(-)-Complanine, an inflammatory substance of marine fireworm: A synthetic study

Article abstract of DOI:10.3762/bjoc.5.12

The synthesis of (-)-complanine, an inflammatory substance of Eurythoe complanata, was accomplished by a "chiral synthon" approach. The absolute configuration of this molecule was determined to be R.

Full text of DOI:10.3762/bjoc.5.12

(−)-Complanine, an inflammatory substance of
marine fireworm: a synthetic study
Kazuhiko Nakamura*,1, Yu Tachikawa2 and Daisuke Uemura*,1,2
Preliminary Communication
Open Access
Address:
Beilstein Journal of Organic Chemistry 2009, 5, No. 12.
1Department of Biosciences and Informatics, Keio University 3-14-1
Hiyoshi Yokohama 223-8622, Japan and 2Graduate School of
Science, Nagoya University Furo-cho Chikusa Nagoya 464-8566,
Japan
doi:10.3762/bjoc.5.12
Received: 03 March 2009
Accepted: 09 April 2009
Published: 16 April 2009
Email:
Kazuhiko Nakamura* - k_nakamura@bio.keio.ac.jp;
Daisuke Uemura* - uemura@bio.keio.ac.jp
Editor-in-Chief: J. Clayden
© 2009 Nakamura et al; licensee Beilstein-Institut.
License and terms: see end of document.
* Corresponding author
Keywords:
chiral synthon; complanine; inflammatory substance; marine fireworm;
total synthesis
Abstract
The synthesis of (−)-complanine, an inflammatory substance of Eurythoe complanata, was accomplished by a “chiral synthon”
approach. The absolute configuration of this molecule was determined to be R.
Introduction
Toxic marine annelids were first referred to in the literature as kinase C (PKC) in the presence of Ca2+ and 12-O-tetra-
“sea scolopendra” in de Materia Medica (A.D. 50) by Dioscor- decanoylphorbol 13-acetate (TPA) has been proved. These
ides, a physician of the Roman Empire [1]. The marine animals, results suggest that complanine can bind PKC at the same site
which are commonly known as “fireworms”, are dangerous to as phosphatidylserine, a co-activation factor with Ca2+ and
humans, as careless handling with bare hands can result in TPA. It is known that signal transduction leads to an inflamma-
serious dermatitis. However the actual toxic substance of these tion mediator TNF-α and its downstream signal molecules,
animals has remained unknown. We recently isolated a novel which occurs by phosphorylation through the action of PKC;
amphipathic substance, named complanine (Figure 1), from an
amphinomid polychaete, Eurythoe complanata (Figure 2).
Complanine has been identified as an inflammatory substance
by bioassay-guided separations; and the substance is thought to
be used as part of the animal’s defense system. In a previous
study the molecular mechanism of inflammation by the action
Figure 1: Structure of (R)-(−)-complanine.
of complanine was examined, and its activation of protein
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Beilstein Journal of Organic Chemistry 2009, 5, No. 12.
product. In this study, the absolute structure of complanine was
unambiguously determined by means of synthetic methodology
by a “chiral synthon” approach. Related amino alcohols
possessing olefins from marine natural resources have been
identified [3,4], but synthetic studies of these compounds have
not been reported.
Results and Discussion
Our synthesis started from the known compound 3 [5,6] that
could be derived from (R)-malic acid, (R)-2, in three steps (1.
BH3·SMe2; 2. cat. TsOH, Et2CO; 3. TsCl, pyridine) (Scheme
1). The resultant tosylate 3 was treated with lithium acetylide
ethylenediamine complex to give the terminal acetylene 4 in
51% yield [7]. The bromomagnesium salt of 4 generated with
EtMgBr was successively treated with 1-iodopent-2-yne in the
presence of CuI to give the corresponding diyne compound 5 in
43% yield [8]. The partial reduction was achieved by using
Figure 2: Marine fireworm Eurythoe complanata (body length 10 cm).
thus, the biological properties of complanine can be understood Lindlar catalyst to give the desired Z olefin, which was then
as controlling this cascade [2].
