Resin glycosides, well known as purgatives, are commonly found in plants of the Convolvulaceae family. These glycosides are characteristic ingredients of crude drugs such as Pharbitis Semen, Mexican Scammoniae Radix, Orizabae Tuber, Jalapae Tuber, and Rhizoma Jalapae Braziliensis.1) They can be roughly divided into an ether-soluble resin glycoside called jalapin and an ether-insoluble one called convolvulin.2) Almost all jalapins hitherto isolated and characterized have common macrolactone structures composed of an oligoglycoside of a hydroxy fatty acid partially acylated by certain organic acids at the sugar moiety (acylated glycosidic acid); some examples are ester-type dimers.3–8) On the other hand, convolvulins are regarded as oligomers of various acylated glycosidic acids.9) However, no genuine convolvulin has thus far been isolated.
Quamoclit pennata BOJER is a Convolvulaceae plant native to tropical regions of South America and is primarily cultivated as an ornamental plant. We earlier reported the isolation and structural elucidation of a glycosidic acid called quamoclinic acid A along with 2S-methylbutyric, n-decanoic, and n-dodecanoic acids, upon alkaline hydrolysis of the crude jalapin fraction of the seeds of the plant.10) Furthermore, we isolated six genuine jalapins, quamoclins I, II, III, IV, V, and VI from the same fraction.10,11) On the other hand, we reported the structures of seven glycosidic acids, quamoclinic acids B, C, D, E, F, G, and H along with isobutyric, 2S-methylbutyric, 2R-methyl-3R-hydroxybutyric (2R,3R-nilic), (E)-2-methylbut-2-enoic (tiglic), 7S-hydroxydecanoic, and 7S-hydroxydodecanoic acids upon alkaline hydrolysis of the crude convolvulin fraction of the seeds.12,13) However, despite numerous attempts, isolation of pure resin glycosides from the crude convolvulin fraction11) of the seeds of Q. pennata has been unsuccessful, until now. Previous results suggested that resin glycosides in the crude convolvulin fraction possessed at least one carboxyl group. Hence, this fraction was treated with indium(III) chloride in methanol (MeOH), which has been reported by Mineno and Kansui to be suitable a catalyst for the mild methyl esterification of carboxylic acids.14) The fraction yielded a number of separate spots on TLC (silica gel) plate after treatment with InCl3–MeOH. Previously, we reported the isolation and structural elucidation of three acylated glycosidic acid methyl esters, QM-1–QM-3, and two acylated methyl glycosides, QM-4 and QM-5, from the above fraction.15) As part of an ongoing study of the resin glycoside of the seeds of Q. pennata, this report details the isolation and structural elucidation of three new acylated methyl glycosides and two new acylated glycosidic acid methyl esters from the above-mentioned treated fraction.
The crude convolvulin fraction15) after treatment with InCl3–MeOH was successively subjected to Diaion HP20, Sephadex LH-20, silica gel, and Chromatorex octadecyl silica (ODS) column chromatography as well as HPLC on ODS and silica gel columns to afford five compounds, referred to as QM-6 (1)–QM-10 (5).
QM-6 (1) was obtained as an amorphous powder and exhibited an [M−H]− ion peak at m/z 1583 in negative-ion FAB-MS and an [M+Na]+ ion peak at m/z 1607 in positive-ion FAB-MS. The molecular formula of 1 was determined as C69H116O40 on the basis of high-resolution (HR)-positive-ion FAB-MS. The 1H-NMR spectrum of 1 indicated signals due to one H-2 of the niloyl residue [δ 2.96 (1H, dq, J=7.0, 7.0 Hz)], one H-3 of the tigloyl residue [δ 7.09 (1H, qq, J=1.5, 7.0 Hz)], one methoxy group [δ 3.29 (3H, s)], eight anomeric protons [δ 6.14 (1H, s), 6.11 (1H, s), 6.01 (1H, d, J=8.0 Hz), 5.93 (1H, d. J=7.5 Hz), 5.31 (1H, d, J=3.0 Hz), 5.20 (1H, d, J=8.0 Hz), 4.91 (1H, d, J=8.0 Hz), 4.79 (1H, d, J=8.0 Hz)], two nonequivalent methylene protons [δ 2.46 (1H, ddd, J=8.0, 8.0, 16.0 Hz), 2.40 (1H, ddd, J=8.0, 8.0, 16.0 Hz)] adjacent to a carbonyl group, one tertiary methyl group [δ 2.00 (3H, br s)] assignable to H3-5 of the tigloyl residue, nine secondary methyl groups [δ 1.80 (3H, d, J=6.0 Hz), 1.75 (3H, d, J=7.0 Hz), 1.62 (1H, d, J=6.0 Hz), 1.60 (3H, d, J=6.5 Hz), 1.60 (3H, d, J=6.0 Hz), 1.55 (3H, d, J=6.0 Hz), 1.45 (3H, d, J=6.5 Hz), 1.39 (3H, d, J=7.0 Hz), 1.38 (3H, d, J=7.0 Hz)], and one primary methyl group [δ 0.95 (3H, t, J=7.0 Hz)]. The 13C-NMR spectrum exhibited signals due to three carboxyl carbons (δ 175.3, 173.4, 167.2), two olefinic carbons (δ 138.1, 128.9), and eight anomeric carbons (δ 106.6, 104.7, 103.3, 102.2, 101.8, 101.6, 100.8, 97.9). The 1H- and 13C-NMR signals were assigned on the basis of 1H–1H correlation spectroscopy (COSY), heteronuclear multiple-quantum coherence (HMQC), and heteronuclear multiple-bond correlation (HMBC) spectra. The spectral data indicated that 1 is a methyl heptaglycoside acylated by 1 mol each of nilic acid, tiglic acid, and quamoclinic acid B (6) (Tables 1, 2). The alkaline hydrolysis of 1 furnished a methyl heptaglycoside (7), temporarily referred to as methyl quamoside B, along with nilic acid, tiglic acid, and 6. The negative-ion FAB-MS of 7 exhibited an [M–H]– ion peak at m/z 1085 along with fragment ion peaks at m/z 939 [1085−46 (methylpentosyl unit)]–, 793 [939−146]−, 631 [793−162 (hexosyl unit)]−, and 339 [631−146×2]−. Upon acidic hydrolysis, 7 afforded a monosaccharide fraction, which was converted into thiocarbamoyl-thiazolidine derivatives and then analyzed using HPLC, according to a procedure reported by Tanaka et al.16) Derivatives of D-glucose, D-fucose, D-qinovose, and L-rhamnose were detected. The 1H- and 13C-NMR spectra of 7 were quite similar to those of methyl quamoside A (8),15) except for the appearance of additional signals due to one terminal α-L-rhamnopyranosyl residue (Rha′)12) and glycosylation shifts17,18) (Δδ=δ7–δ8) of signals due to C-2 (Δδ=0.5), C-3 (Δδ=4.9), and C-4 (Δδ=−1.7) of the second quinovosyl residue (Qui′). In addition, the HMBC spectrum of 7 showed a key cross-peak between H-1 of Rha′ and C-3 of Qui′. From these data, the structure of 7 was assigned as methyl α-L-rhamnopyranosyl-(1→3)-O-β-D-quinovopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→3)-[O-β-D-quinovopyranosyl-(1→4)]-O-α-L-rhamnopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→2)-α-D-fucopyranoside (Fig. 1).
