Platinum(II) complexes of 4-methoxy- and 4-chlorobenzoic acid hydrazides. Synthesis, characterization, and cytotoxic effect

i ELSEVIER

Platinum(lI) Complexes of 4-Methoxy- and 4-Chlorobenzoic Acid Hydrazides. Synthesis, Characterization, and Cytotoxic Effect Nicolay Dodoff, Konstantin Grancharov, and Nadejda Spassovska Institute of Molecular Biology, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria

ABSTRACT The complexes [Pt(NHa)(pmbah)CI2], [Pt(NHa)(pcbah)Cl2], [Pt(pmbah)2X2] and [Pt(pcbah)2X 2] (pmbah = 4-methoxybenzoic acid hydrazide, pcbah = 4-chlorobenzoic acid hydrazide; X = Cl, Br, I) have been synthesized and characterized by elemental analysis, electric conductivity, ~H NMR, IR, and electronic spectra. A cis-square planar structure with hydrazide ligands coordinated via the NH 2 groups has been proposed for these compounds. The complexes, but not the free iigands, have shown a strong growth inhibitory effect in Friend leukemia cells in vitro, most of which are more active than cisplatin.

INTRODUCTION As a result of our research on new analogues of the anticancer drug cisplatin, we recently reported [1] the preparation, spectroscopic characterization, and significant cytotoxic effects of a series of platinum(II) coordination compounds with benzoic- and 3-methoxybenzoic acid hydrazides. The structure of one of these complexes was further confirmed by single crystal x-ray diffraction [2]. The motivation to study platinum complexes of hydrazide ligands was stated in [1]. Here we only note some new communications about the antibacterial and antifungal activity of hydrazide derivatives [3] and their metal complexes [4, 5] that indicates the current interest in such compounds as potential biologically active substances. With the present work we expand the series of platinum complexes mentioned above with those of 4-methoxybenzoic acid hydrazide (pmbah) and of 4-chloro-

Address reprint requests and correspondence to: Dr. N. Dodoff, Institute of Molecular Biology, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Block 21, 1113, Sofia, Bulgaria.

Journal of InorganicBiochemistry, 60, 257-266 (1995) © 1995 Elsevier ScienceInc., 655 Avenue of the Americas, NY, NY 10010

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benzoic acid hydrazide (pcbah). Although two of these complexes, [Pt(pmbah)2C12 ] and [Pt(pmbah)zBr 2], have earlier been reported by Kharitonov et al. [6], we included them in our study for fuller characterization and also to be tested for cytotoxic activity. EXPERIMENTAL

Starting Materials K2[PtCI 4] and c/s-[Pt(NH3)2CI 2] were prepared according to [7], and K[Pt(NH3)C13 ] was prepared according to [8]. The ligands pmbah and pcbah were synthesized following [9]. The remaining reagents and solvents were AR grade commercial products.

Preparation of the Complexes The procedures for preparation of the complexes of pmbah and pcbah were analogous to those described in [1], which was based on the method of Kharitinov et al. [6]. Briefly, the procedure for preparing [Pt(pmbah)2X 2] and [Pt(pcbah)2X 2] (X = C1, Br, I) consists of reacting K2[PtX 4] with an excess (25%) of the ligands in aqueous solution. The solutions of K2[PtBr 4] and KE[PtI 4] were obtained in situ from K2[PtCI 4] and KBr and KI, according to [10] and [11], respectively. KBr was taken in five-fold excess, whereas KI was in 12% excess with respect to KE[PtC14]. For preparation of [Pt(NHa)(pmbah)C12] and [Pt(NH3)(pcbah)Cle], K[Pt(NH3)C13] was reacted with 5% deficiency of the ligands in water. All the complexes separated out as precipitates, which were filtered, washed, and dried in vacuo. Yields were 65-90%.

