Synthesis of novel 1,5-disubstituted pyrrolo[1,2-a]quinazolines and their evaluation for anti-bacterial and anti-oxidant activities

Abstract

A new series of 1,5-disubstituted pyrrolo[1,2-a]quinazoline derivatives were prepared from 2-chloro-4-substituted quinazolines, propargyl alcohol, and secondary amines through novel multi-component reactions. These one-pot reactions, carried out in the presence of a palladium-copper catalyst, provide an efficient method for the synthesis of functionalized pyrrolo[1,2-a]quinazolines in good-to-high yields. A number of synthesized compounds were screened for their in vitro anti-bacterial activity against Gram-positive and Gram-negative bacteria using a well-diffusion method. Also the anti-oxidant activity of the products was evaluated using the DPPH (2,2-diphenyl-2-picrylhydrazyl) assays.

---

Introduction

Heterocycles are of special interest and significant importance in the search for new biologically active scaffolds in pharmaceutical industries. In this area, nitrogen heterocyclic compounds, in particular, display diverse biological and pharmacological activities, in part, due to the similarities with many natural and synthetic molecules with known biological activities. Quinazolines are important nitrogen heterocyclic compounds used in medicine due to their wide spectrum of biological activities. The quinazolinone skeleton is a building block for the preparation of the natural purine base,¹ alkaloids, and many biologically active compounds and intermediates in organic synthesis.² Quinazoline derivatives possess a variety of activities like the anti-bacterial,³ anti-fungal,⁴ anti-HIV,⁵ anthelmintic,⁶ CNS depressant⁷ and anti-tubercular⁸ ones.

Pyrrole derivatives are also extensively used in drug discovery,⁹ exhibiting a variety of pharmacological activities.^10–12 Hence, it is thought to be of interest to merge both the quinazoline and pyrrole moieties, which may enhance the drug activities of the compounds or they might possess some new biological activities. Pyrroloquinazolines are important core structures found in a variety of natural products and other biologically important molecules.¹³ They often possess a wide range of biological properties such as anti-tumor activities,^14,15 modulators of chemokine activity,¹⁶ and anti-inflammatory activities.¹⁷ In addition, some of them are used as thrombin receptor antagonists.¹⁸ Moreover, pyrrolo[1,2-a]quinazolines are an important class of pyrroloquinazolines that have significant applications in medicinal chemistry¹⁹ (Fig. 1).

Fig. 1 Structures of drugs based on pyrrolo[1,2-a]quinazoline moeity.

Compounds of type I are claimed as PARP (poly ADP ribose polymerase) inhibitors, and have a potential as anti-cancer therapeutics.²⁰ Pyrrolo[1,2-a]quinazoline II was tested as a sedative, having potentiating barbiturate properties, and are thus claimed to be useful as adjuvants in the treatment of convulsions, insomnia or mental disorders.²¹ Compounds of general formula III have been reported as anti-edema agents. The tests have been carried out on mice, subjected to strong inflammatory responses induced by carrageenin with 25–100 mg doses of these compounds.²²

To the best of our knowledge, few investigations have been reported on the synthesis of pyrrolo[1,2-a]quinazolines.¹⁹ There are three known strategies for the synthesis of pyrrolo[1,2-a]quinazolines: syntheses starting from substituted quinazolines,²³ synthetic routes starting from substituted N-arylpyrroles,^24,25 and syntheses by double-cyclization of different starting reagents.^26–29 These synthetic procedures have several limitations such as reactions performed in several steps, low yields, and not often readily available starting materials. Thus the use of a new method to synthesize pyrrolo[1,2-a]quinazolines would be attractive.

Results and discussion

Halogenated quinazolines are versatile synthetic intermediates for the metal-catalyzed carbon–carbon bond formation reactions such as the Sonogashira cross-coupling reaction.³⁰ The synthesis of pyrrolo[1,2-a]quinazolines from halogenated quinazolines through palladium-catalyzed reactions has not been studied yet. In continuation our recent studies toward efficient synthesis of fused heterocyclic compounds through palladium-catalyzed reactions,³¹ we carried out the synthesis of new derivatives of 1,5-disubstituted pyrrolo[1,2-a] quinazoline via the multi-component reactions of 2-chloro-4-substituted quinazolines, propargyl alcohol, and secondary amines in the presence of a palladium–copper catalyst (Scheme 1).

Scheme 1 Multi-component synthesis of 1,5-disubstituted pyrrolo[1,2-a]quinazolines via palladium-catalyzed coupling/cyclization reactions.

The starting materials, 2-chloro-4-alkoxyquinazolines and 2-chloro-4-aminoquinazolines, 2a–f, were prepared by the regioselective reactions of 2,4-dichloroquinazoline with sodium alkoxides and amines, respectively (Scheme 2, Table 1).^32,33

Scheme 2 Synthesis of 4-substituted 2-chloroquinazolines from 2,4-dichloroquinazoline and secondary amines or sodium alkoxides.