Table 1.
1H-NMR Spectral Data for
1,
7, and
9 (in Pyridine-
d5, 500 MHz)
| Position | 1 | 7 | 9 |
|---|
| Fuc-1 | 5.31 d (3.0) | 5.33 d (3.5) | 5.33 d (3.5) |
| 2 | 4.45a) | 4.50 dd (3.5, 10.0) | 4.46 dd (3.5, 10.0) |
| 3 | 4.57 dd (3.0, 10.0) | 4.56 dd (3.0, 10.0) | 4.58a) |
| 4 | 4.06 d (3.0) | 4.06a) | 4.06a) |
| 5 | 4.04a) | 4.01 q (7.0) | 4.00a) |
| 6 | 1.39 d (7.0) | 1.42 d (7.0) | 1.39 d (7.0) |
| Glc-1 | 4.91 d (8.0) | 4.99 d (7.5) | 4.93a) |
| 2 | 4.14 dd (8.0, 9.5) | 4.10a) | 4.16a) |
| 3 | 4.03a) | 4.09a) | 4.03a) |
| 4 | 4.05a) | 4.09a) | 4.06a) |
| 5 | 3.56 m | 3.63a) | 3.58 ddd (3.5, 5.5, 9.0) |
| 6 | 4.33a) | 4.36a) | 4.35a) |
| 6 | 4.23 dd (4.0, 12.0) | 4.26 dd (5.0, 11.0) | 4.25 br d (11.0) |
| Glc'-1 | 5.93 d (7.5) | 5.96 d (8.0) | 6.06 d (8.0) |
| 2 | 3.96a) | 3.92 dd (8.0, 9.0) | 3.99a) |
| 3 | 4.29 dd (9.0, 9.0) | 4.35 dd (9.0, 9.0) | 4.36a) |
| 4 | 4.05a) | 4.11a) | 4.06a) |
| 5 | 3.81a) | 3.88 ddd (2.5, 6.0, 9.0) | 3.91a) |
| 6 | 4.32a) | 4.36a) | 4.36a) |
| 6 | 4.05a) | 4.13 dd (6.0, 12.0) | 4.05a) |
| Rha-1 | 6.14 s | 6.17 d (1.5) | 6.20 d (1.5) |
| 2 | 6.07 br s | 4.92a) | 6.03 dd (1.5, 3.5) |
| 3 | 5.34 dd (3.5, 9.0) | 5.16 dd (3.0, 9.0) | 5.43 dd (3.5, 9.0) |
| 4 | 4.50 dd (9.0, 9.0) | 4.70 dd (9.0, 9.0) | 4.56 dd (9.0, 9.0) |
| 5 | 4.94 dq (9.0, 6.0) | 4.90a) | 4.93a) |
| 6 | 1.80 d (6.0) | 1.87 d (6.5) | 1.85 d (6.0) |
| Rha′-1 | 6.11 s | 6.07 d (1.0) | 6.09 d (1.0) |
| 2 | 4.59 br s | 4.65 dd (1.0, 3.5) | 4.56a) |
| 3 | 4.30a) | 4.48 dd (3.5, 9.0) | 4.33a) |
| 4 | 4.16a) | 4.28 dd (9.0, 9.0) | 4.19 dd (9.5, 9.5) |
| 5 | 4.13a) | 4.92a) | 4.16a) |
| 6 | 1.55 d (6.0) | 1.66 d (6.0) | 1.57 d (6.0) |
| Qui-1 | 6.01 d (8.0) | 5.80 d (8.0) | 5.90 d (7.5) |
| 2 | 3.97a) | 3.95 dd (8.0, 9.0) | 3.97a) |
| 3 | 4.45a) | 4.28 dd (9.0, 9.0) | 4.29 dd (9.0, 9.0) |
| 4 | 5.37 dd (9.5, 9.5) | 3.69 dd (9.0, 9.0) | 3.72a) |
| 5 | 4.39a) | 4.08a) | 4.17a) |
| 6 | 1.62 d (6.0) | 1.58 d (6.5) | 1.69 d (6.5) |
| Qui′-1 | 5.20 d (8.0) | 5.03 d (7.5) | 5.16 d (8.0) |
| 2 | 4.20 dd (8.0, 9.5) | 4.08a) | 4.04a) |
| 3 | 4.40 dd (9.5, 9.5) | 4.09a) | 4.39 dd (9.0, 9.0) |
| 4 | 5.37 dd (9.5, 9.5) | 3.64 dd (9.0, 9.0) | 5.37 dd (9.0, 9.0) |
| 5 | 4.02a) | 3.74 dq (9.0, 6.0) | 4.01a) |
| 6 | 1.60 d (6.5) | 1.72 d (6.0) | 1.63 d (6.0) |
| Nla-2 | 2.96 dq (7.0, 7.0) | | |
| 3 | 4.38a) | | |
| 4 | 1.45 d (6.5) | | |
| 5 | 1.38 d (7.0) | | |
| Tig-3 | 7.09 q (7.0) | | 7.10 qq (1.5, 7.0) |
| 4 | 1.75 d (7.0) | | 1.76 d (7.0) |
| 5 | 2.00 br s | | 2.02 br s |
| Hda-2 | 2.46 ddd (8.0, 8.0, 16.0) | | 2.48a) |
| 2 | 2.40 ddd (8.0, 8.0, 16.0) | | 2.45a) |
| 7 | 3.89 m | | 3.90a) |
| 10 | 0.95 t (7.0) | | 0.95 t (7.0) |
| Qui″-1 | 4.79 d (8.0) | | 4.81 d (8.0) |
| 2 | 3.96a) | | 3.97a) |
| 3 | 4.14 dd (9.0, 9.0) | | 4.15 dd (9.0, 9.0) |
| 4 | 3.71 dd (9.0, 9.0) | | 3.72a) |
| 5 | 3.78 dq (9.0, 6.0) | | 3.79 dq (9.0, 6.0) |
| 6 | 1.60 d (6.0) | | 1.64 d (6.0) |
| OCH3 | 3.29 s | 3.29 s | 3.29 s |
δ in ppm from tetramethylsilane (TMS). Coupling constants (J) in Hz are given in parentheses. a) Signals were overlapped with other signals.
