Mechanochemical Synthesis of Diclofenac Conjugates with Glucosamine and Chitosan Exhibiting COX-2 Selective Ulcer Safe Anti-inflammatory Activity

Abstract

Introduction: Non-steroidal anti-inflammatory drugs are associated with severe gastrointestinal irritation upon prolonged use, largely due to their carboxylic (- COOH) functional group. Aim: To address this issue, we aimed to synthesize diclofenac conjugates with glucosamine and chitosan, converting the -COOH group into an amide (-CONH-) via a mechanochemical, environmentally friendly method. Methods: In this study, diclofenac acid was first converted to its acid chloride using thionyl chloride under mechanochemical conditions and subsequently reacted with glucosamine base and chitosan. The resulting conjugates were evaluated for anti-inflammatory activity through the rat-paw edema test, along with ulcerogenicity, COX inhibition assays, and cardiovascular assessment. Results: The mechanochemical approach provided high yields (>90%) and resulted in

conjugates that significantly reduced paw edema (62.3 ± 2.3% for diclofenac- glucosamine and 58.5 ± 1.6% for diclofenac-chitosan) compared to diclofenac sodium

(49.0 ± 1.3%) after 5 h. Notably, the conjugates were ulcer safe, as no gastric lesions were observed, unlike the multiple lesions detected in animals treated with diclofenac sodium. Both conjugates also demonstrated a high degree of COX-2 selectivity and cardiovascular safety. Conclusion: This study highlights the potential of mechanochemical synthesis for efficient amide formation, avoiding the need for hydroxyl group protection.