Concise total synthesis of aplysinellamides A and B

Article abstract of DOI:10.3184/174751915X14326563172262

Concise and efficient total syntheses of bromotyrosine-derived metabolites aplysinellamides A and B, isolated from Australian marine sponge Aplysinella sp., have been accomplished in seven steps. A condensation between cinnamic acid and Boc-D-lysine methyl ester was applied to form the amide skeleton as a key step.

Full text of DOI:10.3184/174751915X14326563172262

336 RESEARCH PAPER
VOL. 39 JUNE, 336–339
JOURNAL OF CHEMICAL RESEARCH 2015
Concise total synthesis of aplysinellamides A and B
Haifeng Gan , Yu Huang , Weiyang Feng , Wentong Zhu and Kai Guo
a
a
a
a
a,b*
a
College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, Nanjing 211816, P.R. China
State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing 210009, P.R. China
b
Concise and efficient total syntheses of bromotyrosine-derived metabolites aplysinellamides A and B, isolated from Australian marine
sponge Aplysinella sp., have been accomplished in seven steps. A condensation between cinnamic acid and Boc-D-lysine methyl ester
was applied to form the amide skeleton as a key step.
Keywords: bromotyrosine, marine sponge, aplysinella species
Among more than 20,000 marine natural products, 2% of them
Results and discussion
1, 2
were discovered from deep-water marine organisms. Deep-
water organisms are expected to produce metabolites having
unique structures with interesting bioactivities, such as
Our initial retrosynthetic analysis of 1 and 2 is outlined in
Scheme 1. We envisaged that the cinnamamide skeleton of 1
and 4 could be constructed through a coupling between amine 9
and the respective acids 11 and 16 (see Scheme 2). Amine 9, in
turn, could be obtained from a cheap starting material D-lysine
(5). Intermediates including methyl N -Boc-D-lysinate 9 and
the cinnamic acids 11 and 16 were synthesised according to
reported literature procedures.
was reacted with ClCOOBn in the presence of CuSO to form
3
4
5
6
cytotoxic, anti-inflammatory, anti-bacterial, anti-malarial,
7
8
9
anti-viral,
anti-thrombotic,
anti-trypanosomal, anti-
10
11
α
neurodegenerative and estrogen. For example, tetracyclic
compound halenaquinone exhibits extremely potent activity
towards farnesyltransferases (IC 0.017–0.031 μM) and malaria
13-18
Accordingly, D-lysine (5)
5
0
(
IC50 0.53–0.62 μM) and meroterpene sulfate fascioquinols A
4
and B displayed promising Gram-positive selective antibacterial
D-lys(Z)-OH 6 in 91% yield, followed by N-protection with
5
13
activity towards Staphylococcus aureus (IC 0.9–2.5 μM).
(Boc) O to afford acid 7 in 96% yield. Acid 7 was alkylated
5
0
2
14
In 2014, Quinn et al isolated four new bromotyrosine
derivatives aplysinellamides A−C (1−3) and aplysamine-1-N-
oxide (4) with ApoE modulation activity from the Australian
marine sponge Aplysinella sp. and assigned their structures by
with CH I smoothly and gave methyl ester 8 in 85% yield.
3
Removal of the Cbz group from 8 by hydrogenation with 10%
α
Pd/C in MeOH smoothly provided methyl N -Boc-D-lysinate
13
9 in 90% yield. Cinnamic acid 11 was prepared through a
12
extensive NMR experiments (Fig. 1). The unique structure of
them intrigues many chemists. We initiated the total synthesis
of aplysinellamides in order to investigate the potential
bioactivity of the derivatives. We now report the first efficient
total syntheses of aplysinellamides A (1) and B (2) from the
accessible starting material D-lysine (5) in seven steps.
two-step sequence. Veratraldehyde was mono-brominated
with Br /AcOH to give 3-bromo-4-methoxybenzaldehyde 10
2
in 70% yield, which was subjected to Doebner–Knoevenagel
condensation with malonic acid in the presence of pyridine
15,16
and piperidine to afford cinnamic acid 11 in 92% yield.
