Polyhedron 50 (2013) 434–442

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Polyhedron

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Synthesis, characterization and cytotoxicity of new gold(III) complexes with1,2-diaminocyclohexane: Influence of stereochemistry on antitumor activity

Said S. Al-Jaroudi a, Mohammed Fettouhi a, Mohammed I.M. Wazeer a, Anvarhusein A. Isab a,⇑,Saleh Altuwaijri b

a Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabiab Clinical Research Laboratory, SAAD Research Development Center, SAAD Specialist Hospital, Al-Khobar 31952, Saudi Arabia

a r t i c l e i n f o

Article history:Received 27 July 2012Accepted 13 November 2012Available online 1 December 2012

Keywords:Gold(III) complex1,2-DiaminocyclohexaneAnticancerGastric carcinogenesis (SGC-7901)Prostate (PC-3)

0277-5387/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.poly.2012.11.034

⇑ Corresponding author.E-mail address: aisab@kfupm.edu.sa (A.A. Isab).

a b s t r a c t

Gold(III) complexes of the type [(DACH)AuCl2]Cl, derived from sodium tetrachloroaurate(III) dihydrateNaAuCl4�2H2O, where DACH is diaminocyclohexane, have been synthesized. These potential metallodrugcompounds were characterized using various spectroscopic and analytical techniques, including elemen-tal analysis, UV–Vis, infrared spectroscopy, solution as well as solid NMR spectroscopy and X-ray crystal-lography. The potential of the synthesized gold(III) complexes as anti-cancer agents was investigated bymeasuring some relevant physicochemical and biochemical properties, such as the stability of the Au–Nbonds by vibrational stretching from far-IR as well as cytotoxicity and the stomach cancer cell inhibitingeffect. The solid-state 13C NMR chemical shift shows that the ligand is strongly bound to the gold(III) cen-ter via N atoms. An X-ray crystallography study of the complexes shows that the cyclohexyl ring adopts achair conformation and the gold coordination sphere adopts a distorted square planar geometry. The cisisomer in solution showed higher activity towards the inhibitory effect of human cancer cell lines such asprostate cancer (PC-3) and gastric carcinoma (SGC-7901) than that of the trans isomer. The cytotoxicity ofthe cis isomer complex has also been estimated in PC-3 and SGC-7901 cells.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

The serendipitous discovery of cisplatin by Rosenberg in 1965heralded a new area of anticancer drug research based on metal-lopharmaceuticals [1]. Cisplatin has been one of the most success-ful chemotherapies in the last 30 years and has been used to treatnumerous types of cancers, including testicular, ovarian, head–neck and bladder tumors. Despite having great utility as a chemo-therapeutic agent, cisplatin does have drawbacks; tumors oftendevelop resistance to the drug and patients routinely experiencesevere side effects throughout the course of the treatment [2].Subsequently, researchers are continually looking for therapeuticalternatives that might alleviate these limitations. Unfortunately,they have several major drawbacks. Common problems includecumulative toxicities of nephrotoxicity and cytotoxicity [3–6]. Inaddition to the serious side effects, the therapeutic efficacy is alsolimited by inherent or treatment-induced resistant tumor cells.These drawbacks have provided the motivation for alternativechemotherapeutic strategies. To circumvent the problem ofdrug-resistance in cisplatin-resistant cells, gold(III)-based com-

ll rights reserved.

plexes have been designed as potential alternatives to cisplatin[7–11].

Gold(III) compounds have greatly attracted researchers’ atten-tion in the last decade for their outstanding cytotoxic actions. Itis a metal ion which typically adopts a four-coordinate, square-pla-nar geometry and is therefore expected to mimic the structural andelectronic properties of platinum(II). Recent studies have shownthat several gold(III) complexes are highly cytotoxic against differ-ent tumor cells [12–14], including some which are active evenagainst the cisplatin-resistant cell lines [8,15–17]. Several lines ofevidence suggest that gold(III) compounds produce their antipro-liferative effects through innovative and non-conventional modesof action. For instance, the hypothesis that their biological effectsare mediated by an antimitochondrial mechanism rather than bydirect DNA damage, as it is the case for cisplatin and its analogs,has gained much credit during the last few years [10].

