The PCA can illustrate the relationship between the different compounds and the different scoring functions. The compounds can be plotted in the space defined by two PCs (score plot, Figure 2 ), which identifies active compounds as a function of inactive compounds. The values of the scores can be understood as the values of the compound in the new variable space, i.e., the principal component space. In Figure 2 , active compounds are depicted as red circles, and inactive compounds are depicted as black squares. The results showed that most of the data were scattered along the PC1 axis. The scattering variation along the PC1 axis is larger than that along the PC2 axis, which corresponds to the values of eigenvalue and reflects the descriptive power of first two PCs scores.