Variability of Molecular Descriptors in Compound Databases Revealed by Shannon Entropy Calculations

A method is introduced to calculate and compare the variability of molecular descriptors in compound databases. Descriptor variability analysis is based on histograms recording the distribution of molecular descriptors and calculation of Shannon entropy (SE), a metric originally applied in digital communication. SE values reflect the variability of descriptor settings. We have calculated a total of 92 molecular descriptors in the ACD and NCI databases and ranked them according to their variability. Significant differences in entropy are observed for a number of descriptors. However, the most variable descriptors are similar in the ACD and NCI databases. Such high-entropy descriptors are preferred tools to discriminate between compounds or account for the diversity of chemical libraries.