Table 2.
13C-NMR Spectral Data for
1–
3,
7, and
9 (in Pyridine-
d5, 125 MHz)
| Position | 1 | 7 | 9 | 2 | 3 | Position | 1 | 7 | 9 | 2 | 3 |
|---|
| Fuc-1 | 100.8 | 100.8 | 100.9 | 100.9 | 100.8 | Qui′-1 | 106.6 | 105.8 | 106.4 | 106.0 | 106.8 |
| 2 | 79.2 | 79.2 | 79.5 | 79.4 | 79.4 | 2 | 77.6 | 76.4 | 77.4 | 77.6 | 74.3 |
| 3 | 70.0 | 70.0 | 70.0 | 70.1 | 70.1 | 3 | 79.3 | 82.9 | 79.2 | 79.1 | 79.0 |
| 4 | 73.0 | 73.0 | 73.2 | 73.0 | 73.1 | 4 | 74.4 | 74.8 | 74.6 | 74.4 | 74.8 |
| 5 | 66.5 | 66.5 | 66.5 | 66.5 | 66.5 | 5 | 71.2 | 74.0 | 71.7 | 71.2 | 73.5 |
| 6 | 16.8 | 16.9 | 16.9 | 16.9 | 16.9 | 6 | 18.3 | 18.6 | 18.4 | 18.2 | 18.5 |
| Glc-1 | 104.7 | 104.9 | 104.8 | 105.0 | 104.7 | Nla-1 | 175.3 | | | 175.4 | 175.5 |
| 2 | 77.6 | 77.9 | 77.9 | 77.9 | 77.6 | 2 | 48.3 | | | 48.4 | 48.4 |
| 3 | 78.3 | 78.4 | 78.5 | 78.5 | 78.4 | 3 | 69.5 | | | 69.6 | 69.3 |
| 4 | 71.6 | 71.5 | 71.6 | 71.6 | 71.6 | 4 | 21.1 | | | 21.1 | 20.9 |
| 5 | 77.8 | 77.9 | 78.0 | 78.0 | 77.9 | 5 | 13.4 | | | 13.4 | 13.2 |
| 6 | 62.4 | 62.5 | 62.5 | 62.4 | 62.4 | Nla′-1 | | | | | 175.0 |
| Glc′-1 | 101.8 | 101.6 | 101.7 | 101.7 | 101.8 | 2 | | | | | 48.4 |
| 2 | 86.1 | 84.8 | 85.8 | 85.6 | 86.2 | 3 | | | | | 69.1 |
| 3 | 77.4 | 77.4 | 77.4 | 77.3 | 77.7 | 4 | | | | | 20.7 |
| 4 | 71.2 | 71.7 | 71.7 | 71.6 | 71.3 | 5 | | | | | 12.9 |
| 5 | 78.1 | 78.3 | 78.6 | 78.4 | 78.2 | Tig-1 | 167.2 | | 167.1 | 167.1 | |
| 6 | 62.3 | 62.4 | 62.5 | 62.5 | 62.5 | 2 | 128.9 | | 129.0 | 128.9 | |
| Rha-1 | 97.9 | 101.4 | 97.8 | 101.4 | 98.0 | 3 | 138.1 | | 137.9 | 138.0 | |
| 2 | 73.8 | 71.6 | 73.8 | 71.8 | 73.7 | 4 | 14.3 | | 14.4 | 14.3 | |
| 3 | 75.9 | 78.4 | 75.6 | 78.5 | 76.0 | 5 | 12.4 | | 12.5 | 12.4 | |
| 4 | 78.5 | 79.1 | 79.0 | 78.8 | 78.7 | Hda-1 | 173.4 | | 173.4 | | 173.4 |
| 5 | 67.9 | 68.8 | 68.3 | 68.5 | 68.0 | 2 | 34.6 | | 34.6 | | 34.6 |
| 6 | 18.7 | 18.8 | 18.7 | 18.8 | 18.8 | 7 | 78.4 | | 78.6 | | 78.6 |
| Rha′-1 | 102.2 | 102.6 | 102.3 | 102.3 | | 10 | 14.3 | | 14.4 | | 14.4 |
| 2 | 72.2 | 72.2 | 72.3 | 72.3 | | Qui″-1 | 103.3 | | 103.4 | | 103.4 |
| 3 | 72.3 | 72.5 | 72.4 | 72.3 | | 2 | 75.5 | | 75.6 | | 75.6 |
| 4 | 73.6 | 73.8 | 73.7 | 73.7 | | 3 | 78.1 | | 78.2 | | 77.9 |
| 5 | 69.8 | 69.8 | 70.1 | 69.9 | | 4 | 76.8 | | 76.9 | | 76.9 |
| 6 | 18.6 | 18.5 | 18.7 | 18.6 | | 5 | 72.6 | | 72.7 | | 72.7 |
| Qui-1 | 101.6 | 102.6 | 102.0 | 102.0 | 101.8 | 6 | 18.7 | | 18.7 | | 18.7 |
| 2 | 76.2 | 76.4 | 76.6 | 76.3 | 76.3 | OCH3 | 55.0 | 55.0 | 55.1 | 55.1 | 55.1 |
| 3 | 75.2 | 78.1 | 78.2 | 75.4 | 75.3 | | | | | | |
| 4 | 77.4 | 77.3 | 77.3 | 77.4 | 77.5 | | | | | | |
| 5 | 69.9 | 72.3 | 72.3 | 69.8 | 69.8 | | | | | | |
| 6 | 18.1 | 18.5 | 18.4 | 18.1 | 18.2 | | | | | | |
Fig. 1. Structures of 1–11
Comparison of the 1H-NMR spectra of 1 and 7 indicated remarkable downfield shifts (Δδ=δ1–δ7) of signals due to H-2 (Δδ=1.15) of the first rhamnosyl residue (Rha), H-4 (Δδ=1.68) of the first quinovosyl residue (Qui), and H-4 (Δδ=1.73) of Qui′ of 1, owing to acylation. In addition, the HMBC spectrum of 1 showed cross-peaks between the methoxy protons and C-1 of the first fucosyl residue (Fuc); H-1 of the first glucosyl residue (Glc) and C-2 of Fuc; H-1 of the second glucosyl residue (Glc′) and C-3 of Rha; H-1 of Qui and C-4 of Rha; H-1 of Qui′ and C-2 of Glc′; H-1 of Rha′ and C-3 of Qui′; H-1 of