Two new tryptamine derivatives, leptoclinidamide and (-)-leptoclinidamine B, from an Indonesian ascidian Leptoclinides dubius

Article abstract of DOI:10.3390/md10020349

Two new tryptamine-derived alkaloids, named as leptoclinidamide (1) and (-)-leptoclinidamine B (2), were isolated from an Indonesian ascidian Leptoclinides dubius together with C²-α-D-mannosylpyranosyl-L- tryptophan (3). The structure of 1 was assigned on the basis of spectroscopic data for 1 and its N-acetyl derivative (4). Compound 1 was an amide of tryptamine with two β-alanine units. Although the planar structure of 2 is identical to that of the known compound (+)-leptoclinidamine B (5), compound 2 was determined to be the enantiomer of 5 based on amino acid analysis using HPLC methods. Compounds 1 to 4 were evaluated for cytotoxicity against two human cancer cell lines, HCT-15 (colon) and Jurkat (T-cell lymphoma) cells, but none of the compounds showed activity.

Full text of DOI:10.3390/md10020349

Mar. Drugs 2012, 10, 349-357; doi:10.3390/md10020349
OPEN ACCESS
Marine Drugs
ISSN 1660-3397
www.mdpi.com/journal/marinedrugs
Article
Two New Tryptamine Derivatives, Leptoclinidamide and
-)-Leptoclinidamine B, from an Indonesian Ascidian
(
Leptoclinides dubius
1
1,2
3
1
Hiroyuki Yamazaki , Defny S. Wewengkang , Teruaki Nishikawa , Henki Rotinsulu ,
2
1,
Remy E. P. Mangindaan and Michio Namikoshi *
1
Department of Natural Product Chemistry, Tohoku Pharmaceutical University, Komatsushima,
Aoba-ku, Sendai 981-8558, Japan; E-Mails: yamazaki@tohoku-pharm.ac.jp (H.Y.);
wdefny@yahoo.com (D.S.W.); rhenki@yahoo.com (H.R.)
2
Faculty of Fisheries and Marine Science, Sam Ratulangi University, Kampus Bahu, Manado 95115,
Indonesia; E-Mail: remysang@yahoo.com
3
Laboratory of Taxonomy, Department of Biology, Faculty of Science, Toho University, Miyama,
Funabashi 274-8510, Japan; E-Mail: nishikawa@bio.sci.toho-u.ac.jp
*
Author to whom correspondence should be addressed; E-Mail: mnami@tohoku-pharm.ac.jp;
Tel./Fax: +81-22-727-0219.
Received: 27 December 2011; in revised form: 23 January 2012 / Accepted: 7 February 2012 /
Published: 10 February 2012
Abstract: Two new tryptamine-derived alkaloids, named as leptoclinidamide (1) and
(
-)-leptoclinidamine B (2), were isolated from an Indonesian ascidian Leptoclinides dubius
2
together with C -α-D-mannosylpyranosyl-L-tryptophan (3). The structure of 1 was assigned
on the basis of spectroscopic data for 1 and its N-acetyl derivative (4). Compound 1 was an
amide of tryptamine with two β-alanine units. Although the planar structure of 2 is identical
to that of the known compound (+)-leptoclinidamine B (5), compound 2 was determined to be
the enantiomer of 5 based on amino acid analysis using HPLC methods. Compounds 1 to 4
were evaluated for cytotoxicity against two human cancer cell lines, HCT-15 (colon) and
Jurkat (T-cell lymphoma) cells, but none of the compounds showed activity.
Keywords: leptoclinidamide; leptoclinidamine; tryptamine; alkaloid; Indonesian ascidian;
Leptoclinides dubius

