Synthesis of New Furothiazolo Pyrimido Quinazolinones from Visnagenone or Khellinone and Antimicrobial Activity.

Substituted-6-methyl-1-thioxo-1,2-dihydro-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-ones (5a,b) were synthesized from condensation of visnagenone (2a) or khellinone (2b) with 6-amino-thiouracil (3) in dimethylformamide or refluxing of (4a) or (4b) in dimethylformamide. Hence, compounds (5a,b) were used as the starting materials for preparing many new heterocyclic compounds such as; furo[3,2-g]pyrimido[1,6-a]quinazoline (6a,b), furo[3,2-g]thiazolo[2',3':2,3]pyrimido[1,6-a]quinazolinone (7a,b), substituted-benzylidene-furo[3,2-g]thiazolo[2',3':2,3]pyrimido[1,6-a]quinazoline-3,5-dione (8a⁻f), 3-oxo-furo[3,2-g]pyrimido[1,6-a]quinazoline-pentane-2,4-dione (9a,b), 1-(pyrazole)-furo[3,2-g]pyrimido[1,6-a]quinazolinone (10a,b), 2-(oxo or thioxo)-pyrimidine-furo[3,2-g]pyrimido[1,6-a]quinazolinone (11a⁻d), 1-(methylthio)-furo[3,2-g]pyrimido[1,6-a]quinazolinone (12a,b), 1-(methyl-sulfonyl)-furo[3,2-g]pyrimido[1,6-a]quinazolinone (13a,b) and 6-methyl-1-((piperazine) or morpholino)-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (14a⁻d). The structures of the prepared compounds were elucidated on the basis of spectral data (IR, ¹H-NMR, 13C-NMR, MS) and elemental analysis. Antimicrobial activity was evaluated for the synthesized compounds against Gram-positive, Gram-negative bacteria and fungi. The new compounds, furothiazolo pyrimido quinazolines 8a⁻f and 11a⁻d displayed results excellent for growth inhibition of bacteria and fungi.

1. Introduction

Physicians confirm the usefulness of adding many naturally occurring drugs. n class="Chemical">Furochromones (visnagin and khellin) compounds are natural products extracted from the plant of Ammi visnaga Lam. and visnagin and khellin are used as therapy for kidney, bladder stones, diuretic infusions [1,2] and are considered essential components of many drugs [3]. As well, furochromone derivatives are reported as anti-atherosclerotic, antineoplastic, anti-gastric, anti-anaphylactic and are used in the treatment of urolithiasis, hypertriglyceridemia [4,5] and vitiligo [6]. Also, the visnaginone derivatives were synthesized using different procedures and elucidated efficient antimicrobial activities [7,8]. Furthermore, furochromones have been used to treat pain in the renal colic [9] and possesses coronary vasodilating activity [10,11]. Moreover, khellin and visnagin have been used in the photo-chemotherapeutic treatment of vitiligo and psoriasis [12], photoreaction with DNA [13] and Khellin displayed important epidermal growth factor receptor (EGFR) inhibitory activity [14]. Benzofurans and furochromones [15,16,17,18] are very exciting heterocycles, which are omnipresent in nature and display a wide range of pharmacological activities. Recently, furochromones and benzofurans derivatives are used as in antiviral and anticancer activities [19,20]. When fused of furochromones with pyrimidine, quinoxaline and pyrazole derivatives showed anti-inflammatory and analgesic activities [21], the cytotoxic activity [22] and used in the protection of DNA [23]. Additionally, some of the moieties heterocyclic such as, chalcones [24], thiazolidinones [25], Mannich bases [26], sulfonamides [27], and isoxazole [28], too, showed several of biological activity with benzofuran derivatives (visnagenone, khellinone) (Figure 1).

Figure 1

Chemical structure of furochromone derivatives.

An extension of our work on the preparation of novel heterocyclic compounds resultant from the naturally occurring n class="Chemical">visnagin and khellin [21,22,23,29], we synthesized and described several derivatives which contained a benzofuran moiety (visnaginone, khellinone) incorporated with thiazole, pyrimidine, pyrazole, and quinazolinone derivatives. The antimicrobial activity of the prepared compounds were evaluated.

2. Results and Discussion

2.1. Synthesis

In the present work, the natural furochromones (n class="Chemical">visnagin 1a or khellin 1b) are highly sensitive to alkali. Hence, aqueous alkaline hydrolysis of 1a and 1b using potassium hydroxide with heating and stirring at 40–50 °C for 1–2 h lead to form visnagenone 2a or khellinone 2b, respectively [22,23]. Moreover, heating under reflux cyclic alfa, beta-unsaturated ketones (visnagenone 2a or khellinone 2b) with 6-aminothiouracil (3) in dimethylformamide solution [21,22] with stirring for 4–6 h or 14–16 h under (TLC) afforded new compounds respectively, 6-((1-(6-hydroxy-(4-methoxy or 4,7-dimethoxy)-benzofuran-5-yl)ethylidene)amino)-2-thioxo-2,3-dihydropyrimidin-4(1H)-one (4a,b) and (7-methoxy or 7,11-dimethoxy)-6-methyl-1-thioxo-1,2-dihydro-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (5a,b) in good yield obtained. Also, another method, stirring under reflux of 4a or 4b in dimethylformamide solution for 8–10 h afforded the same products 5a and 5b, respectively. The 1H-NMR spectrum of compound 4a showed three singlet broad signal at 10.80, 11.19 and 16.11 ppm corresponding to the three protons of the (2NH) and one (OH) groups, which were D2O exchangeable and 1H-NMR spectrum of compound 5a showed one singlet broad signal at 11.20 ppm conforming to the one proton of the one (NH) group (D2O exchangeable) and the mass spectra of 4a, 4b, 5a and 5b showed molecular ion peaks at m/z 331 (M+, 100%) and 361 (M+, 100%), 313 (M+, 100%), 343 (M+, 100%) respectively (Scheme 1).

Scheme 1

Synthesis of furopyrimido quinazolinones from visnagenone and khellinone derivatives.

In this research, simple and convenient methods to the syntheses of n class="Chemical">furopyrimido quinazoline, furothiazolo pyrimido quinazolinone and furothiazolo pyrimido quinazolinone benzylidene derivatives [30]. Thus, refluxing of 5a or 5b with chloroacetic acid in glacial acetic acid/acetic anhydride and anhydrous sodium acetate for 3–5 h or 13–15 h with control via (TLC) to give new compounds followed by, 2-(((7-methoxy or 7,11-dimethoxy)-6-methyl-3-oxo-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-1-yl)thio)acetic acid (6a,b) and (9-methoxy or 9,13-dimethoxy)-8-methyl-2-hydro-5H,14aH-furo[3,2-g]thiazolo[2′,3′:2,3]pyrimido[1,6-a]quinazoline-3,5-dione (7a,b) in high yields. Moreover, the boiling of 6a or 6b in dimethylformamide solution resulted in the same formation of 7a and 7b. The IR spectrum of compounds 6a and 6b exposed the presence of broad band absorption at 3340–3350 cm−1 indicative of one (OH) group and 6a = 1745, 1684 cm−1 and 6b = 1748, 1681 cm−1 of the two carbonyl groups. The 1H-NMR spectrum of 6a showed a singlet broad signal at 13.70 ppm corresponding to the one protons of the one (OH) group, which were D2O exchangeable. Also, 1H-NMR spectrum of 7b displayed a five singlet signal at δ 2.33, 3.97, 4.24, 5.62 and 7.39 ppm conforming to the thirteen protons of the methyl, two methoxy, (CH2), (CH, thiazole) and (CH, pyrimidine) groups, respectively. As well as using one-pot synthesis as follows: when a ternary mixture of 5a or 5b, chloroacetic acid and a proper aldehyde namely; benzaldehyde, 4-chlorobenzaldehyde or 4-methoxybenzaldehyde respectively, was heated under reflux in a mixture of acetic acid and acetic anhydride in the presence of anhydrous sodium acetate afforded the conforming 2-(substituted-benzylidene)-9,(substituted)-methoxy-8-methyl-2-hydro-5H,14aH-furo[3,2-g]thiazolo[2′,3′:2,3]pyrimido[1,6-a]quinazoline-3,5-dione (8a–f) in high yields. In another route, we obtained on the same compounds (8a–f) via refluxing of 7a or 7b with appropriate aromatic aldehyde in dioxane solution containing a catalyst amount of piperidine for 10–12 h. 1H-NMR spectrum of 8a showed six singlets at 2.30, 3.91, 5.59, 7.32, 7.85 and 8.05 ppm conforming to the 10 protons of the methyl, methoxy, thiazole proton, pyrimidine proton, phenyl proton and (CH) proton groups, respectively and two doublet signals at 6.75, 7.72 ppm of the two protons (J = 2.30 Hz, furan). The structures assignments for compounds were established on their elemental analysis and spectral (IR, 1H, 13C-NMR, and MS) data are shown in the experimental section (Scheme 2).

Scheme 2

Synthesis of furothiazolopyrimidoquinazolinone derivatives.

