Y.. Zhou et al. European Journal of Medicinal Chemistry 42(2007)977-98 To assess the predictive power of the 3D-QSAR models between the actual and the predicted activities of the test derived using training set, biological activities of the test set molecules. In addition, the r2y, Ired and number of compo- molecules were predicted. The predictive r(red) value is cal- nents, the conventional correlation coefficient r 2and its stan- culated as follows: dard error were also computed for each model pred=(SD-PRESS)/SD 3. Results and discussion where SD is the sum of squared deviations between the biolog The docked conformations of the molecules in the training ical activity of the test set and the mean activity of training set set are shown in Fig. 1a. The superposition showed that the li molecules, and PRESS is the sum of squared deviations gands fit the binding pocket consisting of critical residues. The PHE221 TYR229 ASN123 TRP178 GLU124 PHE221 TYR229 PHE221 TYR229 GLU231 GL231 TRP178) ASN123 ASN123 TRP178 TRP85 GLU124 TRP85 TYR68 TYR68 icated as a solid surface. (All hydrogen atoms were omitted. )(b)The docked conformations of molecules whose piperazine ring located between pers in- Fig. 1.(a) The docked conformations of the molecules in the training set together with the binding site of 5-HT3 receptor. The solvent-accessible surface yr229 of the receptor and compound 1l was showed as a representative.(c)The docked conformations of molecules whose C-4 substituent located between Trp85 and Tyr229 of the receptor and the representative was compound 15 whose nitrogen atom in the quinoline ring formed hydrogen bond with Asn123 of the receptor. (d) The docked conformations of compound 33 whose phenyl ring was located between Trp85 and Tyr229 of the receptor(the hydrogen bondsTo assess the predictive power of the 3D-QSAR models derived using training set, biological activities of the test set molecules were predicted. The predictive r 2 (r2 pred) value is cal￾culated as follows: r 2 pred ¼ ðSD PRESSÞ=SD where SD is the sum of squared deviations between the biolog￾ical activity of the test set and the mean activity of training set molecules, and PRESS is the sum of squared deviations between the actual and the predicted activities of the test set molecules. In addition, the r2 cv, r2 pred and number of compo￾nents, the conventional correlation coefficient r 2 and its stan￾dard error were also computed for each model. 3. Results and discussion The docked conformations of the molecules in the training set are shown in Fig. 1a. The superposition showed that the li￾gands fit the binding pocket consisting of critical residues. The Fig. 1. (a) The docked conformations of the molecules in the training set together with the binding site of 5-HT3 receptor. The solvent-accessible surface is in￾dicated as a solid surface. (All hydrogen atoms were omitted.) (b) The docked conformations of molecules whose piperazine ring located between Trp85 and Tyr229 of the receptor and compound 11 was showed as a representative. (c) The docked conformations of molecules whose C-4 substituent located between Trp85 and Tyr229 of the receptor and the representative was compound 15 whose nitrogen atom in the quinoline ring formed hydrogen bond with Asn123 of the receptor. (d) The docked conformations of compound 33 whose phenyl ring was located between Trp85 and Tyr229 of the receptor (the hydrogen bonds are shown in yellow lines). Y.-J. Zhou et al. / European Journal of Medicinal Chemistry 42 (2007) 977e984 979