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Acta Chim. Slov. 2016, 63, 638-645
DOI: 10.17344/acsi.2016.2464
Scientific paper
Synthesis of 6-N-^-Tetrazolo[1'5-c]quinazolin-5(6ff)-ones
and Their Anticancer Activity
Oleksii Antypenko,1'* Sergiy Kovalenko,1 Bakhtiyor Rasulev2'3
and Jerzy Leszczynski3
1 Organic and Bioorganic Chemistry Department, Zaporizhzhya State Medical University, 26, Mayakovsky Ave., Zaporizhzhya, 69035, Ukraine
2 Center for Computationally Assisted Science and Technology, North Dakota State University, 1805 NDSU Research Park Dr, Fargo, ND 58108, USA
3 Interdisciplinary Center for Nanotoxicity, Department of Chemistry and Biochemistry, Jackson State University,
1400 John R. Lynch Street, Jackson, MS 17910, USA
* Corresponding author: E-mail: antypenkoan@ gmail.com
Received: 25-03-2016
Abstract
Chemical compounds with tetrazole ring are very interesting systems that can be valuable in pharmaceutical and clinical applications, especially as anticancer agents. In this work, novel 6-N-R-tetrazolo[1,5-c]quinazolin-5(6ff)-ones were synthesized. A large set of IR, LC-, EI-MS, 1H, 13C NMR and elemental analysis data were collected and evaluated for their structures and purity. Details of synthesis, namely the N-alkylation, are discussed, including reactions with secondary and tertiary amides. Four new synthesized compounds (2.7, 3.2, 5.2, 5.3) were tested in vitro for anticancer activity at 10 |M against 60 cell lines of nine different cancer types: leukemia, melanoma, lung, colon, CNS, ovarian, renal, prostate, and breast cancers. Further synthesis of substances within the series of substituted tetrazolo[1,5-c]quinazoline systems will be attempted to develop improved compounds with better anticancer activity.
Keywords: Anticancer activity; 6-N-R-tetrazolo[1,5-c]quinazolin-5(6ff)-ones; organic synthesis
1. Introduction
Tetrazole ring is a very interesting system and chemical compounds with this ring find diverse biological, pharmaceutical, and clinical applications, despite its absence in nature.1 Many highly effective agents have active pharmaceutical ingredients containing the tetrazole ring. During relatively short period of time many such compounds have appeared in the world of pharmaceutical market. Thus, among the drugs with tetrazole ring and agents under trials are the following compounds: hypotensive (Losartan), antimicrobial (Cefamandol), antifungal (TAK-456), anti-inflammatory (Figure 1, a), antiviral (5-CIT-EP), antihistaminic (Tazanoplast, Planlukast), cytostatic (Figure 1, b), central nervous system influence (Co-razolum), and others (Figure 1.).2-5 Also, the anticancer activity of tetrazol was recently reported.6-7 Thus, plati-num(II) complexes (Figure 1, c) with the general formulae
cis-[PtCl2(DMSO)L], where ligands are a Schiff base or hydrazone are derived from tetrazolo[1,5-a]quinoline-4-carboxaldehyde (Figure 1).8 Moreover, fibrinolytic and bronchodilating activities of such compounds were claimed by several US patents.9,10 Our latest investigations of substituted condensed tetrazolo[1,5-c]quinazolines have also proved their potential as pharmaceutical agents, namely anticancer (N-(benzo[d]thiazol-2-yl)-2-(tetrazo-lo[1,5-c]quinazolin-5-ylthio)acetamides against cells of melanoma), antimicrobial (1-(2,5-dimethoxyphenyl)-2-(tetrazolo[1,5-c]quinazolin-5-ylthio)ethanone against Staphylococcus aureus), antifungal (5-(3-chloropropylt-hio)tetrazolo[1,5-c]quinazoline against Candida albicans), and bioluminescence inhibition properties.11,12
So, tetrazolo[1,5-c]quinazolines are of undoubting interest and valuable objects for further research. In this work, as a logical continuation of our previous investigations a range of 6-N-R-tetrazolo[1,5-c]quinazolin-5(6H)-
Antypenko et al.: Synthesis of 6-N-R-Tetrazolo[1,5-c]quinazolin-5(6H)-ones
Acta Chim. Slov. 2016, 63, 638-639	645

Figure 1. Structures of known tetrazole ring containing drugs available on the market and related agents in clinical trials
ones was synthesized. Thus, the aim of this work was the study of tetrazolo[1,5-c]quinazolin-5(6H)-one N-alkyla-tion with subsequent investigation of the 6-N-R-tetrazo-lo[1,5-c]quinazolin-5(6H)-ones for their anticancer activity.
2. Experimental Section
2. 1. Chemistry
2. 1. 1. General Methods
Melting points were determined in open capillary tubes in a «Stuart SMP30» apparatus and are uncorrected. The elemental analyses (C, H, N) were performed using the ELEMENTAR vario EL cube analyzer. IR spectra (4000-600 cm-1) were recorded on a Bruker ALPHA FT-
IR spectrometer using a module ATR eco ZnSe. 1H NMR spectra (400 MHz) and 13C NMR spectra (100 MHz) were recorded at a Varian-Mercury 400 and Bruker Avance DRX-500 spectrometers with SiMe4 as internal standard in DMSO-d6 solution. LC-MS were recorded using chro-matography/mass spectrometric system which consists of high-performed liquid chromatograph «Agilent 1100 Series» equipped with diode-matrix and mass-selective detector «Agilent LC/MSD SL» (atmospheric pressure chemical ionization - APCI). Electron impact mass spectra (EI-MS) were recorded on a Varian 1200 L instrument at 70 eV.
2. 2. Pharmacology
2. 2. 1. Anticancer Assay for Preliminary in vitro Testing
From the newly synthesized compounds 4 substances, namely 2.7, 3.2, 5.2, 5.3 were selected by the NCI Developmental Therapeutic Program for in vitro cell line screening to investigate their anticancer activity. The human tumor cell lines were derived from nine different cancer types: leukemia, melanoma, lung, colon, CNS, ovarian, renal, prostate and breast cancers. Initially, a single high concentration was used (10 pM) in the full NCI 60-cell panel. In the screening protocol, each cell line was inoculated and preincubated for 24-48 h on a microtiter plate. Then test substances were added to the plate and the culture was incubated for further 48 h. End point determinations were made with a protein binding dye, sulforho-damine B. Results for each test agent were reported as the percent growth of the treated cells when compared to the untreated control cells (Table 1).
