328 Acta Chim. Slov. 2005, 52, 328–331 Scientific Paper Synthesis of JV-Substituted Quinazolino[l,4]-benzodiazepine: A Facial Route to JV-Benzylsclerotigenin Naim H. Al-Said* and Zakariyya N. Ishtaiwi Department of Applied Chemical Sciences, Jordan University of Science and Technology. P.O. Box 3030, Irbid 22110, Jordan. Fax: 962-2-7095014. E-mail: naim@just.edu.jo Received 07-04-2005 Abstract Synthesis of JV-benzylsclerotigenin was achieved in four steps. Initially, isatoic anhydride was allovved to react with benzylamine and chloroacetyl chloride, respectively. The generated dipeptide derivative was then cylized to [l,4]benzodiazepinedione. Acylation with o-nitrobenzoyl chloride furnished a labile [l,4]benzodiazepinedione derivative, which upon reduction afforded JV-benzylsclerotigenin in high yield. This methodology can be adopted in combinatorial synthesis of JV-substituted quinazolino[l,4]benzodiazepindione library for biological evaluation. Key words: quinazolino[l,4]benzodiazepine, anthranilic ring system, JV-benzylsclerotigenin, naturally occurring ring system Introduction Broad-spectrum man-made insecticides and fungicides have been found to exhibit serious negative impacts on the fragile ecosvstem. It is well established that, in their mode of action, these chemicals do not differentiate between useful and harmful organisms. Furthermore, insect and fungus usuallv develop resistance to such chemicals making them less effective for continuous use.1 However, recent developments in insecticide and fungicide chemistrv have focused on the use of environmentallv safe bioactive chemicals to which insects and fungus cannot develop resistence.2'3'4 The best source for such novel bioactive chemicals is based on chemical ecologv where living organisms produce and/or sequester secondarv metabolites that serve as chemical defense svstems.2'3'4 Among these potential crop-protecting agents, antiinsectants have recentlv attracted research interest.2 Chemical and biological investigations of different fungal species afforded large number of secondarv metabolites that possess novel and diverse biological effects including sclerotigenin (l),5 benzolmalvine A (2),6 circumdatin F (3),7'8'9 asperlicin A (4)1011 and their derivatives. These alkaloids consist of two anthranilic acid units and an amino acid forming together a novel quinazolino[l,4] benzodiazepine ring svstems. Sclerotigenin (1), isolated in 1999 from Penicllium sclerotigenum Yamamoto, was shown to displav potent antiinsectant activity in dietarv assavs against the crop pest Helicoverpa zea.5 However, it was prepared in 1977 before its identification as a natural product.12 The total svnthesis of Sclerotigenin was recently reported by Thomas,13 Bergman14 and Snider.15 These reports emploved in a key step either ammonia gas at 60 °C which is difficult to handle or 2-azidobenzoyl chloride which requires several step to prepare and demand the use of phosphine derivatives to promote an intramolecular aza-Witting reaction. O o R1- /n-v^nt^ R2 Sclerotigenin (1); R1 = R2 = H Benzomalvin A (2); R1 = H; R2 = CH2Ph Circumdatin F (3); R1 = H; R2 = CH3 Asperlicin C (4); R1 = H; R2 = H In our continuing effort to develop a simple synthetic methods to biological active compounds,161718 we wish to report herein a short and efficient route for the synthesis of the naturally occurring quinazolino[l,4] benzodiazepine system v/a a single reductive-cyclization process using inexpensive 2-nitrobenzoyl chloride. O Al-Said and Ishtaiwi N-Substituted Quinazolino[1,4]benzodiazepine Acta Chim. Slov. 2005, 52, 328–331 329 \ M-z^nT5^ O > O Kl—Z^O X'^ R R 6; X = NH2, 7; X = N02 8 Scheme 1. Retrosynthesis of quinazolino[l,4]benzodiazepine. \1 0=/ ^ and )k>0 02N- O H 10 H T > X P" O 11 Cl H jO 13 H O k^l NH ©\=/ J ^Ph 14 Ph- v/ \ // O .N. Ph~ 12 lil