Biomimetic chichibabin pyridine synthesis of the COPD biomarkers and elastin cross-linkers isodesmosine and desmosine

Article abstract of DOI:10.1021/ol500333t

The tetrasubstituted pyridinium amino acids isodesmosine and desmosine are cross-linkers of elastin and are attractive biomarkers for the diagnosis of chronic obstructive pulmonary disease (COPD). In this study, the biomimetic total synthesis of isodesmosine and desmosine via a lanthanide-promoted Chichibabin pyridine synthesis using the corresponding aldehyde and amine hydrochloride is reported.

Full text of DOI:10.1021/ol500333t

Letter
pubs.acs.org/OrgLett
Biomimetic Chichibabin Pyridine Synthesis of the COPD Biomarkers
and Elastin Cross-Linkers Isodesmosine and Desmosine
Toyonobu Usuki,* Takanori Sugimura, Akira Komatsu, and Yohei Koseki
Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo
102-8554, Japan
*
S Supporting Information
ABSTRACT: The tetrasubstituted pyridinium amino acids isodesmosine and desmosine are cross-linkers of elastin and are
attractive biomarkers for the diagnosis of chronic obstructive pulmonary disease (COPD). In this study, the biomimetic total
synthesis of isodesmosine and desmosine via a lanthanide-promoted Chichibabin pyridine synthesis using the corresponding
aldehyde and amine hydrochloride is reported.
ore than 100 years ago, Chichibabin reported the
thermal cyclocondensation of aldehydes (3 equiv) and1
main component of the elastic fibers that exist in vertebrate
tissues and organs, such as the lung, skin, blood vessels, heart,
etc., and plays an important role in providing their elasticity and
M
ammonia to form 2,3,5-trisubstituted pyridines (Scheme 1).
5
stretchy properties. Elastin is an extremely insoluble
Scheme 1. Typical Chichibabin Pyridine Synthesis
extracellular matrix protein that consists of soluble precursor
tropoelastin monomers (60−72 kDa) connected in a
sophisticated three-dimensional cross-linked network in an
5
,6
inter- and intramolecular fashion by amino acids. Isodesmo-
7
7
sine 1, desmosine 2, desmopyridine, isodesmopyridine,
8
9
9
neodesmosine, oxodesmosine, isooxodesmosine, and penta-
sine, etc. have been identified to date as cross-linker amino
The reaction required intense conditions, such as high
10
1
,2
pressures, high temperatures, and long reaction times. In
997, Wang and co-workers reported that the use of a catalytic
acids for elastin.
The irreversible degradation of lung elastin that occurs in
chronic obstructive pulmonary disease (COPD), which is
1
amount of lanthanide trifluoromethanesulfonate (triflate)
promoted the condensation of aldehydes and amine hydro-
chlorides to give 1,2,3,5-tetrasubstituted dihydropyridinium and
currently the fourth leading cause of death worldwide, is found
11,12
3
to give rise to these two amino acids.
Elastin cross-linkers 1
pyridinium derivatives. The reaction proceeded under mild
and 2 can be measured specifically and sensitively in clinical
samples, such as plasma, urine, and sputum, using liquid
chromatography−mass spectrometry (LC−MS or LC−MS/
conditions (room temperature in aqueous media) to afford the
Chichibabin products.
Isodesmosine (1, Figure 1) and desmosine (2) are 1,2,3,5-
and 1,3,4,5-tetrasubstituted pyridinium amino acids, respec-
11,12
MS).
Therefore, isodesmosine 1 and desmosine 2 are
4
attractive biomarkers for both drug discovery and the rapid
diagnosis of COPD. According to the World Health
Organization, COPD affects over 60 million people worldwide
and is estimated to become the third leading cause of death by
tively, and are found only in the elastin matrix. Elastin is the
13
2
030. The risk for COPD is related to the interaction
between many environmental factors, such as tobacco smoking,
and a genetic factor that is known as α -antitrypsin deficiency
1
14
(
AATD). Presently, there is a lack of effective therapies and
medicines that can prevent progression of the disease, and thus
Received: January 31, 2014
Published: March 5, 2014
Figure 1. Structures of isodesmosine (1) and desmosine (2).
©
2014 American Chemical Society
1672
dx.doi.org/10.1021/ol500333t | Org. Lett. 2014, 16, 1672−1675