General Procedure for the Synthesis of 6-N-R-Tetrazo-lo[1,5-c]quinazolin-5(6H)-ones.
To a solution of 0.9 g (4.8 mmol) of tetrazolo[1,5-c]quina-zolin-5(6#)-one (1.1) in DMF 0.17 g (4.8 mmol) of sodium hydride (60% oil suspension) was added. After 5-10 min, when all hydrogen has been released, the appropriate halogen derivative was added (4.8 mmol). The mixture was refluxed for 2 h and cooled down. Then DMF was evaporated under vacuum and water was added to form the precipitate. It was filtered, washed with water, dried and crystallized from a mixture of propane-2-ol : water (1:1).
Tetrazolo[1,5-c]quinazolin-5(6H)-one (1.1)13'14 Yield 95.6%; mp 295-297°C; IR (cm-1): 3147, 3114, 3085, 3047, 2974, 2916, 2849, 2755, 2709, 1746, 1714, 1660, 1625, 1587, 1547, 1515, 1483, 1463, 1442, 1430, 1415, 1388, 1342, 1304, 1256, 1202, 1167, 1157, 1114, 1088, 1025, 995, 969, 896, 880, 810, 783, 757, 742, 731, 709, 698, 675, 658, 623. 1H NMR: 5 (ppm) 12.68 (s, 1H, NH), 8.27 (d, J = 7.8 Hz, 1H, H-10), 7.71 (t, J = 7.7 Hz, 1H, H-9), 7.50 (d, J = 8.2 Hz, 1H, H-7), 7.42 (t, J = 7.5
Antypenko et al.: Synthesis of 6-N-R-Tetrazolo[1,5-c]quinazolin-5(6H)-ones
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Acta Chim. Slov. 2016, 63, 638-645
Hz, 1H, H-8). LC-MS: m/z 187 [M+H]+. Anal. Calcd. for C8H5N5O: C, 51.34; H, 2.69; N, 37.42. Found: C, 51.38; H, 2.63; N, 37.46.
6-Methyltetrazolo[1,5-c]quinazolin-5(6H)-one (2.1)
Yield 57.0%; mp 224-226 °C; IR (cm1): 1726, 1650, 1620, 1588, 1555, 1518, 1489, 1454, 1423, 1398, 1340, 1315, 1299, 1259, 1235, 1173, 1130, 1108, 1087, 1042, 1013, 1001, 965, 877, 787, 761, 731, 710, 674, 633. 1H NMR: 5 (ppm) 8.39 (d, J = 7.6 Hz, 1H, H-10), 7.87 (t, J = 7.5 Hz, 1H, H-9), 7.71 (d, J = 8.5 Hz, 1H, H-7), 7.54 (t, J = 7.5 Hz, 1H, H-8), 3.80 (s, 3H, CH3). EI-MS: m/z (I% rel) 201 (100, M+0, 173 (50.2), 172 (42.7), 145 (15.8), 144 (88.2), 130 (30.1), 129 (32.4), 106 (11.5), 105 (21.2), 104
(55.5),	103 (38.1), 102 (84.3), 78 (29.4), 77 (90.7), 76 (71.8), 75 (45.1), 74 (45.1), 74 (17.0), 71 (15.3), 70
(10.6),	69 (20.0), 65 (10.3), 50 (26.6), 43 (44.2), 42 (23.1), 41 (28.7), 40 (30.9). LC-MS: m/z 202 [M+H]+. Anal. Calcd. for C9H7N5O: C, 53.73; H, 3.51; N, 34.81. Found: C, 53.71; H, 3.55; N, 34.78.
6-Ethyltetrazolo[1,5-c]quinazolin-5(6H)-one (2.2) Yield 36.8%; mp 214-216 °C; IR (cm-1): 2992, 2916, 2849, 1730, 1714, 1620, 1586, 1554, 1487, 1459, 1447, 1402, 1383, 1370, 1354, 1322, 1296, 1264, 1239, 1216, 1171, 1130, 1106, 1085, 1045, 1021, 970, 859, 781, 757, 732, 710, 671, 628, 608. 1H NMR: 5 (ppm) 8.40 (d, J =
7.4	Hz, 1H, H-10), 7.86 (t, J = 7.5 Hz, 1H, H-9), 7.74 (d, J = 8.3 Hz, 1H, H-7), 7.53 (t, J = 7.1 Hz, 1H, H-8), 4.43 (d, J = 6.7 Hz, 2H, NHCH2), 1.41 (t, J = 6.5 Hz, 3H, CH3). Anal. Calcd. for C10H9N5O: C, 55.81; H, 4.22; N, 32.54. Found: C, 55.84; H, 4.20; N, 32.56.
6-Benzyltetrazolo[1,5-c]quinazolin-5(6H)-one (2.3) Yield 78.1%; mp 203-205 °C; IR (cm-1): 2953, 2918, 2851, 1718, 1619, 1589, 1580, 1556, 1487, 1455, 1400, 1371, 1352, 1324, 1295, 1259, 1227, 1188, 1171, 1161, 1107, 1096, 1050, 1005, 974, 960, 853, 807, 785, 756, 732, 701, 672, 643, 619. 1H NMR: 5 (ppm) 8.41 (d, J =
7.5	Hz, 1H, H-10), 7.73 (t, J = 7.7 Hz, 1H, H-9), 7.50 (dd, J = 13.9, 7.6 Hz, 2H, Bz-3,5), 7.41 (d, J = 6.9 Hz, 2H, H-7,8), 7.36-7.22 (m, 3H, Bz-2,4,6), 5.61 (s, 2H, NCH2). LC-MS: m/z 278 [M+H]+. Anal. Calcd. for C15H11N5O: C, 64.97; H, 4.00; N, 25.26. Found: C, 64.94; H, 4.04; N, 25.22.
