Synthesis and herbicidal activity of 2-cyano-3-substituted-pyridinemethylaminoacrylates

Two series of 2-cyano-3-substituted-pyridinemethylaminoacrylates, namely 12 new (Z)-2-cyano-3-methylthio-3-substituted-pyridinemethaneaminoacrylates and 10 new (Z)-2-cyano-3-alkyl-3-substituted-pyridinemethaneaminoacrylates, were synthesized as herbicidal inhibitors of photosystem II (PSII) electron transport. All of these compounds were confirmed by (1)H NMR, elemental, IR, and mass spectrum analyses. Their herbicidal activities were evaluated. Some compounds exhibited excellent herbicidal activities, even at a dose of 75 g/ha. A suitable substituent at the 2-position of the pyridine ring and the well-fit group at the 3-position of acrylate were essential for high herbicidal activity. 2-Cyanoacrylates containing a substituted pyridine ring provide higher herbicidal activities than parent compounds containing phenyl. These PSII inhibitor herbicides are safe to corn, which is a major crop in China.     

Synthesis, crystal structure, and biological activities of 2-cyanoacrylates containing furan or tetrahydrofuran moieties

A series of novel cyanoacrylates containing furan or tetrahydrofuran moieties were synthesized, and their structures were characterized by 1H NMR, elemental analysis, and single-crystal X-ray diffraction analysis. The herbicidal, plant growth regulatory, fungicidal, and antiviral activities of these cyanoacrylates were evaluated. The results of herbicidal activities showed that most of these cyanoacrylates exhibited higher herbicidal activities against dicotyledonous weeds than monocotyl-edonous weeds, and the compounds containing the tetrahydrofuran moiety gave higher herbicidal activities than corresponding furan analogues; (Z)-ethoxyethyl 2-cyano-3-isopropyl-3-(tetrahydrofuran-3-yl)methaneaminoacrylate showed excellent herbicidal activities against amaranth pigweed in postemergence treatment at a dose of 375 g/ha. At the same time, these cyanoacrylates had interesting plant growth regulatory activities, and some compounds stimulated radicle growth of cucumber, whereas some compounds had an inhibitory effect. These cyanoacrylates showed fungicidal activities as well.     

5-(2,6-difluorobenzyl)oxymethyl-5-methyl-3-(3-methylthiophen-2-yl)- 1,2-isoxazoline as a useful rice herbicide

5-(2,6-difluorobenzyl)oxymethyl-5-methyl-3-(3-methylthiophen-2-yl)-1,2-isoxazoline derivative was synthesized, and its herbicidal activity was assessed under glasshouse and flooded paddy conditions. 5-(2,6-Difluorobenzyl)oxymethyl-5-methyl-3-(3-methylthiophen-2-yl)-1,2-isoxazoline demonstrated good rice selectivity and potent herbicidal activity against annual weeds at 125 g of a.i. ha(-1) under greenhouse conditions. Soil application of this compound showed complete control of barnyard-grass to the fourth leaf stage at 250 g of a.i. ha(-1). Field trials indicated that this compound controlled annual weeds rapidly with a good tolerance on transplanted rice seedlings by post-emergence and soil application. This compound showed a low mammalian and environmental toxicity in various toxicological tests.     

Synthesis and herbicidal activity of diphenyl ether derivatives containing unsaturated carboxylates

A series of novel diphenyl ether derivatives containing unsaturated carboxylates were designed and synthesized. Their structures were identified by (1)H nuclear magnetic resonance and elemental analyses. The bioassays indicated that the compounds 5b and 5c exhibited good herbicidal activities against velvetleaf at a concentration of 30-40 g/hm(2). The relationship between structure and herbicidal activity was also discussed. Among unsaturated carboxylates group, butenoate is the most promising one. Amonst them, 4-ethoxy-4-oxobutenyl 5-(2-chloro-4-(trifluoromethyl)phenoxy)-2-nitrobenzoate 5b was identified as the most promising candidate due to its high protoporphyrinogen IX oxidase inhibition effect (pI(50) = 6.64) and good herbicidal activity against broadleaf weeds with selectivity to soybean and low toxicity to mammals.     

