Journal of Chemistry
Volume 2017 (2017), Article ID 5373049, 7 pages
https://doi.org/10.1155/2017/5373049

Research Article

Synthesis and Pharmacological Activities of Pyrano[2,3-d]pyrimidine and Pyrano[2,3-d]pyrimidine-5-one Derivatives as New Fused Heterocyclic Systems

Naglaa F. H. Mahmoud, Eman A. El-Bordany, and Galal A. Elsayed

Chemistry Department, Faculty of Science, Ain Shams University, Abbassia, Cairo 11566, Egypt

Correspondence should be addressed to Naglaa F. H. Mahmoud; naglaa.fawzy@yahoo.com

Received 7 April 2017; Revised 28 May 2017; Accepted 8 June 2017; Published 17 July 2017

Academic Editor: Orazio Nicolotti

Copyright © 2017 Naglaa F. H. Mahmoud et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Various fused oxazine such as 4-(4-methoxyphenyl)-3,7-dimethyl-1,4-dihydro-5H-pyrazolo [4′,3′:5,6]pyrano[2,3-d][]oxazin-5-one 2 has been prepared and utilized as a starting material for novel pyrazolopyranopyrimidinones 3, 5, 6, and 7a–c and pyrazolopyranopyrimidines 4, 9, 10, and 11 which are expected to possess considerable chemical and pharmacological activities. The structures of the new compounds have been elucidated by spectroscopic data and elemental analysis. The antioxidant and anticancer activities of synthesized products have been evaluated.

1. Introduction

Heterocyclic compounds are one of the most important molecules in the synthesis of pharmacologically active compounds [1–4]. Enaminonitriles have been utilized as starting materials for synthesis of huge number of heterocyclic compounds containing pyranopyrimidine [5–9] and pyridopyrimidine [10–13] moieties. Oxazines [14] and quinazolines [15] are natural products which exhibit a widespread spectrum of biological activity including antitumor [16–18], anti-inflammatory [19], and antiplatelet [20] properties. In view of these reports and as a continuation of our previous work on heterocyclic chemistry [21–27], we aimed to incorporate the pyrano moiety into the 1,5-position of oxazinone and pyrimidinone ring systems to obtain new heterocyclic system which is anticipated to possess notable chemical and pharmacological activities. So we utilized enaminonitrile in the synthesis of pyrano[2,3-d][]oxazin-5-one derivative and pyrano[2,3-d]pyrimidine and pyrano[2,3-d]pyrimidine-5-one derivatives in addition to studying their antioxidant activities.

2. Results and Discussion

2.1. Chemistry

Our present investigation aimed to synthesize of 6-amino-4-(4-methoxyphenyl)-3-methyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile 1 [28], which was used as a precursor for the synthesis of previously unreported 4-(4-methoxyphenyl)-3,7-dimethyl-1,4-dihydro-5H-pyrazolo[4′,3′:5,6]pyrano[2,3-d][]oxazin-5-one 2 as new heterocyclic compound containing oxazine and pyranopyrazole moieties. Compound 1 has been prepared by four-component one-pot reaction [29] and three-component one-pot reaction [30] (Scheme 1).