6-Phenethyltetrazolo[1,5-c]quinazolin-5(6H)-one (2.4) Yield 63.0%; mp 207-209 °C; IR (cm-1): 2937, 2924, 1739, 1679, 1622, 1591, 1555, 1531, 1511, 1489, 1455, 1360, 1326, 1294, 1275, 1251, 1229, 1204, 1183, 1155, 1107, 1095, 1083, 1050, 1034, 1010, 997, 967, 917, 888, 870, 852, 828, 774, 750, 733, 704, 671, 656. 1H NMR: 5 (ppm) 8.42 (d, J = 7.2 Hz, 1H, H-10), 7.87 (t, J = 7.8 Hz, 1H, H-9), 7.79 (d, J = 8.2 Hz, 1H, H-7), 7.54 (t, J = 6.9 Hz, 1H, H-8), 7.38 (d, J = 6.5 Hz, 2H, Ph-2,6), 7.31 (t, 2H, Ph-3,5), 7.23 (d, J = 6.8 Hz, 1H, Ph-4), 4.55 (t, J = 7.6 Hz,
2H, NCH2), 3.08 (t, J = 7.4 Hz, 2H, NCH2CH2). LC-MS: m/z 292 [M+H]+. Anal. Calcd. for C16H13N5O: C, 65.97; H, 4.50; N, 24.04. Found: C, 65.95; H, 4.53; N, 24.01.
2-(5-Oxotetrazolo [1,5-c]quinazolin-6(5H)-yl)acetonitri-le (2.5)
Yield 88.4%; mp 230-235 °C; IR (cm-1): 3117, 3075, 3006, 2917, 2849, 1729, 1620, 1588, 1556, 1485, 1463, 1422, 1400, 1359, 1350, 1317, 1297, 1263, 1239, 1200, 1173, 1107, 1094, 1057, 1024, 1010, 983, 959, 920, 855, 779, 756, 734, 712, 686, 673. 1H NMR: 5 (ppm) 8.43 (d, J = 7.7 Hz, 1H, H-10), 7.95 (t, J = 7.9 Hz, 1H, H-9), 7.85 (d, J = 8.5 Hz, 1H, H-7), 7.61 (t, J = 7.4 Hz, 1H, H-8), 5.54 (s, 2H, CH2). LC-MS: m/z 227 [M+H]+. Anal. Calcd. for C10H6N6O: C, 53.10; H, 2.67; N, 37.15. Found: C, 53.14;
H1,02.665;6 N, 37.18.
6-(2-Oxo-2-phenylethyl)tetrazolo [1,5-c ]quinazolin-5(6H)-one (2.6)
Yield 95.6%; mp 199-201 °C; IR (cm-1): 2919, 2850, 1747, 1696, 1623, 1593, 1557, 1531, 1487, 1465, 1449, 1400, 1377, 1340, 1296, 1259, 1227, 1196, 1174, 1130, 1111, 1098, 1076, 1055, 1026, 997, 970, 835, 812, 750, 728, 708, 687, 670, 632. 1H NMR: 5 (ppm) 8.46 (d, J = 7.6 Hz, 1H, H-10), 8.20 (d, J = 7.5 Hz, 2H, Ph-2,6), 7.78 (t, J = 7.8, Hz, 1H, H-9), 7.72 (d, J = 6.9 Hz, 1H, H-7), 7.59 (m, 4H, Ph-3,4,5, H-8), 6.04 (s, 2H, NCH2). EI-MS: m/z (I% rel) 305 (26.6, M+), 277 (43.7), 207 (13.4), 129 (33.2), 118 (21.2), 117 (20.4), 116 (23.3), 92 (18.4), 91
(64.8),	90 (100), 89 (51.2), 88 (11.9), 65 (29.4), 64 (25.7), 63 (48.0), 62 (28.5), 57 (23.8), 55 (11.7), 52 (17.6), 51
(54.9),	50 (16.2). LC-MS: m/z 306 [M+H]+. Anal. Calcd. for C16H11N5O2: C, 62.95; H, 3.63; N, 22.94. Found: C, 62.99; H, 3.(50; N, 22.97.
6-(2-Oxo-2-(p-tolyl)ethyl)tetrazolo [1,5-c ]quinazolin-5(6H)-one (2.7)
Yield 64.5%; mp 220-222 °C; IR (cm-1): 3045, 2997, 2957, 2916, 2847, 1732, 1684, 1621, 1604, 1589, 1557, 1530, 1488, 1470, 1432, 1354, 1318, 1295, 1264, 1233, 1202, 1185, 1124, 1106, 1091, 1057, 1035, 998, 972, 887, 879, 870, 861, 839, 829, 813, 782, 774, 753, 731, 704, 670, 654, 624. 1H NMR: 5 (ppm) 8.46 (d, J = 7.5 Hz, 1H, H-10), 8.10 (d, J = 6.8 Hz, 2H, Ph-2, 6), 7.80 (t, J = 7.4 Hz, 1H, H-9), 7.58 (d, J = 7.8 Hz, 2H, H-7, 8), 7.43 (d, J = 7.1 Hz, 2H, Ph-3, 5), 6.01 (s, 2H, NCH2), 3.17 (s, 3H, CH3). LC-MS: m/z 320 [M+H]+. Anal. Calcd. for C17H13N5O2: C, 63.94; H, 4.10; N, 21.93. Found: C, 635.90; H, 4.16; N, 21.88.
Methyl 2-(5-oxotetrazolo[l,5-c]quinazolin-6(5H)-yl)ace-tate (3.1)
Yield 14.5%; mp 194-196 °C; IR (cm-1): 2953, 2918, 2851, 1718, 1619, 1589, 1580, 1556, 1487, 1455, 1400, 1371, 1351, 1324, 1295, 1259, 1227, 1188, 1171, 1161, 1107, 1096, 1050, 1005, 974, 960, 853, 807, 785, 756,
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732, 701, 672, 643, 619. 1H NMR: 5 (ppm) 8.43 (d, J = 7.5 Hz, 1H, H-10), 7.85 (t, J = 7.8 Hz, 1H, H-9), 7.64 (d, J = 8.6 Hz, 1H, H-7), 7.57 (t, J = 7.4 Hz, 1H, H-8), 5.22 (s, 2H, NCH2), 3.80 (s, 3H, CH3). Anal. Calcd. for C11H9N5O3: C, 50.97; H, 3.50; N, 27.02. Found: C, 50.95;
H,	3.54; N, 27.01.
