Utility of 2-furan-2-yl-4-mercapto-6-methylpyrimidine-5-carbonitrile as a precursor for the synthesis of some novel pyrimidines: antibacterial activity

Abstract

The starting material 2-furan-2-yl-4-mercapto-6-methylpyrimidine-5-carbonitrile 3 was reacted with various reagents resulting in the formation of a group of new pyrimidines and condensed pyrimidines including quinazoline 6 tetrazolopyrimidine 12, pyrazolopyrimidines 14, 18, and 19, triazolopyrimidine 16, and pyrimidopyridazine 20. The antibacterial activity was evaluated for a group of the synthesized compounds against examples of Gram-positive and Gram-negative bacteria.

Introduction

The chemistry of pyrimidines still attracts the attention and interest of researchers around the world because of their wide applications, especially in the therapeutic field. The literature survey showed that a wide range of pharmacological activities are exhibited by the compounds containing pyrimidine nucleus in their structures, for example, pyrimidines are used for antibacterial [1,2,3] (Fig. 1), antifungal [4, 5], anti-allergic [6], diuretic, antitumor, anti-HIV, and cardiovascular [7], anticonvulsant [8], antileishmanial [9], antihistaminic [10], antidiabetic [11], anti-inflammatory [12], analgesic [13], antihypertensive [14], antipyretic [15], antiviral [16], antioxidant [17], and anticancer activities [18, 19]. In the light of these reports, we have synthesized some new pyrimidines and evaluated the antibacterial activity for a group of the synthesized compounds against examples of Gram-positive and Gram-negative bacteria.

Fig. 1

Antibacterial drugs containing pyrimidines

Results and discussion

As a part of our interest in the synthesis and biological evaluation of new heterocyclic compounds [20, 21], we have synthesized some new pyrimidines using the starting material 2-furan-2-yl-4-mercapto-6-methylpyrimidine-5-carbonitrile 3 which was synthesized by heterocyclization of 2-furoyl isothiocyanate 1 with 3-aminocrotononitrile 2 [22]. The behavior of compound 3 towards benzylidene malononitrile was investigated under different basic conditions, thus reaction of 3 with benzylidene malononitrile in refluxing ethoxide solution did not give the expected thiopyranopyrimidine derivative 4 but instead, it gave 5-ethoxypyrimidine derivative 5 as a sole product. The ¹H NMR of 5 showed a triplet at δ = 1.06 ppm and a quartet at δ = 3.45 ppm for OCH₂CH₃ substituent. The formation of 5 may proceed via the initial addition of SH function to the olefinic double bond of benzylidene malononitrile affording S-alkyl adduct intermediate which was subjected to the nucleophilic attack of ethoxide ion resulting in displacement of S-alkyl substituent to afford 6-ethoxypyrimidine 5 (Scheme 1).

Scheme 1

Reaction of compound 3 with benzylidene malononitrile under different basic conditions

When the previous reaction was carried out under the catalytic effect of piperidine, quinazoline derivative 6 was obtained. The ¹H NMR spectrum of 6 confirmed its structure based on the following data:

• 1. Disappearance of CH₃ signal.

• 2. Appearance of a broad singlet at δ = 3.47 ppm for NH₂.

• 3. The SH signal appeared highly deshielded at δ = 14.53 ppm which indicated that the SH proton is involved in an intramolecular H-bonding with the neighboring NH₂ group.

The formation of compound 6 may proceed via the initial Michael-type addition of the methyl group in position 4 to the double bond of benzylidene malononitrile, followed by an intermolecular cycloaddition to the cyano function and subsequent elimination of HCN to give 6 (Scheme 2).

