Synthetic Approach for Novel Fluorine Substituted α-Aminophosphonic Acids Containing 1,2,4-Triazin-5-One Moiety as Antioxidant Agents

Mohammed S. T. Makki, Reda M. Abdel-Rahman, Abdulrahman S. Alharbi^*

Department of Chemistry, Faculty of Science, King Abdul Aziz University, Jeddah, KSA.

DOI: 10.4236/ijoc.2018.81001                

Abstract

Novel fluorine substituted α-amino phosphonic acids containing 1,2,4-triazin- 5-one (6a-f) have been obtained from fluoroacylation of 6-(2′-amino-5′-nitrophenyl)-3-thioxo-1,2,4-triazin-5(4H)-one (1) followed by ammonilysis to give the corresponding 3-amino-derivative 3. Condensation of compound 3 with nitro/halogenated aromatic aldehydes yielded the Schiff bases 4. The simple addition of diethyl phosphonate to compound 4 produced the α-amino phosphonates 5. Acidic hydrolysis of compound 5 produced the fluorine substituted α-amino acids derivatives 6. Structures of the new compounds have been established with the help of elemental analysis and spectral measurements. Also, the products evaluated as antioxidants, where the fluorinated α-amino phosphonic acids 6 are more active than the other synthesized systems.

Keywords

Synthetic, Fluorine α-Amino Acids, 1, 2, 4-Triazin-5-One Moiety, Antioxidants Activity

1. Introduction

Recently, α-amino phosphonic acids and α-amino phosphonates have a vital importance of research chemists [1] [2] [3] , which is due to these family of compounds display, enzymatic inhibitors for HIV protease antagonists [4] and collagenase inhibitors [5] . Also, they use as anticancer [6] , antibacterial [7] , antiviral [8] and antioxidant [9] agents. On the other hands, functionally 1,2,4-triazines have unique properties for biological, medicinal and pharmacological chemistry [10] [11] [12] . Phosphorus compounds bearing and/or containing 1,2,4-triazine moieties exhibit a significant attention due to the specific biological properties [13] [14] [15] [16] [17] . Also, the introduction of fluorine atoms to heterocyclic nitrogen systems, mostly improve their physical, chemical and medical properties [18] [19] [20] [21] . In the present work, we focused on the reactivity of functional 1,2,4-triazines towards different reagents followed by simple addition of diethyl phosphonate to obtain a novel fluorine substituted α-amino phosphonic acids which considered as α-amino acids analog, in view of antioxidant activity.

α-amino phosphonic acids

2. Chemistry

The phosphorylation of amino-organic heterocyclic systems often improves their biological activity because of the P-O bond stores energy for metabolic processes [1] . Also, the chemistry of N-phosphoryl heterocyclic indicates that these compounds form dimensional polymeric chain via intermolecular P-O⁻・・・・・・⁺NH hydrogen bond [2] . Moreover, the reactivity of the dipolar ion structures of the tautomeric form of α-amino phosphonates is due to the higher electron-withdrawing properties of two phenoxy and P=O groups. Thus, the α-amino-phosphonate group has a high degree of stability against any reagent attack [3] . To deduce the aims of this work, 6-(2ʹ-Amino-5ʹ-nitrophenyl)- 3-thioxo-1,2,4-triazin-5(2H,4H)-one (1) as a starting material obtained from reflux of 5-nitroisatin with thiosemicarbazide in aq. NaOH (Scheme 1).

Fluoroacylation of compound 1 by boiling with ethyl 2,2,2-trifluoroacetate in THF yielded [22] 2,2,2-trifluoro-N-[2-(5-hydroxy-3-thioxo-2,3-dihydro-1,2,4- triazin-6-yl)-4-nitrophenyl] acetamide (2), which upon ammonilysis by reflux with liquid ammonia in ethanol produced [23] 3-amino-6-[2ʹ-(trifluoroaceta- mido-5ʹʹ-nitrophenyl)]-1,2,4-triazin-5(4H)-one (3) (Scheme 2). Condensation of compound 3 with various nitro and halogenated aromatic aldehydes in boiling ethanol yielded the corresponding Schiff bases 4 (Scheme 2).

