English

• 1. INTRODUCTION

  Over the past few decades, increasing research attention has been paid on studying the heterocyclic compounds owing to their important roles in pharmaceuticals and biological processes^[1-3]. Among all heterocycles, the heterocycle-fused 1, 2, 4-triazole scaffold has been identified as one of the privileged structures in drug discovery^[4-7]. In particular, triazolothiadiazines (TTD) containing 3, 6-disubstituents formed from structurally diverse 1, 2, 4-triazoles fused with six-membered ring systems have been claimed to exhibit various biological activities, such as antitubercular, antibacterial, anti-inflammatory, anticancer, antileishmanial, and anti-AIDS^[8-15]. However, most studies have been focused on 3, 6-disubstituted-7H-[1,2,4]triazolo[3, 4-b][1,3,4]thiadiazines, and only limited reports on 3, 6-disubstituted-7-aroyl-6, 7-dihydro-5H-[1,2,4]triazolo[3, 4-b][1,3,4]thiadiazines^[16-22]. Furthermore, available data on the biological activities of the latter and their close structurally related derivatives are rather limited. So far, only two papers have reported that the new compounds showed bactericidal^[16] and anticancer activities^[17], and the biological activities of regulation of plant growth for this type of compounds remain to be studied. Prompted by the above consideration, and as a part of our ongoing research on developing novel TTD scaffolds with more effective bioactivity^[23-25], we proposed that incorporating benzoyl, phenyl and p-methylphenyl groups into heterocycle-fused TTD scaffold might be an effective strategy for discovering novel 1, 2, 4-triazole derivatives with potential novel bioactivity, because these three groups connected to different TTD scaffolds showed a variety of different biological activities respectively^{[16, 17, 26-28]}. Therefore, we are very interested in the design and synthesis of the title compound phenyl(6-phenyl-3-p-tolyl-6, 7-dihydro-5H-[1,2,4]triazolo[3, 4-b][1,3,4]thiadiazin-7-yl)methanone (PTM). In the present work, we described the synthesis, crystal structure and biological activities of a TTD derivative bearing p-methyl-phenyl, benzoyl and phenyl groups. More interestingly, only the crystal structure of the pure trans-isomer of PTM was obtained by X-ray diffraction.

  2. EXPERIMENTAL

  2.1 Reagents and apparatus

  All chemicals and solvents used were of AR grade. The FT-IR spectrum was recorded on a Thermo Scientific NICOLET 5700 FT-IR Spectrometer in ATR mode in the range of 4000~400 cm^-1. NMR spectra were recorded on a Burker 500 MHz Nuclear Magnetic Resonance Spectrometer with TMS as an internal standard and DMSO-d₆ as the solvent. MS spectra were recorded on a Q-Exactive LC-MS/MS. The crystal structures were measured on a Bruker Smart APEX II CCD diffractometer. The melting point was determined on an XT-4A apparatus and uncorrected.

  2.2 Synthesis

  2.2.1   Preparation of 4-amino-3-p-tolyl-1H-1, 2, 4-triazole-5(4H)-thione (1)

  The 1, 2, 4-triazole (1), whose tautomer is 4-amino-5-p-tolyl-4H-1, 2, 4-triazole-3-thiol, was prepared from 4-methyl-benzoic acid (Scheme 1), following the procedure of Zhang et al^[29].

  Scheme 1

  

  Scheme 1.  Synthetic route of compound 1

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  2.2.2   Preparation of (E)-4-(benzylideneamino)-3-p-tolyl-1H-1, 2, 4-triazole-5(4H)-thione (2)

  Benzaldehyde (0.02 mol, distilled under reduced pressure before use) was added to a solution of 4-amino-3-p-tolyl-1H-1, 2, 4-triazole-5(4H)-thione (1, 0.02 mol) in absolute ethanol (30 mL). The pH was adjusted to 5~6 with dilute HCl. The mixture was stirred and refluxed for about 2 h. The crude product was recrystallized from ethanol and gave pure (E)-4-(benzylideneamino)-3-p-tolyl-1H-1, 2, 4-triazole-5(4H)-thione (2, Scheme 2).

