Synthesis of platinum complexes from N-benzyl ethylenediamine derivatives

Abstracts

N-benzylethylenediamine derivatives have been prepared in good yields using methodology diferent than that described in the literature. ¹H and 13C NMR spectra were used to characterize those compounds. Nine new platinum(II) complexes, analogs of cisplatin and carboplatin, containing these ligands have been prepared and characterized. Preliminary in vitro tests against buccal human carcinoma cell lines (KB cells) showed that the complexes are cytotoxic.

platinum(II) complexes; N-benzylethylenediamine; anticancer agents; substitution reactions

O ligante N-benziletilenodiamina e derivados foram preparados em bons rendimentos utilizando-se metodologia diferente da descrita na literatura. Espectros de RMN de ¹H e de 13C foram empregados para a caracterização destes compostos. Nove novos complexos de platina(II) com estes ligantes, análogos da cisplatina e da carboplatina, foram preparados e caracterizados. Testes preliminares in vitro em linhagens celulares de carcinoma bucal humano (células KB) indicam que estes complexos são citotóxicos.

Article

Synthesis of platinum complexes from N-benzyl ethylenediamine derivatives

Mauro V. de Almeida^a,*, Eloi T. Cesar^b,c, Emanoel de C. A. Felício^a, Ana Paula S. Fontes^a and Malka Robert-Gero^d

^aDepartamento de Química, Universidade Federal de Juiz de Fora, 36036-330, Juiz de Fora - MG, Brazil

^bColégio de Aplicação João XXIII, Universidade Federal de Juiz de Fora, 36036-330, Juiz de Fora - MG, Brazil

^cDepartamento de Química, Universidade Federal de Minas Gerais, 31270-901, Belo Horizonte - MG, Brazil

^d ICSN - CNRS - 91190 - Gif/Yvette - France

O ligante N-benziletilenodiamina e derivados foram preparados em bons rendimentos utilizando-se metodologia diferente da descrita na literatura. Espectros de RMN de ¹H e de ¹³C foram empregados para a caracterização destes compostos. Nove novos complexos de platina(II) com estes ligantes, análogos da cisplatina e da carboplatina, foram preparados e caracterizados. Testes preliminares in vitro em linhagens celulares de carcinoma bucal humano (células KB) indicam que estes complexos são citotóxicos.

N-benzylethylenediamine derivatives have been prepared in good yields using methodology diferent than that described in the literature. ¹H and ¹³C NMR spectra were used to characterize those compounds. Nine new platinum(II) complexes, analogs of cisplatin and carboplatin, containing these ligands have been prepared and characterized. Preliminary in vitro tests against buccal human carcinoma cell lines (KB cells) showed that the complexes are cytotoxic.

Keywords: platinum(II) complexes, N-benzylethylenediamine, anticancer agents, substitution reactions

Introduction

cis-Diamminedichloroplatinum(II) (cisplatin)¹ is one of the most widely used and effective oncological agents against cancers of the testicles, ovaries, bladder, head and neck^2-4. It is also an important adjunct for cancers of the lung, cervix and breast². Its most spectacular success has been in the treatment of testicular cancer, a form of cancer previously resistant to any therapy, but now considered to be curable in most cases. However, its clinical usefulness has frequently been limited by severe side effects^5-7, such as nephrotoxicity, ototoxicity and neurotoxicity, and by the emergence of cancer cells resistant to cisplatin.

cis-Diammine(1,1-cyclobutanedicarboxylato) platinum(II) (carboplatin)^8-10 is the only clinically successful second-generation platinum complex, being less nephrotoxic and emetogenic than cisplatin. These properties have been attributed to the greater pharmacokinetic stability of its 1,1-cyclobutanedicarboxylate ligand in solution^11,12. Nonetheless, carboplatin still has drawbacks. Like cisplatin, it only exhibits a relatively narrow spectrum of antitumor activity, and it is not effective in the treatment of cancer cells resistant to cisplatin.