O Ph- N-/>J- 17 ^ O X 15; X = N02 16; X = NH2 Scheme 2. Synthesis of iV-benzylsclerotigenin: a: PhCH2NH2, CH3CN, reflux, 2 h, then ClCH2COCl, Et3N, rt, (78%); b: pyridine, reflux, (30%); c: NaH, THF, (94%); d; 2-02N-PhCOCl, (49%); e: H2/ Pd/(C) (77%). Results and discussion Our route to synthesis of N-substituted quinazo lino[l,4]benzodiazepine ring system 5, summarized in Scheme 1, involves the novel retrosvnthetic approach. This approach is based on cvclization of the intermediate 6, which could be svnthesized after reduction of the nitro group in compound 7. Compound 7 consists of two parts connected by a carbonvl group. Therefore, benzodiazepinedione 8 and 2-nitrobenzoyl choride (9) were predicted to be suitable building blocks for this type of naturally occurring quinazolino[l,4]benzodiaz epine ring system. In connection with this retrosynthetic analysis, we have investigated the implementation of isatoic anhydide (10) as starting material and the benzyl moiety as a protecting group to test our methodology. Thus, the dipeptide ll19 was conveniently prepared by one-pot reaction in good yield (78%) by condensation of 10 with benzylamine in dry acetonitrile followed by acylation with chloroacetyl chloride as shown in Scheme 2. During the step of conversion of dipeptide 11 to benzodiazepinedione 1220 by intramolecular SN2 reaction, it was found that upon heating 11 in pyridine under reflux compound 13 was unexpectedly isolated in 30% yield instead of the anticipated cyclization product 12. The structure of compound 13 was established on the basis of JH and 13C NMR spectroscopy.21'22'23 The formation of 13 is believed to occur via substitution of chloride by pyridine to form the non-isolable intermediate 14, which undergoes intramolecular nucleophilic attack by the nitrogen atom of the benzyl group as shown in Scheme 2. Fortunately, treatment of dipeptide 11 with the non-nucleophilic base, NaH, in THF at room temperature gave the desired benzodiazepinedione 12 in 94% yield. The JH NMR data for compound 12 exhibited two singlets at 4.9 and 3.8 ppm, which are characteristics for the benzylic and seven-membered ring methylene protons, respectively. With our subgoal attained, we advanced toward the synthesis of intermediate 15. This was achieved in moderate yield by benzoylation of 12 with 2-nitrobenzoyl chloride (9) in the presence of DMAP and Et3N in dry CH2C12. The TLC of the reaction mixture indicated the conversion of 12 to the nitro derivative 15 was complete and clean. However, after aqueous work up we observed that the nitro derivative 15 is easily hydrolyzed to the starting materials. Nevertheless, when the reaction mixture was extracted with cold water and purified by silica gel column directly after drying and concentration, the recovered starting material was minimal. The methylene protons of the seven-membered ring in 15 were observed at 5 4.12 (d, 15.7 Hz) and 3.62 o o N N O R 5 9 O d a c O N' O N O H b e N O Al-Said and Ishtaiwi N-Substituted Quinazolino[l,4]benzodiazepine 330 Acta Chim. Slov. 2005, 52, 328–331 (d, 15.7 Hz), indicating that they are non-equivalent on the NMR time scale due to the significant barrier to flipping of the ring. The planned protocol requires reduction of the nitro group in compound 7 to the corresponding amine. Since the nitro derivative 15 dissociates to the starting materials, a very mild reducing agent (Pd/(C) under a balloon filled with hydrogen gas) was applied. When the reaction was stopped before completion TLC showed the presence of both 15 and Ar-benzylsclerotigenin 17, whereas the proposed amine intermediate 16 was not observed. After work up, this reaction furnished the required product 17 in good yield (77%). The structure of the final product Ar-benzylsclerotigenin 17 was assigned based on the JH and 13C NMR spectral