Mar. Drugs 2012, 10
. Introduction
Ascidians are a rich source of biologically-active nitrogenous substances with high chemical
350
1
diversity [1,2]. More than 80% of new compounds from ascidians contained nitrogen, and about 70%
of nitrogenous compounds are alkaloids [3].
In the course of our studies on the bioactive components from marine invertebrates, we found that
the EtOH extract of an Indonesian ascidian Leptoclinides dubius inhibited the growth of Escherichia
coli. Chemical study on the EtOH extract led to the isolation of two tryptamine-derived alkaloids, a
C-glycosylated tryptophan and an antibacterial compound. Two alkaloids were revealed to be new
compounds and named as leptoclinidamide (1) and (-)-leptoclinidamine B (2, Figure 1), and a
2
tryptophan derivative was assigned as C -α-D-mannosylpyranosyl-L-tryptophan (3) [4–8]. The major
bioactive constituent could not be identified because the amount obtained from the ascidian was not
enough to measure 2D NMR spectra.
Figure 1. Structures of leptoclinidamide (1), (-)-leptoclinidamine B (2), and
2
C -α-D-mannosylpyranosyl-L-tryptophan (3).
O 19
O
OH
1
HN
2
HO
1
3
H
O
HN
O
N
10
OH
O
5
14
NH16
5
3
10
OH
3
7
7
HO
OH
N
H
1
N
NH2
O
N
H
1
NH2
18
18
O
HN R
H N
OH
2
2
0
2
R = H: Leptoclinidamide (1)
R = Ac: N-Acetyl leptoclinidamide (4) (+)-Leptoclinidamine B (13S, 5)
(-)-Leptoclinidamine B (13R, 2) C -α-D-mannosylpyranosyl-L-tryptophan (3)
We report herein the isolation and structures of two new tryptamine-derived alkaloids
leptoclinidamide (1) and (-)-leptoclinidamine B (2), which had unique amide moiety with two
β-alanine units and D-arginine moiety, respectively.
2
. Results and Discussion
The EtOH extract of an Indonesian ascidian L. dubius showed antimicrobial activity in the
screening bioassay against Escherichia coli and was separated into nine fractions (fraction 1–fraction 9)
by octadecylsilyl (ODS) column chromatography. Leptoclinidamide (1) was isolated from fraction 6
(
50% MeOH eluate) by HPLC (ODS) and compounds 2 and 3 were obtained from fraction 3 (30%
MeOH eluate) and fraction 2 (water eluate), respectively. The antibacterial activity against E. coli was
detected in fraction 5 (50% MeOH eluate, 10 mm inhibition zone at 250 μg/disk), and HPLC
separation of fraction 5 gave an antibacterial compound as a single HPLC peak.
1
Unfortunately, the antibacterial component did not give an informative H NMR spectrum because
of the small amounts obtained, and, therefore, 2D NMR experiments could not be recorded. The
structure of compound 3 was assigned on the basis of its spectral data and comparison with that of the
2
reported values for C -α-D-mannosylpyranosyl-L-tryptophan [6,7]. Compound 3 was first identified as

Mar. Drugs 2012, 10
351
a novel post-translationally modified tryptophan in human RNases [4] and isolated thereafter from the
ascidian L. dubius in 2000 [8], but the role of compound 3 have not yet been elucidated.
Leptoclinidamide (1) was obtained as a TFA salt. The FAB-MS spectrum of 1 showed a peak at m/z
1
3
13
1
3
03.1821, and 16 C signals were detected in the C NMR spectrum (DMSO-d ). However, the H
6
signals due to amine moiety were observed as broad peak in the NMR spectrum of 1. Therefore, the
molecular weight and formula of 1 were confirmed by the spectroscopic data for an N-acetyl derivative
+
(
4) of 1. Compound 4 gave an [M + H] ion at m/z 345.1930 in the HRFAB-MS, and the molecular
formula of 4 was determined as C H N O . Accordingly, the molecular formula of 1, which revealed
1
8
25
4
3
+
22 4 2
an [M + H] ion at m/z 303.1821 in the HRFAB-MS, were deduced as C16H N O (8 degrees
of unsaturation).
−
1
The IR spectrum of 1 showed absorption bands at 1681 and 1584 cm , which were ascribable to
1
3
2
two amide carbonyl groups. The C signals of 1 were classified into six methylene, four sp methine,
2
2
2
one nitrogenated sp methine, two sp quaternary, one nitrogenated sp quaternary and two amide
13
1
carbonyl carbons by the analysis of C NMR, DEPT and HMQC spectra of 1. The H NMR spectrum
(
DMSO-d
6
) of 1 displayed 22 signals including N-H protons due to a primary amine (δ
H
7.66, 2H), two
1
13
amides (δ
H
7.93 and 8.07), and an indole ring (δ
H
10.8). Table 1 shows H and C NMR data for 1
1
1
1
1
assigned by the analysis of H- H COSY, HMQC and HMBC spectra. The H- H COSY spectrum of 1
revealed the partial structures I through V (Figure 2). The presence of an indole ring was suggested by
1
the H NMR signals at δ 7.09 (H-2), 7.48 (H-5), 6.93 (H-6), 7.02 (H-7), 7.29 (H-8), and 10.8
1
3
(
1-NH) and HMBC correlations from these signals to the expected C NMR signals. HMBC
correlations from H
2
-10 (δ
H
2.77) to C-2 (δ
C
122.5), C-3 (δ
C
111.8), and C-4 (δ
C
127.2) and from
1
H
2
-11 (δ
H
3.29) to C-3 revealed a tryptamine unit in the molecule of 1. The H NMR signals at δ 3.29
(
H
2
-11) showed an HMBC correlation to one of two amide carbonyl carbons at δ
C
170.0 (C-13). The
8.07),
other amide linkage was determined by HMBC correlations to C-17 (δ 169.2) from 16-NH (δ
C
H
H
2
-18 (δ
H
2.38), and H
2
-19 (δ
H
2.93). These data suggested the structure of 1 as shown in Figure 1.
1
The structure of 1 was further confirmed by the analysis of the N-acetyl derivative (4). The H NMR
spectrum of 4 showed new signals corresponding to a methyl proton signal at δ 1.75 and a new amide
proton signal at δ
H NMR spectrum of 1 (δ
H
7.78 and a corresponding loss of two primary amine proton signals detected in the
7.66). These data led to the conclusion that leptoclinidamide has the
1
H
structure 1 as shown in Figure 1.
1
3
1
6
Table 1. C (100 MHz) and H (400 MHz) NMR data for leptoclinidamide (1) in DMSO-d .
No.
δ
C
δ
H
(J in Hz)
10.8 brs
HMBC
3, 4, 9
3, 4, 9
1
-NH
2
-
122.5
111.8
127.2
118.1
118.1
120.8
111.3
136.2
25.1
7.09 d (2.0)
-
3
4
-
5
7.48 d (8.0)
6.93 t (8.0)
7.02 t (8.0)
7.29 d (8.0)
-
9
4
9
4
6
7
8
9
1
0
2.77 brt (7.4)
2, 3, 4