Similarly, 4-hydroxybenzaldehyde was dibrominated to afford
CF
COO
CF
COO
3
NH
3
O
3
O
NH
3
Br
OH
Br
OH
N
N
H
H
O
O
H CO
3
H CO
3
Br
aplysinellamide A
1
ply i ll id B (2)
s ne am
a e
(
)
O
O
HO
N
Br
Br
N
OH
H
CF
3
COO
H
N
O
H CO
3
Br
CF COO
3
aplysinellamide C
3
a l samine-1-N-oxide
p y
4
(
)
( )
Fig. 1 Chemical structures of aplysinellamides A-C (1–3) and aplysamine-1-N-oxide (4).
Br
O
NHB
oc
NHBoc
COOH
Br
N
COOCH3
H
COOC
NH
+
MeO
1
and 2
H
3
2
9
MeO
R
R
1
1
2, R = H
11, R = H
16, R = Br
7, R = Br
NH
2
HOOC
NH
2
5
Scheme 1 Retrosynthetic analysis of aplysinellamides A (1) and B (2).
Correspondent. E-mail: guok@ njtech.edu.cn
*

JOURNAL OF CHEMICAL RESEARCH 2015 337
17
3,5-dibromo-4-hydroxybenzaldehyde 14 in 96% yield,
Experimental
which was methylated with CH I to give 3,5-dibromo-4-
3
Melting points were measured on a microscopic melting point
apparatus. The IR spectra were recorded on a Bruker Tensor 27 FTIR
spectrometer with a KBr disk or film. H NMR and C NMR spectra
were taken on a Bruker AV 300 or AV 400 MHz and 75 or 100 MHz
18
methoxybenzaldehyde 15 in 97% yield. Then, aldehyde
5 was subjected to Doebner–Knoevenagel condensation to
1
13
1
16
provide cinnamic acid 16 in 79% yield. Coupling of 9 with
cinnamic acid 11 was carried out under similar conditions to
give cinnamamide 12, which was saponified with 1M LiOH/
MeOH to give amino acid 13 in 61% yield in two steps. Finally,
removal of the Boc group from 13 with TFA in DCM smoothly
provided aplysinellamide A (1) in 91% yield as a white solid
spectrometer in DMSO-d or CD OD, chemical shifts are given in
6 3
parts per million (ppm) relative to TMS as an internal standard. Mass
spectra and high resolution mass spectra were performed on Agilent
Q TOF 6520 mass spectrometer with electron spray ionisation (ESI)
as the ion mode. Optical rotations were recorded using a sodium lamp
with a Rudolph Autopol I Automatic Polarimeter with 1 dm tube.
19
2
3
o
(
[α]D –3.2 , c 0.007 in MeOH). Likewise, coupling of 9 with
(
R)-Methyl 6-amino-2-(tert-butoxycarbonylamino)hexanoate (9):
cinnamic acid 16 was carried out under similar conditions to
give cinnamamide 17 in a yield of 70%, which was saponified
to give amino acid 18. Subsequently, removal of the Boc group
from 18 with TFA in DCM afforded aplysinellamide B (2) in
Removal of Cbz group from 8 by hydrogenation with 10% Pd/C in
MeOH for 14 h at room temperature smoothly provided methyl
α
13
1
N -Boc-D-lysinate 9 as an oil; yield 90%. H NMR (400 MHz,
DMSO-d ): δ 7.23 (br d, J = 7.7 Hz, 1H, C2NH), 3.88–3.94 (m,
2
3
o
6
6
1% yield in two steps as a white solid ([α]D +0.30 , c 0.017
1
H, C2H), 3.61 (s, 3H, 1-COOCH ), 3.07–3.15 (m, 2H, C6-NH ),
3
2
in MeOH) (Scheme 2). Spectral data of 1 and 2 were consistent
1
.53–1.58 (m, 2H, C1H), 1.37 (s, 9H, C(CH ) ), 1.23–1.32 (m, 6H,
12
3 3
with those described for the natural products.
C3,4,5).
(
E)-3-(3-Bromo-4-methoxyphenyl)acrylic acid (11): 3-Bromo-4-
Conclusions
methoxybenzaldehyde (10) was subjected to Doebner–Knoevenagel
In summary, we have developed a very concise route for the
first total syntheses of aplysinellamides A and B starting from
D-lysine in seven steps (overall yields: 39% for aplysinellamide
A; 31% for aplysinellamide B). Syntheses of these natural
products and their derivatives on a large scale could be realised
by this route, which will facilitate further biological studies.