The strict relationship to platinum(II) compounds makes gold(III) complexes good candidates for development and testing asanticancer drugs, although the relatively high kinetic liability andthe usually high redox potentials have largely hindered suchinvestigations. These problems can possibly be circumvented byforming gold(III) compounds with one or more multidentatenitrogen-donor ligands to enhance the stability of the gold(III)complexes [18–20]. Some recent studies reporting that novel

1, Cis-( )-1,2-(DACH)AuCl± 3

65

43

2

1H2N

H2N

Au

Cl

Cl

65

43

2

1H2N

H2N

Au

Cl

Cl

65

43

2

1H2N

H2N

Au

Cl

Cl

65

43

2

1H2N

H2N

Au

Cl

Cl

2, Trans -( )-1,2-(DACH)AuCl± 3

3, (S,S) -(+)-1,2-(DACH)AuCl3

65

43

2

1H2N

H2N

Au

Cl

Cl

Scheme 2. Chemical structures of the synthesized gold(III) complexes.

S.S. Al-Jaroudi et al. / Polyhedron 50 (2013) 434–442 435

gold(III) compounds show favorable antitumor properties bothin vitro and in vivo have raised new interest in this research area[21–23].

Although, there are a multitude of structural analogs of the anti-tumor agent cis-diamine dichloroplatinum(II) (cisplatin) [24], onlya few are presently used in clinical practice [25], including trans-1,2-diaminocyclohexane (DACH) dichloroplatinum(II) [26]. Sincethe molecule is chiral, the relevance of stereochemical issues hasbeen addressed by a number of investigators [27].The ligand DACHhas three isomeric forms: the enantiomers (IR,2R-DACH) (trans-l-DACH), (lS,2S-DACH) (trans-DACH) and the diastereoisomerPt(1R,2S-DACH) (cis-DACH). In spite of conflicting views [28–32],the consensus is that the (R,R) isomer is generally more active thanthe (S,S) isomer [33,34], although activity has also been demon-strated with the (R,S) isomer [35]. With regard to the stereochem-istry of the complexes, the DACH platinum compounds, Pt(IR,2R-DACH) and Pt(lS,2S-DACH), have a higher antitumor activity thanthe Pt(IR,2S-DACH) complex [36–38].

In the early 1990s, a few gold compounds were prepared andcharacterized for their antitumor activity with positive results[39,40] Recently, the use of various Au(III) complexes with novelfunctionality has elicited more interest due to their distinctphysical and chemical properties, stability under physiologicalconditions and outstanding cytotoxic effects [41,42]. Cis-diamined-ichloroplatinum(II) (cisplatin) is one of the most widely used anti-cancer drugs today. However, platinum compounds possessing the1,2-diaminocyclohexane (DACH) carrier ligand offer advantagesover cisplatin with regard to bioavailability, activity and decreasedrenal toxicity [43]. Furthermore, the success of oxaliplatin, whichincorporates the 1R,2R-DACH carrier ligand as a Pt(II) complex,raised considerable research interest over the past three decadesin platinum–DACH complexes.

Over the past several years, significant effort has been devotedto the study of the antitumor activity of platinum–DACH com-plexes, whereas gold–DACH complexes [44] have received rela-tively little attention, although, Au(III) has a fairly rich biologicalchemistry. For instance, it is redox active, can be coordinated byamino acids and proteins, is able to deprotonate and bind to theamide N of peptides and it is capable of cross-linking histidineimidazole rings [45]. As in the case of the parent cisplatin, the anti-tumor activity of platinum–DACH is accompanied by some toxic-ity. The emergence of resistance and low water solubility, thatcan affect the pharmacokinetics, are additional features that mustbe improved in the quest for a more effective analog [46]. As a con-tinuation of our intrinsic interest in the synthesis of gold(III) com-plexes and to better understand the chemical and physicalbehavior of biologically relevant mono-(DACH) gold(III) com-plexes, the chiral isomers [cis-(±)-1,2-(DACH)AuCl2]Cl (1), [trans-(±)-1,2-(DACH)AuCl2]Cl (2) and [(1S,2S)-(+)-1,2-(DACH)AuCl2]Cl(3) have been synthesized and fully characterized by IR, NMR, ele-mental analysis and UV–Vis. Scheme 1 illustrates the structures ofthe ligands and Scheme 2 shows the structures of the complexes.Their cytotoxicity has been tested in vitro in human gastric carci-noma cell line SGC-7901 and prostate cancer cell line PC-3. In thisstudy, the influence of the relative stereochemistry of (DACH)gold(III) complexes on their antitumor activities was addressed.These compounds are sparingly water soluble.