Scheme 2

Proposed mechanism for formation of compound 6

Hydrolysis of pyrimidine thione 3 afforded pyrimidone 7 whose IR spectrum showed an absorption band at υ = 1651 cm^− 1 for C=O and its ¹H NMR revealed a singlet at δ = 13.52 ppm for NH. Compound 7 was chlorinated with phosphorous oxychloride to give 5-chloropyrimidine 8. IR spectrum of 8 showed disappearance of C=O band, and its ¹H NMR showed disappearance of NH signal. Methylation of pyrimidine thione 3 with methyl iodide gave methyl thiopyrimidine derivative 9. The ¹H NMR of 9 showed a singlet at δ = 2.69 ppm for SCH₃. Hydrazinolysis of 9 gave a mixture of two products, the major product was identified to be the expected 2-furan-2-yl-4-hydrazinopyrimidine 10, and the minor product was identified to be 2-pyridazin-3-yl-4-hydrazinopyrimidine 11. The structure of 10 was confirmed based on the following data:

• 1. ¹H NMR of 10 showed two broad singlets at δ = 4.75 and 9.31 ppm for NH₂ and NH, respectively.

• 2. Mass spectrum of 10 showed a molecular ion peak at m/z = 215.

• 3. Treatment of 10 with nitrous acid gave tetrazolopyrimidine 12 which is identical with that synthesized by treatment of chloropyrimidine 8 with sodium azide.

The structure of 11 was confirmed by its spectral data; ¹H NMR of 11 showed two broad singlets at δ = 4.73 and 9.27 ppm for NH₂ and NH, respectively. Its mass spectrum showed a molecular ion peak at m/z = 227.

Compound 11 may be formed from 9 by ring transformation via attack of two molecules of NH₂NH₂ leading to displacement of methylthio group and ring opening of furan ring, and this was followed by an intramolecular cyclocondensation and subsequent loss of H₂ to give 11 (Scheme 3).

Scheme 3

Proposed mechanism for the formation of compound 11

Treatment of hydrazinopyrimidine 11 with benzaldehyde afforded the hydrazone 13. ¹H NMR of 13 revealed a singlet at δ = 12.38 ppm for NH, and the NH₂ signal disappeared. Heating of compound 11 in sodium ethoxide solution gave the corresponding pyrazolopyrimidine 14. IR spectrum of 14 showed disappearance of the cyano band, and its ¹H NMR spectrum showed two broad singlets at δ = 5.60 and 12.40 ppm for NH₂ and NH, respectively (Scheme 4).

Scheme 4

Synthesis of 2-furan-2-yl-4-hydrazinopyrimidine 10 and 2-pyridazin-3-yl-4-hydrazinopyrimidine 11

The reactivity of 2-furan-2-yl-5-hydrazinopyrimidine 10 was investigated towards various reagents, thus the cyclocondensation of 10 with acetylacetone yielded 6-pyrazolylpyrimidine 15. ¹H NMR of 15 showed three singlets at δ = 2.24, 2.68, and 2.73 ppm for three methyl groups and a singlet at δ = 6.31 ppm for the pyrazole-H. Also, heating of 10 with triethyl orthoformate afforded triazolopyrimidine 16. ¹H NMR of 15 showed a singlet at δ = 8.88 ppm for the triazole-H.

Reaction of 10 with acetic anhydride did not give the expected triazolopyrimidine 17, but it gave N-acetyl aminopyrazolopyrimidine 18. This result was proved by IR spectrum of 18 which revealed disappearance of C≡N and appearance of a C=O band at 1669 cm^− 1, also ¹H NMR of 18 showed three singlets at δ = 2.13, 10.34, and 13.68 ppm for COCH₃ and two NH, respectively. Similarly, when compound 10 was condensed with phthalic anhydride, it gave pyrazolopyrimidine 19. IR of 19 indicated disappearance of C≡N and appearance of C=O. ¹H NMR of 19 showed a highly deshielded singlet at δ = 14.47 ppm for NH which may be involved in an intramolecular H-bonding. The cyclocondensation of 10 with 2-chlorobenzaldehyde in presence of catalytic amount of piperidine yielded pyrimidopyridazine 20. IR of 20 showed disappearance of C≡N, whereas its ¹H NMR showed two NH signals at δ = 9.49 and 13.89 ppm. Compound 20 may be formed by initial formation of the hydrazone which underwent an intramolecular cycloaddition to the cyano function followed by rearrangement to give 20 which is thermodynamically stable by the extended conjugation present in the compound (Scheme 5). Finally, the condensation of 10 with isatin afforded the hydrazone 21. ¹H NMR of 21 revealed two NH signals at δ = 11.33 and 13.00 ppm (Scheme 6).

