Design, synthesis and cytotoxicity of bengamide analogues and their epimers

Article abstract of DOI:10.1039/c6md00587j

Starting from d-glycero-d-gulo-heptonic acid γ-lactone and amino acids, a number of diastereoisomeric bengamide analogues were synthesized. Optimization of the reaction conditions revealed that microwave irradiation assistance is a powerful method for the preparation of aminolactams, as well as for the coupling reactions of the lactone 5 with aminolactams. Cytotoxic activity evaluation against six cancer cell lines (KB, HepG2, LU1, MCF7, HL60, and Hela) demonstrated that the configuration of C-2′ seems to be critical for the cytotoxic activity of compounds 8b (2′R) and 8a (2′S). Additionally, comparison of cytotoxicity of the protected acetonide compounds with that of their corresponding deprotected bengamide analogues suggested that the flexibility of the ketide side chain should be required for their cytotoxic activity.

Full text of DOI:10.1039/c6md00587j

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Thi Mai, V. H. Tran, B. N. Truong, T. A. Tran, V. L. Vu, V. M. Chau and C. V. Pham, Med. Chem. Commun.,
2016, DOI: 10.1039/C6MD00587J.
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DOI: 10.1039/C6MD00587J
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RESEARCH ARTICLE
Design, synthesis and cytotoxicity of bengamide analogues and
their epimers†‡
Received 00th January 20xx,
Accepted 00th January 20xx
a,b
a
a
a
a,c
Thi Dao Phi, Huong Doan Thi Mai, Van Hieu Tran, Bich Ngan Truong, Tuan Anh Tran, Van Loi
a
a
a
Vu, Van Minh Chau and Van Cuong Pham*
DOI: 10.1039/x0xx00000x
Starting from D-glycero-D-gulo-heptonic acid γ-lactone and amino acids, a number of diastereoisomeric bengamide
analogues were synthesized. Optimization of the reaction conditions revealed that microwave irradiation assistance is a
powerful method for the preparation of aminolactams, as well as for the coupling reactions of the lactone 5 with
aminolactams. Cytotoxic activity evaluation against six cancer cell lines, KB, HepG2, LU1, MCF7, HL60, and Hela
demonstrated that the configuration of C-2’ seems to be critical for the cytotoxic activity of compounds 8b (3’R) and 8b
www.rsc.org/
(3’S). Additionlly, comparison of cytotoxicity of the protected acetonide compounds with their corresponding deprotedted
bengamide analogues suggested that the flexibility of the ketide side chain should be require for their cytotoxic activity.
butyl group has proven successful. This modification simplified
the synthesis of their analogues. Also, the introduction of tert-
butyl group at the terminal side chain led to the obtainment of
Introduction
Natural products from terrestrial source play an important
role in biomedical research, as the majority of antibacterial
and cytotoxic anticancer drugs in clinical use are either such
more stable structures by avoiding olefin isomerization. A
bengamide analogue, LAF389 with tert-butyl at terminal side
2
1
1
-3
chain, has been used in a clinical trial. However, the poor
pharmacokinetic properties and unclear side effects of LAF389,
which appeared early in the trial, have prevented its further
secondary metabolites or their derivatives.
Although the
marine environment represents an enormous additional
4
-5
reservoir for novel secondary metabolites. Marine sponges
of the family Jaspidae have proven to be an important source
of bioactive secondary metabolites. The sponge-derived
bengamides, have been firstly reported in 1986, and have a
2
2
development. This prompt the search for new bengamide
analogues with better therapeutic index. To our knowledge,
2
3
except for the ent-bengamide, no synthesis of bengamide
analogues with modification of chirality at C-2’ carbons have
been reported. In this communication, we report the synthesis
of bengamide analogues with replacement of isopropyl by tert-
butyl, and modification of C-2’ or C-5’ of the lactam ring, and
their cytotoxicity evaluation against six cancer cell lines.
6
unique molecular structure. These compounds were found to
have a broad spectrum of biological activities such as
7
-9
antitumor, antibiotic, and anthelmintic properties. Due to
their pharmacological interest, these molecules have attracted
the attention of many organic chemists. The structural
modification of bengamides has focused mainly on improving
their water solubility, stability or biological activity.
Accordingly, the synthetic analogues have been prepared by
modifications of the different stereocenters located at the
OH OMe
O
H
R
1
7'
1
N
2'
N
OH OH
O
5
'
R2
1
0-14
polyketide chain;
changes of the substituent located at the
5-17
Bengamide A: R
1
= H, R
2
= O
2
C(CH
2
)
12CH
3
1
terminal olefinic position;
1
caprolactam unit.
or modification of the
These modifications led to the
B: R1 = Me, R2 = O C(CH ) CH3
2
2 12
7-20
1 2
E: R = R = H
F: R = Me, R = H
obtainment of more potent bengamide derivatives.
1
2
Y: R1 = H, R = OH
2
Modification of side chain by replacement of isopropyl by tert-
Z: R = Me, R = OH
1
2
Fig. 1 Representative bengamide structures
Results and discussion
Synthetic approach of bengamide analogues was described in
Schemes 1 - 4. The general strategy for the preparation of
bengamide analogues is based on the lactone
5 and
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DOI: 10.1039/C6MD00587J
ARTICLE
Journal Name
aminocaprolactam intermediates, via an amide coupling Similarly, the racemic 4a (2S*,5S*) and 4b (2R*,5S*) were also
reaction.
prepared from the corresponding racemic 2a and 2b (Scheme
).
