Structure—activity relationships of pyridylcarbamates active against both benzimidazole-sensitive and -resistant isolates of Botrytis cinerea

A series of pyridylcarbamates showed high potency against cucumber gray mould (Botrytis cinerea Pers.). The most potent compound, propargyl-N-(6-ethyl-5-iodo-2-pyridyl)carbamate was effective against an isolate sensitive to benzimidazole and dicarboximide fungicides as well as against an isolate resistant to both types of compound. QSAR analyses and molecular modelling studies were carried out to investigate the structural requirements for highly active compounds and the structural feature of the binding site of each strain. Significantly different QSAR equations were obtained only for substituents at the 6-position of the pyridine ring. An ethyl-sized pocket or an ethyl terminal recognition was suggested in the case of the sensitive or resistant isolate respectively. These results could explain the phenomenon of negatively correlated cross-resistance between benzimidazoles and N-phenylcarbamate fungicides. Substituent effects at the 5- or 2-position were governed by steric factors. Substituent effects at the 3-position were explained by steric hindrance or by conformational effects. The propargyl-substituted compound above was the most desirable one from the viewpoint of QSAR.     

Bicyclophosphorothionate antagonists exhibiting selectivity for housefly GABA receptors

2,6,7-Trioxa-1-phosphabicyclo[2.2.2]octane 1-sulfides (bicyclophosphorothionates) with various C_1–4 alkyl groups at the 3- and 4-positions were synthesized and tested for their ability to compete with [³H]4′-ethynyl-4-n-propylbicycloorthobenzoate (EBOB), a non-competitive antagonist of γ-aminobutyric acid (GABA) receptors, for specific binding to rat-brain and housefly-head membranes, and for their insecticidal activity against houseflies. Among the 3,4-substituted analogues, 20 compounds were selectively active for housefly GABA receptors versus rat GABA receptors. The 3-alkyl groups of C₃ length and the 4-alkyl groups of C₄ length were tolerated in housefly receptors, whereas such bulky substituents were deleterious in rat receptors. The 4-isobutyl-3-isopropyl analogue was the most potent in housefly receptors (IC₅₀ = 45.2 nM ), and tert-butylbicyclophosphorothionate (TBPS), with the 4-tert-butyl group and no 3-substituent, was the most potent in rat receptors (IC₅₀ = 62.2 nM ). Their receptor selectivities (rat IC₅₀/housefly IC₅₀) were 52 and 0.038, respectively. The insecticidal activity (LD₅₀) of 20 active analogues was well correlated with their potency (IC₅₀) in inhibiting [³H]EBOB binding to housefly-head membranes (r = 0.93). The results obtained in the present study indicate that the introduction of appropriate alkyl groups into the 3- and 4-positions of bicyclophosphorothionate leads to non-competitive antagonists with increased affinity and selectivity for housefly ionotropic GABA receptors versus rat GABA_A receptors. © 1999 Society of Chemical Industry     

10种N-取代氨基香豆素的合成及生物活性

基于结构拼接思想,设计合成了10个N-取代氨基香豆素类化合物,并测定了其抑菌及除草活性。6-硝基香豆素经Fe/NH4Cl还原得6-氨基香豆素,再与不同醛缩合得Schiff碱,最后经硼氢化钠还原制得10个N-取代氨基香豆素类化合物(4a~4J),其中9个未见文献报道,其结构均经红外光谱、核磁共振氢谱和质谱确认。抑菌活性测试结果表明,所有化合物对苹果腐烂病菌Valsa mali、葡萄白腐病菌Coniothyrium diplodiella、棉花枯萎病菌Fusarium oxysporium和柑橘炭疽病菌Citrusanthrax bacteria均有一定抑制作用,其中 4e 的抑菌活性最强,对苹果腐烂病菌和柑橘炭疽病菌的EC50值分别为7.53和12.93 mg/L,对其余2种植物病原菌的EC50值均小于25 mg/L;化合物 4f 次之,对苹果腐烂病菌和葡萄白腐病菌的EC50值均约为11 mg/L。除草活性测试结果表明,除 4f 外,所有目标化合物均有一定除草作用,其中 4c 的活性最强,100 mg/L下对反枝苋Amaranthus retroflexus种子根、茎生长的抑制率均为99%。     

Insecticidal activity of N,N-diethyl-, N,N-dipropyl-, N,n-di-isopropyl-, and n,n-di-isobutylalkanamides against mosquito larvae

