What are substitutions on amine nitrogen?

The nature and bulk of the substituent on the amine nitrogen is important in determining the β selectivity of the adrenergic agonist. For example, epinephrine, with a –CH3 substituent on the amine nitrogen, is more potent at β receptors than norepinephrine, which has an unsubstituted amine. Similarly, isoproterenol, with an isopropyl substituent –CH(CH3)2 on the amine nitrogen is a strong β agonist with little α activity