NH2

NH2

S

R

NH2

NH2

R

R

NH2

NH2

S

S

NH2

NH2

R

S

Trans Cis

Scheme 1. Isomerization structures of diaminocyclohexane (DACH).

2. Experimental

2.1. General procedures

All commercial reagents were purchased from Aldrich and usedas received unless otherwise stated. The 1H and 13C NMR experi-ments were performed on a Bruker Advance 400 or Jeol JNM-LA500 spectrometer. 1H and 13C NMR chemical shifts were given asvalues with reference to tetramethylsilane (TMS) as an internalstandard.

2.2. Synthesis of the Au(III) complexes

Gold complexes of cis-(±)-1,2-diaminocyclohexane (1), trans-(±)-1,2-diaminocyclohexane (2) and the purely optical active iso-mer of (S,S)-(+)-1,2-diaminocyclohexane (3) were synthesized bya general method described in literature for similar compounds[47], by dissolving of 199 mg (0.50 mmol) sodium tetrachloroau-rate(III) dihydrate (NaAuCl4�2H2O) in a minimum amount of abso-lute ethanol at ambient temperature. In a separate beaker, asolution of 57 mg (0.50 mmol) of the diaminocyclohexane in theleast amount of absolute ethanol was prepared, both solutionswere mixed (total of 40 ml) and stirred for around 30 min until aclear solution was obtained, which was filtered and concentratedto 10 ml solvent then left for crystallization in the refrigerator.The produced solid was dried under vacuum. The product was ob-tained in a yield of 91–98%. The complexes prepared in the presentstudy were characterized by their physical properties, NMR, IR, ele-mental analysis and X-ray crystallography. All the data support theformation of the desired DACH complexes. Melting points and ele-mental analyses for the complexes are presented in Table 1 (SeeSupplementary data for Tables 1–7).

2.3. Electronic spectra

Electronic spectra were obtained for the diaminocyclohexanegold(III) complexes using a Lambda 200, Perkin-Elmer UV–Visspectrometer. The resulting absorption data are shown inTable 2.

Table 8Crystal and structure refinement data for compounds (1) and (2).

Compound (1) (2)

CCDC deposit No. 831613 850216Empirical formula C14 H34 Au2 Cl6 N4 O C12 H30 Au2 Cl6 N4 OFormula weight 881.09 853.03T (K) 297(2) 295(2)k (Å) 0.71073 0.71073Crystal system orthorhombic monoclinicSpace group Pbcn P21

Unit cell dimensionsa (Å) 19.792(1) 9.5898(7)b (Å) 12.4662(7) 8.6106(6)c (Å) 10.3212(6) 14.477(1)b (�) 95.307(1)V (Å3) 2546.5(2) 1190.3(2)Z 4 2q (g cm�3) 2.298 2.38l (mm�1) 12.152 12.994F(000) 1656 796Crystal size (mm) 0.40 � 0.37 � 0.26 0.52 � 0.49 � 0.16h range (o) 1.93–28.29 1.41–28.28Limiting indices �26 6 h 6 26 �12 6 h 6 12

�16 6 k 6 16 �11 6 k 6 11�13 6 l 6 13 �19 6 l 6 19

Max and min transmission Tmin = 0.0850 andTmax = 0.1443

Tmin = 0.0564 andTmax = 0.2244

Data/restraints/parameters 3162/0/128 5835/2/230Goodness-of-fit (GOF) on F2 1.051 1.017Final R indices [I > 2r(I)] R1 = 0.0246

wR2 = 0.0631R1 = 0.0308wR2 = 0.0739

R indices (all data) R1 = 0.0288wR2 = 0.0654

R1 = 0.0329wR2 = 0.0747

Largest difference in Peakand hole (e �3)

1.766 and �1.544 0.796 and �1.555

Table 9Selected bond lengths (Å) and bond angles (o) for compounds (1) and (2).

