Novel quinic acid glycerates from Tussilago farfara inhibit polypeptide GalNAc-transferase

The discovery of a bioactive inhibitor tool for human polypeptide N -acetylgalactosaminyl transferases (GalNAc-Ts), the initiating enzyme for mucin-type O -glycosylation, remains challenging. In the present study, we identified an array of quinic acid derivatives, including four new glycerates ( 1 - 4 ) from Tussilago farfara , a traditional Chinese medicinal plant, as active inhibitors of GalNAc-T2 using a combined screening approach with a cell-based T2-specific sensor and purified enzyme assay. These inhibitors dose-dependently inhibit human GalNAc-T2 but did not affect O -linked N -acetylglucosamine transferase (OGT), the other type of glycosyltransferase. Importantly, they are not cytotoxic and retain inhibitory activity in cells lacking elongated O -glycans, which are eliminated by the CRISPR/Cas9 gene editing tool. A structure-activity relationship study unveils a novel quinic acid-caffeic acid conjugate pharmacophore that directs inhibition. Overall, these new natural product inhibitors could serve as a basis for developing an inhibitor tool for GalNAc-T2.