the third quinovosyl residue (Qui″) and C-7 of 7S-hydroxydecanoyl residue (Hda; the aglycone moiety of quamoclinic acid B residue (QaB))12); H-4 of Qui or H-4 of Qui′ and C-1 of the first niloyl residue (Nla); and H-4 of Qui′ or H-4 of Qui and C-1 of the first tigloyl residue (Tig) (Fig. 2). However, the counterparts of C-1 of Nla and C-1 of Tig could not be defined because the 1H-NMR peaks due to H-4 of Qui and H-4 of Qui′ heavily overlapped. Although no cross-peak between H-2 of Rha and C-1 of Hda was observed in the HMBC spectrum of 1, the above data suggested that QaB was attached to OH-2 of Rha.
Fig. 2. 1H-13C Long-Range Correlations Observed in the HMBC Spectra of 1 and 4 (in Pyridine-d5, 500 MHz)
To determine the sites of each ester linkage of nilic acid and tiglic acid, partial deacylation of 1 was conducted. Compound 1 was refluxed with 5% triethylamine–MeOH for 1 h, and the products were purified by HPLC to give 9. The positive-ion FAB-MS of 9 exhibited an [M+Na]+ ion peak at m/z 1507, 100 mass units (niloyl residue) less than that of 1. The 1H-NMR spectrum of 9 showed upfield shift (1.65 ppm) of the signal due to H-4 of Qui as compared to that of 1, along with disappearance of the signals due to the niloyl residue, whereas the signals owing to H-4 of Qui′ and H-2 of Rha were observed at similar chemical shifts (Table 1). These data suggested that Nla and Tig of 1 were located at OH-4 of Qui and OH-4 of Qui′, respectively. The absolute configuration of the nilic acid residue in this crude convolvulin fraction has been previously determined as 2R,3R.12) Accordingly, the structure of 1 was assigned as methyl α-L-rhamnopyranosyl-(1→3)-O-(4-O-tigloyl)-β-D-quinovopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→3)-[O-(4-O-2R,3R-niloyl)-β-D-quinovopyranosyl-(1→4)]-O-(2-O-7S-hydroxydecanoyl-7-O-β-D-quinovopyranoside)-α-L-rhamnopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→2)-α-D-fucopyranoside. The structure of 9 differs by the cleaved Nla residue (Fig. 1).
QM-7 (2) was obtained as an amorphous powder. Alkaline hydrolysis of 2 gave nilic acid, tiglic acid, and 7. Negative- and positive-ion FAB-MS of 2 revealed an [M−H]− ion peak at m/z 1267 and an [M+Na]+ ion peak at m/z 1291, respectively, which were 316 mass units (quamoclinic acid B residue) less than the corresponding peaks for 1. The molecular formula of 2 was determined as C53H88O34 by HR-positive-ion FAB-MS. The 1H- and 13C-NMR spectra of 2 and 1 were superimposable, apart from the absence of signals due to QaB in the spectrum of 2 (Tables 2, 3). When compared to 1H-NMR spectrum of 1, a remarkable upfield shift (1.17 ppm) of the signal assignable to H-2 of Rha was observed. On the other hand, the signals due to H-4 of Qui and H-4 of Qui′ appeared at chemical shifts similar to those of 1. These data suggest that 2 is a derivative of 1 with QaB cleaved. In the HMBC spectrum of 2, key cross-peaks were observed between H-4 of Qui and C-1 of Nla and H-4 of Qui′ and C-1 of Tig. Accordingly, the structure of 2 was assigned as methyl α-L-rhamnopyranosyl-(1→3)-O-(4-O-tigloyl)-β-D-quinovopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→3)-[O-(4-O-2R,3R-niloyl)-β-D-quinovopyranosyl-(1→4)]-O-α-L-rhamnopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→2)-α-D-fucopyranoside (Fig. 1).
Table 3.
