(R)-(+)-Atenolol is the less active enantiomer of the (R,S)-atenolol. (R,S)-atenolol is a β-adrenergic receptor antagonist[1][2].
[1]. Batra S, et al. Bioassay, determination and separation of enantiomers of atenolol by direct and indirect approaches using liquid chromatography: A review. Biomed Chromatogr. 2018 Jan;32(1). [2]. Stoschitzky K, et al. Stereoselective features of (R)- and (S)-atenolol: clinical pharmacological, pharmacokinetic, and radioligand binding studies. Chirality. 1993;5(1):15-9.