Analyses and Physical Measurements The elemental analyses were performed by routine microanalytical procedures (Institute of Organic Chemistry, Bulgarian Academy of Sciences). Melting ranges were determined with a Boetius heating-plate microscope. Electric conductivities of the complexes (1 × 10-3-M solutions) were measured at 25°C in distilled dimethylformamide (DMF) ( A = 9 . 5 × 10 - 7 ~')-1 cm -1) using a Radiometer CDM-3 conductometer. 1n NMR spectra were registered on a Bruker WM-250 spectrometer at 250 MHz in DMF-d 7 solutions and tetramethylsilane (TMS) as internal standard. Infrared spectra (4000-150 cm -1) were taken in CsI disks on a Bruker ISF-113 V spectrophotometer. Electronic spectra of the compounds in DMF solution and in solid state as Nujol mulls were recorded on a Beckman DU-650 spectrophotometer. In Vitro Cytotoxicity Assay The cytotoxic effect of the ligands and complexes on Friend leukemia (FL) cells was determined as described previously [1]. Briefly, FL cells (clone F 4N) were cultured in Dulbecco's modified Eagle medium containing 10% calf serum and passed every day at a concentration of 5 × 105 cells/ml. The compounds studied were dissolved immediately before use in dimethylsulfoxide (DMSO) to obtain stock solutions of various concentra-

PT(II) COMPLEXES OF PMBAH AND PCBAH

259

tions. Each of these solutions was then used at 1% concentration in the experiments. Control cells were incubated in the presence of 1% DMSO. The final concentration of DMSO did not affect the growth and the viability of the cells. The cells were incubated in culture medium with the test compounds for 24, 48, and 72 h and counted thereafter hemocytometrically. The number of dead cells was determined by staining with trypan blue. The average of two determinations was calculated. The 50% inhibitory dose (IDs0) was defined as drug concentration that reduced the number of living cells by 50%. In Vivo Antitumor Evaluation

Complexes I and V were tested against L1210 leukemia. BDF 1 mice (20-22 g) were inoculated i.p. with L1210 cells (1 × 105, suspended in 0.1 ml of saline). The complexes were administrated i.p. as saline suspensions in doses of 21, 42, and 84 mg/kg for I and of 10, 21, and 42 mg/kg for V, at the first, fifth, and ninth day after inoculation. The antileukemic activity was evaluated as the increased survival time of the treated animals (T) in comparison to that of control animals (C), expressed as T/C%. RESULTS AND DISCUSSION Characterization of the Complexes In Table 1 the formulae, analytical results, and some physical data for the prepared complexes are given. The complexes are yellow-colored solids that decompose upon heating; they are soluble in DMF and in DMSO, and are practically insoluble in water.

Electric Conductivity. The freshly prepared DMF solutions of all the complexes exhibited molar electric conductivity values (Table 1) representative for nonelectrolytes [12], which indicates their nonionic character. The A m values measured 24 h after dissolution of the complexes were higher than the initial values, suggesting that solvolysis to ionic species had occurred to some extent. Judging by the conductivity values, the degree of solvolysis should be highest for the iodo complexes.

1H NMR Spectra. The IH NMR spectral data for freshly prepared DMF-d 7 solutions of the compounds studied are presented in Table 2. As a solvent, DMF, being a weaker donor, was preferred to DMSO because in DMSO the platinum(II) complexes undergo considerable solvolysis [1, 13, 14]. The signals in the spectra of the studied complexes were assigned on the basis of literature data for pmbah and pcbah [15, 16] and for some ammonia-containing Pt(II) complexes [8]. D20 exchange was applied to confrm the assignment of nitrogen-bound protons. The most characteristic feature of the spectra is the considerable downfield shift (average 3.6 ppm) of the signals of the NH 2 protons of the complexes in comparison to the free ligands. At the same time, the signals of the NH protons were much less affected (average 1 ppm). The picture is analogous to that observed by us previously [1]. Moreover, a downfield shift of the same order has been registered for the proton signals of coordinated NH 2 groups in the spectra

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'~. ~. ~. ~. ~. ~

. . . . . .

0 0 0

cq

r~

? ×

eq

U

z

U

~.

~

~

z

K

K

K

Z~ z~ ~ U

PT(II) COMPLEXES OF PMBAH AND PCBAH

261

TABLE 2. 1H NMR Spectral Data (6, ppm) for DMF-d 7 Solutions of the Ligands and Complexes Compound

ArH

NH 2a

NH~

3.86 s

6.96-7.07 m

4.55 s

9.64 s

I

3.89 s

7.87 8.03 m 7.01 7.12 m 7.90-8.01 m

8.03 s

10.33 s

II

3.89 s

8.22 s

Ill.60 s

III

3.89 s

8.17 s

10.67 s

IV

3.88 s

m m m m m m

8.02 s

10.78 s

pcbah

7.49 7.65 m

4.61 s

9.86 s

V

7.89-8.05 m 7.54-7.65 m

8.11 s

10.68 s

8.29 s

10.92 s

8.24 s

11.00 s

8.09 s

1 l.l I s

pmbah

VI VII VIII

CH 3

NH 3"

