A convenient method for the one-step synthesis of phosphonic peptides

Article abstract of DOI:10.1016/j.tetlet.2013.07.049

A novel and efficient method for the synthesis of peptidyl derivatives of 1-aminoalkylphosphonate diaryl esters is presented. Phosphonic peptides were obtained in one step via an amidoalkylation reaction using amides of N-protected amino acids or peptides, triphenyl phosphite, and an appropriate aldehyde.

Full text of DOI:10.1016/j.tetlet.2013.07.049

Tetrahedron Letters 54 (2013) 4975–4977
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
A convenient method for the one-step synthesis of phosphonic
peptides
⇑
´
´
Marcin Skorenski, Józef Oleksyszyn, Marcin Sienczyk
_
Division of Medicinal Chemistry and Microbiology, Faculty of Chemistry, Wrocław University of Technology, Wybrzeze Wyspian´skiego 27, 50-370 Wrocław, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel and efficient method for the synthesis of peptidyl derivatives of 1-aminoalkylphosphonate diaryl
esters is presented. Phosphonic peptides were obtained in one step via an amidoalkylation reaction using
amides of N-protected amino acids or peptides, triphenyl phosphite, and an appropriate aldehyde.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 29 May 2013
Revised 26 June 2013
Accepted 5 July 2013
Available online 16 July 2013
Keywords:
1-Aminoalkylphosphonates
Phosphonic peptides
Amidoalkylation
Amides
Serine protease inhibitors
a
-Aminoalkylphosphonate diaryl esters and their peptidyl
Despite the variety of these methods, all require carbamates, thioc-
arbamates, or ureas as a reaction substrate.9
derivatives compose a group of potent, irreversible, and highly
selective inhibitors that exclusively react with the active site of ser-
ine proteases, examples of which include human neutrophil elas-
tase, cathepsin G, dipeptidyl peptidase IV, and chymase.1 Previous
reports have described the usefulness of these compounds to target
serine proteases of viruses2 and bacteria, including proteases with a
non-canonical catalytic triad.3 In general, the elongation of amino-
phosphonates with peptide chains increases significantly their
inhibitory potency toward target proteases, thus the most active
derivatives of this class reported to date contain a peptide sequence
structurally optimized for specific protease binding.4 One of the
Although several methods for the synthesis of
a-amin-
oalkylphosphonate diaryl esters have been reported in the litera-
ture, the synthesis of their peptidyl derivatives relies, to a great
extent, on the stepwise (a successive deprotection-coupling
sequence) synthesis in solution.3 This approach can be limited;
for example, incorporation of an amino acid containing a functional
side chain requires a challenging use of protecting groups. One
solution to overcoming these restrictions is the separate synthesis
of the peptidyl fragment followed by coupling to a 1-amin-
oalkylphosphonate diaryl ester.10 The ideal solution would be the
greatest advantages of
a-aminoalkylphosphonate aromatic esters
application of a-aminoalkylphosphonate diaryl esters in solid
over other classes of inhibitors such as peptide aldehydes, chloro-
methyl ketones, ketoesters, or ketoamides is their complete lack
of reactivity with cysteine, threonine, and metalloproteinases.5
The method for the synthesis of simple Cbz-protected
phase peptide synthesis. Unfortunately, despite extensive research,
this method has yet to be developed. An attempt to use
a-aminoalkylphosphonate diaryl esters in solid phase synthesis
was reported by Haemers et al., but this method did not incorpo-
rate elongation of the peptidyl chain.11 Two interesting approaches
for the synthesis of phosphonic peptides have been reported. The
first method to convert amino acids or peptides into their
corresponding phosphonic analogues is based on the oxidative
decarboxylation, either electrochemical or with lead tetraacetate,
followed by reaction with trialkyl or triaryl phosphite in the
presence of TiCl4.12 The second method, reported only for the prep-
aration of alkyl esters, involves the degradation of amino acids or
dipeptides to bromo derivatives via the Hunsdiecker reaction,
followed by a reaction with sodium diethyl phosphite.13 Although
the electrochemical oxidative decarboxylation approach via the
formation of N-acyl-N,O-acetals is a very efficient method for the
a-aminoalkylphosphonate diphenyl esters was first reported by
Oleksyszyn et al., where triphenyl phosphite underwent an amido-
alkylation reaction with benzyl carbamate and an appropriate
aldehyde in acetic acid.6 Several modifications of this reaction have
since been reported including the addition of acetic anhydride or
acetyl chloride.7 Methods for the preparation of
a-amin-
oalkylphosphonate diphenyl esters under mild conditions including
the application of Lewis acids as catalysts have been developed.8
⇑
Corresponding author. Tel.: +48 71 320 2439; fax: +48 71 320 2427.
