Details of a Researcher - Suenaga, Kiyotake

Papers - Suenaga, Kiyotake

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Komesuamide and odopenicillatamide, two linear lipopeptides from the marine cyanobacterium Caldora penicillata

Ozaki K., Jinno A., Natsume N., Sumimoto S., Iwasaki A., Suenaga K., Teruya T.

Tetrahedron (Tetrahedron) 85 2021.04

ISSN 00404020

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Isolation and identification of three potential phytotoxic compounds from Chrysopogon aciculatus (Retz.) Trin

Islam M.S., Zaman F., Iwasaki A., Suenaga K., Kato-Noguchi H.

Acta Physiologiae Plantarum (Acta Physiologiae Plantarum) 43 ( 4 ) 2021.04

ISSN 01375881

We conducted an investigation to search for the possibility of phytotoxic compounds and then identify them in C. aciculatus. The aqueous methanol extracts of C. aciculatus imposed a strong suppressive effect on the shoots and roots growth of Medicago sativa and Echinochloa crus-galli. The C. aciculatus extracts were subsequently purified through chromatography and three growth-inhibitory compounds were identified by spectral data as methyl cis-p-coumarate, methyl trans-p-coumarate, and trans-ferulaldehyde. The seedlings growth of Lepidium sativum was suppressed by methyl cis-p-coumarate, methyl trans-p-coumarate, and trans-ferulaldehyde. The I50 values (concentration required for 50% growth inhibition) for the seedling growth of L. sativum ranged from 1.25 to 1.73 mM for methyl cis-p-coumarate, 0.74 to 1.23 mM for methyl trans-p-coumarate, and 1.05 to 1.84 mM for trans-ferulaldehyde. Our finding indicates that methyl cis-p-coumarate, methyl trans-p-coumarate, and trans-ferulaldehyde may contribute to the phytotoxic effects of C. aciculatus.

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Identification and application of bioactive compounds from garcinia xanthochymus hook. For weed management

Rob M.M., Hossen K., Khatun M.R., Iwasaki K., Iwasaki A., Suenaga K., Kato-Noguchi H.

Applied Sciences (Switzerland) (Applied Sciences (Switzerland)) 11 ( 5 ) 1 - 10 2021.03

The allelopathic potential of plant species and their related compounds has been increas-ingly reported to be biological tools for weed control. The allelopathic potential of Garcinia xantho-chymus was assessed against several test plant species: lettuce, rapeseed, Italian ryegrass, and timo-thy. The extracts of G. xanthochymus leaves significantly inhibited all the test plants in a concentra-tion-and species-specific manner. Therefore, to identify the specific compounds involved in the allelopathic activity of the G. xanthochymus extracts, assay-guided purification was carried out and two allelopathic compounds were isolated and identified as methyl phloretate {3-(4-hydroxy-phenyl) propionic acid methyl ester} and vanillic acid (4-hydroxy-3-methoxybenzoic acid). Both of the substances significantly arrested the cress and timothy seedlings growth. I50 values (concentra-tions required for 50% inhibition) for shoots and roots growth of the cress and timothy were 113.6– 104.6 and 53.3–40.5 μM, respectively, for methyl phloretate, and 331.6–314.7 and 118.8–107.4 μM, respectively, for vanillic acid, which implied that methyl phloretate was close to 3-and 2-fold more effective than vanillic acid against cress and timothy, respectively. This report is the first on the presence of methyl phloretate in a plant and its phytotoxic property. These observations suggest that methyl phloretate and vanillic acid might participate in the phytotoxicity of G. xanthochymus extract.

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Phytotoxic activity and growth inhibitory substances from Albizia richardiana (Voigt.) King & Prain

Hossen K., Iwasaki A., Suenaga K., Kato-Noguchi H.