N,N-Diethyl-, N,N-dipropyl-, N,N-di-isopropyl, and N,N-di-isobutylalkanamides in which the acyl moiety ranged from C₈ to C₂₁ were synthesised, and their larvicidal activity was determined against the first-instar larvae of the southern house mosquito Culex quinquefasciatus Say. The four homologous series of amides generally showed an increase in their larvicidal activity as the carbon number in the acyl moiety of the amides increased, until the activity reached a maximum. Subsequently, an increment of carbon number resulted in declining activity in the higher homologues, until the activity disappeared. N,N-Diethyltetradecanamide, N,N-dipropylundecanamide, N,N-di-isopropylundecanamide, and N,N-di-isobutlynonanamide or -dodecanamide were the most active compounds in their respective homologous series of amides; however, they were less active than their analogous N,N-dimethylalkanamides previously studied.     

Selective complexometric determination of glyphosate and related compounds

A complexometric method has been developed for the selective determination of glyphosate and related compounds. The method is based upon the different pH-dependence of tridentate and tetradentate ligand-metal complex stabilities. Glyphosate, the tridentate ligand forms a stable copper complex at pH ≥ 8 only, whereas N-carboxymethyl-N-phosphonomethylglycine and N,N-bis(phosphonomethyl)glycine, the tetradentate ligands, form sufficiently stable bismuth complexes even at low pH. The method, therefore, consists of aliquot titrations in basic and acidic media, using metal ion titrant solutions. The first aliquot containing N-(phosphonomethyl)glycine plus N-carboxymethyl-N-phosphonomethylglycine or N,N,-bis(phosphonomethyl)glycine is titrated with bismuth volumetric solution at pH 1.8–2–5 in the presence of methylthymol blue indicator. Quantities of the tetradentate ligands can be calculated from the bismuth consumption. The second aliquot is titrated with copper volumetric solution at pH 8–10, in the presence of murexide indicator. The content of glyphosate can be calculated from the difference between the copper and bismuth consumptions. Efficacy of the method is verified by analyses of standard mixtures and industrial samples.     

Quantitative structure-activity study of insecticidal 2-methoxy-5-(substituted-phenyl)-1, 3, 2-oxazaphospholidine 2-sulfides against Musca domestica L. by topical application

The quantitative relationship between the structure of 2-methoxy-5-(substituted-phenyl)-1, 3, 2-oxazaphospholidine 2-sulfides (5-PMOS) and their insecticidal activity against the house fly. Musca domestica L., was analyzed using reported physicochemical parameters and regression analysis. The electronic nature of the substituent on the phenyl group of 5-PMOS has the most significant effect on the activity, followed by hydrophobic and steric effects; the optimum value of Σρ is zero and the more hydrophobic the substituents on the phenyl group, the higher the insecticidal activity. The plots of observed pLD₅₀, values against calculated pLD₅₀ values for compounds having substituents in the ortho-position deviated downwards from those of compounds having substituents at the meta and/or para positions. This ortho-effect, which reduces the insecticidal activity of compounds having substituents at the ortho-position, was expressed by a dummy parameter D, which has the value 2 for di-ortho-substituted derivatives, 1 for mono-ortho-substituted derivatives and zero for others. Thus, the highest activity was obtained for 2-methoxy-5-phenyl-1, 3, 2-oxazaphospholidine 2-sulfide, and the activity was decreased by the introduction of any substituents on the phenyl group.     

Fungicidal activity of substituted quinoxalines

Twenty substituted quinoxalines based on the structure of 6 (or 7)-methyl-3-phenyl-1, 2-dihydroquinoxalin-2-one, a fungicidally active photodegradation product of quinomethionate, were synthesised. Eleven of these compounds had ED₅₀ values, as protectant sprays against Podosphaera leucotricha, of 0.1 mmol or less; these compounds had an aromatic substituent at the 3-position of the quinoxaline ring. They were less active as protectant leaf dips against Erysiphe graminis f. sp. hordei than against Podosphaera leucotricha; none showed any systemic activity as a soil-applied treatment against Podosphaera leucotricha. One compound was more active than quinomethionate as an eradicant spray. In spore germination tests on fungi from different taxonomic groups, the quinoxaline derivatives were active against only one basidiomycete (Uromyces fabae), whereas quinomethionate showed a broad spectrum of activity. The possible significance of this difference in spectrum of activity with respect to the mode of action is discussed.     

