Design and cytotoxic evaluation of new annonaceous acetogenin analogues

J. Braz. Chem. Soc., Vol. 18, No. 4, 691-695, 2007. Printed in Brazil - ©2007 Sociedade Brasileira de Química 0103 - 5053 $6.00+0.00 Jürgen Krauss,* Franz Bracher, Katrin Synowitz and Doris Unterreitmeier Department Pharmazie, Zentrum für Pharmaforschung Ludwig-Maximilians, Universität München, Butenandtstr. 5-13, 81377 Munich, Germany Acetogeninas anonáceas análogas foram preparadas a partir de 5-iodofurano-2-carbaldeído e ácido undec-10-inoico ou undec-10-inol pela reação de Sonogashira, seguida da reação de Grignard e hidrólise catalizada por mercúrio. A citocidade foi avaliada por ensaios MTT contra células HL e no Instituto Nacional de Câncer (Alemanha). Analogues of annonaceous acetogenins were built up from 5-iodofuran-2-carbaldehyde and undec-10-ynoic acid or undec-10-ynol by a Sonogashira reaction, followed by a Grignard reaction and a mercury catalysed hydratisation. The cytotoxicity was evaluated with MTT assay ((3(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric assay for measuring cellular proliferation) against HL cells and at the National Cancer Institute (NCI). Keywords: Sonogashira reaction, Grignard reaction, cytotoxicity Introduction The tropical plant family of the Annonaceae contains pharmacologically active natural products of the group of alkaloids and acetogenins. These plants are often used in traditional medicine. The annonaceous acetogenins are an interesting target for the development of new anti cancer drugs. Compounds like asitrocin exhibit high selectivity against several cancer cell lines.1,2 On the other hand, the the total syntheses reported up to know are long and expensive,1,7,8 so we tried a simpler approach towards some analogues. The mechanism of action of the annonaceous acetogenins is closed to the cellular mitochondria, following inhibition of the mitochondrial complex I, leading to a lower production of ATP in the tumor cell and subsequent apoptosis. reaction with undec-10-yn-1-ol to give the aldehyde 3. This aldehyde 3 was converted in a Grignard reaction with dodecyl magnesium bromide to the racemic diol 4. Subsequent regioselective hydratisation4 of the triple bond under mercury catalysis led to the corresponding ketone 5. In a second series, undec-10-ynoic acid was esterified via the acid chloride with methanol to give the methyl ester 2a and with lactic acid ethyl ester to give the double ester 2b. These esters 2a and 2b were reacted with 5-iodofuran-2-carbaldehyde (1) under Sonogashira conditions to give the esters 6a and 6b. In a Grignard reaction with one equivalent of dodecylmagnesium bromide 6a and 6b were converted to compounds 7a and 7b. Antimicrobial and cytotoxicity screening Results and Discussion Chemistry In continuation of our work on the synthesis of analogues of annonaceous acetogenin analogues 3 we describe here a new approach towards the acetogenin skeleton. Commercially available 5-iodofuran-2carbaldehyde (Aldrich) (1) was reacted in a Sonogashira *e-mail: The resulting compounds were tested against several bacteria and fungi in an agar diffusion assay, but did not show any significant activities. The cytotoxicity of 3, 4, 6b and 7b was evaluated in MTT assay against a HL 60 cell line using the method of Mosman.5 The results were compared to common alkylating drug cisplatin. Compounds 4 and 7a were also tested at the NCI against 60 cancer cell lines, but showed only weak cytotoxicity