Alkylation of an ethanolic n class="Chemical">potassium hydroxide solution of 5a or 5b with 3-chloro-pentane-2,4-dione(3-chloroacetylacetone) [30], yielded the 3-(((7-methoxy or 7,11-dimethoxy)-6-methyl-3-oxo-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-1-yl)thio)pentane-2,4-dione (9a,b) in high yield. The IR spectra of 9a and 9b showed a strong absorption bands at 9a = 1725, 1721, 1682 cm−1 and 9b = 1728, 1722, 1684 cm−1 characteristic to three carbonyl groups, respectively. The 13C-NMR (DMSO-d6, ppm) of 9a showed signals at 68.2, 91.3 and 96.5 for three carbon atoms of (CH), (CH, phenyl) and (CH, pyrimidine) and signals at 168.6, 184.5 and 188.2 three carbon atoms of the three carbonyl groups, and the molecular ion peaks of 9a and 9b at m/z 411 (95%) and 441 (90%), respectively. On the other hand, compounds 9a and 9b, as a typical 1,3-diketone condensation with each of hydrazine hydrate, urea and thiourea to afford the corresponding 1-((3,5-dimethyl-1H-pyrazol-4-yl)thio)-(7-methoxy or 7,11-dimethoxy)-6-methyl-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (10a,b) and 1-((4,6-dimethyl-2-(oxo or thioxo)-1,2-dihydropyrimidin-5-yl)thio)-(7-methoxy or 7,11-dimethoxy)-6-methyl-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (11a–d), respectively. IR spectrum of 10a and 10b showed absorption of a broad band at 3380–3360 cm−1 corresponding to NH group. Also, the compounds 11a–d exhibited absorption bands at 3390–3370 cm−1 for NH group were detected in the IR spectrum. 1H-NMR spectrum of 10a showed one singlet at 11.50 ppm corresponding to the one proton of NH group and compound 11a revealed one singlet at 10.60 ppm for one proton of NH group (D2O exchangeable). All new compounds were proven by elemental and spectral analysis (IR, 1H, 13C-NMR and MS) which is mentioned in the experimental part (Scheme 3).

Scheme 3

Synthesis of pyrazole, pyrimidine, -furopyrimido quinazolinone derivatives.

Alkylation of an ethanolic n class="Chemical">potassium hydroxide solution of 5a or 5b with methyl-iodide yielded the (7-methoxy or 7,11-dimethoxy)-6-methyl-1-(methylthio)-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (12a,b). Assignment of structures 12a and 12b to the reaction products is based on correct elemental analysis and IR, NMR spectroscopy are in agreement with the structure. Thus, 1H-NMR spectrum of 12a or 12b showed one singlet signal at 2.80 or 2.88 ppm indicative of three protons to (SCH3) group and the molecular ion peaks of 12a or 12b displayed at m/z 327 (M+, 100%) and 357 (M+, 100%), respectively. Moreover, oxidation of 12a or 12b with hydrogen peroxide in acetic acid yielded the (7-methoxy or 7,11-dimethoxy)-6-methyl-1-(methylsulfonyl)-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (13a,b). The IR spectrum of 13a exposed the presence of two bands at 1162, 1340 cm−1 corresponding to (SO2) group, and 1H-NMR spectrum of 13a exhibited one singlet at 2.95 agreeing to the three protons of (SO2CH3) group. Furthermore, heating under refluxing compounds 12a or 12b with secondary aliphatic amines [21,22,30], namely piperazine or morpholine in methanol, produced the (7-methoxy or 7,11-dimethoxy)-6-methyl-1-((piperazin-1-yl) or morpholino)-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (14a–d). IR spectrum of 14a displayed absorption bands at 3390, 1687 cm−1 conforming to NH and carbonyl group, respectively. Additionally, the 1H-NMR spectrum of 14c displayed a singlet broad signal at 10.35 ppm conforming to the one proton of the one (NH) group, which was D2O exchangeable. The mass spectrum of 13a, 13b, 14a, 14b, 14c and 14d revealed molecular ion peaks at m/z 359 (M+, 84%), 389 (M+, 80%), 365 (M+, 83%), 366 (M+, 78%), 395 (M+, 76%) and 396 (M+, 74%), respectively (Scheme 4).

Scheme 4

Synthesis of piperazine, morpholine, -furopyrimido-quinazolinone derivatives.

2.2. Biological Screening

The antimicrobial activity of the compounds was tested in vitro and the results are shown in Table 1 and Table 2. Some of these n class="Chemical">compounds indicated highest antimicrobial activity, comparable to cefotaxime sodium (MIC = 2–5 μmol mL−1). Compounds 8a–f, 11a–d and 10a–b displayed potent antimicrobial activity against Gram-positive bacteria; Staphylococcus aureus (ATCC®6538™), Streptococcus pyogenes (ATCC®19615™) and Gram-negative bacteria; Escherichia coli (ATCC®25922™), Klebsiella pneumoniae (ATCC® 10031™). Also, another compounds; 14a–d, 7a–b and 9a–b exhibited moderate antimicrobial activities. The MIC values in μmol mL−1 of these compounds were as the following, 8a–f (1–8), 11 a–d (6–10), 10a–b (9–12). Compounds 8a–f and 11a–d exposed too higher antifungal activity with MIC in μmol/cm3 of 8a–f (2–9) and 11a–d (7–12) whose results were comparable with the positive control, nystatin (MIC 2-4 μmol mL−1). Some of compounds revealed moderate anti-fungal activity when compared with the nystatin (MIC 2–4 μmol mL−1): 10a–b (10–14), 14a–d (12–18), 7a–b (15–20) and 9a–b (17–22). The tested fungi were Aspergillus niger (ATCC® 16888™), Alternaria alternate, Curvularia lunata and Candida albicans (ATCC®10231™). Thru comparing the observed antimicrobial activities of the furopyrimido quinazolinones, furothiazolo pyrimido quinazolinones obtained in this study to their structures, the (SAR’s) were suggested; the presence of the functional groups linked with visnagenone 2a or khellinone 2b derivatives, such as thioxo, methyl, hydroxyl, methoxy, amino, chloro, substituted-benzylidene, thiazole, quinazoline, pyrimidine, pyrazole, methylsulfonyl, piperazine and morpholine moieties. Remainder the compounds demonstrated a weak activity compared to the antimicrobial activity of the standard drugs (cefotaxime sodium and nystatin). The thiazolopyrimidine derivatives possessing verified to be effective as antimicrobial agents in previous articles [7,8]. Also, they were active against Staphylococcus aureus, E. coli, and Klebsiella pneumoniae [7,31] and they were also effective against Streptococcus pyogenes and species of fungi, namely, Aspergillus niger, Candida albicans [7,32]. In this work and previous reports, most bacteria and fungi types effected susceptible to this class of heterocyclic compounds [33,34,35]. Moreover, previous results and our findings corroboration the promising antimicrobial activity of furothiazolopyrimidoquinazolinone derivatives which can be developed to higher antimicrobial activities

Table 1

A minimum inhibitory concentration of the compounds against bacteria.

MIC (µmol mL−1)
Compounds	Microorganisms
	Gram-Positive Bacteria		Gram-Negative Bacteria
	Staphylococcus Aureus	Streptococcus Pyogenes	E. coli	Klebsiella Pneumoniae
1a	34	33	31	30
1b	33	32	30	29
2a	31	30	29	28
2b	30	29	28	27
3	37	35	34	33
4a	29	28	27	26
4b	28	27	26	25
5a	27	26	25	24
5b	26	25	24	23
6a	23	22	21	20
6b	22	21	20	19
7a	17	16	15	14
7b	16	15	14	13
8a	8	7	7	5
8b	5	4	3	2
8c	7	6	5	4
8d	7	7	6	4
8e	4	3	2	1
8f	6	5	4	3
9a	19	18	17	16
9b	18	17	16	15
10a	12	11	10	10
10b	11	11	10	9
11a	10	10	9	8
11b	9	8	7	7
11c	10	9	8	7
11d	8	8	7	6
12a	25	24	23	22
12b	24	23	22	21
13a	21	20	19	18
13b	20	19	18	17
14a	14	13	12	11
14b	15	14	14	12
14c	13	12	11	10
14d	14	14	13	12
Cefotaxime sodium	5	4	3	2
Negativecontrol	NI	NI	NI	NI

DMSO was used as the negative control and as the solvent for test compounds and the reference drug. NI–No inhibition.

Table 2

A minimum inhibitory concentration of the compounds against fungi.

MIC (µmol mL−1)
Compounds	Microorganisms
	Aspergillus Niger	Alternaria Alternata	Curvularia Lunata	Candida Albicans
1a	39	38	37	36
1b	38	36	34	33
2a	35	34	33	32
2b	33	32	31	30
3	42	40	39	38
4a	31	30	29	28
4b	30	29	27	26
5a	29	28	26	25
5b	29	27	26	25
6a	26	24	23	22
6b	25	23	22	21
7a	20	18	17	16
7b	19	17	16	15
8a	9	8	8	4
8b	6	5	4	3
8c	8	7	6	5
8d	9	8	7	5
8e	5	4	3	2
8f	7	6	5	4
9a	22	20	19	18
9b	21	19	18	17
10a	14	13	12	11
10b	13	12	11	10
11a	12	11	10	9
11b	10	9	8	8
11c	11	10	9	8
11d	9	9	8	7
12a	28	26	25	24
12b	27	25	24	23
13a	24	22	21	20
13b	23	21	20	19
14a	16	15	14	13
14b	18	16	15	15
14c	15	14	13	12
14d	17	16	15	14
Nystatin	4	3	2	2
Negativecontrol	NI	NI	NI	NI

DMSO was used as the negative control and as the solvent for test compounds and the reference drug. NI–No inhibition.

3. Experimental Section

3.1. General Information

All melting points were taken on an Electrothermal IA 9100 series digital melting point apparatus (Shimadzu, Tokyo, Japan). Elemental analyses were performed on Vario EL (Elementar, Langenselbold, Germany). Microanalytical data were processed in the microanalytical center, Faculty of Science, Cairo University and National Research Centre. The IR spectra (KBr disc) were recorded using a Perkin-Elmer 1650 spectrometer (Waltham, MA, USA). NMR spectra were determined using JEOL 270 MHz and JEOL JMS-AX 500 MHz (JEOL, Tokyo, Japan) spectrometers with n class="Chemical">Me4Si as an internal standard. Mass spectra were recorded on an EI Ms-QP 1000 EX instrument (Shimadzu, Japan) at 70 eV. Biological evaluations were done by the antimicrobial unit, Department of Chemistry of Natural and Microbial Products, National Research Centre, Egypt. All starting materials and solvents were purchased from Sigma-Aldrich (Saint Louis, MO, USA).