Synthesis and bioactivity evaluation of novel spiromesifen derivatives

BACKGROUND: The development of environmentally friendly and novel structural pesticides is now an area of intense research in the agriculture field. Spirocyclic tetronic acids such as spiromesifen are typical compounds of this kind. In order to discover novel compounds with improved and broader-spectrum insecticidal activities, a series of spiromesifen derivatives were synthesised and bioassayed. RESULTS: The derivatives were identified by ¹H NMR and MS. Preliminary bioassays demonstrated that some bioactivities of compounds 5a to 5u were better and had a broader spectrum than the lead compound spiromesifen. Moreover, these compounds showed better insecticidal activities against Mythimna sepatara and Aphis fabae than acaricidal activities against Tetranychus cinnabari. Furthermore, LC₅₀ of 5s against Aphis fabae reached 1.09 mg L⁻¹. At the same time, compounds 5g, 5i, 5k and 5r also warrant further study because of their superior bioactivities to spiromesifen. What is more, suitable carbon chain length in the 4-position ester and the log P value of these spiromesifen derivatives dramatically influenced their insecticidal activities. Butyric or pentanoic ester and a log P value of 4.0–6.0 may be preferred. CONCLUSION: The present work demonstrates that some spiromesifen derivatives can be used as potential lead compounds for developing novel insecticides and acaricides. Copyright © 2011 Society of Chemical Industry     

山蒟中脂肪链酰胺类化合物的分离及杀虫活性

采用提取、萃取及柱层析等方法,从山蒟Piper hancei Maxim甲醇提取物的石油醚和氯仿萃取相中分离到6个脂肪链酰胺类化合物,通过核磁共振、质谱并结合相关文献比对,其结构被分别鉴定为已知化合物chingchengenamide A( C1 )、N-异丁基-反-2-反-4-癸二烯酰胺( C2 )、假荜拨酰胺A( C3 )、荜茇宁( C4 )、N-p-香豆酰酪胺( C5 )和N-反式-阿魏酰酪胺( C6 ),其中 C1 为首次从山蒟中获得。利用幼虫浸液法测试了各化合物对白纹伊蚊Aedes albopictus和致倦库蚊Culex pipiens quinquefasciatus幼虫的12 h杀虫活性。结果表明:在20 mg/L下,化合物 C1 对白纹伊蚊的杀虫活性较高,其校正死亡率为100%,LC₅₀值为5.37 mg/L;化合物 C1 、 C2 、 C3 和 C4 对致倦库蚊的杀虫活性较高,20 mg/L下的校正死亡率分别为100%、88.5%、100%和100%,LC₅₀值分别为1.03、9.68、3.08和2.87 mg/L。     

Multifunctionalised benzoxazinones in the systems Oryza sativa–Echinochloa crus‐galli and Triticum aestivum–Avena fatua as natural‐product‐based herbicide leads

BACKGROUND: Fifteen novel derivatives of D‐DIBOA, including aromatic ring modifications and the addition of side chains in positions C‐2 and N‐4, had previously been synthesised and their phytotoxicity on standard target species (STS) evaluated. This strategy combined steric, electronic, solubility and lipophilicity requirements to achieve the maximum phytotoxic activity. An evaluation of the bioactivity of these compounds on the systems Oryza sativa–Echinochloa crus‐galli and Triticum aestivum–Avena fatua is reported here. RESULTS: All compounds showed inhibition profiles on the two species Echinochloa crus‐galli (L.) Beauv. and Avena fatua L. The most marked effects were caused by 6F‐4Pr‐D‐DIBOA, 6F‐4Val‐D‐DIBOA, 6Cl‐4Pr‐D‐DIBOA and 6Cl‐4Val‐D‐DIBOA. The IC₅₀ values for the systems Echinochloa crus‐galli–Oryza sativa and Avena fatua–Triticum aestivum for all compounds were compared. The compound that showed the greatest selectivity for the system Echinochloa crus‐galli–Oryza sativa was 8Cl‐4Pr‐D‐DIBOA, which was 15 times more selective than the commercial herbicide propanil (Cotanil‐35). With regard to the system Avena fatua–Triticum aestivum, the compounds that showed the highest selectivities were 8Cl‐4Val‐D‐DIBOA and 6F‐4Pr‐D‐DIBOA. The results obtained for 6F‐4Pr‐D‐DIBOA are of great interest because of the high phytotoxicity to Avena fatua (IC₅₀ = 6 µM , r² = 0.9616). CONCLUSION: The in vitro phytotoxicity profiles and selectivities shown by the compounds described here make them candidates for higher‐level studies. 8Cl‐4Pr‐D‐DIBOA for the system Echinochloa crus‐galli‐Oryza sativa and 6F‐4Pr‐D‐DIBOA for Avena fatua‐Triticum aestivum were the most interesting compounds. Copyright © 2010 Society of Chemical Industry     

