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The urotensin-II receptor (UTR) is a class A GPCR that predominantly binds to the pleiotropic cyclic peptide urotensin-II (U-II). U-II is constrained by a disulfide bridge that induces a β-turn structure and binds pseudo-irreversibly to UTR and is believed to result in a structural rearrangement of the receptor. However, it is not well understood how U-II binds pseudo-irreversibly and the nature of the reorganization of the receptor that results in G-protein activation. Here we describe a series of U-II peptidomimetics incorporating a non-reducible disulfide bond structural surrogate to investigate the feasibility that native U-II binds to the G protein-coupled receptor through disulfide bond shuffling as a mechanism of covalent interaction. Disubstituted 1,2,3-triazoles were designed with the aid of computational modeling as a non-reducible mimic of the disulfide bridge (Cys5-Cys10) in U-II. Solid phase synthesis using CuAAC or RuAAC as the key macrocyclisation step provided four analogues of U-II(4-11) incorporating either a 1,5-triazole bridge (5, 6) or 1,4-triazole bridge (9, 10). Biological evaluation of compounds 5, 6, 9 and 10 was achieved using in vitro [ 125 I]UII binding and [Ca 2+ ] i assays at recombinant human UTR. Compounds 5 and 6 demonstrated high affinity (K D ∼ 10 nM) for the UTR and were also shown to bind reversibly as predicted and activate the UTR to increase [Ca 2+ ] i . Importantly, our results provide new insight into the mechanism of covalent binding of U-II with the UTR.

The efficient asymmetric synthesis of unnatural alkenyl amino acids required for peptide 'stapling' has been achieved using alkylation of a fluorine-modified Ni(II) Schiff base complex as the key step.

In an effort to understand and enhance the stereochemical outcome of the MOM-ether directed rearrangement of allylic trichloroacetimidates we have investigated various reaction conditions for this process. A range of Pd(ii) and other metal catalysts have been shown to effectively catalyse the rearrangement providing the subsequent allylic amides in high selectivity (up to 11 : 1 ratio of diastereomers). The replacement of THF as a solvent in this reaction with non-coordinating solvents such as toluene has led to an enhancement of the directing effect resulting in a significant increase in the diastereoselective outcome (15 : 1 ratio). The reaction was also carried out for the first time, using a highly coordinating ionic solvent which disrupts binding of the Pd(ii)-catalyst to the MOM-ether yielding the allylic amide in only moderate diastereoselectivity. These results provide further evidence for the ether directed aza-Claisen rearrangement of allylic trichloroacetimidates.

A highly diastereoselective synthesis of (2S,3S)-beta-hydroxy-alpha-amino acids has been developed from enantiopure alpha-hydroxy acids using a MOM-ether-directed, palladium(II)-catalysed, aza-Claisen rearrangement of allylic acetimidates to effect the key step. This highly stereoselective process gave allylic amides in diastereomeric ratios of up to 14 : 1. Problems associated with the isolation of 1,3-products (anti-Claisen) from sterically demanding substrates via an insitu palladium(0)-catalysed rearrangement process were overcome by the addition of a re-oxidant, p-benzoquinone, leading to cleaner reactions and improved yields of the 3,3-products (Claisen). The target beta-hydroxy-alpha-amino acids are an important class of natural products that are also components of more complex organic compounds with significant biological properties.

A highly stereoselective rearrangement of allylic trichloroacetimidates to allylic trichloroamides has been achieved using adjacent ether groups to direct facial coordination of the palladium(II) catalyst.

A synthetic route towards the synthesis of (2S,3S,4R)-gamma-hydroxyisoleucine, the amino acid component of the natural product, funebrine has been developed using as the key step, a palladium(II) catalysed 3,3-sigmatropic rearrangement to create the (2S)-stereogenic centre.