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Osmium NAMI-A analogues: synthesis, structural and spectroscopic characterization, and antiproliferative properties.
Inorg.Chem.2007, 46, 5023- 5033
Osmium NAMI-A Analogues: Synthesis, Structural and Spectroscopic
Characterization, and Antiproliferative Properties
Berta Cebria´n-Losantos, Artem A. Krokhin, Iryna N. Stepanenko, Rene Eichinger, Michael A. Jakupec,
Vladimir B. Arion,* and Bernhard K. Keppler*
Institute of Inorganic Chemistry, Faculty of Chemistry, UniVersity of Vienna, Wa¨hringerstrasse 42,
A-1090 Vienna, Austria
ReceivedMarch2,2007
Theosmium(III)complex[(DMSO)H][trans-OsIIICl(DMSO)](1)hasbeenpreparedviastepwisereductionofOsO
2 4 2 4
inconcentratedHClusingNH(cid:226)2HClandSnCl(cid:226)2HOinDMSO.1reactswithanumberofazoleligands,namely,
2 4 2 2
indazole (Hind), pyrazole (Hpz), benzimidazole (Hbzim), imidazole (Him), and 1H-1,2,4-triazole (Htrz), in organic
solvents, affording novel complexes (Hind)[OsIIICl(Hind)(DMSO)] (2), (Hpz)[OsIIICl(Hpz)(DMSO)] (3), (Hbzim)-
2 4 2 4 2
[OsIIICl(Hbzim)(DMSO)](4),(Him)[OsIIICl(Him)(DMSO)](6),and(Htrz)[OsIIICl(Htrz)(DMSO)](7),whichareclose
4 2 4 2 4
analoguesoftheantimetastaticcomplexNAMI-A.Metathesisreactionof4withbenzyltriphenylphosphoniumchloride
in methanol led to the formation of (PhPCHPh)[OsIIICl(Hbzim)(DMSO)] (5). The complexes were characterized
3 2 4
by IR, UV- vis, ESI mass spectrometry, 1H NMR spectroscopy, cyclic voltammetry, and X-ray crystallography. In
contrasttoNAMI-A,2- 4,6,and7arekineticallystableinaqueoussolutionandresistanttohydrolysis.Surprisingly,
they show reasonable antiproliferative activity in vitro in two human cell lines, HT-29 (colon carcinoma) and SK-
BR-3(mammarycarcinoma),whencomparedwithanalogousrutheniumcompounds.Structure- activityrelationships
and the potential of the prepared complexes for further development are discussed.
Introduction Oneofthereasonsisanoptimalchemicalreactivityofthese
compoundsunderphysiologicalconditions.Certainisostruc-
Currentinterestinrutheniumantitumordrugswasstimu-
turalosmiumanalogues,forexample[(Ł6-biphenyl)Os(en)-
lated by recent phase I clinical studies of two complexes,
Cl]BF ,whichentersubstitutionreactionsmuchmoreslowly
4
namely,(H im)[trans-RuCl (Him)(DMSO)](NAMI-A)1and
2 4 than the corresponding ruthenium complexes, were found
(H ind)[trans-RuCl (Hind) ](KP1019,FFC14),2thefirstas
2 4 2 to be inactive in A2780 ovarian cancer cells.4
anagent,whichinhibitstheprocessofmetastasisformation,
Quite recently Sadler et al.5 have demonstrated that the
andthesecondasaneffectivemeansagainstprimarytumors
reactivityofosmiumcomplexes,particularlythehydrolysis
and metastases, in particular, among others, colon carcino-
and nucleobase binding, can be effectively tuned by sys-
mas. The quest for novel ruthenium compounds with
tematic variation of ancillary ligands. The same authors
potentialantitumorpropertieshasledtosynthesisofalarge
expressedtheopinionthatinusingthisapproachthedesign
varietyofarenecomplexeswithpiano-stoolstructureofthe
andsynthesisofosmiumcomplexeswithpotentialantitumor
type [(Ł6-arene)Ru(L-L)Cl]X, where arene is biphenyl,
properties can be realized. Nevertheless, studies on the
benzene, or p-cymene, and L-L is ethylenediamine or
antitumor activity of osmium complexes are still very
acetylacetone,andXisacounterion.3Thecomplexesshowed scarce.4,6-8
antitumor activity both in vitro and in vivo, which in some
caseswascomparablewiththatofcisplatinandcarboplatin. (3) (a)Morris,R.E.;Aird,R.E.;Murdoch,P.D.S.;Chen,H.;Cummings,
J.;Hughes,N.D.;Parsons,S.;Parkin,A.;Boyd,G.;Jodrell,D.I.;
Sadler,P.J.J.Med.Chem.2001,44,3616-3621.(b)Aird,R.E.;
*To whom correspondence should be addressed. E-mail: Cummings, J.; Ritchie, A. A.; Muir, M.; Morris, R. E.; Chen, H.;
vladimir.arion@univie.ac.at (V.B.A.), bernhard.keppler@univie.ac.at Sadler,P.J.;Jodrell,D.I.Br.J.Cancer2002,86,1652-1657.
(B.K.K.). (4) Dorcier,A.;Dyson,P.J.;Gossens,C.;Rothlisberger,U.;Scopelliti,
(1) Alessio, E.; Mestroni, G.; Bergamo, B.; Sava, G. Curr. Top. Med. R.;Tavernelli,I.Organometallics2005,24,2114-2123.
Chem.2004,4,1525-1535. (5) Peacock, A. F. A.; Habtemariam, A.; Fernandez, R.; Walland, V.;
(2) Hartinger, C. G.; Zorbas-Seifried, S.; Jakupec, M. A.; Kynast, B.; Fabbiani,F.P.A.;Parsons,S.;Aird,R.E.;Jodrell,D.I.;Sadler,P.
Zorbas,H.;Keppler,B.K.J.Inorg.Biochem.2006,100,891-904. J.J.Am.Chem.Soc.2006,128,1739-1748.
10.1021/ic700405y CCC: $37.00 © 2007 American Chemical Society Inorganic Chemistry, Vol. 46, No. 12, 2007 5023
PublishedonWeb05/12/2007
Cebria´n-Losantos et al.
Attempts to extend the synthetic work onto synthesis of
NAMI-A type complexes with metal ions other than ruthe-
nium have also been undertaken and are well documented
intheliterature.Inparticular,complexesofrhodium(III)and
iridium(III)havebeensynthesizedandtheirpropertieshave
been investigated.9,10
Biochemical and cell biological studies show reactivity
andcytotoxicityprofilesdifferentfromthoseofruthenium-
(III)NAMI-Atypecompounds.Inparticular,thecomplexes
neither bind strongly to bovine serum albumin nor inhibit
markedly the proliferation of human tumor cell lines.
Surprisingly,osmiumanaloguesofNAMI-Ahavenotbeen
reportedsofar,althoughtheirsynthesisandcomparisonwith Figure1. Anticancerosmium(III)NAMI-Aanalogues;underlinedcom-
ruthenium compounds appears to be more desirable from plexeshavebeencharacterizedinthisworkbyX-raycrystallography.
the point of view of the position of these metals in the
periodic table. The evaluation of NAMI-A analogues with
metals other than ruthenium, specifically those of osmium-
(III),hasbeenmainlyhinderedbysyntheticlimitations.The
synthesisofNAMI-Aandrelatedrhodium(III)andiridium-
(III) compounds was straightforwardly realized because of
the availability of starting compounds [(DMSO) H] [trans- Figure2. Heterocyclicazoleligands.
2
MCl (DMSO) ](M)Ru,Rh,Ir).11,12Thereactionofthese
4 2
compounds with azole ligands in organic solvents enabled osmium complexes with those of the NAMI-A family of
the synthesis of the desired compound families in good compounds.
yields.Althoughevidencefortheformationof[trans-OsCl 4 - We show in this article that [(DMSO) 2 H][trans-OsIIICl 4 -
(DMSO) 2 ]- (1) in solution was reported,13 the compound (DMSO) 2 ]canbeefficientlypreparedbystepwisereduction
ofOsO withhydrazinedihydrochlorideinconcentratedHCl
has not been isolated as a solid so far. Being intrigued by 4
to OsIV14 and then with SnCl (cid:226)2H O/DMSO to OsIII and
this fact, we directed our efforts on (i) the isolation of this 2 2
OsII.15Wealsodescribethenearestcongeners,resultingfrom
osmiumcompoundanditsfullcharacterization,(ii)thestudy
reactionsof[(DMSO) H][trans-OsCl (DMSO) ]withazole
of the reactivity of [(DMSO) H][trans-OsCl (DMSO) ] 2 4 2
2 4 2
ligands (Figure 2), that are closely related to the well-
towardazoleligandsandfullcharacterizationoftheresulting
characterizedNAMI-Atyperuthenium(III)compounds16-18
osmiumanaloguesofNAMI-Atypecompounds(Figure1),
with a d5 low-spin electronic configuration and show that
(iii)cytotoxicityassaysofthenovelosmium(III)compounds,
osmium(III)complexesarealsoworthbeinginvestigatedas
and (iv) comparison of hydrolytic stability of the prepared
potential antitumor drugs.
(6) Dorcier,A.;Ang,W.H.;Bolan˜o,S.;Gonsalvi,L.;Juillerat-Jeannerat, Experimental Section
L.;Laurenczy,G.;Peruzzini,M.;Phillips,A.D.;Zanobini,F.;Dyson,
P.J.Organometallics2006,25,4090-4096.
Chemicals.OsO (99.8%)waspurchasedfromJohnsonMatthey
(7) (a)Craciunescu,D.G.;Molina,C.;Parrondo-Iglesias,E.;Alonso,M. 4
in 1 g ampoules, NH(cid:226)2HCl from Fluka, and SnCl(cid:226)2HO from
P.;Doadrio-Villarejo,J.C.;GutierrezRios,M.T.;DeFrutos,M.I.; 2 4 2 2
CertadFombona,G.;GastondeIriarte,E.An.RealAcad.Farm.1991, Merck.Theazoleligands,indazole,pyrazole,imidazole,benzimi-
57,221-240.(b)Doadrio,A.;Craciunescu,D.;Ghirvu,C.;Nuno,J.
dazole,and1H-1,2,4-triazole,werefromAldrich.9-Methyladenine
C.An.Quim.1977,73,1220-1223.(b)Craciunescu,D.G.;Parrondo
(MeAde)waspreparedasreportedintheliterature.19
Iglesias,E.;Alonso,M.P.;Molina,C.;DoadrioLopez,A.;Gomez,
A.;Mosquerra,R.M.;Ghirvu,C.;GastondeIriarte,E.An.R.Acad. SynthesisofComplexes.trans-OsIICl 2 (DMSO) 4 and[(DMSO) 2 -
Farm.1988,54,16-45.(c)Craciunescu,D.G.;Molina,C.;Parrondo- H][trans-OsIIICl(DMSO)](1).NH(cid:226)2HCl(0.42g,4.00mmol)
4 2 2 4
Iglesias,E.;Alonso,M.P.;Doadrio-Villarejo,J.C.;GutierrezRios,
wasaddedtoOsO (1.00g,3.93mmol)inHCl(37%,25mL)and
M.T.;DeFrutos,M.I.;DeIriarte,E.;GastonFombona,G.C.;Ercoli, 4
N.An.R.Acad.Farm.1992,58,207-231.
