The discovery of 2,5-dialkylcyclohexan-1,3-diones as a new class of natural products

doi:10.1073/pnas.0900646106

The discovery of 2,5-dialkylcyclohexan-1,3-diones as a new class of natural products

^aDepartment of Chemistry, Organic Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany;
^bDepartment of Chemistry and
^cDepartment of Botany and Zoology, School of Biology, Australian National University, Canberra ACT 0200, Australia; and
^dInstitute of Systematic Botany, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland

Edited by Jerrold Meinwald, Cornell University, Ithaca, NY, and approved March 31, 2009 (received for review January 22, 2009)

Abstract

Orchids employing sexual deceit attract males of their pollinator species through specific volatile signals that mimic female-released sex pheromones. One of these signals proved to be 2-ethyl-5-propylcyclohexan-1,3-dione (chiloglottone1), a new natural product that was shown to be most important in the relations between orchids of the genus Chiloglottis, native to Australia, and corresponding pollinator species. Systematic investigations on the mass spectrometric fragmentation pattern of 2,5-dialkylcyclohexan-1,3-diones identified key ions providing information about the structures of the substituents at positions 2 and 5. Results enabled us to identify 2-ethyl-5-pentylcyclohexan-1,3-dione (chiloglottone2) and 2-butyl-5-methylcyclohexan-1,3-dione (chiloglottone3) as new natural products that play a decisive role in the pollination syndrome of some Chiloglottis species. During field bioassays, pure synthetic samples of chiloglottone1–3 or mixtures thereof proved to be attractive to the corresponding orchid pollinators. Because of their likely biogenesis from ubiquitous fatty acid precursors, 2,5-dialkylcyclohexan-1,3-diones may represent a hitherto overlooked, widespread class of natural products.

Footnotes

¹To whom correspondence should be addressed. E-mail: francke{at}chemie.uni-hamburg.de
Author contributions: W.F. designed research; S.F., F.I., C.M.S., R.T., J.P., R.A.B., R.P., and F.P.S. performed research; S.F., R.T., and W.F. analyzed data; and R.P. and W.F. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.