  Scheme 2

  

  Scheme 2.  Synthetic route of PTM

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  2.2.3   Preparation of phenyl(6-phenyl-3-p-tolyl-6, 7-dihydro-5H-[1,2,4]triazolo[3, 4-b][1,3,4]thiadiazin-7-yl)methanone (PTM)

  The title compound PTM was prepared by the reaction of (E)-4-(benzylideneamino)-3-p-tolyl-1H-1, 2, 4-triazole-5(4H)-thione (2, 2 mmol) and ω-bromoacetophenone (2 mmol) in the mixture of ethanol (40 mL) and triethylamine (1 mL). The mixture was stirred at room temperature for 30 min and the product was obtained by filtration, drying and recrystallization from ethanol (Scheme 2). The obtained target compound PTM was a white powder in a yield of 90%. m.p. 197~199 ˚C. IR (KBr): 3428, 3151, 2946, 1679, 1594, 1448, 1353, 694. ¹H NMR (500MHz, DMSO-d₆) δ: 2.36(s, 3H, CH₃), 5.04~5.07(t, 1H, CH), 5.84~5.85(d, 1H, SCH), 7.25~7.33(m, 6H, NH and ArH), 7.47~7.48(d, 2H, ArH), 7.57~7.60(t, 2H, ArH), 7.70~7.73(t, 1H, ArH), 7.95~7.96(d, 2H, ArH), 8.04~8.05(d, 2H, ArH). ¹³C NMR(125 MHz, DMSO-d₆) δ: 195.14, 152.35, 142.76, 139.97, 137.43, 134.88, 134.78, 129.80, 129.58, 129.31, 129.08, 128.63, 127.88, 127.84, 124.09, 59.24, 44.09, 21.46. MS-ESI (m/z) found (calcd., accuracy): 411.1282 ([M-H]^-) (411.1280, δ 0.49 ppm), 413.1422 ([M+H]⁺) (413.1436, δ 3.39 ppm), 435.1241 ([M+Na]⁺) (435.1256, δ 3.45 ppm), 447.1048 ([M+Cl]^-) (447.1046, δ 0.45 ppm).

  The saturated solution of PTM dissolved in ethanol was stood at room temperature for 7 days by slowing evaporation, yielding colorless single crystals suitable for X-ray analysis.

  2.3 Crystal data and structure determination

  A colorless block crystal of compound PTM with dimensions of 0.28mm × 0.25mm × 0.23mm was selected for X-ray diffraction analysis. The X-ray diffraction data for trans-PTM were obtained on a Bruker Smart APEX II CCD diffractometer equipped with a graphite-monochromatic Mo-Kα radiation (λ = 0.71073 Å) by using an ω-2θ scan mode at 293(2) K. The structure was solved with the olex2.solve structure solution program using Charge Flipping^[30] and refined with the olex2.refine refinement package using Gauss-Newton minimisation^[31]. A total of 12643 reflections were collected in the range of 1.92 < θ < 24.99°, of which 3514 were independent with R_int = 0.0876 and 2044 were observed with I > 2σ(I). The final full-matrix least-squares refinement gave R = 0.0786, wR = 0.2001 (w = 1/[σ²(F_o²) + (0.0445P)² + 0.4252P], where P = (F_o² + 2F_c²)/3), S = 1.0241, (Δρ)_max = 0.6065, (Δρ)_min = –0.5806 e/ų and (Δ/σ)_max = 0.0005.

  2.4 Biological activity

  As far as we know, available data on the biological activities of 3, 6-disubstituted-7-aroyl-6, 7-dihydro-5H-[1,2,4]triazolo[3, 4-b][1,3,4]thiadiazines and their close structurally related derivatives are rather scarce. Although weak bactericidal activities and moderate to potent antiproliferative activities against four cancer cell lines of some new compounds have been reported^{[16, 17]}, the activities of PTM on antimicrobial and the growth regulation of plant remain to be investigated.

  2.4.1   Antimicrobial activity

  The antibacterial activity of PTM was tested against a local Gram positive bacterial species (Bacillus pumilus) on nutrient agar medium (NA) and the effect is compared with that of erythromycin. Pure PTM and erythromycin were prepared into two gradient culture solutions of 60 and 600 ppm, respectively. The culture dishes in 9 cm diameter were placed on the horizontal plane and 20 mL nutrient agar was added as the bottom culture medium. After the nutrient agar was solidified, the fungus medium 10 mL (9 mL agar + 1 mL Bacillus pumilus) was added. Two sterile Oxford cups were put in diagonal. Extraction of 200 μL solutions of two gradient concentrations of PTM and erythromycin was transferred into the different Oxford cups with a liquid transfer gun, respectively. After the culture dishes were incubated at room temperature 27~35 ℃ for 14 h, the diameters of inhibition zones were measured.

