Marked dependence on carrier-ligand bulk but not on carrier-ligand chirality of the duplex versus single-strand forms of a DNA oligonucleotide with a series of G-Pt(II)-G intrastrand cross-links modeling cisplatin-DNA adducts

A Very Rare Example of a Structurally Characterized 3'-GMP Metal Complex. NMR and Synthetic Assessment of Adducts Formed by Guanine Derivatives with [Pt(Ltri)Cl]Cl Complexes with an N,N',N″ Tridentate Ligand (Ltri) Terminated by Imidazole Rings

[Pt(N(R)-1,1'-Me₂dma)Cl]Cl complexes with tridentate ligands (bis(1-methyl-2-methylimidazolyl)amine, R = H; N-(methyl)bis(1-methyl-2-methylimidazolyl)amine, R = Me) were prepared in order to investigate Pt(N(R)-1,1'-Me₂dma)G adducts (G = monodentate N9-substituted guanine or hypoxanthine derivative). Solution NMR spectroscopy is the primary tool for studying metal complexes of nucleosides and nucleotides because such adducts rarely crystallize. However, [Pt(N(H)-1,1'-Me₂dma)(3'-GMPH)]NO₃·5H₂O (5) was crystallized, allowing, to our knowledge, the first crystallographic molecular structure determination for a 3'-GMP platinum complex. The structure is one of only a very few structures of a 3'-GMP complex with any metal. Complex 5 has the syn rotamer conformation, with 3'-GMP bound by N7. All Pt(N(R)-1,1'-Me₂dma)G adducts exhibit two new downfield-shifted G H8 signals, consistent with G bound to platinum by N7 and a syn/anti rotamer mixture. Anticancer-active monofunctional platinum(II) complexes have bulky carrier ligands that cause DNA adducts to be distorted. Hence, understanding carrier-ligand steric effects is key in designing new platinum drugs. Ligand bulk can be correlated with the degree of impeded rotation of the G nucleobase about the Pt-N7 bond, as assessed by the observation of rotamers. The signals of syn and anti rotamers are connected by EXSY cross-peaks in 2D ROESY spectra of Pt(N(H)-1,1'-Me₂dma)G adducts but not in spectra of Pt(N(H)dpa)G adducts (N(H)dpa = bis(2-picolyl)amine), indicating that rotamer interchange is more facile and carrier-ligand bulk is lower in Pt(N(H)-1,1'-Me₂dma)G than in Pt(N(H)dpa)G adducts. The lower steric hindrance is a direct consequence of the greater distance of the G nucleobase from the H4/4' protons in the N(R)-1,1'-Me₂dma carrier ligand in comparison to that from the H6/6' protons in the N(H)dpa carrier ligand. Although in 5 the nucleotide is 3'-GMP (not the usual 5'-GMP) and the N(H)-1,1'-Me₂dma carrier ligand is very different from those typically present in structurally characterized Pt(II) G complexes, the rocking and canting angles in 5 adhere to long-recognized trends.

DNA fragment conformations in adducts with Kiteplatin

The anticancer-active platinum complex with cis-1,4-diaminocyclohexane has proved to be very valuable in detecting multiple conformers in adducts with oligonucleotides.

Guanine nucleobase adducts formed by [Pt(di-(2-picolyl)amine)Cl]Cl: evidence that a tridentate ligand with only in-plane bulk can slow guanine base rotation