The main aims of the present work produce a novel fluorine substituted α-amino acids containing 1,2,4-triazinone moiety. The addition of compounds with phosphorus hydrogen bonds to azomethine (HC=N-Ar) bonds provides an economical method for the synthesis of organophosphorus derivatives. Thus, the addition of diethyl phosphonate to Schiff bases by warm at 80˚C - 100˚C along 6h with a few drops of triethylamine produced [24] α-amino phosphonates 5 which upon acid hydrolysis afforded [25] the novel fluorinated α-amino phosphonic acids 6 as a vital target (Scheme 3). Formation of both compounds 5 & 4

Scheme 1. Synthesis of compounds 1 and 2.

Scheme 2. Synthesis of compounds 3 and 4a-f.

Scheme 3. Synthesis of compounds 5a-f and 6a-f.

may as they shown in Figure 1.

3. Result and Discussion

The former structures of novel fluorinated α-amino phosphonic acids have been deduced from correct their elemental analysis and spectral measurements. IR spectra of both the compounds 1-6 recorded the absorption bands ῡ at 1530, 1350 cm⁻¹for asymmetric and symmetric NO₂ groups, 3200 - 3100 and 1660 cm⁻¹ for NH and C=O of 1,2,4-triazine, also ῡ at 1630 cm⁻¹ attribute to CONH group and 1250 cm⁻¹ of C-F functional groups. IR of compound 3 showed ῡ at 3300 and 1610 cm⁻¹ stretching and bending of NH₂ group, which lacks in all the compounds 4-6. Also, the presence of ῡ at 1600 - 1580 cm⁻¹ for the exocyclic

Figure 1. Formation of compound 5 from 4.

CH=N group in the compound 4. New functional groups at ῡ 1220 - 1215 (P=O) and 1050 (P-O-R) cm⁻¹ observed in the spectrum of 5. In addition, showed ῡ at 2900 - 2880 and 1480 - 1440 cm⁻¹ for stretching and bending of CH₃ & CH₂. On the other hand, IR spectrum of 6 showed ῡ at 2730, 2680 cm⁻¹ attribute for two hydroxy groups bonded to the phosphorus atom. All the fluorinated 1,2,4-tri- azinones 2 - 6 showed a stable true hydroxy group at the position-5 of 1,2,4-tri- azines at ῡ 3500 - 3450 cm⁻¹. Presence of these hydroxy groups may be due to a large withdrawing from both NO₂, CF₃ groups via a type of H-bonding.

The H-bonding form’s of compound 2.

¹H NMR spectra of the novel fluorinated α-amino phosphonic acids give us a good indication of what those structures. Thus, ¹H NMR spectra of compound 1 exhibit δ at 3.5, 13.0, 11.8 ppm for NH₂, NH, NH of 1,2,4-triazinone, in addition to δ 8.8, 8.2, 7.9 ppm for aromatic protons. ¹H NMR spectra of 2 & 4 recorded a lack’s of NH₂ protons while showed δ at 9.22 ppm for methin proton (-CH=N-) in compound 4. Also, ¹H NMR spectrum of compound 5 showed a new resonated signal at δ 1.2(J = 6.8 Hz) and large signal 4.0 - 3.9 ppm for OCH₂CH₃ protons, with a broad signal at 3.0 - 2.95, 2.7, 2.5 and 1.05, 1.03 ppm for CH₂ & CH₃ protons. ¹H NMR spectrum of compound 6f showed lacks both NH protons which is due to a type of F….H bond while reporting the signal at 4.95 ppm attribute to OH proton. ¹H NMR spectra of all new synthetic compounds 1 - 6 recorded the δ at 11.8 ppm for internal NH of 1,2,4-triazine at position-4, and 8.55 ppm for NHCO protons. ³¹P NMR (DMSO) of the 6f exhibit resonated signals at δ 14.0 (O=P-OH) and 20.5 (P-CH) ppm. Also, ¹H NMR spectra of 6 recorded the P-CHAr proton at tow doublets at 4.55 (J_PCH = 21 Hz) and 4.64 (J_PCH = 18 Hz) ppm while that showed the P-OH protons at 3.00 ppm which supported the existence of that structures. ¹³C NMR spectrum of compound 5 supported their structure due to the presence of the characteristic carbon atoms at δ 16, 60.1, 45.2 and 177.5 ppm attributed to CH₃, CH₂, CH-P and C=O of 1,2,4-tri- azines. In addition, signals at δ 155 and 130 - 127 ppm for CONH and aromatic carbons. The aliphatic carbons CH₂, CH₃ of compound 5 disappeared in that of compound 6. Finally, mass spectrometry study of novel fluorinated α-amino phosphonic acids, for example, 6band 6f recorded a molecular ion fragments at low intensity, with base peaks at m/e 231 for (6b) and m/e 95 for (6f) attribute to α-amino phosphonic radicals (Figure 2 & Figure 3).

