89886-42-0

Configurationally pure 9-oxo-10E,12Z,15Z- and 13-oxo-9Z,11E,15E-octadecatrienoic acid are available from linolenic acid via regioselective functionalisation using lipoxygenases from soybean or tomato at specific pH conditions. Reduction of the resulting hydroperoxides followed by oxidation of the resulting allylic alcohols with Bobbitt's reagent yields the configurationally pure but labile ketotrienoic acids 4 and 5 without concomitant isomerisation.

Enzymatic oxidation of (6Z,9Z,12Z)-octadeca-6,9,12-trienoic acid (γ-linolenic acid; 1a) in a preparation of the red alga Lithothamnion corallioides Crouan led to the formation of (6Z,8E,10E,12Z)-octadeca-6,8,10,12-tetraenoic acid 2a and (11R,6Z,9Z,12Z)-hydroxyoctadeca-6,9,12-trienoic acid 3a as the main products. (9Z,12Z,15Z)-Octadeca-(9,12,15)-trienoic acid (α-linolenic acid; 4a) was oxidized in an analogous way to yield (9Z,11E,13E,15Z)-octadeca-9,11,13,15-tetraenoic acid (α-parinaric acid; 5a), (11S,9Z,12Z,15Z)-hydroxyoctadeca-9,12,15-trienoic acid 6a, and (14R,9Z,12Z,15Z)-hydroxyoctadeca-9,12,15-trienoic acid 7a.Isotope studies demonstrated that enzymatic conversion of the acid 1a into the tetraene 2a was accompanied by stereospecific eliminations of the pro-S and pro-R hydrogens from C-8 and C-11, respectively.The bis-allylic hydroxy acid 3a was formed from acid 1a by a reaction involving stereospecific elimination of the pro-S hydrogen from C-11 and incorporation of 1 atom of oxygen from water in the C-11 hydroxy group.Although the bis allylic hydroxy esters 3b, 6b, and 7b were chemically convertible into conjugated tetraenes by rapid acid-catalysed dehydration, enzymatic formation of conjugated tetraenes and hydroxy acids in Lithothamnion occured by independent pathways.