Chiral Recognition of Pharmaceuticals Having a Xanthine Skeleton by (−)-Epigallocatechin-3-O-gallate in Water

A mixture of pharmaceuticals having a xanthine skeleton, theophylline, proxyphylline, diprophylline and (−)-epigallocatechin-3-O-gallate (EGCg) in water created a sticky precipitates, which were thought to be 2 : 2 complexes of the pharmaceuticals and EGCg. The molecular capture ability of the pharmaceuticals having a xanthine skeleton by EGCg was estimated by the amount of the pharmaceuticals included in the precipitates of the complexes, and measured by the integrated value of proton signals in the quantitative 1H-NMR spectra. Based on changes in chemical shifts of proton signals of the pharmaceuticals with a xanthine skeleton in 1H-NMR spectra by adding standard amounts of EGCg, the xanthine skeleton of the pharmaceuticals was considered to exist in the hydrophobic space formed by the three aromatic A, B, B′ rings of EGCg, and a part of the proxyphylline and diprophylline side chains existed out of the hydrophobic space. In the 1H-NMR spectra of the mixture of (R)- and (S)-proxyphylline, (R)- and (S)-diprophylline and an equimolecular amount of EGCg, the N3-CH3 signal of (R)- and (S)-proxyphylline, and (R)- and (S)-diprophylline was clearly observed as two singlets. This suggested that EGCg recognized the chirality of proxyphylline and diprophylline in water.