Characterization of a vector-non-transmissible isolate of Tomato spotted wilt virus

The characteristics of a thrips‐non‐transmissible isolate of Tomato spotted wilt virus (TSWV), designated TSWV‐M, were compared with those of a thrips‐transmissible isolate, designated TSWV‐T. TSWV‐M showed a narrower host range than TSWV‐T. Adult thrips failed to transmit TSWV‐M, although the vector acquired the virus during the larval stages. TSWV‐M was detected by RT‐PCR in adult thrips bodies, but not in thrips heads, suggesting that loss of thrips transmissibility was the result of the absence of virus in adult thrips salivary glands. Whereas N (nucleoprotein), NSs (non‐structural protein) and G_C (the C‐terminal portion of the glycoprotein precursor protein) were present in similar amounts in leaf tissue from TSWV‐M‐ or TSWV‐T‐infected plants, G_N (the N‐terminal portion of the glycoprotein precursor protein) was present at much lower amounts in TSWV‐M‐ than in TSWV‐T‐infected plants. SDS‐PAGE and immunoblotting analysis of TSWV‐M and TSWV‐T virion preparations with G_N‐ and G_C‐specific antibodies revealed similar amounts of the G_N and G_C glycoproteins in TSWV‐T virions, but lower amounts of G_N than G_C in TSWV‐M virions. This resulted in a statistically significant reduction in the G_N/G_C ratio in TSWV‐M virions. In affinoblots, the G_C and G_N glycoproteins of TSWV‐M exhibited weak binding with lectins showing affinity for N‐linked oligosaccharide structures. Sequence analysis of M RNA (medium segment of the TSMV genome) revealed no deletions or frameshift mutations in the G_N/G_C precursor of TSWV‐M. However, five amino acid changes were detected in the G_N/G_C precursor. A single, relatively conservative amino acid substitution (V→I) was observed in the NSm protein. Sequence analysis of S RNA (small portion of the TSMV genome) revealed a large intergenic region with no changes in the N protein and with three amino acid changes in the NSs protein.     

Stereochemistry and active conformation of a novel insecticide,acetamiprid

Acetamiprid, (NI-25; (E)-N¹-[(6-chloro-3-pyridyl)methyl]-N²-cyano-N¹-methylacetamidine), is a novel neonicotinoid insecticide having an N-cyanoacetamidine structure as its characteristic feature. The [¹H] and [¹³C]-NMR spectra indicated the existence of two different structures in acetamiprid at room temperature in solution. The measurement of CH-NOE and C–C coupling constants proved the E-configuration at the cyanoimino group in both existing structures. The [¹³C] chemical shifts of N-CH₃ and the long range C–H coupling in the formamidine analogue of acetamiprid suggested that there exist two conformers generated by the rotation of C–C single bond in the amidine moiety. Dynamic NMR spectra of acetamiprid and the computer simulation of the two-site exchange demonstrated that the two conformers change slowly to each other at room temperature. The conformational analysis by semi-empirical molecular orbital calculations using MNDO-PM3 method predicted four conformers as energy-minimum structures, among which two E-conformers were more stable than Z-conformers. One of the E-conformers in which two methyl groups are in cis configuration was superimposable onto the structure of imidacloprid, which is a known neonicotinoid insecticide having more rigid structure. This E-conformer was assumed as the active conformation of acetamiprid on the basis of the molecular similarity in terms of steric and electrostatic properties. © 1997 SCI     

Isomerization and Beckmann rearrangement reactions in the metabolism of methomyl in rats

Methomyl {S-methyl-N-[(methylcarbamoyl)oxy]thioacetimidate}, also known as Lannate, may exist in two geometric configurations but the more stable syn isomer is the form applied as an insecticide. In the rat, syn[¹⁴CN]methomyl [CH₃S(CH₃)CNOC(O)NHCH₃] was metabolized to respiratory ¹⁴CO₂ and $\text{CH}{}_3{}^{14}\text{CN}$ in a ratio of about 2 to 1. Studies with the anti isomer showed that it was metabolized predominately to $\text{CH}{}_3{}^{14}\text{CN}$. These and other data are presented supporting the contention that syn methomyl is partially isomerized to the anti isomer in the animal prior to the hydrolysis of the ester linkage. After hydrolysis, the syn oxime [CH₃S(CH₃)¹⁴CNOH] is further metabolized to ¹⁴CO₂ while the anti oxime is metabolized to $\text{CH}{}_3{}^{14}\text{CN}$. Proposed immediate precursors to the carbon dioxide and acetonitrile, formed by Beckmann rearrangement of the syn and anti oximes, are CH₃S¹⁴C(O)NHCH₃ and $\text{[}\text{CH}{}_3{}^{\mathrm{14\oplus }}\text{CNSCH}{}_3\text{]x}{}^{\mathrm{?}}$, respectively.     