(8) Peacock,A.F.A.;Parsons,S.;Sadler,P.J.J.Am.Chem.Soc.2007, (14) Brauer,G.HandbuchderPra¨paratiVenAnorganischenChemie;Bd.
129,3348-3357. III,1981;pp1742-1744.
(9) Mestroni,G.;Alessio,E.;SessantaoSanti,A.;Geremia,S.;Bergamo, (15) McDonagh,A.M.;Humphrey,M.G.;Hockless,D.C.R.Tetrahe-
A.;Sava,G.;Boccarelli,A.;Schettino,A.;Coluccia,M.Inorg.Chim. dron: Asymmetry1997,8,3579-3583.
Acta1998,273,62-71. (16) (a)Reisner,E.;Arion,V.B.;GuedesdaSilva,M.F.C.;Lichtenecker,
(10) Messori,L.;Marcon,J.;Orioli,P.;Fontani,M.;Zanello,P.;Bergamo, R.;Eichinger,A.;Keppler,B.K.;Kukushkin,V.;YuPombeiro,A.J.
A.;Sava,G.;Mura,P.J.Inorg.Biochem.2003,95,37-46. L.Inorg.Chem.2004,43,7083-7093.
(11) (a)Alessio,E.;Balducci,G.;Calligaris,M.;Costa,G.;Attia,W.M.; (17) (a) Alessio, E.; Balducci, G.; Lutman, A.; Mestroni, G.; Calligaris,
Mestroni, G. Inorg. Chem. 1991, 30, 609-618. (b) Alessio, E.; M.;Attia,W.M.Inorg.Chim.Acta1993,203,205-217.(b)Mura,
Sessanta o Santi, A.; Faleschini, P.; Calligaris, M.; Mestroni, G. J. P.;Camalli,M.;Messori,L.;Piccioli,F.;Zanello,P.;Corsini,M.Inorg.
Chem.Soc.,DaltonTrans.1994,13,1849-1855.(c)Haddad,Y.M. Chem.2004,43,3863-3870.
Y.;Henbest,H.B.;Trocha-Grimshaw,J.J.Chem.Soc.,PerkinTrans. (18) Alessio,E.;Mestroni,G.;Pacor,S.;Sava,G.;Spinelli,S.PCTInt.
11974,5,592-595. Appl.WO9013553,1990.
(12) Jaswal,J.S.;Rettig,S.J.;James,B.R.Can.J.Chem.1990,68,1808- (19) (a)Talman,E.G.;Bruening,W.;Reedijk,J.;Spek,A.L.;Veldman,
1817. N.Inorg.Chem.1997,36,854-861.(b)Charland,J.P.;PhanViet,
(13) (a)Komozin,P.N.Zh.Neorg.Khim.2000,45,662-674.(b)Komozin, M.T.;St-Jacques,M.;Beauchamp,A.L.J.Am.Chem.Soc.1985,
P.N.Zh.Neorg.Khim.1998,43,547-553. 107,8202-8211.
5024 InorganicChemistry,Vol.46,No.12,2007
OsmiumNAMI-Aanalogues
water(3mL).Thesolutionwasstirredatroomtemperaturefor7 ether(5mL),anddriedinvacuo.Yield: 0.06g,60%.Anal.Calcd
days. Afterward, the solvent was removed by rotary evaporation forC H ClNOOsS(M )647.45g/mol): C,29.68;H,2.96;N,
16 19 4 4 r
underreducedpressureat60(cid:176) C.Totheredresidue,SnCl (cid:226)2HO 8.65; S, 4.95. Found: C, 29.61; H, 3.04; N, 8.47; S, 4.82. ESI-
2 2
(0.80 g, 3.54 mmol) and DMSO (8 mL) were added, and the MSinMeOH(negative):m/z528[OsIIICl(Hbzim)(DMSO)]-,410
4
solution was held at 87 (cid:176) C for 1 h. The precipitated yellow solid [OsIIICl(DMSO)]-,332[OsIIICl]-.IR(KBr),selectedbands,cm-1:
4 4
trans-OsIICl(DMSO) wasfilteredoff,washedwithacetone(4(cid:2) 426(w),(cid:238)(Os-S);1016(s),F(CH);1067(vs),(cid:238)(SdO).UV-vis
2 4 3
15mL)andEt 2 O(4(cid:2)15mL),anddriedinvacuo.TheIRspectrum (MeOH), (cid:236) max , nm ((cid:15), M-1 cm-1): 377 (1186), 334 (6324), 279
of this compound was identical to that of trans-OsCl 2 (DMSO) 4 (13747)sh,273(19763),267(20553).UV-vis(H 2 O),(cid:236) max ,nm
prepared as described in the literature.15 The filtrate was allowed ((cid:15),M-1cm-1): 406(599)sh,370(1367),330(5096),277(11690),
tostandatroomtemperatureovernight,producingyellow-orange 270(13488),250(11091)sh.
crystalsoftheproduct.Thesewereseparatedbyfiltrationanddried (Ph PCH Ph)[trans-OsIIICl (Hbzim)(DMSO)] (5). Benzyl-
in vacuo. Yield: trans-OsIICl(DMSO) 0.34-0.56 g, 15-25%; 3 2 4
2 4 triphenylphosphoniumchloride(0.06g,0.15mmol)wasaddedto
[(DMSO)H][trans-OsIIICl(DMSO)]0.50-0.76g,20-30%.Anal.
2 4 2 asolutionof4(0.05g,0.10mmol)inmethanol(20mL),andthe
CalcdforCH ClOOsS (M )645.59g/mol): C,14.88;H,3.90;
8 25 4 4 4 r mixturewasstirredatroomtemperaturefor2h.Slowremovalof
S,19.87;Cl,21.97.Found: C,14.63;H,3.79;S,19.67;Cl,21.67.
solvent by rotary evaporation under reduced pressure led to
ESI-MSinMeOH(negative):m/z488[OsIIICl(DMSO)]-,410
4 2 precipitationofayellowsolid,whichwasfilteredoff,washedwith
[OsIIICl 4 (DMSO)]-,332[OsIIICl 4 ]-.IR(KBr),selectedbands,cm-1: diethylether(2(cid:2)5mL),anddriedinvacuo.Yield: 0.05g,60%.
416(w),(cid:238)(Os-S);909(vw),916(vw),936(w),947(w),969(vw),
Anal.CalcdforC H ClNOOsPS(M )881.73g/mol): C,46.31;
977 (vw), 1017 (s), F(CH 3 ); 1080 (s), (cid:238)(SdO); 1292 (vw), 1304 H,3.89;N,3.18. 3 F 4 o 3 u 4 nd: 4 C 2 ,46.61;H, r 3.64;N,3.17.ESI-MSin
(vw),1318(w),(cid:228)(CH 3 ).UV-vis(MeOH),(cid:236) max ,nm((cid:15),M-1cm-1): MeOH (negative): m/z 528 [OsIIICl (Hbzim)(DMSO)]-, 410
419(351)sh,348(4189),268(5077)sh.UV-vis(H 2 O),(cid:236) max ,nm [OsIIICl(DMSO)]-, 332 [OsIIICl]-. E 4 SI-MS in MeOH (posi-
((cid:15),M-1cm-1): 410(666)sh,374(2516)sh,344(6162),300(757) tive): m 4 /z 353, [PhPCHPh]+. X 4 -ray diffraction-quality crystals
3 2
sh,257(1174).SuitablecrystalsforX-raydiffractionstudywere
were grown by slow diffusion of methanol solutions of 4 and
selecteddirectlyfromthereactionvessel.
benzyltriphenylphosphoniumchlorideinanH-tube.
(Hind)[trans-OsIIICl(Hind)(DMSO)] (2). Indazole (0.04 g,
2 4 (Him)[trans-OsIIICl(Him)(DMSO)] (6). Imidazole (0.03 g,
0.31mmol)wasaddedto1(0.10g,0.15mmol)indryethanol(10 2 4
0.45mmol)wasaddedtoasuspensionof1(0.10g,0.15mmol)in
mL), and the mixture was held at 53 (cid:176) C for 2 h. The orange-red
acetone(10mL),andthemixturewasheldat53(cid:176) Cfor20h.The
solutionwasfilteredtoremovesolidimpuritiesandthenevaporated
reactionmixturewascooledtoroomtemperature,andtheyellow
almostcompletelyunderreducedpressure.Additionofhexaneto
solidwasfilteredoff,washedwithacetone(2(cid:2)5mL)anddiethyl
the remaining residue led to the formation of red crystals, which
ether(5mL),anddriedinvacuo.Yield: 0.07g,80%.Anal.Calcd
were filtered off, washed with diethyl ether (5 mL), and dried in
forCH ClNOOsS(M )547.34g/mol): C,17.55;H,2.76;N,
vacuo.Yield: 0.05g,50%.Anal.CalcdforC H ClNOOsS(M 8 15 4 4 r
)647.45g/mol): C,29.68;H,2.96;N,8.65 1 ; 6 S, 19 4.9 4 5. 4 Found: C, r 10.24;S,5.85;Found: C,17.61;H,2.64;N,10.18;S,5.47.ESI-
29.26; H, 2.96; N, 8.35; S, 4.83. ESI-MS in MeOH (negative): MS in MeOH (negative): m/z 478 [OsIIICl 4 (Him)(DMSO)]-, 410
m/z 528 [OsIIICl(Hind)(DMSO)]-, 410 [OsIIICl(DMSO)]-, 332
[OsIIICl
4
(DMSO)]-,332[OsIIICl
4
]-.IR(KBr),selectedbands,cm-1:
[OsIIICl]-. IR (K
4
Br), selected bands, cm-1: 43
4
2 (w), (cid:238)(Os-S);
435(m),(cid:238)(Os-S);1016(s),F(CH
3
);1065(vs),(cid:238)(SdO).UV-vis
1023(m 4 ),F(CH);1058(vs),(cid:238)(SdO).UV-vis(MeOH),(cid:236) ,nm (MeOH), (cid:236) max , nm ((cid:15), M-1 cm-1): 373 (869), 334 (3913). UV-
((cid:15),M-1cm-1): 3 378(1650),332(7317),298(21255)sh.U m V ax -vis vis(H 2 O),(cid:236) max ,nm((cid:15),M-1cm-1): 409(192)sh,371(1275),330
(HO),(cid:236) ,nm((cid:15),M-1cm-1): 408(168)sh,370(330),330(815),
(4996),254(2025).X-raydiffraction-qualitycrystalsof6Æ0.5EtOH
2 max
were grown by vapor diffusion of diethyl ether into an ethanol
296 (1361) sh, 285 (1485), 258 (1260). X-ray diffraction-quality
solutionofthecomplex.
