O-[(Triorganostannyl)methyl] derivatives of 1,2-O-isopropylidene-α-D-xylofuranose

The synthesis, mass, IR and NMR spectra of 3-O-benzyl-1,2-O-isopropylidene-5-O-[(triphenylstannyl)methyl]--D-xylofuranose (9) and 1,2-O-isopropylidene-3-O-(R₃SnCH₂)-5-O-triphenylmethyl--D-xylofuranose (10, R=Bu or Ph) are reported, as is the X-ray structure of10 (R=Ph). Compound10 (R=Ph), crystallizes in the orthorhombic space groupP2₁2₁2₁ (Z=4), witha=11.006(4) Å,b=17.096(6) Å,c=21.164(7) Å. The conformation of the furanose ring in solid10 (R=Ph) is a 8218 mixture of the envelope (E₄) and twist (³T₄) forms: the isopropylidene ring conformation is similarly a mixture of envelope and twist forms, with the former dominant. On dissolution, the furanose ring of10 (R=Ph) undergoes a conformation change, with the³T₂ conformation becoming the major form. The tin center in10 is four-coordinate and has a tetrahedral geometry.     

Orientational disorder in 4‐chloronitrobenzene

The crystal structure of 4‐chloronitrobenzene, C₆H₄ClNO₂, a material that exhibits disorder in the solid state, is re‐examined using multiple‐temperature single‐crystal X‐ray diffraction. Our results show a marked improvement on previous crystal structure determinations and our comprehensive multiple temperature measurements help to rationalize the structural anomalies. 4‐Chloronitrobenzene exhibits twofold orientational disorder of the NO₂/Cl substituents, with the molecule lying across an inversion centre. There is also evidence of large thermal motion, which exists at all temperatures and reflects the presence of significant disorder in this material. The nitro group shows possible libration, with one O atom exhibiting larger thermal motion than the other across the whole temperature range. This is explained by a difference in hydrogen‐bonding environment.     

Biocatalytically oligomerized epicatechin with potent and specific anti-proliferative activity for human breast cancer cells

Catechins, naturally occurring flavonoids derived from wine and green tea, are known to exhibit multiple health benefits. Epigallocatechin gallate (EGCG) is one of the most widely investigated catechins, but its efficacy in cancer therapy is still inconsistent and limited. The poor stability of EGCG has contributed to the disparity in the reported anti-cancer activity and other beneficial properties. Here we report an innovative enzymatic strategy for the oligomerization of catechins (specifically epicatechin) that yields stable, water-soluble oligomerized epicatechins with enhanced and highly specific anti-proliferative activity for human breast cancer cells. This one-pot oxidative oligomerization is carried out in ambient conditions using Horseradish Peroxidase (HRP) as a catalyst yielding water-soluble oligo(epicatechins). The oligomerized epicatechins obtained exhibit excellent growth inhibitory effects against human breast cancer cells with greater specificity towards growth-inhibiting cancer cells as opposed to normal cells, achieving a high therapeutic differential. Our studies indicate that water-soluble oligomeric epicatechins surpass EGCG in stability, selectivity and efficacy at lower doses.     

Tripeptide self-assembled hydrogels: unexpected twists of chirality

Change of chirality of the first N-terminal amino acid of tripeptides VFF and FFV from l to d results in self-assembled hydrogels at physiological pH from non-assembling l-analogues. Interestingly, changing the chirality of F yields very different nanostructures; nanotapes are observed for (D)VFF, twisted fibers for (D)FFV.     

Nuclear magnetic resonance spectroscopy of rat ventricles following chronic hypoxia: A model of right ventricular hypertrophy

Nuclear magnetic resonance spectroscopy was used to study the effect of chronic hypoxia on both right (RV) and left ventricular and septal (LV + S) muscle. Rats in the hypoxic group, kept in a hypobaric chamber at $\text{1}\text{2}$ atm pressure for 2 weeks, developed right, but not left, ventricular hypertrophy (p < 0.001). Tissues were studied within 2.5 h of return to air. T₁ and T₂ relaxation times of RV, LV + S and thigh muscle (Th) from hypoxic and control rats were compared. The T₂ value distinguished hypoxic from control RV (p < 0.002), but not hypoxic from control LV + S or Th, indicating that the change in relaxation time reflects cellular hypertrophy, and not hypoxemia. For hypoxic rats only the T₂ value distinguished each muscle type: RV from LV + S (p < 0.009), RV from Th (p < 0.001) and LV + S from Th (p < 0001). The T₁ value did not identify either the hypoxic or control group or the type of muscle. Percent water content was similar for all tissues. For hypoxic RV, T₂ correlated with the percent water content (r = 0.89; p < 0.01). The sensitivity of T₂ to the cellular changes associated with hypoxic RV hypertrophy could provide a means of detecting right ventricular hypertrophy.     