Studies towards the structure modifications of these natural
products for further pharmacological investigation are ongoing
and will be reported elsewhere.
condensation with malonic acid in the presence of pyridine and
16
piperidine to afford cinnamic acid 11 as a yellow solid; yield 92%;
o
1
m.p. 240–242 C; H NMR (400 MHz, DMSO-d ): δ 12.31 (br s, 1H,
6
COOH), 7.96 (s, 1H, C2’H), 7.70 (d, J = 8.6 Hz, 1H, C6’H), 7.51 (d, J =
16.0 Hz, 1H, C3H), 7.14 (d, J = 8.6 Hz, 1H, C5’H), 6.46 (d, J = 16.0 Hz,
1H, C2H), 3.89 (s, 3H, 4’-OCH ).
3
(R,E)-6-[3-(3-bromo-4-methoxyphenyl)acrylamido]-2-[(tert-
butoxycarbonyl)amino]hexanoic acid (13): Compound 11 (0.08 g,
0.3 mmol) was dissolved in anhydrous DMF (2 mL) and anhydrous
NHBoc
NHBoc
Br
O
NH
2
NH
2
O
(
a)
(b)
HO
HO
HO
N
H
O
NH
2
N
H
O
O
O
O
5
6
7
(
c)
NHBoc
O
H
3
CO
(d)
NH
2
3
H CO
N
H
O
O
O
9
O
8
3
CF COO
O
NH
3
NHBoc
OH
Br
OH
N
H
N
(k)
H
O
O
H
3
CO
H
3
CO
R = H, 13
R = Br, 18
R
R
R = H, aplysinellamide A (1)
R = Br, aplysinellamide B (2)
(j)
O
O
NHBoc
CHO
Br
CHO
(h)
Br
Br
OCH
3
9
N
H
(e)
OH
O
H
3
CO
H
3
CO
H
3
CO
(i)
H
3
CO
R = H, 12
R = Br, 17
11
R
10
(i)
9
O
Br
CHO
Br
CHO
Br
CHO
OH
(f)
(g)
(h)
HO
H
3
CO
3
H CO
HO
Br
Br
15
Br
16
14
Scheme 2 Synthesis of aplysinellamide A and B. Reagents and conditions: (a) CuSO , aq. NaOH, r.t., 5h; ClCOOBn, EDTA, r.t., 3h, 91%; (b) (Boc) O,
4
2
4
M NaOH, Dioxane, H O, r.t., 14h; MeOH, r.t., 12h, 96%; (c) NaHCO , CH I, DMF, r.t., 36h, 85%; (d) 10% Pd/C (15 w/w %, MeOH, r.t., 14h, 95%; (e) Br ,
2 3 3 2
o
AcOH, r.t., 14h, 70%; (f) Br , AcOH, NaOAc, r.t., 1h, 96%; (g) CH I, K CO , DMF, 55 C, 3h, 97%; (h) Malonic acid, pyridine, piperidine, reflux 12h, 92%
2
3
2
3
for 11 and 79% for 16; (i) EDC.HCl, HOBt, TEA, dry DMF, dry DCM, r.t., 16h, 70% for 17; (j) LiOH.H O, MeOH, r.t., 16h, 61% for 13 in two steps; (k)
2
TFA, dry DCM, r.t., 40min, 91% for 1; 62% for 2 in two steps.

338 JOURNAL OF CHEMICAL RESEARCH 2015
DCM (2 mL) and cooled to
0
°C. 1-Hydroxy-benzotriazole
J = 8.6 Hz, 1H, C5”H), 6.47 (d, J = 15.6 Hz, 1H, C2’H), 3.95–3.98
hydrate (0.05 g, 0.37 mmol), N-(3-dimethylaminopropyl)-N’-
ethylcarbodiimide hydrochloride (0.07 g, 0.37 mmol) and TEA (0.11
mL, 0.74 mmol) were added to the solution and the mixture was
stirred at 0 °C for 1 h. Then compound 9 (0.07 g, 0.27 mmol) was
dissolved in anhydrous DCM (2 mL) and added to the mixture. The
mixture was stirred while warming to room temperature for 16 h.
