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Three New Caffeoyl Glycosides from the Roots of Picrorhiza Scrophulariiflora

From the underground parts of Picrorhiza scrophulariiflora, three new caffeoyl glycosides, scrocaffeside A-C (1-3), together with two caffeic acid derivates, 4-O-β-D-glucopyranosyl caffeic acid (4) and 4-methoxycaffeic acid (5) and a phenylethanoid glycoside, scroside D (6), were isolated. Their structures were elucidated on the basis of chemical and spectroscopic evidence and comparisons with literature data of related compounds.


Introduction
The plant Picrorhiza scrophulariiflora (Scrophulariaceae) grows in the high altitude regions (over 4400 m) in the southeast of Tibet and the northwest of Yunnan in China. The roots of this plant are used in traditional Chinese medicine for the treatment of damp-heat dysentery, jaundice and steaming bone disorder [1]. Previous phytochemical investigations of this plant led to the isolation of terpenoids [2,3,4], iridoid glycosides [5,6,7], phenolic glycosides and phenylethanoid glycosides [8][9][10][11][12][13][14]. Here we report the isolation and characterization of three new caffeoyl glycosides 1-3, as well as three known compounds.
The 1 H-NMR spectrum of 1 (Table 1) exhibited the characteristic signals of two (trans)-caffeoyl units and two β-glucose unites [anomeric protons at δ H 5.50 (1H, d, J = 8.0 Hz) and 4.78 (1H, d, J = 6.8 Hz)]. Twenty nine signals were exhibited in the 13 C-NMR spectrum. The carbon resonances at δ C 115.8 represent two methines, based on the HMQC experiment. Comparison of the 13 C-NMR data with those of 4 also suggested the presence of two glucopyranosyl and two (trans)-caffeoyl moieties [15].
The presence of the glucopyranosyl and (trans)-caffeoyl moieties were further confirmed by the acid hydrolysis of 1, which resulted in a release of glucose and caffeic acid, identified by TLC comparison with the authentic samples. The configuration of the glucopyranosyl was assigned to be β-Daccording to the procedure of Oshima, Yamauchi and Kumanotani [18] and the coupling constant of the anomeric proton [19].

was concluded to be E-caffeoyl-6-O-[4-O-(β-D-glucopyranosyl) E-
caffeoyl]-β-D-glucopyranoside, for which the trivial name scrocaffeside A is proposed.  (Table 1). Notable differences were signals from a (trans)-caffeoyl moiety in 2. Comparison of the NMR spectra of 2 and 1 also showed a conspicuous deshielding of H-1′′ (Δδ H 0.64) and C-1′′ (Δδ C 7.1) of the central glucose core (Glc 1), indicating the diferent glycosidic linkage between the glucopyranosyl moiety and caffeoyl moiety 1. In the HMBC spectrum correlations between H-1′′ (Glc 1-1) and C-4 demonstrated that the glucose 1 attached at C-4 of caffeoyl moiety 1. Thus, the structure of compound 2 was established as  1 H-NMR and the 13 C-NMR spectroscopic data of 3 together with the chemical test results were very similar to those of 1, suggesting a close relationship. Structural assessment of 3 was accomplished using a combination of NMR techniques, along with comparisons to the assignments of analogues 1 and 2.
The 13 C-NMR spectra experiments gave a total of 29 resonance lines, of which 12 signals (δ C 102~60) could be assigned to three glucosy moieties by the aid of DEPT and HMQC experimrnts. Analysis of 1 H-NMR, TCOSY, 13 C-NMR, HSQC and HMBC spectra of 3 indicated again the glycosidic linkages between the glucopyranosyl and caffeoyl moieties. The connections between glucose 1, glucose 2 and the two caffeoyl moieties of 3 shared the same pattern with those of 1. The glucose 3 should be linked to C-4, as indicated by the HMBC crosspeak between this carbon (δ C 147.7) and the anomeric proton (δ H 4.80).

Experimental
General UV spectra were recorded on a Milton Roy Spectronic 1201 spectrophotometer, and FTIR spectra were measured on a Perkin-Elmer 157G infrared spectrophotometer. Optical rotations were obtained using a Perkin-Elmer 241-MC polarimeter. 1 H-NMR (400 MHz) and 13 C-NMR (100 MHz) spectra were obtained on a Bruker AV400 spectrometer with DMSO-d 6

Acid hydrolysis of 1, 2 and 3
A solution of the compound (8 mg) in 2 N TFA (3 mL) was refluxed at 100°C for 3 h. The reaction mixture was extracted with EtOAc. The EtOAc extract was proven to contain caffeic acid by direct TLC comparison with authentic samples. D-Glucose was found as the only sugar present in the water part following the procedure of Oshima, Yamauchi and Kumanotani [18].