DNA-binding and molecular mechanics modelling studies of the bulky chiral platinum(II) complex [PtCl2(mepyrr)] (mepyrr = N-methyl-2-aminomethylpyrrolidine)

Detailed studies were carried out on the binding of the enantiomers of [PtCl₂(mepyrr)] (mepyrr = N-methyl-2-aminomethylpyrrolidine) to dG, d(GpG) and a 52-mer oligonucleotide. The pyrrolidine ligand structure was found to be neither sufficiently rigid nor bulky to enforce a single chirality at the exocyclic amine site in this complex, resulting in the presence of diastereomers that complicated the binding studies. Reaction of the (GpG) dinucleotide with R- and S-[PtCl₂(mepyrr)] resulted in formation of four [Pt{d(GpG)}(mepyrr)] isomers for each enantiomer as a consequence of the existence of two orientational isomers and two diastereomers. These isomers formed in different amounts most likely as a consequence of the unequal formation of the diastereomers together with stereoselectivity induced by interactions between the dinucleotide and the mepyrr ligand. The [PtCl₂(mepyrr)] complexes displayed stereoselectivity and enantioselectivity in their reactions with a 52-mer duplex designed to allow formation of only GpG intrastrand adducts. All four bifunctional adducts formed for each enantiomer, providing further evidence of the lack of directing ability of the ligand in formation of the 1,2-intrastrand adduct. Significant amounts of monofunctional species remained in these assays suggesting that the introduction of the methyl substituent to the exocyclic amine inhibited ring-closure to the bifunctional adduct. This was not sufficient to achieve enantiospecificity, but in the case of the R-enantiomer, one of the bifunctional adducts formed in only small amounts.     

Steric control of stereoselective interactions between the platinum(II) complex [PtCl2(1,4-diazacycloheptane)] and DNA: comparison with cis-[PtCl2(NH3)2] and [PtCl2(ethane-1,2-diamine)] using DNA binding and molecular modeling studies

The rate and extent of binding of [PtCl2(hpip)] (hpip=homopiperazine-1,4-diazacycloheptane) and cis-[PtCl2(NH3)2] to calf thymus DNA was measured using atomic absorption spectroscopy and it was found that [PtCl2(hpip)] bound both more rapidly and to a greater extent than did cis-[PtCl2(NH3)2]. The binding of [PtCl2(hpip)] and [PtCl2(en)] (en=ethane-1,2-diamine) to salmon sperm DNA and to synthetic, self-complementary 10-base-pair and 52-base-pair oligonucleotides was studied using enzymatic digestion and HPLC analysis of the products. [PtCl2(hpip)] forms approximately two-fold fewer GpG and ApG intrastrand adducts and concomitantly more monofunctional adducts than does [PtCl2(en)]. In the case of [PtCl2(hpip)], two GpG adducts, corresponding to the different orientations of the hpip ligand with respect to the DNA, were observed in a 1:3.3 ratio. The minor product corresponds to the orientation in which the bulkier propylene chain of the hpip ligand is adjacent to, and makes close contacts with, the floor of the major groove. When the reaction was repeated with a synthetic oligonucleotide decamer duplex, the ratio of the two forms was approximately 1:1.9 and with the 52-mer duplex it was 1:2.4, revealing an apparent systematic dependence of stereoselectivity on nucleotide size. Computer modeling of the two adducts formed by [PtCl2(hpip)] and those formed by [PtCl2(en)] and cis-[PtCl2(NH3)2] revealed that non-bonded interactions between the hpip ligand and the DNA were probably responsible for both the decreased proportion of GpG adducts formed by [PtCl2(hpip)] and the stereoselectivity exhibited in the formation of these adducts. This is the first case in which the stereoselectivity can be ascribed to steric factors alone.     

Structure and characterization of platinum(II) and platinum(IV) complexes with protonated nucleobase ligands