3.2. General Procedure for Synthesis of 6-((1-(6-Hydroxy-(4-methoxy or 4,7-dimethoxy)-benzofuran-5-yl)ethylidene)amino)-2-thioxo-2,3-dihydropyrimidin-4(1H)-one (,)

A mixture of visnaginone n class="Chemical">2a (2.06 g, 0.01 mol) or khellinone 2b (2.36 g, 0.01 mol) with 6-amino-2-thioxo-2,3-dihydropyrimidin-4(1H)-one 3 (1.43 g, 0.01 mol) in dimethylformamide (40 mL) was refluxed for 4–6 h. The solid formed was filtered off, dried, and crystallized from the proper solvent to give 4a and 4b, respectively.

3.3. Synthesis of 6-((1-(6-Hydroxy-4-methoxybenzofuran-5-yl)ethylidene)amino)-2-thioxo-2,3-dihydro pyrimidin-4(1H)-one ()

The compound was obtained from the reaction of n class="Chemical">visnaginone (2a) with 6-amino-thiouracil (3) as yellow crystals, crystallized from methanol in 90% yield, m.p. 231 °C. IR (ν, cm−1) KBr: 3370 (brs, 2NH), 3030 (CH-aryl), 2960 (CH-aliph), 1685 (CO, amide), 1630 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.38 (s, 3H, CH3), 3.92 (s, 3H, OCH3), 6.79 (d, 1H, J = 2.35 Hz, furan), 7.80 (d, 1H, J = 2.38 Hz, furan), 7.92 (s, 1H, phenyl), 7.94 (s, 1H, pyrimidine), 10.80, 11.19 (br, 2H, 2NH, D2O exchangeable), 16.11 (br, 1H, OH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 21.3 (1C, CH3), 61.7 (1C, OCH3), 93.1 (1C, CH, pyrimidine), 98.9 (1C, CH, phenyl), 100.5, 104.5, 108.9, 146.6, 146.9, 154.5, 160.9, 163.2, (8C, Ar-C), 164.1 (1C, C=N-ph), 168.1(1C, C=O), 173.5 (1C, C=S); MS (70 eV, %) m/z 331 (M+, 100%); Anal. Calc. (Found) for C15H13N3O4S (331.35): C, 54.37 (54.30); H, 3.95 (3.91); N, 12.68(12.60).

3.4. Synthesis of 6-((1-(6-Hydroxy-4,7-dimethoxybenzofuran-5-yl)ethylidene)amino)-2-thioxo-2,3-dihydro pyrimidin-4(1H)-one ()

The compound was obtained from the reaction of khellinone (2b) with 6-amino-thiouracil (3) as yellowish crystals, crystallized from dioxane in 84% yield, m.p. 211 °C. IR (ν, cm−1) KBr: 3371(brs, 2NH), 3032 (CH-aryl), 2965 (CH-aliph), 1682 (CO, amide), 1631 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.39 (s, 3H, CH3), 3.94 (s, 6H, 2OCH3), 6.80 (d, 1H, J = 2.34 Hz, furan), 7.83 (d, 1H, J = 2.37 Hz, furan), 7.95 (s, 1H, pyrimidine), 10.81,11.20 (br, 2H, 2NH, D2O exchangeable), 16.12 (br, 1H, OH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 21.4 (1C, CH3), 61.6 (2C, OCH3), 93.2 (1C, CH, pyrimidine), 100.5, 104.7, 109.9, 129.3, 146.2, 147.1, 153.8, 158.9, 164.7, (9C, Ar-C), 165.2 (1C, C=N-ph), 167.9 (1C, C=O), 173.8 (1C, C=S); MS (70 eV, %) m/z 361 (M+, 100%); Anal. Calc. (Found) for C16H15N3O5S (361.37): C, 53.18 (53.23); H, 4.18 (4.13); N, 11.63 (11.68).

3.5. General Procedure for Synthesis of (7-Methoxy or 7,11-dimethoxy)-6-methyl-1-thioxo-1,2-dihydro-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (,)

Method A: A mix of visnaginone n class="Chemical">2a (2.06 g, 0.01 mol) or khellinone 2b (2.36 g, 0.01 mol) with 6-amino-2-thiouracil (3) in DMF (40 mL) was refluxed for 14–16 h. The product precipitated was filtered off and washed with 100 mL water, dried and crystallized from the proper solvent to give 5a and 5b, respectively. Method B: A refluxing of 4a (3.31 g, 0.01 mol) or 4b (3.61 g, 0.01 mol) in DMF (40 mL) was refluxed for 8–10 h under control (TLC). The final precipitated was filtered off and washed with 50 mL ethanol, dried, and crystallized from the proper solvent to give 5a and 5b, respectively.

3.6. Synthesis of 7-Methoxy-6-methyl-1-thioxo-1,2-dihydro-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of n class="Chemical">visnaginone (2a) with 6-aminothiouracil (3) or compound (4a) in dimethylformamide, as yellowish crystals, crystallized from benzene in 85% yield, m.p. 271 °C. IR (ν, cm−1) KBr: 3350 (brs, NH), 3028 (CH-aryl), 2955 (CH-aliph), 1680 (CO, amide), 1635 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.32 (s, 3H, CH3), 3.92 (s, 3H, OCH3), 6.75 (d, 1H, J = 2.33 Hz, furan), 7.33 (s, 1H, pyrimidine), 7.80 (d, 1H, J = 2.36 Hz, furan), 8.29 (s, 1H, phenyl), 11.20 (br, 1H, NH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 24.5 (1C, CH3), 61.8 (1C, OCH3), 79.7 (1C, CH, pyrimidine), 99.1 (1C, CH, phenyl), 104.9, 108.9,116.6, 140.9, 146.6, 148.9, 160.1, 161.2, 164.1 (9C, Ar-C), 168.2 (1C, C=O), 173.6 (1C, C=S); MS (70 eV, %) m/z 313 (M+, 100%); Anal. Calc. (Found) for C15H11N3O3S (313.33): C, 57.50 (57.58); H, 3.54 (3.59); N, 13.41(13.50).

3.7. Synthesis of 7,11-Dimethoxy-6-methyl-1-thioxo-1,2-dihydro-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of n class="Chemical">khellinone (2b) with 6-amino- thiouracil (3) or compound (4b) in dimethylformamide, as yellow crystals, crystallized from toluene in 82% yield, m.p. 251 °C. IR (ν, cm−1) KBr: 3352 (brs, NH), 3029 (CH-aryl), 2957 (CH-aliph), 1681 (CO, amide), 1633 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.35 (s, 3H, CH3), 3.95 (s, 6H, 2OCH3), 6.77 (d, 1H, J = 2.31 Hz, furan), 7.30 (s, 1H, pyrimidine), 7.82 (d, 1H, J = 2.37 Hz, furan), 11.25 (br, 1H, NH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 24.6 (1C, CH3), 61.9 (2C, 2OCH3), 80.2 (1C, CH, pyrimidine), 105.1, 109.2, 115.9, 125.8, 137.5, 142.8, 146.5, 149.2, 161.7, 164.8 (10C, Ar-C), 168.4 (1C, C=O), 173.8 (1C, C=S); MS (70 eV, %) m/z 343 (M+, 100%); Anal. Calc. (Found) for C16H13N3O4S (343.36): C, 55.97 (55.90); H, 3.82 (3.75); N, 12.24 (12.29).

3.8. General Procedure for Synthesis of 2-(((7-Methoxy or 7,11-dimethoxy)-6-methyl-3-oxo-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-1-yl)thio) Acetic Acid (,)

A mixture from 5a (3.13 g, 0.01 mol) or 5b (3.43 g, 0.01 mol), chloroacetic acid (0.94 g, 0.01 mol) and (0.02 mol) of anhydrous n class="Chemical">sodium acetate was stirred under reflux in 40 mL of glacial acetic acid and 20 mL of acetic anhydride for 3–5 h. The reaction mixture was cooled and poured into cold water (100 mL). The deposited precipitate was filtered off, and crystallized from appropriate solvent to produce 6a and 6b, respectively.

3.9. Synthesis of 2-((7-Methoxy-6-methyl-3-oxo-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-1-yl)thio) Acetic Acid ()

The compound was obtained from the reaction of (5a) with n class="Chemical">chloroacetic acid, as brownish crystals, crystallized from hexane in 88% yield, m.p. 294 °C. IR (ν, cm−1) KBr: 3340 (brs, OH), 3025 (CH-aryl), 2950 (CH-aliph), 1745 (CO, acid), 1684 (CO, amide), 1631 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.30 (s, 3H, CH3), 3.91 (s, 3H, OCH3), 4.27 (s, 2H, CH2), 6.77 (d, 1H, J = 2.32 Hz, furan), 7.35 (s, 1H, pyrimidine), 7.78 (d, 1H, J = 2.35 Hz, furan), 7.90 (s, 1H, phenyl), 13.70 (br, 1H, OH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 23.6 (1C, CH3), 32.8 (1C, CH2), 61.7 (1C, OCH3), 97.2 (1C, CH, phenyl), 100.6 (1C, CH, pyrimidine), 103.4, 105.3, 108.5, 143.7, 146.5, 152.2,158.4, 160.6, 163.9,164.8 (10C, Ar-C), 169.1, 172.8 (2C, 2C=O); MS (70 eV, %) m/z 371 (M+, 100%); Anal. Calc. (Found) for C17H13N3O5S (371.37): C, 54.98 (54.91); H, 3.53 (3.58); N, 11.32(11.40).

