Extended Summaries: IUPAC Congress
1
INTRODUCTION
of the pyranols 3 and 4 generated (6S)- and (6R)-
tetrahydro-2,2,6-trimethyl-6-vinyl-2H-pyran-3-ones
9 and 10 respectively. Coinjection by chiral GC
showed (6S)-tetrahydro-2,2,6-trimethyl-6-vinyl-2H-
pyran-3-one 9 to be identical to the component
produced by Sissinghurst Pink and Pink Parfait. In
olfactometer studies, WFT were attracted to 5 but not
to 3 or to a mixture of 5 and 3 in the ratio produced by
Sissinghurst Pink cultivar, suggesting that there may
be separate olfactory receptors for the two diastereo-
isomers of linalool oxide and that other components of
the ¯ower volatiles must contribute to the attractive-
ness of the odours from Tapien Pink and Pink Parfait.
The indiscriminate use of herbicides has provoked an
increasing incidence of resistance in weeds and new,
more ef®cient and speci®c herbicides are needed.
Plants and micro-organisms contain allelochemicals
which act as their defence system and may act as
herbicides. Thus naturally occurring allelochemicals
may act as templates for the synthesis of active
compounds for use as herbicides1±5 There have been
several reports of the action of sesquiterpene lactones,
which occur as allelochemicals in some plants, as
inhibitors of plant germination and growth.6,7 This
activity has been attributed to analogues of com-
pounds containing a methylene-g-lactone moiety. We
have isolated such compounds from the leaves of
sun¯owers (Helianthus annuus L)8,9 and have synthe-
sised a number of guaianolide, eudesmanolide, ger-
macranolide, cis,cis-germacranolide, heliangolide and
melampolide analogues.10 As part of an on-going
search for new agrochemicals based on allelopathic
properties, we have synthesised some guaianolides and
heliannuols based on those present as biocommuni-
cators in selected sun¯ower cultivars and tested them
for their ability to affect germination and root and
shoot growth of some test plants.
ACKNOWLEDGEMENTS
This work was carried out with the ®nancial support of
the Ministry for Agriculture Food and Fisheries.
IACR-Rothamsted receives grant-aided support from
the Biotechnology and Biological Sciences Research
Council of the United Kingdom.
REFERENCES
1 Meou A, Bouanah N, Archelas A, Zhang XM, Guglielmetti R and
Furstoss R, Synthesis of all four stereoisomers of enantiomeri-
cally pure tetrahydro-2,2,6-trimethyl-6-vinyl-2H-pyran-3-ols.
Synthesis 681 (1991).
2
EXPERIMENTAL
2.1 Compounds
Figure 1 shows a selection of sesquiterpene lactones
isolated from natural sources and/or synthesised from
the readily available compound dehydrocostuslactone.
Developing new herbicide models from
allelochemicals†
2.2 Seed germination and root and shoot growth
bioassays
Stock test solutions in water (10 M) of pure test
Francisco A Mac´ıas,* Juan CG Galindo,
3
´
´
Jose MG Molinillo, Diego Castellano, Raul F Velasco
compound, or of the commercial herbicide mixture
terbutryntriasulfuron (Logran, Novartis), were di-
luted to the appropriate concentration and adjusted to
pH 6.0, using 2-(N-morpholino)ethanesulfonic acid.
The test solution (5ml), or a water control, was added
to a sheet of ®lter paper contained in a Petri dish, seeds
of the appropriate test plant were added and the dish
was then incubated in the dark in a growth chamber at
25°C. The test species were as follows (number of
seeds and incubation time in parentheses): lettuce,
Lactuca sativa L cvs Nigra and Roman (25; ®ve days);
tomato, Lycopersicon esculentum L (25; ®ve days);
onion, Allium cepa L (25; ®ve days); cress, Lepidum
sativum L (25; three days); barley, Hordeum vulgare L
(10; ®ve days) and wheat, Triticum aestivum L (10; ®ve
days). There were four replicate dishes per treatment,
except for wheat and barley, which had 20 replicates.
A similar number of controls incorporating seeds
incubated on ®lter paper treated with water was
included. The extent of germination, root and shoot
length were recorded and subjected to Welch's test
which determines differences, signi®cant at P =0.01,
between the treatment and the control.
and David Chinchilla
Departamento de Quı´mica Organica, Facultad de Ciencias,
Universidad de Cadiz, Apdo 40, 11510-Puerto Real, Cadiz, Spain
Abstract: Plants contain allelochemicals which are
their own defence systems and can act as herbicides.
Selected examples of guaianolides and heliannuols,
which are sesquiterpenes, are discussed in the
context of their potential use as natural herbicide
templates.
Keywords: Allelopathy; sesquiterpene; herbicide;
bioassay; standard target species
* Correspondence to: Francisco A Mac´ıas, Departamento de
Quimica Organica, Facultad de Ciencias, Universidad de Cadiz,
Apdo 40, 11510 Puerto Real, Cadiz, Spain
† Part 9 in the series ‘Natural Products as Allelochemicals’:
Part 8 – Macias FA, Simonet AM, Galindo JCG and Castellano, D,
Phytochemistry 50: 35–46 (1999)
Contract/grant sponsor: Secretaria General del Plan Nacional de I
and D, Spain; contract/grant number: CIYCT;AGF97-1230-C02-02
(Received 3 July 1998; accepted 17 February 1999)
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662
Pestic Sci 55:633±675 (1999)
Macias, Francisco A.
