Fig. 2. Molecular assembly and chemical space.

a Schematic of assembly paths for four example molecules (hydrogens and charges omitted for clarity). b The computed MA of molecules from the Reaxys database shown by molecular weight. The color scale indicates the frequency, with increasing frequency from dark purple (0.0) to green and yellow (1.0) of molecules in a given molecular weight range with a given MA. 2.5 million MA were calculated, in the figure shown here that data has been subsampled to control for bias, see SI. The overlaid plot with the white labels shows how the MA varies for some compound types where some natural products, pharmaceuticals, and metabolites have a wide range of values (these molecules are listed in Supplementary Information Section 7, table 2). Note that the range of MA for the amino acids is limited. The molecular masses are binned in 50 Dalton sections. c Example organic molecular structures and the corresponding MA values calculated.