2-[4-[Bis(2-chloroethyl)amino]benzyl]-5,5-dimethyl-2,5-dihydro-4H-benzo[e]isoindol-4-one (Cytotoxic Oxonaphthalene-Pyrroles, Part I)

Abstract

A bis(chloroethyl)amine containing side chain is attached to an oxonaphthalene-annelated pyrrol in expectation of DNA alkylating properties. The cytotoxicity is evaluated against two cell lines, KB-31 and KB-8511, respectively.

1. Introduction

Nitrogen mustards were the first clinically effective cancer therapeutic agents. Chlorambucil and melphalan are two of numerous aromatic derivatives of compounds with a nitrogen mustard moiety that have been synthesized. They have been a clinical agent for many years and remains in common use at the present time. The cytotoxic effects are based on the highly active 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] we are reporting in this paper the synthesis of the oxonaphthalene annelated pyrrole 3 with an attached side chain containing a bis(2-chloroethyl)amine group. The cytotoxic activity of 3 was evaluated.

2. Results and Discussion

As previously published the N-alkylation of 1 [9,10] with BOC-protected 4-aminobenzyl bromide with NaH in DMF afforded selectively 2 [8], following deprotection with trifluoroacetic acid [11] furnished the amine which was treated with ethylene oxide [4]. The resulting diol was converted via its mesylate and subsequent reaction with LiCl [12] to target compound 3. The biological activity of 3 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 3 are >10.00 (KB-31) and 7.138 (KB-8511), respectively [for experimental details see[13,14]).

3. Experimental

3.1. 2-[4-[Bis(2-chloroethyl)amino]benzyl]-5,5-dimethyl-2,5-dihydro-4H-benzo[e]isoindol-4-one (3)

(a) To a solution of 2 [8] (1.07 g, 2.56 mmol) in 11.7 mL of dry CH₂Cl₂ were added dropwise under argon 2.3 mL (30.25 mmol) of triflouroacetic acid. After stirring for 2 h at room temperature the reaction mixture was concentrated under vacuum and the residue was dissolved in ethyl acetate. The organic phase was washed with aqueous NaHCO₃-solution and brine, dried (Na₂SO₄) and concentrated.

(b) The resulting crude product was purified by column chromatography (aluminium oxide, light petro­leum/ethyl acetate, 60/40) to afford a solid residue which was dissolved in 25 mL of EtOH/H₂O (3/1). 0.55 mL (0.61 g, 1.40 mmol) of oxirane were added to the reaction mixture at 0 ^oC. After heating for 12 h under reflux the reaction mixture was concentrated under vacuum and the residue was dissolved in ethyl acetate. The organic phase was dried (Na₂SO₄) and concentrated. The resulting crude product was used for the next reaction step without further purification.

(c) To a solution of the obtained crude product in 5.5 mL of dry CH₂Cl₂ and 0.5 mL of triethylamine were added dropwise under argon 0.23 mL (2.90 mmol) of methanesulfonicacid chloride. After stirring for 15 min the reaction mixture was washed with H₂O, dried (Na₂SO₄) and concentrated under vacuum. The residue was dissolved in 5.0 mL DMF and after addition of 0.9 g LiCl (21.5 mmol; dried over P₂O₅ at 100 ^oC for 12 h) the reaction mixture was heated for 5 min at 120 ^oC. The cooled reaction mixture was diluted with H₂O and extracted with ethyl acetate. The combined organic layers were washed with H₂O, dried (Na₂SO₄) and concentrated. The crude product was purified by column chromatography (silica gel, light petroleum/ethyl acetate 60/40 + 0.3% TEA) to afford 112 mg (11%) of 3. M.p. 50-52 ^oC (light petroleum/ethyl acetate). IR (KBr): 1654, 1615, 1523, 1353, 1148. MS (EI, 70 eV) m/z: 442 (M⁺ + 2, 2), 440 (M⁺, 3), 234 (11), 232 (66), 231 (14), 230 (100), 118 (58), 63 (9). ¹H NMR (CDCl₃, 200 MHz) = 7.53 (m, 1H, 9-H), 7.43 (m, 1H, 6-H), 7.38 (d, J = 2.0 Hz, 1H, 3-H), 7.21 (m, 2H, 7-H, 8-H), 7.14 (d, J = 8.8 Hz, 2H, 2_phenyl-H, 6_phenyl-H), 7.0 (d, J = 2.0 Hz, 1H, 1-H), 6.65 (d, J = 8.8 Hz, 2H, 3_phenyl-H, 5_phenyl-H), 5.0 (s, 2H, NCH₂), 3.71 (m, 4H, 2 × CH₂CH₂Cl), 3.64 (m, 4H, 2 × CH₂CH₂Cl), 1.51 (s, 6H, (CH₃)₂). ¹³C NMR (CDCl₃, 50 MHz) = 198.4 (C-4), 146.1 (C_phenyl-4), 144.1 (C-5a), 129.5 (C_phenyl-2, C_phenyl-6), 127.0 (C-6), 126.9 (C-9a), 126.6 (C-7), 126.1 (C-8), 125.3/124.5 (C_phenyl-1, C-9b), 123.3 (C-3), 122.6 (C-9), 118.3 (C-3a), 115.0 (C-1), 112.1 (C_phenyl-3, C_phenyl-5), 53.7/53.3 (NCH₂, 2 × CH₂CH₂Cl), 47.6 (C-5), 40.2 (2 × CH₂Cl), 28.1 ((CH₃)₂). HRMS calc. for C₂₅H₂₆N₂OCl₂: 440.1422. Found: 440.1425.