Organic Letters
Letter
survival rates cannot be improved. As a result, intensive drug
discovery activities are underway to find an effective treatment.
The development of biomarkers that can act as indicators of the
severity of COPD and the level of patient response to therapy
Scheme 2. Synthesis of Aldehyde 3
15
would thus aid these efforts.
Many pharmaceutical companies and academic researchers
have attempted to establish a methodology for the biomarker
analysis of desmosines using LC−MS or LC−MS/MS
11
techniques for the diagnosis of COPD. However, due to a
lack of specific internal standards, such as isotopic labeled
compounds, the precise analysis of desmosines has not yet been
achieved. Recently, we reported the isotope-dilution LC−MS/
MS analysis of desmosines using a stable deuterium internal
12d
standard that was chemically synthesized.
As a result, the
demand for the efficient chemical synthesis of desmosines has
increased.
The total synthesis of 1,3,4,5-tetrasubstituted pyridine
desmosine 2 starting from 4-hydroxypyridine or 3,5-dibromo-
16
pyridine was recently achieved in our laboratory. The
synthesis relied on palladium-catalyzed cross-coupling reactions
between the pyridine cores and the corresponding segments as
key steps. However, the chemical synthesis of 1,2,3,5-
tetrasubstituted pyridine isodesmosine 1 has not been reported
yet. It has been proposed that the formation of the cross-linkers
1
and 2 occurs spontaneously via Mannich reactions and aldol
condensations after oxidative transformation of the lysine
17
residues of tropoelastin by lysyl oxidase. Considering the
1
−3
above-mentioned Chichibabin pyridine synthesis,
we
[(tert-butoxycarbonyl)amino]pentanedionic acid 1-benzyl ester
hypothesized that 1 and 2 could be chemically prepared from
the corresponding aldehyde and amine hydrochloride. The
Chichibabin pyridine synthesis has, in fact, previously been
utilized in the synthesis of other natural products, such as
juliprosine and haouamine A, etc. Herein we report the
biomimetic total synthesis of isodesmosine 1 and desmosine 2
in the aqueous phase via a lanthanide-promoted Chichibabin
pyridine synthesis.
in 38% yield over eight steps.
Next, the synthesis of amine hydrochloride 11, lysine
derivative, was achieved in 95% yield over two steps starting
from commercially available 6-(benzyloxycarbonyl)amino-2-
1
8
19
20
24
(S)-[(tert-butoxycarbonyl)amino]hexanoic acid. With alde-
hyde 3 and amine hydrochloride 11 in hand, we then turned
our attention to the lanthanide-promoted Chichibabin pyridine
synthesis (Table 1). Reactions with 4 equiv of aldehyde 3 and 1
equiv of amine hydrochloride 11 were run using 0.5 equiv of
Our synthesis commenced with preparation of aldehyde 3
starting from commercially available 2-(S)-[(tert-
butoxycarbonyl)amino]pentanedionic acid 1-benzyl ester
2
5
several types of lanthanide triflates (Ln(OTf)3) in H O for 24
2
h at room temperature (entries 1−7). Although more than 10
spots were identified via thin-layer chromatography (TLC)
(CH Cl /MeOH = 10/1) analysis, both isodesmosine-type
2
1
(
Scheme 2). Protection of the carboxyl group via reaction
with methyl chloroformate in the presence of 4-(N,N′-
2
2
dimethylamino)pyridine (DMAP) in triethylamine gave methyl
pyridinium 12 and desmosine-type pyridinium 13 were
generated and could be separated and isolated using column
chromatography. Of the Ln(OTf)3 catalysts investigated,
22
ester 4, glutamic acid derivative, in 99% yield. Removal of the
benzyl group under Pd/C hydrogenation conditions provided
carboxylic acid 5 quantitatively. Reaction of 5 with tert-butyl
alcohol (t-BuOH), 1-ethyl-3-(3-dimethylaminopropyl)-
carbodiimide (EDC), and DMAP afforded compound 6 in
Pr(OTf) gave the best yields (34% for 12, 3% for 13, total
3
37%). When the reaction was run with Sc(OTf) and Y(OTf) ,
3
3
which are typical Lewis acids in the aqueous phase, the total
yields of 12/13 were 10% and 20%, respectively (entries 8 and
9).
6
7% yield. However, the specific rotation of the product was
20
found to be [α] −10.2, indicating that partial racemization
D
2
0
23
occurred (literature data: [α] −28.2 ). Fortunately, the use
The milder Lewis acids (Sc > Y > Yb > Er > Dy > Gb > Nd >
D
26
of di-tert-butyl dicarbonate ((Boc) O), DMAP, and t-BuOH
Pr > La) gave better yields in this reaction, probably
suggesting that the Mannich reaction and aldol condensation
were promoted under milder conditions. While Wang and co-
workers reported generation only of the 1,2,4,5-tetrasubstituted
pyridine skeleton in the lanthanide-promoted reaction of
2
gave the desired product 6 in 75% yield with a good optical
2
0
rotation value ([α] −32.5). Additional Boc protection of the
D
amine group was then achieved using (Boc) O and DMAP in
2
acetonitrile (MeCN), providing compound 7 in 82% yield.
Reduction of the methyl ester using diisobutylaluminum
hydride (DIBAL-H) afforded aldehyde 8 in 98% yield, followed
by formation of the terminal olefin 9 in 77% yield via a Wittig
reaction. Hydroboration−oxidation of 9 then afforded the anti-
Markovnikov alcohol 10 in 82% yield. Oxidation of 10 with
Dess−Martin periodinane (DMP) led to the desired compound
3
hexanal and benzylamine hydrochloride, desmosine-type
1,3,4,5-tetrasubstituted pyridines were also obtained from the
reaction of 3 and 11. The cross-linkers isodesmosine 1 and
desmosine 2 are formed naturally in elastin in approximately a
1:1 ratio. Although the ratio of 12 and 13 obtained in the
present reaction did not follow the same trend as that of the
Lewis acidity of the catalysts, a ratio close to 1:1 was observed
for Dy(OTf) , Sc(OTf) , and Y(OTf) . Therefore, a route
3
quantitatively. Thus, aldehyde 3, a precursor for the
Chichibabin pyridine synthesis, was prepared from 2-(S)-
3
3
3
1
673
dx.doi.org/10.1021/ol500333t | Org. Lett. 2014, 16, 1672−1675