E-mail address: marcin.sienczyk@pwr.wroc.pl (M. Sien´ czyk).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.07.049

´
M. Skorenski et al. / Tetrahedron Letters 54 (2013) 4975–4977
4976
O
R
O
R
O
R
O
Route A:
R CHO, P(OPh) , AcOH
H
N
O
O
1
NH2
P
Boc O, (NH )HCO , py
OH
2
4
3
3
X
N
H
X
N
H
X
N
H
Route B:
ref. 14
O
O
R1
O
1
R CHO, P(OPh) ,
3
t
X = Cbz, Boc, or protected amino acid;
R = amino acid side chain
Cu(OTf) , CH Cl
1
2
2
2
R
= amino acid side chain
Scheme 1. The general synthesis of peptidyl derivatives of
a-aminophosphonate diphenyl esters from N-protected amino acid or peptide amides—routes A and B.
by SPPS on Rink amide resin using HBTU in the presence of DIEA as
the coupling agent. Fmoc deprotection was performed using 20%
piperidine/DMF solution. Peptides were cleaved from the resin
with TFA/H2O/TIPS (95:2.5:2.5, v/v) and used in the next step with-
out any further purification.
Table 1
Yields and products obtained via amide-based amidoalkylation
Product
Formula
Isolated yield (%)
Route A Route B
Cbz-Pro-AlaP(OPh)2
4
15
8
9
15
19
7
12
8
<4%
<4%
<4%
<4%
<4%
<4%
<4%
<4%
<4%
<4%
<4%
<4%
<4%
<4%
25
38
31
11
30
36
19
31
16
26
16
29
29
11
19
19
31
12
24
18
26
15
21
An amidoalkylation of simple N-protected amides of amino
acids resulted in the formation of phosphonic dipeptides 1–9, with
higher yields being obtained when the synthesis followed route B
(11–38%, Table 1). The preparation of tripeptides 10–19 as well
as polypeptides 20–23 required milder reaction conditions (Route
B) since the amidoalkylation in acetic acid resulted in poor yields of
isolated products (<4%). The one-step preparation of phosphonic
peptides was performed with the application of copper(II) triflate
in dichloromethane at room temperature. In general, the yields
were higher and the products more easily isolated for all the reac-
tions performed under mild conditions with Cu(OTf)2 as the reac-
tion mixture were less complex.
