Synthesis, Crystal Structure and Bioactivity of 1-(3-((Benzo[d][1,3]dioxol-5-yloxy)methyl)- phenethyl)-4-phenylpiperidin-4-ol 1

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1 34 卷 12 期 结构化学 (JIEGOU HUAXUE) Vol. 34, No Chinese J. Struct. Chem Synthesis, Crystal Structure and Bioactivity of 1-(3-((Benzo[d][1,3]dioxol-5-yloxy)methyl)- phenethyl)-4-phenylpiperidin-4-ol 1 XU Xing-Jie XU Wei 2 CHEN Hong SHAO Bin-Hao (Pharmaceutical Research Center, Guangzhou Medical University, Guangzhou , China) ABSTRACT The title compound 1-(3-((benzo[d][1,3]dioxol-5-yloxy)methyl)phenethyl)-4- phenylpiperidin-4-ol (4, C 27 H 29 NO 4, M r = ) was synthesized by a four-step reaction and characterized by 1 H NMR, 13 C NMR, elemental analysis and single-crystal X-ray diffraction. The crystal is of triclinic, space group P1 with a = (12), b = (2), c = (4) Å, α = 83.44(3), β = 82.71(3), γ = (3)º, V = (4) Å 3, Z = 1, D c = g/cm 3, S = 1.070, μ = mm -1, F(000) = 460, R = and wr = for 6452 observed reflections with I > 2σ(I). Geometry conformations revealed that the dihedral angle between benzodioxole and aromatic planes contributed to the formation of C H π interactions. Hydrogen bonds and van der waals interactions were observed to stabilize the three-dimensional packing structure. The compound showed a moderate inhibitory activity against the prostate cancer cells. Keywords: crystal structure, phenylpiperidin, prostate cancer, C H π interactions, synthesis; DOI: /j.cnki INTRODUCTION Prostate cancer is the fifth most commonly diagnosed cancer in the world, and the incidence of prostate cancer has increased considerably over the past two decades. Researches in the United States indicated that the death rate of prostate cancer was just less than that of lung cancer with an increment of men ages, from 8.6% in men aged <45 years to 46% in men aged >70 years [1]. The current treatment methods for this cancer include chemotherapy, radiotherapy, and/or surgery [2]. However, the disease with metastatic property frequently develops even after potentially curative surgery [3]. Developing novel anti-prostate cancer drugs with better effectiveness is thus urgently desired. Compounds with arylpiperazine moiety show extensive bioactivities comprising of anti-prostate cancer [4, 5]. In this study, we investigated a potent agent of arylpiperazine analogue (4) on the activity of anti-prostate cancer, and presented the description of crystal structure. Our work will provide a valuable clue to further explore the structure-activity relationship (SAR) of arylpiperidine derivatives. 2 EXPERIMENTAL All reagents and solvents were of analytical grade Received 27 April 2015; accepted 15 September 2015 (CCDC ) 1 The project was supported by the Natural Science Foundation of Guangdong Province (No. S ) and the Postdoctoral Science Foundation of Guangzhou City (Q188) 2 Corresponding author. Xu Wei, born in 1980, Post-Ph.D, majoring in structure biology. xwnail2003@163.com

2 XU X. J. et al.: Synthesis, Crystal Structure and Bioactivity of 1-( ((Benzo[d][1,3]dioxol-5-yloxy)methyl)-phenethyl)-4-phenylpiperidin-4-ol No. 12 and commercially available. NMR spectra were accomplished on a Bruker AVANCE-400 spectrometer using TMS as the internal standard, and coupling constants (J) were in Hz. Single-crystal X-ray diffraction data of 4 were collected on an R-AXIS RAPID II diffractometer with Cu-Kα radiation Synthesis of compound 4 The title compound 4 was synthesized in four steps shown in Scheme 1 starting from the commercially available 2-(3-(bromomethyl)phenyl)acetic acid (98%, Aladdin). Borane-dimethyl sulfide complex (BH 3 S(CH 3 ) 2, 21.9 ml, 42 mmol) was added to