Association patterns of platinated purine nucleobases in metal-modified pairs and triples

Blocking of Watson-Crick or Hoogsteen edges in purine nucleobases by a metal entity precludes involvement of these sites in interbase hydrogen bonding, thereby leaving the respective other edge or the sugar edge as potential H bonding sites. In mixed guanine, adenine complexes of trans-a2PtII (a = NH3 or CH3NH2) of composition trans-[(NH3)2Pt(9-EtA-N1)(9-MeGH-N7)](NO3)2 (1a), trans-[(NH3)2Pt(9-EtA-N1)(9-MeGH-N7)](ClO4)2 (1b), and trans,trans-[(CH3NH2)2(9-MeGH-N7)Pt(N1-9-MeA-N7)Pt(9-MeGH-N7)(CH3NH2)2](ClO4)4*2H2O (2) (with 9-EtA = 9-ethyladenine, 9-MeA= 9-methyladenine, 9-MeGH = 9-methylguanine), this aspect is studied. Thus, in 1b pairing of two adenine ligands via Hoogsteen edges and in 2 pairing of two guanine bases via sugar edges is realized. These situations are compared with those found in a series of related complexes.     

Syntheses and structural and electrochemical characterizations of vanadatricarbadecaboranyl analogues of vanadocene and the structural characterization of the [Li(CH(3)CN)2+](6-CH(3)-nido-5,6,9-C(3)B(7)H(9-) tricarbadecaboranyl anion.

A single-crystal X-ray determination of the [Li(CH(3)CN)(2)(+)](6-CH(3)-nido-5,6,9-C(3)B(7)H(9)(-)) salt has shown that the 6-CH(3)-nido-5,6,9-C(3)B(7)H(9)(-) tricarbadecaboranyl anion has a nido-cage geometry based on an octadecahedron missing the unique six-coordinate vertex. The resulting six-membered open face is puckered, with two of the cage carbons (C6 and C9) occupying the low-coordinate cage positions above the plane of the four remaining atoms (C5, B7, B8, and B10). The Li(+) ion is centered over the open face and is solvated by two acetonitrile molecules. The reactions of the 6-CH(3)-nido-5,6,9-C(3)B(7)H(9)(-) anion with various vanadium halide salts, including VCl(4), VCl(3), and VBr(2), each resulted in the isolation of the same five paramagnetic products (2-6) of composition V(CH(3)-C(3)B(7)H(9))(2). X-ray crystallographic determinations of 2-5 showed that the complexes consist of two octadecahedral VC(3)B(7) fragments sharing a common vanadium vertex and established their structures as commo-V-(1-V-4'-CH(3)-2',3',4'-C(3)B(7)H(9))(1-V-2-CH(3)-2,3,4-C(3)B(7)H(9)) (2), commo-V-(1-V-5'-CH(3)-2',3',5'-C(3)B(7)H(9))(1-V-4-CH(3)-2,3,4-C(3)B(7)H(9)) (3), commo-V-(1-V-5'-CH(3)-2',3',5'-C(3)B(7)H(9))(1-V-2-CH(3)-2,3,4-C(3)B(7)H(9)) (4), and commo-V-(1-V-2-CH(3)-2,3,4-C(3)B(7)H(9))(2) (5). These complexes can be considered as tricarbadecaboranyl analogues of vanadocene, (eta(5)-C(5)H(5))(2)V. However, unlike vanadocene, these complexes are air- and moisture-stable and have only one unpaired electron. The five complexes differ with respect to one another in that they either (1) contain different enantiomeric forms of the CH(3)-C(3)B(7)H(9) cages, (2) have a different twist orientation of the two cages, or (3) have the methyl group of the CH(3)-C(3)B(7)H(9) cage located in either the 2 or 4 position of the cage. Subsequent attempts to oxidize the compounds with reagents such as Br(2) and Ag(+) were unsuccessful, illustrating the ability of the tricarbadecaboranyl anion to stabilize metals in low oxidation states. Consistent with this, both the electrochemical oxidation and the reduction of 2 were much more positive than those of the same oxidation state changes in vanadocene. The one-electron reduction of 2 is a remarkable 2.9 V positive of that of Cp(2)V.     

Simultaneous N7,O6-binding of guanine to two zinc centers and its possible biological significance

The reaction of ZnCl(2) with 9-ethylguanine (9-EtGH) produced a novel dinuclear Zn(II) complex, [Zn(2)Cl(4)(H(2)O)(mu-9-EtGH-N7,O6)(9-EtGH-N7), 1. The X-ray structure analysis (monoclinic, P2(1) (No. 4), a = 11.0636(6) A, b = 6.6546(4) A, c = 15.9630(9) A, beta = 101.069(1) degrees, V = 1153.4(1) A(3), Z = 2) revealed that one of the tetrahedrally coordinated Zn(II) atoms binds to the N7 site of 9-EtGH and to the exocyclic O6 atom of another 9-EtGH molecule. The remaining Zn(II) atom binds to the N7 site of the second 9-EtGH moiety.     

