Kolokol-1

Kolokol-1 (Russian: Колокол meaning "bell") is a synthetic opioid developed for use as an aerosolizable incapacitating agent. The exact chemical structure has not yet been revealed by the Russian government. It was originally thought by some sources to be a derivative of the potent opioid fentanyl, most probably 3-methylfentanyl dissolved in an inhalational anaesthetic as an organic solvent. However, independent analysis of residues on the Barricade Theater hostage crisis hostages' clothing or in one hostage's urine found no fentanyl or 3-methyl fentanyl. Two much more potent and shorter-acting agents, carfentanil (a large animal tranquilizer) and remifentanil (a surgical painkiller) were found in the samples. They concluded that the agent used in the Barricade Theater hostage rescue contained two fentanyl derivatives much stronger than fentanyl itself, sprayed in an aerosol mist.

According to Lev Fyodorov, a former Soviet chemical weapons scientist who now heads the independent Council for Chemical Security in Moscow, the agent was originally developed at a secret military research facility in Leningrad (now restored to its historic name of Saint Petersburg), during the 1970s. Methods of dispersing the compound were reportedly developed and tested by releasing harmless bacteria through subway system ventilation shafts, first in Moscow and then in Novosibirsk. Fyodorov also claimed that leaders of the failed August 20, 1991 Communist coup considered using the agent in the Russian parliament building.

...
Wikipedia