Intramolecular Acylal Cyclisation (IAC) as an Efficient Synthetic Strategy towards the Total Synthesis of Erythrina Alkaloid Derivatives

Compounds that comprise the erythrina alkaloid class of natural products are based on a tetracyclic spiroamine framework and exhibit a range of biological activities on the central nervous system. Herein, we report a new and efficient total synthesis of this multiple-ring system based on an intramolecular acylal cyclisation (IAC) approach. Using this methodology, the tetracyclic core was rapidly assembled over a two-step domino process catalysed by a Lewis acid. The effect of heteroatoms, substituents and ring size on the IAC has also been investigated, and the broad application of this procedure is demonstrated by the synthesis of a library of derivatives in good yields with excellent regioselectivity

Regioselective Dihalohydration Reactions of Propargylic Alcohols: Gold-Catalyzed and Non-Catalyzed Reactions

The regioselective conversion of propargylic alcohols into previously unreported α,α-diiodo-β-hydroxyketones was achieved by treatment with N-iodosuccinimide in the presence of a gold catalyst. The corresponding α,α-dichloro-β-hydroxyketones were obtained by treatment with trichloroisocyanuric acid in the absence of a catalyst. The latter reaction can be extended to other alkynols. These transformations can be used to prepare potentially useful halogenated building blocks. Preliminary mechanistic studies suggest that the reaction involves participation of the acetonitrile solvent in the formation of a 5-halo-1,3-oxazine intermediate

The structure of tagetitoxin

Based on detailed analysis of newly acquired NMR data, we show that the previously revised structure of tagetitoxin is incorrect. A new structure of tagetitoxin is proposed which is consistent with the NMR and MS data

Intramolecular amidocyclopropanation reactions using diethoxymethyl-functionalised lactams as organozinc carbenoid precursors

Intramolecular amidocyclopropanation reactions of diethoxymethyl-lactams containing a pendant alkene were examined using zinc/TMSCI. With a range of 4-6-membered lactams, bicyclic amidocyclopropanes were obtained with very high diastereoselectivity with a preference for the formation of the More hindered endo-cyclopropane. (C) 2009 Elsevier Ltd. All rights reserved

Synthesis of substituted benzooxaborinin-1-ols via palladium-catalysed cyclisation of alkenyl- and alkynyl-boronic acids

Two new palladium-catalysed reactions have been developed for the synthesis of stable 4-substituted benzooxaborinin-1-ols. A palladium-catalysed cyclisation of ortho-alkenylbenzene boronic acids can be used to access 4-chlorobenzooxaborinin-1-ols via a Wacker-type oxidation and chlorination. Alternatively, ortho-alkynylbenzene boronic acids undergo a palladium-catalysed oxyallylation reaction to provide 4-allylbenzooxaborinin-1-ols

A lactate-derived chiral aldehyde for determining the enantiopurity of enantioenriched primary amines

In this paper we describe the use of a chiral aldehyde derived from lactate esters for determining the enantiopurity of primary amines, via the formation of diastereomeric imines. The method was shown to be suitable for reproducibly determining the enantiopurity of a diverse set of chiral amines. Both enantiomers of the aldehyde can be prepared in two steps from commercially available materials

Water scaffolding in collagen: Implications on protein dynamics as revealed by solid-state NMR.

Solid-state NMR studies of collagen samples of various origin confirm that the amplitude of collagen backbone and sidechain motions increases significantly on increasing the water content. This conclusion is supported by the changes observed in three different NMR observables: (i) the linewidth dependence on the (1) H decoupling frequency; (ii) (13) C CSA changes for the peptide carbonyl groups, and (iii) dephasing rates of (1) H-(13) C dipolar couplings. In particular, a nearly three-fold increase in motional amplitudes of the backbone librations about C-C(α) or N-C(α) bonds was found on increasing the added water content up to 47 wt%D2 O. Based on the frequencies of NMR observables involved, the timescale of the protein motions dependent on the added water content is estimated to be of the order of microseconds. This estimate agrees with that from wideline T2 (1) H NMR measurements. Also, our wideline (1) H NMR measurements revealed that the timescale of the microsecond motions in proteins reduces significantly on increasing the added water content, i.e., an approximately 15-fold increase in protein motional frequencies is observed on increasing the added water content to 45 wt%D2 O. The observed changes in collagen dynamics is attributed to the increase in water translational diffusion on increasing the amount of added water, which leads to more frequent "bound water"/"free water" exchange on the protein surface, accompanied by the breakage and formation of new hydrogen bonds with polar functionalities of protein

Motional timescale predictions by molecular dynamics simulations: Case study using proline and hydroxyproline sidechain dynamics.

We propose a new approach for force field optimisations which aims at reproducing dynamics characteristics using biomolecular MD simulations, in addition to improved prediction of motionally averaged structural properties available from experiment. As the source of experimental data for dynamics fittings, we use (13) C NMR spin-lattice relaxation times T1 of backbone and sidechain carbons, which allow to determine correlation times of both overall molecular and intramolecular motions. For structural fittings, we use motionally averaged experimental values of NMR J couplings. The proline residue and its derivative 4-hydroxyproline with relatively simple cyclic structure and sidechain dynamics were chosen for the assessment of the new approach in this work. Initially, grid search and simplexed MD simulations identified large number of parameter sets which fit equally well experimental J couplings. Using the Arrhenius-type relationship between the force constant and the correlation time, the available MD data for a series of parameter sets were analyzed to predict the value of the force constant that best reproduces experimental timescale of the sidechain dynamics. Verification of the new force-field parameters against NMR J couplings and correlation times showed consistent and significant improvements compared to the original force field in reproducing both structural and dynamics properties. The results suggest that matching experimental timescales of motions together with motionally averaged characteristics is the valid approach for force field parameter optimisation. Such a comprehensive approach is not restricted to cyclic residues and can be extended to other amino acid residues, as well as to the backbone. © Proteins 2013;. © 2013 Wiley Periodicals, Inc

Synthesis of novel and potent vorapaxar analogues

Vorapaxar is a first-in-class PAR-1 antagonistic drug based on the ent-himbacine scaffold. Detailed in this article are enantioselective and racemic routes to various novel vorapaxar analogues. Biological testing revealed these compounds to have moderate to excellent potencies against PAR-1 with the most potent analogue demonstrating an IC50 of 27 nM

Characterising plasticised cellulose acetate-based historic artefacts by NMR spectroscopy: a new approach for quantifying the degree of substitution and diethyl phthalate contents

As one of the first semi-synthetic plastics produced industrially, cellulose acetate (CA)-based artefacts represent valued items in museum collections and archives which, however, present stability issues. High temperature and relative humidity conditions have long been known to promote changes in CA properties, for instance, due to the deacetylation of CA polymer chains and the loss of plasticiser from the polymer matrix. However, there is a need for improved methods for the quantification of plasticiser loss and CA deacetylation. In this context, this contribution presents a new approach for enabling the investigation of plasticiser loss and deacetylation degradation processes in historic plasticised CA-based artefacts which is based on high-resolution proton nuclear magnetic resonance spectroscopy (1H NMR). The proposed methods allow for simple and fast quantification of diethyl phthalate contents and average degree of substitution (DS), while requiring no need for extractive separation between the plasticiser and the CA polymer matrix prior to analysis. Both methods are demonstrated by their application towards a series of reference samples, historic artefacts and artificially aged plasticised CA materials. Our analysis indicates that plasticiser content and DS can be accurately quantified by using high-resolution 1H NMR and both methods have been compared to analyses performed using infrared spectroscopy