Journal of Natural Products
ARTICLE
Lavaudioside A (2a) was obtained as an amorphous solid,
[R]20D ꢀ30. The molecular formula was C31H42O18, as deduced
from the 13C NMR data and the quasimolecular ion obtained
by LC-HRESIMS (observed m/z 720.2713 [M þ NH4]þ). The
1H NMR spectrum (Table 1) in methanol-d4 showed five
resonances corresponding to the presence of a caffeoyl group
(δH 7.51 to 6.24). An additional resonance at δH 7.53 (s, H-3), as
well as two more at δH 5.55 (d, H-1) and 4.68 (d, H-10),
suggested that 2a was a carboxylated iridoid glucoside. Further-
more, the three-proton doublet at δH 1.10 showed the presence
of a C-10 methyl group. In the 13C NMR spectrum, 30 reso-
nances were observed, of which one (δC 169.0) was of double
intensity. Nine of the resonances were consistent with the
presence of a caffeoyl group. Of the remaining resonances in
the spectrum, 16 were similar to those reported for a 7-O-acyl
derivative of the iridoid glucoside epiloganic acid (2),8 including
those from the 1-O-β-glucopyranosyl group. The remaining six
resonances were all in the δC 65ꢀ73 region, which suggested
the presence of a hexityl moiety. This was consistent with the
1H NMR spectrum, where the signals not accounted for were
observed in the shift interval δH 3.65ꢀ4.44. The HMBC
spectrum allowed the carbons of attachment between the iridoid
moiety and the peripheral parts to be discerned. Thus, the
position of the ester group was confirmed by an HMBC
correlation between H-7 (δH 4.9) and the carbonyl carbon of
the caffeoyl group (δC 169.0). The 1000-CH2 resonances of the
hexityl moiety at δH 4.44 and 4.21 showed correlations with the
carbonyl carbon (δC 169.0) of the iridoid core and with a
carbinol signal (δC 70.5), which could therefore be assigned as
C-2000. The HSQC spectrum designated the remaining reso-
nances at δC 65.1, 72.8, 70.9, and 70.8 as one CH2OH and three
CHOH groups, respectively, thereby fulfilling the molecular
formula determined by the MS. The first three shift values closely
matched those of mannitol (1). Confirmation that the hexitol
was indeed mannitol was achieved by an in-NMR tube hydrolysis
similar to that of 2a, but resonances from two caffeoyl groups
were present. Also, two β-hexopyranosyl groups were considered
present due to the two doublets at δH 4.69 and 4.36. In the 13
C
NMR spectrum (Table 1) of 4, 39 resonances were observed, of
which five were of double and one (δC 71.6) was of triple
intensity, as also confirmed by the HSQC data. Eighteen of the
resonances could be assigned to the two caffeoyl groups, and
comparing with the data for 2a, a further 16 could be assigned
to an epiloganyl moiety including its 1-O-glucosyl group. This left
12 13C NMR resonances to be accounted for. That at δC 105.0
was assigned to an anomeric carbon atom, and the remaining 11,
resonating at δC 64ꢀ78, suggested the presence of a hexopyr-
anosyl and a hexityl moiety. 2D NMR data suggested that the
hexopyranosyl moiety was an additional β-glucopyranosyl group,
but the full structure of 4 could be resolved only in relation to that
of hebitol II (5).
The sugar esterhebitol II(5) was considered to be composed of
a 6-O-caffeoyl-β-D-glucopyranose moiety with a 1-glucityl group as
the aglucone.10 The structure of 5 was originally elucidated
by comparison of the NMR data of an analogue, the feruloyl
ester globularitol (5b) isolated from Globularia orientalis.11 The
structure of 5b was in turn inferred by deacylation and com-
parison by TLC of the resulting disaccharide with authentic β-D-
glucopyranosyl-(1f6)-glucitol (5d), obtained by NaBH4 reduc-
tion of gentiobiose. However, because the corresponding 13C
NMR shift values of 5 (for C-1000 to C-3000 in Table 1) compared
better with those of β-D-glucopyranosyl-(1f6)-mannitol (5c)12
than with those of the glucitol derivative, we therefore decided to
re-examine the structure of 5. Thus, treatment of 5 with ammonia
in D2O gave a disaccharide with a 13C NMR spectrum (see
Supporting Information) identical to that reported for 5c. The
similar levorotatory activity of5 and 5aꢀc pointed to the β-D-form
of the glucose moiety in the four compounds (see Supporting
Information). Consequently, the structures of the three analogues
hebitol II (5), hebitol I (5a),10 and globularitol (5b)11 must be
revised to the β-D-glucosylmannitol derivatives shown in the
formula chart.
