ANTIFUNGAL ACTIVITY OF FLAVONOIDS ISOLATED FROM ULEX SPECIES

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ANTIFUNGAL ACTIVITY OF FLAVONOIDS ISOLATED FROM
ULEX SPECIES P. Máximo, A. Lourenço, S. Feio
and J. Roseiro Departamento de Química, Centro
de Química Fina e Biotecnologia, Faculdade de
Ciências e Tecnologia Universidade Nova de
Lisboa, Quinta da Torre, 2825-114 Caparica,
Portugal. Instituto Nacional de Engenharia e
Tecnologia Industrial IBQTA, Laboratório de
Microbiologia Industrial Azinhaga dos Lameiros,
1699 Lisboa Codex, Portugal.
ACTIVE COMPOUNDS
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INTRODUCTION Isoflavonoids are described in
Leguminosae as phytoallexins and defence agents
against insects. There are different structural
factors in isoflavonoid molecules that are
important for their antimicrobial activity. The
presence of isoprenoid groups proved to increase
activity in isoflavons and pterocarpans and the
relative acidity and number of hydroxyl groups
are important in structure-activity relations
1,2.
RESULTS
AND DISCUSSION The fungicidal activity of 18
isoflavonoids together with 2 chalcones, 1
flavone and 1 isoflavanone, isolated from Ulex
species, was tested by the bioautographic method
against Cladosporium cucumerinum. Most of the
test compounds showed antifungal activity and
inhibited the fungal growth at 100 µg
concentration. From the experimental results some
structure-activity comments can be drawn. Among
the 11 isoflavones tested (1-4,13-17,20,21) the
structures with an open chain isoprenoid
substituent at C-8 were active (1,2,4). The C-6
substituted compounds (13-15,17) had no activity,
except for one dimethylpyrano substituted
compound 21 that partially inhibited the fungal
growth. All the pterocarpans studied (5-9,12,22)
have an 8,9-methylenodioxy group and their
structural differences are in ring A
substitution. The presence of a C-2 hydroxyl
group imparts lack (22) or only partial
fungicidal activity (18). The presence of
hydroxyl groups seems to play an important role
for antifungal behaviour of this kind of
compounds.
NON ACTIVE COMPOUNDS
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EXPERIMENTAL Cell suspension for
thin-layer chromatography (TLC) bioassay
Cladosporium cucumerinum CCMI 206 was grown on
malt extract agar at 25ºC in pyrex Petri dishes
for ten days. The mycelium was harvested from the
agar plates in a small volume of fresh Homans and
Fuchs nutrient broth 3, filtered through four
layers of sterilised gauze and diluted in
nutrient broth in order to obtain 106 cell
ml-1. Bioautographic TLC bioassay Aliquots of the
test compounds (100 mg) were spotted, in
quadruplicate, on silica gel 60 F254 TLC plates
(Merck 5554), which were eluted with the
appropriate eluent for each sample (CHCl3-MeOH
0.6 - 1.25 mixts). Developed chromatograms
were dried and the spots of each compound were
marked under 254 nm UV light. A 20 ml sample of
the cell suspension was sprayed evenly over each
plate, in a glove box. Plates were incubated in
closed pyrex trays lined with moist paper at 25ºC
for two-three days, protected from light.
Bioautograms were evaluated by clear spots,
indicating zones of inhibition.
SLIGHTLY ACTIVE COMPOUNDS
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Acknowledgments We wish to thank the people from
Herbário, Museu, Jardim Botânico, Faculdade de
Ciências, Universidade de Lisboa (Portugal) for
collecting plant material. One of us (P. M.)
wishes to thank FCT (Portugal) for a PRAXIS XXI
fellowship.
References 1 Tahara, S. and Ibrahim, R.K.
(1995) Phytochemistry 38, 1073. 2 Tahara, S.,
Katagiri, Y., Ingham, J.L. and Mizutani, (1994)
Phytochemistry 36, 1261. 3 Homans A.L. and
Fushs A. (1970) J. Chromatogr. 51, 327-329.