  2.4.2   Activity of regulating the growth of plant

  PTM was also investigated for its biological activity on regulating the growth of plant. We selected wheat and radish to represent monocotyledonous and dicotyledonous plants, respectively. The effects of PTM on the growth regulation of wheat and radish were tested at the same time. Twenty seeds of each species were carefully chosen and individually placed in culture dishes of 9 cm diameter containing two pieces of filter paper and 8 mL solution of PTM (10, 20 and 50 μg/mL, respectively), and were incubated in a growth chamber at 25 ℃. The set of controls in distilled water was prepared simultaneously. After 5 days, the germination percentage and the growth in each culture dish were investigated both for the treated plants and for the set controls. The lengths of the stalks and the radicels of 10 plants with the most prosperous growth were measured in each culture dish and the average lengths of them were calculated, respectively. The equations of the germination percentage (the wheat and the radish in each culture dish) are: (the number of the germinated seeds/the total number of seeds) × 100%. The equations of the growth regulating percentage (the stalk and radicel of the wheat and radish) are: [the average of sample length (cm) – the average of the controls (cm)]/the average of the controls (cm) × 100%. The positive result (expressed as "+") means PTM possesses a growth-promoting effect, while a negative value (represented by "–") suggests an inhibitory effect on growth. The magnitude of a numerical value represents the degree of promotion or inhibition.

  3. RESULTS AND DISCUSSION

  3.1 Synthesis

  The target compound we originally predicted was compound 3. Surprisingly, however, it turned out to be PTM when synthesized and characterized. Conceivably, due to the acidity of the carbonyl α-H, the α-C becomes a carbanion under alkaline conditions, which attacks C=N as a nucleophilic reagent to form the six-membered thiadiazine ring. The proposed reaction mechanism is shown in Scheme 3.

  Scheme 3

  

  Scheme 3.  Cyclization mechanism of PTM formation proposed

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  The absence of NH₂, S–H and C=S absorption bands in the IR spectrum has confirmed that PTM was obtained via cyclocondensation. The broad band around 3428 cm^-1 is due to the symmetric stretching vibration of N–H, while aromatic C–H stretching vibration is observed at 3151 cm^-1. The C–H stretching and bending vibration peaks of the CH₃ group are at 2946 and 1353 cm^-1, respectively. Sharp band observed at 1679 cm^-1 is obviously attributed to C=O stretching vibration. In the ¹H NMR spectrum of PTM, there are a double and a triple peaks in the ranges of δ 5.84~5.85 and 5.04~5.07, corresponding to S–C–H and N–C–H, respectively, consistent with the thiadiazine ring-closure. In the ¹³C NMR spectrum of PTM, the peaks at δ 195.14, 152.35, 142.76 assigned to be C=O, N=C–S and N=C–N respectively also prove the formation of the title compound.

  3.2 Crystal structure of trans-PTM

  The molecular structure and packing diagram in a unit cell of trans-PTM are illustrated in Figs. 1 and 2, respectively. In the crystal structure there is no typical hydrogen bonding, and all bond lengths, bond angles and dihedral angles are in normal ranges. Crystal data for trans-PTM: C₂₄H₂₀N₄OS, M_r = 412.52, monoclinic system, space group P2₁/c, a = 16.650(3), b = 13.876(3), c = 8.812(2) Å, β = 100.340(3)°, V = 2002.8(7) ų, F(000) = 865, Z = 4, D_c = 1.3680 g/cm³, λ = 0.71073 Å, μ = 0.186 mm^‑1 and the final R = 0.0786 for 3514 unique reflections with 2044 observed ones (I > 2σ(I)). The selected bond lengths, bond angles and dihedral angles are shown in Tables 1, 2 and 3, respectively. More interestingly, we can see clearly two chiral carbon atoms (6- and 7-positions) in the crystal structure. The configurations of them are just opposite (6-position R and 7-position S) and the two largest groups (the benzene ring and the benzoyl group) are located on the opposite sides of the thiadiazine ring respectively to reduce their mutual repulsion. Moreover, the parallel benzene rings (C(19)~C(24)) of the adjacent molecules of trans-PTM interact with each other by π-π stacking interactions, leading to the formation of a two-dimensional network.

