title: Size estimation of chemical space: how big is it?
abstract: OBJECTIVE
  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.
  
  
  RESULTS
  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.
authors.affiliation: School of Chemical Sciences, The University of Auckland, Auckland, New Zealand.
authors.forename: Kurt L M
authors.initials: KL
authors.lastname: Drew
authors.forename: Hakim
authors.initials: H
authors.lastname: Baiman
authors.forename: Prashanna
authors.initials: P
authors.lastname: Khwaounjoo
authors.forename: Bo
authors.initials: B
authors.lastname: Yu
authors.forename: Jóhannes
authors.initials: J
authors.lastname: Reynisson
mesh_terms: D001682:Biological Availability; D003627:Data Interpretation, Statistical; D006801:Humans; D008956:Models, Chemical; D015394:Molecular Structure; D009930:Organic Chemicals / Q000737:chemistry*; D004364:Pharmaceutical Preparations / Q000737:chemistry* / Q000378:metabolism
chemical_list: D009930:Organic Chemicals; D004364:Pharmaceutical Preparations