Phytotoxic and Antimicrobial Activities of Catechin Derivatives

Article abstract of DOI:10.1021/jf030653+

(±)-Catechin is a potent phytotoxin, with the phytotoxicity due entirely to the (-)-catechin enantiomer. (+)-Catechin, but not the (-)-enantiomer, has antibacterial and antifungal activities. Tetramethoxy, pentaacetoxy, and cyclic derivatives of (±)-catechin retained phytotoxicity. The results indicate that antioxidant properties of catechins are not a determining factor for phytotoxicity. A similar conclusion was reached for the antimicrobial properties. Centaurea maculosa (spotted knapweed) exudes (±)-catechin from its roots, but the flavanol is not re-absorbed and hence the weed is not affected. The much less polar tetramethoxy derivative may, however, be absorbed and hence be able to cause toxicity. Because of the combination of phytotoxicity and antimicrobial activity, (±)-catechin could be a useful natural herbicide and antimicrobial.

Full text of DOI:10.1021/jf030653+

J. Agric. Food Chem. 2004, 52, 1077−1082 1077
Phytotoxic and Antimicrobial Activities of Catechin Derivatives
RAVIKANTH VELURI,†,§ TIFFANY L. WEIR,† HARSH PAL BAIS,†
FRANK R. STERMITZ,§ AND JORGE M. VIVANCO*,†
Department of Horticulture and Landscape Architecture and Department of Chemistry,
Colorado State University, Fort Collins, Colorado 80523-1173
(()-Catechin is a potent phytotoxin, with the phytotoxicity due entirely to the (-)-catechin enantiomer.
(+)-Catechin, but not the (-)-enantiomer, has antibacterial and antifungal activities. Tetramethoxy,
pentaacetoxy, and cyclic derivatives of (()-catechin retained phytotoxicity. The results indicate that
antioxidant properties of catechins are not a determining factor for phytotoxicity. A similar conclusion
was reached for the antimicrobial properties. Centaurea maculosa (spotted knapweed) exudes (()-
catechin from its roots, but the flavanol is not re-absorbed and hence the weed is not affected. The
much less polar tetramethoxy derivative may, however, be absorbed and hence be able to cause
toxicity. Because of the combination of phytotoxicity and antimicrobial activity, (()-catechin could be
a useful natural herbicide and antimicrobial.
KEYWORDS: Catechin derivatives; herbicide; phytotoxicity; antimicrobial activity
INTRODUCTION
(5, 6). (+)-Catechin is also a well-known antioxidant free radical
scavenger, and antifungal, antitumor, and insect repellant
properties have been attributed to it as well. Previous papers
have speculated that the antioxidant properties of (+)-catechin
are increased by converting the freely rotating, flexible catechin
to a rigid, planar molecule (7).
We have begun a series of studies to explore relative
phytotoxicity and antimicrobial potencies among these and other
common flavonoids. The flavones kaempferol and dihydroquer-
cetin and the flavanol (+)-epicatechin were phytotoxic, but less
so than (-)-catechin, whereas quercetin, naringenin, and (-)-
epicatechin were devoid of such activity (6). To investigate
structure-activity relationships for root phytotoxicity and
antimicrobial activity among the catechins, we compared several
synthetic derivatives of (+)- and (()-catechin (Figure 1) for
these properties.
Natural products have become increasingly more sought after
as ecologically safer alternatives to herbicides and pesticides,
as well as a source of new medicines. However, the biological
activity of these compounds is often affected by their stereo-
chemistry, lipophilicity, and other factors. Slight modifications
can alter the bioactivity either positively or negatively. For
example, (-)-boscialin, which is a natural product found in a
number of medicinal plants, was less active against various
bacterial and fungal pathogens than its (+) isomer, whereas (-)-
epiboscialin was more active than (+)-epiboscialin (1). This
structure-dependent activity has also been noted in a number
of synthetic molecules used as herbicides and insecticides
(2-4).