Synthesis, insecticidal, and acaricidal activities of novel 2-aryl-pyrrole derivatives containing ester groups

A series of novel 2-aryl-pyrrole derivatives containing ester groups were synthesized, and their structures were characterized by (1)H NMR spectroscopy and elemental analysis. The insecticidal activities against oriental armyworm, mosquito, diamondback moth, green rice leafhopper, and bean aphids and acaricidal activities against spider mite of these new compounds were evaluated. The results of bioassays indicated that some of these title compounds exhibited excellent insecticidal and acaricidal activities. The insecticidal activities against oriental armyworm of compounds IVa, IVd, IVe, IVf, IVg, IVi, IVk, and IVp were equal to commercialized Chlorfenapyr, and the insecticidal activities of most of compounds IVb, IVc, IVd, IVf, IVg, IVj, IVk, IVl, IVs, IVt, IVu, IVw, IVx, IVz, and Chlorfenapyr against mosquito at 0.10 mg kg (-1) were 100%, and the acaricidal activities of compounds IVd, IVe, IVf, IVg, IVh, IVi, and IVk were equal or superior to Chlorfenapyr. Especially, the results indicated that the acaricidal activity of [4-bromo-2-(4-chlorophenyl)-3-cyano-5-(trifluoromethyl)pyrrol-1-yl]methyl 3-methylbutanoate ( IVg) against spider mite was 2.65-fold as high as that of Chlorfenapyr from the value of LC 50.     

Syntheses and herbicidal activities of novel triazolinone derivatives

Protoporphyrinogen oxidase (Protox, EC 1.3.3.4) has been identified as one of the most important action targets of herbicides. To search for novel Protox inhibitors, a series of title compounds 1, 2, and 3 were designed and synthesized by introducing three types of pharmacophores, cyclic imide, phenylurea, and ( E)-methyl 2-methoxyimino-2- o-tolylacetate, into the scaffold of triazolinone. The bioassay results indicated that the resulting cyclic imide-type triazolinones 1 displayed much better herbicidal activities than phenylurea-type triazolinones 2. Most fortunately, compound 3, methyl 2-[3-methyl-(2-fluoro-4-chloro-5-ethylsulfonamidephenyl)-4,5-dihydro-5-oxo-1 H-1,2,4-triazol-4-yl]methylenephenyl-2-( E)-methoxyiminoacetate, was found to be the most promising candidate due to its comparable herbicidal activity at 75-150 g of active ingredient/ha with the commercial product sulfentrazone. On the basis of test results of herbicidal spectrum and crop selectivity, compound 3 could be developed as a postemergent herbicide used for the control of broadleaf weeds in rice fields.     

Design and syntheses of novel N-(benzothiazol-5-yl)-4,5,6,7-tetrahydro-1H-isoindole-1,3(2H)-dione and N-(benzothiazol-5-yl)isoindoline-1,3-dione as potent protoporphyrinogen oxidase inhibitors

Discovery of protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors has been one of the hottest research areas in the field of herbicide development for many years. As a continuation of our research work on the development of new PPO-inhibiting herbicides, a series of novel N-(benzothiazol-5-yl)-4,5,6,7-tetrahydro-1H-isoindole-1,3(2H)-diones (1a-p) and N-(benzothiazol-5-yl)isoindoline-1,3-diones (2a-h) were designed and synthesized according to the ring-closing strategy of two ortho-substituents. The bioassay results indicated that some newly synthesized compounds exhibited higher PPO inhibition activity than the control of sulfentrazone. Compound 1a, S-(5-(1,3-dioxo-4,5,6,7-tetrahydro-1H-isoindol-2(3H)-yl)-6-fluorobenzothiazol-2-yl) O-methyl carbonothioate, was identified as the most potent inhibitor with k(i) value of 0.08 μM, about 9 times higher than that of sulfentrazone (k(i) = 0.72 μM). Further green house assay showed that compound 1b, methyl 2-((5-(1,3-dioxo-4,5,6,7-tetrahydro-1H-isoindol-2(3H)-yl)-6-fluorobenzothiazol-2-yl)thio)acetate, exhibited herbicidal activity comparable to that of sulfentrazone even at a concentration of 37.5 g ai/ha. In addition, among six tested crops, wheat exhibited high tolerance to compound 1b even at a dosage of 300 g ai/ha. These results indicated that compound 1b might have the potential to be developed as a new herbicide for weed control of wheat field.     