The higher stability of their base peak may be due to the tautomeric forms present and the free delocalization from HN to P=O centers (Figure 4).

4. Experimental

The melting point recorded on Stuart scientific SMP3 (Bibby, UK) melting point

Figure 2. Mass fragmentation pattern of compound 6b.

Figure 3. Mass fragmentation pattern of compound 6f.

Figure 4. The stability of α-amino phosphonic acids 6b.

apparatus and reported as uncorrected. A Perkin Elmer (Lambda EZ-2101) double beam spectrophotometer (190 - 1100 nm) used for recording the electronic spectra. A Perkin Elmer model RXI-FT-IR 55,529 cm⁻¹ used for recording the IR spectra. A Brucker advance DPX 400 MHz using TMS as an internal standard for recording the ¹H/¹³C NMR spectra in deuterated DMSO (δ in ppm). AGC-MS-QP 1000 Ex model used for recording the mass spectra. Hexafluorobenzene used as an external standard for ¹⁹FNMR at 84.25 MHz and ³¹P (in CDCl₃, 101.25 MHZ). Elemental analysis performed on Micro Analytical Center of National Reaches Center-Dokki, Cairo, Egypt.

6-(2ʹ-Amino-5ʹ-nitrophenyl)-3-thioxo-1,2,4-triazin-5(2H,4H)one (1) [26]

A mixture of 5-nitroisatin (0.1 mol, in 100 ml of 5% aq. NaOH) and thiosemicarbazide (0.1 mol, in 10 ml hot water) refluxed for 2 h, cooled then poured onto ice-AcOH. The solid produced filtered off, and crystallization from MeOH to give compound 1 as reddish brown solid, yield 85%, m.p. 290˚C - 291˚C. IR spectrum ῡ(cm⁻¹): 3255(NH), 3138(NH), 3082(NH), 3020(aromatic CH), 1608 (binding NH₂), 1595(C=N), 1509, 1310(asym. & sym. NO₂), 1173(C=S), 837, 817, 750 (aromatic CH). Calculated C₉H₇N₅O₃S(M⁺ 265): C, 40.75; H, 2.66; N, 26.40; S, 12.09%. Found: C, 40.34; H, 2.60; N, 26.31; S, 11.99%.

2,2,2-Trifluoro-N-[2-(5-hydroxy-3-thioxo-2,3-dihydro-1,2,4-triazin-6-yl)- 4-nitrophenyl]acetamide (2)

Equimolar amounts of compound 1 and ethyl 2,2,2-trifluoroacetate in THF (100 ml) refluxed for 4h, cooled. The solid obtained filtered off and crystallized from EtOH to give compound 2 as deep green solid, yield 76%, m.p: 270˚C - 272˚C. IR spectrum ῡ(cm⁻¹): 3448(OH), 3324, 3191(NH), 3080(aromatic CH), 1703(COCF₃), 1615(C=N), 1519, 1321(asym. & sym. NO₂), 1242(C-F), 850, 810, 780(aromatic CH). ¹H NMR(400 MHz, DMSO-d₆) δ(ppm): 14.64(s, 1H, OH), 13.72(s, 1H, NH), 12.45(s, 1H, NH), 9.1, 8.9, 8.5, 8.3(m, 4H, aromatic protons), 3.56(s, OH).¹³C NMR(100 MHz, DMSO-d₆) δ(ppm): 173.32(C=S), 153.61, 153.75(2C=O), 145.7, 143.10(C-F), 135.07(NCN), 128.0-121(aromatic carbons), 118.47, 114.54, 113.52(C₅, C₆ of 1,2,4-triazine). Calculated C₁₁H₆F₃N₅O₄S(M⁺ 361): C, 36.57; H, 1.67; F, 15.78; N, 19.39; S, 8.87%. Found: C, 36.40; H, 1.61; F, 15.49; N, 19.15; S, 8.75%.

