Resolution of racemic carboxylic acids via the lipase‐catalyzed irreversible transesterification of vinyl esters

The lipase‐catalyzed irreversible transesterification procedure using vinyl esters was applied to the resolution of racemic 2‐phenoxypropanoic acids. Aspergillus niger lipase showed high enantioselectivities and reasonable reaction rates. The enantioselectivity was found to be affected profoundly by several variables, e.g., the alcohol as nucleophile, the organic solvent used, and the reaction temperature. A gram‐scale resolution of (RS)‐2‐phenoxypropanoic acid was achieved after optimization of the reaction conditions. Then this irreversible transesterification procedure was applied to the resolution of some related 2‐substituted carboxylic acids. Thus, racemic 2‐methoxy‐2‐phenylacetic acid was resolved via the A. niger lipase‐catalyzed transesterification of the corresponding vinyl ester. 2‐Phenylpropanoic acid and 2‐phenylbutanoic acid were resolved using Pseudomonas sp. lipase. A gram‐scale resolution of 2‐phenylbutanoic acid was achieved by this procedure coupled with the porcine liver esterase‐catalyzed hydrolysis of the resulting methyl ester. Chirality 11:554–560, 1999. © 1999 Wiley‐Liss, Inc.     

Lipase‐Catalyzed Kinetic Resolution of (±)‐1‐(2‐Furyl) Ethanol in Nonaqueous Media

S‐1‐(2‐Furyl) ethanol serves as an important chiral building block for the preparation of various natural products, fine chemicals, and is widely used in the chemical and pharmaceutical industries. In this work, lipase‐catalyzed kinetic resolution of (R/S)‐1‐(2‐furyl) ethanol using different acyl donors was investigated. Vinyl esters are good acyl donors vis‐à‐vis alkyl esters for kinetic resolution. Among them, vinyl acetate was found to be the best acyl donor. Different immobilized lipases such as Rhizomucor miehei lipase, Thermomyces lanuginosus lipase, and Candida antarctica lipase B were evaluated for this reaction, among which C. antarctica lipase B, immobilized on acrylic resin (Novozym 435), was found to be the best catalyst in n‐heptane as solvent. The effect of various parameters was studied in a systematic manner. Maximum conversion of 47% and enantiomeric excess of the substrate (ee_s) of 89% were obtained in 2 h using 5 mg of enzyme loading with an equimolar ratio of alcohol to vinyl acetate at 60°C at a speed of 300 rpm in a batch reactor. From the analysis of progress curve and initial rate data, it was concluded that the reaction followed the ordered bi–bi mechanism with dead‐end ester inhibition. Kinetic parameters were obtained by using nonlinear regression. This process is more economical, green, and easily scalable than the chemical processes. Chirality 26:286–292, 2014. © 2014 Wiley Periodicals, Inc.     

Multi‐steps green process for synthesis of six‐membered functional cyclic carbonate from trimethylolpropane by lipase catalyzed methacrylation and carbonation,and thermal cyclization

A highly functionalized six‐membered cyclic carbonate, methacrylated trimethylolpropane (TMP) cyclic carbonate, which can be used as a potential monomer for bisphenol‐free polycarbonates and isocyanate‐free polyurethanes, was synthesized by two steps transesterifications catalyzed by immobilized Candida antarctica lipase B, Novozym^®435 (N435) followed by thermal cyclization. TMP was functionalized as 70 to 80% selectivity of mono‐methacrylate with 70% conversion was achieved, and the reaction rate was evaluated using various acyl donors such as methacrylic acid, methacrylate‐methyl ester, ‐ethyl ester, and ‐vinyl ester. As a new observation, the fastest rate obtained was for the transesterfication reaction using methacrylate methyl ester. Byproducts resulted from leaving groups were adsorbed on the molecular sieves (4Å) to minimize the effect of leaving group on the equilibrium. The difference of reaction rate was explained by molecular dynamic simulations on interactions between carbonyl oxygen and amino acid residues (Thr 40 and Glu 157) in the active site of lipase. Our docking studies revealed that as acyl donor, methyl ester was preferred for the initial conformation of the first tetrahederal intermediate with hydrogen bonding interactions. TMP‐monomethacrylate (TMP‐mMA) cyclic carbonate was obtained in 63% yield (74.1% calculated in 85% conversion) from the lipase‐catalyzed carbonation reaction of TMP‐mMA with dimethylcarbonate, and followed by thermal cyclization of the monocarbonate at 90°C. From the multiple reactions demonstrated in gram scale, TMP‐mMA cyclic carbonate was obtained as a green process without using chlorinated solvent and reagent. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 32:83–88, 2016     

