Sesterterpenoids from the sponge Sarcotragus sp.

Article abstract of DOI:10.1021/np0780147

Nineteen new sesterterpenoids and eight known compounds were isolated from the sponge Sarcotragus sp. collected from Soheuksan Island, Korea. The structures of these compounds were determined to be linear sesterterpenoids containing furan or related oxygenated functionalities on the basis of combined chemical and spectroscopic analyses. In addition, the configurations of several previously undetermined compounds were assigned. Several compounds exhibited moderate to major antibacterial activity (compounds 1-3, 17, 18) and cytotoxicity (3, 11, 12) against the K562 cell line and inhibitory activity against isocitrate lyase (6, 13).

Full text of DOI:10.1021/np0780147

J. Nat. Prod. 2008, 71, 551–557
551
Sesterterpenoids from the Sponge Sarcotragus sp.
Nan Wang,†, Jueun Song,† Kyoung Hwa Jang,† Hyi-Seung Lee,§ Xian Li,‡ Ki-Bong Oh,*,0 and Jongheon Shin*,†
Natural Products Research Institute, College of Pharmacy, Seoul National UniVersity, 599 Gwanangno, Gwanak-gu, Seoul 151-742, Korea,
School of Traditional Chinese Materia Medica, Shenyang Pharmaceutical UniVersity, Shenyang 110016, People’s Republic of China, Marine
Natural Products Laboratory, Korea Ocean Research & DeVelopment Institute, Ansan P.O. Box 29, Seoul 425-600, Korea, and School of
Agricultural Biotechnology, Seoul National UniVersity, San 56-1, Sillim, Gwanak, Seoul 151-921, Korea
ReceiVed September 19, 2007
Nineteen new sesterterpenoids and eight known compounds were isolated from the sponge Sarcotragus sp. collected
from Soheuksan Island, Korea. The structures of these compounds were determined to be linear sesterterpenoids containing
furan or related oxygenated functionalities on the basis of combined chemical and spectroscopic analyses. In addition,
the configurations of several previously undetermined compounds were assigned. Several compounds exhibited moderate
to major antibacterial activity (compounds 1–3, 17, 18) and cytotoxicity (3, 11, 12) against the K562 cell line and
inhibitory activity against isocitrate lyase (6, 13).
Sponges produce a wide variety of terpenoids and related
metabolites containing polyprenyl moieties.1 One of the most
distinctive characteristics of sponge-derived terpenoids is the
abundance and structural diversity of sesterterpenoids, a structure
class rarely found in other marine or terrestrial organisms. Several
compounds of this structural class exhibit various bioactivities, for
example, antimicrobial, anti-inflammatory, antiviral, and cytotoxic
activities, as well as inhibitory actions against diverse biosystems.1,2
Sesterterpenoids have also been isolated from specimens of the
genera Psammocinia, Sarcotragus, Smenospongia, and Spongia
from Korean waters.3–9 During the course of our search for bioactive
metabolites, we encountered a sponge of the genus Sarcotragus,
the organic extracts of which showed considerable toxicity against
brine shrimp larvae (LC50 87 ppm). We describe the isolation and
structure determination of 19 new sesterterpenoids and eight
previously reported compounds of the same structural class. All of
the compounds contained furan and/or related oxygenated func-
tionalities such as γ-lactone, γ-lactam, or corresponding methyl
acetals at one end of the linear molecule, while the other end was
occupied by tetronic acid, carboxylic acid, or dimethyl diester
moieties. Additionally, the absolute stereochemistry of several
previously reported compounds was examined by chemical deg-
radation and CD measurements. Several compounds exhibited
moderate to significant antibacterial activity, and cytotoxicity and
inhibitory activity against isocitrate lyase (ICL) from Candida
albicans.
Scheme 1. Oxidative Cleavage of 1 to 2-Methyl-6-oxo-heptanoic
Acid
and (8Z,13Z,18R,20Z)-strobilinin, respectively, on the basis of
combined spectroscopic analyses and comparison of the NMR data
with those in the literature.10–12 In addition, compounds 4–6 and
10 were also structurally defined and found to have been previously
reported.7,12,13 The sesterterpenoids 1–5 and 10 have frequently
been isolated from sponges of the genera Ircinia, Psammocinia,
and Sarcotragus, while compound 6, previously reported as a
synthetic analogue, was isolated for the first time as a natural
product.1,13 Compounds 1–6 possess a common asymmetric carbon
center at C-18. The stereochemistry at this center in 1–3 was
assigned to be R, as in the known compounds, by chemical
degradation followed by comparison of the optical rotations with
those in the literature (Scheme 1).7,14–19 The absolute configuration
at C-18 of compounds 4 and 6, previously unassigned, was also
determined to be R in both cases. Although the limited amounts of
compound 5 prevented a stereochemical assignment, comparison
of the optical rotation with those of the other compounds suggested
the 18R configuration. Compound 10, a furan-containing C21
norsesterterpene, also possessed an asymmetric center at the same
position. The absolute configuration at this center was determined
to be R using the PGME method for a ꢀ,ꢀ-dialkyl carboxylic acid
(Scheme 2).20
The molecular formula of compound 7 was deduced to be
C25H34O6 by combined HRFABMS and 13C NMR analyses. The
NMR data for this compound were very similar to those of known
sesterterpenoids. In particular, the hydroxy-γ-lactone and tetronic
acid moieties of compound 6 were found to be intact in 7 on the
basis of 1H COSY, TOCSY, HSQC, and gHMBC experiments
(Table 1). Thus, the structural difference had to be in the prenyl
chain connecting these terminal functionalities. Two-dimensional
(2-D) NMR data placed the double bonds at C-8 and C-13 of the
carbon framework. From the characteristic chemical shifts of C-9
and C-14 in the 13C NMR data at δ 23.5 and 23.7, respectively,
we assigned the Z geometry for both double bonds. Although the
Results and Discussion
Freeze-dried specimens were exhaustively extracted with CH2Cl2
and MeOH. Guided by the combined results of brine shrimp
lethality and 1H NMR analyses, the crude extract was sequentially
separated by solvent partitioning, ODS vacuum flash chromatog-
raphy, and ODS HPLC to yield 27 compounds.
The structures of compounds 1, 2a, 2b (unseparable mixture),
and 3, the major constituents, were identified to be (7E,12E,18R,20Z)-
variabilin, (7E,13Z,18R,20Z)-felixinin, (8E,13Z,18R,20Z)-strobilinin,
* To whom correspondence should be addressed. (J.S.) Tel: 82 2 880
2484. Fax: 82 2 762 8322. E-mail: shinj@snu.ac.kr. (K.-B.O.) Tel: 82 2
880 4646. Fax: 82 2 873 3112. E-mail: ohkibong@snu.ac.kr.
† College of Pharmacy, Seoul National University.
Visiting Student from Shenyang Pharmaceutical University. Present
address: Institute of Applied Ecology, Chinese Academy of Sciences,
Shenyang 110016, China.
‡ Shenyang Pharmaceutical University.
§ Korea Ocean Research and Development Institute.
