Structure-activity relationship development of dihaloaryl triazole compounds as insecticides and acaricides. 1. Phenyl thiophen-2-yl triazoles

An extended lipophilic system that incorporated some key elements of first-generation 2,6-dihaloaryl actives, such as 1, demonstrated desirable efficacy against chewing insects as well as sap-feeding insects. These four-ring systems, based on 2, were accessed primarily via Suzuki couplings of halothiophene derivatives with appropriately substituted boronic acids. In particular, phenylthiophene systems that incorporated haloxyether groups, such as those in 3, 4, and 5, had the broadest spectrum of activity across chewing and sap-feeding insect pests. Expansion of this structure-activity relationship to include compounds with differing substitution patterns on the thiophene-C-ring and aryl-D-rings was undertaken. The synthesis and insecticidal activity of 3-aryl-5-(thiophen-2-yl)-1-methyl-1H-[1,2,4]triazoles will be described.     

Insect nicotinic acetylcholine receptors: neonicotinoid binding site specificity is usually but not always conserved with varied substituents and species

The diversity of neonicotinoid insecticides acting as insect nicotinic acetylcholine (ACh) receptor (nAChR) agonists is illustrated by imidacloprid (IMI) with chloropyridinylmethyl (CPM) and N-nitroimine substituents, dinotefuran (DIN) with tetrahydrofurylmethyl (TFM) and N-nitroimine moieties, and acetamiprid (ACE) with CPM and N-cyanoimine groups. These three neonicotinoids are used here as radioligands to test the hypothesis that they all bind to the same site in the same way in both fruit flies (Drosophila melanogaster) and a leafhopper pest (Homalodisca coagulata): that is, neonicotinoid binding site specificity is conserved in the insect nAChRs. Multiple approaches show that [3H]IMI and [3H]ACE interact with an identical site in both species. However, although [3H]DIN binds with high affinity in both insects, its pharmacological profile in Homalodisca is surprisingly unique, with high sensitivity to some TFM-containing compounds and ACh. The TFM moiety of DIN may bind in a different orientation compared to the CPM group of IMI and ACE.     

Insect muscarinic acetylcholine receptor: pharmacological and toxicological profiles of antagonists and agonists

The insect muscarinic acetylcholine receptor (mAChR) is evaluated as a potential target for insecticide action. The mammalian M2/M4-selective antagonist radioligand [3H]AF-DX 384 (a pirenzepine analogue) binds to Drosophila mAChR at a single high-affinity site identical to that for the nonselective antagonist [3H]quinuclidinyl benzilate (QNB) and with a pharmacological profile distinct from that of all mammalian mAChR subtypes. Three nonselective antagonists (QNB, scopolamine, and atropine) show the highest affinity (Ki=0.5-2.4 nM) at the Drosophila target, and AF-DX 384 and M3-selective 4-DAMP (dimethyl-4-(diphenylacetoxy)piperidinium iodide) rank next in potency (Ki=5-18 nM). Eleven muscarinic antagonists generally exhibit higher affinity than eight agonists. On injection into houseflies, the antagonists 4-DAMP and (S)-(+)-dimethindene produce suppressed movement, the agonist (methyloxadiazolyl)quinuclidine causes knockdown and tremors, and all of them inhibit [3H]QNB binding ex vivo, indicating possible mAChR-mediated intoxication. The insect mAChR warrants continuing study in lead generation to discover novel insecticides.     

Design, synthesis, crystal structure analysis, and insecticidal evaluation of phenylazoneonicotinoids

On the basis of research of the proposed modes of action between neonicotinoids and insect nicotinic acetylcholine receptor (nAChR), a series of phenylazoneonicotinoids were designed and synthesized to further promote the π-π interaction between molecule and amino acid residues. The target compounds have been identified on the basis of satisfactory analytical and spectral ((1)H NMR, (13)C NMR, HRMS, and X-ray) data. The preliminary results revealed that tiny differences in substitutes resulted in different configurations and great bioactivity variations. Some compounds with electron-donating groups on positions 2 and 6 of the phenyl ring presented higher insecticidal activity than imidacloprid against cowpea aphids ( Aphis craccivora ). The impressive crystal structure of the excellent insecticidal activity compound 9q clearly proved that the functional electronegative pharmacophore was approximately vertical to the methyleneimidazolidine plane. The differences in the mode of interaction on nAChR of typical compounds 9h and 9q remain unclear.     