Intrinsic acid-base properties of purine derivatives in aqueous solution and comparison of the acidifying effects of platinum(II) coordinated to N1 or N7: acidifying effects are reciprocal and the proton "outruns" divalent metal ions

The effect of Pt(2+) coordination, in particular of (dien)Pt(2+) or cis-(NH(3))(2)Pt(2+), on the acid-base properties of the purine ligands 9-ethylguanine (9EtG), 9-methylhypoxanthine (9MeHx), inosine (Ino), 9-methyladenine (9MeA), and N6',N6',N9-trimethyladenine (TriMeA) is quantitatively evaluated. The corresponding acidity constants of the complexes are calculated by curve-fitting procedures using previously published (1)H NMR shift data which had been measured in aqueous solution (D(2)O) in dependence on pH (pD). Comparison of the pK(a) values of the ligands with those of the Pt(2+) complexes reveals the expected behavior for the (N7)-platinated complexes; i.e., the (N1)H(0/+) sites are acidified due to charge repulsion. However, Pt(2+) coordination at (N1)(-)(/0) sites leads to an (already previously observed) apparent increase in the basicity of the N7 sites for the guanine, hypoxanthine, and adenine residues; this is also the case if Pt(2+) is bound to N3. Coordination of Pt(2+) to both the (N1)(-) and N7 sites of 9EtG results apparently in an enhanced basicity of N3 if compared with the release of the proton from the (N3)H(+) site in H(2)(9EtG)(2+). For the former cases in aqueous solution (H(2)O) it is now proven for a comprehensive set of data (seven examples), by taking into account the intrinsic basicities of the various N7 sites via micro acidity constants, that the acidifications are reciprocal and identical. This means Pt(2+) coordinated to (N1)(-)(/0) sites in guanine, hypoxanthine, or adenine residues acidifies the (N7)H(+) unit to the same extent as (N7)-coordinated Pt(2+) acidifies the (N1)H(0/+) site. In other words, the apparently increased basicity of N7 upon Pt(2+) coordination at (N1)(-)(/0) sites disappears if the micro acidity constants of the appropriate isocharged tautomers of the ligand are properly taken into account. It is further proven, on the basis of the evaluations of the nucleotide analogue 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA), that these given conclusions are also valid for nucleotides. In addition, it is shown that the mentioned apparent basicity increase, which results from the use of macro acidity constants, has its origin in the fact that the proton-metal ion (Pt(2+)) interaction (the extent of which depends on the kind of metal ion involved) is less pronounced than the proton-proton interaction. Finally, the proven reciprocal behavior will now allow one to determine micro acidity constants of ligands by studying complexes formed with kinetically inert metal ions. A further result of interest is the proof that the competition of Pt(2+) (or Pd(2+)) with the proton for the (N1)(-) and N7 binding sites of inosinate results in the isomer where the metal ion is at N7 with the proton relegated to (N1)(-); this isomer is favored by a factor of about 2000 compared with the one having the metal ion at (N1)(-) and the proton at N7.     

Complexes of platinum(II) containing neutral and deprotonated 9-methyladenine. Synthesis, x-ray structures, and NMR studies on the cyclic trimer cis-[L2Pt[9-MeAd([bond]H)]]3(NO3)3 and the Dinuclear cis-[L2Pt(ONO2)[9-MeAd([bond]H)]PtL2](NO3)2 (L = PMePh2)

The dinuclear hydroxo complex cis-[L(2)Pt(mu-OH)](2)(NO(3))(2) (L = PMePh(2), 1), in CH(2)Cl(2), CH(3)CN, or DMF solution, deprotonates the NH(2) group of 9-methyladenine (9-MeAd) to give the complex cis-[L(2)Pt[9-MeAd(-H)]](3)(NO(3))(3), 2, which was isolated in good yield. The X-ray structure shows that the nucleobase binds symmetrically the metal centers through the N(1),N(6) atoms forming a cyclic trimer with Pt...Pt distances in the range 5.202(1)-5.382(1) A. Dissolution of 2 in DMSO or DMF determines the partial (or total) dissociation of the cyclic structure to form several fragments. A multinuclear NMR analysis of the resulting mixture supports the presence of the mononuclear species cis-[L(2)Pt[9-MeAd(-H)]](+), 3, in which the deprotonated nucleobase chelates the metal center with the N(6),N(7) atoms. Addition of a stoichiometric amount of the nitrato complex cis-[L(2)Pt(ONO(2))(2)] (L = PMePh(2), 4) to a DMSO or DMF solution of 2 affords quantitatively the diplatinated compound cis-[L(2)Pt(ONO(2))[9-MeAd(-H)]PtL(2)](NO(3))(2), 5. The single-crystal X-ray analysis shows that the adenine behaves as a tridentate ligand bridging two cis-L(2)Pt units at the N(1) and N(6),N(7) sites, respectively [Pt(1)-N(1) = 2.109(5) A, Pt(2)-N(6) = 2.095(7) A, Pt(2)-N(7) = 2.126(7) A]. The N(1)-bonded metal center completes the coordination sphere through an oxygen atom of a nitrate group, and its coordination plane is arranged orthogonally with respect the second one. The Pt-O distance [2.109(5) A] is similar to those found in the nitrato complex 4 [2.110 A, average]. The related complex cis-[[L(2)Pt(ONO(2))](2)(9-MeAd)](NO(3))(2), 6, containing the neutral adenine platinated at the N(1),N(7) atoms, was isolated and its stability in solution investigated by NMR spectroscopy. In DMSO, 6 undergoes decomposition forming a mixture of the species 4, 5, and the adenine mono- and bis-adducts cis-[L(2)Pt(9-MeAd)(DMSO)](2+), 7, and cis-[L(2)Pt(9-MeAd)(2)](2+), 8, respectively. This last complex, quantitatively formed upon addition of 9-MeAd (Pt/adenine = 1:2) to the mixture, was also isolated and characterized.     

