Pergamon 0031-9422(94)00761-6 Phytochemistry, Vol. 38, No. 4, pp. 821 823, 1995 Copyright ((~ 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0031 9422/95 $9.50 + 0.00 BIOLOGICAL ACTIVITY OF METHYL 7-METHYL-JASMONATES YASUNORI KODA, JANE L. WARD* and MICHAEL H. BEALE*t Department of Botany, Faculty of Agriculture, Hokkaido University, Sapporo 060, Japan; *Department of Agricultural Sciences, University of Bristol, Institute of Arable Crop Research, Long Ashton Research Station, Bristol BS18 9AF, U.K. (Received in revisedform 23 August 1994) Key Word Index--Solanum tuberosum; Solanaceae; Bryonia dioica; Cucurbitaceae; Glycine max; Leguminosae; Arena sativa; Gramineae; methyl 7-methyl-jasmonates; methyl jasmonate; bioassay. Abstract--Stereochemically-locked cis- and trans-7-methyl derivatives of methyl jasmonate were found to have low biological activity in several assays, including that with Bryonia dioica. This suggests that the introduction of the locking methyl group at position 7 considerably lowers affinity for the jasmonate receptor, presumably owing to a steric effect. INTRODUCTION Jasmonic acid (1) and the corresponding methyl ester (2) are endogenous signalling compounds involved in plant reactions to stresses such as wounding and pathogen attack. These ~,fl-disubstituted-cyclopentanones are bio- synthesized from ~-linolenic acid, apparently as the cis- stereoisomer [1]. However, isolated and synthetic jasmonate exists with the ~- and fl-substituents mainly (ca 95%) in the more thermodynamically stable trans-config- uration. We have attempted to determine which of the stereoisomers is responsible for the observed biological activities ofjasmonic acid by synthesizing analogues that cannot be interconverted by enolization. Recently, we described the synthesis and preliminary biological evalu- ation of the cis- and trans-7-methyl derivatives of methyl jasmonate (3) and (4) [2]. In this work, we examined the derivatives for induction of tendril coiling in shoots of Bryonia dioica exposed to airborne compound. In this paper, we describe a more detailed quantitative assess- ment of the bioactivity of these derivatives using a number ofjasmonate-responsive systems. RESULTS AND DISCUSSION The assay of the airborne activity of methyl jasmonate for the induction of tendril coiling has been described by Falkenstein et al. [3]. Owing to differences in volatility between derivatives of differing [M] +, this bioassay cannot give accurate quantitative data on their relative bioactivity. However, our initial experiments indicated that methyl 7-methyl-7-epi-jasmonate (3) was active and that the trans-isomer (4) was not [2]. In order to quantify this activity, we needed to examine the relative activities +Author to whom correspondence should be addressed. of 2-4 in other well characterized jasmonate responses. The 7-methyl epimers were prepared and purified by silica gel flash chromatography as described previously [2]. These new samples of 3 and 4 were further purified by preparative HPLC. Both showed little activity in the airborne induction of tendril coiling in Bryonia dioica. This is in contrast to our previous observation that the cis-isomer (3) had activity in this assay [2]. A possible explanation for our initial observations of bioactivity in our original sample of 3 was contamination with methyl jasmonate. Methyl jasmonate impurities were difficult to distinguish from methyl 7-methyl-jasmonate (4) by NMR. GC mass spectroscopic analysis revealed traces of methyl jasmonate in our original preparation of 3. This arises from incomplete reaction in the alkylation step, and co-purification of the starting materials through the rest of the synthetic sequence. Purification by preparative HPLC was necessary to ensure complete purity of 3. Further investigation of the effects of 2-4 on Bryonia tendrils was carried out with cut tendrils floating in Petri dishes containing solutions of the jasmonate derivatives, as described by Falkenstein et al. [3]. The results were inconclusive as far as 3 and 4 were concerned, but methyl jasmonate at 100 #M was clearly active. One problem that we encountered with this assay was reproducibility, with even some untreated cut tendrils tending to coil, presumably owing to a response to wounding or mechan- ical shock. Thus, we found it difficult to assess com- pounds of low to medium activity in this assay. In order to define more clearly the activity of the 7- methylated isomers, they were assayed in potato tuberiza- tion, senescence promotion and inhibition of cell division assays as described previously [4]. The results are shown in Figs 1-3. Methyljasmonate is known to be as active as the natural agonists, tuberonic acid and its glycoside, in the induction of tubers in potato shoots [5]. It has also 821