4.34 s, br

6.98-7.13 7.89 8.03 6.98-7.10 7.87-8.03 6.99-7.15 7.80-8.01

4.32 s, br

7.90-8.(12 7.55-7.62 7.88 8.08 7.56-7.65

m m m m

7.90-8.03 m 7.59 7.70 m 7.85-8.07 m

" In the s p e c t r a o f t h e c o m p l e x e s , a d d i t i o n a l m i n o r signals w e r e o b s e r v e d in the r a n g e s of 4.18-4.55, 7.52-8.82, a n d 9 . 2 6 - 1 1 . 1 3 p p m , respectively.

of a number of Pt(II) amine complexes [17]. This gives us a reason to consider that in the complexes discussed, the ligands pmbah and pcbah are coordinated through the NH 2 groups. The signals of the NH 3, NH 2, and NH protons were accompanied by several weaker peaks in the regions of 4.18-4.55, 7.52-8.82, and 9.26-11.13 ppm, respectively; they were most intensive for the iodo complexes. As mentioned previously, the iodo complexes exhibited the highest electric conductivity. Upon standing, the intensity of these minor peaks increased at the expense of the major peaks. The features described resemble those observed for DMSO solutions of similar Pt(II) complexes [1], except for the much lower intensity of the additional signals in the present case, and are in accordance with the regularities found by Kerrison and Sadler [13, 14] for DMSO solvolysis of diamminedihalogenoplatinum(II) complexes. The above-mentioned regularities allow us to suppose that the additional signals in the spectra of the studied complexes are due to their solvolysis products.

Infrared Spectra. IR spectral data for the ligands and complexes as CsI disks are collected in Table 3. The assignments were done by taking into account the data for benzoic acid hydrazide [18, 19] and its Pt(II) complexes [20], 4-chlorobenzoic acid hydrazide [21], 2-, 3-, and 4-methoxybenzoic acid hydrazides and their Pt(II) [6] and other metal complexes [22, 23], as well as data for some ammine Pt(II) complexes [24, 25]. Here we should mention that some differences were observed between the spectra of our complex III and that reported in [6], e.g., in the range of 1335-1300 c m - 1 and in the far IR region (vide infra).

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T A B L E 3. I R Spectral Data (~, c m - 1 ) for the Ligands and Complexes

Compound pmbah

I

II

III

IV

pcbah

V

VI

VII

VIII

v(NH3), v(NH2), v(NH)

A m i d e I, 8(NH2), ~a(NH3)

3332 s 3325 s 3260 sh 3210 w 3293m 3232 m 3200 m 3162 sh 3108 w 3284 s 3199m 3165 sh 3076m 3287m 3180m 3127m 3090m 3251m 3205m 3173 sh 3093m 3308 s 3226 s 3158 sh 3288 s 3191m 3134m 3098m 3296m 3187m 3168 sh 3100m 3294 s 3181m 3101m 3306m 3187m 3087m

to(NH2), tSs(NH3) , v(C-C)Ar, t~(C-H)Ar

v(Pt-X)

