Synthesis of sulfur-Containing derivatives from olefinic fatty esters

The reaction of 3-mercaptopropan-l,2-diol with methyl 10-undecenoate (Ib) yielded three products, methyl 11-(3′-mercaptopropan-l′,2′-diacetoxy) undecanoate (II, 48.9%), methyl 11-(1-oxapropan-2′-acetoxy-3′-mercaptoacetyl) undecanoate (III, 27.4%) and methyl 10-(3′-mercaptopropan-1′-acetoxy-2′-ol) undecanoate (IV, 23.0%) along with hydrolyzed starting material (Ia, 5.4%). The same reaction with methyl 9-octadecenoate (Vb) gave an isomeric product, 9(10)-(3′-mercaptopropan-l′-acetoxy-2′-ol) octadecanoic acid (VI, 78.5%) and oleic acid (Va, 21.4%). Reaction withtrans-2-octadecenoic acid (VII) afforded 2(3)-(3′-mercaptopropan-l′-acetoxy-2′-ol) octadecanoic acid (VIII, 85.7%).     

Derivatization of keto fatty acids: V. Synthesis and characterization of 1,3-dioxolanes

The synthesis of substituted 1,3-dioxolanes from oxo fatty acid esters using 1,2-propanediol is described. This reagent, besides forming dioxolanes, also converts the methyl ester to the 2′-hydroxy propyl ester. Methyl 10-oxoundecanoate gives 2′-hydroxy propyl 10-(2″-methyl ethylene dioxolane) undecanoate (Ia, 75%) as a major product. Methyl 9-oxooctadecanoate reacts similarly and yields 2′-hydroxy propyl 9-(2″-methyl ethylene dioxolane) octadecanoate (IIb, 60%), along with the minor products (IIa, IIc). Methyl 2-oxooctadecanoate, after prolonged refluxing, affords only 2′-hydroxy propyl 2-(2″-methyl ethylene dioxolane) octadecanoate (IIIa) in 70% yield. Structures of each reaction product were established on the basis of elemental analysis, IR, NMR and a study of mass spectrometry.     

Novel vitamin E derivative with 4-substituted resorcinol moiety has both antioxidant and tyrosinase inhibitory properties

A novel vitamin E derivative, (6″-hydroxy-2″,5″,7″,8″-tetramethylchroman-2″-yl) methyl 3-(2′,4′-dihydroxyphenyl)propionate (TM4R), which has a chromanoxyl ring and 4-substituted resorcinol moieties, was synthesized; and its inhibitory effects on tyrosinase, antioxidant ability, and lightening effect of ultraviolet B (UVB)-induced hyperpigmentation were estimated. TM4R showed potent inhibitory activity on tyrosinase, which is the rate-limiting enzyme in melanogenesis. The scavenging activities of TM4R on 1,1-diphenyl-2-picrylhydrazyl and hydroxyl radicals were found to be nearly the same as those of α-tocopherol. Furthermore, an efficient lightening effect was observed following topical application of TM4R to UVB-stimulated hyperpigmented dorsal skin of brownish guinea pigs. These results suggest that TM4R may be a candidate for an efficient whitening agent, possibly by inhibiting tyrosinase activity and biological reactions caused by reactive oxygen species.     

New Sphingolipids with a Previously Unreported 9-Methyl-C<Subscript>20</Subscript>-sphingosine Moiety from a Marine Algous Endophytic Fungus <Emphasis Type="Italic">Aspergillus niger</Emphasis> EN-13

Asperamides A (1) and B (2), a sphingolipid and their corresponding glycosphingolipid possessing a hitherto unreported 9-methyl-C₂₀-sphingosine moiety, were characterized from the culture extract of Aspergillus niger EN-13, an endophytic fungus isolated from marine brown alga Colpomenia sinuosa. The structures were elucidated by spectroscopic and chemical methods as (2S,2′R,3R,3′E,4E,8E)-N-(2′-hydroxy-3′-hexadecenoyl)-9-methyl-4,8-icosadien-1,3-diol (1) and 1-O-β-d-glucopyranosyl-(2S,2′R,3R,3′E,4E,8E)-N-(2′-hydroxy-3′-hexadecenoyl)-9-methyl-4,8-icosadien-1,3-diol (2). In the antifungal assay, asperamide A (1) displayed moderate activity against Candida albicans.     