高比活度碳-14标记氟噻草胺的合成与分析

为开展除草剂氟噻草胺在我国的登记代谢试验,本研究以4-氟[U-¹⁴C]苯胺为同位素原料,经还原胺化、缩合、取代、水解和醚化五步放化反应获得N-(4-氟[U-¹⁴C]苯基)-N-异丙基-2-((5-(三氟甲基)-1,3,4-噻二唑-2-基)氧基)乙酰胺(2,总活度201.65 MBq;比活度2 049.80 MBq·mmol^-1;化学纯度和放化纯度均大于98%,总放化收率39%);以[¹⁴C]硫氰酸钠为同位素原料,经加成、水解、环化、重氮化和醚化五步放化反应获得N-(4-氟苯基)-N-异丙基-2-((5-(三氟甲基)-1,3,4-[2-¹⁴C]噻二唑-2-基)氧基)乙酰胺(3,总活度287.86 MBq;比活度2 042.40 MBq·mmol^-1;化学纯度和放化纯度均大于98%,总放化收率14%)。两种标记物的结构经核磁共振氢谱(¹H NMR)和质谱(MS)分析确认,质量指标经高效液相色谱(HPLC-PDA)、放射性薄层成像分析(TLC-IIA)、在线放射性高效液相色谱(HPLC-FSA)和液体闪烁法(LSC)测定,均可作为放射性示踪剂。本研究结果为氟噻草胺的同位素示踪研究(包括该除草剂在我国的登记代谢试验)奠定了物质基础。     

氟啶虫胺腈在棉花和土壤中的检测方法与残留动态研究

研究和建立了氟啶虫胺腈在土壤、棉籽和棉叶中的高效液相色谱检测方法,并在天津和杭州两地开展了氟啶虫胺腈在棉花中的田间残留试验研究。样品采用乙腈提取,正己烷萃取,氟罗里硅土柱层析净化,正己烷/丙酮(体积比6∶4)混合液洗脱,减压浓缩至干,甲醇定容,高效液相色谱配可变波长紫外检测器进行检测。当分别在空白土壤、棉籽和棉叶样品中添加浓度为0.05~2.5mg·kg-1的氟啶虫胺腈标准品时,其平均添加回收率在76.81%~94.43%之间,相对标准偏差(RSD)在0.54%~7.20%之间;氟啶虫胺腈的最小检出量为1 ng,在所有样品中的最低检出浓度均为0.05mg·kg-1。田间残留试验结果表明,氟啶虫胺腈在土壤和棉叶中的消解规律符合一级动力学模型Ct=C0e-kt,消解半衰期分别为1.36~5.10 d和6.13~9.37d。最终残留试验结果表明,在棉花田手动喷雾施用50%氟啶虫胺腈水分散粒剂,按推荐剂量和1.5倍推荐剂量施药,兑水喷雾处理2~3次,每次施药间隔7 d,在距最后1次施药7、14 d和21d时,氟啶虫胺腈在棉籽和土壤中的残留量均小于方法最低检出浓度0.05mg·kg-1。     

Unique neonicotinoid binding conformations conferring selective receptor interactions

Neonicotinoid agonists selectively act on the insect nicotinic acetylcholine receptor (nAChR). The molecular basis for this specificity is deciphered by comparisons of two acetylcholine binding proteins (AChBPs) with distinct pharmacological profiles that serve as structural homologues for the nAChR subtypes. Aplysia AChBP has high neonicotinoid sensitivity, whereas Lymnaea AChBP has low neonicotinoid sensitivity, pharmacologies reminiscent of insect and vertebrate nAChR subtypes, respectively. The ligand-receptor interactions for these AChBPs were established by chemical and structural neurobiology approaches. Neonicotinoids and nicotinoids bind in a single conformation with Aplysia AChBP, wherein the electronegative nitro or cyano pharmacophore of the neonicotinoid faces in a reversed orientation relative to the cationic nicotinoid functionality. For Lymnaea AChBP, the neonicotinoids have two binding conformations in this vertebrate receptor model, which are completely inverted relative to each other, whereas nicotinoids are nestled in only one conserved conformation. Therefore, the unique binding conformations of nicotinic agonists determine the selective receptor interactions.     

