Syn–Anti Conformational Equilibrium of Indomethacin: A Combined NOESY and Quantum Chemical Study
Pharmaceutical Research, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Basım Tarihi: 2026
- Doi Numarası: 10.1007/s11095-026-04162-9
- Dergi Adı: Pharmaceutical Research
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, BIOSIS, Chemical Abstracts Core, Chimica, EMBASE, INSPEC, MEDLINE, Academic Search Ultimate (EBSCO), Biomedical Reference Collection: Corporate Edition (EBSCO), Health Research Premium Collection (ProQuest), Pharma Collection (ProQuest)
- Anahtar Kelimeler: conformational analysis, cross-relaxation rates, density functional theory, drug solid forms, indomethacin, NOESY NMR, polymorphism, solvent effects
- Sivas Cumhuriyet Üniversitesi Adresli: Evet
Özet
Purpose: To elucidate the conformational equilibrium of Indomethacin in solution and to establish its relationship with solvent environment and solid-state polymorphism. Methods: A combined experimental–computational approach was employed. One- and two-dimensional NOESY NMR spectroscopy were used to quantify cross-relaxation rates and derive conformation-sensitive internuclear distances in DMSO-d6 and CDCl3. Conformer populations were determined using the initial rate approximation and isolated spin-pair approximation. Quantum-chemical calculations based on Density Functional Theory (B3LYP-D3(BJ)/def2-TZVP, SMD solvation model) were performed to evaluate conformer energetics and solvent effects. Results: Two conformer families, syn- and anti-, were identified as key structural motifs governing indomethacin behavior. InDMSO-d6, the syn-conformer dominates (80.8%), whereas in CDCl3 the equilibrium shifts toward nearly equal populations (51.5% syn, 48.5% anti), revealing a strong solvent-dependent effect. Experimentally derived NOESY distances showed excellent agreement with computed geometries. DFT calculations confirmed the energetic preference of syn-type conformers while demonstrating significant solvent-induced changes in relative stability. Importantly, a direct correlation between solution-phase conformational equilibrium and known polymorphic forms was established. Conclusion: This study demonstrates that solvent-controlled conformational equilibria play a probable role in determining the solid-state forms of indomethacin. The integrated NOESY-DFT methodology provides a robust and quantitative framework for conformational analysis and offers a predictive tool for rational design and optimization of pharmaceutical solid forms.