Luminescence investigation on ultraviolet-emitting rare-earth-doped phosphors using synchrotron radiation

Three series of new ultraviolet-emitting Ca(9)Y(PO(4))(7):Ln(3+) (Ln = Ce, Gd, Pr) phosphors were synthesized, and their luminescence was investigated. Under vacuum ultraviolet excitation Ca(9)Y(PO(4))(7):Ce(3+) phosphors emit UVA light with one broad emission centered at 346 nm, on account of the 5d(1) → 4f(1) transition of Ce(3+) ions; the optimal doping concentration of these phosphors is 0.2 mol. Ca(9)Y(PO(4))(7):Gd(3+) phosphors show a strong 4f(7) → 4f(7) transition and a sharp UVB emission band at 312 nm; the optimal doping concentration of these phosphors is 0.7 mol. The PL spectra of Ca(9)Y(PO(4))(7):Pr(3+) show two broad UVC emission bands centered between 230 and 340 nm, owing to the 4f(1)5d(1) → 4f(2) transition of Pr(3+) ions; the optimal doping concentration of these phosphors is 0.2 mol. Under 172 nm excitation, we found that the luminescence intensity of the UVA-emitting Ca(9)Y(PO(4))(7):0.2Ce(3+) is 0.3675 times that of BaSi(2)O(5):0.05Pb(2+), that of the UVB-emitting Ca(9)Y(PO(4))(7):0.7Gd(3+) is 1.7 times that of YAl(3)(BO(3))(4):0.25Gd(3+), and that of the UVC-emitting Ca(9)Y(PO(4))(7):0.2Pr(3+) is 1.5 times that of LaPO(4):0.1Pr(3+). The thermal stability investigation indicated that the luminescence decay was only 9.2%, 18.2%, and 10.3% for Ca(9)Y(PO(4))(7):0.2Ce(3+), Ca(9)Y(PO(4))(7):0.7Gd(3+), and Ca(9)Y(PO(4))(7):0.2Pr(3+) at 250 °C relative to that at ambient temperature, respectively. The Ca(9)Y(PO(4))(7):Ln(3+) (Ln = Ce, Gd, Pr) phosphors exhibit high emission efficiency and excellent thermal stability.     

7-Methylguanine: protonation, formation of linkage isomers with trans-(NH3)2Pt(II), and base pairing properties

Three protonated forms of 7-methylguanine (7-MeGH, 1) with different counter ions, [7-MeGH(2)]X (X = NO(3), 1a; ClO(4), 1b; BF(4), 1c) and two Pt(II) complexes, trans-[Pt(NH(3))(2)(7-MeGH-N9)(2)](ClO(4))(2) (4) and trans-[Pt(NH(3))(2)(7-MeGH-N9)(7-MeGH-N3)](ClO(4))(2)·3H(2)O (5) are described and their X-ray crystal structures are reported. 1a-1c form infinite ribbons via pairs of intermolecular hydrogen bonds between N1H···O6 and N3···N2H(2) sites, with anions connecting individual ribbons, thereby generating extended sheets. 4 and 5 do not display unusual features, except that 5 represents a rare case of a bis(nucleobase) complex of Pt(II) in which linkage isomers occur. Unlike in a previously reported compound, [Pt(dien)(7-MeGH-N9)](NO(3))(ClO(4)), the Pt coordination planes and the 7-MeGH planes are not coplanar in 4 and 5. The hydrogen bonding behaviour of 7-MeGH, free and when platinated at N9 (complex 4), was studied in Me(2)SO-d(6). It revealed the following: (i) there is no detectable self-association of 1 in Me(2)SO solution. (ii) 1 and 1-methylcytosine (1-MeC) form Watson-Crick pairs. (iii) 4 does not self-associate. (iv) 4 associates with 1-MeC in the Watson-Crick fashion. (v) 4 and 1 interact in solution, but no model can be proposed at present. (vi) Remarkable interaction shifts between 4 and 1 occur when NH(3) is liberated from trans-(NH(3))(2)Pt(II) to give NH(4)(+) in Me(2)SO-d(6). Feasible models, which imply the presence of deprotonated 7-MeG(-) species are proposed. Finally, DFT calculations were carried out to qualitatively estimate the effect of 7-MeGH acidity in [Pt(dien)(7-MeGH-N9)](2+) in dependence of the dihedral angle between the Pt coordination plane and the nucleobase.     