Novel Magnetic Cross‐Linked Lipase Aggregates for Improving the Resolution of (R,S)‐2‐octanol

Novel magnetic cross‐linked lipase aggregates were fabricated by immobilizing the cross‐linked lipase aggregates onto magnetic particles with a high number of ‐NH₂ terminal groups using p‐benzoquinone as the cross‐linking agent. At the optimal fabrication conditions, 100% of immobilization efficiency and 139% of activity recovery of the magnetic cross‐linked lipase aggregates were achieved. The magnetic cross‐linked lipase aggregates were able to efficiently resolve (R, S)‐2‐octanol, and retained 100% activity and 100% enantioselectivity after 10 cycles of reuse, whereas the cross‐linked lipase aggregates only retained about 50% activity and 70% enantioselectivity due to insufficient cross‐linking. These results provide a great potential for industrial applications of the magnetic cross‐linked lipase aggregates. Chirality 27:199–204, 2015. © 2014 Wiley Periodicals, Inc.     

One‐pot synthesis of (R)‐1‐(pyridin‐4‐yl)ethyl acetate using tandem catalyst prepared by co‐immobilization of palladium and lipase on mesoporous foam: Optimization and kinetic modeling

The synthesis of (R )‐1‐(pyridin‐4‐yl)ethyl acetate was achieved over tandem palladium‐lipase catalyst with 100% selectivity using 4‐acetyl pyridine as a reactant. The 2% w /w palladium and lipase catalyst was successfully co‐immobilized in the microenvironment of the mesocellular foam and characterized by various techniques. The palladium metal from catalyst hydrogenated 4‐acetyl pyridine to form 1‐(pyridin‐4‐yl)ethanol. The generated intermediate product then underwent kinetic resolution over lipase and selectively gave (R )‐1‐(pyridin‐4‐ yl)ethyl acetate. The catalytic conditions were then studied for optimal performance of both steps. The reaction conditions were optimized to 50 °C and toluene as a solvent. Both chemical and enzymatic kinetic models of the reaction were developed for a given set of reaction conditions and kinetic parameters were predicted. At optimal conditions, the obtained selectivity of intermediate (1‐(pyridin‐4‐yl)ethanol) was 51.38%. The final product yield of ((R )‐1‐(pyridin‐4‐yl)ethyl acetate) was 48.62%.     

Optimized butyl butyrate synthesis catalyzed by Thermomyces lanuginosus lipase

Butyl butyrate is an ester present in pineapple flavor, which is very important for the food and beverages industries. In this work, the optimization of the reaction of butyl butyrate synthesis catalyzed by the immobilized lipase Lipozyme TL‐IM was performed. n‐Hexane was selected as the most appropriate solvent. Other reaction parameters such as temperature, substrate molar ratio, biocatalyst content and added water, and their responses measured as yield, were evaluated using a fractional factorial design, followed by a central composite design (CCD) and response surface methodology. In the fractional design 2^4–1, the four variables were tested and temperature and biocatalyst content were statistically significant and then used for optimization on CCD. The optimal conditions for butyl butyrate synthesis were found to be 48°C; substrate molar ratio 3:1 (butanol:butyric acid); biocatalyst content of 40% of acid mass. Under these conditions, over 90% of yield was obtained in 2 h. Enzyme reuse was tested by washing the biocatalyst with n‐hexane or by direct reuse. The direct reuse produced a rapid decrease on enzyme activity, while washing with n‐hexane allowed reusing the enzyme for five reactions cycles keeping approximately 85% of its activity. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1416–1421, 2013     

Chemical Defense in Millipedes (Myriapoda,Diplopoda): Do Representatives of the Family Blaniulidae Belong to the ‘Quinone’ Clade?

