Amino-acids and peptides. Part XVII. Synthesis of cyclo-[(O-t-butyl)-L-seryl-β-alanyl-glycyl-(O-methyl)-L-β-aspartyl], and observations on the rearrangement of β-aspartyl peptide esters

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Abstract
The title fourteen-membered ring system was synthesised by cyclisation of the corresponding linear tetrapeptide p-nitrophenyl ester. When ring closure of the related tetrapeptide with terminal β-alanine and glycine residues was attempted, no cyclic peptide was formed; the aspartyl residue rearranged remarkably readily from β- to α-. The synthesis of several peptides containing β-aspartyl residues established that the sequence O-methyl-L-β-aspartyl(O-t-butyl)-L-seryl-β-alanyl particularly favoured this rearrangement.
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