Synthesis and structural characterization of trivalent amino acid derived chiral phosphorus compounds

Reaction of the N-toluenesulfonyl derivatives of (S)-alanine, phenylalanine, and valine (4-6) with PhPCl(2) gave in high yield the 4-methyl, benzyl, and isopropyl derivatives (7-9) of 2-phenyl-1-p-toluenesulfonyl-1,3,2-oxazaphospholidin-5-one. The ratios of the (2S,4S)/(2R,4S) diastereomers (cis/trans isomers) were 1:1, 2:1, and 10:1 for the methyl, benzyl, and isopropyl derivatives 7a,b, 8a,b, and 9a,b, respectively. For 7a,b, both isomers could be crystallized, but for the others only the major isomers were isolable. The X-ray crystal structure of 9a shows that the isopropyl and phenyl groups are mutually cis and that the tolyl moiety is oriented s-trans to both the isopropyl and phenyl groups. Reaction of 6 with Cl(2)PCH(2)CH(2)PCl(2) (10) gave a 56:38:7 mixture of the cis/cis, cis/trans, and trans/trans diphosphorus heterocycles 11a-c. The major isomer could be crystallized and isolated free of the other diastereomers. Reaction of 6 with EtPCl(2) gave a 6:1 mixture of cis/trans isomers of the ethyl-substituted heterocycles 12a,b as an inseparable oil but allowed confirmation of the structure of 11a. Slow epimerization at phosphorus may occur by inversion but more likely by ring opening/closure, since 7b, 9a, and 11a give rise upon standing in solution to mixtures containing starting material and 7a, 9b, and 11b, respectively, along with the free amino acid derivatives 4 and 6. The NMR spectra, and in particular the coupling constants between the alpha-hydrogen atom of the amino acid moiety and phosphorus, were used to establish the identities of the cis and trans isomers. Reaction of 9a with (THF)W(CO)(5) gave the phosphorus-ligated adduct (9a)W(CO)(5) (13), and the IR spectrum of this complex shows that 9a is a strongly electron-withdrawing ligand. The geometry of the sulfonamide moiety is discussed in detail, as are the (1)H NMR coupling constants. The data are consistent with the presence of little steric interaction between the cis isopropyl and phosphorus substituent in 9a, 11a, and 12a and orientation of the tolyl moiety s-cis to the isopropyl group in 9b, 12b, and 13.     

Structure and magnetism of the tetra-copper(II)-substituted heteropolyanion [Cu(4)K(2)(H(2)O)(8)(alpha-AsW(9)O(33))(2)](8-)

The novel heteropolyanion [Cu(4)K(2)(H(2)O)(8)(alpha-AsW(9)O(33))(2)](8)(-) (1) has been synthesized and characterized by IR spectroscopy, elemental analysis, and magnetic studies. Single-crystal X-ray analysis was carried out on [K(7)Na[Cu(4)K(2)(H(2)O)(6)(alpha-AsW(9)O(33))(2)].5.5H(2)O](n)(K(7)Na-1), which crystallizes in the tetragonal system, space group P42(1)m, with a = 16.705(4) A, b = 16.705(4) A, c = 13.956(5) A, and Z = 2. Interaction of the lacunary [alpha-AsW(9)O(33)](9)(-) with Cu(2+) ions in neutral, aqueous medium leads to the formation of the dimeric polyoxoanion 1 in high yield. Polyanion 1 consists of two alpha-AsW(9)O(33) units joined by a cyclic arrangement of four Cu(2+) and two K(+) ions, resulting in a structure with C(2)(v)() symmetry. All copper ions have one terminal water molecule, resulting in square-pyramidal coordination geometry. Three of the copper ions are adjacent to each other and connected via two micro(3)-oxo bridges. EPR studies on K(7)Na-1 and also on Na(9)[Cu(3)Na(3)(H(2)O)(9)(alpha-AsW(9)O(33))(2)].26H(2)O (Na(9)-2) over 2-300 K yielded g values that are consistent with a square-pyramidal coordination around the copper(II) ions in 1 and 2. No hyperfine structure was observed due to the presence of strong spin exchange, but fine structure was observed for the excited (S(T) = 3/2) state of Na(9)-2 and the ground state (S(T) = 1) of K(7)Na-1. The zero-field (D) parameters have also been determined for these states, constituting a rare case wherein one observes EPR from both the ground and the excited states. Magnetic susceptibility data show that Na(9)-2 has antiferromagnetically coupled Cu(2+) ions, with J = -1.36 +/- 0.01 cm(-)(1), while K(7)Na-1 has both ferromagnetically and antiferromagnetically coupled Cu(2+) ions (J(1) = 2.78 +/- 0.13 cm(-)(1), J(2) = -1.35 +/- 0.02 cm(-)(1), and J(3) = -2.24 +/- 0.06 cm(-)(1)), and the ground-state total spins are S(T) = 1/2 in Na(9)-2 and S(T) = 1 in K(7)Na-1.     

