NotesCleistocalyx operculatus (ROXB.) MERR. et PERRY (Myrtaceae) is a large green tree that grows in rural areas of North Vietnam where it is commonly called Voi. The flower buds (name as Nu Voi) and leaves (La Voi) have been used to make a beverage since ancient times.1) It is also a wellknown medicinal plant whose buds are commonly used as an ingredient for tonic drinks in Southern China.2) The water extract of C. operculatus buds has been shown to increase the contractility and decrease the frequency of contraction in an isolated rat heart perfusion system.3) It showed strong protective effects on lipid peroxidation in rat liver microsomes, and the H 2 O 2 -induced trauma of rat pheochromocytima (PC12) cells. 4) C. operculatus extract showed inhibitory activity against the a-glucosidase, rat-intestinal maltase, and sucrase activities. It is also considered a promising material for preventing and treating diabetes. 5) Previous phytochemical attention characterized the oleanane-type triterpenes, 6,7) and flavonoids.2) Analysis of its leaf oil by gas chromatography (GC) and chromatography/mass spectrometry (GC/MS) has also been reported. 8) Chalcone compounds from this plant possess antioxidant and anticancer activities. [9][10][11] In this report, we describe the isolation and structural determination of four new flavonoids (1-4), and evaluate their DPPH radical scavenging activity.
Results and DiscussionThe MeOH extract of the buds of C. operculatus was partitioned into hexane-, EtOAc-, and BuOH-soluble fractions. Chromatographic purification of the EtOAc-soluble fraction led to the isolation of four compounds (1-4) (Fig. 1).Compound 1 was isolated as a yellow amorphous powder. In the positive ion mode, electrospray ionization mass spectrometry (ESI-MS), a quasimolecular ion peak at m/z 329 [MϩH] ϩ was observed, and high-resolution ESI-MS (HR-ESI-MS) analysis indicated an ion peak at 329.1813 which corresponded to the molecular formula, C 18 H 16 O 6 . The infrared (IR) absorptions at 3452, 2873 and 2758 cm Ϫ1 showed the presence of hydroxy and aldehyde groups. The 1 H nuclear magnetic resonance (NMR) spectrum of 1 indicated the presence of methoxy group at d 3.82 (3H, s), aldehyde group at d 10.41 (1H, s), and methyl group at d 2.04 (3H, s). Proton signals were also observed at d 7.54 (2H, dd, Jϭ8.5, 2.0 Hz, H-2, 6) and d 6.94 (2H, dd, Jϭ8.5, 1.8 Hz, H-3, 5) and assigned to 4-substituted phenyl in the B ring of chalcone.12) An AB spin system with Jϭ15.8 Hz at d 7.73 and 7.78 indicated the presence of protons of an a,b-unsaturated ketone moiety.2) The 13 C-NMR and distortionless enhancement by polarization transfer (DEPT) spectrum of 1 showed 18 signals, including three oxygenated aromatic carbons at d 165.7 (C-2Ј), 169.8 (C-6Ј) and 160.7 (C-4), one carbonyl carbon at d 193.8 (CϭO), one aldehyde carbon at d 191.7 (3Ј-CHO), one methyl carbon at d 10.6 (5Ј-CH 3 ), and four aromatic carbons at d 130.2 (C-2, 6) and 118.3 (C-3, 5). The 1 H-and 13 C-NMR spectra (Table 1) were very similar to those of 3Ј-formyl-4Ј,...