Additionally, we checked to see if any stereoselectivity could be
induced when structurally diverse chiral amides were used. Sur-
prisingly, we noticed a 1:1 ratio of both diastereoisomers. This con-
trasted with the previous report by Oshikawa et al. who observed
the formation of an excess of one diastereoisomer when chiral car-
bamates [(ꢀ)-menthyl carbamate; 1,7,7-trimethylspiro[bicy-
clo[2.2.1]heptane-3,20-indan)-2-yl carbamate) or chiral ureas
((R)-(+)- and (R)-(ꢀ)-(1-phenylethyl)urea] were used in the amido-
alkylation reaction.15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Cbz-Pro-LeuP(OPh)2
Cbz-Pro-PhgP(OPh)2
Cbz-Ala-AlaP(OPh)2
Cbz-Ala-nValP(OPh)2
Cbz-Ala-LeuP(OPh)2
Cbz-Phe-AlaP(OPh)2
Cbz-Phe-LeuP(OPh)2
Cbz-Phe-nValP(OPh)2
tBoc-Abu-Gly-LeuP(OPh)2
Cbz-Val-Pro-ValP(OPh)2
Cbz-Val-Pro-nValP(OPh)2
Cbz-Val-Pro-LeuP(OPh)2
Cbz-Val-Pro-AlaP(OPh)2
Cbz-Val-Pro-AbuP(OPh)2
Cbz-Val-Pro-PheP(OPh)2
Cbz-Val-Pro-hPheP(OPh)2
Cbz-Phe-Pro-ValP(OPh)2
Cbz-Phe-Pro-LeuP(OPh)2
Ac-VFLLAlaP(OPh)2
Ac-VFLLLeuP(OPh)2
Ac-PVFLLAlaP(OPh)2
Ac-PVFLLLeuP(OPh)2
In comparison to the classical approach to phosphonic oligopep-
tide synthesis in solution, our amide-based method presents a clear
advantage. The standard synthesis of Cbz-Val–Pro-PheP(OPh)2 (16)
in solution requires five steps, whereas in our amide-based protocol
the target peptide can be synthesized in a single step from the cor-
responding protected dipeptide amide Cbz-Val–Pro-NH2. More-
over, when the synthesis of longer phosphonic peptides is
required [Ac-PVFLLLeuP(OPh)2, 23], peptide amides can be prepared
simply on a solid support followed by a modified amidoalkylation
reaction with triphenyl phosphite and the appropriate aldehyde
(Scheme 2, method III). This also represents an improvement on
the classical three-step protocol where the peptide synthesized
by SPPS is next coupled to a deprotected 1-aminoalkylphosphonate
diaryl ester (Scheme 2, method II). When we compared the yield of
Ac-VFLLLeuP(OPh)2 (21) synthesized by the three approaches, we
determined that the most efficient methods were II and III (approx.
synthesis of phosphonic diaryl ester derivatives, it requires access
to specialized electrochemical equipment that may limit its broad-
er application.
Herein we present a novel method for the synthesis of phos-
phonic peptides using amides of N-protected amino acids or pep-
tides as the starting substrates.
The general synthetic approach is outlined in Scheme 1. The
starting amides of N-protected amino acids or dipeptides were pre-
pared using ammonium hydrogen carbonate in the presence of
pyridine and di-tert-butyl dicarbonate (Boc2O) according to a pre-
viously described procedure.14 In the next step an amidoalkylation
reaction was performed either following the conditions of the ori-
ginal Oleksyszyn protocol (Scheme 1, route A), or a modified proce-
dure under mild conditions using copper(II) triflate as the catalyst
(Scheme 1, route B). The peptides used in this study were prepared
Method I
O
2 steps
ref.6
OPh
OPh
P(OPh)3
HBr*H2N
P
+
H
O
NH2
+
9 steps
O
O
Method II
coupling
Ac-Pro-Val-Phe-Leu-Leu-LeuP(OPh)2
Ac-Pro-Val-Phe-Leu-Leu-OH
23
solid phase
peptide synthesis
(CH3)2CHCHO, P(OPh)3, Cu(OTf)2, CH2Cl2
1 step
Ac-Pro-Val-Phe-Leu-Leu-NH2
Method III
Scheme 2. Different approaches for the synthesis of peptide derivatives of a-aminoalkylphosphonate diphenyl esters.

´
4977
M. Skorenski et al. / Tetrahedron Letters 54 (2013) 4975–4977
25% and 26% yields, respectively, with the assumption of 100% yield
References and notes
for the starting peptide synthesis on solid support), whereas the to-
tal yield using method I was estimated not to exceed 5%.
1. Grzywa, R.; Sien´ czyk, M. Curr. Pharm. Des. 2013, 19, 1154.
2. (a) Lazic, A.; Goetz, D. H.; Nomura, A. M.; Marnett, A. B.; Craik, C. S. J. Mol. Biol.
2007, 373, 913; (b) Ogilvie, W.; Bailey, M.; Poupart, M. A.; Abraham, A.;
Bhavsar, A.; Bonneau, P.; Bordeleau, J.; Bousquet, Y.; Chabot, C.; Duceppe, J. S.;
Fazal, G.; Goulet, S.; Grand-Maître, C.; Guse, I.; Halmos, T.; Lavallée, P.; Leach,
M.; Malenfant, E.; O’Meara, J.; Plante, R.; Plouffe, C.; Poirier, M.; Soucy, F.;
Yoakim, C.; Déziel, R. J. Med. Chem. 1997, 40, 4113.
