Syntheses and beta-adrenergic binding affinities of (R)- and (S)-fluoronaphthyloxypropanolamines

The beta-adrenergic receptors mediate several physiological processes including heart rate (beta 1), bronchodilation (beta 2), and lipolysis (beta 3). Therefore, selectivity is important for a possible therapeutic agent acting via these receptors. Aryloxypropanolamines are beta-receptor agonists or antagonists, depending on the aryl group and its substituents. We therefore hypothesized that fluorine substitution on the aromatic ring in this class could lead to significant biological effects because of the unique chemical characteristics of fluorine. Because the target compound has a chiral center, we set out to synthesize the two enantiomers so that effects of stereochemistry on biological activity could be evaluated. Syntheses of the enantiomers were performed starting with commercially available fluoronaphthalene and subsequent use of the chiral synthon (2R)- or (2S)-glycidyl 3-nitrobenzenesulfonate, depending on the desired enantiomer. High-pressure liquid chromatography (HPLC) methods were used to characterize %ee. Each enantiomer was synthesized. They exhibited nanomolar binding activities on beta-adrenergic receptors. The (S)-enantiomer was found to be up to 310 times more potent than the (R). It was also found to be about five-fold more selective for beta 2- than for beta 1-receptors. The current report demonstrates the importance of stereochemistry for the fluoroaromatic beta-receptor ligands.