<unk>  is a short-acting β2 adrenoreceptor agonist — a class of medication used for smooth muscle relaxation (other similar drugs are used in asthma or other pulmonary diseases such as salbutamol (albuterol)). Since<unk>  has a bulky N-substituent, it has high β2 selectivity. Also, the 4-hydroxy group on the benzene ring is important for activity as it is needed to form hydrogen bonds. However, the 4-hydroxy group makes it susceptible to metabolism by catechol-O-methyl transferase (COMT). Since it is β2-selective it is used for premature labor.
Ritodrine
Midodrine
Amixetrine
Minaprine
Methylergometrine
Chloroxylenol
Ergometrine
Erythrocrine