Recently, we have reported that (()-catechin is secreted into
the soil rhizosphere from the roots of an invasive weed,
Centaurea maculosa L. (5). Bioassays revealed that (-)-
catechin, (-)-1, but not (+)-catechin, (+)-1, is potently phyto-
toxic (5, 6). (-)-Catechin inhibits seed germination in addition
to killing plant seedlings via the roots and is as potent as the
herbicide 2,4-D when applied to broad-leaf plants. When
naturally secreted by the roots of C. maculosa, (-)-catechin
undoubtedly plays a role in the invasive behavior of the plant.
Because catechins are present in many plants, including food
plants, the use of either (()- or (-)-catechin as a herbicide could
be ecologically benign.
MATERIALS AND METHODS
Plant Culture Conditions. Seeds of C. maculosa were obtained
from natural populations in Missoula, MT, and seeds of Potentilla
arguta were obtained from Dr. Ruth Hufbauer (Colorado State
University). Seeds of Gaillardia aristata, Arabidobsis thaliana (Col-
0), Lycopersicum lycopersicon, and Ocimum basilicum were purchased
from Wind River Seed (Manderson, WY), Lehle Seeds (Round Rock,
TX), The Rocky Mountain Seed Co. (Denver, CO), and Shepherd’s
Garden Seeds (Torrington, CT). Seeds were washed in running tap water
and surface sterilized using sodium hypochlorite (0.3% v v-1) for 30
min, followed by three or four washes in sterile distilled water. Surface-
sterilized seeds were inoculated on static Murashige and Skoog (MS)
(8) basal medium in Petri dishes for germination. Seeds were allowed
to germinate for 10 days after roots and shoots emerged. The
temperature within the growth chamber was 27 ( 2 °C, and the light
intensity was 4.41 J m-2 s-1. Ten-day-old seedlings were transferred
to sterile 50 mL culture tubes with 5 mL of liquid MS basal medium.
Alternatively, (+)-catechin produced by the plant, but not
(-)-catechin, was found to have strong antimicrobial properties
* Author to whom correspondence should be addressed [e-mail
jvivanco@lamar.colostate.edu; fax (970) 491-7745].
† Department of Horticulture and Landscape Architecture.
§ Department of Chemistry.
10.1021/jf030653+ CCC: $27.50 © 2004 American Chemical Society
Published on Web 02/10/2004

1078 J. Agric. Food Chem., Vol. 52, No. 5, 2004
Veluri et al.
derivatives was added to the liquid PDB media and serially diluted to
provide tested concentrations ranging from 0.05 to 100 µL. One hundred
microliters of the spore suspensions was then added to the wells to
determine the minimum concentration of each derivative required to
inhibit fungal germination. Control wells contained 100 µL of fungal
spores alone with the highest volume of DMSO used or serial dilutions
of a 1 mg mL-1 stock solution of (+)-catechin. The plates were covered
with sterile lids and placed in a polystyrene box lined with moistened
filter paper to maintain high humidity and incubated at 37 °C. The
absorbance of each well was determined at OD630 nm with an Opsys
MR, microtiter plate reader (Dynex Technologies) after 96 h of
incubation.
Microscopy. To check activity against bacterial plant pathogens,
bacterial cells in microtiter plates treated with the catechin derivatives
were stained with Molecular Probes BacLight bacterial viability kit
(Eugene, OR) by incubation at room temperature in the dark for 20
min, according to the manufacturer’s manual. The samples were
mounted with Citifluor antifading (Sigma) and observed for fluorescence
with a fluorescent microscope (Fluroview LGPS-2, Olympus).
Synthesis of Pentaacetylcatechins, (+)- and (()-2. (+)-Catechin
(Sigma, 100 mg) was dissolved in 0.5 mL of pyridine, and 0.5 mL of
acetic anhydride was added; the solution was allowed to stand overnight
at room temperature. The solution was then poured into 15 mL of water
and extracted with EtOAc (10 mL × 3). The extract was evaporated
Figure 1. Structures of catechins and derivatives.