Modification of lysine amino groups by the lipid peroxidation product 4,5(E)-Epoxy-2(E)-hepteal

The reaction between 4,5(E)-epoxy-2(E)-heptenal (EH) andl-lysine was studied to characterize some of the compounds that may be produced when proteins react with peroxidizing lipids. A mixture of EH and lysine was incubated overnight at room temperature and then fractionated by high-performance liquid chromatography (HPLC). Fractions were freeze-dried and characterized by¹H and¹³C nuclear magnetic resonance (NMR) and mass spectrometry. Four major pyrrole derivatives were obtained, namely 1-(5′-amino-1′-carboxypentyl)-pyrrole (3), 1-(5′-amino-1′-carboxypentyl)-2-(1″-hydroxypropyl)pyrrole (diastereomers 5 and 8), 1-(5′-amino-5′-carboxypentyl)pyrrole (7), and 1-(5′-amino-5′-carboxypentyl)-2-(1″-hydroxypropyl)pyrrole (9). In addition, several lysine complexes were detected. A polymer (1b) that was responsible for the color and the fluorescence produced in the reaction was isolated by gel filtration chromatography from a fraction obtained by HPLC. Formation of pairs of analogs (5 and 3, 9 and 7) with and without a substituent in position 2 of the pyrrole ring suggested that the compounds were produced by the same mechanism, with the formation of the 2-unsubstituted pyrroles corresponding to the loss of the 2-substituent as propanal; propanal was detected by headspace capillary gas chromatography. A reaction mechanism is proposed based on the NMR data obtained when the reaction was monitored in real time in an NMR tube. The results suggest that pyrrolic amino acids 7 and 9 may be present in proteins that have been damaged by peroxidizing lipids.     

Synthesis and antimicrobial activity of fatty 2-morpholinones prepared from epoxy fatty acid methyl esters

Reactions of methyl 10,11-epoxyundecanoate (I), methyl 9,10-epoxyoctadecanoate (II) methyl 12,13-epoxy-cis-9-octadecenoate (III) and methyltrans-2,3-epoxyhexadecenoate (IV) with glycine in dimethylformamide (DMF) in the presence of anhydrous AlCl₃ as catalyst have yielded 5(6)-[8′-carbomethoxyoctyl]-2-morpholinone (V); 5(6)-[7′'-carbomethoxyheptyl]-6(5)-octyl-2-morpholinone (VI);5(6)-[10′-carbomethoxydec-cis-2-enyl)-6(5)-pentyl-2-morpholinone (VII), and 5-tridecyl-6-carbomethoxy 2-morpholinone (VIII), respectively in excellent yield. The products have been characterized with the help of spectral data and microanalysis. Antifungal and antibacterial screening of (V–VIII) showed pronounced activity against four bacteria and seven fungal species. Presented in part at the 43rd Annual Convention of the Oil Technologists' Association of India (OTAI) held in Bombay, India In February 1988.     

Divinyl ethers and hydroxy fatty acids from three species ofLaminaria (brown algae)

Three species of brown algae,Laminaria sinclairii, L. saccharina andL. setchellii, have been investigated for the presence of oxylipins. From one,L. sinclairii, three new divinyl ether fatty acids have been characterized as methyl ester derivatives (methyl 12-[1′ (Z),3′(Z)-hexadienyloxy]-6(Z), 9(Z), 11(E)-dodecatrienoate, methyl 12-[1′ (Z), 3′ (Z)-hexadienyloxy]-9(Z), 11(E)-dodecatrienoate, and methyl 14-[1′ (Z),3′ (Z)-hexadienyloxy]-9(Z),11(E)-dodecadienoate, and methyl 14-[1′ (Z),3′(Z)-hexadienyloxy]-5(Z),8(Z),11(Z),13(E)-tetradecatetraenoate) by a variety of spectroscopic methods. In addition, one new [13(S)-hydroxy-6(Z),9(Z),11(E),15(Z)-octadecatetraenoic acid] and four known monohydroxy polyunsaturated fatty acids have been isolated from all three species as their methyl ester derivatives. The occurrence of these compounds in brown algae strongly suggests that these organisms possess an active lipoxygenase(s) with ω6 specificity. A preliminary summary of this work was presented at the XIVth International Seaweed Symposium, Brest, France, August 1992 (10).     

