Properties of known drugs. 2. Side chains

We continue our study of the common features present in drug molecules by l ooking in detail at drug side chains. Using shape description methods, we d ivide a database of commercially available drugs into a list of common drug side chains. On the basis of the atom pair shape descriptor (taking into a ccount atom type, hybridization, and bond order), there are 1246 different side chains among the 5090 compounds analyzed. The average number of side c hains per molecule is 4, and the average number of heavy atoms per side cha in is 2. If we ignore the carbonyl side chain, then there are approximately 15 000 occurrences of side chains. Of these 15 000 approximately 11 000 ar e from the "top 20" group of side chains. This suggests that the diversity that side chains provide to drug molecules is quite low. We discuss ways th at this work could be used to provide guidance for molecular design efforts .