Applied Sciences (Switzerland) (Applied Sciences (Switzerland)) 11 ( 4 ) 1 - 13 2021.02

Albizia richardiana, a fast-growing, large deciduous tree belonging to the Fabaceae family, grows well in hot and humid areas but mainly grows in the tropics of the Old World. The medicinal and other uses of Albizia richardiana are well documented, but the phytotoxic effects of this tree have not yet been investigated. We conducted this study to investigate the phytotoxic activity of Albizia richardiana leaves and to identify growth inhibitory substances for controlling weeds in a sustainable way. Aqueous methanol extracts of Albizia richardiana leaves greatly suppressed the growth of cress and barnyard grass seedlings in a concentration- and species-dependent manner. Two phytotoxic substances were separated using several purification steps and characterized through spectral analysis as dehydrovomifoliol and loliolide. Dehydrovomifoliol and loliolide significantly arrested the seedling growth of cress in the concentrations of 0.1 and 0.01 mM, respectively. The extract concentrations needed for 50% growth inhibition (I50 values) of cress seedlings were 3.16-3.01 mM for dehydrovomifoliol and 0.03-0.02 mM for loliolide. The results suggest that these two allelopathic substances might play a vital role in the phytotoxicity of Albizia richardiana leaves.

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Bioorganic Study ofNew Natural Products Isolatedfrom Marine Cyanobacteria

Iwasaki A., Suenaga K.

Yuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry (Yuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry) 79 ( 2 ) 133 - 144 2021.02

ISSN 00379980

Natural products, well known for unique chemical diversity and bioactivity, are the compounds that organisms have acquired in evolutionary history. They have attracted attentions from not only organic chemists but also scientists in related fields and have provided breakthroughs for science. Against this background, we have investigated the secondary metabolites of marine organisms, especially cyanobacteria, and have discovered various novel bioactive compounds. In this account, our recent research activities regarding the isolation, structure determination, total syntheses and biological activities of our novel natural products are described.

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Isolation, structure determination, and total synthesis of hoshinoamide c, an antiparasitic lipopeptide from the marine cyanobacterium caldora penicillata

Suenaga K., Iwasaki A., Ohtomo K., Kurisawa N., Shiota I., Rahmawati Y., Jeelani G., Nozaki T.

Journal of Natural Products (Journal of Natural Products) 2021

ISSN 01633864

© 2020 American Chemical Society. All rights reserved. Hoshinoamide C (1), an antiparasitic lipopeptide, was isolated from the marine cyanobacterium Caldora penicillata. Its planar structure was elucidated by spectral analyses, mainly 2D NMR, and the absolute configurations of the α-amino acid moieties were determined by degradation reactions followed by chiral-phase HPLC analyses. To clarify the absolute configuration of an unusual amino acid moiety, we synthesized two possible diastereomers of hoshinoamide C and determined its absolute configuration based on a comparison of their spectroscopic data with those of the natural compound. Hoshinoamide C (1) did not exhibit any cytotoxicity against HeLa or HL60 cells at 10 μM, but inhibited the growth of the parasites responsible for malaria (IC50 0.96 μM) and African sleeping sickness (IC50 2.9 μM).

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Odookeanynes A and B, Acetylene-Containing Lipopeptides from an Okeania sp. Marine Cyanobacterium

Yamano A., Asato Y., Natsume N., Iwasaki A., Suenaga K., Teruya T.

Journal of Natural Products (Journal of Natural Products) 2021

ISSN 01633864

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Phytotoxic activity of Clerodendrum indicum (L.) Kuntze and its potential phytotoxic substance

Kyaw E.H., Iwasaki A., Suenaga K., Kato-Noguchi H.

Emirates Journal of Food and Agriculture (Emirates Journal of Food and Agriculture) 33 ( 10 ) 884 - 892 2021

ISSN 2079052X

Clerodendrum indicum (L.) Kuntze (Lamiaceae), an annual shrub, is renowned for being used in folk medicine in South Asian countries. Several pharmacological properties and many bioactive secondary metabolites from C. indicum have been well documented. However, the phytotoxic activities and the related phytotoxic substances with the allelopathic activity of C. indicum have not yet been reported. Thus, we explored the phytotoxic activity of C. indicum and identified its phytotoxic substance. In the experiment, the dry C. indicum leaves were extracted with aqueous methanol, and then the filtrate of the extracts was concentrated using a rotary evaporator to obtain crude extracts. The C. indicum crude extracts significantly inhibited the shoots and roots of six target species: alfalfa, cress, lettuce, barnyard grass, Italian ryegrass, and timothy. The inhibition increased when the extract concentration was increased. The crude extracts of C. indicum were separated in several chromatography steps, and a phytotoxic substance was isolated and characterized using spectroscopy as p-coumaric acid. p-Coumaric acid significantly suppressed the growth of lettuce and timothy seedlings at concentrations greater than 0.3 and 1 mM, respectively. The concentrations of p-coumaric acid required for 50% inhibition (I50) of the shoots and roots of lettuce and timothy were 0.65 and 0.17 mM, and 0.81 and 0.67 mM, respectively. This study is the first report on isolating p-coumaric acid in C. indicum. The results, therefore, suggest that p-coumaric acid may partly contribute to the phytotoxic properties of C. indicum.

