An isotopic study (2H and 18O) of the enzymic conversion of linoleic acid into colneleic acid with carbon chain fracture: the origin of shorter chain aldehydes

Contrary to earlier reports, the divinyl 9-ether oxygen of colneleic acid is shown by experiment with 18O2 to originate from oxygen, not water. Using [9,10,12,13-2H4]-9(S)-hydroperoxyoctadeca-1O(E), 12(Z)-dienoic acid, made enzymically from synthetic [9,10,12,13-2H4]Iinoleic acid, it is found that the distribution of deuterium as determined by NMR and mass spectrometry in the fractured carbon chain of colneleic acid formed by potato enzyme, is consistent with the intervention of an epoxycarbonium ion intermediate. Though divinyl acids such as colneleic and colnelenic acid give the expected shorter chain aldehydes on treatment with aqueous acid, it is likely that the latter are formed in most plants by trapping of a monovinyl oxonium ion rather than by rehydration of colneleic and colnelenic acid.