Robert Faure

Interspecific variation in terpenoid composition of defensive secretions of European Reticulitermes termites

Sixteen terpene compounds were isolated from the soldier defensive secretions of seven European termite taxa of the genus Reticulitermes (Isoptera, Rhinotermitidae). We describe species-specific mixtures of monoterpenes (α-pinene, β-pinene, limonene), sesquiterpenes (germacrene C, germacrene A, germacrene B, β-selinene, δ-selinene, γ-selinene, (E)-β-farnesene, γ-cadinene, nerolidol), diterpenes (geranyl linalool, geranyl geraniol, geranyl geranial), and one sesterterpene (geranyl farnesol). Compounds were purified by HPLC and their structures determined by means of MS spectrometry, or 1D and 2D NMR spectroscopy. Comparison of two different analytical approaches, GC-MS and HPLC with subsequent NMR spectroscopy, revealed Cope rearrangement of germacrene A, germacrene B, and germacrene C to the respective β-elemene, γ-elemene, and δ-elemene under GC conditions, thus demonstrating the limits for this analytical approach. The species-specific compound composition provides insight into taxonomy and species origin of European Reticulitermes. The biological significance of the species-specific composition of Reticulitermes defensive secretions is briefly discussed.

Structure of bis-, tris- and tetrakispyrazolylborates in the solid state (sodium and potassium salts of tetrakispyrazolylborate by X-ray crystallography) and in solution (1H, 11B, 13C and 15N NMR)

Abstract The knowledge of the properties of pyrazolylborates has been considerably improved both in the solid state and in solution. The hydrates of the sodium and the potassium salts of tetrakis(l-pyrazolyl)borate crystallize in the space group C2/c, both salts being isomorphous. Regular pyrazole rings conform with a pseudosymmetry plane around a distorted tetrahedral boron atom. Chains along the b axis of two different octahedra of coordination, sharing water oxygens, are linked by H bonds. In solution, a careful 1H, 13C, 11B and 15N NMR study was carried out. The applicability of the rules used to assign H(3) versus H(5) and C(3) vcrsus C(5) in the case of pyrazolylborates was reevaluated. Only for tetrakis(1- pyrazolyl)borate were couplings observed with 1B in 1H, 3C and 5N resonances. The regularity of the properties of bis-, tris- and tetrakispyrazolylborates, allows the calculation of the spectral parameters of the still unknown tris-hydrido(1-pyrazolyl)borate, pzBH3−. Finally, the electronic properties, as measured by σp, of the substituents BH3−, pzBH2−, pz2BH− and pz3B− were estimated.

Complete energy profile of a chiral propeller compound: Tris-(2′-methylbenzimidazol-1′-yl) Methane (TMBM). Chromatographic resolution on triacetyl cellulose, x-ray structures of the racemic and one enantiomer, and dynamic NMR study

Abstract Tris-(2′-methylbenzimidazol-1 ′-y) methane (TMBM) presents an interesting example of propeller-like chirality, which is discussed according to Mislows and Dunitzs descriptions. Fortunately, the two most stable isomers (the three methyl groups “up”, i . e . on the same side of the methine proton, and two methyl groups “up” and the third one “down”) were present in the solid state, thus allowing the determination of their molecular structure by x-ray crystallography. The activation barrier which separates both isomers (9.8 kcal.mol −1 ) was determined by dynamic 1 H n.m.r., whereas that corresponding to enantiomers (28.5 kcal. mol −1 ) was determined kinetically by racemization, after pure enantiomers were resolved by chromatography on microcrystalline triacetyl cellulose. Both the racemic TMBM and its enantiomers crystallize with a larger number of water molecules, six and seven respectively, forming cyclic structures.

Sulphonyl radical addition to non-conjugated dienes regio- and stereoselective cyclizations

Abstract Addition of TsBr to diallyl malonates and allyl methallyl malonates is described. These cyclization reactions exhibit high stereoselectivity and very high regioselectivity. The structure of the reaction products is elucidated using 2D NMR.

Eudesmane sesquiterpenes from laggera alata

Two new eudesmane-type sesquiterpenoids (7-epi-γ-eudesmol and 7-epi-β-eudesmol) were isolated and characterized along with five other sesquiterpene compounds (β-selinene, 7-epi-α-eudesmol, isointermedeol, juniper camphor and β-dihydroagarofuran) from the essential oil of Laggera alata var. alata grown in Madagascar. The assigned structures were based on their spectral data.

Michael Addition Initiated Carbocyclization Sequences with Nitroolefins for the Stereoselective Synthesis of Functionalized Heterocyclic and Carbocyclic Systems

The synthesis of various heterocycles and carbocycles (tetrahydrofurans, pyrrolidines, cyclopentanes) has been achieved by using new and efficient ionic addition/cyclization sequences. Nitroolefins play an important role in the Michael addition induced ring-closing reactions (MIRC) reported in the present article, with various substituted alcohols, amines, Grignard reactants, or malonate derivatives acting as the nucleophile partner. The optimized cascade reactions were high yielding in most cases and highly stereoselective, creating up to three stereogenic centers starting from achiral substrates.

13C NMR study of annular tautomerism of azoles in the solid state

Etude par spectrometrie RMN de 13 C de la tautomerie prototropique des triazole, tetrazole, indazole, benzimidazole et benzotriazole, de la tautomerie de fonction de la benzoxazolidinethione-2, et du tautomerisme non prototropique du trimethylsilyl-1 benzimidazole

Diastereoselective Access to 3-Nitro-4-vinylidenetetrahydrofurans and 3-Nitro-4-vinylidenetetrahydropyrans and Their Conversion into 3,6-Dihydro-1,2-oxazines by Reverse Cope Elimination of Hydroxylamine Precursors

A new approach to the synthesis of unsaturated nitro-allenyl-tetrahydrofurans 3 and -tetrahydropyrans 5 has been developed, involving oxa-Michael addition/SN2′ substitution of propargyl and homopropargyl alcohol derivatives 2a and 4h on nitroalkenes 1a−g. Complete allylic 1,3-strain control during the cyclization accounts for the observed diastereoselectivity. Reduction of nitro compounds 3 and 5 with SmI2 provided new α−allenylhydroxylamines 7 and 8, which were easily isomerized into 3,6-dihydro-1,2-oxazines 9 and 10 by reverse Cope elimination.

Trikentramine, an unusual pyrrole derivative from the sponge trikentrion loeve carter

Abstract Trikentramine, an unusual pyrrole, has been isolated from the Senegalese sponge Trikentrion loeve and characterized by spectroscopic and X-ray diffraction techniques.

Spectrometric identifications of sesquiterpene alcohols from niaouli (Melaleuca quinquenervia) essential oil

Oxidation and reduction reactions on alloaromadendrene and aromadendrene sesquiterpene hydrocarbons have been investigated in order to produce alcohols with an aromadendrene skeleton for checking the chemical structure and therefore the identity of one main alcohol present in niaouli (Melaleuca quinquenervia) essential oil. Oxidation using m-chloroperbenzoic acid was carried out to produce two diastereoisomer epoxides and two corresponding aldehyde isomers for each sesquiterpene. Epoxide reductions yielded two alcohols ledol and viridiflorol, from alloaromadendrene and globulol and epiglobulol from aromadendrene. The structure determination of all compounds, i.e. epoxides, aldehydes, and alcohols, was achieved using spectrometric methods: 2D-NMR and mass spectroscopy. The stereochemistry of known sesquiterpenic alcohols, viridiflorol and ledol, has been unambiguously established.