0 School of Agricultural Biotechnology, Seoul National University.
10.1021/np0780147 CCC: $40.75
2008 American Chemical Society and American Society of Pharmacognosy
Published on Web 03/15/2008

552 Journal of Natural Products, 2008, Vol. 71, No. 4
Wang et al.
Scheme 2. PGME Amidation of 10 and ∆δ(10R - 10S) Values
(ppm)
Table 1. 13C NMR Assignments for Compounds 7–9 and 11–13
(in CD3OD solutions)
position
7
8
9
11
12a
12b
13
1
2
3
4
99.0 173.7 109.1 144.0
146.3 117.7 124.9 111.8
138.2 172.5 146.8 126.3
174.0 101.1 108.1 140.1
142.8d 143.9d 173.7
112.0
126.2
111.9
126.4
117.8
172.4
140.0c 140.1c 101.5
5
6
7
8
25.9
26.8
32.1
26.1
28.3
32.1
27.2
26.7
32.3
25.6
29.7
32.3
26.0
29.6
125.2
25.2
29.5
40.3
136.0
16.0
125.6
27.4
32.8
136.2
23.6
126.3
26.3e
38.2
28.3
26.1
32.2
135.4
23.4
127.1
27.5
33.1
136.0
23.7
126.5
26.5
38.3
135.6 135.4 135.8 136.3a 136.6
9
23.5
23.4
23.5
23.7b
16.1
40.6
27.4
32.2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
1-OMe
4-OMe
126.8 127.0 126.6 126.3
27.4
33.1
27.5
33.1
27.5
33.2
27.5
33.2
136.3 136.3 136.3 136.2a 136.6
23.7
23.7
23.7
23.6b
23.6
126.0
26.4e
38.2
31.2
20.1
126.1 126.2 126.1 126.3
27.1
38.7
31.8
21.1
27.1
38.7
31.8
21.2
27.1
38.7
31.8
21.1
26.4
38.2
31.3
20.0
42.9
31.2
20.1
42.8
177.4
31.4
20.1
43.7
178.5
115.4 114.9 114.9
145.5 145.9 145.9 177.4
166.0 168.0 167.1
42.8
177.4
98.2
98.2
97.4
174.0 174.5 174.5
6.1
6.1
6.1
54.2
54.2
a Assignments may be interchanged. b Assignments may be
interchanged. c Assignments may be interchanged. d Assignments may be
interchanged. e Assignments may be interchanged.
limited amounts of the isolated material prevented application of a
chemical degradation method, the 18R configuration was assigned
to this compound on the basis of a comparison of the optical rotation
with other metabolites and biogenetic considerations. Because of
interference by the tetronic acid moiety, however, the absolute
stereochemistry at C-1 could not be assigned using CD measure-
ments.5
The molecular formula of compound 8 was found to be C25H34O6,
identical to 7, by HRFABMS and 13C NMR analyses. The NMR
data of this compound were also very similar to those of 7.
However, close inspection of the 13C NMR data revealed noticeable
differences in the carbon signals of the γ-hydroxy-γ-lactone ring:
δ 173.7 (C), 172.5 (C), 117.7 (CH), and 101.1 (CH) (Table 1).
Corresponding differences were also observed in the 1H NMR
spectra in which the lactone proton signals were moved from δ
6.96 (1 H, br s) and 6.06 (1 H, br s) in 7 to δ 6.00 (1 H, br s) and
5.87 (1 H, s) in 8 (Table 2). These changes were accommodated
by the exchange of the carbonyl and hemiacetal carbons and
supported by a combination of 2-D experiments. Thus, the carbonyl
and hemiacetal carbons were placed at C-4 and C-1, respectively,
on the basis of long-range correlations between these carbons and
neighboring protons in the gHMBC data. The absolute configuration
at C-18 was assigned as R, as in the other compounds, on the basis
of chemical degradation, followed by measurement of specific
rotation.
The molecular formula of compound 9 was determined to be
C27H40O6 by HRFABMS and was consistent with the 13C NMR
data. The NMR data for this compound were very similar to those
of compound 5. Combined 2-D NMR analyses revealed that the
C-7 and C-12 double bonds of 5 were instead at C-8 and C-13 in
9. The Z configuration was assigned at both double bonds on the

Sesterterpenoids from the Sponge Sarcotragus sp.
Journal of Natural Products, 2008, Vol. 71, No. 4 553
Table 2. 1H MMR Assignments for Compounds 7–9 and 11–13 (in CD3OD solutions)
position
7
8
9
11
7.38, br s
6.29, br s
7.26, br s
2.44, t (7.5)
1.65, m
2.07, t (7.5)
1.68, s
5.15, t (7.0)
2.03, m
2.02, m
1.66, s
5.11, t (6.5)
2.00, m
1.21, m; 1.37, m
1.92, m
12a
12b
13
5.88, br s
6.01, br s
2.39, t (7.5)
1.72, m
2.15, t (7.5)
1.69, br s
5.21, t (7.0)
2.08, m
2.05, m
1.67, s
5.13, t (7.0)
2.02, m
1.35, m; 1.22, m
1.92, m
0.94, d (6.6)
2.25, dd (14.3, 5.8)
2.03, m
1
2
4
5
6
7
9
10
11
12
14
15
16
17
18
19
20
6.06, br s
6.96, br s
5.39, br s
5.66, br s
5.52, br s
2.09, m
7.36, br sa
6.29, br sb
7.23, br s
2.44, t (7.5)
2.24, q (7.5)
5.17, t (7.5)
1.58, s
1.97, m
1.47, m
1.97, m
1.67, s
5.10, m
2.00, m
1.35, m; 1.22, m
1.91, m
0.94, d (6.6)
2.28, m; 2.05, m
7.35, br sa
6.27, br sb
7.23, br s
2.37, t (7.5)
1.64, m
2.03, m
1.61, s
5.17, m
2.07, m
2.07, m
1.68, s
5.10, m
2.00, m
1.35, m; 1.22, m
1.91, m
0.94, d (6.6)
2.28, m; 2.05, m
5.87, s
6.00, br s
2.37, m
2.23, t (7.7)
1.65, m
2.09, t (7.7)
1.67, s
5.15, t (6.6)
2.03, m
1.69, m
1.57, m
2.06, m
2.11, t (7.5)
1.67, s
5.16, t (6.8)
2.03, m
1.65, br s
5.13, m
2.02, m
1.99, m
2.00, m
1.67, s
2.00, m
1.66, s
1.66, br s
5.12, t (7.7)
1.97, m
1.44, m; 1.38, m
2.72, m
5.12, t (6.9)
1.97, m
1.38, m; 1.46, m
2.73, m
1.06, d (6.7)
5.28, d (10.1)
5.11, t (6.6)
1.95, m
1.44, m; 1.35, m
2.72, m
1.05, d (6.7)
5.26, d (10.0)
1.05, d (6.7)
5.26, d (10.0)
0.94, d (6.6)
2.27, dd (14.7, 6.0)
2.07, m
25
1-OMe
4-OMe
1.73, s
1.71, s
1.71, s
3.35, s
3.34, s
a Assignments may be interchanged. b Assignments may be interchanged.
basis of downfield shifts of the vinyl methyl carbons: δ 23.5 (C-9)
and 23.7 (C-14). The 18R configuration was assigned by comparing
the optical rotation (+23.2) with that of other sesterterpene tetronic
acids, compound 5 (+21.2) in particular.