Mar. Drugs 2012, 10
352
Table 1. Cont.
No.
δ
C
δ
H
(J in Hz)
HMBC
1
1
39.2
-
3.29 brt (7.4)
7.93 brt (5.8)
-
3, 13
1
1
2-NH
1
1
1
3
4
5
170.0
35.2
35.3
-
2.24 brt (7.4)
3.23 brt (7.4)
8.07 brt (5.8)
-
13
13
17
6-NH
1
1
1
7
8
9
169.2
31.9
35.3
-
2.38 brt (7.4)
2.93 brt (7.4)
7.66 brs
17
17
2
0-NH
2
1
1
Figure 2. H- H COSY and HMBC correlations of leptoclinidamide (1).
O
III
0
13
HN
1
5
I
IV
1
1
1
5
H- H COSY
Key HMBC
7
NH
7
1
N
O
II
H
1
V
NH2
+
Compound 2 showed a molecular ion peak at m/z 362 [M + H] in the FAB-MS, and the molecular
formula C16 was deduced from HRFAB-MS. The NMR spectrum of 2 revealed the presence
of a disubstituted indole ring and an arginine moiety. A literature to search suggested the structure of
20 5 5
H N O
1
13
(
+)-leptoclinidamine B (5) as a candidate, and this structure was confirmed by comparing H and C
NMR data for 2 with those for the reported values [9]. Compound 5 was originally isolated from an
ascidian Leptoclinides durus and showed no apparent antiprotozoal or cytotoxic activity [9]. Although
1
13
H and C NMR spectra of 2 were identical to those of 5, the sign of the specific rotation of 2 was
negative ([α] −20.6 in MeOH), suggesting that compound 2 was the enantiomer of 5 ([α] +27.0 in
D
D
MeOH) [4]. To determine the absolute configulation of 2, amino acid analysis was carried out by the
methods described in the Experimental Section. The acid hydrolysate of 2 was analyzed by using
chiral HPLC. In the analysis, an amino acid in the hydrolysate of 2 was detected at 3.7 min, which
corresponded to D-Arg (L-Arg eluted at 11.3 min). This result was confirmed by Marfey’s method [10,11].
The hydrolysate of 2 was treated with Marfey’s reagent, 5-fluoro-2,4-dinitrophenyl-L-leucine amide
(
L-FDLA), and the resulting derivative was analyzed by HPLC using an ODS column. An L-FDLA
derivative of an amino acid in the hydrolysate of 2 showed the same retention time as that of the
derivative from D-Arg (13.4 min), whereas the L-FDLA derivative of L-Arg eluted at 15.9 min.
Consequently, the absolute stereochemistry of 2 was determined to be 13R, as shown in Figure 1. Very
recently, herdmanines A-D containing a D-Arg unit were isolated from a solitary ascidian
Herdmania momus [12].
No biological activities have been reported for compound 3. Compounds 1–4 were tested for their
cytotoxicity against two human cancer cell lines (colon adenocarcinoma HCT-15 and T-cell leukemia