Table 1 Melting points and yields of 4-substituted 2-chloroquinazolines 2a–f obtained from reaction of 2,4-dichloroquinazoline with secondary amines or alkoxides

Entry	Amine/alkoxide	Mp (°C)	Product	Yield (%)
1	Morpholine	112–114	2a	90
2	Piperidine	120–125	2b	80
3	Methoxide	99–100	2c	90
4	Ethoxide	92–93	2d	85
5	Propoxide	89–91	2e	80
6	Butoxide	87–90	2f	80

---

Initially, stirring of a mixture of 2-chloro-4-methoxyquinazoline, propargyl alcohol, and morpholine in refluxing CH₃CN in the presence of bis-triphenylphosphine palladium(II) chloride and copper(I) iodide under an argon atmosphere for 15 h afforded the desired 5-methoxy-1-morpholino-H-pyrrolo[1,2-a]quinazoline in only 50% yield (Table 2, entry 8). Inspired by this result, the reaction was thoroughly optimized in terms of the solvent, catalyst, and addition various bases (Table 2). We screened DMF, CH₃CN, and water, as solvents, in the presence of the organic and inorganic bases such as Et₃N, DIPEA, and carbonate salts. We found CH₃CN to be an efficient solvent for the reaction. Et₃N was found to be the most suitable base, giving a clean product and a better yield. The Pd(PPh₃)₂Cl₂–CuI catalytic system was found to be the best one. Moreover, the use of copper(I) iodide was found to be essential for the reaction progress; the reaction carried out without CuI led to only 10% product yield. It turned out that a yield of 79% could be obtained if the reaction was run in refluxing CH₃CN in the presence of Et₃N (4 mmol), Pd(PPh₃)₂Cl₂ (0.05 mmol), and CuI (0.1 mmol) for 15 h (Table 2, entry 6).

Table 2 Optimization conditions for one-pot synthesis of 5-methoxy-1-(morpholin-4-yl)pyrrolo[1,2-a]quinazoline^a

Entry	Solvent	Base^b	Catalyst	Co-catalyst	Yield (%)
a Reaction conditions: 2a–e (1 mmol), 3 (1.2 mmol), secondary amine (3 mmol), base (4 mmol), Pd(Ph3P)2Cl2 (0.05 mmol), CuI (0.1 mmol), distilled solvent (5 mL), 80 °C, 15 h, argon atmosphere.b Base (3 mmol).c SDS (10 mol%).
1	DMF	Et3N	PdCl2(PPh3)2	CuI	75
2	DMF	Morpholine	PdCl2(PPh3)2	CuI	45
3	DMF	K2CO3	PdCl2(PPh3)2	CuI	50
4	DMF	DIPEA	PdCl2(PPh3)2	CuI	65
5	CH3CN	Et3N	PdCl2	CuI	33
6	CH3CN	Et3N	PdCl2(PPh3)2	CuI	79
7	CH3CN	Et3N	PdCl2(PPh3)	—	10
8	CH3CN	Morpholine	PdCl2(PPh3)2	CuI	50
9	CH3CN	DIPEA	PdCl2(PPh3)2	CuI	65
10	CH3CN	Et3N	Pd/C (10 mol%)	CuI	25
11	H2O	K2CO3/SDS^c	PdCl2(PPh3)2	CuI	10
12	H2O	Cs2CO3/SDS	PdCl2(PPh3)2	CuI	10

---

Having the optimized reaction conditions in hand, we focused our attention on the exploration of the substrate scope. With other substrates of 2-chloro-4-alkoxy quinazolines, the corresponding products were isolated successfully (Table 3, entries 2–7). Similarly, 2-chloro-4-aminoquinazoline substrates could be handled without any trouble, giving the corresponding pyrrolo[1,2-a]quinazolines in good yields (Table 3, entries 8 and 9).

Table 3 Synthesis of 1,5-disubstituted pyrrolo[1,2-a]quinazolines^a

Entry	Substrate	Product	Yield (%)
a Reaction conditions: 2 (1 mmol), 3 (1.2 mmol), secondary amine (3 mmol), Et3N (4 mmol), Pd(Ph3P)2Cl2 (0.05 mmol), CuI (0.1 mmol) distilled CH3CN (5 mL), 80 °C, 15 h, argon atmosphere.
1	2c		79
2	2c		72
3	2d		80
4	2e		75
5	2e		69
6	2f		72
7	2f		65
8	2a		75
9	2b		70

---

The structural assignments of compounds 4a–i were based on the spectroscopic data and mass analysis. The ¹H NMR spectrum for 4b showed a doublet of doublet (dd) at δ 8.91, which was characteristic of an aromatic proton at position 6 of the heterocyclic system, and was deshielded by the diamagnetic pyrrole ring current. The other three aromatic protons in the quinazoline ring appeared at δ 7.04–7.64. The two doublets at δ 6.62–6.64 and δ 6.20–6.22 were assigned to the two protons at the 2- and 3-positions in the fused pyrrole ring. In the aliphatic region, we observed 13 protons at δ 1.51–4.02 that were related to the piperidine and methoxy substituents in the 1- and 5-positions of this heterocyclic system.

Mechanistically, the present one-pot coupling/cyclization process seems to proceed through the initial Pd(0)-catalyzed coupling of 2a–f with copper(I) acetylide generated in situ from propargyl alcohol to afford the heteroaryl alkyne A. This compound was isomerized to the allene intermediate B, continuing to an enone aldehyde C and an iminium ion D, followed by an intramolecular cyclization to the fused ring system E, and finally, a base-induced aromatization to afford the product (Scheme 3).

Scheme 3 Proposed mechanism for formation of 1,5-disubstituted pyrrolo[1,2-a]quinazolines from 4-substituted 2-chloroquinazoline, propargyl alcohol, and secondary amines.