3.73 (×2) and 1.45 (Table 4). In addition, the IR and UV spectra
indicated the presence of a hydroxyl-bearing group (νmax 3500 cm-1
and the loss of the tetronic acid moiety (λmax 250 and 210 nm),
)
respectively.
The molecular formula of compound 11 was deduced to be
C21H32O3 by combined HRFABMS and 13C NMR analyses. The
NMR data for this norsesterterpene were similar to those of
compound 10. Structural differences were traced to the replacement
of the 7E and 12E double bonds in 10 with the 8Z and 13Z double
bonds in 11 on the basis of combined 2-D NMR experiments. The
18R configuration was assigned by the PGME method.
A mixture of compounds 12a and 12b was isolated as a colorless
oil, which was analyzed as C21H32O3 by HRFABMS and 13C NMR
spectrometry. Although these compounds were obtained as an
unseparable mixture, detailed examination of 2-D NMR data
coupled with chemical shifts of vinyl methyl carbons revealed that
they were indeed 7E, 13Z and 8E, 13Z isomers, respectively, of 10
and 11. The configuration at the common asymmetric center at C-18
was determined to be R, the same as the other compounds, after
applying the PGME method to the mixture.
Aided by this information, the structure of 14 was determined
by combined 2-D NMR analyses. The 1H COSY, TOCSY, gHSQC,
and gHMBC experiments showed that 14 possessed the same furan
ring and 8Z and 13Z double bonds as compounds 3 and 11. Starting
at the furan ring, the proton spin system was traced to the H-19
methyl protons at δ 0.94 and the H-20 methylene protons at δ 1.94
and 1.83 on the basis of TOCSY and gHMBC data (Table 4). The
remaining part consisted of newly appearing NMR signals that were
also examined in the gHMBC experiment. Specifically, the long-
range correlations of the methyl proton at δ 1.45 with the carbons
at δ 175.5, 84.4, and 81.8 indicated the presence of a carbonyl-
bearing isopropyl equivalent at the terminus of the molecule. The
linkage of this group to the prenyl chain was determined by long-
range couplings of the H-20 protons with the carbons at δ 84.4
and 81.8. An additional coupling of these protons with the carbonyl
carbon at δ 175.3 revealed the presence of an additional methyl
equivalent, a rearranged terpene skeleton. Finally, long-range
couplings of the two methyl protons at δ 3.75 with the carbonyl
carbons at δ 175.5 and 175.3 showed the presence of two methyl
esters. Consideration of the molecular formula, coupled with the
hydroxyl absorption band in the IR data, revealed that each of the
quaternary carbons at δ 84.4 and 81.8 carried a hydroxyl group.
Thus, the structure of compound 14 was determined to be a
rearranged furanosesterterpene containing a 1,2-dicarbomethoxy-
1,2-dihydroxy group. A literature study showed that a compound
possessing the same terminal structure was reported as a chemical
degradation product of a tetronic acid using a strong base.22 To
our knowledge, however, this is the first isolation of a natural
product with this carbon skeleton. The stereochemistry of the
asymmetric centers at C-18, C-21, and C-23 is discussed later.
The molecular formula of compound 13 was established to be
C21H32O5 by HRFABMS and 13C NMR spectrometry. Although a
1
norsesterterpene carboxylic acid was evident from its H and 13C
NMR spectra, carbon signals for the furan ring of other compounds
were markedly changed in both chemical shifts and multiplicity.
Combined 2-D NMR analyses, including long-range correlations
of the newly appearing downfield carbons at δ 173.7 (C) and 172.4
(C) with the neighboring protons in the gHMBC data, established
a γ-hydroxy-γ-lactone ring. The 8Z, 13Z, 18R configuration was
assigned by the downfield shifts of the vinyl methyls and PGME
analysis. In addition, the absolute stereochemistry at the C-4
hemiacetal was assigned to be S by CD measurement: a positive
Cotton effect, 204 (-1.82), 212 (-0.07), 219 (+0.53), 228 (+0.56)
nm.21 Thus, the structure of compound 13 was determined to be a
C21 norsesterterpene acid containing a γ-lactone moiety.
Compound 14 was isolated as a colorless oil, which was analyzed
as C27H42O7 by HRFABMS and 13C NMR spectrometry. Although
the sesterterpene nature of this compound was evident from its
spectroscopic data, the loss of the C-20 tetronic acid moiety, present
in compounds 1–9, was readily observed in the 13C NMR spectra.
Carbon signals of this functional group were replaced with others
appearing at δ 175.5 (C), 175.3 (C), 84.4 (C), 81.8 (C), 52.8 (2 ×
CH3), and 21.3 (CH3) in the 13C NMR spectra (Table 3).
Corresponding differences were also observed in the 1H NMR
spectra, in which signals of singlet methyl protons appeared at δ
The molecular formula of compound 15 was determined to be
C27H42O7 by HRFABMS and was consistent with the 13C NMR
data. The spectroscopic data for this compound were very similar
to those of 14 (Tables 3 and 4). Because the 2-D NMR data
demonstrated that 15 had the same planar structure as 14, this
compound was defined to be an epimer of 14.
Also obtained by HPLC were compounds 16a–16c (mixture of
three), 17, and 18a and 18b (mixture), all having the same molecular
formula as 14 and 15. Combined 2-D NMR analyses of these
compounds revealed that they were 7E, 12E (16a and 17), 7E, 13Z

554 Journal of Natural Products, 2008, Vol. 71, No. 4
Wang et al.
