A diverse suite of spiroacetals, including a novel branched representative, is released by female Bactrocera tryoni (Queensland fruit fly)

Abstract

A remarkably diverse suite of spiroacetals including a novel member of the rare, branched chain class has been identified in the glandular secretions of Bactrocera tryoni, the most destructive horticultural pest in Australia.

Biosynthesis of the Spiroacetal Suite in Bactrocera tryoni

“…[7] Incorporation However, the E,E and E,Z isomers of known spiroacetal 2-ethyl-7-propyl-1,6-dioxaspiro [4.5]decane (80) [21] were identified Thorough scrutiny of the GC-MS data from the pentane extract of female B. tryoni glands [6,7] revealed no presence of spiroacetals 80, whereas spiroacetal (E,E)-5 is known to occur naturally. [7] Therefore, as it is logical that the true, bona fide precursors should only produce naturally occurring spiroacetals, it was concluded that the 2,6-dioxygenated precursors were the biosynthetic intermediates, providing both spiroacetals (E,E)-3 and (E,E)-5.…”

“…Spiroacetals (E,E)-2 and (E,E)-3 are naturally present at levels of 5 and < 1 %, respectively, in the abdominal extract of female B. tryoni. [6] Thus, the incorporation levels can be gauged firstly from the relative peak intensities of the minor spiroacetal under investigation and the major spiroacetal ((2S,6R,8S)-1, 83 %), which acts as an internal standard. Additionally, (E,E)-2 acts as a second internal standard for assessing the incorporation levels into (E,E)-3.…”

“…P450-catalysed oxidation of a fatty acid at the positions corresponding to C2 and C6 of the predicted C 11 fragment could be followed by b-oxidation and chain shortening to give the C 12 b-ketoacid, which upon decarboxylation furnishes a diketone. C2 reduction then affords 2-hydroxyundecan-6-one (6). The putative P450 involved in the final hydroxylation has been determined in B. cucumis to S hydroxylate the S substrate preferentially at the (wÀ1) position; [8,11] this accounts for the biosynthesis of (2S,6R,8S)-1.…”

“…[6] Enantioselective GC-MS analysis of this extract identified (2S,6R,8S)-1 as the major component, with unusual even carbon-numbered spiroacetals (e.g., (2S,6R,8S)-2), and novel branched chain ((2S,6R,8S)-4) [6] and [5.6]spiroacetals ((2S,6R,8S)-5) [7] also being present.…”

“…However, the enzyme involved is also capable of S hydroxylation of the R substrate and R hydroxylation of the S substrate, [11] and so (2S,6S,8R)-1, (2R,6R,8S)-1 and (2R,6S,8R)-1, other naturally occurring B. tryoni spiroacetals can be generated. [6,10] Furthermore, a degree of site flexibility in the proposed, final P450-catalysed hydroxylation [8] at the (wÀ2) position would result in the biosynthesis of the other naturally occurring C 11 spiroacetals, (E,E)-7 and (E,Z)-7. [5] We now describe the first investigations of the biosynthesis of the minor C 12 and C 13 spiroacetals released by female B. tryoni.…”