(1) (2)

Au1–N1 2.029(4) Au1–N1 2.029(6) Au2–N3 2.029(6)Au1–N2 2.030(3) Au1–N2 2.031(5) Au2–N4 2.054(7)Au1–Cl1 2.261(1) Au1–Cl1 2.274(2) Au2–Cl3 2.259(3)Au1–Cl2 2.268(1) Au1–Cl2 2.276(2) Au2–Cl4 2.266(2)

N1–Au1–N2 83.9(2) N1–Au1–N2 84.3(2) N3–Au2–N4 84.1(2)N1–Au1–Cl1 91.7(1) N1–Au1–Cl1 92.0(2) N3–Au2–Cl3 92.2(2)N2–Au1–Cl1 175.4(1) N2–Au1–Cl1 176.2(2) N4–Au2–Cl3 176.2(2)N1–Au1–Cl2 176.0(1) N1–Au1–Cl2 174.2(2) N3–Au2–Cl4 176.4(2)N2–Au1–Cl2 92.6(1) N2–Au1–Cl2 89.9(2) N4–Au2–Cl4 92.3(2)Cl1–Au1–Cl2 91.83(5) Cl1–Au1–Cl2 93.81(8) Cl3–Au2–Cl4 91.4(1)

436 S.S. Al-Jaroudi et al. / Polyhedron 50 (2013) 434–442

2.4. IR and far-IR studies

The solid-state IR spectra of the ligands and their gold(III) com-plexes were recorded on a Perkin-Elmer FTIR 180 spectrophotom-eter using KBr pellets over the range 4000–400 cm�1. The selectedIR frequencies are given in Table 3. Far-infrared spectra were re-corded for complexes (1)–(3) at 4 cm�1 resolution at room temper-ature in cesium chloride disks on a Nicolet 6700 FT-IR with a far-IRbeam splitter. Far-IR data for the complexes studied are depicted inTable 4.

2.5. Solution NMR measurements

All NMR measurements were carried out on a Jeol JNM-LA 500NMR spectrophotometer at 297 K. The 1H NMR spectra were re-corded at a frequency of 500.00 MHz. The 13C NMR spectra wereobtained at a frequency of 125.65 MHz with 1H broadband decou-pling and they were referenced relative to TMS. The spectral condi-tions were: 32 k data points, 0.967 s acquisition time, 1.00 s pulsedelay and 45� pulse angle. The 1H and 13C NMR chemical shifts aregiven in Tables 5 and 6, respectively, according to Scheme 2.

2.6. Solid state NMR studies

13C solid-state NMR spectra were recorded on a Bruker400 MHz spectrometer at an ambient temperature of 25 �C. Sam-ples were packed into 6 mm zirconium oxide rotors. Cross polari-zation and high power decoupling were employed. A pulse delayof 7.0 s and a contact time of 5.0 ms were used in the CPMASexperiments. The magic angle spinning rates were 4 and 8 kHz.Carbon chemical shifts were referenced to TMS by setting the highfrequency isotropic peak of solid adamantane to 38.56 ppm. Thesolid NMR data are given in Table 7.

2.7. X-ray crystallography

For each of (1) and (2), an X-ray quality single crystal, whichwas obtained from EtOH solution, was mounted in a thin-walledglass capillary on a Bruker-Axs Smart Apex diffractometerequipped with graphite monochromatized Mo Ka radiation(k = 0.71073 Å). The data were collected using SMART [48]. The dataintegration was performed using SAINT [49]. An empirical absorp-tion correction was carried out using SADABS [50]. The structurewas solved with direct methods and refined by full matrix leastsquare methods based on F2, using the structure determinationpackage SHELXTL [51] based on SHELX 97 [52]. Graphics were gener-ated using ORTEP-3 [53] and MERCURY [54]. For compound (1), someof the hydrogen atoms of the disordered ethanol molecule couldnot be placed. For compound (2), one hydrogen atom of the watermolecule was located on a Fourier Difference map and refined iso-tropically, the second one could not be placed reliably. All other Hatoms were placed a calculated positions using a riding model.Crystal and structure refinement data are given in Table 8. Selectedbond lengths and bond angles are given in Table 9.