crystalsweregrownbyvapordiffusionofn-hexaneintoasaturated
EtOHsolutionofthecomplex. (H 2 trz)[trans-OsIIICl 4 (Htrz)(DMSO)] (7). 1-H-1,2,4-Triazole
(Hpz)[trans-OsIIICl(Hpz)(DMSO)](3).Pyrazole(0.025g,0.37 (0.03g,0.45mmol)wasaddedtoasuspensionof1(0.10g,0.15
mmol 2 ) was added to 1 4 (0.10 g, 0.15 mmol) in dry methanol (10 mmol)inacetone(10mL),andthemixturewasheldat53(cid:176) Cfor
mL), and the mixture was held at 53 (cid:176) C for 2 h. Afterward the 1h.Aclearsolutionformedonheatingproducedayellowsolid,
yellowsolutionwasevaporatedunderreducedpressure,anddiethyl
whichwasfilteredoff,washedwithacetone(2(cid:2)5mL)anddiethyl
etherwasaddeddropwise.Theresultingredcrystalswerefiltered ether(5mL),anddriedinvacuo.Yield: 0.05g,60%.Anal.Calcd
off,washedwithdiethylether(5mL),anddriedinvacuo.Yield: forC 6 H 13 Cl 4 N 6 OOsS(M r )549.31g/mol): C,13.12;H,2.38;N,
0.05 g, 60%. Anal. Calcd for CH ClNOOsS (M ) 547.34 15.30;S,5.84.Found: C,13.32;H,2.31;N,15.61;S,5.81.ESI-
8 15 4 4 r
g/mol): C,17.55;H,2.76;N,10.24;S,5.86.Found: C,17.62;H, MSinMeOH(negative): m/z479[OsIIICl 4 (Htrz)(DMSO)]-,410
2.69; N, 10.23; S, 5.95. ESI-MS in MeOH (negative): m/z 478 [OsIIICl 4 (DMSO)]-,332[OsIIICl 4 ]-.IR(KBr),selectedbands,cm-1:
[OsIIICl 4 (Hpz)(DMSO)]-,410[OsIIICl 4 (DMSO)]-,332[OsIIICl 4 ]-. 434 (m), (cid:238)(Os-S); 1026 (br), F(CH 3 ); 1057 (vs), (cid:238)(SdO). UV-
IR (KBr), selected bands, cm-1: 436 (w), (cid:238)(Os-S); 1016 (s), vis (MeOH), (cid:236) max , nm ((cid:15), M-1 cm-1): 370 (2778), 336 (5555).
F(CH 3 ); 1056 (s), (cid:238)(SdO). UV-vis (MeOH), (cid:236) max , nm ((cid:15), M-1 UV-vis(H 2 O),(cid:236) max ,nm((cid:15),M-1cm-1): 409(329)sh,371(2983),
cm-1): 377 (330), 335 (5280). UV-vis (HO), (cid:236) , nm ((cid:15), M-1 333 (5786), 256 (2026). X-ray diffraction-quality crystals were
2 max
cm-1): 408(237)sh,372(1168),330(4865),236(6568).Suitable grownbyvapordiffusionofdiethyletherintoamethanolsolution
crystalsforX-raydiffractionstudywereselecteddirectlyfromthe ofthecomplex.
reactionvessel. Physical Measurements. Elemental analyses were carried out
(Hbzim)[trans-OsIIICl(Hbzim)(DMSO)] (4). Benzimidazole attheMicroanalyticalServiceoftheInstituteofPhysicalChemistry
2 4
(0.05g,0.45mmol)wasaddedtoasuspensionof1(0.10g,0.15 of the University of Vienna. Infrared spectra were obtained from
mmol)inacetone(10mL),andthemixturewasheldat53(cid:176) Cfor KBrpelletswithaPerkin-Elmer370FTIR2000instrument(4000-
2h.Theclearsolutionformedonheatingproducedayellowsolid, 400 cm-1). UV-vis spectra were recorded on a Perkin-Elmer
whichwasfilteredoff,washedwithacetone(2(cid:2)5mL),diethyl Lambda 20 UV-vis spectrophotometer using samples dissolved
Inorganic Chemistry, Vol. 46, No. 12, 2007 5025
Cebria´n-Losantos et al.
Table1. CrystalDataandDetailsofDataCollectionfor1-3and5-7
complex 1 2 3 5 6Æ0.5EtOH 7
empirical C8H25Cl4O4OsS4 C16H19Cl4N4OOsS C8H15Cl4N4OOsS C34H34Cl4N2OOsPS C9H18Cl4N4O1.5OsS C6H13Cl4N6OOsS
formula
fw 645.59 647.45 547.34 881.73 570.37 549.31
spacegroup P1h P21/n P21/c P21/n P21/c P1h
a(Å) 9.1652(4) 10.5903(4) 8.4670(2) 10.6249(17) 10.1758(4) 7.4444(4)
b(Å) 13.8866(14) 8.6393(3) 14.9489(4) 15.416(3) 16.1069(7) 8.0206(4)
c(Å) 16.4116(8) 22.6247(9) 13.0000(3) 20.809(3) 20.9749(9) 13.1209(7)
R(deg) 90.201(5) 92.973(3)
(cid:226)(deg) 90.130(2) 103.068(2) 97.585(1) 93.677(10) 92.605(3) 103.329(3)
(cid:231)(deg) 100.651(1) 93.293(3)
V(Å3) 2052.8(2) 2016.39(13) 1631.04(7) 3401.5(9) 3434.2(2) 759.36(7)
Z 4 4 4 4 8 2
(cid:236)(Å) 0.71073 0.71073 0.71073 0.71073 0.71073 0.71073
F calcd(gcm-3) 2.089 2.133 2.229 1.722 2.206 2.402
crystsize(mm3) 0.20(cid:2)0.10(cid:2)0.08 0.26(cid:2)0.20(cid:2)0.06 0.14(cid:2)0.14(cid:2)0.14 0.36(cid:2)0.26(cid:2)0.14 0.16(cid:2)0.05(cid:2)0.02 0.18(cid:2)0.14(cid:2)0.12
T(K) 100 100 296 296 100 100
(cid:237)(cm-1) 71.47 69.73 85.97 42.03 81.73 92.37
R1a 0.0320 0.0212 0.0183 0.0271 0.0328 0.0201
wR2b 0.0845 0.0577 0.0358 0.0617 0.0627 0.0451
GOFc 1.094 1.048 1.026 1.005 1.029 1.010
aR1)(cid:229) jjFo j-jFc jj/(cid:229) jFo j.bwR2){(cid:229) [w(Fo 2-Fc 2)2]/(cid:229) [w(Fo 2)2]}1/2.cGOF){(cid:229) [w(Fo 2-Fc 2)2]/(n-p)}1/2,wherenisthenumberofreflections,
andpisthetotalnumberofparametersrefined.
inmethanolorinwaterat298K.Theaqueoussolutionbehavior methodsandrefinedbyfull-matrixleast-squarestechniques.Non-
withrespecttohydrolysisof2-4,6,and7wasstudiedat298K hydrogen atoms were refined with anisotropic displacement pa-
over48hbyUV-visspectroscopy.Electrosprayionizationmass rameters.Hatomswereplacedatcalculatedpositionsandrefined
spectrometrywascarriedoutwithaBrukerEsquire3000instrument asridingatomsinthesubsequentleast-squaresmodelrefinements.
(Bruker Daltonic, Bremen, Germany) in methanol and methanol/ The isotropic thermal parameters were estimated to be 1.2 times
water(30/70).Expectedandexperimentalisotopedistributionswere the values of the equivalent isotropic thermal parameters of the
compared.The1HNMRspectrawererecordedat400.13MHzon non-hydrogen atoms to which hydrogen atoms are bonded. The
aBrukerDPX400(UltrashieldMagnet)spectrometer.Thesolution following computer programs were used: structure solution,
behaviorof6wasstudiedby1HNMRinaqueoussolution(D O, SHELXS-97;22 refinement, SHELXL-97;23 molecular diagrams,
2
pH(cid:24)5.5,37(cid:176) C)for2daysandinphysiologicalmedium(phosphate ORTEP;24computer,PentiumIV.Scatteringfactorsweretakenfrom
buffer 0.05 M, pH 7.4; 0.15 M NaCl, 37 (cid:176) C) for 3 days. The theliterature.25
interaction of 6 with 9-methyladenine (1:1.5 molar ratio) in Cell Lines and Culture Conditions. Human HT-29 (colon
phosphate buffer (pH 6.0, 37 (cid:176) C) was followed by 1H NMR carcinoma)andSK-BR-3(mammarycarcinoma)cellswerekindly
spectroscopyfor4days.Acetone(1(cid:237)L/mL)wasusedasreference providedbyBrigitteMarian(InstituteofCancerResearch,Medical
fortheNMRexperiments.Cyclicvoltammogramsweremeasured University of Vienna, Austria) and Evelyn Dittrich (General
inatwo-compartmentthree-electrodecellusinga1.0-mm-diameter Hospital,MedicalUniversityofVienna,Austria),respectively.All
glassy-carbon-diskworkingelectrode,probedbyaLuggincapillary, of the cell culture media and supplements were purchased from
and connected to a silver-wire pseudoreference electrode and a Sigma-Aldrich,Vienna,Austria,unlessindicatedotherwise.Cells
platinumauxiliaryelectrode.Measurementswereperformedatroom were grown in 75 cm2 culture flasks (Iwaki/Asahi Technoglass,
temperatureusinganEG&GPARC273Apotentiostat/galvanostat. Gyouda,Japan)asadherentmonolayerculturesincompleteculture
Deaerationofsolutionswasaccomplishedbypassingastreamof medium,thatis,minimalessentialmedium(MEM)supplemented
argon through the solution for 10 min prior to the measurements with10%heat-inactivatedfetalbovineserum(Invitrogen,Paisley,
and then maintaining a blanket atmosphere of argon over the U.K.), 1 mM sodium pyruvate, 4 mM l-glutamine, and 1% non-
solution during the measurements. The potentials were measured essentialaminoacids(100(cid:2)).Culturesweremaintainedat37(cid:176) C
in0.2Mphosphatebuffersolutions(pH7.0),usingmethylviologen inahumidifiedatmospherecontaining5%CO.
