Structurally Diverse Phenolic Amides from the Fruits of Lycium barbarum with Potent α-Glucosidase, Dipeptidyl Peptidase-4 Inhibitory, and PPAR-γ Agonistic Activities

A total of nine new phenolic amides (1-9), including four pairs of enantiomeric mixtures (3-5 and 8), along with ten known analogues (10-19) were identified from the fruits of Lycium barbarum using bioassay-guided chromatographic fractionation. Their structures were elucidated by comprehensive spectroscopic and spectrometric analyses, chiral HPLC analyses, and quantum NMR, and electronic circular dichroism calculations. Compounds 5-7 are the first example of feruloyl tyramine dimers fused through a cyclobutane ring. The activity results indicated that compounds 1, 11, and 13-17 exhibited remarkable inhibition against α-glucosidase with IC50 of 1.11-33.53 μM, 5-150 times stronger than acarbose (IC50 = 169.78 μM). Meanwhile, compounds 4a, 4b, 5a, 5b, 13, and 14 exerted moderate agonistic activities for peroxisome proliferator-activated receptor (PPAR-γ), with EC50 values of 10.09-44.26 μM. Especially,compound 14 also presented inhibitory activity on dipeptidyl peptidase-4 (DPPIV), with an IC50 value of 47.13 μM. Furthermore, the banding manner of compounds 14 and 17 with the active site of α-glucosidase, DPPIV, and PPAR-γ was explored by employing molecular docking analysis.