Structural chemistry of polycyclic heteroaromatic compounds. Part XI. Photoelectron spectra and electronic structures of tetracyclic hetarenes of the triphenylene type

The UV photoelectron spectra of several tetracyclic heteroaromatic compounds (2-9) which are pi-isoelectronic with triphenylene (1) have been recorded and analysed making use of semiempirical AM1 and PM3 as well as ab initio/DFT B3LYP calculations. In one series of compounds (2-7), the peripheral benzene rings of 1 are successively substituted by thiophene rings that are either [b]- or [c]-annellated with the central benzene unit. In 2-7 only marginal shifts are found for most of the IPs of electrons. In the benzotrithiophenes 5-7, a systematic variation is displayed by IP(pi7). Compared to 1, the pi electron system of benzo[c]trithiophene (7) is approximately two times as much destabilized as in the isomers 5 and 6 with [b]annellated thiophene rings. The IP[n(S)] values of the thiophene derivatives 2-7 indicate that these orbitals are clearly destabilized relative to thiophene. The same holds for the n(O) orbital of the furane derivative 9 in comparison with that of furane. In 9, only the higher pi MOs (pi7-pi9) are destabilized whereas the lower levels (pi1-pi4) are stabilized, and those in between (pi5-pi6) remain essentially unshifted. In the pyrrole derivative 8, all pi MOs are substantially destabilized by about 0.5-1.6 eV relative to 1.     

Synthese von 4(5)-acyl-5(4)-alkylimidazolen aus symmetrischen 1,3-dicarbonylverbindungen

Synthesis of 4(5)-Acyl-5(4)-alkylimidazoles from Symmetrical 1,3-Diones A new synthesis of 4(5)-acyl-5(4)-alkylimidazoles 1 is described. The symmetrical 1,3-diones 5a and 5b were reacted with N₂O₄ to give the nitro compounds 7a and 7b , respectively; 5c was treated with NaNO₂ to give the nitroso compound 7c (Scheme 2). Hydrogenation of 7a , 7b and 7c over Pd/C in acetic acid/acetic formic anhydride yielded the formamides 9a , 9b and 9c , whose cyclization in formamide/formic acid afforded the 4(5)-acyl-5(4)-alkylimidazoles 1a, 1b and 1c , respectively. Oxazoles 11a and 11b were obtained from the corresponding formamides 9a and 9b with methanesulfonic acid/P₂O₅.     

Fused s-triazino heterocycles. X. Displacement reactions of 7,9-dibromo-2-tribromomethyl-5-trichloromethyl-1,3,4,6,9b-pentaazaphenalene and 7,9-dibromo-2,5-bis(tribromomethyl)- 1,3,4,6,9b-pentaazaphenalene

The preparation of 7, 9-dibromo-2-tribromomethyl-5-trichloromethyl-1, 3, 4, 6, 9b-pentaazaphenalene ( 1c ) and 7, 9-dibromo-2, 5-bis(tribromomethyl)-1, 3, 4, 6, 9b-pentaazaphenalene ( 1d ) is described. Reaction of 1c with various nucleophiles converted it to the corresponding 7, 9-dibromo-2, 5-bis-substituted derivatives, the tri-halomethyl groups serving as leaving groups. Displacement, first of one tribromomethyl group on 1d by pyrrolidine, and then by various nucleophiles on the remaining tribromomethyl group led to several mixed 2, 5-disubstituted derivatives.     

Syntheses, characterizations, and coordination chemistry of the 10-vertex phosphadicarbaboranes 6-R-arachno-6,8,9-PC2B7H11 and 6-R-arachno-6,5,7-PC2B7H11

The 10-vertex phosphadicarbaboranes, 6-R-arachno-6,8,9-PC(2)B(7)H(11) (1) (R = Ph 1a or Me 1b) and 6-R-arachno-6,5,7-PC(2)B(7)H(11) (2) (R = Ph 2a or Me 2b) have been synthesized using in situ dehydrohalogenation reactions of RPCl(2) (R = Ph or Me) with the arachno-4,5-C(2)B(7)H(13) and arachno-4,6-C(2)B(7)H(13) carboranes, respectively. X-ray crystallographic determinations in conjunction with DFT/GIAO/NMR calculations and NMR spectroscopic studies have established that both 1 and 2 have open cage structures based on an icosahedron missing two vertexes. The two isomeric compounds differ in the positions of the carbons and bridging hydrogens on the open face. Studies of the reactions of 2a with BH(3).THF, S(8), and hydrogen peroxide demonstrated that 2a shows strong donor properties yielding the compounds endo-6-H(3)B-exo-6-Ph-arachno-6,5,7-PC(2)B(7)H(11) (3), endo-6-S-exo-6-Ph-arachno-6,5,7-PC(2)B(7)H(11) (4), and endo-6-O-exo-6-Ph-arachno-6,5,7-PC(2)B(7)H(11) (5) in which the BH(3), S, and O substitutents are bonded to an electron lone pair localized at the phosphorus endo-position. The reaction of 2a with an excess of S(8) results in the loss of a framework boron to produce the unique open-cage compound micro(7,8)-[HS(Ph)P]-hypho-7,8-C(2)B(6)H(11) (6). 2a also formed the donor complexes cis-(eta(1)-[6-Ph-arachno-6,5,7-PC(2)B(7)H(11)])(2)PtBr(2) (7) and trans-(eta(1)-[6-Ph-arachno-6,5,7-PC(2)B(7)H(11)])(2)PdBr(2) (8) in which the metal fragment is bonded in an eta(1)-fashion at the phosphorus endo-position. In these complexes, 2a is functioning as a two-electron sigma donor to the metals and can thus be considered as an analogue of the PR(3) ligands in the classical cis-(PPh(3))(2)PtBr(2) and trans-(PPh(3))(2)PdBr(2) coordination complexes. Although 1a did not show the donor properties exhibited by 2a, its dianion 6-Ph-6,8,9-PC(2)B(7)H(9)(2)(-) (1a(2)()(-)()) readily formed eta(4)-coordinated complexes with late transition metals including 8-Ph-7-(Ph(3)P)(2)-nido-7,8,10,11-PtPC(2)B(7)H(9) (9), 7-Ph-11-(eta(5)-C(5)H(5))-nido-11,7,9,10-CoPC(2)B(7)H(9) (10), and commo-Ni-(7-Ni-8'-Ph-nido-8',10',11'-PC(2)B(7)H(9))(7-Ni-8-Ph-nido-8,10,11-PC(2)B(7)H(9)) (11).     