Scheme 5

Proposed mechanism for formation of compound 20

Scheme 6

Reactivity of 2-furan-2-yl-4-hydrazinopyrimidine 10 towards various reagents

Antibacterial activity

Compounds 5, 7, 8, 9, 10, 11 and 14 were tested in vitro for antibacterial activity against Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa) using disc diffusion method [23] at 1 mg/ml disc concentration. Ciprofloxacin was used as antibacterial agent standard. DMSO was used as solvent. The zone of inhibition of bacterial growth was observed.

The results given in Table 1 indicated that:

Table 1 In vitro antibacterial activity for a group of the synthesized compounds

• 1. Compounds 5, 10 and 11 have high antibacterial activity against the tested microorganisms.

• 2. Compounds 7 and 8 have moderate antibacterial activity against the tested microorganisms.

• 3. Compounds 9 and 14 have no antibacterial activity against the tested microorganisms.

Experimental

All melting points are uncorrected. IR spectra (KBr) were run on a Unicam SP 1200G infrared spectrophotometer. ¹H NMR and ¹³C NMR spectra (DMSO-d6) were run on a Bruker spectrometer (400 MHz) with a TMS as internal standard. Elemental analyses and in vitro antimicrobial activities were carried out at Micro Analytical Center, Cairo University. Compound 3 was prepared by the procedure described in the literature [22].

4-Ethoxy-2-(furan-2-yl)-6-methylpyrimidine-5-carbonitrile (5)

A mixture of 3 (0.01 mol) and benzylidene malononitrile (0.01 mol) in sodium ethoxide solution (50 ml) was refluxed for 3 h, cooled then poured into cold water and neutralized with dil. HCl. The solid formed was filtered off, dried and recrystallized from ethanol to give 5 as yellow crystals. m.p. = 250–252 °C, Yield: 71%. IR (KBr) υ_max: 2222 (C≡N), 1596 (C=N) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 1.06 (t, 3H, OCH₂CH₃), 2.72 (s, 3H, CH₃), 3.46 (q, 2H, OCH₂CH₃), 6.84–8.16 (m, 3H, furan-H). ¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 23.9 (CH₃), 39.3, 40.6 (OCH₂CH₃), 110.7, 149.7, 168.8, 182.9 (pyrimidine carbons), 114.1, 120.2, 144.7, 148.5 (furan carbons), 116.4 (C≡N). MS: m/z = 229 (M⁺), 228 (M⁺–H), 214 (M⁺–CH₃), 200 (M⁺–CH₂CH₃), 184 (M⁺–OCH₂CH₃). Anal. Calc. for C₁₂H₁₁N₃O₂ (229.24): C, 62.87; H, 4.84; N, 18.33; Found: C, 62.74; H, 4.69; N, 18.41.

5-Amino-2-(furan-2-yl)-4-mercapto-7-phenylquinazoline-6-carbonitrile (6)

A mixture of 3 (0.01 mol) and benzylidene malononitrile (0.01 mol) in absolute ethanol (50 ml) and 3 drops of piperidine was refluxed for 4 h, cooled then poured into cold water. The solid formed was filtered off, dried and recrystallized from ethanol to give 6 as orange crystals. m.p. = 278–280 °C, Yield: 82%. IR (KBr) υ_max: 3107, 3021 (NH₂), 2217 (C≡N), 1592 (C=N) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 3.48 (s, br., 2H, NH₂), 6.85–8.22 (m, 9H, furan-H + phenyl-H + quinazoline-H), 14.53 (s, 1H, SH). ¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 108.2, 136.5, 144.1, 145.1, 148.4, 149.6, 160.6, 183.2 (quinazoline carbons), 114.0, 120.1, 121.9, 129.1 (furan carbons), 129.3, 129.7, 131.4, 134.9, (phenyl carbons) 115.9 (C≡N). Anal. Calc. for C₁₉H₁₂N₄OS (344.40): C, 66.26; H, 3.51; N, 16.27; Found: C, 66.34; H, 3.42; N, 16.19.

