Scientists Redesign Naproxen in Silico to Beat Its Own Side Effects

Naproxen is one of the most widely used non-steroidal anti-inflammatory drugs in the world, a propionic acid derivative that millions of people reach for when pain and swelling strike. Yet the very chemical feature that makes it work, a free carboxylic acid group, is also the source of its most troublesome liabilities: acid reflux, stomach lining ulcers, gastrointestinal bleeding, and, with frequent use, even kidney damage. A new computational study published in Results in Chemistry by Afia Abdullah and Mahwish Akhtar takes aim at this paradox, using a battery of structure-based design tools to rationally redesign the drug so that it binds cyclooxygenase enzymes more tightly while shedding the acidity that irritates the gut.

The research team designed ten new naproxen derivatives, labeled ND1 through ND10, by replacing the drug’s terminal carboxylic acid with an amide linkage attached to a variety of aromatic, heterocyclic, and aliphatic fragments. The naphthalene methoxy backbone that the cyclooxygenase enzymes recognize was left untouched, preserving the pharmacophore responsible for anti-inflammatory action. The logic is rooted in well-established medicinal chemistry: the acidic group anchors classical NSAIDs inside the COX channel through a salt bridge with the conserved Arg120 residue, but that same ionizable acid undergoes ion trapping in the acidic gastric lumen, directly irritates the epithelial barrier, and inhibits mitochondrial oxidative phosphorylation in stomach lining cells. Swapping the acid for a neutral amide could, in principle, keep the anchoring interactions while eliminating the gastric toxicity, and the amide’s terminal fragment could even reach into the less conserved side pocket that distinguishes COX-2 from COX-1, a strategy long used to convert non-selective NSAIDs into COX-2-preferring inhibitors.

To test this idea without synthesizing a single molecule, the researchers deployed a multi-layered computational pipeline. Density functional theory calculations at the B3LYP/6-31+G(d,p) level probed the electronic character of each derivative, yielding frontier molecular orbital energies, chemical hardness, softness, electronegativity, and electrophilicity. The results were striking: derivatives ND1 and ND4 showed the smallest HOMO-LUMO energy gaps, around 0.30 and 0.31 electron volts, compared with 0.87 electron volts for naproxen itself, indicating far greater electronic softness and reactivity. Soft molecules polarize more readily, which favors effective dispersion forces and electronic redistribution during non-covalent binding within the hydrophobic COX-2 pocket. ND2, meanwhile, posted the highest dipole moment at over 30 Debye, suggesting the strongest potential for polar interactions with the receptor. Molecular electrostatic potential mapping reinforced the picture, revealing that the high-polarization derivatives, including ND1, ND4, ND5, ND6, and ND9, retained sharply localized electron-rich and electron-poor regions capable of directional hydrogen bonding, effectively replacing the electrostatic role of the discarded carboxylic acid.

Before any binding predictions could be trusted, the docking protocol itself had to be validated. The researchers re-docked the co-crystallized ligands into the active sites of COX-1 and COX-2, using crystal structures 3KK6 and 3NT1 from the Protein Data Bank, and obtained root-mean-square deviations of 1.48 and 0.936 angstroms respectively, well within accepted thresholds. With the protocol confirmed, all ten derivatives were docked against both enzymes using AutoDock Vina and AutoDock4, alongside reference drugs including diclofenac, aspirin, mefenamic acid, and indomethacin. Every single derivative outperformed the parent drug. Naproxen scored roughly minus 7.5 kilocalories per mole against COX-2, while the derivatives ranged from minus 8.3 to minus 10.1 kilocalories per mole under Vina scoring. ND10, bearing an aminomethyl benzoic acid terminus, achieved the most favorable AutoDock4 score of minus 11.49 kilocalories per mole, driven largely by superior van der Waals contacts, while ND5’s bulky cycloheptylethyl group delivered a minus 10.43 kilocalories per mole result.

The docking poses revealed how the amide modification preserves potency through a clever molecular sleight of hand. Although converting the carboxylate into an amide removes the classical ionic salt bridge with Arg120, the amide carbonyl steps in as an alternative hydrogen-bond partner for the Arg120 guanidinium group in complexes ND3, ND5, and ND10. This neutral interaction, combined with deep penetration of the derivatives into the hydrophobic core near GLY526 and ALA527, provides a rational basis for COX-2 selectivity. Several complexes, including ND2, ND4, ND5, ND6, ND7, ND9, and ND10, reproduced the essential binding pattern of naproxen through pi-pi stacking with aromatic residues such as PHE381, TYR385, and TRP387, while ND4, ND6, and ND10 added hydrogen bonds and pi-sigma interactions with TYR385. By replacing the ionic anchor essential for COX-1 recognition with amide-based hydrogen bonding and expanded aromatic stacking, the derivatives exploit the larger active-site volume of COX-2 while potentially reducing the COX-1-mediated gastrointestinal harm of the parent acid.