3.10. Synthesis of 2-((7,11-Dimethoxy-6-methyl-3-oxo-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-1-yl)thio) Acetic Acid ()

The compound was obtained from the reaction of (5b) with chloroacetic acid, as yellowish crystals, crystallized from ethanol in 86% yield, m.p. 283 °C. IR (ν, cm−1) KBr: 3345 (brs, OH), 3027 (CH-aryl), 2952 (CH-aliph), 1748 (CO, acid), 1681 (CO, amide), 1632 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.31 (s, 3H, CH3), 3.95 (s, 6H, 2OCH3), 4.25 (s, 2H, CH2), 6.79 (d, 1H, J = 2.35 Hz, furan), 7.38 (s, 1H, pyrimidine), 7.80 (d, 1H, J = 2.35 Hz, furan), 13.75 (br, 1H, OH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 23.4 (1C, CH3), 32.6 (1C, CH2), 61.3 (2C, 2OCH3), 100.1 (1C, CH, pyrimidine), 101.2, 105.4, 108.8, 124.1, 130.1, 146.2, 146.7, 150.5, 160.1, 164.4, 166.9 (11C, Ar-C), 169.5, 172.9 (2C, 2C=O); MS (70 eV, %) m/z 401 (M+, 100%); Anal. Calc. (Found) for C18H15N3O6S (401.39): C, 53.86 (53.80); H, 3.77 (3.71); N, 10.47 (10.42).

3.11. General Procedure for Synthesis of (9-Methoxy or 9,13-dimethoxy)-8-methyl-2-hydro-5H,14aH-furo[3,2-g]thiazolo[2′,3′:2,3] pyrimido[1,6-a]quinazoline-3,5-dione (,)

Method A: A mixture from 5a (3.13 g, 0.01 mol) or 5b (3.43 g, 0.01 mol), chloroacetic acid (0.94 g, 0.01 mol) and (0.02 mol) of anhydrous n class="Chemical">sodium acetate was stirred under reflux in 40 mL of glacial acetic acid and 20 mL of acetic anhydride on a water bath (60–70 °C) for 13–15 h (TLC). The reaction mixture was allowed to cool to room temperature and poured into water (100 mL). The solid precipitate was filtered off, and crystallized from appropriate solvent to produced 7a and 7b in good yields, respectively. Method B: A mixture of 6a (3.71 g, 0.01 mol) or 6b (4.01 g, 0.01 mol) in dimethylformamide (35 mL) was refluxed for 6–8 h with (TLC). The final product was filtered off, dried and crystallized from the proper solvent to give 7a and 7b, respectively.

3.12. Synthesis of 9-Methoxy-8-methyl-2-hydro-5H,14aH-furo[3,2-g]thiazolo[2′,3′:2,3]pyrimido[1,6-a]quinazoline-3,5-dione ()

The compound was obtained from the reaction of (5a) with n class="Chemical">chloroacetic acid or compound (6a) in DMF, as white crystals, crystallized from dioxane in 82% yield, m.p. 338 °C. IR (ν, cm−1) KBr: 3035 (CH-aryl), 2962 (CH-aliph), 1688, 1680 (2CO, amide), 1635 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.37 (s, 3H, CH3), 3.93 (s, 3H, OCH3), 4.21 (s, 2H, CH2), 5.57 (s, 1H, CH, thiazole), 6.78 (d, 1H, J = 2.34 Hz, furan), 7.38 (s, 1H, pyrimidine), 7.75 (d, 1H, J = 2.32 Hz, furan), 7.88 (s, 1H, phenyl); 13C-NMR (DMSO-d6) δ 23.3 (1C, CH3), 32.6 (1C, CH2), 61.8 (1C, OCH3), 76.1 (1C, CH, thiazole), 94.5 (1C, CH, phenyl), 98.8 (1C, CH, pyrimidine), 101.2, 105.5, 107.9, 142.2, 146.4, 153.5, 159.7, 160.4, 164.5 (9C, Ar-C), 166.4, 170.1 (2C, 2C=O); MS (70 eV, %) m/z 355 (M+, 90%); Anal. Calc. (Found) for C17H13N3O4S (355.37): C, 57.46 (57.40); H, 3.69 (3.62); N, 11.82 (11.88).

3.13. Synthesis of 9,13-Dimethoxy-8-methyl-2-hydro-5H,14aH-furo[3,2-g]thiazolo[2′,3′:2,3]pyrimido[1,6-a]quinazoline-3,5-dione ()

The compound was obtained from the reaction of (5b) with chloroacetic acid or compound (6b) in DMF, as yellowish crystals, crystallized from methanol in 80% yield, m.p. 303 °C. IR (ν, cm−1) KBr: 3038 (CH-aryl), 2966 (CH-aliph), 1685, 1682 (2CO, amide), 1632 (C=N). 1H-NMR (DMSO-d, ppm) δ 2.33 (s, 3H, CH3), 3.97 (s, 6H, 2OCH3), 4.24 (s, 2H, CH2), 5.62 (s, 1H, CH, thiazole), 6.74 (d, 1H, J = 2.33 Hz, furan), 7.39 (s, 1H, pyrimidine), 7.77 (d, 1H, J = 2.31 Hz, furan); 13C-NMR (DMSO-d) δ 23.1 (1C, CH3), 32.3 (1C, CH2), 61.7 (2C, 2OCH3), 76.4 (1C, CH, thiazole), 97.5 (1C, CH, pyrimidine), 101.4, 105.6, 108.2, 123.6, 127.8, 146.3, 146.8, 152.9, 160.1, 164.7 (10C, Ar-C), 166.2, 170.5 (2C, 2C=O); MS (70 eV, %) m/z 385 (M+, 95%); Anal. Calc. (Found) for C18H15N3O5S (385.39): C, 56.10 (56.18); H, 3.92 (3.85); N, 10.90 (10.98).

3.14. General Procedure for Synthesis of 2-(Substituted-benzylidene)-9,(substituted)-methoxy-8-methyl-2-hydro-5H,14aH-furo[3,2-g]thiazolo[2′,3′:2,3]pyrimido[1,6-a]quinazoline-3,5-dione (–)

Method A: One pot synthesis: A mixture from 5a (3.13g, 0.01 mol) or 5b (3.43 g, 0.01 mol), chloroacetic acid (0.94 g, 0.01 mol), the appropriate aromatic n class="Chemical">aldehyde (10 mmol) and (0.02 mol) of anhydrous sodium acetate was stirred under reflux in 40 mL of glacial acetic acid and 20 mL of acetic anhydride for 24–26 h. The reaction mixture was cooled and poured into ice water. The deposited precipitate was filtered off, and crystallized from appropriate solvent to give (8a–f).

Method B: A mixture of compound 7a (3.55 g, 10 mmol) or 7b (3.85 g, 10 mmol) and the appropriate aromatic n class="Chemical">aldehyde (10 mmol) in dioxane (40 mL) containing a catalyst amount of piperidine (0.5 mL) was stirred and heated under reflux for 10–12 h (TLC control). The reaction mixture was cooled, the formed precipitate filtered off, dried and recrystallized from the appropriate solvent to afford (8a–f).

3.15. Synthesis of 2-Benzylidene-9-methoxy-8-methyl-2-hydro-5H,14aH-furo[3,2-g]thiazolo[2′,3′:2,3] pyrimido[1,6-a]quinazoline-3,5-dione ()

The compound was obtained from the reaction of (5a) and n class="Chemical">benzaldehyde (1.06 g, 10 mmol) with chloroacetic acid or compound (7a) with benzaldehyde, as yellowish crystals, crystallized from dimethylformamide in 75% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3050 (CH-aryl), 2945 (CH-aliph), 1685, 1672 (2CO, amide), 1630 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.30 (s, 3H, CH3), 3.91 (s, 3H, OCH3), 5.59 (s, 1H, CH, thiazole), 6.75 (d, 1H, J = 2.31 Hz, furan), 7.32 (s, 1H, pyrimidine), 7.40–7.67(m, 5H, phenyl), 7.72 (d, 1H, J = 2.30 Hz, furan), 7.85 (s, 1H, phenyl), 8.05 (s, 1H, CH); 13C-NMR (DMSO-d6) δ 23.1 (1C, CH3), 61.6 (1C, OCH3), 77.5 (1C, CH, thiazole), 90.8 (1C, CH, phenyl), 92.9 (1C, CH, pyrimidine), 100.7, 104.8, 105.6, (3C, benzofurane), 121.9 (1C, CH), 127.2, 128.1, 128.7, 133.9 (6C, phenyl), 137.5 (1C, thiazole), 140.3, 146.4, 153.8, 160.1, 160.4, 164.2 (6C, pyrimidobenzo furane), 165.6, 168.4 (2C, 2C=O); MS (70 eV, %) m/z 443 (M+, 88%); Anal. Calc. (Found) for C24H17N3O4S (443.48): C, 65.00 (65.10); H, 3.86 (3.80); N, 9.48 (9.41).

