The development of novel myosin inhibitors

Abstract

This thesis describes a structure activity relationship (SAR) study on the recently discovered small molecule tool blebbistatin (S)-21 with particular emphasis on the development of novel synthetic protocols suitable for the rapid synthesis of libraries of blebbistatin analogues. These analogues are potentially of use as novel myosin inhibitors Chapter 1 introduces the concept of chemical biology with particular emphasis on chemical genetics. This approach has rekindled the search for new chemical tools for the investigation of biological systems. The success of blebbistatin (S)-21, which was identified in a chemical genetic study, as a research tool was also discussed. The link between several myosin classes and genetic diseases such as coeliac disease, Crohn’s disease, deafness, dermatitis, familial hypertrophic cardiomyopathy, Griscelli disease and ulcerative colitis indicate that potent inhibitors which show selectivity towards specific myosin isoforms may be of great value as tools for the study of these conditions. The plan for the SAR study around (S)-21 was outlined. Chapter 2 describes the studies undertaken to develop an efficient synthetic route to N1-alkyl analogues of (S)-21 suitable for the parallel synthesis of chemical collections. These studies culminated in the synthesis of an intermediate (S)-66 from which novel N1-alkyl analogues were synthesised. The biological evaluation of these N1-alkyl analogues was discussed. Chapter 3 describes the development of a protocol suitable for the parallel synthesis of collections of N1-aryl analogues of (S)-21 via the intermediate 66. The application of this protocol to the synthesis of a collection of racemic N1-aryl and heteroaryl analogues of (S)-21 and their biological evaluation was presented. Chapter 4 describes the successful rational design and synthesis of a novel fused thiophene ring containing inhibitor of myosin II. The structure of this compound was proposed by modelling of the existing co-crystal structure of (S)-21 bound to the metastable state of Dictyostelium discoideum myosin II (S1dC) and sought to optimise the π-π stacking interaction displayed by (S)-21 with the tyrosine 261 residue within its binding site. The biological evaluation of this novel analogue was discussed. In Chapter 5 the studies conducted to investigate the contribution of ring-C to the binding affinity of (S)-21 were described. The development of alternate routes to (S)-21, in an attempt to avoid difficulties experienced during the synthesis of some analogues of (S)-21, are described. The synthesis and biological investigation of the fluorescent dye PPBA whose binding site has been suggested to overlap with that of (S)-21 was also reported.