subjected to acidic deprotection to afford the diol 6 in 43%
yield (2 steps). The primary alcohol was converted into the
From a structural perspective, complanine possesses amphi- azide via the mesylate (79%), which was then successfully
pathic properties due to its characteristic unsaturated carbon converted into the corresponding amino alcohol 7 (78%). From
chain and a γ-aminobutyric acid (GABA)-derived trimethylam- a spectral perspective, the amino alcohol 7 was identical to the
monium substructure. Natural complanine shows negative degradation product of natural complanine (NMR, MS and Rf
optical rotation ([α]D25 = −10.0 (c 1.0, H2O)), but the configur- value of TLC).
ation of the hydroxy-substituted carbon atom has not been
revealed because derivatization to determine the absolute The activated ester (hydroxysuccinimide ester) of 4-(trimethyl-
configuration failed due to the lack of availability of the natural ammonio)butanoate was synthesized from the commercially
Scheme 1: Total synthesis of complanine. Keys: a) 1. BH3·SMe2 (71%); 2. cat. TsOH, Et2CO (59%); 3. TsCl, pyridine (80%) [5,6]; b) lithium acetylide
ethylenediamine complex (1.2 equiv), DMSO, rt, 3 h (51%); c) 1-iodopent-2-yne (2.0 equiv), EtMgBr (1.6 equiv), CuI (cat.), THF, 0 °C to rt, 12 h
(43%); d) H2, Lindlar catalyst, EtOH, rt, 30 min; e) AcOH, H2O, rt, 12 h (43% in 2 steps); f) MsCl (1.1 equiv), pyridine, CH2Cl2, 0 °C, 2 h; g) NaN3 (4.0
equiv), DMF, 80 °C, 11 h (79% in 2 steps); h) PPh3 (1.0 equiv), THF, H2O, rt, 12 h (78%); i) N-[4-(trimethylammonio)butyryloxy]succinimide iodide
(see text and [9]) (2.0 equiv), MeOH, rt, 18 h (44%).
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Beilstein Journal of Organic Chemistry 2009, 5, No. 12.
available γ-aminobutyric acid (GABA) in two steps (1. MeI, Synthesis of diyne 5: To a solution of the alkyne (4, 445 mg,
NaHCO3, MeOH, rt, 24 h; 2. HOSu; DCC, CH3CN, rt, 24 h) 2.45 mmol) in THF (2.0 ml), 1.6 M solution of ethylmag-
[9]. A reaction occurred between the amino alcohol and the nesium bromide (Aldrich, 2.45 ml, 3.92 mmol) was added
activated ester (2.0 equiv) in MeOH to give the desired (−)- under N2, and the resulting solution was stirred at ambient
complanine in 44% yield. The synthesized product was temperature. After 15 min, copper(I) iodide (2.0 mg, catalytic)
identical to the natural material in all its spectral data, including was added, and the solution was stirred for additional 12 h. The
optical rotation ([α]D20 = −9.9 (c 0.12, H2O)). The configura- solution was cooled to 0 °C, and 1-iodopent-2-yne (950 mg,
tion of the hydroxy-substituted carbon atom was determined to 4.90 mmol) was added to the reaction mixture and gradually
be R. The configuration is comparable to that of the related warmed to room temperature. After stirring for 12 h, an
compound, obscuraminol, isolated from an ascidian from Tarifa extractive workup and column chromatography (SiO2, hexane/
Island, Spain. Obscuraminol possesses a vic-amino alcohol and ethyl acetate 98 : 2 to 95 : 5) gave the desired diyne compound
an unsaturated carbon chain; its absolute configuration (of the 5 as a pale yellow oil (258 mg, 43%). 5: [α]D26 +2.7 (c 0.26,
OH adjacent carbon atom) is R [4]. The similarity of the struc- CHCl3); HRMS (ESI) calcd for C16H24O2Na [(M + Na)+]
tures suggests a close relationship in their biosynthetic path- 271.1674, found 271.1696; 1H NMR (600 MHz, CDCl3) δ 4.17
ways. It can be hypothesized that complanine is biosynthesized (1H, m), 4.09 (1H, dd, J = 6.0, 7.6 Hz), 3.52 (1H, dd, J = 7.6,
from glycine, based on comparison with serine- or alanine- 7.6 Hz), 3.11 (2H, t, J = 2.2 Hz), 2.29 (2H, m), 2.17 (2H, m),
derived natural products [3,4,10,11].