In recent years, extensive efforts have been made to develop third-generation platinum complexes with a broader spectrum of activity, improved clinical effectiveness, lack of cross-resistance to cisplatin, and enhanced water solubility¹³. Since some substituted ethylenediamine platinum complexes have shown antitumor activity against a variety of cell tumors^14,15, and since aromatic compounds have shown the possibility of intercalation between DNA bases¹⁶, we sought to synthesize several complexes containing N-benzylethylenediamine and derivatives as ligands, which are analogs of cisplatin and carboplatin.

Experimental

IR spectra were obtained on a Bomem FT IR MB-102 spectrometer in KBr pellets. ¹H NMR (200 and 400 MHz), ¹³C NMR (50 and 100 MHz) and ¹⁹⁵Pt NMR (86 MHz) spectra were recorded on a Bruker Avance DRX 200 and DRX 400 spectrometers at the Federal University of Minas Gerais. Elemental analyses were done at the Microanalyses Laboratory at ICSN/CNRS, Gif/Yvette, France. The cytotoxicity studies were done at ICSN/CNRS, Gif/Yvette, France.

Reagents:

All chemicals were reagent grade and were used without further purification.

Synthesis of ligands PhCH₂NH(CH₂)₂NH ₂(a), ClPhCH₂NH(CH₂)₂NH ₂(b) and CH₃OPhCH₂NH(CH₂) ₂ NH₂(c)

To ethylenediamine (6.7 mL, 100 mmol) in ethanol (30 mL), the corresponding benzyl chloride (20 mmols) was slowly added during 4 h. The reaction mixture was stirred for 24 h. at room temperature, after which time, it was evaporated under reduced pressure, and the residue purified on silica gel 60 G (0.2-0.5 mm), using dichloromethane/methanol 9/1 as eluent. Yields: 2.70 g, 90 % for compound a; 3.14 g, 85 % for compound b and 2.95 g, 82 % for compound c.

a: IR n_max KBr (cm^-1): 3294, 3027, 2934, 2850, 1568, 1453, 1312, 740, 699; ¹H NMR (200 MHz DMSO-d₆) d 2.19 (s, 3H, NH, NH₂), 2.45 (m, 2H, CH₂NH₂), 2.60 (m, 2H, CH₂NH), 3.68 (s, 2H, CH₂Ar), 7.28 (m, 5H, Ar); ¹³C NMR (50 MHz DMSO-d₆) d 41.4, 51.9, 52.9 (CH₂), 126.4, 127.8, 128.0, 141.1 (Ar); MS (m/z, %): 151(100); 134(12); 120(16); 106(2); 91(20).

b: IR n_max KBr (cm^-1): 3287, 2934, 2830, 1595, 1489, 1089, 1016, 803; ¹H NMR (200 MHz DMSO-d₆) d 2.28 (s, 3H, NH, NH₂), 2.54 (m, 2H, CH₂NH₂), 2.62 (m, 2H, CH₂NH), 3.67 (s, 2H,CH₂Ar), 7.35 (m, 4H, Ar); ¹³C NMR (50 MHz DMSO-d₆) d 41.4, 51.8, 52.0 (CH₂), 127.9, 129.6, 130.8, 140.2 (Ar); MS (m/z, %): 185(100); 168(6); 154(28); 140(3); 125(99).

c: IR n_max KBr (cm^-1): 3290, 3001, 2936, 2837, 1613, 1513, 1461, 1245, 1178, 1036, 820; ¹H NMR (200 MHz DMSO-d₆) d 2.30 (s, 3H, NH, NH₂), 2.50 (m, 2H, CH₂NH₂), 2.60 (m, 2H,CH₂NH), 3.63 (s, 2H, CH₂Ar), 3.72 (s, 3H, OCH₃), 6.85 (d, 2H, H3, H3', J_3-2 8.6Hz), 7.22 (d, 2H, H2, H2'); ¹³C NMR (50 MHz DMSO-d₆) d 51.7, 52.3, 54.9 (CH₂), 113.4, 129.4, 133.0, 157.9 (Ar); MS (m/z, %): 181(92); 163(3); 150(4); 136(4); 121(100).