Table 3. 13C NMR Assignments for Compounds 14–21 (in CD3OD solutions)
position
14
15
16a
16b
16c
17
18a
18b
19
20a
20b
21
1
2
3
4
144.0
109.6
126.4
140.1
25.6
144.0
111.9
126.3
140.1
25.6
143.8b
112.0c
126.2d
140.1
26.0
143.8b
112.0c
126.2d
140.1
26.0
143.9b
111.9c
126.4d
140.1
25.2
143.8
112.0
126.2
140.1
26.0
143.9i
112.0j
126.4k
140.1
26.0
143.8i
111.9j
126.2k
140.1
25.2
53.2
138.2
139.9
174.1
27.1
53.2q
138.2
139.9
174.1
27.1
53.3q
138.0
140.3
174.1
26.4
53.3
137.9
140.2
174.0
26.7
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
29.7
32.3
136.3
23.7
126.3
27.5
33.2
135.9
23.7
126.5
26.3
39.5
29.7
32.3
136.2
23.66
126.3
27.5
29.6
29.6
29.5
40.3
135.9
16.0
125.6
27.5
32.8
135.8
23.7
126.7
26.4f
40.0
29.6
29.6
29.5
40.3
136.0
16.0
125.6
27.5
32.9
136.0
23.6
27.1
27.1
27.1
40.4
27.3
32.4
136.0
23.6
126.47
27.5
33.2
135.9
23.7
126.54
26.3
39.5
125.2
136.5
16.1
125.2
136.7
16.1
40.7
27.5
32.2
136.1
23.6
126.5
26.3f
40.0
125.3g
136.6
16.1
125.2
136.6
16.0
40.7
27.5
32.3
136.3
23.7
124.8
137.1
16.2
40.8
27.6
125.4
136.1
16.0
40.8
26.2
124.8
137.1
16.0
135.9
16.1
125.8
27.6r
32.9
40.8e
27.5
40.8h
27.5
40.7
27.5r
32.4
33.2
125.4
136.0
16.0
125.2g
136.1
16.0
135.7
23.71
126.7
26.4
39.9
29.4
136.3
23.7
136.0
23.7
40.9e
26.2
40.9h
26.3
126.3
26.3l
39.5
126.5
26.2l
39.5
126.3
26.2s
39.5
126.5
26.3s
39.5
38.4
30.7
22.1
40.6
39.1
29.4
20.2
40.6
38.4
30.7
22.1
40.6
30.6
22.0
40.6
29.4
20.1
40.6
29.4
20.1
40.6
30.7m
21.9n
40.6
30.6m
22.0n
40.6
30.6t
22.0
30.5t
22.0
30.6
22.0
40.6
20.1
40.7
40.6
40.6
21
22
23
84.4
83.3
175.6
82.0
84.3
175.5
81.9
83.3
175.6
82.0
83.3
175.6
82.0
83.3
175.7
82.0
84.4
84.4
84.3
175.5
81.8
84.4
175.5
81.8
84.4
175.5
81.8
84.4
175.5
81.8
175.5a
81.8
175.3o
81.8
175.3o
81.8
24
25
22-OMe
25-OMe
1′
21.3
21.3
175.4
52.7
21.3
175.4
52.8
21.3
175.4
52.7
21.3
175.4
52.7
21.2
175.4
52.7
21.3
21.3
21.3
175.4
52.8
52.8
47.1
21.4
175.3
52.9
52.8
47.1
21.4
175.3
52.9
52.8
47.1
21.3
175.3
52.8
52.8
47.1
175.3a
52.8
175.5p
52.8
175.5p
52.8
52.8
52.9
52.8
52.9
52.9
52.9
52.8
52.8
2′
174.1
174.1
174.1
174.0
a Assignments may be interchanged. b Assignments may be interchanged. c Assignments may be interchanged. d Assignments may be interchanged.
e Assignments may be interchanged. f Assignments may be interchanged. g Assignments may be interchanged. h Assignments may be interchanged.
i Assignments may be interchanged. j Assignments may be interchanged. k Assignments may be interchanged. l Assignments may be interchanged.
m Assignments may be interchanged. n Assignments may be interchanged. o Assignments may be interchanged. p Assignments may be interchanged.
q Assignments may be interchanged. r Assignments may be interchanged. s Assignments may be interchanged. t Assignments may be interchanged.
Table 4. 1H NMR Assignments for Compounds 14–18b (in CD3OD solutions)
position
14
15
16a
16b
16c
17
18a
18b
1
2
4
5
6
7
9
7.38, br s
6.29, br s
7.25, br s
2.40, t (7.5)
1.65, m
7.37, br s
6.29, br s
7.25, br s
2.40, t (7.6)
1.65, m
7.36, br s
6.29, br s
7.24, br s
2.44, t (7.3)a
2.24, m
7.36, br s
6.29, br s
7.24, br s
2.43, t (7.4)a
2.24, m
5.17, m
1.58, s
7.37, br s
6.28, br s
7.24, br s
2.37, t (7.6)
1.65, m
2.01, m
1.61, s
7.36, br s
6.29, br s
7.23, br s
2.43, t (7.4)
2.23, q (7.4)
5.16, t (6.6)
1.58, s
7.37b
7.36b
6.29c
6.28c
7.24, br s
2.43, t (7.6)
2.25, m
5.18, t (7.6)
1.58, s
7.24, br s
2.37, t (7.6)
1.65, m
2.01, m
1.61, s
2.07, t (7.5)
1.68, s
2.06, t (7.6)
1.67, s
5.17, m
1.58, s
10
11
12
14
15
16
17
5.15, m
5.15, m
2.01, br s
1.99, m
1.64, s
5.09, t (7.7)
1.93, m
1.37, m
1.14, m
1.57, m
0.76, d (6.7)
2.16, dd
(14.1, 4.4)
1.72, dd
(14.1, 7.9)
1.45, s
1.99, m
2.08, m
5.08, m
1.57, s
1.90, t (7.8)
1.37, m
1.15, m
1.03, m
1.38, m
0.94, d (6.6)
1.93, m
1.98, m
1.47, m
1.96, m
1.65, s
5.15, m
2.08, m
2.06, m
1.67, s
1.99, t (7.2)
2.07, q (7.2)
5.08, t (6.6)
1.59, s
1.92, t (7.3)
1.38, m
1.33, m
1.12, m
1.57, m
0.75, d (6.6)
2.17, dd
1.98, m
1.46, m
1.96, m
1.65, s
5.06, t (7.2)
1.93, m
1.21, m
1.10, m
1.38, m
5.14, t (7.4)
2.08, m
2.06, m
1.67, s
5.08, t (7.7)
1.93, m
1.21, m
1.10, m
1.38, m
0.94, d (6.6)
1.94, m
2.01, br s
2.01, br s
1.65, s
5.06, t (6.9)
1.91, m
1.21, m
1.10, m
1.38, m
0.94, d (6.6)
1.94, dd
(14.2, 4.4)
1.83, dd
(14.2, 7.2)
1.45, s
5.09, m
1.95, m
1.39, m
1.15, m
1.57, m
0.76, d (6.6)
2.17, dd
(14.1, 3.4)
1.72, dd
(14.1, 8.0)
1.45, s
5.11, m
1.95, m
1.39, m
1.15, m
1.57, m
0.75, d (6.6)
2.17, dd
(14.1, 3.4)
1.72, dd
(14.1, 8.0)
1.45, s
18
19
20
0.94, d (6.6)
1.94, m
(14.0, 4.1)
1.69, dd
(14.0, 8.1)
1.45, s
1.83, dd
(14.2, 7.1)
1.45, s
1.83, dd
(14.1, 7.2)
1.46, s
1.83, dd
(14.1, 7.2)
1.46, s
24
22-OMe
25-OMe
3.73, s
3.73, s
3.74, s
3.72, s
3.73, s
3.73, s
3.74, s
3.72, s
3.74, s
3.72, s
3.74, s
3.72, s
3.73, s
3.73, s
3.73, s
3.73, s
a Assignments may be interchanged. b Assignments may be interchanged. c Assignments may be interchanged.
(16b and 18a), and 8E and 13Z (16c and 18b) configurational
isomers of 14 and 15, respectively.
similar to each other (Tables 3 and 4). In trying to assign the
stereochemistry at C-18, C-21, and C-23, several attempts at
converting the natural products to the corresponding cyclic ketals
or lactones were unsuccessful.23 This problem was addressed by
NOESY experiments; cross-peaks were found at H-18/H-20ꢀ (δ
2.16), H-19/H-20R (δ 1.72), H-19/22-OMe, H-20R/22-OMe, and
H-24/22-OMe for 15 (Figure 1). In contrast, cross-peaks were found
at H-18/22-OMe, H-19/H-20R (δ 1.83), and H-20R/H-24 for 14.
