The Uracil C(5) Position as a Metal Binding Site: Solution and X-ray Crystal Structure Studies of Pt(II) and Hg(II) Compounds

1,3-Dimethyluracil (1,3-DimeU) reacts with trans-[(CH(3)NH(2))(2)Pt(H(2)O)(2)](+) to give trans-[(CH(3)NH(2))(2)Pt(1,3-DimeU-C5)(H(2)O)]X (X = NO(3)(-), 1a, ClO(4)(-), 1b) and subsequently with NaCl to give trans-(CH(3)NH(2))(2)Pt(1,3-DimeU-C5)Cl (2) or with NH(3) to yield trans-[(CH(3)NH(2))(2)Pt(1,3-DimeU-C5)(NH(3))]ClO(4) (3). In a similar way, (dien)Pt(II) forms [dienPt(1,3-DimeU-C5)](+) (4). Reactions leading to formation of 1 and 4 are slow, taking days. In contrast, Hg(CH(3)COO)(2) reacts fast with 1,3-DimeU to give (1,3-DimeU-C5)Hg(CH(3)COO) (5). Both 1-methyluracil (1-MeUH) and uridine (urdH) react with (dien)Pt(II) initially at N(3) and subsequently with either (dien)Pt(II) or Hg(CH(3)COO)(2) also at C(5) to give the diplatinated species 7 and 9 or the mixed PtHg complex 8. C(5) binding of either Pt(II) or Hg(II) is evident from coupling of uracil-H(6) with either (195)Pt or (199)Hg nuclei and (3)J values of 47-74 Hz (for Pt compounds) and 185-197 Hz (for Hg compounds). J values of Pt compounds are influenced both by the ligands trans to the uracil C(5) position and by the number of metal entities bound to a uracil ring. Both 2 and 5 were X-ray structurally characterized. 2: monoclinic system, space group P2(1)/c, a = 15.736(6) ?, b = 11.481(6) ?, c = 25.655 (10) ?, beta = 145.55(3) degrees, V = 2621.9(28) ?(3), Z = 4. 5: monoclinic system, space group P2(1)/c, a = 4.905(2) ?, b = 18.451(6) ?, c = 11.801(5) ?, beta = 94.47(3) degrees, V = 1064.77(72) ?(3), Z = 4.     

Resolution of four k-region arene imines and mutagenicity of the optically pure aziridines

Racemic K-region imines of benz[a]anthracene, 7-methylbenz[a]anthracene, chrysene and benzo[a]pyrene ( 1–4 , respectively) have been resolved by high performance liquid chromatography on a column packed with amylose tris(3,5-dimethylphenylcarbamate) on silica gel. The absolute configuration of the resolved aziridines was assigned by comparison of their circular dichromism spectra to those of the corresponding enantiomerically pure arene oxides. The mutagenicity of the enantiomers of the arene imines was investigated using Salmonella typhimurium strains TA98 and TA100. Although all arene imines investigated were potent mutagens, quantitative and qualitative differences in the mutagenic activity were observed between enantiomers.     

Determination of metal concentration in fat supplements for swine nutrition by atomic absorption spectroscopy

The presence of some essential and toxic metals in fat supplements for swine diet was investigated. Collected samples represented a relevant production of the Italian industry. In particular, some samples were enriched with antioxidants or waste cooking oils. The method for the determination of Ca, Cu, Cd, Fe, Mg, Mn, Ni, Pb, and Zn in fat samples was developed by means of a certified reference material (CRM 186) and a representative fatty sample (RFS). All samples were digested in closed vessels in a microwave oven and then analyzed by flame atomic absorption or graphite furnace atomic absorption spectrometry. The entire analytical method provided a satisfactory repeatability and reproducibility confirmed by agreement between the experimental recovery data obtained for the CRM 186 sample and, with the method of standard additions, for the RFS material. The samples generally showed a small amount of metals compared with the recommended daily intake for the essential elements. On the other hand, some samples contained a significant concentration, from an analytical point of view, of Cd, Ni, and Pb. Principal component analysis (PCA) was applied to inspect the experimental data obtained from samples analysis. Basically no differences were detected in terms of metal concentration among the fat supplements analyzed.     

Condensed heterocycles containing the pyrimidine nucleus

Continuing earlier studies designed to obtain derivatives of 1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one and of the isomeric 7-one of pharmacological interest, some novel compounds 2 and derivatives of 6,7,8,9-tetrahydro-5H-1,3,4-thiadiazolo[2,3-b]quinazolin-5-one ( 3 ) were prepared. Derivatives of pyrimido[2,1-b]benzothiazol-2-one ( 6 ) and of the isomeric 4-one derivatives 8 were also synthesized. Structural identification was obtained by ¹H-nmr, ir and mass spectra.     

