Constituents from Litsea japonica leaves and their inhibitory effects on ages formation and aldose reductase

In our continuing efforts to identify effective naturally sourced agents for diabetic complications, two new (1 and 2) and 15 known compounds (3 – 17) were isolated from the 80% EtOH extract of Litsea japonica leaves. The structures of the new compounds were established by spectroscopic and chemical studies. These isolates (1 – 17) were subjected to an in vitro bioassay evaluating their inhibitory activity on advanced glycation end-product (AGE) formation and rat lens aldose reductase (RLAR) activity. Of the tested compounds, flavonoids (4, 6 – 8, 11, and 12) markedly inhibited AGE formation with IC₅₀ values of 7.42 – 72.05µM, compared with that of a positive control, aminoguanidine (IC₅₀= 975.9µM). In the RLAR assay, consistent with the inhibition of AGE formation, flavonoids (4, 6 – 8, 11, and 12) exhibited considerable inhibition of RLAR with IC₅₀ values of 1.10 – 12.5µM.