Total synthesis of the COPD biomarker desmosine via Sonogashira and Negishi cross-coupling reactions

Article abstract of DOI:10.1016/j.tetlet.2012.08.084

Desmosine, a crosslinking pyridinium amino acid of elastin, is an attractive biomarker for the diagnosis of chronic obstructive pulmonary disease (COPD). In this study, the total synthesis of (+)-desmosine is reported utilizing chemo- and regioselective S

Full text of DOI:10.1016/j.tetlet.2012.08.084

Tetrahedron Letters 53 (2012) 5920–5922
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Tetrahedron Letters
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Total synthesis of the COPD biomarker desmosine via Sonogashira
and Negishi cross-coupling reactions
⇑
Hiroto Yanuma, Toyonobu Usuki
Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo 102-8554, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Desmosine, a crosslinking pyridinium amino acid of elastin, is an attractive biomarker for the diagnosis of
chronic obstructive pulmonary disease (COPD). In this study, the total synthesis of (+)-desmosine is
reported utilizing chemo- and regioselective Sonogashira and Negishi cross-coupling reactions in 15%
yield over six steps.
Received 19 July 2012
Revised 20 August 2012
Accepted 22 August 2012
Available online 30 August 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Desmosine
Biomarker
Elastin
Total synthesis
Sonogashira cross-coupling
Negishi cross-coupling
Chronic obstructive pulmonary disease (COPD) is a respiratory
disorder and is a leading cause of morbidity and mortality. Accord-
ing to the World Health Organization (WHO), COPD, affecting over
60 million people, is currently the fourth leading cause of death
worldwide, and is estimated to become the third leading cause
by 2030. The risk for COPD is related to the interaction between
many environmental factors, such as tobacco smoking, and a ge-
attractive biomarkers for both drug discovery and rapid diagnosis
of COPD.
Despite the potential application of these compounds as bio-
markers for COPD, rigid quantitation of 1 and 2 has not been
achieved due to a lack of promising internal standards for strict
analysis by LC–MS.5,6 The total synthesis of desmosine 1 has been
recently achieved in 13 steps in 11% overall yield in our labora-
tory.8 The synthesis relied on stepwise and regioselective Sono-
gashira cross-coupling reactions between the pyridine core and
the corresponding alkynes. After the preparation of the tri-alkyl-
ated pyridine, several steps were required for conversion from
the oxazolidine rings into the corresponding amino acid moieties.
Herein, utilizing Sonogashira and Negishi cross-coupling reactions
as key steps in order to avoid further conversions, we report a
netic factor that is known as
a
1-antitrypsin deficiency (AATD).1
Presently, there is a lack of effective therapies and medicines that
can prevent progression of the disease, and thus survival rates can-
not be improved. As a result, intensive drug discovery activities are
underway to find an effective treatment. The development of bio-
markers that can act as indicators of the severity of COPD and the
level of patient response to therapy would thus aid these efforts.2
Elastin fibers are a part of the extracellular matrix and are an
essential structural component of the lungs, ligaments, skin, blood
vessels, and so on. Desmosine (1) and isodesmosine (2), which ex-
ist only in the elastin matrix, are pyridinium amino acids that serve
as the crosslinking molecules that bind the polymeric chains in
elastin into a sophisticated 3-D network (Fig. 1).3,4 The irreversible
degradation of lung elastin that occurs in COPD is known to give
rise to these two amino acids, which can be measured specifically
and sensitively in clinical samples, such as plasma, urine, and spu-
tum, by liquid chromatography–mass spectrometry (LC–MS) anal-
ysis.5–7 Therefore, the elastin crosslinking amino acids 1 and 2 are
⇑
Corresponding author. Tel.: +81 3 3238 3446; fax: +81 3 3238 3361.
E-mail address: t-usuki@sophia.ac.jp (T. Usuki).
Figure 1. Structures of desmosine (1) and isodesmosine (2).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.08.084