Scheme 1

Treatment of 1 by freshly distilled acetic anhydride afforded 2 as a sole product. The structure of 2 was elucidated by spectral analysis. The IR spectrum showed a strong absorption band at 1732 cm⁻¹ corresponding to lactonic carbonyl group and the disappearance of the cyano group. Also the structure was confirmed by elemental analysis; ¹H-NMR spectrum showed a singlet at δ 12.52 ppm of NH, a doublet at δ 7.162–7.136 ppm and δ 6.84–6.81 ppm of aromatic protons, a singlet at δ 4.7 ppm of benzylic proton, and a singlet at δ 3.68 ppm of three protons for OCH₃ group. Ammonolysis of 2 by fusion with ammonium acetate and/or formamide afforded 4-(4-methoxyphenyl)-3,7-dimethyl-4,6-dihydro-pyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-5(1H)-one 3. The structure of 3 was confirmed by the IR spectrum which exhibited strong absorption bands at 3200, 3281, 1664, and 1610 cm⁻¹ corresponding to , , and , respectively and lacked a band corresponding to lactonic carbonyl group and also the presence of acidic hydrogen in the ¹H-NMR spectrum at δ 12.38. The electrophilicity of the lactonic carbonyl group of compound 2 was studied by nucleophilic reaction with 1,2-diaminobenzene and thiosemicarbazide, as 1,4-dinucleophile, to afford 4-(4-methoxyphenyl)-3,7-dimethyl-4-hydrobenzimidazolo[1,2,c]pyrazolo[4′3′:5,5]pyrano[2,3-d]pyrimidine 4 and N-[4-(4-methoxyphenyl)-3,7-dimethyl-5-oxo-1,4-dihydro-pyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidin-6(5H)-yl]thiourea 5, as sole products. The pyrazolopyranopyrimidine derivative 4 was formed via ring opening of the oxazine ring by an amino group followed by ring closer and then dehydration with the other amino group. The IR spectrum of compound 4 showed strong absorption bands at 3180 and 1609 cm⁻¹ corresponding to and . The IR spectrum of compound 5 showed well defined absorption bands at 3251, 3158, 3121, 1665, 1619, and 1254 cm⁻¹ corresponding to , , , , and . Compound 2 was allowed to react with primary amines, namely, hydrazine hydrate, 4-methylaniline, 4-methoxyaniline, and/or 4-aminoaniline, to afford the pyrazolopyranopyrimidine derivatives 6 and 7a–c, respectively (Scheme 2).

Scheme 2

4-(4-Methoxyphenyl)-3,7dimethy-l-4,6-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidin-5(1H)-thione 8 was synthesized by sulfurization of 3 using Lawson’s reagent or by reaction of thiourea with 5-chloro-4-(4-methoxyphenyl)-3,7-dimethyl-1,4-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine 9. Compound 9 was prepared by chlorination of 3 by POCl₃ and PCl₅ mixture. Hydrazinolysis of 9 afforded 5-hydrazino-4-(4-methoxyphenyl)-3,7-dimethyl-1,4-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine 10.

IR spectrum of compound 10 showed strong absorption bands at 3215, 3156, 3161, and 1612 cm⁻¹ corresponding to , , and . Also the structure was confirmed by ¹H-NMR spectrum that showed a singlet at δ 12.01 ppm of NH, multiplet at δ 7.83 ppm of aromatic protons, a singlet at δ 4.8 ppm of benzylic proton, a singlet at δ 3.7 ppm of three protons for OCH₃ group, and a singlet at δ 5.354 of NH₂.

Acetylation of 10 by refluxing with acetic anhydride gave the diacetyl derivative 11 and not the expected triazolo derivative 12. The structure of 11 was confirmed by the spectral data such as the IR which showed the absorbance for the carbonyl group at 1732 and 1695 cm⁻¹ and the two methyl groups signals at δ 2.678 ppm for 2CH₃ in ¹H-NMR spectrum (Scheme 3).

Scheme 3

2.2. Pharmacological Activity

Antioxidant activity using 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) inhibition. The prepared compounds were tested for antioxidant activity as reflected in their ability to inhibit oxidation in rat brain and kidney homogenates, from the result in Table 1. Compounds 1, 4, 7a, and 10 exhibit a similar antioxidant activity to ascorbic acid, used as standard. Compounds 8 and 11 exhibited moderate antioxidant activity, while 2, 3, 7b, 5, and 9 showed lower activity.

Table 1: The antioxidant activities of the synthesized compounds.

Compound number
Antioxidant activity
Bleomycin dependent DNA damage

Absorbance
Inhibition %

1
0.111
78.6
0.098

2
0.427
17.9
0.127

3
0.419
19.4
0.135

4
0.062
88.1
0.083

5
0.393
24.4
0.138

7a
0.083
84.0
0.091

7b
0.428
17.7
0.151

8
0.274
47.3
0.089

9
0.446
14.2
0.142

10
0.060
88.5
0.066

11
0.355
31.7
0.112

Ascorbic acid
0.065
89.2
0.076

ABTS
0.520
—
—

Bleomycin Dependent DNA Damage. The bleomycins are a family of glycopeptides antibiotics [31] that are routinely used as antitumor agents. The bleomycin assay has been adopted for assessing the prooxidant activity of food antioxidants. The antitumor antibiotic bleomycin binds iron ions and DNA. If the samples are able to reduce bleomycin–Fe³⁺ to bleomycin–Fe, DNA degradation in the system will be stimulated, resulting in a positive test for prooxidant activity. DNA degradation is accompanied by the formation of a product similar to malondialdehyde.

