Design, Synthesis, and Biological Activities of Spirooxindoles

Article pubs.acs.org/JAFC

Design, Synthesis, and Biological Activities of Spirooxindoles Containing Acylhydrazone Fragment Derivatives Based on the Biosynthesis of Alkaloids Derived from Tryptophan Linwei Chen,† Jialin Xie,† Hongjian Song,*,† Yuxiu Liu,† Yucheng Gu,Δ Lizhong Wang,† and Qingmin Wang*,†,§ †

State Key Laboratory of Elemento-Organic Chemistry, Research Institute of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, People’s Republic of China § Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Tianjin 300071, People’s Republic of China Δ Syngenta, Jealott’s Hill International Research Centre, Bracknell, Berks RG42 6EY, United Kingdom S Supporting Information *

ABSTRACT: On the basis of the biosynthesis of alkaloids derived from tryptophan and considering the wide use of spirooxindole in drug molecular design, a series of novel spirooxindole derivatives containing an acylhydrazone moiety were designed, synthesized, and first evaluated for their biological activities. The results of bioassays indicated that the target compounds possessed good activities against tobacco mosaic virus (TMV); especially compound 4, containing a tert-butyl at the benzene ring, exhibited the best antiviral activity in vitro and inactivation, curative, and protection activities in vivo (48.4%, 58 ± 0.4, 55.2 ± 2.3, and 49.7 ± 1.1% at 500 μg/mL, respectively) compared with ribavirin (38.2, 36.4 ± 0.2, 37.5 ± 0.2, and 36.4 ± 0.1% at 500 μg/mL, respectively) and harmine (44.6, 40.5 ± 0.2, 38.6 ± 0.8, and 42.4 ± 0.6% at 500 μg/mL, respectively). At the same time, these compounds exhibited fungicidal activity selectively against certain fungi; most of these derivatives exhibited >60% fungicidal activity against Physalospora piricola at 50 mg/kg. Additionally, compounds 25 and 14 displayed excellent insecticidal activities (60% motality against C. pipiens pallens at 0.25 mg/kg) even at very low concentrations. KEYWORDS: tryptophan, biosynthesis, spirooxindole, acylhydrazone, antiviral activity, fungicidal activity, insecticidal activity

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As we all know, β-carbolines are synthesized in organisms using tryptophan as a precursor via the catalysis of enzymes. Furthermore, there are varieties of other fused or spiro indole alkaloids such as spirotryprostatin A and paraherquamide A (Figure 1) using tryptophan as a precursor for biosynthesis.8−12 Meanwhile, the spirooxindole scaffold is rather common in drug design, and spirooxindole compounds frequently exhibit a wide range of biological activities such as obviously analgesic and antihypertensive effects, usually served as mammalian cell cycle inhibitors, etc.13−15 Furthermore, in an effort to break through the limitation of the intrinsic structure and the physicochemical property of natural product and make the molecular structure simpler and more diverse, we intend to select tryptophan to design and synthesize pseudo-spiro-indole natural products with structural diversity, based on the experience of β-carbolines’ antiviral inhibitor and the preliminary results of tryptophan biological activity.16 On the other hand, the biological activities of acylhydrazone compounds have attracted more and more attention in recent years;17−20 for example, pymetrozine,21 metaflumizone,22 and diflufenzopyr23 (Figure 2) show desirable insecticidal or herbicidal activities. Our previous studies revealed that the

INTRODUCTION Plant viral diseases cause enormous detrimental effects on agriculture and horticulture worldwide.1 As one of the most well-studied plant viruses, tobacco mosaic virus (TMV), which is made up of a piece of nucleic acid (ribonucleic acid; RNA) and a surrounding protein coat, is known to infect at least 125 individual species that are economically important plants, such as tobacco, tomato, pepper, cucumber, and many ornamental flowers.2,3 What is worse, although TMV can proliferate only inside a living cell, it can survive in dead tissue in a dormant state, retaining its ability to infect growing plants for years after the infected plant part died. Because plants do not have the same immune system as animals, the control of plant diseases is still a challenge.4 In the search for an effective agent to protect plants from TMV infection, natural products from plants have been proved to be a rich resource. In comparison to synthetic chemicals, natural-product-based TMV inhibitors feature structural diversity and complexity, low mammalian toxicity, friendliness to the environment, specificity to targeted species, unique mode of action, and so on.5,6 In our previous work, we found that natural product harmine (Figure 1), one of the β-carboline alkaloids isolated from Peganum harmala L., exhibited antiTMV activity (antiviral activity against TMV in vitro and inactivation, curative, and protection activities in vivo were 44.6, 40.5 ± 0.2, 38.6 ± 0.8, and 42.4 ± 0.6%, respectively, at 500 μg/mL).7 © XXXX American Chemical Society

Received: June 14, 2016 Revised: August 12, 2016 Accepted: August 13, 2016

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DOI: 10.1021/acs.jafc.6b02683 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Journal of Agricultural and Food Chemistry

Figure 1. Tryptophan and alkaloids using tryptophan as biosynthesis precursors.

