In the course of our serial studies on bioactive constituents from Chinese natural medicines, we have characterized the structures of aliphatic alcohol and monoterpene oligo- glycosides and cyanogenic glycosides from the roots of Rhodiola (R) quadrifida,

from Chinese natural medicines, we have characterized the structures of aliphatic alcohol and monoterpene oligoglycosides and cyanogenic glycosides from the roots of Rhodiola (R) quadrifida, R. sacra, and R. crenulata. Among the isolated compounds, several monoterpene oligoglycosides were found to show histamine release from rat exudate cells induced by an antigen–antibody reaction. Furthermore, from the extracts of R. sachalinensis with a protective effect an D-galactosamine-induced cytotoxicity in primary cultured mouse hepatocytes, we isolated monoterpene oligoglycosides, flavonol bisdesmosides, and cyanogenic glycoside named sachalosides I—VIII and reported their structures and hepatoprotective effects. As a continuing study on R. sachalinensis, we isolated three new ( )-rosiridol glycosides termed rosiridosides A (3), B (4), and C (5) together with rosiridin (2) [( )-rosiridol 1-O-b-D-glucopyranoside]. The absolute configuration of the 4-position in ( )-rosiridol (1) was first reported to be S by the total enantioselective synthesis and chemical transformation to ( )-eldanolide. However, the absolute configuration of the 4-position in ( )rosiridol and rosiridin was recently revised to be R (1 , 2 ) by the application of the modified Mosher’s method. In order to determine the absolute stereostructures of rosiridosides (3—5), we began with a reinvestigation of the absolute configuration of ( )-rosiridol. This paper deals with the application of the modifiel Mosher’s method for ( )and ( )rosiridol pivalate (6, 11), which supported the previous synthetic evidence to be S configuration (1, 2) rather than R form (1 , 2 ). Furthermore, we described the isolation and structure elucidation of three new ( )-rosiridol glycosides (3, 4, 5). Isolation of Rosiridin and Rosiridosides A, B, and C The methanolic extract from the roots of R. sachalinensis was partitioned into an EtOAc–H2O mixture to furnish an EtOAc-soluble phase (3.5% from the roots) and aqueous layer, which was further extracted with n-BuOH to give a nBuOH-soluble phase. The EtOAc-soluble fraction was subjected to normal-phase and reverse-phase column chromatographies, and finally HPLC to give rosiridoside C (5, 0.0013%). The n-BuOH-soluble phase was subjected to Diaion HP-20 column chromatography to afford a methanoleluted fraction (3.5%) as previously reported. The methanol-eluted fraction was separated by normaland reversed-phase column chromatography, and finally HPLC to give rosiridosides A (3, 0.00019%) and B (4, 0.00032%) together with rosiridin (2, 0.49%). Reinvestigation of the Absolute Configuration of ( )Rosiridol Rosiridin (2) was obtained as a colorless viscous oil with a negative optical rotation {[a]D 32.1° (c 2.06 in MeOH), [a]D 31.3° (c 4.65 in acetone)} and the IR spectrum of 2 showed absorption bands at 3450, 1638, and 1045 cm 1 assignable to hydroxyl, olefin, and ether functions. The positive-ion first atom bombardment (FAB)-MS of 2 exhibited a quasimolecular ion peak at m/z 355 (M Na) . The high resolution (HR) MS analysis revealed the molecular formula of 2 to be C16H28O7. Acid hydrolysis of 2 with HCl 1 M liberated D-glucose, which was identified by HPLC analysis using an optical rotation detector. On the basis of this evidence and by comparison of the physical data with reported values {[a]D 16.9° (c 0.087 in MeOH), [a]D 32.7° (c 1.1 in acetone), Hand C-NMR, MS}, 2 was identified to be rosiridin, which was isolated from R. rosea and R. sachalinensis, in which the absolute stereostructure of rosiridin was reported to be 2 . Enzymatic hydrolysis of 2 with b-glucosidase furnished ( )-rosiridol, {1, [a]D 7.7° (c 1.98 in acetone), [a]D 14.2° (c 0.42 in CHCl3)}, whose molecular formula C10H18O2 was determined from a molecular ion peak at m/z 170 (M) and by HR-MS measurement. The H-NMR (CD3OD) and CNMR (Table 1) spectra of 1 showed signals assignable to three methyls [d 1.65, 1.69, 1.74, (3H each, both s, H3-8, 10, May 2008 695