Synthesis of complexes [PtCl₂(PhCH₂NH(CH₂ )₂NH₂)] (1), [PtCl₂(ClPhCH₂NH(CH₂)₂NH₂)] (2) and [PtCl₂ (CH₃OPhCH₂NH(CH₂ )₂NH₂)] (3)

To a solution of K₂PtCl₄ (0.415 g, 1 mmol) in water (10 mL), the appropriate ligand (1 mmol) was dissolved in water (5 mL), and added slowly with stirring. After 24 h in the dark at room temperature, the yellow solid that formed was filtered off, washed with water, and dried. Yields: 0.37 g, 90% for compound 1; 0.36 g, 80 % for compound 2 and 0.35 g, 80% for compound 3.

1: IR n_max KBr (cm^-1): 3294, 3180, 3119, 3027, 2951, 2889, 2863, 1579, 1453, 1282, 1191, 1062, 1017, 760; ¹H NMR (400 MHz DMSO-d₆) d 2.01, 2.22 (2 s, 4H, CH₂NH₂, CH₂NH), 3.86, 4.20 (2 dd, 2H, CH₂Ar), 5.30 (2 s, 2H, NH₂), 6.60 (s, 1H, NH), 7.40 (m, 5H, Ar); 13C NMR (100 MHz DMSO-d₆) d 46.3, 54.3, 55.3 (CH₂), 127.9, 128.4, 130.0, 135.1 (Ar); ¹⁹⁵ Pt NMR (DMSO-d₆) d - 2357; Anal. Calcd. for C₉H₁₄Cl₂N₂ Pt: C, 25.97; N, 6.73; H, 3.39; Cl, 17.04; found: C, 25.76; N, 6.91; H, 3.43; Cl, 16.94.

2: IR n_max KBr (cm^-1): 3299, 3188, 3108, 2949, 2889, 1597, 1575, 1493, 1188, 1153, 1093, 1066, 1018, 840, 796, 753, 602, 496; ¹H NMR (400 MHz DMSO-d₆) d 2.05, 2.21 (2 s, 4H, CH₂NH₂, CH₂NH), 4.01 (dd, 2H, CH₂Ar), 5.27 (2 s, 2H, NH₂), 6.65 (s, 1H, NH); 7.37 (d,2H, H3, H3'), 7.57 (d, 2H, H2, H2', J_2-3 7.6 Hz); ¹³C NMR (100 MHz DMSO-d₆) d 46.4, 54.1, 54.3 (CH₂), 128.3, 132.03, 132.7, 134.1 (Ar); ¹⁹⁵ Pt NMR (DMSO-d₆) d - 2361; Anal. Calcd. for C₉H₁₃Cl₃N₂ Pt: C, 23.99; N, 6.22; H, 2.91; found: C, 24.21; N, 6.19; H, 2.97.

3: IR n_max KBr (cm^-1): 3280, 3193, 3135, 2970, 2932, 2837, 1612, 1513, 1452, 1245, 1180, 1113, 1010, 835, 762, 629, 513; ¹H NMR (400 MHz DMSO-d₆) d 1.88, 2.10 (2 s, 4H, CH₂NH₂, CH₂NH); 3.70 (s, 3H, OCH₃), 3.90 (dd, 1H, H7'), 5.26, 5.34 (2 s, 2H, NH₂), 6.53 (s, 1H, NH), 6.93 (d, 2H, H3, H3a, J_3-2= 8,0 Hz), 7.46 (d, 2H, H2, H2a); ¹³C NMR (100 MHz DMSO-d₆) d 46.1, 54.1, 54.5 (CH₂), 55.0 (OCH₃), 113.7, 127.0, 131.4, 158.9 (Ar); ¹⁹⁵Pt NMR (DMSO-d₆) d -2359; Anal. Calcd. for C₁₀H₁₆Cl₂N₂ OPt: C, 26.92; H, 3.61; N, 6.28; found: C, 27.25; H, 3.71; N, 6.25.

