Synthesis and Functionalization of Azetidine-Containing Small Macrocyclic Peptides.

Cyclic peptides are increasingly important structures in drugs but their development can be impeded by difficulties associated with their synthesis. Here, we introduce the 3-aminoazetidine (3-AAz) subunit as a new turn-inducing element for the efficient synthesis of small head-to-tail cyclic peptides. Greatly improved cyclizations of tetra-, penta- and hexapeptides (28 examples) under standard reaction conditions are achieved by introduction of this element within the linear peptide precursor. Post-cyclization deprotection of the amino acid side chains with strong acid is realized without degradation of the strained four-membered azetidine. A special feature of this chemistry is that further late-stage modification of the resultant macrocyclic peptides can be achieved via the 3-AAz unit. This is done by: (i) chemoselective deprotection and substitution at the azetidine nitrogen, or by (ii) a click-based approach employing a 2-propynyl carbamate on the azetidine nitrogen. In this way, a range of dye and biotin tagged macrocycles are readily produced. Structural insights gained by XRD analysis of a cyclic tetrapeptide indicate that the azetidine ring encourages access to the less stable, all-trans conformation. Moreover, introduction of a 3-AAz into a representative cyclohexapeptide improves stability towards proteases compared to the homodetic macrocycle.

Stimuli responsive asymmetric catalysis by triggered pseudo-enantiomeric proligand release.

Complex stimuli responsive systems are the basis for molecular machines and computing. A dual psuedo-enantiomer system was conceived, where the combination of two 'switch-on' asymmetric catalytic cycles could be selectively triggered to afford an enantioenriched product. Two pseudo-enantiomeric proligands were designed and synthesised for selective activation by fluoride and alkaline phosphatase. The proligands were firstly incorporated into single proligand systems, and then into a dual proligand system, where enantioselectivity of up to 98 : 2 was achieved in the reduction of prochiral ketone following external stimulation.

Ratiometric Electrochemistry: Improving the Robustness, Reproducibility and Reliability of Biosensors.

Electrochemical biosensors are an increasingly attractive option for the development of a novel analyte detection method, especially when integration within a point-of-use device is the overall objective. In this context, accuracy and sensitivity are not compromised when working with opaque samples as the electrical readout signal can be directly read by a device without the need for any signal transduction. However, electrochemical detection can be susceptible to substantial signal drift and increased signal error. This is most apparent when analysing complex mixtures and when using small, single-use, screen-printed electrodes. Over recent years, analytical scientists have taken inspiration from self-referencing ratiometric fluorescence methods to counteract these problems and have begun to develop ratiometric electrochemical protocols to improve sensor accuracy and reliability. This review will provide coverage of key developments in ratiometric electrochemical (bio)sensors, highlighting innovative assay design, and the experiments performed that challenge assay robustness and reliability.

Ratiometric electrochemical detection of ß-galactosidase.

A novel ferrocene-based substrate for the ratiometric electrochemical detection of ß-galactosidase was designed and synthesised. It was demonstrated to be an excellent electrochemical substrate for ß-Gal detection with sensitivity as low as 0.1 U mL-1.