3.16. Synthesis of 2-(4-Chlorobenzylidene)-9-methoxy-8-methyl-2-hydro-5H,14aH-furo[3,2-g]thiazolo[2′,3′:2,3]pyrimido[1,6-a]quinazoline-3,5-dione ()

The compound was obtained from the reaction of (5a) and n class="Chemical">4-chlorobenzaldehyde (1.40 g, 10 mmol) with chloroacetic acid or compound (7a) with 4-chloro- benzaldehyde, as yellow crystals, crystallized from dioxane in 80% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3052 (CH-aryl), 2948 (CH-aliph), 1687, 1674 (2CO, amide), 1631 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.31 (s, 3H, CH3), 3.90 (s, 3H, OCH3), 5.60 (s, 1H, CH, thiazole), 6.74 (d, 1H, J = 2.32 Hz, furan), 7.33 (s, 1H, pyrimidine), 7.45–7.50 (dd, 2H, J = 7.60, 7.64 Hz, 4-chlorophenyl), 7.55–7.60 (dd, 2H, J = 7.62, 7.66 Hz, 4-chloro phenyl),7.70 (d, 1H, J = 2.34 Hz, furan), 7.83 (s, 1H, phenyl), 8.08 (s, 1H, CH); 13C-NMR (DMSO-d6) δ 23.2 (1C, CH3), 61.4 (1C, OCH3), 77.8 (1C, CH, thiazole), 90.2 (1C, CH, phenyl), 92.1 (1C, CH, pyrimidine), 100.3, 104.9, 105.5, (3C, benzofurane), 122.1 (1C, CH), 128.4, 129.2, 132.5, 132.8 (6C, 4-chlorophenyl), 137.9 (1C, thiazole), 140.6, 146.3,153.5, 160.3, 160.7, 164.3 (6C, pyrimidobenzo furane), 165.8, 168.7 (2C, 2C=O); MS (70 eV, %) m/z 477 (M+, 90%); Anal. Calc. (Found) for C24H16ClN3O4S (477.92): C, 60.32 (60.39); H, 3.37 (3.44); N, 8.79 (8.85).

3.17. Synthesis of 9-Methoxy-2-(4-methoxybenzylidene)-8-methyl-2-hydro-5H,14aH-furo[3,2-g]thiazolo[2′,3′:2,3]pyrimido[1,6-a]quinazoline-3,5-dione ()

The compound was obtained from the reaction of (5a) and n class="Chemical">4-methoxy- benzaldehyde (1.36 g, 10 mmol) with chloroacetic acid or compound (7a) with 4-methoxybenzaldehyde, as brownish crystals, crystallized from ethanol in 78% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3054 (CH-aryl), 2944 (CH-aliph), 1683, 1671 (2CO, amide), 1636 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.29 (s, 3H, CH3), 3.92 (s, 3H, OCH3), 4.10 (s, 3H, OCH3), 5.59 (s, 1H, CH, thiazole), 6.71 (d, 1H, J = 2.32 Hz, furan), 7.28 (s, 1H, pyrimidine), 7.48–7.53 (dd, 2H, J = 7.61, 7.65 Hz, 4-methoxyphenyl), 7.58–7.63 (dd, 2H, J = 7.63, 7.67 Hz, 4-methoxyphenyl), 7.69 (d, 1 H, J = 2.37 Hz, furan), 7.86 (s, 1 H, phenyl), 8.06 (s, 1H, CH); 13C-NMR (DMSO-d6) δ 23.4 (1C, CH3), 58.5 (1C, OCH3), 61.7 (1C, OCH3), 77.2 (1C, CH, thiazole), 90.5 (1C, CH, phenyl), 92.4 (1C, CH, pyrimidine), 100.4, 105.1, 105.5, (3C, benzofurane), 122.6 (1C, CH), 123.1, 127.7, 130.1, 155.5 (6C, 4-methoxyphenyl), 137.4 (1C, thiazole), 140.8, 146.2,153.6, 160.1, 160.4, 164.3 (6C, pyrimidobenzofurane), 165.1, 168.6 (2C, 2C=O); MS (70 eV, %) m/z 473 (M+, 87%); Anal. Calc. (Found) for C25H19N3O5S (473.50): C, 63.42 (63.49); H, 4.04 (4.12); N, 8.87 (8.95).

3.18. Synthesis of 2-Benzylidene-9,13-dimethoxy-8-methyl-2-hydro-5H,14aH-furo[3,2-g]thiazolo [2′,3′:2,3]pyrimido[1,6-a]quinazoline-3,5-dione ()

The compound was obtained from the reaction of (5b) and n class="Chemical">benzaldehyde (1.06 g, 10 mmol) with chloroacetic acid or compound (7b) with benzaldehyde, as yellow crystals, crystallized from acetone in 79% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3060 (CH-aryl), 2950 (CH-aliph), 1688, 1678 (2CO, amide), 1638 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.33 (s, 3H, CH3), 3.97 (s, 6H, 2OCH3), 5.60 (s, 1H, CH, thiazole), 6.74 (d, 1H, J= 2.30 Hz, furan), 7.34 (s, 1H, pyrimidine), 7.45–7.65 (m, 5H, phenyl), 7.74 (d, 1H, J = 2.35 Hz, furan), 8.02 (s, 1H, CH); 13C-NMR (DMSO-d6) δ 23.5 (1C, CH3), 61.8 (2C, 2OCH3), 77.7 (1C, CH, thiazole), 91.7 (1C, CH, pyrimidine), 101.4, 105.3, 108.8, 120.7 (4C, benzo furane), 122.2 (1C, CH), 126.1 (1C, pyrimidine), 127.7, 128.3, 128.8, 134.6 (6C, phenyl), 137.7 (1C, thiazole), 146.2, 146.7, 151.9, 160.6, 164.8 (5C, pyrimidobenzofurane), 165.1, 168.3 (2C, 2C=O); MS (70 eV, %) m/z 473 (M+, 84%); Anal. Calc. (Found) for C25H19N3O5S (473.50): C, 63.42 (63.50); H, 4.04 (4.10); N, 8.87 (8.80).

3.19. Synthesis of 2-(4-Chlorobenzylidene)-9,13-dimethoxy-8-methyl-2-hydro-5H,14aH-furo[3,2-g]thiazolo [2′,3′:2,3]pyrimido[1,6-a]quinazoline-3,5-dione ()

The compound was obtained from the reaction of (5b) and n class="Chemical">4-chlorobenzaldehyde (1.40 g, 10 mmol) with chloroacetic acid or compound (7b) with 4-chlorobenzaldehyde, as yellowish crystals, crystallized from methanol in 88% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3055 (CH-aryl), 2945 (CH-aliph), 1686, 1674 (2CO, amide), 1634 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.30 (s, 3H, CH3), 3.98 (s, 6H, 2OCH3), 5.59 (s, 1H, CH, thiazole), 6.73 (d, 1H, J= 2.31 Hz, furan), 7.35 (s, 1H, pyrimidine), 7.47–7.52 (dd, 2H, J = 7.68, 7.62 Hz, 4-chlorophenyl), 7.57–7.62 (dd, 2H, J = 7.61, 7.65 Hz, 4-chloro phenyl), 7.75 (d, 1H, J = 2.36 Hz, furan), 8.04 (s, 1H, CH); 13C-NMR (DMSO-d6) δ 23.7 (1C, CH3), 61.9 (2C, 2OCH3), 77.6 (1C, CH, thiazole), 91.2 (1C, CH, pyrimidine), 100.5, 105.6, 108.4, 120.8 (4C, benzo furane), 122.4 (1C, CH), 126.3 (1C, pyrimidine), 128.2, 128.8, 131.5, 131.9 (6C, 4-chloro phenyl), 137.5 (1C, thiazole), 146.3, 146.9, 150.8, 160.4, 164.9 (5C, pyrimidobenzofurane), 165.3, 168.1 (2C, 2C=O); MS (70 eV, %) m/z 507 (M+, 98%); Anal. Calc. (Found) for C25H18ClN3O5S (507.94): C, 59.12 (59.22); H, 3.57 (3.50); N, 8.27 (8.35).

3.20. Synthesis of 9,13-Dimethoxy-2-(4-methoxybenzylidene)-8-methyl-2-hydro-5H,14aH-furo[3,2-g]thiazolo [2′,3′:2,3]pyrimido[1,6-a]quinazoline-3,5-dione ()

The compound was obtained from the reaction of (5b) and n class="Chemical">4-methoxy- benzaldehyde (1.36 g, 10 mmol) with chloroacetic acid or compound (7b) with 4-methoxybenzaldehyde, as brownish crystals, crystallized from benzene in 73% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3052 (CH-aryl), 2944 (CH-aliph), 1685, 1672 (2CO, amide), 1630 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.28 (s, 3H, CH3), 3.95 (s, 6H, 2OCH3), 4.12 (s, 3H, OCH3), 5.55 (s, 1H, CH, thiazole), 6.71 (d, 1H, J= 2.32 Hz, furan), 7.37 (s, 1H, pyrimidine), 7.49–7.54 (dd, 2H, J = 7.65, 7.61 Hz, 4-methoxyphenyl), 7.58–7.63 (dd, 2H, J = 7.62, 7.66 Hz, 4-methoxyphenyl), 7.76 (d, 1H, J = 2.35 Hz, furan), 8.06 (s, 1H, CH); 13C-NMR (DMSO-d6) δ 23.4 (1C, CH3), 58.2 (1C, OCH3), 61.8 (2C, 2OCH3), 77.3 (1C, CH, thiazole), 91.5 (1C, CH, pyrimidine), 100.2, 105.5, 108.6, 120.5 (4C, benzofurane), 122.7 (1C, CH), 126.1 (1C, pyrimidine), 127.2, 128.4, 129.1, 152.2 (6C, 4-methoxyphenyl), 137.8 (1C, thiazole), 146.1, 146.7, 150.6, 160.5, 164.8 (5C, pyrimidobenzo furane), 165.7, 168.2 (2C, 2C=O); MS (70 eV, %) m/z 503 (M+, 91%); Anal. Calc. (Found) for C26H21N3O6S (503.53): C, 62.02 (62.10); H, 4.20 (4.28); N, 8.35 (8.27).

3.21. General Procedure for Synthesis of 3-(((7-Methoxy or 7,11-dimethoxy)-6-methyl-3-oxo-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-1-yl)thio)pentane-2,4-dione (,)

To a warmed ethanolic n class="Chemical">potassium hydroxide solution (prepared by dissolving 10 mmol of KOH in 50 mL ethanol) was added each of 5a (3.13 g, 0.01 mol) or 5b (3.43 g, 0.01 mol), the heating was continued for 40 min and the mixture was allowed to cool to room temperature, and the proper 3-chloro-pentane-2,4-dione (3-chloroacetylacetone, 1.12 mL, 0.01 mol) was added. The mixture was stirred under reflux for 6–8 h (control TLC), and then cool to room temperature, poured into cold water (100 mL). The solid product precipitated was filtered off, washed with 100 mL water; the product was dried and crystallized from the suitable solvent to afford 9a and 9b in good yields, respectively.