3
Scheme 1 Main reported methods for synthesis of 3a from L-lysine
H
O
N
2
H N
2
O
3
a
Scheme 4 Reagents and conditions: (a) THF, MW at 100 W, 60 - 120 min, 6a (95%), 6b
76%), 7a (48%), 7b (44%) (93% overall yield for 7a+7b), 7c (28%) and 7d (25%) (53%
H N
2
2
OH
(
o
NH2
overall yield for 7c+7d); (b) TFA, H O, THF, 0 C, 1 h, 8a (69%), 8b (58%), 9a (45%), 9b
H
N
2
O
1
a (L-lysine)
(63%), 9c (42%) and 9d (40%).
1b (D-lysine)
2
H N
2
3b
Scheme 2 Reagents and conditions: Ethylene glycol, MW at 284 W, 60 min;
a (79%), 3b (82%).
3
Fig. 2 Structures of the synthetic bengamide analogues.
Coupling reaction of the lactone
5 (which was prepared
0,21
2
according to the previously reported method)
with each
enantiomeric aminolactams 3a and 3b, and two racemic
mixtures, rac-4a and rac-4b was optimized. Initial attempt for
the coupling of
according to the previously described method by using sodium
-ethylhexanoate as a base at room temperature for 15 – 20
5 with these aminolactams was performed
Scheme 3 Reagents and conditions: Ethylene glycol, MW at 284 W, 60 min;
rac-4a (51%), rac-4b (39%).
2
2
1
In the first step, the aminocaprolactams were synthesized h. The lactone ring opening by aminolactams was then
from the corresponding amino acids. Several methods for examined under microwave irradiation. Accordingly, treatment
synthesis of α-aminolactams from the corresponding amino of
5
with the aminolactams 3a and 3b under microwave
2
4-26
acids have been reported.
However, these methods irradiation at 100 W for 1 - 2 h to afford the corresponding
involved to use expensive reagents or need performing under compounds 6a and 6b in 95 and 76% yield, respectively. Thus,
high pressure, at high temperature and long reaction time with microwave irradiation assistance, the coupling reaction
(
methods a, b and c, Scheme 1). In this work, the preparation occurred significantly faster with the yields comparable with
of α-aminolactams were examined under microwave previously described method. By using the same procedure
irradiation. With the aid of microwave irradiation, the with microwave irradiation assistance, the lactone reacted
cyclization reactions proceed faster under mild condition with the racemic 4a (2S*,5S*), affording two diastereoisomers
Scheme 2). The α-aminolactams 3a and 3b were obtained 7a and 7b, while the coupling reaction of with the racemic 4b
from L-lysine and D-lysine in 79 and 82 % yields, respectively. (2R*,5S*) provided the two diastereoisomers 7c and 7d
5
(
5
.
2
| Med. Chem. Commun.
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Pleas Me de od Cn oh te amd Cj u os tm mma rgins
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DOI: 10.1039/C6MD00587J
Journal Name
ARTICLE
Finally, acetonide deprotection of compounds 6a-b and 7a-d
,
hydroxyl groups at C3, C-4 and C-5 of the polyketide chain are
o
O in THF at 0 C to involved in the activity of bengamides by forming complex
was achieved by treatment with TFA and H
2
2
with MetAps, enzymes playing important roles in cell
7
afford the corresponding bengamide analogues 8a-b and 9a-d
The absolute configuration of C-2’ and C-5’ of compounds 7a
and 9a was established by comparison of their NMR data
.
2
8-29
-d
proliferation and angiogenesis.
-d
and optical rotation activity with the previously reported
compound (in case of 7c) or related structures. Accordingly, for
the 2’,5’-trans-isomer series, 9a had a positive rotation activity
Conclusions
Six diastereoisomeric bengamide analogues were synthesized.
Microwave irradiation assistance was found to be useful for
the preparation of aminolactams, and especially for the
2
5
{
[α]
D
+7.0 (c 0.1, MeOH)}, while this value was -20.0 (c 0.1,
MeOH) for 9b. The bengamide Y (2’S,5’S), a related structure
2
5
with 9a and 9b displayed a positive rotation activity {[α]
D
coupling reactions of the lactone
5 with aminolactams.
9
+
14.0 (c 0.11, MeOH)}. This observation suggested the
absolute configurations 2’S and 5’S for 9a, as well as for 7a
Thus, the configurations 2’R and 5’R were assigned for 9b and
Similarly, for the 2’,5’-cis-isomers 7c and 9c
comparison of NMR data revealed that 7c was identical with
Cytotoxicity evaluation of these diastereoisomeric bengamide
analogues revealed that the analogue 8b was remarkably more
active than its 2’-epimer (8a) which represented similar
configuration at C-2’ as natural bengamides. Furthermore,
since the acetonide compounds were much less active than
their corresponding acetonide deprotection analogues, the
flexibility of the ketide side chain should be require for their
cytotoxic activity. This is consistent with the previous study on
mode of action for bengamides in which the hydroxyl groups
at C-2, C-4 and C-5 are required for forming complex with
MetAps.
