N-Methylation of adamantane-substituted oxalamide unit affects its conformational rigidity: A skew conformation of the oxalamide bridge

The synthesis of adamantane functionalized retropeptides, N,N′-bis(2-adamantyl-2-carboxylic acid methyl ester)oxalamide (1) and N-methyl-N,N’-bis(2-adamantyl-2-carboxylic acid methyl ester)oxalamide (2), as well as the influence of the N-methylation on the conformational preferences of oxalamide group are described. In the solid state the oxalamide group of 1 is planar while in the retropeptide 2 adopts a skew-conformation.