a cooled (0 ) solution of carboxylic acid (5 g, 21 mmol) in dry tetrahydrofuran (THF, 100 ml). The progress of the reactions was monitored by TLC with ethylacetate-petroleum ether (1:3, v/v) as a developing solvent. When the reaction was completed, THF was removed by distillation at reduced pressure. The residue including compound 1 was obtained. Without further purification, 3,4-metylendioxyfenol (2.58 g, 18.7 mmol) was added into 1 with the presence of potassium carbonate (10.32 g, 74.8 mmol) in THF at reflux for 16 h. After evaporation of the solvent, the residue was washed with water and purified by normal column chromatography to give compound 2 in 67% yield. Triethylamine (5.94 g, 58.8 mmol) and 4-dimethyl-aminopyridine (0.18 g, 1.47 mmol) in dry dichloromethane (CH 2 Cl 2, 10 ml) were added dropwise to a solution of 2 (4 g, 14.7 mmol) and 4-toluenesulfonyl chloride (TsCl, 4.19 g, 22.1 mmol) in CH 2 Cl 2 (100 ml) at 0. After the reaction was complete (monitored by TLC), the solvent was removed under reduced pressure. The purification was performed on silica gel (400 mesh, ethyl acetate/petroleum ether, 1/15) to afford compound 3 (5.76 g) as a white solid. Then, the phenylpiperidine (49.31 mg, 0.28 mmol) and potassium carbonate ( mg, 1.38 mmol) were added to a solution of 3 (100 mg, 0.23 mmol) in acetonitrile (10 ml). The reaction mixture was stirred at reflux for 16 h. Acetonitrile was removed by evaporation. The residue was washed with water and purified by recrystallization from trichloromethane and n-hexane (1/3, v/v) to give the final compound 4 with 80% yield as a white crystal [6]. 1 H-NMR (400 MHz, DMSO-d6) δ in ppm: (s, 1H, N+H), 7.55~7.20 (m, 9H, Ar-H), 6.80 (d, J = 8.5 Hz, 1H, Ar-H), 6.69 (d, J = 2.5 Hz, 1H, Ar-H), 6.43 (dd, J = 8.5, 2.5 Hz, 1H, Ar-H), 5.95 (s, 2H, CH 2 ), 5.47 (s, 1H, OH), 5.00 (s, 2H, CH 2 ), 3.49 (d, J = 11.0 Hz, 2H, CH 2 ), 3.43~3.06 (m, 8H, CH 2 ), 1.82 (d, J = 11.0 Hz, 2H, CH 2 ). 13 C-NMR (100 MHz, DMSO-d6) δ in ppm: , , , , , , , , , , , , , , 98.07, 69.71, 68.00, 56.32, 48.25, 34.96, Anal. Calcd. for C 27 H 29 NO 4 1HCl: C, 69.29; H, 6.46; N, 2.99%. Found: C, 69.20; H, 6.45; N, 2.85%. Reagents and conditions: (i) BH 3 S(CH 3 ) 2, THF, 0 C for 1 h; (ii) 3,4-metylendioxyfenol, K 2 CO 3, CH 3 CN, reflux, 16 h; (iii) TsCl, Et 3 N and 4-dimethylaminopyridine, Cl 2 CH 2, 0 C, 16 h; (iv) Phenylpiperidine, K 2 CO 3, CH 3 CN, reflux, 16 h Scheme 1. Synthesis of the title compound 4

3 2015 Vol. 34 结构化学 (JIEGOU HUAXUE)Chinese J. Struct. Chem Crystal data and structure determination Suitable crystals were obtained by slowly evaporating a mixture of trichloromethane and n-hexane solution at ambient temperature with dimensions of 0.30mm 0.20mm 0.20mm. A colorless crystal of the title compound 4 was mounted on a glass fiber in a random orientation. The data were collected by a R-AXIS RAPID II diffractometer at room temperature equipped with a graphite-monochromatic CuKα radiation (λ = Å) by using an ω scan mode. The structure was solved by direct methods, and the non-hydrogen atoms were located from the trial structure and then refined anisotropically with SHELXL-97 using a fullmatrix least-squares procedure based on F 2[7]. The hydrogen atoms were fixed geometrically at the calculated distances and allowed to ride on the parent atoms. A total of reflections were collected in the range of 4.16 θ 68.23º, in which 7405 were independent with R int = and 6452 observed reflections with I > 2σ(I) were used in the structure determination and refinements. The final R = and wr = (w = 1/[σ 2 (F 2 o ) + (0.0918P) P], where P = (F 2 o + 2F 2 c )/3) with S = (Δρ) max = 0.23 and (Δρ) min = 0.21 e/å 