A hydrogen bond is the bond formed between the hydrogen of one molecule and an electronegative atom of another molecule. Hydrogen involved in the bond formation is attached to the electronegative atom, which can be oxygen, nitrogen, or fluorine.
On comparing the structures of isoprenaline and the inactive metabolite, the only difference found is the presence of phenol group and methyl ether group. As it is known that isoprenaline is an active molecule.