Conversion of dipeptides and a tetrapeptide to macrocyclic ionophores by means of caesium aided ring closure of the N-2-chloroacetyl derivatives

Abstract

Three di-, (Gly)2, (Val)2 and (Leu)2, and one tetra-peptide, (Gly)4, have been acylated with 2-chloroacetyl chloride and the resulting products treated with Cs2CO3 in dimethylformamide (DMF) solution; (Gly)2 and (Leu)4 provided strained 9-membered rings whereas (Val)2 dimerized to the 18-membered ring.