Organic Letters
Letter
Table 1. Chichibabin Pyridine Synthesis of 12 and 13 from
Aldehyde 3 and Amine Hydrochloride 11
when the reaction was run without Pr(OTf) , TLC analysis
indicated the presence of the two starting materials and
numerous other compounds, but not the desired products
3
(
2
entry 6). Notably, when the reaction time was extended from
4 to 48 h, the total yield reached a maximum of 40% (entry 7).
Changing the pH of the solution to acidic or basic conditions,
however, had a negative effect. Under acidic conditions
(
AcOH), the yield of products dropped to 21% (entry 8),
whereas under basic conditions (added K CO or NaHCO )
2
3
3
the desired products were obtained in 20% and 33% yields,
respectively (entries 9 and 10). Not surprisingly, when the ratio
of aldehyde 3 and amine hydrochloride 11 was changed from
4
:1 to 3:1, 2:1, or 1:1, the total yield steadily decreased to 13%,
9
%, and 8%, respectively (entries 11−13). As a result, reaction
conditions used for entry 7 were determined to be the optimum
conditions for the synthesis of isodesmosine-type product 12.
The seven tert-butoxycarbonyl groups and four tert-butyl
groups of 12 and 13 were quantitatively and simultaneously
removed using trifluoroacetic acid (TFA) to provide the natural
products isodesmosine 1 and desmosine 2, respectively
yield (%)
a
b
c
entry
M(OTf)3
temp (°C)
12
13
total
ratio (12/13)
1
2
3
4
5
6
7
8
9
La
Pr
rt
rt
rt
rt
rt
rt
rt
rt
rt
21
34
18
11
12
7
3
6
5
8
28
37
24
16
20
17
17
10
20
3
11.3
3
(
Scheme 3, counter anions: TFA). Spectroscopic data obtained
Nd
Gb
Dy
Er
for 1 and 2 were in good agreement with those of naturally
derived 1 and 2.
2.2
1.5
7.5
16
d
d
15
16
6
2
Scheme 3. Total Synthesis of 1 and 2
d
d
d
Yb
Sc
1
d
4
1.5
1.5
Y
12
8
a
Reactions between 4 equiv of 3 and 1 equiv of 11 were run in H O
2
b
c
d
for 24 h. 0.5 equiv for each reaction. Isolated yield. Determined by
1
H NMR analysis.
employing one of these catalysts can be regarded as a
biomimetic synthesis.
Optimization of the reaction conditions using Pr(OTf) in
3
H O was then investigated (Table 2). When the temperature
2
was increased to 40 °C, the total yield was slightly decreased to
3
1
0% (entry 2). However, when the reaction was run at 80 and
00 °C, isodesmosine-type product 12 was obtained in 32%
and 15% yield, respectively, along with a trace amount of 13
(
0
entries 3 and 4). Increasing the equivalents of Pr(OTf) from
.5 to 2.0 led to a decrease in the product yield (entry 5),
3
In summary, the biomimetic total synthesis of isodesmosine
suggesting that Pr(OTf) may act as a catalytic reagent. In fact,
1 and desmosine 2 was achieved for the first time via a
3
Table 2. Optimization of the Chichibabin Pyridine Synthesis of 12 and 13 from Aldehyde 3 and Amine Hydrochloride 11
yield (%)
a
b
entry
Pr(OTf) (equiv)
ratio (3/11)
time (h)
additive
temp (°C)
12
13
total
3
c
1
0.5
0.5
0.5
0.5
2.0
0
4:1
4:1
4:1
4:1
4:1
4:1
4:1
4:1
4:1
4:1
3:1
2:1
1:1
24
24
24
24
24
24
48
24
24
24
24
24
24
rt
40
80
100
rt
34
24
32
15
10
0
3
6
0
0
0
0
3
6
4
3
2
37
30
32
15
10
0
2
3
4
5
6
7
8
9
rt
0.5
0.5
0.5
0.5
0.5
0.5
0.5
rt
37
15
16
30
11
40
21
20
33
13
9
AcOH
rt
K CO3
2
rt
10
11
12
13
NaHCO3
rt
rt
d
d
rt
7
6
2
d
d
rt
2
8
a
b
c
d
1
Reactions were run in H O. Isolated yield. Same as Table 1, entry 2. Determined by H NMR analysis.
2
1
674
dx.doi.org/10.1021/ol500333t | Org. Lett. 2014, 16, 1672−1675

