The Parent Hexacarbaborane arachno-C6B6H12 and a Methylated Pentacarbaborane arachno-CH3C5B7H12: Domains of Incipient Hydrocarbon Behavior within Borane Clusters

Increasingly pronounced hydrocarbon character is exhibited by C₆H₆B₁₂, the first unsubstituted hexacarbaborane, and CH₃C₅B₇H₁₂, the first cluster pentacarbaborane. These compounds shed light on the structural dichotomy between open hydrocarbon skeletons and polyhedral borane frameworks for high-carbon carboranes.     

Selectivity of 1-O-Propargyl-d-Mannose Preparations

Thanks to their ability to bind to specific biological receptors, mannosylated structures are examined in biomedical applications. One of the most common ways of linking a functional moiety to a structure is to use an azide-alkyne click reaction. Therefore, it is necessary to prepare and isolate a propargylated mannose derivative of high purity to maintain its bioactivity. Three known preparations of propargyl-α-mannopyranoside were revisited, and products were analysed by NMR spectroscopy. The preparations were shown to yield by-products that have not been described in the literature yet. Our experiments showed that one-step procedures could not provide pure propargyl-α-mannopyranoside, while a three-step procedure yielded the desired compound of high purity.     

Estimation of partition coefficients by MEKC part 2: anthocyanins

The octanol-water partition coefficients of seven anthocyanins (in neutral form, pH = 7.0) were measured by means of MEKC. A new iterative method for the estimation of migration time of electroosmotic flow (EOF) and micelles in MEKC is presented. This calculation is based on Gauss-Newton linearization of the dependence between migration indices and migration times of a set of suitable standards and the application of an advanced statistical evaluation procedure. The values of partition coefficients obtained with the aid of an iterative process are compared with values obtained on use of EOF and micelle markers.     

Synthesis and rearrangements of aminosubstituted ferra- and ruthenatricarbaboranes

A room-temperature reaction between the [7-tBuNH-nido-7,8,9-C3B8H10]- anion (1a) and [Cp*RuCl]4 leads to the ruthenatricarbollide [1-Cp*-12-tBuNH-1,2,4,12-RuC3B8H10] (2) (yield 85%). Analogously, the room-temperature photochemical reaction of 1a with [CpFe(C6H6)]PF6 gives the previously reported iron complex [1-Cp-12-tBuNH-1,2,4,12-FeC3B8H10] (3) (yield 82%). Both reactions are associated with extensive polyhedral rearrangement, which occurs under very mild conditions and brings the carbon atoms to positions of maximum separation within the framework. Compounds 2 and 3 were also surprisingly obtained via complexation of the isomeric [8-tBuNH-nido-7,8,9-C3B8H10]- (1b) anion. Complex 2 rearranges further to [1-Cp*-10-tBuNH-1,2,4,10-RuC3B8H10] (4) upon refluxing in xylene (145 degrees C). Density functional theory calculations at the B3LYP/SDD level were used to estimate relative stabilities of these metallacarborane isomers. Compounds 2 and 4, along with the 11-vertex closo compounds [1-Cp*-1,2,3,10-RuC3B7H10] (5) and [1-Cp*-10-tBuNH-1,2,3,10-RuC3B7H9] (6), were also isolated from the reaction between [Cp*RuCl2]2 and 1a in boiling xylene. The structure of 2 was established by an X-ray diffraction study, and the constitution of all compounds was determined unambiguously by multinuclear NMR spectroscopy, mass spectrometry, and elemental analyses.     

Chirality-Controlled Self-Assembly of Amphiphilic Dibenzo[6]helicenes into Langmuir–Blodgett Thin Films

Racemic and highly enantioenriched 3-methoxycarbonyl, 3-carboxy, and 3-hydroxymethyl derivatives of dibenzo[6]helicene were prepared. The Langmuir layers of these helicenes were formed at the air–water interface and transferred onto solid substrates to afford Langmuir–Blodgett films, which were then studied by ambient atomic force microscopy and (chir)optical spectroscopy. Significant differences were found in the behaviour of the Langmuir layers as well as in the morphology, UV/Vis, electronic circular dichroism (ECD), and fluorescence spectra of the Langmuir–Blodgett thin films depending on the molecular chirality and nature of the polar group. The experimental results were supported by molecular dynamics simulations.     

Guanine Substitutions Prevent Conformational Switch from Antiparallel to Parallel G-Quadruplex

Guanine quadruplexes, recently reported to form in vivo, represent a broad spectrum of non-canonical conformations of nucleic acids. The actual conformation might differ between water solutions and crowding or dehydrating solutions that better reflect the conditions in the cell. Here we show, using spectroscopic techniques, that most guanine substitutions prevent the conformational switch from antiparallel or hybrid forms to parallel ones when induced by dehydrating agents. The inhibitory effect does not depend on the position of the substitution, but, interestingly, on the type of substitution and, to some extent, on its destabilising potential. A parallel form might be induced in some cases by ligands such as N-methyl mesoporphyrin IX and even this ligand-induced switch is inhibited by guanine substitution. The ability or inability to have a conformation switch, based on actual conditions, might significantly influence potential conformation-dependent quadruplex interactions.     

Enantioselective Catalytic Crotylboration Based Syntheses of the C(7)–C(18(20)) Fragments of Polyketides Isolated from Streptomyces gramineus

A general modular enantioselective synthetic approach to the C(7)–C(18) and the C(7)–C(20) fragment belonging to E-492, actinofuranone A, and JBIR-108 was developed. The crucial synthetic step relies on highly enantioselective crotylboration of aldehydes catalyzed by a chiral TRIP PA giving rise to highly enantioenriched terminal alkenes (86 and 88 % ee on the preparative scale). The alkenes were subsequently converted into the title products. Further important synthetic steps included Ru-catalyzed alkene cross-metathesis and Suzuki coupling reactions. The approach consists of five synthetic steps starting from easily available aldehydes and other reaction partners.     

Influence of various spices on acrylamide content in buckwheat ginger cakes

The aim of this work was to study the effect of various spices (cloves, cinnamon, allspice, white pepper, anise, star anise, coriander, fennel, nutmeg, cardamom, vanilla, and ginger) on acrylamide formation in buckwheat ginger cakes. The spices were characterised by their free radical scavenging activity and applied to formulation of the buckwheat ginger cakes in the same portions. After baking, the acrylamide content was determined by LC/ESI-MS-MS. The results showed a reduction in acrylamide content of up to 23 % in the buckwheat ginger cakes with the addition of nutmeg, fennel, anise, or cloves. A decrease in acrylamide content from 5 % to 11 % was found in the buckwheat ginger cakes with vanilla, cardamom, white pepper, or ginger. By contrast, the acrylamide content in the buckwheat ginger cakes with cinnamon or coriander increased by up to 29 %. No change in the acrylamide content was observed in the buckwheat ginger cakes with star anise or allspice. Only a slight correlation between the di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium (DPPH^·) free radical scavenging activity of the added spices and the final acrylamide content in the buckwheat ginger cakes (0.68) was observed. The final acrylamide content was probably influenced not only by the free radical scavenging activity of the spices added, but also by their chemical composition and the reactiveness of particular constituents with synergistic/antagonistic effect in the matrix studied.