data and also by elemental analysis. The benzylic methylene protons of the target compound 17 exhibited two different signals at 5 5.37 (d, 14.8 Hz) and 4.35 (d, 14.8 Hz. The methylene protons of the seven-membered-ring were observed at 5 4.32 (d, 15.1 Hz) and 4.13 (d, 15.1 Hz). In this context, it is important to mention that aH attempts to convert Ar-benzylsclerotigenin to the natural sclerotigenin 1 by cleavage of the benzyl group using H2/Pd(C) were unsuccessful. However, the facile formation of 17 directly from 15 prompted us to investigate the synthesis of quinazolino[l,4]benzodiazep indione alkaloids employing other N-protecting groups. The implementation of this methodology presently is under investigation. Conclusions We have developed a short, simple and highly reliable route to the synthesis of N-substituted quinaz olino[l,4]benzodiazepin-5,13-dione ring system using cheap starting materials. This strategy was successfully applied to the preparation of Ar-benzylscleroteginin. This procedure can also be applied to prepare a wide range of N-substituted sclerotigenin derivatives for biological evaluation. In fact, one can adopt this methodology for the combinatorial synthesis of quinazolino[l,4]benzodi azepine libraries for biological evaluation. Experimental Melting points (mp) were determined on electrothermal digital melting point apparatus and are uncorrected. Infrared (FT IR) spectra were recorded using a Nicolet-Impact 410 FT IR spectrophotometer. JH NMR and 13C NMR spectra were recorded on Bruker, advance DPX-300. The spectral data are reported in ppm (5) relative to TMS reference line. Mass spectra were recorded on a sector field double focusing unit VG 7070E G.C. mass spectrometer. Ali the reactions were monitored by thin layer chromatography (TLC). iV-Benzyl-2-(2-chloroacetylamino)benzamide (11). Benzylamine (0.214 g, 2.0 mmol) was added to a solution of isatoic anhydride (10) (0.326 g, 2.0 mmol) in acetonitrile (10 mL). The obtained solution was heated under reflux for 3h and then cooled to 0°C. The reaction mixture was treated with triehylamine (0.404g, 4.0mmol) followed by addition of chloroacetyl chloride (0.294 g, 2.6 mmol) in acetonitrile (5 mL). The resulting mixture was stirred at room temperature for 24 h and then concentrated. The residue was dissolved in ethyl acetate. The solution was washed with 5% HC1, water and brine. The separated organic layer was dried (MgS04) and concentrated giving a dark red residue. The residue was purified on a silica gel column (35% ethyl acetate in hexane) to give 11 (0.472 g). Yield: 78%, mp 153-155 °C. FT IR: (KBr) 3296 (v,^), 1679 and 1627 (vc=0), 1597, 1597, 1522 cm4. JH NMR (200 MHz, CDC13) 511.9.(br, 1H), 8.7 (d, 8.5 Hz, 1H), 7.5-7.3 (m, 7H), 7.1 (t, 8.3 Hz, 1H), 6.6 (br, 1H), 4.7 (bs, 2H), 4.2 (s, 2H, CH2). 13C NMR (75 MHz, CDC13) 5 168.4, 165.3, 138.6, 137.5, 132.7, 128.9, 128.0, 127.9, 126.5, 123.7, 121.6, 121.2, 44.2, 43.3. MS (EI) m/z (relative intensity %): 302.3 (M+ (C16H1502N2C1), 1), 196.2 (4), 161.3 (6), 146.2 (9), 132 (14), 120.2 (100). 4-Benzyl-3,4-dihydro-lff-benzo[e] [l,4]diazepine-2,5-dione (12). Sodium hydride (NaH, 60%, 0.384 g, 9.6 mmol) was added portion-wise to a solution of chloride derivative 11 (1.210 g, 4 mmol) in dry THF (20 mL). The resulting mixture was stirred at room temperature overnight and then concentrated. The residue was dissolved in ethyl acetate. The resulting solution was washed with 5% HC1 and brine. The separated organic layer was dried (MgS04) and concentrated. The residue was purified on a short column of silica gel (0-30% ethyl acetate in CHC13) to furnish 12 (1.004 g). Yield: 94%, mp 173-174 °C. FT IR (KBr): 3246 (Vnh), 1696 and 1628 (vc=o)> 1603, 1483 cm4. JH NMR (200 MHz, CDC13) 5 8.5 (br, 1H), 8.2-6.8 (m, 9H), 4.9 (s, 2H), 3.8 (s, 2H). 