VR (Russian VX, VXr, Soviet V-gas, GOSNIIOKhT substance No. 33, Agent "November")  is a "V-series" unitary
nerve agent closely related (it is an isomer) to the better-known VX nerve agent. It became a prototype for the series of Novichok agents. According to chemical weapons expert Jonathan Tucker, the first binary formulation developed under the Soviet Foliant program was used to make Substance 33, differing from VX only in the alkyl substituents on its nitrogen and oxygen atoms. "This weapon was given the code name Novichok."