Biosynthesis of Dodecano‐4‐lactone in Ripening Fruits: Crucial Role of an Epoxide‐Hydrolase in Enantioselective Generation of Aroma Components of the Nectarine ( Prunus persica var. nucipersica ) and the Strawberry ( Fragaria ananassa )

Early steps in the biosynthesis of dedecano‐4‐lactone in ripening nectarines ( Prunus persica var. nucipersica ) and strawberries ( Fragaria ananassa ) were studied using cis ‐9,10‐([ 18 O]epoxy)heptadecanoic acid ( 5 ), instead of the natural C 18 ‐precursor epoxystearic acid 1 . In nectarines, an epoxide hydrolase catalyzed, in a highly regio‐ and enantioselective reaction, the attack of H 2 O at C(9) of epoxy acid 5 yielding preferentially (9 R ,10 R )‐dihydroxyheptadecanoic acid 6a as an early intermediate and, after further metabolization, undecano‐4‐lactone 7a . In strawberries, the same transformation exhibited only a moderate regio‐ and enantioselectivity. Besides the previously established function of phytogenic epoxide hydrolases involved in generating oxygenated fatty‐acid derivatives, which are used in cutin monomer production and plant defence, a new rǒle for these enzymes now emerges in the enantioselective production of aroma components of ripening fruits. The cis ‐9,10‐([ 18 O]epoxy)heptadecanoic acid (≥ 98% 18 O; 5 ) was obtained in good overall yield (68%) from isopropyl (9 Z )‐heptadec‐9‐enoate using 18 O 2 gas in a free‐radical chain reaction in the presence of 2‐methylbutanal.