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Characterization of Macroscopic Colony-Forming Filamentous Cyanobacteria from Okinawan Coasts as Potential Sources of Bioactive Compounds

Nuryadi H., Sumimoto S., Teruya T., Suenaga K., Suda S.

Marine Biotechnology (Marine Biotechnology) 22 ( 6 ) 824 - 835 2020.12

ISSN 14362228

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. Marine macroscopic colony-forming filamentous (MMCFF) cyanobacteria are considered as prolific producers of bioactive compounds. Thus, knowledge of the diversity of MMCFF cyanobacteria as related to bioactive compound production has become very important. However, basic taxonomic studies of MMCFF cyanobacteria are lacking. Many cyanobacterial taxa are still misidentified or undescribed. In this study, a total of 32 cyanobacterial colonies from nine coastal regions of Okinawa Prefecture were investigated for a diversity assessment. A polyphasic approach including morphological and molecular studies based on 16S rRNA gene sequences was performed to characterize Okinawan MMCFF cyanobacteria. Both morphological and molecular phylogenetic results showed that MMCFF cyanobacteria from Okinawan coasts are very diverse. We found morphotypes of Lyngbya-like, Phormidium-like, and Leptolyngbya-like groups among Okinawan cyanobacterial samples. Genetically, samples were distributed in various clades in the phylogenetic tree, including within Moorena, Okeania, Caldora, Neolyngbya, Dapis, as well as several unknown clades. In addition, cytotoxic activities of three samples from Kiyan coast were tested against HeLa cells. All three crude extracts of these samples showed strong cytotoxic activity with IC50 < 1 μg/ml.

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Allelopathic potential and active substances from wedelia chinensis (Osbeck)

Hossen K., Das K.R., Okada S., Iwasaki A., Suenaga K., Kato-Noguchi H.

Foods (Foods) 9 ( 11 ) 2020.11

Wedelia chinensis (Asteraceae) is a wetland herb native to India, China, and Japan. It is a valuable medicinal plant recorded to have pharmaceutical properties. However, the phytotoxic potential of Wedelia chinensis has not yet been examined. Thus, we carried out this study to establish the allelopathic effects of Wedelia chinensis and to identify its phytotoxic substances. Extracts of Wedelia chinensis exhibited high inhibitory activity against the root and shoot growth of cress, alfalfa, rapeseed, lettuce, foxtail fescue, Italian ryegrass, timothy, and barnyard grass. The inhibition was varied with species and was dependent on concentrations. The extracts were separated through several purification steps, and the two effective substances were isolated and characterized as vanillic acid and gallic acid using spectral analysis. Vanillic acid and gallic acid significantly arrested the growth of cress and Italian ryegrass seedlings. The concentrations of vanillic acid and gallic acid needed for 50% inhibition (I50 values) of the seedling growth of the cress and Italian ryegrass were 0.04–15.4 and 0.45–6.6 mM, respectively. The findings suggest that vanillic acid and gallic acid may be required for the growth inhibitory activities of Wedelia chinensis.

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Irijimasides A-E, Macrolide Glycosides from an Okeania sp. Marine Cyanobacterium

Yamano A., Natsume N., Yamada M., Sumimoto S., Iwasaki A., Suenaga K., Teruya T.

Journal of Natural Products (Journal of Natural Products) 83 ( 5 ) 1585 - 1591 2020.05

ISSN 01633864

Copyright © 2020 American Chemical Society and American Society of Pharmacognosy. Irijimasides A-E (1-5), a series of new 14-membered macrolide glycosides, were isolated from a marine cyanobacterium collected in Okinawa. The gross structures of 1-5 were established by spectroscopic analysis, including 2D NMR, while absolute stereostructures were determined based on NOESY spectra, chemical derivatization, and ECD data. All five macrolides suppressed receptor activator of nuclear factor-κB ligand (RANKL)-induced tartrate-resistant acid phosphatase (TRAP) activity in mouse RAW264 macrophage cells, indicating that these compounds inhibit osteoclast formation.

