The present invention provides polyunsaturated fatty acid compounds having antimalarial and/or neutrophil stimulatory activity. The polyunsaturated fatty acids contain 18-25 carbons and 1-6 double bonds and are characterized in that they have one or two substitutions selected from the group consisting of &bgr; oxa, &ggr; oxa, &bgr; thia and &ggr; thia. It is also preferred that the polyunsaturated fatty acid compound includes a further substitution selected from the group consisting of hydroxy, hydroperoxy, peroxy, carboxymethyl substitutions or attached to an amino acid. The invention also provides a method of producing an unsaturated oxa substituted fatty acid comprising reacting an unsaturated fatty acid alcohol with a carbene that is inserted in the OH bond of the alcohol, the invention further provides a method of treating inflammation with a composition comprising at least one hydroxy, hydroperoxy or peroxy derivative of a polyunsaturated fatty acid having a C18-24 carbon chain and 1-6 cis or trans double bonds.