Pt(II) complexes bind preferentially at N7 of G residues of DNA, causing DNA structural distortions associated with anticancer activity. Some distortions induced by difunctional cisplatin are also found for monofunctional Pt(II) complexes with carrier ligands having bulk projecting toward the guanine base. This ligand bulk can be correlated with impeded rotation about the Pt-N7(guanine) bond. Pt(N(H)dpa)(G) adducts (N(H)dpa = di-(2-picolyl)amine, G = 5'-GMP, 5'-GDP, 5'-GTP, guanosine, 9-EtG, and 5'-IMP) were used to assess whether a tridentate carrier ligand having bulk concentrated in the coordination plane can impede guanine nucleobase rotation. Because the Pt(N(H)dpa) moiety contains a mirror plane but is unsymmetrical with respect to the coordination plane, Pt(N(H)dpa)(G) adducts can form anti or syn rotamers with the guanine O6 and the central N-H of N(H)dpa on the opposite or the same side of the coordination plane, respectively. The observation of two sharp, comparably intense guanine H8 NMR signals provided evidence that these Pt(N(H)dpa)(G) adducts exist as mixtures of syn and anti rotamers, that rotational interchange is impeded by N(H)dpa, and that the key interactions involves steric repulsions between the pyridyl and guanine rings. The relative proximity of the guanine H8 to the anisotropic pyridyl rings allowed us to conclude that the syn rotamer was usually more abundant. However, the anti rotamer was more abundant for the Pt(N(H)dpa)(5'-GTP) adduct, in which a hydrogen bond between the 5'-GTP γ-phosphate group and the N(H)dpa central N-H is geometrically possible. In all previous examples of the influence of hydrogen bond formation on rotamer abundance in Pt(II) guanine adducts, these hydrogen bonding interactions occurred between ligand groups in cis positions. Thus, the role of a trans ligand group in influencing rotamer abundance, as found here, is unusual.

Effects of amine ligand bulk and hydrogen bonding on the rate of reaction of platinum(II) diamine complexes with key nucleotide and amino acid residues

NMR spectroscopy has been used to observe the effects of the amine ligand on the rate of reaction of platinum diamine and triamine complexes with DNA and protein residues. Whereas [Pt(dien)Cl]Cl and [Pt(dien)(D(2)O)](2+) have been known to react faster with thioether residues such as N-AcMet than with 5'-GMP, we found that [Pt(Me(4)en)(D(2)O)(2)](2+) appeared to react faster with 5'-GMP. To quantitatively assess the factors influencing the rates of reaction, rate constants at pH 4 were determined for the reactions of [Pt(en)(D(2)O)(2)](2+) [en = ethylenediamine] and [Pt(Me(4)en)(D(2)O)(2)](2+) with N-AcMet, N-AcHis, 5'-GMP, and Guo (guanosine). In each case the less bulky complex ([Pt(en)(D(2)O)(2)](2+)) reacts more quickly than does the bulkier [Pt(Me(4)en)(D(2)O)(2)](2+), as expected. Both complexes reacted faster with 5'-GMP; however, analysis of the rate constants suggests that the [Pt(en)(D(2)O)(2)](2+) complex favors reaction with 5'-GMP due to hydrogen bonding with the 5'-phosphate, whereas [Pt(Me(4)en)(D(2)O)(2)](2+) disfavors reaction with N-AcMet due to steric clashes. Bulk had relatively little effect on the rate constant with N-AcHis, suggesting that peptides or proteins that coordinate via His residues would not have their reactivity affected by bulky diamine ligands.

Single-stranded oligonucleotide adducts formed by Pt complexes favoring left-handed base canting: steric effect of flanking residues and relevance to DNA adducts formed by Pt anticancer drugs

Platinum anticancer drug binding to DNA creates large distortions in the cross-link (G*G*) and the adjacent XG* base pair (bp) steps (G* = N7-platinated G). These distortions, which are responsible for anticancer activity, depend on features of the duplex (e.g., base pairing) and of the cross-link moiety (e.g., the position and canting of the G* bases). The duplex structure stabilizes the head-to-head (HH) over the head-to-tail (HT) orientation and right-handed (R) over left-handed (L) canting of the G* bases. To provide fundamental chemical information relevant to the assessment of such duplex effects, we examine (S,R,R,S)-BipPt(oligo) adducts (Bip = 2,2'-bipiperidine with S,R,R,S chiral centers at the N, C, C, and N chelate ring atoms, respectively; oligo = d(G*pG*) with 3'- and/or 5'-substituents). The moderately bulky (S,R,R,S)-Bip ligand favors L canting and slows rotation about the Pt-G* bonds, and the (S,R,R,S)-BipPt(oligo) models provide more useful data than do dynamic models derived from active Pt drugs. All 5'-substituents in (S,R,R,S)-BipPt(oligo) adducts favor the normal HH conformer (∼97%) by destabilizing the HT conformer through clashes with the 3'-G* residue rather than through favorable H-bonding interactions with the carrier ligand in the HH conformer. For all (S,R,R,S)-BipPt(oligo) adducts, the S pucker of the 5'-X residue is retained. For these adducts, a 5'-substituent had only modest effects on the degree of L canting for the (S,R,R,S)-BipPt(oligo) HH conformer. This small flanking 5'-substituent effect on an L-canted HH conformer contrasts with the significant decrease in the degree of R canting previously observed for flanking 5'-substituents in the R-canted (R,S,S,R)-BipPt(oligo) analogues. The present data support our earlier hypothesis that the distortion distinctive to the XG* bp step (S to N pucker change and movement of the X residue) is required for normal stacking and X·X' WC H bonding and to prevent XG* residue clashes.

