A study of the pharmacological properties of pyrrolo[2,1-c][1,4]benzodiazepine derivatives led to the choice of (+)-1,2,3,11a-tetrahydro-10-methyl-5H-pyrrolol[2,1-c][1,4]benzodiazepine-5,11)10H)-dione as a candidate for anxiolytic evaluation in a limited clinical trial in man. Metabolism studies in laboratory animals have pointed to rapid hydroxylation, possibly in the 3 and 11a positions. A series of compouds containing methyl groups in one or more of these positions has been prepared in an effort to block metabolism and thereby obtain more active or longer acting compounds. All of these derivatives were less active than the parent compound.

A series of 1-aryl-3-azabicyclo[3.1.0]hexanes was synthesized by hydride reduction of 1-arylcyclopropanedicarboximides. Hydroxyphenyl analogues 20, 22, and 24 were prepared by EtSNa--DMF ether cleavage of the corresponding methoxyphenyl analogues 2m, 2n, and 23, respectively, with the secondary amines 20 and 22 going through the N-formyl intermediate 19 and 21. The p-ethoxy analogue 26 was obtained by O-ethylation of 19, followed by base hydrolysis of the amide 25. The greatest analgesic potency in mouse writhing and rat paw-pain assays was observed for para-substituted compounds. Bicifadine, 1-(4-methylphenyl)-3-azabicyclo[3.1.0]hexane (2b), was the most potent member of the series and is presently undergoing clinical trials in man. Analgesic activity of 2b is limited to the (+) enantiomer 2v, which has the 1R,5S absolute configuration as determined by single-crystal X-ray analysis. The N-methyl analogue (27d) of 2b showed significant analgesic potency, whereas the N-allyl (27a), N-(cyclopropylmethyl) (27b), and N-(n-hexyl) (27c) analogues were inactive. Bicifadine (2b) showed a nonnarcotic profile different from analogous azabicycloalkane and 3-phenylpyrrolidine analgesics.

2‐Aminobenzimidazoles were reacted with enaminones in acetic acid to give pyrimido[1,2‐a]benzimidazoles. With a substituted enaminone only one regioisomer was obtained. Structural assignments based on nmr and uv spectroscopy are presented. Possible pathways leading to the products are discussed.

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