.
7b
.
-d
-d,
2
0
the reported values for 2’S,5’R-isomer. The configurations 2’S
and 5’R were distributed for 7c and 9c. Therefore, 7d and 9d
had the configurations 2’R and 5’S.
Table 1 Cytotoxicity of the synthetic bengamide analogues (IC50 values are expressed in
µM)
Compd
KB
LU1
4.3
HepG2
21.1
MCF7
1.3
HL60
83.3
5.3
Hela
60.7
2.1
8
8
9
9
9
9
6
6
a
b
a
b
c
21.0
1.1
0.5
1.1
0.2
Experimental
19.8
5.1
10.0
17.2
23.4
36.3
103.1
21.3
144.5
164.9
23.4
>150.0 >150.0
12.1 15.4
General information
62.6
23.7
>150.0
137.6
>150.0
>150.0
1.2
>150.0 >150.0
>150.0 >150.0
>150.0 >150.0
>150.0 >150.0
Optical rotations were recorded on a Polax-2L polarimeter in
d
a
b
80.4
CHCl
10 spectrometer. NMR spectra were recorded on a Bruker
AM500 FT-NMR spectrometer operating at 500.13 MHz and
3
or MeOH. HRESIMS data were recorded on a VARIAN
>150.0 >150.0
>150.0 >150.0
>150.0
>150.0
2.4
9
Ellipticine
1.2
1.6
2.0
1.6
1
13
1
1
25.76 MHz for H NMR and C NMR spectra, respectively. H
NMR chemical shifts were referenced to CHCl at 7.27 ppm,
and C NMR chemical shifts to the central peak of CDCl at
7.0 ppm. The HMBC measurements were optimized to 7.0 Hz
long-range couplings, and NOESY experiments were run with
50 ms mixing time. All chemicals were purchased from Sigma-
Aldrich and used without further purification.
3
The synthetic bengamide analogues were evaluated for their
cytotoxicity against six cancer cell lines, KB (mouth epidermal
carcinoma cells), HepG2 (human liver hepatocellular
carcinoma cells), LU (human lung adenocarcinoma cells), MCF7
1
3
3
7
1
(human breast cancer cells), HL60 (human promyelocytic
leukemia cells), and Hela (human cervical carcinoma cells).
Compound 8b (2’R) was the most active against six tested Synthetic procedures
cancer cell lines and exhibited slightly selective inhibition
Synthesis of the aminolactams 3a-b, rac-4a and rac-4b
toward MCF7 cells (Table 1). Comparison of the compound 8b
2’R) with its 2’-epimer 8a which had the same
stereochemistry at C-2’ as natural bengamides revealed that
(2’R) was more active than 8a (2’S) against almost tested
To a solution of each amino acid, L-lysine, D-lysine, rac-2a and
rac-2b (0.3 mmol) in ethylene glycol (0.1 mL) was added
pyridine (0.1 mL). The mixture was irradiated with microwaves
at 284 W for 60 min. The corresponding aminolactam
compounds were obtained by chromatographic purification on
(
(
)
8
b
cancer cell lines. Additionally, in order to understand the
flexibility effects of the ketide side chain to the cytotoxicity,
the acetonide compounds were also tested for their activity
against six above cancer cell lines. However, all of them were
much less active than their corresponding deprotected
compounds. No inhibition was observed for the restricted
compounds even at the concentration of 150 µM. As an
example indicated in Table 1, the two compounds 6a and 6b
with restricted C-3/C-4/C-5 bonds are significantly less active
than 8a and 8b which had free rotation bonds for C-3/C-4/C-5.
This suggested that the flexibility of the polyketide side chain
of bengamides seems to be critical for their cytotoxicity. This
observation is in agreement with the previous report that the
silica gel (gradient acetone/MeOH). NMR data for 3b and 3b
1
:
H-NMR (500 MHz, DMSO-d
6
): 1.17 (1H, m), 1.32 (1H, m), 1.56
(
1H, m), 1.68 (2H, m), 1.83 (1H, m), 3.05 (2H, m), 3.41 (1H, dd,
13
J = 1.5, 11.0 Hz), 7.56 (1H, br. s, NH). C-NMR (125 MHz,
DMSO-d ): 27.9 (CH ), 29.1 (CH ), 34.1 (CH ), 40.5 (CH ), 52.8
CH), 177.9 (C=O); NMR data for rac-4a: H-NMR (500 MHz,
6
2
2
2
2
1
(
6
DMSO-d ): 1.36-1.67 (m,3H), 1.95 (m, 1H), 2.90-3.50 (m, 4H),
13
4
.85 (br. s, 1H), 7.55 (br. s, 1H). C-NMR (125 MHz, DMSO-d
2.5 (CH ), 36.9 (CH ), 47.4 (CH
6
):
3
2
2
2
), 52.6 (CH), 69.3 (CH), 177.8
1
C=O); NMR data for rac-4b: H-NMR (500 MHz, DMSO-d
(
6
):
1.44 (m,1H), 1.58-1.78 (m, 3H), 2.98-3.66 (m, 4H), 7.18 (br. s,
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ARTICLE
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1
3
NH). C-NMR (125 MHz, DMSO-d6): 28.3 (CH
5.2 (CH ), 52.9 (CH), 64.3 (CH), 177.6 (C=O).
