Total synthesis of chloptosin: a dimeric cyclohexapeptide

Here we describe in full our investigations into the synthesis of the dimeric cyclohexapeptide chloptosin in 17 linear steps. Particularly, this work features an organocatalytic tandem process for the synthesis of the embedded piperazic acids, in which a differentially protected azodicarboxylate is used together with pyrrolidinyl tetrazole as the catalyst. The central biaryl bond is being formed by Stille coupling of two sterically demanding ortho-chloropyrroloindole fragments. The inherent flexibility of the synthetic strategy proved beneficial as the route could be adjusted smoothly during the progression of the synthesis programme.     

Cylindrical Algebraic Sub-Decompositions

Cylindrical algebraic decompositions (CADs) are a key tool in real algebraic geometry, used primarily for eliminating quantifiers over the reals and studying semi-algebraic sets. In this paper we introduce cylindrical algebraic sub-decompositions (sub-CADs), which are subsets of CADs containing all the information needed to specify a solution for a given problem. We define two new types of sub-CAD: variety sub-CADs which are those cells in a CAD lying on a designated variety; and layered sub-CADs which have only those cells of dimension higher than a specified value. We present algorithms to produce these and describe how the two approaches may be combined with each other and the recent theory of truth-table invariant CAD. We give a complexity analysis showing that these techniques can offer substantial theoretical savings, which is supported by experimentation using an implementation in Maple.     

PhPAd‐DalPhos: Ligand‐Enabled,Nickel‐Catalyzed Cross‐Coupling of (Hetero)aryl Electrophiles with Bulky Primary Alkylamines

The base metal‐catalyzed C?N cross‐coupling of bulky α,α,α‐trisubstituted primary alkylamines with (hetero)aryl electrophiles represents a challenging and under‐developed class of transformations that is of significant potential utility, including in the synthesis of lipophilic active pharmaceutical ingredients. Herein, we report that a new, air‐stable Ni(II) pre‐catalyst incorporating the optimized ancillary ligand PhPAd‐DalPhos enables such transformations of (hetero)aryl chloride, bromide, and tosylate electrophiles to be carried out for the first time with substrate scope rivalling that achieved using state‐of‐the‐art Pd catalysts, including room temperature cross‐couplings of (hetero)aryl chlorides that are unprecedented for any catalyst (Pd, Ni, or other).     

Generation and measurement of relativistic electron bunches characterized by a linearly ramped current profile

We report the first successful attempt to generate ultrashort (1-10 ps) relativistic electron bunches characterized by a ramped longitudinal current profile that rises linearly from head to tail and then falls sharply to zero. Bunches with this type of longitudinal shape may be applied to plasma-based accelerator schemes as an optimized drive beam, and to free-electron lasers as a means of reducing asymmetry in microbunching due to slippage. The scheme used to generate the ramped bunches employs an anisochronous dogleg beam line with nonlinear correction elements to compress a beam having an initial positive time-energy chirp. The beam current profile is measured using a deflecting mode cavity, and a pseudoreconstruction of the beam's longitudinal phase space distribution is obtained by using this diagnostic with a residual horizontal dispersion after the dogleg.     

The Diels-Alder reactions of quinone imine ketals: a versatile synthesis of highly substituted 5-methoxyindoles

[reaction: see text]. N-benzoylated quinone imine ketals undergo smooth cycloadditions in a [4 + 2] sense to yield the expected cycloadducts. The crude cycloadducts, when subjected to a short series of simple transformations, produce synthetically useful quantities of 5-methoxyindoles in excellent overall yields.     

The elastic scattering of 33 MeV He particles from Ni,Cu and Zn

Differential cross sections have been measured for the elastic scattering of 33 MeV ³He particles from targets of ^58,60,62,64Ni,^63,65Cu and ^64,66,68Zn over the angular range 5° to 175°. The data have been analysed with the optical model, with particular emphasis on the investigation of the ambiguities in the real potential, the form of the imaginary potential and the use of a spin-orbit term.     

Investigation of 91Zr by high resolution (d,p), (p,p′) and (p,d) reactions

Energy spectra and angular distributions of light particles (Z = 3–8) produced in the reactions ¹³C+^{58, 60, 64}Ni have been measured at 105 MeV. Coincidence events between light outgoing particles Li, Be, B and α, p have been observed for the first time in the ¹³C+⁵⁸Ni and ¹³C+⁶⁴Ni reactions. The results show that at least part of the ‘deep-inelastic’ events are due to many-particle reactions.     

Improving the power to detect differentially expressed genes in comparative microarray experiments by including information from self-self hybridizations

Our ability to detect differentially expressed genes in a microarray experiment can be hampered when the number of biological samples of interest is limited. In this situation, we propose the use of information from self-self hybridizations to acuminate our inference of differential expression. A unified modelling strategy is developed to allow better estimation of the error variance. This principle is similar to the use of a pooled variance estimate in the two-sample t-test. The results from real dataset examples suggest that we can detect more genes that are differentially expressed in the combined models. Our simulation study provides evidence that this method increases sensitivity compared to using the information from comparative hybridizations alone, given the same control for false discovery rate. The largest increase in sensitivity occurs when the amount of information in the comparative hybridization is limited.