The reaction of H₂[PtCl₆] · 6H₂O and (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O (18C6 = 18-crown-6) with 9-methylguanine (MeGua) proceeded with the protonation of MeGua forming 9-methylguaninium hexachloroplatinate(IV) dihydrate (MeGuaH)₂[PtCl₆] · 2H₂O (1).The same compound was obtained from the reaction of Na₂[PtCl₆] with (MeGuaH)Cl.On the other hand, the reaction of guanosine (Guo) with (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O in methanol at 60 °C proceeded with the cleavage of the glycosidic linkage and with ligand substitution to give a guaninium complex of platinum(IV), [PtCl₅(GuaH)] · 1.5(18C6) · H₂O (2).Within several weeks in aqueous solution a slow reduction took place yielding the analogous guaninium platinum(II) complex, [PtCl₃(GuaH)] · (18C6) · 2Me₂CO (3).H₂[PtCl₆] · 6H₂O and guanosine was found to react in water, yielding (GuoH)₂[PtCl₆] (4) and in ethanol at 50 °C, yielding [PtCl₅(GuoH)] · 3H₂O (5).Dissolution of complexes 2 and 5 in DMSO resulted in the substitution of the guaninium and guanosinium ligands, respectively, by DMSO forming [PtCl₅(DMSO)]⁻.Reactions of 1-methylcytosine (MeCyt) and cytidine (Cyd) with H₂[PtCl₆] · 6H₂O and(H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O resulted in the formation of hexachloroplatinates with N3 protonated pyrimidine bases as cation (MeCytH)₂[PtCl₆] · 2H₂O (6) and (CydH)₂[PtCl₆] (7), respectively. Identities of all complexes were confirmed by ¹H, ¹³C and ¹⁹⁵Pt NMR spectroscopic investigations, revealing coordination of GuoH⁺ in complex 5 through N7 whereas GuaH⁺ in complex 3 may be coordinated through N7 or through N9. Solid state structure of hexachloroplatinate 1 exhibited base pairing of the cations yielding (MeGuaH⁺)₂, whereas in complex 6 non-base-paired MeCytH⁺ cations were found. In both complexes, a network of hydrogen bonds including the water molecules was found. X-ray diffraction analysis of complex 3 exhibited a guaninium ligand that is coordinated through N9 to platinum and protonated at N1, N3 and N7. In the crystal, these NH groups form hydrogen bonds N–HO to oxygen atoms of crown ether molecules.     

Molecular structures and some properties of tris(2-aminoethyl) amine cobalt(III) complexes with thiocarboxylato-O,S such as 3-mercaptopropionato, 2-mercaptoacetato and their derivatives

Cobalt(III) complexes with a thiolate or thioether ligand, t-[Co(mp)(tren)]⁺ (2), t-[Co(mtp)(tren)]²⁺ (1Me) and t-[Co(mta)(tren)]²⁺ (2Me), (mp = 3-mercaptopropionate, MA = 3-(methylthio)propionate and MTA = 2-(methylthio)acetate) have been prepared in aqueous solutions. The crystal structures of 1, 2, 1Me and 2Me were determined by X-ray diffraction methods. The crystal data are as follows, t-[Co(mp)(tren)]ClO₄ (1CIO₄): monoclinic, P2₁/n, A = 10.877(8), B = 11.570(4), c = 12.173(7) Å, β = 92.20(5)°, V = 1531(1) ų, Z = 4 and R = 0.060; t-[Co(ma)(tren)]Cl·3H₂O (2Cl·3H₂O): monoclinic, P2₁/n, a = 7.7688(8), B = 27.128(2), C = 7.858(1) Å, β = 100.63(1)°, V = 1627.7(3) ų, Z = 4 and R = 0.066; (+)₄₆₅^CD-t-[Co(mtp)(tren)](ClO₄)₂ ((+)₄₆₅^CD-1Me(ClO₄)₂): orthorhombic, P2₁2₁2₁, A = 10.6610(7), B = 11.746(1), C = 15.555(1) Å, V = 1947.9(3) ų, Z = 4 and R = 0.068; (+)₄₆₅^CD-t-[Co(mta)(tren)](ClO₄)₂ ((+)₄₆₅^CD-2Me(ClO₄)₂): orthorhombic, P2₁2₁2₁, a = 10.564(1), B = 11.375(1), C = 15.434(2) Å, V = 1854.7(4) ų, Z = 4 and R = 0.047. All central Co(III) atoms have approximately octahedral geometry, coordinated by four N, one O, and one S atoms. All of the complexes are only isomer, of which the sulfur atom in the didentate-O,S ligands are located at the trans position to the tertiary amine nitrogen atom of tren. 1 and 1Me contain six-membered chelate ring, and 2 and 2Me do five-membered chelate ring in the didentate ligand. The chirality of the asymmetric sulfur donor atom in (+)₄₆₅^CD-1Me is the S configuration and that in (+)₄₆₅^CD-2Me is the R one. The ¹H NMR, ¹³C NMR and electronic absorption spectral behaviors and electrochemical properties of the present complexes are discussed in relation to their stereochemistries.     

