Synthesis and biological activity of allenic analogues of abscisic acid

Novel allenic analogues of abscisic acid (ABA) were synthesized and tested for ABA activity. The allene functional group was introduced by one of two methods: base catalysed isomerization of an enyne to an enallene conjugated to a ketone, or reduction of a 2-butyn-1,4-diol to an allenic alcohol. A 3:1 mixture of ( E)- and ( Z)-3-methyl-5-(4′,4′-ethylenedioxy-2′,6′,6′-trimethylcyclohex-2′-en-1′-ylidene)-2,4,5-pentatrienoic acids strongly inhibited growth of axenic duckweed ( Lemna gibba) causing a 50% reduction in frond number at 60 μg 1 −1 over 7 days in continuous light. Racemic ABA caused the same inhibition at 130 μ 1 −1. The mixture caused the production of turion-like structures, an effect known hitherto to be induced only by short photoperiods or by certain concentrations of ABA.