A new and efficient synthetic method of a liquid crystalline epoxy resin with biphenol and aromatic ester group

This article describes a high efficient and economical method to synthesize a liquid crystalline epoxy resin (LCER) containing biphenol and aromatic ester group, 3,3′,5,5′-tetramethylbiphenyl-4,4′-diyl bis(4-(oxiran-2-ylmethoxy) benzoate) (4). First, 3,3′,5,5′-tetramethylbiphenyl-4,4′-diyl bis(4-hydroxybenzoate) (3) was prepared by direct esterification of 3,3′,5,5′-tetramethylbiphenyl-4,4′-diol (2) with p-hydroxybenzoic acid (1) in the presence of a certain amount of p-toluene sulfonic acid (p-TSA) as catalyst. And then (4) was synthesized by the reaction of (3) with epichlorohydrin. The chemical structure, melting range, and liquid crystalline phase transition behavior of (4) were characterized by FT-IR, ¹H-NMR, ¹³C-NMR, mass spectroscopy, differential scanning calorimetry (DSC), and polarized optical microscopy (POM).     

Positional distribution of fatty acids in cardiolipin of mitochondria from 21-day-old rats

Pure cardiolipins (1,3-diphosphatidylglycerol) were prepared from mitochondria of heart, liver and kidney from 21-day-old male Wistar rats and submitted toNaja naja venom phospholipase A₂ (EC 3.1.1.4) action. Incubation conditions were controlled carefully, and a complete hydrolysis of cardiolipin to lysocardiolipin {di [1 (1″) acylsn-glycero-3-phosphoryl] 1′, 3′-sn-glycerol} and fatty acids from positions 2 (2″) was obtained in less than two hr practically without side reactions. Cardiolipins from the three organs contained low levels of saturated fatty acids; stearic acid accounted for 0.4–0.7% and palmitic acid for 1.4–3.5% of total fatty acids. These percentages apparently depended on the organ. In all three cases, linoleic acid was the major component, but its percentage varied from 62–78% of total fatty acids. Acyl chains linked to positions 1 (1″) of all three cardiolipin preparations exhibited a similar pattern; they were composed of linoleic acid for 85–89%. This fatty acid also was the main component esterified at position 2 (2″), but its percentage was much more variable: from 39.8% in heart to 51.2% in kidney and 67.8% in liver mitochondria. The remaining acids comprised octadecenoic and polyunsaturated fatty acids with more than 18 carbon atoms in different proportions. As opposed to other phospholipids,cis-vaccenic acid, and not oleic acid, was the main octadecenoic acid present in cardiolipins. Octadecenoic acids were nine- to 10-fold more concentrated at positions 2 (2″) than at positions 1 (1″). The percentage ofcis-vaccenic acid was four- to five-fold higher than that of oleic acid at positions 2 (2″), whereas oleic acid dominated at positions 1 (1″). From results presented in this study and selected literature data, it may be concluded that fatty acids are asymmetrically distributed in cardiolipins of different origins, with linoleic acid showing a definite preference for position 1 (1″).     

The structure of the core polyol of the ether lipids fromSulfolobus acidocaldarius

The major ether-type lipid structures ofSulfolobus acidocaldarius (ATCC33909) were composed of caldarchaeol and calditoglycerocaldarchaeol. However, the characterization by nuclear magnetic resonance spectroscopy and mass spectrometry showed that the structure of calditol in calditoglycerocaldarchaeol is not nonitol, 2-(1′,2′,3′-trihydroxypropyl)1,2,3,4,5,6-hexahydroxyhexane, but 2-hydroxymethyl-1-(2,3-dihydroxypropoxy),2,3,4,5-cyclopentanetetraol with an ether linkage in the molecule. Such an intermolecular ether linkage was resistant, to BCl₃ treatment, but nonresistant to 57% HI degradation treatment conducted at 100°C for 60 h, producting 2-hydroxymethyl-1,2,3,4,5-cyclopentanepentaol from calditol as reaction product. Further, it was confirmed that the structure of calditol is essentially a derivative of glycerol, and hydrocarbon chains were conjugated to the glycerol-like site in the structure. The calditol with an ether linkage in the molecule suggested an important role regarding the properties of heat-resistance and acid-resistance observed inSulfolobales. Presented at the international workshop on “Molecular Biology and Biotechnology of Extremophiles and Archaebacteria,” Wako, Japan, August 1993.     