Reactions of the haloalcohols HO(CH2)nCl (n = 2, 3) with platinum(II) - alkynyl and -alkyne complexes. X-ray crystal structure of trans-[Pt(Me) {C(OCH2CH2Cl) (CH2Ph)} (PPh3)2] [BF4]

The chloro complexes trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄, react with 1-alkynes HC---C---R in the presence of NEt₃ to afford the corresponding acetylide derivatives trans-[Pt(Me) (C---C---R) (PPh₃)₂] (R = p-tolyl (1), Ph (2), C(CH₃)₃ (3)). These complexes, with the exception of the t-butylacetylide complex, react with the chloroalcohols HO(CH₂)_nCl (n = 2, 3) in the presence of 1 equiv. of HBF₄ to afford the alkyl(chloroalkoxy)carbene complexes trans-[Pt(Me) {C[O(CH₂)_nCl](CH₂R) } (PPh₃)₂][BF₄] (R = p-tolyl, N = 2 (4), N = 3 (5); R=Ph, N = 2 (6)). A similar reaction of the bis(acetylide) complex trans-[Pt(C---C---Ph)₂(PMe₂Ph)₂] with 2 equiv. HBF₄ and 3-chloro-1-propanol affords trans-[Pt(C---CPh) {C(OCH₂CH₂CH₂Cl)(CH₂Ph) } (PMe₂Ph)₂][BF₄] (7). T alkyl(chloroalkoxy)-carbene complex trans-[Pt(Me) {C(OCH₂CH₂Cl)(CH₂Ph) } (PPh₃)₂][BF₄] (8) is formed by reaction of trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄ in HOCH₂CH₂Cl, with phenylacetylene in the presence of 1 equiv. of n-BuLi. The reaction of the dimer [Pt(Cl)(μ-Cl)(PMe₂Ph)]₂ with p-tolylacetylene and 3-chloro-1-propanol yields cis-[PtCl₂{C(OCH₂CH₂CH₂Cl)(CH₂C₆H₄-p-Me}(PMe₂Ph)] (9). The X-ray molecular structure of (8) has been determined. It crystallizes in the orthorhombic system, space group Pna2₁, with a = 11.785(2), B = 29.418(4), C = 15.409(3) Å, V = 4889(1) ų and Z = 4. The carbene ligand is perpendicular to the Pt(II) coordination plane; the PtC(carbene) bond distance is 2.01(1) Å and the short C(carbene)-O bond distance of 1.30(1) Å suggests extensive electronic delocalization within the Pt---C(carbene)---O moietry.     

Differential genotoxic effects of antitumor trans-[PtCl(2)(E-iminoether)(2)] and cisplatin in Escherichia coli

In the present work, we measured survival and the platinum on the genome after treatment of repair-proficient or repair-deficient Escherichia coli strains with trans-[PtCl₂(E-iminoether)₂] and compared these results with the effects of “classical” cisplatin. We found that toxicity of antitumor trans-[PtCl₂(E-iminoether)₂] in repair-deficient trains was much less than that of cisplatin. This markedly reduced toxicity was not a consequence of the reduced uptake or low levels of DNA binding in the bacteria cells but rather appeared to reflect DNA binding mode of this trans-platinum drug different from that of cisplatin.     

Synthesis, crystal and molecular structure, spectroscopic and electrochemical studies of trichloro-oxo(4,6-dimethylpyrimidine-2(1H)-thione)(triphenylphosphine oxide)rhenium(V) complex

Reaction of 4,6-dimethylpyrimidine-2(1H)-thione (Me₂pymSH) with mer-[ReOCl₃(Me₂S)(OPPh₃)] synthon in 1:1 molar ratio in refluxing acetone, results in the replacement of the Me₂S ligand to form the mer-[ReOCl₃(Me₂pymSH)(OPPh₃)] species. X-ray diffraction shows that the structure of the title compound consists of monomeric units with a distorted octahedral coordination around the rhenium(V) centre which includes the axial ReO and Re---OPPh₃ bonds, and in which three Cl⁻ ions and a S-monodentate neutral Me₂pymSH ligand act as equatorial ligands. The compound was also characterised using electrochemical measurements and UV–Vis–NIR and IR spectroscopy.     

Cytotoxicity, mutagenicity, cellular uptake, DNA and glutathione interactions of lipophilic trans-platinum complexes tethered to 1-adamantylamine

Cytotoxicity and mutagenicity of trans,trans,trans-[PtCl₂(CH₃COO)₂(NH₃)(1-adamantylamine)] [trans-adamplatin(IV)] and its reduced analog trans-[PtCl₂(NH₃)(1-adamantylamine)] [trans-adamplatin(II)] were examined. In addition, the several factors underlying biological effects of these trans-platinum compounds using various biochemical methods were investigated. A notable feature of the growth inhibition studies was the remarkable circumvention of both acquired and intrinsic cisplatin resistance by the two lipophilic trans-compounds. Interestingly, trans-adamplatin(IV) was considerably less mutagenic than cisplatin. Consistent with the lipophilic character of trans-adamplatin complexes, their total accumulation in A2780 cells was considerably greater than that of cisplatin. The results also demonstrate that trans-adamplatin(II) exhibits DNA binding mode markedly different from that of ineffective transplatin. In addition, the reduced deactivation of trans-adamplatin(II) by glutathione seems to be an important determinant of the cytotoxic effects of the complexes tested in the present work. The factors associated with cytotoxic and mutagenic effects of trans-adamplatin complexes in tumor cell lines examined in the present work are likely to play a significant role in the overall antitumor activity of these complexes.     