Plants were then allowed to stabilize in the liquid medium for 5 days
prior to treatment with (+)/(()-catechin derivatives.
1
to yield (+)-2 (104 mg), the H and 13C NMR and mass spectra of
Plant Growth Inhibitory Bioassay. A stock solution of 10 mg mL-1
of each catechin (Sigma, St. Louis, MO) and catechin derivative was
prepared in methanol. To ensure that maximum activity was retained,
fresh stock was prepared prior to each experiment. The solutions were
filter sterilized using 0.22 µm filters (Millipore, Cork County, Ireland)
and added to the liquid media containing the various plant species at
concentrations of 10, 50, 100, and 200 µg mL-1. Control plants were
treated with a filter-sterilized solution of methanol added at the same
volume as the highest concentration of treated plants. Plant cultures
were maintained at 27 ( 2 °C on an orbital platform shaker set at 90
rpm and exposed to 24 µmol m-2 s-1 light intensity for 7 days. After
7 days, root length, shoot number, and fresh weight were recorded,
and all plants were scored for mortality.
which were identical to those in the literature (9). Acetylation of (()-
catechin (Sigma) was similarly carried out to yield (()-2.
Synthesis of Tetramethoxycatechins, (+)- and (()-3. A mixture
of (+)-catechin (100 mg) and trimethylsilyldiazomethane (2.0 M
solution in n-hexane, 5 mL) in methanol (5.0 mL) was stirred at room
temperature overnight. After the excess of trimethylsilyldiazomethane
was decomposed with acetic acid, the reaction mixture was evaporated
to dryness. The residue was purified by column chromatography using
silica gel with hexane/ethyl acetate (80:20) to yield (+)-3 (45 mg), the
1H and 13C NMR spectra of which were identical with those in the
literature (10). Similarly, methylation of (()-catechin yielded (()-3.
Synthesis of 6a,12a-trans-2,3,8,10-Tetrahydroxy-5,5-dimethyl-
5,6a,7,12a-tetrahydro[1]benzopyrano[3,2-c][2]benzopyrans (+)- and
(()-4. These were prepared similarly to literature methods (7, 11, 12).
(+)-Catechin (100 mg) was dissolved in moist acetone. p-Toluene-
sulfonic acid (60 mg) was added and the solution stirred for 3 days at
room temperature. The solvent was evaporated (N2 gas) and the mixture
subjected to preparative layer chromatography in CHCl3/MeOH (90:
Antibacterial Assays. Bacterial isolates from a broad phylogenetic
range were tested for inhibition of growth with catechin and synthesized
catechin derivatives. Initial stock solutions of (1 mg mL-1) of each
compound were prepared in dimethyl sulfoxide (DMSO). Bacterial
suspension cultures of Erwinia carotoVora, Erwinia amyloVora, Xan-
thomonas campestris pv. Vesicatoria, and Pseudomonas fluorescens
were grown overnight at 37 °C to OD600 ) 0.2. Assays were performed
in 96-well, sterile, flat-bottom microtiter plates (Nalge Nunc Interna-
tional, Roskilde, Denmark). Test wells contained 5 µL of the bacterial
suspension and serial dilutions of the tested derivatives ranging from
100 to 0.05 µg. Control wells contained 5 µL of bacterial isolates alone
with the highest volume of DMSO used or serial dilutions of a 1 mg
mL-1 stock solution of (+)-catechin, which has known antifungal
activity (2). Bacterial isolates were incubated at 37 °C for 24 h. The
absorbance of each well was determined at OD600 nm with an Opsys
MR, microtiter plate reader (Dynex Technologies). Each isolate was
tested against all compounds at the total range of concentrations (100-
0.05 µg) in two separate replicates.