Ethyl 2-(5-oxotetrazolo[1,5-c]quinazolin-6(5H)-yl)ace-tate (3.2)
Yield 54.4%; mp 172-174 °C; IR (cm-1): 2984, 2918, 1730, 1621, 1588, 1558, 1488, 1467, 1444, 1428, 1377, 1354, 1297, 1268, 1223, 1202, 1107, 1093, 1057, 1032, 1018, 990, 958, 887, 854, 814, 772, 752, 726, 707, 683, 672, 647. 1H NMR: 5 (ppm) 8.44 (d, J = 7.7 Hz, 1H, H-10), 7.88 (t, J = 7.8 Hz, 1H, H-9), 7.67 (d, J = 8.5 Hz, 1H, H-7), 7.59 (t, J = 7.2 Hz, 1H, H-8), 5.22 (s, 2H, NCH2), 4.27 (dd, J = 13.1, 6.2 Hz, 2H, OCH2), 1.32 (t, J = 6.9 Hz, 2H, CH3). 13C NMR: 5 167.38 (s, CO), 150.01 (s, C-5), 142.93 (s, C-6a), 137.83 (s, C-1a), 134.68 (s, C-8), 125.68 (s, C-9), 125.09 (s, C-10), 116.20 (s, C-7), 108.19 (s, C-10a), 61.75 (s, OCH2), 45.59 (s, NCH2), 14.07 (s, CH3). LC-MS: m/z 275 [M+H]+. Anal. Calcd. for C12H11N503: C, 52.75; H, 4.06; N, 25.63. Found: C, 52.71; H, 4.09; N, 25.60.
Propyl 2-(5-oxotetrazolo[1,5-c]quinazolin-6(5H)-yl)ace-tate (3.3)
Yield 72.5%; mp 108-110 °C; IR (cm-1): 3128, 3060, 3019, 2959, 2918, 2873, 2849, 1730, 1620, 1589, 1557, 1519, 1487, 1466, 1426, 1395, 1351, 1298, 1267, 1220, 1199, 1106, 1093, 1058, 1029, 1010, 991, 958, 934, 876, 841, 827, 749, 707, 671, 648. 1H NMR: 5 (ppm) 8.44 (d, J = 7.6 Hz, 1H, H-10), 7.85 (t, J = 7.7 Hz, 1H, 1H, H-9), 7.62 (d, J = 8.5 Hz, 1H, H-7), 7.57 (t, J = 7.4 Hz, 1H, H-8), 5.20 (s, 2H, NCH2), 4.19 (t, J = 6.5 Hz, 2H, OCH2),
I.38	(dd, J = 14.7, 7.3 Hz, 2H, OCH2CH2CH3), 0.93 (t, J = 7.2 Hz, 3H, OCH2CH2CH3). Anal. Calcd. for C13H13N5O3: C, 54.35; H, 42.56; N, 24.38. Found: C, 5^1.37; H, 4.54; N, 24.41.
2-((2-(1H-tetrazol-5-yl)phenyl)amino)acetic acid (4.1) Yield 75.8%; mp 260-270 °C; IR (cm-1): 3546, 3356, 3191, 2890, 2582, 1908, 1616, 1575, 1564, 1517, 1480, 1436, 1408, 1307, 1281, 1257, 1166, 1095, 1052, 984, 938, 845, 746, 721, 703, 665. 1H NMR: 5 (ppm) 8.227.93 (br.s, 1H, NHtetr.), 7.80 (d, J = 7.6 Hz, 1H, Ph-3), 7.30 (t, J = 7.6 Hz, 1H, Ph-4), 6.72 (t, J = 7.4 Hz, 1H, Ph-5), 6.66 (d, J = 8.3 Hz, 1H, Ph-6), 4.01 (s, 2H, NCH2). LC-MS: m/z 220 [M+H]+. Anal. Calcd. for C10H7N5O3: C, 49.31; H, 4.14; N, 31.95. Found: C, 49.34; H, 43.11; N, 31.99.
N-(2-methoxyphenyl)-N-(2-((2-methoxyphenyl)amino)-2-oxoethyl)-2-(5-oxotetrazolo[1,5-c ]quinazolin-6(5H)-yl)acetamide (5.1)
Yield 72.2%; mp 184-186 °C; IR (cm-1): 3324, 3004,
2953, 2919, 2850, 1771, 1710, 1683, 1600, 1539, 1486, 1453, 1417, 1379, 1360, 1321, 1290, 1264, 1253, 1237, 1199, 1179, 1159, 1080, 1037, 996, 970, 950, 907, 864, 841, 827, 815, 799, 784, 747, 723, 698, 682, 668, 644, 621. 1H NMR: 5 (ppm) 10.42 (s, 1H, NH), 8.26 (d, J = 7.0 Hz, 1H, H-10), 7.64 (dd, J = 13.1, 5.0 Hz, 3H, H-7,8,9), 7.32-7.23 (m, 2H, Ph'-3, Ph-3), 7.17 (t, J = 8.1 Hz, 1H, Ph'-4), 7.05 (d, J = 7.8 Hz, 1H, Ph'-6), 6.97-6.83 (m, 3H, Ph'-5, Ph-4,5), 6.60 (d, J = 6.8 Hz, 1H, Ph-6), 5.66 (s, 2H, NCH2CO), 4.46 (s, 2H, NCH2CONH), 3.77 (s, 1H, Ph'-OCH3), 3.75 (s, 1H, Ph-OCH3). EI-MS: m/z (I% rel) 513 (33.0, M+*), 3 3 5 (51.9), 3(39 (10.9), 308 (32.7), 307 (26.3), 178 (17.9), 150 (34.0), 149 (100), 148 (17.2), 147 (15.5), 123 (10.1), 119 (19.9), 92 (12.9), 91 (18.9), 88 (10.2), 86 (39.6), 84 (41.2), 57 (18.1), 55 (10.7). LC-MS: m/z 513 [M+H]+. Anal. Calcd. for C26H17F6N7O3: C, 60.81; H, 4.51; N, 19.09. Found: C, 60.85; H, 4.473; N, 19.12.
N-(2-Oxo-2-((4-(trifluoromethyl)phenyl)amino)ethyl)-2-(5-oxotetrazolo [1,5-c ]quinazolin-6(5H)-yl)-N-(4-(trif-luoromethyl)phenyl)acetamide (5.2) Yield 51.2%; mp 249-251 °C; IR (cm-1): 3304, 3213, 3166, 3141, 3081, 3014, 2921, 2851, 1777, 1716, 1704, 1609, 1550, 1491, 1441, 1416, 1386, 1358, 1328, 1285, 1258, 1230, 1181, 1162, 1113, 1067, 1044, 1017, 1005, 992, 968, 951, 868, 851, 834, 805, 785, 748, 738, 726, 690, 674, 660, 643, 624. 1H NMR: 5 (ppm) 10.95 (s, 1H, NH), 8.29 (d, J = 7.4 Hz, 1H, H-10), 7.80 (t, J = 7.4 Hz, 1H, H-9), 7.73 (br.s, 4H, Ph-2,3,5,6), 7.70-7.64 (m, 4H, Ph'-2,3,5,6), 7.59 (d, J = 8.2 Hz, 1H, H-7), 7.49 (dd, J = 15.5, 7.9 Hz, 1H, H-8), 5.82 (s, 2H, NCH2CO), 4.56 (s, 2H, NCH2CONH). LC-MS: m/z 590 [M+H]+. Anal. Calcd. for C26H17F6N7O3: C, 52.98; H, 2.91; N, 16.63. Found: C, 52.93; H, 2.95; N, 16.60.
