N-Butylisatoic Anhydride is an intermediate used in the synthesis of 1-Butyl-3-(1,1-dioxido-2H-1,2,4-benzothiadiazin-3-yl)-4-hydroxy-2(1H)-quinolinone (B691765), which is a heterocyclic inhibitor of the RNVIP(LA)dependent RNA polymerase enzyme transcribed by the Hepatitis C virus.