The quantitative differences in biological activity between the two enantiomers of a compound are sometimes quite large. for example, the d isomer of the drug isoproterenol, used to treat mild asthma, is 50 to 80 times more effective as a bronchodilator than the l isomer. identify the chiral center in isoproterenol. why do the two enantiomers have such radically different bioactivity?

The Chiral center is show in the figure

Explanation:

If a carbon atom is bonded to four differents groups as in isoproterenol (-OH, -Ph, -H and -CH2-R), it is a chiral carbon, which means that the molecule has two enantiomers, D and L.

Each enantiomer will have a different bioactivity, the bioctivity is the interaction of the D or L enantiomer with a biological receptor which also is chiral. The two enantiomers have different bioactivity because each one interact  different with the biological receptor.