Two New Norphenylpropanoid Glucosides and Hemipholin from the Flowers of Ononis vaginalis

Do extrato butanólico das flores de Ononis vaginalis Vahl. Symb. foram isolados dois novos glicosídeos norfenilpropanóides: 1 β-D-glicopiranosil-2-(4’hidroxifenil) ( E)-eteno ( trans-vaginosídeo) e 1 β-D-glicopiranosil-2-(4’hidroxifenil) ( Z)-eteno ( cis-vaginosídeo), e a flavanona C-glicosilada (+) 6-Cβ-D-glicopiranosil (2S) naringenina (hemifolina). As estruturas destes compostos foram determinadas por métodos químicos e espectroscópicos.


Introduction
The genus Ononis (Fabaceae) is represented in Egypt by eight species 1,2 .Several plants belonging to the genus are known to be used in the treatment of jaundice, urinary tract inflammations and kidney stones 3 .Recently, a number of alkyl resorcinols were isolated from Ononis species 4 .This class of naturally occurring compounds are glycerol-3-phosphate dehydrogenase inhibitors 5 and cleave DNA through selective strand scission 6 .Previous investigation of the non polar ether fractions of the flowers of Ononis vaginalis resulted in the isolation of seven flavonoids 7.Among these, eupatilin is known to have a cytotoxic action against human carcinoma of nasopharynx 8 and trifolin proved to have an insect growth regulator like action 9 .However, the more polar butanol fraction was not subjected to more detailed investigation.

Results and Discussions
Compound 1 was isolated in the form of a yellowish gum.The UV λmax absorption at 263 nm indicated its aromatic nature.In the 1 H-NMR of 1 (Table 1), the two doublets at 7.08 and 7.46 ppm (J = 8.4 Hz, 2H each) as well as their correlated carbons (base on a HETCOR experiment) at 117.7 and 130.4 ppm respectively, (see experimental) were diagnostic for a p-substituted benzene ring.Another two doublets at 6.39, 7.37 ppm (J =16 Hz, 1H each) and their correlated carbons at 131.0 and 141.9 ppm were assigned for conjugated methines with their protons having the transorientation 10 .The chemical shifts of the carbons equivalent to C-1 in cinnamic acid and its derivatives is usually around 115 ppm 11 , while the 141.9 ppm resonance in 1 indicates that C-1 is oxygenated.The quaternary carbon resonances at 136.1 and 158.5 ppm were in complete agreement with carbon and oxygen substitutions on the aromatic system.Both 1 H-and 13 C-NMR showed signals diagnostic for β-D-glucopyranoside.FABMS showed an [M + +H] at 299 m/z (100%) consistent with the molecular formula C14H18O7 as indicated from 1 H, 13 C-NMR and DEPT experiments.Positive reaction to FeCl3, 12 nm UV bathochromic shift after the addition of NaOMe and the instability of the enol form (if the sugar part was attached to the phenolic OH) all support the position of glucose to be at C-1. Acid hydrolysis of 1 generated β-D-glucose (identified by TLC comparison with authentic material) and an aglycone identified as (4-hydroxyphenyl)-acetaldehyde through comparing its 1 H-NMR data with those in the literature 12 .As in cyanogentic glycosides; the glycosidic linkage is the main stabilizing factor for the aglycone.Consequently, hydrolysis of 1 resulted in the formation of the stable (4-hydroxy-phenyl)-acetaldehyde (keto form) rather than the unstable enol form.
Compound 2 showed essentially similar spectral characteristics to those of 1 (Table 1 and experimental).The major significant differences are in the J1,2 value (16 Hz in 1 and 12 Hz in 2) as well as H-1 and H-2 chemical shift (6.39, 7.37 ppm in 1 and 5.94, 6.33 ppm in 2) indicating that 2 is the cis -isomer of 1 10 .
Compound 3 was identified as hemipholin (6-C-β-Dglucopyranosyl (2S) naringenin) through comparison of its data (see experimental) with those in the literature 13,14 as well as its positive reaction with Gibb's reagent eliminating the possibility of the sugar to be attached to C-8 15 .The assignment of the unreported 13 C-NMR data for 3 were performed based on HETCOR experiments as well as comparison with the data of 6,8-di-C-β-D-glucopyranosyl (2S) naringenin 16 .

General procedure
The melting point was determined using a Griffin melting point apparatus and was uncorrected.UV spectra were obtained in MeOH on a Pye Unicam Sp8-100 spectrometer.CD spectrum was recorded using a Jasco J-720 spectropolarimeter.NMR spectra were measured with a Bruker Ac-300 spectrometer at 300 and 75 MHz for 1 H-and 13 C-NMR respectively.Proton and carbon chemical shifts are reported in parts per million (ppm) relative to residual undeuterated solvent.The carbon chemical shifts for 1 in D2O are reported relative to C-6 of glucose at 61.5 ppm.FAB and Electrospray mass spectra were recorded using a Quattro-SQ mass spectrometer.β-D-Glucose was obtained from Sigma Chemical Co.