Anti-bacterial assay

Some reports have shown the anti-bacterial activity of pyrroloquinazoline. For example, Singh and co-workers³⁴ have studied the anti-bacterial activity of several pyrroloquinazoline alkaloids, finding that these compounds show moderate anti-bacterial activities against Bacillus subtilis and some other bacteria. Products 4a, 4d, 4e, 4f, and 4h were screened for their in vitro anti-bacterial activity against Gram-positive and Gram-negative bacteria strains including Micrococcus luteus (M. luteus), Pseudomonas aeruginosa (Ps. aeruginosa), and Bacillus subtilis (B. subtilis) using a well-diffusion method. DMSO was used as the negative control, and showed no activity against the above-mentioned bacterial strains. Penicillin G was used as the positive control (Table 4). According to the results obtained, 4a, 4e, and 4h were active against all the three bacterial strains. Compounds 4e and 4h were more active against Pseudomonas aeruginosa, and 4h had the highest anti-bacterial activity against M. luteus.

Table 4 Anti-bacterial activities of pyrrolo[1,2-a]quinazolines (1000 μg mL⁻¹) as inhibition zone in mm

Compound	B. subtilis	M. luteus	Ps. aeruginosa
4e	8	8	8
4h	7	10	8
4a	8	8	7
4d	7	8	—
4f	8	9	—
DMSO	—	—	—
Penicillin G	25	55	—

---

Anti-oxidant assay

The anti-oxidant assay using DPPH (diphenylpicrylhydrazyl) is one of the simplest methods used to evaluate an anti-oxidant activity. DPPH is a stable free radical of violet color. When a compound donates a radical hydrogen atom to a DPPH molecule, it reduces DPPH, and thus the absorbance of DPPH is decreased. In brief, the higher the anti-oxidant activity, the lighter is the violet hue. The anti-oxidant activities of a number of pyrrolo[1,2-a]quinazolines were evaluated by the DPPH radical scavenging activity method. In this method, a decrease in the absorption band at 517 nm indicates that the test compound possesses an anti-oxidant activity. The radical scavenging activities of 4a, 4d, 4e, 4f, and 4h were screened at concentrations in the range of 4000–125 μg mL⁻¹ and monitored at 517 nm (Table 5). Also the IC₅₀ values (the concentrations of 4a, 4d, 4e, 4f, and 4h to scavenge 50% of the DPPH radical concentration) were calculated using the line equation obtained from Scheme 4 (Table 5). Ascorbic acid was used as the standard. The IC₅₀ values for the measured compounds were in the range 0.59–0.27 μM. It is worth noting that among the evaluated pyrrolo[1,2-a]quinazolines, compound 4d had the lowest IC₅₀ value (0.27 μM), while compound 4e had the highest IC₅₀ value (0.59 μM), compared to the IC₅₀ value for ascorbic acid, the anti-oxidant compound (0.13 μM). A higher anti-oxidant activity is reflected in a lower IC₅₀ value. Compounds 4a, 4d, 4e, 4f, and 4h were determined to exhibit a potent radical scavenging activity in a DPPH assay with IC₅₀ values in the 4d, 4h, 4a, 4f, and 4e order, respectively.

Table 5 IC₅₀ values for DPPH radical scavenging activity of pyrrolo[1,2-a]quinazolines

Compound	DPPH assay IC50 (μM)
4a	1.25
4d	0.81
4e	0.75
4f	0.41
4h	0.28
Ascorbic acid	0.13

---

Scheme 4 DPPH radical scavenging activities of pyrrolo[1,2-a]quinazolines.

Conclusions

In this work, we developed a rare one-pot reaction for the construction of a variety of novel pyrrolo[1,2-a]quinazolines from 2-chloro-4-substituted quinazolines, propargyl alcohol, and secondary amines. The Sonogashira coupling reaction and hetero-annulation were realized in a cascade. A wide range of these fused heterocycles bearing different substitutions at positions 1 and 5 were elaborated from suitable substrates. A number of synthesized compounds were screened for their in vitro anti-bacterial and anti-oxidant activities.

Experimental part

General information

Melting points were recorded on a Thermocouple digital melting point apparatus. IR spectra were recorded on a Shimadzu IR-435 grating spectrophotometer. For column chromatography, Merck Kieselgel 100 was used as the stationary phase. NMR spectra were obtained as CDCl₃ solutions using a Bruker 400 and 300 MHz NMR spectrometer. ¹H NMR signals were reported relative to Me₄Si (δ 0.0) or residual CHCl₃ (δ 7.26). ¹³C NMR signals were reported relative to CDCl₃ (δ 77.16). Multiplicities were described using the following abbreviations: s = singlet, d = doublet, t = triplet and m = multiplet. The mass spectra were measured with a MS (EI), 5973 quadrupole Analyzer spectrometer, manufactured by Agilent Technologies Company (HP) and ESI Wasters Q-T of Ultima.

