X-ray crystallographic and proton nuclear magnetic resonance studies of β-hydroxy-N-nitrosamines derived from α-amino acids and ephedrine

beta -Hydroxy-N-nitrosamines derived from L-leucine, L-valine, L-phenylalanine, D-phenylglycine and (IR,2S)-ephedrine have been synthesized and analyzed. These compounds all exhibit rotameric populations of (E)- and (Z)-stereoisomers that are a result of the barrier to rotation about the N-nitroso (N-N=O) group. A correlation is made between the X-ray crystallographic data of the N-nitroso-ephedrine derivative 6 and the H-1 NMR of the N-nitrosamines 4a-4d. From this comparison, the identities and ratios of (E)- and (Z)-rotamers were unambiguously assigned. Finally, the H-1 NMR also provides some insight into the conformational changes that occur when the nitrosamine rotamers interconvert. (C) 2000 Elsevier Science Ltd. All rights reserved.