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2-[2-(Aziridin-1-yl)ethyl]-5,5-dimethyl-2,5-dihydro-4H-benzo [e]isoindol-4-one (Cytotoxic Oxonaphthalene-Pyrroles, Part IV)

Department of Drug and Natural Product Synthesis, Faculty of Life Sciences, University of Vienna, Althanstraße 14, A- 1090 Vienna, Austria
*
Author to whom correspondence should be addressed.
Molbank 2012, 2012(4), M781; https://doi.org/10.3390/M781
Submission received: 27 June 2012 / Accepted: 27 September 2012 / Published: 1 October 2012

Abstract

:
An aziridine-containing side chain is attached to an oxonaphthalene-annelated pyrrole in expectation of DNA alkylating properties. The cytotoxicity is evaluated against two cell lines, KB-31 and KB-8511, respectively.

Graphical Abstract

Introduction

Chlorambucil and melphalan are chemotherapy drugs belonging to the class of nitrogen mustard alkylating agents. Both compounds are believed to exert their antitumor effects by cross-linking DNA via aziridinium cation intermediates arising from the bis(2-chloroethyl)amine moiety [1]. In continuation of our department’s previous studies in the field of antitumor agents [2,3,4,5,6,7,8,9,10], we are reporting in this paper the synthesis of the oxonaphthalene-annelated pyrrole 2 with an attached side chain containing an aziridine group. The rationale is that the three-membered aziridine ring is structurally analogous to the ammonium-intermediate formed from the nitrogen mustards. The aziridine moiety is not charged and the reactivity results from the strain on the three-member ring structure [11]. Recent studies with aziridine substituted quinones showed promising results against breast cancer tumor cells [12,13,14,15,16]. The cytotoxic activity of 2 was evaluated.

Results and Discussion

Reaction of 1 [17] with t-BuPh2Si-protected hydroxyethyl bromide [18] with NaH in THF afforded the N-alkylated product. The following deprotection with tetrabutylammonium fluoride [19] furnished the alcohol which was treated with methansulfonic chloride [20]. The resulting mesylate was converted via reaction with aziridine into the target compound 2 (Scheme 1). The biological activity of 2 was tested against two cancer cell lines, KB-31 and KB-8511, respectively. KB-31 is a drug-sensitive human epidermoid cell line, whereas KB-8511 is a multi-drug resistant subline, typically over­expressing P-glycoprotein. The IC50[μM] values of 2 are >10.000 (KB-31) and 8.680 (KB-8511), respectively (3 days incubation time; staining with 0.05% methylene blue; optical density measured at 665 nm; for further experimental details, see [21,22]).

Experimental

2-[2-(Aziridin-1-yl)ethyl]-5,5-dimethyl-2,5-dihydro-4H-benzo[e]isoindol-4-one (2)

