1452
R.-X. Zheng et al.
peak at m/z 754.5445 [M þ Na]þ (Calcd for C40H77NO10 þ Na, 754.5446). The IR spectrum
of 1 showed absorption peaks typical for a hydroxyl (3380 cmꢁ1), a carbonyl group of an
amide (1645 cmꢁ1), an amino (1540 cmꢁ1), C–O (1080 cmꢁ1) and (CH2)n (720 cmꢁ1
function groups, and is suggestive of a glycosphingolipid. The sugar moiety was determined
)
20
as D-glucose (½ꢀꢂD þ 45.2, c 0.36, H2O) by acid hydrolysis and comparison with an authentic
sample. The stereochemistry of the anomeric carbon of glucose was determined as ꢁ
according to the coupling constant of the anomeric proton (J ¼ 8.0 Hz). The linkage of
glucose to the aglycone was established unambiguously by an HMBC experiment, in which
long-range correlation between H-100 (ꢂ 4.94) and C-1 (ꢂ 70.5) was observed. The presence of
a 1,3,4-trihydroxy unsaturated 18 member chain base was deduced from the 1H–1H COSY
and MS spectra data. The EIMS of 1 showed three fragments at m/z 263, 272, 298, indicating
the presence of the 18 member chain of amide. The signal at ꢂH 8.54 gave a cross peak with
the signal at ꢂH 5.27 (H-2) in the 1H–1H COSY spectrum of 1, which, in turn, showed cross
peaks with methylene protons (H-1) at ꢂH 4.70 and 4.51 and ꢂH 4.28 (H-3). The latter
correlated with the signal at ꢂH 4.18 (H-4). The positive FABMS of 1 showed a molecular ion
peak at m/z 754.3 [M þ Na]þ, and fragments at m/z 569 [754-Na-162]þ, indicating the loss of
glucose. The EIMS of 1 showed a molecular ion peak at m/z 754 [M þ Na]þ and fragment
ion peaks at m/z 713 [M ꢁ H2O]þ, 569 [754-Na-162]þ, 551 [754-Na ꢁ 162-H2O]þ, 355, 344,
309, 298, 272 (100%), 262 and 180, respectively, indicting the presence of a 16 member chain
of fatty acids and another 18 member chain of amides. Furthermore, this result was also
confirmed by the HMBC experiment (Table 1).
The characteristic fragment peak at EI m/z 180 from the ꢁ-cleavage of the double bond
indicated that the position of the olefinic group in the long-chain was at C-6. This
conclusion was further confirmed by EIMS analysis of the corresponding dimethyl
disulfide derivative of 1, showing the fragment ions at m/z 211 from cleavage of the
carbons bearing the methylthio group.
The trans (E ) configuration of the double bond in 1 was evidenced by the coupling
constant of H-6 and H-7 (J ¼ 13.5 Hz), as well as by the chemical shifts of the carbons (32–
33ppm) next to the double band (Sugiyama, Honda, & Komori, 1990; Sugiyama, Honda,
Higuchi, & Komorim, 1991). The signal of the H-2 (ꢂH 5.27), and the signals at ꢂC 70.5 (C-1),
51.7 (C-2), 75.9 (C-3), 72.4 (C-4), 175.9 (C-1) and 72.4 (C-20) were virtually identical with
those of the reported data of other (2S,3S,4R)-phytosphingosine moieties (Sam , Ju, Yong,
1
& Young, 1999). When carefully comparing the H and 13C-NMR data of 1 to aralia
cerebroside reported in the literature, which is the isomeric compound of 1 (Sam et al.,
1999), that the 1,3,4-trihydroxy phytosphingosine moiety in 1 possesses the 2S,3S,4R
configuration could be deduced. Based on the above evidence, the structure of 1 was
established as 1-O-ꢁ-D-glucopyranosyl-(2S,3S,4R,6E)-[20(R)-20-hydroxypalmitoylamino]-6-
octadecene-1,3,4-triol, and named hippophae cerebroside (Figure 1).
Several compounds: oleanolic acid, urosolic acid and dulcioic acid, isolated from H.
rhamnoides, possess moderate antitumour activity in three common solid tumour cell lines.
This indicates that the fruit of H. rhamnoides might be useful for anticancer therapy.
3. Experimental
3.1. General experimental procedures
Melting points were determined on a Fisher–Johns apparatus (Fisher Scientific
International, Hampton, NH, USA) and are uncorrected. The IR spectrometer