Figure 2. Acylhydrazone compounds.

Figure 3. Synthesis of compounds 1−18. HRMS data were obtained on an FTICR-MS instrument (Ionspec 7.0 T). The melting points were determined on an X-4 binocular microscope melting point apparatus and are uncorrected. Reaction progress was monitored by thin-layer chromatography on silica gel GF-254 with detection by UV. General Synthesis. Reagents were purchased from commercial sources and were used as received. All anhydrous solvents were dried and purified according to standard techniques just before use. The synthetic routes are given in Figures 3 and 4. The operating steps and physical data in detail of intermediates A− H and target compounds 1−25 can be found in the Supporting Information. Biological Assay. The anti-TMV, fungicidal, and insecticidal activities of the synthesized compounds were tested using our previously reported methods.27,28

introduction of an acylhydrazone fragment could dramatically boost the antivirus activities.24 Reasonably, we speculate that the hydrogen bond donor and acceptor of acylhydrazone could obviously enhance the interaction between the agents and the TMV receptor.25,26 On the basis of the above two points, here a series of spirooxindole derivatives containing an acylhydrazone fragment were designed, synthesized, and characterized in detail. Meanwhile, their anti-TMV, fungicidal, and insecticidal activities were evaluated for the first time. The structure− activity relationship (SAR) study of these new spirooxindoles was also discussed.

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MATERIALS AND METHODS

Instruments. 1H NMR spectra and 13C NMR spectra were obtained at 400 MHz using a Bruker AV400 spectrometer in CDCl3 or DMSO-d6 solution with tetramethylsilane as the internal standard. B


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Figure 4. Synthesis of compounds 19−25.

Figure 5. Possible mechanism for the spirocyclization reaction.

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RESULTS AND DISCUSSION Synthesis. The synthesis of the compound 1 is depicted in Figure 3. Using L-tryptophan as starting material, the tetrahydrocarboline skeleton was constructed via Pictet− Spengler cyclization. Then the obtained carboxylic acid A was reacted with thionyl chloride and methanol to form methyl

ester B, which was subsequently reacted with (Boc)2O and Et3N to afford compound C in 94% yield. As a key step, the spirocyclization reaction of the tetrahydrocarboline skeleton was carried out in the presence of N-bromosuccinimide (NBS) and glacial acetic acid to successfully form the spirooxindole architecture. It is worth mentioning that the reaction C


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through reductive amination reaction gave F in 71% yield, and then F was reacted with NBS using a similar procedure as for the preparation of D, followed by hydrazinolysis and condensation with benzaldehyde, to give 19 in 84% yield. To investigate the influence of the spatial configuration and substituents on bioactivities, compounds 24 and 25 were synthesized using the method shown in Figure 4. Configuration. Interestingly, the 1H and 13C NMR spectra of compounds 1−18 exhibited two sets of signals (the ratio approximately was 1:1), whereas compounds 20−23 showed mostly one set of signals (dr was more than 10:1), which aroused our attention. At first, it should be noted that in both kinds of compounds the carbon at the spiro center was stereospecific with one enantiomer, which had been investigated by elegant work,30−32 and the reaction mechanism depicted in Figure 5 could also make sense. Second, in both kinds of compounds the imine bond was always in trans position not a mixture of cis and trans. Third, there were also two sets of signals for 19 in which N−H bond was substituted by a methyl group, whereas there was mostly one set of signals for compounds 20−23 in which a new ring formed. On the basis of the above information we speculate reasonably that the NMR phenomenon of compounds 1−18 may be attributed to the rotamers induced by the amide bond: there were two stable configurations (Figure 6); after further cyclization, the orientation of the carbonyl group was fixed, therefore giving one set of peaks in the NMR spectra. However, a newly generated stereocenter (C3′) in compounds 20−23 resulted in a pair of diastereoisomers, and the diastereoisomeric mixture ratio was more than 10:1. To investigate the absolute configuration of the main diastereoisomer, compound 20 was taken, for example, to carry out a NOESY experiment (Figure 7). As depicted in the 2D NOE spectrum, there were no obvious correlation signals between δ 4.42 and 5.76, so we speculated that the H of δ 4.42 and 5.76 were trans to each other. Indirectly, δ 4.42 had correlation signals with δ 2.48, not δ 2.80, so the H of δ 4.42 and 2.48 is cis and trans, respectively, with the H of δ 2.80; there was a weak correlation signal