Crosslinking and grafting ethylene vinyl acetate copolymer with accelerated electrons in the presence of polyfunctional monomers

In this study, we have studied the effects of polyfunctional monomers (PFMs) on physical properties of ethylene vinyl acetate (EVA) copolymer crosslinked with electron beam (EB) or peroxides. The PFMs used were triallylcyanurate, triallylisocyanurate, trimethylolpropane trimethacrylate, zinc diacrylate, and ethylene glycol dimethacrylate. Using PFMs has led to (1) optimum cure time t ₉₀ decrease from 19′25″ to 17′30″–18′45″, (2) scorch time increase from 2′ to maximum 3′45″, (3) increasing the crosslink density of peroxide or EB-cured systems by increasing the efficiency of productive radical reactions. The most efficient PFM for EVA copolymer blends has been triallylisocyanurate. Tensile strength and tear strength of samples crosslinked with EB for all irradiation doses are significantly better than those obtained for samples crosslinked with peroxides (differences up to 190%). The results show that EB irradiation gave the best results     

Synthesis and fluorescence properties of polystyrene via atom transfer radical polymerization using a coumarin derivate as initiator

Well-defined polystyrene was successfully synthesized via atom transfer radical polymerization, using a novel coumarin derivate, 2-bromo-2-methyl-propionic acid 4-methyl-2-oxo-2H-chromen-7-yl ester (BMP), synthesized in our lab as an initiator, and CuBr/N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) as the catalyst at 110 °C. The kinetics of the polymerization was studied in detail. The fluorescence properties of the resultant polystyrenes were studied in N,N-dimethylformamide (DMF). It is very interesting that the adding of Fe³⁺ has significant effect on the fluorescence intensities, which decreased with increasing the concentration of iron in solutions. The obtained polystyrenes can be used as fluorescent probe molecules for Fe³⁺.     

Synthesis of novel tri- and tetrasubstituted C<Subscript>18</Subscript> furan fatty esters

A methylene-interrupted C₁₈ keto-acetylenic fatty ester (methyl 12-oxo-9-octadecynoate) was obtained from methyl ricinoleate by bromination-dehydrobromination followed by oxidation. Reaction of methyl 12-oxo-9-octadecynoate with bis(benzonitrile) palladium(II) chloride, allyl bromide, or methyl-allyl bromide furnished methyl 8-[5-hexyl-3-allyl-furan-2-yl]-octanoate (1, 56%) or methyl 8-[5-hexyl-3-(2-methyl-allyl)-furan-2-yl]-octanoate (2, 55%). Reaction of methyl 12-oxo-11-chloro-or 11-fluoro-9-octadeyynoate (prepared from methyl santalbate-methyl 11-E-9-octadecynoate, found in sandalwood, Santalum album, seed oil) with bis(benzonitrile) palladium(II) chloride gave methyl 8-(4-fluoro-5-hexyl-furan-2-yl)-octanoate (3, 50%) or methyl 8-(4-fluoro-5-hexyl-furan-2-yl)-octanoate (4, 50%), respectively. And when methyl 12-oxo-11-chloro- or 11-fluoro-9-octadecynoate was treated with a mixture of bis(benzonitrile) palladium(II) chloride, allyl bromide, or methyl-allyl bromide, the reaction yielded tetrasubstituted C₁₈ furan derivatives, viz, methyl 8-(3-allyl-4-chloro-5-hexyl-furan-2-yl)-octanoate (5, 54%), methyl 8-[4-chloro-5-hexyl-3-(2-methyl-allyl)-furan-2-yl)-octanoate (6, 54%), methyl 8-(3-allyl-4-fluoro-5-hexyl-furan-2-yl]-octanoate (7, 10%), and methyl 8-[4-fluoro-5-hexyl-3-(2-methyl-allyl)-furan-2-yl]-octanoate (8, 10%). The presence of a fluorine atom in the furan derivatives 4, 7, and 8 was readily characterized by the appearance of doublets for carbon nuclei, which were coupled to the fluorine atom in the ¹³C NMR spectra. All furan fatty derivatives from this work were characterized by NMR spectroscopic and mass spectrometric analyses. The yields of compounds 7 and 8 were very low (10%) despite attempts to improve the procedure by increasing the amounts of the reactants and catalyst.     

