13C CPMAS NMR studies and DFT calculations of triterpene xylosides isolated from Actaea racemosa

13C CPMAS NMR spectra of four triterpene glycosides: cimigenol xyloside (1), 26-deoxyactein (2), cimicifugoside H-1 (3) and 24-acethylhydroshengmanol xyloside (4) were recorded and analyzed to characterize their solid-state structure. Experimental data were supported by theoretical calculations of NMR shielding constants with the GIAO/6-31G**-su1 approach. A number of methods for the conformational search and a number of functionals for the DFT calculations were applied to (1). The best method was proven to be MMFF or MMFFAQ for the conformational search and the PBE1PBE functional for the DFT calculations. Extra calculations simulating C16O⋯HOH hydrogen bond yield the isotropic shielding closer to the experimental solid-state value. For all the compounds CP kinetics parameters were calculated using either the I-S or the I-I*-S model. The analysis of CP kinetics data for methyl groups revealed differences in the T2 time constant for two methyl groups (C29 and C30) linked at C4.