The defensive secretions of two blaniulid millipedes, Nopoiulus kochii and Cibiniulus phlepsii, were characterized by GC‐FID and GC/MS analyses, which showed the presence of a complex mixture of benzoquinones, hydroquinones, and oleates. Altogether, 13 compounds were identified. The major compound in the secretions of both analyzed species was 2‐methyl‐1,4‐benzoquinone (toluquinone). The second major constituent in the N. kochii secretion was 2‐methyl‐3,4‐(methylenedioxy)phenol, while in that of C. phlepsii, it was 2‐methoxy‐3‐methyl‐1,4‐benzoquinone. The defensive secretion of N. kochii also showed a high content of hydroquinones (13.5%) in comparison to that of C. phlepsii (0.8%). Hexyl oleate and octyl oleate were detected for the first time in defensive millipede fluids. The chemical composition of the defensive secretions supports the chemotaxonomic position of the family Blaniulidae in the ‘quinone’ millipede clade.     

Disposable luciferase‐based microfluidic chip for rapid assay of water pollution

In the present study, we demonstrate the use of a disposable luciferase‐based microfluidic bioassay chip for environmental monitoring and methods for fabrication. The designed microfluidic system includes a chamber with immobilized enzymes of bioluminescent bacteria Photobacterium leiognathi and Vibrio fischeri and their substrates, which dissolve after the introduction of the water sample and thus activate bioluminescent reactions. Limits of detection for copper (II) sulfate, 1,3‐dihydroxybenzene and 1,4‐benzoquinone for the proposed microfluidic biosensor measured 3 μM, 15 mM, and 2 μM respectively, and these values are higher or close to the level of conventional environmental biosensors based on lyophilized bacteria. Approaches for entrapment of enzymes on poly(methyl methacrylate) (PMMA) plates using a gelatin scaffold and solvent bonding of PMMA chip plates under room temperature were suggested. The proposed microfluidic system may be used with some available luminometers and future portable luminescence readers.     

Stereoselective enzymatic esterification of 3-benzoylthio-2-methylpropanoic acid

Summary A key intermediate, S-(–)-3-benzoylthio-2-methylpropanoic acid (1) was made in high optical purity by the lipase-catalyzed stereoselective esterification of racemic 1 with methanol in an organic solvent system. Among various lipases evaluated, Amano P-30 lipase from Pseudomonas sp. efficiently catalyzed the esterification of 1 to yield R-(+) methyl ester and unreacted S-(–) 1. A reaction yield of 40 mol% and an optical purity of 97.2% were obtained for compound 1 at a substrate concentration of 0.1 m (22 mg/ml). Lipase P-30 was immobilized on Accurel polypropylene (PP) and the immobilized enzyme was reused (23 cycles) in the esterification reaction without loss of enzyme acitivity, productivity or optical purity. Among various solvents evaluated, toluene was found to be the most suitable organic solvent and methanol was the best alcohol for the esterification of racemic 1 by immobilized lipase. Substrate concentrations as high as 1.0 m were used in the esterification reaction. When the temperature was increased from 28° C to 60° C, the reaction time required for the esterification of 0.1 m substrate decreased from 16 h to 2 h. On increasing the methanol to substrate molar ratio from 1:1 to 4:1, the rate of esterification decreased. A lipase fermentation using Pseudomonas sp. ATCC 21 808 was developed. In the batch-fermentation process, 56 units/ml of extracellular lipase activity was obtained. A fed-batch process using soybean oil gave a significant increase in the lipase activity (126 units/ml). Crude lipase recovered from the filtrate by ethanol precipitation and immobilized on Accurel PP was also effective: S-(–) compound 1 was obtained in 35 mol% yield and 95% optical purity. Offsprint requests to: R. N. Patel     

Biodiesel production using Aspergillus niger as a whole‐cell biocatalyst in a packed‐bed reactor

Enzymatic lipase transesterification of palm oil to biodiesel in a packed‐bed reactor (PBR) using a novel strain of the fungus Aspergillus niger, immobilized within polyurethane biomass support particles (BSPs), was investigated. A three‐step addition of methanol was used to reduce lipase inhibition by immiscible methanol. The influence of water content and PBR flow rate was investigated. FAME yield was enhanced with an increase of PBR flow rate in the range of 0.15–30 L h^?1, where inefficient mixing of the reaction mixture at lower flow rates resulted in low conversion rates i.e. 69% after 72‐h reaction. Adding the third mole equivalent of methanol resulted in lipase inhibition due to methanol migration into the accumulated glycerol layer. Glutaraldehyde (GA) solution (0.5 vol.%) was used to stabilize lipase activity, which led to a high FAME yield (>90%) in the PBR after 72‐h of reaction time at a flow rate of 15 L h^?1, and a water content of 15%. Moreover, a high conversion rate (>85%) was maintained after four palm oil batch conversion cycles in the PBR. In contrast, lipase activity of non‐GA‐treated cells decreased with each PBR batch cycle, where only 70% FAME was produced after the forth PBR cycle. Transesterification of palm oil in a PBR system using BSPs‐immobilized A. niger as a whole‐cell biocatalyst is a viable process for enzymatic biodiesel production.     