INFLUENCE OF NEONICOTINOID INSECTICIDES ON THE PLANT GROWTH ATTRIBUTES OF COTTON AND OKRA

Neonicotinoids are crop protection agents used against sucking pests acting on receptor proteins of insect nervous system. Although many reports detail their insecticidal properties, reports on the effect on plant growth are minimal. We investigated the effect of neonicotinoids viz. imidacloprid, thiamethoxam, acetamiprid and thiacloprid on plant height, chlorophyll, and soluble protein of cotton and okra. Thiamethoxam was found to exert an influence on the plant height of cotton and okra. There was no marked influences of neonicotinoids on the total chlorophyll content of cotton leaves, whereas acetamiprid recorded a gradual increase in the total chlorophyll content of okra leaves at 7, 14 and 21 days after treatment. All the neonicotinoid insecticides under study showed an increase in the soluble protein content of cotton and okra. An increase in soluble protein content is reported to increase the ability of plants to fix carbon dioxide (CO₂) effectively and thus increase photosynthesis.     

Synthesis of haptens and development of an immunoassay for the olive fruit fly pheromone

An enzyme-linked immunosorbent assay (ELISA) for the olive fruit fly pheromone, Bactrocera oleae Gmelin, was developed. The assay uses polyclonal antibodies, raised in rabbits, against (+/-)-beta-[3-(1,7-dioxaspiro[5.5]undecane)]propionic acid, 2 (hapten I), conjugated to the KLH (keyhole limpet hemocyanin) by the carbodiimide method. A second hapten, (+/-)-delta-[3-(1,7-dioxaspiro[5.5]undecane)]butylamine, 3 (hapten II), after conjugation to a biotin moiety, was used for indirect immobilization onto ELISA microwells precoated with the glycoprotein avidin. The developed ELISA method measures the synthetic olive fruit fly pheromone in concentrations ranging between 0.08 and 10 microg/mL and shows great promise for practical applications for pheromone detection in environmental and biological samples. The results obtained strongly indicate that this technique, to our knowledge the first insect pheromone enzyme-linked immunosorbent assay so far reported, is a fast, sensitive, inexpensive, and highly convenient method for the analysis of a volatile and low molecular weight compound such as 1,7-dioxaspiro[5.5]undecane, 1.     

Synthesis and structure-activity relationships of 1-phenyl-1H-1,2,3-triazoles as selective insect GABA receptor antagonists

To study the interaction of phenylheterocycles with gamma-aminobutyric acid (GABA) receptors, 4- or 5-alkyl(or phenyl)-1-phenyl-1H-1,2,3-triazoles were synthesized and examined for their ability to inhibit the specific binding of [3H]-4'-ethynyl-4-n-propylbicycloorthobenzoate (EBOB), a noncompetitive antagonist, to the housefly and rat GABA receptors, as well as to the beta3 subunit homo-oligomer of the human GABA receptor investigated as a model receptor. 4-Substituted 1-phenyl-1H-1,2,3-triazoles were found to be more potent competitive inhibitors than the 5-substituted regioisomers in the case of all receptors. The 4-tert-butyl or 4-n-propyl analogue of 1-(2,6-dichloro-4-trifluoromethylphenyl)-1H-1,2,3-triazole exhibited the highest level of inhibition of [3H]EBOB binding to all receptors. Most of the synthesized analogues were more active in terms of the inhibition of EBOB binding to the housefly and human beta3 GABA receptors than to the rat receptor. The 4-cyclohexyl analogue showed the highest (185-fold) housefly versus rat receptor selectivity. A three-dimensional quantitative structure-activity relationship (3D-QSAR) analysis demonstrated that both the 4-trifluoromethyl-2,6-dichloro substitution on the phenyl ring and a small, bulky, hydrophobic substituent at the 4-position of the triazole ring played significant roles in conferring high potency in cases involving the housefly and human beta3 receptors. The human beta3 receptor resembled the housefly receptor in terms of their recognition of phenyltriazoles, whereas 3D-QSAR analysis revealed a slight difference between the two receptors in terms of their mechanisms of recognition of the para-substituent on the phenyl moiety. Some of the triazoles synthesized here exhibited insecticidal activity, which was correlated with their ability to inhibit [3H]EBOB binding to the housefly receptor. Thus, 1-phenyl-1H-1,2,3-triazoles with the appropriate substituents exert insecticidal activity by selectively acting at the site for noncompetitive antagonism of insect GABA receptors.     

