv, known INH-sensitive and INH-resistant strains were selected, sub-cultured on LJ Medium and serial diluted to achieve 1:10, 1:100, 1:1000 and 1:10000 from calibrated bacterial suspension Mcfarland No. 1. Dilutions of 1:100 and 1:10000 were added to drug free medium and 1:100 bacterial suspension was added to each of the test concentrations and finally incubated for 4-6 weeks at 37°C. It was observed that only compounds II and XI were active against MTb. Compounds III, IX and X also showed activity but were less potent. Ligand Scout 3.02[il_10] was used to perform pharmacophore-based screening where important pharmacophoric features were identified in the structures of these compounds which could be related to their observed antimycobacterial activity. Keywords: Pyridine-4-carbohydrazide, antitubercular activity, dilution method, pharmacophore mapping. INTRODUCTION Tuberculosis TB is one of the most ancient diseases and is still commonly found around the globe. It is caused by obligate aerobic acid fast bacilli called Mycobacterium tuberculosis Mtb, which grow very slowly and mostly cause pulmonary infections (Smith, 2003). In 1993, World Health Organization WHO declared TB as a global crisis. It is considered as a foremost reason of mortality after HIV & malaria, and an economic burden for developing countries. Re-emergence of this life-threatening disorder associated with the interface of AIDS/HIV also present an alarming situation. Another dilemma is the emergence of multi drug-resistant strains of TB. (Baker, 1994; Kremer and Besra, 2002). Despite these, no fresh antitubercular treatment came into the clinical site for the past decades. The researchers have been trying to develop new vaccines and drugs for complete eradication of this deadliest disease. For rational drug designing the study of pharmacophoric features in bioactive molecules might help and guide us in highlighting their important binding regions (Mason et al., 2001; Cavalli et al., 2002; Khedkar et al., 2007). Pharmacophore modeling is commonly employed where active ligand is known but target’s (receptor/protein) 3D structure is unclear. It is believed that agents with same structural domains bind to the target in the same way as the compounds for known biological activity. Determination of pharmacophoric features, their active conformations which are required to interact with the target and establishment of a 3D relationship are the components of pharmacophore mapping (Hou and Xu, 2004; Vyas et al., 2008) Various analogues of isoniazid were synthesized in the past with the aim to develop lead molecules for antitubercular drug discovery (Ferreira et al., 2008; Hearn et al., 2009; Sankar and Pandiarajan, 2010; Rodrigues et al., 2013; Rychtarčíková et al., 2014). Considering this, we have reported the synthesis of novel seventeen sulphonyl, benzoyl and phenacyl INH derivatives I-XVII (table 1) with antimicrobial activity (Naeem et al., 2015; Naeem et al., 2016). Here we have attempted to test the potential of these analogues against sensitive and resistant strains of mycobacterium. MATERIALS AND METHOD Dimethyl sulfoxide (DMSO), glycerol and LJ base were purchased from Musaji Adam & Sons, Karachi, Pakistan. Sterile Distilled Water was used to perform Serial dilution of the test compounds under Telsar AH-100 Laminar Flow. Inspissation was carried out in INSPI Max *Corresponding author: e-mail: sabahat.naeem30@gmail.com