1H-NMR Spectral Data for
2 and
3 (in Pyridine-
d5, 500 MHz)
| Position | 2 | 3 |
|---|
| Fuc-1 | 5.33 d (3.5) | 5.32 d (3.5) |
| 2 | 4.48 dd (3.5, 10.0) | 4.46 dd (3.5, 10.0) |
| 3 | 4.55 dd (3.0, 10.0) | 4.59 dd (3.0, 10.0) |
| 4 | 4.04 d (3.0) | 4.08a) |
| 5 | 4.03 q (6.5) | 4.03a) |
| 6 | 1.41 d (6.5) | 1.39 d (7.0) |
| Glc-1 | 4.96a) | 4.92 d (7.5) |
| 2 | 4.07a) | 4.16 dd (7.5, 9.0) |
| 3 | 4.08a) | 4.05a) |
| 4 | 4.07a) | 4.06a) |
| 5 | 3.61 m | 3.57 ddd (3.0, 5.0, 9.0) |
| 6 | 4.35a) | 4.34a) |
| 6 | 4.26 dd (4.5, 11.0) | 4.25a) |
| Glc′-1 | 6.02 d (7.5) | 5.94 d (7.5) |
| 2 | 3.92 dd (7.5, 9.0) | 3.96a) |
| 3 | 4.37a) | 4.31a) |
| 4 | 4.12a) | 4.05a) |
| 5 | 3.87 dd (2.5, 6.0, 9.0) | 3.82a) |
| 6 | 4.35a) | 4.32a) |
| 6 | 4.12a) | 4.05a) |
| Rha-1 | 6.15 d (1.5) | 6.16 d (1.5) |
| 2 | 4.90 dd (1.5, 3.0) | 6.08 dd (1.5, 3.5) |
| 3 | 5.15 dd (3.0, 9.0) | 5.35 dd (3.5, 9.0) |
| 4 | 4.66 dd (9.0, 9.0) | 4.51 dd (9.0, 9.0) |
| 5 | 4.86 dq (9.0, 6.5) | 4.97a) |
| 6 | 1.81 d (6.5) | 1.82 d (6.5) |
| Rha′-1 | 6.05 d (1.5) | |
| 2 | 4.59 dd (1.5, 3.0) | |
| 3 | 4.30 dd (3.0, 9.0) | |
| 4 | 4.18 dd (9.0, 9.0) | |
| 5 | 4.11a) | |
| 6 | 1.54 d (6.5) | |
| Qui-1 | 5.90 d (7.5) | 6.00 d (8.0) |
| 2 | 3.97 dd (7.5, 9.5) | 3.99a) |
| 3 | 4.38 dd (9.5, 9.5) | 4.49 dd (9.5, 9.5) |
| 4 | 5.34 dd (9.5, 9.5) | 5.38 dd (9.5, 9.5) |
| 5 | 4.23 dq (9.5, 6.5) | 4.37a) |
| 6 | 1.53 d (6.5) | 1.53 d (6.5) |
| Qui′-1 | 5.08 d (8.0) | 5.26 d (8.0) |
| 2 | 4.12a) | 4.28a) |
| 3 | 4.18 dd (9.5, 9.5) | 5.78 dd (9.5, 9.5) |
| 4 | 5.28 dd (9.5, 9.5) | 3.83a) |
| 5 | 3.83 dq (9.5, 6.5) | 3.95a) |
| 6 | 1.44 d (6.5) | 1.79 d (6.0) |
| Nla-2 | 2.94 dq (7.0, 7.0) | 2.92 dq (7.0, 7.0) |
| 3 | 4.36a) | 4.41 m |
| 4 | 1.43 d (6.5) | 1.45 d (7.0) |
| 5 | 1.36 d (7.0) | 1.36 d (7.0) |
| Nla′-2 | | 2.81 dq (7.0, 7.0) |
| 3 | | 4.29a) |
| 4 | | 1.37 d (7.0) |
| 5 | | 1.18 d (7.0) |
| Tig-3 | 7.04 qq (1.5, 7.0) | |
| 4 | 1.73 d (7.0) | |
| 5 | 1.97 br s | |
| Hda-2 | | 2.43 a) |
| 2 | | 2.39 a) |
| 7 | | 3.88 m |
| 10 | | 0.94 t (7.0) |
| Qui″-1 | | 4.81 d (8.0) |
| 2 | | 3.95a) |
| 3 | | 4.16 dd (9.0, 9.0) |
| 4 | | 3.72 dd (9.0, 9.0) |
| 5 | | 3.82a) |
| 6 | | 1.63 d (6.0) |
| OCH3 | 3.30 s | 3.29 s |
δ in ppm from TMS. Coupling constants (J) in Hz are given in parentheses. a) Signals were overlapped with other signals.
QM-8 (3) was obtained as an amorphous powder and exhibited an [M−H]− ion peak at m/z 1455 in negative-ion FAB-MS and an [M+Na]+ ion peak at m/z 1479 in positive-ion FAB-MS. HR-positive-ion FAB-MS indicated C63H108O37 for the molecular formula of 3. Upon alkaline hydrolysis, 3 furnished nilic acid, 6, and 8. The 1H- and 13C-NMR spectra indicated that 3 is composed of 2 mol of nilic acid and 1 mol each of 6 and 8 (Tables 2, 3). Comparison of the chemical shifts of the 1H-NMR signals of the sugar moieties in 3 and 815) showed that the signals due to H-2 of Rha, H-4 of Qui, and H-3 of Qui′ of 3 exhibited remarkable downfield shifts of 1.14, 1.70, and 1.77 ppm, respectively. In addition, the HMBC spectrum of 3 showed key cross-peaks between H-4 of Qui and C-1 of Nla and H-3 of Qui′ and C-1 of the second niloyl residue (Nla′). Consequently, the structure of 3 was assigned as methyl (3-O-2R,3R-niloyl)-β-D-quinovopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→3)-[O-(4-O-2R,3R-niloyl)-β-D-quinovopyranosyl-(1→4)]-O-(2-O-7S-hydroxydecanoyl-7-O-β-D-quinovopyranoside)-α-L-rhamnopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→2)-α-D-fucopyranoside (Fig. 1).