13C NMR (75 MHz, CDC13) 5 170.7, 167.3, 136.2, 135.9, 132.6, 132.0, 128.8, 128.3, 127.9, 126.4, 125.3, 120.7, 52.0, 52.0. Anal. Calcd. for C16H1402N2: C 72.17, H 5.29, N 10.52. Found: C 71.95, H 5.28, N 10.55. 3-Benzyl-lff-quinazoline-2,4-dione (13). A solution of chloride derivative 11 (0.908 g, 3 mmol) in pyridine (15 mL) was heated under reflux for 20 min then concentration under reduced pressure. The residue was chromatographed on a silica column (30-40% ethyl acetate in hexane) to give 13 (0.227 g). Yield: 30%, mp 220-222 °C. FT IR (KB): 3438 (v,^), Al-Said and Ishtaiwi N-Substituted Quinazolino[l,4]benzodiazepine Acta Chim. Slov. 2005, 52, 328–331 331 1713 (?C=O), 1653 (?C=O), 1452 cm–1. 1H NMR (300 MHz, CDCl3) ? 10.16 (br s, 1H), 8.14 (d, 7.7 Hz, 1H), 7.6 (m, 1H), 7.53 (d, 6.8 Hz, 2H), 7.33–7.21 (m, 4H), 7.06 (d, 8.1 Hz, 1H), 5.28 (s, 2H). 13C NMR (75 MHz, CDCl3) ? 162.3, 152.1, 138.5, 136.9, 135.1, 128.9, 128.6, 128.5, 127.7, 123.5, 114.9, 114.7, 44.2. Acknowledgements We thank the Deanship of Research at Jordan University of Science and Technology for financial support, Grant No.7/2000. We also thank Deeb T. Deeb for assistance in doing some spectroscopic data. 4-Benzyl-l-(2-nitrobenzoyl)-3,4-dihydro-l//-benzo [e][l,4]diazepine-2,5-dione (15). Triethylamine (0.303 g, 3 mmol) was added to a solution of benzodiazepinedione 12 (0.532 g, 2.0 mmol) in dry CH2C12 (40 mL). The resulting mkture was stirred for 15 min and then treated with DMAP (0.244 g, 2.0 mmol). Freshly prepared 2-nitrobenzoyl chloride (0.557 g, 3.0 mmol) in dry CH2C12 (2 mL) was added drop-wise to the solution and the resulting mixture was stirred for 2 h at room temperature. The solution was washed with water (3x40 mL), dried and concentrated. The residue was purified on a silica gel column (35% ethyl acetate in hexane) to afford 15 (0.406 g). Yield: 49%, mp 168-169 °C. FT IR (KBr) 1740 (vc=0), 1710 (vc=0), 1642 (vc=0), 1600, 1519, 1459, 1346 cm4. JH NMR (300 MHz, CDC13) 5 8.26 (d, 7.9 Hz, 1H), 7.99 (dd, 1.5 Hz, 7.7 Hz, 1H), 7.74 (d, 7.3 Hz, 1H), 7.68-7.53 (m, 4H), 7.30 (s, 5H), 7.01 (dd, 1.5 Hz, 7.5 Hz, 1H), 4.85 (d, 14.6 Hz, 1H), 4.72 (d, 14.6 Hz, 1H), 4.12 (d, 15.7 Hz, 1H), 3.62 (d, 15.7 Hz, 1H). iV-Benzylsclerotigenin (17). A solution of 15 (0.112 g, 0.27 mmol) in ethyl acetate (12 mL) in the presence of Pd/C (10%) was stirred at 50 °C under pressure of hydrogen balloon until the reaction was completed. The reaction mkture was filtered over band of celite, evaporated and purified by a silica gel column (30-35% ethyl acetate in hexane) to furnish Ar-benzylscleroteginin 17 (76 mg). Yield: 77%, mp 173-174 °C. FT IR (KBr): 1697 (vc=0), 1610 (vc=0), 1593 (vc=N), 1465, 1142 cm4; JH NMR (300 MHz, CDCI3) 5 8.33 (d, 7.9 Hz, 1H), 8.02 (d, 7.9 Hz, 1H), 7.79 (m, 1H), 7.67-7.51 (m, 5H), 7.37-7.22 (m, 5H), 5.37 (d, 14.8 Hz, 1H), 4.35 (d, 14.8 Hz, 1H), 4.32 (d, 15.00 Hz), 4.13 (d, 15.00 Hz); MS (EI) m/z (relative intensity %): 367.5 (M+ (C23H1702N3), 62), 261.4 (100), 235.4 (66), 91.2 (54). 13C NMR (75 MHz, CDC13) 5 166.4, 161.2, 152.2, 146.3, 136.2, 134.9, 133.6, 131.1, 131.0, 130.6, 128.9, 128.8, 128.4, 127.9, 127.7, 127.7, 127.6, 127.5, 121.6, 51.9, 50.4. Anal. Calcd. for C23H1702N3: C 75.19, H 4.66, N 11.44. Found: C 74.91, H 4.55, N 11.53. Povzetek References 1. J. A. Pickett, Chem. Ber. 1988, 24, 137-130. 2. H.-J. Wang, J. B. Gloer; D. T. Wacklow, P. F. Dov/d, App. Environ. 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Nastali dipeptid smo ciklizirali v [1,4]benzodiazepindion. Tega smo acilirali z o-nitrobenzoil kloridom v labilni derivat, ki smo ga nato reducirali v N-benzilsklerotigenin z dobrim izkoristkom. To metodologijo lahko uporabimo v kombinatorni sintezi knjižnice N-substituiranih kinazolino[1,4] benzodiazepindionov za biološko vrednotenje. Al-Said and Ishtaiwi N-Substituted Quinazolino[l,4]benzodiazepine