In addition, an amide-based amidoalkylation procedure can be
used successfully for combinatorial applications. By using a mix-
ture of aldehydes, two or four phosphonic peptides were obtained
in one reaction mixture (see Supplementary data). Such an ap-
proach can be used for combinatorial screening of serine proteases
with a preference for an optimal peptidyl inhibitor P1 residue.
In conclusion we have demonstrated a novel method for the
3. (a) Burchacka, E.; Skoren´ ski, M.; Sien´ czyk, M.; Oleksyszyn, J. Bioorg. Med. Chem.
Lett. 2013, 23, 1412; (b) Burchacka, E.; Walczak, M.; Sien´ czyk, M.; Dubin, G.;
_
Zdzalik, M.; Potempa, J.; Oleksyszyn, J. Bioorg. Med. Chem. Lett. 2012, 22, 5574;
(c) Irgolic, K. J. In Houben-Weyl; Klamann, D., Ed., 4th Ed.; ; Thieme: Stuttgart,
one-step synthesis of peptidyl derivatives of a-aminoalkylphosph-
´
1990; Vol E12b, p 150; (d) Pietrusewicz, E.; Sienczyk, M.; Oleksyszyn, J. J.
Enzyme Inhib. Med. Chem. 2009, 24, 1229.
onate diphenyl esters. Importantly, this procedure allows for the
preparation of short peptidyl derivatives and can be used success-
fully to synthesize longer phosphonic peptides in a single step,
even when peptide labile side protecting groups are present. The
target compounds were obtained in good to moderate yields. Our
results suggest a combinatorial application of this method and fur-
ther research on this subject will be published in due course.
4. Winiarski, L.; Oleksyszyn, J.; Sien´ czyk, M. J. Med. Chem. 2012, 55, 6541.
5. Powers, J. C.; Asgian, J. L.; Ekici, O. D.; James, K. E. Chem. Rev. 2002, 102, 4639.
6. Oleksyszyn, J.; Subotkowska, L.; Mastalerz, P. Synthesis 1979, 985.
7. Oleksyszyn, J. J. Prakt. Chem. 1987, 329, 19.
8. (a) Van der Veken, P.; El Sayed, I.; Joossens, J.; Stevens, C. V.; Augustyns, K.;
Haemers, A. Synthesis 2005, 634; (b) Soroka, M.; Goldeman, W. Chem. Abstr.
2008, 149, 556785.
9. Birum, G. H. J. Org. Chem. 1974, 39, 209.
10. Marnett, A. B.; Nomura, AM.; Shimba, N.; Ortiz de Montellano, P. R.; Craik, CS.
Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 6870.
11. Senten, K.; Daniëls, L.; Van der Veken, P.; De Meester, I.; Lambeir, A. M.;
Scharpé, S.; Haemers, A.; Augustyns, K. J. Comb. Chem. 2003, 5, 336.
12. (a) Seebach, D.; Charczuk, R.; Gerber, C.; Renaud, P.; Bener, H.; Schneider, H.
Helv. Chim. Acta 1989, 72, 401; (b) Corcoran, R. C.; Green, JM. Tetrahedron Lett.
1990, 31, 6827.
13. Ösapay, G.; Dzilagyi, I.; Seres, J. Tetrahedron 1987, 43, 2997.
14. Pozdnev, V. F. Tetrahedron Lett. 1995, 36, 7115.
15. Oshikawa, T.; Yamashita, M. Bull. Chem. Soc. Jpn. 1989, 62, 3177.
Acknowledgments
The work was supported by the Wroclaw University of Technol-
ogy Statute Funds S10156/Z0313. This research is co-financed by
the European Union as part of the European Social Fund. The
authors would like to thank Dr Keri Csencsits-Smith (University
of Texas Health Science Center at Houston, TX, USA) for critical
reading of the manuscript.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.07.
049.