5'-Guanylyl imidodiphosphate
5'-Guanylyl imidodiphosphate (GDPNP) is a purine nucleotide. It is an analog of guanosine triphosphate in which one of the oxygen atoms is replaced with an amine, producing a non-hydrolyzable functional group.
Source: Wikipedia — 5'-Guanylyl imidodiphosphate (CC BY-SA 4.0)