Figure 6. Compound 6 and its rotamer.

temperature and the dosage of NBS are crucial to the desired product. The brominated byproduct29, featuring a bromo substituent on the benzene ring, was inevitably obtained when the temperature was >0 °C or the NBS was in excess. The possible mechanism that characterized an oxidative rearrangement of indole C mediated by NBS is shown in Figure 5. We surmised that the oxindole would have arisen from the rearrangement of a bromohydrin derivative J.30−32 Satisfactorily, compound D was prepared in excellent yield with stereospecificity due to self-chirality induction of the Ltryptophan moiety. Next the hydrazide 1 was formed from the spirooxindole D by deprotection and hydrazinolysis reaction sequentially. Compounds 2−25 containing the acylhydrazone fragment can be synthesized from the condensation of compound 1 with the corresponding aldehydes under different reaction conditions (Figures 3 and 4). To be specific, when the usage of aldehyde was 1 equiv at room temperature for 6 h, compounds 2−18 could be easily obtained in moderate to good yields when the aldehyde was in excess, and when the reactions were carried out in ethanol under reflux conditions, compounds 20−23 with a new N-heteroacetal ring were obtained efficiently. To study the effect of hydrogen bonding of the amino on the anti-TMV activity, compound 19 was designed and synthesized. First, the methylation of B

Figure 7. NOE spectra and chemical shift assignment of compound 20. D


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Journal of Agricultural and Food Chemistry Table 1. In Vitro and in Vivo Antiviral Activity of Compounds 1−25 against TMV

between δ 5.76 and 2.80, thus indicating they are on the same side of the ring, and therefore δ 4.42 and 5.76 are on the opposite side accordingly. In conclusion, we presume the absolute configuration of 20 to be (3S,3′R,7a′S), and the chemical shift assignment is given in Figure 7. However, this is only reasonable speculation yet to be confirmed by crystal structure determination. As for compounds 24 and 25, they were mixtures of rotamers and diastereoisomers deduced from the analysis of NMR spectra and the structure. Antiviral Activities. The results of antiviral activities, in vitro and in vivo (inactivation, curative, and protection), of these compounds are listed in Table 1. Overall, compared with

ribavirin, most of the newly designed compounds displayed desirable antiviral activity in vitro, of which 4, 5, 9−11, 13, 19, and 22 exhibited higher inhibition than ribavirin (38.2%, 500 μg/mL); especially, compounds 4 (48.4%, 500 μg/mL) and 19 (45.9%, 500 μg/mL) exhibited higher activities than harmine (44.6%, 500 μg/mL). Furthermore, it was noteworthy that the substituents of the acylhydrazone moiety had a significant impact on the anti-TMV activity, indicated by a set of representative compounds (2−12) containing different substituted benzyl structures. The result demonstrated that the electronic effect of substituents on the benzene ring did have an effect on anti-TMV activity. For E


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Journal of Agricultural and Food Chemistry Table 2. Fungicidal Activity of Compounds 1−9, 12, 14−19, 21, 22, 24, and 25 against 14 Kinds of Phytopathogensa

a

F.C., Fusarium oxysporum sp. cucumeris; C.H., Cercospora arachidicola Hori; P.P., Physalospora piricola; R.C., Rhizoctonia cerealis; B.M., Bipolaris maydis; C.O., Colletotrichum orbiculare; F.M., Fusarium moniliforme; A.S., Alternaria solani; F.G., Fusarium graminearum; P.I., Phytophthora infestans; P.C., Phytophthora capsici; S.S., Sclerotinia sclerotiorum; B.C., Botrytis cinerea. R.S., Rhizoctonia solani.

