Asymmetric allylboration of alpha,beta-enals as a surrogate for the enantioselective synthesis of allylic amines and alpha-amino acids

[reaction: see text] Optically pure allylic amines have been synthesized from alpha,beta-unsaturated aldehydes via allylboration with (-)-B-allyldiisopinocampheylborane, followed by Overman rearrangement. By incorporating crotyl and alkoxyallylboration, functionalization at delta-position was readily accomplished. By applying this methodology, the synthesis of several chiral alpha-amino acids has been achieved.     

Regio- and stereoselective transfer of p-toluenesulfonamido group from sulfur to carbon: preparation of aminoalcohol derivatives from allylalcohols

A novel methodology for the regio- and stereoselective synthesis of amino alcohol derivatives from allylalcohols/ethers via intramolecular nucleophilic participation by the sulfilimine moiety is disclosed. The sulfilimine moiety is stereospecifically transformed to a sulfinyl moiety with an inverted configuration. The reaction is general and affords highly functionalised products.     

Negative ion electrospray ionization mass spectral study of dicarboxylic acids in the presence of halide ions

The negative ion electrospray ionization (ESI) mass spectra of a series of dicarboxylic acids, a pair of isomeric (cis/trans) dicarboxylic acids and two pairs of isomeric (positional) substituted benzoic acids, including a pair of hydroxybenzoic acids, were recorded in the presence of halide ions (F(-), Cl(-), Br(-) and I(-)). The ESI mass spectra contained [M--H](-) and [M+X](-) ions, and formation of these ions is found to be characteristic of both the analyte and the halide ion used. The analytes showed a greater tendency to form adduct ions with Cl(-) under ESI conditions compared with the other halide ions used. The isomeric compounds yielded distinct spectra by which the isomers could be easily distinguished. The collision-induced dissociation mass spectra of [M+X](-) ions reflected the gas-phase basicities of both the halide ion and [M--H](-) ion of the analyte. However, the relative ordering of gas-phase basicities of all analyte [M--H](-) and halide ions could not account for the dominance of chloride ion adducts in ESI mass spectra of the analytes mixed with equimolar quantities of the four halides.     

Stereoselective synthesis of (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone

A stereoselective synthesis of the pentaketide lactone (3R,4S,5S,9S)-3,5,9-trihydroxy-4-methylundecanoic acid δ-lactone has been achieved.     

9,9‐Dimethoxy‐7,11‐diphenyl‐2,4‐diazaspiro[5.5]undecane‐1,3,5‐trione monohydrate

Due to steric repulsions, the cyclo­hexane ring in the title compound, C₂₃H₂₄N₂O₅·H₂O, shows some bond‐length abnormalities and adopts a chair conformation. The pyrimidine and cyclo­hexane rings are approximately perpendicular to each other, and the phenyl rings are equatorial. C—H?π and N—H?O intermolecular interactions, as well as C—H?O inter‐ and intramolecular interactions, occur between the mol­ecules. In addition to van der Waals interactions, the water mol­ecule interacts with the pyrimidine­trione ring to stabilize the structure.     

A model for surfactant distribution in latex coatings

The presence of surfactants in dried latex films can adversely affect the adhesive, water-resistant, and gloss properties, so investigating the surfactant distribution in latex coatings is of prime industrial relevance. Here we present a model that predicts the distribution of surfactant in a latex coating during the solvent evaporation stage. The conservation equation for surfactant during solvent evaporation is solved in the limit of infinite particle Peclet numbers, a dimensionless quantity giving the measure of relative magnitudes of evaporative to diffusive fluxes. A parametric analysis using the model reveals that the surfactant adsorption isotherm is the determining physical parameter. The model always predicts surfactant excesses at the top surface and either excess or depletion at the bottom surface depending on the isotherm. Uniform distributions are predicted for low surfactant Peclet numbers. Attenuated total reflection Fourier transform infrared spectroscopic probes on film surfaces conform to the behavior predicted by the model.     