General procedure for preparation of 2-chloro-4-alkoxyquinazoline

A mixture of sodium (1 mmol) and an alcohol (3 mL) was stirred for 15 min at room temperature, then 2,4-dichloroquinazoline (1 mmol) was added to the mixture until the complete consumption of the starting materials (monitored by TLC). After evaporation of the solvent, the resulting precipitate was washed with H₂O; it did not require any further purification.³²

General procedure for preparation of 2-chloro-4-aminoquinazoline

A mixture of 2,4-dichloroquinazoline (1 mmol) and a secondary amine (2 mmol) in acetonitrile was refluxed for 5 h until the complete consumption of the starting materials (monitored by TLC). After evaporation of the solvent, the resulting precipitate was washed with H₂O; it did not require any further purification.³³

General experimental procedure for synthesis of 1,5-disubstituted pyrrolo[1,2-a] quinazoline

A mixture of 4-substituted-2-chloroquinoxaline 2 (1 mmol), a secondary amine (3 mmol), Pd(Ph₃P)₂Cl₂ (0.05 mmol, 0.03 g), CuI (0.1 mmol, 0.03 g), and Et₃N (4 mmol, 0.4 g) was stirred in CH₃CN (5 mL) at room temperature under an argon atmosphere. Propargyl alcohol (1.2 mmol, 0.07 g) was added, and the resulting mixture was stirred at 80 °C for 15 h. After completion of the reaction, the mixture was filtered, and the remaining solid was washed with H₂O and then dried. The crude product was purified by column chromatography (silica-gel 100) using CHCl₃–CH₃OH (99 : 1) as the eluent.

5-Methoxy-1-(morpholin-4-yl)pyrrolo[1,2-a]quinazoline (4a). Dark yellow solid; mp, 145–147 °C; ¹H NMR (300 MHz, CDCl₃): δ 2.45–2.59 (m, 2H, NCH₂), 3.25–3.39 (m, 2H, NCH₂), 3.84–4.05 (m, 7H, 2OCH₂, OCH₃), 6.24 (d, J = 3.9 Hz, 1H, CH of pyrrole), 6.64 (d, J = 3.9 Hz, 1H, CH of pyrrole), 7.15–7.38 (m, 2H, Ar–H), 7.65–7.73 (m, 1H, Ar–H), 8.96 (d, J = 8.0 Hz, 1H, 9-H); ¹³C NMR (75 MHz, CDCl₃): δ 52.45, 66.35, 67.27, 100.21, 104.34, 115.27, 122.63, 125.60, 125.88, 127.81, 134.87, 152.54, 163.65, 175.36; IR (KBr): 2940, 2830, 1610, 1500, 1120 cm⁻¹; m/z [M]⁺ 283; HRMS for C₁₆H₁₇N₃O₂ calculated [MH] 283.1321; found m/z = 283.1323.

5-Methoxy-1-(piperidin-1-yl)pyrrolo[1,2-a]quinazoline (4b). Orange solid; mp, 139–141 °C; ¹H NMR (300 MHz, CDCl₃): δ 1.51–1.91 (m, 6H, 3CH₂), 2.51–2.58 (m, 2H, NCH₂), 3.21–3.43 (m, 2H, NCH₂), 4.02 (s, 3H, OCH₃), 6.21 (d, J = 3.9 Hz, 1H, CH of pyrrole), 6.63 (d, J = 4.1 Hz, 1H, CH of pyrrole), 7.04–7.21 (m, 1H, Ar–H), 7.31–7.47 (m, 1H, Ar–H), 7.56–7.64 (m, 1H, Ar–H), 8.93 (d, J = 8.0 Hz, 1H, 9-H); ¹³C NMR (75 MHz, CDCl₃): δ 24.71, 25.15, 52.77, 67.12, 99.39, 104.53, 115.14, 121.86, 125.10, 125.48, 127.41, 135.40, 152.54, 163.75, 175.32; IR (KBr): 2944, 2830, 1620, 1505, 1125 cm⁻¹; m/z [M]⁺ 281; HRMS for C₁₇H₁₉N₃O calculated [MH] 281.1528; found m/z = 281.1532.

5-Ethoxy-1-(piperidin-1-yl)pyrrolo[1,2-a]quinazoline (4c). Orange solid; mp, 139–141 °C; ¹H NMR (300 MHz, CDCl₃): δ 1.33 (t, J = 7.2 Hz, 3H, CH₃), 1.60–1.80 (m, 6H, 3CH₂), 2.47–2.54 (m, 2H, NCH₂), 3.18–3.22 (m, 2H, NCH₂), 4.44 (q, J = 7.1 Hz, 2H, OCH₂), 6.17 (d, J = 4.2 Hz, 1H, CH of pyrrole), 6.58 (d, J = 4.2 Hz, 1H, CH of pyrrple), 7.10–7.19 (m, 1H, Ar–H), 7.21–7.32 (m, 1H, Ar–H), 7.53–7.61 (m, 1H, Ar–H), 8.91 (d, J = 9.0 Hz, 1H, 9-H); ¹³C NMR (75 MHz, CDCl₃): δ 14.43, 24.87, 25.94, 53.85, 62.36, 100.39, 105.63, 116.21, 122.86, 126.11, 126.76, 127.75, 136.50, 154.22, 162.51, 176.62; IR (KBr): 2950, 2850, 1615, 1510, 1120 cm⁻¹; m/z [M]⁺ 295; HRMS for C₁₈H₂₁N₃O calculated [MH] 295.1685; found m/z = 295.1686.