On the lability of dimethylsulfoxide (DMSO) coordinated to the [Ru(II)-NO(+)] species: X-ray structures of mer-[RuCl(3)(DMSO)(2)(NO)] and mer-[RuCl(3)(CD(3)CN)(DMSO)(NO)

The syntheses of nitrosyl–dimethylsulfoxide–ruthenium(II) complexes with general formula mer-[RuCl₃(L)(DMSO)(NO)] (L=DMSO or CD₃CN) is reported. The mer-[RuCl₃(DMSO)₂(NO)] (1) complex was obtained from the reaction of [RuCl₃(NO)] with the sulfoxide ligand in acetone. The mer-[RuCl₃(CD₃CN)(DMSO)(NO)] (2) compound was obtained from mer-[RuCl₃(DMSO)₂(NO)] maintained in deuterated acetonitrile. These data suggest a slow kinetic reaction due the low lability of the DMSO ligand coordinated to the {Ru^II–NO⁺} species. The crystal and molecular structures of (1) and (2) have been determined from X-ray studies. Crystal data: for (1), monoclinic, P2₁/c, a=8.8340(2) Å, b=12.0230(3) Å, c=13.7064(4) Å, β=114.546(2)°, Z=4, R1=0.0429; for (2), monoclinic, P21/n, a=10.0180(7) Å, b=9.5070(7) Å, c=13.3340(9) Å, β=102.264(4)°, Z=4, R1=0.0472. The spectroscopic characterization of (1), in solid state (infrared spectrum) and in solution (nuclear magnetic resonance and cyclic voltammetry) is also described.     

Characterization of adducts produced in DNA by isomeric 1,2-diaminocyclohexaneplatinum(II) complexes

The cancer chemotherapeutic drug cis-diamminedichloroplatinum(II) (cis-DDP) is active as a result of its bifunctional reactions with DNA. Many other platinum complexes also have therapeutic activity. Of current interest are complexes containing 1,2-diaminocyclohexane (DACH). The DACH ligand exists in three isomeric forms with reported differences in therapeutic activity in the order R,R greater than S,S greater than R,S-DACH-Pt. The reaction of the sulphate form of each of these three isomers with DNA has been characterized as a possible explanation for the apparent differences in antitumor activity. These reactions have been characterized by platinating pure DNA followed by enzyme digestion, HPLC separation and analysis by atomic absorption and nuclear magnetic resonance. The spectrum of adducts produced was similar for each isomer and similar to that reported for cis-DDP with adduction at d(GpG), d(ApG) and (dG)2. The R,S-isomer additionally demonstrated isomeric adducts at d(GpG) and d(ApG). The kinetics of formation of the various adducts was the same for each isomer; total platination of DNA was complete in 15 min as were bifunctional adducts at d(GpG) and (dG)2. However, rearrangement to bifunctional adducts took several hours in the case of adducts at d(ApG) sequences. These results did not provide a reason for the different activities of the isomers. It is suggested that the interaction of these adducts with metabolic processes such as DNA repair might explain these differences.     

Bending studies of DNA site-specifically modified by cisplatin, trans-diamminedichloroplatinum(II) and cis-[Pt(NH3)2(N3-cytosine)Cl]+

Duplex oligonucleotides containing a single intrastrand [Pt(NH3)2]2+ cross-link or monofunctional adduct and either 15 or 22 bp in length were synthesized and chemically characterized. The platinum-modified and unmodified control DNAs were polymerized in the presence of DNA ligase and the products studied on 8% native polyacrylamide gels. The extent of DNA bending caused by the various platinum-DNA adducts was revealed by their gel mobility shifts relative to unplatinated controls. The bifunctional adducts cis-[Pt(NH3)2[d(GpG)]]+, cis-[Pt(NH3)2[d(ApG)]]+, and cis-[Pt(NH3)2[d(G*pTpG*)]], where the asterisks denote the sites of platinum binding, all bend the double helix, whereas the adduct trans-[Pt(NH3)2[d(G*pTpG*)]] imparts a degree of flexibility to the duplex. When modified by the monofunctional adduct cis-[Pt(NH3)2(N3-cytosine)(dG)]Cl the helix remains rod-like. These results reveal important structural differences in DNAs modified by the antitumor drug cisplatin and its analogs that could be important in the biological processing of the various adducts in vivo.     