L-Ascorbic acid was used as the reducing agent to reduce Fe³⁺ to Fe²⁺. The synthesized compounds were selected for bleomycin dependent DNA damage testing (Table 1).

Results in Table 1 showed that compounds 1, 4, 7a, 8, and 10 have the ability to protect DNA from the damage induced by bleomycin. On the other hand, the rest of the compounds exhibited weak activities.

Cytotoxic Activity of Some Compounds against Human Tumor Cells. The prepared compounds were tested for cytotoxic activity against four human tumor cells. Best results were observed for compounds 1, 4, 7a, and 10 which were found to very strong cytotoxic compounds. Compound 8 was also considered strongly cytotoxic. Finally, compounds 3, 5, and 11 were moderate in their cytotoxic activity and compounds 2, 7b, and 9 were weakly cytotoxic (Table 2).

Table 2: The cytotoxic activity of some compounds against human tumor cells.

Compounds
In vitro cytotoxicity IC50 (µg/ml)

HePG2
HCT-116
PC3
MCF-7

5-FU

1

2

>100
>100

3

4

5

7a

7b

>100

8

9

10

11

IC50 (µg/ml): 1–10 (very strong), 11–20 (strong), 21–50 (moderate), 51–100 (weak), and above 100 (noncytotoxic); 5-FU = 5-fluorouracil.

2.3. Experimental

All melting points were measured on a Gallenkamp electric melting point apparatus and are uncorrected. The infrared spectra were recorded in potassium bromide disks on a pyeUnicam SP-3-300 and Shimdazu FTIR 8101 PC infrared spectrophotometers.

The ¹H-NMR and ¹³C-NMR were recorded at a Varian Mercury VX-300 MHz and 75 MHz, respectively, using TMS as internal standard in deuterated chloroform (CDCl₃) or deuterated dimethyl sulfoxide (DMSO-d6). Chemical shifts are measured in ppm. The mass spectra were recorded on a Shimadzu GCMS-QP-1000EX mass spectrometer at 70 eV. Elemental analyses were carried out at the Microanalytical Center of Cairo University. All the reactions and the purity of the new compounds were followed and checked by TLC using TLC aluminum sheets silica gel F₂₅₄.

2.4. Synthesis of 6-Amino-4-(4-methoxyphenyl)-3-methyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (1)

Method 1. An equimolar mixture of anisaldehyde (10 mmol, 1.36 mL), ethyl acetoacetate (10 mmol, 1.3 mL), hydrazine hydrate (0.5 mL), and malononitrile (10 mmol, 0.66 g) was stirred for 30 min at room temperature in the presence of triethyl amine and water (5 ml). The precipitate was filtered off and recrystallized from ethanol, yield (81%).

Method 2. A mixture of 3-methyl-5-pyrazolone (10 mmol, 0.98 g) and arylidine (10 mmol, 1.1 g) was refluxed in (30 mL) ethanol and 5 drops of piperidine for 2 h. The precipitate was filtrated off and recrystallized from ethanol to give solid 1, yield (87%).

