Design, Synthesis and Pharmacological Profiling of Amino Acid-based Indomethacin Conjugates: A Strategy to Mitigate...

A major limitation of conventional non-steroidal anti-inflammatory drugs (NSAIDs) is their tendency to cause significant gastrointestinal complications, such as hemorrhage and ulceration. This toxicity arises mainly from their preferential inhibition of COX-1 over COX-2, combined with the inherent acidity of their carboxylic acid groups, which directly irritate the gastric mucosa. A more pragmatic strategy for developing safer anti-inflammatory agents involves optimizing the physicochemical, toxicological, and pharmacokinetic properties of established NSAIDs. One effective approach is the synthesis of prodrugs or conjugates, in which the active drug is linked to biocompatible carriers to mask its adverse effects and improve its overall therapeutic profile.

Amino acid conjugates of indomethacin were successfully synthesized by chemically linking the carboxylic acid group of indomethacin, in its acid chloride form, with amino acid methyl ester hydrochlorides using the DCC coupling method. The designed compounds were evaluated for their binding affinity to the COX-2 enzyme (PDB ID: 5F1A) using molecular docking. Drug-likeness and ADMET properties of these compounds were predicted using PreADMET and SwissADME software. The synthesized derivatives were characterized by spectral analyses (FTIR, NMR, and MS) and physicochemical evaluations, including solubility and partition coefficient determination. The anti-inflammatory and ulcerogenic activities of indomethacin and its conjugates were evaluated in Sprague-Dawley rats.

The in silico study demonstrated that the designed compounds exhibited superior binding affinity toward the COX-2 enzyme compared with the parent drug. ADMET predictions indicated favourable pharmacokinetic and safety profiles of all the compounds. Conjugation with amino acids significantly enhanced the aqueous solubility of indomethacin. FTIR, 1HNMR, and mass spectrometric analyses confirmed the structures of synthesized derivatives. All the amino acid conjugates exhibited anti-inflammatory activity comparable to that of the parent drug, along with a substantial reduction in ulcerogenic activity.

The improved selectivity of the designed compounds toward COX-2 may be attributed to the increased molecular size resulting from amino acid conjugation, which facilitates accommodation within the larger active site of the COX-2 enzyme. Enhanced aqueous solubility following amino acid conjugation may offer formulation-related advantages. Furthermore, the intrinsic antiinflammatory properties of the amino acids helped maintain the parent drug's anti-inflammatory efficacy. The gastrointestinal toxicity of indomethacin was significantly reduced in all synthesized amino acid conjugates, as evidenced by lower ulcer index values compared with the parent drug.

The findings of this study suggest that amino acid conjugation can overcome the limitations of conventional NSAIDs and represents an effective strategy for developing safer, more selective COX-2 inhibitors.