1-(Morpholin-4-yl)-5-propoxypyrrolo[1,2-a]quinazoline (4d). Orange solid; mp, 127–129 °C; ¹H NMR (300 MHz, CDCl₃): δ 0.81 (t, J = 7.3 Hz, 3H, CH₃), 1.58–1.77 (m, 2H, CH₂), 2.44–2.58 (m, 2H, NCH₂), 3.29–3.32 (m, 2H, NCH₂), 3.74–3.92 (m, 4H, 2OCH₂), 4.24 (t, J = 6.6 Hz, 2H, OCH₂), 6.18 (d, J = 4.2 Hz, 1H, CH of pyrrole), 6.59 (d, J = 4.2 Hz, 1H, CH of pyrrole); 7.23–7.47 (m, 2H, Ar–H), 7.53–7.65 (m, 1H, Ar–H), 8.93 (d, J = 8.1 Hz, 1H, 9-H); ¹³C NMR (75 MHz, CDCl₃): δ 10.90, 14.76, 52.03, 66.19, 68.26, 100.36, 104.22, 117.89, 121.00, 126.12, 126.42, 128.90, 136.76, 154.19, 163.37, 175.42; IR (KBr): 2950, 2840, 1620, 1500, 1110 cm⁻¹; m/z [M]⁺ 311; HRMS for C₁₈H₂₁N₃O₂ calculated [MH] 311.1634; found m/z = 311.1629.

1-(Piperidin-1-yl)-5-propoxypyrrolo[1,2-a]quinazoline (4e). Brown solid; mp, 125–126 °C; ¹H NMR (300 MHz, CDCl₃): δ 0.82 (t, J = 7.3 Hz, 3H, CH₃), 1.18–1.37 (m, 2H, CH₂), 1.57–1.71 (m, 6H, 3CH₂), 2.51–2.59 (m, 2H, NCH₂), 3.22–3.25 (m, 2H, NCH₂), 4.14 (t, J = 6.6 Hz, 2H, OCH₂), 6.21 (d, J = 4.2 Hz, 1H, CH of pyrrole), 6.63 (d, J = 4.2 Hz, 1H, CH of pyrrole), 7.15–7.18 (m, 1H, Ar–H), 7.43–7.47 (m, 1H, Ar–H), 7.55–7.63 (m, 1H, Ar–H), 8.93 (d, J = 8.4 Hz, 1H, 9-H); ¹³C NMR (75 MHz, CDCl₃): δ 10.98, 14.08, 23.76, 25.77, 53.83, 68.16, 100.40, 104.38, 116.19, 122.87, 126.61, 127.68, 128.81, 135.46, 154.11, 165.78, 175.28; IR (KBr): 2955, 2840, 1615, 1515, 1110 cm⁻¹; m/z [M]⁺ 309; HRMS for C₁₉H₂₃N₃O calculated [MH] 309.1841; found m/z = 309.1846.

5-Butoxy-1-(piperidin-1-yl)pyrrolo[1,2-a]quinazoline (4f). Orange solid; mp, 117–119 °C; ¹H NMR (300 MHz, CDCl₃): δ 0.85 (t, J = 7.4 Hz, 3H, CH₃), 1.17–1.47 (m, 4H, 2CH₂), 1.65–1.79 (m, 6H, 3CH₂), 2.51–2.58 (m, 2H, NCH₂), 3.21–3.25 (m, 2H, NCH₂), 4.14 (t, J = 6.6 Hz, 2H, OCH₂), 6.21 (d, J = 4.2 Hz, 1H, CH of pyrrole), 6.62 (d, J = 4.0 Hz, 1H, CH of pyrrole), 7.12–7.18 (m, 1H, Ar–H), 7.44–7.56 (m, 2H, Ar–H), 8.93 (d, J = 7.8 Hz, 1H, 9-H); ¹³C NMR (75 MHz, CDCl₃): δ 10.96, 13.94, 19.34, 24.06, 26.20, 57.34, 68.04, 100.38, 105.69, 116.20, 122.85, 126.66, 127.71, 128.82, 135.05, 154.18, 168.20, 175.18; IR (KBr): 2950, 2850, 1615, 1525, 1110 cm⁻¹; m/z [M]⁺ 323. HRMS for C₂₀H₂₅N₃O calculated [MH] 323.1998; found m/z = 323.1995.

5-Butoxy-1-(morpholin-4-yl)pyrrolo[1,2-a]quinazoline (4g). Orange solid; mp, 121–123 °C; ¹H NMR (300 MHz, CDCl₃): δ 0.82 (t, J = 7.4 Hz, 3H, CH₃), 1.15–1.37 (m, 2H, CH₂), 1.57–1.72 (m, 2H, CH₂), 2.51–2.56 (m, 2H, NCH₂), 3.22–3.57 (m, 2H, NCH₂), 4.14 (t, J = 6.6 Hz, 2H, OCH₂), 6.21 (d, J = 4.2 Hz, 1H, CH of pyrrole), 6.64 (d, J = 4.2 Hz, 1H, CH of pyrrole), 7.17–7.21 (m, 1H, Ar–H), 7.43–7.47 (m, 1H, Ar–H), 7.55–7.64 (m, 1H, Ar–H), 8.93 (d, J = 8.1 Hz, 1H, 9-H); ¹³C NMR (75 MHz, CDCl₃): δ 10.98, 14.08, 19.38, 57.56, 66.75, 68.17, 101.84, 104.14, 116.31, 121.44, 126.43, 126.72, 128.82, 136.36, 155.01, 167.80, 175.83; IR (KBr): 2955, 2850, 1610, 1520, 1115 cm⁻¹; m/z [M]⁺ 325; HRMS for C₁₉H₂₃N₃O₂ calculated [MH] 325.1790; found m/z = 325.1794.