2-(Furan-2-yl)-1,6-dihydro-4-methyl-6-oxopyrimidine-5-carbonitrile (7)

Compound 3 (0.01 mol) was dissolved in a solution of NaOH (20 ml, 5%), then H₂O₂ (60 ml) was added and the mixture was stirred for 1 h. The solid obtained after neutralization with HCl was filtered off, dried and recrystallized from ethanol to give 7 as white crystals. m.p. = 228–230 °C, Yield: 43%. IR (KBr) υ_max: 3429 (NH), 2223 (C≡N), 1651(C=O), 1591 (C=N) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.70 (s, 3H, CH₃), 6.81–8.12 (m, 3H, furan-H), 13.52 (s, 1H, NH). ¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 23.8 (CH₃), 97.4, 150.3, 160.8 (pyrimidine carbons), 113.9, 118.9, 145.5, 149.1 (furan carbons), 115.7 (C≡N), 172.8 (C=O). Anal. Calc. for C₁₀H₇N₃O₂ (201.19): C, 59.70; H, 3.51; N, 20.89; Found: C, 59.57; H, 3.62; N, 20.96.

4-Chloro-2-(furan-2-yl)-6-methylpyrimidine-5-carbonitrile (8)

A mixture of 7 (0.01 mol) and POCl₃ (15 ml) was heated gently under reflux for 3 h, cooled and poured into crushed ice. The solid formed was filtered off, dried and recrystallized from ethanol to give 7 as brown crystals.

m.p. = 164–166 °C, Yield: 81%. IR (KBr) υ_max: 2220 (C≡N), 780 (C–Cl) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.70 (s, 3H, CH₃), 6.81–8.11 (m, 3H, furan-H).¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 23.7 (CH₃), 97.3, 150.2, 156.8, 162.0 (pyrimidine carbons), 113.9, 118.9, 145.5, 149.3 (furan carbons), 115.6 (C≡N). Anal. Calc. for C₁₀H₆ClN₃O (219.63): C, 54.69; H, 2.75; N, 19.13; Found: C, 54.51; H, 2.83; N, 19.21.

2-(Furan-2-yl)-4-methyl-6-(methylthio)pyrimidine-5-carbonitrile (9)

A mixture of 3 (0.01 mol), K₂CO₃ (0.01 mol), and CH₃I (0.01 mol) in DMF (15 ml) was stirred at room temperature for 3 h, then the reaction mixture was poured into cold water and the solid formed was filtered off, dried and recrystallized from ethanol to give 9 as pale brown crystals.

m.p. = 170–172 °C, Yield: 76%. IR (KBr) υ_max: 2208 (C≡N), 1585 (C=N) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.58 (s, 3H, CH₃), 2.69 (s, 3H, SCH₃), 6.78–8.06 (m, 3H, furan-H).¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 12.8, 23.5 (2 CH₃), 102.0, 155.8, 170.0, 173.2 (pyrimidine carbons), 113.6, 117.9, 148.3, 150.9 (furan carbons), 115.0 (C≡N). MS: m/z = 231 (M⁺), 230 (M⁺–H), 216 (M⁺–CH₃), 184 (M⁺-SCH₃). Anal. Calc. for C₁₁H₉N₃OS (231.28): C, 57.13; H, 3.92; N, 18.17; Found: C, 57.04; H, 3.81; N, 18.09.

2-(Furan-2-yl)-4-hydrazinyl-6-methylpyrimidine-5-carbonitrile (10) and 4-hydrazinyl-6-methyl-2-(pyridazin-3-yl)pyrimidine-5-carbonitrile (11)

A mixture of 9 (0.01 mol) and hydrazine hydrate (2 ml) in ethanol (30 ml) was heated under reflux for 5 h. the solid formed on hot was filtered off, dried and recrystallized from n-butanol to give 10 as pale yellow crystals. The mother liquor was poured into water and the solid formed was filtered off, dried and recrystallized from ethanol to give 11 as brown crystals.