3.22. Synthesis of 3-((7-Methoxy-6-methyl-3-oxo-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-1-yl)thio)pentane- 2,4-dione ()

The compound was obtained from the reaction of () with n class="Chemical">3-chloro-pentane-2,4-dione (3-chloroacetylacetone), as white crystals, crystallized from hexane in 92% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3035 (CH-aryl), 2945 (CH-aliph), 1725, 1721 (2CO, acetyl), 1682 (CO, amide), 1638 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.26 (s, 6H, 2COCH3), 2.34 (s, 3H, CH3), 3.90 (s, 3H, OCH3), 4.08 (s, 1H, CH), 6.73 (d, 1H, J = 2.31 Hz, furan), 7.37 (s, 1H, pyrimidine), 7.62 (s, 1H, phenyl), 7.75 (d, 1H, J = 2.33 Hz, furan), 13C-NMR (DMSO-d6) δ 23.8(1C, CH3), 26.5 (2C, 2COCH3), 61.6 (1C, OCH3), 68.2 (1C, CH), 91.3 (1C, CH, phenyl), 96.5 (1C, CH, pyrimidine), 100.1, 105.3, 108.5, 142.6, 146.1, 153.5, 157.4, 160.3, 163.8, 165.7 (10C, Ar-C), 168.6, 184.5, 188.2 (3C, 3C=O); MS (70 eV, %) m/z 411 (M+, 95%); Anal. Calc. (Found) for C20H17N3O5S (411.43): C, 58.39 (58.32); H, 4.16 (4.10); N, 10.21 (10.16).

3.23. Synthesis of 3-((7,11-Dimethoxy-6-methyl-3-oxo-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-1-yl)thio)pentane-2,4-dione ()

The compound was obtained from the reaction of (5b) with 3-chloro-pentane-2,4-dione (3-chloroacetylacetone), as white crystals, crystallized from dioxane in 90% yield, m.p. 348 °C. IR (ν, cm−1) KBr: 3038 (CH-aryl), 2949 (CH-aliph), 1728, 1722 (2CO, acetyl), 1684 (CO, amide), 1636 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.28 (s, 6H, 2COCH3), 2.37 (s, 3H, CH3), 3.98 (s, 6H, 2OCH3), 4.15 (s, 1H, CH), 6.72 (d, 1H, J = 2.34 Hz, furan), 7.35 (s, 1H, pyrimidine), 7.79 (d, 1H, J = 2.37 Hz, furan), 13C-NMR (DMSO-d6) δ 23.4 (1C, CH3), 26.1 (2C, 2COCH3), 61.9 (2C, 2OCH3), 68.5 (1C, CH), 97.1 (1C, CH, pyrimidine), 100.2, 105.7, 108.9, 122.5, 130.2, 146.3, 146.8, 150.7, 159.6, 164.2, 166.4 (11C, Ar-C), 168.8, 185.1, 188.7 (3C, 3C=O); MS (70 eV, %) m/z 441 (M+, 90%); Anal. Calc. (Found) for C21H19N3O6S (441.46): C, 57.14 (57.20); H, 4.34 (4.39); N, 9.52 (9.60).

3.24. General Procedure for Synthesis of 1-((3,5-Dimethyl-1H-pyrazol-4-yl)thio)-(7-methoxy or 7,11-dimethoxy)-6-methyl-3H-furo[3, 2-g]pyrimido[1,6-a]quinazolin-3-one (,)

A mixture of 9a (4.11 g, 0.01 mol) or 9b (4.41 g, 0.01 mol), and hydrazine hydrate (99–100%) in n class="Chemical">dioxane (30 mL) and ethanol (20 mL) was stirred under reflux for 13–15 h. The reaction mixture was allowed to cool to room temperature, poured into cold water (100 mL). The deposited precipitate was filtered off, dried, and crystallized from the proper solvent to give 10a and 10b in good yields, respectively.

3.25. Synthesis of 1-((3,5-Dimethyl-1H-pyrazol-4-yl)thio)-7-methoxy-6-methyl-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (9a) with n class="Chemical">hydrazine hydrate, as yellow crystals, crystallized from dimethylformamide in 95% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3375 (brs, NH), 3030 (CH-aryl), 2940 (CH-aliph), 1684 (CO, amide), 1633 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.28 (s, 3H, CH3), 2.38 (s, 3H, CH3), 2.40 (s, 3H, CH3), 3.92 (s, 3H, OCH3), 6.75 (d, 1H, J = 2.32 Hz, furan), 7.32 (s, 1H, pyrimidine), 7.60 (s, 1H, phenyl), 7.72 (d, 1H, J = 2.37 Hz, furan), 11.50 (brs, NH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 20.1, 20.3, 23.2 (3C, 3CH3), 61.4 (1C, OCH3), 91.1 (1C, CH, phenyl), 96.3 (1C, CH, pyrimidine), 100.2, 105.1, 107.2, 108.4, 142.3, 144.5, 146.6, 154.1, 158.2, 160.5, 164.4, 166.3 (13C, Ar-C), 168.8 (1C, C=O); MS (70 eV, %) m/z 407 (M+, 100%); Anal. Calc. (Found) for C20H17N5O3S (407.45): C, 58.96 (58.88); H, 4.21 (4.15); N, 17.19 (17.10).

3.26. Synthesis of 1-((3,5-Dimethyl-1H-pyrazol-4-yl)thio)-7,11-dimethoxy-6-methyl-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (9b) with hydrazine hydrate, as yellowish crystals, crystallized from dioxane in 91% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3370 (brs, NH), 3032 (CH-aryl), 2943 (CH-aliph), 1682 (CO, amide), 1635 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.30 (s, 3H, CH3), 2.39 (s, 3H, CH3), 2.41 (s, 3H, CH3), 3.98 (s, 6H, 2OCH3), 6.77 (d, 1H, J = 2.36 Hz, furan), 7.38 (s, 1H, pyrimidine), 7.79 (d, 1H, J = 2.34 Hz, furan), 11.55 (brs, NH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 20.4, 20.6, 23.5 (3C, 3CH3), 61.9 (2C, 2OCH3), 96.7 (1C, CH, pyrimidine), 100.3, 105.6, 107.8, 108.5, 122.5, 130.4, 144.8, 146.1, 146.8, 151.4, 160.5, 164.2, 166.6 (14C, Ar-C), 168.9 (1C, C=O); MS (70 eV, %) m/z 437 (M+, 100%); Anal. Calc. (Found) for C21H17N5O4S (437.47): C, 57.66 (57.72); H, 4.38 (4.30); N, 16.01 (16.10).

3.27. General Procedure for Synthesis of 1-((4,6-Dimethyl-2-(oxo or thioxo)-1,2-dihydropyrimidin-5-yl)thio)-(7-methoxy or 7,11-dimethoxy)-6-methyl-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (–)

A mixture of 9a (4.11 g, 0.01 mol) or 9b (4.41 g, 0.01 mol), and urea (0.60 g, 0.01 mol) or n class="Chemical">thiourea (0. 76 g, 0.01 mol) was stirred under reflux in dioxane (40 mL) in the presence of catalytic amount of piperidine (1 mL) for 16–18 h. The reaction mixture was allowed to cool to room temperature, poured into water (100 mL), the deposited precipitate was filtered off, washed with ethanol (40 mL), dried and crystallized from proper solvent to afford (11a–d).

3.28. Synthesis of 1-((4,6-Dimethyl-2-oxo-1,2-dihydropyrimidin-5-yl)thio)-7-methoxy-6-methyl-3H-furo[3,2- g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (9a) with n class="Chemical">urea, as yellowish crystals, crystallized from dioxane in 86% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3380 (brs, NH), 3032 (CH-aryl), 2942 (CH-aliph), 1685, 1680 (2C=O, amide), 1635 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.11 (s, 3H, CH3), 2.28 (s, 3H, CH3), 2.37 (s, 3H, CH3), 3.94 (s, 3H, OCH3), 6.72 (d, 1H, J = 2.31 Hz, furan), 7.36 (s, 1H, pyrimidine), 7.63 (s, 1H, phenyl), 7.79 (d, 1H, J = 2.38 Hz, furan), 10.60 (brs, NH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 20.6, 20.9, 23.5 (3C, 3CH3), 61.8 (1C, OCH3), 85.4 (1C, pyrimidine), 91.5 (1C, CH, phenyl), 97.7 (1C, CH, pyrimidine), 100.4, 105.7, 108.2, 143.1, 146.1, 153.6, 158.5, 160.4, 163.8, 164.7, 165.2, 166.8 (12C, Ar-C), 169.2, 172.5 (2C, 2C=O); MS (70 eV, %) m/z 435 (M+, 92%); Anal. Calc. (Found) for C21H17N5O4S (435.46): C, 57.92 (57.85); H, 3.94 (3.99); N, 16.08 (16.15).

