Enantiospecific synthesis of the ABC and ABD ring systems of the marine diterpenes aberraranes

Enantiospecific synthesis of the ABC and ABD ring systems present in the marine diterpenes aberraranes, starting from the readily available (S)-campholenaldehyde, has been accomplished.     

Regioselective intramolecular N1-C3 cyclizations on pyrrole-proline to ABC tricycles of dibromophakellin and ugibohlin

Pyrrole N1-C and C3-C regioselective linkage to the fused tricycle ABC system present in the marine metabolites ugibohlin and dibromoisophakellin is described. The cyclization is closely dependent on the electrophilic function, bromination degree of the pyrrole moiety and pH conditions. The mechanism of the functionalization of the ABC olefin by oxidative agents was found to occur through an N-acyliminium intermediate as showed by the natural chemical connection between ugibohlin and dibromoisophakellin.     

Predicting the R/S absolute configuration in asymmetric bifunctional catalysis (ABC)

A predictive model for assigning the R/S absolute configuration in chiral Lewis base-dependent asymmetric bifunctional catalysis (ABC) has been developed. Chiral Lewis base (LB^∗)-dependent ABC abolishes the chiral Lewis acid (LA^∗) component as the stereochemical determining factor in asymmetric catalysis. By correlating the constant LB^∗ chirality to the facial preference for the LA^∗-bound carbonyl group for nucleophile delivery, the R/S absolute configuration of the products can be predicted a priori.     

One pot conversion of azido arenes to N-arylacetamides and N-arylformamides: synthesis of 1,4-benzodiazepine-2,5-diones and fused [2,1-b]quinazolinones

Sodium iodide in acidic media has been employed for the synthesis of N-arylformamides and N-arylacetamides. The NaI/acetic acid reagent system has also been extended for the synthesis of 1,4-benzodiazepine-2,5-diones, pyrrolo[2,1-c][1,4]benzodiazepine-5,11-diones, and fused [2,1-b]quinazolinones.     

An expedient stereoselective synthesis of (Z)- and (E)-allyl iodides from Baylis-Hillman adducts along with selective iodination of benzylic alcohols using the polymethylhydrosiloxane-iodine system

A stereoselective method has been developed for the synthesis of (Z)- and (E)-allyl iodides from Baylis-Hillman adducts using polymethylhydrosiloxane (PMHS) and iodine in chloroform at room temperature. In addition, the reagent system has been utilized for the iodination of benzylic alcohols selectively.     

First observation of intra-5f fluorescence from an actinyl center: Np(VI) near-IR emission in Cs2U(Np)O2Cl4

Fluorescence from an excited 5f state of Np(VI) has been observed in the doped impurity system Cs₂U(Np)O₂Cl₄. This is the first intra-5f fluorescence transition that has been detected at room temperature in a condensed-phase system with an actinyl (An(VI)O₂²⁺) core, and it is a rare example of fluorescence of any kind from non-uranyl ions of this type. The emission originates from an excited state approximately 6890 cm⁻¹ above the ground state. Its emission spectrum and fluorescence lifetime at 295 K will be discussed. Vibronic structure in the emission spectrum is assigned based on comparison with the detailed analysis of the absorption spectra published by Denning et al.     

Synthesis of the ABC and IJ ring fragments of yessotoxin

Synthesis of a 6/6/6 tricyclic ether system (3) corresponding to the ABC ring fragment of yessotoxin (1) has been achieved via coupling of a triflate and a 2-lithiofuran followed by intramolecular hetero-Michael addition. The IJ ring fragment (4) of 1 was readily synthesized via successive Sharpless epoxidation and 6-endo cyclization of the resulting vinyl epoxide.     

