We also performed analysis of the drugs approved by the FDA between 1951 and 2021 as summarized by Scott et al. Overall, the averages of Fsp3, FCstereo and nSPS values do not appear to change appreciably over the years, and show no apparent increasing or decreasing trends (Figure ). The average nSPS of the approved drugs in time period is relatively high and equals 21 units, which seems to correspond well with the optimal nSPS range found for the compound potency and selectivity in the ChEMBL data set. Thus, for compounds intended for biological investigations and in the absence of any other indications, we suggest that molecules with nSPS values in the range of 20 to 40 units will be particularly promising. Similarly to the Böttcher complexity index, the un-normalised SPS can also be applied for the assessment of spacial modifications occurring during generalised chemical transformations. The difference in SPS (ΔSPS) between the product and the starting material(s) for a particular reaction type can be easily calculated and used for comparison and ranking of contributions to spacial changes between different chemical reactions (Table ).