1,5-Di(4-yl)pyrrolo[1,2-a]quinazoline (4h). Yellow solid; mp, 149–151 °C; ¹H NMR (400 MHz, CDCl₃): δ 2.45–2.60 (m, 2H, NCH₂), 3.16–3.18 (m, 2H, NCH₂), 3.33–3.56 (m, 4H, 2NCH₂), 3.68–4.10 (m, 8H, 4OCH₂), 6.38 (d, J = 4.0 Hz, 1H, CH of pyrrole), 6.83 (d, J = 4.0 Hz, 1H, CH of pyrrole), 7.25–7.27 (m, 1H, Ar–H), 7.48–7.50 (m, 1H, Ar–H), 7.65–7.67 (m, 1H, Ar–H), 8.90 (d, J = 9.0 Hz, 1H, 9H); ¹³C NMR (75 MHz, CDCl₃): δ 52.12, 54.38, 66.25, 64.37, 100.26, 105.31, 115.23, 122.51, 125.37, 126.11, 127.48, 136.05, 152.89, 162.28, 171.23; IR (KBr): 2950, 2850, 1610, 1520, 1115 cm⁻¹; m/z [M]⁺ 338; HRMS for C₁₉H₂₂N₄O₂ calculated [MH] 338.1743; found m/z = 338.1745.

1-(Morpholin-4-yl)-5-(piperidin-1-yl)pyrrolo[1,2-a]quinazoline (4i). Yellow solid; mp, 145–147 °C; ¹H NMR (300 MHz, CDCl₃): δ 1.61–1.85 (m, 6H, 3CH₂), 2.34–2.49 (m, 2H, NCH₂), 3.10–3.21 (m, 2H, NCH₂), 3.61–3.72 (m, 4H, 2NCH₂), 3.96–4.09 (m, 4H, 2OCH₂), 6.38 (d, J = 4.2 Hz, 1H, CH of pyrrole), 6.75 (d, J = 4.2 Hz, 1H, CH of pyrrole), 7.19–7.42 (m, 2H, Ar–H), 7.64–7.69 (m, 1H, Ar–H), 8.86 (d, J = 8.0 Hz, 1H, 9 H); ¹³C NMR (75 MHz, CDCl₃): δ 24.84, 25.94, 51.20, 53.37, 66.42, 100.39, 104.83, 115.42, 122.74, 125.53, 126.12, 135.84, 153.07, 161.27, 171.13; IR (KBr): 2950, 2850, 1600, 1510, 1100 cm⁻¹; m/z [M]⁺ 336; HRMS for C₂₀H₂₄N₄O calculated [MH] 336.1950; found m/z = 336.1951.

Anti-bacterial assay

The anti-bacterial activities of pyrrolo[1,2-a]quinazolines were evaluated biologically using a well-diffusion method. First the nutrient agar and nutrient broth cultures were prepared according to the manufacturer's instructions, and they were then incubated at 37 °C. After incubation for the appropriate time period, a suspension of 30 μL of each bacterium was added to the nutrient agar plates. Cups (5 mm in diameter) were cut in the agar using a sterilized glass tube. Each well received 30 μL of the test compounds at a concentration of 1000 μg mL⁻¹ in DMSO. Then the plates were incubated at 37 °C for 24 h, after which time, the inhibition zone was measured. The values were expressed in millimeters (mm). The anti-bacterial activity of each pyrrolo[1,2-a]quinazoline was compared with that for penicillin G and as the standard. DMSO was used as the negative control.

DPPH radical scavenging assay

The DPPH radical scavenging activities of 4a, 4d, 4e, 4f, and 4h were evaluated according to the literature.²³ The DPPH solution was prepared by dissolving an appropriate amount of DPPH in MeOH to give a concentration of 6.25 × 10⁻⁵ M. Compounds 4a, 4d, 4e, 4f, 4h, and DPPH with different concentrations (4000, 2000, 1000, 500, 250, and 125 μg mL⁻¹) in MeOH were prepared. Then 0.1 mL of each pyrrolo[1,2-a]quinazoline solution was added to 3.9 mL of the DPPH solution, and was shaken vigorously. The samples were kept in dark for 30 min, and then their absorbance was measured at 517 nm. MeOH was used as the blank. The radical scavenging activity was calculated as follows:

Radical scavenging activity (%) = [(A_control − A_sample)/A_control] × 100

where A_control is the absorbance of the negative control (containing all reagents except the test compounds) and A_sample is the absorbance of the test compounds. IC₅₀ values of the test compounds were determined by plotting the radical scavenging activity percentage against the concentration of the test compound.

Acknowledgements

The authors wish to express their thanks to the Research Council of Shahrood University of Technology for the financial support of this research work.

