Stereochemistry of oxidized fatty acids generated during catalytic oxygenation of lauric acid and unsaturated analogs by plant microsomes

The capacity of microsomes from aminopyrine-induced Jerusalem artichoke ( Helianthus tuberosus L.) to oxidize saturated and unsaturated fatty acids has been investigated using lauric acid and a series of unsaturated lauric acid analogs (7-, 8-, 9- and 10-dodecenoic acids) as radiolabeled substrates. In the presence of NADH, lauric acid was mono-hydroxylated principally at carbon 9. Steric analysis of this product showed a low enantiomeric excess of 28%. Mono-hydroxylated and mono-epoxidated reaction products were formed from the unsaturated analogs. The epoxidation/hydroxylation ratio was related to the position of the double bond in the aliphatic chain. The oxidation of 7-dodecenoic acid (7-DDNA) and 10-DDNA produced mainly 9-hydroxy-7-DDNA and 9-hydroxy-10-DDNA plus minor amounts of 7,8-epoxy- or 10,11-epoxylauric acid, respectively. In contrast, 8- and 9-DDNAs yielded essentially 8,9-epoxy- and 9,10-epoxylauric acids and smaller amounts of 10-hydroxy-9-DDNA and 8-hydroxy-9-DDNA, respectively. The optical purity and the absolute configuration of the major metabolites were investigated. Epoxidation of Z 8-DDNA and Z 9-DDNA occurs with high enantiomeric excesses. When the double bond was in the Z configuration, (8 S,9 R)/(8 R,9 S) 8,9-epoxylauric acid (93/7) or (9 R,10 S)/(9 S,10 R) 9,10-epoxylauric acid (89/11) were produced. In contrast, when the double bond was in the E configuration, steric analysis showed an enantiomeric ratio of 52/48 for E 8,9-epoxide and of 59/41 for E 9,10-epoxide, Z 7-DDNA led to the formation of 98% of the 9( S)-hydroxy- Z 7-DDNA enantiomer, while 9-hydroxy- Z 10-DDNA derived from Z 10-DDNA was 35% ( R) and 65% ( S).