The reaction mixture was diluted with DCM (2mL) and washed with
(m, 1H, C2H), 3.90 (s, 3H, OCH ), 3.33–3.35 (m, 2H, C6H), 1.90–2.01
3
(m, 2H, C3H), 1.57–1.65 (m, 2H, C5H), 1.43–1.54 (m, 2H, C4H);
13
C NMR (100 MHz, CD OD and one drop of TFA): δ 172.0 (C1),
3
169.0 (C1’), 158.8 (C4”), 140.4 (C3’), 133.4 (C2”), 130.5 (C1”), 130.1
(C6”), 120.8 (C2’), 113.5 (C5”), 113.3 (C3”), 57.1 (4”-OCH ), 54.0
3
(C2), 40.2 (C6), 31.4 (C3), 30.3 (C5), 23.6 (C4); HRMS (ESI) calcd
for C H BrN O (M+H) m/z 385.0765; found: 385.0775.
16
22
2
4
saturated NaHCO (2×4 mL). The DCM layer was washed with water
Aplysinellamide B (2): Compound 17 (0.10 g, 0.17 mmol) was
3
(
4 mL), brine (4 mL), dried (Na SO ), filtered, and evaporated under
dissolved in methanol (3 mL) and water (1 mL) and cooled to 0 °C.
2
4
reduced pressure, yielding 0.1 g crude product (12) which was used
LiOH.H O (0.04 g, 0.98 mmol) was added to the solution and the
2
for next step without further purification. The residue was dissolve in
mixture was stirred at room temperature for 16 h. The methanol was
evaporated under reduced pressure and the pH of the remaining water
was adjusted to 3 with 3 M HCl. The aqueous solution was extracted
with DCM (2×10 mL). The DCM layers were dried with Na SO and
methanol (3 mL), water (1 mL) and cooled to 0 °C. LiOH.H O (0.04 g,
2
0.98 mmol) was added to the solution and stirred at room temperature
for 16 h. The methanol was evaporated under reduced pressure,
and the pH of the remaining water was adjusted to 3 with 3 M HCl.
The aqueous solution was extracted with DCM (2×10 mL). The
DCM layers were dried with Na SO and evaporated under reduced
2
4
evaporated under reduced pressure, yielding crude product (0.08
g). The residue was dissolved in DCM: TFA (1 mL:1 mL) and the
reaction was stirred at r.t. for 40 min. The solvents were subsequently
evaporated and the product crystallised with diethyl ether to give
aplysinellamide B (2) (0.056 g, 62% yield in two steps) as a pale
2
4
pressure. The residue was purified by column chromatography on
silica gel to give 13 (0.084 g, 61% yield in two steps) as a white solid;
o
1
o
23
12
23
m.p. 119–120 C; H NMR (400 MHz, DMSO-d ): δ 8.00 (t, J = 5.6
powder; m.p.>250 C; [α]D +0.30 (c 0.017, MeOH) (lit. [α]D
+0.29 (c 0.017, MeOH); IR (KBr): 2927, 2857, 1634, 1419, 1260,
6
Hz, 1H, N1H), 7.78 (d, J = 2.0 Hz, 1H, C2”H), 7.55 (dd, J = 8.8, 2.0
Hz, 1H, C6”H), 7.32 (d, J = 15.8 Hz, 1H, C3’H), 7.15 (d, J = 8.8 Hz,
−1
1
1
205cm ; H NMR (400 MHz, CD OD and one drop of TFA): δ 7.79
3
1
3
H, C5”H), 6.97–7.03 (m, 1H, N2H), 6.52 (d, J = 15.8 Hz, 1H, C2’H),
.88 (s, 3H, OCH ), 3.80–3.84 (m, 1H, C2H), 3.12–3.17 (m, 2H,
(
s, 2H, C2”,6”H), 7.39 (d, J = 15.8 Hz, 1H, C3’H), 6.56 (d, J = 15.8 Hz,
3
1H, C2’H), 3.97 (t, J = 6.4 Hz, 1H, C2H), 3.88 (s, 3H, C4”–OCH ),
3
C6H), 1.55–1.65 (m, 2H, C3H), 1.41–1.47 (m, 2H, C5H), 1.37 (s, 9H,
3
.31–3.33 (m, 2H, C6H), 1.92–2.00 (m, 2H, C3H), 1.62–1.66 (m, 2H,
13
C(CH ) ), 1.35–1.32 (m, 2H, C4H); C NMR (100 MHz, DMSO-d ):
13
3
3
6
C5H), 1.46–1.58 (m, 2H, C4H); C NMR (100 MHz, CD OD and
3
δ 174.3 (C1), 164.8 (C1’), 156.1 (C4”), 155.6 (C=O of Boc), 136.6
C3’), 131.6 (C2”), 129.1 (C1”), 128.4 (C6”), 121.4 (C2’), 112.9 (C3”),
one drop of TFA): δ 172.0 (C1), 168.2 (C1’), 156.6 (C4”), 138.4 (C3’),
(
135.6 (C1”), 133.2 (C2”,6”), 124.1 (C2’), 119.8 (C3”,5”), 61.4 (4”-
1
11.1 (C5”), 77.9 (C(CH ) ), 56.4 (C2), 53.5 (C4”-OCH ), 38.4 (C6),
3
3
3
OCH ), 54.0 (C2), 40.2 (C6), 31.3 (C3), 30.2 (C5), 23.6 (C4); HRMS
3
3
0.5 (C3), 28.8 (C(CH ) ), 28.2 (C5), 23.1 (C4); HRMS (ESI) calcd
3
3
(ESI) calcd for C H Br N O Na (M+Na) m/z = 484.9679; found:
16
20
2
2
4
for C H BrN O Na (M+Na) m/z 507.1101; found: 507.1123.