2.8. Cell lines and reagents

Human gastric cancer SGC-7901 and prostate cancer PC-3 cellswere incubated. Trypan blue dye exclusion analysis and MTT assaywere used to detect cell proliferation and to assess the inhibitoryeffect of the compounds (1)–(3) on the proliferation of the SGC-7901 and PC-3 cells. In one culture plate, human gastric cancerSGC-7901 and PC-3 cells were treated with various concentrationsof compounds (1)–(3), and the control (water), Figs. 1–3.

In one set of plates, Figs. 4–6, compounds (1)–(3) and SGC-7901cells were kept for an entire day (24 h) and for 72 h (3 days).

Similarly, in another set, compounds (1)–(3) and PC3 cells werekept for an entire day (24 h) and for 72 h (3 days). In the remainingset, Fig 7, compounds (1) and (2), with fixed concentrations, wereemployed to determine the growth inhibitory effect for both PC-3and SGC-7901 cells. After being treated with (1) and (2), the cellviability was examined by an MTT assay.

2.9. Assessment of cell proliferation

An MTT assay was used to obtain the number of living cells inthe sample. SGC-7901 and PC-3 cells were seeded on 96-wellplates at a predetermined optimal cell density to ensure exponen-tial growth for the duration of the assay. After 24 h pre incubation,the growth medium was replaced with an experimental mediumcontaining the appropriate drug or control. Six duplicate wellswere set up for each sample, and cells untreated with drug servedas a control. Treatment was conducted for 24 and 72 h. After incu-bation, 10 lL MTT (6 g/L, Sigma) was added to each well and theincubation was continued for 4 h at 37 �C. After removal of the

Fig. 1. Effect of the cis-(±)1,2-(DACH)–gold(III) complex on cell growth in (A) PC-3and (B) SGC-7901 cells. The cells were treated with 10 lM of compound (1) for1 day and 3 days. The anti-proliferative effect was measured by an MTT assay. Theresults are expressed as the mean, SD. ⁄P < 0.05.

Fig. 2. Effect of the trans-(±)1,2-(DACH)–gold(III) complex on cell growth in (A) PC-3 and (B) SGC-7901 cells. The cells were treated with 10 lM of compound (2) for1 day and 3 days. The anti-proliferative effect was measured by an MTT assay. Theresults are expressed as the mean, SD. ⁄P < 0.05.

Fig. 3. Effect of the (S,S)-(+)-1,2-(DACH)–gold(III) complex on cell growth in (A) PC-3 and (B) SGC-7901 cells. The cells were treated with 10 lM of compound (3) for1 day and 3 days. The anti-proliferative effect was measured by an MTT assay. Theresults are expressed as the mean, SD. ⁄P < 0.05.

Fig. 4. Effect of the cis-(±)-1,2-(DACH)–gold complex on cell growth in (A) PC-3 and(B) SGC-7901 cells. The cells were treated with various concentrations of compound(1) for 24 h. The anti-proliferative effect was measured by an MTT assay. The resultsare expressed as the mean, SD. ⁄P < 0.05.

S.S. Al-Jaroudi et al. / Polyhedron 50 (2013) 434–442 437

medium, MTT stabilization solution (dimethylsulfoxide:etha-nol = 1:1) was added to each well, and shaken for 10 min until allcrystals were dissolved. Then, the optical density was detected ina micro plate reader at 550 nm wavelength using an ELISA reader.Each assay was performed in triplicate. The cell number and viabil-ity were determined by trypan blue dye exclusion analysis.

3. Results and discussion

3.1. Electronic spectra

The kmax values for the complexes studied are shown in Table 2.The Au(III) complexes show absorptions in the region 250–350 nm

(40000–28570 cm�1), which correspond to LMCT transitions, asignal at 300 nm that could be assigned to a Cl ? Au charge trans-fer by analogy to the absorption spectrum of auric acid, whichgives a band at 320 nm [55], where this transition has a highextinction coefficient and cannot be assigned to the symmetry for-bidden d–d transition. According to crystal field theory for d8 com-plexes, the LUMO orbital is dx2—y2 , so the ligand to metal chargetransfer could be due to a pr ? dx2—y2 transition [56]. It is evidentthat the electronic spectra of these compounds are stable and con-sistent, which means that the gold centers remain in the +3 oxida-tion states.