Hydride complexes of platinum(II) containing unsymmetrical di(phosphine) ligands: synthesis, characterization and evidence for pairwise addition of hydrogen based on parahydrogen induced polarization

Unsymmetrical di(phosphine) ligands (dpp)₂Rop (1a, b = bis(diphenylphosphino)-2-alkyl-3-oxapropane (alkyl = methyl and ethyl)) and (dpp)₂oCy (1c = trans-2-diphenylphosphinocyclohexyl diphenylphosphinite) and their Pt(II) dichloride complexes, PtCl₂((dpp)₂mop) (2a), PtCl₂((dpp)₂eop) (2b) and PtCl₂((dpp)₂oCy) (2c), have been synthesized and characterized by NMR spectroscopy. The crystal structures of 2b and 2c show that the geometry about the platinum centers is square planar. In 2b, the metal and di(phosphine) ligand chelate ring are in a chair conformation, whereas in 2c, the chelate ring conformation is a skewed boat. Initial reaction of sodium borohydride with 2a, b, c yields the monohydride monochloride complexes PtHCl((dpp)₂mop) (5a), PtHCl((dpp)₂eop) (5b) and PtHCl((dpp)₂oCy) (5c). At longer reaction times, fluxional dimeric species are obtained, [PtH((dpp)₂mop)]₂ (4a), [PtH((dpp)₂eop)]₂ (4b) and [PtH((dpp)₂oCy)]₂ (4c),and in the case of 4c two different isomers exist. The dihydride complexes PtH₂((dpp)₂mop) (3a), PtH₂((dpp)₂eop) (3b) and PtH₂((dpp)₂oCy) (3c), are prepared by further reaction of NaBH₄ and 2. Hydrogen cycling is facile in the dihydride complexes 3a, b, c, and oxidative addition of H₂ proceeds in a pairwise manner as determined by the observation of parahydrogen induced polarization (PHIP) in the ¹H NMR spectra. The reductive elimination of H₂ is also shown to be concerted by reaction of dihydride complexes with D₂. Crystal data: 2b (C₃₀H₃₂Cl₆OP₂Pt), monoclinic, space group P2₁/c (No. 14), a = 13.7040(1), b = 11.3430(7), c = 21.3880(9) Å, β = 97.923(9)°, V = 3292.9(2) ų and Z = 4; 2c (C₃₀H₃₀Cl₂OP₂Pt), monoclinic, space group P2₁ (No. 4), a = 11.7360(2), b = 8.4311(2), c = 14.2789(2) Å, β = 101.290(1)°, V = 1385.52(4) ų and Z = 2.     

Platinum(II) complexes of chelating and monodentate thiourea monoanions incorporating chiral, fluorescent or chromophoric groups

The reaction of cis-[PtCl₂(PPh₃)₂] with trisubstituted thioureas [R¹R²NC(=S)NHR³] in refluxing methanol with triethylamine base, followed by addition of NaBPh₄ gives the salts [Pt{SC(=NR¹R²)NR³}(PPh₃)₂]BPh₄ in high yield; a range of thiourea substituents, including chiral, fluorescent and chromophoric groups can be incorporated. The azo dye-derived complex [Pt{SC(=N(CH₂CH₂)₂O)NC₆H₄N=NC₆H₄NMe₂}(PPh₃)₂]BPh₄ has been characterised by a single-crystal X-ray diffraction study. The formation of a fluorescein-derivatised platinum–thiourea complex is also described. Reaction of cis-[PtCl₂(PPh₃)₂] with PhNHC(S)NHPh or EtNHC(S)NHEt, triethylamine and NaBPh₄ gives, respectively, [Pt{SC(=NHPh)NPh}(PPh₃)₂]⁺ and the known cation [Pt{SC(=NHEt)NEt}(PPh₃)₂]⁺, isolated as tetraphenylborate salts. Reaction of cis-[PtCl₂(PPh₃)₂] with an excess of Na[MeNHC(S)NCN] in methanol gives the bis(thiourea monoanion) complex trans-[Pt{SC(=N---CN)NHMe}₂(PPh₃)₂], characterised by NMR spectroscopy and an X-ray crystal structure determination. When cis-[PtCl₂(PPh₃)₂] is reacted with 1 equiv. of Na[MeNHC(S)N---CN] in methanol, with added NaBPh₄, a mixture of isomers of the [Pt{SC(=NHCN)NMe}(PPh₃)₂]⁺ cation is obtained.     