N-(4-Fluorobenzyl)-N-(2-((4-fluorobenzyl)amino)-2-ox-oethyl)-2-(5-oxotetrazolo [1,5-c ]quinazolin-6(5H)-yl)acetamide (5.3)
Yield 54.4%; mp 152-154 °C; IR (cm-1): 3296, 1770, 1737, 1705, 1659, 1621, 1604, 1556, 1520, 1487, 1455, 1433, 1417, 1381, 1369, 1352, 1296, 1258, 1217, 1203, 1154, 1095, 1044, 1005, 995, 959, 917, 851, 829, 782, 770, 757, 744, 732, 711, 680, 659, 641, 617. 1H NMR: 5 (ppm) 8.86 (br.s, 1H, NH), 8.19 (d, J = 7.2 Hz, 1H, H-10), 7.62 (m, 3H, H-9,8,7), 7.35 (m, 4H, Ph-2,3,5,6), 7.09 (m, J = 8.4 Hz, 4H, Ph'-2,3,5,6), 5.43 (s, 2H, NCH2C(O)N), 4.59 (s, 2H, NCH2C(O)NH), 4.39 (s, 2H NCH2Ph), 4.35 (d, J = 5.0 Hz, 2H, NHCH2Ph'). EI-MS: m/z (I% rel) 517 (3.2, M+), 337 (26.6), 165 (20.5), 150 (30.8), 137 (11.8), 136 (19.7), 131 (18.0), 122 (21.4), 110 (47.0), 109 (100), 107 (17.5), 105 (11.5), 104 (14.2), 103 (30.6), 89 (10.9), 86 (14.9), 84 (20.4), 83 (47.0), 77 (16.9), 76 (13.3), 75 (19.6), 51 (17.8). LC-MS: m/z 518 [M+H]+. Anal. Calcd. for C26H21F2N7O3: C, 60.35; H, 4.09; N, 18.95. Found: C, 60.39; H, 4.05; N, 18.98.
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N-(2-Oxo-2-((4-(trifluoromethyl)benzyl)amino)ethyl)-2-(5-oxotetrazolo [1,5-c ]quinazolin-6(5H)-yl)-N-(4-(trif-luoromethyl)benzyl)acetamide (5.4) Yield 31.1%; mp 166-168 °C; IR (cm-1): 3293, 2916, 1774, 1708, 1671, 1621, 1558, 1486, 1452, 1439, 1422, 1412, 1374, 1324, 1260, 1203, 1178, 1158, 1114, 1080, 1067, 1044, 1019, 953, 925, 817, 784, 762, 744, 735, 712, 679, 635, 613. 1H NMR: 5 (ppm) 8.99 (br.s, 1H, NH), 8.20 (d, J = 6.8 Hz, 1H, H-10), 7.63 (m, 7H, H-7,8,9, Ph-2,3,5,6), 7.52 (m, 4H, Ph'-2,3,5,6), 5.52 (m, 2H, NCH2C(O)N), 4.70 (s, 2H, NCH2C(O)NH), 4.46 (d, J = 4.9 Hz, 2H, NHCH2Ph'), 4.42 (s, 2H, NCH2Ph). LC-MS: m/z 590 [M+H]+. Anal. Calcd. for C28H21F6N7O3: C, 54.46; H, 3.43; N, 15.88. Found: C, 54.41; H, 3.40; N, 15.85.
6-(2-Morpholino-2-oxoethyl)tetrazolo [1,5-c]quinazolin-5(6H)-one (6.1)
Yield 73.3%; mp 217-219 °C; IR (cm-1): 2981, 2917, 2868, 2848, 1733, 1665, 1620, 1587, 1556, 1485, 1454, 1422, 1399, 1365, 1344, 1329, 1314, 1299, 1269, 1261, 1226, 1213, 1198, 1163, 1120, 1104, 1091, 1060, 1037, 1024, 1008, 987, 949, 908, 872, 842, 801, 780, 760, 730, 709, 669, 621. 1H NMR: 5 (ppm) 8.43 (d, J = 7.5 Hz, 1H, H-10), 7.91 (t, J = 7.5 Hz, 1H, H-9), 7.63 (d, J = 8.7 Hz, 1H, H-7), 7.59 (t, J = 7.4 Hz, 1H, H-8), 5.38 (s, 2H, NCH2), 3.75 (s, 2H, H-3 morph), 3.71 (s, J = 3.1 Hz, 2H, H-5 morph), 3.63 (s, 2H, H-2 morph), 3.48 (s, 2H, H-6 morph). EI-MS: m/z (I% rel) 314 (1.4, M+*), 286 (17.9), 228 (49.8), 172 (26.0), 131 (15.1), 130 (26.6), 129 (57.4), 127 (19.1), 103 (43.9), 102 (49.0), 99 (18.9), 77 (19.2), 76 (18.5), 75 (16.4), 70 (100). LC-MS: m/z 315 [M+H]+. Anal. Calcd. for C14H14N6O3: C, 53.50; H, 4.49; N, 26.74. Found: C, 53.53; H, 4.45; N, 26.77.