NMR studies of models having the Pt(d(GpG)) 17-membered macrocyclic ring formed in DNA by platinum anticancer drugs: Pt complexes with bulky chiral diamine ligands

The highly distorted Pt(d(G*pG*)) (G* = N7-platinated G) 17-membered macrocyclic ring formed by cisplatin anticancer drug binding to DNA alters the structure of the G*G* base pair steps, canting one base, and increases dynamic motion, complicating solution structural studies. However, the ring appears to favor the HH1 conformation (HH1 denotes head-to-head guanine bases, 1 denotes the normal direction of backbone propagation). Compared to cisplatin, analogues with NH groups in the carrier ligand replaced by bulky N-alkyl groups are more toxic and less active and form less dynamic adducts. To examine the molecular origins for the biological effects of steric bulk, we evaluate Me(4)DABPt(d(G*pG*)) models; the bulk and chirality of Me(4)DAB (N,N,N',N'-tetramethyl-2,3-diaminobutane with S,S or R,R configurations at the chelate ring carbons) impede dynamic motion and enhance the utility of NMR methods for identifying and characterizing conformers. Unlike past studies of adducts with such bulky carrier ligands, in which no HH conformer was found, the Me(4)DABPt(d(G*pG*)) adducts did form the HH1 conformer, providing compelling evidence that the sugar-phosphate backbone can impose constraints sufficient to overcome the alkyl-group steric effects. The HH1 conformer exhibits no significant canting. The (S,S)-Me(4)DABPt(d(G*pG*)) adduct has the least amount of the "normal" HH1 conformer and the greatest amount of the ΔHT1 conformer (ΔHT1 = head-to-tail G* bases with Δ chirality) ever observed (88% under some conditions). Thus, our results lead us to hypothesize that the low activity and high toxicity of analogues of cisplatin having carrier ligands with N-alkyl groups arise from the low abundance and minimal canting of the HH1 conformer and possibly from the adverse effects of an abundant ΔHT1 conformer. The new findings advance our understanding of the chemistry of the Pt(d(G*pG*)) macrocyclic ring and of the effects of carrier-ligand steric bulk on the properties of the ring.

Metals in anticancer therapy: copper(II) complexes as inhibitors of the 20S proteasome

Selective 20S proteasomal inhibition and apoptosis induction were observed when several lines of cancer cells were treated with a series of copper complexes described as [Cu(L(I))Cl] (1), [Cu(L(I))OAc] (2), and [Cu(HL(I))(L(I))]OAc (3), where HL(I) is the ligand 2,4-diiodo-6-((pyridine-2-ylmethylamino)methyl)phenol. These complexes were synthesized, characterized by means of ESI spectrometry, infrared, UV-visible and EPR spectroscopies, and X-ray diffraction when possible. After full characterization species 1-3 were evaluated for their ability to function as proteasome inhibitors and apoptosis inducers in C4-2B and PC-3 human prostate cancer cells and MCF-10A normal cells. With distinct stoichiometries and protonation states, this series suggests the assignment of species [CuL(I)](+) as the minimal pharmacophore needed for proteasomal chymotryspin-like activity inhibition and permits some initial inference of mechanistic information.