Assuming the 18R configuration, based on biogenetic consider-
1
Close examination of the H and 13C NMR data of compounds
14–18 revealed that chemical shifts of the carbons and protons in
the region of C-17 to C-25 were unambiguously divided into two
groups. That is, chemical shifts of carbons and protons in
compounds 14, 16a, 18a, and 18b were almost identical to each
other, while they were noticeably shifted from those of compounds
15, 16b, 16c, and 17, the chemical shifts of which were also very

Sesterterpenoids from the Sponge Sarcotragus sp.
Journal of Natural Products, 2008, Vol. 71, No. 4 555
were active against the fungal strains Aspergillus fumigatus
HIC6094, A. niger ATCC9642, A. niger IFO6661, or C. albicans
SC5314, several compounds, in particular, 6 and 13, showed
moderate inhibitory activity against isocitrate lyase (ICL), an
enzyme that plays a key role in fungal metabolism derived from
C. albicans.24 In addition, 3, 11, and 12 displayed moderate
cytotoxicity against the K562 cell line. Although the bioactivity
tests displayed somewhat scattered results, a general trend was
revealed; the bioactivity of these sesterterpenoids was apparently
attributable to the presence of tetronic acid or carboxylic acid
moieties.
Figure 1. NOE correlations of the 1,2-dicarbomethoxy-1,2-dihy-
droxy moiety of 14 and 15.
ations, these NOESY results indicated 21S and 21R configurations
for 14 and 15, respectively. Because of the lack of reliable NOE
correlations, however, the configuration at the terminal C-23 could
not be assigned.
Experimental Section
General Experimental Procedures. Optical rotations were measured
on a JASCO P-1020 polarimeter using a 1 cm cell. CD data were
obtained on a JASCO J-715 spectropolarimeter in MeOH solutions,
UV spectra were recorded on a Hitachi U-3010 spectrophotometer, and
IR spectra were recorded on a JASCO 300E FT-IR spectrometer. NMR
spectra were recorded in CD3OD solutions containing Me4Si as an
internal standard on Bruker Avance 500 and Varian Gemini 2000
spectrometers. Proton and carbon NMR were measured at 500 and 125
MHz, respectively. Mass spectra were obtained on a JEOL JMS-700
high-resolution mass spectrometer for FAB experiments, provided by
the Basic Science Research Institute, Seoul Branch, Seoul, Korea. All
solvents used were spectral grade or distilled from glass prior to use.
Animal Material. Specimens of Sarcotragus sp. (voucher number
97J-4) were collected by hand using scuba (25 m) off the shore of Jeju
Island in July 1997. The morphological characteristics of this sponge
have been reported previously. Similar specimens (voucher number
01SH-15) were also collected (25–30 m) off the shore of Soheuksan
Island, Korea, in June 2001. Gross morphological features, such as
color and shape of this sponge, were very similar to those collected
previously at a nearby area. The voucher specimens are deposited at
the Sponge Collection, KORDI, under the curatorship of H.-S.L.
Extraction and Isolation. Freshly collected specimens were im-
mediately frozen and kept at –25 °C until chemical investigation. The
combined specimens were lyophilized (dry wt 560 g), macerated, and
repeatedly extracted with CH2Cl2 (4 L × 3) and MeOH (4 L × 3). The
combined crude extracts were successively partitioned between H2O
and n-BuOH, and then the latter was repartitioned between 15% aqueous
MeOH (26.4 g) and n-hexane (10.1 g). The aqueous MeOH layer was
separated by C18 reversed-phase vacuum flash chromatography using
a sequential mixture of MeOH and H2O as eluents (elution order: 50%,
40%, 30%, 20%, 10% aqueous MeOH, 100% MeOH), acetone, and
finally EtOAc.
The molecular formula of compound 19 was deduced to be
C29H45NO9 by combined HRFABMS and 13C NMR analyses.
Although the terpenoid nature of this compound was evident from
its spectroscopic data, the 13C NMR spectra showed the appearance
of additional carbon signals at δ 174.1 (C) and 47.1 (CH2) (Table
1
3). Because a preliminary examination of the H and 13C NMR
data revealed that this compound possessed the same C-5 to C-25
portion as compound 14, the structural difference was thought to
be related to the remaining portion having the partial formula of
C6H6NO3. A small spin coupling between the olefinic proton at δ
6.84 and methylene protons at δ 4.05, coupled with the HMBC
correlations of these protons with the carbonyl carbon at δ 174.1,
allowed us to construct a five-membered carbonyl-bearing ring
(Table 5). The IR absorption band at 1670 cm-1 suggested this
moiety to be an R,ꢀ-unsaturated γ-lactam. Furthermore, isolated
methylene protons at δ 4.04 exhibited long-range couplings with
another carbonyl carbon at δ 175.5. The linkage of this carboxy-
methylene with the lactam moiety was determined by the mutual
HMBC couplings of the methylene protons at δ 4.05 and 4.04 with
the carbons bearing these protons (Figure 2). The configurations
of the C-7 and C-12 double bonds were assigned as E for both on
the basis of the upfield shifts of vinyl methyl carbons. Thus, the
structure of compound 19 was determined to be a sesterterpene
lactam containing a carboxymethylene group. Sesterterpenoids
containing this kind of lactam moiety were previously isolated from
Korean sponges of the genus Sarcotragus.3,5
The molecular formula of three closely related compounds, 20a,
20b (mixture), and 21, were all found to be C29H45NO9, identical
to 19, by HRFABMS, and consistent with their 13C NMR data.
The spectroscopic data of these compounds were also very similar
to those of 19. Combined 2-D NMR experiments defined that these
were configurational isomers of each other, and on the basis of the
13C chemical shifts of the vinyl methyls, 7E, 13Z (20a), 8E, 13Z
(20b), and 8Z, 13Z (21) geometries were assigned for these
On the basis of the combined results of the bioassay and 1H NMR
analysis, the fractions eluted with 10% aqueous MeOH (6.22 g) from
flash chromatography were separated by Sephadex LH-20 gel-
permeation chromatography using MeOH as an eluent. The fractions
containing sesterterpenoids were combined and separated by semi-
preparative silica HPLC (YMC-Pack silica column, 1 cm × 25 cm,
20% EtOAc/n-hexane). Purification of these metabolites was then
accomplished by reversed-phase HPLC (15% aqueous MeCN and
then 15% aqueous MeOH) to yield compounds 11, 12, and 10, in
order of elution, as colorless oils. Another terpenoid-containing LH-
20 fraction was also separated and purified by reversed-phase HPLC
(20% aqueous MeCN for 4, 17.5% aqueous MeOH for 5, 9, 14–18,
15% aqueous MeOH for 1–3). The purified metabolites were isolated
in the following amounts: 100.2, 109.3, 107.6, 16.5, 2.8, 4.6, 14.7,
20.2, 17.1, 8.5, 10.9, 15.2, 8.2, and 8.4 mg of 1–5, 9–12, and 14–18,
respectively.