2
), 34.4 (CH
2
), 2’), 47.0 (C-6’), 35.9 (C-4’), 32.1 (C-8), 28.5 (C-3’), 28.3 (C-9, 10
and 11), 28.6 (C-15), 17.9 (C-16).
4
2
2
5
7
b
: C21
H
36
N
2
O
7
; White amorphous; [α]
D
+23.4 (c 0.3 CHCl
ESIMS: m/z 451 [M+Na] ; H-NMR (500 MHz, CDCl ): 7.57 (1H,
d, J = 6.0 Hz, NH-13), 6.19 (1H, t, J = 6.0, NH-7’), 5.78 (1H, d, J =
6.0 Hz, H-7), 5.52 (1H, dd, J = 7.0, 16.0 Hz, H-6), 4.62 (1H, br.
dd, J = 6.0 and 9.5 Hz, H-2’), 4.28 (1H, br. d, J = 7.0 Hz, H-5),
3
),
General procedure for coupling reaction of lactone 5 with
aminolactams
+
1
3
To a solution of each amino lactam, 3a
-b
, rac-4a and rac-4b
1
(
0.5 mmol, 5.0 eq) in 0.2 mL anhydrous THF was added the
ketide
5 (1.0 eq) and sodium-2-ethylhexanoate (1.2 eq) under
4
.06 (1H, br. d, J = 7.5 Hz, H-3), 3.88 (1H, d, J = 7.5 Hz, H-2),
.61 (1H, m, H-5’), 3.53 (1H, br. s, J = 5.5 Hz, H-4), 3.48 (3H, s,
nitrogen atmosphere. The solution mixture was irradiated with
microwaves at 100 W for 60 - 120 min. The solvent was
removed in vacuum. The residue was chromatographed on a
silica gel column, eluting with gradient mixture of
3
OMe-12), 3.35 (1H, m, H
-4’), 2.13 (1H, m, H -3’), 1.88 (1H, m, H
’), 1.46 (3H, s, Me-15), 1.45 (3H, s, Me-16), 1.03 (9H, s, Me-9,
b
a
-6’), 3.28 (1H, m, H -6’), 2.22 (1H, m,
H
b
b
a
-4’), 1.63 (1H, m, H -
a
3
1
CH
bengamide analogues.
; White amorphous solids, [α]
2 2
Cl /MeOH to afford the corresponding protected
1
3
3
0 and 11). C-NMR (125 MHz, CDCl ): 174.7 (C-1’), 169.7 (C-
2
5
1), 145.4 (C-7), 121.5 (C-6), 99.7 (C-14), 80.7 (C-2), 74.4 (C-5),
73.2 (C-3), 69.9 (C-5’), 65.8 (C-4), 59.3 (OMe-12), 51.7 (C-2’),
6
a
: C21
H
36
N
2
O
6
D
-7.0 (c 0.8
); ESIMS: m/z 413 [M+H] ; H-NMR (500 MHz, CDCl ):
.78 (1H, d, J = 6.0 Hz, NH-13), 5.91 (1H, br. s, NH-7’), 5.77 (1H,
d, J = 16.0 Hz, H-7), 5.56 (1H, dd, J = 7.0 and 16.0 Hz, H-6), 4.58
1H, ddd, J = 1.5, 6.0 and 10.5 Hz, H-2’), 4.26 (1H, br. d, J = 7.0
+
1
CHCl
3
3
4
1
7
8.1 (C-6’), 36.8 (C-4’), 33.1 (C-8), 29.6 (C-15), 29.4 (C-9, 10 and
1), 29.3 (C-3’), 19.1 (C-16).