  Figure 1

  

  Figure 1.  Molecular structure of trans-PTM

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  Figure 2

  

  Figure 2.  Packing diagram in a unit cell of trans-PTM

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  Table 1

  

  Table 1.  Selected Bond Lengths (Å) for trans-PTM

  DownLoad: CSV

  Bond	Dist.		Bond	Dist.
  N(1)–N(2)	1.361(5)		N(3)–N(4)	1.381(4)
  N(1)–C(8)	1.296(5)		N(4)–C(10)	1.450(5)
  N(2)–C(9)	1.298(5)		C(10)–C(11)	1.526(6)
  N(3)–C(8)	1.341(5)		S(1)–C(11)	1.813(4)
  N(3)–C(9)	1.336(5)		S(1)–C(9)	1.696(5)
  C(5)–C(8)	1.435(6)		C(10)–C(12)	1.460(4)
  C(5)–C(6)	1.357(6)		C(11)–C(18)	1.513(5)
  C(6)–C(7)	1.350(7)		O(1)–C(18)	1.207(5)
  C(2)–C(7)	1.375(6)

  Table 2

  

  Table 2.  Selected Bond Angles (º) for trans-PTM

  DownLoad: CSV

  Angle	(°)		Angle	(°)
  C(7)–C(2)–C(3)	116.7(5)		N(3)–C(9)–S(1)	124.2(3)
  C(2)–C(7)–C(6)	120.8(5)		C(9)–S(1)–C(11)	100.0(2)
  C(7)–C(6)–C(5)	122.4(5)		S(1)–C(11)–C(10)	114.7(3)
  C(6)–C(5)–C(4)	116.7(5)		N(4)–C(10)–C(11)	113.3(3)
  C(8)–N(1)–N(2)	108.9(4)		N(3)–N(4)–C(10)	108.9(3)
  C(9)–N(2)–N(1)	106.3(4)		N(4)–N(3)–C(9)	123.5(4)
  N(2)–C(9)–N(3)	110.0(4)		C(11)–C(18)–C(19)	118.2(4)
  C(9)–N(3)–C(8)	106.5(3)		C(20)–C(19)–C(24)	120.0
  N(1)–C(8)–N(3)	108.2(4)		C(17)–C(12)–C(13)	120.0

  Table 3

  

  Table 3.  Selected Dihedral Angles (º) for trans-PTM

  DownLoad: CSV

  Groups		Dihedral angle (º)
  Benzene ring (C(2)~C(7))	Triazole ring	9.69(0.22)
  Triazole ring	Thiadiazine ring	22.56(0.16)
  Benzene ring (C(12)~C(17))	Thiadiazine ring	81.74(0.14)
  Benzene ring (C(19)~C(24))	Thiadiazine ring	61.07(0.14)
  Benzene ring (C(19)~C(24))	Benzene ring (C(12)~C(17))	69.29(0.15)

  3.3 Biological activity

  3.3.1   Antimicrobial activity

  In an effort to gain insight into the biological activity of PTM, PTM was subjected to a preliminary in vitro antimicrobial susceptibility test against a local Gram positive bacterial species (Bacillus pumilus). The results indicated that PTM showed a weak inhibitory effect on Bacillus pumilus. Compared with erythromycin, PTM has a lower bacteriostatic effect (equivalent to 57% of erythromycin), suggesting that the inhibitory effect of PTM on Gram positive bacteria was not significant. The data of biological activity test are presented in Table 4. And the two similar compounds reported by Awad et al also have weak effects on Micrococcus roseus and Staphylococcus citereus of seven strains of bacteria tested^[16]. Surprisingly, most of the nearly 30 similar compounds reported by Zhang et al showed moderate to potent antiproliferative activities against four cancer cell lines, PC-3, HepG2, A549, and MCF-7^[17]. These data may suggest that this type of compounds generally have poor antibacterial effect, but have potent anticancer activity. PTM needs to be further developed in anticancer activity.

  Table 4

  

  Table 4.  Antimicrobial Activity of PTM

  DownLoad: CSV

  	PTM		Erythromycin
  Concentration (ppm)	60	600	60	600
  Bacteriostasis diameter (cm)	0.8	1.2	1.4	2.1

  3.3.2   Activity of regulating the growth of plant

  We next investigated PTM in regulating the growth of wheat (monocotyledon) and radish (dicotyledon) with reference of distilled water. After treating with culture solutions of 10, 20 and 50 μg/mL of PTM for 5 days, the growth regulating percentages have been calculated. The data of biological activity test are presented in Table 5.

