A novel flavonoid glycoside acylated with a sesquiterpene. dihydrophaseic acid, was obtained from the seeds of Astragalus complanatus R. BR. Astragali Semen, the seeds of Astragalus complanatus R. BR. (Leguminosae), has been used as a tonic in the traditional Chinese medicine. In the preceding paper,*) we reported the occurrence of the oleanene qlycosides in the methanolic extract of the title plant. We now present a paper of a novel flavonoid glycoside acylated with an absc::sic acid-type sesquiterpene, designated as complanatin.Complanatin (11, pale yellow needles, mp 192-4"C, [01lD +0.50 (MeOH), showed a peak due to [M+l]+ at m/z 889 in the positive FAB-MS, UV absorption peaks [hmax 267 (log & 4.88), 340 (log & 4.39)1, and IR absorptions(cm-1) at 3428 (OH), 1705 (ester carbonyl), 1658 (conjugated carbonyl) and 1602 (aromatic ring). The lH- and 13C-NMR spectra of 13) displayed that it was constituted with a flavonoid portion, glycosidic parts and a sesquiterpene moiety as listed in Table I. Since the appearance of the ester linkage was suggested, 1 was saponified with alkaline to afford a flavonoid derivative (2), pale yellow crystals, mp 271-3'C, [a]D +28.0c (DMSO-d6), positive FAB-MS (m/z): 625 [M+l]+ and a sesquiterpene moiety (3), a resin, [a]D -72.6" (CHC13), EI-MS (m/z): 296 CM+).The IH-NMR signals (in DMSO-d6) c86.38 (lH, d, J-2.2 Hz), 6.77 (lH, d, 512.2 Hz), 7.17 (ZH, d, J=8.8 Hz), 8.17 (2H, d, J=8.8 Hz), 12.56 (lH, s) I 3.87 (3H, s) I of 2 could assign its structure to be a 3,5,1,4' tetrahydroxyflavone (kaempferol) derivative. It was furthermore suggested to possess one methoxyl group at C-7 by the NOE experiment and subsequently two terminal glucosyl moieties [two anomeric proton signals at 2; 5.50 (lH, d, J=7.3 Hz) and 5.04 (lH, d, J-7.3 Hz) 1 to attach to C-3-OH and C-4'-OH, respectively, by the 13C-NMR spectrum.On the other hand, the 'H-NMR spectrum (in CDCl3) of 3 s.howed signals due to two methyl groups (6 0.89, 1.11, each s), one vinyl methyl (61.99, d, Jz1.5 Hz), one methoxyl group (6 3.65, s), three olefinic protons [6 5.69 (lH, s), 6.36 (111, d, ~=16.1 Hz), 7.95 (lH, d, J=16.1 Hz)], a methylene group bearing oxygen atom [6 3.69 (lH, d, 5~7.7 Hz), 3.14 (lH, dd, J=l.7, 2.2 Hz)], methine group adjacent to the hydroxyl group [8 4.22 (lH, dddd, J=10.6, 10.3, 7.0, 7.0 Hz), and other methylene signals [6 1.60 (lH, dd, J=13.6, 10.6 Hz), 1.67 (lH, dd, J=13.6, 10.3 Hz), 1.84 (lH, ddd, J=13.6, 7.0, 1.5 Hz), 2.10 (lH, ddd, JE13.6, 7.0, 1.5 Hz)] attrjbutable to a sesquiterpene moiety, methyl dihydrophaseate,5) which was der:ved from (-) methyl phaseate 6*7) by reduction with NaBH4. Oxidation of 3 with chromic acid yielded a product (4),8) [@ID -26.7" (CHC13), being ident:cal with (-) methyl phaseate in respects with specific rotation, IH- and 13C-NMR spectra.Meanwhile, enzymatic hydrolysis of 1 provided a sole product (5),g) which was estimated as a deglucosyl compound of 1 by the FAB-MS { [M+ll+ at m/z 727) and 13C-NMR spectrum. Moreover, the 13C-NMR spectrum revealed that the acylated glucosyl moiety attached to the C-4'-OH and furthermore the sesquiterpene residue linked to the C-2 hydroxyl group of gl-ucosyl moiety [acylation shifts (ppm): C-l, 6 97.6(-2.3); C-2, 6 74.0(+0.8); C-3, 6 72.6 (-3.8)],10) whose lH-NMR spectrum also supported by the fact that signals due to H-l and H-2 appeared at 65.83 (lH, d, J=8.1 Hz) and 5.94 (lH, dd, Jz8.1, 9.5 Hz), respectively, being substantiated by the lH-lH COSY.Consequently, the structure of complanatin (1) was determined as shown in the formula. A novel flavonoi~d glycosj_de acylated with sesquiterpene is firstly reported.