Synthesis and pharmacological assessment of pyrrole carboxylic acid derivatives: unexpected pro-inflammatory action of a hexanoic analogue in rats

• Pyrrole derivatives were tested for analgesic and anti-inflammatory effects • BB and CC series compounds lacked significant pain or inflammation reduction. • CC1 exhibited unexpected pro-inflammatory activity in carrageenan model. • Side-chain length and para -substitution did not enhance pharmacological efficacy. • In vivo findings highlighted scaffold limitations for drug design. Pyrrole-based carboxylic acid derivatives are a promising scaffold in medicinal chemistry due to their potential anti-inflammatory and analgesic properties. In this study, we synthesized two series of novel pyrrole derivatives (BB and CC) and evaluated their in vivo antinociceptive and anti-inflammatory activity using male Wistar rats. Compounds were administered intraperitoneally at 40 mg/kg, with metamizole and diclofenac serving as reference drugs. Thermal nociception was assessed via the plantar test, and acute inflammation was induced by carrageenan-mediated paw edema. Reference drugs produced the expected analgesic and anti-inflammatory effects, confirming model reliability. In contrast, none of the BB or CC compounds significantly altered paw withdrawal latency or edema, indicating a lack of analgesic and anti-inflammatory efficacy. Notably, CC1 , a hexanoic acid derivative, caused a significant increase in paw swelling at 3–4 h post-carrageenan, suggesting a pro-inflammatory effect. Structure-activity analysis revealed that variations in side-chain length and para -substitution on the phenyl ring did not enhance pharmacological activity. The absence of efficacy may be due to limited tissue penetration, insufficient target engagement, or metabolic factors, while the pro-inflammatory effect of CC1 may involve local accumulation, reactive oxygen species generation, and activation of pro-inflammatory signaling pathways. These findings highlight critical limitations of the current pyrrole scaffold and emphasize the need for thorough in vivo assessment during drug development. Overall, while pyrrole carboxylic acids remain a chemically versatile platform, substantial structural optimization is required to achieve effective analgesic or anti-inflammatory activity.