  Table 5

  

  Table 5.  Effect of PTM on the Plant Growth-regulating of Wheat and Radish

  DownLoad: CSV

  	Wheat			Radish
  Concentration (μg/mL)	Germination percentage (%)	Stalk (%)	Radicel (%)	Germination percentage (%)	Stalk (%)	Radicel (%)
  10	50	–33	–7.1	50	+2	+4.2
  20	80	–26.5	+5.7	90	+20	+29.2
  50	70	–31.4	+19.4	75	+4	+45.8

  The results indicated that when the concentration of PTM was increased from 10 to 20 μg/mL, the germination rates of wheat and radish were both significantly increased. PTM also significantly promoted the growth of stalk and the radicel of radish, and generally the higher the concentration, the stronger the promotion. When the concentration reached 50 μg/mL, the promoting effect of PTM on the growth of the radicel of radish reached 45.8%, while on the stalk it was not obvious, only 4%.

  Interestingly, the effect of PTM on wheat is basically the opposite of that on radish. The three gradient concentration solutions of PTM all showed good inhibitory effects on the growth of the stalk of wheat. Surprisingly, the effect on the growth of the radicel of wheat changes from the initial weak inhibitory effect (–7.1%) to the promotion effect until 19.4% following the increase of concentration.

  In general, PTM promoted the growth of radish, while inhibited that of wheat in a dose-dependent manner. Therefore, PTM may be developed as a drug to promote the growth of dicotyledonous plants or as an herbicide to inhibit that of monocotyledonous plants in the future. And the relationship between the structure of PTM and the activity of regulating the growth of plant is worth studying further.

  4. CONCLUSION

  In conclusion, PTM was prepared and characterized by FT-IR, NMR, single-crystal X-ray diffraction and MS techniques. The crystal structure of the trans-isomer of PTM was obtained from X-ray diffraction. Furthermore, by introducing p-methylphenyl, benzoyl and phenyl groups into the scaffold of heterocycle-fused TTD, PTM exhibited weak antimicrobial activity on Bacillus pumilus, while promoted the growth of radish and inhibited that of wheat in a dose-dependent manner. At present, the most promising thing is that PTM may be developed as a drug to promote the growth of dicotyledonous plants or as an herbicide to inhibit that of monocotyledonous plants in the future. Further research on the mechanisms of this kind of compounds and modification is underway.

  
  
• 1. [1]

     Khillare1, L. D.; Pratap1, U. R.; Bhosle1, M. R.; Dhumal1, S. T.; Bhalerao1, M. B.; Mane, R. A. Syntheses of biodynamic heterocycles: baker's yeast-assisted cyclocondensations of organic nucleophiles and phenacyl chlorides. Res. Chem. Intermed. 2017, 43, 4327–4337. doi: 10.1007/s11164-017-2880-0

  2. [2]

     Kattimani, P. P.; Kamble, R. R.; Dorababu, A.; Hunnur, R. K.; Kamble, A. A.; Devarajegowda, H. C. C₅-alkyl-1, 3, 4-oxadiazol-2-ones undergo dealkylation upon nitrogen insertion to form 2H-1, 2, 4-triazol-3-ones: synthesis of 1, 2, 4-triazol-3-one hybrids with triazolothiadiazoles and triazolothiadiazines. J. Heterocycl. Chem. 2017, 54, 2258–2265. doi: 10.1002/jhet.2813

  3. [3]

     Hamama, W. S.; Ibrahim, M. E.; Ghaith, E. A.; Zoorob, H. H. Peculiar reaction chemical reactivity behavior of 1, 3-oxathiolane-5-one towards various reagents: assisted by molecular modeling studies and in vitro antioxidant and cytotoxicity evaluation. Synth. Commun. 2017, 47, 566–580. doi: 10.1080/00397911.2016.1276190

  4. [4]

     Aouad, M. R.; Al-Saedi, A. M. H.; Ali, A. A.; Rezki, N.; Messali, M. Preparation of novel 3-fluorophenyl triazolothiadiazoles and of triazolothiadiazines. Org. Prep. Proced. Int. 2016, 48, 355–370. doi: 10.1080/00304948.2016.1194134

  5. [5]

     Nikpour, M.; Motamedi, H. Сonvenient access to 1, 3-dimethyl[1, 2, 4]triazolo[3, 4-b][1, 3, 4]-thiadiazol-1-ium and 7H-[1, 2, 4]triazolo[4, 3-b][1, 2, 4]-triazol-1-ium salts. Chem. Heterocycl. Compd. 2015, 51, 159–161. doi: 10.1007/s10593-015-1674-9

  6. [6]

     Aly, H. M.; Moustafa, M. E.; Nassar, M. Y.; Abdelrahman, E. A. Synthesis and characterization of novel Cu(II) complexes with 3-substituted-4-amino-5-mercapto-1, 2, 4-triazole Schiff bases: a new route to CuO nanoparticles. J. Mol. Struct. 2015, 1086, 223–231. doi: 10.1016/j.molstruc.2015.01.017

