Martin Murray

Formation of a dihydropyridine derivative as a potential cross-link derived from malondialdehyde in physiological systems

Malondialdehyde is a major oxidation product of lipids which is capable of cross‐linking the collagen of the cardiovascular system. Identification of cross‐links usually involves degradative procedures. In this paper, we use a novel, direct, approach using nuclear magnetic resonance to identify early and labile products. Initial model studies show that malondialdehyde reacts with lysine to form a dihydropyridine derivative rather than the unstable imidopropene Schiff base previously reported. The aldehydes on the pyridine ring could react further to cross‐link collagen and stiffen the aorta, thereby promoting further glycation, a process that would be accelerated in diabetes.

Porphyrins with a novel exocyclic ring system in an oil shale

Abstract A C32 and a C31 alkyl porphyrin, each present in Serpiano oil shale as the vanadyl complex, have been -isolated as the demetallated compounds and their structures determined by 1H NMR spectroscopic analysis of the zinc complexes, using selective decoupling and nuclear Overhauser effects. The occurrence of these chiral optically inactive compounds with a methyl-substituted, six membered exocyclic ring extends the known series of isomeric structural types of sedimentary alkyl porphyrins.

Synthesis and crystal and molecular structure of tris-µ-(t-butyl isocyanide)-tris(t-butyl isocyanide)-triangulo-triplatinum

Reaction of t-butyl isocyanide with bis(cyclo-octa-1,5-diene)platinum gives the orange crystalline complex [Pt3(ButNC)6] in essentially quantitative yield. Methyl, ethyl, and cyclohexyl isocyanides react with [Pt(1,5-C8H12)2] in a similar manner to give [Pt3(RNC)6](R = Me, Et, or C6H11). The structural identity of [Pt3(ButNC)6] has been established by analysis of single-crystal X-ray data recorded at room temperature on a four-circle diffractometer. The complex is monoclinic, space group P21/n, Z= 4, a= 18.213(7), b= 11.811 (5), c= 21.996(6)A, β= 110·21(3)°. Using 3 543 reflections, the refinement has converged to R 0.057 (R′0.070). The molecule contains an essentially equilateral triangle of platinum atoms each of which carries a terminal isocyanide ligand, with the remaining three isocyanide groups bridging the sides of the triangle. The former are effectively linear and the latter bent [CNC(mean) 132.7°]. The platinum atoms and the six attached carbon atoms are effectively coplanar with maximum deviation 0.08 A. Hydrogen-1 and 13C n.m.r. studies between room temperature and 120 °C reveal that [Pt3(ButNC)6] undergoes dynamic behaviour via an intermolecular process involving terminal and bridge isocyanide site exchange catalysed by free ligand.

Stereochemical course of the action of the cellobioside hydrolases I and II of Trichoderma reesei

With β-cellobiosyl fluoride as substrate, CBHI gives β-cellobiopyranose as the first product, whereas CBHI gives α-cellobiopyranose (CBH = cellobioside hydrolase).

Homoallyl-substituted vinylcyclopropanes from alpha,beta-unsaturated ketones and allylindium derivatives

Simply reversing the order of addition of aqueous acid and Et2 O to the Barbier intermediate 1 of the known indium-mediated allylation leads to unprecedented deoxygenative rearrangements [Eq. (a)].

The Azomethine Ylid Strategy in β-Lactam Synthesis. Application to Selenapenams

Abstract Using azomethine ylid reactivity available from the β-lactam-based oxazolidinone 1 , selenoketones 6a – e react as 1,3-dipolarophiles to give racemic selenapenams 7a – e in a single step. The cycloaddition sequence proceeds with complete control of regiochemistry and the thermodynamically more stable C (3)/ C (5) relationship is observed. The selenothiocarboxylate 9a and the selenocarboxylate 9b also function as effective dipolarophiles, but attempts to convert the resulting cycloadducts 10a and 10b to the corresponding selenapenems were unsuccessful. Other selenium-containing dipolarophiles failed to give characterizable cycloadducts.

Synthesis of bis-µ-diorganosilanediyl-af-dihydridobis(triorganophosphine)diplatinum complexes: crystal and molecular structure of [{PtH(µ-SiMe2)[P(C6H11)3]}2]

