13C CP MAS NMR and DFT study of vascular-selective drugs felodipine and amlodipine

Amlodipine besylate (AM) and felodipine (FL) have been studied in solid by C-13 CP MAS NMR and DFT. The spectra have been successfully reproduced from the theoretical calculations of the nuclear magnetic shielding tensors, using the GIAO method, after the SCF partial geometry optimisation. A very good correlation between the 13C chemical shifts and quadrupole coupling constants for chlorobenzene, AM and FL was obtained. 13C NMR as well as Cl-35 NQR do not differentiate between S and R enantiomers of AM and FL due to the symmetry of the 4-aryl ring comprising one (AM) or two (FL) chlorine atoms oriented in a perpendicular fashion over the 1,4-DHP ring. (c) 2008 Elsevier B.V. All rights reserved.