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Iheyamides A-C, Antitrypanosomal Linear Peptides Isolated from a Marine Dapis sp. Cyanobacterium

Kurisawa N., Iwasaki A., Jeelani G., Nozaki T., Suenaga K.

Journal of Natural Products (Journal of Natural Products) 83 ( 5 ) 1684 - 1690 2020.05

ISSN 01633864

© 2020 American Chemical Society and American Society of Pharmacognosy. Iheyamides A (1), B (2), and C (3), new linear peptides, were isolated from a marine Dapis sp. cyanobacterium. Their structures were elucidated by spectroscopic analyses and degradation reactions. Iheyamide A (1) showed moderate antitrypanosomal activities against Trypanosoma brucei rhodesiense and Trypanosoma brucei brucei (IC50 = 1.5 μM), but the other two analogues, iheyamides B (2) and C (3), did not (IC50 > 20 μM, respectively). The structure-activity relationship clarified that an isopropyl-O-Me-pyrrolinone moiety was necessary for the antitrypanosomal activity. Furthermore, the cytotoxicity of 1 against normal human cells, WI-38, was 10 times weaker than its antitrypanosomal activity (IC50 = 18 μM).

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A kaurene-type novel phytotoxic substance in Wedelia chinensis

Rany Das K., Iwasaki A., Suenaga K., Kato-Noguchi H.

Tetrahedron Letters (Tetrahedron Letters) 61 ( 11 ) 2020.03

ISSN 00404039

© 2020 Elsevier Ltd Wedelia chinensis has been widely used as a traditional medicine and several bioactive compounds have been isolated. We investigated phytotoxic property and phytotoxic substances in the species. An aqueous methanol extract of W. chinensis inhibited the growth of roots and shoots of cress. The extracts were then purified by several chromatographic runs with monitoring the inhibitory activity and a phytotoxic substance was isolated. The substance was determined by spectral data to be a novel kaurene-type compound, wedelienone. Wedelienone inhibited the growth of cress and timothy (Phleum pratense L) at concentrations greater than 10–30 μM. These results suggest that wedelienone may contribute to the phytotoxic effects caused by the extracts.

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Isolation and identification of two phytotoxic compounds from the medicinal plant Cassia alata L.

Das K.R., Iwasaki K., Suenaga K., Kato-Noguchi H.

Weed Biology and Management (Weed Biology and Management) 20 ( 1 ) 3 - 11 2020.03

ISSN 14446162

© 2020 Weed Science Society of Japan Cassia alata (Caesalpiniaceae), an ornamental shrub, has many biological properties such as antifungal and antibacterial activities. Several bioactive and phytotoxic compounds have already been isolated from C. alata. Phytotoxic substances from plants have drawn attention as an alternative biological approach to control weeds. Thus, we conducted this research to explore other phytotoxic compounds in C. alata leaves. Aqueous methanol extracts of C. alata leaves strongly inhibited the seedling growth of broccoli, cabbage, cress, radish and rapeseed, in which the level of inhibition correlated with concentration. Two active compounds were isolated through chromatographies and identified using spectral data as (S)-4-(3-hydroxybutyl)phenol [(+)-rhododendrol] and (E)-4-((1R,4R)-4-hydroxy-2,6,6-trimethylcyclohex-2-en-1-yl)but-3-en-2-one [3-hydroxy-α-ionone]. These two active compounds inhibited the growth of cress seedlings in a concentration-dependent manner. The required concentrations for 50% growth inhibition (I50 value) of cress seedlings were 192.0–296.1 μM for (+)-rhododendrol and 132.4–195.3 μM for 3-hydroxy-α-ionone. These results indicate that the two phytotoxic compounds play a part in the phytotoxic activity of C. alata leaves.

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Ikoamide, an Antimalarial Lipopeptide from an Okeania sp. Marine Cyanobacterium

Iwasaki K., Iwasaki A., Sumimoto S., Matsubara T., Sato T., Nozaki T., Saito-Nakano Y., Suenaga K.

Journal of Natural Products (Journal of Natural Products) 83 ( 2 ) 481 - 488 2020.02

ISSN 01633864

Copyright © 2020 American Chemical Society and American Society of Pharmacognosy. An antimalarial lipopeptide, ikoamide, was isolated from an Okeania sp. marine cyanobacterium. Its gross structure was established by spectroscopic analyses, and the absolute configuration was clarified based on a combination of chiral-phase HPLC analyses, spectroscopic analyses, and derivatization reactions. Ikoamide showed strong antimalarial activity with an IC50 value of 0.14 μM without cytotoxicity against human cancer cell lines at 10 μM.

