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F. Feistel et al. / Phytochemistry 143 (2017) 170e179
be oxygenated due to its 13C chemical shift value. Further long-
range CH-correlations suggested an aliphatic ring structure as
corroborated by 3JCH correlations of H-5000a/b to C-6000 and H-5000b to
3), dC 123.5 (C-4), dC 131.0 (C-5) and dC 116.6 (C-6). The 1,2-
disubstitution was determined from characteristic HMBC correla-
tions of H-6 and H-4 with a quaternary carbon atom at dC 126.0 (C-
2) and of H-3 and H-5 with C-1. The HMBC correlation between the
protons H-7a/b at dH 5.28/5.40 (3JHH ¼ 12.6) of the hydroxy-
methylene group to C-3 (dC 130.6) indicated that this substituent is
attached to C-2 of the aromatic ring. Thus, the fragment was
characterized as a salicylic alcohol moiety. Further 3JCH correlations
3
C-1000. The geometry was also supported by JCH correlations of H-
3000/H-2000 to C-4000 and H-3000 to C-5000. An additional HMBC correlation
of H-3000 to a third quaternary carbon atom at dC 171.5 (C-7000) indi-
cated the linkage to a carboxyl functionality tethered to position C-
1000 of the aliphatic ring structure, which led to the characterization
of the subunit as 1-hydroxy-cyclohex-2-en-6-onoyl moiety (HCH).
Because another long-range CH-correlation from the methylene
group of the aromatic ring at H-7a/b (dH 5.54/5.30; dC 64.7) to C-7000
established the ester linkage of the HCH unit with the rest of the
molecule, the structure was characterized as an idescarpin deriv-
ative (Fig. 1) with an additional p-coumaric acid linked to the 40-OH
between position H-7a/b and the carboxyl carbon atom C-7000
(dC
171.5) revealed the linkage to the HCH moiety via an ester bond.
Accordingly, the structure of compound 8 was assigned as 40-O-(E)-
p-coumaroyl-salicortin. Except for the signals of its CG unit, com-
pound 9 showed very similar chemical shift values compared to 8
(Table 2). Although most signals were overlapping, the connectiv-
ities of the particular subsystems appeared to be identical.
Accordingly, the structure of compound 9 was assigned as 40-O-(Z)-
p-coumaroyl-salicortin.
of the b-glucopyranosyl moiety. Determination of the configuration
at position C-1000 in the HCH moiety was achieved by circular di-
chroism (CD) spectroscopy. The differential dichroic absorption of
D
ε ¼ ꢀ6.9 mdeg (lmax ¼ 216 nm, c ¼ 0.75 mM, MeOH) of compound
As for compounds 6 and 7, the configuration at the stereogenic
6 was compared with the reported value of
D
ε ¼ ꢀ13.4 mdeg
position C-1000 in the HCH moieties of 8 and 9 was determined by CD
(
lmax ¼ 224 nm, c ¼ 1.61 mM) for (S)-idescarpin (Feistel et al., 2015;
spectroscopy. A differential dichroic absorption of
lmax ¼ 219 nm, c ¼ 1.19 mM, MeOH) was found for the mixture and
compared with the reported value of
ꢀ26.7 mdeg
D
ε ¼ ꢀ3.5 mdeg
Kim et al., 2014). The negative
Dε values reveal the same stereo-
(
chemistry of 6 and idescarpin. Hence, we concluded that com-
pound 6 had an (S)-configuration at the stereogenic position C-1000.
Accordingly, the structure of compound 6 was assigned as 40-O-(E)-
p-coumaroyl-idescarpin.
Dε
¼
(
lmax ¼ 224 nm, c ¼ 1.61 mM) for salicortin (Fig. 1) (Feistel et al.,
2015). Accordingly, (S)-configuration at position C-1000 was
concluded. Usually, determination of the configuration demands
The HRESIMS data of compound 7 showed a molecular ion peak
of m/z 585.1601 [M-H]-. As for compound 6, its mass was consistent
with a molecular formula of C29H30O13 (calcd for C29H29O13, m/z
585.1614), suggesting isomeric structures for compounds 6 and 7.