v(C-C)Ar

A m i d e II

1670 sh 1620 s

1610 sh 1578m

1538m

1342m 1327m 1308m

--

1675m 1650 sh 1545 sh

1606 s 1578 m

1530m

1324m 1317 sh 1302 s

331 s 325 s

1664 s

1606 s 1592 sh 1570m

1533m

1323m 1314 sh 1300 s

340 s 328 s

1665 s 1636 sh 1618 s

1609 sh 1577m

1550 sh 1536m

237 s 227 s

1665 sh 1635 s

1610 s 1585 sh 1568m

1545m

1335m 1326m 1314 sh 1300m 1325m 1308m

200 s 192 s

1664 s 1619 s

1600 sh 1563 s

--

1348 s

--

1670 s 1651 s

1593 s 1570m

1524m

1320 s 1304 sh

332 s 326 s

1670 s 1650 sh

1594 s 1569m

1524m

1322 s 1304m

336 s 328 sh

1669 s 1648m

1593m 1578m 1568m 1598m 1565m

1518m

1314 s 1303m

237m 230m

1522m

1320 s 1301 sh

188m 185m

1667 s

T h e b a n d s in t h e r a n g e o f a b s o r p t i o n o f t h e N - H s t r e t c h i n g v i b r a t i o n s in t h e s p e c t r a o f t h e c o m p l e x e s w e r e s h i f t e d (as a w h o l e by 1 0 0 - 4 0 c m - 1 ) to l o w e r f r e q u e n c y as c o m p a r e d t o t h e f r e e ligands. T h i s shift s h o u l d b e a t t r i b u t e d to t h e p a r t i c i p a t i o n o f t h e N H 2 g r o u p s in c o o r d i n a t i o n to t h e p l a t i n u m [6, 20]. It is m o r e difficult t o assign t h e v i b r a t i o n s o f t h e c o m p l e x e s in t h e r e g i o n b e l o w 1670 c m -1 w i t h c e r t a i n t y . E s p e c i a l l y f o r t h e r a n g e o f 1 6 7 0 - 1 5 8 0 c m -1, d i f f e r e n t r e s e a r c h e r s h a v e g i v e n d i f f e r i n g a s s i g n m e n t s f o r t h e b a n d s in t h e s p e c t r a o f a r o m a t i c h y d r a z i d e m e t a l c o m p l e x e s ; cf., f o r e x a m p l e , [6], [20], [23], [26], a n d [27]. T h e i n t e r p r e t a t i o n o f t h e s p e c t r a is c o m p l i c a t e d by t h e a b s o r p -

PT(II) COMPLEXES OF PMBAH AND PCBAH

263

tions of the aromatic ring in the intervals 1610-1320 cm 1 [skeletal v(C-C)], 1300-1020 cm -1 [6(C-H)], and below 1000 cm-1 (mostly out-of-plane deformations) [20, 28]. Nevertheless, due to the relatively small influence of the coordination, the bands in the range of 1610-1565 cm -~ in the spectra of the studied complexes should be ascribed to v(C-C) vibrations, rather than to the 6(NH 2) modes. The mutual position of the amide I and 6(NH 2) bands is affected by the coordination, and in some cases (complexes II and VIII) their overlapping results in the registration of only one band in the range of 1670-1618 cm We could not pick out the bands of the NH 3 vibrations (v, 6,~, and 8~), since in the ranges where they should appear [24, 29, 30], the absorptions of the v(NH2), v(NH), 6(NH2), and 6o(NH2) modes, respectively, were registered. However, in the spectrum of V, a band was observed at 806 cm--~ which lacks the spectra of pcbah and its remaining complexes. This band could be ascribed to p(NH 3) vibration [24, 25, 30]. In accordance with literature data [6, 20, 31], the bands assignable to Pt-C1 and Pt-Br stretching vibrations were found in the intervals of 340-325 and 237-227 cm 1, respectively. Due to their relatively high intensity they were easily identified, despite the absorption of the ligands themselves. Kharitonov et al. [6] have pointed out three bands (at 248, 238, and 230 cm l) of v(Pt-Br) for their complex of the formula [Pt(pmbah)zBr2], whereas we observed only two bands (at 237 and 227 cm -l) assignable to v(Pt-Br) in the spectrum of III. Taking into account the literature data for some diaminediiodoplatinum(II) complexes [32, 33], the bands in the range of 200-185 cm ~ registered in the spectra of IV and VIII could be assigned to Pt-I stretching vibrations. Their assignment is, however, less certain (especially in the case of VIII) because of overlap with ligand absorptions. The appearance of two bands (u~ and v,,) for the platinum-halogen stretching vibrations is an indication of the cis configuration [31, 34] of the complexes. Some of the weak bands in the range of 583-490 cm-1 in the spectra of the complexes could tentatively be ascribed to Pt-N stretchings [6, 35].

Electronic spectra. In water solution pmbah and pcbah exhibited a strong absorption with maxima at 39,800 cm-1 (e = 14,800 l mol 1 cm 1) and 42,400 cm ~ ( e = 13,500 1 mol 1 cm 1), respectively, and shoulders in the range of 37,000-35,000 cm -1. According to [36], the peaks should correspond to 7r ~ ~*, and the shoulders should correspond to n ~ ~r* transitions. This intensive absorption of the ligands should mask the high energy bands of the metal chromophore in the spectra of the complexes. Data from the electronic spectra of the complexes in DMF solution and in solid state (Nujol mulls) are presented in Table 4. Because of the scatter of the mull, the relatively weak absorption of the chloro and bromo complexes in the near UV and visible region could not be registered in the solid state spectra. This was, however, possible for the highly absorbing iodo complexes. In the spectra of all the complexes a couple of shoulders were observed in the ranges of 31,100-27,000 and 28,100-23,600 cm -1 on the low frequency contour of the ligand absorption. They should be attributed to d-d transitions of the metal ion. The positions of these bands are in good agreement with an assignment to lAlg--) 1A2g and 1Alg--~ 3A2g , 3Big transitions, respectively, in square planar PtN2Hal 2 chromophores (effective symmetry D4h) [37, 38]. The red shift of the