The role of p53 in the cellular toxicity by active trans-platinum complexes containing isopropylamine and hydroxymethylpyridine

Despite some initial research that reported a lack of activity of trans geometry, complexes with general formula trans-[PtCl2(L)(L')] exhibit an important cytotoxic activity in cisplatin-sensitive and resistant cell lines. Based on the proposed mechanism of action for the trans-platinum compounds, they might form DNA adducts initiating a DNA-damage response and ultimately ending in the activation of the p53 protein. In the present work, we have studied the biochemical properties of the trans-[PtCl2(isopropylamine)(L)] complexes (where L is 3- or 4-(hydroxymethyl)-pyridine) against several cell lines and the relationship between cytotoxicity and the protein p53. Both complexes showed different antitumoral properties depending on the presence or absence of protein p53 in isogenic colon carcinoma HCT116 cell lines. Cell cycle studies with the complexes in these cell lines were performed to investigate their antitumoral activity. Apoptosis was observed to be launched from G1 or G2/M accumulations. Confocal microscopy showed the different behaviour of isogenic tumoral cell lines treated with the trans-platinum complexes. Our data suggest that small differences in the carrier ligands could play an important role in the overall biological effects. The body of the research regarding structure-activity relationships such as the different position of groups in the carrier ligands will provide new rational basis for the design of new platinum antitumor drugs.

Comparison of the electronic properties, and thermodynamic and kinetic parameters of the aquation of selected platinum(II) derivatives with their anticancer IC50 indexes

Three potential anticancer agents {trans-[PtCl(2)(NH(3))(thiazole)], cis-[PtCl(2)(NH(3))(piperidine)], and PtCl(2)(NH(3))(cyclohexylamine) (JM118)} were explored and compared with cisplatin and the inactive [PtCl(dien)](+) complex. Basic electronic properties, bonding and stabilization energies were determined, and thermodynamic and kinetic parameters for the aquation reaction were estimated at the B3LYP/6-311++G(2df,2pd) level of theory. Since the aquation process represents activation of these agents, the obtained rate constants were compared with the experimental IC(50) values for several tumor cells. Despite the fact that the processes in which these drugs are involved and the way in which they affect cells are very complex, some correlations can be deduced.

Metal-ion-coordinating properties of the dinucleotide 2'-deoxyguanylyl(5'-->3')-2'-deoxy-5'-guanylate (d(pGpG)3-): isomeric equilibria including macrochelated complexes relevant for nucleic acids

The interaction between divalent metal ions and nucleic acids is well known, yet knowledge about the strength of binding of labile metal ions at the various sites is very scarce. We have therefore studied the stabilities of complexes formed between the nucleic acid model d(pGpG) and the essential metal ions Mg2+ and Zn2+ as well as with the generally toxic ions Cd2+ and Pb2+ by potentiometric pH titrations; all four ions are of relevance in ribozyme chemistry. A comparison of the present results with earlier data obtained for M(pUpU)- complexes allows the conclusion that phosphate-bound Mg2+ and Cd2+ form macrochelates by interaction with N7, whereas the also phosphate-coordinated Pb2+ forms a 10-membered chelate with the neighboring phosphate diester bridge. Zn2+ forms both types of chelates with formation degrees of about 91% and 2.4% for Zn[d(pGpG)]cl/N7 and Zn[d(pGpG)]-cl/PO, respectively; the open form with Zn2+ bound only to the terminal phosphate group, Zn[d(pGpG)]-op, amounts to about 6.8 %. The various intramolecular equilibria have also been quantified for the other metal ions. Zn2+, Cu2+, and Cd2+ also form macrochelates in the monoprotonated M[H;d(pGpG)] species (the proton being at the terminal phosphate group), that is, the metal ion at N7 interacts to some extent with the P(O)2(OH)- group. Thus, this study demonstrates that the coordinating properties of the various metal ions toward a pGpG unit in a nucleic acid differ: Mg2+, Zn2+, and Cd2+ have a significant tendency to bridge the distance between N7 and the phosphate group of a (d)GMP unit, although to various extents, whereas Pb2+ (and possibly Ca2+) prefer a pure phosphate coordination.

