Isolation and Characterization of Glycosidic Tyrosinase Inhibitors from Typhonium giganteum Rhizomes

A new hydrocinnamoyl glucoside, 1-O-(4-hydroxyhydrocinnamoyl)-β-D-glucopyranose (1), together with fifteen known glycosides, including two phenylethanoid glycosides (2–3), two cinnamoyl glycosides (4–5), six phenolic glycosides (6–11), one lignan glycoside (12) and four megastigmane glycosides (13–16) were isolated from a 95% EtOH extract of the Typhonium giganteum rhizomes. The sixteen glycosides were structurally characterized by NMR, HRESIMS, enzymatic hydrolysis and comparison with literature. Upon evaluating inhibitory activities of compounds 1–16 against mushroom tyrosinase at 25 μM, compounds 10 and 11 exhibited obvious inhibitory activities, with %inhibition values of 20.94±0.59%, 23.28±1.09%, respectively, with arbutin used as the positive control (26.21±0.58%).

Analysis of Antioxidant Polyphenols in Loquat Leaves using HPLC-based Activity Profiling

Leaves of Eriobotrya japonica (loquat) have been used in Traditional Chinese Medicine with beneficial effects in numerous diseases. Extracts from loquat leaves are rich in antioxidants, containing among others: triterpenes, sesquiterpenes, flavonoids, tannins, and megastigmane glycosides. However, there is no conclusive study revealing which of these compounds are the main bioactive principles. The goal of this study was to pinpoint compounds responsible for strong antioxidant activity. Eriobotryae folium was extracted and fractionated between solvents of increasing polarity. All extracts and fractions were screened for total polyphenols and tannins, and antioxidant activity was checked by DPPH, phosphomolybdenum and linoleic acid tests. The ethyl acetate fraction demonstrated the highest antioxidant activity and contained the largest amount of polyphenols. Applying HPLC-based activity profiling to localize antioxidants revealed that cinchonain IIb, as well as flavonoid glycosides such as hyperoside, isoquercitrin, kaempferol glycosides, quercetin-rhamnoside, as well as two tentatively identified protocatechuic acid derivatives are the main substances responsible for the strong antioxidant activity of the ethyl acetate fraction.