6-(2-(4-(2-Fluorophenyl)piperazin-1-yl)-2-oxoethyl)te-trazolo[1,5-c]quinazolin-5(6H)-one (6.2)
Yield 96.8%; mp 247-249 °C; IR (cm-1): 2995, 2963, 2917, 2849, 1727, 1656, 1618, 1589, 1557, 1504, 1485, 1463, 1447, 1435, 1397, 1377, 1359, 1341, 1329, 1294, 1279, 1262, 1235, 1213, 1199, 1166, 1149, 1106, 1091, 1057, 1039, 1025, 1009, 994, 960, 937, 927, 912, 803, 779, 755, 730, 670, 616. 1H NMR: 5 (ppm) 8.44 (d, J = 7.8 Hz, 1H, H-10), 7.91 (t, J = 7.9 Hz, 1H, H-9), 7.65 (d, J = 8.4 Hz, 1H, H-7), 7.60 (t, J = 7.3 Hz, 1H, H-8), 7.21-7.15 (m, 2H, Ph-5,6), 7.12 (t, J = 8.2 Hz, 1H, Ph-4), 7.04 (dd, J = 12.3, 5.9 Hz, 1H, Ph-3), 5.43 (s, 2H, NCH2), 3.87 (s, 2H, ppz-3), 3.67 (s, 2H, ppz-5), 3.21 (s, 2H, ppz-2), 3.05 (s, 2H, ppz-6). 13C NMR: 5 (ppm) 164.20 (s, CO ppz), 150.38 (s, CF), 143.30 (s, C-5), 140.09 (s, Ph-1), 138.74 (s, C-6), 135.00 (s, C-1a), 125.90 (s, C-9), 125.38 (s, Ph-5), 125.24 (s, C-8), 123.49 (s, C-7), 120.14 (s, C-10), 116.95 (s, Ph-6), 116.65 (s, Ph-4), 116.48 (s, Ph-3), 108.42 (s, C-10a), 50.97 (s, C-3 ppz), 50.49 (s, C-5 ppz), 46.02 (s, NCH2), 44.97 (s, C-2, ppz), 42.31 (s, C6 ppz). LC-MS: m/z 408 [M+H]+. Anal. Calcd. for C20H18FN7O2: C, 58.96; H, 4.45; N, 24.07. Found: C, 58.98; H, 4.42; N, 24.09.
6-(2-(3,5-Diphenyl-4,5-dihydro-1H-pyrazol-1-yl)-2-ox-oethyl)tetrazolo[1,5-c]quinazolin-5(6H)-one (6.3) Yield 87.2%; mp 248-250 °C; IR (cm-1): 2932, 1734, 1675, 1622, 1592, 1558, 1487, 1455, 1445, 1398, 1385,
1356,	1302, 1261, 1195, 1173, 1161, 1143, 1106, 1092, 1060, 1042, 1023, 1012, 955, 884, 864, 788, 776, 752, 731, 694, 672, 659, 644, 618. 1H NMR: 5 (ppm) 8.41 (d, J = 7.6 Hz, 1H, H-10), 7.92-7.82 (m, 2H, H-9,7), 7.78 (t, J = 7.6 Hz, 1H, H-8), 7.56-7.44 (m, 5H, 3-Ph(2-6)-5pyr.), 7.35-7.20 (m, 5H, 5-Ph(2-6)-5pyr.), 5.76-5.51 (m, 3H, NCH2, pyr.-5), 3.98 (dd, J = 17.9, 11.8 Hz, 1H, pyr.-4), 3.22 (dd, J = 17.9, 4.4 Hz, 1H, pyr.-4). LC-MS: m/z 450 [M+H]+. Anal. Calcd. for C^H^N^: C, 66.81; H, 4.26; N, 21.81. Found: C, 66.85; H, 4.22; N, 21.85.
6-(2-Oxo-2-(3-phenyl-5-(thiophen-2-yl)-4,5-dihydro-1H-pyrazol-1-yl)ethyl)tetrazolo [1,5-c]quinazolin-5(6H)-one (6.4)
Yield 91.5%; mp 264-265 °C; IR (cm-1): 2918, 2850, 1738, 1669, 1621, 1589, 1556, 1525, 1487, 1462, 1419,
1357,	1344, 1306, 1261, 1196, 1172, 1142, 1105, 1094, 1083, 1059, 1036, 1020, 1010, 996, 964, 954, 878, 863, 839, 787, 774, 753, 725, 699, 673, 643, 612. 1H NMR: 5 (ppm) 8.41 (d, J = 7.3 Hz, 1H, H-10), 7.78 (t, J = 8.1 Hz, 1H, H-9), 7.64 (s, 1H, H-7), 7.52 (s, 2H, Ph-2,6), 7.45 (s, 1H, H-8), 7.31 (d, J = 6.1 Hz, 2H, thioph.-4, pyr.-5), 7.26 (s, 3H, Ph-3,4,5), 7.13 (s, 1H, thioph.-3), 5.63 (s, 2H, NCH2), 5.53 (s, 1H, thioph. -2), 4.99 (m, 1H, pyr.-4), 3.22 (d, J = 16.1 Hz, 1H, pyr.-4). LC-MS: m/z 456 [M+H]+. Anal. Calcd. for C23H17N7O2S: C, 60.65; H, 3.76; N, 21.53. Found: C, 60.(52; H, 3.79; N, 21.51.
3. Results and Discussion
3. 1. Chemistry
The tetrazolo[1,5-c]quinazoline synthesis was described in detail in our previous works.11,12 5-(2'-Aminop-henyl)-1H-tetrazole (Scheme 1, c) was cyclized with car-bonyldiimidazole with formation of tetrazolo[1,5-c]qui-nazolin-5(6H)-one (1.1), which was used as the starting compound for further modifications at position 6. N-Alkylation of tetrazolo[1,5-c]quinazolin-5(6H)-one (1.1) was carried out using chloro derivatives, namely substances 2.1-2.7 (Cl-R) and 3.1-3.3 (Cl-R1) (Scheme 1).
To find the most efficient way of synthesis, various reaction conditions were explored. At first, tetrazolo[1,5-c]quinazolin-5(6H)-one (1.1) was dissolved in DMF with equimolar amount of sodium hydride. The corresponding halogen derivative was added only after all hydrogen has been released. The resulting mixture was refluxed for 2 h. Alternatively, the reaction was performed by the addition of potassium carbonate in DMF or sodium bicarbonate in dioxane. The best yields and purity of derivates 2 were observed in the presence of sodium hydride. This method was chosen as the primary one.
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Scheme 1. Synthesis of tetrazolo[1,5-c]quinazolin-5(6H)-one (1.1) and its N-substitued derivatives
The next step was the synthesis of acetamides. Firstly 2-(5-oxotetrazolo[1,5-c]quinazolin-6(5H)-yl)ace-tic acid should be obtained with further aminolysis. The direct alkylation of tetrazolo[1,5-c]quinazolin-5(6H)-one (1.1) with chloroacetic acid has not resulted in the desirable product. Thus, an alkaline hydrolysis of 2-(5-oxote-trazolo[1,5-c]quinazolin-6(5H)-yl)acetate esters 3.1-3.3 was necessary (Scheme 1). However, the cleavage of qui-nazoline cycle was observed, and the product of the cleavage turned out to be 2-((2-(1H-tetrazol-5-yl)phenyl)ami-no)acetic acid (4.1) (see further discussion on spectral data).