Synthesis and herbicidal activity of 2-(7-fluoro-3-oxo- 3,4-dihydro-2H-benzo[b][1,4]oxazin-6-yl)isoindoline-1,3-diones

The mode of action of 2-(7-fluoro-3-oxo-3,4-dihydro-2H-benzo[b][1,4]oxazin-6-yl)-4,5,6,7-tetrahydro-2H-isoindoline-1,3-diones, including the commercial herbicide flumioxazin, had been identified as inhibition of protoporphyrinogen oxidase (protox). As part of continuous efforts to search for new herbicides with high efficacy, broad-spectrum activity, and safety to crops, flumioxazin and its iodo analogue (B2055) were used as lead compounds for further optimization. Series of novel compounds were prepared by multistep synthetic procedures starting from 5-fluoro-2-nitrophenol. All of the test compounds were structurally confirmed by 1H NMR, IR, mass spectroscopy, and elemental analysis. Preliminary bioassay data showed that some of them possess commercial levels of herbicidal activity comparable to those of other protox-inhibiting herbicides. One of the best compounds, 5-fluoro-2-(7-fluoro-3-oxo-4-(prop-2-ynyl)-3,4-dihydro-2H-benzo[b][1,4]oxazin-6-yl)isoindoline-1,3-dione (8e), has IC50 values for velvetleaf (Abutilon theophrasti Medic) and crabgrass (Digitaria sanguinalis) comparable to thos of B2055. With respect to crop selectivity, compound 8e is similar to flumioxazin. Compound 8e is safe to cotton and maize at a rate of 150 g of active ingredient (ai)/ha or less when applied at pre-emergent stage, and it has the best safety to wheat among the tested crops, showing no injury after post-emergent application at 7.5-30 g of ai/ha.     

In vitro inhibition studies of phytoene desaturase by bleaching ketomorpholine derivatives

The herbicidal activities of homochiral steroisomeric 5-methy1-2-(3-trifluoromethybenzyl)-3-keto- morpholine derivatives were investigated in vitro as inhibitors of phytoene desaturase, a key enzyme in carotenoid biosynthesis. It was demonstrated that ketomorpholines are classical bleaching compounds which directly inhibit phytoene desaturase, accumulating phytoene at the expense of colored carotenoids. Ketomorpholines interact with phytoene desaturase in a noncompetitive manner with respect to phytoene. A structure-activity investigation for in vitro inhibition of phtoene desaturase activity revealed that the relative and absolute stereochemistry is important for optimum inhibition for the 5-methyl derivatives, and that the distance of the phenyl group from the ketomorpholine ring is critical for the inhibitory potential. The average herbicidal score on 7 weeds and the in vitro I(50) values related very well with the exception of two compounds. It was postulated that the discrepancies may possibly occur through modification in plants to compounds that are either more or less active herbicides.     

Synthesis and Herbicidal Activity of 2-(Substituted phenoxyacetoxy)alkyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one

A series of 2-(substituted phenoxyacetoxy)alkyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-ones IIa-s were designed and synthesized on the basis of the previous work for the modification of alkylphosphonates I, and their structures were confirmed by (1)H NMR, (31)P NMR, (13)C NMR, IR, MS, and elemental analysis. Their herbicidal activities against seven species of weeds were evaluated in a greenhouse. A part of the title compounds such as IIa-g, IIk, IIo, and IIr exhibited significant postemergence herbicidal activity against Abutilon theophrasti , Brassica juncea , Amaranthus retroflexus , and Eclipta prostrate at a dosage of 150 g ai/ha. Structure-activity relationship analyses indicated that the introduction of a phosphorus-containing heterocyclic ring had a favorable effect on herbicidal activity, and their herbicidal activity could be further increased by a reasonable combination of X, Y, and R in parent structure II. It could be found that the title compounds IIa 2-[(2,4-dichlorophenoxy)acetoxy](methyl)methyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one and IIr 2-[(4-chloro-2-methyl-phenoxy)acetoxy](methyl)methyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one possess high activity and a broad spectrum against all of the test broadleaf weeds with 70-100% inhibition effect at a dosage of 75 g ai/ha, and the title compounds IIa and IIr are safe for corn and wheat at a dosage of 150 g ai/ha. Furthermore, the title compound IIa possesses low rat toxicity. These results suggest that the title compounds IIa and IIr could be potential and selective postemergence herbicides for further development.     