References

1. D. L. Dreyer and R. C. Brenner, Phytochemistry, 1980, 19, 935–939.
2. V. Alagarsamy, V. R. Solomon and K. Dhanabal, Bioorg. Med. Chem., 2007, 15, 235–241.
3. M. S. Malamas and J. Millen, J. Med. Chem., 1991, 34, 1492–1503.
4. Z. Tetere, D. Zicane, I. Ravina, I. Mierina and I. Rijikure, Material Science and Applied Chemistry, 2014, 30, 51–54.
5. V. Alagarsamy, R. Giridhar, H. R. Yadav, R. Revathi, K. Rukmani and E. De Clercq, Indian J. Pharm. Sci., 2006, 68, 532–535.
6. D. P. Gupta, S. Ahmed, A. Kumar and K. Shankar, Indian J. Chem., 1988, 27, 1060–1062.
7. H. J. Wang, C. X. Wei, X. Q. Deng, F. L. Li and Z. S. Quan, Arch. Pharm., 2009, 342, 671–675.
8. V. Joshi and R. P. Chaurasia, Indian J. Chem., 1978, 26, 602–604.
9. E. Toja, A. Depaoli, G. Tuan and J. Kettenring, Synthesis, 1987, 3, 272–274.
10. F. Bellina and R. Rossi, Tetrahedron, 2006, 62, 7213–7256.
11. (a) M. Joseph, H. Muchowski Stefan, T. Unger, J. Ackrell, P. Cheung, F. Gary and C. J. Cook, J. Med. Chem., 1985, 28, 1037–1049; (b) G. Dannhardt, W. Kiefer, G. Kramer, S. Maehrlein, U. Nowe and B. Fiebich, Eur. J. Med. Chem., 2000, 35, 499–510; (c) I. K. Khanna, R. M. Weier, Y. Yu, P. W. Collins, J. M. Miyashiro, C. M. Koboldt, A. W. Veenhuizen, J. L. Currie, K. Seibert and P. C. Isakson, J. Med. Chem., 1997, 40, 1619–1633; (d) B. S. Burnham, J. T. Gupton, K. E. Krumpe, T. Webb, J. Shuford, B. Bowers, A. E. Warren, C. Barnes and I. H. Hall, Arch. Pharm., 1998, 331, 337–341; (e) J. T. Gupton, B. S. Burnham, B. D. Byrd, K. E. Krumpe, C. Stokes, J. Shuford, S. Winkle, T. Webb, A. E. Warren, C. Barnes, J. Henry and I. H. Hall, Pharmazie, 1999, 54, 691–697.
12. (a) M. H. Justin, K. O'Toole-Colin, A. Getzel, A. Argenti and A. Michael, Molecules, 2004, 9, 134–157; (b) K. Krowicki, T. Jan Balzarini, E. De Clercq, A. Robert and J. William Lawn, J. Med. Chem., 1988, 31, 341–345; (c) A. M. Almerico, P. Diana, P. Barraja, G. Dattolo, F. Mingoia, A. G. Loi, F. Scintu, C. Milia, I. Puddu and P. La Colla, Farmaco, 1998, 53, 33–40; (d) D. T. Dannhar, G. Kiefer, W. Kramer, G. Maehrlein, S. Nowe and U. Fiebich, Eur. J. Med. Chem., 2000, 35, 499–510; (e) M. A. Evans, D. C. Smith, J. M. Holub, A. Argenti, M. Hoff and G. A. Dalglish, Arch. Pharm., 2003, 336, 181–190.
13. T. Harayama, Y. Morikami, Y. Shigeta, H. Abe and Y. Takeuchi, Synlett, 2003, 6, 847–848.
14. P. Barraja, V. Spano, P. Diana and A. Carbone, Tetrahedron Lett., 2009, 50, 5389–5391.
15. S. Sarno, M. Ruzzene, P. Frascella, M. A. Pagano, F. Meggio, A. Zambon, M. Mazzorana, G. Di Maira, V. Lucchini and L. A. Pinna, Mol. Cell. Biochem., 2005, 274, 69–76.
16. R. Anderskewitz, H. Dollinger, C. Heine, P. Pouzet, F. Birke and T. Bouyssou, PCT Int. Appl Chem Abstr, WO 2004072074 A1 26, 2004, vol. 141, p. 225527.
17. I. Rioja, M. C. Terencio, A. Ubeda, P. Molina, A. Tarraga, A. Gonzalez-Tejero and M. Alcaraz, Eur. J. Pharmacol., 2002, 434, 177–185.
18. (a) A. Dixit, S. K. Kashaw, S. Gaur and A. K. Saxena, Bioorg. Med. Chem., 2004, 12, 3591–3598; (b) B. E. Maryanoff, H. C. Zhang and D. F. McComsey, PCT Int. Appl. Chem. Abstr, WO 2002068425 A1 6, 2002, vol. 137, p. 216956; (c) H. S. Ahn, C. Foster, G. Boykow, A. Stamford, M. Manna and M. Graziano, Biochem. Pharmacol., 2000, 60, 1425–1434.
19. F. Dumitrascu and M. M. Popa, ARKIVOC, 2014, i, 428–452.
20. T. Honda, H. Enomoto, K. Kawashima, S. Takaoka, Y. Fujioka, M. Matsuda, K. Ohashi, Y. Fujita, S. Hirai and H. Kurashima, WO Patent 2013008872/A1, 2013.
21. F. K. Krichner and A. W. Zalay, US Pat., 3 843 654, 1974.
22. S. C. Bell and G. T. Conklin, US Pat., 3 707 468, 1972.