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Tree fern cyathea lepifera may survive by its phytotoxic property

Ida N., Iwasaki A., Teruya T., Suenaga K., Kato-Noguchi H.

Plants (Plants) 9 ( 1 ) 2020.01

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. Cyatheaceae (tree ferns) appeared during the Jurassic period and some of the species still remain. Those species may have some morphological and/or physiological characteristics for survival. A tree fern was observed to suppress the growth of other ligneous plants in a tropical forest. It was assumed that the fern may release toxic substances into the forest floor, but those toxic substances have not yet been identified. Therefore, we investigated the phytotoxicity and phytotoxic substances of Cyathea lepifera (J. Sm. ex Hook.) Copel. An aqueous methanol extract of C. lepifera fronds inhibited the growth of roots and shoots of dicotyledonous garden cress (Lepidum sativum L.), lettuce (Lactuca sativa L.), and alfalfa (Medicago sativa L.), and monocotyledonous ryegrass (Lolium multiflorum Lam.), timothy (Phleum pratense L.), and barnyardgrass (Echinochloa crus-galli (L.) P. Beauv.). The results suggest that C. lepifera fronds may have phytotoxicity and contain some phytotoxic substances. The extract was purified through several chromatographic steps during which inhibitory activity was monitored, and p-coumaric acid and (-)-3-hydroxy-β-ionone were isolated. Those compounds showed phytotoxic activity and may contribute to the phytotoxic effects caused by the C. lepifera fronds. The fronds fall and accumulate on the forest floor through defoliation, and the compounds may be released into the forest soils through the decomposition process of the fronds. The phytotoxic activities of the compounds may be partly responsible for the fern’s survival.

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Phytotoxic activity and identification of phytotoxic substances from Schumannianthus dichotomus

Rob M.M., Hossen K., Iwasaki A., Suenaga K., Kato-Noguchi H.

Plants (Plants) 9 ( 1 ) 2020.01

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. The phytotoxic potential of plants and their constituents against other plants is being increasingly investigated as a possible alternative to synthetic herbicides to control weeds in crop fields. In this study, we explored the phytotoxicity and phytotoxic substances of Schumannianthus dichotomus, a perennial wetland shrub native to Bangladesh, India, and Myanmar. Leaf extracts of S. dichotomus exerted strong phytotoxicity against two dicot species, alfalfa and cress, and two monocot species, barnyard grass and Italian ryegrass. A bioassay-driven purification process yielded two phenolic derivatives, syringic acid and methyl syringate. Both constituents significantly inhibited the growth of cress and Italian ryegrass in a concentration-dependent manner. The concentrations required for 50% growth inhibition (I50 value) of the shoot and root growth of cress were 75.8 and 61.3 μM, respectively, for syringic acid, compared with 43.2 and 31.5 μM, respectively, for methyl syringate. Similarly, to suppress the shoot and root growth of Italian rye grass, a greater amount of syringic acid (I50 = 213.7 and 175.9 μM) was needed than methyl syringate (I50 = 140.4 to 130.8 μM). Methyl syringate showed higher phytotoxic potential than syringic acid, and cress showed higher sensitivity to both substances. This study is the first to report on the phytotoxic potential of S. dichotomus and to identify phytotoxic substances from this plant material.

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Allelopathic potential and identification of two allelopathic substances in Eleocharis atropurpurea

Zaman F., Iwasaki A., Suenaga K., Kato-Noguchi H.

Plant Biosystems (Plant Biosystems) 2020

ISSN 11263504

© 2020, © 2020 Societá Botanica Italiana. Eleocharis atropurpurea is an annual weed and distributed widely in pantropical and subtropical regions. Yet, there have been no studies on the allelopathy of E. atropurpurea. Therefore, we investigated the allelopathic potential of E. atropurpurea to identify allelopathic substances from it. The aqueous methanolic extracts of E. atropurpurea showed an inhibitory effect on the seedling growth of lettuce, rapeseed, barnyard grass and foxtail fescue. Inhibition was species- and concentration-dependent. Two substances, syringaldehyde and acetosyringone, were isolated by using chromatography and using spectroscopy their structures were determined. Syringaldehyde and acetosyringone inhibited the shoot and root growth of cress and barnyard grass at concentrations greater than 3.0 mM except shoot growth of barnyard grass by acetosyringone. Concentration and seedling growth of cress and barnyard grass displayed a negative correlation. The I50 values of syringaldehyde and acetosyringone for the shoot and root growth of cress were 1.67 and 1.61 mM, and 1.49, and 1.29 mM, respectively, whereas for the shoot and root growth of barnyard grass the values were 4.09 and 2.41 mM, and 4.54 and 1.92 mM, respectively. Therefore, it is suggested that these compounds may contribute to the inhibitory effects of E. atropurpurea.