Furthermore, a comparison of 1H NMR, 1H-1H COSY, 1H-13C HSQC
and 1H-13C HMBC data with those of compound 6 (Table 2) also
suggested both compounds have very similar structures. Signals of
compound 6 were also observed in the NMR spectra of compound
7, which might be due to spontaneous isomerization. Compared to
signals seen in the 1H NMR spectrum of compound 6, the proton
pure substances. However, here we determined Dε for a mixture of
the isomeric compounds 8 and 9; these differ only in the configu-
ration of their double bond system, which does not interfere with
the stereogenic position of interest. The very similar NMR spectra of
these compounds highlight their close electronic similarity. How-
ever, in contrast to the reference compound salicortin, compounds
8 and 9 have stronger UV absorption due to the presence of addi-
tional chromophores, and these in turn influence the CD mea-
surement. As a result, the determined
Dε is still negative, but
smaller compared to ε of salicortin. Furthermore, the (S)-config-
D
signals of the p-coumaroyl
p
-system of compound 7 appeared at a
uration of the main HCH-containing compounds idescarparide (14)
and idescarpin (15) was determined earlier by X-ray crystallog-
raphy (Kim et al., 2014).
higher field at dH 6.92 (H-700) and dH 5.81 (H-800). Both doublet
3
signals showed a coupling constant of JHH ¼ 12.6 Hz, which in-
dicates Z-configuration. CD spectroscopy resulted in
Dε ¼ ꢀ5.6
The HRESIMS of compound 12 showed a molecular ion peak of
mdeg (lmax ¼ 218 nm, c ¼ 0.98 mM, MeOH), which is in accordance
with the stereochemical description of compound 6 ((S)-configu-
ration at position C-1000). Accordingly, the structure of compound 7
was assigned as 40-O-(Z)-p-coumaroyl-idescarpin.
Compounds 8 and 9 were obtained as a mixed fraction from
HPLC-SPE-separation. UPLC-HRESIMS showed two molecular ions
of m/z 569.1650 [M-H]- and m/z 569.1652 [M-H]-, both corre-
m/z 423.1651 [M-H]-, which corresponds to a molecular formula of
C21H28O9 (calcd for C21H27O9, m/z 423.1661). According to reported
data (Si et al., 2009), the observed NMR signals suggest that this
compound is an isograndidentatin isomer. The 1,2-cyclohexanediol
ring of this structure features two stereogenic centers at positions
C-1 and C-2. NMR data were inconsistent with (1R,2S)-cis-config-
uration (Si et al., 2009) and (1S,2S)-trans-configuration (Pichette
et al., 2010). To the best of our knowledge (SciFinder® search,
May 2017), no information about a possible (1R,2R)-trans-config-
ured 1,2-cyclohexanediol has been reported. Therefore, compound
12 was hydrolyzed and the resulting aglycon was compared to
authentic standards by chiral GC-MS measurements. The hydrolysis
product was determined to be (1R,2S)-cis-1,2-cyclohexanediol.
Accordingly, we identified 12 as isograndidentatin A.
The structures of compounds 1e15 from I. polycarpa resemble
those of compounds reported from Salix (Thieme, 1964) and Pop-
ulus species (Boeckler et al., 2011; Dommisse et al., 1986; Si et al.,
2009). However, a typical Idesia feature is the presence of com-
pounds with an additional hydroxyl group in the aromatic part of
sponding to a molecular formula of C29H30O12 (calcd for C29H29O12
,
m/z 569.1664). The NMR data (Table 2) of compounds 8 and 9
showed close similarities with the data of compounds 6 and 7
described above. Matching signals for the presence of HCH rings as
well as the Z-CG and E-CG moieties were found, indicating com-
pounds 8 and 9 were a pair of cis-trans isomers. Comparative
integration of the 1H NMR signals of E-CG (8) (dH 6.39 with
3JHH ¼ 15.6, H-800) and Z-CG (9) (dH 5.83 with JHH ¼ 12.9, H-800)
3
revealed a molar ratio of 2 to 1. Structure elucidation of compound
8 started from the NMR signals of its E-CG unit. The 1H NMR signal
of the proton (H-10) at the anomeric position of a
b-glucopyranosyl
unit appeared at dH 5.01 (3JHH ¼ 7.8 Hz). This signal showed a 1H-13
C
HMBC correlation to a quaternary carbon atom at dC 156.8. The
chemical shift assigned the latter signal to the oxygenated C-1 of an
aromatic system. The aromatic proton signals were assigned to a
four-spin system (ABCD) consisting of dH 7.31 (3JHH ¼ 7.2 Hz, H-3),
dH 7.04 (3JHH ¼ 7.2/8.0 Hz, H-4), dH 7.33 (3JHH ¼ 8.0/8.6 Hz, H-5) and
dH 7.24 (3JHH ¼ 8.6 Hz, H-6). The corresponding 13C chemical shifts
were determined from 1H-13C HSQC correlations to be dC 130.6 (C-
the parent salicinoids (4, 6, 7 and 14, 15). Whereas b-glucopyranose
substituents in compounds isolated from Populus are typically
found on position C-20 or C-60, the corresponding Idesia compounds
are acylated exclusively at position C-4' (1e9 and 11e13).
Little is known about the ecological functions of Idesia constit-
uents. Like Populus salicinoids, which are generally accepted as
defense compounds with feeding-deterrent and anti-fungal
Feistel, Felix