Method 3. A mixture of 3-methyl-5-pyrazolone (10 mmol, 0.98 g), anisaldehyde (10 mmol, 1.36 mL), and malononitrile (10 mmol, 0.66 g) was refluxed in (30 mL) ethanol in presence of 5 drops of piperidine for 2 h. The precipitate was filtrated off and recrystallized from ethanol to give solid 1, yield (80%)

2.5. Synthesis of 4-(4-Methoxyphenyl)-3,7-dimethyl-1,4-dihydro-5H-pyrazolo[4′,3′:5,6]pyrano[2,3-d][1,3]oxazin-5-one (2)

A mixture of 1 (10 mmol, 2.82 g) and freshly distilled acetic anhydride (20 mL) was heated under reflux for 3 h. The solid that deposited after distilling the excess solvent was collected and recrystallized from ethanol to give (2).

m.p. over 300°C. Anal. Calcd. for C₁₇H₁₅N₃O₄ (325.32): C, 62.76; H, 4.65; N, 12.92. Found: C, 63.07; H, 4.29; N, 13.10. FTIR (KBr) (cm⁻¹): 3157 (NH), 1732 (C=O), 1624 (C=N), 1606 (C=C). ¹H-NMR (DMSO-d ₆): (ppm) 12.52 (s, 1H, NH, D₂O exchangeable), 7.162–7.136 (d, , 2H, Ar-H), 6.84–6.81 (d, , H, Ar-H), 4.7 (s, 1H, benzylic proton), 3.68 (s, 3H, OCH₃), 2, 16 (s, 3H, CH₃) and 1.831 (s, 3H, CH₃). ¹³C-NMR (75 MHz, DMSO-d ₆):δ 173.7, 165, 163.4, 161.9, 157.2, 138.6, 134.2, 130.3, 130.3, 114.4, 114.5, 112.9, 99.8, 55.5, 34.4, 15.7, 13.4. MS, m/z (%): 325 (M•+, 6), 281 (27), 241 (13), 218 (100), 107 (28).

2.6. Synthesis of 4-(4-Methoxyphenyl)-3,7-dimethyl-4,6-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-5-(1H)-one (3)

A mixture of 2 (10 mmol, 3.25 g) and formamide (10 mL) or excess ammonium acetate was refluxed for 4 h. After cooling white solid was collected, washed with water, dried, and recrystallized from benzene: ethanol mixture (1 : 1) to give (3).

m.p. over 300°C Anal. Calcd. for C₁₇H₁₆N₄O₃ (324.33): C, 62.95; H, 4.97; N, 17.27. Found: C, 62.07; H, 4.92; N, 17.10. FTIR (KBr) (cm⁻¹): 3200, 3281 (NH), 1664 (C=O), 1610 (C=N) ¹H-NMR (DMSO-d ₆): (ppm) 12.381 (s, 1H, NH, D₂O exchangeable), 12.01 (s, 1H, NH, D₂O exchangeable), 7.359–7.334 (d, , 2H, Ar-H), 6.790–6.762 (d, , 2H, Ar-H), 4.899 (s, 1H, benzylic proton), 3.668 (s, 3H, OCH₃), 2.176 (s, 3H, CH₃) and 1.791 (s, 3H, CH₃). MS, m/z (%): 324 (M•+, 16), 281 (19), 240 (24), 217 (100), 107 (51).

2.7. Synthesis of 4-(4-Methoxyphenyl)-3,7-dimethyl-4-hydrobenzoimidazolo[1,2-c]pyrazolo[4′,3′:5,5]pyrano[3,2-d]pyrimidine (4)

A mixture of 2 (10 mmol, 3.25 g) and 2-amino aniline (10 mmol, 1.08 g) in n-butanol (20 mL) was heated under reflux for 4 h. The solid that separated after concentration and cooling was filtered off and recrystallized from petroleum ether at 60–80°C.

m.p. 102–104°C Anal. Calcd. For C₂₃H₁₉N₅O₂ (397): C, 69.51; H, 4.82; N, 17.62. Found: C, 69.26; H, 4.78; N, 17.23. FTIR (KBr) (cm⁻¹): 3180 (NH), 1609 (C=N) ¹H-NMR (DMSO-d ₆): (ppm) 11.252 (s, 1H, NH, D₂O exchangeable), 8.023–7.215 (m, 8H, Ar-H), 5.099 (s, 1H, benzylic proton), 3.212 (s, 3H, OCH₃), 2.801 (s, 3H, CH₃) and 2,176 (s, 3H, CH₃). MS, m/z (%): 395 (M•+, 7), 317 (9), 290 (12), 267 (10), 181 (25), 80 (100).