The fractions eluted with 20% MeOH(aq) (2.76 g) were separated
by Sephadex LH-20 gel-permeation chromatography (4 × 35 cm) using
MeOH (20 mL/fraction) as an eluent to yield 25 fractions. Fraction
LH3 was separated by reversed-phase HPLC (YMC-Pack CN column,
60% MeOH(aq)) to yield compounds 19–21, in order of elution, as
pale yellow oils. On the basis of the TLC results, fractions LH9–11
were combined and separated by semipreparative reversed-phase HPLC
(YMC-Pack ODS-A column, 1 cm × 25 cm, 22.5% MeOH(aq)) to
yield compounds 13, 8, 7, and 6, in order of elution, as colorless oils.
The purified metabolites were obtained in the following amounts: 11.8,
12.7, 3.8, 5.8, 23.5, 23.3, and 22.9 mg of 6–8, 13, and 19–21,
respectively.
1
compounds. Comparison of the H and 13C NMR data of these
compounds in the region of C-18 to C-25 revealed a very close
similarity with those of 14, 16a, 18a, and 18b, suggesting 18R,
21S configurations for these compounds. Because of the lack of
relevant NOESY cross-peaks, however, the configuration at the
terminal C-23 asymmetric center was not assigned.
Sesterterpenoids containing tetronic acid and/or related functional
groups frequently exhibit diverse bioactivities.1 In our measurements
of bioactivity, compounds 1–3, 17, and 18 exhibited moderate to
major activity against diverse Gram-positive and Gram-negative
strains, including MRSA (Supporting Information). Although none
Figure 2. Key HMBC correlations (H f C) of the R,ꢀ-unsaturated
γ-lactam moiety of 19.

556 Journal of Natural Products, 2008, Vol. 71, No. 4
Wang et al.
Table 5. 1H NMR Assignments for Compounds 19–21 (in CD3OD solutions)
position
19
20a
20b
4.06, br s
21
4.06, br s
1
4.05, br s
4.06, br s
2
5
6
7
6.84, br s
2.26, m
2.26, m
5.16, t (6.0)
1.61, s
2.01, m
2.07, m
5.09, t (6.5)
1.57, s
1.91, m
1.37, m
1.15, m
1.03, m
1.38, m
0.93, d (6.6)
1.93, dd (14.1, 4.7)
1.83, dd (14.1, 7.2)
1.45, s
6.85, br s
2.27, m
2.06, m
5.17, m
1.61, s
1.96, m
1.49, m
1.97, m
1.65, s
5.07, m
1.93, m
1.21, m
1.11, m
1.38, m
0.94, d (6.6)
1.94, m
1.83, dd (14.2, 7.2)
1.46, s
6.85, br s
2.21, t (7.7)
1.67, m
2.04, m
1.62, s
5.17, m
2.08, m
2.06, m
1.67, s
5.07, m
1.93, m
1.21, m
1.11, m
1.38, m
0.94, d (6.6)
1.94, m
1.83, dd (14.2, 7.2)
1.46, s
6.85, br s
2.23, t (7.4)
1.65, m
2.11, t (7.5)
1.68, br s
5.16, t (6.8)
2.06, m
9
10
11
12
14
15
16
17
2.03, m
1.66, br s
5.07, t (6.8)
1.92, m
1.21, m
1.11, m
1.38, m
0.94, d (6.6)
1.94, dd (14.1, 4.7)
1.83, dd (14.1, 7.1)
1.45, s
18
19
20
24
1′
4.04, s
4.03, br s
3.73, s
3.73, s
4.03, br s
3.73, s
3.73, s
4.04, s
3.73, s
3.72, s
22-OMe
25-OMe
3.73, sa
3.74, sa
a Assignments may be interchanged.
Compound 1: colorless oil; [R]2D0 +36.4 (c 1.15, MeOH) {lit. +
33.3 (c 1.1, MeOH)};12 IR (KBr) νmax 2950, 1760, 1635, 1500, 1425,
1285 cm-1; UV (MeOH) λmax (log ꢀ) 290 (3.71), 253 (4.04) nm.
Compound 2 (2a and 2b): colorless oil; [R]2D0 +50.7 (c 1.14, MeOH)
{lit. + 44.6 (c 0.01, MeOH)};11 IR (KBr) νmax 2950, 1760, 1630, 1505,
1425, 1280 cm-1; UV (MeOH) λmax (log ꢀ) 297 (3.73), 255 (3.97) nm.
Compound 3: colorless oil; [R]2D0 +46.4 (c 0.87, MeOH); IR (KBr)
Compound 13: colorless oil; [R]2D0 +6.4 (c 0.51, MeOH); IR (KBr)
ν
max 3400 (br), 2960, 2930, 1730, 1455, 1285 cm-1; UV (MeOH) λmax
1
(log ꢀ) 297 (3.08), 251 (3.42), 210 (4.15) nm; H and 13C NMR data,
see Tables 1 and 2; HRFABMS m/z 387.2148 [M + Na]+ (calcd for
C21H32O5Na, 387.2147).
Compound 14: colorless oil; [R]2D0 –7.6 (c 0.52, MeOH); IR (KBr)
ν
max 3500 (br), 2925, 1735, 1460, 1280, 1125 cm-1; UV (MeOH) λmax
ν
max 2950, 1760, 1635, 1500, 1425, 1280 cm-1; UV (MeOH) λmax (log
1
(log ꢀ) 250 (3.15), 210 (4.00) nm; H and 13C NMR data, see Tables
3 and 4; HRFABMS m/z 479.2991 [M + H]+ (calcd for C27H43O7,
479.3009).
ꢀ) 307 (3.74), 253 (3.98) nm.
Compound 4: colorless oil; [R]2D0 +9.4 (c 0.48, MeOH) {lit. –24.5
(c 0.22, MeOH)};13 IR (KBr) νmax 3400 (br), 2945, 1815, 1760, 1640,
1460, 1260, 1125 cm-1; UV (MeOH) λmax (log ꢀ) 307 (4.05), 250 (4.32),
209 (4.24) nm.
Compound 15: colorless oil; [R]2D0 +0.6 (c 0.45, MeOH); IR (KBr)
ν
max 3500 (br), 2930, 1730, 1465, 1280, 1125 cm-1; UV (MeOH) λmax
1
(log ꢀ) 210 (3.98) nm; H and 13C NMR data, see Tables 3 and 4;
HRFABMS m/z 479.3007 [M + H]+ (calcd for C27H43O7, 479.3009).
Compound 16 (16a, 16b, and 16c): colorless oil; [R]2D0 +13.2 (c
0.54, MeOH); IR (KBr) νmax 3500 (br), 2960, 2925, 1730, 1460, 1280,
1125 cm-1; UV (MeOH) λmax (log ꢀ) 211 (3.99) nm; 1H and 13C NMR
data, see Tables 3 and 4; HRFABMS m/z 479.3011 [M + H]+ (calcd
for C27H43O7, 479.3009).
Compound 5: colorless oil; [R]2D0 +21.2 (c 0.52, MeOH) {lit. +
16.3 (c 0.1, MeOH)};14 IR (KBr) νmax 2955, 1760, 1640, 1545, 1455,
1310 cm-1; UV (MeOH) λmax (log ꢀ) 313 (3.60), 250 (3.93), 209 (3.87)
nm.