Synthesis of compounds [PtI₂(PhCH₂NH(CH₂) ₂NH₂)] (4), [PtI₂(ClPhCH₂NH(CH₂ )₂NH₂)] (5) and [PtI₂ (CH₃OPhCH₂NH(CH₂ )₂NH₂)] (6)

A solution of K₂PtCl₄ (0.415 g, 1 mmol) and KI (0.664 g, 4 mmol) in water (10 mL) was stirred in the dark at room temperature for 30 min, after which the appropriate ligand (1 mmol) dissolved in water (5 mL) was added slowly. After stirring 24 h in the dark at room temperature, the brown product was isolated by filtration and recrystalized from acetone/water. Yields: 0.50g, 83% for compound 4; 0.62 g, 95% for compound 5 and 0.57 g, 91% for 6.

4: IR n_max KBr (cm^-1): 3253, 3180, 3025, 2945, 2923, 1567, 1455, 1148, 1057, 1112, 1007, 748, 702; ¹H NMR (400 MHz acetone-d₆) d 2.70 (m, 4H, CH₂NH₂, CH₂NH), 4.09 (dd, 1H, H7, J_7-7' 13.8 Hz, J_7-NH 10.3 Hz), 4.80 (s, 2H, NH₂), 4.90 (dd, 1H, H7', J_7'-NH 2.3Hz), 5.50 (s, 1H, NH), 7.50 (m, 5H, Ar); ¹³C NMR (100 MHz acetone-d₆) d 48.3, 54.5, 57.0 (CH₂), 129.2, 129.6, 130.8, 131.0 (Ar); Anal. Calcd. for C₉H₁₄I₂ N₂ Pt: C, 18.04; H, 2.36; N, 4.68; found: C, 18.44; H, 2.37; N, 4.67.

5: IR n_max KBr (cm^-1): 3250, 3189, 3145, 2950, 2885, 1599, 1567, 1494, 1447, 1141, 1090, 1066, 1009, 841, 796, 491; ¹H NMR (400 MHz DMSO-d₆) d 2.50 (m, 4H, CH₂NH₂, CH₂NH), 4.05 (dd, 1H, H7, J_7-7' 13.2 Hz, J_7-NH 9.2 Hz), 4.52 (dd, 1H, H7', J_7'-NH 4.8Hz), 6.06 (s, 2H, NH₂), 7.04 (s, 1H, NH), 7.55 (m, 4H, Ar); ¹³C NMR (100 MHz DMSO-d₆) d 46.7, 53.9, 54.6 (CH₂), 128.6, 131.8, 132.0, 133.7 (Ar); ¹⁹⁵Pt NMR (DMSO-d₆) d - 3313; Anal. Calcd. for C₉H₁₃ClI₂ N₂Pt.H₂O: C, 16.57; N, 4.29; H, 2.30; found: C, 16.16; N, 3.98; H, 1.96.

6: IR n_max KBr (cm^-1): 3238, 3185, 3000, 2951, 2827, 1609, 1512, 1458, 1254, 1176, 1030, 835, 804, 571;¹H NMR (400 MHz DMSO-d₆) d 2.50 (m, 4H, CH₂NH₂, CH₂NH), 3.75 (s, 3H, OCH₃), 3.95 (d, 1H, H7, J_7-7' 13.2 Hz), 4.50 (d, 1H, H7'), 6.01, 6.05 (2 s, 2H, NH₂), 6.27 (s, 1H, NH), 6.95 (d, 2H, H₃, H₃^,, J_3-2 8.4Hz), 7.42 (d, 2H, H₂, H₂^,); ¹³C NMR (100 MHz DMSO-d₆) d 46.5, 53.6, 54.9 (CH₂), 55.1 (OCH₃), 113.9, 126.5, 131.2, 159.3 (Ar); ¹⁹⁵ Pt NMR (DMSO-d₆) d - 3313; Anal. Calcd. for C₁₀H₁₆I₂N₂ OPt: C, 19.09; N, 4.45; H, 2.56; found: C, 19.52; N, 4.26; H, 2.57.

