Design, Synthesis, Crystal Structure, and Antimicrobial Evaluation of 6- Amino-4-phenyl-3-propyl-1,4-dihydropyrano2,3-cpyrazole-5-carbonitrileDerivatives: A Structure Activity Relationship Study

Introduction: A new library of 6-amino-4-phenyl-3-propyl-1,4-dihydropyrano2,3- cpyrazole-5-carbonitrile derivatives (4a–j) was synthesized with the objective of developing eco-friendly synthetic routes and evaluating their potential antimicrobial activity, along with establishing structure–activity relationships (SAR). Methods: The target compounds were synthesized via a catalyst-free, one-pot, three-component reaction performed at room temperature under green conditions using an ethanol–water solvent system. The synthesized derivatives were characterized using standard spectroscopic techniques, and the molecular structure of compound 4h was confirmed by single-crystal X-ray diffraction analysis. Antimicrobial activity was assessed against selected Gram-positive bacteria, Gramnegative bacteria, and fungal strains using minimum inhibitory concentration (MIC) assays. Results: Several derivatives demonstrated significant antimicrobial activity. Compound 4g exhibited the highest antibacterial potency against Escherichia coli with an MIC value of 62.5 μg/mL, while compound 4e showed strong inhibition against Streptococcus pyogenes. Among the tested compounds, 4b displayed the most pronounced antifungal activity. SAR analysis revealed that derivatives bearing electron-withdrawing substituents on the aryl ring enhanced antibacterial activity, whereas electron-donating groups resulted in moderate antifungal effects. Discussion: The observed antimicrobial trends underscore the crucial role of aryl substitution patterns in modulating biological activity. Compared to previously reported pyranopyrazole derivatives, the synthesized compounds demonstrate comparable or improved antimicrobial efficacy under milder and greener reaction conditions. However, further mechanistic studies and cytotoxicity evaluations are required to validate their therapeutic potential. Conclusion: This study presents an efficient and environmentally benign synthetic protocol for structurally diverse pyranopyrazole derivatives with promising antimicrobial properties. The combined biological evaluation, SAR insights, and crystallographic analysis support these compounds as potential lead candidates for further medicinal chemistry optimization.