7
2
5
c
: C21
H
36
N
2
O
7
; White amorphous, [α]
+
D
+26.9 (c 0.45 CHCl
3
);
(
1
ESIMS: m/z 451 [M+Na] ; H-NMR (500 MHz, CDCl
3
): 7.60 (1H,
Hz, H-5), 4.07 (1H, br. d, J = 6.0 Hz, H-3), 3.88 (1H, d, J = 6.0 Hz,
H-2), 3.54 (1H, br. d, J = 7.5 Hz, H-4), 3.51 (3H, OMe-12), 3.39
d, J = 7.0 Hz, NH-13), 6.27 (1H, t, J = 5.0 Hz, NH-7’), 5.78 (1H, d,
J = 16.0 Hz, H-7), 5.53 (1H, dd, J = 7.0 and 16.0 Hz, H-6), 4.57
(
1H, d, J = 7.5 Hz, OH), 3.28 (2H, m, CH
.01 (1H, m, H -3’), 1.85 (2H, m, H -4’, H
’), 1.48 (3H, s, Me-15), 1.45 (3H, s, Me-16), 1.42 (1H, m, H
2
-6’), 2.06 (1H, m, H
b
-4’),
(
1H, m, H-2’), 4.28 (1H, br. d, J = 7.0 Hz, H-5), 4.07 (1H, br. d, J
7.0 Hz, H-3), 4.01 (1H, m, H-5’), 3.90 (1H, d, J = 7.0 Hz, H-2),
3.55 (1H, br. s, H-4), 3.50 (1H, m, H -6’), 3.48 (3H, s, OMe-12),
2
3
5
1
8
5
2
6
b
a
b
-5’), 1.53 (1H, m, H
a
-
-
=
b
1
3
b
3
’), 1.03 (9H, s, Me-9, 10 and 11). C-NMR (125 MHz, CDCl ):
3
1
1
.35 (1H, m, H
.89 (1H, m, H
.45 (3H, s, Me-15), 1.03 (9H, s, Me-9, 10 and 11). C-NMR
): 175.1 (C-1’), 169.7 (C-1), 145.4 (C-7), 121.5
a
-6’), 2.05 (1H, m, H
b
-4’), 2.00 (1H, m, H
a
-4’),
75.0 (C-1’), 169.5 (C-1), 145.3 (C-7), 121.7 (C-6), 99.7 (C-14),
1.6 (C-2), 74.7 (C-5), 73.3 (C-3), 66.3 (C-4), 59.6 (OMe-12),
1.9 (C-2’), 42.2 (C-6’), 33.1 (C-8), 31.7 (C-3’), 29.5 (Me-15),
9.4 (C-9, 10 and 11), 28.9 (C-5’), 27.9 (C-4’), 19.0 (C-16).
b
-3’), 1.84 (1H, m, H
a
-3’), 1.46 (3H, s, Me-16),
1
3
(
125 MHz, CDCl
3
2
5
(C-6), 99.7 (C-14), 80.6 (C-2), 74.5 (C-5), 73.2 (C-3), 65.8 (C-4),
64.7 (C-5’), 59.2 (OMe-12), 51.8 (C-2’), 46.0 (C-6’), 34.6 (C-4’),
b
: C21
H
36
N
2
O
6
; White amorphous solids; [α]
D
+8.8 (c 1.05
); ESIMS: m/z 413 [M+H] ; H-NMR (500 MHz, CDCl ):
.55 (1H, d, J = 6.0 Hz, NH-13), 6.05 (1H, t, J = 5.5 Hz, NH-7’),
.77 (1H, d, J = 16.0 Hz, H-7), 5.52 (1H, dd, J = 6.5 and 16.0 Hz,
+
1
CHCl
3
3
3
3.1 (C-8), 29.6 (C-15), 29.3 (C-9, 10 and 11), 25.1 (C-3’), 19.1
7
5
(
C-16).
2
D
5
7
d
: C21
H
36
N
2
O
7
; White amorphous, [α]
-19.7 (c 0.3 CHCl
3
);
H-6), 4.59 (1H, br. dd, J = 6.0 and 10.5 Hz, H-2’), 4.27 (1H, br. d,
J = 6.5 Hz, H-5), 4.06 (1H, br. d, J = 7.5 Hz, H-3), 3.87 (1H, d, J =
+
ESIMS: m/z 451 [M+Na] ; H-NMR (500 MHz, CDCl ): 7.78 (1H,
1
3
d, J = 6.0 Hz, NH-13), 6.10 (1H, br. s, H-7’), 5.78 (1H, d, J = 15.5
Hz, H-7), 5.55 (1H, dd, J = 7.0, 15.5 Hz, H-6), 4.55 (1H, m, H-2’),
7
.5 Hz, H-2), 3.54 (1H, br. s, H-4), 3.48 (3H, s, OMe-12), 3.27
2H, m, CH -6’), 2.09 (1H, m, H -4’), 2.01 (1H, m, H -3’), 1.85
2H, m, H -4’, H -5’), 1.65 (1H, m, H -3’), 1.46 (3H, s, Me-15),
.45 (3H, s, Me-16), 1.44 (1H, m, H -5’), 1.02 (9H, s, Me-9, 10
): 175.2 (C-1’), 169.4 (C-1),
45.3 (C-7), 121.6 (C-6), 99.7 (C-14), 80.7 (C-2), 74.5 (C-5), 73.2
(
(
2
b
b
4
.26 (1H, br. d, J = 7.0 Hz, H-5), 4.06 (1H, br. d, J = 6.5 Hz, H-3),
.01 (1H, m, H-5’), 3.89 (1H, d, J = 6.5 Hz, H-2), 3.53 (1H, br. s,
a
b
a
4
1
b
1
3
H-4), 3.51 (1H, m, H -6’), 3.50 (3H, s, OMe-12), 3.34 (1H, m, H -
b
a
and 11). C-NMR (125 MHz, CDCl
3
6
’), 2.04 (1H, m, H
.84 (1H, m, H
b
-4’), 2.01 (1H, m, H
a
-4’), 1.88 (1H, m, H
b
-3’),
1
1
a
-3’), 1.47 (3H, s, Me-15), 1.45 (3H, s, H-16), 1.03
(
C-3), 65.9 (C-4), 59.2 (OMe-12), 52.0 (C-2’), 42.1 (C-6’), 33.1
C-8), 31.3 (C-3’), 29.6 (Me-15), 29.4 (C-9, 10 and 11), 28.9 (C-
1
9H, s, Me-9, 10 and 11). C-NMR (125 MHz, CDCl
3
(
3
): 175.0 (C-
(
1’), 169.7 (C-1), 145.4 (C-7), 121.6 (C-6), 99.7 (C-14), 81.4 (C-2),
5
’), 27.9 (C-6’), 19.1 (C-16).
