Robin A. E. Carr

Oxidation State of the Active-Site Cysteine in Protein Tyrosine Phosphatase 1B

Protein tyrosine phosphatases regulate signal transduction pathways involving tyrosine phosphorylation and have been implicated in the development of cancer, diabetes, rheumatoid arthritis and hypertension. Increasing evidence suggests that the cellular redox state is involved in regulating tyrosine phosphatase activity through the reversible oxidization of the catalytic cysteine to sulphenic acid (Cys-SOH). But how further oxidation to the irreversible sulphinic (Cys-SO2H) and sulphonic (Cys-SO3H) forms is prevented remains unclear. Here we report the crystal structures of the regulatory sulphenic and irreversible sulphinic and sulphonic acids of protein tyrosine phosphatase 1B (PTP1B), an important enzyme in the negative regulation of the insulin receptor and a therapeutic target in type II diabetes and obesity. We also identify a sulphenyl-amide species that is formed through oxidation of its catalytic cysteine. Formation of the sulphenyl-amide causes large changes in the PTP1B active site, which are reversible by reduction with the cellular reducing agent glutathione. The sulphenyl-amide is a protective intermediate in the oxidative inhibition of PTP1B. In addition, it may facilitate reactivation of PTP1B by biological thiols and signal a unique state of the protein.

Structure-based screening of low-affinity compounds

Conventional bioassay-based screening remains a mainstream approach for lead discovery. However, its limitations have meant that other, more biophysical methods, such as X-ray crystallography and NMR, are now being developed as lead discovery tools. These methods are particularly effective at detecting the binding of low affinity, low molecular weight compounds and transforming them into novel potent leads using structure-guided chemistry. Here, we describe some of the technologies and approaches that are being developed in structure-based screening using X-ray crystallography, which promise to have a major impact on lead discovery.

A photolabile carbamate based dual linker analytical construct for facile monitoring of solid phase chemistry: ‘TLC’ for solid phase?

Abstract A dual linker analytical construct based on a photolabile carbamate is described. Photochemical cleavage from the solid support can be effected to afford an analytical fragment, containing the substrate, which is sensitised to electrospray mass spectrometry. We believe this simple construct now renders all substrates visible to high throughput mass specroscopic analysis.

Enantioselective synthesis of (R)-(-)-2,6-dimethyl heptanoic acid:the first application of the DITOX asymmetric building block

Abstract The 1,3-dithiane 1-oxide (DITOX) asymmetric building block/chiral auxiliary has been used to prepare (R)-(−)-2,6-dimethyl heptanoic acid (1), a simple derivative of citronellal, in two steps from (2).

Diastereoselective electrophilic amination of ketone enolates in 2-substituted 2-acyl-1,3-dithiane 1-oxides

Abstract Enolate anions derived from 2-substituted 2-acyl-1,3-dithiane 1-oxides react readily with the nitrogen electrophile di- tert -butyl azodicarboxylate (DBAD) to give α-aminoketones with good diastereoselectivity and in reasonable yields; in some cases diastereoselectivity appears sufficiently high that the minor isomer cannot be detected by 400 MHz 1 H NMR spectroscopy.

Rapid reaction scanning of solid phase chemistry using resins incocorporating analytical constructs

Abstract Two analytical constructs, based on orthogonally cleavable linkers, are reported which facilitate the mass spectral analysis of solid phase chemistry. The chemical compatibility and orthogonality of the linkers were established in a parallel reaction study using contructs prepared specifically for the purpose.

Total synthesis of (+)-milbemycin β3

(+)-Milbemycin β3(1) was prepared by total synthesis from (6S,8R,9S)-methyl 8,9-dimethyl-4-oxo-1,7-dioxaspiro[5.5]undeco-2-ene-2-carboxylate (2), (4R,6R)-4-methyl-6-phenylsulphonyl-(E)-hept-2-en-1-ol (3a), and 2-ethyl-4-methoxy-5-methylbenzoic acid (4) using Julia–Lythgoe and benzylic anion chemistry to establish the carbon framework and a Mitsunobu reaction to close the lactone ring.

Enolate bromination in 2-acyl-1,3-dithiane 1-oxides

Abstract Enolates derived from 2-acyl-2-ethyl-1,3-dithiane 1-oxides react readily and diastereoselectively with N-bromosuccinimide to give α-bromoketones. In addition, halide displacement by treatment with nitrogen nucleophiles has been briefly investigated, but induces loss of stereochemical integrity by equilibration under the reaction conditions.