Chemistry of the azine phosphine ligand Z,E-PPh2CH2C(Bu)=N-N=CMe(C6H4NO2-4): crystal structure of [Mo(CO)4{PPh2CH2C(Bu)=N-N=CMe(C6H4NO2-4)}]

Condensation of Z-PPh₂CH₂C(Bu^t)=NNH₂ with 4-nitroacetophenone gave the azine phosphine Z,E-PPh₂CH₂C(Bu^t)=N-N=CMe(C₆H₄NO₂-4) (I). The corresponding phsophine oxide II was prepared by treatment of I with H₂O₂. The phosphine I with [Mo(CO)₄(nbd)] (nbd=norbornadiene) gave [Mo(CO)₄{PPh₂CH₂C(Bu^t)=N-N=CMe(C₆H₄NO₂-4)}] (1a); the corresponding tungsten 1b and chromium 1c complexes were made similarly. The crystal structure of 1a was determined by X-ray diffraction and showed the presence of a six-membered chelate ring with the bulky 4-nitrophenyl group held close to the metal. Oxidation of 1a with bromine gave the seven-coordinate molybdenum (II) complex 2. Treatment of [PtMe₂(cod)] (cod=cycloocta-1,5-diene) with I at 20°C gave the dimethyl-platinum (II) complex [PtMe₂{PPh₂CH₂C(Bu^t)=N-N=CMe(C₆H₄NO₂-4)}] (3a) which with MeI gave the iodotrimethylplatinum(IV) complex 4. Treatment of 3a with C≡O opened the chelate ring to give the dimethyl(carbonyl)platinum(II) complex 5 containing a monodentate phosphine ligand. When 3a was heated in toluene solution at 110°C it gave the cyclometallated methylplatinum(II) complex [PtMe{PPh₂CH₂C(Bu^t)=N-N=CMe(C₆H₃NO₂-4)}] (6). Treatment of 6 with MeI gave the platinum(IV) complex 7. The dichloropalladium(II) complex [PdCl₂{PPh₂CH₂C(Bu^t)=N-N=CMe(C₆H₄NO₂-4)}] (3b) was prepared by treatment of [PdCl₂(NCPh)₂] with I in CH₂Cl₂. Treatment of [PtCl₂(NCMe)₂] with 2 equiv. of I gave the trans-bis(phosphine) complex 8. When 2 equiv. of I were treated with [PtCl₂(cod)] followed by NH₄PF₆ this gave the salt 9a containing two six-membered chelate rings; the analogous palladium(II) 9b) salt was also prepared. Treatment of 2 equiv. of I with [PtCl₂(cod)] followed by NH₄PF₆ gave the PF₆ salt 10 containing a six-membered chelate ring and a monodentate ligand. When 10 was treated with AgNO₃ followed by NH₄PF₆ this gave the bis-chelate complex 11 containing five- and six-membered chelate rings. Treatment of [IrCl(CO)₂(p-toluidine)] with I gave the cyclometallated iridium(III) hydride complex [IrHClCO{PPh₂CH₂C(Bu^t)=N-N=CMe(C₆H₃NO₂-4)}] (12). [RuCl₂(PPh₃)₃] with the phosphine I resulted in the Ru(II) complex 13 in which the ortho hydrogens of the 4-nitrophenyl group are agostically interacting with ruthenium. Proton, Phosphorus-31, some carbon-13 NMR and IR data have been obtained. Crystals of 1a are orthorhombic, space group Pna2₁, with a = 1819.3(2), b = 1050.0(1), c = 1614.8(2) pm and Z = 4; final R = 0.0191 for 2616 observed reflections.     

Geometrical configuration of monomethyl–platinum(II) complexes driven by the size of entering nitrogen ligands

The reaction of the monoalkyl complex trans-[Pt(DMSO)₂Cl(CH₃)] with a large variety of heterocyclic nitrogen bases L, in chloroform solution, leads to the formation of uncharged complexes of the type [Pt(DMSO)(L)Cl(CH₃)], containing four different groups coordinated to the metal center. Only two out of the three different possible isomers were detected in solution. These two trans(C,N) and cis(C,N) species can be unambiguously identified through ¹H NMR spectroscopy. For the trans(C,N) isomers, average values of ²J_PtH=75±4 Hz and ³J_PtH=36±4 Hz have been observed for the coordinated methyl and DMSO ligands, respectively. In the case of the cis(C,N) isomers, these values increase to ²J_PtH=83±2 Hz, and decrease to ³J_PtH=26±3 Hz due to the mutual exchange of ligands in trans position to CH₃ and DMSO. In the case of bulky asymmetric ligands, such as quinoline, 2-quinolinecarboxaldehyde, 2-methylquinoline, 5-aminoquinoline, 2-phenylpyridine and 2-chloropyridine, slow rotation of the hindered group around the Pt---N bond makes the coordinated DMSO ligand prochiral. NMR experiments have shown that the first reaction product is the trans(C,N) isomer as a consequence of the very fast removal of one DMSO ligand by the nitrogen bases from the starting complex trans-[Pt(DMSO)₂Cl(CH₃)]. This trans kinetic product undergoes a geometrical conversion into the more stable cis(C,N) isomer through the intermediacy of fast exchanging aqua-species. The rate of isomerization and the relative stability of the two isomers depends essentially on the rate of aquation and on the steric congestion imposed by the new L ligand on the metal.     