Mar. Drugs 2012, 10
353
Jurkat cells). However, none of the four compounds displayed activity against these cell lines at
0 μM. Since fractions 2, 3, and 6, from which respective compounds 3, 2, and 1 were isolated, did not
show growth inhibitory activity against four microorganisms (see Experimental Section), compounds
–3 will not have antimicrobial activity. Further study on biological activity of 1 is now in progress.
3
1
More L. dubius will be collected from the same site to provide sufficient amounts of the antibacterial
component for structural characterization.
3. Experimental Section
3.1. General
1
FAB-MS spectra were obtained using a JEOL JMS-MS 700 mass spectrometer (Tokyo, Japan). H
1
3
1
and C NMR spectra were recorded on a JEOL JNM-AL-400 NMR spectrometer (400 MHz for H
1
3
and 100 MHz for C) in DMSO-d (δ 2.46, δ 39.5) or CD OD (δ 3.31, δ 49.0). Optical rotations
6
H
C
3
H
C
were measured with a JASCO P-2300 digital polarimeter (Tokyo, Japan). UV spectra were recorded
on a Hitachi U-3310 UV-Visible spectrophotometer (Tokyo, Japan) and IR spectra on a PerkinElmer
Spectrum One Fourier transform infrared spectrometer (Waltham, MA, USA). Preparative HPLC was
carried out with a Hitachi L-6200 system.
3.2. Materials
Fetal bovine serum (FBS) and other culture materials were purchased from Invitrogen (Carlsbad,
CA, USA). 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) was purchased from
Sigma-Aldrich (St. Louis, MO, USA). All other chemicals and organic solvents were purchased from
Wako Pure Chemical Industries Ltd. (Osaka, Japan).
3
.3. Ascidian
The ascidian was collected by scuba diving at the coral reef in the Lembeh Strait, North Sulawesi,
Indonesia in October 2009 and identified as Leptoclinides dubius by T. N. The voucher specimen is
deposited at the National Museum of Nature and Science, Tokyo as NSMT Pc-1123.
3.4. Extraction and Isolation
The ascidian (250 g, wet weight) was cut into small pieces and soaked in EtOH on a boat
immediately after collection. The organism was further extracted twice with EtOH. The EtOH extract
3.57 g) was suspended in H O and adsorbed on an ODS column (100 g). The ODS column was eluted
stepwise with 0, 30, 50, 70, and 100% MeOH in 0.10% TFA aqueous solution into nine fractions
(
2
(
(
(
2
fraction 1–fraction 9). Fraction 2, eluted with H O, was concentrated to yield a red brown oil
108.0 mg), and 20.0 mg of the fraction was purified by preparative HPLC column, PEGASIL ODS
10 mm × 250 mm); solvent, 35% MeOH containing 0.10% TFA; flow rate, 2.0 mL/min; detection,
UV at 210 nm] to give compound 3 (eluted at 9.9 min) as a colorless solid (6.0 mg). Fraction 3, eluted
with 30% MeOH, was concentrated to yield a red brown oil (399.5 mg), and 20.0 mg was fractionated
by preparative HPLC (same conditions as Fraction 2) to yield compound 2 (eluted at 11.0 min) as a
pale yellow oil (4.0 mg). Fraction 5 (95. 0 mg), eluted with 50% MeOH, was active against E. coli and

