Atropisomers of 3-substituted-4-arylquinolin-2-one derivatives having the general formula ##STR1##

wherein R, R¹, R², R³, R⁴ and R⁵, are as defined herein, or a non-toxic pharmaceutically acceptable salt, solvate or prodrug thereof. The atropisomers can modulate the large conductance calcium-activated K⁺ channels and are useful in the treatment of disorders which are responsive to the opening of the potassium channels. In addition, the atropisomers can be stable, i.e., do not interconvert, for periods of up to one month, or more.