The synthesis and biological evaluation of labelled karrikinolides for the elucidation of the mode of action of the seed germination stimulant Adrian Scaffidi a, * , Gavin R. Flematti a , David C. Nelson a, b , Kingsley W. Dixon c, d , Steven M. Smith a, b , Emilio L. Ghisalberti a a School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, Crawley, Western Australia 6009, Australia b Plant Energy Biology, The University of Western Australia, Crawley, Western Australia 6009, Australia c Kings Park and Botanic Garden, West Perth, Western Australia 6005, Australia d School of Plant Biology, The University of Western Australia, Crawley, Western Australia 6009, Australia article info Article history: Received 15 August 2010 Received in revised form 1 October 2010 Accepted 1 November 2010 Available online 5 November 2010 Keywords: Karrikinolide Karrikins Germination stimulant Smoke Seed dormancy abstract Karrikins are a novel class of naturally occurring plant growth regulators that promote seed germination among a diverse range of species. Currently little is known about the mechanism by which these compounds overcome seed dormancy and initiate germination. The preparation of various karrikinolide derivatives provides an opportunity to investigate the karrikinolide mode of action at the cellular and molecular level. The first synthesis and biological evaluation of analogues suitable for use in metabolic labelling, affinity chromatography, photoaffinity labelling and NanoSIMS experiments are reported. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Plant-derived smoke has a remarkable ability to increase the germination success of more than 1200 species from over 80 gen- era 1 located in various regions around the world including Aus- tralia, 2 South Africa, 3 North America 4 and Europe. 5 Interestingly, this response is not limited to species present in fire-prone regions as smoke-stimulated germination has also been observed for spe- cies from regions not frequented by fire. 6 The key germination stimulant from smoke was first isolated and identified by Flematti et al. as 3-methyl-2H-furo[2,3-c]pyran-2- one 1 , now termed karrikinolide 1 (Fig. 1). 7 This naturally occurring germination stimulant displays activity in a variety of species at concentrations as low as one-part-per-billion. 1,8 Recently it has been revealed that at least five other analogues are present in smoke leading to the collective name ‘karrikins’. 9 The mode of action of karrikinolide remains unknown, however interactions with factors influencing germination such as light, gibberellic acid and abscisic acid have all been observed. 10,11 Unlocking the secrets behind karrikinolide perception may result in a better understanding of the processes involved in regulating seed dormancy and germination, thus facilitating broader environ- mental and commercial applications. The potential for promoting a more uniform release from seed dormancy, improving germina- tion rates and widening the range of species that respond, will allow for more effective plant regeneration and conservation in restora- tion programs. In addition, novel approaches to weed control through initiating germination followed by treatment with knock- down herbicides offers great potential for reducing weed seed levels in agricultural settings. 1 Since the discovery of 1 , only four syntheses have been pub- lished. These include the preparation of 1 from pyromeconic acid 2, 12 ethyl-4-methyl-2-oxo-2,5-dihydro-furan-3-carboxylate 3, 13 2- furfurylmethanol 4 14 and D-xylose 5 15 (Scheme 1). O O O 1 1 3 4 5 7 Fig. 1. Karrikinolide. * Corresponding author. E-mail address: adrian.scaffidi@uwa.edu.au (A. Scaffidi). Contents lists available at ScienceDirect Tetrahedron journal homepage: www.elsevier.com/locate/tet 0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2010.11.006 Tetrahedron 67 (2011) 152e157