Antioxidative Flavonoids from Cleistocalyx operculatus Buds

Abstract

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,...

Flavonoids from Cleistocalyx operculatus Buds and their Cytotoxic Activity

“…[10][11][12] In our previous study, 3'-formyl-4,4',6'-trihydroxy-2'-methoxy-5'-methylchalcone, 3'-formyl-4,6'-dihydroxy-2'-methoxy-5'-methylchalcone 4'-O-β-D-glucopyranoside, (2S)-8-formyl-6-methylnaringenin, and (2S)-8-formyl-6-methylnaringenin 7-O-β-D-glucopyranoside were isolated from EtOAcsoluble fraction and their radical scavenging activities were reported. 13 In the present study, further phytochemical investigation of the water-soluble fraction of this plant led to the isolation of a new flavonoid glycosides (1), and six known compounds (2-7). Details of the isolation, structural determination and cytotoxic activity are described herein.…”

“…NMR experiments were conducted on a Varian Unity INOVA 400 spectrometer. 1 H and 13 C NMR spectra were recorded at 400 and 100 MHz, respectively, and tetramethylsilane was used as the internal standard. FAB-MS and HR-FAB-MS analyses were performed on a Micromass QTQF2 mass spectrometer.…”

“…In addition, the 1 H NMR spectrum showed seven characteristic signals typical of a sugar moiety, including a peak at δ 6.41 (1H, d, J = 7.6 Hz) for an anomeric proton (H-1''). The 13 C NMR and DEPT spectra of 1 showed 23 signals, including nine oxygenated carbons, one carbonyl carbon at δ 179.6 (C=O), two methoxy carbons, and six carbon signals between δ 62.4 and 104.6, which could be assigned to a sugar unit. The full NMR assignments and connectivities of 1 were determined by HMQC and HMBC spectroscopic data analysis.…”

VB1 Promoted Green Synthesis of Chalcones and Its Neuroprotection Potency Evaluation

“…Inspired by this phenomenon, to increase the yield of 3a, the condensation reaction was carried out under similar conditions in a mixed solvent of EtOH-H2O. To our delight, the yields of 3a were increased substantially (78-84%) when using EtOH-H2O as a solvent (Table 1, entries [7][8][9][10][11], and EtOH-H2O (v/v, 1:1) gave the best result (Table 1, entry 8). Furthermore, the recyclable character of VB1 was also investigated.…”

“…2 ,4 -Dihydroxy-6 -methoxy-3 ,5 -dimethylchalcone (3f) (Figure 1), featuring a 3,5-dimethylsubstitution ring A, is the major active component in the buds of Cleistocalyx operculatus [5]. It has been shown to have antidrug efflux [6,7], antioxidant [8][9][10], antitumor [11][12][13], and antivirus effects [14] and antiacute liver injury [4]. Due to the poor accessibility of this material (0.69 g per 5 kg of dried flower buds) [15], the organic synthesis to get greater quantities of 3f was demanded.…”