This Issue is Dedicated to the Memory of Professor Ivano Morelli

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1090 Natural Product Communications Vol. 1 (12) 2006 Vassallo et al. the methanol extract was the active one, while all the other residues were inactive (data not shown). Subsequent fractionation and analysis of the methanol extract led to the isolation and structural characterization of three new flavonoids (1-3), together with some known compounds, including five flavonoids (4-7 and 9), one phenolic derivative (8), and three megastigmane glycosides (10-12). Compound 1 was isolated as a yellow amorphous powder. Its molecular formula was established as C 36 H 36 O 20 by means of ESI-MS ([M-H] - peak at m/z 787), 13 C, 13 C-DEPT NMR, and elemental analysis. Analysis of 600 MHz NMR spectra suggested a flavonoid skeleton for compound 1. The 1 H-NMR spectrum (Table 1) indicated a 5,7-dihydroxylated pattern for ring A (two meta-coupled doublets at δ 6.16 and 6.33, J = 1.5 Hz) and a 3’,4’- dihydroxylation pattern for ring B (ABX system signals at δ 6.80, d, J = 8.5 Hz; 7.58, dd, J = 8.5, 2.5 Hz; 7.67, d, J = 2.5 Hz), allowing the aglycon to be recognized as quercetin [5]. The 1 H-NMR spectrum of 1 also showed signals ascribable to sugar moieties and a caffeoyl residue (Table 1). Two anomeric protons arising from the sugar moieties appeared at δ 5.26 and 4.88 each (1H, d, J = 7.5 Hz), which correlated respectively with signals at δ 103.4 and 104.7 ppm in the HSQC spectrum. All the 1 H- and 13 C-NMR signals of 1 were assigned using 1D-TOCSY, DQF-COSY, HSQC, and HMBC experiments. Complete assignments of proton and carbon chemical shifts of the sugar portion were accomplished by DQF-COSY and 1D-TOCSY experiments and allowed the identification of the sugars as two terminal β-D-glucopyranosyl units. The configurations of the sugar units were assigned after hydrolysis of 1 with 1 N HCl. The hydrolysate was trimethylsilylated, and GC retention times compared with those of authentic sugar samples prepared in the same manner. The lower field shifts of H 2 -6''' (δ 4.32 and 4.23) of one glucosyl unit suggested the substitution site of the caffeoyl moiety. Unequivocal information could be obtained by 2D-NMR spectra; the HMBC experiment indicated correlations between δ 5.26 (H-1''') and 135.6 (C-3), δ 4.88 (H-1'') and 149.0 (C-3'), δ 4.32 and 4.23 (H 2 -6''') and 170.0 (COO). Thus, the structure of 1 was determined as quercetin 3-O-(6''-caffeoyl)-β-D-glucopyranoside-3'- O-β-D-glucopyranoside. The molecular formula C 37 H 38 O 18 for compound 2 was determined by ESI-MS ([M-H] - at m/z 769), 13 C, Table 1: 1 H and 13 C NMR data of compound 1 (CD 3 OD, 600 MHz) a . position δ H δ C 2 159.0 3 135.6 4 179.0 5 163.5 6 6.16 d (1.5) 100.0 7 166.3 8 6.33 d (1.5) 94.2 9 159.0 10 105.8 1' 123.1 2' 7.67 d (2.5) 117.2 3' 149.0 4' 146.4 5' 6.80 d (8.5) 116.0 6' 7.58 dd (2.5, 8.5) 123.5 3'-O-Glc 1'' 4.88 d (7.5) 104.7 2'' 3.58 dd (7.5, 9.0) 74.8 3'' 3.52 t (9.0) 77.3 4'' 3.42 t (9.0) 71.2 5'' 3.53 m 78.4 6''a 3.95 dd (5.0, 12.0) 62.4 3-O-Glc1''' 5.26 d (7.5) 103.4 2''' 3.56 dd (7.5, 9.0) 73.6 3''' 3.49 t (9.0) 77.7 4''' 3.40 t (9.0) 71.8 5''' 3.59 m 75.6 6'''a 4.32 dd (5.0, 12.0) 64.2 trans-caffeoyl 1 128.4 2 7.00 d (1.5) 115.4 3 147.5 4 150.1 5 6.81 d (8.8) 116.2 6 6.82 dd (1.5, 8.8) 123.1 α 6.07 d (16.0) 114.6 β 7.39 d (16.0) 147.4 COO 170.0 a Coupling pattern and coupling constants (J in Hertz) are in parentheses. 