Synthesis of compounds [Pt(CBDCA)(PhCH₂NH(CH₂)₂ NH₂)].H₂O (7), [Pt(CBDCA)(ClPhCH₂NH(CH₂) ₂ NH₂)].2H₂O (8) and [Pt(CBDCA)(CH₃OPhCH₂ NH(CH₂)₂NH₂)].3H ₂O (9), (CBDCA = 1,1-cyclobuta-nedicarboxylate)

To a solution of 1 mmol of the appropriate iodide complex (compounds 4, 5 and 6) in 5 mL of acetone was added 1 mmol of silver 1,1-cyclobutanedicarboxylate previously prepared by reaction of 1,1-cyclobutanedicarboxylic acid with silver nitrate in water. After stirring for 48 h at room temperature in the dark, the silver iodide formed was filtered off. The volume of the filtrate was reduced and after 24 h in the freezer, a white powder was isolated. Yields: 0.16 g, 33 % for compound 7; 0.17 g, 31 % for compound 8 and 0.18 g, 31 % for compound 9.

7: IR n_max KBr (cm^-1): 3204, 3170, 3105, 2991, 2954, 2883, 1652, 1364, 1115, 755, 708, 472; ¹H NMR (400 MHz CD₃OD) d 1.69 (m, 2H, CH₂ cyclobutane), 2.25 (m, 4H, 2 CH₂ cyclobutane), 2.73 (m, 4H, CH₂NH, CH₂NH₂), 3.80 (dd, 1H, H7, J_7-7' 10.8 Hz; J_7-NH 8.4 Hz), 3.93 (dd, 1H, H7', J_7'-NH 2.8 Hz), 5.47, 5.72 (2 s, 2H, NH₂), 6.81 (s, 1H, NH), 7.45 (m, 5H, Ar); ¹³C NMR (100 MHz DMSO-d₆) d15.0, 30.2, 30.3 (CH₂ cyclobutane), 45.8, 54.4, 55.3, 55.4 [CH₂N, C(CH₂)₂], 128.1, 128.5, 130.1, 134.3 (Ar), 177.2, 177.4 (C=O); Anal. Calcd. for C₁₅H₂₀N₂O₄ Pt. 1 H₂O: C, 35.65; H, 4.39; N, 5.54, found: C, 35.66; H, 4.48; N, 5.43.

8: IR n_max KBr (cm^-1): 3268, 3144, 3013, 2995, 1658, 1548, 1377, 1305, 1098; ¹H NMR (200 MHz DMSO-d₆) d 1.67, 2.20 (2 m, 6H, 3CH₂ cyclobutane), 2.70 (m, 4H, CH₂NH, CH₂NH₂), 3.83 (m, 2H, CH₂Ar), 5.44, 5.68 (2 s, 2H, NH₂), 6.85 (s, 1H, NH), 7.45 (d, 2H, H3, H3', J_3-2 8.4 Hz), 7.60 (d, 2H, H2, H2'); ¹³C NMR (50 MHz DMSO-d₆) d 15.0, 30.0, 30,4 (CH₂ cyclobutane), 45.0, 54.2, 55.4 [CH₂N, C(CH₂)₂], 128.4, 132.2, 133.0, 133.3 (Ar), 177.1, 177.3 (C=O); Anal. Calcd. for C₁₅H₁₉ClN₂O₄ Pt.2H₂O: C, 32.26; N, 5.01; H, 4.12; found: C, 32.36; N, 4.51; H, 4.51.

9: IR n_max KBr (cm^-1): 3252, 3109, 3001, 2946, 1651, 1612, 1515, 1253, 1181, 1115, 1025, 842, 469l; ¹H NMR (400 MHz DMSO-d₆) d 1.64 (s, 2H, CH₂ cyclobutane), 2.15 (m, 4H, 2 CH₂ cyclobutane), 2.66 (m, 4H, CH₂NH₂, CH₂NH), 3.70 (s, 3H, OCH₃), 3.75 (m, 2H, CH₂Ar), 5.40, 5.63 (2 s, 2H, NH₂), 6.67 (s, 1H, NH), 6.87 (d, 2H, H3, H3', J_3-2 8 Hz), 7.40 (d, 2H, H2, H2');¹³C NMR (100 MHz DMSO-d₆) d 15.0, 30.2, 30.3 (CH₂ cyclobutane), 45.8, 54.2, 54.7, 55.1, 55.4 [CH₂N, C(CH₂)_2, OCH₃], 113.8, 126.2, 131.6, 159.1 (Ar), 177.3, 177.5 (C=O); 195Pt NMR (DMSO-d₆) d -1996; Anal. Calcd. for C₁₆H₂₂N₂O₅ Pt.3H₂O: C, 33.62; N, 4.89; H, 4.93; found: C, 33.77; N, 4.92; H, 4.83.