Synthesis and herbicidal evaluation of novel 3-[(alpha-hydroxy-substituted)benzylidene]pyrrolidine-2,4-diones

A series of 3-[(alpha-hydroxy-substituted) benzylidene]pyrrolidine-2,4-dione derivatives were synthesized as candidate herbicides by reacting different aroyl acetates with N-substituted glycine esters. The new compounds were identified by 1H NMR spectroscopy and elemental analyses. Their herbicidal activities were evaluated. Some compounds exhibited excellent herbicidal activities at a dose of 187.5 g/ha. A suitable electron-donating substituent at the 2- and/or 4-position of the phenyl ring was essential for high herbicidal activity, a result that has not been reported before. It was also found that the title compound's structure-activity relationships were different from those of other similar kinds of earlier compounds, a result that may depend on the enol structure difference.     

Design and syntheses of novel phthalazin-1(2H)-one derivatives as acetohydroxyacid synthase inhibitors

A series of 2-substituted-8-(4,6-dimethoxypyrimidin-2-yloxy)-4-methylphthalazin-1-one derivatives, 7a-7w, were designed via an ortho-substituent cyclization strategy to discover a new herbicidal lead structure. These compounds were synthesized by a seven-step route using 3-hydroxy-acetophenone as a starting material. Determination of the Ki values against wild-type A. thaliana acetohydroxyacid synthase (AHAS) (EC 4.1.3.18) indicated that some of the compounds displayed good enzyme inhibition activity comparable to that of KIH-6127. The further preliminary bioassay data on weeds showed that the synthesized compounds exhibited typical injury symptoms of AHAS-inhibiting herbicides, and some of them showed broad-spectrum and high herbicidal activities in postemergence treatments against Echinochloa crusgalli, Digitaria sanguinalis, Setaria viridis, Brassica juncea, Amaranthus retroflexus, and Chenopodium album at an application rate of 150 g ai/ha. To our knowledge, this is the first report of methylphthalazin-1-one derivatives as AHAS inhibitors.     

Preparation and biological activity of four epiprogoitrin myrosinase-derived products

(5R)-5-Vinyl-1,3-oxazolidine-2-thione, (2S)-1-cyano-2-hydroxy-3-butene, and two diastereoisomeric erythro-(2S)- and threo-(2S)-1-cyano-2-hydroxy-3,4-epithiobutanes were prepared in pure form starting from (2S)-2-hydroxybut-3-enyl glucosinolate (epiprogoitrin). This glucosinolate was isolated in almost pure form using ripe seeds of Crambe abyssinica and then hydrolyzed under different conditions. The hydrolysis was carried out using either myrosinase immobilized on nylon, to produce (5R)-5-vinyl-1,3-oxazolidine-2-thione, or the endogenous myrosinase contained in defatted crambe meals, to produce the other epiprogoitrin-derived products. After purification and physicochemical characterization, all four myrosinase degradation products were tested for their biological activity. A bioassay on Lactuca sativa was chosen as a simple test to determine their apparent action on living tissues. (5R)-5-Vinyl-1,3-oxazolidine-2-thione negatively affected mainly root growth, whereas (2S)-1-cyano-2-hydroxy-3-butene affected the early phase of germination, and both (2S)-1-cyano-2-hydroxy-3,4-epithiobutane diastereoisomers appeared to negatively affect both germination and root growth at doses 5-10 times lower than those of (2S)-1-cyano-2-hydroxy-3-butene or (5R)-5-vinyl-1,3-oxazolidine-2-thione.     

Synthesis and herbicidal activities of novel 3-N-substituted amino-6-methyl-4-(3-trifluoromethylphenyl)pyridazine derivatives

4-(3-Trifluoromethylphenyl)pyridazine is a new series of compounds with bleaching and herbicidal activities. Starting from ethyl 2-(3-trifluoromethylphenyl)acetate, an important intermediate 7 was synthesized in five steps with a moderate total yield of 51.5% in a safe and practical way. Twenty-six novel 3-N-substituted amino-6-methyl-4-(3-trifluoromethylphenyl)pyridazine derivatives were synthesized and evaluated through a Spirodela polyrrhiza test and greenhouse test. Some compounds can completely inhibit Chl at 1 microg/mL and exhibit equal or higher herbicidal activities with the commercial bleaching herbicide diflufenican against dicotyledonous plants at a rate of 75 g/ha.     