  7. [7]

     Nami, N.; Zareyee, D.; Ghasemi, M.; Asgharzadeh, A.; Forouzanib, M.; Mirzad, S.; Hashemi, S. M. An efficient method for synthesis of some heterocyclic compounds containing 3-iminoisatin and 1, 2, 4-triazole using Fe₃O₄ magnetic nanoparticles. J. Sulfur Chem. 2017, 38, 279–290. doi: 10.1080/17415993.2017.1278761

  8. [8]

     Li, Z. Q.; Bai, X. G.; Deng, Q.; Zhang, G. N.; Zhou, L.; Liu, Y. S.; Wang, J. X.; Wang, Y. C. Preliminary SAR and biological evaluation of antitubercular triazolothiadiazine derivatives against drug-susceptible and drugresistant Mtb strains. Bioorg. Med. Chem. 2017, 25, 213–220. doi: 10.1016/j.bmc.2016.10.027

  9. [9]

     Iradyan, M. A.; Iradyan, N. S.; Minasyan, N. S.; Paronikyan, R. V.; Stepanyan, G. M. Synthesis and antibacterial activity of 3, 6-diaryl-7H-[1, 2, 4]triazolo[3, 4-b][1, 3, 4]thiadiazines. Pharm. Chem. J. 2016, 50, 10–15. doi: 10.1007/s11094-016-1389-y

  10. [10]

      Morsy, R. M. I.; Salem, O. I. A.; Abdel-Moty, S. G.; Kafafy, A. H. N. Synthesis, molecular modeling study and anti-inflammatory activity of novel benzimidazole derivatives with promising cyclooxygenase inhibitory properties. Pharma Chemica 2016, 8, 213–231.

  11. [11]

      Sever, B.; Altıntop, M. D.; Kuş, G.; Özkurt, M.; Özdemir, A.; Kaplancıklı, Z. A. Indomethacin based new triazolothiadiazine derivatives: synthesis, evaluation of their anticancer effects on T98 human glioma cell line related to COX-2 inhibition and docking studies. Eur. J. Med. Chem. 2016, 113, 179–186. doi: 10.1016/j.ejmech.2016.02.036

  12. [12]

      Aytaç, P. S.; Durmaz, I.; Houston, D. R.; Cetin-Atalay, R.; Tozkoparan, B. Novel triazolothiadiazines act as potent anticancer agents in liver cancer cells through Akt and ASK-1 proteins. Bioorg. Med. Chem. 2016, 24, 858–872. doi: 10.1016/j.bmc.2016.01.013

  13. [13]

      Ibrar, A.; Zaib, S.; Jabeen, F.; Iqbal, J.; Saeed, A. Unraveling the alkaline phosphatase inhibition, anticancer, and antileishmanial potential of coumarin-triazolothiadiazine hybrids: design, synthesis, and molecular docking analysis. Arch. Pharm. Chem. Life Sci. 2016, 349, 1–13. doi: 10.1002/ardp.201500337

  14. [14]

      Winton, V. J.; Aldrich, C.; Kiessling, L. L. Carboxylate surrogates enhance the antimycobacterial activity of UDP-galactopyranose mutase probes. ACS Infect. Dis. 2016, 2, 538–543. doi: 10.1021/acsinfecdis.6b00021

  15. [15]

      Khan, I.; Hameed, S.; Al-Masoudi, N. A.; Abdul-Reda, N. A.; Simpson, J. New triazolothiadiazole and triazolothiadiazine derivatives as kinesin Eg5 and HIV inhibitors: synthesis, QSAR and modeling studies. Z. Naturforsch. 2015, 70, 47–58.

  16. [16]

      Awad, I. M. A.; Rahman, A. E. A.; Bakite, E. A. Synthesis and application of some new heterocyclo-s-triazole derivatives as antimicrobial agents. J. Clirrn. Tech. Bioteclniol. 1991, 51, 483–495.

