Strigolactones (SLs) constitute a new class of plant hormones of increasing importance in plant science. The structure of natural SLs is too complex for ready access by synthesis. Therefore, much attention is being given to design of SL analogues and mimics with a simpler structure but with retention of bioactivity. Here new hybrid type SL mimics have been designed derived from auxins, the common plant growth regulators. Auxins were simply coupled with the butenolide D-ring using bromo (or chloro) butenolide. D-rings having an extra methyl group at the vicinal C-3' carbon atom, or at the C-2' carbon atom, or at both have also been studied. The new hybrid type SL mimics were bioassayed for germination activity of seeds of the parasitic weeds S. hermonthica, O. minor and P. ramosa using the classical method of counting germinated seeds and a colorimetric method. For comparison SL mimics derived from phenyl acetic acid were also investigated. The bioassays revealed that mimics with a normal D-ring had appreciable to good activity, those with an extra methyl group at C-2' were also appreciably active, whereas those with a methyl group in the vicinal C-3' position were inactive (S. hermonthica) or only slightly active. The new hybrid type mimics may be attractive as potential suicidal germination agents in agronomic applications.

Palacký University Faculty of Science Centre of the Region Haná for Biotechnological and Agricultural Research Department of Chemical Biology and Genetics Šlechtitelů 241 27 CZ 783 71 Olomouc Czech Republic

Palacký University Faculty of Science Centre of the Region Haná for Biotechnological and Agricultural Research Department of Chemical Biology and Genetics Šlechtitelů 241 27 CZ 783 71 Olomouc Czech Republic; Radboud University Institute for Molecules and Materials Cluster of Organic Chemistry Heyendaalsweg 135 6525AJ Nijmegen The Netherlands

Radboud University Institute for Molecules and Materials Cluster of Organic Chemistry Heyendaalsweg 135 6525AJ Nijmegen The Netherlands

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Hybrid-type strigolactone analogues derived from auxins