3.2. IR and far-IR spectroscopic studies

Table 3 lists the significant IR bands of the free DACH ligandsand the gold(III) complexes. The N–H stretching band, which

Fig. 5. Effect of the trans-(±)-1,2-(DACH)–gold complex on cell growth in (A) PC-3and (B) SGC-7901 cells. The cells were treated with various concentrations ofcompound (2) for 24 h. The anti-proliferative effect was measured by an MTT assay.The results are expressed as the mean, SD. ⁄P < 0.05.

Fig. 6. Effect of the (S,S)-(+)-1,2-(DACH)–gold(III) complex on cell growth in (A) PC-3 and (B) SGC-7901 cells. The cells were treated with various concentrations ofcompound (3) for 24 h. The anti-proliferative effect was measured by an MTT assay.The results are expressed as the mean, SD. ⁄P < 0.05.

438 S.S. Al-Jaroudi et al. / Polyhedron 50 (2013) 434–442

occurs around 3300 cm�1 for the free ligands, shifts towards ahigher frequency (blue shift) upon complexation by about150 cm�1. Another important vibrational band observed in IR spec-tra is the C–N stretching, which also showed a slight shift to higherwavenumber, indicating a shorter C–N bond in the complexes thanin the free ligands.

Far-IR spectra showed absorption bands at 353 and 367 cm�1

for the symmetric and asymmetric stretching of the Au–Cl bond,which is consistent with an Au–Cl stretching mode trans to nitro-gen [57,58]. Another group of bands at 395 and 437 cm�1 couldbe assigned to the symmetric and asymmetric stretching of the

Au–N bond [59]. The red shift of the DACH complexes with respectto auric acid shows a weakening of the Au–Cl bond.

3.3. Solution NMR characterization

The 1H and 13C NMR chemical shifts of compounds (1)–(3),along with the free ligands, are listed in Tables 5 and 6, respec-tively. Also, the 1H and 13C NMR spectra of complexes (1)–(3) de-picted one half of the total expected signals because of the C2

symmetry axis. The 1,2-diaminocyclohexane ring is considered asa rigid conformer that allows the equatorial H3 and H4 protonsto be distinguished from the axial H3 and H4 protons at room tem-perature. A 1H NMR downfield shift was observed for the com-plexes with respect to the free diamine ligands. A significantdownfield shift was observed at 3.59 ppm for complex (1) with re-spect to the free DACH ligand at 2.23 ppm. This can be attributed todonation of nitrogen lone pairs to the gold center that causes desh-ielding of the proton(s) next to the bonding nitrogen. On the otherhand, the 13C NMR downfield shift was observed only for the car-bon next to the bonding nitrogen and the other carbons in thecomplex showed an upfield shift. For instance, the chemical shiftsof C3 and C4 for complex 1 were observed at 26.78 and 21.43 ppm,respectively, whereas for the free diamine ligand they occur at35.26 and 26.36 ppm. It is also worth mentioning that complexes(1)–(3), even though they have same DACH skeleton, their NMRchemical shifts are not the same due to differences in their stereo-chemistry upon complexation.

3.4. Solid-state NMR

At the spinning rate of 8 kHz, only the isotropic signals were ob-served for the carbons, indicating a small anisotropy due to the sp3

hybridization of these atoms. Compared to the solution chemicalshifts, substantial deshielding in the solid state is observed, witha similarity in the chemical shifts amongst all the synthesized com-plexes (Table 7), which is a clear indication of the stability of theprepared complexes. The solid state NMR spectrum of complex(1) showed two sets of peaks with equal intensity, which supportsthe idea of the inequivalency of all six carbon atoms of DACH. Thisindicates that complex (1) lacks C2 symmetry in the solid state.