Activity of lycorine analogues against the fish bacterial pathogen Flavobacterium columnare

In a continuing effort to discover natural products and natural product-based compounds for the control of columnaris disease in channel catfish (Ictalurus punctatus), 17 lycorine analogues were synthesized, including new benzoyl analogues 6-16, and evaluated for antibacterial activity against two isolates (ALM-00-173 and BioMed) of Flavobacterium columnare using a rapid bioassay. Two of the lycorine analogues had greater antibacterial activity than 1-O-acetyllycorine, an analogue of lycorine evaluated previously that is highly active against both isolates. Carbamate analogue 18 (1S,2S,3a(1)S,12bS)-2,3a(1),4,5,7,12b-hexahydro-1H-[1,3]dioxolo[4,5-j]pyrrolo[3,2,1-de]phenanthridin-1,2-diylbis(o-tolylcarbamate) had the strongest antibacterial activity toward both F. columnare isolates ALM-00-173 and BioMed, with 24-h IC(50) values of 3.0 ± 1.3 and 3.9 ± 2.2 mg/L, respectively, and a MIC of 5.5 ± 0 mg/L for both isolates. Compound 18 appears to be the most promising lycorine analogue for future efficacy studies to determine its potential for use as an alternative to the currently used compounds to control columnaris disease in channel catfish.     

Natural fungicides from Ruta graveolens L. leaves,including a new quinolone alkaloid

Bioassay-directed isolation of antifungal compounds from an ethyl acetate extract of Ruta graveolens leaves yielded two furanocoumarins, one quinoline alkaloid, and four quinolone alkaloids, including a novel compound, 1-methyl-2-[6'-(3' ',4' '-methylenedioxyphenyl)hexyl]-4-quinolone. The (1)H and (13)C NMR assignments of the new compound are reported. Antifungal activities of the isolated compounds, together with 7-hydroxycoumarin, 4-hydroxycoumarin, and 7-methoxycoumarin, which are known to occur in Rutaceae species, were evaluated by bioautography and microbioassay. Four of the alkaloids had moderate activity against Colletotrichum species, including a benomyl-resistant C. acutatum. These compounds and the furanocoumarins 5- and 8-methoxypsoralen had moderate activity against Fusarium oxysporum. The novel quinolone alkaloid was highly active against Botrytis cinerea. Phomopsis species were much more sensitive to most of the compounds, with P. viticola being highly sensitive to all of the compounds.     

旅游踩踏对五台山东台山地草甸土壤酶活性的影响

[目的]研究旅游踩踏对五台山东台山地草甸土壤酶活性的影响,旨在为五台山旅游资源的开发、保护和管理提供科学依据。[方法]采用野外采样调查与室内研究分析相结合的方法。[结果](1)在不同海拔高度处,踩踏对土壤脲酶和蔗糖酶活性有显著的抑制作用,表现为:无踩踏区酶活性踩踏轻微区酶活性踩踏严重区酶活性;表层(0—20cm)土层酶活性下表层(20—40cm)土层酶活性;(2)在不同海拔高度处,两个土壤层的踩踏严重区脲酶、蔗糖酶活性与无踩踏区的脲酶、蔗糖酶活性差异显著,但轻微区蔗糖酶活性与无踩踏区无显著差异;(3)在不同的海拔处,表层和下表层的踩踏严重区土壤过氧化氢酶活性、磷酸酶活性显著低于无踩踏区土壤过氧化氢酶活性、磷酸酶活性(p0.05);表层轻微区的过氧化氢酶活性、磷酸酶活性与无踩踏区的过氧化氢酶活性、磷酸酶活性均无显著差异。[结论]五台山东台山地草甸土壤酶活性已受到人为踩踏的破坏,应采取相应措施保护景区健康发展。     

Rapid, semimicro method for determination of polycyclic aromatic hydrocarbons in shellfish by automated gel permeation/liquid chromatography