Organic Letters
Letter
lanthanide-promoted Chichibabin pyridine synthesis using the
corresponding aldehyde and amine hydrochloride. The total
synthesis of 1 and 2 was achieved in 35% (under the condition
of entry 7 in Table 2) and in 8% (under the condition of entries
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These results may provide insight into possible mechanisms
for elastin reformation (repair) from degraded elastin peptides
that are detected in patients with elastin-related diseases. In
addition, this lanthanide-promoted pyridine synthesis in water
can be applied as an environmentally benign approach to the
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route described above can provide access to isotopically labeled
desmosines as internal standards for the precise isotope-
dilution LC−MS/MS analysis of clinical COPD samples and
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*
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Supporting Information
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Experimental procedures and H and 13C NMR spectra. This
material is available free of charge via the Internet at http://
pubs.acs.org.
1
(16) (a) Usuki, T.; Yamada, H.; Hayashi, T.; Yanuma, H.; Koseki, Y.;
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AUTHOR INFORMATION
Corresponding Author
■
*
3
782. (b) Akagawa, M.; Suyama, K. Connect. Tissue Res. 2000, 41,
1
31−141.
E-mail: t-usuki@sophia.ac.jp.
(18) Baran, P. S.; Burns, N. Z. J. Am. Chem. Soc. 2006, 128, 3908−
3
909.
Notes
(
19) Burns, N. Z.; Baran, P. S. Angew. Chem., Int. Ed. 2008, 47, 205−
The authors declare no competing financial interest.
208.
(20) Dagorn, F.; Yan, L.-H.; Gravel, E.; Leblanc, K.; Maciuk, A.;
ACKNOWLEDGMENTS
Poupon, E. Tetrahedron Lett. 2011, 52, 3523−3526.
■
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21) Koseki, Y.; Yamada, H.; Usuki, T. Tetrahedron: Asymmetry 2011,
We thank Dr. Yong Y. Lin (Columbia University) for invaluable
discussions and Prof. Sergei V. Dzyba (Texas Christian
University) for suggestions regarding the manuscript. This
work was supported by a Grant-in-Aid for Young Scientists (B)
from JSPS (KAKENHI Grant Nos. 22710224 and 25750388),
the Shimadzu Science Foundation, and the Naito Science
Foundation.
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dx.doi.org/10.1021/ol500333t | Org. Lett. 2014, 16, 1672−1675