Fungal Bioassay Procedures. Five fungal isolates, Aspergillus niger,
Trichoderma reesi, Trichoderma Viridens, Pennicillium sp., and
Fusarium oxysporum, were tested for inhibition of spore germination
with synthetic derivatives of catechin. Initial stock solutions of (1 mg
mL-1) of each derivative were prepared in DMSO. Fungal isolates were
maintained on potato dextrose agar (PDA) in the dark at 24 °C until
sporulation occurred. Spore suspensions were prepared from 4-week-
old fungal cultures by rinsing the plates with 5 mL of sterile distilled
water. Spore suspension concentration was estimated using an Ultra
Plane Improved Neubauer cell counting chamber (Scientific Products,
West Sussex, U.K.) and adjusted to 1 × 105 spores mL-1 with sterile
distilled water. Fungal spore germination assays were performed in
96-well, sterile, flat-bottom microtiter plates (Nalge Nunc International).
One hundred microliters of the 1 mg mL-1 stock solutions of catechin
1
10) to yield (+)-4 (18 mg), 0.35 Rf, the H and 13C NMR and mass
spectra of which were identical to those in the literature (7, 11, 12).
Similarly, (()-catechin was converted to (()-4.
Statistical Analysis. Due to the incremental nature of the treatment
concentrations, standard deviations for bacterial minimum inhibitory
concentrations (MICs) are expressed as (5% of the mean MIC, and
all other standard deviations are calculated on the basis of the square
root of the variance from the mean.
RESULTS AND DISCUSSION
Comparative phytotoxicities at the 200 µg mL-1 level, as
measured by inhibition of shoot and root differentiation, varied
depending on both derivative structure and test plant (Figure
2). The MICs for some derivatives against some plants were as
low as 50 µg mL-1; however, the results at 200 µg mL-1
allowed presentation of all data on a single graph (Figure 2).
All of the synthesized derivatives were screened for phytotox-
icity. The general results were that only (()-3 and (()-4 were
active phytotoxins, usually equal to the potency of (-)-catechin
(Figure 2). Because the same derivatives of (+)-catechin were
inactive, the inhibitions observed for the (()-derivatives un-
derestimate the true activity of (-)-catechin by about half. One
of the more striking results was the inhibition of root dif-
ferentiation of C. maculosa by the (()-3 and (()-4 derivatives
(Figure 2B). C. maculosa is very resistant to its own exuded

Phytotoxic and Antimicrobial Activities of Catechin Derivatives
J. Agric. Food Chem., Vol. 52, No. 5, 2004 1079
Figure 2. Effect of 200 µg mL-1 of (−)-catechin (1), (±)-1, tetramethoxycatechin [(±)-3], and the isopropylidylcatechin [(±)-4] on shoot (A) and root (B)
differentiation of selected plant species on the seventh day after treatment. Data represent the percent inhibition relative to the untreated control in
shooting and rooting efficiency response in various tested seedlings. Values are mean ± SD, n ) 5.
(-)-catechin (5), but here we find that root differentiation is
potently inhibited (Figure 2B) by both (()-3 and (()-4.
Although C. maculosa is not susceptible to exogenous (-)-
catechin in the growth medium, if the flavanol is directly injected
into plant cells, mortality occurs (13). Thus, it is possible that
conversion of (-)-catechin to the much less polar methoxy and
acetyl derivatives now allows penetration of the phytotoxin into
the root, thus inhibiting growth at the cellular level.

1080 J. Agric. Food Chem., Vol. 52, No. 5, 2004
Veluri et al.
Figure 3. Antibacterial activities of (+)-catechin (1), pentaacetylcatechin -(+)- and (±)-2], tetramethoxycatechin [(+)-3 and (±)-3], and the isopropylidylcatechin
[(+)-4 and (±)-4] on different bacteria. The concentration of compounds was administered at one dose below their respective MIC levels (see Table 1).