Then, N-alkylation of tetrazolo[1,5-c]quinazolin-5(6H)-one (1.1) with chloroacetamides was used to synthesize amides 5.1-5.4. The reaction was quite interesting, since the products obtained were disubstituted compounds 5.1-5.4. In this reaction NH proton of acetamide was acting as a competitive acid moiety, which results in the alkylation of the quinazolin-5(6H)-one NH group, and of acetamide NH group of intermediate alkylated product (Scheme 2). This was confirmed by LC-MS and 1H NMR spectra of the synthesized compounds with intensive peaks of molecular ions with a mass of two acetamide residues. Alkylation with tertiary amides 6.1-6.4 has not revealed any unexpected products (Scheme 2).
The identity of the synthesized compounds was confirmed by IR, LC-, EI-MS, 1H, 13C NMR, and elemental
Scheme 2. Alkylation of tetrazolo[1,5-c]quinazolin-5(6H)-one (1.1) with secondary and tertiary amines
analysis. LC-MS of the synthesized compounds in a »soft« ionization (chemical ionization at atmospheric pressure) allowed to register the molecular ion peak [M+1] in high intensity. For compound 4.1 the ion with molecular weight of 220 was observed, confirming cleavage of the quinazoline ring.
In the 1H NMR spectra of tetrazolo[1,5-c]quinazo-lin-5(6H)-ones the clear splitting of aromatic quinazoline protons' signals was observed. Thus, H-10 signal can be found at a range of 8.19-8.46 ppm, H-9 at 7.71-7.95 ppm, H-7 at 7.50-7.85 ppm, and H-8 at 7.42-7.61 ppm. The signals for these protons for some compounds were overlapping with each other (2.3, 2.7) or with other aromatic substituents protons (5.4). At the same time, for compound 4.1 the diamagnetic shift of aromatic protons was observed, obviously due to the absence of electron-deficient tetrazoloquinazoline system. Thus, Ph-3 signal was registered at 7.80 ppm as a doublet, Ph-4 at 7.30 ppm as a triplet, Ph-5 at 6.72 ppm as a triplet, and Ph-6 as a doublet at 6.66 ppm. Besides that, the NH tetrazole proton was detected as a broad singlet at 8.22-7.93 ppm.
The signal of the NCH2 group can be used as a confirmation of N-alkylation. For compounds 2.1-2.7 it was registered as a two-proton singlet at 5.54-3.80 ppm, except for compound 2.4, where it was as a two-proton triplet at 4.55 ppm. Due to electron acceptor influence of 2-oxo-2-phenylethyl and 2-oxo-2-(p-tolyl)ethyl moiety the signal of NCH2 group was observed in the weak field at 6.04-6.01 ppm for substances 2.6 and 2.7. Esters 3.1-3.3 displayed two-proton singlet signal at 5.20-5.22 ppm. For 2-(5-oxotetrazolo[1,5-c]quinazolin-6(5H)-yl)acetic acid the signal of NCH2 group was detected in the stronger field at 4.01 ppm. Moreover, for acetamides 5.1-5.4 and
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tertiary amides 6.1-6.4 the signal of NCH2 group was also shifted to the weak field and observed at 5.82-5.38 ppm as a two-proton singlet. Only for compound 6.3 the NCH2 signal was overlapped with H-5 of pyrazol and registered as a multiplet at 5.76-5.51 ppm. The signal of NH proton of phenylacetamides 5.1 and 5.2 was located as a singlet at 10.42-10.95 ppm, whereas for benzylacetamides 5.3 and 5.4 as an unsplitted triplet at 8.86-8.99 ppm. All alkyl groups are located in the strong field.
As for the IR spectra, the main tetrazolo[1,5-c]qui-nazoline ring and C-H deformations were detected at 1623-1485 cm-1 and at 917-608 cm-1. Azo fragments had stretchings at 1604-1400 cm-1. Moderate absorptions caused by cyclic N-C(=O)-N stretching were overlapped with ester and amide carbonyl vibrations. Vibrations of the vC=O in esters 3.1-3.3 were found at 1746-1730 cm-1. Wide stretchings of C-O-C appeared at 1250-1188 cm-1. Vibrations of vOH of 4.1 were found at 3546-3191 cm-1 and 5OH at 938-845 cm-1. Secondary amides 5.1-5.4 had two stretching signals of the N-H group: strong at 3324-3296 cm1 and mild at 3330-3070 cm1; and deformations at 1550-1520 cm-1. The carbonyl stretchings we-
re overlapped at 1683-1621 cm-1 for secondary and tertiary amides fragments in the substances 5.1-5.4, and were at 1669-1618 cm-1 for substances 6.1-6.4.
In EI-MS spectra the characteristic peaks of M+^ were observed, with different intensity, depending on the moiety of synthesized compounds (2.1 m/z 201 (100%), 2.6 m/z 305 (26.6%), 5.1 m/z 513 (33.0%), 5.3 m/z 517 (3.2%), 6.1 m/z 314 (1.4%)). The first step of M+ fragmentation was associated with N1-N2 and N3-N4 of te-trazole fragment cleavages (2.1 m/z 173 (50.2%), 2.6 m/z 277 (43.7%), 6.1 m/z 286 (7.9%)). Whereas for compounds 5.1 and 5.3 the fragmentation of molecular ion was caused by the concurrent processes: tetrazole ring destruction and a-scission of the second acetamide moiety (5.1 m/z 335 (51.9%) and 5.3 m/z 337 (26.6%)).
3. 2. Anticancer Assay for Preliminary in vitro Testing
Among all newly synthesized compounds substances 2.7, 3.2, 5.2, 5.3 were selected by the National Cancer Institute (NCI) Developmental Therapeutic Program for
Table 1. Percentage of in vitro tumor cell lines growth at 10 |M exposed to 6-A-R-tetrazolo[1,5-c]quinazolin-5(6ff)-ones (2.7, 3.2, 5.2, 5.3)
Cmpd. Mean	Range	Most sensitive cell lines"
2.7	103.29	81.02-	-127.01	94.69 (HOP-62/nscLC), 87.49 (HOP-92/nscLC), 89.53 (NCI-H226/nscLC), 99.73 (NCI-H23/nscLC), 97.44 (NCI-H322M/nscLC), 97.56 (SF-539/CNSC), 93.50 (SNB-75/CNSC), 92.85 (U251/CNSC), 97.21 (LOX IMVI/M), 97.99 (SK-MEL-5/M), 92.55 (SK-OV-3/OV), 99.52 (SN12C/RC), 81.02 (UO-31/RC), 91.05 (PC-3/PC), 94.11 (MCF7/BC), 91.80 (MDA-MB-231/ATCC/BC), 97.43 (HS 578T/BC), 98.86 (BT-549/BC), 96.83 (T-47D/BC).
