238
CMLS 53 (1997), Birkha¨user Verlag, CH-4010 Basel/Switzerland
Research Articles
Figure 1. Diglucosides from Morus alba cell cultures.
out under the same conditions as with [1,3- between two olefinic protons at l 6.55 and 6.40 ppm,
13C2]glycerol. Mulberroside D (20 mg) was obtained less than that between the relevant protons of mulberro-
from the lyophilized cells (5.4 g). Incorporation of the
precursor into mulberroside D (1) was estimated by
comparing the 13C signal intensity of 1 from the feeding
experiment with that of naturally occurring 1.
side A (4, J =16 Hz), indicated that mulberroside D is
a geometric isomer of 4. The 13C-NMR spectrum also
supported this suggestion (table 1). Furthermore,
photo-irradiation of the methanol solution of 4 with a
100 W high-pressure mercury lamp gives mulberroside
D in 90% yield. Thus the molecular structure of mulber-
roside D was represented by the formula 1.
Results and discussion
Mulberroside D (1), [h]D22 – 76°, was obtained as a white
amorphous powder and its molecular formula was de-
termined to be C26H33O14 {(M +H)+, m/z 569.1864}
from the high-resolution FABMS spectrum. The 1H
NMR spectrum of 1 (lppm) showed the proton signals
due to the oxyresveratrol moiety [l 7.01 (1H, d, J =8
Hz, C-6-H), 6.59 (1H, d, J =2 Hz, C-3-H), 6.45 (1H,
dd, J =2 and 8 Hz, C-5-H), 6.52 (1H, br d, J =2 Hz,
C-2%-H), 6.38 (1H, br d, J =2 Hz, C-6%-H), 6.34 (1H, t,
J =2 Hz, C-4%-H), 6.55 (1H, d, J =12 Hz, C-h-H), 6.40
(1H, d, J =12 Hz, C-i-H)] and two glycosyl moieties [l
4.88 (1H, d, J =7 Hz, G1-H), 4.56 (1H, d, J =7 Hz,
G1%-H), 3.10–3.95 (12 H, m)]. These data suggested 1 to
be an oxyresveratrol diglycoside like mulberroside A
Mulberroside E (2), [h]D22 – 75°, was obtained as a white
amorphous powder and its molecular formula was de-
termined to be C26H32O13Na {(M +Na)+, m/z
575.1743} by the high-resolution FABMS spectrum.
1
The signal pattern of 2 in the H NMR spectrum was
closely similar to that of 4, except the A2B2 type of
signal in the A ring of 2, indicating that 2 is a resvera-
trol diglucoside [resveratrol moiety: l 7.46, 7.08 (each
2H, d, J =8 Hz, C-2 and 6-H, C-3 and C-5-H), 6.81,
6.63 (each 1H, br d, J =2 Hz, C-6% and 2%-H), 6.46 (1H,
t, J =2 Hz, C-4%-H), 7.06, 6.93 (each 1H, d, J =16 Hz,
C-h and i-H); two glucosyl moieties: l 4.89, 4.92 (each
1H, d, J =7 Hz), 3.30–3.95 (12H, m)]. The value of the
coupling constant (J =16 Hz) between two olefinic pro-
tons at l 7.06 and 6.93 ppm indicated that 2 has a
trans-stilbene skeleton. The 2D NOESY spectrum indi-
cated the correlation between one of two anomeric
protons at l 4.89 ppm (G1%-H) and two aromatic pro-
tons at l 6.46 (C-4%-H) and 6.81 ppm (C-2%-H) as well as
between the other anomeric proton at l 4.92 (G1-H)
and two aromatic protons at l 7.08 ppm (C-3 and 5-H),
indicating that the two glucose residues are linked with
different aromatic rings. The 13C NMR spectrum of 2
supported the formula 2 for the structure of mulber-
roside E (table 1).
1
(4). Assignments of the protons in the H NMR spec-
trum as well as the carbons in the 13C NMR spectrum
1
(table 1) were performed by 2D H-1H correlation spec-
troscopy (COSY) and 2D 13C-1H COSY. The 2D nu-
clear Overhauser effect shift correlation spectroscopy
(NOESY) demonstrated the correlation between one of
two anomeric protons at l 4.56 ppm (G1%-H) and two
aromatic protons at l 6.34 (C-4%-H) and 6.52 ppm
(C-2%-H), as well as between the other anomeric proton
at l 4.88 ppm (G1-H) and two aromatic protons at l
6.45 (C-5-H) and 6.59 (C-3-H) ppm, indicating that the
two glycosyl residues are linked with different aromatic
rings. The value of the coupling constant (J =12 Hz)
Mulberroside F (3), C26H30O14, [h]2D2 – 75°, is a diglu-
coside of a 2-arylbenzofuran derivative. The molecular
formula was determined by the FABMS {(M +Na)+,
Table 1. 13C-NMR chemical shifts (ppm).
1
m/z 589.1510}. The H NMR spectrum of 3 disclosed
Solvent a; CD3OD c; DMSO-d6
the presence of a 2-arylbenzofuran moiety [l 7.46 (1H,
d, J =8 Hz, C-4-H), 7.32 (1H, br d, J =2 Hz, C-7-H),
7.05 (1H, dd, J =2 and 8 Hz, C-5-H), 7.05 (1H, s,
b, The multiplicities by 13C-13C spin-spin coupling were observed
in [U-13C6]-D-glucose-derived 1