Enantioselective synthesis of (S)‐naproxen using immobilized lipase on chitosan beads

S‐naproxen by enantioselective hydrolysis of racemic naproxen methyl ester was produced using immobilized lipase. The lipase enzyme was immobilized on chitosan beads, activated chitosan beads by glutaraldehyde, and Amberlite XAD7. In order to find an appropriate support for the hydrolysis reaction of racemic naproxen methyl ester, the conversion and enantioselectivity for all carriers were compared. In addition, effects of the volumetric ratio of two phases in different organic solvents, addition of cosolvent and surfactant, optimum pH and temperature, reusability, and inhibitory effect of methanol were investigated. The optimum volumetric ratio of two phases was defined as 3:2 of aqueous phase to organic phase. Various water miscible and water immiscible solvents were examined. Finally, isooctane was chosen as an organic solvent, while 2‐ethoxyethanol was added as a cosolvent in the organic phase of the reaction mixture. The optimum reaction conditions were determined to be 35 °C, pH 7, and 24 h. Addition of Tween‐80 in the organic phase increased the accessibility of immobilized enzyme to the reactant. The optimum organic phase compositions using a volumetric ratio of 2‐ethoxyethanol, isooctane and Tween‐80 were 3:7 and 0.1% (v /v/v), respectively. The best conversion and enantioselectivity of immobilized enzyme using chitosan beads activated by glutaraldehyde were 0.45 and 185, respectively.     

Effect of ionic liquids activation on laccase from Trametes versicolor: Enzymatic stability and activity

The stability and activity of laccase from Trametes versicolor in two water‐soluble ionic liquids (ILs), namely 1‐butyl‐3‐methylimidazolium methyl sulfate, [bmim][MeSO₄] and 1,3‐dimethylimidazolium methyl sulfate, [mmim][MeSO₄], were investigated in this study. Thermal inactivation of laccase was characterized in the presence of these both ILs and as expected first‐order kinetics was followed. Inactivation rate constant (k), half‐life time (t_1/2), and energy of activation (Ea) were determined. Kinetics of 2,2′‐azino‐bis(3‐ethylbenzthiazoline‐6‐sulfonic acid) oxidation by laccase in the presence of these ILs was studied and Michaelis–Menten parameters were calculated. There is no enzymatic inactivation since the maximum reaction rate remained constant for IL concentrations up to 25%, and surprisingly, it was found that laccase was activated for concentrations of 35% of ILs, since the reaction rate increased 1.7 times.     

Direct Asymmetric anti‐Mannich‐Type Reactions Catalyzed by Cinchona Alkaloid Derivatives

A series of cinchona alkaloid derivatives were used to catalyze the asymmetric anti‐Mannich‐type reaction of 3‐methyl‐2‐oxindole with N‐tosyl aryl aldimines. The resulting anti‐3,3‐disubstituted 2‐oxindole products were obtained in good yields (up to 92%) with high diastereo‐ and enantioselectivities (anti/syn up to 97:3 and 91% ee). Chirality 26:801–805, 2014. © 2014 Wiley Periodicals, Inc.     

Stability and kinetic behavior of immobilized laccase from Myceliophthora thermophila in the presence of the ionic liquid 1‐ethyl‐3‐methylimidazolium ethylsulfate

The use of ionic liquids (ILs) as reaction media for enzymatic reactions has increased their potential because they can improve enzyme activity and stability. Kinetic and stability properties of immobilized commercial laccase from Myceliophthora thermophila in the water‐soluble IL 1‐ethyl‐3‐methylimidazolium ethylsulfate ([emim][EtSO₄]) have been studied and compared with free laccase. Laccase immobilization was carried out by covalent binding on glyoxyl–agarose beads. The immobilization yield was 100%, and the activity was totally recovered. The Michaelis‐Menten model fitted well to the kinetic data of enzymatic oxidation of a model substrate in the presence of the IL [emim][EtSO₄]. When concentration of the IL was augmented, the values of V_max for free and immobilized laccases showed an increase and slight decrease, respectively. The laccase–glyoxyl–agarose derivative improved the laccase stability in comparison with the free laccase regarding the enzymatic inactivation in [emim][EtSO₄]. The stability of both free and immobilized laccase was slightly affected by small amounts of IL (<50%). A high concentration of the IL (75%) produced a large inactivation of free laccase. However, immobilization prevented deactivation beyond 50%. Free and immobilized laccase showed a first‐order thermal inactivation profile between 55 and 70°C in the presence of the IL [emim][EtSO₄]. Finally, thermal stability was scarcely affected by the presence of the IL. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:790–796, 2014     

