N+-C-H Center Dot Center Dot Center Dot O Hydrogen Bonds In Protein-Ligand Complexes

In the context of drug design, C-H center dot center dot center dot O hydrogen bonds have received little attention so far, mostly because they are considered weak relative to other noncovalent interactions such as O-H center dot center dot center dot O hydrogen bonds, pi/pi interactions, and van der Waals interactions. Herein, we demonstrate the significance of hydrogen bonds between C-H groups adjacent to an ammonium cation and an oxygen atom (N+-C-H center dot center dot center dot O hydrogen bonds) in protein-ligand complexes. Quantum chemical calculations revealed details on the strength and geometrical requirements of these N+-C-H center dot center dot center dot O hydrogen bonds, and a subsequent survey of the Protein Data Bank (PDB) based on these criteria suggested that numerous protein-ligand complexes contain such N+-C-H center dot center dot center dot O hydrogen bonds. An ensuing experimental investigation into the G9a-like protein (GLP)-inhibitor complex demonstrated that N+-C-H center dot center dot center dot O hydrogen bonds affect the activity of the inhibitors against the target enzyme. These results should provide the basis for the use of N+-C-H center dot center dot center dot O hydrogen bonds in drug discovery.