3-Amino-6-[2ʹ-(trifluoroacetamido-5ʹʹ-nitrophenyl)]-1,2,4-triazin-5(4H) one (3)

A mixture of 2(0.1 mol) and a liquid NH₃(20 ml, 39%), with ethanol (100 ml), refluxed 6 h, cooled then poured onto ice-drops AcOH. The resulting solid, filtered off and crystallized from EtOH to give light green solid, yield 86%, m.p: 305˚C - 307˚C. IR spectrum ῡ(cm⁻¹): 3448(OH), 3323(NH), 3090(NH), 1702 (C=O), 1615(deformation NH₂), 1557(C=N), 1531, 1312(asym. & sym. NO₂), 1241(C-F), 988, 830, 749(aromatic CH), 607(C-F). ¹H NMR(400 MHz, DMSO-d₆) δ(ppm): 13.59, 12.41(each s, 2NH), 9.1(1H, OH-triazine), 8.95 - 8.60, 8.53 - 8.35 (each d, d, 2H, aromatic adjacent of NO₂), 8.27 - 8.01, 7.99 - 6.76(d, d 2H, aromatic), 3.44(s, 2H, NH₂), protons. ¹³C NMR(100 MHz, DMSO-d₆) δ(ppm): 173.3(C=O), 153, 152(C-O), 145(C-F), 153(NCN), 128 - 121(aromatic carbons), 114, 113(triazine). Calculated C₁₁H₇F₃N₆O₄(M⁺ 344): C, 38.38; H, 2.05; F, 16.56; N, 24.42%. Found: C, 38.18; H, 1.99; F, 16.36; N, 24.21%.

Schiff bases 4a-f

A mixture of 3 (0.01 mol) and (o-, m-, p-nitrobenzaldehydes, p-bromo, p-chloro, and p-fluoro benzaldehydes) (0.01 ml) refluxed in AcOH (50 ml) for 1h, cooled then poured onto ice. The yielded solids filtered off and crystallized from a suitable solvent (EtOH, MeOH & Isopropyl alcohol) to give 4a-f.

4a: Brown green solid, yield 83%, m.p: 270˚C - 272˚C. IR spectrum ῡ(cm⁻¹): 3447(OH), 3323(NH), 3080(aromatic CH), 1703(C=O), 1615(C=C), 1557(C=N), 1479(exo CH=N), 1519, 1322(asym., sym. NO₂), 1270(C-F), 927, 831, 749(aromatic CH), 607(C-F). Calculated C₁₈H₁₀F₃N₇O₆(M⁺ 477): C, 45.29; H, 2.11; F, 11.94; N, 20.54%. Found: C, 44.78; H, 2.08; F, 11.79; N, 20.27%.

4b: Deep brown solid, yield 76%, m.p: 268˚C - 270˚C. IR spectrum ῡ(cm⁻¹): 3446(OH), 3322.55(NH), 3083(aromatic CH), 1702.56(C=O), 1615.21(C=N), 1531, 1307(asym., sym. NO₂), 1478(CH=N), 1453, 1427(deformation CH=N), 1270(C-F), 1239(C-F), 987, 928, 830, 749(aromatic CH), 607(C-F). ¹H NMR(400 MHz, DMSO-d₆) δ(ppm): 10.13(s, 1H, NH), 12.42 - 12.23(NHCO), 10.13(s, 1H, CH=N), 9.2 - 8.5, 8.4 - 6.75(each d, d, 8H, aromatic protons), 3.48(s, 1H, OH). ¹³C NMR(100 MHz, DMSO-d₆) δ(ppm): 173(C=O), 153(CONH), 145(C-F), 137(CH=N), 130-123(aromatic carbons), 114, 113(carbons of 1,2,4-triazine). Calculated C₁₈H₁₀F₃N₇O₆(M⁺ 477): C, 45.29; H, 2.11; F, 11.94; N, 20.54%. Found: C, 44.89; H, 2.00; F, 11.81; N, 20.39%.

4c: Brown green solid, yield 88%, m.p: 274˚C - 276˚C IR spectrum ῡ(cm⁻¹): 3447(OH), 3324(NH), 3084(aromatic CH), 1703(C=O), 1615(C=C), 1557(C=N), 1479(exo CH=N), 1531, 1322(asym., sym. NO₂), 1270(C-F), 900, 880, 850 (aromatic CH), 610(C-F). Calculated C₁₈H₁₀F₃N₇O₆(M⁺ 477): C, 45.29; H, 2.11; F, 11.94; N, 20.54%. Found: C, 44.71; H, 2.01; F, 11.64; N, 20.12%.