QM-9 (4) was obtained as an amorphous powder, and upon alkaline hydrolysis afforded tiglic acid, 6, and quamoclinic acid E (10).12) Negative- and positive-ion FAB-MS of 4 exhibited an [M−H]− ion peak at m/z 1807 and an [M+Na]+ ion peak at m/z 1831, respectively. The molecular formula of 4 was determined as C83H140O42 by HR-positive-ion FAB-MS. The 1H-NMR spectrum of 4 indicated signals due to one methoxy group, two tigloyl residues, two nonequivalent methylene protons assignable to H2-2 of Hda, two nonequivalent methylene protons assignable to H2-2 of 3S,11S-dihydroxytetradecanoyl (ipuroloyl) residue (Ipu; the aglycone moiety of quamoclinic acid E),12,19) eight anomeric protons, and two primary methyl groups. The 13C-NMR spectrum exhibited signals of four carboxyl carbons and eight anomeric carbons. These 1H- and 13C-NMR spectra suggested that 4 is composed of 2 mol of tiglic acid and 1 mol each of 6 and 10. Comparison of the 1H-NMR spectra12) due to the sugar moiety in 4 and 10 indicated acylation shifts (Δδ=δ4–δ10) of signals due to H-2 (Δδ=1.12) of Rha, H-4 (Δδ=1.71) of the second fucosyl residue (Fuc′), and H-4 (Δδ=1.81) of Qui′. In addition, the HMBC spectrum of 4 showed cross-peaks between H-4 of Fuc′ and C-1 of the second tigloyl residue (Tig′) and H-4 of Qui′ and C-1 of Tig. Accordingly, the structure of 4 was assigned as methyl 3S,11S-dihydroxytetradecanoate 11-O-β-D-fucopyranosyl-(1→3)-O-(4-O-tigloyl)-β-D-quinovopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→3)-[O-(4-O-tigloyl)-β-D-fucopyranosyl-(1→4)]-O-(2-O-7S-hydroxydecanoyl-7-O-β-D-quinovopyranoside)-α-L-rhamnopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→2)-β-D-fucopyranoside (Fig. 1).
QM-10 (5) was obtained as an amorphous powder, and its molecular formula was determined as C67H118O36 by HR-positive-ion FAB-MS. Upon alkaline hydrolysis, 5 furnished 6 and quamoclinic acid C (11).12) The 1H- and 13C-NMR spectra of 5 exhibited signals due to one methoxy group, one QaB, and one quamoclinic acid C residue (Tables 4, 5). Comparison of the 1H-NMR spectra12) of the sugar moieties in 5 and 11 indicated acylation shift (1.11 ppm) of the signal due to H-2 of Rha in 5. Accordingly, the structure of 5 was assigned as methyl 3S,11S-dihydroxytetradecanoate 11-O-β-D-quinovopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→3)-[O-β-D-quinovopyranosyl-(1→4)]-O-(2-O-7S-hydroxydecanoyl-7-O-β-D-quinovopyranoside)-α-L-rhamnopyranosyl-(1→2)-O-β-D-glucopyranosyl-(1→2)-β-D-fucopyranoside (Fig. 1).
Table 4.
1H-NMR Spectral Data for
4 and
5 (in Pyridine-
d5, 500 MHz)
| Position | 4 | 5 |
|---|
| Fuc-1 | 4.81 d (7.5) | 4.82 d (7.5) |
| 2 | 4.49a) | 4.49a) |
| 3 | 4.51a) | 4.56 dd (3.5, 9.5) |
| 4 | 4.11a) | 4.15a) |
| 5 | 3.98a) | 3.96a) |
| 6 | 1.43 d (6.5) | 1.39 d (6.5) |
| Fuc′-1 | 5.87 d (8.0) | |
| 2 | 4.25 dd (8.0, 9.5) | |
| 3 | 4.40 dd (3.0, 9.5) | |
| 4 | 5.69 d (3.0) | |
| 5 | 4.31a) | |
| 6 | 1.43 d (6.5) | |
| Fuc″-1 | 4.96 d (7.5) | |
| 2 | 4.22 dd (7.5, 8.5) | |
| 3 | 4.03a) | |
| 4 | 3.96a) | |
| 5 | 3.77a) | |
| 6 | 1.45 d (6.5) | |
| Glc-1 | 5.61 d (8.0) | 5.63 d (7.5) |
| 2 | 4.18 dd (8.0, 9.0) | 4.21 dd (7.5, 9.0) |
| 3 | 4.10a) | 4.14a) |
| 4 | 4.01a) | 4.02a) |
| 5 | 3.58 ddd (4.0, 5.0, 9.0) | 3.58 ddd (3.5, 5.0, 9.0) |
| 6 | 4.29 dd (4.0, 12.0) | 4.30 dd (3.5, 11.5) |
| 6 | 4.19a) | 4.18a) |
| Glc′-1 | 6.10 d (8.0) | 6.06a) |
| 2 | 3.98a) | 4.01a) |
| 3 | 4.37 dd (9.0, 9.0) | 4.39 dd (9.0, 9.0) |
| 4 | 4.04a) | 4.04 dd (9.0, 9.0) |
| 5 | 3.96a) | 3.94a) |
| 6 | 4.45 br d (11.5) | 4.49a) |
| 6 | 4.11a) | 4.15a) |
| Rha-1 | 6.27 d (2.0) | 6.32 s |
| 2 | 6.07 dd (2.0, 3.5) | 6.04a) |
| 3 | 5.35 dd (3.5, 9.0) | 5.39 dd (3.5, 9.5) |
| 4 | 4.51 dd (9.0, 9.0) | 4.62 dd (9.5, 9.5) |
