NPC
Natural Product Communications
Synthesis of Neolamellarin A, an Inhibitor of Hypoxia-inducible Factor-1
2009 Vol. 4 No. 7 925 - 926
Khaled M. Arafeh and Nisar Ullah* Chemistry Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
[email protected] Received: April 12th, 2009; Accepted: June 14th, 2009
Neolamellarin A, a metabolite isolated from the sponge Dendrilla nigra, was found to inhibit hypoxia-inducible factor-1 (HIF-1) activation by 26% at 10 µM concentration and inhibition of HIF-1 has become a major antitumor molecular target. Herein the first synthesis of neolamellarin A is described. The synthetic strategy features the condensation of vinylogous amide with aminomalonate to construct the 3,4-bis(4-methoxyphenyl)-1H-pyrrole core and the subsequent acylation and deprotection rendered the target compound in 18% over all yield. Keywords: hypoxia-inducible factor-1, antitumor agent, acylation, natural product.
The prevalence of heterogeneously distributed hypoxic regions in advanced solid tumors is known to reduce cellular metabolism and cell proliferation which subsequently leads to cell death, as well as promoting tumor growth by selecting highly mutated and malignant tumor cells [1a]. The poor clinical outcome and treatment resistance in tumor hypoxia makes it difficult to target such a process [1a]. The transcription factor hypoxia-inducible factor-1 (HIF1) is one of the key antitumor molecular targets [1b] and studies have demonstrated that HIF-1 inhibition coupled with radiation and chemotherapeutic agents have resulted in reduction of tumor growth and improved treatment outcome [1c-e]. Currently there is no approved drug which targets tumor hypoxia and the challenge lies in the discovery of a potent HIF-1 inhibitor with high efficacy and low toxicity [1f]. In the search for potent and small molecule HIF-1 inhibitors, the extract of the sponge Dendrilla nigra (Aplysillidate) has led to the isolation of a new lamellarin-like phenolic pyrrole, neolamellarin A (1) [2]. The effect of 1 on HIF-1 activity in a T47D cellbased reporter assay revealed that it exerts inhibition of HIF-1 activation by 26% at 10 µM concentration. Herein we wish to report the first synthesis of neolamellarin A (1) [2]. Our synthesis started from the known methyl ester 4, which was synthesized in 56% yield by condensation
Scheme 1: Synthesis of neolamellarin A (1).
of vinylogous amide (2) with dimethyl aminomalonate hydrochloride (3) [3a]. Hydrolysis of the ester 4 with LiOH at room temperature generated the corresponding acid and subsequent decarboxylation with CF3CO2H at room temperature yielded pyrrole 5 in 90% yield [3b]. The acylation of 5 with acid chloride 6 was tried with triethyl amine, K2CO3 and NaHMDS as bases and DMF, DMSO or THF at different reaction temperatures ranging from room temperature to 80oC. However, the use of NaH as a base in DMF, and heating the reaction at 50oC for 5 hours gave compound 7 in 30% yield. The
926 Natural Product Communications Vol. 4 (7) 2009
coupled product 7 was reacted with BBr3 in CH2Cl2 at -78oC for 1 hour, followed by stirring the reaction mixture at room temperature for 15 minutes to produce 1 in 82% yield [2] (Scheme: 1). Experimental 3,4-Bis(4-methoxyphenyl)-1H-pyrrole (5): Ester 4 (1.18 g, 1.76 mmol) was dissolved in a 1:2:1 mixture of 24 mL of MeOH, THF and H2O, followed by the addition of LiOH.H2O (0.23 g, 5.4 mmol) and the reaction mixture was stirred for 12 h at room temperature. The mixture was concentrated in vacuo, Water (15 mL) was added and extracted with diethyl ether (2 x 10 mL). The aqueous layer was acidified to pH 4 with 2 N HCl and re-extracted with EtOAc (2 x 15 mL) and the organic layer was washed with brine (10 mL), dried over Na2SO4 and evaporated to afford acid (0.53 g, 92%) [4]. The acid (0.4 g, 1.24 mmol) was dissolved in CH2Cl2 (4 mL), CF3CO2H (4 mL) was added, the mixture was stirred at room temperature for 2 h, and then evaporated under vacuum, after which 1N NaOH (10 mL) was added and the mixture extracted with EtOAc (20 mL). The organic layer was washed with brine (10 mL), dried over Na2SO4 and evaporated to dryness. Column chromatography of the dark brown oily material on silica gel eluting with EtOAc: n-hexane (2:8) gave the pyrrole (5) as a yellow solid (0.31 g, 90%) [3b]. 1-(3,4-Bis(4-methoxyphenyl)-1H-pyrrole-1-yl)-2(4-methoxyphenyl)ethanone (7): A solution of 5 (72 mg, 0.26 mmol) in DMF (2 mL) was cooled to 10oC. NaH (12 mg, 0.52 mmol) was added and after being stirred for 15 minutes, a solution of acid chloride (72 mg, 0.39 mmol) in DMF (1 mL) was added dropwise