Net bacterial growth was calculated by subtracting the OD at the beginning from the OD after 24 h of incubation. Percent inhibition (%I) was
600
600
calculated using net bacterial growth based on OD600 readings with the following formula: [(untreated − treated)/untreated] × 100. Values are mean ±
SD, n ) 5.
The catechins are widely known as strong antioxidants, with
those properties being derived from the ortho-disubstituted
phenolic groups (14 and references cited therein). Blocking these
functions with methyl groups [as in (()-3] removes the
antioxidant properties. Because (()-3 was still potently phyto-
toxic, this property must not stem from antioxidant activity.
The potent antibacterial activity of (+)-catechin does not
appear to have been previously recognized. This may stem from
a general focus on Gram-positive bacteria of direct importance
in human health and the fact that (+)-catechin has little or no
effect on those organisms previously tested. Thus, (+)-catechin
was reported to be completely inactive against Bacillus cereus,
Staphylococcus aureus, Staphylococcus coagulans, and Citro-
bacter freundii and showed only minimal activity against
Escherichia coli (17). Very weak activity was reported against
Lactobacillus rhamnosus, but none against other Lactobacillus
species, E. coli, Salmonella enterica, Enterococcus faecalis, or
Bifidobacterium lactis (18). These results are to be contrasted
with those of Table 1, where potent activity was observed
against a group of Gram-negative plant pathogens. It seems
likely that part of the ecological imperative (13) for C. maculosa
invasiveness is its root exudation of a potent inhibitor of such
pathogens.
That bioactivity of catechins, in some cases, is not dependent
on antioxidant power has also been noted by others (15, 16).
The enantiospecificity of phytotoxicity suggested an important
role for the C-2/C-3 stereochemistry and/or the presence of a
free 3-OH group. Compound (()-4 has a blocked 3-OH group
and, because it is planar (13), has an altered spatial arrangement
between the B and C rings. Because (()-4 was active in all
systems (Figure 2), it is clear that a free 3-OH is not necessary
and that some modification of spatial relationships in the C-2/
C-2′ region (through cyclization) is also not detrimental.
(+)-Catechin had significant antibacterial activity against all
four organisms and was similarly potent against each (Figure
3). All of the (+)-derivatives were also active, but none were
quite as active as (+)-catechin. The activities of (+)-2, (+)-3,
and (+)-4 were essentially equal to each other. As compared
to (+)-catechin, the absence of phenolic character as in (+)-2
and (+)-3 or lack of a free C-3 OH as in (+)-2 and (+)-4 had
some detrimental effect on activity but did not eliminate it. In
each case the (+)-derivative was, as expected, more active than
the (()-derivative. Fluorescence microscopy of bacterial cultures
treated with the synthetic catechin derivatives and stained with
the BacLight bacterial viability kit revealed that all of the tested
derivatives had bactericidal activity. Figure 4 shows an example
for compound (+)-4.
(+)-Catechin and the derivatives were also tested for anti-
microbial activity against root-colonizing fungi: Trichoderma
reesi, Trichoderma Viridins, Fusarium oxysporum, Aspergillus
niger, and Penicillium sp. (+)-1 was active against all five fungi
at 12.5-25 µg mL-1, (+)-2 was active only against F.
oxysporum (25 µg mL-1), and (+)-3 showed activity against
Penicillium sp. and A. niger (25 µg mL-1). None of the other
derivatives showed antifungal activity. (+)-Catechin was previ-
ously reported to be inactive against the crop plant fungi Botrytis
cinerea, Cladosporium echinulatum, and Penicillium griseo-
flulVum (17). Our results extend the view that (+)-catechin
exudation can be an ecologically important plant defense.
Both (()- and (-)-catechin are commercial products and
hence could be available as herbicides. As a very rare plant

Phytotoxic and Antimicrobial Activities of Catechin Derivatives
J. Agric. Food Chem., Vol. 52, No. 5, 2004 1081
commercial development of (()-catechin would provide a
compound with both potent herbicidal and antimicrobial activi-
ties.