1.80 (1H, m), 1.69 (1H, m), 1.62 (4H, m), 1.12 (3H, t, J = 7.6
Hz), 0.89 (3H + 3H, t, J = 7.4 Hz, overlapped).
The enantiomer of the natural product, (+)-complanine, was
also successfully synthesized from the corresponding (S)-malic Synthesis of diol 6: To the solution of the diyne 5 (103 mg,
acid, (S)-2, in 10 steps, including coupling with 4-(trimethylam- 0.410 mmol) in ethanol (4.0 ml), Lindlar catalyst (206 mg) was
monio)butanoate. (S)-1 (ent-complanine) showed positive added. The mixture was stirred under hydrogen atmosphere for
optical rotation ([α]D23 = 11.1 (c 0.65, H2O)); which was in 30 min. After filtration of the catalyst, the concentrated residue
reasonably good agreement with the absolute configuration of was dissolved in an AcOH/H2O (4.0 : 3.5 ml) mixture and then
the natural product. The biological activities of both enan- stirred for 13 h. The concentrated residue was subjected to
tiomers were examined, but no significant difference between column chromatography (SiO2, hexane/ethyl acetate 1 : 1) to
them was observed based on the inflammatory activity on a give the desired diol 6 as a colorless oil. 6: [α]D20 −2.0 (c 0.40,
mouse foot pad. Detailed biological properties (for example, CHCl3); HRMS (ESI) calcd for C11H20O2Na [(M + Na)+]
PKC activation) of both enantiomers are under consideration at 207.1361, found 207.1346; 1H NMR (600 MHz, CD3OD) δ
the present time.
5.24–5.35 (4H, m), 3.53 (1H, br, s), 3.41 (2H, m), 2.77 (2H, t, J
= 5.2 Hz), 2.17 (1H, m), 2.12 (1H, m), 2.03 (2H, m), 1.50 (1H,
In conclusion, (−)-complanine was successfully synthesized m), 1.39 (1H, m), 0.92 (3H, t, J = 7.7 Hz); 13C NMR (CD3OD)
from (R)-malic acid by acetylene coupling and catalytic hydro- δ 132.6, 130.4, 129.6, 128.4, 72.7, 67.4, 34.4, 26.4, 24.3 21.4,
genation as key steps. The absolute configuration of the natural 14.6.
product was determined to be R.
Synthesis of amino alcohol 7 via an azide: To the solution of
Experimental
the diol (6, 16.2 mg, 88 μmol) in dichloromethane (2.0 ml),
Synthesis of alkyne 4: To a solution of tosylate (3, 3.00 g, 9.1 pyridine (1.2 ml) and mesyl chloride (11.1 mg, 97 μmol) were
mmol) in DMSO (10 ml), a lithium acetylide ethylene diamine added. After stirring for 2 h, the extractive workup was carried
complex (1.00 g, 11.0 mmol) was added under nitrogen atmo- out to give a colorless oil (24.2 mg). This crude material was
sphere. After stirring for 3 h, an extractive workup and column successively dissolved in DMF (0.4 ml), and sodium azide (23
chromatography (SiO2, hexane/ethyl acetate 99 : 1) gave the mg, 330 μmol) was then added. The reaction mixture was main-
desired alkyne 4 as a pale yellow oil (850 mg, 51%). 4: [α]D26 tained at 80 °C for 11 h. An extractive workup and preparative
+2.1 (c 1.0, CHCl3); HRMS (ESI) calcd for C11H18O2Na [(M + TLC (SiO2, ethyl acetate) gave the desired azide as a colorless
Na)+] 205.1204, found 205.1201; 1H NMR (400 MHz, CDCl3) oil (14.6 mg, 79% in 2 steps). IR (CHCl3): 2105 cm−1.