Mar. Drugs 2012, 10
354
subjected to ODS HPLC with 40% MeOH containing 0.10% TFA (the other conditions were the same
as above) into six fractions (Fraction 5-1–Fraction 5-6). Fraction 5-6 showed the growth inhibition
1
against E. coli, but the amounts were not enough to obtain a good H NMR spectrum. Fraction 6,
eluted with 50% MeOH, was concentrated to dryness (50.5 mg), and 20.0 mg was separated by
preparative HPLC with the same conditions as Fraction 5 and afforded compound 1 (eluted at
1
5.0 min) as a colorless oil (2.0 mg).
Leptoclinidamide (1): obtained as TFA salt; UV λ (MeOH) nm (log ε): 202 (4.47), 221 (4.31);
max
−1
IR νmax (KBr) cm : 3418, 2938, 1680, 1584, 1556, 1457; HRFAB-MS (m/z) found: 303.1821, calcd:
+
1
13
3
03.1821 [M + H] for C16
23 4 2
H N O ; H and C NMR data, see Table 1.
2
0
(
-)-Leptoclinidamine B (2): obtained as TFA salt; [α]
−20.6 (c = 0.033, MeOH); UV λmax
D
−1
(
MeOH) nm (log ε): 203 (4.38), 247 (3.78), 284 (3.78), 334 (3.22); IR νmax (KBr) cm : 3384, 1684,
638, 1450, 1275, 1131; HRFAB-MS (m/z) found: 362.1465, calcd: 362.1464 [M + H] for
+
1
1
C H N O ; H-NMR (DMSO-d ) δ 1.53 (2H, m, H-15), 1.77, 1.86 (2H, m, H-14), 3.14 (2H, m,
1
6
20
5
5
6
H
H-16), 4.28 (1H, brs, H-13), 6.75 (1H, d, J = 8.0 Hz, H-6), 6.87 (1H, s, H-8), 7.12 (4H, brs, 18-N H ),
2
4
7
.62 (1H, brs, 17-NH), 7.97 (1H, d, J = 8.0 Hz, H-5), 8.52 (1H, s, 12-NH), 8.72 (1H, brd, H-2), 9.33
1
3
(
(
(
6 C
1H, brs, 7-OH), 11.9 (1H, brs, 1-NH); C-NMR (DMSO-d ) δ 2 5.2 (C-15), 27.9 (C-14), 40.3
C-16), 51.9 (C-13), 97.2 (C-8), 112.4 (C-6), 112.5 (C-3), 118.8 (C-4), 121.7 (C-5), 137.3 (C-2), 137.5
C-9), 154.6 (C-7), 156.7 (C-18), 163.5 (C-11), 173.0 (C-20), 181.3 (C-10).
2
20
C -α-D-mannosylpyranosyl-L-tryptophan (3): obtained as TFA salt; [α]
D
+15.5 (c = 0.52,
3.31, 3.65 (2H, m), 3.65 (1H, m), 3.65,
.29 (2H, m), 3.89 (1H, m), 3.97 (1H, m), 4.05 (1H, brd), 4.25 (1H, brdd), 5.04 (1H, brd), 7.07 (1H, t,
J = 7.8 Hz), 7.11 (1H, t, J = 7.8 Hz), 7.38 (1H, d, J = 7.8 Hz), 7.63 (1H, d, J = 7.8 Hz).
+
1
3 H
MeOH); FAB-MS (m/z): 367 [M + H] ; H-NMR (CD OD) δ
4
3
.5. Synthesis of N-Acetyl Derivative (4) of Compound 1
Acetic anhydride (120 μL) was added to a solution of fraction 6 (20 mg) in MeOH (340 μL) at room
temperature. The mixture was stirred for 12 h and evaporated. The residue was purified by preparative
HPLC (40% MeOH containing 0.10% TFA) using ODS column (PEGASIL ODS) to give 1.0 mg of 4:
+
1
HRFAB-MS (m/z) found: 345.1930, calcd: 345.1927 [M + H] for C18
25 4 3 6
H N O ; H-NMR (DMSO-d )
δ
H
1.75 (3H, s), 2.17 (2H, t, J = 7.6 Hz), 2.21 (2H, t, J = 7.6 Hz), 2.79 (2H, t, J = 7.6 Hz), 3.18 (2H, t,
J = 7.6 Hz), 3.22 (2H, t, J = 7.6 Hz), 3.31 (2H, t, J = 7.6 Hz), 6.95 (1H, t, J = 7.4 Hz), 7.04 (1H, t,
J = 7.4 Hz), 7.11 (1H, d, J = 8.3 Hz), 7.31 (1H, d, J = 8.3 Hz), 7.50 (1H, d, J = 2.0 Hz), 7.78 (NH, 1H,
brt, J = 5.4 Hz), 7.85 (NH, 1H, brt, J = 5.8 Hz), 7.93 (NH, 1H, brt, J = 5.8 Hz), 10.8 (NH, 1H, brs).
3
.6. Acid Hydrolysis of Compound 2
Compound 2 (0.5 mg) was suspended in 6.0 N HCl (1.0 mL) and heated at 100 °C for 8 h. The
mixture was cooled to room temperature and evaporated to dryness.

