13C and 15N chemical shift anisotropy of ampicillin and penicillin-V studied by 2D-PASS and CP/MAS NMR

The principal values of the chemical shift tensors of all C-13 and N-15 sites in two antibiotics, ampicillin and penicillin-V, were determined by 2-dimensional phase adjusted spinning sideband (2D-PASS) and conventional CP/MAS experiments. The C-13 and N-15 chemical shift anisotropies (CSA), and their confidence limits, were evaluated using a Mathematica program. The CSA values suggest a revised assignment of the a-methyl C-13 sites in the case of ampicillin. We speculate on a relationship between the chemical shift principal values of many of the C-13 and N-15 sites and the beta-lactam ring conformation. (C) 1998 Academic Press.