Size estimation of chemical space: How big is it?

Abstract

Objectives To estimate the size of organic chemical space and its sub-regions, i.e. drug-like chemical space and known drug space (KDS). Methods Analysis of the growth of organic compounds as a function of their carbon atoms based on a power function (f(x) = A×B, C = x) and an exponential function (f(x) = AeBx). Also, the statistical distribution of KDS and drug-like chemical space (drugs with good oral-bioavailability) based on their carbon atom count was used to deduce their size. Key findings The power function (f(x) = A×B, C = x) gives a superior fit to the growth of organic compounds leading to an estimate of 3.4 × 109 populating chemical space. KDS is predicted to be 2.0 × 106 molecules and drug-like chemical space is calculated to be 1.1 × 106 compounds. Conclusions The values here are much smaller than previously reported. However, the numbers are large but not astronomical. A clear rationale on how we reach these numbers is given, which hopefully will lead to more refined predictions. © 2011 Royal Pharmaceutical Society.