Optimization of a two‐step process comprising lipase catalysis and thermal cyclization improves the efficiency of synthesis of six‐membered cyclic carbonate from trimethylolpropane and dimethylcarbonate

Six‐membered cyclic carbonates are potential monomers for phosgene and/or isocyanate free polycarbonates and polyurethanes via ring‐opening polymerization. A two‐step process for their synthesis comprising lipase‐catalyzed transesterification of a polyol, trimethylolpropane (TMP) with dimethylcarbonate (DMC) in a solvent‐free system followed by thermal cyclization was optimized to improve process efficiency and selectivity. Using full factorial designed experiments and partial least squares (PLS) modeling for the reaction catalyzed by Novozym®435 (N435; immobilized Candida antarctica lipase B), the optimum conditions for obtaining either high proportion of monocarbonated TMP and TMP‐cyclic‐carbonate (3 and 4), or dicarbonated TMP and monocarbonated TMP‐cyclic‐carbonate (5 and 6) were found. The PLS model predicted that the reactions using 15%–20% (w/w) N435 at DMC:TMP molar ratio of 10–30 can reach about 65% total yield of 3 and 4 within 10 h, and 65%–70% total yield of 5 and 6 within 32–37 h, respectively. High consistency between the predicted results and empirical data was shown with 66.1% yield of 3 and 4 at 7 h and 67.4% yield of 5 and 6 at 35 h, using 18% (w/w) biocatalyst and DMC:TMP molar ratio of 20. Thermal cyclization of the product from 7 h reaction, at 110°C in the presence of acetonitrile increased the overall yield of cyclic carbonate 4 from about 2% to more than 75% within 24 h. N435 was reused for five consecutive batches, 10 h each, to give 3+4 with a yield of about 65% in each run. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2013.     

Synthesis and chemiluminescence of copolymers of 5-amino-8-vinyl-phthalazine-1, 4(2H,3H)-dione with methyl methacrylate or styrene,and of α, ω-bis[5-amino-phthalazine-1,4 (2H,3H)-dion-]8-yl alkanes [=α, ω-bis(6-luminyl) alkanes]: Investigations on an intramolecular ‘distance effect’

Oligomers of 5-amino-8-vinyl-phthalazine-1,4(2H,3H)-dione exhibit about 0.05% of the chemiluminescence quantum yield of the corresponding ‘monomer unit’, i.e. 5-amino-8-ethyl-phthalazine-1,4(2H,3H)-dione which has a similar quantum yield to luminol. The quantum yields of copolymers of 5-amino-8-vinyl-phthalazine-1,4(2H,3H)-dione (1a) with methyl methacrylate or with styrene increase up to 1000-fold, relative to the quantum yield of oligomers of (1a). Thus the monomer units of methyl methacrylate or styrene appear to act as ‘spacers’ between the lumigenic groups. α,ω-Bis[(5-amino-phthalazine-1,4(2H,3H)-dion-)8-yl] alkanes show an analogue ‘distance’ effect: the chemiluminescence quantum yield increases with increasing alkane chain length. As the fluorescence of the corresponding amino phthalates (which are intermediates in the synthesis of the phthalazine diones) is only slightly influenced by the distance between the lumigenic groups it is suggested that a mainly chemical ‘distance effect’ is working here: the smaller the intramolecular distance between the hydrazide groups the more inhibition exists in respect of the oxidative reaction producing the luminol-type chemiluminescence.     