4d: Brown solid, yield 79%, m.p: 260˚C - 262˚C. IR spectrum ῡ(cm⁻¹): 3448 (OH), 3324(NH), 3085(NH), 1704(C=O), 1616(C=C),1558(C=N), 1480(exo CH=N), 1515, 1324(asym. & sym. NO₂), 1272(C-F), 988, 929, 749(aromatic CH), 690(C-Br), 640(C-F). Calculated C₁₈H₁₀BrF₃N₆O₄(M⁺ 509): C, 42.29; H, 1.97; Br, 15.63; F, 11.15; N, 16.44%. Found: C, 41.97; H, 1.71; Br, 15.54; F, 10.99; N, 16.24%.

4e: Brownish yellow solid, yield 77%, m.p: 267˚C - 269˚C. IR spectrum ῡ(cm⁻¹): 3447(OH), 3320(NH), 3089(NH), 1701(C=O), 1614(C=C), 1553(C=N), 1477(exo CH=N), 1516, 1322(asym. & sym. NO₂), 1269.9(C-F), 986, 929, 749.7(aromatic CH), 688(C-Cl), 646(C-F). Calculated C₁₈H₁₀ClF₃N₆O₄(M⁺ 466): C, 46.32; H, 2.16; Cl, 7.59; F, 12.21; N, 18.01%. Found: C, 45.89; H, 2.13; Cl, 7.28; F, 11.96; N, 17.71%.

4f: Reddish brown solid, yield 84%, m.p: 271˚C - 273˚C. IR spectrum ῡ(cm⁻¹): 3446(OH), 3321(NH), 3081(NH), 1702(C=O), 1557(C=N), 1517, 1320(asym. & sym. NO₂), 1239(C-F), 928, 931, 749(aromatic CH), 647(C-F). ¹H NMR(400 MHz, DMSO-d₆) δ(ppm): 13.44(s, 1H, NH), 9.52(s, 1H, CH=N), 8.35 - 7.99 & 7.01 - 6.75(each d, d 7H, aromatic protons), 3.41(s, 1H, OH of C₅-1,2,4-triazine). ¹³C NMR(100 MHz, DMSO-d₆) δ(ppm): 173(C=O), 153, 152(C-OR), 145.7(C-F), 135(NCN of 1,2,4-triazine), 128-126(aromatic carbons), 114, 113(C₅, C₆ of 1,2,4-triazine). Calculated C₁₈H₁₀F₄N₆O₄(M⁺ 450): C, 48.01; H, 2.24; F, 16.88; N, 18.66%. Found: C, 47.83; H, 2.19; F, 16.66; N, 18.46%.

Diethyl [6-(2ʹ-trifluoroacetamido-5ʹ-nitrophenyl)-5-hydroxy-1,2,4-triazin- 3-yl]-amino-(aryl) methyl phosphonates (5a-f)

A mixture of 4a-e and/ or 4f (0.01 mol) and diethyl phosphonate (0.01 mol) in few drops of TEA, fused at 80˚C - 100˚C for 6 - 8 h, cooled the treated with dioxan. The solid obtained crystallized from a suitable solvent to give 5a-f.

5a: Deep brown solid, yield 82%, m.p: 263˚C - 265˚C. IR spectrum ῡ(cm⁻¹): 3447(OH), 3321(NH), 3085(aromatic CH), 2970(aliphatic CH), 1701(C=O), 1615(C=N), 1532, 1309(asym., sym. NO₂), 1481, 1428(deformation CH₂, CH₃), 1237(C-F), 1159(P=O), 1100(O-P-O-R), 840, 805(aromatic CH), 610(C-F). Calculated C₂₂H₂₁F₃N₇O₉P(M⁺ 615): C, 42.94; H, 3.44; F, 9.26; N, 15.93; P, 5.03%. Found: C, 42.59; H, 3.38; F, 9.15; N, 15.70; P, 4.93%.