Glycosylidene Carbenes. Part 18. Insertion of glycosylidene carbenes into the Sn?H bond of tributyl- and triphenylstannane: A synthesis of stannoglycosides

Insertion of the glycosylidene carbenes, derived from the gluco- and the manno-diazirines 1 and 2 , into the Sn? H bond of R₃SnH (R = Bu or Ph) leads to the fully substituted stannoglycosides 3 – 8 (53–77%). The 1,2-cis-configurated products are formed preferentially (α-D /β -D ranges from 2.5:1 to 5.1:1 with 1 , and 1:1.3 to 1:4.2 with 2 ). Relative to CH₂Cl₂, THF favors formation of the equatorial Sn-glycosides. The stannylated (benzyloxy)glucals 9 and 10 were isolated as side products. The reaction of 1 with (Bu₃Sn)₂ yielded 9 (17% in CH₂Cl₂; 36% in CCl₄) together with the azines 11 and the benzyloxyglucal 12 . NMR Data of the Sn-glycosides 3 – 8 show evidence for an anomeric effect, ¹J(C(1),H) being larger in the axial and ¹J(Sn,C(1)) larger in the equatorial anomers.     

o-quinone methides 2. Stereoselectivity in cycloaddition reactions of o-quinone methides with vinyl ethers

Cycloaddition reactions between vinyl ethers 3 and $\text{o}$-quinone methides 2, thermally generated from 2-hydroxybenzyl alcohols 1, have been studied. The structure and conformational preferences of the 4-substituted 2-ethoxy-(2,3)-dihydro-2$\text{H}$-benzopyrans 4–9 obtained, which show new interesting features, are discussed together with competitive kinetic data. The cycloaddition process is concerted and involves $\text{o}$-quinone methides in the $\text{E}$-configuration. The OEt-$\text{endo}$ transition state seems to be preferred with ethyl vinyl ether and $\text{Z}$-1-propenyl ethyl ether, whereas with $\text{E}$-1-propenyl ethyl ether the stereoselectivity of the cycloaddition process depends on substituents on the methylene group of the starting alcohol 1. These results are discussed in terms of $\text{endo}$ and $\text{exo}$ preference of the propenyl ether methyl group.     

Formation and characterization of the hexanuclear platinum cluster [Pt6(mu-PBu(t)2)4(CO)6](CF3SO3)2 through structural, electrochemical, and computational analyses

The reaction between equimolar amounts of Pt(3)(mu-PBu(t)()(2))(3)(H)(CO)(2), Pt(3)()H, and CF(3)SO(3)H under CO atmosphere affords the triangular species [Pt(3)(mu-PBu(t)()(2))(3)(CO)(3)]X, [Pt(3)()(CO)(3)()(+)()]X (X = CF(3)SO(3)(-)), characterized by X-ray crystallography, or in an excess of acid, [Pt(6)(mu-PBu(t)()(2))(4)(CO)(6)]X(2), [Pt(6)()(2+)()]X(2)(). Structural determination shows the latter to be a rare hexanuclear cluster with a Pt(4) tetrahedral core formed by joining the unbridged sides of two orthogonal Pt(3) triangles. The dication Pt(6)()(2+)() features also extensive redox properties as it undergoes two reversible one-electron reductions to the congeners [Pt(6)(mu-PBu(t)()(2))(4)(CO)(6)](+) (Pt(6)()(+)(), E(1/2) = -0.27 V) and Pt(6)(mu-PBu(t)()(2))(4)(CO)(6) (Pt(6)(), E(1/2) = -0.54 V) and a further quasi-reversible two-electron reduction to the unstable dianion Pt(6)()(2)()(-)() (E(1/2) = -1.72 V). The stable radical (Pt(6)()(+)()) and diamagnetic (Pt(6)()) species are also formed via chemical methods by using 1 or 2 equiv of Cp(2)Co, respectively; further reduction of Pt(6)()(2+)() causes fast decomposition. The chloride derivatives [Pt(6)(mu-PBu(t)()(2))(4)(CO)(5)Cl]X, (Pt(6)()Cl(+)())X, and Pt(6)(mu-PBu(t)()(2))(4)(CO)(4)Cl(2), Pt(6)()Cl(2)(), observed as side-products in some electrochemical experiments, were prepared independently. The reaction leading to Pt(3)()(CO)(3)()(+)() has been analyzed with DFT methods, and identification of key intermediates allows outlining the reaction mechanism. Moreover, calculations for the whole series Pt(6)()(2+)() --> Pt(6)()(2)()(-)()( )()afford the otherwise unknown structures of the reduced derivatives. While the primary geometry is maintained by increasing electron population, the system undergoes progressive and concerted out-of-plane rotation of the four phosphido bridges (from D(2)(d)() to D(2) symmetry). The bonding at the central Pt(4) tetrahedron of the hexanuclear clusters (an example of 4c-2e(-) inorganic tetrahedral aromaticity in Pt(6)()(2+)()) is explained in simple MO terms.     

A new bicyclic proline-mimetic amino acid

A new constrained bicyclic α-amino acid proline-mimetic was developed. The synthesis was achieved starting from derivatives of the chiral pool, thus allowing to prepare analogues of either l- or d-proline by choosing appropriate stereoisomers of serine and α,β-isopropylidene-glycerol derivatives. The scaffolds were prepared as N-Fmoc-amino acid suitable for solid-phase peptide synthesis.     

A Theoretical Study of Amine Bonding in Titanium Alkoxide Adducts

Summary. DFT calculations were carried out on Ti₂(OCH₃)₈ (NH₂CH₃)₂ and Ti₂(OCH₃)₈(NH₃)₂, which are model compounds for the previously isolated amine adducts Ti₂(OR)₈(NH₂ R′)₂. The calculations show that the Ti–N bond strength is weak; however, coordination of the amine to the metal center is supported by a N–H···O hydrogen bond of the amine with the neighboring alkoxo ligand. The Ti–N interaction is purely σ in nature, while the Ti–O interactions include both σ and π contributions. The lowest unoccupied molecular orbitals are mainly localized on Ti t_2g-like orbitals.