Michel Geoffroy

α-Deoxy-α-hydroxyamino sugar phosphonates and the corresponding nitroxide free-radicals☆

Abstract Treatment of sugar aldonitrones with dialkyl phosphites gave sugar α-deoxy-α-( N -hydroxy- N -methylamino)phosphonates, often highly stereoselectively. Repeated nucleophilic addition to a nitrone followed by oxidation of the resulting hydroxylamine allows the “first generation” nitrone, 1,2- O -isopropylidene-α- d - xylo -pentodialdo-1,4-furanose 5-( N -methyloxime), to be converted into the “third generation” cyclic nitrone, [(4 R )-4-diethoxyphosphoryl-5 H ,6 H -1,3-oxazino][6,5- c ](1,2- O -isopropylidene-α- d - xylo -tetrofuranose) N -oxide. The configurational and conformational assignments for all the new compounds prepared were based on short and long-range H,H, H,P, and P,C couplings, and new empirical rules regarding long-range H,P couplings are proposed. The sugar α-deoxy-α-hydroxyamino-phosphonates spontaneously oxidised in the air to give the corresponding nitroxide free-radicals, which afforded good e.s.r. spectra that allowed epimers at the α-carbon atom to be discriminated.

Mono- and Bis(tetrathiafulvalene)-1,3,5-Triazines as Covalently Linked Donor-Acceptor Systems: Structural, Spectroscopic, and Theoretical Investigations

Reaction of 2,4,6-trichloro-1,3,5-triazine with lithiated tetrathiafulvalene (TTF) in stoichiometric conditions, followed by treatment with sodium methanolate, provides mono- and bis(TTF)-triazines as new covalently linked (multi)donor-acceptor systems. Single-crystal X-ray analyses reveal planar structures for both compounds, with formation of peculiar segregated donor and acceptor stacks for the mono(TTF)-triazine compound, while mixed TTF-triazine stacks establish in the case of the bis(TTF) derivative. Cyclic voltammetry measurements show reversible oxidation of the TTF units, at rather low potential, with no splitting of the oxidation waves in the case of the dimeric TTF, whereas irreversible reduction of the triazine core is observed. Intramolecular charge transfer is experimentally evidenced through solution electronic absorption spectroscopy. Time-dependent DFT calculations allow the assignment of the charge transfer band to singlet transitions from the HOMO of the donor(s) to the LUMO of the acceptor. Solution EPR measurements correlated with theoretical calculations were performed in order to characterize the oxidized species. In both cases the spectra show very stable radical species and contain a triplet of doublet pattern, in agreement with the coupling of the unpaired electron with the three TTF protons. The dication of the bis(TTF)-triazine is paramagnetic, but no spin-spin exchange interaction could be detected.

Synthesis of new chelating agents : association of a phosphaalkene moiety with a pyridine

Molecules containing a Pyridine ring located in α from one or two phosphaalkene moieties have been synthesized. The E isomer (L1) and the E,E isomer (L2) are well suited for acting as a bidentate and a trindentate ligand respectively. The crystal structure ofthe E isomer (L1) is determined.

Copper(I) and copper(II) complexes of entwined or interlocked phenanthroline type ligands : ESR and crystallographic investigations

The crystal structure of [Cu(dap) 2 ]BF 4 has been determined and single crystals of 63 Cu(dap) 2 BF 4 were doped with [ 63 Cu(dap) 2 ] 2+ ions and studied by ESR. The resulting spectra are compared with those obtained with frozen solutions containing [ 63 Cu(dap) 2 ] 2+ or [Cu(cat-30)] 2+ . The complex [Cu(dap) 2 ] + is pseudotetrahedral (crystal structure) as is [Cu(dap) 2 ] 2+ in frozen solution. The 63 Cu hyperfine coupling shows however that this coordination is not maintained for the dication in a crystalline environment, and the single crystal ESR study suggests the presence of a fifth ligand. Such a versatility of the structure is not observed for the Cu(II) catenate in agreement with the more pronounced rigidity of the interlocked system as compared to its open chain analogue.

3′-Deoxy-3′-Hydroxyamino-β-D-Xylofuranosyluracil and Derivatives Thereof

Abstract The title compound was prepared by reduction of the oxime of the 3′-ketouridine. Condensation with aldehydes gave a series of nitrones whose reduction afforded “second generation” hydroxylamines, some of which showing antiviral activity. The nitroxide free radicals formed upon oxidation of hydroxylamines gave good e.s.r. spectra useful for configurational and conformational assignments.

Terminal Deoxy Hydroxyamino Sugars

Abstract Reduction of sugar aldoximes gave in good yield the corresponding terminal deoxy hydroxyamino sugars. These compounds were found to be reasonably stable (they could be kept for some weeks at 4° C). On standing in the air, these compounds in solution were spontaneously oxidized to the corresponding nitroxide free radicals whose ESR spectra gave useful structural information.

Spin-labelled glycolipid analogues" D-glucose series

Abstract Neoglycolipids bearing a paramagnetic probe in their lipophilic aglycon have been prepared. All belong to the d -glucose series, both anomers for the glucoside representatives, respectively β and α anomers in the S - and C -glucosyl series. Two different types of radical sites have been used, a relatively short-lived imino N -oxyl group for glucosides and a more stable N -acylamino N -oxyl moiety in the other cases. EPR spectra of these radical species afforded information on the conformation of the lipophilic chain in the vicinity of the paramagnetic probe.

EPR and DFT studies of the one-electron reduction product of phospholium cations

Cyclic voltammetry and EPR spectroscopy show that cationic phospholium groups are good electron acceptors whose reduction leads to a neutral radical where the unpaired electron is mainly delocalized on the carbon atoms of the five-membered ring. DFT calculations together with the crystal structure of phospholiums indicate that the electron addition causes a drastic diminution of the exocyclic CPC angle. The SOMO of reduced phospholium is compared to the SOMO of the phosphole radical anion.

Phosphaalkene derivatives of furane and thiophene: Synthesis, crystal structure, electrochemistry and EPR study of their radical anions

Two phosphaalkenes containing either a furane or a thiophene ring bound to the carbon atom of the −Pdouble bond; length as m-dashC < bond have been synthesized. The crystal structure of the furane derivative has been determined and the electrochemistry of both compounds has been investigated. THF solutions of these compounds react at 255 K with a potassium mirror to yield the corresponding radical anions which have been studied by EPR in both the liquid and solid states. The resulting hyperfine constants are compared with the values predicted by ab initio calculations on radical anions formed from model phosphaalkenes.

The diphenylphosphino radical, (C6H5)2˙P

The diphenylphosphino radical, (C6H5)2P, has been observed at room temperature in X-irradiated single crystals of triphenylphosphine oxide and diphenylphosphine sulphide and in ultra-violet irradiated polycrystalline diphenylphosphine at 77 K. The isotropic 31P coupling constant is deduced to be +252 MHz and the anisotropic components are approximately 504, -252, -252 MHz. The largest value of the g tensor lies perpendicularly to the direction of the largest hyperfine coupling constant, the values in diphenylphosphine sulphide being 2·0094, 2·0035 and 2·0021. X-irradiated triphenylphosphine oxide also contains the (C6H5)2PO radical.