(a) To a solution of 0.3 g (12.38 mmol) NaH (60% in mineral oil, washed twice with hexane) in 20 mL of dry THF was added dropwise under argon a solution of 1 [8] (2.61 g, 12.38 mmol) in 20 mL of dry THF. After stirring for 0.5 h at 0 °C at room temperature, a solution of 6.74 g (18.58 mmol) of 2-(bromoethoxy)(tert-butyl)diphenylsilane in 30 mL of dry THF was added. After stirring for 20 h under reflux the reaction mixture was treated with a saturated aqueous solution of ammonium chloride and extracted with ether. The organic phase was dried (Na2SO4) and concentrated. Yield 3.34 g (55%) of colorless crystals (m.p. 117–118 °C, TLC, silica gel, light petroleum/ethyl acetate 70/30).
(b) The resulting product from (a) (3.34 g, 6.78 mmol) was dissolved under argon in a mixture of 40 mL of dry THF and 13.5 mL of a 1M solution of TBAF in THF and stirred for 2 h at room temperature. Subsequently after addition of H2O the resulting mixture was extracted with ether. The ether extract was dried (Na2SO4) and concentrated. Yield 1.23 g (71%) of colorless crystals (m.p. 112–113 °C, TLC, silica gel, ethyl acetate/light petroleum 80/20).
(c) The obtained product from (b) (1.23 g, 4.88 mmol) was dissolved under argon in a mixture of 1.0 mL (7.39 mmol) of dry TEA and 16 mL of dry CH2Cl2. Afterwards 0.46 mL (5.89 mmol) of freshly distilled methanesulfonic chloride under argon was added dropwise and the resulting reaction mixture was stirred for 1 h at 0 °C. Subsequently the reaction mixture was extracted with CH2Cl2, dried (Na2SO4) and concentrated. Yield: 1.56 g (96%) of colorless crystals (m.p. 122–123 °C, TLC, silica gel, ethyl acetate/light petroleum 80/20).
(d) The resulting crude product from (c) (1.56 g, 4.67 mmol) was dissolved under argon in a dry mixture of acetonitrile/triethyl amine (18 mL, 1:1) and treated with 9.69 mL (18.7 mmol) of aziridine. After stirring for 20 h at room temperature the reaction mixture was diluted with a mixture of CH2Cl2/EtOH (9/1) and subsequently filtered by use of 125 g of silica gel. Evaporation furnished 1.27 g of crude product which was purified by column chromatography (silica gel, ethyl acetate/triethylamine 95/5) to afford 0.29 g (22%) of colorless crystals of 2. M.p. 96–98 °C (ethyl acetate). IR (KBr): 3350, 2950, 1643, 1523, 1207, 1160 cm−1. MS (EI, 70 eV) m/z: 280 (M+, 10%), 224 (M+-56, 1), 88 (17), 73 (20), 70 (67), 61 (81), 56 (59), 45 (100). 1H-NMR (CDCl3, 200 MHz) δ = 7.56 (m, 1H, 9-H), 7.46 (m, 1H, 6-H), 7.41 (d, J = 2.0 Hz, 1H, 3-H), 7.21 (m, 2H, 7-H, 8-H), 7.07 (d, J = 2.0 Hz, 1H, 1-H), 4.15 (t, J = 5.9 Hz, 2H, 1'-H), 2.60 (t, J = 5.9 Hz, 2H, 2'-H) 1.72 (m, 2H, aziridine-H), 1.51 (s, 6H, (CH3)2), 1.03 (m, 2H, aziridine-H). 13C-NMR (CDCl3, 50 MHz) δ = 198.4 (C-4), 144.1 (C-5a), 127.0 (C-6), 126.9 (C-9a), 126.6 (C-7), 126.2 (C-8), 125.1 (C-9b), 123.5 (C-3), 122.6 (C-9), 118.5 (C-3a), 115.5 (C-1), 61.6 (C-2'), 50.8 (C-1'), 47.6 (C-5), 28.1 ((CH3)2), 27.0 (aziridine-CH2). HRMS calc. for C18H20N2O: 280.1576. Found: 280.1569.

Supplementary materials

Supplementary File 1Supplementary File 2Supplementary File 3

Acknowledgement

We are indebted to Novartis AG (Vienna, Austria) for the evaluation of the cytotoxic activity.

References and Notes

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Scheme 1. Synthesis of target compound 2.
Scheme 1. Synthesis of target compound 2.
Molbank 2012 m781 sch001

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MDPI and ACS Style

Spreitzer, H.; Puschmann, C. 2-[2-(Aziridin-1-yl)ethyl]-5,5-dimethyl-2,5-dihydro-4H-benzo [e]isoindol-4-one (Cytotoxic Oxonaphthalene-Pyrroles, Part IV). Molbank 2012, 2012, M781. https://doi.org/10.3390/M781

AMA Style

Spreitzer H, Puschmann C. 2-[2-(Aziridin-1-yl)ethyl]-5,5-dimethyl-2,5-dihydro-4H-benzo [e]isoindol-4-one (Cytotoxic Oxonaphthalene-Pyrroles, Part IV). Molbank. 2012; 2012(4):M781. https://doi.org/10.3390/M781

Chicago/Turabian Style

Spreitzer, Helmut, and Christiane Puschmann. 2012. "2-[2-(Aziridin-1-yl)ethyl]-5,5-dimethyl-2,5-dihydro-4H-benzo [e]isoindol-4-one (Cytotoxic Oxonaphthalene-Pyrroles, Part IV)" Molbank 2012, no. 4: M781. https://doi.org/10.3390/M781

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