Direct photons,dimuons and nuclear effects

Largep _T direct photon and dimuon production in experiments using nuclear targets have been studied in detail. We show that, by a careful choice of kinematic configurations in these experiments, very good estimates of nuclear quark and gluon densities can be obtained. Information on the cumulative region of the nuclear structure functions i.e. the regionx>1 can also be obtained by considering semi-integrated cross sections.     

The influence of fluorine on the asymmetric reduction of fluoromethyl ketones

A comparative study of the asymmetric reduction of representative aryl and alkyl α-fluoro- and α-chloromethyl ketones using (−)-diisopinocampheylchloroborane [(−)-DIP-Chloride™] and (−)-B-isopinocampheyl-9-borabicyclo[3.3.1]nonane [R-Alpine-Borane^®] has been made. It was observed that DIP-Chloride™ is superior in terms of the rate and enantioselectivity for both classes of halo-ketones. While the reduction of monofluoroacetone and trifluoroacetone with DIP-Chloride™ provided the product alcohols in 61% ee and 96% ee, respectively, the reduction of difluoroacetone yielded only 5% ee. The influence of a lone halogen atom was not observed for monochloroacetone, all of which point towards a chelating effect of monofluoroacetone on the Lewis acidic chloroborane.     

The first polymorph in the family of nucleobases: a second form of cytosine

A new polymorph of cytosine, C₄H₅N₃O, is reported half a century after the report of its first known crystal structure [Barker & Marsh (1964). Acta Cryst. 17 , 1581–1587]. Cytosine thus provides the first polymorphic example in the category of parent nucleobases. The new form, denoted (Ib), was observed unexpectedly during an attempt to cocrystallize cytosine with catechol. Form (Ib) crystallizes in the orthorhombic centrosymmetric space group Pccn with two molecules in the asymmetric unit. The previously known form, denoted (Ia), crystallizes in the orthorhombic noncentrosymmetric space group P2₁2₁2₁. The cytosine molecule is planar in both forms. Hydrogen‐bonding interactions are also similar for both forms. Infinite one‐dimensional ribbons composed of cytosine base‐pair dimers in R₂²(8) arrangements are observed in both (Ia) and (Ib). However, the way that the ribbons are packed differs in (Ia) and (Ib). This appears to guide the centrosymmetric versus noncentrosymmetric space‐group selection through the formation of an inversion‐related motif in polymorph (Ib) and a helical propagation in polymorph (Ia). A few selected polymorphic systems have been gathered from the Cambridge Structural Database to understand possible structural features responsible for achiral molecules adopting centro‐ and noncentrosymmetric space groups.     

Four oxoindole‐linked α‐alkoxy‐β‐amino acid derivatives

Four structures of oxoindolyl α‐hydroxy‐β‐amino acid derivatives, namely, methyl 2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐methoxy‐2‐phenylacetate, C₂₄H₂₈N₂O₆, (I), methyl 2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐ethoxy‐2‐phenylacetate, C₂₅H₃₀N₂O₆, (II), methyl 2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐[(4‐methoxybenzyl)oxy]‐2‐phenylacetate, C₃₁H₃₄N₂O₇, (III), and methyl 2‐[(anthracen‐9‐yl)methoxy]‐2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐phenylacetate, C₃₈H₃₆N₂O₆, (IV), have been determined. The diastereoselectivity of the chemical reaction involving α‐diazoesters and isatin imines in the presence of benzyl alcohol is confirmed through the relative configuration of the two stereogenic centres. In esters (I) and (III), the amide group adopts an anti conformation, whereas the conformation is syn in esters (II) and (IV). Nevertheless, the amide group forms intramolecular N—H...O hydrogen bonds with the ester and ether O atoms in all four structures. The ether‐linked substituents are in the extended conformation in all four structures. Ester (II) is dominated by intermolecular N—H...O hydrogen‐bond interactions. In contrast, the remaining three structures are sustained by C—H...O hydrogen‐bond interactions.     

A Magneto-Mechanically Coupled Phase-Field Model at Large Deformation

The aggregate magneto-mechanical behavior of magneto-rheological elastomers (MREs) stems from the magnetic properties of the ferromagnetic inclusion and the mechanical properties of the matrix material. We propose a large deformation micro-magnetic theory, to predict the behavior and interaction of ferromagnetic particles inside an elastomeric matrix. A rate-type variational principle, with the magnetization as the order parameter is proposed. A large deformation Landau-Lifshitz-Gilbert equation for the time evolution of the magnetization, is obtained directly from the proposed variational principle. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analysis of the ketosynthase-chain length factor heterodimer from the fredericamycin polyketide synthase

The pentadecaketide fredericamycin has the longest carbon chain backbone among polycyclic aromatic polyketide antibiotics whose biosynthetic genes have been sequenced. This backbone is synthesized by the bimodular fdm polyketide synthase (PKS). Here, we demonstrate that the bimodular fdm PKS as well as its elongation module alone synthesize undecaketides and dodecaketides. Thus, unlike other homologs, the fdm ketosynthase-chain length factor (KS-CLF) heterodimer does not exclusively control the backbone length of its natural product. Using sequence- and structure-based approaches, 48 CLF multiple mutants were engineered and analyzed. Unexpectedly, the I134F mutant was unable to turn over but could initiate and partially elongate the polyketide chain. This unprecedented mutant suggests that the KS-CLF heterodimer harbors an as yet uncharacterized chain termination mechanism. Together, our findings reveal fundamental mechanistic differences between the fdm PKS and its well-studied homologs.     

Fluoroallylboration-olefination for the synthesis of (Z)-4,4-difluoropent-2-enoates and 5,5-difluoro-5,6-dihydropyran-2-ones

Horner-Wadsworth-Emmons (HWE) or Still-Gennari olefination of TBS-protected 3,3-difluoro-4-hydroxy-2-ones, derived from the difluoroallylboration of aldehydes, provides the Z-isomer of 4,4,-difluoropent-2-enoates. These, upon hydrolysis, followed by Yamaguchi cyclization, afford 5,5-difluoro-4-methyl-5,6-dihydro-α-pyrones in high yields.     

Tandem Prins/Friedel–Crafts cyclization for stereoselective synthesis of heterotricyclic systems

Homoallylic substrates such as (E)-6-arylhex-3-enyl alcohols, N-tosylamides, and thiols undergo smooth cross-coupling with various aldehydes in the presence of 10 mol % Sc(OTf)(3) and 30 mol % TsOH to afford the trans-fused hexahydro-1H-benzo[f]isochromenes, N-tosyloctahydrobenzo[f]isoquinolines, and hexahydro-1H-benzo[f]isothiochromenes, respectively. However, the cross-coupling of (Z)-olefins such as 6-arylhex-3-enyl alcohols, N-tosylamides, and thiols with aldehydes affords the corresponding hexahydro-1H-benzo[f]isochromenes, N-tosyloctahydrobenzo[f]isoquinolines, and hexahydro-1H-benzo[f]isothiochromenes with complete cis selectivity via intramolecular Prins-, aza-Prins-, and thia-Prins/Friedel-Crafts cyclizations, respectively. Though the Prins cyclization proceeds smoothly under the influence of Sc(OTf)(3), high conversions and enhanced reaction rates are achieved using a mixture of Sc(OTf)(3) and TsOH (1:3).