Structural requirements for the binding affinity of some small, non–peptide C5a receptor antagonists

Complement anaphylatoxin 5a (C5a) has been recognized as a potent therapeutic target for anti-inflammatory therapy, thus, blocking the action of C5a on its binding receptors may provide an effective treatment of a variety of inflammatory diseases. However, there have been few clinically available non-peptide C5a receptor antagonists disclosed at present. In pursuit of better anti-inflammatory drugs, quantitative structure–activity relationship studies were carried out in a series of non-peptide C5a receptor antagonists with binding activity using different physicochemical descriptors. The conventional best 2D-QSAR models were developed using a training set of 35 molecules and an external test set of 8 molecules by genetic function approximation (GFA) and stepwise multiple linear regression (Stepwise-MLR) with acceptable r^2^ of 0.773 and 0.863, r^2^~CV~ of 0.752 and 0.775, and r^2^~pred~ of 0.801 and 0.888, respectively, indicating binding activity strongly depends on thermodynamic properties as expressed by the hydrophobicity of molecules.