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International audience; In order to mimic the first steps of lignification, pectin/synthetic lignin (dehydrogenation polymers (DHPs)) interactions were investigated using reconstructing approaches. In artificially lignified bacterial cellulose(BC)/pectin composites, DHP nodules display a more dispersed distribution than in BC mats. Occurrence of covalent linkages between pectin and DHP was investigated by solid state NMR. Non-covalent bonds seem to govern the associative behaviour and stability of the complexes. Studied by small angle neutron scattering, a compaction process of DHP/pectin clusters occurs during polymerization and phase separation of the two polymers was shown at the nanometer scale.

Aldol condensations on α,β-epoxyaldehyde having a remote alkoxy group have been realized. A rationalization of the outcome of this condensation is discussed, relying on the dominant conformers revealed by molecular modeling of anti and syn γ,δ-epoxy β-hydroxyesters and their NMR and IR spectrostroscopic properties.

The cyclisation process leading stereoselectively to six and/or five membered ring lactones and lactone ethers from optically active epoxy or diepoxy β-hydroxyesters, or diastereoisomeric epoxy lactones obtained from nerol and geraniol has been developed. The ring closure leading to lactones mirrors the well-known iodolactonisation process while for the cyclic ether formation, Baldwin's rules are obeyed. 13C NMR data are helpful for determining the relative stereochemistry of different carbon chiral centers.

The reaction between acetic acid derivatives and α-substituted cinnamic acid derivatives has been studied inTHF andTHF:HMPT (80:20) as an alternative pathway of theMichael addition of phenylacetic and cinnamic acid derivatives. The regioselectivity observed is found to depend on the acceptor functional group and its geometry but not on the solvent used. The diastereoselectivity of the conjugate addition results from kinetic protonation of diastereotopic enolates (1,2-asymmetric induction). It varies from low in the presence ofHMPT to considerable or even high in pureTHF. The favouredanti orsyn configuration inTHF depends on the nature of the enolate. The results obtained are rationalized in terms of protonationvia transition structures different in type (openvs. chelated) and geometry.

Aldol condensations on α,β-epoxyaldehyde having a remote alkoxy group have been realized. A rationalization of the outcome of this condensation is discussed, relying on the dominant conformers revealed by molecular modeling of anti and syn γ,δ-epoxy β-hydroxyesters and their NMR and IR spectrostroscopic properties.

Reacting Zn(CF3SO3)2 with the title ligand (ON) yields a 1:2 complex which precipitates from methanol as the [Zn(ON)2(CH3OH)2](CF3SO3)2 salt. The crystal structure of this complex (P11/c, a=13.711(2), b=10.401(2), c=16.358(2) A, β=124.27(1)°, R=0.059, 1918 observed reflections) reveals the presence of a centrosymmetric, nearly octahedral, complex cation. The all-trans configuration about Zn2+ is achieved by two methanol hydroxyl groups and two bidentate ligands bonded via their pyridyl nitrogens and amide oxygens. The amide group nitrogen is not coordinated to the metal, but it forms an NH.…O hydrogen bond to the CF3SO3− counterions. The influence of the amide substituent on the structure is discussed on the basis of comparisons with the [Zn{N-(2-pyridyl)acetamide}2(H2O)2]2+ ion containing a similar amidopyridine chelate ring.

5′-C-substituted nucleosides with an hydroxyalkyl chain are synthesized. The stereochemistry of the new stereogenic center is defined. After introduction of a tosyl group, dimer models are prepared to evaluate the conjugation with amines used as nucleophiles.

The equilibrium adduct from the Michael reaction between lithium dimethylphenylacetamide enolate and methyl cinnamate has been studied by means of 7Li, 13C and 1H NMR and IR spectroscopy as well as by electrical conductivity measurements in THF and diethyl ether. The 7Li NMR and the electrical conductivity measurements data are consistent with a triple ion structure of [A−M+A−]− M+ type, favoured in THF. All other spectral data support an intramolecular chelation in the triplet fragment.

The crystal structure of a trimeric lignin model 1 presenting the characteristic pattern of biphenyl (5,5') and aryl-alkyl-ether (beta-O-4) linkages has been determined. The crystal system is triclinic and the crystallographic unit cell consists of two monomeric molecules. These results are compared with crystal data from the literature of simple models of the 5,5' and beta-O-4 structure type. The availability of a terminal aldehyde function on the model affords some interesting intermolecular interactions by weak hydrogen bonding which controls the conformation of the molecule and the aromatic ring orientation in particular; an unexpected cisoïd conformation of the biaryl unit is observed based on the 64.4 degrees value found for the torsion angle between the two 5,5' aromatic rings.