Polyhedral monocarbaborane chemistry. Some C-phenylated seven, eight, nine, ten, eleven and twelve-vertex species

Some synthetic and structural systematics for monocarbaboranes, using the C-phenylated motif as the example, are investigated. The 10-vertex [6-Ph-nido-6-CB(9)H(11)](-) anion 1, from reaction of PhCHO with B(10)H(14) in KOH/H(2)O, is a useful entry synthon into C-phenyl monocarbaborane chemistry. Treatment of anion 1 with Na/thf yields the 10-vertex [1-Ph-closo-1-CB(9)H(9)](-) anion 2a, whereas treatment of anion 1 with iodine in alkaline solution yields the isomeric 10-vertex [2-Ph-closo-2-CB(9)H(9)](-) anion 2b, which isomerises quantitatively to 2a on heating under reflux in DME. Thermolysis of anion 1 yields the 9-vertex [4-Ph-closo-4-CB(8)H(8)](-) anion 5, whereas treatment of anion 1 with FeCl(3)/HCl gives neutral 9-vertex [4-Ph-arachno-4-CB(8)H(13)] 3. Compound 3 gives neutral 9-vertex [1-Ph-nido-1-CB(8)H(11)] 4 in refluxing toluene, and gives the 7-vertex [2-Ph-closo-2-CB(6)H(6)](-) anion 7 and the 8-vertex [1-Ph-closo-1-CB(7)H(7)](-) anion 6 in refluxing toluene with NEt(3). Reaction of 1 with [BH(3)(thf)] yields the 11-vertex [7-Ph-nido-7-CB(10)H(12)](-) anion 8 which can be converted to the 12-vertex [1-Ph-closo-1-CB(11)H(11)](-) anion 10 using [BH(3)(SMe(2))]; alternatively, anion 1 yields anion 10 directly on treatment with [BH(3)(NEt(3))]. Treatment of anion 8 with I(2)/KOH yields the 11-vertex [2-Ph-closo-2-CB(10)H(10)](-) anion 9. The structures of anions 1, 2a, 2b, 5, 6, 7, 8, 9 and 10 have been established by single-crystal X-ray diffraction analyses of their [NEt(4)](+) salts, and those of neutral 3 and 4 estimated by DFT calculations at the B3LYP/6-31G* level; similar calculations have also been applied to the new anionic closo species 2a, 2b, 5, 6, 7, 9 and 10. Crystals of the [NEt(4)](+) salt of the [2-Ph-closo-2-CB(6)H(6)](-) anion 7 required synchrotron X-radiation for sufficient diffraction intensity for molecular-structure elucidation. The syntheses are in principle generally applicable to give extensive derivative C-aryl and C-alkyl chemistries.     

New chemistry of 1,2-closo-P2B10H10 and 1,2-closo-As2B10H10; in silico and gas electron diffraction structures, and new metalladiphospha- and metalladiarsaboranes

