Epibatidine( Cilazapril (10) Captopril(11) 1.6.Bioassay: Once a compound is synthesized or isolated,it needs to be screened for its biological activity.Screening is an attractive and key area towards the drug discovery programmes.28 It is crucial for successful isolation of bioactive compounds.Generally,bioassays are broadly classified into two types.They are mechanism based assays and cell based assays.29 1.6.1.Mechanism based assays: It involves the testing of a specific drug against a specific enzyme, DNA,receptor etc.As these assays are conducted in artificial environment which is different from physiological environment,it must be properly configured for accuracy.A properly handled assay can determine the activity of a compound even at lower concentrations.30 Though these assays are useful in determining the biological activity of the compounds,the disadvantage is that they approximate the in vivo environment due to incomplete system generated from the absence of certain pathways 1.6.2.Cell based assays It involves a drug-cell interaction with the complete intact cell rather than just isolated system and is by far more superior to the mechanism based assay.This method has the advantage of screeningCl N H N Epibatidine (9) N N HO NH O O O O Cilazapril (10) HS N O Captopr il (11) HOOC 1.6. Bioassay: Once a compound is synthesized or isolated, it needs to be screened for its biological activity. Screening is an attractive and key area towards the drug discovery programmes.28 It is crucial for successful isolation of bioactive compounds. Generally, bioassays are broadly classified into two types. They are mechanism based assays and cell based assays.29 1.6.1. Mechanism based assays: It involves the testing of a specific drug against a specific enzyme, DNA, receptor etc. As these assays are conducted in artificial environment which is different from physiological environment, it must be properly configured for accuracy. A properly handled assay can determine the activity of a compound even at lower concentrations.30 Though these assays are useful in determining the biological activity of the compounds, the disadvantage is that they approximate the in vivo environment due to incomplete system generated from the absence of certain pathways. 1.6.2. Cell based assays: It involves a drug-cell interaction with the complete intact cell rather than just isolated system and is by far more superior to the mechanism based assay. This method has the advantage of screening