2.8. Synthesis of N-[4-(4-Methoxyphenyl)-3,7-dimethyl-5-oxo-1,4-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-6(5H)-yl]thiourea (5)

A mixture of 2 (10 mmol, 3.25 g) and thiosemicarbazide (10 mmol, 0.91 g) in dimethylformamide (20 mL) was heated under reflux for 6 h. The solid that was separated after concentration and cooling was filtered off, washed with water, and recrystallized from ethanol to give (5).

m.p. 265–267°C Anal. Calcd. for C₁₈H₁₈N₆O₃S (398.44): C, 54.26; H, 4.55; N, 21.09; S, 8.05. Found: C, 53.70; H, 4.19; N, 20.83. FTIR (KBr) (cm⁻¹): 3251, 3158, 3121 (NH₂, NH), 1665 (CO), 1619 (C=N) and 1254 (C=S). ¹H-NMR (DMSO-d ₆): (ppm) 11.912 (s, 1H, NH, D₂O exchangeable), 7.923–7.751 (m, 4H, Ar-H), 8.213 (s, 1H, NH, D₂O exchangeable), 6.754 (s, 2H, NH₂, D₂O exchangeable), 5.013 (s, 1H, benzylic proton), 3.934 (s, 3H, OCH₃), 2.178 (s, 3H, CH₃) and 1.987 (s, 3H, CH₃). ¹³C-NMR (75 MHz, DMSO-d ₆):δ182.7, 163.2, 161.9, 160.3, 158.5, 157.1, 139.8, 135.2, 130.3, 130.3, 114.6, 114.6, 113.8, 102.9, 55.9, 35.7, 22.3, 13.3,. MS, m/z (%): 398 (M•+, 23), 323 (20), 291 (18), 107 (100), 75 (21).

2.9. Synthesis of 6-Amino-4-(4-methoxyphenyl)-3,7-dimethyl-4,6-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidin-5(1H)-one (6)

To a solution of 2 (10 mmol, 3.25 g) in 20 mL of ethanol, hydrazine hydrate (0.5 mL) was added. The reaction mixture was refluxed for 4 h. The separated solid was filtered, dried, and recrystallized from ethanol to give (6).

m.p. 268–290°C Anal. Calcd. for C₁₇H₁₇N₅O₃ (339.35): C, 60.17; H, 5.05; N, 20.64. Found: C, 60.07; H, 4.94; N, 20.53. FTIR (KBr) (cm⁻¹): 3325, 3210, 3154 (NH₂, NH), 1669 (CO), 1609 (C=N). ¹H-NMR (DMSO-d ₆): (ppm) 12.012 (s, 1H, NH, D₂O exchangeable), 7.632–7.115 (m, 4H, Ar-H), 6.845 (s, 2H, NH₂, D₂O exchangeable), 5.013 (s, 1H, benzylic proton), 3.798 (s, 3H, OCH₃), 2.867 (s, 3H, CH₃) and 1.872 (s, 3H, CH₃). MS, m/z (%): 322 (M•+ -NH₃, 23), 282 (19), 240 (10), 80 (100).

2.10. General Procedure for the Synthesis of Pyrazolopyranopyrimidine (7a–c)

A solution of 2 (10 mmol, 3.25 g) in dimethylformamide (20 mL) and (10 mmol) of 4-methyl aniline, 4-methoxyaniline, and/or 4-amino aniline was heated under reflux for 5 h. The solid that was separated out after concentration and cooling was recrystallized from the proper solvent to give (7a–c).

2.11. 4-(4-Methoxyphenyl)-3,7-dimethyl-6-(p-tolyl)-4,6-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidin-5(1H)-one (7a)

Solvent: ethanol m.p. 278–280°C. Anal. Calcd. for C₂₄H₂₂N₄O₃ (414.46): C, 69.55; H, 5.35; N, 13.52. Found: C, 68.67; H, 4.89; N, 12.98. FTIR (KBr) (cm⁻¹): 3191 (NH), 1682 (CO), 1608 (C=N). ¹H-NMR (DMSO-d ₆): (ppm) 10.972 (s, 1H, NH, D₂O exchangeable), 7.963–7.785 (m, 8H, Ar-H), 4.876 (s, 1H, benzylic proton), 3.912 (s, 3H, OCH₃), 2.911 (s, 3H, CH₃) and 2.176 (s, 3H, CH₃) and 1.987 (s, 3H, CH₃). MS, m/z (%): 414 (M•+, 17), 386 (8), 307 (19), 107 (100).