Enantiomeric resolution of asymmetric glycol by a lipase‐catalyzed transesterification reaction

The lipase catalyzed enantiomeric resolution of syn‐glycol was carried out to confirm the sector method, which can determine the absolute configuration of anti‐ and syn‐glycol from the ¹H‐NMR spectra of bis‐2‐methoxy‐2‐trifluoromethyl‐2‐phenylacetic acid (MTPA) esters. The lipase catalyzed transesterification reaction was most reactive at the C2 position (C2–OH) of (2R;3R)‐2,3‐octanediol. Both (2S;3S)‐ and (2R;3R)‐2,3‐octanediol were prepared using lipase. The ¹H‐NMR spectra of their bis‐(R)‐MTPA esters agreed well with those prepared previously via mono‐(R)‐MTPA esters. The result suggests the retention of the Mosher plane in MTPA esters possessing a hydroxyl group at the β position. The reaction rate and the stereoselectivity decreased at C2–OH with the addition of 18‐crown‐6. Chirality 11:338–342, 1999. © 1999 Wiley‐Liss, Inc.     

A novel enzymatic route for biodiesel production from renewable oils in a solvent-free medium

A new enzymatic route for biodiesel production from soybean oil was developed using methyl acetate as a novel acyl acceptor. Novozym 435 (immobilized Candida antarctica lipase) gave the highest methyl ester (ME) yield of 92%. The optimum conditions of the transesterification were 30% enzyme based on oil weight; a molar ratio of methyl acetate/oil of 12:1; temperature 40 °C and reaction time 10 h. Since no glycerol was produced in the process, this method is very convenient for recycling the catalyst and by-product triacetylglycerol showed no negative effect on the fuel property.     

Solvent selection and optimization of α‐chymotrypsin‐catalyzed synthesis of N‐Ac‐Phe‐Tyr‐NH2 using mixture design and response surface methodology

A peptide, N‐Ac‐Phe‐Tyr‐NH₂, with angiotensin I‐converting enzyme (ACE) inhibitor activity was synthesized by an α‐chymotrypsin‐catalyzed condensation reaction of N‐acetyl phenylalanine ethyl ester (N‐Ac‐Phe‐OEt) and tyrosinamide (Tyr‐NH₂). Three kinds of solvents: a Tris–HCl buffer (80 mM, pH 9.0), dimethylsulfoxide (DMSO), and acetonitrile were employed in this study. The optimum reaction solvent component was determined by simplex centroid mixture design. The synthesis efficiency was enhanced in an organic‐aqueous solvent (Tris‐HCl buffer: DMSO: acetonitrile = 2:1:1) in which 73.55% of the yield of N‐Ac‐Phe‐Tyr‐NH₂ could be achieved. Furthermore, the effect of reaction parameters on the yield was evaluated by response surface methodology (RSM) using a central composite rotatable design (CCRD). Based on a ridge max analysis, the optimum condition for this peptide synthesis included a reaction time of 7.4 min, a reaction temperature of 28.1°C, an enzyme activity of 98.9 U, and a substrate molar ratio (Phe:Tyr) of 1:2.8. The predicted and the actual (experimental) yields were 87.6 and 85.5%, respectively. The experimental design and RSM performed well in the optimization of synthesis of N‐Ac‐Phe‐Tyr‐NH₂, so it is expected to be an effective method for obtaining a good yield of enzymatic peptide. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012     

Amino‐substituted para‐Benzoquinones as Potential Herbicides

Although quinones present a large array of biological activities, a few studies on the herbicidal potential of 2,5‐bis(alkyl/arylamino)‐1,4‐benzoquinones have been reported to date. In this work, starting from benzoquinone, 13 2,5‐bis(alkyl/arylamino)‐1,4‐benzoquinones were prepared in 46 – 93% yield. The products were fully characterized by spectroscopic analyses and their phytotoxicity against Cucumis sativus and Sorghum bicolor seedlings was investigated. At 100 ppm, compounds caused 10 – 88% growth inhibition of the dicotyledonous species, whereas the monocotyledon was less affected. Most compounds exerted little inhibitory effect on a cyanobacterial model strain. However, at 100 μm , compounds 8  –  10 caused about 50% inhibition of algal growth, and compounds 1 and 2 reduced cell viability in the 1 – 10 μm range. The ability of benzoquinone derivatives to interfere with the light‐driven ferricyanide reduction by isolated spinach chloroplasts was evaluated. Some substances showed a moderate effect as uncouplers, but no relationship was found between this property and their biological activity, indicating that the herbicidal effect is not associated with the inhibition of the photosynthetic electron transport chain. Phytotoxic compounds were not toxic to insects, strengthening the possibility that they may serve as lead for the development of eco‐friendly herbicides.