3.2	101.85	85.49-	118.12	97.93 (RPMI-8226/L), 92.84 (A549/ATCC/nscLC), 93.56 (HOP-62/nscLC), 88.43 (HOP-92/nscLC), 96.75 (NCI-H226/nscLC), 94.74 (NCI-H322M/nscLC), 98.04 (HCT-116/ColC), 96.07 (SNB-75/CNSC), 86.66 (U251/CNSC), 98.42 (M14/M), 95.12 (SK-MEL-5/M), 85.49 (UACC-257/M), 89.08 (OVCAR-8/OV), 97.26 (CA-KI-1/RC), 99.65 (SN12C/RC), 89.59 (UO-31/RC), 98.76 (PC-3/PC), 96.76 (MCF7/BC), 99.85 (HS 578T/BC), 98.24 (BT-549/BC), 97.86 (T-47D/BC).
5.2	102.25	84.19-	128.99	89.75 (A549/ATCC/nscLC), 97.40 (HOP-62/nscLC), 93.88 (HOP-92/nscLC), 93.84 (NCI-H226/nscLC), 90.72 (NCI-H23/nscLC), 86.55 (NCI-H522/nscLC), 99.58 (COLO 205/ColC), 93.31 (SF-539/CNSC), 98.98 (SNB-75/CNSC), 88.56 (U251/CNSC), 97.77 (SK-MEL-2/M), 95.35 (SK-MEL-5/M), 86.93 (UACC-257/M), 88.58 (OVCAR-5/OV), 84.93 (OVCAR-8/OV), 97.41 (SK-OV-3/OV), 97.74 (786-0/RC), 84.19 (UO-31/RC), 97.38 (PC-3/PC), 97.16 (HS 578T/BC), 97.66 (BT-549/BC), 93.67 (T-47D/BC).
5.3	95.34	65.64-115.96		85.49 (CCRF-CEM/L), 90.41 (HL-60(TB)/L), 88.03 (K-562/L), 88.98 (MOLT-4/L),
				65.64 (RPMI-8226/L), 94.18 (SR/L), 93.21 (A549/ATCC/nscLC), 94.52 (HOP-
				62/nscLC), 84.56 (HOP-92/nscLC), 78.93 (NCI-H226/nscLC), 91.43 (NCI-
				H322M/nscLC), 90.50 (HCT-116/ColC), 97.47 (HCT-15/ColC), 92.86 (SF-295/CN-
				SC), 97.98 (SNB-19/CNSC), 88.72 (SNB-75/CNSC), 90.50 (U251/CNSC), 98.39
				(LOX IMVI/M), 95.76 (M14/M), 78.17 (SK-MEL-5/M), 94.08 (UACC-257/M),
				98.92 (UACC-62/M), 98.00 (OVCAR-4/OV), 78.84 (OVCAR-8/OV), 82.75
				(NCI/ADR-RES/OV), 95.22 (786-0/RC), 77.20 (ACHN/RC), 94.36 (CAKI-1/RC),
				92.08 (RXF 393/RC), 66.45 (UO-31/RC), 81.19 (PC-3/PC), 96.59 (MCF7/BC),
				91.55 (BT-549/BC), 70.81 (T-47D/BC), 99.64 (MDA-MB-468/BC).
a L - leukemia, nscLC - non-small cell lung cancer, ColC - colon cancer, CNSC - CNS cancer, M - melanoma, OV - ovarian cancer, RC - renal cancer, PC - prostate cancer, BC - breast cancer, bold values - the most sensitive ones.
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the in vitro cell line screening to investigate their anticancer activity1516 (Table 1).
The most sensitive cell line turned out to be UO-31 of renal cancer. It should be mentioned that N-(4-fluoro-benzyl)-N-(2-((4-fluorobenzyl)amino)-2-oxoethyl)-2-(5-oxotetrazolo[1,5-c]quinazolin-6(5H)-yl)acetamide (5.3) had the highest inhibition at 33.55%. Besides, this compound also negatively influenced RPMI-8226 of leukemia cell line, displaying inhibition at 34.36%.
4.	Conclusions
Due to their unique characteristics, compounds with tetrazole ring have been used in pharmaceutical and clinical applications especially as anticancer agents. In this work, novel 6-N-R-tetrazolo[1,5-c]quinazolin-5(6H)-ones were synthesized. N-Alkylation reaction of tetrazolo[1,5-c]quinazolin-5(6H)-one (1.1) with various chloro-deriva-tives was performed under various reaction conditions. As the best option a reflux in DMF with an equimolar amount of sodium hydride was selected. Spectral data confirm molecular structures of investigated compounds. These investigations will be continued for other activities and core structures.
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Povzetek
Spojine, ki vsebujejo tetrazolski obroč, so zelo zanimivi sistemi s pomembnimi farmacevtskimi in kliničnimi uporabami, zlasti kot učinkovine proti raku. V tem članku predstavljamo sintezo novih 6-N-R-tetrazolo[1,5-c]kinazolin-5(6ff)-onov, katerih strukturo in čistost smo ugotovili s pomočjo zbranih IR, LC-, EI-MS, 1H in 13C NMR podatkov ter rezultatov elementnih analiz. Opisujemo podrobnosti sinteze, torej N-alkiliranja, vključno z reakcijami s sekundarnimi in terciarnimi amidi. Štiri nove pripravljene spojine (2.7, 3.2, 5.2, 5.3) smo in vitro testirali za protirakavo učinkovitost pri 10 |M na 60 celičnih linij devetih vrst rakov: levkemije in melanoma ter raka pljuč, debelega črevesja, centralnega živčnega sistema, jajčnika, ledvice, prostate in dojke. V prihodnosti bomo poizkušali izvesti še dodatne sinteze spojin iz serije tetrazolo[1,5-c]kinazolinskih sistemov z namenom izboljšanja protirakave učinkovitosti.
Antypenko et al.: Synthesis of 6-N-R-Tetrazolo[1,5-c]quinazolin-5(6H)-ones