2
(E(cid:239)x ) -0.44 V vs NHE in water)20 as an internal standard and Cytotoxicity Tests in Cancer Cell Lines. Cytotoxicity was
1/2
arequotedrelativetoNHE. determined by means of the colorimetric MTT assay (MTT )
CrystallographicStructureDetermination.X-raydiffraction 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazoliumbromide;
measurementswereperformedonanX8APEXIICCDdiffracto- purchasedfromFluka,Vienna,Austria).HT-29andSK-BR-3cells
meterat100or296K.Singlecrystalswerepositionedat37.5,40, were harvested from culture flasks by trypsinization and seeded
37.5,40,40,and40mmfromthedetector,and1793,5247,1134, into96-wellmicrocultureplates(Iwaki/AsahiTechnoglass,Gyouda,
948,3201,and1973framesweremeasured,eachfor20,5,60,8, Japan).Aseedingdensityof4(cid:2)103cells/wellwaschosentoensure
50,and3sovera1(cid:176) scanwidthfor1-3and5-7,correspondingly. exponential growth throughout drug exposure. After a 24 h
The data were processed using SAINT software.21 Crystal data,
datacollectionparameters,andstructurerefinementdetailsfor1-3 (22) Sheldrick,G.M.SHELXS-97,ProgramforCrystalStructureSolution;
and5-7aregiveninTable1.Thestructuresweresolvedbydirect UniversityofGo¨ttingen,Germany,1997.
(23) Sheldrick,G.M.SHELXL-97,ProgramforCrystalStructureRefine-
ment;UniversityofGo¨ttingen: Go¨ttingen,Germany,1997.
(20) GuedesdaSilva,M.F.C.;Pombeiro,A.J.L.;Geremia,S.;Zangrando, (24) Johnson,C.K.ReportORNL-5138;OakRidgeNationalLaboratory:
E.; Calligaris, M.; Zinchenko, A. V.; Kukushkin, V. Yu. J. Chem. OakRidge,TN,1976.
Soc.,DaltonTrans.2000,1363-1371. (25) International Tables for X-ray Crystallography; Kluwer Academic
(21) SAINT-Plus, version 7.06a and APEX2; Bruker-Nonius AXS Inc.: Press: Dordrecht,TheNetherlands,1992;Vol.C,Tables4.2.6.8and
Madison,WI,2004. 6.1.1.4.
5026 InorganicChemistry,Vol.46,No.12,2007
OsmiumNAMI-Aanalogues
preincubation,cellswereexposedtosolutionsofthetestcompounds
in 200 (cid:237)L/well complete culture medium for 96 h. At the end of
exposure,drugsolutionswerereplacedby100(cid:237)L/wellRPMI1640
culture medium (supplemented with 10% heat-inactivated fetal
bovine serum) plus 20 (cid:237)L/well MTT solution (5 mg/mL) in
phosphate-buffered saline. After incubation for 4 h, the medium/
MTT mixtures were removed, and the formazan crystals formed
by the mitochondrial dehydrogenase activity of vital cells were
dissolvedin150(cid:237)LDMSOperwell.Opticaldensitiesat550nm
weremeasuredwithamicroplatereader(TecanSpectraClassic),
usingareferencewavelengthof690nmtocorrectforunspecific
absorption. The quantity of vital cells was expressed in terms of
T/Cvaluesbycomparisontountreatedcontrolmicrocultures,and
IC values were calculated from concentration-effect curves by
50
interpolation.Evaluationisbasedonthemeansfromatleastthree
independent experiments, each comprising six microcultures per
concentrationlevel. Figure3. ORTEPdiagramofthestructureof1withatomlabelingscheme
showing two crystallographically independent complex anions and one
Results and Discussion
[(DMSO)2H]+ cation. The second cation present in the asymmetric unit
wasomittedforclarity;thermalellipsoidsweredrawnat50%probability
level.Selectedbondlengths(Å)andangles(deg): Os1-S12.3301(9),Os1-
SynthesisandCharacterizationoftheComplexes.1was S22.3345(9),Os1-Cl12.3693(11),Os1-Cl22.3629(7),Os1-Cl32.3632-
synthesized by two consecutive reductions. The first one is (10),Os1-Cl42.3569(7),Os2-S32.3303(10),Os2-S42.3364(10),Os2-
the reduction of OsVIIIO to [OsIVCl ]2- by hydrazine Cl52.3726(9),Os2-Cl62.3496(8),Os2-Cl72.3490(9),Os2-Cl82.3704(8),
4 6 S1-O11.466(3),S2-O21.469(3),S3-O31.479(3),S4-O41.469(3),S5-
dihydrochloride in the presence of concentrated HCl, and O51.538(3),S6-O61.567(3).
the second is the reduction of [OsIVCl ]2- to OsIII and OsII
6
by SnCl (cid:226)2H O in the presence of dimethyl sulfoxide with
2 2
theformationof[(DMSO) H][OsIIICl (DMSO) ](20-30%)
2 4 2
and trans-OsIICl (DMSO) (15-25%). trans-OsIICl -
2 4 2
(DMSO) ,15whichprecipitatedfirst,wasfilteredoff,whereas
4
the filtrate produced nice orange needles of 1, which were
suitable for X-ray crystallography (vide infra). It should be
alsonotedthattherelatedruthenium(III)complex[(DMSO)H]-
2
[RuIIICl (DMSO) ] was originally isolated from the mother
4 2
liquorofcis-RuIICl (DMSO) .262-4,6,and7weresynthe-
2 4
sized by reaction of [(DMSO) H][trans-OsIIICl (DMSO) ]
2 4 2
(1) with an excess of the corresponding azole ligand in
acetone,ethanol,ormethanolbyusingthedestabilizingtrans
effectofthetwoaxiallyS-bound(cid:240)-acceptingDMSOligands
Figure 4. ORTEP view of 2 with atom labeling scheme; the thermal
in1,whereas5wasobtainedbymetathesisreactionof(H 2 - ellipsoidsareshownat50%probabilitylevel.Selectedbondlengths(Å)
bzim)[trans-OsIIICl (Hbzim)(DMSO)](4)andPh PCH PhCl andbondangles(deg): Os1-N12.090(2),Os1-Cl12.3530(7),Os1-Cl2
4 3 2 2.3511(7),Os1-Cl32.3603(7),Os1-Cl42.3928(7),Os1-S12.2690(7),
inmethanol.Thereactionof[(DMSO) 2 H][OsIVCl 5 (DMSO)]27 S1-O1 1.495(2) Å, N1-Os1-S1 176.02(6), Cl3-Os1-N1-N2
with pyrazole in 1:2 molar ratio in isoamylalcohol at 105 -39.1(2)(cid:176) .
(cid:176) C for 1 h yielded a mixture of different products, one of between 1600 and 1100 cm-1 and an intense broad band
which was shown by X-ray diffraction to be (H
2
pz)[trans- between900and600cm-1.In1,thisintensebandwasfound
OsIIICl 4 (Hpz)(DMSO)] (3). at844cm-1,verysimilartothatfor[(DMSO) 2 H] 2 [OsCl 6 ]27
The infrared spectrum of 1 showed one SdO (S-bonded (845 cm-1) and was blue shifted when compared to that
DMSO)stretchingvibrationat1080cm-1typicalforatrans observed for [(DMSO) H][trans-RuIIICl (DMSO) ] at 730
2 4 2
configuration.Thelightercongener[(DMSO) 2 H][trans-RuIII- cm-1. DMSO possesses rather strong (cid:240)-acceptor properties
Cl 4 (DMSO) 2 ] revealed this vibration at 1082 cm-1.12 Band and, compared to azole ligands, shows the greater trans-
assignment was also confirmed by replacement of DMSO labilizingeffectalongthevectorS-Os-N.Asaresult,the
withDMSO-d 6 .Thehydrogen-bridgedcation[(DMSO) 2 H]+ positions of stretching vibrations Os-S (426-436 cm-1),
hasbeenpreviouslydiscoveredfor[(DMSO)
2
H][trans-MCl
4
- SdO(S-bondedDMSO)(1056-1067cm-1),anddeforma-
(DMSO) 2 ], where M ) Ru,12 Rh.28 The IR spectra of these tion vibrations C-H (1016-1026 cm-1) in IR spectra of
complexes display a very broad band of medium intensity 2-4,6,and7donotchangesignificantlyafterthereplace-
ment of one azole by another. In the case of starting
(26) Alessio,E.;Mestroni,G.;Nardin,G.;Attia,W.M.;Calligaris,M.; compound1,amutuallabilizationofDMSOligandsonthe
Sava,G.;Zorzet,S.Inorg.Chem.1988,27,4099-4106.
vectorS-Os-SexpressedinOs-Sbondlengthening(2.33
(27) Rudnitskaya,O.V.;Buslaeva,T.M.;Lyalina,N.N.Zh.Neorg.Khim.
1994,39,922-924. Å (1), 2.26-2.27 Å (2-7)) (Figures 3-8) resulted in the
(28) (a)James,B.R.;Morris,R.H.;Einsten,F.W.B.;Willis,A.J.Chem.
decrease of its strength as evidenced by lowering the
Soc.,Chem.Commun.1980,1,31-32.(b)James,B.R.;Morris,R.
H.Can.J.Chem.1980,58,399-408. absorptionfrequency(cid:238)(Os-S)to416cm-1(1).Themarginal
Inorganic Chemistry, Vol. 46, No. 12, 2007 5027
Cebria´n-Losantos et al.
Figure 5. ORTEP view of 3 with atom labeling scheme; the thermal Figure 8. ORTEP view of a centrosymmetric fragment of the crystal
ellipsoidsareshownat50%probabilitylevel.Selectedbondlengths(Å) structure of 7 with atom labeling scheme; the thermal ellipsoids are
andbondangles(deg): Os1-N12.109(2),Os1-Cl12.3542(6),Os1-Cl2 shownat50%probabilitylevel.Selectedbondlengths(Å)andbondangles
2.3646(6),Os1-Cl32.3591(6),Os1-Cl42.3640(6),Os1-S12.2656(7), (deg): Os1-N12.095(3),Os1-Cl12.3548(8),Os1-Cl22.3724(8),Os1-
S1-O11.482(2)Å,N1-Os1-S1179.09(5),Cl4-Os1-N1-N2-40.65- Cl32.3574(8),Os1-Cl42.3497(8),Os1-S12.2592(8),S1-O11.492(2),
(18). N1-N21.383(4),N2-C31.302(4),C3-N41.350(4),N4-C51.353(4),
C5-N1 1.307(4) Å, N1-Os1-S1 177.71(7), Cl3-Os1-N1-N2
39.13(22)(cid:176) .