The molecular structures of 1,2-closo-P(2)B(10)H(10) (1) and 1,2-closo-As(2)B(10)H(10) (2) have been determined by gas electron diffraction and the results obtained compared with those from computation at the MP2/6-31G** level of theory. The level of agreement is good for 2 (root-mean-square [rms] misfit for As and B atoms 0.0297 ?) and very good for 1 (rms misfit for P and B atoms 0.0082 ?). In comparing the structures of 1 and 2 with that of 1,2-closo-C(2)B(10)H(12) (I) it is evident that expansion of the polyhedron from I to 1 to 2 is restricted only to the heteroatom vertices and the B(6) face to which these are bound. Following deboronation (at B3) and subsequent metallation, compounds 1 and 2 have been converted into the new metalladiheteroboranes 3-(η-C(9)H(7))-3,1,2-closo-CoAs(2)B(9)H(9) (4), 3-(η-C(10)H(14))-3,1,2-closo-RuAs(2)B(9)H(9) (5), 3-(η-C(5)H(5))-3,1,2-closo-CoP(2)B(9)H(9) (6), 3-(η-C(9)H(7))-3,1,2-closo-CoP(2)B(9)H(9) (7) and 3-(η-C(10)H(14))-3,1,2-closo-RuP(2)B(9)H(9) (8), the last three constituting the first examples of metalladiphosphaboranes. Together with the known compound 3-(η-C(5)H(5))-3,1,2-closo-CoAs(2)B(9)H(9) (3), compounds 4-8 have been analysed by NMR spectroscopy and (except for 8) single-crystal X-ray diffraction. The (11)B NMR spectra of analogous pairs of metalladiphosphaborane and metalladiarsaborane (6 and 3, 7 and 4, 8 and 5) reveal a consistently narrower (9-10 ppm) chemical shift range for the metalladiarsaboranes, the combined result of a deshielding of the lowest frequency resonance (B6) and an increased shielding of the highest frequency resonance (B8) via an antipodal effect. In crystallographic studies, compounds 3 and 5B (one of two crystallographically-independent molecules) suffer As/B disorder, but in both cases it was possible to refine distinct, ordered, components of the disorder, the first time this has been reported for metalladiarsaboranes. Moreover, whilst the Cp compounds 6 and 3 are disordered, their indenyl analogues 7 and 4 are either ordered or significantly less disordered, a consequence of both the reduced symmetry of an indenyl ligand compared to a Cp ligand and the preference of the former for a distinct conformation relative to the cage heteroatoms. Unexpectedly, whilst this conformation in the cobaltadiphosphaborane 7 is cis-staggered (similar to that previously established for the analogous cobaltadicarborane), in the cobaltadiarsaborane 4 the conformation is close to cis-eclipsed.     

Synthesis and biological activity of [MeTyr1,MeArg7,D-Leu8]-dynorphin A(1-9)-NHEt and [D-Cys2-Cys5,MeArg7,D-Leu8]-dynorphin A(1-9)-NH2

The opioid activities of [MeTyr1]-Dyn(1-7)-NH2, [MeTyr1,D-Leu8]-Dyn(1-8)-NH2, [MeTyr1,D-Leu8]-Dyn(1-9)-NH2, [MeTyr1,D-Leu8]-Dyn(1-10)-NH2, [MeTyr1,D-Leu8]-Dyn(1-11)-NH2, and [MeTyr1,D-Leu8,12]-Dyn(1-13)-NH2 were examined in the bioassays (guinea pig ileum, mouse vas deferens and rabbit vas deferens). Because [MeTyr1,D-Leu8]-Dyn(1-9)-NH2 showed the most potent opioid activity of the peptides tested, the biological activities of two kinds of Dyn(1-9) analogues, [MeTyr1,MeArg7,D-Leu8]-Dyn(1-9)-NHEt and [D-Cys2-Cys5,MeArg7,D-Leu8]-Dyn(1-9)-NH2 were determined and compared with those of [MeTyr1,MeArg7,D-Leu8]-Dyn(1-8)-NHEt and [D-Cys2-Cys5,MeArg7,D-Leu8]-Dyn(1-8)-NHEt in the three bioassays, in the receptor binding assays, and in the mouse tail pinch test after subcutaneous administration. The results suggest that the extension of the C-terminal in the peptide chain of [MeArg7,D-Leu8]-Dyn(1-8)-NH2 analogues by Arg is ineffective for increasing the kappa-opioid activities, kappa-receptor selectivity and/or analgesic effects of the peptides.     

Migration of a cis-(NH3)2PtII moiety along two adenine nucleobases, from N1 to N6, is markedly facilitated by additional PtII entities coordinated to N7

Adenine acidification as a consequence of simultaneous PtII binding to N1 and N7 facilitates deprotonation of the exocyclic N(6)H2 group and permits PtII migration from N1 to N6 under mild conditions. Starting from the trinuclear complex cis-[(NH3)2Pt(N1-9-MeA-N7)2{Pt(NH3)3)}2]6+ (3), stepwise migration of cis-(NH3)2PtII takes place in the alkaline aqueous solution to give initially cis-[(NH3)2Pt(N1-9-MeA-N7)(N6-9-MeA--N7){Pt(NH3)3}2]5+ (4) and eventually cis-[(NH3)2Pt(N6-9-MeA--N7)2{Pt(NH3)3}2]4+ (5) (with 9-MeA = neutral 9-methyladenine, 9-MeA- = 9-methyl-adenine monoanion, deprotonated at N6). The migration process has been studied by 1H NMR spectroscopy, and relevant acid-base equilibria have been determined. 5 has been crystallized as its nitrate salt and has been characterized by X-ray crystallography. The precursor of 3, [(NH3)3Pt (9-MeA-N7)]Cl2.2H2O (2) has likewise been studied by X-ray analysis.     