Design, synthesis, and quantitative structure-activity relationship study of herbicidal analogues of pyrazolo[5,1-d][1,2,3,5]tetrazin-4(3H)ones

A series of pyrazolo[5,1-d][1,2,3,5]tetrazin-4(3H)one derivatives were designed, synthesized, and evaluated for their herbicidal activities where some of these compounds provided >80% control of Brassica campestris at 10 microg/mL. Quantitative structure-activity relationship studies were performed on these compounds using physicochemical parameters (electronic, Verloop, or hydrophobic) as independent parameters and herbicidal activity as a dependent parameter, where herbicidal activity correlated best (r > 0.8) with physicochemical parameters in this set of molecules. The herbicidal activity against B. campestris was mainly affected by the molar refractivity (MR) for R1, Taft (Eso) for R2 or R6, Verloop (Lm) for R3 or R5, and electronic parameters (Hammett's constants) for R4. The optimal MR for herbicidal activity is 0.95. The herbicidal activity against Echinochloa crus-galli was mainly related with the substituents' hydrophobic parameter. The optimal pi parameters for R1 and R4 for herbicidal activity are 0.72 and 0.68, respectively. In general, these compounds showed greater herbicidal activity toward B. campestris than E. crus-galli.     

Dihydropiperazine neonicotinoid compounds. Synthesis and insecticidal activity

Syntheses of various isomeric dihydropiperazines can be approached successfully by taking advantage of the regioselective monothionation of their respective diones. Preparation of the precursor unsymmetrical N-substituted piperazinediones from readily available diamines is key to this selectivity. The dihydropiperazine ring system, as exemplified in 1-[(6-chloropyridin-3-yl)methyl]-4-methyl-3-oxopiperazin-2-ylidenecyanamide (4) and 1-[(2-chloro-1,3-thiazol-5-yl)methyl]-4-methyl-3-oxopiperazin-2-ylidenecyanamide (25), has been shown to be a suitable bioisosteric replacement for the imidazolidine ring system contained in neonicotinoid compounds. However, placement of the cyanoimino electron-withdrawing group further removed from the pyridine ring, as in 4-[(6-chloropyridin-3-yl)methyl]-3-oxopiperazin-2-ylidenecyanamide (3a), or relocation of the carbonyl group, as in 1-[(6-chloropyridin-3-yl)methyl]-4-methyl-5-oxopiperazin-2-ylidenecyanamide (5), results in significantly decreased bioisosterism. The dihydropiperazine ring system of 4 and 25 also lends a degree of rigidity to the molecule that is not offered by the inactive acyclic counterpart 2-[(6-chloropyridin-3-yl)-methyl-(methyl)amino]-2-(cyanoimino)-N,N-dimethylacetamide (6). A pharmacophore model is proposed that qualitatively explains the results on the basis of good overlap of the key pharmacophore elements of 4 and imidacloprid (1); the less active regioisomers of 4 (3a, 5, and 6) feature a smaller degree of overlap.     

Synthesis of glucose-fipronil conjugate and its phloem mobility

Phloem-mobile insecticides are preferred to achieve economically useful activity. However, only a few phloem-mobile synthetic insecticides are available. One approach to converting nonmobile insecticides into phloem-mobile types is introducing sugar to the parent compound. To test whether the addition of a glucose group to a non-phloem-mobile insecticide enables conversion into phloem-mobile, N-[3-cyano-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazol-5-yl]-1-(β-D-glucopyranosyl)-1H-1,2,3-triazole-4-methanamine (GTF) was prepared through click chemistry. A phloem-mobility test in Ricinus communis L. seedlings confirmed that GTF was mobile in the sieve tubes. Although GTF exhibited lower insecticidal activity against the third-instar larvae of Pzlutella xylostella than fipronil did, it can be reconverted into fipronil in adult plants of castor bean, thereby offsetting the decrease of insecticidal activity. Therefore, the presence of a glucose core confers phloem mobility to fipronil.     