H. Yanuma, T. Usuki / Tetrahedron Letters 53 (2012) 5920–5922
5921
the ligand may cause the decomposition of the substrates and/or
product. When the Negishi cross-coupling reaction between
3,4,5-triiodopyridne and iodo amino acid 7 was carried out under
the same conditions as used in entry 1 (Table 1), however, no cou-
pling products were observed.
Toward the total synthesis, a Sonogashira cross-coupling reac-
tion was then attempted with compound 8 and alkyne 6 using
10 mol % Pd2(dba)3, 40 mol % P(2-furyl)3, and 40 mol % CuI in
DMF and iPr2NEt at 50 °C with the hope of obtaining 3,4,5-tri-
alkylated pyridine 3 (Scheme 2). However, recovery of the starting
material was confirmed in 92% yield, while the desired coupling
product was not observed. Meanwhile, in order to obtain the tri-
alkylated pyridine 10, the Negishi cross-coupling reaction between
8 and d-iodoalkylated L
-glycine 99 under the same conditions as
entry 2 (Table 1) did not proceed. Instead, starting material 8
was recovered in 71% yield. These results are probably due to steric
repulsion of the 3,5-di-sp3-carbon atom in the oxidative addition of
palladium to the 4-bromo-position on the pyridine ring, while the
Sonogashira cross-coupling reaction to 4-bromo-3,5-dialkynylpyri-
dine (i.e., 3,5-di-sp-carbon) was successful.8 This synthetic route
was thus ruled out.
As an alternative strategy, 3,5-dibromo-4-iodopyridine 5b and
commercially available 3,5-dichloro-4-iodopyridine 5c were se-
lected as the substrates for the cross-coupling reactions (Scheme 3).
Preparation of 5b was accomplished in 70% yield from 3,5-
dibromopyridine 11 by regioselective iodination using LDA and
I2.12 Chemo- and regioselective Sonogashira cross-coupling
reactions between alkyne 6 and the 4-position of 5b and 5c were
carried out using 10 mol % Pd2(dba)3 with 40 mol % P(2-furyl)3 to
afford the corresponding monoalkynes 12b and 12c in 58% and
80% yield, respectively.13 The different reactivities might be due
to the extents of steric hindrance of the neighboring iodine groups,
which prevents the oxidative addition of the palladium.
Scheme 1. Retrosynthetic analysis of desmosine (1).
shortened and improved total synthesis of the COPD biomarker
desmosine 1 that crosslinks elastin.
As illustrated in Scheme 1, it was envisioned that 1 would be
derived from 3,4,5-tri-alkylated pyridine 3 and
x-iodoalkylated
L
-glycine 49 through late-stage formation of the pyridinium salt.
Synthesis of 3 would then involve chemo- and regioselective palla-
dium-catalyzed Sonogashira and Negishi cross-coupling reactions
of trihalogenated pyridines 5, the corresponding terminal alkyne
6,8 and -glycine 7.9 The key strategy was to utilize
c-iodoalkylated L
the different reactivities of each compound as determined by the
substituent position and the halogen species on the pyridine ring.
Firstly, the Negishi cross-coupling reaction between 4-bromo-
3,5-diiodopyridne 5a8 and
c-iodoalkylated L-glycine 7 was investi-
Incorporation of c-iodoalkylated L-glycine 7 into the 3,5-positons
gated (Table 1). 3,5-Chemo- and regioselective introduction of 7
into 5a using 10 mol % Pd2(dba)3 with 40 mol % P(2-furyl)3 at
50 °C for 20 h afforded the desired di-coupled product 8 in 44%
yield (entry 1). In the Negishi reaction, we have applied a modified
protocol in which an extra Zn from the organozinc reagent can be
removed via centrifugation.10 When the reaction was shortened to
5 h under the same conditions, the yield was slightly improved to
49% (entry 2). Replacing the P(2-furyl)3 ligand with AsPh3, which is
known to be more effective in the palladium-catalyzed reaction,11
led to a decrease in the yield to 33% when the reaction was run for
20 h, but a reaction time of just 5 h resulted in a significant in-
crease in the yield to 71% (entries 3 and 4, respectively). With
AsPh3, the longer reaction time led to a lower yield, suggesting that
of the obtained 12b and 12c was attempted via a Negishi
cross-coupling reaction using Pd-PEPPSI-IPr, which was developed
by Organ and co-workers.14 When the reaction was conducted
with 3,5-dibromopyridine 12b, the desired tri-alkylated pyridine
3 was obtained in 60% yield, along with the mono coupling product
13 in 10% yield.15 However, the Negishi cross-coupling with
3,5-dichloropyridne 12c using Pd-PEPPSI-IPr did not provide the
product, while the starting material was recovered in 44% yield.
These results suggested that the reactivity of the chloropyridine
is reduced compared to those of the bromopyridine and
iodopyridine.10
Table 1
Negishi cross-coupling of 5a and 7.
Entry
Ligand (40 mol %)
Time (h)
Yield (%)
1
2
3
4
P(2-furyl)3
P(2-furyl)3
AsPh3
20
5
20
5
44
49
33
71
AsPh3
Scheme 2. Attempts at the cross-coupling reactions of 8.