of 2a with ammonia in D2O. After 48 h at room temperature, 13
C
NMR resonances corresponding to mannitol were observed
at δC 64.5 (C-1 and C-6), 72.1 (C-2 and C-5), and 70.5
(C-3 and C-4).9 These increased in intensity following the
addition of authentic mannitol (see Supporting Information).
Lavaudioside B (3a) was obtained as an amorphous solid,
[R]22D ꢀ24. The molecular formula was C31H40O18, as deduced
from the 13C NMR data and LC-HRESIMS (observed m/z
718.2558 [M þ NH4]þ). The NMR data (Table 1) in methanol-
d4 was assigned as above. The 1H NMR spectrum was similar to
that of 2a, including a caffeoyl and a mannityl group, as well as the
resonance at δH 7.62 (1H, s, H-3) and others at δH 5.41 and 4.70,
assigned to H-1 and H-10, respectively. The major differences
were in the iridoid moiety. Thus, additional resonances (δH 5.48
and 5.45) were present, while that from a methyl group was
missing. In the 13C NMR spectrum of 3a, the expected 31
resonances were observed. When compared with the spectrum of
2a, only the resonances for the iridoid aglucone differed. The two
resonances at δC 148.9 and 116.5 suggested an iridoid with an
Returning to the structure of 4, the resonances of the caffeoyl
and β-glucopyranosyl groups found in 4, but not in 2a, were
coincident with the corresponding resonances of 5. In addition,
those from C-1000 through C-3000 for 4 were almost coincident
with the resonances of the corresponding carbon atoms of 2a,
and the resonances of C-4000 to C-6000 were coincident with those
of 5. This provided the hypothetical structure for 4. In the
HMBC spectrum, correlations could be seen between the 1000-
CH2 group (δH 4.42 and 4.20) and C-2000 (δC 70.7) as well as
C-11 of the iridoid core (δC 169.0) since a cross-peak with H-5
(δH 3.13) was also found at this shift value. Other correlations
were seen between the 6000-CH2 group (δH 4.14 and 3.76) and
C-5000 (δC 71.6) as well as the anomeric carbon atom C-10000 of
the central β-glucopyranosyl moiety (δC 105.0). Also, H-50000
(δH 3.55) displayed a correlation with C-10000, and furthermore,
cross-peaks could be found between 60000-CH2 (δH 4.52 and
4.28) and C-50000 (δC 75.5) as well as one of the low-field
carbonyl carbon atoms (δC 169.1). Therefore, it was concluded
that the latter could be assigned to one of the caffeic acid
moieties. The structure of lavaudioside C has therefore been
established as that shown by 4.
1
8,10-double bond, in accordance with the H NMR data. A
comparison with the data reported8 for a 7-O-acyl derivative of
gardoside (3) showed a satisfactory coincidence for the chemical
shift values.
Lavaudioside C (4) was isolated as an amorphous solid,
Compound 7e was obtained as an amorphous solid, [R]22D ꢀ70,
and the molecular formula was C24H28O13, determined by the
13C NMR data and LC-HRESIMS (observed m/z 523.1465
[M ꢀ H]ꢀ). The 1H NMR data (Table 2) were somewhat similar
[R]22 ꢀ48, and the molecular formula was C46H58O26, de-
D
duced by the 13C NMR data and LC-HRESIMS (observed m/z
1027.3269 [M þ H]þ). The 1H NMR spectrum (Table 1) was
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dx.doi.org/10.1021/np200233p |J. Nat. Prod. 2011, 74, 1477–1483