The compound [{Pt(µ-H)(SiMe2Ph)[P(C6H11)3]}2] decomposes in hexane at reflux to give in low yield (10%) the diplatinum complex [{PtH(µ-SiMe2)[P(C6H11)3]}2]. A single-crystal X-ray diffraction study shows that the crystals are monoclinic, space group P21/c, with Z= 2 in a unit cell of dimensions a= 9.158(2), b= 11.725(3), c= 20.252(9). A, and β= 92.37(3)°. The structure has been solved by heavy-atom methods from automated diffractometer data, and refined to R 0.065 (R′ 0.080) for 5 998 reflections. The molecule is constrained crystalographically to Ci, symmetry, and the two platinum atoms are asymetrically bridged by two dimethylsilyl groups, giving two distinct Pt–Si bond lengths [2.420(2) and 2.324(2)A]. The Pt, Si, and P atoms are essentially coplanar, with a P–Pt–Pt angle of 159.5(1)° and a Pt–Pt distance of 2.708(1)A. Hydrido-ligands have been located trans to the shorter Pt–Si bonds at a distance of 1.78 A from the Pt atoms, sites which are also only 1.72 A from the other Si atoms. These hydrido-ligands might therefore be considered to bridge the longer Pt–Si bonds, and in any case complete very distorted ‘square’ planar configurations around the Pt atoms. The tricyclohexylphosphine ligands show no unusual features, and possess the usual chair conformation for the C6 rings. The complex [{PtH(µ-SiMe2)[P(C6H11)3]}2] may be synthesised in high yield by treating [Pt(C2H4)2{P(C6H11)3}] with SiMe2H2, and similar reactions afford the compounds [{PtH(µ-SiR2)(PR′3)}2][R = Me, PR′3= PMeBut2, PPri2Ph, or PPh3; R = Ph, PR′3= P(C6H11)3, PPh3, PPri2Ph, or PMeBut2] from, SiR2H2(R = Me or Ph). These hydridoplatinum complexes do not show 1H n.m.r. resonances above τ 10, but the 2H spectrum of [{Pt2H(µ-SiMe2)(PMeBut2)}2] has a signal due to 2HPt at τ 8.13. This property, and the occurrence in the i.r. spectra of all the complexes [{PtH(µ-SiR2)(PR3)}2] of ν(PtH) bands at ca. 1 650 cm–1, are interpreted as indicating the presence of delocalised three-centre two-electron Pt–H–Si bonding in the title compounds.

The synthesis and x-ray crystal structure of the hexanuclear metal cluster complex [Ir3Pt3(μ-CO)3(CO)3(η-C5Me5)3]

Abstract The compounds [Ir(CO)2(η-C5Me5)] and [Pt(C2H4)3] in diethylether at 0°C react to give the cluster complex [Ir3Pt3(μ-CO)3(CO)3(η-C5Me5)3] in quantitative yield. The structure of the hexanuclear metal species was established by X-ray diffraction. The main feature is a near-planar array of metal atoms with a central triangle of platinum atoms [PtPt (mean), 2.703(3) A] each edge-bridged by an iridium atom [IrPt (mean) 2.667(3) A]. The iridium atoms are each ligated by an η5-C5Me5 group and by two CO ligands. Three of the latter are essentially terminally bound to Ir and lie approximately orthogonal to the Ir3Pt3 plane, and three bridge between Pt and Ir and lie close to the hexametal plane. The 13C-{1H&} NMR data for the cluster reveal that the carbonyl groups and η5-C5Me5 ligands undergo dynamic behaviour in solution and possible mechanisms for ligand site exchange are discussed.

Sacredicene, a novel monocyclic C33 hydrocarbon from sediment of Sacred Lake, a tropical freshwater lake, Mount Kenya

Abstract A new isoprenoidal hydrocarbon, Sacredicene ( 1 ), has been isolated from a lacustrine sediment deposited 10280 years ago ( 14 C dating) and its structure determined by 1 H and 13 C NMR and mass spectroscopy.

Entropy-Driven Hydrogen Bonding: Stereodynamics of a Protonated, N,N-Chiral “Proton Sponge”

The C2-symmetric ([DL]) and achiral ([meso]) diastereoisomers of the hydrogen iodide salt of 1,8-bis-(N-benzyl-N-methylamino)naphthalene ([2H]-[I] ) interconvert in solution. Direct interconversion of the diastereoisomers of [2H]+ must involve hydrogen bond fission (to give [nonHB-2H+]) and rotation-inversion of the non-protonated nitrogen centre. The global activation parameters (deltaH++ and deltaS++) for diastereoisomer interconversion in [D7]DMF have been determined from rate data obtained by temperature-drop and magnetisation-transfer 13C NMR spectroscopy over a temperature range of 170 degrees C. The process is found to have a high entropy of activation in both directions (deltaS++=163(+/-4) and 169(+/-4) JK(-1)mol(-1)) and this is suggested to arise through hydrogen bonding of the ammonium centre in [nonHB-2H+] with the solvent ([D7]DMF). Comparison of the enthalpy of activation (deltaH++) with that earlier found for diastereoisomer interconversion of the free-base form 2 suggests that the intramolecular hydrogen bond in [2H]+ is roughly equal in enthalpic strength (deltaH) with that made with the solvent ([D7]DMF) in the non-hydrogen-bonded intermediate [nonHB-2H+]. As such, the hydrogen bonding in [2H]+ may be considered as predominantly an entropically driven process, without any unusual enthalpic strength.