LiBF4-Catalyzed three-component coupling of an aldehyde, acetic anhydride and allyltrimethylsilane/TMSCN

Lithium tetrafluoroborate is found to be an efficient catalyst for allylation and cyanation of aldehydes with allyltrimethylsilane and trimethylsilyl cyanide in the presence of acetic anhydride at room temperature to produce homoallylic acetates and α-cyano acetates in excellent yields. A solution of 10 mol % of LiBF₄ in acetonitrile provides a convenient reaction medium to carry out allylation and cyanation reactions under very mild and neutral conditions.     

Solid-phase synthesis of positively charged deoxynucleic guanidine (DNG) tethering a Hoechst 33258 analogue: triplex and duplex stabilization by simultaneous minor groove binding

Deoxynucleic guanidine (DNG), a DNA analogue in which positively charged guanidine replaces the phosphodiester linkages, tethering to Hoechst 33258 fluorophore by varying lengths has been synthesized. A pentameric thymidine DNG was synthesized on solid phase in the 3' --> 5' direction that allowed stepwise incorporation of straight chain amino acid linkers and a bis-benzimidazole (Hoechst 33258) ligand at the 5'-terminus using PyBOP/HOBt chemistry. The stability of (DNA)(2).DNG-H triplexes and DNA.DNG-H duplexes formed by DNG and DNG-Hoechst 33258 (DNG-H) conjugates with 30-mer double-strand (ds) DNA, d(CGCCGCGCGCGCGAAAAACCCGGCGCGCGC)/d(GCGGCGCGCGCGCTTTTTGGGCCGCGCGCG), and single-strand (ss) DNA, 5'-CGCCGCGCGCGCGAAAAACCCGGCGCGCGC-3', respectively, has been evaluated by thermal melting and fluorescence emission experiments. The presence of tethered Hoechst ligand in the 5'-terminus of the DNG enhances the (DNA)(2).DNG-H triplex stability by a DeltaT(m) of 13 degrees C. The fluorescence emission studies of (DNA)(2).DNG-H triplex complexes show that the DNG moiety of the conjugates bind in the major groove while the Hoechst ligand resides in the A:T rich minor groove of dsDNA. A single G:C base pair mismatch in the target site decreases the (DNA)(2).DNG triplex stability by 11 degrees C, whereas (DNA)(2).DNG-H triplex stability was decreased by 23 degrees C. Inversion of A:T base pair into T:A base pair in the center of the binding site, which provides a mismatch selectively for DNG moiety, decreases the triplex stability by only 5-6 degrees C. Upon hybridization of DNG-Hoechst conjugates with the 30-mer ssDNA, the DNA.DNG-H duplex exhibited significant increase in the fluorescence emission due to the binding of the tethered Hoechst ligand in the generated DNA.DNG minor groove, and the duplex stability was enhanced by DeltaT(m) of 7 degrees C. The stability of (DNA)(2).DNG triplexes and DNA.DNG duplexes is independent of pH, whereas the stability of (DNA)(2).DNG-H triplexes decreases with increase in pH.     

A new sphingolipid from the gorgonian Junceella juncea of the Indian Ocean

A new sphingolipid, (2S,3R,4E)-1,3-dihydroxy-2-[(nonadecanoyl) amino]-octadec-4-ene (1) along with ubiquitous batyl alcohol is isolated from the gorgonian, Junceella juncea Pallas (Gorgonaceae) of the Indian Ocean. The structure of 1 is determined on the basis of 1H- and 13C-NMR, COSY, FABMS, and GC-EIMS experiments.     

Intramolecular nucleophilic activation promoting efficient hydrolytic cleavage of DNA by (aqua)bis(dipyridoquinoxaline)copper(II) complex

The axial aqua bound copper(II) complex [Cu(dpq)2(H2O)](ClO4)2, having a planar NN-donor heterocyclic base dipyridoquinoxaline (dpq) as the DNA minor groove binder, shows efficient hydrolytic cleavage of supercoiled DNA in the dark and in the absence of any external reagents, as evidenced from T4 ligase experiments, with a rate of 5.58 +/- 0.4 h(-1) and a rate enhancement of 1.55 x 10(8).