; White amorphous; ESIMS: m/z 451 [M+Na] ;
): 7.77 (1H, d, J = 6.0 Hz, NH-13), 6.09
1H, t, J = 6.0 Hz, NH-7’), 5.77 (1H, d, J = 16.0 Hz, H-7), 5.54 (1H,
dd, J = 6.5 and 16.0 Hz, H-6), 4.61 (1H, m, H-2’), 4.26 (1H, br. d, General procedure for synthesis of compounds 8a-b and 9a-d
J = 6.5 Hz, H-5), 4.05 (1H, br. d, J = 6.5 Hz, H-3), 3.88 (1H, d, J = A solution of each protected compound, 6a , and 7a , (0.02
.5 Hz, H-2), 3.62 (1H, m, H-5’), 3.53 (1H, br. s, H-4), 3.50 (3H, mmol) in THF (0.15 mL) was cooled down to 0 C. To this
s, OMe-12), 3.33 (1H, m, H -6’), 3.29 (1H, m, H -6’), 2.21 (1H, solution, TFA (8 eq) and H O (30 µL) were successively added.
m, H -4’), 2.10 (1H, m, H -3’), 1.89 (1H, m, H -4’), 1.65 (1H, m, The solution was stirred at 0 C for 1 h, and passed through a
-3’), 1.47 (3H, s, Me-15), 1.45 (3H, s, Me-16), 1.02 (9H, s, Me- Sephadex LH-20 column (eluting with MeOH). The solvent was
+
74.6 (C-5), 73.3 (C-3), 66.3 (C-4), 64.7 (C-5’), 59.6 (OMe-12),
51.7 (C-2’), 46.1 (C-6’), 34.6 (C-4’), 33.1 (C-8), 29.5 (C-15), 29.4
7
1
36 2 7
a: C21H N O
H-NMR (500 MHz, CDCl
3
(C-9, 10 and 11), 25.4 (C-3’), 19.0 (C-16).
(
-b
-d
o
6
b
a
2
o
b
b
a
H
a
1
3
9
, 10 and 11). C-NMR (125 MHz, CDCl
3
): 173.6 (C-1’), 168.8 removed under diminished pressure and the residue was
(C-1), 144.4 (C-7), 120.6 (C-6), 98.7 (C-14), 80.4 (C-2), 73.6 (C- purified by preparative TLC to give the corresponding title
5), 72.3 (C-3), 68.9 (C-5’), 65.2 (C-4), 58.6 (OMe-12), 50.6 (C- compounds.
4
| Med. Chem. Commun.
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Pleas Me de od Cn oh te amd Cj u os tm mma rgins
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DOI: 10.1039/C6MD00587J
Journal Name
ARTICLE
2
5
25
+5.0 (c 0.4 9c: White amorphous solid; [α]
D
8
a
: C18
H
32
N
2
O
6
; White amorphous solid; [α]
+
D
+16.0 (c 0.1, MeOH);
+
3
CHCl ); HRESI-MS: m/z 395.2135 [M+Na] (calcd 395.2158 for HRESIMS: m/z 411.2108 [M+Na] (calcd 411.2107 for
1
Na); H-NMR (500 MHz, CDCl
1
C
18
H
32
N
2
O
6
3
): 7.96 (1H, d, J = 6.5
18 32 2 7 3
C H N O Na); H-NMR (500 MHz, CD OD): 5.82 (1H, d, J =
Hz, NH-13), 6.13 (1H, br. s, NH-7’), 5.82 (1H, d, J = 15.5 Hz, H- 15.5 Hz, H-7), 5.43 (1H, dd, J = 7.0 and 15.5 Hz, H-6), 4.59 (1H,
7
6
3
3
), 5.41 (1H, dd, J = 7.5 and 15.5 Hz, H-6), 4.55 (1H, br. dd, J = br. d, J = 9.0 Hz, H-2’), 4.14 (1H, dd, J = 7.0 and 7.0 Hz, H-5),
.5 and 10.5 Hz, H-2’), 4.22 (1H, dd, J = 5.0 and 7.5 Hz, H-5), 3.83 (1H, overlap, H-2), 3.79 (1H, m, H-5’), 3.76 (1H, m, H-3),
.80 (1H, br. d, J = 7.0 Hz, H-3), 3.75 (1H, d, J = 7.0 Hz, H-2), 3.59 (1H, m, H-4), 3.44 (3H, s, OMe-12), 3.03 (1H, m, H
.62 (1H, br. d, J = 5.0 Hz, H-4), 3.55 (3H, s, OMe-12), 3.28 (2H, 2.80 (1H, m, H -6’), 1.96 (2H, m, CH -3’), 1.61 (2H, m, CH
-6’), 2.03 (1H, m, H -4’), 2.01 (1H, m, H -3’), 1.87 (1H, m, 1.06 (9H, s, Me-9, 10 and 11). C-NMR (125 MHz, CD
-5’), 1.82 (1H, m, H -4’), 1.56 (1H, m, H -3’), 1.42 (1H, m, H 174.7 (C-1’), 172.2 (C-1), 146.0 (C-7), 125.4 (C-6), 83.4 (C-2),
’), 1.02 (9H, s, Me-9, 10 and 11). C-NMR (125 MHz, CDCl ): 75.2 (C-5), 74.3 (C-4), 72.6 (C-3), 68.4 (C-5’), 58.7 (OMe-12),
b
-6’),
a
2
2
-4’),
1
3
CH
2
b
b
3
OD):
H
b
a
a
a
-
1
3
5
1
7
4
3
74.8 (C-1’), 171.5 (C-1), 145.7 (C-7), 123.2 (C-6), 81.3 (C-2), 53.1 (C-2’), 45.9 (C-6’), 35.4 (C-3’), 33.8 (C-8), 32.2 (C-4’), 29.9
4.5 (C-5), 72.7 (C-3), 72.3 (C-4), 59.9 (OMe-12), 51.9 (C-2’), (C-9, 10 and 11).