2.12. 4,6-Bis(4-methoxyphenyl)-3,7-dimethyl-4,6-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidin-5(1H)-one (7b)

Solvent: ethanol. m.p. over 300°C Anal. C; alcd. for C₂₄H₂₂N₄O₄ (430.46): C, 66.97; H, 5.15; N, 13.02. Found: C, 66.17; H, 4.98; N, 13.41 FTIR (KBr) (cm⁻¹): 3154 (NH), 1685 (CO), 1611 (C=N). ¹H-NMR (DMSO-d ₆): (ppm) 11.241 (s, 1H, NH, D₂O exchangeable), 8.054–7.815 (m, 8H, Ar-H), 5.045 (s, 1H, benzylic proton), 3.912 (s, 6H, 2 OCH₃), 2.832 (s, 3H, CH₃), 2.092 (s, 3H, CH₃) and 1.898 (s, 3H, CH₃). MS, m/z (%): 430 (M•+, 8), 402 (7), 295 (19), 80 (100).

2.13. 6-(4-Aminophenyl)-4-(methoxyphenyl)-3,7-dimethyl-4,6-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidin-5(1H)-one (7c)

Solvent: dioxane. m.p. over 300°C Anal. Calcd. for C₂₃H₂₁N₅O₃ (415.44): C, 66.49; H, 5.09; N, 16.86. Found: C, 66.16; H, 4.92; N, 16.16. FTIR (KBr) (cm⁻¹): 3312, 3215, 3145 (NH₂, NH), 1679 (CO), 1611 (C=N). ¹H-NMR (DMSO-d ₆): (ppm) 9.471 (s, 1H, NH, D₂O exchangeable), 7.439–7.005 (m, 8H, Ar-H), 6.450 (s, 2H, NH₂, D₂O exchangeable), 4.713 (s, 1H, benzylic proton), 3.803 (s, 3H, OCH₃), 2.367 (s, 3H, CH₃) and 1.912 (s, 3H, CH₃). MS, m/z (%): 415 (M•+, 10), 398 (9), 372 (20), 77 (100).

2.14. Synthesis of 4-(4-Methoxyphenyl)-3,7-dimethyl-4,6-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine-5(1H)-thione (8)

A mixture of 9 (10 mmol, 3.4 g) and thiourea (10 mmol, 0.76 g) in ethanol (20 mL) was heated under reflux for 6 h. The separated solid was filtered, dried, and recrystallized from ethanol to give (8).

m.p. 218–220°C. Anal. Calcd. for C₁₇H₁₆N₄O₂S (340): C, 59.98; H, 4.74; N, 16.46. Found: C, 60.03; H, 4.91; N, 16.10. FTIR (KBr) (cm⁻¹): 3158, 3121 (NH), and 1225 (C=S). ¹H-NMR (DMSO-d ₆): (ppm) 11.912 (s, 1H, NH, D₂O exchangeable), 10.112 (s, 1H, NH, D₂O exchangeable), 7.923–7.751 (m, 4H, Ar-H), 4.731 (s, 1H, benzylic proton), 3.876 (s, 3H, OCH₃), 2.112 (s, 3H, CH₃) and 1.831 (s, 3H, CH₃). MS, m/z (%): 340 (M•+, 16), 281 (19), 241 (23), 233 (100), 107 (18).

