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Synthesis and beta-adrenergic receptor blocking potency of 1-(substituted amino)-3-(4-indolyloxy)propan-2-ols.

Although (-)-[125I]iodopindolol (IPIN) can be used to label beta-adrenergic receptors in the central nervous system in vivo, use of this ligand for receptor imaging studies in humans may be limited due to its relatively poor penetration into the brain. As a first step toward the development of radioligands for imaging studies, we report the synthesis and measurement of in vitro binding affinity to beta-receptors of a series of 1-(substituted amino)-3-(4-indolyloxy)-propan-2-ol derivatives. The synthesized compounds vary widely in their lipophilicity as measured by their distribution coefficients between phosphate buffer and octanol at pH 7.4. The affinity of these compounds for beta-receptors, as measured by their inhibition of binding of IPIN to rat cortical and cerebellar membranes in vitro, ranges from 2- to 100-fold less potent than pindolol; the most potent compounds have Ki values of 2-5 nM. The radiolabeled analogues of some of these compounds may prove useful for receptor imaging studies.