exhibited significantly higher activity. The position of the substituent also affected the anti-TMV activity; the order of activities of chloro-substituted compounds was ortho > para > meta. It was noteworthy that the antivirus activity was tremendously improved when a sterically hindered group was introduced on the benzene ring (14.7%, 500 μg/mL), such as 4 (tert-butyl, 48.4% at 500 μg/mL), partly due to the increase of the molecular lipid solubility. When the benzene ring was changed to other aromatic (13− 16) or aliphatic (17−18) substituents, their activities were

instance, it was advantageous to anti-TMV activity when the electron-withdrawing group (nitro, 5 (40.8%, 500 μg/mL)) was introduced to the benzene ring compared with the activity of compounds bearing an electron-donating group (methoxyl, 3 (0, 500 μg/mL)). Additionally, monosubstitution or multisubstitution on the benzene ring affected anti-TMV activity to a certain extent; for example, compared with compounds 6 (28.9%, 500 μg/mL), 7 (25.5%, 500 μg/mL), and 8 (32.1%, 500 μg/mL), the multisubstituted compounds 9 (38.1%, 500 μg/mL), 10 (37.2%, 500 μg/mL), and 11 (43.4%, 500 μg/mL) F


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compounds 6−8, and 17. For example, 22 (44.2%, 500 μg/mL) displayed obviously higher activity than most of the other compounds. Additionally, the SAR demonstrated that the chirality at the 3,5′-position of spirooxindole affected the antiviral activity slightly. For instance, compound 24 (3S,5′S, 25.2%, 500 μg/mL) derived from L-tryptophan was more active than 25 (3R,5′R, 14.3%, 500 μg/mL) derived from Dtryptophan. With regard to compounds 2 and 24, the result indicated that the introduction of a substituent at the 2′position had little influence on the bioactivity. Further anti-TMV bioassay was conducted to investigate their inactivation, curative, and protection effects in vivo (Table 1). The result showed that most of the compounds exhibited good antiviral activity and similar SAR to the activity in vitro. The activities of compounds 4, 5, 8−11, 13, 18, 19, and 22 were much superior to those of ribavirin (36.4 ± 0.2, 37.5 ± 0.2, and 36.4 ± 0.1% at 500 μg/mL) and harmine (40.5 ± 0.2, 38.6 ± 0.8, and 42.4 ± 0.6% at 500 μg/mL); especially compounds 4 (58 ± 0.4, 55.2 ± 2.3, and 49.7 ± 1.1% at 500 μg/mL), 9 (53.8 ± 3.3, 46.2 ± 2.0, and 51.4 ± 1.7% at 500 μg/ mL), and 22 (51.4 ± 1.0, 48.1 ± 3.7, and 54 ± 0.8% at 500 μg/ mL) displayed higher activities than the others. Interestingly, compound 18 showed moderate activity in vitro but desirable activities in vivo. Of all, compound 4, the N′-benzylidene-2oxospiro[indoline-3,3′-pyrrolidine]-5′-carbohydrazide containing a tert-butyl at the benzene ring, exhibited the best antiviral activity both in vitro and in vivo. Considering its good solubility, stability, and simple chemical structure, it is worthy of further research and exploitation. Through the modification of the spirooxindole skeleton, as we can see, the introduction of an acylhydrazone moiety favors the antiviral activities. These results indicate that the hydrogen bond donor and acceptor of acylhydrazone could obviously enhance the interaction between the agents and the TMV receptor and then improve the activities. This verified that our initial design ideas are reasonable. Fungicidal Activity. Overall, these derivatives exhibited broad-spectrum fungicidal activities against 14 kinds of plant fungi (Table 2). Most of these derivatives exhibited >60% fungicidal activity against Physalospora piricola at 50 mg/kg. To our surprise, the compound containing a hydrazide structure (1) showed low anti-TMV activity but excellent fungicidal activity against Physalospora piricola (96.6% at 50 mg/kg). Noteworthily, those compounds containing aryl groups exhibited fungicidal activities to certain fungi selectively: they showed apparently higher activities against Physalospora piricola, Rhizoctonia cerealis, and Sclerotinia sclerotiorum than the others. Addtionally, the chlorinated compounds 6−9 generally showed good fungicidal activities against Physalospora piricola and Rhizoctonia cerealis. Insecticidal Activity. Some derivatives also showed broadspectrum insecticidal activities (Table 3). It was noteworthy that the chirality played an important role in the insecticidal activities. For example, compound 25, which derived from Dtryptophan, displayed excellent activities (60% against C. pipiens pallens at 0.25 mg/kg) compared with 24 (20% against C. pipiens pallens at 5 mg/kg) derived from L-tryptophan. Although the antivirus activities of compound 14 was far less effective, the insecticidal activities were extremely higher than those of other tested compounds even at very low concentration (60% against C. pipiens pallens at 0.25 mg/kg and 100% against M. separata at 600 mg/kg).