2
5
2.1 (C-6’), 33.0 (C-8), 31.4 (C-3’), 29.4 (C-9, 10 and 11), 28.8 9d: White amorphous solid; [α]
D
-35.0 (c 0.1, MeOH);
+
HRESIMS: m/z 411.2107 [M+Na] (calcd 411.2107 for
(C-5’), 27.9 (C-4’).
2
D
5
1
8b
: C18
H
32
N
2
O
6
; White amorphous solid; [α]
+37.7 (c 0.26
18 32 2 7 3
C H N O Na); H-NMR (500 MHz, CD OD): 5.80 (1H, d, J =
+
); HRESIMS: m/z 395.2161 [M+Na] (calcd 395.2158 for 15.5 Hz, H-7), 5.42 (1H, dd, J = 7.5 and 15.5 Hz, H-6), 4.59 (1H,
CHCl
3
1
C
18
H
32
N
2
O
6
Na); H-NMR (500 MHz, CDCl
3), 5.84 (1H, d, J = 15.5 Hz, H-7), 5.39 (1H, dd, J = 7.5 and 15.5 5’), 3.83 (1H, d, J = 7.5 Hz, H-2), 3.74 (1H, dd, J = 1.7 and 7.5 Hz,
Hz, H-6), 4.53 (1H, br. dd, J = 6.5 and 9.5 Hz, H-2’), 4.16 (1H, H-3), 3.60 (1H, dd, J = 1.7 and 7.5 Hz, H-4), 3.51 (1H, br. d, J =
dd, J = 5.0 and 7.5 Hz, H-5), 3.93 (1H, m, H-3), 3.72 (1H, m, H- 15.0 Hz, H -6’), 3.42 (3H, s, OMe-12), 3.26 (1H, dd, J = 6.5 and
-6’), 1.99 (2H, m, CH -4’), 1.94 (1H, m, H -3’), 1.77
3
): 7.88 (1H, br. s, NH- m, H-2’), 4.15 (1H, dd, J = 7.5 and 7.5 Hz, H-5), 3.92 (1H, m, H-
1
b
2
2
1
1
1
7
4
), 3.67 (1H, m, H-4), 3.47 (3H, s, OMe-12), 3.30 (2H, CH
2
b
a
-6’), 15.0 Hz, H
-5’), (1H, m, H
-5’), MHz, CD
a
2
b
1
3
.03 (1H, m, H
.78 (1H, m, H
b
-4’), 2.02 (1H, m, H
-4’), 1.67 (1H, m, H
b
-3’), 1.85 (1H, m, H
-3’), 1.44 (1H, m, H
a
-3’), 1.04 (9H, s, Me-9, 10 and 11). C-NMR (125
3
OD): 176.6 (C-1’), 173.1 (C-1), 146.1 (C-7), 125.4 (C-6),
a
a
1
3
3
.01 (9H, s, Me-9, 10 and 11). C-NMR (125 MHz, CDCl ): 83.5 (C-2), 75.5 (C-5), 74.2 (C-4), 72.8 (C-3), 65.7 (C-5’), 58.8
75.1 (C-1’), 171.8 (C-1), 146.0 (C-7), 123.3 (C-6), 81.5 (C-2), (OMe-12), 53.2 (C-2’), 46.5 (C-6’), 35.4 (C-4’), 33.8 (C-8), 29.8
4.1 (C-5), 72.7 (C-4), 72.1 (C-3), 59.1 (OMe-12), 52.2 (C-2’), (C-9, 10 and 11), 25.9 (C-3’).
1.9 (C-6’), 33.0 (C-8), 30.3 (C-3’), 29.4 (C-9, 10 and 11), 28.6
Cytotoxic activity assay
(C-5’), 27.9 (C-4’).
The cytotoxicity assays were carried out in triplicate in 96-well
microtiter plates against KB, HepG2, LU, MCF7, HL60, and Hela.
