Benzophenones and biflavonoids from Rheedia edulis

Abstract

Two new polyisoprenylated benzophenones, 32-hydroxy-ent-guttiferone M (1) and 6-epi-guttiferone J (2), along with seven known compounds, 6-epi-clusianone (3), guttiferone A (4), xanthochymol (5), guttiferone E (6), isoxanthochymol (7), (+)-volkensiflavone (8), and (+)-morelloflavone (9), were identified from the seeds and rinds of Rheedia edulis. Compounds 1-3 and 5-9 have been isolated and identified from this species for the first time. The structures of the new compounds were elucidated mainly by analysis of their 1D and 2D NMR spectroscopic data, and their absolute configurations were determined by comparison of their experimental optical rotation and electronic circular dichroism measurements with those values predicted by DFT calculations. Compound 1 showed significant antioxidant activity in both DPPH and ABTS free radical scavenging assays, whereas compound 2 was inactive.

Figure 1

New compounds isolated from R. edulis

Figure 2

Key COSY, HMBC, and NOESY correlations of 1 and 2

Figure 3

DFT B3LYP/6-31G++(d,p) geometry optimized conformers of 1 (1a-1c) and 2 (2a-2c) at 298 K and 1 atm, accounting for ca. 90% of the conformational population of each compound

Figure 4

Calculated ECD spectra of 1 (A, red) and 2 (B, red) and its experimental (black) at the B3LYP/6-31G++(d,p) level in MeOH