Molecular phylogenetic study and expression analysis of ATP-binding cassette transporter gene family in Oryza sativa in response to salt stress

ATP-binding cassette (ABC) transporter is a large gene superfamily that utilizes the energy released from ATP hydrolysis for transporting myriad of substrates across the biological membranes. Although many investigations have been done on the structural and functional analysis of the ABC transporters in Oryza sativa, much less is known about molecular phylogenetic and global expression pattern of the complete ABC family in rice. In this study, we have carried out a comprehensive phylogenetic analysis constructing neighbor-joining and maximum-likelihood trees based on various statistical methods of different ABC protein subfamily of five plant lineages including Chlamydomonas reinhardtii (green algae), Physcomitrella patens (moss), Selaginella moellendorffii (lycophyte), Arabidopsis thaliana (dicot) and O. sativa (monocot) to explore the origin and evolutionary patterns of these ABC genes. We have identified several conserved motifs in nucleotide binding domain (NBD) of ABC proteins among all plant lineages during evolution. Amongst the different ABC protein subfamilies, ‘ABCE’ has not yet been identified in lower plant genomes (algae, moss and lycophytes). The result indicated that gene duplication and diversification process acted upon these genes as a major operative force creating new groups and subgroups and functional divergence during evolution. We have demonstrated that rice ABCI subfamily consists of only half size transporters that represented highly dynamic members showing maximum sequence variations among the other rice ABC subfamilies. The evolutionary and the expression analysis contribute to a deep insight into the evolution and diversity of rice ABC proteins and their roles in response to salt stress that facilitate our further understanding on rice ABC transporters.     

An intramolecular para-phenolic allylation free radical cyclization strategy for the synthesis of alkaloids and terpenes with spiro[4.5]decane architectures

A Tsuji-Trost variant of the Winstein-Masamune reaction has been investigated for the synthesis of the AC spirocyclic ring system 9 bearing a quaternary carbon found in the fawcettimine type Lycopodium alkaloids magellanine 1 and lycojaponicumin B 2 and cyclopiane diterpenes such as conidiogenone 3. Annulation of the B ring for the synthesis of tricyclic ABC cores was demonstrated utilizing a 5-exo-trig free radical cyclization of a primary carbon radical onto a cyclohexadienone generated with tri-n-butylgermanium hydride (9 → 11).     

A palladium complex with a new hemilabile amino- and sulfur-containing phosphinite ligand as an efficient catalyst for the Heck reaction of aryl bromides with styrene. The effect of the amino group

A palladium complex with a new hemilabile amino- and sulfur-containing phosphinite ligand has been synthesised and its crystal structure determined. This system efficiently catalyses the Heck reaction of aryl bromides with styrene at 130°C after 24 h, with turnover numbers of up to 100000 and with a selectivity towards trans-stilbenes ranging from 91.5 to 96.3%. The analogous sulfur-containing phosphinite without the amino group has also been synthesised and subjected to the Heck reaction. The constructive role of the amino group on the formation of the P,S-chelate palladium complex as well as in the Heck reaction is discussed.     

Leucolusine, a tetracyclic alkaloid with a novel ring system incorporating an oxindole moiety and fused piperidine-tetrahydrofuran rings

A tetracyclic ring-opened oxindole alkaloid, possessing an unprecedented ring system incorporating fused piperidine-tetrahydrofuran rings, has been isolated from the Malayan species, Leuconotis griffithii. The structure was established by analysis of the spectroscopic data and a possible biogenetic pathway from an Aspidosperma precursor is presented.     

Daphniglaucin C, a novel tetracyclic alkaloid from Daphniphyllum glaucescens

A novel Daphniphyllum alkaloid with an unprecedented tetracyclic ring system consisting of an octahydroindole and a hexahydroazulene rings, daphniglaucin C (1), has been isolated from the leaves of Daphniphyllum glaucescens and the structure and relative stereochemistry were elucidated on the basis of spectroscopic data. Daphniglaucin C (1) inhibited the polymerization of tubulin.     

Direct,simple derivatization of disulfide bonds in proteins with organic mercury in alkaline medium without any chemical pre-reducing agents

In this work we have studied the derivatization of protein disulfide bonds with p-Hydroxymercurybenzoate (pHMB) in strong alkaline medium without any preliminary reduction. The reaction has been followed by the determination of the protein–pHMB complex using size exclusion chromatography coupled to a microwave/UV mercury oxidation system for the on-line oxidation of free and protein-complexed pHMB and atomic fluorescence spectrometry (SEC–CVG–AFS) detection. The reaction has been optimized by an experimental design using lysozyme as a model protein and applied to several thiolic proteins.     