3.5. X-ray crystal structure

Fig. 8 shows the crystal structure of complex (1). The gold(III)ion is bonded to two nitrogen atoms of the cis-cyclohexane-1,2-diamine ligand and two chloride ions in a distorted square planargeometry. The two Au–N bond distances are not significantly dif-ferent (2.029(4) Å), while the Au–Cl bond distances are 2.261(1)and 2.268(1) Å (Tables 8 and 9). The Cl-Au-Cl and N-Au-N bond an-gles are 91.83(5) and 83.9(2)�, respectively. The later value reflectsthe chelation strain of the diamine ligand. These values are similarto those found in dichloro-(ethylenediamine-N,N0)-gold(III) chlo-ride dihydrate [47] and dichloro-(1,2-ethanediamine)-gold(III) ni-trate [60]. The cyclohexyl ring adopts a chair conformation. Thesquare planar geometry and the five-membered ring strain imposean N1–C1–C2–N2 torsion angle of 49.80�. All the amine hydrogenatoms are engaged in hydrogen bonding with the Cl� counterion. To the best of our knowledge, this is the first X-ray structureof a gold complex based on cyclohexane-1,2-diamine [61]. A mol-ecule of ethanol is present in the lattice. It presents an orientationdisorder on a twofold rotation axis. The metal complex moleculespack head to tail to generate molecular chains along the c axis,which in turn pack into layers parallel to the ac plane (Fig. 9). Theseare separated by sheets hosting columns of disordered ethanolmolecules and Cl� counter ions, having hydrogen bonding interac-tions with the NH2 groups of adjacent layers.

Fig. 7. Effect of compounds 1 and 2 on cell growth in (A) PC-3 and (B) SGC-7901 cells. The cells were treated with 10 lM of compounds 1 and 2 for 1 day, 2 days and 3 days.The anti-proliferative effect was measured by an MTT assay. The results were expressed as the mean, SD. ⁄P < 0.05.

Fig. 8. X-ray structure of compound (1).

S.S. Al-Jaroudi et al. / Polyhedron 50 (2013) 434–442 439

The crystal structure of complex (2) is depicted in Fig. 10. In thiscase, the asymmetric unit contains two cationic molecules of thegold complex, two chloride counter ions and one crystallization

water molecule. Similarly to (1), in both molecules the gold(III)ion is bonded to two nitrogen atoms of the trans-cyclohexane-1,2-diamine ligand and two chloride ions (Fig. 10). The geometry

Fig. 9. Molecular packing in compound (1).

Fig. 10. X-ray structure of compound (2).

440 S.S. Al-Jaroudi et al. / Polyhedron 50 (2013) 434–442

is distorted square planar, with Au–N and Au–Cl bond distances inthe ranges 2.029(6)–2.054(7) and 2.259(3)–2.276(2) Å, respec-tively, and with similar N–Au–N bond angles of 84.1(2) and84.3(2)�, in addition to Cl–Au–Cl bond angles in the range91.4(1)–93.81(8)�. The coordination sphere bond distances andbond angles are similar to those of compound (1). The two cyclo-hexyl rings adopt a chair conformation with N1–C1–C6–N2 andN3–C7–C12–N4 torsion angles of 55.78 and 52.33�, respectively.Hydrogen bonding interactions take place between the aminogroups and the chloride counter ions.

3.6. Effect of compounds (1), (2) and (3) on cell proliferation

The bioassay tests were completed for compounds (1)–(3) un-der various experimental conditions. The cytotoxicity assay wasperformed with various concentrations of the synthesized gold(III)

complexes on PC-3 and SGC-7901 cells. The experimental PC-3 andSGC-7901 cells were treated with various concentrations of (1), (2)and (3) for 24–72 h, the cell viability was determined as describedabove by an MTT assay and the results are shown in Tables 10 and11, as well as in Figs. 1–7. As depicted in Figs. 1–3, the cis-(±)-1,2-(DACH)-gold complex exhibited potentially high activity againstthe gastric cancer cell SGC-7901 and human prostate cancer cellsafter 24 and 72 h of treatment with 10 lM, whereas, trans-(±)-1,2-(DACH) and purely chiral trans-(�)-1,2-(DACH) gold complexesshowed moderate inhibition against SGC-7901 and PC-3 cell linesunder the same assay experimental conditions. From Figs. 4–6, itis also quite clear that the gold(III) complexes under study showeda concentration dependent cytotoxic effect on cancerous PC-3 andSGC-7901 cells. It can be concluded from Figs. 2, 3, 5 and 6 thatthere is no significant difference in the bioactivity between thetrans-(1R,2R)-(DACH) isomer and the trans-(1S,2S)-(DACH) isomer.