A simple, rapid, easily automated method is described for the determination of polycyclic aromatic hydrocarbons (PAHs) in shellfish such as American lobster (Homarus americanus) and blue mussel (Mytilus edulis). PAHs are extracted from small amounts (1-8 g) of tissue by saponification in 1N ethanolic potassium hydroxide followed by partitioning into 2,2,4-trimethylpentane. This solution is evaporated just to dryness by rotary evaporation and the residue is dissolved in cyclohexane-dichloromethane (1 + 1) for gel permeation chromatography (GPC) on Bio-Beads SX-3. The GPC procedure is ideal as a screening method in the range 25-18 000 ng PAHs/g tissue. If individual PAH measurements are required, the appropriate GPC fraction is collected and PAHs are separated by reverse phase liquid chromatography (LC) with fluorometric detection. Individual PAHs at concentrations as low as 0.25-10 ng/g can be determined. Recoveries of added fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[e]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene, benzo[ghi]perylene, and indeno[1,2,3-cd]pyrene were quantitative, with relative standard deviations ranging from 0.0 to 16.9%.     

Synthesis and insect antifeedant activity of aurones against Spodoptera litura larvae

A series of aurones were prepared from various phenols via phenoxy acetic acids and coumaranones and evaluated for insect antifeedant activity against the common cutworm (Spodoptera litura). The naturally occurring aurone was most active at an ED50 of 0.12 micromol/cm2. The synthetic precursor, coumaranones, showed that the introduction of methoxyl and methyl groups to the benzene ring increased insect antifeedant activity. Similarly, the tested aurones showed that the introduction of methoxyl group to the A and/or B rings increased the insect antifeedant activity, but 4,5,6- and 3',4',5'-trisubstituted compounds did not show this activity in this test. The hydroxylation of aurones in the B ring should be disadvantageous for insect antifeedant activity against S. litura. Although the melting points did not correlate well with the insect antifeedant activity, compounds that were nearly inactive had high melting points. A significant correlation was noted between biological activity (pED50) and a hydrogen-bonding parameter calculated from the Rf value obtained from SiOH thin-layer chromatography and a lipophilicity parameter (log k) calculated from the retention time in ODS high-performance liquid chromatography. The respective correlation coefficients (r) were -0.83 and -0.70. The introduction of alkoxy and alkyl groups along with adequate hydrogen bonding seems to contribute to the antifeedant activity of the compounds tested.     

Rapid magnetic solid-phase extraction based on magnetic multiwalled carbon nanotubes for the determination of polycyclic aromatic hydrocarbons in edible oils

In this study, magnetic multiwalled carbon nanotubes were fabricated by a simple method and applied to magnetic solid-phase extraction (MSPE) of eight heavy molecular weight polycyclic aromatic hydrocarbons (PAHs) including chrysene, benzo[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene, dibenzo[a,h]anthracene and benzo[g,h,i]perylene from edible oil samples. Several parameters affecting the extraction efficiency were investigated, including the type and volume of desorption solvent, extraction and desorption time, washing solution and the amount of sorbent. Under the optimized conditions, a simple and effective method for the determination of PAHs in edible oils was developed by coupling with gas chromatography-mass spectrometry (GC-MS). The whole pretreatment process was rapid, and it can be accomplished within 10 min. The limits of quantitation for the target PAHs were found to be 0.34-2.9 ng/g. The recoveries in oil sample were in the range 87.8-122.3% with the RSDs less than 6.8% (intraday) and 9.6% (interday). This method was successfully applied to the analysis of PAHs in seven kinds of edible oils from local markets.     

Insecticidal, anti-juvenile hormone, and fungicidal activities of organic extracts from different Penicillium species and their isolated active components.

Organic extracts from mycelium and culture broth of 21 Penicillium isolates have been tested for insecticidal, insect anti-juvenile hormone (anti-JH), and antifungal activities. Culture broth extracts were the most active, mainly against insects; nearly 25% of them have shown high entomotoxicity (100% mortality at 100 microg/cm(2)). A strong in vivo anti-JH activity against Oncopeltus fasciatus Dallas was detected in the culture broth extracts from P. brevicompactum P79 and P88 isolates. The two new natural products isolated from P79, N-(2-methyl-3-oxodec-8-enoyl)-2-pyrroline (1) and 2-hept-5-enyl-3-methyl-4-oxo-6,7,8,8a-tetrahydro-4H-pyrrolo[2,1-b]-1, 3-oxazine (2), possessed anti-JH and insecticidal activity, respectively, against O. fasciatus. Synthesized natural compound 1 has shown an ED(50) of 0.7 microg/nymph when assayed on newly molted fourth-instar nymphs of O. fasciatus. Promising biological activities have also been detected in the synthetic precursors.     

