5.35 ppm (H-12) and a double doublet at d 2.86 ppm (H-18, J 13, 4 Hz).7 The ß-configuration of the sugar moiety was apparent from the coupling value found for the anomeric proton (d 5.58 ppm, d, J 8 Hz). The structure of compound 5 can therefore be defined as 29- hydroxyarjunglucoside II octaacetate or 2,3,4,6-tetra-O-acetyl-ß-D-glucopyranosyl 2,3,23,29- tetra-O-acetyl-2a,3ß,23,29-tetrahydroxyolean-12-en-28-oate. Hence compound 5 is the octaacetyl derivative of the natural triterpene quadranoside III (6),8 ß-D-glucopyranosyl 2a,3ß,23,29-tetrahydroxyolean-12-en-28-oate.
Compounds 7 and 8 were isolated as an inseparable mixture (3:2), which presented a similar 1H NMR spectrum as that from the mixture 1, 2 prepared by separate heating of 3 with acetic anhydride in pyridine. From the disappearance of the AB quartets at d 3.50-3.90 corresponding to the oxymethylene protons H-23 in 1, 2, compounds 7, 8 were presumed to be the 23-H analogues of 1, 2. In the 13C NMR spectrum, the 23-deoxy structure was supported by the absence of the signal at d 65.3 corresponding to the oxymethylene carbon C-23, and the appearence of a peak at d 28.4 attributed to the C-23 methyl group. Further comparison of the 13C NMR data of 7, 8 to those of 1, 2 confirmed their identical structures except for the ring A substituents while comparison to data published for 22 and 26 having a C-23 methyl group (Table 3) revealed identical ring A substituents (Table 1). The structures of compounds 7 and 8 are therefore defined as 2,3,4,6-tetra-O-acetyl-ß-D-glucopyranosyl 2,3-di-O-acetyl-19-O-[(E)-3- acetoxybut-2-enoyl]-2a,3ß,19a-trihydroxyolean-12-en-28-oate and 2,3,4,6-tetra-O-acetyl-ß-D- glucopyranosyl 2,3-di-O-acetyl-19-O-[(Z)-3-acetoxybut-2-enoyl]-2a,3ß,19a-trihydroxyolean-12- en-28-oate, respectively. These new compounds 7 and 8 are derived from the known natural glucoside arjunetin (9),9 in the same way as compounds 1 and 2 from arjunglucoside I (4).
Compound 10 was isolated as an inseparable mixture (4:1) along with compound 3. The mass spectrum of 10 displayed a pseudo-molecular ion at m/z 978 ([M + NH4]+). The molecular formula C50H72O18 was inferred from the MS and 13C NMR data. The 1H NMR spectrum of 10 showed signals for one secondary (d 0.94 ppm) and five tertiary (d 1.26, 1.20, 1.10, 0.91 and 0.72 ppm) methyl groups, and an olefinic proton signal at d 5.38 ppm (t, J 4 Hz). The presence of this olefinic proton and a secondary methyl group suggested that compound 10 is a .12-ursene derivative. A broad singlet detected at d 2.53 corresponds to H-18ß of an ursane type structure with 19a-O-substitution.26-28 Compound 10 is therefore a derivative of a 19a-hydroxyurs-12-en type triterpenoid. Further absorptions in the region of 3.50-5.60 ppm were similar to those observed for compound 3 (Table 2). The AB quartet (J 12 Hz) centered at 3.87 and 3.57 ppm was due to the oxymethylene protons H-23. The diaxial coupling observed for H-3a (d 5.09, d, J 10 Hz) indicated the presence of an 2a-OAc substitutent. These data suggested that compound 10 is a derivative of 2a,3ß,19a,23-tetrahydroxyurs-12-en triterpenoid. The coupling value found for a doublet due to the anomeric proton (d 5.58, J 8 Hz) indicated the presence of a ß- hexopyranosyl ester moiety. The sugar attached to C-28 of the aglycone was identified as ß-D- glucopyranose by comparison of the 13C NMR data of 10 to those of 1, 2, and 3. The 13C NMR spectrum of 10 provides further support for the ursene type triterpenoid structure of the aglycone. The peaks at d 128.9 (-CH=) and 137.5 (=C<) ppm are characteristic of a .12-ursene