3. In the final circle of refinement, the largest parameter shift (Δ/σ) max is Biological activity Human prostate cancer cell lines PC-3 (androgeninsensitive), DU145 (androgen-insensitive) and LNCaP (androgen-sensitive) were cultured in rational mediums, and incubated at 37 in a humidified atmosphere with 5% CO 2. Cell viability was evaluated by a CCK-8 assay, and cell growth inhibition was determined by measuring the absorbance at λ = 450 nm. The half maximal inhibitory concentrations (IC 50 ) were obtained from non-linear regression analysis of the concentrationresponse curves plotted for compound 4. Bioactivity of 4 is in comparison with that of naftopidil acting as a control agent. 3 RESULTS AND DISCUSSION 3. 1 Crystal structure description An asymmetric unit of 4 comprises two crystallographically independent molecules shown in Fig. 1. The crystal structure is similar to our previously reported arylpiperazine derivatives that showed good potency for treating with benign prostatic hyperplasia [8]. Fig. 1. A view of the molecules of 4 in an asymmetric unit, showing atomic numbering scheme. Intramolecular hydrogen bonds are presented in black dashed lines

4 XU X. J. et al.: Synthesis, Crystal Structure and Bioactivity of 1-( ((Benzo[d][1,3]dioxol-5-yloxy)methyl)-phenethyl)-4-phenylpiperidin-4-ol No. 12 Selected bond lengths and bond angles are listed in Table 1. Geometric structure analysis of molecule A shows that the O(1A) C(4A) and O(3A) C(1A) bonds (1.382(4) and 1.372(4) Å, respectively) are slightly shorter than the O(4A) C(19A) bond (1.431(4) Å). The case can be also observed in molecule B. In addition, the measured O(2A) C(5A) C(6A) C(1A) ando(2b) C(5B) C(6B) C(1B) torsion angles are (4) and (3), respectively. Such cases can be rationally explained that the lone-pair electrons in O atoms participate in forming a π bond with adjacent aromatic rings. Piperidine ring, a non-planar five-membered heterocyclic ring, presents an ideal chair conformer that is assigned as the lowest-energy conformation. The dihedral angle between planes 1 (C(1A) ~ C(6A)) and 2 (C(9A)~C(14A)) is 77.61(13), but that of benzodioxole ring and the aromatic plane (C(22A)~C(27A)) is 40.32(14), which contributes to the C H π interactions (Fig. 2). For molecule B, the corresponding dihedral angles are 78.13(12) and 42.66(13), indicating that the two conformers of an asymmetric unit are distinct. Fig. 2. Crystal packing diagraph for 4. Red dashed lines show the intermolecular O H N hydrogen bonds, and black dashed lines indicate the C H π interactions. Dummy atoms represent the centroids of aromatic rings Table 1. Selected Bond Lengths (Å) and Bond Angles ( ) for the Title Compound 4 Bond Dist. Bond Dist. O(1A) C(4A) 1.382(4) O(1B) C(4B) 1.383(4) O(3A) C(1A) 1.372(4) O(3B) C(1B) 1.376(4) O(4A) C(19A) 1.431(4) O(4B) C(19B) 1.434(4) N(1A) C(16A) 1.474(4) N(1B) C(16B) 1.474(4) C(8A) C(9A) 1.509(5) C(8B) C(9B) 1.518(5) C(10A) C(11A) 1.387(5) C(10B) C(11B) 1.395(5) C(17A) C(18A) 1.520(4) C(17B) C(18B) 1.519(4) Angle ( ) Angle ( ) C(1A) O(3A) C(8A) 118.6(3) C(1B) O(3B) C(8B) 117.4(3) C(5A) C(4A) O(1A) 108.6(3) C(5B) C(4B) O(1B) 109.6(3) C(9A) C(10A) C(11A) 120.3(4) C(9B) C(10B C(11B) 120.3(4) C(10A) C(9A) C(8A) 122.0(4) C(10B) C(9B) C(8B) 122.2(4) N(1A) C(16A) C(15A) 119.3(3) N(1B) C(16B) C(15B) 115.9(3) To further confirm whether the two independent molecules had different conformations, superposition was performed to demonstrate a significant discrepancy between them (see Fig. 3). The two conformers are distinguished by rotation of the benzodioxole ring around the O(3) C(8) bonds as well as phenylpiperidin-4-ol moiety around the C(15) C(16) bonds.