The synthesis of substituted bis[(diarylphosphinomethyl)cyclopentadienyl]zirconocene dichloride complexes for the preparation of heterodimetallic complexes containing early/late transition metal combinations

Fulvenes (1a–e) derived from condensation of cyclopentadiene with acetone or a variety of aldehydes were treated with LiPAr₂ (Ar = phenyl, p-tolyl) to yield the respective substituted (diarylphosphinomethyl)cyclopentadienides (2, 3). Subsequent reaction with ZrCl₄(THF)₂ gave the respective bis[(diarylphosphinomethy])cyclopentadienyl]zirconium dichlorides ( Ar = phenyl (4), p-tolyl (5)). The complex rac-[C₅H₄-CH(CH₃)-PPh₂]₂ZrCl₂ (rac-4b) was characterized by X-ray diffraction. The reaction of complexes 4a and 5a [(Cp-CMe₂-PAr₂)₂ZrCl₂] with PdCl₂(NCPh)₂ or PtCl₂(NCPh)₂ leads to the formation of the trans-(metallocene-chelate-phosphane)metal complexes 6–9 (e.g. trans-Cl₂Pd(Ph₂P-CMe₂-Cp)₂ZrCl₂]. Chloride abstraction from the reaction product of [Cp-CH(CMe₃)PPh₂]₂ZrCl₂ with PdCl₂(NCPh)₂ eventually gave the cationic complex [meso,trans-(Cp-CH(CMe₃)PPh₂)₂(Cl)Zr(μ-Cl)Pd(Cl)]⁺ (10) that was also characterized by X-ray diffraction. It features a dimetallabicyclic framework with two Cp-CHR-PPh₂ ligands and a chloride bridging between the early and the late transition metal center.     

Enantioselectivity and stereoselectivity in the reactions of the enantiomers of the platinum complex [PtCl2(ahaz)] (ahaz = 3(R)- or 3(S)-aminohexahydroazepine) with DNA

The platinum-DNA adduct profile formed by the R- and S-enantiomers of [PtCl₂(ahaz)] (ahaz = 3(R)-aminohexahydroazepine or 3(S)-aminohexahydroazepine) on reaction with salmon sperm DNA were characterised using HPLC and GFAAS (graphite furnace atomic absorption spectrometry) analyses. At a platinum to nucleotide ratio (R_t) equalling 0.05, the R-enantiomer forms a substantially larger amount (approximately 60%) of monofunctional adducts than the S-enantiomer (less than 35%). Fewer intrastrand GpG adducts are formed by the R-enantiomer (approximately 21%) than the S-enantiomer (approximately 37%). For both enantiomers, two isomeric GpG adducts, corresponding to the different orientations of the primary amine of ahaz ligand with respect to the O6 atom of the 5′ guanine, were observed in the ratios of 1:1.3 and 1:4.3 for the R- and S-enantiomers, respectively. The reasons for this enantioselectivity and stereoselectivity are discussed.     

Effect of (6R)- and (6S)-tetrahydrobiopterin on L-3,4-dihydroxyphenylalanine (DOPA) formation in NRK fibroblasts transfected with human tyrosine hydroxylase type 2 cDNA