IR spectra of 2-7 compares well with those of ruthenium
NAMI-A analogues.
The electronic absorption spectra of 1 in water and
methanol are very similar. The band with an absorption
maximumat348nminmethanolisslightlyblueshifted(344
nm)whenwaterisusedassolvent.Theseresultsagreewell
withthespectraforthelightercongener[(DMSO) H][trans-
2
RuIIICl (DMSO) ],11a which shows a maximum absorption
4 2
at 402 (methanol) and 396 nm (water). The bands at 194
and 204 nm for 1 in water are due to the (cid:240)-(cid:240)* transitions
of the DMSO ligands. UV-vis spectra of the aqueous
solutions of 2-4, 6, and 7 are characterized by four
absorption bands with maxima near 200 nm ((cid:240)-(cid:240)* transi-
tions of the ligands) within 236-298, 323-336, 370-378
nmandashoulderat406-409nm.Inaddition,thesecond
Figure6. Fragmentofthecrystalstructureof5showingtheformationof
band of 2 and 4 is typical for a free or annelated benzene
interanionic bifurcated hydrogen bond. Atoms marked with i are at the
symmetrypositions(-x+1.5,y+0.5,-z+1.5).Selectedbondlengths ringandhasanoscillatorycharacter29(TableS1).Veryweak
(Å)andangles(deg): Os1-N12.120(3),Os1-Cl12.3536(9),Os1-Cl2 d-dtransitionsofoctahedralosmium(III)complexes,which
2.3704(8),Os1-Cl32.3604(9),Os1-Cl42.3634(8),Os1-S12.2632(9),
aresolventindependent,canbeobservedveryrarelybecause
S1-O11.475(3)Å,N1-Os1-S1177.74(8),Cl3-Os1-N1-C741.2(3)(cid:176) .
they are obscured by more intense charge transfer absorp-
tions.30Theobservedsolvatochromism(ahypsochromicshift
(blue)withincreasingsolventpolarity,inourcasethechange
from methanol to water and a change of band intensity)
indicates the presence of metal-ligand charge-transfer
(MLCT) bands, which also overlap with intraligand transi-
tions in coordinated azole and DMSO ligands. Taking into
consideration the presence of a hole in the t subshell of
2g
low-spin OsIII and the presence of ligands with electron-
donatingpropertiesinitscoordinationsphere,theappearance
Figure7. Partofthecrystalstructureof6showingthebridgingroleof of low-energy LMCT bands is expected. However, there is
oneoftheimidazoliumcationsbetweentwo[trans-RuCl4(Him)(DMSO)]-
nocleardependenceofcharge-transferenergyfromthenet
anions.Atomsmarkedwithiareatthesymmetrypositions(-x+1.5,y+
0.5,-z+1.5).Selectedbondlengths(Å)andangles(deg): Os1-N12.097- electron-donor character of the azole ligands (the third and
(4), Os1-Cl1 2.3626(11), Os1-Cl2 2.3494(11), Os1-Cl3 2.3640(11), fourth bands for 2-4, 6, and 7 show very close maxima).
Os1-Cl42.3748(11),Os1-S12.2648(11),S1-O11.482(3)Å,N1-Os1-
Just as for [(DMSO) H][trans-MIIICl (DMSO) ], upon re-
S1 177.55(11), N3-Os2-S2 178.96(11), Cl1-Os1-N1-C3 -38.8(4), 2 4 2
Cl8-Os2-N3-C6-37.4(4)(cid:176) .
(29) Lambert,J.B.;Shurvell,H.F.;Lightner,D.A.;Cooks,R.G.Organic
shortening of SdO bond length (1.47-1.48 Å (1), 1.48- StructuralSpectroscopy;PrenticeHall: UpperSaddleRiver,NJ,1998;
1.49 Å (2-7)) (Figures 3-8) did not affect the position of pp568.
(30) Lever,A.B.P.InorganicElectronicSpectroscopy,2ndEd.;Elsevi-
the stretching vibration (cid:238)(SdO). The general character of er: Amsterdam,TheNetherlands,1984;p862.
5028 InorganicChemistry,Vol.46,No.12,2007
OsmiumNAMI-Aanalogues
placementofRuIIIbyOsIIIinalloftheNAMI-Aanalogues, 2.3304(19),and2.3365(10)Å]withDMSOligandstransto
a blue shift of all of the absorption bands with preserved eachother.ReplacementofoneoftheDMSOligandsbyan
generalcharacterofthespectraisobserved.Thisisprobably indazole or pyrazole ligand results in a shortening of the
due to the stronger ligand field splitting for third row other Os-DMSO bond because of a diminished (cid:240) back-
transition-metal complexes (Table S1). bonding competition between the two trans ligands or
Crystal Structures. The structures of the complexes decreased (cid:243)-directed trans influence of the nitrogen ligand.
reported herein are of interest because of the paucity of
TheSdObondlengthof1.495(2)Åin2isequalwithin3(cid:243)
documentedX-raydiffractiondataforosmium(III)-sulfoxide with that of metal-free DMSO [1.492(1) Å], whereas it is
complexes31 and lack of such data for osmium(III)-azole 5(cid:243) shorter in 3 [1.482(2) Å]. It should, however, be noted
derivatives.32 1 crystallizes in the triclinic space group P1h thattheX-raydiffractionstudiesfor2and3wereperformed
withcellparametersveryclosetothoseofrelatedRu,Ir,or atdifferenttemperatures(Table1).Thecrystalstructuresof
Rh compounds, the structures of which were solved in the 2and3consistofazoliumcationsandcomplexanions,which
monoclinic space group P2/n. The crystal structure of 1 are involved in hydrogen bonding interactions. Two such
consistsof[(DMSO)H]+cationsand[trans-OsCl(DMSO)]- hydrogen bonds, a weak N3-H(cid:226)(cid:226)(cid:226)Cl3 [N3-H ) 0.88 Å,
2 4 2
anions. Figure 3 displays a perspective view of two crys- H(cid:226)(cid:226)(cid:226)Cl3)2.672Å,N3(cid:226)(cid:226)(cid:226)Cl33.134Å,— N3HCl3)113.94(cid:176) ]
tallographicallyindependentcomplexanionsandoneofthe
andastrongN4-H(cid:226)(cid:226)(cid:226)O1[N4-H)0.88Å,H(cid:226)(cid:226)(cid:226)O1)1.905
two independent [Me SO(cid:226)(cid:226)(cid:226)H(cid:226)(cid:226)(cid:226)OSMe ]+ cations. Selected Å,N4(cid:226)(cid:226)(cid:226)O1)2.750Å,— N4HO1)160.41(cid:176) ]in2,areshown
2 2
bond lengths (Å) and angles (deg) are quoted in the legend
inFigure4,whereastwoothers,N6-H(cid:226)(cid:226)(cid:226)O1[N6-H)0.86
toFigure3.Thestructureofthe[(DMSO) H]+cationisthe Å, H(cid:226)(cid:226)(cid:226)O1 ) 1.874 Å, N6(cid:226)(cid:226)(cid:226)O1 ) 2.733 Å, — N6HO1 )
2
sameasinthecomplexes[(DMSO)H][trans-MCl(DMSO)], 176.27(cid:176) ]andabifurcatedhydrogenbondinvolvingN7Has
2 4 2
where M ) Ru, Ir, Rh or in [(DMSO) H][trans-OsCl - the donor and Cl1 and Cl2 as acceptors [N7-H ) 0.86 Å;
2 4
(DMSO)NO].33 H(cid:226)(cid:226)(cid:226)Cl1 ) 2.722 Å, N7(cid:226)(cid:226)(cid:226)Cl1 ) 3.378 Å, — N7HCl1 )
Theosmium(III)ionsin[trans-OsCl (Hind)(DMSO)]-of 134.13(cid:176) ;H(cid:226)(cid:226)(cid:226)Cl4)2.876Å,N7(cid:226)(cid:226)(cid:226)Cl4)3.319Å,— N7HCl4
4
2andin[trans-OsCl (Hpz)(DMSO)]-of3havetheexpected )113.88(cid:176) ],in3areshowninFigure5.TheresultsofX-ray
4
distorted octahedral coordination geometry (Figures 4 and diffraction studies of the crystal structures of 5 and 6 are
5),withfourchlorideligandsintheequatorialpositionsand shown in Figures 6 and 7, respectively. Selected bond
a DMSO molecule bound through its sulfur atom trans to distances(Å)andbondangles(deg)arequotedinthelegends
theindazoleorpyrazoleligandinaxialpositions.TheOs1- to Figures 6 and 7.