5922
H. Yanuma, T. Usuki / Tetrahedron Letters 53 (2012) 5920–5922
reactions as a key transformation in 15% yield over six steps start-
ing from 3,5-dibromopyridine 11. The straightforward synthetic
route is greatly shortened compared to the previous synthesis of
1 (11% yield over 13 steps). The improved synthetic strategy de-
scribed above is currently being applied to the preparation of other
crosslinking amino acids4 in order to elucidate the 3-D structure of
elastin fiber, including the structure of the degraded elastin pep-
tides that are generated due to COPD that can be indicative of
the severity of the disease.
Acknowledgments
We thank Dr. Yong Y. Lin (Columbia University), Prof. Gerard M.
Turino (Columbia University), Prof. Yoshiro Masuyama (Sophia
University), Prof. Noriyuki Suzuki (Sophia University), and Prof.
Kyozo Suyama (Tohoku University) for their suggestions. This work
was supported by a Grant-in-Aid for Young Scientists (B) from the
Ministry of Education, Culture, Sports, Science and Technology
(MEXT) of Japan, the Sophia University Collaborative Research
Grant, the Shimadzu Science Foundation, the SEI Group CSR Foun-
dation, and the Naito Science Foundation.
Supplementary data
Supplementary data (experimental procedures and character-
ization data) associated with this article can be found, in the online
version, at http://dx.doi.org/10.1016/j.tetlet.2012.08.084.
References and notes
1. (a) Yoshida, T.; Tuder, R. M. Physiol. Rev. 2007, 87, 1047–1082; (b) Mannino, D.
M.; Buist, A. S. Lancet 2007, 370, 765–773.
2. (a) Turino, G. M.; Ma, S.; Lin, Y. Y.; Cantor, J. O.; Luisetti, M. AJRCCM 2011, 184,
637–641; (b) Martinez, F. J.; Donohue, J. F.; Rennard, S. I. Lancet 2011, 378,
1027–1037.
3. (a) Partridge, S. M.; Elsden, D. F.; Thomas, J. Nature 1963, 197, 1297–1298; (b)
Thomas, J.; Elsden, D. F.; Partridge, S. M. Nature 1963, 200, 651–652.
4. Akagawa, M.; Suyama, K. Connect. Tissue Res. 2000, 41, 131–141.
5. (a) Kaga, N.; Soma, S.; Fujimura, T.; Seyama, K.; Fukuchi, Y.; Murayama, K. Anal.
Biochem. 2003, 318, 25–29; (b) Boutin, M.; Berthelette, C.; Gervais, F. G.;
Scholand, M.-B.; Hoidal, J.; Leppert, M. F.; Bateman, K. P.; Thibault, P. Anal.
Chem. 2009, 81, 1881–1887; (c) Albarbarawi, O.; Barton, A.; Lin, Z.; Takahashi,
E.; Buddharaju, A.; Brady, J.; Miller, D.; Palmer, C. N. A.; Huang, J. T.-J. Anal.
Chem. 2010, 82, 3745–3750; (d) Shiraishi, K.; Matsuzaki, K.; Matsumoto, A.;
Hashimoto, Y.; Iba, K. J. Oleo Sci. 2010, 59, 431–439.
Scheme 3. Total synthesis of desmosine 1.
6. Analysis of 1 and 2 as possible biomarkers for COPD has been among the topics
of two recent FDA workshops (2009, 2010).
Formation of the pyridinium salt of 3 with
x
-iodoalkylated
L
-
7. (a) Ma, S.; Lieberman, S.; Turino, G. M.; Lin, Y. Y. Proc. Natl. Acad. Sci. U.S.A. 2003,
100, 12941–12943; (b) Ma, S.; Lin, Y. Y.; Turino, G. M. Chest 2007, 131, 1363–
1371; (c) Ma, S.; Turino, G. M.; Lin, Y. Y. J. Chromatogr. B 2011, 879, 1893–1898.
8. Usuki, T.; Yamada, H.; Hayashi, T.; Yanuma, H.; Koseki, Y.; Suzuki, N.;
Masuyama, Y.; Lin, Y. Y. Chem. Commun. 2012, 48, 3233–3235.
9. Koseki, Y.; Yamada, H.; Usuki, T. Tetrahedron: Asymmetry 2011, 22, 580–586.
10. Usuki, T.; Yanuma, H.; Hayashi, T.; Yamada, H.; Suzuki, N.; Masuyama, Y. J.
Heterocycl. Chem., accepted for publication
11. Farina, V.; Krishnan, B. J. Am. Chem. Soc. 1991, 113, 9585–9595.
12. Baxter, P. N. W. Chem. Eur. J. 2003, 9, 2531–2541.
13. On the other hand, Negishi cross-coupling reaction between 5b and 9 gave a
complex mixture.
glycine 4 in MeNO2 at 60 to 80 °C was then conducted to produce
14 in 99% yield.16 After reduction of the benzyl and alkyne groups
with H2 and Pd/C, the t-butoxycarbonyl protecting groups were
successfully removed using TFA to give crude 1. Purification on
C18 column chromatography afforded pure desmosine 1 in 63%
yield over two steps. Spectroscopic data for obtained 1 including
the optical rotation were in good agreement with those measured
for natural 1.8
14. Valente, C.; Belowich, M. E.; Hadei, N.; Organ, M. G. Eur. J. Org. Chem. 2010, 23,
4343–4354.
15. Negishi cross-coupling reaction between 13 and 7 using Pd-PEPPSI-IPr gave a
trace amount of 3.
Conclusion
In summary, the total synthesis of (+)-desmosine 1, a crosslink-
ing pyridinium amino acid of elastin, has been achieved via
chemo- and regioselective Sonogashira and Negishi cross-coupling
16. (a) Ren, R. X.-F.; Sakai, N.; Nakanishi, K. J. Am. Chem. Soc. 1997, 119, 3619–3620;
(b) Sicre, C.; Cid, M. M. Org. Lett. 2005, 7, 5737–5739.