Compound (10)

m.p. = 194–196 °C, Yield: 52%. IR (KBr) υ_max: 3324, 3241 (NH₂, NH), 2205 (C≡N) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.51 (s, 3H, CH₃), 4.75 (s, br., 2H, NH₂), 6.69–7.93 (m, 3H, furan-H), 9.31 (s, br., 1H, NH) .¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 23.6 (CH₃), 84.8, 156.8, 162.9, 171.2 (pyrimidine carbons), 113.0, 117.2, 146.8, 151.8 (furan carbons), 115.9 (C≡N). MS: m/z = 215 (M⁺), 214 (M⁺–H), 200 (M⁺–CH₃), 199 (M⁺–NH₂), 184 (M⁺–NHNH₂), 67 (furan-2-yl). Anal. Calc. for C₁₀H₉N₅O (215.22): C, 55.81; H, 4.22; N, 32.54; Found: C, 55.69; H, 4.15; N, 32.63.

Compound (11)

m.p. = 186–188 °C, Yield: 11%. IR (KBr) υ_max: 3325, 3244 (NH₂, NH), 2206 (C≡N) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.46 (s, 3H, CH₃), 4.73 (s, br., 2H, NH₂), 6.68–7.91 (m, 3H, pyridazine-H), 9.27 (s, br., 1H, NH) .¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 23.5 (CH₃), 84.8, 156.8, 162.4, 170.8 (pyrimidine carbons), 112.7, 113.0, 146.8, 151.7 (pyridazine carbons), 115.9 (C≡N). MS: m/z = 227 (M⁺), 226 (M⁺–H), 212 (M⁺–CH₃), 211 (M⁺–NH₂), 196 (M⁺–NHNH₂), 79 (pyridazin-3-yl). Anal. Calc. for C₁₀H₉N₇ (227.23): C, 52.86; H, 3.99; N, 43.15; Found: C, 52.79; H, 3.87; N, 43.21.

5-(Furan-2-yl)-7-methyltetrazolo[1,5-f]pyrimidine-8-carbonitrile (12)

Method (a)

A solution of NaNO₂ (0.01 mol) in H₂O (5 ml) was added drop wise to a cold solution of 10 (0.01 mol) in acetic acid (20 ml). The mixture was stirred for 1 h then poured into cold water and the solid formed was filtered off, dried and recrystallized from ethanol to give 12 as pale brown crystals.

Method (b)

A mixture of 8 (0.01 mol) and NaN₃ (0.01 mol) in acetic acid (20 ml) was heated under reflux for 3 h. the reaction mixture was cooled then poured into cold water and the solid formed was filtered off, dried and recrystallized from ethanol.

m.p. = 174–176 °C, Yield: 67%. IR (KBr) υ_max: 2219 (C≡N) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.85 (s, 3H, CH₃), 6.79–8.08 (m, 3H, furan-H). ¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 23.7 (CH₃), 93.6, 164.1, 173.1, 173.3 (pyrimidine carbons), 113.8, 148.6, 150.2, 156.7 (furan carbons), 118.4 (C≡N). MS: m/z = 226 (M⁺), 225 (M⁺–H), 211 (M⁺–CH₃), 199 (M⁺–HCN). Anal. Calc. for C₁₀H₆N₆O (226.20): C, 53.10; H, 2.67; N, 37.15; Found: C, 53.19; H, 2.75; N, 37.04.

4-(2-Benzylidenehydrazinyl)-6-methyl-2-(pyridazin-3-yl)pyrimidine-5-carbonitrile (13)

A mixture of 11 (0.01 mol) and benzaldehyde (0.01 mol) in ethanol acid (30 ml) was heated under reflux for 3 h. the reaction mixture was cooled and the solid formed was filtered off, dried and recrystallized from ethanol to give 13 as white crystals.

m.p. = 206–208 °C, Yield: 72%. IR (KBr) υ_max: 3313 (NH), 2206 (C≡N) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.59 (s, 3H, CH₃), 6.72–8.17 (m, 9H, pyridazine-H + phenyl-H + N=CH), 12.38 (s, 1H, NH). ¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 24.0 (CH₃), 86.0, 156.6, 160.1, 173.3 (pyrimidine carbons), 127.7, 129.2, 130.4, 134.8 (phenyl carbons), 113.2, 116.2, 147.1, 151.3 (pyridazine carbons), 117.3 (C≡N), 145.4 (N=CH). Anal. Calc. for C₁₇H₁₃N₇ (315.34): C, 64.75; H, 4.16; N, 31.09; Found: C, 64.84; H, 4.09; N, 31.03.