Head-to-head cross-linked adduct between the antitumor unit bis(mu-N,N'-di-p-tolylformamidinato)dirhodium(II,II) and the DNA fragment d(GpG)

Reactions of the compound cis-[Rh2(DTolF)2(CH3CN)6](BF4)2, a formamidinate derivative of the class of antitumor compounds [Rh2(O2CR)4] (R=Me, Et, Pr), with 9-ethylguanine (9-EtGuaH) or the dinucleotide d(GpG) proceed by substitution of the acetonitrile groups, with the guanine bases spanning the Rh--Rh bond, in a bridging fashion, through sites N7/O6. In the case of 9-EtGuaH, both head-to-head (HH) and head-to-tail (HT) isomers are formed, whereas with the tethered bases in d(GpG), only one right-handed conformer HH1R [Rh2(DTolF)2{d(GpG)}] is present in solution. For both cis-[Rh2(DTolF)2(9-EtGuaH)2](BF4)2 and [Rh2(DTolF)2{d(GpG)}], the absence of N7 protonation at low pH and the substantial decrease of the pKa values for N1-H deprotonation, support N7/O6 binding of the bases to the dirhodium core. The N7/O6 binding of the bases is further corroborated by the downfield shift by Deltadelta approximately 4.0 ppm of the 13C NMR resonances for the C6 nuclei as compared to the corresponding resonances of the free ligands. The HH arrangement of the guanine bases in [Rh2(DTolF)2{d(GpG)}] is indicated by the intense H8/H8 ROE cross-peaks in the 2D ROESY NMR spectrum. Complete characterization of the [Rh2(DTolF)2{d(GpG)}] conformer by 2D NMR spectroscopy supports anti-orientation and N (C3'-endo) conformation for both deoxyribose residues. The N-pucker for the 5'-G base is universal in such cross-links, but it is very unusual for platinum and unprecedented for dirhodium HH cross-linked adducts to have both deoxyribose residues in the N-type conformation. The bulk, the nonlabile character, and the electron-donating ability of the formamidinate bridging groups spanning the dirhodium core affect the nature of the preferred dirhodium DNA adducts. Molecular modeling studies performed on [Rh2(DTolF)2{d(GpG)}] corroborate the structural features obtained by NMR spectroscopy.

The first pure LambdaHT rotamer of a complex with a cis-[metal(nucleotide)2] unit: a cis-[Pt(amine)2(nucleotide)2] LambdaHT rotamer with unique molecular structural features

cis-[PtA2(nucleotide)2] complexes (A2 stands for two amines or a diamine) have been extensively investigated as model compounds for key cisplatin-DNA adducts. All cis-[metal(nucleotide/nucleoside)2] complexes with guanine and related purines characterized in the solid state thus far have the DeltaHT conformation (head-to-tail orientation of the two bases and right-handed chirality). In sharp contrast, the LambdaHT conformation (left-handed chirality) dominates in acidic and neutral aqueous solutions of cis-[PtA2(5'-GMP)2] complexes. Molecular models and solution experiments indicate that the LambdaHT conformer is stabilized by 5'-phosphate/N1H hydrogen-bond interactions between cis nucleotides with the normal anti conformation. However, this evidence, while compelling, is indirect. At last, conditions have been defined to allow crystallization of this elusive conformer. The structure obtained reveals three unique features not present in all other cis-[PtA2(nucleotide)2] solid-state structures: a LambdaHT conformation, very strong hydrogen-bond interactions between the phosphate and N1H of cis nucleotides, and a very small dihedral angle between the planes of the two guanines lying nearly perpendicular to the coordination plane. These new results indicate that, because there are no local base-base repulsions precluding the LambdaHT conformer, global forces rather than local interactions account for the predominance of the DeltaHT conformer over the LambdaHT conformer in the solid state and in both inter- and intrastrand HT crosslinks of oligonucleotides and DNA.

