New antimicrobial terpenoids and phloroglucinol glucosides from Syzygium szemaoense

Six new terpenoids (1-6) and two new phloroglucinol glucosides (7 and 8) were isolated from the extract of Syzygium szemaoense leaves. Among the isolates, compounds 1 and 2 (named syzygiumursanolides A and B) were unusual 28-norursane type triterpenoids with 19(18 -> 17)-abeo spirocyclic skeleton. And syzygiumone B (8) was rare ascorbyl-modified phloroglucinol glucoside. Their structures were elucidated on the basis of comprehensive 1D and 2D NMR, HRESIMS spectroscopic data analysis, as well as experimental and calculated ECD spectra and acid hydrolysis. Antimicrobial bioassay revealed that syzygiumursanolide D (4) displayed the most potent antifungal activities with MIC values ranging from 6.25 to 25 mu g/mL against a panel of fungi.