Table 3. Larvacidal Activities against Oriental Armyworm (Mythimna separata), Cotton Bollworm (Helicoverpa armigera), Corn Borer (Ostrinia nubilalis), and Mosquito (C. pipiens pallens) of Compounds 1−9, 12, 14−19, 21, 22, 24, and 25

slightly higher than or comparable to that of compound 2. However, the activity was greatly improved when the naphthalene ring was introduced to the molecules, maybe also attributed to the molecular lipid solubility. For the aliphatic substituent, the number of branched chains affected anti-TMV activity; the more branched was the aliphatic chain, the better was the activity. For example, compound 17 (16.3%, 500 μg/ mL) containing a cyclohexyl displayed lower anti-TMV activities than 18 (36%, 500 μg/mL) containing a tert-butyl group. To investigate the role of the N−H bond to the bioactivity, we designed and synthesized compound 19, which has a methyl at the nitrogen. To our delight, it showed better antivirus activities (45.9%, 500 μg/mL) than compound 2, ribavirin, and harmine. Thus, the result turned out that the N−H bond is not indispensable. Similarl results can be found for the imidazolone compounds 20−23; the activity could be kept or increased substantially compared with the corresponding acylhydrazone G


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(5) Qian, X. H.; Lee, P. W.; Cao, S. China: Forward to the green pesticides via a basic research program. J. Agric. Food Chem. 2010, 58, 2613−2623. (6) Seiber, J. N. Sustainability and agricultural and food chemistry. J. Agric. Food Chem. 2011, 59, 1−21. (7) Song, H. J.; Liu, Y. X.; Liu, Y. X.; Wang, L. Z.; Wang, Q. M. Synthesis and antiviral and fungicidal activity evaluation of β-carboline, dihydro-β-carboline, tetrahydro-β-carboline alkaloids, and their derivatives. J. Agric. Food Chem. 2014, 62, 1010−1018. (8) Berlin, J.; Rügenhagen, C.; Greidziak, N.; Kuzovkina, I.; Witte, L.; Wray, V. Biosynthesis of serotonin and β-carboline alkaloids in hairy root cultures of Peganum harmala. Phytochemistry 1993, 33, 593−597. (9) Nettleship, L.; Slaytor, M. Limitations of feeding experiments in studying alkaloid biosynthesis in Peganum harmala callus cultures. Phytochemistry 1974, 13, 735−742. (10) Ding, Y. S.; de Wet, J. R.; Cavalcoli, J.; Li, S. Y.; Greshock, T. J.; Miller, K. A.; Finefield, J. M.; Sunderhaus, J. D.; McAfoos, T. J.; Tsukamoto, S.; Williams, R. M.; Sherman, D. H. Genome-based characterization of two prenylation steps in the assembly of the stephacidin and notoamide anticancer agents in a marine-derived Aspergillus sp. J. Am. Chem. Soc. 2010, 132, 12733−12740. (11) Haynes, S. W.; Gao, X.; Tang, Y.; Walsh, C. T. Complexity generation in fungal peptidyl alkaloid biosynthesis: a two-enzyme pathway to the hexacyclic MDR export pump inhibitor ardeemin. ACS Chem. Biol. 2013, 8, 741−748. (12) Lin, H. C.; Chiou, G.; Chooi, Y. H.; McMahon, T. C.; Xu, W.; Garg, N. K.; Tang, Y. Elucidation of the concise biosynthetic pathway of the communesin indole alkaloids. Angew. Chem., Int. Ed. 2015, 54, 3004−3007. (13) Yu, S.; Qin, D.; Shangary, S.; Chen, J.; Wang, G.; Ding, K.; McEachern, D.; Qiu, S.; Nikolovska-Coleska, Z.; Miller, R.; Kang, S.; Yang, D.; Wang, S. Potent and orally active small-molecule inhibitors of the MDM2−p53 interaction. J. Med. Chem. 2009, 52, 7970−7973. (14) Zhou, J.; Zhou, S. Antihypertensive and neuroprotective activities of rhynchophylline: the role of rhynchophylline in neurotransmission and ion channel activity. J. Ethnopharmacol. 2010, 132, 15−27. (15) Cui, C. B.; Kakeya, H.; Osada, H. Novel mammalian cell cycle inhibitors, spirotryprostatins A and B, produced by Aspergillus f umigatus, which inhibit mammalian cell cycle at G2/M phase. Tetrahedron 1996, 52, 12651−12666. (16) Huang, Y. Q.; Liu, Y. X.; Liu, Y. X.; Song, H. J.; Wang, Q. M. C ring may be dispensable for β-carboline: design, synthesis, and bioactivities evaluation of tryptophan analog derivatives based on the biosynthesis of β-carboline alkaloids. Bioorg. Med. Chem. 2016, 24, 462−473. (17) Zhao, P. L.; Li, J.; Yang, G. F. Synthesis and insecticidal activity of chromanone and chromone analogues of diacylhydrazines. Bioorg. Med. Chem. 2007, 15, 1888−1895. (18) Chen, Q.; Liu, Z. M.; Chen, C. N.; Jiang, L. L.; Yang, G. F. Synthesis and fungicidal activities of new 1,2,4-triazolo[1,5-a]pyrimidines. Chem. Biodiversity 2009, 6, 1254−1265. (19) Jin, Y. X.; Zhong, A. G.; Zhang, Y. J.; Pan, F. Y. Synthesis, crystal structure, spectroscopic properties, antibacterial activity and theoretical studies of a novel difunctional acylhydrazone. J. Mol. Struct. 2011, 1002, 45−50. (20) Liu, X. H.; Liu, H. J.; Tan, C. X.; Weng, J. Q. Application of acylhydrazonederivatives as fungicide. Faming Zhuanli Shenqing, CN 101874496 A, 2010. (21) Fuog, D.; Fergusson, S. J.; Flückiger, C. Pymetrozine: a novel insecticide affecting aphids and whiteflies. In Insecticides with Novel Modes of Action; Springer: Berlin, Germany, 1998; pp 40−49. (22) Jose, L.; Armes, N. J.; Farlow, R.; Aldridge, K.; Robin, F.; Tedeschi, L. Metaflumizone, a new broad-spectrum insecticide for crop protection. Congress Proceedings 2007 of the XVI International Plant Protection Congress; British Crop Protection Council: Hampshire, UK, 2007; Vol. 1, pp 74−81. (23) Lym, R. G.; Christianson, K. M. Diflufenzopyr increases perennial weed control with auxin herbicides. Proceedings of the Western