Compound 6: colorless oil; [R]2D0 +38.6 (c 0.52, MeOH); IR (KBr)
ν
max 3400 (br), 2955, 2925, 1735, 1640, 1455, 1280 cm-1; UV (MeOH)
λmax (log ꢀ) 307 (3.80), 254 (3.98) nm.
Compound 17: colorless oil; [R]2D0 +5.2 (c 0.67, MeOH); IR (KBr)
Compound 7: colorless oil; [R]2D0 +36.4 (c 0.37, MeOH); IR (KBr)
ν
max 3450 (br), 2960, 2925, 1730, 1465, 1280 cm-1; UV (MeOH) λmax
ν
max 3400 (br), 2925, 1735, 1645, 1545, 1310, 1140 cm-1; UV (MeOH)
1
(log ꢀ) 210 (3.83) nm; H and 13C NMR data, see Tables 3 and 4;
HRFABMS m/z 501.2821 [M + Na]+ (calcd for C27H42O7Na, 501.2828).
Compound 18 (18a and 18b): colorless oil; [R]2D0 +7.5 (c 0.50,
1
λmax (log ꢀ) 307 (3.79), 253 (3.97) nm; H and 13C NMR data, see
Tables 1 and 2; HRFABMS m/z 453.2250 [M + Na]+ (calcd for
C25H34O6Na, 453.2253).
MeOH); IR (KBr) νmax 3450 (br), 2950, 1735, 1460, 1280, 1125 cm-1
;
Compound 8: colorless oil; [R]2D0 +21.2 (c 0.46, MeOH); IR (KBr)
νmax 3400 (br), 2925, 1740, 1645, 1545, 1455, 1310, 1135 cm-1; UV
(MeOH) λmax (log ꢀ) 310 (3.73), 210 (4.85) nm; 1H and 13C NMR data,
see Tables 1 and 2; HRFABMS m/z 453.2233 [M + Na]+ (calcd for
C25H34O6Na, 453.2253).
1
UV (MeOH) λmax (log ꢀ) 210 (3.99) nm; H and 13C NMR data, see
Tables 3 and 4; HRFABMS m/z 501.2824 [M + Na]+ (calcd for
C27H42O7Na, 501.2828).
Compound 19: pale yellow oil; [R]2D0 –2.4 (c 0.58, MeOH); IR (KBr)
ν
max 3450 (br), 2960, 2925, 1735, 1670, 1460, 1280 cm-1; UV (MeOH)
Compound 9: colorless oil; [R]2D0 +23.2 (c 0.55, MeOH); IR (KBr)
1
λmax (log ꢀ) 250 (3.11), 211 (3.92) nm; H and 13C NMR data, see
Tables 3 and 5; HRFABMS m/z 574.2993 [M + Na]+ (calcd for
C29H45NO9Na, 574.2992).
νmax 2960, 2925, 1760, 1640, 1545, 1455, 1305, 1140 cm-1; UV
1
(MeOH) λmax (log ꢀ) 308 (3.70), 250 (3.96), 213 (3.70) nm; H and
13C NMR data, see Tables 1 and 2; HRFABMS m/z 483.2716 [M +
Na]+ (calcd for C27H40O6Na, 483.2723).
Compound 20 (20a and 20b): pale yellow oil; [R]2D0 –2.5 (c 0.73,
MeOH); IR (KBr) νmax 3450 (br), 2955, 2925, 1735, 1670, 1460, 1280
cm-1; UV (MeOH) λmax (log ꢀ) 211 (3.92) nm; 1H and 13C NMR data,
see Tables 3 and 5; HRFABMS m/z 574.2995 [M + Na]+ (calcd for
C29H45NO9Na, 574.2992).
Compound 10: colorless oil; [R]2D0 +8.8 (c 0.47, MeOH); IR (KBr)
ν
max 2960, 2930, 1730, 1580, 1460, 1285 cm-1; UV (MeOH) λmax (log
ꢀ) 210 (4.03) nm.
Compound 11: colorless oil; [R]2D0 +7.0 (c 0.60, MeOH); IR (KBr)
Compound 21: pale yellow oil; [R]2D0 –2.8 (c 0.47, MeOH); IR (KBr)
ν
max 2960, 2925, 1730, 1575, 1460, 1285 cm-1; UV (MeOH) λmax (log
ꢀ) 307 (3.74), 253 (3.99) nm; 1H and 13C NMR data, see Tables 1 and
2; HRFABMS m/z 355.2249 [M + Na]+ (calcd for C21H32O3Na,
355.2249).
ν
max 3500 (br), 2955, 2925, 1730, 1670, 1460, 1280 cm-1; UV (MeOH)
1
λmax (log ꢀ) 247 (3.16), 211 (3.92) nm; H and 13C NMR data, see
Tables 3 and 5; HRFABMS m/z 574.2994 [M + Na]+ (calcd for
C29H45NO9Na, 574.2992).
Compound 12 (12a and 12b): colorless oil; [R]2D0 +7.8 (c 0.51,
MeOH); IR (KBr) νmax 2925, 1735, 1575, 1455, 1285 cm-1; UV
(MeOH) λmax (log ꢀ) 274 (2.84), 209 (3.90) nm; 1H and 13C NMR data,
see Tables 1 and 2; HRFABMS m/z 355.2245 [M + Na]+ (calcd for
C21H32O3Na, 355.2249), 355.2419 [M + H]+ (calcd for C21H33O3,
355.2430).
Oxidative Cleavage of Sesterterpenoids to 2-Methyl-6-oxo-
heptanoic Acid (1, 4, and 6). The reaction was carried out following
the general procedure for compound 1. From 6.5 mg (0.016 mmol) of
1, we obtained 1.0 mg (0.006 mmol, 39% yield) of (R)-(-)-2-methyl-
1
6-oxo-heptanoic acid: [R]2D0 –5.2 (c 0.08, MeOH); H NMR (CD3OD)

Sesterterpenoids from the Sponge Sarcotragus sp.
Journal of Natural Products, 2008, Vol. 71, No. 4 557
δ 2.50 (1 H, m, H-2), 2.45 (2 H, t, J ) 6.8 Hz, H-5), 2.14 (3 H, s,
H-7), 1.61 (2 H, m, H-4), 1.44 (2 H, m, H-3), 1.20 (3 H, d, J ) 7.2
Hz, 2-CH3). Authentic 2-methyl-6-oxo-heptanoic acid prepared from
2,6-dimethylcyclohexanone following the procedure reported previously
ppm; H-15, –0.026 ppm; H-16, –0.005 ppm; H-17, –0.014 to –0.010
ppm; H-18, –0.023 ppm; H-19, +0.063 ppm; H-2′, –0.015 ppm; OCH3,
0 ppm.
PGME Amidation of 12. Prepared as described for 10. We obtained
7,12,13
1
1.6 and 1.5 mg of 12R and 12S from 2.4 and 2.2 mg of 12 (mixture of
gave identical H NMR data.
The same degradation with 4 and
1
6 yielded (R)-(-)-2-methyl-6-oxo-heptanoic acid with [R]2D0 values of
–6.7 (c 0.03, MeOH) and –8.3 (c 0.06, MeOH), respectively.
