Isoprostanes (IsoPs) 3 are cyclic derivatives of arachidonic acid (1a) and are diastereomeric to the enzymatically formed prostaglandins (PGs) 2.[1] They form in vivo by a free-radical- induced cascade, which consists of peroxidation/double 5-exo radical cyclization/ oxygenation, predominately from membrane-or low-density lipoprotein (LDL)-bound arachidonic acid derivatives 1b and 1c, in much larger quantities than PGs (Scheme1).[2] ...