3.29. Synthesis of 1-((4,6-Dimethyl-2-thioxo-1,2-dihydropyrimidin-5-yl)thio)-7-methoxy-6-methyl-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (9a) with n class="Chemical">thiourea, as yellow crystals, crystallized from dimethylformamide in 82% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3385 (brs, NH), 3035 (CH-aryl), 2944 (CH-aliph), 1681 (C=O, amide), 1632 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.10 (s, 3H, CH3), 2.27 (s, 3H, CH3), 2.36 (s, 3H, CH3), 3.91 (s, 3H, OCH3), 6.70 (d, 1H, J = 2.30 Hz, furan), 7.34 (s, 1H, pyrimidine), 7.61 (s, 1H, phenyl), 7.78 (d, 1H, J = 2.36 Hz, furan), 12.30 (brs, NH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 21.4, 21.8, 23.7 (3C, 3CH3), 61.7 (1C, OCH3), 84.6 (1C, pyrimidine), 91.8 (1C, CH, phenyl), 98.2 (1C, CH, pyrimidine), 100.2, 105.8, 108.1, 143.7, 146.3, 153.8, 158.9, 160.5, 163.9, 164.2, 165.8, 169.6 (12C, Ar-C), 170.1 (1C, C=O), 177.8 (1C, C=S); MS (70 eV, %) m/z 451 (M+, 90%); Anal. Calc. (Found) for C21H17N5O3S2 (451.52): C, 55.86 (55.78); H, 3.80 (3.88); N, 15.51 (15.60).

3.30. Synthesis of 1-((4,6-Dimethyl-2-oxo-1,2-dihydropyrimidin-5-yl)thio)-7,11-dimethoxy-6-methyl-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (9b) with urea, as yellow crystals, crystallized from methanol in 80% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3377 (brs, NH), 3039 (CH-aryl), 2937 (CH-aliph), 1687, 1683 (2C=O, amide), 1638 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.09 (s, 3H, CH3), 2.27 (s, 3H, CH3), 2.33 (s, 3H, CH3), 3.99 (s, 6H, 2OCH3), 6.75 (d, 1H, J = 2.32 Hz, furan), 7.38 (s, 1H, pyrimidine), 7.76 (d, 1H, J = 2.37 Hz, furan), 10.74 (brs, NH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 20.5, 20.7, 23.7 (3C, 3CH3), 61.9 (2C, 2OCH3), 87.1(1C, pyrimidine), 98.9 (1C, CH, pyrimidine), 100.2, 105.4, 108.8, 122.3, 130.5, 146.1, 146.9, 152.1, 158.2, 164.1, 164.5, 166.2, 168.5 (13C, Ar-C), 169.8, 171.4 (2C, 2C=O); MS (70 eV, %) m/z 465 (M+, 88%); Anal. Calc. (Found) for C22H19N5O5S (465.48): C, 56.77 (56.70); H, 4.11 (4.05); N, 15.05 (15.14).

3.31. Synthesis of 1-((4, 6-Dimethyl-2-thioxo-1,2-dihydropyrimidin-5-yl)thio)-7,11-dimethoxy-6-methyl-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (9b) with thiourea, as yellowish crystals, crystallized from dioxane in 80% yield, m.p. > 350 °C. IR (ν, cm−1) KBr: 3388 (brs, NH), 3034 (CH-aryl), 2945 (CH-aliph), 1683 (C=O, amide), 1630 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.13 (s, 3H, CH3), 2.25 (s, 3H, CH3), 2.32 (s, 3H, CH3), 4.01 (s, 6H, 2OCH3), 6.73 (d, 1H, J = 2.34 Hz, furan), 7.36 (s, 1H, pyrimidine),7.80 (d, 1H, J = 2.38 Hz, furan), 12.50 (brs, NH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 21.5, 21.9, 23.8 (3C, 3CH3), 62.01 (2C, 2OCH3), 86.1 (1C, pyrimidine), 99.3 (1C, CH, pyrimidine), 100.4, 105.2, 108.7, 122.7, 130.4, 146.3, 146.7, 151.9, 159.1, 164.3, 164.5, 166.9, 168.2 (13C, Ar-C), 169.8(1C, C=O), 178.5 (1C, C=S); MS (70 eV, %) m/z 481 (M+, 86%); Anal. Calc. (Found) for C22H19N5O4S2 (481.54): C, 54.87 (54.95); H, 3.98 (3.90); N, 14.54 (14.47).

3.32. General Procedure for Synthesis of (7-Methoxy or 7,11-dimethoxy)-6-methyl-1-(methylthio)-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (,)

To a warmed ethanolic n class="Chemical">KOH solution (prepared by dissolving 10 mmol of KOH in 50 mL ethanol) was added each of 5a (3.13 g, 0.01 mol) or 5b (3.43 g, 0.01 mol), the heating was continued for 30 min and the mixture was allowed to cool to room temperature, and methyl iodide (0.62 mL, 0.01 mol) was added. The mixture was stirred under reflux for 5–7 h, then cool to room temperature, poured into cold water (100 mL). The solid product precipitated was filtered off, washed with water; the product was dried and crystallized from the proper solvent to produce 12a and 12b, respectively.

3.33. Synthesis of 7-Methoxy-6-methyl-1-(methylthio)-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (5a) with n class="Chemical">methyl iodide, as yellow crystals, crystallized from methanol in 90% yield, m.p. 329 °C. IR (ν, cm−1) KBr: 3035 (CH-aryl), 2962 (CH-aliph), 1685 (CO, amide), 1630 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.30 (s, 3H, CH3), 2.80 (s, 3H, SCH3), 3.90 (s, 3H, OCH3), 6.73 (d, 1H, J = 2.31 Hz, furan), 7.34 (s, 1H, pyrimidine), 7.64 (s, 1H, phenyl), 7.78 (d, 1H, J = 2.35 Hz, furan); 13C-NMR (DMSO-d6) δ 18.9 (1C, SCH3), 23.8 (1C, CH3), 61.4 (1C, OCH3), 92.7 (1C, CH, phenyl), 98.9 (1C, CH, pyrimidine), 100.3, 105.2, 108.5, 145.2, 146.4, 153.7, 158.3, 160.9, 164.6, 167.8 (10C, Ar-C), 169.1 (1C, C=O); MS (70 eV, %) m/z 327 (M+, 100%); Anal. Calc. (Found) for C16H13N3O3S (327.36): C, 58.71 (58.78); H, 4.00 (4.10); N, 12.84 (12.90).

3.34. Synthesis of 7,11-Dimethoxy-6-methyl-1-(methylthio)-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (5b) with methyl iodide, as yellowish crystals, crystallized from ethanol in 86% yield, m.p. 311 °C. IR (ν, cm−1) KBr: 3038 (CH-aryl), 2965 (CH-aliph), 1683 (CO, amide), 1633 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.35 (s, 3H, CH3), 2.88 (s, 3H, SCH3), 3.97 (s, 6H, 2OCH3), 6.78 (d, 1H, J=2.32 Hz, furan), 7.38 (s, 1H, pyrimidine), 7.80 (d, 1H, J = 2.34 Hz, furan); 13C-NMR (DMSO-d6) δ 19.2 (1C, SCH3), 23.6 (1C, CH3), 61.8 (2C, 2OCH3), 99.4 (1C, CH, pyrimidine), 100.1, 105.7, 108.2, 122.7, 130.5, 146.1, 146.8, 151.5, 159.7, 164.4, 168.2 (11C, Ar-C), 169.7 (1C, C=O); MS (70 eV, %) m/z 357 (M+, 100%); Anal. Calc. (Found) for C17H15N3O4S (357.38): C, 57.13 (57.22); H, 4.23 (4.28); N, 11.76 (11.66).

3.35. General Procedure for Synthesis of (7-Methoxy or 7,11-dimethoxy)-6-methyl-1-(methylsulfonyl)-3H- furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (,)

A mixture of 12a (3.27 g, 0.01 mol) or 12b (3.57 g, 0.01 mol), and excess amount of n class="Chemical">hydrogen peroxide (5 mL) in acetic acid (40 mL) was heated gently with stirring for 12–14 h with (TLC). The reaction mixture was allowed to cool to 0 °C. The deposited precipitate was filtered off, and crystallized from the proper solvent to afford 13a and 13b, respectively.

3.36. Synthesis of 7-Methoxy-6-methyl-1-(methylsulfonyl)-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (1n class="Chemical">2a) with hydrogen peroxide, as yellowish crystals, crystallized from benzene in 75% yield, m.p. 241 °C. IR (ν, cm−1) KBr: 3032 (CH-aryl), 2920 (CH-aliph), 1687 (CO, amide), 1632 (C=N), 1162, 1340 (SO2). 1H-NMR (DMSO-d6, ppm) δ 2.34 (s, 3H, CH3), 2.95 (s, 3H, SO2CH3), 3.92 (s, 3H, OCH3), 6.76 (d, 1H, J = 2.36 Hz, furan), 7.37 (s, 1H, pyrimidine), 7.61 (s, 1H, phenyl), 7.81 (d, 1H, J = 2.32 Hz, furan); 13C-NMR (DMSO-d6) δ 23.5 (1C, CH3), 35.6 (1C, SO2CH3), 61.3 (1C, OCH3), 93.5 (1C, CH, phenyl), 99.4 (1C, CH, pyrimidine), 100.2, 105.4, 108.7, 140.3, 145.5, 146.2, 153.9, 160.8, 164.4, 168.1 (10C, Ar-C), 169.5 (1C, C=O); MS (70 eV, %) m/z 359 (M+, 84%); Anal. Calc. (Found) for C16H13N3O5S (359.36): C, 53.48 (53.40); H, 3.65 (3.57); N, 11.69 (11.61).

