Studies Towards a Model ϐ-Sheet

The construction of de novo proteins is a long time goal of many researchers into the protein folding problem. In order to design and construct "tertiary" structure from scratch, an understanding of the forces involved in the lower levels of structure is necessary. Simple models are needed to confidently study the factors involved in stabilizing the secondary and super-secondary structure of proteins. One way in which this can be done is by template assembly. The template limits the degrees of freedom afforded to the attached peptide chains, directing them into pre-determined folding patterns. The long term aim of this project is to model (ϐ-sheets using a cyclotriveratrylene (CTV) molecule as template. The challenge in making this template-assembled synthetic protein is to covalently link six unprotected peptides to the macrocycle. Model studies, using amino acids protected at their C-terminus, were directed towards finding an efficient method that could be used for linking unprotected peptides. This was achieved by first bromoacetylating the amino terminus of the amino acid models using bromoacetyl bromide in methylene chloride with potassium carbonate as base. These functionalised amino acid models were subsequently coupled to the six hydroxyl moieties on the cyclotriveratrylene template using potassium carbonate as base in degassed dimethylformamide. Thus we have succeeded in coupling six single amino acid esters to a C T V macrocycle in a 90% yield. This represents the first model of a hexasubstituted de novo protein. To successfully nucleate the hydrogen bonding pattern associated with p-sheet formation the template must possess a suitable inter-strand distance. This was investigated by looking for the presence of an internal hydrogen bonding network between the six amino acid strands on the template. This was done using N M R and IR spectroscopy and comparing the results to those obtained for single stranded analogues. An internal hydrogen bonding network was observed, indicating the suitability of the cyclotriveratrylene macrocycle as a template for modeling (ϐ-sheets.Science, Faculty ofChemistry, Department ofGraduat