LITERATURE CITED
(1) Busch, J.; Grether, Y.; Ochs, D.; Sequin, U. Total synthesis and
biological activities of (+)- and (-)-boscialin and their 1′-
epimers. J. Nat. Prod. 1998, 61, 591-597.
(2) Luo, X. Y.; Matsumoto, H. Susceptibility of a broad-leaved weed,
Acanthospermum hispidum, to the grass herbicide fluazifop-butyl.
Weed Biol. Manag. 2002, 2, 98-103.
(3) Grossmann, K.; Tresch, S.; Plath, P. Triaziflam and diamino-
triazine derivatives affect enantioselectively multiple herbicide
target sites. Z. Naturforsch., Sect. C: J. Biosci. 2001, 56, 559-
569.
(4) Wing, K. D.; Sacher, M.; Kagaya, Y.; Tsurubuchi, Y.; Mulderig,
L.; Connair, M.; Schnee, M. Bioactivation and mode of action
of the oxadiazine indoxacarb in insects. Crop Prot. 2000, 19,
537-545.
(5) Bais, H. P.; Walker, T. S.; Stermitz, F. R.; Ruh, A. H.; Vivanco,
J. M. Enantiomeric-dependent phytotoxic and antimicrobial
activity of (()-catechin. A rhizosecreted racemic mixture from
spotted knapweed. Plant Physiol. 2002, 128, 1173-1179.
(6) Bais, H. P.; Walker, T. S.; Kennan, A. J.; Stermitz, F. R.;
Vivanco, J. M. Structure-dependent phytotoxicity of catechins
and other flavonoids: flavonoid conversions by cell-free protein
extracts of Centaurea maculosa (spotted knapweed) roots. J.
Agric. Food Chem. 2003, 51, 897-901.
(7) Kiyoshi, F.; Ikuo, N.; Hisao, K.; Etsuko, S.; Mitsihiro, K.;
Tomokazu, S.; Shiro, U.; Kentaro, Y.; Naoki, M. Enhanced
radical scavenging activity of a planar catechin analogue. J. Am.
Chem. Soc. 2002, 124, 5952-5953.
(8) Murashige, T.; Skoog, F. A revised medium for rapid growth
and bioassay with tissue culture. Physiol. Plant. 1962, 15, 473-
476.
(9) Balde, A. M.; Pieters, L. A.; Gergely, A.; Kolodziel, H.; Claeys,
M.; Vlietinck, A. J. A-Type proanthocyanidins from stem-bark
of PaVetta owariensis. Phytochemistry 1991, 30, 337-342.
(10) Liu, H.; Yamazaki, Y.; Sasaki, T.; Uchida, M.; Tanaka, H.; Oka,
S. A-type proanthocyanidins from peanut skins. Phytochemistry
1999, 51, 297-308.
(11) Van der Westhuizen, J. H.; Steenkamp, J. A.; Ferreira, D. An
unusual reaction of flavan-3-ols with acetone of relevance to
the formation of the tetracyclic ring system in peltogynoids.
Tetrahedron 1990, 46, 7849-7854.
(12) Ngnokam, D.; Massiot, G.; Nuzillard, J.-M.; Tsamo, E. (+)-
7′,7′-Dimethyl-5-hydroxy-2R,3S-trans-pubeschin from Entan-
drophragma cylindricum. Phytochemistry 1994, 37, 529-531.
(13) Bais, H. P.; Vepachedu, R.; Gilroy, S.; Callaway, R. M.; Vivanco,
J. M. Allelopathy and exotic plant invasion: from molecules
and genes to species interactions. Science 2003, 301, 1377-
1380.
Figure 4. Fluorescence microscopic visualization of live−dead staining
to show bactericidal activity of the isopropylidylcatechin, (+)-4, against
different bacteria in a titer plate assay. Bacterial suspensions were treated
with the MIC of (+)-4 against each organism and stained with propidium
iodide and SYTO9 for visualizing the polysaccharides and nuclei,
respectively. Green fluorescence depicts live material surrounding/inside
the bacterial colony. Red fluorescence shows dead cells. The scale bars
indicate 20 µm.
