Postprandial hyperglycemic excursion has been implicated as an independent risk factor for cardiovascular disease, not only among diabetes patients, but also among other pre-diabetic subjects in the general population with pre-diabetic states. 1,2) Therefore, sustained postprandial hyperglycemia (PPHG) also results in postprandial oxidative stress (PPOS). PPOS is characterized by an increased susceptibility of the organism toward oxidative damage after consumption of a meal rich in lipids and/or carbohydrates, and is associated with a higher risk for atheroscleroses, diabetes and obesity. 3) Hence, combinations of agents that reduce PPHG and PPOS are becoming therapeutics of interest to combat diabetes and its related complications. a-Glucosidase inhibitors are used in the management of non-insulin-dependent diabetes mellitus, acting by reversible inhibition of the gastrointestinal sucrases, glucoamylase, dextrinase, maltase, and isomaltase. These enzymes normally catalyze the conversion of dietary starch and sucrose into absorbable monosaccharides; therefore, enzyme inhibition delays and reduces the peak of postprandial blood glucose. 4) In a recent study, it was reported that oral administration of the Acer extract to mice caused their blood glucose level to be lower than control at 30 min. 5,6) Additionally, it was suggested that the effect is also involved in a-glucosidase inhibitory activity, and ginnalins B (3) and C (4) from A. pycnanthum were found to be a portion of the active compounds. 7) In this study, we report the isolation and structure determination of a new compound, pycnalin (1), and investigated of its a-glucosidase inhibitory and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activities.
Results and DiscussionIsolation and Structure Elucidation The leaves of A. pycnanthum were extracted with hot water. The hot water extract was partitioned among EtOAc, BuOH, and H 2 O and ginnalin A (2, 4.4%) was obtained from the EtOAc-insoluble portion. The BuOH-soluble portion was separated by octadecylsilyl ( The molecular formula of pycnalin (1), C 13 H 16 O 9 , was established by high resolution-electrospray ionization-mass spectra (HR-ESI-MS) [m/z 339.0949 (MϩNa) ϩ , Dϩ0.7 mmu]. IR spectrum implied the presence of hydroxyl (3423 cm Ϫ1 ) and ester carbonyl (1699, 1237 cm Ϫ1 ) groups. The gross structure of 1 was deduced from detailed analyses of the 1 H-and 13 C-NMR data (Table 1) aided by 2D-NMR ( 1 H-1 H correlation spectroscopy (COSY), 1 H-detected heteronuclear multiple quantum coherence (HMQC), and heteronuclear multiple bond connectivity (HMBC)). The 1 H-NMR spectral data showed nine proton signals. A singlet at d H 7.13, integrating for two protons, was attributed to the two aromatic protons of a galloyl group. Eight proton signals at d H 3.40-4.52 suggested the presence of a structure similar to that of a sugar moiety. The 13 C-NMR and distortionless enhancement by polarization transfer (DEPT) spectra of 1 indicated the presence of two oxymethylene carbons, four oxymethine carbons,...