  17. [17]

      Zhang, B.; Li, Y. H.; Liu, Y.; Chen, Y. R.; Pan, E. S.; You, W. W.; Zhao, P. L. Design, synthesis and biological evaluation of novel 1, 2, 4-triazolo[3, 4-b][1, 3, 4]thiadiazines bearing furan and thiophene nucleus. Eur. J. Med. Chem. 2015, 103, 335–342. doi: 10.1016/j.ejmech.2015.08.053

  18. [18]

      Al-Etaibi, A.; John, E.; Ibrahim, M. R.; Al-Awadi, N. A.; Ibrahim, Y. A. Stereoselective synthesis of dihydrothiadiazinoazines and dihydrothiadiazinoazoles and their pyrolytic desulfurization ring contraction. Tetrahedron 2011, 67, 6259–6274. doi: 10.1016/j.tet.2011.06.034

  19. [19]

      Gaponenko, N. I.; Kolodina, A. A.; Lesin, A. V.; Kurbatov, S. V.; Starikova, Z. A.; Nelyubina, Y. V. Synthesis of spiro[indole-3, 3´-[1, 3, 4]thiadiazino[3, 2-a]benzimidazoles] and spiro[indole-3, 6´-[1, 2, 4]triazolo[3, 4-b][1, 3, 4]thiadiazines]. Russ. Chem. Bull. Int. Ed. 2010, 59, 838–844. doi: 10.1007/s11172-010-0170-8

  20. [20]

      Kolodina, A. A.; Lesin, A. V. Intramolecular cyclization of 4-amino-3-alkylsulfanyl-1, 2, 4-triazoles as a method for annelation of thiadiazine and thiadiazole rings. Russ. J. Org. Chem. 2009, 45, 139–145. doi: 10.1134/S1070428009010199

  21. [21]

      Ibrahim, Y. A.; Elwahy, A. H. M.; El-Fiky, A. E. M. Stereospecific synthesis of 6, 7-dihydro-5H-1, 2, 4-triazolo[3, 4-b] [1, 3, 4]thiadiazines. Heteroat. Chem. 1994, 5, 321–325. doi: 10.1002/hc.520050402

  22. [22]

      Molina, P.; Alajarin, M.; De Vega, M. J. P. Synthesis of 6, 7-dihydro-5H-1, 2, 4-triazoIo[3, 4-b][1, 3, 4]thiadiazines by a C–C ring cyclization under mild conditions. J. Chem. Soc. Perkin Trans. I. 1987, 1853–1860.

  23. [23]

      Ding, Q. C.; Dai, S. D.; Zhang, L. X. Crystal structure of 3, 6-diphenyl-7H-[1, 2, 4]-triazolo[3, 4-b][1, 3, 4]thiadiazine, C₁₆H₁₂N₄S. Z. Kristallogr. New Cryst. Struct. 2018, 233, 849–851. doi: 10.1515/ncrs-2018-0051

  24. [24]

      Ding, Q. C.; Zhang, L. X.; Zhang, H. L. Synthesis and biological activities of some novel triazolothiadiazines and Schiff bases derived from 4-amino-3-(4-hydroxyphenyl)-1H-1, 2, 4-triazole-5(4H)-thione. Phosphorus, Sulfur Silicon Relat. Elem. 2010, 185, 567–572. doi: 10.1080/10426500902848393

  25. [25]

      Ding, Q. C.; Lei, X. X.; Jin, J. Y.; Zhang, L. X.; Du, H. A.; Zhang, H. L. Synthesis and structure of novel 1, 2, 4-triazole derivatives containing the 2, 4-dinitrophenylthio group. J. Chem. Res. 2009, 114–119.

  26. [26]

      Parmar, K. A.; Patel, R. P.; Prajapati, S. N.; Joshi, S. A. A versatile approach for the synthesis of some new [1, 2, 4] triazolo derivatives of 1, 3, 4 thiadiazine and their biological activities. J. Ultra Chem. 2011, 7, 21–28.

  27. [27]

      Miao, R. D.; Wei, J.; Lv, M. H.; Cai, Y.; Du, Y. P.; Hui, X. P.; Wang, Q. Conjugation of substituted ferrocenyl to thiadiazine as apoptosis-inducing agents targeting the Bax/Bcl-2 pathway. Eur. J. Med. Chem. 2011, 46, 5000–5009. doi: 10.1016/j.ejmech.2011.08.007

  28. [28]

      Baeeri, M.; Foroumadi, A.; Motamedi, M.; Yahya-Meymandi, A.; Firoozpour, L.; Ostad, S. N.; Shafiee, A.; Souzangarzadeh, S.; Abdollahi, M. Safety and efficacy of new 3, 6-diaryl-7H-[1, 2, 4]triazolo[3, 4-b][1, 3, 4]thiadiazine analogs as potential phosphodiesterase-4 inhibitors in NIH-3T3 mouse fibroblastic cells. Chem. Biol. Drug Des. 2011, 78, 438–444. doi: 10.1111/j.1747-0285.2011.01167.x

  29. [29]

      Zhang, L. X.; Zhang, A. J.; Hu, M. L.; Lei, X. X.; Xu, Z. X.; Zhang, Z. Y. Synthesis and crystal structure of 3-phenoxymethyl-6-(2, 4-difluorophenyl)-7H-1, 2, 4-triazolo[3, 4-b][1, 3, 4]thiadiazine. Acta Chim. Sin. 2003, 61, 917–921.

