A new dihydrofurocoumarin from the fruits of Pandanus tectorius Parkinson ex Du Roi

Abstract From the fruit of Pandanus tectorius Parkinson ex Du Roi, one new dihydrofurocoumarin, named pandanusin A (1) and 15 known compounds, including one furanocoumarin (2), two coumarins (3, 4), four lignans (5–8), one neolignan (9), two flavonoids (10, 11), three phenolics (12–14), one monoglyceride (15) and one monosaccharide (16) were isolated by various chromatography methods. Among them, compounds (3–5) were obtained from the Pandanus genus for the first time and compounds (9–14, 16) were reported from this species for the first time. Their structures were elucidated by HR–ESI–MS, NMR 1D and 2D experiments and comparison with previous reported data. The α-glucosidase inhibitory activity of all compounds was measured. The isolated compounds (1–12, 14) showed better α-glucosidase inhibitory activity (IC50 = 42.2, 36.5, 84.7, 73.2, 40.8, 26.7, 76.5, 33.8, 68.1, 14.4, 22.1, 81.5, 43.8 μM, respectively) than the standard drug acarbose (IC50 = 214.5 μM).


General experimental procedures
The optical rotations were determined on a Krüss-optronic gmbH polarimeter equipped with a sodium lamp (589 nm). The HR-ESI-MS was performed on a Bruker MicrOTOF-QII spectrometer. The 1 H NMR (500 MHz), 13 C NMR (125 MHz), DEPT, COSy, HSQC and HMBC spectra were recorded on a Bruker AM500 FT-NMR spectrometer using tetramethylsilane as internal standard. CD spectrum were recorded on Jasco J-815 CD spectropolarimeter. Column chromatography was carried out using Merck Silica gel normal-phase (230-240 mesh) and reversed-phase C 18 (Merck). Analytical thin-layer chromatography was carried out in silica gel plates (Merck DC-Alufolien 60 F 254 ). Compounds were visualised by spraying with aqueous 10% H 2 SO 4 and heating for 3-5 min.

Plant material
The fruits of P. tectorius were collected in Binh Thuan province, Vietnam in February 2013 and authenticated by Mr Dang Van Son, Institute of Tropical Biology, Vietnam Academy of Science and Technology. A voucher specimen (No PT-125) was deposited in Bioactive Compounds Laboratory, Institute of Chemical Technology, Vietnam Academy of Science and Technology, Vietnam.

α-Glucosidase inhibition assay
The inhibitory activity of α-glucosidase was determined according to the modified method of Kim et al. (2008) and 3 mM p-Nitrophenyl-α-d-glucopyranoside (25 μL) and 0.2 u/mL α-glucosidase (25 μL) in 0.01 M phosphate buffer (pH 7) were added to the sample solution (625 μL) to start the reaction. Each reaction was carried out at 37 °C for 30 min and stopped by adding 0.1 M Na 2 CO 3 (375 μL). Enzymatic activity was quantified by measuring absorbance at 401 nm. One unit of α-glucosidase activity was defined as amount of enzyme liberating p-nitrophenol (1.0 μM) per min. The IC 50 value was defined as the concentration of α-glucosidase inhibitor that inhibited 50% of α-glucosidase activity. Acarbose, a known α-glucosidase inhibitor, was used as positive control.

Conclusion
This phytochemical investigation on the ethyl acetate extract of the fruit of P. tectorius has led to the isolation and structure elucidation of one new dihydrofurocoumarin (1) and 15 known compounds (2-16). This study indicated that phenolic compounds are the main components of the fruits of P.tectorius. Moreover, we investigated the inhibitory activity against enzyme α-glucosidase of isolated compounds. As a result, the isolated compounds except for 13, 15 and 16 showed promoting effects on enzyme α-glucosidase. via inhibition of carbohydrate-hydrolysing enzyme α-glucosidase, the isolated compounds from this plant retarded absorption of glucose known to be beneficial in therapy in type-II diabetes. In conclusion, this species can be completely appropriated with the good antidiabetic drug.

Disclosure statement
No potential conflict of interest was reported by the authors.

Funding
This work was supported by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) [grant number 104.01-2012.72].