Cl4 and Os1-Cl3 bonds in 2 are significantly longer than Theasymmetricunitof5containsanessentiallyoctahedral
Os1-Cl1andOs1-Cl2(legendtoFigure4).Theelongation anion[trans-RuCl
4
(Hbzim)(DMSO)]-andthe(Ph
3
PCH
2
Ph)+
ofthefirsttwobondsisprobablyduetotheinvolvementof cation,whereasthatof6consistsoftwocrystallographically
bothCl4andCl3asprotonacceptorsintwointermolecular distinct[trans-RuCl 4 (Him)(DMSO)]-anions,twoimidazo-
and one intramolecular hydrogen-bonding interactions, re- lium cations, and a disordered ethanol molecule. The
spectively, namely, Cl4(cid:226)(cid:226)(cid:226)H2-N2(-x + 1, -y + 1, -z + osmium(III) atoms in 5 and 6 are bound to four chlorido
1)[Cl4(cid:226)(cid:226)(cid:226)N23.336Å],Cl4(cid:226)(cid:226)(cid:226)H3-N3(-x+1,-y+1,-z ligands in the equatorial plane and to DMSO and benzimi-
+1)[Cl4(cid:226)(cid:226)(cid:226)N33.226Å]andCl3(cid:226)(cid:226)(cid:226)H3-N3(theparameters dazoleorimidazolemoleculesinaxialpositions.TheN2-H
ofthisHbondarequotedbelow).Theaveragevalueofthe group of the benzimidazole ring in 5 appears to form a
Os-Clbondlengthin3[2.361(2)Å]isclosetothosefound bifurcated hydrogen bond involving O1i as well as Cl4i
in [(DMSO) H][trans-OsCl (DMSO) ] (1) [2.3617(32) Å] (N2-H 0.86 Å, H(cid:226)(cid:226)(cid:226)O1i ) 2.029 Å, N2(cid:226)(cid:226)(cid:226)O1i ) 2.795 Å,
2 4 2
and in mer-[OsCl (NH ) (Me S)] [2.368(8) Å].20 The Os- — N2HO1i ) 147.81(cid:176) ; N2-H 0.86 Å, H(cid:226)(cid:226)(cid:226)Cl4i ) 2.827 Å,
3 3 2 2
N1bondof2.090(2)and2.109(2)Åin2and3,correspond- N2(cid:226)(cid:226)(cid:226)Cl4i ) 3.412 Å, — N2HCl4i ) 126.82(cid:176) ) (Figure 6).
ingly, compares well with Ru-N1 in the related complex Bond lengths and angles in the (Ph 3 PCH 2 Ph)+ cation are
(H ind)[trans-RuCl (Hind)(DMSO)]at2.0901(13)Å16aand similar to those reported in the literature.35
2 4
is significantly shorter than similar bonds trans to sulfur- Afragmentofthesolid-statestructureof7showninFigure
boundDMSOintheosmium(II)complexestrans,cis,cis-OsII- 8 features an S-bonded DMSO ligand trans to the N-donor
Cl (Hind) (DMSO) andtrans,cis,cis-OsIICl (Hpz) (DMSO) atom of Htrz. The Os1-S1 bond distance is 2.2592(8) Å,
2 2 2 2 2 2
at2.130(4),2.137(4)and2.1202(17),2.1365(17)Å,respec-
andtheS1-O1bondlengthis1.492(2)Å.Thefirstbondis
tively.34 The Os-S1 bond lengths of 2.2690(7) Å (2) and shorter than Ru1-S1 [2.2730(8) Å] in (Ph 3 PCH 2 Ph)[trans-
2.2656(7)Å(3)(sulfurbeingtranstotheindazoleorpyrazole RuCl 4 (Htrz)(DMSO)].16Thelatterbondispracticallyidenti-
nitrogen)aremarkedlyshorterthanthosefoundin[(DMSO)H]- caltothatinfreeDMSO[1.492(1)Å].36Thedistributionof
2
[OsCl (DMSO) ] [2.3300(9), 2.3343(9), electron density over the triazole ring indicates a pre-
4 2
vailing double bond character of N1-C5 and N2-C3. The
(31) (a)Alessio,E.Chem.ReV.2004,104,4203-4242. analysisofthecrystalstructureof7showedthepresenceof
(32) Chiorescu,I.;Stepanenko,I.N.;Arion,V.B.;Krokhin,A.A.;Scaffidi- hydrogenbondinginteractionswithparticipationoftriazole-
Domianello,Y.Y.;Keppler,B.K.,manuscriptinpreparation.
(33) Rudnitskaya,O.V.;Buslaeva,T.M.;Stash,A.I.;Kisin,A.V.Russ.
J.Coord.Chem.1995,21,136-140. (35) Cifuentes,M.P.;Waterman,S.M.;Humphrey,M.G.;Heath,G.A.;
(34) Stepanenko,I.N.;Cebria´n-Losantos,B.;Arion,V.B.;Krokhin,A. Skelton,B.W.;White,A.H.;Perera,M.P.S.;Williams,M.L.J.
A.;Nazarov,A.A.;Keppler,B.K.Eur.J.Inorg.Chem.2007,400- Organomet.Chem.1998,565,193-200.
411. (36) Calligaris, M.; Carugo, O. Coord. Chem. ReV. 1996, 153, 83-154.
Inorganic Chemistry, Vol. 46, No. 12, 2007 5029
Cebria´n-Losantos et al.
Table2. CyclicVoltammetricDataforComplexes2-4,6and7in
AqueousPhosphateBuffer(pH7)
E1/2(OsII/III)a, E1/2(OsIII/IV)a,
complex (¢Ep)b (¢Ep)b “EL/VvsNHE pKa(H2azole+)
2 0.17(60) 1.41(70) -0.23 1.25
3 0.16(60) 1.40(70) -0.29 2.64
4 0.12(70) 1.27(60) -0.39 5.63
6 0.12(60) 1.33(80) -0.37 6.65
7 0.15(80) 1.35(70) -0.31 2.55
aPotentialsE1/2(E1/2 )(Epa +Epc)/2,whereEpaandEpcaretheanodic
and cathodic peak potential, respectively) are given in V and measured
at a scan rate 0.2 V s-1 in aqueous phosphate buffer (pH 7) using
methylviologen(E(cid:239)x )-0.44VvsNHEinwater)asinternalstandard
andarequotedrelat 1 iv /2 etoNHE.b¢Epvalues(¢Ep )Epa -Epc)aregiven
inmV.
Figure9. Multiplecyclicvoltammogramof0.5mM(H2trz)[trans-OsCl4-
ring nitrogen atoms N2 and N4. The first one acts as an (Htrz)(DMSO)] in aqueous phosphate buffer at pH 7 at a carbon-disk
acceptorinthehydrogenbondN8-H(cid:226)(cid:226)(cid:226)N2withthefollow- working electrode and at a scan rate of 0.2 V/s, starting with a scan in
cathodicdirection.
ing parameters: N8-H ) 0.88 Å, H(cid:226)(cid:226)(cid:226)N2 ) 2.089 Å, N8(cid:226)
(cid:226)(cid:226)N2 ) 2.811 Å, — N8HN2 ) 138.71(cid:176) . The second acts as > E (Him) > E (Hbzim)] and their basicity [pK(H ind+)
L L a 2
a donor in the hydrogen bond N4-H(cid:226)(cid:226)(cid:226)Cl2 (-x + 1, -y, <pK(Htrz+)<pK(Hpz+)<pK(Hbzim+)<pK(Him+)]43-46
a 2 a 2 a 2 a 2
-z) with the following parameters: N4-H ) 0.88 Å, H(cid:226)(cid:226) (Table 2). The reversible responses are characterized by a
(cid:226)Cl2)2.538Å,N4(cid:226)(cid:226)(cid:226)Cl2)3.350Å,— N4HCl2)153.91(cid:176) . peak-to-peakseparation(¢E )of60-80mVandananodic
p
All of this indicates that, in contrast to [trans-RuCl 4 (Htrz)- peak current (i pa ) that is almost equal to the cathodic peak
(DMSO)]-where1H-1,2,4-triazoleiscoordinatedtoruthe-
current (i ), as expected for reversible electron-transfer
pc
nium(III) via N4, the triazole ligand in 7 is stabilized as a processes. The one-electron nature of electron-transfer
4Htautomer.Hence,coordinationoftriazoleviaN1(orN2 processeswasverifiedbycomparingthepeak-currentheight
in the nomenclature used for 1H- or 4H-1,2,4-triazole) (i ) with that of standard methyl viologen couples under
p
is proposed. The N2 atom in triazole is less basic than identical experimental conditions.
N4,37 therefore such behavior is rather unexpected. 1,2,4- The linear relationships between the redox potentials for
Triazole behaves as a monodentate ligand coordinating to the OsIII f OsII and OsIII f OsIV processes and (cid:229) E (E -
L L
the first-row or second-row transition metal ion in the (Cl) ) -0.24,47 E (DMSO) ) 0.47,48 E (Hind) ) 0.26,16
L L
majority of cases via N4 ([MnII(SO 4 )(Htrz)(H 2 O) 4 ],38 [Cd- E L (Hpz) ) 0.20,48 E L (Htrz) ) 0.18,48 E L (Hbzim) ) 0.1,47
(NCS) 2 (Htrz) 2 ],39 [FeCl 3 (bpy)(Htrz)],40 or Zn(II) in human E L (Him))0.1248),expressedbygeneralLever’sequation48
carbonic anhydrase.41 Only in two cases, namely, (H 2 trz)- (eq 1)
[cis-RuCl(Htrz)]and(PhPCHPh)[trans-RuCl(Htrz)],has
4 2 3 2 4 2
crystallographic evidence for coordination via N2 been E)S (cid:229) E +I (1)
M L M
provided.42
andwasobtainedfromtheplotsinFigures10and11.This
ElectrochemicalBehaviorinAqueousPhosphateBuffer
atpH7.Thecyclicvoltammogramsof2-4,6,and7in0.2 expression enabled for the first time the estimate of the S
M
andI values,whicharedependentuponthemetalandredox
M phosphate buffer (pH 7) at a carbon-disk working M
couple,thespinstate,andthestereochemistryfortheOsII/III
electrodeandatascanrateof0.2V/sdisplayonereversible,
single-electronoxidationwave(I(cid:239)x)assignedtotheOsIIIf (eq2)andOsIII/IV(eq3)redoxcouplesinaqueousphosphate
OsIVprocesswithE(cid:239)x potentialvaluesrangingfrom1.27to buffer at pH 7 as follows:
1/2
1.41 V and one reversible single-electron reduction wave
(cid:229)
(Ired) attributed to the OsIII f OsII process with E 1 re / d 2 E(OsII/III))0.35 (cid:229) E L +0.26 (2)
potential values ranging from 0.12 to 0.17 V versus NHE E(OsIII/IV))0.82 E +1.61 (3)
L
(Table 2). The redox potentials of the complexes are in the
following rank order: E (2) > E (3) > E (7) > E (6)
g E (4) (in the case o 1/ f 2 OsIII f 1/2 OsII pro 1 c / e 2 ss E (4 1/ ) 2 ) (43) Reedijk,J.HeterocyclicNitrogen-DonorLigands.InComprehensiVe
1/2 1/2 CoordinationChemistry;Wilkinson,G.,Gillard,R.D.,McCleverty,
E (6)), which agrees well with the relative electron-donor J.A.,Eds.;PergamonPress: Elmsford,NY,1987;Vol.2,pp73-98.
ch 1/ a 2 racteroftheN-ligands[E (Hind)>E (Hpz)>E (Htrz) (44) Potts,K.T.Chem.ReV.1961,61,87-127.
L L L (45) Catala´n,J.;Claramunt,R.M.;Elguero,J.;Laynez,J.;Mene´ndez,M.;
Anvia, F.; Quian, J. H.; Taagepera, M.; Taft, R. W. J. Am. Chem.
(37) Meot-Ner,M.;Liebman,J.F.;DelBene,J.E.J.Org.Chem.1986, Soc.1988,110,4105-4111.