New oleanane saponins in Chenopodium quinoa

Six triterpenoid saponins were isolated from the seeds of Chenopodium quinoa (Chenopodiaceae). Their structures were as follows: phytolaccagenic acid 3-O-[alpha-L-arabinopyranosyl-(1' '-->3')-beta-D-glucuronopyranosyl]-28-O-beta-D-glucopyranoside (1); spergulagenic acid 3-O-[beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl-(1-->3)-alpha-L-arabinopyranosyl-28-O-beta-D-glucopyranoside (2); hederagenin 3-O-[beta-D-glucopyranosyl-(1-->3)-alpha-L-arabinopyranosyl]-28-O-beta-D-glucopyranoside (3); phytolaccagenic acid 3-O-[beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranosyl]-28-O-beta-D-glucopyranoside (4); hederagenin 3-O-[beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranosyl]-28-O-beta-D-glucopyranoside (5); and spergulagenic acid 3-O-[alpha-L-arabinopyranosyl-(1' '-->3')-beta-D-glucuronopyranosyl]-28-O-beta-D-glucopyranoside (6). Saponins 5 and 6 are new. The structures were characterized on the basis of hydrolysis and spectral evidence, including IR, UV, optical rotations, 1D- and 2D-NMR (HMQC and HMBC), ESIMS, and FABMS analyses.     

In vitro actions on human cancer cells and the liquid chromatography-mass spectrometry/mass spectrometry fingerprint of phytochemicals in rice protein isolate

Rice protein isolate (RPI) has been reported to reduce the incidence of 7,12-dimethylbenz[a]anthracene-induced mammary tumors in rats. To determine the potential role of phytochemicals associated with the RPI, we studied in vitro antitumor activities of an ether fraction from RPI using human tumor cell lines, including two human breast carcinoma cell lines (MDA-MB-453 and MCF-7) and two myeloma cell lines (RPMI-8226 and IM-9). Concentration-dependent antiproliferative effects of the ether fraction were observed in all cell lines using the standard 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. Fraction-induced apoptosis (P < 0.05) was detected in all cell lines, and this was associated with the induction of proapoptotic bax protein and cdk inhibitors (p21) and the suppression of cdk4 and cyclin D1 activity. Liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) with both positive and negative modes was used to analyze the phytochemicals in the ether fraction from RPI. Fifty-seven phytochemicals were identified or characterized by their diagnostic fragmentation patterns and direct comparison with the authentic standards on the basis of electrospray ionization-MS/MS data. The major components bound to RPI were lysoglycerophospholipids, fatty acids, and fatty acid 3-[2-(2,3-dihydroxy-propoxycarbonyl)-2-hydroxy-ethoxy]-2-hydroxy-propyl esters.     

Microbial degradation of penoxsulam in flooded rice field soils

The degradation of penoxsulam [2-(2,2-difluoroethoxy)-N-5,8-dimethoxy[1,2,4]triazolo[1,5-C]pyrimidin-2-yl-6-(trifluoromethyl)benzene-sulfonamide] was studied in flasks simulating flooded rice field conditions using four representative rice field soils from the Sacramento Valley. Degradation half-lives (t(1/2) values) ranged between 2 and 13 days. Increased degradation rates were observed in flask systems with steeper redox gradients between the flooded soil layer and the overlaying water. Two transient metabolites were identified that were temporarily formed in amounts exceeding 5% of the total initial mass of penoxsulam. The results of high-performance liquid chromatography/(14)C radiodetection studies indicate that the degradation of the triazolopyrimidine system and its substituents is the main pathway of microbial transformation processes. Microbial activity, as measured by dehydrogenase activity, was not affected by penoxsulam concentrations corresponding to the proposed maximum annual use rate of 40 g active ingredient/ha.