Results and Discussion

The syntheses of ligands PhCH₂NH(CH₂)₂NH ₂(a), ClPhCH₂NH(CH₂)₂NH ₂ (b) and CH₃OPhCH₂NH (CH₂)₂NH₂(c) are described in the literature^17-19 from the reactions of the corresponding benzaldehyde with ethylenediamine, followed by reduction of the resulting Schiff bases with formic acid. We found that these ligands can be prepared in satisfactory yields by treatment of ethylenediamine with the corresponding benzyl chloride in ethanol at room temperature for 24 h (Scheme 1). The IR spectra of all the ligands showed the characteristic absorptions at n_N-H at 3294 cm^-1, n_{C-H(aromatic)} at 3027 cm^-1 and n_{C-H(aliphatic)} at 2934 cm^-1 for compound a, for instance. In addition to these absorptions, the IR spectrum of compound b showed n_{Cl-C(aromatic)} at 1089 cm^-1 and for compound c one can observe n_C-O-C at 1036 cm^-1. These ligands were also characterized using ¹H and ¹³C NMR spectroscopy. In the ¹H NMR spectrum, signals were observed at d 2.19, 2.45, 2.60, 3.68 and 7.28, corresponding to the NH, CH₂NH₂, CH₂NH, CH₂Ar and aromatic hydrogens. For compound c, a signal at d 3.72 attributable to the OCH₃ was also observed. In the ¹³C NMR spectrum, signals at d 41.4, 51.9, 52.9 corresponding to the methylenic carbons and signals in the d 113 to 160 region, due to the aromatic carbons were observed. For compound c, the OCH₃ was observed at d 54.9. The mass spectra showed the following principal fragments. For compound a, m/z: 151 (M+H)⁺; 134 (ArNHCH₂CH₂); 120 (ArNHCH₂); 106 (ArCH₂NH) and 91 (ArCH₂). For compound b, m/z: 185 (M+H)⁺; 168 (ClArNHCH₂CH₂); 154 (ClArCH₂NHCH₂); 140 (ClArCH₂NH) and 125 (ClArCH₂). For compound c, m/z: 181(M+H)⁺; 163 (OCH₃ArCH₂NCH₂ CH₂); 150 (CH₃OArCH₂NHCH₂); 136 (CH₃OArCH₂NH) and 121 (CH₃OArCH₂).

The dichloro platinum(II) complexes [PtCl₂(PhCH₂ NH(CH₂)₂NH₂)] (1), [PtCl₂(ClPhCH₂NH(CH₂ )₂NH₂)] (2) and [PtCl₂(CH₃OPhCH₂NH(CH ₂)₂NH₂)] (3) were synthesized by reaction of the corresponding ligands with K₂[PtCl₄] in water at room temperature for 12 h, and isolated by simple filtration. For these complexes, one can see in the IR spectra the absorptions corresponding to n_Pt-N and n_Pt-Cl at 495 and 322 cm^-1, respectively, in addition to the absorptions observed for the ligand. In the ¹H NMR spectra one observes that there is a marked downfield shift for the NH and NH₂ signals compared to those for the ligands. The ¹⁹⁵Pt NMR spectra showed only one signal at d -2357, -2361 and -2359 for compounds 1, 2 and 3, respectively. These chemical shift values can be expected based on data for similar compounds described in the literature. For instance, the spectrum of [Pt(DACH)Cl₂] shows a signal at d - 2287 (DACH= 1,2-diaminocyclohexane)²⁰.