Cells were maintained in Dulbecco's D-MEM medium,
2
D
5
9a
: White amorphous solid; [α]
+7.0 (c 0.1, MeOH);
+
HRESIMS: m/z 411.2111 [M+Na] (calcd 411.2107 for
1
Na); H-NMR (500 MHz, CD
C
18
H
32
N
2
O
7
3
OD): 5.82 (1H, d, J =
supplemented with 10% fetal calf serum,
penicillin (100 UI/mL), streptomycin (100 μg/mL) and
gentamicin (10 μg/mL). Stock solutions of compounds were
prepared in DMSO/H O (1/9), and the cytotoxicity assays were
L-glutamine (2 mM),
16.0 Hz, H-7), 5.43 (1H, dd, J = 8.0 and 16.0 Hz, H-6), 4.64 (1H,
G
dd, J = 1.5 and 11.5 Hz, H-2’), 4.16 (1H, dd, J = 8.0 and 8.0 Hz,
H-5), 3.83 (1H, d, J = 7.0 Hz, H-2), 3.74 (1H, dd, J = 1.5 and 7.0
Hz, H-3), 3.60 (1H, dd, J = 1.5 and 8.0 Hz, H-4), 3.51 (1H, m, H-
2
carried out in 96-well microtiter plates against cancer or
3
normal cells (3 x 10 cells/mL) using a modification of the
5
6
1
’), 3.43 (3H, s, OMe-12), 3.32 (1H, m, H
’), 2.20 (1H, m, H -4’), 2.03 (1H, m, H -3’), 1.82 (1H, m, H
.73 (1H, m, H -3’), 1.05 (9H, s, Me-9, 10 and 11). C-NMR
OD): 176.7 (C-1’), 173.1 (C-1), 146.0 (C-7), 125.4
C-6), 83.6 (C-2), 75.4 (C-5), 74.3 (C-4), 72.7 (C-3), 70.5 (C-5’),
b
-6’), 3.26 (1H, m, H
a
-
30
published method. After 72 h incubation at 37 °C in air/CO
b
b
a
-4’),
2
1
3
a
(
95:5) with or without test compounds, cell growth was
(125 MHz, CD
3
estimated by colorimetric measurement of stained living cells
by neutral red. Optical density was determined at 540 nm with
a Titertek Multiscan photometer. The IC50 value was defined as
the concentration of sample necessary to inhibit the cell
growth to 50% of the control. Ellipticine was used as a
reference compound.
(
5
3
9
8.8 (OMe-12), 53.0 (C-2’), 48.6 (C-6’), 37.5 (C-4’), 33.7 (C-8),
0.2 (C-3’), 29.8 (C-9, 10 and 11).
2
D
5
+
b
: White amorphous solid; [α]
-20.0 (c 0.1, MeOH);
HRESIMS: m/z 411.2103 [M+Na] (calcd 411.2107 for
1
Na); H-NMR (500 MHz, CD
C
18
H
32
N
2
O
7
3
OD): 5.83 (1H, d, J =
16.0 Hz, H-7), 5.42 (1H, dd, J = 7.0 and 16.0 Hz, H-6), 4.58 (1H,
dd, J = 6.5 and 11.0 Hz, H-2’), 4.23 (1H, dd, J = 7.0 and 7.0 Hz,
H-5), 3.84 (1H, br. d, J = 6.5 Hz, H-3), 3.79 (1H, d, J = 6.5 Hz, H-
Acknowledgements
The authors thank the National Foundation for Science and
Technology (NAFOSTED), and the Ministry of Science and
Technology of Vietnam (MOST) for financial support (NCCB-
ĐHUD.2012-G/05).
2
3
1
), 3.63 (1H, m, H-5’), 3.62 (1H, m, H-4), 3.53 (3H, s, OMe-12),
.23 (2H, m, CH -6’), 2.22 (1H, m, H -4’), 2.12 (1H, m, H -3’),
.87 (1H, m, H -4’), 1.67 (1H, m, H -3’), 1.02 (9H, s, Me-9, 10
OD): 174.3 (C-1’), 172.2 (C-1),
45.8 (C-7), 123.2 (C-6), 81.4 (C-2), 74.5 (C-5), 72.7 (C-3), 72.5
2
b
b
a
a
1
3
and 11). C-NMR (125 MHz, CD
3
1
(
C-4), 69.8 (C-5’), 59.8 (OMe-12), 51.7 (C-2’), 48.0 (C-6’), 36.8
C-4’), 33.0 (C-8), 29.4 (C-9, 10 and 11), 28.9 (C-3’).
References
(
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DOI: 10.1039/C6MD00587J
ARTICLE
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MedChemComm
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DOI: 10.1039/C6MD00587J
Table of contents
The C-2’ of the lactam rings and the flexibility of polyketide chain should be critical for the cytotoxicity of
bengamides.
OH OMe
O
H
N
2'
NH
8
a: R = H
R
O
OH OH
O
9a (2'S,5'S): R = OH
9c (2'S,5'R): R = OH
5
'
H2N
2
R
OH
NH2
1
a: R = H (L-lysine)
1b: R = H (D-lysine)
OH OMe
O
8
b: R = H
NH 9b (2'R,5'R): R = OH
d (2'R,5'S): R = OH
H
N
rac-2a (2S*,5S*)
rac-2b (2R*,5S*)
9
OH OH
O
R