264

N. Dodoff et aL

TABLE 4. Electronic Spectral Data for the Complexes ~'× 10 -3 (cm -1) (e, 1 m o 1 - 1 c m - 1 ) a Complex

Medium

I II III IV

1Alg --)

DMF DMF DMF DMF Solid DMF DMF DMF DMF Solid

V VI VII VIII

1A2g

1Alg --~ 3A2g , 3Big

31.1 (230) 30.8 (256) 29.4 (345) 27.8 (952) 27.5 31.0 (290) 30.9 (315) 29.5 (370) 27.5 (1190) 27.0

28.1 (79) 27.7 (11 l) 26.0 (141) 24.3 (470) 23.6 27.5 (90) 27.5 (120) 26.0 (143) 24.6 (707) 23.8

Shoulders; the wave numbers and extinction coefficients in the inflection points are given.

spectral bands in the order chloro, bromo, iodo complexes is in accordance with the positions of the halide ligands in the spectrochemical series [39]. By taking into account the stoichiometry, molar electric conductivity values, and spectroscopic characteristics of the complexes prepared, the structures in Figure 1 could be ascribed. Cytotoxic Effect The cytotoxic efficacy of the ligands pmbah and pcbah and their complexes was examined on FL cells in culture. The results, as expressed by the IDs0 values for different times of drug exposure are presented in Table 5. From a comparison of the numbers, the following conclusions could be drawn: As a whole, the complexes of 4-methoxy- and 4-chlorobenzoic acid hydrazides are more cytotoxic than those of benzoic- and 3-methoxybenzoic acid hydrazides [1]. The ammonia-containing complexes I and V are less toxic than the corresponding complexes II and VI, without NH 3 ligands. The complexes of pcbah are more inhibitory in comparison with those of pmbah. Concerning the effect of the anionic ligands, the following order of increasing activity was established: Cl < Br < I. It is worth noting that compounds III, IV, and VI-VIII were more toxic against FL cells than cisplatin, used as a positive control; complex VIII exerted the highest cytotoxicity in this study. The ligands pmbah and pcbah did not show any appreciable activity at concentrations up to 100 ~M.

H 31'4

Cl

"pt ~

/

\

R~

O C-N'H-NI-I2

~

X

~Pt( x

0

0 R -- H3CO, CI; X -- Cl, Br, I FIGURE I.

PT(II) COMPLEXES

OF PMBAH

AND PCBAH

265

TABLE 5. In Vitro Cytotoxicity of the Ligands and Complexes in Friend Leukemia Cells ID~o (/.tM) Compound

24 h b

pmbah I

II III IV pcbah V VI VII VIII Cisplatin

6.8 6.5 4.0 3.2 5.5 4.0 3.8 2.5 5.8

48 h b c 6.8 3.9 3.7 2.5 c 5.0 3.9 3.5 1.3 4.9

72 h b 6.9 4.4 3.7 3.5 3.9 2.9 3.1 1.2 3.9

a Drug concentration that reduces the number of living cells by 50%. b Time after drug treatment. c No inhibition of cell growth at concentration up to 100 /zM.

C o m p l e x e s I a n d V w e r e t e s t e d in vivo against L1210 l e u k e m i a . T h e s e p r e l i m i n a r y e x p e r i m e n t s r e v e a l e d a m o d e r a t e activity ( m a x i m u m value o f T / C = 137%, at a d o s e o f 84 m g / k g ) for c o m p l e x I a n d a m a r g i n a l activity ( m a x i m u m value o f T / C = 125%, at a d o s e of 42 m g / k g ) for c o m p l e x V. A full a c c o u n t o f the in vivo a n t i t u m o r effect of the s t u d i e d c o m p l e x e s will be p r e s e n t e d at a l a t e r stage.

The authors thank Mrs. R. Gugova for preparing the ligands pmbah and pcbah, Dr. M. Spassoca for recording some of the NMR spectra, and the National Fund for Scientific Research at the Bulgarian Ministry of Education and Science for the financial support (grant Ch-lll).

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Received September 30, 1994; accepted January 17, 1995