64 Original Papers
(δH 7.08); and MeO-3 (δH 3.88) and H-4 (δH 7.08) implied that 2
was a derivative of 1, sharing the same aromatic ring system. The
HMBC correlations (l Fig. 2) from H-4 (δH 7.08), H-6 (δH 7.08),
and H-2′ (δH 2.91) to C-1′ (δC 200.2) established the location of a
ketone in 2. Based upon the above data, compound 2 was a keto
derivative of 1 and its structure was established as shown.
Table 2 Anticubercular activities of compounds from A. cornudentata against
M. tuberculosis H37RV.
"
Compounds#
MIC (µg/mL)
3-Methoxy-2-methyl-5-pentylphenol (1)
1,3-Dimethoxy-2-methyl-5-pentylbenzene (1a)
3-Methoxy-2-methyl-5-(1′-ketopentyl)phenol (2)
1-(3,5-Dihydroxyphenyl)heptan-1′-one (4)†
1-(3,5-Dihydroxyphenyl)nonan-1′-one (5)
3-Methoxy-5-pentylphenol (6)
Ardisinone (7)
≤ 2.58
≤ 2.50
12.8
19.0
6.0
Cornudoside (3) was obtained as colorless needles. The ESI MS
gave a dehydrated pseudo-molecular ion [M ‑ H2O + Na]+ at m/z
335, and from the analysis of HR ESIMS its formula corresponded
to C14H16O8Na (m/z 335.0741). Together with spectral data, the
molecular formula of 3 was inferred to be C14H18O9. UV absorp-
tions at 215, 269, 321 nm and a bathochromic shift after addition
of KOH aq. solution suggested the presence of a phenolic conju-
gated benzenoid moiety [12]. The 1H‑NMR spectrum revealed
one singlet proton at δH 7.02 (1H, s, H-6) in the aromatic region,
suggesting the presence of a pentasubstituted benzene ring in 3.
These five substituents were identified as a methyl group [δH 2.10
(3H, s, Me-4)], a glucosyl group [δH 4.96 (1H, d, J = 10.4 Hz, H-1′),
4.05 (1H, m, H-2′), 4.02 (1H, t, J = 9.0 Hz, Ha − 6′), 3.82 (1H, t,
J = 8.9 Hz, H-3′), 3.69 (1H, m, H-5′), 3.68 (1H, m, Hb − 6′), 3.42 (1H,
t, J = 8.9 Hz, H-4′)], two sp2 hydroxy groups at C-3 (δC154.9) and C-
5 (δC 157.9), and a carboxylic acid [δC 166.2 (C-1′′)] attached at C-1
(δC 122.2). The presence of these substituents was supported by
the 13C‑NMR experiment and IR absorptions at 3334 (OH) and
60
≥ 150
≥ 200
20.8
19.6
59.4
19.3
33.8
47.1
25.6
160
Cornudentanone (8)
5-(8′Z-pentadecenyl)resorcinol (9)†
5-(8′Z-heptadecenyl)resorcinol (10)†
2-Methyl-5-(8′Z-heptadecenyl)resorcinol (11)†
2-Methylcardol (12)†
Belamcandol B (13)
Kusukuenol A1 (14)†
Kusukuenol A2 (15)†
Oncostemonol D (20)
Dehydrobisgravillol (21) †
50.2
150
(+)-Catechin (24)
Ethambutol*
6.25
* Positive control; † previous data from ref. 5; # purity (%) of tested compounds was
> 90%
1714 (C = O) cm−1. The HMBC spectrum (l Fig. 2) showed correla-
"
tions between H-1′ (δH 4.96), H-2′ (δH 4.05), and C-2 (δC 115.2),
thus establishing that the glucosyl group was connected at C-2.