Compounds a, b and c were reacted with an equimolar amount of potassium tetraiodoplatinate(II), generated in situ, to produce the diiodo platinum(II) complexes [PtI₂(PhCH₂NH(CH₂) ₂NH₂)] (4), [PtI₂(ClPhCH₂NH (CH₂)₂NH₂)] (5) and [PtI₂(CH₃OPhCH₂NH(CH ₂)₂NH₂)] (6). Besides the absorptions observed in the spectra of the ligands, the IR spectra of the iodide complexes showed one absorption due to n_Pt-N at 491 cm^-1. The ¹H and ¹³C NMR spectra are analogous to those of compounds 1, 2 and 3. The ¹⁹⁵Pt NMR spectra of these complexes showed one signal at d -3313, supporting the proposed structure. Compared to compounds 1, 2 and 3, the replacement of chloride by iodide causes an upfield shift of the signal in the ¹⁹⁵Pt NMR spectrum, as expected^21,22.

Reactions of 4, 5 and 6 with an aqueous silver 1,1-cyclobutanedicarboxylate (Ag₂CBDCA) suspension afforded the corresponding carboplatin analogs [Pt(CBDCA) (PhCH₂NH(CH₂)₂NH ₂)].H₂O (7), [Pt(CBDCA)(ClPhCH₂ NH(CH₂)₂NH₂)].2 H₂O (8) and [Pt(CBDCA)(CH₃OPhCH₂ NH(CH₂)₂NH₂)].3H ₂O (9), (Scheme 1). The IR spectra showed absorptions at 3204 cm^-1 (n_NH), 3064 cm^-1 (n_{CH aromatic}), 2954 cm^-1 (n_{CH aliphatic}) and 1652 cm^-1 (n_C=O), as well as the n_Pt-N and n_Pt-O at 472 cm^-1 and 535 cm^-1, respectively. In the ¹H NMR spectrum, multiplets at d 1.69 and 2.25 corresponding to the CH₂ groups of the cyclobutane ring were evident. The downfield shift of the NH and NH₂ signals was also evident, as mentioned previously for compounds 1, 2 and 3. In the ¹³C NMR spectrum the signals corresponding to the CH₂ groups of the cyclobutane ring appear at d 15.0, 30.2 and 30.3. The quaternary carbon exhibits a resonance at d 55.4, and the carbonyl carbons at d 177.2 and 177.4. The ¹⁹⁵Pt NMR spectra, as expected, showed only one signal at d - 1996. Compared to compounds 1, 2 and 3, the coordination of the oxygen atoms in these complexes causes a downfield shift of the signal in the ¹⁹⁵Pt NMR spectra, as expected. For instance, the spectrum of [Pt(DACH)(ox)] shows a signal at d - 1857 (DACH= 1,2-diaminocyclohexane and ox= oxalate anion)²³. Figure 1 shows the ¹⁹⁵Pt NMR spectra of compounds 3, 6 and 9. One can see the upfield and downfield shifts of the signal when chloride 3 is replaced for iodide 6 or carboxylate 9.

The results of elemental analysis for all the complexes prepared are in agreement with the calculated values.

Preliminary cytotoxicity tests for complexes 1, 2 and 3 were undertaken to verify their potencial as anticancer agents. A standard test using buccal human carcinoma cell lines (KB cells)^24,25 was performed in vitro along with cisplatin, as the reference drug, using a colorimetric method. These compounds are not cytotoxic at 1 and 10mg mL^-1 concentrations. Complexes 1 and 2 show 30% and 65% cytotoxicity, respectively, at a concentration of 50mg mL^-1.

Conclusion

This work describes the synthesis and characterization of three N-benzylethylenediamine analogs used as ligands for the preparation of nine new platinum(II) complexes. These complexes were fully characterized and have potential for acting as cytotoxic agents, which was demonstrated by a preliminary test done using KB cells. Further investigation of the biological properties of the new compounds is desirable to determine their possible utility as anticancer agents.

Acknowledgments

E. T. C. gratefully acknowledges CAPES (Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for a fellowship. The authors are grateful to Dr. Richard Grazul for his review of this paper.

Received: May 31, 1999

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Publication Dates

• Publication in this collection
  23 Oct 2000
• Date of issue
  Apr 2000

History

• Received
  31 May 1999