Abstract
Curating the data underlying quantitative structure–activity relationship models is a never-ending struggle. Some curation can now be automated but much cannot, especially where data as complex as those pertaining to molecular absorption, distribution, metabolism, excretion, and toxicity are concerned (vide infra). The authors discuss some particularly challenging problem areas in terms of specific examples involving experimental context, incompleteness of data, confusion of units, problematic nomenclature, tautomerism, and misapplication of automated structure recognition tools.
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Notes
Supplemental material provided by O’Reilly et al. [29] provides an excellent overview of how to interconvert the various types of specifications and half-life measurements.
Variously attributed to Bill Vaughn and Paul Ehrlich.
The particular problematic “compounds” found revealed incidental limitations in the SMILES parser used that have little practical relevance but that have since been addressed.
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Acknowledgments
The authors wish to thank Jinhua Zhang, Michael S. Lawless, Jayeeta Ghosh, and Michael Bolger for their help in ferreting out errors over the years. We also thank the Simulations Technology colleagues at Simulations Plus for their ongoing real-world testing of the models that were the ultimate product of our efforts: nothing is so effective an inducement to careful curation as knowing that the person across the hall depends on your getting it right. Thanks are also due to Ian Haworth (University of Southern California) and Terry Stouch (Science for Solutions, LLC) for the insight, inspiration, encouragement, and useful information they have provided us.
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Appendix
Appendix
Endpoint | Some things to worry about |
---|---|
Solubility | Units: mg/mL (ppt) versus mg/L (ppm) versus M Temperature Miscibility and solubility are somewhat different things Mixed solvents Salts & other mixtures Ionic strength Use of buffers without checking the final pH Precipitation of insoluble salts (e.g., phosphates) |
Melting point | Decomposition Salts versus free acids or bases |
Structures | Esters versus salts Spelling variants Primes & double primes in names Synonyms Stereoisomers Names match but structures do not Strange amidine and guanidine valence isomers Inverted tetrahedral & planar trisubstituted sp3 carbons |
Tautomers | Electron-deficient amidines & aminopyridines Hydroxypyridines usually exist as pyridones Triketones usually enolize Amides and esters only rarely enolize |
pKa | Temperature Solvent Ionic strength Tautomeric representation Multiple closely spaced pKa’s Protonated nitro groups Doubly protonated piperazines at physiological pH Identification of pKa’s with specific groups may be problematic in some cases |
CYP assays | Complex kinetics Substrate inhibition Nonstandard recombinant assay systems Mutant isoforms Interference from other oxidases or hydrolases Aromatic epoxidation versus hydroxylation Disappearance of parent versus appearance of product CLint determinations at single substrate concentrations |
UGT assays | Reactive or unstable products Endoplasmic reticulum accessibility artifacts |
In vivo metabolites | Prodrugs Unstable or reactive metabolites Secondary metabolites |
Units | Satellite peaks in distribution near three log units away from the average Negative log units: M versus mM versus μM Typographical errors: “m” for “μ” Discrepancies between units in tables and in the text |
Enzyme & binding assays | IC50 versus Ki Comparability of assay conditions Substrate or displaced ligand identity Substrate or displaced ligand concentration Source of the enzyme or receptor Limit values like “>10 μM” becoming “10.00 μM” |
General | The fact that internet sources agree does not make something true If something looks too high or too low to be true: check it out |
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Waldman, M., Fraczkiewicz, R. & Clark, R.D. Tales from the war on error: the art and science of curating QSAR data. J Comput Aided Mol Des 29, 897–910 (2015). https://doi.org/10.1007/s10822-015-9865-0
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DOI: https://doi.org/10.1007/s10822-015-9865-0