In the 13C‑NMR spectrum, C-1′ (δC 74.4) of 3, which shifted to high
field, was determined as C-linkage. The coupling constant of H-1′
of 3 was 10.4 Hz, suggesting that the glucosyl group was β-form.
tubercular activities against Mycobacterium tuberculosis H37Rv
in vitro. Data on antitubercular activities data are shown in
l Table 2. The clinically used antitubercular agent, ethambutol,
"
was used as a positive control. Results of the antitubercular ac-
tivities indicated that (a) 3-methoxy-2-methyl-5-pentylphenol
(1) and its O-methylation product (1a) exhibited more potent
antitubercular activities against Mycobacterium tuberculosis
H37RV in vitro, showing MIC values of ≤ 2.58 and ≤ 2.50 µg/
mL, respectively, than did the clinical drug, ethambutol; (b)
the methyl group at C-2 of compounds 1 and 1a plays an im-
portant role due to 3-methoxy-5-pentylphenol decreasing the
activity 25-fold; and (c) compound 2, with a ketone group at
C-1′, is 5-fold weaker compared to 1. Some isolates were tested
for cytotoxicity against MCF-7, NCI-H460, and SF-268 cancer
cell lines in vitro. The clinically applied anticancer agent, acti-
nomycin D, was used as a positive control for cytotoxicity as-
says at concentrations of 10 nM and 10 µM in each 96-well
plate. The values represent averages of three independent ex-
periments, each with duplicate samples. 5-(8′Z-Pentadecenyl)-
resorcinol (9), 2-methyl-5-(8′Z-heptadecenyl)resorcinol (11),
and 2-methylcardol (12) previously reported to have cytotoxic
activity against the MCF-7 cancer cell line (IC50 : 6.7, 6.9,
6.0 µg/mL) [5]. Ardisianone (7) and cornudentanone (8) were
reported for their selective cytotoxic activity against the NCI-
H460 cancer cell line (IC50 values of 2.3, 2.5 µg/mL) in our pre-
vious study [4].
"
The NOESY spectrum (l Fig. 3) showed correlations between H-
1′, H-3′, and H-5′; and between H-2′ and H-4′, and the coupling
constants of above protons displayed large values (J > 8.8 Hz), in-
dicating axial orientation of all the above protons. These spectro-
scopic data readily confirmed the presence of β-glucose in 3. The
location of each substituent was further confirmed by the HMBC
"
spectrum (l Fig. 2) showing correlations from Me-4 (δH 2.10) to
C-3 (δC 154.9), C-4 (δC 120.7), and C-5 (δC 157.9); and from H-6 (δH
7.02) to C-1 (δC 122.2), C-5 (δC 157.9), and C-1′′ (δC 166.2). On the
basis of these data, the structure of cornudoside (3) was estab-
lished as shown.
The twenty-six known compounds including three alkyl phenols,
1-(3,5-dihydroxyphenyl)heptan-1′-one (4) [4], 1-(3,5-dihy-
droxyphenyl)nonan-1′-one (5) [4], 3-methoxy-5-pentylphenol
(6) [4], two benzoquinones, ardisianone (7) [8], cornudentanone
(8) [8], thirteen alkenyl resorcinols, 5-(8′Z-pentadecenyl)resorci-
nol (9) [5], 5-(8′Z-heptadecenyl)resorcinol (10) [5], 2-methyl-5-
(8′Z-heptadecenyl)resorcinol (11) [5], 2-methylcardol (12) [5],
belamcandol B (13) [13], kusukuenol A1 (14) [5], kusukuenol A2
(15) [5], kusukuenol B1 (16) [5], kusukuenol B2 (17) [5], kusukue-
nol C1 (18) [5], kusukuenol C2 (19) [5], oncostemonol D (20) [5],
dehydrobisgravillol (21) [5], an α-tocopheranoid, α-tocopheryl
quinone (22) [4], three steroids, a mixture of β-sitosterol and stig-
masterol [5], α-spinasterol (23) [5], a flavan, (+)-catechin (24)
[14], three alkanoid derivatives, a mixture of methyl pentadeca-
noate, methyl palmitate, and methyl heptadecanoate [15] were
readily identified by comparison of physical and spectroscopic
Acknowledgements
!
This work was supported by a grant from the National Science
Council of the Republic of China.
1
data (UV, IR, H‑NMR, and MS) with those of corresponding au-
thentic samples or values found in the literature.
3-Methoxy-2-methyl-5-pentylphenol (1) and its O-methylation
product (1a) and 3-methoxy-2-methyl-5-(1′-ketopentyl)phenol
(2), along with seven known compounds, were tested for anti-
Chang C-P et al. Antitubercular Resorcinol Analogs… Planta Med 2011; 77: 60–65