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Thursday Dec 16 11:45 AM StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications) Article: 316

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Inorganic Chemistry Communications 3 (2000) 32–34

Synthesis, antiapoptotic biological activity and structure of anoxo–vanadium(IV) complex with an OOO ligand donor set

Diego del Rıo a, Agustın Galindo a,*, Juan Tejedo b, Francisco J. Bedoya b, Andrea Ienco c,´ ´Carlo Mealli c

a Departamento de Quımica Inorganica, Universidad de Sevilla, Aptdo 553, 41071 Sevilla, Spain´ ´b Departamento de Bioquımica Medica y Biologıa Molecular, Universidad de Sevilla, 41009 Sevilla, Spain´ ´ ´

c ISSECC, CNR, Via Nardi 39, 50132 Florence, Italy

Received 22 October 1999

Abstract

The oxo–vanadium(IV) complex VO(oda)(H2O)2 (1) (odasoxydiacetate, O(CH2COOy)2) was obtained by reaction ofaerobicaqueoussolutions of VO(acac)2 with oxydiacetic acid, O(CH2COOH)2. The antiapoptotic biological activity of 1 was studied in insulin-producingcells. Chemically generated nitric oxide (NO) triggers apoptotic events, such as the appearance of oligonucleosomes in cytosol, and thisresponse was prevented by the presence of 1 in the culture medium. The molecular structure of 1 has been determined by X-ray diffractionanalysis. q2000 Elsevier Science S.A. All rights reserved.

Keywords: Vanadium complexes; Oxo complexes; Oxydiacetate complexes; Apoptosis; Crystal structures

Interest in the chemistry of oxo–vanadium complexes hasgrown enormously in recent decades. The increasing atten-tion given to this type of compound is mainly due to thefunction of vanadium in several biological processes [1–7]such as the regulation of carbohydrate metabolism [8–11].Basic research on the coordination chemistry of oxo–vana-dium complexes has become essential for the knowledge ofthe behaviour of these systems [12–16]. The present studydescribes the synthesis, the antiapoptotic biological activityof 1 in insulin-producing cells and the structural characteri-zation of the oxo–vanadium(IV) complex VO(oda)(H2O)2

(1) (odasO(CH2COOy)2) containing an OOO donorligand set. As far as we know, this is the first study of theantiapoptotic activity of an oxo–vanadium complex;although, while our work was in progress, vanadate has beenshown [17] to inhibit apoptosis in malignant glioma cells.

Specific studies on the stability of the vanadyl–oxydiaceticacid aqueous system were reported early [18,19], but theexact nature of the vanadium(IV) complex was never elu-cidated. Treatment of aerobic aqueous solutions ofVO(acac)2 with oxydiacetic acid, O(CH2COOH)2, affords,after the appropriate work-up, blue crystals of complex

* Corresponding author. Fax: q34 95 455 7156; e-mail: galindo@cica.es

VO(oda)(H2O)2 (1) in good yields 1. The IR spectrum of1 displays the characteristic absorptions due to the vanadylgroup, the carboxylate groups and the water ligands (con-firmed by the preparation of deuterated VO(oda)(D2O)2

complex). The measured effective magnetic moment, bothin solution and in the solid state, is ca. 1.7 mB, consistent witha d1 ground-state electronic configuration.

Complex 1 in the solid state is stable in air. Aqueous solu-tions of 1 also show a great stability to oxidation in air,remaining unaltered (UV–Vis control) after bubbling of oxy-gen for 1 day. However, a slow oxidation process wasobserved when solid 1 was dissolved in MeOH, under aerobicconditions. Oxidation seems to be suppressed in water, whichacts as a good donor ligand, in a similar manner to theobserved behaviour of the complex VO(maltolato)2 [11].

1 To the mixture of VO(acac)2 (10.6 g, 40 mmol) and O(CH2COOH)2

(5.36 g, 40 mmol) was added water (100 ml). The mixture was heated atreflux for 3 h. The hot solution was filtered, concentrated (in order toeliminate Hacac by evaporation) and slowly cooled. Blue crystals of 1 werefiltered off, washed with acetone and Et2O, and dried (7.5 g, 80%). IR(KBr): 3056–2887 very br n(OH), 1590 s br n(CO), 994 s n(VO) cmy1.meff (solid state)s1.71 mB. meff (H2O/tBuOH solution, 9:1)s1.68 mB.UV–Vis (H2O): lmaxs275, 790 nm. Anal. Calc. for C4H8O8V: C, 20.4; H,3.4. Found: C, 20.6; H, 3.2%.

D. del Rıo et al. / Inorganic Chemistry Communications 3 (2000) 32–34´ 33

Thursday Dec 16 11:45 AM StyleTag -- Journal: INOCHE (Inorganic Chemistry Communications) Article: 316

Fig. 1. Antiapoptotic effect in RINm5F cells: prevention of NO-inducedoligonucleosamal DNA fragmentation by complex 1.