| 5 | 5.03 dq (9.0, 6.5) | 5.12a) |
| 6 | 1.89 d (6.5) | 1.96 d (6.0) |
| Qui-1 | | 5.91 d (8.0) |
| 2 | | 3.98a) |
| 3 | | 4.30 dd (9.0, 9.0) |
| 4 | | 3.72a) |
| 5 | | 4.15a) |
| 6 | | 1.66 d (6.0) |
| Qui′-1 | 5.24 d (7.5) | 5.13a) |
| 2 | 4.08a) | 4.11a) |
| 3 | 4.32 dd (9.5, 9.5) | 4.13a) |
| 4 | 5.33 dd (9.5, 9.5) | 3.73a) |
| 5 | 4.03a) | 3.84a) |
| 6 | 1.63 d (6.0) | 1.76 d (6.0) |
| Tig-3 | 7.16 qq (1.0, 7.0) | |
| 4 | 1.61 d (7.0) | |
| 5 | 1.93 br s | |
| Tig′-3 | 7.11 qq (1.0, 7.0) | |
| 4 | 1.73 d (7.0) | |
| 5 | 1.97 br s | |
| Hda-2 | 2.50a) | 2.56 ddd (6.5, 8.5, 16.0) |
| 2 | 2.46a) | 2.43 ddd (6.5, 8.5, 16.0) |
| 7 | 3.91a) | 3.88a) |
| 10 | 0.96 t (7.0) | 0.93 t (7.0) |
| Qui″-1 | 4.79 d (8.0) | 4.78 d (8.0) |
| 2 | 3.96a) | 3.96a) |
| 3 | 4.14 dd (9.0, 9.0) | 4.14a) |
| 4 | 3.72 dd (9.0, 9.0) | 3.72a) |
| 5 | 3.79a) | 3.78 dq (9.0, 6.0) |
| 6 | 1.63 d (6.0) | 1.62 d (6.0) |
| Ipu-2 | 2.73 dd (8.0, 15.0) | 2.73 dd (7.5, 15.0) |
| 2 | 2.69 dd (4.5, 15.0) | 2.69 dd (5.0, 15.0) |
| 3 | 4.41a) | 4.40a) |
| 11 | 3.91a) | 3.87a) |
| 14 | 0.93 t (7.0) | 0.89 t (7.0) |
| OCH3 | 3.63 s | 3.63 s |
δ in ppm from TMS. Coupling constants (J) in Hz are given in parentheses. a) Signals were overlapped with other signals.
Table 5.
13C-NMR Spectral Data for
4 and
5 (in Pyridine-
d5, 125 MHz)
| Position | 4 | 5 | Position | 4 | 5 | Position | 4 | 5 |
|---|
| Fuc-1 | 102.6 | 102.4 | Glc′-1 | 101.6 | 101.5 | Tig-1 | 167.3 | |
| 2 | 78.6 | 78.4 | 2 | 86.2 | 84.7 | 2 | 129.0 | |
| 3 | 76.0 | 76.0 | 3 | 77.4 | 76.9 | 3 | 137.7 | |
| 4 | 73.4 | 73.0 | 4 | 71.8 | 71.6 | 4 | 14.2 | |
| 5 | 71.1 | 71.0 | 5 | 78.1 | 78.2 | 5 | 12.5 | |
| 6 | 17.0 | 17.1 | 6 | 62.6 | 62.7 | Tig′-1 | 168.1 | |
| Fuc′-1 | 102.4 | | Rha-1 | 97.7 | 97.4 | 2 | 129.3 | |
| 2 | 73.7 | | 2 | 74.0 | 73.7 | 3 | 137.2 | |
| 3 | 72.7 | | 3 | 75.3 | 75.8 | 4 | 14.3 | |
| 4 | 74.6 | | 4 | 79.1 | 79.2 | 5 | 12.3 | |
| 5 | 69.5 | | 5 | 68.0 | 67.9 | Hda-1 | 173.4 | 173.7 |
| 6 | 16.9 | | 6 | 19.1 | 18.8 | 2 | 34.7 | 34.6 |
| Fuc″-1 | 107.1 | | Qui-1 | | 102.4 | 7 | 78.6 | 78.7 |
| 2 | 73.5 | | 2 | | 76.5 | 10 | 14.4 | 14.4 |
| 3 | 75.2 | | 3 | | 78.3 | Qui″-1 | 103.4 | 103.4 |
| 4 | 72.7 | | 4 | | 77.3 | 2 | 75.6 | 75.6 |
| 5 | 71.5 | | 5 | | 72.4 | 3 | 78.3 | 78.2 |
| 6 | 17.1 | | 6 | | 18.6 | 4 | 76.9 | 76.9 |
| Glc-1 | 102.2 | 102.2 | Qui′-1 | 106.0 | 105.6 | 5 | 72.7 | 72.7 |
| 2 | 76.6 | 77.1 | 2 | 77.8 | 75.9 | 6 | 18.8 | 18.8 |
| 3 | 78.6 | 78.8 | 3 | 84.7 | 77.6 | Ipu-1 | 172.9 | 172.9 |
| 4 | 72.5 | 72.5 | 4 | 74.8 | 76.6 | 2 | 43.4 | 43.4 |
| 5 | 77.2 | 77.2 | 5 | 71.5 | 73.9 | 3 | 68.2 | 68.2 |
| 6 | 63.0 | 63.0 | 6 | 18.4 | 18.7 | 11 | 80.2 | 80.2 |
| | | | | | 14 | 14.5 | 14.4 |
| | | | | | OCH3 | 51.2 | 51.2 |
Mannich and Schumann9) have speculated that the convolvulin from Ipomoea purga is an oligomer of acylated glycosidic acid. However, herein we describe both QM-9 and QM-10 as methyl ester monomers of acylated glycosidic acid, as in the case of QM-1–QM-3. On the other hand, QM-6, QM-7, and QM-8 are all acylated methyl glycosides, as in the case of QM-4 and QM-5. Two acylated trisaccharides closely related to the resin glycosides were previously reported as natural constituents of the seeds of Cuscuta chinensis (Convolvulaceae).20) Therefore, QM-6–QM-8 are presumably formed from the corresponding acylated saccharides with a reducing terminal during the treatment with InCl3–MeOH. Although QM-6–QM-10 appear to be artifacts formed during the treatment, they present new information about the structures of genuine convolvulins of Q. pennata. In addition, methyl quamoside B has the new carbohydrate chain; furthermore, QM-10 is the first representative of the quamoclinic acid C as the component glycosidic acid.