fac-[Re(CO)3(H2O)3]+ nucleoside monophosphate adducts investigated in aqueous solution by multinuclear NMR spectroscopy

The fac-[Re(CO)3(H2O)3]+ cation, the putative DNA-binding species accounting for the biological activity of related Re(I) complexes, binds reversibly to N7 of 6-oxopurine nucleotide monophosphates (NMPs), in contrast to Pt(II) anticancer drugs. A relatively high amount of NMP is needed to convert all of the fac-[Re(CO)3(H2O)3]+ to adducts. The Re/nucleotide 1:1 adduct forms more rapidly and builds up to a higher concentration for guanosine 5'-monophosphate (5'-GMP) and inosine 5'-monophosphate (5'-IMP) than for the respective 3'-monophosphates (3'-GMP and 3'-IMP). These results are attributable to the 5'-positioning of the 5'-NMP phosphate group that allows it to approach the metal inner sphere for more favorable cation electrostatic and aqua ligand H-bonding interactions, both in the initial productive ion pair encounter complexes and in the N7-bound 1:1 adducts. A higher reactivity of 5'-GMP over 3'-GMP is known for cisplatin. In contrast, more Re/nucleotide 1:2 adduct was formed by 3'-GMP (and 3'-IMP) than by 5'-GMP (and 5'-IMP). Because the 3'-phosphate group cannot closely approach the metal inner coordination sphere, the greater stability for the 3'-GMP 1:2 adduct reflects the more favorable G N1H-phosphate interligand GMP-GMP interactions for 3'-GMP vs 5'-GMP (G=guanine base derivative). This type of interaction is known for platinum adducts. In 1:2 adducts the bound nucleotides are inequivalent, prompting us to perform mixed 5'-GMP/3'-GMP experiments, leading to the observation of major (M) and minor (m) mixed Re/5'-GMP/3'-GMP 1:1:1 adducts. The order of abundance at equilibrium in a typical experiment was M>bis 3'-GMP>m>or=bis 5'-GMP. This stability order was rationalized by invoking the phosphate interactions described above. When methionine and 5'-GMP were allowed to compete for fac-[Re(CO)3(H2O)3]+, the Re/5'-GMP 1:1 adduct was the kinetic product and the S-bound Re/methionine adduct was the thermodynamic product, a result opposite to that typically found for cisplatin.

Effect of the diamine nonleaving group in platinum-acridinylthiourea conjugates on DNA damage and cytotoxicity

The following complexes of type [PtCl(R)(ACRAMTU)](NO3)2 (ACRAMTU = 1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea)), derived from prototype 1 (with R = ethane-1,2-diamine), were synthesized: 2 (with R = (1R,2R)-1,2-diaminocyclohexane), 3 (with R = propane-1,3-diamine), 4 (with R = N1,N1,N2,N2-tetramethylethane-1,2-diamine), and 5 (with R = 2,2'-bipyridine). The DNA sequence specificity of the conjugates and their antiproliferative potential in HL-60 and H460 cells were investigated. Conjugate 3 showed the strongest non-cisplatin-type DNA damage in polymerase stop assays and superior cell kill efficacy in H460 lung cancer (IC50 = 70 nM).

Pt-bridges in various single-strand and double-helix DNA sequences. DFT and MP2 study of the cisplatin coordination with guanine, adenine, and cytosine

In this study, various platinum cross-links in DNA bases were explored. Some of these structures occur in many cis/trans-platinated double-helixes or single-stranded adducts. However, in the models studied, no steric hindrance from sugar-phosphate backbone or other surroundings is considered. Such restrictions can change the bonding picture partially but hopefully the basic energy characteristics will not be changed substantially. The optimization of the structures explored was performed at the DFT level with the B3LYP functional and the 6-31G(d) basis set. Perturbation theory at the MP2/6-31++G(2df,2pd) level was used for the single-point energy and 6-31+G(d) basis set for the electron-property analyses. It was found that the most stable structures are the diguanine complexes followed by guanine-cytosine Pt-cross-links, ca 5 kcal mol(-1) less stable. The adenine-containing complexes are about 15 kcal mol(-1) below the stability of diguanine structures. This stability order was also confirmed by the BE of Pt-N bonds. For a detailed view on dative and electrostatic contributions to Pt-N bonds, Natural Population Analysis, determination of electrostatic potentials, and canonical Molecular Orbitals description of the examined systems were used.