Mar. Drugs 2012, 10
.7. Chiral HPLC of Peptide Hydrolysate
Hydrolysate of 2 was dissolved in H O (0.4 mL) and 5.0 μL was analyzed by HPLC using the
355
3
2
following condition (A): L-6200 system; column, SUMICHIRAL OA-6000 (Sumika Chemical
Analysis Service, Ltd., Tokyo, Japan), 4.6 × 150 mm; flow rate, 1.0 mL/min; detection, UV 254 nm;
mobile phase, 2 mM CuSO in 2.0% CH CN. Authentic L- and D-Arg were eluted at 11.3 and 3.7 min,
4
3
respectively. An amino acid in the hydrolysate of 2 was detected at 3.7 min.
3
.8. Marfey’s Analysis
Hydrolysate of 2 was dissolved in 1 M NaHCO (200 μL) and reacted with 1% L-FDLA (100 μL in
3
acetone) at 40 °C for 2 h. After cooling, the sample was quenched with 1 N HCl and dried under
vacuum. The solid residue was dissolved in 50% aq CH CN (400 μL) and analyzed under the
3
following condition (B): L-6200 system; column, Pegasil ODS SP100 (Senshu Scientific), 4.6 × 250 mm;
flow rate, 0.8 mL/min; detection, UV 340 nm; mobile phase, a liner gradient from 30% to 60%
CH CN containing 0.05% TFA. L-FDLA derivatives of authentic L- and D-Arg eluted at 15.9 and
3
1
3.4 min, respectively, and the L-FDLA derivative in the hydrolysate of 2 was detected at 13.4 min.
3.9. Antimicrobial Assay
The growth inhibitory activity was examined by the paper disk method against Mucor hiemalis
IAM 6088 (fungus), Saccharomyces cerevisiae IAM 1438T (yeast), Staphylococcus aureus IAM
2544T (Gram-positive bacterium), and Escherichia coli IAM 12119T (Gram-negative bacterium) as
test microorganisms. A paper disk containing 250 μg of the test sample was placed on a test plate.
1
3.10. Cytotoxicity Assay
HCT-15 and Jurkat cells were obtained from the Center for Biomedical Research, Institute of
Development, Aging, and Cancer, Tohoku University (Miyagi, Japan). Two cell lines were cultured in
RPMI-1640 medium. The medium was supplemented with 10% fetal bovine serum, 100 units/mL
penicillin, and 100 μg/mL streptomycin. Exponentially growing cells cultured in a humidified chamber
2
at 37 °C containing 5.0% CO were used for the experiments.
Cytotoxic activity was evaluated using the colorimetric MTT assay [13]. HCT-15 cells
4
4
(
1.0 × 10 cells in 100 μL) or Jurkat cells (2.0 × 10 cells in 100 μL) were added to each well of a
6-well plastic plate (Corning Inc., Corning, NY, USA). A sample (1.0 μL in MeOH) was added to
each well to make the final concentration from 0 to 27 μM and the cells were incubated for 48 hours at
7 °C. MTT (10 μL of 5.5 mg/mL stock solution) and a cell lysate solution (90 μL, 40%
N,N-dimethylformamide, 20% sodium dodecyl sulfate, 2.0% CH COOH and 0.030% HCl) were added
9
3
3
to each well, and the plate was shaken thoroughly by agitation at room temperature for overnight. The
optical density of each well was measured at 570 nm using an MTP-500 microplate reader (Corona
Electric Co., LTD., Ibaraki, Japan).

Mar. Drugs 2012, 10
. Conclusions
Two new tryptamine derivatives, leptoclinidamide (1) and (-)-leptoclinidamine B (2), were isolated
356
4
from the EtOH extract of an Indonesian ascidian Leptoclinides dubius together with a known
2
compound, C -α-D-mannosylpyranosyl-L-tryptophan (3). Biological activity of compound 3 has not
been clarified, and, in this study, we found that compounds 1–4 were not active against two human
cancer cell lines (HCT-15 and Jurkat) and four microorganisms (Gram positive and negative bacteria,
yeast, and fungus). An antibacterial component against E. coli was also obtained from the EtOH
extract, but the structure has not been determined because the amounts were not enough to measure 2D
NMR spectra.
Acknowledgments
This work was supported in part by a Grant-in-aid for Scientific Research (21603012) from the
Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan to MN and by a
Colab. Res. & Int. Pub. Project No. 492/SP 2H/PL/2011 from DGHE, Ministry of National Education
of Indonesia to REPM. We are grateful to the Center for Biomedical Research, Institute of
Development, Aging and Cancer, Tohoku University for kindly providing human cancer cell lines.
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