21
29
2
6
484.9672.
(
R,E)-Methyl 2-[(tert-butoxycarbonyl)amino]-6-[3-(3,5-dibromo-
-methoxyphenyl)acrylamido] hexanoate (17): Compound 16
0.20 g, 0.6 mmol) was dissolved in anhydrous DMF (3 mL) and
4
(
The authors thank the National High Technology Research
and Development Program of China (863 Program, grant
No. 2012AA02A701) and the National High Technology
Research and Development Program of China (863
Program, grant No. 2013AA031901) for financial support
in a Project Funded by the Priority Academic Program
Development of Jiangsu Higher Education Institutions (PAPD).
anhydrous DCM (3 mL) and cooled to 0 °C. 1-Hydroxy-benzotriazole
hydrate (0.10 g, 0.73 mmol), N-(3-dimethylaminopropyl)-N’-
ethylcarbodiimide hydrochloride (0.14 g, 0.73 mmol) and TEA
(
0.20 mL, 1.4 mmol) were added to the solution and the mixture
was stirred at 0 °C for 1 h. Then compound 9 (0.19 g, 0.72 mmol)
was dissolved in anhydrous DCM (2 mL) and added to the mixture.
The mixture was stirred while warming to room temperature for 16
h. The reaction mixture was diluted with DCM (5 mL) and washed
with saturated NaHCO3 (2×5 mL). The DCM layer was washed
with water (10 mL) and brine (10 mL), dried (Na SO ), filtered, and
Electronic Supplementary Information
1
13
Supplementary information including H NMR and C NMR
2
4
data and spectra of aplysinellamide A (1), aplysinellamide B
evaporated under reduced pressure. The residue was purified by
(
2) and compounds 13 and 17, has been deposited online, at
column chromatography on silica gel to give 17 (0.24 g, 70% yield)
o
1
as a white solid; m.p. 100–102 C; H NMR (400 MHz, DMSO-d ): δ
stl.publisher.ingentaconnect.com/content/stl/jcr/supp-data
6
8
.04 (t, J = 5.8 Hz, 1H, N1H), 7.87 (s, 2H, C2”,6”H), 7.32 (d, J = 15.8
Hz, 1H, C3’H), 7.23 (d, J = 8.0 Hz, 1H, N2H), 6.63 (d, J = 15.8 Hz, 1H,
Received 13 May 2015; accepted 20 May 2015
Paper 1503360 doi: 10.3184/174751915X14326563172262
Published online: 4 June 2015
C2’H), 3.87–3.96 (m, 1H, C2H), 3.82 (s, 3H, C4”OCH ), 3.61 (s, 3H,
3
C1OCH ), 3.12–3.17 (m, 2H, C6H), 1.53–1.66 (m, 2H, C3H), 1.41–1.48
3
(
m, 2H, C5H), 1.37 (s, 9H, C(CH ) ), 1.30–1.33 (m, 2H, C4H);
3 3
1
3
C NMR (100 MHz, DMSO-d ): δ 173.2 (C1), 164.2 (C1’), 155.5
6
References
(
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1
2
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o
23
(
0.13 g, 91% yield) as a pale powder; m.p.>250 C; [α] –3.2 (c 0.007
D
12 23
MeOH) (lit. [α]D –3.1 (c 0.007, MeOH); IR (KBr): 2923, 2854,
-1
1
1650, 1595, 1499, 1260, 1050 cm ; H NMR (400 MHz, CD OD and
3
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1

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