A new norlignan glycoside from Cestrum diurnum L.

From the methanolic extract of Cestrum diurnum L. leaves, a new 9-norlignan glucoside (cestrumoside) ( 1 ) was isolated in addition to six known glycosides ( 2-7 ). The structures of the isolated compounds were determined on the bases of NMR spectral analysis ( 1 H NMR, 13 C NMR, HSQC, HMBC, COSY) in addition to MS and CD to infer the stereochemistry of the compounds.


Results and Discussion
The aerial parts of Cestrum diurnum L. were collected from the plants cultivated in the Experimental Station of Faculty of Agriculture, Assiut University, Assiut, Egypt, in December 2004.The plant was kindly authenticated by Prof. Naeem El-Keltawy, Prof. of Horticulture, Faculty of Agriculture, Assiut University, Assiut, Egypt.A voucher sample was kept in the Herbarium of Pharmacognosy Department, Faculty of Pharmacy, Assiut University, Assiut, Egypt.
The position of the hydroxyl groups in compound 1 was confirmed from the HMBC analysis (Fig. 2a,b).
The relative trans configuration between the methine protons at C-7 and C-8; C-8 and C-8′; C-8′ and C-7′ were established by the 2D ROESY spectral analysis.Additionally, the configuration of C-7 and C-7′ were characterized as 7S and 7′S, respectively by the CD spectrum [10][11] .
To the best of our knowledge, this is the first report about the isolation of a 9-norlignan glycoside derivative from a natural source.
In conclusion, compound 1 is a new natural product, while known compounds (2-7) are reported here for the first time from the genus Cestrum.

Experimental Section
General Procedures.Optical rotations were measured on Union PM-101 automatic digital polarimeter.FT−IR spectra were recorded on a Horiba FT-710 spectrophotometer.HR-FABMS was recorded with JEOL JMS-SX 102 spectrophotometer. 1 H NMR and 13 C NMR spectra were measured on JEOL JNM A400 spectrophotometer (400 and 100 MHz, respectively) using TMS as an internal standard.Column chromatography was performed on Kieselgel 60 (60-230 mesh, Merck), Lichroprep RP-18 (Merck) and Diaion HP-20 (Mitsubishi).Preparative HPLC was carried out on columns of Polyamine and ODS (each 150x20 mm i.d., YMC) with JASCO PU-1580 Pump and TOYO SODA RI-8000 refractive index detector.TLC was carried out with silica gel 60 pre-coated plates F-254s.

Extraction and Isolation
The air-dried powdered aerial parts of Cestrum diurnum (900 g) was exhaustively extracted with methanol at room temperature.The methanolic extract was concentrated under reduced pressure till dryness.The residue (80 g) was suspended in water and fractionated with CHCl 3 .The aqueous layer, after evaporation to a minimum volume, was subjected to a Diaion HP-20 CC and eluted with water, MeOH and finally with acetone.The residue of the MeOH eluate (22 g) was subjected to a silica gel CC using CHCl 3 -MeOH-H 2 O (80: 20: 2 to 65: 35: 5) gradient as eluting systems to give four fractions (Fractions I, II, III and IV).From fraction IV, the steroidal saponins cesdiurins I-IV were isolated using prep.HPLC with polyamine column and 75%, 77% and 80% MeCN as a mobile phase where cesdiurin IV, III, I and II were obtained respectively as previously reported 8 .On the other hand, Fraction II (1.3 g) was chromatographed on RP-18 CC using 30% to 70% MeOH gradient as solvent systems, where 13 sub-fractions were obtained (F-1 to F-13).F-2 (63 mg) was chromatographed on prep.HPLC using ODS column and 20% MeCN as a mobile phase where compound 3 (38 mg) was obtained.F-5 (36 mg) was subjected to prep.HPLC using polyamine column and 80% MeCN as a solvent system to afford compound 7 (8 mg).F-6 (115 mg) was chromatographed on prep.HPLC using Polyamine column and 82% MeCN as a mobile phase where compounds 2 (9 mg), 5 (18 mg) and 6 (15 mg) were isolated.F-10 (48 mg) was chromatographed on prep.HPLC using Polyamine column and 85% MeCN as a mobile phase where compound 4 (22 mg) was obtained.F-12 (33 mg) was subjected to prep.HPLC using ODS column and 25% MeCN as a solvent system to afford compound
2a. H-H COSY and important HMBC correlations of compound 1.