Both syn- and anti-4-amido-2,4-dimethylbutyric acid derivatives 5 and 6 were found to populate a conformation in which the amido group is gauche to the main chain of the molecule. In the anti series (6) a single conformation predominates, in which the acid carbonyl group is also gauche to the main chain. In the syn series (5) two local conformers prevail about the C-2–C-3 bond.