5 2015 Vol. 34 结构化学 (JIEGOU HUAXUE)Chinese J. Struct. Chem Fig. 3. Superposition of the two independent molecules. Molecule A is in red, and molecule B in blue. H atoms are omitted for clarity Another particular interest in studying the crystal structure of 4 is to investigate the intra- and intermolecular interactions. Intramolecular hydrogen bonds (C(21A) H(21A) O(4A) and C(21B) H(21D) O(4B)) (Fig. 1) result in the formation of two pseudo five-membered rings with envelope conformations [9]. Intermolecular H-bonds shown in Table 2 are to stabilize the three-dimensional packing structure (Fig. 2). A double chain along the b-axis is constructed by the connection of two molecules through O H N hydrogen bonds. The accumulation unit is reinforced by C H π interactions (Table 3). Additionally, weak Van der Waals interactions can be easily formed by intermolecular aggregation, thus providing structural evidence for high density of the crystal (1.273 g cm -3 ) [10] Bioactivity evaluation As shown in Table 4, the title compound 4 exhibited a moderate inhibitory activity against DU145 and LNCaP cells with the µm level of IC 50, but displayed a poor activity against PC-3 cells in comparison to the inhibitory activity of naftopidil. Table 2. Hydrogen Bonds for the Title Compound 4 (Å, º) D H A d(d H) d(h A) d(d A) D H A Symmetry code Compound 4 O(4A) H(4A) N(1B) (0) x, y, z O(4B) H(4B) N(1A) (5) x, 1 + y, z C(21A) H(21A) O(4A) (7) 100 C(21B) H(21D) O(4B) (6) 100 Table 3. C H π Interaction Geometry (Å, ) C H π H Cg X Cg X H Cg ( ) Symmetry code C(7A) H(7AB) Cg(1) (5) x, 1+ y, 1+z C(7B) H(7BA) Cg(2) (0) 128 x, y, 1+ z C(26A) H(26A) Cg(3) (8) x, y, 1+ z C(26B) H(26B) Cg(4) (0) 145 x, 1+ y, 1+ z Ring Cg(1): C(22B) C(23B) C(24B) C(25B) C(26B) C(27B); Ring Cg(2): C(22A) C(23A) C(24A) C(25A) C(26A) C(27A); Ring Cg(3): O(1B) C(4B) C(5B) O(2B) C(7B); Ring Cg(4): O(1A) C(4A) C(5A) O(2A) C(7A) Table 4. Inhibitory Activity against Human Prostate Cancers Cells of Compound 4 Compd. IC 50 a (µmol L -1 ) PC-3 b DU145 b LNCaP b 4 > ± ± 7.58 Naftopidil 42.1 ± ± ± 0.61 a IC 50 values are taken as means ± standard deviation from three experiments; b PC-3, DU145 and LNCaP, human prostate cancer cell line

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