Abstract
2-Phenylhistamines with various substituents at the phenyl ring were synthesized and the influence of substitution in ortho, meta or para position on histamine H 1-agonistic activity was investigated. Compounds with high activity occurred in the meta phenyl series. Increased activity in the guinea-pig ileum assay was achieved by monosubstitution with halogen on the phenyl ring. 2-[2-(3-Fluorophenyl)-4-imidazolyl]ethanamine ( 12) is the most potent highly selective H 1-agonist known so far, showing 87% relative potency compared with histamine and full efficacy at the H 1-receptor. Relative activities of the 3-chloro analogue ( 11) and the 3-methyl analogue ( 13) are 81% and 29%, respectively. Histamine H 2-activity could not be detected. 2-Phenylhistamines are available via reaction of the corresponding benzimidates with 2-oxo-4-phthalimido-1-butyl acetate ( 6) in liquid ammonia.
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