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S.R. Gedara and A.A. Galala
1994), 3b-O-trans-p-coumaroyl-erythrodiol (Xue et al. 1988), myricetin-3-O-rhamnoside and
quercetin-3-O-rhamnoside (Agrawal 1989). Quercetin-3-O-a-L-rhamnoside (3) and myricetin-
3-O-a-L-rhamnoside (5) were separated before from the leaves and flowers of A. saligna
(El-Sawi 2001), and erythrodiol (1) was isolated as erythrodiol diacetate from the hexane extract
of A. saligna (El-Sawi et al. 2003). This is the first report for the isolation of 3b-O-trans-p-
coumaroyl-erythrodiol (2) from genus Acacia, in addition to the new compounds 4 and 6.
Compound 4 was isolated as amorphous yellow powder. 13C NMR (see experimental
section) revealed the presence of 15 countable carbon signals alongside with the sugar signals
which were identical to that of myricetin-3-O-rhamnoside (Agrawal 1989). However, 1H NMR
showed two 3H signals at dH 0.91 (d, J ¼ 6.4 Hz) and 0.95 (d, J ¼ 6 Hz) suggesting two methyl
residues and hence two rhamnose moieties. This finding was further confirmed by the presence
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of two anomeric proton singlets at dH 5.30 and 5.29. H NMR also showed the presence of a
singlet signal at dH 6.92 (H- 20, 60 I, II) integrated for four protons, besides the presence of two
doublets at dH 6.18 (H-6 I, II) and dH 6.36 (H-8 I, II) each integrated for two protons. This result
indicated the probable presence of a symmetrical flavonoid dimer. EI-MS gave a molecular ion
peak at m/z 910 consistent with the molecular formula C42H38O23. The EI-MS and the mass
fragmentation pattern depicted in Figure S1 were additional supports of the presence of
biflavonoid glycoside. The establishment of the connection of both flavonol glycoside moieties
through a [C7-O-C7] ether linkage was determined by UV spectral data (see Section 3) as the
absence of a significant bathochromic shift in band II (þ3.5) upon addition of NaOAc indicated
that the hydroxyl group at C-7 is blocked. The upfield shift of H-6 and H-8 at dH 6.18 and dH
6.36, respectively, indicated the absence of glycosylation at C-7 (Nyandat et al. 1990) and the
presence of (C7-O-C7) ether linkage biflavonoid. Based on these findings, compound 4 was
confirmed to be biflavonoid glycoside, myricetin-3-O-rhamnoside (C7-O-C7) myricetin-3-O-
rhamnoside, which is a new natural product.
Compound 6 was obtained as a yellowish-white amorphous powder. Its molecular formula
was deduced to be C43H70O16 from HR-ESI-MS data (m/z 865.6085 [M þ Na]þ). The 1H NMR
spectrum of 6 exhibited two tertiary methyl signals at dH 0.71 (s, C-18), 0.89 (s, C-19) and two
secondary methyl signals at dH 0.93 (d, J ¼ 6.9 Hz, C-21), 1.00 (d, J ¼ 7.1 Hz, C-27), which
were recognised as typical steroid methyls (Lu et al. 2010). The 13C NMR signals showed 43
carbon signals, 27 of which were assigned to the aglycone moiety consisted in 2 tertiary methyls,
2 secondary methyls, 11 methylenes (including one oxygenated at dC 64.0), 9 methines
(including two oxygenated at dC 81.2 and 72.8) and 3 quaternary carbons (including one
oxygenated at dC 110.0) as concluded from the DEPT experiment. The remaining signals were
due to the carbons of the three sugar units. All the information mentioned above together with
the HMBC correlations (Figure S2) indicates the probable presence of a spirostane saponin
(Agrawal et al. 1985). The 25S configuration was confirmed by the upfield shift of C-23, C-24,
C-25, C-26 and C-27 to dC 26.9, 25.7, 26.7, 64.0 and 16.3, respectively, comparable to those of
25R (Agrawal et al. 1985). The 5b configuration was deduced from the higher field resonance of
C-5 to dC 35.6 (Zhou et al. 2007). From the above data, the aglycone of compound 6 was
identified as 25S-5b-spirostan-3b-ol (sarsasapogenin). The 1H NMR and 13C NMR of 6
exhibited three sugar anomeric protons at dH 4.25 (d, J ¼ 7.7 Hz), 4.34 (d, J ¼ 7.7 Hz) and 4.40
(d, J ¼ 7.3 Hz) and carbon atoms at dC 103.9, 98.9 and 105.0, respectively. The sugar part of 6
was determined to be a combination of one galactose and two xylose moieties on the bases of
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NMR data (including 13C NMR, HSQC, H,1H COSY and HMBC) and by acid hydrolysis
followed by investigation of the sugar part alongside with authentic sugars. The b-anomeric
configurations of both galactose and xylose moieties were judged from their coupling constants
(J1,2 . 7.0 Hz) (Su et al. 2009). The sequence of the trisaccharide chain at C-3 was deduced
from the following HMBC correlations: H-10 (dH 4.34) of galactose with C-3 (dC 72.8) of the
aglycone, H-100 (dH 4.25) of the first xylose moiety with C-30 (dC 79.3) of galactose and H-1000 (dH