Using recombinant cinnamyl alcohol dehydrogenase isoform 2 (CAD2, EC 1.1.1.195), an NADPH-dependent aromatic alcohol dehydrogenase involved in lignification in vascular plants, we have investigated the detailed steady-state kinetic mechanism of CAD2 and the role of a serine residue in determining the cofactor specificity of CAD2. Site-directed mutagenesis (S212D) and overexpression of the WT and mutant S212D forms of CAD2 in Escherichia coli, followed by kinetic studies on the purified WT and mutant proteins, confirmed the involvement of S212D in recognizing the phosphate group of NADPH and provided information on the structural requirements for NADPH specificity. From substrate kinetic patterns and product inhibition studies both WT and S212D mutant forms of CAD2 have been shown to follow rapid equilibrium random bireactant kinetics with the value of the interaction factor (alpha) for WT (0.25) being significantly less than that for S212D CAD2 (0.45). The changes in binding energy arising from the mutation on the binding of the 2'-phosphate site of the coenzyme were assessed. A marked degree of physical interaction was detected between the enzymatic binding sites of the coniferyl alcohol substrate and the 2'-phosphate binding region, which are quite distant in the three-dimensional structure. The inhibition by 2',5'-ADP and 5'-AMP was found to be weak for both WT and S212D CAD2. Strong substrate inhibition was detected for CAD2, and its implications for plant physiological studies were assessed.(ABSTRACT TRUNCATED AT 250 WORDS)

The nucleophilic additions of hindered organometallic compounds to polycyclic ketones with trans ring junctions involve predominant axial attack when flattening of the ring containing the carbonyl group occurs. The influence of nucleophile structure (O-Por C-metallated character) on equatorial or axial attack is discussed.

Organomercuric compounds of the general formula and [RCOCH(R′)] 2 Hg, obtained from three ketones, 2,2-dimethyl 3-pentanone, 1-mesityl 1-propanone and 1-mesityl 1-ethanone, have been studied by 13 C and 199 Hg NMR techniques. Coupling constants J (CHg) and J (HgH) are consistent with C-metalated species; in each case the values of δ(C(2)) and J (C(2)H) observed are higher than expected for purely sp 3 carbon. The contribution of O-metalated species and hyperconjugative effects are discussed. For two dioxomercuric compounds (R′  Me, R  t-Bu, mesityl) the existence of diastereoisomers is suggested from 199 Hg NMR data.

Interactions between boric acid and Shikimic acid and quinic acid or (and) its methyl esters, have been studied by means of 11B and 13C NMR, in aqueous solution, and in presence of potassium hydroxyde. Monocyclic and spiranic borates have been isolated allowing a better understanding of the equilibria which take place.

The behavior of metallated imines and hydrazones toward α,β-unsaturated ketones was studied, using different reaction times and temperatures. Dissociation of the functional group (imine or hydrazone) in the adducts and regioselectivity in their condensation reactions are discussed. The first example of reversible addition to the carbonyl group of an enone is demonstrated for the reaction between trans chalcone and

The ZnBr2 complexes of the four title sulfinamoylesters were formed and investigated by NMR and i.r. techniques. The stoichiometry of the complexes greatly depends on the position of the amino or hydroxyl substituents on the aromatic ring. Nevertheless, the occurrence of a tetracoordinated zinc atom is suggested for all the complexes.

The zinc(II) complexes of the title sulfinamoyl compounds L 2 ·ZnX 2 (X = Cl, Br) were prepared and studied by NMR and i.r. methods. All the complexes have a tetrahedral [O 2 X 2 ] coordination and NH . . X hydrogen bonding.

Tert -butyl N-aryl sulfinamoyl acetates are hydrolysed in aqueous basic media following a bimolecular elimination process, via an intermediate sulfine species. The use of sulfinamoyl compounds as irreversible inactivators for zinc-metallo-enzymes is emphasized.

Association capabilities of oxobromomercuric and dioxomercuric compounds I and II have been investigated by cryoscopic methods, 1 H NMR, IR and Raman spectroscopy. The association degree n is concentration dependent for I in C 6 H 6 while no variation of n is observed in the case of II for which the value of n is close to one. Similarly 1 H NMR data show diminuation of 2 J (HgH) and 3 J (HgH) upon solution of I in C 6 D 6 or CDCl 3 while no modification of 2 J and 3 J is noticed for II. Using C 6 D 6 as solvent, important shielding of δ(CH) and δ(CH 3 ) is found in the spectra; these effects are smaller for δ(CH 3 ) than for δ(CH) and less clear for II than for I. IR and Raman spectra of I and II in the solid state show associative intermolecular interactions Hg…Br (in I), Hg…O intramolecular interactions and a linear structure of CHgC in II. The splitting of v (CO) frequencies for solutions of I and II in C 6 D 6 is attributed to Fermi resonances. These results, in connection with the variation of n in I, are consistent with an equilibrium between monomeric and associated HgBr species for the oxobromomercuric compound I and with an intramolecularly associated monomer for the dioxomercuric compound II.

Die Chalkone (I) reagieren mit einem Uberschus an Chlorrnagnesiumenolaten der Ketone (II) bzw. (IV) zu den Diketonen (III) bzw. (V).