2.15. Synthesis of 5-Chloro-4-(4-methoxyphenyl)-3,7-dimethyl-1,4-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine (9)

A mixture of 3 (10 mmol, 3.24 g), phosphorus oxychloride (15 mL), and phosphorus pentachloride (150 mmol, 3.13 g) was heated in water bath at 80°C for 8 h. The reaction mixture after cooling was poured onto crushed ice and the solid obtained was filtered off and recrystallized from ethanol to give pale brown solid (9).

m.p. 198–200°C. Anal. Calcd. for C₁₇H₁₅ClN₄O₂ (342): C, 59.57; H, 4.41; N, 10.34. Found: C, 58.97; H, 3.95; N, 10.10. FTIR (KBr) (cm⁻¹): 3123 (NH), 1620 (C=N) ¹H-NMR (DMSO-d ₆): (ppm) 12.012 (s, 1H, NH, D₂O exchangeable), 7.832–7.615 (m, 4H, Ar-H), 4.832 (s, 1H, benzylic proton), 3.843 (s, 3H, OCH₃), 2.546 (s, 3H, CH₃) and 1.687 (s, 3H, CH₃). MS, m/z (%): 342 (M•+, 10), 344 (25), 235 (12), 237 (30), 214 (28), 201 (100), 107 (30).

2.16. Synthesis of 5-Hydrazino-4-(4-methoxyphenyl)-3,7-dimethyl-1,4-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine (10)

A mixture of 9 (10 mmol, 3.4 g) and hydrazine hydrate (0.5 mL) in (30 mL) ethanol was heated under reflux for 5 h. The solid separated after concentration and cooling was filtered off and recrystallized from ethanol to give (10).

m.p. 243–245°C Anal. Calcd. for C₁₇H₁₈N₆O₂ (338.36): C, 60.34; H, 5.36; N, 24.84. Found: C, 61.07; H, 5.23; N, 24.73. FTIR (KBr) (cm⁻¹): 3215, 3156, 3161 (NH₂, NH), 1612 (C=N) and. ¹H-NMR (DMSO-d ₆): (ppm) 12.012 (s, 1H, NH, D₂O exchangeable), 8.123–7.836 (m, 4H, Ar-H), 6.013 (s, 1H, NH, D₂O exchangeable), 5.354 (s, 2H, NH₂, D₂O exchangeable), 4.803 (s, 1H, benzylic proton), 3.734 (s, 3H, OCH₃), 2,576 (s, 3H, CH₃) and 2.087 (s, 3H, CH₃). MS, m/z (%): 338 (M•+, 12), 307 (21), 244 (11), 201 (100), 107 (18).

2.17. Synthesis of 5-(2N,N-diacetylhydrazino)-4-(4-methoxyphenyl)-3,7-dimethyl-1,4-dihydropyrazolo[4′,3′:5,6]pyrano[2,3-d]pyrimidine (11)

A mixture of 10 (10 mmol, 3.3 g) was heated under reflux with 30 mL of fresh distilled acetic anhydride for 8 h. The excess acetic anhydride was removed by distillation and the separated product was filtered off and recrystallized from ethanol to give (11).

m.p. 278–280°C Anal. Calcd. for C₂₁H₂₂N₆O₄ (422.44): C, 59.71; H, 5.25; N, 19.81. Found: C, 60.17; H, 4.96; N, 19.23. FTIR (KBr) (cm⁻¹): 3211, 3198 (NH), 1732, 1695 (CO), and 1619 (C=N). ¹H-NMR (DMSO-d ₆): (ppm) 12.901 (s, 1H, NH, D₂O exchangeable), 7.902–7.714 (m, 4H, Ar-H), 6.213 (s, 1H, NH, D₂O exchangeable), 5.630 (s, 1H, benzylic proton), 3.919 (s, 3H, OCH₃), 2.013 (s, 3H, CH₃), 2.678 (s, 6H, 2CH₃) and 1.987 (s, 3H, CH₃). ¹³C-NMR (75 MHz, DMSO-d₆): δ 176.6, 174.6, 173.8, 171.8, 163.5, 160.2, 157.2, 138.7, 130.7, 130.0, 130.0, 114.6, 114.6, 113.1, 98.2, 56.0, 39.3, 25.2, 21.4, 21.4, 12.8. MS, m/z (%): 422 (M•+, 13), 322 (17), 307 (100), 201 (23), 107 (28), 101 (16).

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

The authors would like to express their appreciation for Ain Shams University.

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