13C CP (cross-polarization) MAS (magic angle spinning) NMR and GIAO-CHF calculations of buspirone analogues part 1.: 3a,4,7,7a-Tetrahydro-2-{4-[4-(2-quinolinyl)-1-piperazinyl]butyl}-4,7-ethane-1H-isoindole-1,3(2H)-dione hydrochloride and hydrobromide

C-13 CP (cross-polarization) MAS (magic angle spinning) solid state NMR spectra of buspirone analogue 3a,4,7,7a-tetrahydro-2-{4-[4-(2-quinolinyl)-1-piperazinyl]butyl}-4,7-ethane-1H-isoindole-1,3(2H)-dione were recorded. In the spectra of hydrochloride and hydrobromide, two sets of signals appeared, in agreement with single crystal X-ray diffraction data indicating that in each of the salts two independent cations were present in the crystal unit. The largest shielding differences of 3.2-4.6 ppm between two sets of signals were found for quinoline aromatic carbons C3 and C2. Ab initio calculations of the carbon and nitrogen shielding constants were performed with the use of the GIAO-CHF method for structural fragments: N-butylsuccinimide, quinoline-(N-methyl) piperazine hydrochloride and hydrobromide. Linear correlations between theoretical and solid state results were obtained, thus enabling a reasonable assignment of carbon resonances of the conformations present in the solid state. Due to the fast dynamics in solution, the carbon chemical shifts corresponded to the averaged values of the forms present in the solid state. (C) 1998 Elsevier Science B.V. All rights reserved.