16.4 Applications of PUFA hydroperoxides in fine
chemistry
16.4.1 Reduction of PUFA hydroperoxides
In living cells, PUFA-HPODs are potentially toxic compounds which may initiate
radical chain reactions. They are detoxified rapidly in both plants (Gardner, 1991)
and mammals (Pace-Asciak and Asostra, 1989) by various catabolic pathways, lead-
ing to physiologically active molecules such as jasmonic acid, leukotrienes, and
lipoxins. They can also be reduced simply to their corresponding alcohols. In certain
cases, the formed alcohol accumulates, as in the case of rice suffering from rice blast
disease (coriolic acid) (Kato et al., 1984) or in seed oil ofDimorphotheca aurantiaca
(dimorphecolic acid or 9(S)-HODE) (Smith et al., 1960). These two natural com-
pounds, as well as other HPOD-derived alcohols, could be easily synthesized in
a two-step chemo-enzymatic procedure. After lipoxygenation, the hydroperoxide
could be reduced in the reaction medium (using NaBH 4 or SnCl 2 ) or after extraction
(for example with diethyl ether) by triphenylphosphine (TPP). In the synthesis of
both coriolic acid (Martini et al., 1994) and dimorphecolic acid (Martini et al.,
1996b), the latter procedure is preferred since the reaction is clean and easy to per-
form, and the excess of TPP as well as its formed oxide are easily separated from the
alcohol by flash column chromatography over silica.
16.4.2 Lactonization of hydroxy-acids
Coriolic acid, for example, possesses both an alcohol and a carboxylic acid function
which might give rise after cyclization to a macrocyclic C 13 lactone (Figure 14).
Roberts and colleagues synthesized such a lactone (Maguire et al., 1991) from cor-
iolic acid in 40 % yield (di-2-pyridyl disulfide, TPP, xylenes, 140 8 C, 20 h), the cyclic
ester being used further in a Diels-Alder reaction.
352 16 Properties and Applications of Lipoxygenases
Figure 14. Lactonization of coriolic acid (Maguire et al., 1991).