and no cellular selectivity.6 Article Design and Cytotoxic Evaluation of New Annonaceous Acetogenin Analogues 692 Design and Cytotoxic Evaluation of New Annonaceous Acetogenin Analogues OH J. Braz. Chem. Soc. OH O H H OH OH O O asitrocin Scheme 1. Annonaceae acetogenin asitrocin. OH O O O H I O H a [69 %] HO 3 1 MgBr b [48 %] OH O HO 4 OH O O c [28 %] OH 5 Scheme 2. a: EDMA, Pd((PPh3)2)Cl2, CuI; b: THF; c: HgO, H2O, HOAc. O O OH OR R = Me R= a [95 %] 2a 2b O O O O H OR 2 O I O O H a [90 %] 1 R = Me R= MgBr O RO O RO O 6a 6b O c [62-78 %] OH O R = Me R= O Scheme 3. a: C2Cl2O2, EDMA, methanol. b: EDMA, Pd((PPh3)2)Cl2, CuI. c: THF. O 7a 7b Vol. 18, No. 4, 2007 Krauss et al. Table 1. Cytotoxicity aganist HL 60 cell line determined with MTT test compound IC50 /μM compound IC50 /μM 2a 3 4 cisplatin 1000 30 30 5 2b 6a 6b 7b 4000 400 2000 200 Table 2. Cytotoxicity determined by the NCI (USA) compound 4 IC50 /μM compound IC50 /μM 20 7a > 100 Conclusions In this paper we report the synthesis and cytotoxic evaluation of new annonaceous acetogenine analogues containing a furan ring instead of the naturally occuring tetrahydrofuran ring. The cytotoxic acitivity of the resulting compounds is only in µM range and so much than that the natural products with a cytotoxicity in nM range. In summary, we describe here a shorter and more efficient way towards the annoceous acetogenine skeleton. The resulting compounds might be an interesting starting material for the synthesis of enantiomeric pure tetrahydrofuran analogues. Experimental IR-Spectra: Jasco FT-IR Paragon; MS: Hewlett Packard MS-Engine, electron ionisation (EI) 70 eV, chemical ionisation (CI) with CH4 (300 eV); NMR (400 MHz): Jeol GSX 400 (1H: 400 MHz, 13C: 100 MHz); GLCMS: Shimadzu GC 17 A; flash column chromatography (FCC): silica gel 60 (230-400 mesh, E. Merck, Darmstadt). 5-(11-Hydroxy-undec-1-ynyl)-furan-2-carbaldehyde (3) 2.2 g (10.0 mmol) 5-iodofuran-2-carbaldehyde, 1.7 g (10.0 mmol) undec-10-yn-1-ol, 200 mg CuI and 800 mg PdCl2(PPh3)2 were dissolved in 20 ml EDMA and stirred for 12 h at room temperature. The solvent was evaporated and the residue was dissolved in 20 mL 5% aqueous Na2S2O3 solution. The solution was extracted with diethyl ether (3×25 mL). The combined organic layers were dried over Na 2 SO 4 , the solvent was evaporated and the residue was purified by FCC (n-hexane/ethyl acetat 5:1) to give 1.8 g (69%) of 3 as a brown solid. IR(KBr disc) νmax/cm-1: 3405, 3337, 3101, 2920, 2835, 2223, 1677, 1510, 1271, 819, 763. EI-MS 693 m/z (rel. int.): 262 (M+, 20), 190 (25), 136 (100). HRMS: Calc.: 262.1569. Found: 262.1578. 1H NMR (400 MHz, CDCl3) δ (J, Hz) 1.38 (m, 10 H, 5 CH2), 1.59 (m, 4 H, 2 CH2), 2.46 (t, J 7.6, 2 H, CH2), 3.65 (t, J 7.2, 2 H, CH2O), 6.60 (d, J 3.6, 1 H, aromat. CH), 7.20 (d, J 3.6, 1 H, aromat. CH), 9.58 (s, 1 H, CHO). 13C NMR (400 MHz, CDCl 3) δ 21.1 (CH 2), 25.7 (CH 2), 28.0 (CH2), 28.8 (CH2), 29.0 (CH2), 29.3 (CH2), 29.4 (CH2), 32.8 (CH2), 63.0 (CH2), 70.4 (quat. C), 99.0 (quat. C), 115.9 (2 aromat. CH), 142.6 (quat. C), 151.9 (quat. C), 177.1 (CHO). 1-[5-(11-Hydroxy-undec-1-ynyl)-furan-2-yl]tridecan-1-ol (4) 1.7 g (6.5 mmol) of 3 were dissolved in 10 mL dry THF and 13 mL of 1 mol L-1 (13 mmol) dodecylmagnesium bromide solution in n-hexane were added dropwise. The mixture was stirred for 10 h, was diluted with 20 mL saturated NH4Cl solution and was extracted with diethyl ether (3×30 mL). The combined organic layers were dried over Na2SO4, (...truncated)