51,1105-1110. (46) Reisner, E.; Arion, V. B.; Eichinger, A.; Kandler, N.; Giester, G.;
(38) Gorter, S.; Engelfriet, D. W. Acta Crystallogr. 1981, B37, 1214- Pombeiro, A. J. L.; Keppler, B. K. Inorg. Chem. 2005, 44, 6704-
1218. 6716.
(39) Haasnoot, J. G.; De Keyzer, G. C. M.; Verschoor, G. C. Acta (47) (a)Lever,A.B.P.Inorg.Chem.1990,29,1271-1285.(b)Lever,A.
Crystallogr.1983,C39,1207-1209. B.P.;Dodsworth,E.S.InorganicElectronicStructureandSpectros-
(40) Driessen,W.L.;DeGraaff,R.A.G.;Vos,J.G.ActaCrystallogr. copy;Wiley: NewYork,1999;pp227-290.
1983,C39,1635-1637. (48) (a)Bacac,M.;Hotze,A.C.G.;vanderSchilden,K.;Haasnoot,J.
(41) Mangani,S.;Liljas,A.J.Mol.Biol.1993,232,9-14. G.; Pacor, S.; Alessio, E.; Sava, G.; Reedijk, J. J. Inorg. Biochem.
(42) Arion,V.B.;Reisner,E.;Fremuth,M.;Jakupec,M.A.;Keppler,B. 2004,98,402-412.(b)Bouma,M.;Nuijen,B.;Jansen,M.T.;Sava,
K.; Kukushkin, V. A.; Pombeiro, A. J. L. Inorg. Chem. 2003, 42, G.; Flaibani, A.; Bult, A.; Beijnen, J. H. Int. J. Pharm. 2002, 248,
6024-6031. 239-246.
5030 InorganicChemistry,Vol.46,No.12,2007
OsmiumNAMI-Aanalogues
Figure10. PlotofE1/2(OsII/III)for2-4,6,and7inaqueousphosphate
buffer(pH7)against(cid:229) EL(inVvsNHE).E(OsII/III))0.35(cid:229) EL +0.26(r
) 0.97) (eq 2). (H2ind)[OsIIICl4(Hind)(DMSO)] 2; (H2pz)[OsIIICl4(Hpz)-
(DMSO)]3;(H2bzim)[OsIIICl4(Hbzim)(DMSO)]4;(H2im)[OsIIICl4(Him)- Figure12. 1HNMRspectraof6(5.5mM)inphosphatebuffer(0.05M
(DMSO)] 6; (H2trz)[OsIIICl4(Htrz)(DMSO)] 7, where EL(Hind) ) 0.26; phosphate,0.15MNaCl),pH7.4,37(cid:176) Cfort)0and3dayswithchemical
EL(Hpz))0.20;EL(Hbzim))0.10;EL(Him))0.12;EL(Htrz))0.18. formula and atom numbering scheme. For signal integration, acetone (1
(cid:237)L/mL)wasaddedtothebuffersolutionasreference(2.16ppm).
NMRspectraof6inD O(pH(cid:24)5.5,37(cid:176) C)weremonitored
2
over 2 days. The spectra obtained immediately after dis-
solutionof6andafter2dayswerealmostidentical.Avery
small signal (<2%) at 2.63 ppm was attributed to free
DMSO.Additionof1(cid:237)LofDMSOresultedinanincrease
ofthissignal.TheintegrationoftheDMSOsignalobserved
for a freshly prepared solution of 6 after 2 days showed an
increaseofonly3%,indicatingthataverysmallamountof
the expected hydrolysis product [OsCl (Him)(H O)]- is
4 2
presumably formed. In contrast, NAMI-A under similar
Figure11. PlotofE1/2(OsIII/IV)for2-4,6,and7inaqueousphosphate conditions hydrolyzes to a larger extent with formation of
b ( (r D u ) f M fe S 0 r . O 9 (p ) 3 ] H ) 3 (e 7 ; q ) ( , H 3 a 2 ) g b . a z ( i H i n m 2 s i t ) n [ (cid:229) O d) E s [ I O L IIC s ( I i l I n I 4 C (H V l4 b ( v H z s i i m n N d ) H ( ) D ( E D M ) M . S E S O ( O O )] ) s ] 4 II 2 ; I/ ; I ( V ( H ) H 2 ) 2 im pz 0 ) ) [ . [ O 8 O 2 s s “ I I I I I E I C C L l l 4 4 + ( ( H H 1 i p m . z 6 ) ) 1 - - t o h f e R c u o - m C pl l e b x o [ n R d u s C w l 4 a ( s H f i o m u ) n ( d H . 2 T O h )] e - 1 . H Ho N w M e R ver s , p n ec o tr h u y m dr o o f ly t s h i e s
(DMSO)] 6; (H2trz)[OsIIICl4(Htrz)(DMSO)] 7, where EL(Hind) ) 0.26; anion[OsCl(Him)(DMSO)]-showedabroadsignalcentered
EL(Hpz))0.20;EL(Hbzim))0.10;EL(Him))0.12;EL(Htrz))0.18.
at -20 ppm
4
attributed to the protons of S-bonded DMSO
ResistancetoHydrolysisinAqueousandPhysiological (by comparison with the spectrum of 1), two broad reso-
Media. The aqueous solution behavior with respect to nancesaround-17and-15ppm(Him,H ),andasharper
4,5
hydrolysisof2-4,6,and7wasstudiedat298Kover48h resonanceat-5.26ppm(Him,H ).Twosharpsignalsat(cid:228)
2
byUV-visspectroscopyand1HNMRspectroscopy.Allof 8.61 and 7.39 ppm (1:2 integration ratio) correspond to H
2
thecomplexeswerequitestableinaqueoussolution,ascan andH oftheH im+counterion,respectively.Otherpeaks
4,5 2
beseenfromtheirelectronicabsorptionspectra(FiguresS2- observed in the 1H NMR spectrum of 6 have not been
S6). Immediate hydrolysis can be excluded by comparison identified (a sharp peak at 7.67 ppm shifted to 7.38 ppm
ofUV-visspectraofthecomplexesinmethanolandwater. after 2 days, a very broad signal at about 3.38 ppm, a peak
Inaddition,thenegativeionESImassspectraofcomplexes at3.58,andasharpsignalat2.13ppm).Allofthesepeaks
2-4, 6, and 7 in methanol/water (30/70) showed a similar wereofmarginalintensityinthespectrumoffreshlyprepared
pattern with three different peaks, which can be attributed solutionsof6anddidnotchangetheirintensityafter2days.
to[OsIIICl(L)(DMSO)]-,[OsIIICl(DMSO)]-,and[OsIIICl]-, 1HNMRspectraof6inphysiologicalmedium(phosphate
4 4 4
where L is the respective azole ligand. The presence of the buffer0.05M,pH7.4;0.15MNaCl,37(cid:176) C)weremonitored
parentpeakdueto[OsIIICl(azole)(DMSO)]-providesfurther over3days.The1HNMRspectrarecordedimmediatelyafter
4
evidence against immediate hydrolysis of the complexes dissolution(t)0)andafter3dayswerepracticallyidentical,
studied in aqueous solution (Figure S8). as can be seen in Figure 12. Acetone (1 (cid:237)L/mL) was used
1HNMRexperimentsinaqueoussolution(D O,pH(cid:24)5.5, asreference,asitgivesasharpsignalat2.16ppmthatdoes
2
37(cid:176) C)andinphysiologicalmedium(phosphatebuffer0.05 not overlap with the signals of 6. The integration of the
M,pH7.4;NaCl0.15M,37(cid:176) C)werecarriedoutwith6for DMSO signal observed (2.66 ppm) for a freshly prepared
direct comparison with the earlier reported data for solution of 6 after 3 days showed an increase of only 5%.
[RuIIICl (Him)(DMSO)]-(NAMI-A).48Becauseofthepara- The spectrum showed a broad signal centered at -20 ppm
4
magnetismoftheOsIIIion(d5,lowspin),afullidentification fortheprotonsofS-bondedDMSO,twobroadbandsaround
oftheNMRsignalswasnotaccomplished.Themainpeaks -17and-15ppm(Him,H ),andasharperpeakat-5.18
4,5
observedwereassignedtakingintoaccounttheNMRspectra ppm (Him, H ). The signals of the H im+ counterion seen
2 2
of NAMI-A49 and the osmium(II) complexes trans,cis,cis- at 8.33 and 7.30 ppm (1:2 integration ratio) correspond to
OsCl(Him)(DMSO) andcis,fac-OsCl(Him)(DMSO).351H H and H , respectively. Two other minor peaks at 3.42
2 2 2 2 3 2 4,5
Inorganic Chemistry, Vol. 46, No. 12, 2007 5031
Cebria´n-Losantos et al.
