Content text 1. A BRIEF INTRODUCTION TO QUANTITATIVE STRUCTURE ACTIVITY RELATIONASHIP (QSAR).pdf
PHARMD GURU Page 1 QSAR: It is said to be a mathematical relationship in the form of an equation between the biological activity and measurable physiochemical parameters. QSAR attempts to identify and quantify the physicochemical properties of a drug and to see whether any of these properties has an effect on the drugs biological activity. Biological activity= function(parameters) Activity is expressed as log (1/c). Where C is the minimum concentration required to cause a defined biological response. PARAMETERS: The parameter is the measure of the potential contribution of its group to a particular property of the parent drug. Various parameters used in QSAR studies are: 1. Lipophilic parameters: partition coefficient, π-substitution constant 2. Polarizability parameters: molar refractivity, parachor 3. Electronic parameters: Hammet constant, dipole moment. 4. Steric parameters: Taft’s constant. 5. Miscellaneous parameters: molecular weight, geometric parameters. LIPOPHILIC PARAMETERS: Lipophilicity is one of the most studied physicochemical properties. Methods for lipophilicity have been in use for many years. An extensive set of published lipophilicity values for drugs and other compounds has been compiled by Hansch et al. Reliable and inexpensive in silico lipophilicity tools are commonly used in drug discovery. Partition coefficients (P): The partition coefficient is the measure of the lipophilicity of a drug and an indication of its ability to cross the cell membrane. It is defined as the ratio between unionized drugs distributed between the organic and aqueous layers at equilibrium. Drugs with high partition-coefficient value can easily permeate through biological membrane. The diffusion of drug molecules across rate- controlling membrane or through the matrix system essentially relies on the partition-coefficient. Drugs having lower partition-coefficient value are not suitable for translating in to oral controlled release formulations and drugs that have higher partition-coefficient are also A BRIEF INTRODUCTION TO QUANTITATIVE STRUCTURE ACTIVITY RELATIONASHIP (QSAR)
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