Fig. 2. Molecular structure of VO(oda)(H2O)2 (1). Selected bond lengths(A): V(1)–O(5), 1.590(7); V(1)–O(3), 2.016(3); V(1)–O(4),˚

2.053(3); V(1)–O(2), 2.180(6); O(3)–C(1), 1.266(5); O(6)–C(1),1.242(5). Selected bond angles (8): O(5)–V(1)–O(3), 107.03(11);O(5)–V(1)–O(4), 92.92(11); O(3)–V(1)–O(4), 89.55(11); O(5)–V(1)–O(2), 180.000(1); O(3)–V(1)–O(2), 72.97(11); O(4)–V(1)–O(2), 87.08(11); O(4)–V(1)–O(49), 174.2(2).

Solutions of 1 have an acidic nature and chemical transfor-mations were observed at basic pH [20].

The antiapoptotic biological activity of 1 has been studiedin insulin-producing RINm5F cells 2. Nitric oxide (NO) hasbeen reported to trigger the apoptotic death program in rodentpancreatic b cells [21–24]. We have found that exposure ofcells to NO, chemically generated from sodium nitroprusside(NPS), triggered apoptotic events in the cells such as thefragmentation of DNA into oligonucleosomes. This actionwas prevented by addition of 1 to the culture medium. Fig. 1shows the antiapoptotic biological effect caused by complex1, in terms of the prevention of NO-induced oligonucleosa-mal DNA fragmentation 3.

Phosphorylation of proteins has been found to participatein the control of the apoptotic death program in several cellsystems [25–27]. NO-dependent apoptosis in insulin-pro-ducing HIT-T15 cells has been reported to be dependent onthe cGMP/protein kinase G system [28]. It has also beenreported recently that NO-dependent apoptosis in HL-60 cellsis potentiated by vanadate [29–32]. Actions of vanadate onapoptosis might be cell dependent [33–35], since we havefound [36] that it blocks NO-dependent apoptosis inRINm5F cells. Our finding that 1 blocks NO-dependentapop-tosis also confirms the notion that tryrosine phosphorylationis involved in the activation of antiapoptotic proteins in pan-creatic b-cells.

The crystal structure 4 of 1 has been determined by X-raydiffraction methods. The molecular structure (Fig. 2) hasapproximate C2v symmetry. The coordination geometryaround the vanadium atom is a distorted octahedron. Thewater ligands are mutually trans (O(4)–V(1)–O(49),174.2(2)8) while the oxydiacetate ligand is meridionally dis-tributed. Similar mer disposition of the oxydiacetate ligandhas been noticed in other structurally characterized transitionmetal complexes [37–41]. The main distortion from the octa-hedral geometry is imposed by the bites of the tridentate odaligand (O(3)–V(1)–O(2) angles of 72.97(11)8) and alsocomes from the typical [42] deviation of the oxo–V–(cisatom) angles from the ideal 908 value (for example,107.03(11)8 for O(5)–V(1)–O(3)). The vanadyl bondlength is 1.590(7) A and compares well with the mean V_O˚

bond length value of 1.614(2) A (CSD search [43]). The˚

other vanadium–oxygen bond distances are 2.053(3) A(water ligands), 2.016(3) A (carboxy groups) and 2.180(6)˚

A (for the ethereal oxygen atom O(2)). The structure˚

2 RINm5F cells were maintained in RPMI 1640 supplemented with 100mg/ml streptomycin, 100 U/ml penicillin G, 2.5 mg/ml amphotericin B, 2mM glutamine, 10% fetal bovine serum in a humidified atmosphere of 5%CO2 at 378C.

3 5=104 cells were incubated with 1 mM SNP for 2 h. When necessary,150 mM of complex 1 was added 0.5 h before exposing cells to SNP, andDNA fragmentation was measured with a cell death detection ELISAPLUS

kit. Complex 1 does not react with NO or SNP. No antiapoptotic effect wasobserved by adding only oxydiacetic acid.

4 Crystal data for 1: C4H8O8V, orthorhombic, space group Aba2,as8.919(3), bs10.889(2), cs8.593(3) A, Vs834.5(4) A3, Zs4,˚ ˚

Dcalcs1.616 g cmy3, ms1.172 mmy1, Rs0.0288, wRs0.0817.

resembles that reported [44] for the analogous com-plex VO(pdc)(H2O)2 (pdcspyridine-2,6-dicarboxylate).Although many related oxo–vanadium(IV) complexes withtridentate ligands have been structurally characterized, to ourknowledge the presence of a tridentate OOO ligand donor setis unprecedented.

Supplementary material

Tables of crystal and refinement data, bond lengths andangles, atomic coordinates and thermal parameters for 1 areavailable from the author on request.

Acknowledgements

This work was supported by the DGES (PB97-740) andDGCYT (SAF96-0205) and Junta de Andalucıa.´

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