Pharmacokinetic profiling through SwissADME and ProTox 3.0 added a crucial safety dimension. All ten derivatives fell safely below the 500 grams per mole Lipinski ceiling, satisfied hydrogen-bond donor and acceptor limits, and showed topological polar surface areas between 38 and 76 square angstroms, comfortably within the threshold for passive oral absorption. Predicted gastrointestinal absorption was high across the series, and all compounds were predicted non-cardiotoxic. The toxicity results were particularly encouraging: naproxen showed an LD50 of 248 milligrams per kilogram in toxicity class 3, whereas ND1 and ND8 exhibited LD50 values of 4000 and 5000 milligrams per kilogram in the far safer class 5. ND1, ND8, and ND10 were additionally predicted to be non-neurotoxic, and nearly all compounds showed inactive nephrotoxicity predictions, in contrast to active nephrotoxicity for naproxen itself. Caveats remain, however, as several analogues were predicted to inhibit multiple cytochrome P450 isoforms, flagging a potential risk of drug-drug interactions that will require experimental confirmation.

The three most promising candidates, ND2, ND4, and ND10, were then subjected to 100-nanosecond molecular dynamics simulations in GROMACS using the CHARMM36 force field, solvated in explicit water with physiological ion concentrations. The trajectories told a dramatic story. Naproxen repeatedly dissociated and rebounded at three distinct binding-site regions over the simulation, maintaining only intermittent hydrogen bonding of zero to two bonds and showing the highest conformational fluctuation of any system studied. ND4, by contrast, locked into its binding pose almost immediately and maintained a steady four to six hydrogen bonds, occasionally reaching seven, throughout the entire 100 nanoseconds. Its average root-mean-square deviation of 0.215 nanometers was the lowest of the series, and its solvent-accessible surface area of 255.90 square nanometers indicated the most compact, tightly bound complex. ND10 required roughly 50 nanoseconds to settle but then held its final pose with remarkable rigidity, achieving the steadiest plateau in the RMSD analysis.

Free-energy calculations using the MM/GBSA method over 501 trajectory snapshots quantified these differences with impressive precision. Naproxen’s binding free energy averaged minus 13 kilocalories per mole, while ND2 reached minus 16.5 and ND10 minus 25.4 kilocalories per mole. ND4 was in a class of its own at minus 46 kilocalories per mole, powered by an enormous van der Waals contribution of nearly minus 49 kilocalories per mole and an electrostatic term of minus 27 kilocalories per mole, reflecting its extended hydrogen-bond network with TYR324, ARG89, and ARG120. Per-residue energy decomposition confirmed that Arg120 contributed favorably to ND4 binding, demonstrating that the amide linkage had successfully recreated the anchoring interaction that the carboxylic acid once provided. Conformational analysis added a final layer of insight: 75 percent of the ND4 trajectory occupied a single conformational family, compared with only 43 percent for naproxen, whose energy landscape was fragmented across many shallow, poorly defined basins.

The authors are careful to frame these findings as exploratory rather than conclusive. Computational docking, dynamics, and ADMET predictions cannot fully capture the complexity of living systems, and predicted binding affinities do not always translate to in vitro or in vivo efficacy and safety. Experimental verification of the amide modification’s impact on cyclooxygenase selectivity, anti-inflammatory activity, metabolic stability, and gastrointestinal protection remains essential. Still, the study stands as a compelling demonstration of modern computer-aided drug design, showing how density functional theory, electrostatic mapping, validated docking, long-timescale simulation, and ensemble free-energy calculations can converge to identify ND4 and ND10 as lead candidates worthy of synthesis and biological testing. If laboratory work confirms what the simulations suggest, the humble painkiller in millions of medicine cabinets could one day be replaced by a safer, more potent descendant of itself.

Subject of Research: Computational design of naproxen amide derivatives as improved anti-inflammatory COX inhibitors

Article Title: Structure-based computational design of naproxen analogues with improved anti-inflammatory activity by DFT analysis, ADMET assessment, molecular docking, and molecular dynamics simulations

Article References: Abdullah, A., & Akhtar, M. (2026). Structure-based computational design of naproxen analogues with improved anti-inflammatory activity by DFT analysis, ADMET assessment, molecular docking, and molecular dynamics simulations. Results in Chemistry, 31, Article 103933. https://doi.org/10.1016/j.rechem.2026.103933

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103933

Keywords: naproxen, NSAIDs, COX-2 inhibition, computer-aided drug design, molecular docking, molecular dynamics simulation, DFT, ADMET, MM/GBSA, amide derivatives, gastrointestinal toxicity, drug discovery