N-Phenylnaphthalen-1-amine (NPN) is an aromatic amine with the chemical formula .
This molecule is notable for its binding affinity in mouse major urinary protein (MUP). This ligand has the greatest binding affinity of all MUP binding ligand discovered, including 2-sec-butyl-4,5-dihydrothiazole (SBT), 6-hydroxy-6-methyl-3-heptanone (HMH), and 3-isobutyl-2-methoxypyrazine (IBMP). NPN binds 28 times tighter than SBT. It also makes 38 nonpolar contacts to MUP, whereas IBMP only makes 15 contacts which are the next most nonpolar contacts.[1] There is a slight difference in the binding affinities and forms for NPN bound in wild-type MUP and the Y120F MUP mutant. In wild-type MUP there is just enough room for the amine group of NPN to makes a water mediated hydrogen bond to Tyr120, whereas in Y120F MUP mutant, there is a slight shift and the amine group makes a direct hydrogen bond to Tyr120. Much is still unknown about the entropic and enthalpic effects of the MUP binding site.[2]