3.37. Synthesis of 7,11-Dimethoxy-6-methyl-1-(methylsulfonyl)-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin- 3-one ()

The compound was obtained from the reaction of (12b) with hydrogen peroxide, as yellow crystals, crystallized from toluene in 75% yield, m.p. 221 °C. IR (ν, cm−1) KBr: 3029 (CH-aryl), 2918 (CH-aliph), 1684 (CO, amide), 1628 (C=N), 1160, 1342(SO2). 1H-NMR (DMSO-d6, ppm) δ 2.29 (s, 3H, CH3), 2.97 (s, 3H, SO2CH3), 4.01 (s, 6H, 2OCH3), 6.80 (d, 1H, J = 2.30 Hz, furan), 7.31 (s, 1H, pyrimidine), 7.75 (d, 1H, J = 2.33 Hz, furan); 13C-NMR (DMSO-d6) δ 23.3 (1C, CH3), 35.8 (1C, SO2CH3), 61.9 (2C, 2OCH3), 99.8 (1C, CH, pyrimidine), 100.4, 105.7, 108.9, 122.4, 130.1, 140.6, 146.3, 146.8, 151.5, 164.7, 168.5(11C, Ar-C), 169.5 (1C, C=O); MS (70 eV, %) m/z 389 (M+, 80%); Anal. Calc. (Found) for C17H15N3 O6S (389.38): C, 52.44 (52.50); H, 3.88 (3.80); N, 10.79 (10.71).

3.38. General Procedure for Synthesis of (7-Methoxy or 7,11-dimethoxy)-6-methyl-1-((piperazin-1-yl) or morpholino)-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one (–)

In a warm solution of 12a (3.27 g, 0.01 mol) or 12b (3.57 g, 0.01 mol), in methanol (50 mL) was added the freshly distilled 2nd amine, namely piperazine (0.95 mL, 0.01 mol) or morpholine (0.86 mL, 0.01 mol). The reaction mixture was stirred under reflux for 7–9 h, then allowed to cool to 0 °C for 14 h and the solid obtained was filtered, washed with water (100 mL) dried and recrystallized from appropriate solvent to produce (14a–d).

3.39. Synthesis of 7-Methoxy-6-methyl-1-(piperazin-1-yl)-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (1n class="Chemical">2a) with piperazine, as pale yellow crystals, crystallized from dioxane in 79% yield, m.p. 202 °C. IR (ν, cm−1) KBr: 3390 (br, NH), 3044 (CH-aryl), 2940 (CH-aliph), 1687 (CO, amide), 1620 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.29 (s, 3H, CH3), 2.82–2.91 (m, 8H, piperazine), 3.92 (s, 3H, OCH3), 6.78 (d, 1H, J = 2.36 Hz, furan), 7.38 (s, 1H, pyrimidine), 7.66 (s, 1H, phenyl), 7.81 (d, 1H, J = 2.37 Hz, furan), 10.30 (brs, NH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 23.2 (1C, CH3), 48.3 (2C, 2CH2, piperazine), 52.5 (2C, 2CH2, piperazine), 61.7 (1C, OCH3), 91.8 (1C, CH, phenyl), 98.4 (1C, CH, pyrimidine), 100.1, 105.3, 108.2, 144.6, 146.1, 153.8, 154.9, 160.3, 164.4, 168.1(10C, Ar-C), 169.3 (1C, C=O); MS (70 eV, %) m/z 365 (M+, 83%); Anal. Calc. (Found) for C19H19N5O3 (365.39): C, 62.46 (62.55); H, 5.24 (5.18); N, 19.17 (19.24).

3.40. Synthesis of 7-Methoxy-6-methyl-1-morpholino-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (1n class="Chemical">2a) with morpholine, as yellow crystals, crystallized from methanol in 75% yield, m.p. 171 °C. IR (ν, cm−1) KBr: 3040 (CH-aryl), 2936 (CH-aliph), 1685 (CO, amide), 1622 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.30 (s, 3H, CH3), 3.14–3.23 (m, 8H, morpholine), 3.90 (s, 3H, OCH3), 6.76 (d, 1H, J = 2.34 Hz, furan), 7.33 (s, 1H, pyrimidine), 7.64 (s, 1H, phenyl), 7.80 (d, 1H, J = 2.35 Hz, furan); 13C-NMR (DMSO-d6) δ 23.1 (1C, CH3), 51.5 (2C, 2CH2, morpholine), 55.8 (2C, 2CH2, morpholine), 61.9 (1C, OCH3), 91.5 (1C, CH, phenyl), 99.5 (1C, CH, pyrimidine), 100.7, 105.6, 108.4, 144.7, 146.3, 153.9, 155.2, 160.7, 164.8, 168.9 (10C, Ar-C), 169.8 (1C, C=O); MS (70 eV, %) m/z 366 (M+, 78%); Anal. Calc. (Found) for C19H18N4O4 (366.38): C, 62.29 (62.37); H, 4.95 (4.88); N, 15.29 (15.22).

3.41. Synthesis of 7,11-Dimethoxy-6-methyl-1-(piperazin-1-yl)-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (12b) with piperazine, as yellowish crystals, crystallized from ethanol in 74% yield, m.p. 184 °C. IR (ν, cm−1) KBr: 3395 (br, NH), 3048 (CH-aryl), 2944 (CH-aliph), 1689 (CO, amide), 1624 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.31 (s, 3H, CH3), 2.85–2.94 (m, 8H, piperazine), 3.97 (s, 6H, 2OCH3), 6.81 (d, 1H, J = 2.32 Hz, furan), 7.36 (s, 1H, pyrimidine), 7.84 (d, 1H, J = 2.30 Hz, furan), 10.35 (brs, NH, D2O exchangeable); 13C-NMR (DMSO-d6) δ 23.5 (1C, CH3), 48.6 (2C, 2CH2, piperazine), 52.8 (2C, 2CH2, piperazine), 61.8 (2C, 2OCH3), 99.6(1C, CH, pyrimidine), 100.5, 105.7, 108.9, 122.3, 130.2, 146.4, 146.5, 151.8, 154.1, 164.8, 168.5 (10C, Ar-C), 169.7(1C, C=O); MS (70 eV, %) m/z 395 (M+, 76%); Anal. Calc. (Found) for C20H21N5O4 (395.42): C, 60.75 (60.82); H, 5.35 (5.43); N, 17.71 (17.78).

3.42. Synthesis of 7,11-Dimethoxy-6-methyl-1-morpholino-3H-furo[3,2-g]pyrimido[1,6-a]quinazolin-3-one ()

The compound was obtained from the reaction of (12b) with morpholine, as yellowish crystals, crystallized from n-hexane in 72% yield, m.p. 156 °C. IR (ν, cm−1) KBr: 3039 (CH-aryl), 2934 (CH-aliph), 1683 (CO, amide), 1626 (C=N). 1H-NMR (DMSO-d6, ppm) δ 2.32 (s, 3H, CH3), 3.16–3.25 (m, 8H, morpholine), 3.97 (s, 6H, 2OCH3), 6.79 (d, 1H, J = 2.33 Hz, furan), 7.37 (s, 1H, pyrimidine), 7.82 (d, 1H, J = 2.37 Hz, furan); 13C-NMR (DMSO-d6) δ 23.7 (1C, CH3), 53.8 (2C, 2CH2, morpholine), 57.6 (2C, 2CH2, morpholine), 61.9 (2C, 2OCH3), 99.8 (1C, CH, pyrimidine), 100.4, 105.3, 108.7, 122.6, 130.1, 146.2, 146.8, 151.3, 154.2, 164.5, 168.6 (11C, Ar-C), 169.4 (1C, C=O); MS (70 eV, %) m/z 396 (M+, 74%); Anal. Calc. (Found) for C20H20N4O5 (396.40): C, 60.60 (60.68); H, 5.09 (5.16); N, 14.13 (14.20).

3.43. Biological Screening

The antimicrobial activity of the newly prepared compounds was tested in vitro against Gram-positive bacteria n class="Species">Staphylococcus aureus (ATCC®6538™), Streptococcus pyogenes (ATCC®19615™), Gram-negative bacteria Escherichia coli (ATCC®25922™), Klebsiella pneumoniae (ATCC® 10031™) and the fungi Aspergillus niger (ATCC® 16888™), Alternaria alternate, Curvularia lunata and Candida albicans (ATCC®10231™). The newly prepared compounds were dissolved in dimethyl sulfoxide (DMSO) and tested for their antimicrobial activity by the agar disk diffusion technique. Cefotaxime sodium and nystatin [34,35] were used as the standard drugs for antibacterial and antifungal assays, respectively. A solution of 100 μg mL−1 of the tested compound was practical and microplate-wells, 1 cm in diameter, were used. Zones of inhibition were measured with calipers or automated scanners and were paralleled with those of the standards. Cefotaxime sodium (0.15 μmol mL−1) and nystatin (0.037 μmol mL−1) were used as the standard drugs for antibacterial and antifungal activity, respectively. Compound-impregnated disks were placed on an agar plate containing a standard suspension of microorganisms. The plate was incubated for 24 h at 37 °C. For the assessment of the minimum inhibitory concentration (MIC) by the serial plate dilution way [34,35], 5 mg of each tested compound was dissolved in 1 mL of DMSO separately to prepare stock solutions. Serial dilutions were prepared from each stock solution. The plates were incubated at 37 °C for 24 h. MIC is defined as the lowest concentration (μmol mL−1) of the tested compound that results in no visible growth on the plates. DMSO was used as the solvent control to ensure that the solvent had no effect on bacterial growth. The results are shown in Table 1 and Table 2.

4. Conclusions

In this work, we synthesized novel heterocyclic compounds with potent antimicrobial activity starting from n class="Chemical">furochromones (visnagenone 2a or khellinone 2b). New derivatives were prepared in good yields such as; furopyrimido quinazolinones, furothiazolo pyrimido quinazolinones, substituted-benzyliden-furothiazolo pyrimido quinazolinones, pyrazolo furopyrimido quinazolin-ones, oxo or thioxo-pyrimidin-furopyrimido quinazolinones and methylthio, methylsulfonyl, piperazino or morpholino-furopyrimido quinazolinones. Some new prepared compounds such as substituted-benzylidene-furothiazolo pyrimido quinazolinones 8a–f showed higher activity against the tested microorganisms (bacteria and fungi).