Table 10Effect of compound (1) on cell/proliferation and the cell cycle of the PC3 and SGC-7901 cell lines (Mean, SD) after incubation for 24 and 72 h.

PC3 Cell line SGC-7901 Cell line

Group Day 1 (24 h) Day 3 (72 h) Day 1 (24 h) Day 3 (72 h)Control 0.75016 ± 0.02511 1.3910 ± 0.11711 0.54516 ± 0.02483 1.091 ± 0.068(1) 0.70412 ± 0.29933 0.81748 ± 0.17350 0.79107 ± 0.40634 0.85672 ± 0.23955

Table 11Cytotoxicity of compound (1) towards different tumor cell lines. The data werecollected after 72 h exposure to the compound.

Compound SGC-7901 PC3

(1) 8.5 ± 0.23 8.1 ± 0.17

S.S. Al-Jaroudi et al. / Polyhedron 50 (2013) 434–442 441

To the best of our knowledge, these are the first bioassay tests thathave been reported for gold(III) complexes based on cyclohexane-1,2-diamine.

In the time dependent activity studies, it is revealed that after72 h of the experiment for (1) on the PC-3 cell, the cell proliferationis bit higher than that of the SGC-7901 cells at a fixed 10 lM con-centration (Fig. 1). Furthermore, in Fig. 7, the cytotoxicity resultsdemonstrate that compound (1) at 10 lM concentration has ahigher cytotoxic effect in comparison with the same concentrationof compound (2).

4. Conclusion

Gold, along with its therapeutic and beneficial effect on humanhealth, is amongst the most ancient of all metals used in medicine.The use of gold complexes in modern medicine has allowed infor-mation regarding toxicological and clinical administration to be-come available, along with valuable studies concerning itsmetabolism and molecular targets. Therefore, gold has becomeone of the most promising metals for drug development in medi-cine. Three mono gold(III) complexes based on DACH with differentconfigurational structures were prepared. These gold(III) com-plexes were characterized using elemental analyses, solution andsolid NMR, UV, IR, far-IR spectroscopy and X-ray crystallography.The analytical data strongly support the formation of the[(DACH)AuCl2]Cl type complex. Also, X-ray crystallography dem-onstrates that the gold coordination sphere of this complex has adistorted square planar geometry. According to our biological as-says, complex (1), with a cis configuration, is a more promisingcandidate as an anti-cancer agent than the trans isomers, com-plexes (2) and (3). The exact mechanisms are not clearly known,but the inhibitory effect of [(cis-DACH)AuCl2]Cl on the proliferationof rapidly dividing cells may be attributed to the induction of cellcycle blockage, interruption of the cell mitotic cycle, programmedcell death (apoptosis) or premature cell death (necrosis). Therefore,[(cis-DACH)AuCl2]Cl might be a promising chemo preventative andchemotherapeutic agent against human gastric carcinogenesis. Asthe cytotoxic activity of the [(cis-DACH)AuCl2]Cl complex is hightowards some cancer cell lines, further biological evaluation forthis class of complex is worthy of effort, especially in order to eval-uate activities in vivo.

Acknowledgement

The author(s) would like to acknowledge the support providedby King Abdulaziz City for Science and Technology (KACST)through the Science & Technology Unit at King Fahd Universityof Petroleum & Minerals (KFUPM) for funding this work throughProject No. 10-BIO1368-04 as part of the National Science, Tech-nology and Innovation Plan.

Appendix A. Supplementary data

CCDC numbers 831613 and 850216 contain the supplementarycrystallographic data for complexes 1 and 2, respectively. Thesedata can be obtained free of charge from The Cambridge Crystallo-graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif Sup-plementary data associated with this article can be found, in theonline version, at http://dx.doi.org/10.1016/j.poly.2012.11.034.

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