Thermal alteration of a cyclic fatty acid produced by a flaxseed extract

Methyl 8-[2-(cis-pent-2′-enyl)-3-oxo-cis-cyclopent-4-enyl] octanoate (I) is the methyl ester of a cyclic fatty acid synthesized enzymically from an incubation of linolenic acid with an extract of flaxseed (Linum usitatissimum L.). A proposed trivial name for I is methyl 12-oxo-cis-10, 15-phytodienoate (12-oxo-PDA). The evidence presented indicated that compound I has thecis configuration of the carbon chains with respect to the cyclopentenone ring. Treatment with acid, base, or heat isomerized I to a second product (II) that has thetrans configuration of the carbon chains. Prolonged heat treatment of II yielded a third cyclic product, methyl 12-oxo-9(13),cis-15-phytodienoate (III).     

Radical Scavenging Activity and Performance of Novel Phenolic Antioxidants in Oils During Storage and Frying

Novel phenolic antioxidants: 2a (6′-hydroxy-2′,5′,7′,8′-tetramethylchroman-2′-yl)methyl 3-methoxy-4-hydroxycinnamate, 2b (6′-hydroxy-2′,5′,7′,8′-tetramethylchroman-2′-yl)methyl 3,5-dimethoxy-4-hydroxycinnamate, 2c (6′-hydroxy-2′,5′,7′,8′-tetramethylchroman-2′-yl)methyl 3,4-dihydroxycinnamate, and 3 (6-hydroxy-2,5,7,8-tetramethylchroman-2-yl)methyl (6′-hydroxy-2′,5′,7′,8′-tetramethylchroman-2′-carboxylate) have been prepared in good yields and fully characterized by ¹H and ¹³C NMR, and HRMS. Their radical scavenging activities have been evaluated by DPPH and ORAC assays. Each of the synthesized antioxidants exhibited significantly higher radical scavenging activities than trolox and α-tocopherol. These novel antioxidants efficiently protected canola oil triacylglycerides (CTG) during accelerated storage and frying. Compounds 2c and 3 were significantly more efficient than α-tocopherol protecting CTG under accelerated storage. All new antioxidants were more efficient than α-tocopherol under frying conditions and present significantly higher thermal stability.     

Two Novel Ceramides with a Phytosphingolipid and a Tertiary Amide Structure from <Emphasis Type="Italic">Zephyranthes candida</Emphasis>

Two novel ceramides, Candidamide A (1) with a phytosphingolipid structure, and Candidamide B (2) with a tertiary amide structure, together with 12 known compounds (3–14) have been isolated from the bulbs of Zephyranthes candida, The structures of 1 and 2 have been elucidated to be 1,3,5,6-tetrahydroxy-2-(2′-hydroxytetracosanoyl amino)-8-(E)-octadecadiene (1) and (2S,3S,4R,8E,2′R)-2-[N-(2′-hydroxyoctadecanoyl)-N-(1′′,2′′-dihydroxyethyl)-amino]-8-hexacosene-1,3,4-triol (2) on the basis of spectroscopic evidence including IR, MS, NMR (¹H-NMR, ¹³C-NMR, DEPT, ¹H–¹H COSY, HSQC, HMBC). The known compounds were identified as (2S)-3′,7-dihydroxy-4′-methoxyflavan (3), (2S)-4′-hydroxy-7-methoxyflavan (4), (2S)-4′,7-dihydroxyflavan (5), 7-hydroxy-3′, 4′-methylenedioxyflavan (6), ambrettolide (7), β-sitostero1 (8), β-daucosterin (9), rutin (10), pancratistatin (11), lycorine (12), haemanthidine (13), and haemanthamine (14). In the antimicrobial assay, candidamide A (1) and candidamide B (2) displayed moderate activities against bacteria Staphylococcus aureus and Escherichia coli, and fungi Aspergillus niger, Candida albicans and Trichophyton rubrum.     

Synthesis and free radical polymerization of 4-{1′-(2″-methacryloyloxyethoxy)-5′-naphthyliminomethylidene}-4′-nitrostilbene for nonlinear optical applications

4-{1′-(2″-Methacryloyloxyethoxy)-5′-naphthyliminomethylidene}-4′-nitro-stilbene 6 was prepared by the reactions of methacryloyl chloride with 4-{1′-(2″-hydroxyethoxy)-5′-naphthyliminomethylidene}-4′-nitrostilbene 5. Compound 5 was synthesized from 4′-methyl-4-nitrostilbene by several reaction steps. Monomer 6 was polymerized with DTBP as a radical initiator to obtain polymer with 4-(1′-oxy-5′-naphthyliminomethylidene)-4′-nitrostilbene, which is presumably effective chromophore for second-order nonlinear optical applications in the side chain. The resulting polymethacrylate 7 showed a thermal stability up to 300 °C in TGA thermogram, and the T_g value obtained from DSC thermogram was 120 °C, which is acceptable for NLO device applications. Received: 14 October 1996/Accepted: 11 December 1996     

