Oxidation of cholesterol and O-protected derivatives by the environmental pollutant NO2.

Exposure of O-protected and free cholesterol to NO2˙ under exclusion of water leads to nitroimine nitrates through a non-radical mechanism, which reveals the high susceptibility of the π system to oxidative damage. In the presence of moisture the reaction leads to 6-nitrocholesterols , which result from hydrolysis and oxidation of 2.