Regiospecific N9 alkylation of 6-(heteroaryl)purines: shielding of N7 by a proximal heteroaryl C-H1

Purine alkylations have been plagued with formation of mixtures of N9 (usually desired), N7, and other regioisomers. We have developed methods for synthesis of 6-(azolyl)purine derivatives whose X-ray crystal structures show essentially coplanar conformations of the linked azole-purine rings. Such ring orientations position the C-H of the azole above N7 of the purine, which results in protection of N7 from alkylating agents. Treatment of 6-(2-butylimidazol-1-yl)-2-chloropurine (9) with sodium hydride in DMF followed by addition of ethyl iodide resulted in exclusive formation of 6-(2-butylimidazol-1-yl)-2-chloro-9-ethylpurine (10), whereas identical treatment of 2-chloro-6-(4,5-diphenylimidazol-1-yl)purine (11) produced a regioisomeric mixture 12/13 (N9/N7, approximately 5:1). The linked imidazole and purine rings are coplanar in 9 (the butyl side chain is extended away from the purine ring and C-H is over N7) but are rotated approximately 57 degrees in 11, and the more bulky azole substituent in 11 did not prevent formation of the minor N7 regioisomer 13. Access to various regioisomerically pure 9-alkylpurines is now readily available.     

Syntheses of functionalized ferratricarbadecaboranyl complexes

The reactions of nitriles (RCN) with arachno-4,6-C(2)B(7)H(12)(-) provide a general route to functionalized tricarbadecaboranyl anions, 6-R-nido-5,6,9-C(3)B(7)H(9)(-), R = C(6)H(5) (2(-)), NC(CH(2))(4) (4(-)), (p-BrC(6)H(4))(Me(3)SiO)CH (6(-)), C(14)H(11) (8(-)), and H(3)BNMe(2)(CH(2))(2) (10(-)). Further reaction of these anions with (eta(5)-C(5)H(5))Fe(CO)(2)I yields the functionalized ferratricarbadecaboranyl complexes 1-(eta(5)-C(5)H(5))-2-C(6)H(5)-closo-1,2,3,4-FeC(3)B(7)H(9) (3), 1-(eta(5)-C(5)H(5))-2-NC(CH(2))(4)-closo-1,2,3,4-FeC(3)B(7)H(9) (5), 1-(eta(5)-C(5)H(5))-2-[(p-BrC(6)H(4))(Me(3)SiO)CH]-closo-1,2,3,4-FeC(3)B(7)H(9) (7), 1-(eta(5)-C(5)H(5))-2-C(14)H(11)-closo-1,2,3,4-FeC(3)B(7)H(9) (9), and 1-(eta(5)-C(5)H(5))-2-H(3)BNMe(2)(CH(2))(2)-closo-1,2,3,4-FeC(3)B(7)H(9) (11). Reaction of 11 with DABCO (triethylenediamine) resulted in removal of the BH(3) group coordinated to the nitrogen of the side chain, giving 1-(eta(5)-C(5)H(5))-2-NMe(2)(CH(2))(2)-closo-1,2,3,4-FeC(3)B(7)H(9) (12). Crystallographic studies of complexes 3, 5, 7, 9, and 11 confirmed that these complexes are ferrocene analogues in which a formal Fe(2+) ion is sandwiched between the cyclopentadienyl and tricarbadecaboranyl monoanionic ligands. The metals are eta(6)-coordinated to the puckered six-membered face of the tricarbadecaboranyl cage, with the exopolyhedral substituents bonded to the low-coordinate carbon adjacent to the iron.     

Examination of cucurbit[7]uril and its host-guest complexes by diffusion nuclear magnetic resonance

The self-diffusion of cucurbit[7]uril (CB[7]) and its host-guest complexes in D2O has been examined using pulsed gradient spin-echo nuclear magnetic resonance spectroscopy. CB[7] diffuses freely at a concentration of 2 mM with a diffusion coefficient (D) of 3.07 x 10(-10) m(2) s(-1). At saturation (3.7 mM), CB[7] diffuses more slowly (D = 2.82 x 10(-10) m(2) s(-1)) indicating that it partially self-associates. At concentrations between 2 and 200 mM, CsCl has no effect on the diffusion coefficient of CB[7] (1 mM). Conversely, CB[7] (2 mM) significantly affects the diffusion of 133Cs+ (1 mM), decreasing its diffusion coefficient from 1.86 to 0.83 x 10(-9) m(2) s(-1). Similar changes in the rate of diffusion of other alkali earth metal cations are observed upon the addition of CB[7]. The diffusion coefficient of 23Na+ changes from 1.26 to 0.90 x 10(-9) m(2) s(-1) and 7Li+ changes from 3.40 to 3.07 x 10(-9) m(2) s(-1). In most cases, encapsulation of a variety of inorganic and organic guests within CB[7] decreases their rates of diffusion in D2O. For instance, the diffusion coefficient of the dinuclear platinum complex trans-[[PtCl(NH3)2}2mu-dpzm](2+) (where dpzm is 4,4'-dipyrazolylmethane) decreases from 4.88 to 2.95 x 10(-10) m(2) s(-1) upon encapsulation with an equimolar concentration of CB[7].