4-Methyl-6-(pyridazin-3-yl)-1H-pyrazolo[3,4-d]pyrimidin-3-amine (14)

Compound 11 (0.01 mol) in sodium ethoxide solution (20 ml) was heated under reflux for 3 h. the reaction mixture was cooled, poured into cold water, then neutralized with dil. AcOH. The solid formed was filtered off, dried and recrystallized from ethanol to give 14 as orange crystals.

m.p. = 218–220 °C, Yield: 64%. IR (KBr) υ_max: 3119, 3011 (NH₂, NH) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.73 (s, 3H, CH₃), 5.60 (s, br., 2H, NH₂), 6.68–7.99 (m, 3H, pyridazine-H), 12.40 (s, br., 1H, NH). Anal. Calc. for C₁₀H₉N₇ (227.23): C, 52.86; H, 3.99; N, 43.15; Found: C, 52.93; H, 3.91; N, 43.06.

2-(Furan-2-yl)-4-methyl-6-(3,5-dimethyl-1H-pyrazol-1-yl)pyrimidine-5-carbonitrile (15)

A mixture of 10 (0.01 mol) and acetylacetone (0.01 mol) in n-butanol (30 ml) was heated under reflux for 6 h. the reaction mixture was cooled and the solid formed was filtered off, dried and recrystallized from n-butanol to give 15 as white crystals.

m.p. = 166–168 °C, Yield: 81%. IR (KBr) υ_max: 2216 (C≡N) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.24 (s, 3H, CH₃), 2.68 (s, 3H, CH₃), 2.73 (s, 3H, CH₃), 6.31 (s, 1H, pyrazole-H), 6.80–8.08 (m, 3H, furan-H) .¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 13.9 (CH₃), 14.9 (CH₃), 24.4 (CH₃), 95.4, 156.1, 157.9, 174.8 (pyrimidine carbons), 111.9, 113.8, 143.7, 148.4 (furan carbons), 115.7, 150.7, 151.9 (pyrazole carbons), 117.9 (C≡N). MS: m/z = 279 (M⁺), 278 (M⁺–H), 264 (M⁺–CH₃), 252 (M⁺–HCN). Anal. Calc. for C₁₅H₁₃N₅O (279.30): C, 64.51; H, 4.69; N, 25.07; Found: C, 54.60; H, 4.58; N, 25.13.

5-(Furan-2-yl)-7-methyl-[1, 2, 4] triazolo[4,3-f]pyrimidine-8-carbonitrile (16)

Compound 10 (0.01 mol) in triethyl orthoformate (50 ml) was heated under reflux for 6 h. the solid formed on hot was filtered off, dried and recrystallized from ethanol to give 16 as brown crystals.

m.p. = 230–232 °C, Yield: 45%. IR (KBr) υ_max: 2223 (C≡N), 1597 (C=N) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.79 (s, 3H, CH₃), 6.99–8.33 (m, 3H, furan-H), 8.88 (s, 1H, triazole-H).¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 23.5 (CH₃), 93.7, 156.5, 160.1, 161.9 (pyrimidine carbons), 121.1, 124.3, 145.4, 152.3 (furan carbons), 139.8 (triazole carbon), 114.6 (C≡N). MS: m/z = 225 (M⁺), 224 (M⁺–H), 198 (M⁺–HCN). Anal. Calc. for C₁₁H₇N₅O (225.21): C, 58.67; H, 3.13; N, 31.10; Found: C, 58.73; H, 3.04; N, 31.17.

N-(6-(Furan-2-yl)-4-methyl-1H-pyrazolo[3,4-d]pyrimidin-3-yl)acetamide (18)

Compound 10 (0.01 mol) in acetic anhydride (30 ml) was heated under reflux for 8 h, then the reaction mixture was cooled and poured into crushed ice. The solid formed was filtered off, dried and recrystallized from ethanol to give 18 as white crystals.

m.p. > 300 °C, Yield: 51%. IR (KBr) υ_max: 3428, 3253 (NH), 1669 (C=O) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.13 (s, 3H, COCH₃), 2.65 (s, 3H, CH₃), 6.72–7.93 (m, 3H, furan-H), 10.34 (s, 1H, NH), 13.68 (s, 1H, NH).¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 22.3 (CH₃), 23.1 (CH₃), 107.5, 154.2, 154.9, 163.9 (pyrimidine carbons), 112.9, 114.3, 139.8, 146.2 (furan carbons), 152.4 (pyrazole carbon), 171.2 (C=O). Anal. Calc. for C₁₂H₁₁N₅O₂ (257.25): C, 56.03; H, 4.31; N, 27.22; Found: C, 56.12; H, 4.25; N, 27.18.