A quantitative structure-activity relationship study of herbicidal analogues of alpha-hydroxy-substituted 3-benzylidenepyrrolidene-2,4-diones

A series of pyrrolidine-2,4-dione and piperidine-2,4-dione derivatives were prepared and evaluated for their herbicidal activities where some of these compounds exhibited good bioactivity against Echinochloa crus-galli in comparison with sulcotrione. Quantitative structure-activity relationship studies were performed on these compounds using physicochemical parameters (hydrophobic, electronic, and Taft) as independent parameters and herbicidal activity as a dependent parameter, where herbicidal activity correlated best (r > 0.8) with hydrophobic (pi(o) + pi(p)), steric (Es), STERIMOL (B4), indicator (H(M)), van der Waals volume (V), and electronic parameter (sigma(m) + sigma(p)) in this set of molecules; the optimum van der Waals volume for R(2) is about 41.8 A3; when B4 is equal to 3, the target molecule possessed the lowest herbicidal activity.     

Abscisic acid related compounds and lignans in prunes (Prunus domestica L.) and their oxygen radical absorbance capacity (ORAC)

Four new abscisic acid related compounds (1-4), together with (+)-abscisic acid (5), (+)-beta-D-glucopyranosyl abscisate (6), (6S,9R)-roseoside (7), and two lignan glucosides ((+)-pinoresinol mono-beta-D-glucopyranoside (8) and 3-(beta-D-glucopyranosyloxymethyl)-2- (4-hydroxy-3-methoxyphenyl)-5-(3-hydroxypropyl)-7-methoxy-(2R,3S)-dihydrobenzofuran (9)) were isolated from the antioxidative ethanol extract of prunes (Prunus domestica L.). The structures of 1-4 were elucidated on the basis of NMR and MS spectrometric data to be rel-5-(3S,8S-dihydroxy-1R,5S-dimethyl-7-oxa-6-oxobicyclo[3,2,1]oct-8-yl)-3-methyl-2Z,4E-pentadienoic acid (1), rel-5-(3S,8S-dihydroxy-1R,5S-dimethyl-7-oxa-6-oxobicyclo[3,2,1]oct-8-yl)-3-methyl-2Z,4E-pentadienoic acid 3'-O-beta-d-glucopyranoside (2), rel-5-(1R,5S-dimethyl-3R,4R,8S-trihydroxy-7-oxa-6-oxobicyclo[3,2,1]oct-8-yl)-3-methyl-2Z,4E-pentadienoic acid (3), and rel-5-(1R,5S-dimethyl-3R,4R,8S-trihydroxy-7-oxabicyclo[3,2,1]- oct-8-yl)-3-methyl-2Z,4E-pentadienoic acid (4). The antioxidant activities of these isolated compounds were evaluated on the basis of oxygen radical absorbance capacity (ORAC). The ORAC values of abscisic acid related compounds (1-7) were very low. Two lignans (8 and 9) were more effective antioxidants whose ORAC values were 1.09 and 2.33 micromol of Trolox equiv/micromol, respectively.     

Metabolism of furametpyr. 1. Identification of metabolites and in vitro biotransformation in rats and humans

Urinary and fecal metabolites in male rats treated with a (14)C-labeled fungicide, furametpyr [N-(1,3-dihydro-1,1, 3-trimethylisobenzofuran-4-yl)-5-chloro-1, 3-dimethylpyrazole-4-carboxamide, Limber], were purified by a combination of chromatographic techniques, and chemical structures of 14 metabolites were identified by spectroanalyses (NMR and MS). The major biotransformation reactions of furametpyr in rats were found to be (1) N-demethylation, (2) oxidation of the methyl group at C3 of the pyrazole ring, (3) oxidation of the methyl group at C1 of the 1,3-dihydroisobenzofuran ring, (4) hydroxylation at C3 of the 1,3-dihydroisobenzofuran ring, and (5) hydroxylation at C7 of the 1, 3-dihydroisobenzofuran ring. In vitro metabolism by recombinant human cytochrome P450 revealed that a major biotransformation in humans is N-demethylation, catalyzed by CYP1A1, 1A2, 2C19, and 3A4.