Chemistry of HIV-1 Virucidal Pt Complexes Having Neglected Bidentate sp2 N-Donor Carrier Ligands with Linked Triazine and Pyridine Rings. Synthesis, NMR Spectral Features, Structure, and Reaction with Guanosine

Complexes of the types LPtCl2 and [L2Pt]X2 [L = substituted 3-(pyridin-2'-yl)-1,2,4-triazine] were synthesized and characterized by NMR spectroscopy and, for the first time, by X-ray crystallography in an effort to determine the coordination properties of this novel class of inorganic medicinal agents possessing HIV-1 virucidal activity. The agents containing either one or two sp2 N-donor bidentate ligands are referred to as ptt (platinum triazine) agents. The X-ray structures of three LPtCl2 compounds revealed the expected pseudo-square-planar geometry. The X-ray structure of [(pyPh2t)2Pt](BF4)2 [pyPh2t = 3-(pyridin-2'-yl)-5,6-diphenyl-1,2,4-triazine] has the expected trans relationship of the unsymmetrical L and is essentially planar, an unusual property for a Pt(II) complex with two bidentate sp2 N donors. HIV-1 is an RNA virus; the guanosine ribonucleoside (Guo) binds (MepyMe2t)PtCl2 at both (inequivalent) available coordination sites to form [(MepyMe2t)Pt(Guo)2]2+ [MepyMe2t = 3-(4'-methylpyridin-2'-yl)-5,6-dimethyl-1,2,4-triazine]. This adduct has four nearly equally intense Guo H8 signals attributed to two pairs of head-to-tail (HT) and head-to-head (HH) conformers, which interchange rapidly within each pair. However, equilibration between pairs requires rotation of the Guo cis to the MepyMe2t pyridyl ring, and the H6' proton on this ring projects toward the Guo and hinders Guo rotation about the Pt-N7 bond. Thus, the HT/HH pairs do not interchange; such behavior is rare. Guo did not add to [(MepyMe2t)2Pt]2+, a result suggesting the possibility that the virucidal activity of LPtCl2 and [L2Pt]2+ ptt agents arises respectively from covalent and noncovalent (possibly intercalative interactions favored by [L2Pt]2+ planarity) binding to biomolecular targets.

Synthesis and Cytotoxicity of Enantiomerically Pure [1,2-Diamino-1-(4-fluorophenyl)-3-methylbutane]platinum(II) Complexes

A series of leaving group derivatives of enantiomerically pure [1,2-diamino-1-(4-fluorophenyl)-3-methylbutane]platinum(II) complexes were synthesized and tested for cytotoxicity. The enantiomeric purity was determined by 1H NMR spectroscopy on the final diamines after derivation with (1R)-myrtenal. For coordination to platinum, the diamines were reacted with K2PtI4. The treatment of diiodoplatinum(II) complexes (4F-Ph/iProp-PtI2) with Ag2SO4 resulted in the sulfatoplatinum(II) complexes (4F-Ph/iProp-PtSO4), which can be easily transformed to dichloroplatinum(II) complexes (4F-Ph/iProp-PtCl2) with 2 n HCl. The importance of the leaving groups and the configuration at the diamine ligand on the antiproliferative effects was evaluated on the hormone-dependent MCF-7 and the hormone-independent MDA-MB 231 breast cancer cell lines as well as the LNCaP/FGC prostate cancer cell line. (R,R)-4F-Ph/iProp-PtCl2 was identified as the most active platinum(II) complex. The 3-methyl group increased antiproliferative effects relative to the [1,2-diamino-1-(4-fluorophenyl)butane]platinum(II) complexes described in an earlier study.