Design, semisynthesis and insecticidal activity of novel podophyllotoxin derivatives against Brontispa longissima in vivo

In an attempt to find the effective phytopesticides, a series of novel podophyllotoxin derivatives were firstly synthesized and preliminarily tested for their antifeedant and insecticidal effects against the fifth-instar larvae of Brontispa longissima. The different antifeedant and insecticidal activity ranges of compounds 3a-l showed that variations of NR₁R₂ groups in the 4-position of podophyllotoxin skeleton markedly affected the activity profiles of this compound class, and some important SAR information has been revealed from it. To clarify their mode of action of insecticidal activity, the docking models as well as tubulin inhibitory effect of representative compound 3i were also investigated, and the result indicated that the insecticidal activity of these compounds was due to the tubulin inhibitory effect of these derivatives, thereby possibly providing some useful information for rational designs of novel podophyllotoxin-based insecticides.     

Mechanism of hydantoin ring opening in iprodione in aqueous media

The hydrolysis kinetics of iprodione in alkaline solutions of pH 8.3 to 12 at 25°C have been determined by ultraviolet spectrophotometry. Under these conditions, iprodione leads quantitatively and irreversibly to N-(3,5-dichloroanilinocarbonyl)-N-(isopropylaminocarbonyl)glycine. The reaction is not subject to a general basic catalysis and the rate law takes the form K_obs = K_OH- [OH^?1]. The activation entropy of -77 J mol^?1deg^?1, the value of the kinetic solvent isotope effect k_OH?/k_OD? of 0.79 and the value of 0.60 for the Hammett parameter σ, obtained for the hydrolysis of a series of 3-aryl-N-isopropyl-2,4-dioxoimidazolidine-1-carboxamides are all in agreement with the rate-determining attack by the hydroxyl ion on the carbonyl in the 4-position of the hydantoin ring of the fungicide.     

The genetic and molecular basis of b-proteins in the genus Nicotiana

Screening for the pathogenesis-related (b) protein patterns of 11Nicotiana species and 30N. tabacum varieties has revealed both inter- and intraspecific variability and 7 different b-proteins (b₀, b₁, b_1′, b_1″, b₂, b₃ and b₄) have been clearly defined. Their genetic determinants are sexually transmitted independently of theN gene conferring resistance to TMV, and a monogenic inheritance has been demonstrated for one of them (b_1′). Grafting experiments have revealed the existence of a species-aspecific ‘mobile compound’ responsible for the expression of the b-protein genes, the production of which is probably under the control of theN gene. Among the 5 intraspecific and 6 interspecific hybrids studied, one of them, theN. glutinosa x N. debneyi together with its amphidiploid, synthesizes b-protein (b_1″) in a constituve way and possesses a high level of resistance to necrosis-inducing viruses. The amphidiploid is able to transfer these two properties to otherNicotianae not only by crossing but also by grafting; it therefore appears to permanently synthesize the ‘mobile compounds’. Furthermore, the hypersensitive reaction to TMV in these hybrids is only completely broken down at 35 °C, whereas this normally occurs at 30 °C in plants with theN gene.     

Structure—activity relationships of organotin biocides and Ceratocystis ulmi

The effect of organotin compounds on the growth of Ceratocystis ulmi, the causative agent of Dutch elm disease, was studied in shake culture. Triphenyltin, (C₆H₅)₃SnX, tricyclohexyltin, (C₆H₁₁)₃SnX, and tributyltin, (C₄H₉)₃SnX, compounds were all effective in the inhibition of C. ulmi in vitro. The anionic group, X, did not play a major role in the inhibitory activities of these compounds, suggesting that the species involved in the inhibition is R₃Sn⁺ or the hydrated cation.     