Male pheromone protein components activate female vomeronasal neurons in the salamander Plethodon shermani

Background  

The mental gland pheromone of male Plethodon salamanders contains two main protein components: a 22 kDa protein named Plethodon Receptivity Factor (PRF) and a 7 kDa protein named Plethodon Modulating Factor (PMF), respectively. Each protein component individually has opposing effects on female courtship behavior, with PRF shortening and PMF lengthening courtship. In this study, we test the hypothesis that PRF or PMF individually activate vomeronasal neurons. The agmatine-uptake technique was used to visualize chemosensory neurons that were activated by each protein component individually.     

An unusual phenomenon observed when anodising CP titanium to produce coloured surfaces for jewellery and other decorative uses

The unpredictability of the evenness of colour developed on titanium surfaces for use in jewellery has led to a research project at Central Saint Martin's College of Art and Design (CSM) to investigate the detailed structure of the thin oxide films that produce the interference colours.In the course of some initial investigations an unusual phenomenon was observed when a specific material was anodised. Examination of the anodised surface by scanning electron microscopy (SEM) showed a profusion of flower-like ‘oxide growths’ developed in random orientations from about 30 V with increasing density up to 110 V.In honour of the late Professor Harvey Flower these features are currently referred to as ‘Flower oxides’ or ‘flowers’.Further work is continuing to clarify the nature of these growth features and their structure and composition.     

Chemical Alterations in Native Histone Octamer Complexes Induced by the Attak of · OH and · N3 Radicals

·OH Radicals generated by short electron-beam pulses were allowed to attack histone octamer complexes (extracted from calf-thymus chromatin) in N₂O-saturated dilute solution (0.5–1.3 g/l, [NaClO₄] = 1 – 2M , pH 9). They induced a volume contraction due to intra-complex cross-linking. In this process, essentially non-tyrosine moieties of the proteins were involved. Phenol coupling via tyrosyl radicals occurred mainly as an intramolecular reaction, i.e., it was restricted to single histone moelecules. Furthermore, it turned out that only about 55% of the tyrosine moieties were accessible to attacking ·OH and/or ·N₃ radicals. When ·N₃ radicals were generated via continuous irradiation of N₂O-saturated octamer solutions containing NaN₃ with ⁶⁰Co-γ-rays, dimers, trimers, and tetramers were detected by SDS gel electrophoresis, in contrast to pulse radiolysis where only dimers were found. These results were explained in terms of denaturation being induced by small chemical changes and causing partial or complete dissociation of the complexes thus permitting, in the course of the γ-irradiation, the attack and conversion of amino-acid moieties non-accessible in the native octamer complexes. Removal of steric restrictions for the combination of tyrosyl radicals may also play a role. By time-resolved absorption measurements, it was shown that, upon the attack of intact octamer complexes by ·OH radicals, tyrosyl radicals were formed which were converted to dityrosine groups according to two modes with half-lives of several 100 m?s and 1–2 ms, respectively. Cross-linking of histone molecules occurred with a definitely lower rate (1st half-life: 50 100 ms). This process was detectable both by optical absorption measurements at λ = 300 400 nm and by light-scattering measurements.     

Cyclo-β-peptides: Structure and tubular stacking of cyclic tetramers of 3-aminobutanoic acid as determined from powder diffraction data

The solid-state structures of three stereoisomer, 1–3 , of the cyclic tetramer of 3-aminobutanoic acid are presented. These cyclo-β-peptides were found to be highly insoluble materials, and it proved to be impossible to grow crystals of sufficient quality for X-ray single-crystal analysis. The samples of 1–3 were, however, suitable candidates for structure determination from powder diffraction data (Fig. 1), and the application of this method is described. All three isomers have been found to adopt tubular structures (Figs. 2–4) in a fashion similar to those already observed for certain cyclo-α-peptides. The stacks of 16-membered rings are held together by four nonlinear C?O…?H? N H-bonds between pairs of molecules (Fig.5).     

Lithium enolates from a (−)-quinic acid-derived cyclohexanone with a β-alkoxy leaving group: regioselective preparation and evaluation of enolate stability towards β-elimination

Deprotonation of a (−)-quinic acid-derived ketone {(2S,3S,4aR,8R,8aS)-8-[(tert-butyl(dimethyl)silyl)oxy]-2,3-dimethoxy-2,3-dimethylhexahydro-1,4-benzodioxin-6(5H)-one} using lithium hexamethyldisilazide (LHMDS) at −78 °C gave one regioisomeric enolate. The regiocontrol is governed by the axial β-silyloxy substituent and the resulting lithium enolate is stable towards β-elimination at temperatures up to −40 °C. It was found that the axial β-silyloxy group could be conveniently eliminated using 2.1 equiv of LHMDS at 0 °C for 1 h and that an equatorial β-alkoxy group was much more resistant to β-elimination. A chiral lithium amide base was used to overturn the inherent regioselectivity of ketone deprotonation with LHMDS.