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Potential use of Schumannianthus dichotomus waste: the phytotoxic activity of the waste and its identified compounds

Rob M.M., Iwasaki A., Suenaga K., Ozaki K., Teruya T., Kato-Noguchi H.

Journal of Environmental Science and Health - Part B Pesticides, Food Contaminants, and Agricultural Wastes (Journal of Environmental Science and Health - Part B Pesticides, Food Contaminants, and Agricultural Wastes) 2020

ISSN 03601234

© 2020 Taylor & Francis Group, LLC. The phytotoxic potential of the leaves and twigs of Schumannianthus dichotomus, discarded in the mat-making industry against four test plants (lettuce (Lactuca sativa L.), rapeseed (Brassica napus L.), foxtail fescue (Vulpia myuros (L.) C.C. Gmel.) and timothy (Phleum pratense L.)) was investigated and found strong phytotoxic activity. An assay-guided fractionation of S. dichotomus extarcts against cress (Lepidium sativum L.) through a series of column chromatography steps yielded two compounds, 8-(5-oxo-2,5-dihydrofuran-2-yl) octanoic acid (ODFO) and (E)-6-hydroxy-2,6-dimethylocta-2,7-dienoic acid (8-carboxylinalool). ODFO and 8-carboxylinalool showed strong phytotoxic activity against cress and timothy. The concentrations required for 50% growth inhibition (I 50 value) of the seedlings of cress and timothy were 111.94–128.01 and 36.30–91.75 µM, respectively, for ODFO, but the values were much higher at 315.98–379.13 and 107.92–148.41 µM, respectively, for 8-carboxylinalool, indicating the stronger phytotoxic activity of ODFO. This study is the first to isolate ODFO and 8-carboxylinalool from S. dichotomus and their phytotoxic potential while ODFO is firstly encountered from any natural source. The growth inhibitory activity of the identified compounds may explain their role in the phytotoxic activity of S. dichotomus, which suggests the possible use of its leaves and twigs or its active constituents as natural bioherbicides.

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Assessment of allelopathic potential of Dalbergia cochinchinensis Pierre and its growth inhibitory substance

Krumsri R., Iwasaki A., Suenaga K., Kato-Noguchi H.

Emirates Journal of Food and Agriculture (Emirates Journal of Food and Agriculture) 32 ( 7 ) 513 - 521 2020

ISSN 2079052X

In forestry systems, many types of forest trees possess allelopathic properties and release a wide variety of allelochemicals that influence the growth and development of surrounding species. Dalbergia cochinchinensis, a forest tree distributed in Southeast Asia, is reputed to possess several biological properties and contain several secondary compounds. However, there have been no studies on the allelopathy of D. cochinchinensis. Therefore, D. cochinchinensis leaf extracts were examined for allelopathic potential. The present study showed that D. cochinchinensis extracts significantly inhibited the seedling growth of six test plant species: timothy, Italian ryegrass, barnyard grass, cress, alfalfa, and lettuce. Concentrations of the D. cochinchinensis extracts negatively correlated with the shoot length (r = −0.50 to −0.89) and root length (r = −0.65 to −0.89) of all the test plant species. The extracts were then purified using several chromatographic steps and the growth inhibitory substance was isolated. The chemical structure of the substance was identified through spectroscopic analysis as 3,4-dihydroxybenzoic acid (protocatechuic acid). Protocatechuic acid at a concentration higher than 3 mM significantly inhibited the growth of cress seedlings, whereas barnyard grass seedlings were inhibited at concentrations higher than 0.3 mM. As the protocatechuic acid concentration increased, the seedling growth of cress and barnyard grass was significantly reduced. I50 values showed the effectiveness of protocatechuic acid against both test plant species was apparently greater on root growth than shoot growth. Results of this study suggest that protocatechuic acid isolated from D. cochinchinensis might be responsible for its inhibitory effects.

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