Structural characterization of the Ta-rich part of the Ta-Al system

The Ta-rich part of the Ta-Al system has been investigated. On the one hand, the accommodation of the non-stoichiometry in the σ phase has been studied by Rietveld refinement of X-ray powder data obtained from different samples on both sides of the ideal composition (Ta₂Al, P4₂/mnm, tP30). On the other hand, the structure of the β phase has been determined ab initio from powder synchrotron data (analyzed composition Ta_50.7Al_49.3, refined composition Ta_52.6(5)Al_47.4(5) (Ta_45.2(4)Al_40.8(4)), stoichiometric composition Ta₄₈Al₃₈, mP86, P2₁/c, a=9.8707(1) Å, b=9.8766(1) Å, c=16.3539(2), β=116.478(1), R_B=2.6%). This phase is shown to be closely related to the group of the topologically close packed phases. In addition, phase relations have been accurately determined in the Ta-rich end of the system.     

Syntheses of indolo[3,2,1-d,e]phenanthridines and isochromeno[3,4-a] carbazoles: palladium catalyzed intramolecular arylation via C-H functionalization

A new synthetic route has been developed for the preparation of indolo[3,2,1-d,e]phenanthridines and isochromeno[3,4-a]carbazoles via palladium catalyzed intramolecular biaryl coupling reactions. The coupling reactions proceeded smoothly and in high yields under ligand-free conditions with the catalytic system Pd(OAc)₂/Cs₂CO₃/TBAB. Under optimized reaction conditions no halogen-reduced products were observed.     

Convenient method for the synthesis of C-phosphorylated N-arylformamidines

C-Phosphorylated (P^V) arylformamidines have been prepared by the reaction of N-arylamidotrichloromethyl derivatives of phosphorus, thiophosphorus, and selenophosphorus acids with secondary amines. Dependence of the reaction on the nature of chalcogene, electronic and steric factors has been studied. By reduction of N-arylformamidinophosphonoselenides the corresponding C-phosphorylated (P^III) arylformamidines have been synthesized.     

The O + O2 reaction: quantum detailed probabilities and thermal rate coefficients

The detailed quantum probabilities of the O + O₂ reactive system have been computed at zero total angular momentum using the time-independent quantum program ABC thanks to the restructuring of the code and its implementation on the EGEE production Grid. Their main features are discussed and out of them J-shifting thermal rate coefficients have been computed to compare with the experiment and quasiclassical trajectory results over a wide range of temperatures.     

Concavine, an unusual diterpenic alkaloid produced by the fungus Clitocybe concava

A novel alkaloid with an unprecedented ring system consisting of a dodecahydro-7-oxa-9a-aza-benzo[a]azulene ring (1), has been isolated from cultures of Clitocybe concava (Basidiomycetae). Its structure and relative stereochemistry were elucidated on the basis of spectroscopic data. Concavine presents a weak antibacterial activity.     

Diastereoselective synthesis of homo-N,O-nucleosides

A new class of homo-N,O-nucleosides has been designed, based on the 1,3-dipolar cycloaddition of C-substituted nitrones with allyl nucleobases. The N-methyl-C-ethoxycarbonyl nitrone 1, and the C-α-silyloxymethyl-N-methyl nitrone 7 have been exploited: the stereochemical features of the obtained nucleosides are dependent on the nature of the dipole. The results obtained with DFT calculations fully agree with the experimental results and successfully reproduce the experimentally observed reversal of endo/exo selectivity for nitrones 1 and 7.     

Ab initio ground and the first excited adiabatic and quasidiabatic potential energy surfaces of H + CO system

Ab initio global adiabatic as well as quasidiabatic potential energy surfaces for the ground and the first excited electronic states of the H⁺ + CO system have been computed as a function of the Jacobi coordinates (R, r, γ) using Dunning’s cc-pVTZ basis set at the internally contracted multi-reference (single and double) configuration interaction level of accuracy. In addition, nonadiabatic coupling matrix elements arising from radial motion, mixing angle and coupling potential have been computed using the ab initio procedure [Simah et al. (1999) [66]] for the purpose of dynamics study. The geometrical properties corresponding to the minimum energy of the bound HCO⁺ and HOC⁺ isomers have been obtained and compared with those predicted by previous theoretical and experimental results. The HCO⁺ has been found to be more stable than the HOC⁺. The minimum energy pathway in the ground electronic state for the isomerization process, HCO⁺ ? HOC⁺ has also been obtained as a function of γ.