4H-Imidazo[2,1-c][1,4]benzoxazine-2-carboxylic acid (3) was found to possess potent activity in the IgE-induced rat passive cutaneous anaphylaxis model which may be predictive of clinical antiallergic activity. Compared to disodium cromoglycate (DSCG, 1), 3 was less active following iv administration but unlike DSCG showed very significant oral activity. To explore the structural requirements for this activity, a range of tricyclic compounds was prepared and their activities were measured. Individual 2-carboxylic acids derived from imidazo[1,2-a]quinolines, imidazo[1,2-a]quinoxalines, imidazo[1,2-a]quinoxalinones, pyrrolo[1,2-a]quinoxalinones, pyrrolo[2,3-a]quinoxalinones, and imidazo[2,1-b]benzothiazoles showed iv activities up to 10(3) times as potent as DSCG and many of them showed significant oral activity. From these, imidazo[1,2-a]quinoxaline-2-carboxylic acid 114 has been chosen for further development.
Several series of heterocyclic carboxylic esters were found to be active in the benzodiazepine receptor binding assay, a typical example being ethyl 7-ethyl-5-methoxyimidazo[1,2-a]quinoline-2-carboxylate (4b) with an IC50 of 150 nM. The corresponding phenylmethanone 5d was more potent with an IC50 of 14 nM and was orally active in animal models thought to predict anxiolytic effects. The synthesis of a large number of compounds resulted in the optimization of this activity in a series of (imidazo[1,2-a]pyrimidin-2-yl)phenylmethanones of which compounds 7e, 8b, 8h, 8j, and 8k were equipotent with chlordiazepoxide while exhibiting reduced anticonvulsant activity, little or no muscle relaxation, and negligible sedative effects.
4‐Pyrimidinamines have been reacted with 3‐bromo‐1‐phenylpropane‐1,2‐dione to give a series of (imidazo[1,2‐c]pyrimidin‐2‐yl)phenylmethanones. The dione also reacted with ethyl amidinoacetate to yield ethyl 2‐amino‐5‐benzoylpyrrole‐2‐carboxylate which was used to prepare a series of 6‐benzoylpyrrolo[2,3‐a]pyrimidines.
The synthesis and CNS activity of a noval class of annelated 1,4-benzodiazepines, the aminomethylene-2,4-dihydro-1H-imidazo[1,2-a][1,4]benzodiazepines, are described. An investigation of the structure--activity relationships in the series derived from 8-chloro-2,4-dihydro-2-dimethylaminomethylene-6-phenyl-1H-imidazo[1,2-a][1,4]-benzodiazepin-1-one (10) led to the synthesis of a group of compounds with potent minor tranquillizer activity.
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