Treatment of the Convolvulin Fraction with Indium(III) Chloride in MeOH, and Isolation of 1–5
The crude covolvulin fraction (15.032 g) previously obtained13) from the seeds of Quamoclit pennata was dissolved in MeOH (300 mL), and indium(III) chloride (7.500 g) was added to the solution at the room temperature. The mixture was heated at reflux for 27 d, while being monitored by TLC. The concentrated reaction mixture was chromatographed on a Diaion HP20 (Mitsubishi Chemical Industries) column, eluted with H2O and MeOH. The MeOH eluate (11.162 g) was subjected to Sephadex LH-20 (Pharmacia Fine Chemicals) colum chromatography (CC) eluted with MeOH to give fractions 1 (1.630 g) and 2 (8.113 g). CC of fraction 2 on silica gel eluted with a gradient of mixtures of CHCl3–MeOH–H2O (14 : 2 : 0.1, 10 : 2 : 0.1, 8 : 2 : 0.2, 7 : 3 : 0.5, 6 : 4 : 1, 0 : 1 : 0) afforded fractions 2-1–2-15. Fraction 2-9 (1.431 g) was chromatographed on a Chromatorex ODS (Fuji Silysia Chemical, Ltd.) column using a gradient of mixtures of MeOH–H2O (60% MeOH, 65% MeOH, 70% MeOH, 75% MeOH, 80% MeOH, 85% MeOH, 90% MeOH, 95% MeOH, 100% MeOH) as eluents to give fractions 2-9-1–2-9-52. Fraction 2-9-46 (68 mg) was subjected to HPLC [COSMOSIL 5C18-AR-II(Nacalai Tesque, Inc., 20 mm i.d.×250 mm, column 1)] using 90% MeOH as eluent to give fractions 2-9-46-1–2-9-46-5. HPLC [COSMOSIL 5SL-II (Nacalai Tesque, Inc., 20 mm i.d.×250 mm, column 2)] of fractions 2-9-46-2 (22 mg) using CHCl3–MeOH–H2O (7 : 3 : 0.5) as eluent afforded 4 (8 mg). Fraction 2-10 (2.142 g) was chromatographed on a Chromatorex ODS column using a gradient of mixtures of MeOH–H2O (60% MeOH, 70% MeOH, 80% MeOH, 85% MeOH, 90% MeOH, 100% MeOH) as eluents to give fractions 2-10-1–2-10-18. HPLC (column 1) of fraction 2-10-7 (53 mg) using 65% MeOH as eluent afforded 3 (10 mg). Fraction 2-10-12 (121 mg) was subjected to HPLC (column 1) using 80% MeOH as eluent to give 5 (10 mg) and fractions 2-10-12-1–2-10-12-5. Fraction 2-11 (2.666 g) was chromatographed on a Chromatorex ODS column using a gradient of mixtures of MeOH–H2O (60% MeOH, 65% MeOH, 70% MeOH, 75% MeOH, 80% MeOH, 85% MeOH, 90% MeOH, 95% MeOH, 100% MeOH) as eluents to give fractions 2-11-1–2-11-38. Fraction 2-11-7 (32 mg) was subjected to HPLC (column 1) using 65% MeOH as eluent to give 2 (12 mg). HPLC (column 2) of fraction 2-11-19 (156 mg) using CHCl3–MeOH–H2O (7 : 3 : 0.5) as eluent afforded 1 (73 mg).
QM-6 (1): Amorphous powder. [α]D19 −33.9° (c=1.2, MeOH). Positive-ion FAB-MS m/z: 1607 [M+Na]+. HR-positive-ion FAB-MS m/z: 1607.6921 (Calcd for C69H116O40Na+, 1607.6941). Negative-ion FAB-MS m/z: 1583 [M−H]−, 1337 [1583−100−146]−, 631 [1337−82−146−162−316]−, 339 [631−146×2]−, 333 [quamoclinic acid B−H]−. 1H-NMR spectral data: see Table 1. 13C-NMR spectral data: see Table 2.
QM-7 (2): Amorphous powder. [α]D19 −36.2° (c=0.6, MeOH). Positive-ion FAB-MS m/z: 1291 [M+Na]+. HR-positive-ion FAB-MS m/z: 1291.5062 (Calcd for C53H88O34Na+, 1291.5055). Negative-ion FAB-MS m/z: 1267 [M−H]−, 1021 [1267−100−146]−, 631 [1021−82−146−162]−, 485 [631−146]−, 339 [485−146]−. 1H-NMR spectral data: see Table 3. 13C-NMR spectral data: see Table 2.
QM-8 (3): Amorphous powder. [α]D24 −23.7° (c=1.7, MeOH). Positive-ion FAB-MS m/z: 1479 [M+Na]+. HR-positive-ion FAB-MS m/z: 1479.6495 (Calcd for C63H108O37Na+, 1479.6467). Negative-ion FAB-MS m/z: 1455 [M−H]−, 1355 [1455−100]−, 1255 [1355−100]−, 1209 [1355−146]−, 1109 [1209−100]−, 793 [1109−316]−, 631 [793−162]−, 485 [631−146]−. 1H-NMR spectral data: see Table 3. 13C-NMR spectral data: see Table 2.
QM-9 (4): Amorphous powder. [α]D26 −27.5° (c=0.7, MeOH). Positive-ion FAB-MS m/z: 1831 [M+Na]+. HR-positive-ion FAB-MS m/z: 1831.8704 (Calcd for C83H140O42Na+, 1831.8717). Negative-ion FAB-MS m/z: 1807 [M−H]−, 333. 1H-NMR spectral data: see Table 4. 13C-NMR spectral data: see Table 5.
QM-10 (5): Amorphous powder. [α]D24 −39.7° (c=1.8, MeOH). Positive-ion FAB-MS m/z: 1521 [M+Na]+. HR-positive-ion FAB-MS m/z: 1521.7324 (Calcd for C67H118O36Na+, 1521.7300). Negative-ion FAB-MS m/z: 1497 [M−H]−, 333. 1H-NMR spectral data: see Table 4. 13C-NMR spectral data: see Table 5.