Table3. AntiproliferativeEffectsof1-4,6,and7andThree
Ruthenium(III)AnaloguesinTwoHumanCancerCellLines
compound L IC50((cid:237)M)a
HT-29 SK-BR-3
1 DMSO 75(11 241(57
2 Hind 21(1 119(41
3 Hpz 39(10 325(141
4 Hbzim 36(2 194(19
6 Him 103(15 930(46
7 Htrz 214(61 >1000
Ruanaloguesb Hind 212(22 169(10
Him 339(68 472(25
Htrz 322(32 415(48
aFiftypercentinhibitoryconcentrationsafterexposurefor96hinthe
MTT assay. Values are means ( standard deviations from at least three
independentexperiments.bDatatakenfromthepreviouspublication.49
dazoleresultsinincreasedantiproliferativeactivity,whereas
replacement by imidazole or triazole weakens it. A com-
parison with ruthenium analogues (presented in a previous
Figure13. Antiproliferativeeffectsof1-4,6,and7inthehumancancer paper)49 reveals that replacement of ruthenium(III) by
celllinesHT-29(A)andSK-BR-3(B).Concentration-effectcurveswere osmium(III)increasestheactivityinHT-29cellsinallthree
obtainedbytheMTTassay;valuesaremeans(standarddeviationsfrom pairsofcomplexes(L)Hind,Him,orHtrz).WhereasIC
atleastthreeindependentexperiments. 50
values>100(cid:237)Mindicatethatthepotenciesoftheruthenium
and 1.37 ppm have not been identified, but remained analogues are rather modest, osmium confers a reasonable
unchangedover3days.The1HNMRspectrumofNAMI-A activitywithIC valuesmostlyinthe10-5Mrangeinthese
50
(-15ppmforS-bondedDMSO,-3.5,-5.6,and-7.8ppm cells. This effect is most pronounced in the case of 2 (L )
for coordinated Him, and 8.69 and 7.49 ppm for H im+) Hind), which is 10 times more potent than its ruthenium
2
showed notably downfield-shifted signals when compared congener.Thesetendenciesarenotparalleledbythefindings
to 6. Moreover, the 1H NMR spectrum of NAMI-A in incelllineSK-BR-3,however.Butgenerally,thevariation
physiologicalmediumwastimedependentandshowedfast of the azole ligand seems to have greater consequences for
replacementofthecoordinatedchlorideandDMSObywater, biologicalactivityintheosmiumseriesthanintheruthenium
as evidenced by the appearance of signals at -10 ppm (S- series. The observed effects are all the more remarkable
bondedDMSO)andat0.6ppm(Him)former-[RuCl (Him)- becauseoftheinertnessoftheseosmium(III)complexesin
3
(H O)(DMSO)] and free DMSO (2.7 ppm) within a few general and especially their resistance to hydrolysis (even
2
minutes.NAMI-AunderwentchlorideandDMSOhydrolysis in chloride-free solution) and lack of reactivity toward
responsibleforthedisappearanceofNAMI-Aafteronly15 9-methyladenine,whichsharplycontrastswiththebehavior
min.49aIncontrast,theosmiumNAMI-Aanalogueremained of ruthenium analogues, in particular NAMI-A, under
intact after 3 days in physiological medium. comparableexperimentalconditions.49Whereastheantime-
1H NMR spectra of a mixture of 6 and 9-methyladenine tastatic activity of NAMI-A in vivo has been attributed
(as a DNA model base) in 1:1.5 molar ratio in phosphate specifically to hydrolyzed species, the lack of cytotoxicity
buffer (pH 6.0, 37 (cid:176) C) were measured. The absence of a observedwithvariousosmium(II)arenecompoundshasbeen
newsetofsignalsexpectedforcoordinated9-methyladenine attributed to either too slow or too rapid hydrolysis, in the
evenafter4daysindicatedinertnessof6towardthepurine latter case resulting in the predominant formation of stable
nucleobase under the conditions employed (Figure S7). hydroxo-bridgeddimers.5Eventhoughthelattercompounds
AntiproliferativeActivity.1-4,6,and7weretestedfor differ distinctly from those presented here in terms of
theirantiproliferativeactivityintwohumancancercelllines oxidationstateandligandsphere,itisquiteremarkablethat
usingacolorimetricMTTassay.Concentration-effectcurves our findings conversely suggest that hydrolysis is not at all
are depicted in Figure 13, and IC values are listed in anessentialprerequisiteforantiproliferativeactivityofthis
50
comparisonwiththreeruthenium(III)analoguesinTable3. classofosmiumcomplexes.Thisalsocontrastswithconclu-
Structure-activityrelationshipsaresimilarinbothcelllines. sions drawn from the behavior of rhodium and iridium
In the more sensitive cell line HT-29 (colon carcinoma), analogues of NAMI-A, the inactivity of which has been
antiproliferative activity decreases in the following rank attributed to their inertness to hydrolysis.9,10
order: 2 > 4 (cid:25) 3 > 1 g 6 > 7. In the less sensitive cell NAMI-Areducestheformationandgrowthofmetastases
line SK-BR-3 (mammary carcinoma), the rank order is as in experimental tumor models but has little impact on the
follows: 2>4g1g3>6g7.Taking1asareference, growth of primary tumors.50 This behavior is in line with a
replacement of one DMSO ligand by indazole or benzimi- modest cytotoxicity but a pronounced and rapid impact on
(49) Groessl,M.;Reisner,E.;Hartinger,C.G.;Eichinger,R.;Semenova, (50) Sava,G.;Zorzet,S.;Turrin,C.;Vita,F.;Soranzo,M.R.;Zabucchi,
O.;Timerbaev,A.R.;Jakupec,M.A.;Arion,V.B.;Keppler,B.K. G.;Cocchietto,M.;Bergamo,A.;DiGiovone,S.;Pezzoni,G.;Sartor,
J.Med.Chem.2007,50,2185-2193. L.;Garbisa,S.Clin.CancerRes.2003,9,1898-1905.
5032 InorganicChemistry,Vol.46,No.12,2007
OsmiumNAMI-Aanalogues
theinteractionsoftumorcellswiththeextracellularmatrix, andmigrationwithacytotoxiccomponentinprimaryaswell
suggesting a target located in the cell membrane. In assecondarysitesofmalignanttumorswouldbeparticularly
particular,NAMI-Aincreasesactin-dependentcelladhesion attractiveforfurtherdevelopment.Inanycase,thesuggestion
by a mechanism probably involving integrin activation,51,52 ofMessorietal.touseanaloguesnotamenabletohydrolysis
it inhibits matrix degradation by reducing the release of asmodelcompoundsforstudyingthebiodistributionprofile
matrixmetalloproteinasesratherthanbyitsdirectinhibitory ofunhydrolysedNAMI-A10isapplicablealsototheosmium
effect on these enzymes,53 and it reduces cell invasiveness complexes presented here.
andmigration,50,53,54altogethermanifestinginalessmalig- Final Remarks. Investigation of stepwise reduction of
nant cell phenotype. In endothelial cells, inhibition of OsO withN H (cid:226)2HClandSnCl (cid:226)2H O/DMSOenabledthe
4 2 4 2 2
proliferation,chemotacticbehavior,andmatrixmetallopro- preparationandcharacterizationof[(DMSO) H][trans-OsIII-
2
teinasesecretionhavebeenobserved,suggestingacontribu- Cl(DMSO)],thecompoundwhichremainedelusive(atleast
4 2
tion of antiangiogenic effects to the antimetastatic proper- in terms of solid-state isolation) for quite a long time. The
ties.55 Furthermore, NAMI-A is capable of inducing a latter proved to be a suitable precursor for the synthesis of
transientcellcyclearrest55andbindingtoDNAtoacertain osmium NAMI-A analogues, which showed reasonable
degree,56butneitheroftheseeffectsislikelytoaccountfor antiproliferative activity in vitro. The full characterization
the antimetastatic activity. of prepared compounds, both in the solid state and in
NAMI-A is transformed under physiological conditions solution, permitted the elucidation of essential differences
intoseveraldifferentrutheniumspecies,buttheirindividual between related osmium and ruthenium complexes. In
contributions to the pharmacological effects remain elu- particular, we found that osmium complexes, which are
sive.48a,57Rapidhydrolysistopolyoxospeciesinphysiologi- markedly more inert than related ruthenium compounds
cal buffer, their higher cellular uptake, and their unaltered toward substitution reactions (hydrolysis, interaction with
effects on the cell cycle of metastatic cells have prompted DNA bases), in accord with their position in the periodic
investigatorstoattributetheactivityofNAMI-Atohydroly- table, partially show a higher antiproliferative activity than
sis products.48a Furthermore, reduction to ruthenium(II) therelatedrutheniumcompounds.Thisisevenmoreintrigu-
species does not alter the effects on cell cycle distribution ing, if we take into account that other related compounds
and metastasis growth to a meaningful extent.57 Because it based on iridium and rhodium do not exhibit any antipro-
remains unclear which molecular effects account for the liferative activity.
antimetastaticactivityandwhethertheydependonhydrolysis Theslope,S ,andintercept,I ,ofLever’sequationwere
M M
and/or reduction, it is impossible to predict whether this determinedfortheOsII/OsIIIandOsIII/OsIVcouplesinaqueous
activityispreservedintheosmiumanalogues.Experiments medium, which will allow the prediction of the redox
insuitablerodenttumormodelswithreliablemetastasizing potential of other osmium complexes with the same redox
propensityareplannedinordertoexaminethesecompounds couples.
fortheirantimetastaticcapacity,alongwiththeirimpacton The work also made a notable crystallographic contribu-
primarytumorsinvivo.Fromatherapeuticalpointofview, tion.2,3,and5-7expandtherelativelysmallclassofOsIII-
a compound endowed with a dual mechanism combining DMSO-azolecomplexescharacterizedbyX-raydiffraction.
inhibitory effects on the processes of tumor cell invasion The binding mode of triazole (monofunctional via N2) and
the tautomer stabilized (4H) are distinct from those found
(51) Sava,G.;Frausin,F.;Cocchietto,M.;Vita,F.;Podda,E.;Spessotto, in related ruthenium compounds (coordination via N4 and
P.;Furlani,A.;Scarcia,V.;Zabucchi,G.Eur.J.Cancer2004,40,
1383-1396. 1H tautomer).
(52) Frausin,F.;Scarcia,V.;Cocchietto,M.;Furlani,A.;Serli,B.;Alessio,
E.;Sava,G.J.Pharmacol.Exp.Ther.2005,313,227-233. Acknowledgment. WethankA.Rollerforcollectionof
(53) Pacor,S.;Zorzet,S.;Cocchietto,M.;Bacac,M.;Vadori,M.;Turrin, X-ray data and Dr. S. Shova for discussion of the crystal-
C.;Gava,B.;Castellarin,A.;Sava,G.J.Pharmacol.Exp.Ther.2004, lographic part of the work.
310,737-744.
(54) Zorzet,S.;Bergamo,A.;Cocchietto,M.;Sorc,A.;Gava,B.;Alessio, SupportingInformationAvailable: UV-visspectraofcom-
E.; Iengo, E.; Sava, G. J. Pharmacol. Exp. Ther. 2000, 295, 927- plexes [HL][MCl(HL)(DMSO)], where M ) Os, Ru, UV-vis
933. 2 4
(55) Vacca, A.; Bruno, M.; Boccarelli, A.; Coluccia, M.; Ribatti, D.;
spectrumof1inwater,UV-visspectraof2-4,6,and7inwater
Bergamo,A.;Garbisa,S.;Sartor,L.;Sava,G.Br.J.Cancer2002, monitoredover48h,1HNMRspectrumof6with9-MeAde,ESI
86,993-998.
mass spectrum of 6 in methanol/water (30/70), X-ray crystal-
(56) Pluim,D.;vanWaardenburg,R.C.A.M.;Beijnen,J.H.;Schellens,
J.H.M.CancerChemother.Pharmacol.2004,54,71-78.
lographicfilesinCIFformatfor1-3,5,6,and7.Thismaterialis
(57) Sava,G.;Bergamo,A.;Zorzet,S.;Gava,B.;Casarsa,C.;Cocchietto, availablefreeofchargeviatheInternetathttp://pubs.acs.org.
M.;Furlani,A.;Scarcia,V.;Serli,B.;Iengo,E.;Alessio,E.;Mestroni,
G.Eur.J.Cancer2002,38,427-435. IC700405Y
Inorganic Chemistry, Vol. 46, No. 12, 2007 5033