Phloroglucinol-derived lipids from the leaves of Syzygium cumini and their neuroprotective activities.

Abstract Based on the typical HPLC-UV-MS profiles and characteristic 1H NMR signals, twelve new phloroglucinol-derived lipids (1−12), featuring a long linear aliphatic side chain, together with three known ones (13–15) were isolated from the ethanol extract of the leaves of Syzygium cumini. Their structures were elucidated on the basis of extensive NMR spectroscopic analyses and mass spectrometric data. Compounds 1–5 characterize an enolizable β,β'-tricarbonyl motif with a cyclohexa-3,5-dien-1-one core that is hitherto undescribed in phloroglucinol-derived lipids. Compounds 4 and 10–12 are novel phloroglucinol-derived lipids containing an uncommon methylene interrupted trans double bond in their polyunsaturated aliphatic side chains. A polyketide biogenetic pathway for those phloroglucinol-derived lipids was also proposed. In addition, the isolates were evaluated for their neuroprotective activities against oxygen-glucose deprivation and re‑oxygenation (OGD/R)-induced Neuro-2a cell injury. Notably, compounds 1, 5, and 10–12 significantly improved viability of Neuro-2a cells after OGD/R damage.