Synthesis of new diacid monomers and poly(amide-imide)s: study of structure–property relationship and applications

Two diimide-diacid monomers 4,4′-bis[4″-(trimellitimido)phenyl isopropylidene-4″′-phenoxy]diphenyl sulfone and 4,4′-bis[4″-(trimellitimido)phenylisopropylidene-4″′-phenoxy] were synthesized. The structures of the monomers were characterized by FT-IR and ¹H-NMR spectroscopy. A series of novel poly(amide-imide)s were prepared from this two diacids and aromatic diamines through phosphorylation reaction. The PAIs were characterized by FT-IR, ¹H-NMR, XRD, TGA, and DSC, solution viscosity, solubility test and electrical properties. Poly(amide-imide)s showed excellent solubility due to the presence of flexible groups and isopropylidene unit in the polymer backbone. They also exhibited good thermal stability and the temperatures at which 10% weight loss occurred in the range 385–465 °C. These PAIs found to have a dielectric constant in the range 3.25–4.20 at 10 kHz and have excellent electrical insulation character and can be used as insulation materials for electrical items operating at elevated temperatures.     

Soil wetting agents from fatty nonionic tertiary amides: “Aromatic adducts without aminoester”

Tertiary amides RCONR'K, where K is a hydroxy function and R,R′ are aliphatic and/or aromatic groups, were oxyethylated to adducts containing 5, 10, 15, and 20 moles of ethylene oxide. The hydroxy function K was derived from CH₂CHR″OH,-(CH₂)_yOH, or (CH₂CH₂O)_zH, where R″ is methyl, ethyl, or octyl, y is 4 or 6 methylenes, and z is 2 or 3 ethoxy groups. Structural variations in R,R′ and K permitted the oxyethylation of aromatic amides with minimal aminoester formation. When K was diethoxy and R,R′ were linear aliphatic groups, no aminoester accompanied oxyethylation. Minimal aminoester formed when R,R′ were mixed aliphatic/ aromatic or when R was phenethyl and R′ aromatic. For aromatic amides where K was dior triethoxy, large aminoester concentrations accompanied oxyethylation. For aromatic amides where K was (CH₂)₄OH or (CH₂)₆OH smaller aminoester concentrations were observed. For branched alphatic amides where R″ is methyl, ethyl, or octyl, aminoester concentration remained at the level found where R″ is hydrogen. The increasing size of R″ decreased solubility and Draves wetting times. The adducts of this study were wetting agents for Idylwild hydrophobic soil and cotton skeins. The availability of aromatic substrates should permit formulation of soil wetting agents with greater stability to biodegradation than would be expected with aliphatic substrates.     

Chemical Defenses Promote Persistence of the Aquatic Plant Micranthemum umbrosum

Five of the most common macrophytes from an aquaculture facility with high densities of the herbivorous Asian grass carp (Ctenopharyngodon idella) were commonly unpalatable to three generalist consumers—grass carp and the native North American crayfishes Procambarus spiculifer and P. acutus. The rooted vascular plant Micranthemum umbrosum comprised 89% of the total aboveground plant biomass and was unpalatable to all three consumers as fresh tissues, as homogenized pellets, and as crude extracts. Bioassay-guided fractionation of the crude extract from M. umbrosum led to four previously known compounds that each deterred feeding by at least one consumer: 3,4,5-trimethoxyallylbenzene (1) and three lignoids: β-apopicropodophyllin (2); (−)-(3S,4R,6S)-3-(3′,4′-methylenedioxy-α-hydroxybenzyl)-4-(3″,4″-dimethoxybenzyl)butyrolactone (3); and (−)-hibalactone (4). None of the remaining four macrophytes produced a chemically deterrent extract. A 16-mo manipulative experiment showed that the aboveground biomass of M. umbrosum was unchanged when consumers were absent, but the biomass of Ludwigia repens, a plant that grass carp preferentially consumed over M. umbrosum, increased over 300-fold. Thus, selective feeding by grass carp effectively eliminates most palatable plants from this community and promotes the persistence of the chemically defended M. umbrosum, suggesting that plant defenses play critical yet understudied roles in the structure of freshwater plant communities.