A series of prostaglandin-like compounds that are produced by the attack of free-radical species on unsaturated fatty acids, especially arachidonic acid, of cellular membranes. Once cleaved from the lipid membrane by the action of phospholipases they can circulate into various bodily fluids and eventually be excreted. Although these compounds resemble enzymatically synthesized prostaglandins their stereoisometric arrangement is usually different than the "naturally occurring" compounds.