Reliable Machine Learning for DPPH Antioxidant QSAR: Scaffold- and Study-Aware Validation with an Out-of-Domain Sulfonamide-Tyr-Gly Case Study
Year: 2026
Type: preprint
Abstract: Machine-learning QSAR models can prioritize antioxidant compounds, but apparent accuracy depends strongly on how chemical data are partitioned for validation. This study develops a reproducible DPPH antioxidant QSAR workflow using 1,891 curated molecules from a public 30 min DPPH dataset. Molecular structures were represented by nine RDKit physicochemical descriptors and 2,048-bit Morgan fingerprints (radius 2), giving 2,057 combined features.Random Forest regression was evaluated as the primary model,with Extra Trees as an independent ensemble comparator.Random Forest achieved mean R-squared = 0.712 and MAE = 0.297 pIC50 units under random five-fold cross-validation, but performance decreased to R-squared = 0.447 and MAE = 0.433 under Bemis-Murcko scaffold-aware validation, and to R-squared = 0.124 and MAE = 0.545 under DOI-grouped validation. In an internal held-out set, molecules with scaffolds represented during training performed better than those with unseen scaffolds(R-squared=0.824 versus 0.580).Nearest-neighbour Morgan Tanimoto analysis further separated structurally supported predictions from extrapolation: inside-domain molecules achieved R-squared = 0.830, whereas outside-domain performance was R- squared =-0.031. The workflow was then applied to two experimentally investigated sulfonamide-Tyr-Gly derivatives. Both had low maximum Tanimoto similarity(0.364 and 0.333), unseen scaffolds,and were overpredicted by approximately one pIC50 unit.The results show that random-split performance alone is insufficient for judging DPPH-QSAR reliability and that chemically informed validation and applicability-domain analysis are necessary when predictions are extended to structurally novel compounds.
Source: ChemRxiv
Institution: Enugu State University of Science and Technology
Language: English
Subfield: Drug Discovery
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7212043616