Synthesis and structure-activity relationships among alpha-adrenergic receptor agonists of the phenylethanolamine type.

Nineteen arylethanolamine derivatives related to norepinephrine were prepared and tested for alpha-adrenergic stimulant activity. In one series the analogues possess a p-hydroxy function, while the meta position is substituted by methyl, ethyl, isopropyl, chlohexyl, fluoro, chloro, iodo, carboxy, carbomethoxy, and methylsulfamido groups. The other series is meta hydroxylated with the para position substituted by the same groups. The influence of these groups upon the alpha-adrenergic activity is discussed, and the compounds are compared to octopamine, normetanephrine, norepinephrine, and norphenylephrine. It has been found that the introduction of an isopropyl, cyclohexyl, and fluoro group in the meta position of octopamine improves its affinity by three, five, and six times, respectively, whereas when these groups are introduced in the para position of norphenylephrine their effects are always detrimental. The most active compound, alpha-(aminomethyl)(4-fluoro-3-hydroxyphenyl)methanol (44), has about one-hundredth the affinity and the same intrinsic activity as norepinephrine.