-erythro-5,6,7,8-Tetrahydrobiopterin (BH₄), which is the cofactor of aromatic amino acid hydroxylases, plays an important role in the biosyntheses of monoamine neurotransmitters. BH₄ exists as natural (6R)- and unnatural (6S)-isomers. In our previous reports, only (6R)-isomer significantly stimulated cofactor activity for tyrosine, tryptophan and phenylalanine hydroxylases (TH, TPH, PAH) in whole animals or in tissue slices. In this study we have compared the in situ cofactor activity on TH between natural (6R)- and unnatural (6S)-isomers in clonal cells. We have transfected human TH type 2 cDNA into the normal rat kidney (NRK) fibroblasts. These cells expressed TH protein, but had neither DOPA decarboxylase (DDC) nor BH₄. Thus, TH activity was observed only in the presence of exogenous BH₄. We compared the difference in in situ DOPA formation by TH activity in the presence of (6R)- or (6S)-BH₄ in the human TH-transfected cells. The effect of exogenous BH₄ was also compared between (6R)- and (6S)-isomers in rat pheochromocytoma PC12h cells, which contained approximately 100 μM endogenous (6R)-BH₄. The rate of uptake of both BH₄ isomers into these cells increased in proportion to the pterin cofactor concentrations in the incubation medium up to 400 μM but was nearly saturated at 1 mM BH₄. TH-transfected NRK fibroblasts formed DOPA only in the presence of exogenously added (6R)- or (6S)-BH₄ dose-dependently and released DOPA into the medium. At a saturating concentration of 1 mM, (6R)-BH₄ was approximately three times as active as (6S)-BH₄. In contrast, in PC12h cells which contained endogenous (6R)-BH₄ (approximately 100 μM), exogenous (6R)-BH₄ activated DOPA formation maximally at 500 μM about 10-fold, while (6S)-BH₄ activated it only slightly, about 2.5-fold. These results suggest that (6S)-isomer has lower cofactor activity with TH in the cells than (6R)-isomer. This TH transfected fibroblasts should be useful to assess cofactor activities of tetrahydropteridines in the cell.     

Circular dichroism spectra of the individual rotamers of [Pt(N,N-dmen)(GpG)]+ (N,N-dmen=N,N-dimethylethylenediamine) indicate that the base-base oscillator coupling is not the main source of ellipticity in cis-PtG2L2 head-to-head complexes

The asymmetrical platinum complex [PtCl2(N,N-dmen)] (N,N-dmen = N,N-dimethylethylenediamine) reacts with the dinucleotide GpG to form two isomeric chelates of the formula [Pt(N,N-dmen)(GpG)]+ [9]. One of the isomers forms two stable rotamers separable by HPLC, whereas the other apparently prefers one single rotameric form. The favored conformations of these three forms were elucidated by means of molecular mechanics and dynamics techniques. In parallel, we have prepared the adduct, isolated the three rotamers, and recorded their solution circular dichroism (CD) spectra. For the first time we were thus able to correlate the CD features of individual rotamers of a cis-Pt(GpG) chelate with their structures. We show here that the two forms labeled in Inagaki's paper 1'e and 2e have the same right-handed helicoidal arrangement of the guanine bases but display different CD spectra in which the prominent bands have inverted signs. Thus, base-base interactions cannot be the principal cause of the CD of these compounds.     

Fixing the conformations of diamineplatinum(II)-GpG chelates: NMR and CD signatures of individual rotamers

The bulky, asymmetric analog of the antitumor drug cisplatin, [PtCl(2)(tmen)] (tmen = N,N,N'-trimethylethylenediamine), was used to produce crosslinks with the dinucleotide d(GpG), modeling the most frequent lesions that cisplatin and its analogs cause to DNA. The ligand tmen was chosen because it is expected to constrain the guanine cis to the NMe(2) group in the adduct [Pt(tmen){d(GpG)}](+) to an orientation perpendicular to the coordination plane and to stabilize the other guanine in an oblique orientation, thus maintaining a head-to-head geometry typical of cisplatin-d(GpG) crosslinks within single- and double-stranded DNA. Of the four possible combinations of tmen chirality (R or S symmetry of the coordinated NHMe group) and crosslink direction (5'-G bound cis to the secondary or the tertiary amino group of tmen), two isomers were preponderantly formed, [Pt(R-tmen){d(GpG)}](+) with 5'-G bound cis to NMe(2) and [Pt(S-tmen){d(GpG)}](+) with 5'-G bound cis to NHMe. The former was shown to have a right-handed R2 orientation of guanines similar to that found in duplex DNA, whereas the latter had a left-handed L1 orientation that modeled cisplatin-d(GpG) adducts within single-stranded DNA. The R2 rotamer was found to be in an equilibrium (as observed using EXSY spectroscopy) with a minor fraction (< or =4%) of a Delta-HT rotamer related to R2 by rotation of the 3'-G about the Pt-N7 bond. The major rotamers R2 and L1 were isolated using reverse-phase HPLC, and their NMR and CD signatures were compared to those of the corresponding rotamers of the less hindered adduct [Pt(dmen)(GpG)](+) (dmen = N,N-dimethylethylenediamine). From this and other comparisons with previously reported platinum dinucleotide complexes, and from molecular modeling, it could be concluded that both steric repulsion between guanine and substituents of the cis amino group and N-H...O6 hydrogen bonding are significant effects favoring the oblique orientation of one guanine base typical of the HH rotamers of [Pt(diamine){d(GpG)}](+) and [Pt(diamine)(GpG)](+) complexes.