2-(6-(Furan-2-yl)-4-methyl-2H-pyrazolo[3,4-d]pyrimidin-3-yl)isoindoline-1,3-dione (19)

A mixture of 10 (0.01 mol) and phthalic anhydride (0.01 mol) in acetic acid (50 ml) was heated under reflux for 6 h. the reaction mixture was cooled and the solid formed was filtered off, dried and recrystallized from DMF to give 19 as pale brown crystals.

m.p. > 300 °C, Yield: 61%. IR (KBr) υ_max: 3323 (NH), 1786, 1731 (C=O) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.73 (s, 3H, CH₃), 6.73–8.11 (m, 7H, furan-H + isoindoline-H), 14.47 (s, 1H, NH). ¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 22.2 (CH₃), 107.9, 154.7, 155.4, 163.3 (pyrimidine carbons), 113.1, 115.1, 135.9, 146.6 (furan carbons), 152.1 (pyrazole carbon), 124.7, 131.6, 133.1 (isoindoline carbons), 167.2 (C=O). Anal. Calc. for C₁₈H₁₁N₅O₃ (345.32): C, 62.61; H, 3.21; N, 20.28; Found: C, 62.55; H, 3.13; N, 20.37.

3-(2-Chlorophenyl)-7-(furan-2-yl)-5-methylpyrimido[4,5-c]pyridazin-4(8H)-imine (20)

A mixture of 10 (0.01 mol), 2-chlorobenzaldehyde (0.01 mol), and catalytic amount of piperidine in DMF (30 ml) was heated under reflux for 6 h. the reaction mixture was cooled and the solid formed was filtered off, dried and recrystallized from DMF to give 20 as yellow crystals.

m.p. = 296–298 °C, Yield: 76%. IR (KBr) υ_max: 3433, 3159 (NH) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.91 (s, 3H, CH₃), 6.74–8.58 (m, 7H, furan-H + 2-chlorophenyl-H), 9.49 (s, 1H, NH), 13.89 (s, 1H, NH). MS: m/z = 337 (M⁺), 236 (M⁺–H), 322 (M⁺–CH₃). Anal. Calc. for C₁₇H₁₂ClN₅O (337.77): C, 60.45; H, 3.58; N, 20.73; Found: C, 60.52; H, 3.67; N, 20.80.

2-(Furan-2-yl)-4-methyl-6-[2-(2-oxo-1,2-dihydro-3H-indol-3-ylidene)hydrazinyl]pyrimidine-5-carbonitrile (21)

A mixture of 10 (0.01 mol) and isatin (0.01 mol) in n-butanol (50 ml) was heated under reflux for 3 h. The solid formed on hot was filtered off, dried and recrystallized from acetic acid to give 21 as yellow crystals.

m.p. = 290–292 °C, Yield: 82%. IR (KBr) υ_max: 3432 (NH), 2211 (C≡N), 1695 (C=O) cm^{− 1. 1}H NMR (400 MHz, DMSO-d₆) δ (ppm): 2.67 (s, 3H, CH₃), 6.77–8.03 (m, 7H, furan-H + indole-H), 11.33 (s, 1H, NH), 13.00 (s, 1H, NH). ¹³C NMR (400 MHz, DMSO-d₆) δ (ppm): 23.9 (CH₃), 111.6, 157.0, 159.0, 163.3 (pyrimidine carbons), 113.5, 131.9, 142.6, 150.8, (furan carbons), 120.2, 121.3, 124.5., 129.4, 123.1, 135.0, 147.8 (isatin carbons), 117.3 (C≡N), 173.0 (C=O). Anal. Calc. for C₁₈H₁₂N₆O₂ (344.34): C, 62.79; H, 3.51; N, 24.41; Found: C, 62.71; H, 3.42; N, 24.34.