Alumina catalyzed transformations of O-(3-oxobutyl) urethanes

The alumina-catalyzed transformations of urethane to a secondary amine and a sulfonyl urethane to a sulfonamide are described. Alumina is also shown to catalyze the conjugate addition of p-toluenesulfonamide to methyl vinyl ketone.     

A DFT study on the regioselectivity of the reaction of dichloropropynylborane with isoprene

This theoretical study deals with the reaction of isoprene and dichloropropynylborane. We report the results of the DFT calculations applied to the two processes involved, Diels-Alder cycloaddition and 1,4-alkynylboration. The boron influences both the chemoselectivity and the regioselectivity of this reaction through secondary orbital interactions (SOI hereafter) that give rise to transition structures with strong [4 atom + 3 atom] character. The "meta" regioselectivity observed experimentally for the reaction between 2-substituted 1,3-dienes and alkynyldihaloboranes has been explained as a result of the higher stabilization of these transition structures with "meta" orientation. Intrinsic reaction coordinate calculations were performed to determine connectivities and established the remarkable result that the geometrically very similar transition structures leading to both regioisomeric 1,4-alkynylboration products correspond to different pathways. For the "meta" orientation a direct alkynylboration of the diene through a concerted transition structure was found.     

Introduction to the Proceedings of the Fourteenth Symposium on Biotechnology for Fuels and Chemicals

Applied Biochemistry and Biotechnology -     

Tilted amides in amino acid and peptide derivatives

Background: Amide bonds in peptides and proteins typically adopt planar cis or trans conformations. Conversions between cis and trans amide conformations are necessary for protein folding and for many other processes, but are difficult to achieve since they involve disruption of the planarity of the bond. As a first step to understanding cis-trans isomerization, we set out to synthesize and characterize peptides that mimic the tilted or twisted amide structures that are postulated to form the intermediate states in this process.Results: We have synthesized a model amino acid and four dipeptide derivatives containing a methyl-substituted aziridine residue. Single crystals of phenacyl (2R, 3R)-benzyloxycarbonyl-3-methyl-2-aziridinecarboxylate and phenacyl (2R, 3R)-acetyl-glycyl-3-methyl-2-aziridine-carboxylate were obtained. Using X-ray diffraction analysis, we determined that the amide nitrogens of the aziridine rings have tetrahedral sp³-like geometry with tilt angles in the range of 37–38°. The ¹³C-NMR spectra indicate that the amide carbonyl is dramatically shifted downfield as a consequence of the tilt.Conclusions: In peptides containing a substituted aziridine ring, the orbitals of the amide nitrogen are constrained into a tilted configuration. These peptides may mimic the transition state between cis and trans amide conformations. This technique thus provides a novel strategy for the study of isomerization and other biorecognition processes.     

Surface states in electrochemisorption

The recursive Green function (RGF) method is used to obtain the surface and adatom RGFs for an electrified substate. The electrochemisorption (ECS) process is described, by invoking the Anderson–Newns (AN) model, whereby a self-consistent treatment of the ECS energy and charge transfer is provided. The role of the electric field, and the presence of surface states (SS), in governing magnetic and non-magnetic ECS is discussed in the case of H–Cr.     

An alternative synthesis of the lipophilic tail portion of abediterol using linear-selective hydroformylation

Abediterol is a compound currently in development for the treatment of respiratory disease at AstraZeneca. In this work we employ hydroformylation, an under-utilised reaction in the synthesis of pharmaceutical intermediates, as a key step to access the lipophilic amine portion of this molecule. The route described herein addresses some of the issues identified in the original route. Namely, hazardous materials are avoided and increased levels of control – from a process chemistry point of view – are demonstrated, with isolation of intermediates possible at multiple points in the synthesis. This work provides ‘proof-of-concept’ for an alternative synthetic route and provides high-quality material using a series of robust transformations.