Quantitative Structure-Activity Relationship (QSAR) connects molecular structure and properties to biological activity through numerical descriptors and mathematical functions. A successful QSAR is both explanatory for known activity and predictive for unknowns, utilizing various physicochemical parameters such as partition coefficients and electronic properties. Key elements include steric effects, electronic characteristics, and molecular lipophilicity, relevant for understanding and optimizing molecular behaviors.

1. QSAR- simplified
M H Ghante
Asst prof
Dept of Pharmacy
GGV, Bilaspur

2. What is QSAR
• A QSAR relates a numerical description of molecular structure or
properties to known biological activity
• Activity = f (molecular descriptors)
• Success of QSAR: right descriptors + right method (form of f )
• A QSAR should be
• explanatory (for structures with activity data)
• predictive (for structures without activity data)
• A QSAR can be used to explain or optimise:
• localised properties of molecules such as binding properties
• whole molecule properties such as uptake and distribution

3. Physicochemical parameters used in quantitative structure activity
relationship (QSAR)- such as
•Partition coefficient,
•Hammet’s electronic parameter,
•Tafts steric parameter and
•Hansch analysis.

4. Main stereoelectronic properties used in CADD
Steric L (Substituent length)
B5 ( Substituent width)
MR (Molar refractivity)
Volume
Surface area
Electronic σ (Hammet constant)
F, R (Field and resonance parameters)
pKa (Ionization constants)
q (atomic charges)
MEP (Molecular Electrostatic Potential)…
Lipophilic π (Hansch constant)
f (Hydrophic fragmental constant)
LogP (partition coefficients)
Logkw (capacity factor values from RP-HPLC)
CLOGP (calculated log P values)
MLP (Molecular lipophilic potential)
H-bonding HA (number of H-bond acceptors)
HD (number of H-bond donors)
ΔlopP (oct-hex) (H-bond capability)…