Oxidative Cleavage of Sesterterpenoids to Dimethyl-2-methyl-
glutarate (2, 3, and 8). The reaction was carried out following the
general procedure for 3: 26.3 mg of RuCl3 ·xH2O was added to a
biphasic solution of 7.8 mg (0.02 mmol) of 3 and 50.3 mg (0.24 mmol)
of NaIO4 in a mixture of 1 mL of CCl4, 1 mL of MeCN, and 1.5 mL
of H2O. After vigorously stirring the mixture for 2 h at room
temperature, the solvents were removed under vacuum. The residue
was redissolved in acetone and filtered on an ODS Sep-Pak column.
One milliliter of HCl ·MeOAc was added to the filtrate under N2 and
stirred for 12 h. The solvent was removed under vacuum, and the
residue was separated by reversed-phase HPLC (20% MeOH(aq)) to
yield 1.4 mg (0.008 mmol, 40.0% yield) of dimethyl-2-methyl glutarate
at a retention time of 7.4 min (flow rate 0.5 mL/min): [R]2D0 –9.1 (c
0.1, MeOH); 1H NMR (CD3OD) δ 3.63 (6 H, s, OCH3), 2.48 (1 H, m,
H-2), 1.89 (2 H, t, J ) 7.5 Hz, H-4), 1.72 (2 H, m, H-3), 1.14 (3 H, d,
J ) 7.2 Hz, 2-CH3). Authentic glutarates prepared similarly from (R)-
(-)-2-methylglutaric acid and (S)-(+)-2-methylglutaric acid gave [R]2D0
–20.8 (c 0.53, MeOH) and +19.1 (c 0.79, MeOH), respectively. The
same process with 2 and 8 gave (R)-(-)-dimethyl-2-methylglutarate
with [R]2D0 values of –16.0 (c 0.07, MeOH) and –13.1 (c 0.15, MeOH),
respectively.
12a and 12b), respectively. 12R H NMR (CD3OD) δ 7.377–7.337
(H-1, Ar), 7.231 (H-4), 6.276 (H-2), 5.452 (H-2′), 5.087 (H-15), 3.689
(OCH3), 1.652 (H-14), 1.582 (H-9), 0.942 (H-19); 12S 1H NMR
(CD3OD) δ 7.379–7.348 (H-1, Ar), 7.234 (H-4), 6.279 (H-2), 5.466
(H-2′), 5.087 (H-15), 3.687 (OCH3), 1.666 (H-14), 1.590 (H-9), 0.878
(H-19); ∆δ (12R – 12S) H-1, Ar, –0.011 to –0.002 ppm; H-2, –0.003
ppm; H-4, –0.003 ppm; H-9, –0.008 ppm; H-14, –0.008 ppm; H-15, 0
ppm; H-19, +0.064 ppm; H-2′, –0.014 ppm; OCH3, +0.020 ppm.
Acknowledgment. We thank the Seoul Branch of the Basic Science
Research Institute, Korea, for providing mass data. J.-E.S. and K.H.J.
are the recipients of a fellowship from the Ministry of Education through
the Brain Korea 21 Project. This study was partially supported by the
Korea Ocean Research & Development Institute (grant PE97802) and
the Ministry of Maritime Affairs and Fisheries, Korea (grant PM44700).
Supporting Information Available: Antibacterial activity and
cytotoxicity against the K562 cell line and inhibitory activity against
isocitrate lyase. This material is available free of charge via the Internet
at http://pubs.acs.org.
References and Notes
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PGME Amidation of 10. The reaction was carried out following
the general procedure reported previously for the stereochemical
assignment of ꢀ,ꢀ-dialkylcarboxylic acid.6,20 Four milligrams of (R)-
PGME·Cl (phenylglycine methyl ester chloride), 10.4 mg of PyBOP
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1
sponding (S)-PGME amide (10S) from 1.7 mg of 10: 10R H NMR
data (CDCl3) δ 7.397–7.338 (H-1, Ar), 7.231 (H-4), 6.283 (H-2), 5.455
(H-2′), 5.154 (H-7), 5.067 (H-12), 3.690 (OCH3), 2.426 (H-5), 2.253
(H-6), 2.210 (H-20), 1.996 (H-20), 1.975 (H-11), 1.937 (H-10), 1.913
(H-15), 1.889 (H-18), 1.571 (H-9), 1.547 (H-14), 1.432–1.231 (H-16,
H-17), 0.946 (H-19); 10S 1H NMR (CDCl3) δ 7.378–7.336 (H-1, Ar),
7.231 (H-4), 6.282 (H-2), 5.466 (H-2′), 5.164 (H-7), 5.087 (H-12), 3.689
(OCH3), 2.429 (H-5), 2.264 (H-6), 2.218 (H-20), 2.009 (H-20), 1.966
(H-10), 1.987 (H-11), 1.943 (H-15), 1.917 (H-18), 1.574 (H-9, H-14),
1.476–1.280 (H-16, H-17), 0.946 (H-19); ∆δ (10R - 10S) H-1, Ar,
+0.001 to +0.002 ppm; H-2, +0.001 ppm; H-4, 0 ppm; H-5, -0.003
ppm, H-6, –0.011 ppm, H-7, –0.010 ppm, H-9, –0.003 ppm; H-10,
–0.029 ppm, H-11, –0.012 ppm; H-12, –0.020 ppm; H-14, –0.027 ppm;
H-15, –0.030 ppm; H-16, H-17, –0.044 to –0.049 ppm; H-18, –0.028
ppm; H-19, +0.064 ppm; H-20, –0.013 ppm; H-20, –0.008 ppm; H-2′,
–0.011 ppm; OCH3, +0.001 ppm.
PGME Amidation of 11. Prepared as described for 10. We obtained
1.1 and 1.4 mg of 11R and 11S from 2.3 and 2.3 mg of 11, respectively.
1
11R H NMR (CD3OD) δ 7.364–7.342 (H-1, Ar), 7.248 (H-4), 6.276
(H-2), 5.452 (H-2′), 5.093 (H-10, H-15), 3.687 (OCH3), 2.390 (H-5),
2.255 (H-20), 2.219 (H-7), 2.100 (H-11), 2.055 (H-12), 2.024 (H-20),
2.006 (H-16), 1.664 (H-9), 1.660 (H-14), 1.635 (H-6), 1.412–1.154 (H-
1
17), 0.937 (H-19); 11S H NMR data (CD3OD) δ 7.376–7.347 (H-1,
Ar), 7.249 (H-4), 6.279 (H-2), 5.467 (H-2′), 5.119 (H-10, H-15), 3.687
(OCH3), 2.396 (H-5), 2.265 (H-20), 2.101 (H-11), 2.055 (H-12), 2.023
(H-20), 2.011 (H-16), 1.940 (H-18), 1.671 (H-9), 1.668 (H-9, H-14),
1.644 (H-6), 1.426–1.164 (H-17), 0.874 (H-19); ∆δ (11R – 11S) H-1,
Ar, –0.120 to –0.005 ppm; H-2, –0.003 ppm; H-4, –0.001 ppm; H-5,
–0.006 ppm; H-6, –0.009 ppm; H-7, –0.046 ppm; H-9, –0.007 ppm;
H-10, –0.026 ppm; H-11, –0.001 ppm; H-12, 0 ppm; H-14, –0.008
NP0780147