23. (a) K. I. Ozaki, Y. Yamada and T. Oine, Chem. Pharm. Bull., 1983, 31, 2234–2245; (b) M. Volovenko and E. V. Resnyanska, Mendeleev Commun., 2002, 12, 119–120; (c) E. S. Vostrov, D. V. Gilev and A. N. Maslivets, Chem. Heterocycl. Compd., 2004, 40, 532–535; (d) H. A. Soleiman, Open Catal. J., 2011, 4, 18–26.
24. (a) E. E. Garcia, J. G. Riley and R. I. Fryer, J. Org. Chem., 1968, 33, 1359–1363; (b) F. Ishikawa, A. Kosayama and K. Abiko, JP Pat., 53 044 592, 1978; (c) F. Ishikawa, A. Kosayama and K. Abiko, JP Pat., 53 044 593, 1978; (d) A. M. Salah Eldin, Heteroat. Chem., 2003, 14, 612–616.
25. (a) J. Cobb, N. L. Demetropoulos, D. Korakas, S. Skoulika and G. Varvounis, Tetrahedron, 1996, 52, 4485–4498; (b) F. M. Abdelrazek and M. S. Bahbouh, Phosphorus, Sulfur Silicon Relat. Elem., 1996, 116, 235–240; (c) F. Abdelrazek and N. Metwally, Synth. Commun., 2006, 36, 83–89; (d) H. Schaefer and K. Gewald, Monatsh. Chem., 1989, 120, 315–322.
26. (a) D. Zicane, I. Ravina, Z. Tetere and M. Turks, LV Pat., 14 663, 2013; (b) D. Zicane, Z. Tetere, I. Ravina and M. Turks, Chem. Heterocycl. Compd., 2013, 49, 310–316; (c) E. Feng, Y. Zhou, D. Zhang, L. Zhang, H. Sun, H. Jiang and H. Liu, J. Org. Chem., 2010, 75, 3274–3282; (d) N. T. Patil, P. G. V. V. Lakshmi, B. Sridhar, S. Patra, M. P. Bhadra and C. R. Patra, Eur. J. Org. Chem., 2012, 36, 1790–1799.
27. (a) N. T. Patil, R. D. Kavthe, V. S. Raut, V. Shinde and B. J. Sridhar, Org. Chem., 2010, 75, 1277–1280; (b) M. M. Zhang, L. Lu, Y. J. Zhou and X. S. Wang, Res. Chem. Intermed., 2013, 39, 3327–3335; (c) E. M. Campi, W. R. Jackson and A. E. Trnacek, Aust. J. Chem., 1997, 50, 1031–1034.
28. (a) F. M. Abdelrazek and N. H. Metwally, Synth. Commun., 2009, 39, 4088–4099; (b) M. Langlois, C. Guilloneau, T. Vovan, R. Jolly and J. Maillard, J. Heterocycl. Chem., 1983, 20, 393–398; (c) C. G. Dave and R. D. Shah, Heterocycles, 1998, 48, 529–536; (d) F. Fulop, F. Miklos and E. Forro, Synlett, 2008, 1687–1689.
29. (a) R. T. Iminov, A. V. Tverdokhlebov, A. A. Tolmachev, M. Volovenko Yu, A. N. Kostyuk, A. Chernega and E. B. Rusanov, Heterocycles, 2008, 75, 1673–1680; (b) M. Wang, G. Dou and D. J. Shi, J. Comb. Chem., 2010, 12, 582–586; (c) X. Zhao and D. J. Shi, Heterocycl. Chem., 2011, 48, 634.
30. (a) Y. Kitano, T. Suzuki, E. Kawahara and T. Yamazaki, Bioorg. Med. Chem. Lett., 2007, 17, 5863–5867; (b) M. J. Mphahlele and M. M. Maluleka, Molecules, 2014, 19, 17435–17463; (c) C. Kieffer, P. Verhaeghe, N. Primas, C. Castera-Ducros, A. Gellis, R. Rosas, S. Rault, P. Rathelot and P. Vanelle, Tetrahedron, 2013, 69, 2987–2995; (d) Y. Peng, P. Huang, Y. Wang, Y. Zhou, J. Yuan, Q. Yang, X. Jiang and Z. Deng, Org. Biomol. Chem., 2014, 12, 5922–5927.
31. (a) A. Keivanloo, M. Bakherad, H. Nasr-Isfahani and S. Esmaily, Tetrahedron Lett., 2012, 53, 3126–3130; (b) A. Keivanloo, M. Bakherad and A. Rahimi, Synthesis, 2010, 10, 1599–1602; (c) M. Bakherad, H. Nasr-Isfahani, A. Keivanloo and N. Doostmohammadi, Tetrahedron Lett., 2008, 49, 3819–3822.
32. H. J. Wang, C. X. Wei, X. Q. Deng, F. L. Li and Z. S. Quan, Arch. Pharm. Chem. Life Sci., 2009, 342, 671–675.
33. (a) J. Odingo, T. O'Malley, E. A. Kesicki, T. Alling, M. A. Bailey, J. Early, J. Ollinger, S. Dalai, N. Kumar, R. V. Singh and P. A. Hipskind, Bioorg. Med. Chem., 2014, 22, 6965–6979; (b) V. J. Ram, B. K. Tripathi and A. K. Srivastava, Bioorg. Med. Chem., 2003, 11, 2439–2444.
34. B. Singh and R. A. Sharma, Phytomedicine, 2013, 20, 441–445.

---

Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ra21219k

---