5b: Deep brown solid, yield 78%, m.p: 260˚C - 262˚C. IR spectrum ῡ(cm⁻¹): 3433(OH), 3316(NH), 3083(aromatic CH), 2969(aliphatic CH), 1698(C=O), 1616(C=N), 1532, 1311(asym., sym. NO₂), 1481, 1428(deformation CH₂, CH₃), 1245(C-F), 1159(P=O), 1098(O-P-O-R), 860, 810(aromatic CH), 600(C-F). ¹H NMR(400 MHz, DMSO-d₆) δ(ppm): 13.59(NH), 8.37(CH-NH), 8.36 - 8.0, 7.99 - 6.76(each d, d, aromatic protons), 3.82(s, 1H, OH), 3.76 - 3.44(b, NH), 2.89, 2.53 & 1.05, 1.03(each s, 2 CH₂ & CH₃). ¹³C NMR(100 MHz, DMSO-d₆) δ(ppm): 173.3(C=O), 153, 152(C-OR), 145.80(C-F), 135(NCN), 128 - 126(aromatic carbons), 114, 113.59(C₅, C₆ of 1,2,4-triazine), 38.30(carbons of CH₂, CH₃). Calculated C₂₂H₂₁F₃N₇O₉P(M⁺ 615): C, 42.94; H, 3.44; F, 9.26; N, 15.93; P, 5.03%. Found: C, 42.66; H, 3.25; F, 9.11; N, 15.78; P, 4.85%.

5c: Brown sold, yield 87%, m.p: 270˚C - 272˚C. IR spectrum ῡ(cm⁻¹): 3446(OH), 3320(NH), 3082(aromatic CH), 2970(aliphatic CH), 1700(C=O), 1614(C=N), 1528, 1310(asym., sym. NO₂), 1477, 1427(deformation CH₂, CH₃), 1238(C-F), 1159(P=O), 1104(O-P-O-R), 850, 810(aromatic CH), 608(C-F). Calculated C₂₂H₂₁F₃N₇O₉P(M⁺ 615): C, 42.94; H, 3.44; F, 9.26; N, 15.93; P, 5.03%. Found: C, 42.69; H, 3.44; F, 9.26; N, 15.93; P, 5.03%.

5d: Deep brown solid, yield 92%, m.p: 302˚C - 305˚C. IR spectrum ῡ(cm⁻¹): 3434(OH), 3317(NH), 3081(aromatic CH), 2970(aliphatic CH), 1700(C=O), 1553(C=N), 1532, 1311(asym. & sym. NO₂), 1479, 1427(deformation aliphatic), 1242(C-F), 1223(P=O), 1100(P-O-Et) 987, 780, 749(aromatic CH), 700(C-Br), 605(C-F). Calculated, C₂₂H₂₁BrF₃N₆O₇P(M⁺ 649): C, 40.70; H, 3.26; Br, 12.31; F, 8.78; N, 12.94; P, 4.77%. Found: C, 40.39; H, 3.11; Br, 12.16; F, 8.61; N, 12.80; P, 4.66%.

5e: Black brown solid, yield 86%, m.p: 296˚C - 298˚C. IR spectrum ῡ(cm⁻¹): 3434(OH), 3317(NH), 3084(aromatic CH), 2970(aliphatic CH), 1700(C=O), 1553(C=N), 1532, 1311(asym. & sym. NO₂), 1480, 1427(deformation aliphatic), 1242(C-F), 1210(P=O), 1099(P-O-Et) 987, 780, 749(aromatic CH), 730(C-Cl), 600(C-F). Calculated C₂₂H₂₁ClF₃N₆O₇P(M⁺ 604): C, 43.69; H, 3.50; Cl, 5.86; F, 9.42; N, 13.89; P, 5.12%. Found: C, 43.48; H, 3.43; Cl, 5.57; F, 9.22; N, 13.69; P, 4.98%.

5f: Light brown solid, yield 78%, m.p: 285˚C - 287˚C. IR spectrum ῡ(cm⁻¹): 3447(OH), 3284(NH), 3198(NH), 3084(aromatic CH), 2970(aliphatic CH), 1695(C=O), 1556(C=N), 1516, 1304(asym. & sym. NO₂), 1478, 1427(deformation aliphatic), 1240(C-F), 1222(P=O), 1070(P-O-Et) 983, 787, 749(aromatic CH), 608(C-F). ¹H NMR(400 MHz, DMSO-d₆) δ(ppm): 12.25(s, 1H, NH), 10.76(s, 1H, OH), 9.9(s, 1H, CH-N), 9.05 - 8.01 & 7.99 - 6.54(each d, d 7H, aromatic protons), 3.44(s, 1H, OH), 2.52, 1.24(each m, 10H, O-CH₂CH₃).¹³C NMR(100 MHz, DMSO-d₆) δ(ppm): 173(C=O), 152(C-OH), 150(C-NH), 147(C-F), 145(C₆ of 1,2,4-triazine), 142(C-NO₂), 137(C₃ of 1,2,4-triazine)130 - 126(aromatic carbons), 116(Ar-CH-P), 113(CH₂-O), 40(CH₃-CH₂). Calculated C₂₂H₂₁F₄N₆O₇P(M⁺ 588): C, 44.91; H, 3.60; F, 12.92; N, 14.28 P, 5.26%. Found: C, 44.66; H, 3.58; F, 12.71; N, 14.11 P, 5.01%.