  30. [30]

      Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. OLEX2: a complete structure solution, refinement and analysis program. J. Appl. Cryst. 2009, 42, 339–341. doi: 10.1107/S0021889808042726

  31. [31]

      Bourhis, L. J.; Dolomanov, O. V.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. The anatomy of a comprehensive constrained, restrained refinement program for the modern computing environment – Olex2 dissected. Acta Cryst. 2015, A71, 59–75. http://pubmedcentralcanada.ca/pmcc/articles/PMC4283469/

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  Scheme 1  Synthetic route of compound 1

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  Scheme 2  Synthetic route of PTM

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  Scheme 3  Cyclization mechanism of PTM formation proposed

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  Figure 1  Molecular structure of trans-PTM

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  Figure 2  Packing diagram in a unit cell of trans-PTM

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  Table 1.  Selected Bond Lengths (Å) for trans-PTM

  Bond	Dist.		Bond	Dist.
  N(1)–N(2)	1.361(5)		N(3)–N(4)	1.381(4)
  N(1)–C(8)	1.296(5)		N(4)–C(10)	1.450(5)
  N(2)–C(9)	1.298(5)		C(10)–C(11)	1.526(6)
  N(3)–C(8)	1.341(5)		S(1)–C(11)	1.813(4)
  N(3)–C(9)	1.336(5)		S(1)–C(9)	1.696(5)
  C(5)–C(8)	1.435(6)		C(10)–C(12)	1.460(4)
  C(5)–C(6)	1.357(6)		C(11)–C(18)	1.513(5)
  C(6)–C(7)	1.350(7)		O(1)–C(18)	1.207(5)
  C(2)–C(7)	1.375(6)

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  Table 2.  Selected Bond Angles (º) for trans-PTM

  Angle	(°)		Angle	(°)
  C(7)–C(2)–C(3)	116.7(5)		N(3)–C(9)–S(1)	124.2(3)
  C(2)–C(7)–C(6)	120.8(5)		C(9)–S(1)–C(11)	100.0(2)
  C(7)–C(6)–C(5)	122.4(5)		S(1)–C(11)–C(10)	114.7(3)
  C(6)–C(5)–C(4)	116.7(5)		N(4)–C(10)–C(11)	113.3(3)
  C(8)–N(1)–N(2)	108.9(4)		N(3)–N(4)–C(10)	108.9(3)
  C(9)–N(2)–N(1)	106.3(4)		N(4)–N(3)–C(9)	123.5(4)
  N(2)–C(9)–N(3)	110.0(4)		C(11)–C(18)–C(19)	118.2(4)
  C(9)–N(3)–C(8)	106.5(3)		C(20)–C(19)–C(24)	120.0
  N(1)–C(8)–N(3)	108.2(4)		C(17)–C(12)–C(13)	120.0

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  Table 3.  Selected Dihedral Angles (º) for trans-PTM

  Groups		Dihedral angle (º)
  Benzene ring (C(2)~C(7))	Triazole ring	9.69(0.22)
  Triazole ring	Thiadiazine ring	22.56(0.16)
  Benzene ring (C(12)~C(17))	Thiadiazine ring	81.74(0.14)
  Benzene ring (C(19)~C(24))	Thiadiazine ring	61.07(0.14)
  Benzene ring (C(19)~C(24))	Benzene ring (C(12)~C(17))	69.29(0.15)

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  Table 4.  Antimicrobial Activity of PTM

  	PTM		Erythromycin
  Concentration (ppm)	60	600	60	600
  Bacteriostasis diameter (cm)	0.8	1.2	1.4	2.1

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  Table 5.  Effect of PTM on the Plant Growth-regulating of Wheat and Radish

  	Wheat			Radish
  Concentration (μg/mL)	Germination percentage (%)	Stalk (%)	Radicel (%)	Germination percentage (%)	Stalk (%)	Radicel (%)
  10	50	–33	–7.1	50	+2	+4.2
  20	80	–26.5	+5.7	90	+20	+29.2
  50	70	–31.4	+19.4	75	+4	+45.8

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