Arafeh & Ullah
and the reaction mixture stirred at 50oC for 5 h. The reaction was quenched with H2O (5 mL) and extracted with EtOAc (10 mL). The organic layer was washed with 1 N HCl (2 x 5 mL), H2O (5 mL), brine (5 mL), dried over Na2SO4 and evaporated. Purification on a silica gel column of the crude product using EtOAc: n-hexane (2:8 →3:7) as eluent afforded 5 as an off white solid (0.05 g, 30%). MP: 114-115ºC. IR (neat) 3035, 2950, 1696, 1614, 1510, 1440, 1387, 1221, 1172 cm-1. 1 H NMR (500 MHz, CDCl3): δ 3.72 (2H, s, H-7), 3.88 (6H, s, 2 x OCH3), 3.89 (3H, s, OCH3), 6.78 (2H, d, J = 8.4 Hz, H-3', H-5'), 7.01 (4H, d, J = 8.5 Hz, H-3'', H-5'', H-3''', H-5'''), 7.08 (2H, d, J = 8.4 Hz, H-2', H-6'), 7.52 (4H, d, J = 8.5 Hz, H-2'', H-6'', H-2''', H-6'''), 7.56 (2H, s, H-2, H-5). 13 C NMR (125 MHz CDCl3): δ 39.2 (CH2), 56.1 (CH3), 56.2 (CH3), 114.2 (CH), 114.3 (CH), 116.8 (CH), 122.9 (C), 126.8 (C), 127.2 (C), 128.4 (CH), 129.6 (CH), 158.7 (C), 158.9 (C), 168.7 (C). Anal. Calcd for C27H25NO4: C, 75.86; H, 5.89; N, 3.28. Found C, 75.82; H, 5.93, N, 3.24. Neolamellarin A (1): A stirred solution of 8 (0.04 g, 0.094 mmol) in CH2Cl2 (1 mL) at -78°C was treated with BBr3 (0.85 mL as a 1 M solution CH2Cl2) dropwise over a 10 min period. The solution was stirred at -78°C for 1 h and gradually warmed to 25°C and stirred for 10 minutes. The solution was diluted with EtOAc (15 mL) and washed with H2O (2 x 5 mL) and saturated aqueous sodium chloride (5 mL). Column chromatography of the orange oily material on silica gel eluting with EtOAc: n-hexane (35:65) afforded 1 (0.022 g, 60%) [2].
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[2]
[3]
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(a) Vaupel P, Mayer A. (2007) Hypoxia in cancer: significance and impact on clinical outcome. Cancer and Metastasis Reviews, 26, 225–239; (b) Semenza GL. (2003) Targeting HIF-1 for cancer therapy. Nature Reviews Cancer, 3, 721–732; (c) Kung AL, Zabludoff SD, France DS, Freedman SJ, Tanner EA, Vieira A, Cornell-Kennon S, Lee J, Wang B, Wang J, Memmert K, Naegeli HU, Petersen F, Eck MJ, Bair KW, Wood AW, Livingston DM. (2004) Small molecule blockade of transcriptional coactivation of the hypoxia-inducible factor pathway. Cancer Cell, 6, 33–43; (d) Unruh A, Ressel A, Mohamed HG, Johnson RS, Nadrowitz R, Richter E, Katschinski DM, Wenger RH. (2003) The hypoxia-inducible factor-1 is a negative factor for tumor therapy. Oncogene, 22, 3213–322; (e) Moeller BJ, Dreher MR, Rabbani ZN, Schroeder T, Cao Y, Li CY, Dewhirst MW. (2005) Pleiotropic effects of HIF-1 blockade on tumor radiosensitivity. Cancer Cell, 8, 99–110; (f) Semenza GL. (2006) Development of novel therapeutic strategies that target HIF-1. Expert Opinion on Therapeutic Targets, 10, 267–280. Rui L, Yang L, Yu-Dong Z, Dale GN. (2007) Molecular-targeted antitumor agents. 15. Neolamellarins from the marine sponge Dendrilla nigra inhibit hypoxia-inducible factor-1 activation and secreted vascular endothelial growth factor production in breast tumor cells. Journal of Natural Products, 70, 1741–1745. (a) Sanghee K, Soonjoo S, Heonjoong K. (2001) Efficient synthesis of 2-carbomethoxy-3,4-disubstituted pyrroles by the condensation of vinylogous amides with aminomalonate. Bulletin of the Korean Chemical Society, 22, 1403-1406; (b) Noboru O, Hirokazu M, Takahiro U, Takuji O, Hiroyuki T. (1998) Synthesis of 3,4-diarylpyrroles and conversion into dodecaarylporphyrins; a new approach to porphyrins with altered redox potentials. Journal of the Chemical Society Perkin Transactions 1, 1595-1601. Michael S, Holger U, Andreas M, Jan-Peter K, Werner K, Gerd D. (2008) Investigations concerning the correlation of COX-1 inhibitory and hydroxyl radical scavenging activity. Archiv der Pharmazie, 341, 281–287.
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Continued inside back cover
