The 13C NMR resonances corresponding to the C-Me group of C-6 and/or C-8 C-methylated-flavonoids absorb between 6.7–10.0 ppm and typically between 6.7–8.7 ppm. A comparative 13C NMR study reflects that the 13C NMR chemical shifts reported for 6-hydroxy-5-methyl-3′,4′,5′-trimethoxyaurone-4-O-α-L-rhamnoside from Pterocarpus santalinus and 8-C-methyl-5,7,2′,4′- tetramethoxyflavanone from Terminalia alata are inconsistent with the assigned structures, and therefore need reconsideration.
Structural Analysis of Glycans by NMR Chemical Shift Prediction