[((6-(5ʹ-nitro-2ʹ-(2ʹʹ,2ʹʹ,2ʹʹ-trifluoroacetamido)phenyl)-5-oxo-2,5-dihydro-1,2,4-triazin-3-yl)amino)(phenyl)methyl]phosphonic acids(6a-f)

A mixture of 5 (0.01 mol) and dil. HCl (10 ml, 5%) refluxed for 2 h, cooled, then neutralized with diluted NaHCO₃. The solid poured, filtered off and crystallized from suitable solvents to give (6a-f).

6a: Brown solid, yield 85%, m.p: 282˚C - 284˚C. IR spectrum ῡ(cm⁻¹): 3446(OH), 3321(NH), 3080(aromatic CH), 2970(aliphatic CH), 1701(C=O), 1614(C=N), 1557, 1305(asym., sym. NO₂), 1269(C-F), 1160(P=O), 1090(O-P-O), 980, 840(aromatic CH), 610(C-F). Calculated C₁₈H₁₃F₃N₇O₉P(M⁺ 559): C, 38.65; H, 2.34; F, 10.19; N, 17.53; P, 5.54%. Found: C, 38.41; H, 2.08; F, 9.99; N, 17.30; P, 5.28%.

6b: Brown solid, yield 94%, m.p: 289˚C - 291˚C. IR spectrum ῡ(cm⁻¹): 3447(OH), 3323(NH), 1702(C=O), 1615(C=N), 1531, 1308(asym., sym. NO₂), 1270(C-F), 1159(P=O), 1090(O-P-O), 987, 850(aromatic CH), 606(C-F). ¹H NMR(400 MHz, DMSO-d₆) δ(ppm): 13.5, 13.19, 12.24(each s, 3NH), 9.0(s, 1H, CH-P), 8.61 - 8.14, 7.98 - 6.75(each d, d, 7H, aromatic protons), 5.95(s, 1H, P-OH). ¹³C NMR(100 MHz, DMSO-d₆) δ(ppm): 173.3(C=O), 153, 152(C-O), 145.80(C-F), 135.1(NCN), 128.02 - 126.68(aromatic carbons), 114.48, 113.48 (carbons of 1,2,4-triazine). Calculated C₁₈H₁₃F₃N₇O₉P(M⁺ 559): C, 38.65; H, 2.34; F, 10.19; N, 17.53; P, 5.54%. Found: C, 38.38; H, 2.11; F, 9.98; N, 17.35; P, 5.39%. M/S(Int.%): 555(M+3, 1.00), 234(11.11), 231(100), 136(18.2), 69(5.00).

6c: Deep brown solid, yield 88%, m.p: 273˚C - 275˚C. IR spectrum ῡ(cm⁻¹): 3446(OH), 3323(NH), 3078(aromatic CH), 2970(aliphatic CH), 1704(C=O), 1615(C=N), 1555, 1307(asym., sym. NO₂), 1271(C-F), 1158(P=O), 1093(O-P-O), 970, 825(aromatic CH), 604(C-F). Calculated C₁₈H₁₃F₃N₇O₉P(M⁺ 559): C, 38.65; H, 2.34; F, 10.19; N, 17.53; P, 5.54%. Found: C, 38.40; H, 2.13; F, 10.01; N, 17.40; P, 5.33%.

6d: Deep brown solid, yield 78%, m.p: 251˚C - 253˚C. IR spectrum ῡ(cm⁻¹): 3447(OH), 3323(NH), 3080(aromatic CH), 2970(aliphatic CH), 1702(C=O), 1614(C=N), 1557, 1304(asym. & sym. NO₂), 1269(C-F), 1218(C-P=O), 1060 (P-O-H) 975, 900, 880, 790(aromatic CH), 729(C-Br), 600(C-F). Calculated C₁₈H₁₃BrF₃N₆O₇P(M⁺ 593): C, 36.45; H, 2.21; Br, 13.47; F, 9.61; N, 14.17; P, 5.22%. Found: C, 36.15; H, 2.15; Br, 13.47; F, 9.39; N, 14.05; P, 5.11%.

