Synthesis and biological evaluation of isoxazole derivatives aspre-mRNA splicing inhibitors

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Abstract

It is now known that eukaryotic pre-mRNA splicing is catalysed by complex molecularmachinery called the spliceosome which consists of five U-type (snRNAs) and nearly 300supplemental protein and non-protein snRNP groups. However, the exact mechanism bywhich the ends and branch point of introns of nuclear pre-mRNA are recognized andeliminated in order to produce complementary messenger RNA (mRNA) is as yetunknown. Tackling this complex issue is of immense importance as a number of inheritedhuman diseases result from faults in pre-mRNA splicing.Prp8 is the largest and one of the essential spliceosomal proteins. This protein isimplicated in splicing reactions although its exact biological role and structure remainlargely undefined. That said it is known that Pre-mRNA splicing is associated withchromatin modification and that chromatin modification can modulate spliceosomeactivity. Structural bioinformatics analysis has been used to gain additional insights intothe molecular structure of Prp8. From these studies it has been concluded that the Prp8N-terminal region contains a putative bromodomain. The bromodomain is an importantchromosomal protein which is associated with chromatin modification, a hypothesiswhich should lend itself to practical investigation.Recent studies have shown that isoxazole derivatives have remarkable potency asinhibitors for bromodomains, an observation which may be reflected in the continuedinterest in the development of isoxazole-based structures as ethical pharmaceuticals.The outcomes of splicing assays indicate that isoxazole 183c shows complete inhibitionfor in vitro pre-mRNA splicing in both yeast and human cells at 250 μM with effectsbeginning at 100 μM. Hence, the existence of putative bromodomain or bromodomainlikestructure in Prp8 N-terminal region have been confirmed by biochemicalinvestigation. This was based on a comparative bioinformatics analysis which combinedwith X-ray crystallographic studies of bromodomain-isoxazole interactions.The current programme of research has investigated novel approaches to the synthesis ofisoxazole derivatives. The use of a radical Truce-Smiles rearrangement reaction has beeninvestigated for the synthesis of isoxazoles containing a bi-aryl axis. An indication of therate of these rearrangement reactions has been gained from intramolecular andintermolecular radical trapping reactions.

Keyword(s)

Pre-mRNA splicing, Isoxazoles, Radical rearrangement reaction, Bromodomains, Antimicrobial agent

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