title: 13C-nuclear magnetic resonance investigations of xanthine and some of its N-methylated derivatives.
mesh_terms: D002110:Caffeine / Q000032:analysis*; D002247:Carbon Isotopes; D009682:Magnetic Resonance Spectroscopy; D008745:Methylation; D011522:Protons; D013805:Theobromine / Q000032:analysis*; D013806:Theophylline / Q000032:analysis*; D014970:Xanthines / Q000032:analysis*
chemical_list: D002247:Carbon Isotopes; D011522:Protons; D014970:Xanthines; D002110:Caffeine; D013806:Theophylline; D013805:Theobromine