In summary, according to the biosynthesis of alkaloids derived from tryptophan and the wide use of spirooxindole in drug molecular design, as well as by drawing from the experience of our previous study on derivatives containing acylhydrazone fragment, we designed and synthesized a series of novel spirooxindole derivatives containing an acylhydrazone moiety and first evaluated their biological activities. The results of bioassays indicated that most of the target compounds showed good anti-TMV activity both in vitro and in vivo (inactivation, curative, and protection) in the laboratory; the activities of compounds 4, 5, 9−11, 13, 19, and 22 were much higher than that of ribavirin (38.2, 36.4 ± 0.2, 37.5 ± 0.2, and 36.4 ± 0.1% at 500 μg/mL); especially compound 4 (48.4, 58 ± 0.4, 55.2 ± 2.3, and 49.7 ± 0.2% at 500 μg/mL) exhibited the best antiviral activity compared with ribavirin and harmine (44.6, 40.5 ± 0.2, 38.6 ± 0.8, and 42.4 ± 0.6% at 500 μg/mL), and the relevant SAR was summarized. In addition, we were pleased to find that these compounds also showed broadspectrum fungicidal activity and insecticidal activity. For instance, most of these derivatives exhibited >60% fungicidal activity against Physalospora piricola at 50 mg/kg. Compounds 25 and 14 displayed excellent insecticidal activities (60% against C. pipiens pallens at 0.25 mg/kg) even at very low concentrations. The experimental data above proved the rationality of our speculation and design ideology preliminarily, and further study on their antiviral mechanism is in progress in our labratory.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jafc.6b02683. Experimental details and characterization of intermediates A−H and target compounds 1−25 (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*(H.S.) Phone/fax: +86-(0)22-23503952. E-mail: [email protected]. *(Q.W.) Phone/fax: +86-(0)22-23503952. E-mail: wangqm@ nankai.edu.cn. Funding

We are grateful to the National Natural Science Foundation of China (21132003, 21421062, 21372131, 21602117), the Specialized Research Fund for the Doctoral Program of Higher Education (20130031110017), and the Tianjin Natural Science Foundation (16JCZDJC32400). Notes

The authors declare no competing financial interest.

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Design, Synthesis, and Biological Activities of Spirooxindoles

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