6e: Deep brown solid, yield 74%, m.p: 263˚C - 265˚C. IR spectrum ῡ(cm⁻¹): 3446(OH), 3321(NH), 3080(aromatic CH), 2970(aliphatic CH), 1702(C=O), 1615(C=N), 1557, 1307(asym. & sym. NO₂), 1269(C-F), 1219(C-P=O), 1060 (P-O-H) 980, 900, 870, (aromatic CH), 748(C-Cl), 605(C-F). Calculated C₁₈H₁₃ClF₃N₆O₇P(M⁺ 548): C, 39.40; H, 2.39; Cl, 6.46; F, 10.39; N, 15.32; P, 5.64%. Found: C, 39.15; H, 2.19; Cl, 6.31; F, 10.15; N, 15.20; P, 5.45%.

6f: Brown solid, yield 83%, m.p: 245˚C - 247˚C. IR spectrum ῡ(cm⁻¹): 3448(OH), 3325(NH), 3088(NH), 1703(C=O), 1616(C=N), 1517, 1324(asym. & sym. NO₂), 1240(C-F), 1216(C-P=O), 1060(P-O-H) 988, 910, 880, 790(aromatic CH), 607(C-F). ¹H NMR(400 MHz, DMSO-d₆) δ(ppm): 8.35(s, 1H, CH-N), 8.04 - 7.48 & 7.47 - 6.75(each d, d, 7H, aromatic protons), 4.98(s, 1H, OH), 4.95(s, 1H, OH), 4.011(s, 1H, OH). ¹³C NMR(100 MHz, DMSO-d₆) δ(ppm): 173.44 (C=O), 153, 152(C-O), 145.81(C-F), 135.12(NCN), 129.28 - 126.47(aromatic carbons), 114.68, 113.67(C₅, C₆ of 1,2,4-triazine). Calculated C₁₈H₁₃F₄N₆O₇P(M⁺ 532): C, 40.62; H, 2.46; F, 14.28; N, 15.79; P, 5.82%. Found: C, 40.45; H, 2.30; F, 14.12; N, 15.56; P, 5.69%. M/S(Int.%): 534(M+2, 5.18), 234(43.1), 204(80.33), 136(22.15), 121(8.9), 96(12.15), 95(100).

5. The Antioxidant Evaluation

1,1-Diphenyl-2-picrylhydrazyl (DPPH) use to produce and reduce the odd electron stable-free radical which showed a strong UV-absorption maximum at λ = 517 nm. The new systems obtained dissolved in DMSO/EtOH at 150 & 300 μmol∙L⁻¹ added to DPPH at 100 μmol∙L⁻¹. The tube kept at room temperature for 20 minutes and the absorption measured at λ 517 nm. The difference between the test and the control taken as the percent scavenging of the DPPH radical by use the formula: % inhibition = $\left(AB-AA\right)/AB\times 100$

where AB: absorption of blank; AA: absorption of the tested compound. The radical scavenging activity of ascorbic acid also measured and compared with that of the different synthesized compounds [27] . The observed data on the antioxidant-activated of the compounds and control shown in Table 1.

From the results obtained (Table 1) we can conclude that:

Presence of CF₃ and NO₂ of 6-aryl-1,2,4-triazinone and α-amino phosphonate bearing 3-substituted amino-1,2,4-triazinones deployed a good to perfect scavenging activities. The ordering activity is 6f > 6e > 6d > 6b > 6a > 6c, which mainly attribute to the presence of C-halogen and C-NO₂ of aryl-amino derivatives. The activity of α-amino phosphonic acids 6 is higher than the activity of α-amino phosphonates 5. Also, high activity of 6f comparing with the other systems is may be due to a rich of fluorine atoms bonded to a 1,2,4-triazinone moiety, and the phosphonate groups are the potent antioxidant agent.

6. Conclusion

In the search for new antioxidant agents, the present work reports a simple route to synthetic novel fluorine substituted nitroaryl-1,2,4-triazine bearing α-amino phosphonic acids. Presence of rich aliphatic/aromatic fluorine atoms and nitro

Table 1. The DPPH radical scavenging activity of the novel fluorinated α-amino phosphonates and the related α-amino phosphonic acids at 150 and 300 μmol∙L⁻¹.

groups bonded to 1,2,4-triazinone bearing α-amino phosphonic acids enhance the antioxidant activities, which may use the feature of medicinal treatments.

Conflicts of Interest

The authors declare no conflicts of interest.

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