Eudesmane-type sesquiterpene glycosides: sonneratiosides A–E and eudesmol β-d-glucopyranoside from the leaves of Sonneratia alba

Five eudesmane-type sesquiterpene glycosides, named sonneratiosides A–E ( 1 – 5 ), were isolated from the leaves of Sonneratia alba (Lythraceae). The aglycone of sonneratioside A was identified as cryptomeridiol also known as proximadiol. X-ray crystallographic analysis of sonneratioside A confirmed its structure and its absolute stereochemistry. Eudesmol β - d -glucopyranoside ( 6 ) was also isolated from nature for the first time. The tyrosinase inhibitory activity was assayed for the new compounds together with seven known compounds. Among them, arbutin ( 12 ) showed the expected activity and luteolin 7- O -rutinoside ( 10 ) showed comparable activity to arbutin.