13 C-DEPT NMR analyses and was supported also by elemental analysis. Its 1 H- and 13 C-NMR spectra (see Table 2) indicated that it was a quercetin 3-methyl ether derivative [5]. Its 1 H-NMR spectrum further displayed signals for two sugar residues that were easily clarified with the help of 1D-TOCSY and DQF-COSY experiments, leading to the identification of one β-D-glucopyranosyl and one α- L-rhamnopyranosyl residue. The configuration of sugar units was determined as reported for compound 1. The presence of one p-coumaroyl moiety was shown in the 1 H-NMR spectrum by the signals at δ 7.45 and 6.73 each (2H, d, J = 8.5 Hz) and δ 7.41 and 6.38 each (1H, d, J = 16.0 Hz). The HSQC spectrum showed glycosidation shifts for C-6'' (δ 67.5) and acylation shift for H-2'' (δ 4.74) and C-2'' (δ 74.5) of the β-D-glucopyranosyl unit. An unambiguous determination of the sequence and linkage sites was obtained from an HMBC experiment, showing cross peak correlations between δ 5.06 (H-1'') and 164.5
Flavonoid glycosides from Chrozophora senegalensis Natural Product Communications Vol. 1 (12) 2006 1091 OH OMe RO O OR 2 RO O OR 1 OH O OH O 1 R = H R 1 = (6''-caffeoyl)glc R 2 = glc 3 R= (6''-p-coumaroyl)glc 2 R = (2''-p-coumaroyl)-glc-(6-1)rha R 1 = Me R 2 = H Figure 1: Structures of compounds 1-3. Table 2: 1 H- and 13 C-NMR data of compounds 2-3 (CD 3 OD, 600 MHz) a . position 2 3 δ H δ C δ H δ C 2 157.9 164.5 3 139.9 6.70 s 103.7 4 180.0 184.0 5 164.3 164.0 6 6.54 d (2.0) 101.2 6.56 d (2.0) 100.2 7 164.5 165.3 8 6.73 d (2.0) 95.8 6.77 d (2.0) 95.6 9 158.8 158.6 10 107.1 106.0 1' 123.6 122.8 2' 7.71 d (1.5) 116.2 7.94 d (8.5) 129.4 3' 145.0 7.06 d (8.5) 116.3 4' 149.6 159.0 5' 6.90 d (8.0) 117.3 7.06 d (8.5) 116.3 6' 7.65 dd (1.5, 8.0) 123.3 7.94 d (8.5) 129.4 OMe 3.90 s 56.1 3.92 s 56.3 7-O-Glc 1'' 5.06 d (7.5) 100.0 5.05 d (7.5) 100.3 2'' 4.74 dd (7.5, 9.0) 74.5 3.55 dd (7.5, 9.0) 74.0 3'' 3.47 t (9.0) 77.0 3.47 t (9.0) 77.5 4'' 3.45 t (9.0) 71.0 3.43 t (9.0) 71.5 5'' 3.30 m 77.7 3.61 m 75.8 6''a 4.00 dd (5.0, 12.0) 67.5 4.64 dd (4.5, 12.0) 64.3 6''b 3.60 dd (3.0, 12.0) 4.25 dd (2.5, 12.0) Rha 1''' 4.80 d (1.5) 101.9 2''' 3.94 dd (1.5, 3.4) 72.2 3''' 3.88 dd (3.4, 9.5) 71.8 4''' 3.55 t (9.0) 74.5 5''' 4.20 m 69.6 6''' 1.12 d (6.5) 17.6 p-coumaroyl 1 124.9 127.0 2,6 7.45 d (8.5) 130.2 7.45 d (8.5) 129.5 3,5 6.73 d (8.5) 116.5 6.75 d (8.5) 116.0 4 161.0 150.1 α 6.38 d (16.0) 118.0 6.38 d (16.0) 118.0 β 7.41 d (16.0) 146.8 7.43 d (16.0) 147.0 COO 168.7 168.8 a Coupling pattern and coupling constants (J in Hertz) are in parentheses. (C-7), δ 4.74 (H-2'') and 168.7 (COO), and δ 4.80 (H-1''') and 67.5 (C-6''). Therefore, the structure quercetin 3-methyl ether-7-O-α-L-rhamnopyranosyl- (1→6)-(2''-p-coumaroyl)-β-D-glucopyranoside was assigned to compound 2. Compound 3 was obtained as a yellow amorphous powder and its ESI-MS showed an [M-H] - ion peak at m/z 591. The molecular formula C 31 H 28 O 12 was confirmed by elemental analysis. In the 1 H-NMR spectrum (Table 2) two singlets at δ 6.70 and 3.92, two doublets at δ 6.77 and 6.56 each (1H, d, J = 2.0 Hz), and two o-coupled protons at δ 7.94 and 7.06 each (2H, d, J = 8.5 Hz) were present permitting the identification of the aglycon as apigenin 4'-methyl ether or acacetin [5]. Additionally for 3, resonances of one anomeric proton and one p-coumaroyl residue were observed in the 1 H-NMR spectrum at δ 5.05
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