Time,concentration and temperature relationships for phosphine activity in tests on diapausing larvae of Ephestia elutella (Hübner) (Lepidoptera: Pyralidae)

The activity of phosphine against diapausing larvae of Ephestia elutella was shown to depend on several different interactions of duration of exposure, temperature and gas concentration. Using the model proposed by Knight, (C? C₀) × (t? t₀) = k, a constant for mortality, the minimum effective concentration C₀ was raised and the minimum effective exposure t₀ extended as temperatures were increased. The effect of temperature on these thresholds was reduced at higher mortality levels. A range of concentration levels, influenced by temperature, elicited an increase in tolerance at the LD₉₉ level over that evident at higher or lower concentrations. These concentration ranges were 0.9–2-1 mg litre-¹at 25°C,0.7–2.3 mg litre-¹ at 20°C and 0.1–1.5 mg litre-¹ at 15°C. A mathematical model was fitted to relate concentration and time thresholds, mortality and temperature. At the LD₅₀ level, values for t₀ ranged from 2.5 h at 15°C to 5.0 h at 25°C. C₀ values increased from about 0.6 to 7.0 μg litre-¹ over this temperature range. At the LD₉₉ level, t₀ values ranged from 21 to 28 h and C₀ values from 11 to 19 μg litre-¹. Phosphine appeared most effective at each temperature at concentrations from about 40 to 60–100 μg litre-¹.     

The antifungal activity of some sulphonyl derivatives of isoxazole,pyrazole, thiazole and thiophene

Fifty-three heterocyclic sulphonyl derivatives including eight sulphonamides, three sulphonyl azides, nine sulphonohydrazides and twenty sulphonohydrazones of substituted thiophenes, and a smaller range of analogous isoxazoles pryazoles and thiazoles, were tested as potential fungicides in a simple screening procedure against Mucor mucedo, Septoria nodorum, Trichoderma viride, Chaetomium globosum and Aspergillus niger. Several thiophene-2-sulphonyl based compounds exhibited a high level of antifungal activity at 100 mg litre^?1 against the five test species, especially the mono-halogen-substituted sulphonamides and sulphonohydrazines, in which a single chlorine or bromine atom was substituted in the para position of an attached phenyl ring. The most active compound, against all five species of fungus was N-(4-chlorophenyl)-N-(trichloromethylthio) thiophene-2-sulphonamide which had average MIC₅₀ and MIC₁₀₀ values of 86 and 180 μmol respectively. (MIC₅₀ and MIC₁₀₀ values are, respectively, the concentrations required to inhibit fungal growth by 50% and to inhibit it totally.) In general, the isoxazole analogues of the thiophene-2-sulphonyl compounds exhibited a much lower fungitoxic activity, whilst the pyrazole and thiazole based compounds had little or no activity. Compared with the other results, the considerable activity shown by 4-[2′-(3,4-dichlorobenzylidene)hydrazinosulphonyl]thiophene-2-carboxylic acid was unexpected.     

Mode of action of new diethylamines in lycopene cyclase inhibition and in photosystem II turnover

The new bleaching herbicidal compound N,N‐diethyl‐N‐(2‐undecynyl)amine (NDUA) is identified here as an inhibitor of lycopene cyclase and is compared with the known cyclase inhibitors N,N‐diethyl‐N‐[2‐(4‐chlorophenylthio)ethyl]amine (CPTA) and N,N‐diethyl‐N‐[2‐(4‐methylphenoxy)ethyl]amine (MTPA). HPLC separation of chloroplast pigments shows lycopene accumulation in NDUA treated tissue. Variation in chain length of the undecynylamine moeity of NDUA from 7 to 21 C atoms reveals an optimum of 11 to 14 C atoms for herbicidal activity. A series of seven further analogues of NDUA and CPTA reveals the structural elements necessary for inhibition of lycopene cyclase. The effect of NDUA derivatives on photosynthesis has been studied in Chlamydomonas reinhardtii. Photosynthesis is highly sensitive, particularly towards the C14 and longer chain length analogues at nanomolar concentrations. It is shown that the breakdown of photosynthesis by NDUA is due to interference with the turnover of the D1 protein of the photosystem II reaction centre that requires the continous biosynthesis of the two reaction‐centre β‐carotene moieties in the reassembly phase. The D1 protein disappearance is most marked under strong light conditions. The depletion of photosystem II occurs before total pigment bleaching. This newly recognized mechanism in herbicidal activity is also the basis for the mode of action of other lycopene cyclase inhibitors as well as phytoene desaturase inhibitors. © 2001 Society of Chemical Industry