(14) Sang, S.; Cheng, X.; Stark, R. E.; Rosen, R. T.; Yang, C. S.;
Ho, C.-T. Chemical studies on antioxidant mechanism of tea
catechins: analysis of radical reaction products of catechin and
epicatechin with 2,2-diphenyl-1-picrylhydrazyl. Bioorg. Med.
Chem. 2002, 10, 2233-2237.
Table 1. Minimum Inhibitory Concentration (MIC), Expressed in
Micrograms per Milliliter, of (+)-1 and Synthetic Derivatives against
Various Plant Pathogenic Bacteria (Standard Deviations Are ±5% of
the Mean)
(15) Schroeter, H.; Spencer, J. P. E. Flavonoids: neuroprotective
agents? Modulation of oxidative stress-induced map kinase signal
transduction. In FlaVonoids in Health and Disease; Rice-Evans,
C. A., Packer, L., Eds.; Dekker: New York, 2003; pp 253-
272.
(16) Boyd, C. S.; Cadenas, E. Mitochondrial actions of flavonoids
and isoflavonoids. In FlaVonoids in Health and Disease; Rice-
Evans, C. A., Packer, L., Eds.; Dekker: New York, 2003; pp
273-301.
tested compd E. carotovora E. amylovora X. campestris P. fluorescens
(+)-4
(±)-4
(+)-3
(±)-3
(+)-2
(±)-2
(+)-1
1.6 ± 0.08
12.5 ± 0.63
6.3 ± 0.32
6.3 ± 0.32
6.3 ± 0.32
25 ± 1.25
1.6 ± 0.08
3.1 ± 0.16
12.5 ± 0.63
25 ± 1.25
12.5 ± 0.63
6.3 ± 0.32
25 ± 1.25
1.6 ± 0.08
6.3 ± 0.32
12.5 ± 0.63
25 ± 1.25
12.5 ± 0.63
6.3 ± 0.32
25 ± 1.25
1.6 ± 0.08
3.1 ± 0.16
12.5 ± 0.63
6.3 ± 0.32
12.5 ± 0.63
6.3 ± 0.32
12.5 ± 0.63
1.6 ± 0.08
(17) Palma, M.; Taylor, L. T.; Varela, R. M.; Cutler, S. J.; Cutler, H.
G. Fractional extraction of compounds from grape seed by
supercritical fluid extraction and analysis for antimicrobial and
agrochemical activities. J. Agric. Food Chem. 1999, 47, 5044-
5048.
compound, the price of (-)-catechin is currently very high, but
it could be made semisynthetically by epimerization of the more
common and cheaper (-)-epicatechin (19). On the other hand,

1082 J. Agric. Food Chem., Vol. 52, No. 5, 2004
Veluri et al.
(18) Puupponen-Pimisˇ; Nohynek, L.; Meier, C.; Ksˇhksˇnene, M.;
Hopia, A.; Oksman-Caldentey, K.-M. Antimicrobial properties
of phenolic compounds from berries. J. Appl. Microbiol. 2001,
90, 494-507.
(19) Nay, B.; Monti, J.-P.; Nuhrich, A.; Deffieux, G.; Me´rillon, J.-
M.; Vercauteren, J. Methods in synthesis of flavonoids. Part 2.
High yield access to both enantiomers of catechin. Tetrahedron
Lett. 2000, 41, 9049-9051.
Received for review September 10, 2003. Revised manuscript received
December 12, 2003. Accepted December 15, 2003. This work was
supported by the Colorado State University Agricultural Experiment
Station Invasive Weeds Initiative to F.R.S. and J.M.V. and by an NSF-
CAREER Award (MCB-0093017) to J.M.V.
JF030653+