Indazolinones, a new series of redox-active 5-lipoxygenase inhibitors with built-in selectivity and oral activity
摘要:
Since the hypothetical mechanisms of hydroperoxydation of arachidonic acid by, respectively, 5-lipoxygenase (5-LPO) and cyclooxygenase (CO) involve a redox cycle, a compound which reduces 5-LPO and CO to their inactive state would give a nonselective inhibitor of both enzymes. Structural modifications of such a compound could be expected to give improved potency and selectivity for 5-LPO and oral activity. Such an approach has led to the discovery of 1,2-dihydroindazol-3-ones which are potent 5-LPO inhibitors with various degrees of selectivity. Structure-activity relationship studies indicated that while N-1,N-2-unsubstituted and N-1-substituted derivatives are orally inactive, N-2-alkyl derivatives are orally active and inhibit both 5-LPO and CO. In contrast, N-2-benzyl derivatives are selective for 5-LPO but possess only weak oral activity. Further structural modifications have identified ICI 207968 [1,2-dihydro-2-(3-pyridylmethyl)-3H-indazol-3-one, 21a] which combines potent oral activity and high selectivity. Methemoglobin (MHb) induction by 21a in dog blood precluded its development for clinical use. Attempts at dissociating 5-LPO inhibitory properties and MHb formation showed that MHb formation in vitro seemed to be related to the redox potential of the compounds whereas 5-LPO inhibition was not. This study led to a series of 4-(N-n-pentylcarbamoyl)indazolinones which maintained in vitro 5-LPO potency but did not induce MHb.
A convenient photocatalyst‐free method for the synthesis of redox‐active 1,2‐dihydro‐3H‐indazol‐3‐one derivatives from (2‐nitroaryl)methanol and amines was developed. The reaction proceeded efficiently at room temperature by irradiation of UV lightunder CO2 atmosphere (1.0 atm, flow) without any photocatalysts or additives. This mild, operationally simple method shows wide functional tolerance. The