δ 4.14 (1H, m), 4.04 (1H, dd, J = 6.2, 7.6 Hz), 3.48 (1H, t, J =
7.6 Hz), 2.27 (2H, m), 1.91 (1H, t, J = 2.8 Hz), 1.78 (1H, m), The solution of the resultant azide (14.6 mg, 70 μmol) in THF
1.69 (1H, m), 1.57 (4H, m), 0.84 (3H + 3H, t, J = 7.6 Hz, over- (1.0 ml), H2O (25 μl) and triphenylphosphane (18.3 mg, 70
lapped).
μmol) were added. After stirring for 12 h, the reaction mixture
was concentrated, and the desired product (10.0 mg, 78%) was
obtained by chromatography on SiO2 (eluent: CHCl3/MeOH/
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Beilstein Journal of Organic Chemistry 2009, 5, No. 12.
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doi:10.1021/ol0613721
H2O 10 : 5 : 1) as a colorless oil. 7: HRMS (ESI) calcd for
C11H22NO [(M + H)+] 184.1701, found 184.1707; 1H NMR
(600 MHz, CD3OD) δ 5.25–5.37 (4H, br m), 3.75 (1H, br s),
2.96 (1H, dd, J = 3.1, 12.4 Hz), 2.79 (2H, t, J = 6.6 Hz), 2.73
(1H, dd, J = 9.6, 12.4 Hz), 2.23 (1H, m), 2.16 (1H, m), 2.06
(2H, m), 1.49 (2H, m), 0.95 (3H, t, J = 7.6 Hz); 13C NMR (150
MHz, CD3OD) δ 131.4, 129.0, 128.3, 127.0, 71.4, 46.9, 34.5,
25.0, 23.0, 20.1, 13.3.
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10.Brady, R. N.; Di Mari, S. J.; Snell, E. E. J. Biol. Chem. 1969, 244,
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License and Terms
Synthesis of (R)-complanine, (R)-1: To the solution of the
amino alcohol 7 (1.8 mg, 9.9 μmol) in MeOH (150 μl), N-[4-
(trimethylammonio)butyryloxy]succinimide iodide [9] (5.5 mg,
20 mmol) in MeOH (150 μl) was added. The reaction mixture
was stirred for 18 h. The resultant mixture was concentrated,
and the residue was purified by column chromatography (SiO2,
CHCl3/MeOH/H2O/AcOH 10 : 5 : 1 : 0.06) to give the
synthetic complanine (1.4 mg, 44%) as a colorless oil. (R)-1
(synthetic complanine): HRMS (ESI) calcd for C18H35N2O2+
[(M)+] 311.2693, found 311.2698; [α]D20 = −9.9 (c 0.12, H2O);
1H NMR (600 MHz, D2O) δ 5.31–5.37 (4H, br m), 3.64 (1H, br
m), 3.22 (2H + 1H, m), 3.09 (1H, dd, J = 6.9, 13.8 Hz), 3.02
(9H, s), 2.43 (2H, t, J = 6.5 Hz), 2.28 (2H, t, J = 7.6 Hz), 2.08
(2H, m), 1.98 (2H, m), 1.41 (2H, m), 0.84 (3H, t, J = 7.6 Hz);
13C NMR (150 MHz, D2O) δ 180.9, 174.3, 129.6, 129.1, 127.6,
69.5, 65.5, 52.9 (3C), 45.9, 33.8, 31.7, 25.2, 23.3, 20.2, 18.8,
13.8.
This is an Open Access article under the terms of the
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(http://creativecommons.org/licenses/by/2.0), which
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The license is subject to the Beilstein Journal of Organic
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The definitive version of this article is the electronic one
which can be found at:
doi:10.3762/bjoc.5.12
Synthesis of (S)-complanine, (S)-1: The enantiomer of natural
complanine was also synthesized from (S)-malic acid. (S)-1
(ent-complanine): [α]D23 = 11.1 (c 0.65, H2O).
Acknowledgments
The authors are thankful for the financial support from a Grant-
in-Aid for the Creative Scientific Research program of the
Ministry of Education, Science, Culture, and Sports of Japan.
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