Communications
DOI: 10.1002/anie.200903510
Synthetic Methods
Solvent-Free Synthesis of Peptides**
Valꢀrie Declerck, Pierrick Nun, Jean Martinez, and Frꢀdꢀric Lamaty*
The chemistry of peptides has been continuously growing
during the last few decades. Peptides are now not only
considered as pharmacological tools but also as active
pharmaceutical ingredients, in connection to their high
therapeutic index and low toxicity.[1] The market for ther-
apeutic bulk peptides is expected to grow rapidly in the next
few years.[2] In spite of the well-established procedures[3] for
peptide synthesis by chemical ways, that is, stepwise synthesis
in solution and solid-phase peptide synthesis, one of the major
problems related to peptide preparation concerns the huge
amount of solvent needed, particularly for synthesis on solid
supports (2000–5000 kg for a large peptide). There is still a
need to explore efficient, convenient, and environmentally
friendly methods for peptide synthesis, particularly when the
time for the scale-up of peptide production comes.
Scheme 1. Synthesis of dipeptides under solvent-free conditions. Boc:
tert-butoxycarbonyl; Fmoc: 9-fluorenylmethoxycarbonyl; PG: protecting
group.
The field of “green chemistry” has recently grown at a
rapid pace. Some major thematic areas have emerged: use of
alternative feedstock and of innocuous reagents, employment
of natural processes, use of substitute solvents, design of safer
chemicals, development of alternative reaction conditions,
and minimization of energy consumption.[4] One particularly
active area is in the use of substitute solvents such as aqueous,
ionic, fluorous, or supercritical fluids to replace volatile
organic and chlorinated solvents and to solve the problems of
treating or recycling solvent waste.[5] An alternative approach
would be to carry out chemical reactions in the absence of
solvent.[6] Techniques such as mixing, grinding, or ball-milling
have proved their efficiency in the field of organic chemistry
in the solid state.[7] We report herein a new strategy for the
preparation of peptides under solvent-free conditions by
using ball-milling technology.[8] This strategy has been exem-
activated forms of amino acids that have proved to be useful
in peptide[10] and organic synthesis.[11]
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The reaction was tested for the coupling of Boc Val
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NCA (1a, 1 equiv) with HCl·H Leu OMe (2a, 1 equiv) in
the presence of NaHCO3 (1.5 equiv) in a hardened-steel
vessel with steel balls. The vessel was agitated for 1 h at a
frequency of 30 Hz. Analysis of the reaction mixture after this
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time showed the exclusive presence of the dipeptide Boc
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Val Leu OMe, obtained in quantitative yield. To our knowl-
edge, this represents the first example of peptide bond
formation in solvent-free conditions. The results obtained
with various UNCAs and amino acid derivatives are pre-
sented in Table 1.
The various UNCA derivatives do not present the same
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reactivity profile. Boc Val NCA (1a) reacted quantitatively
with amino acid derivatives to yield the corresponding
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plified by the synthesis of the sweetener dipeptide H Asp
dipeptides (Table 1, entries 1–5) whereas Fmoc Val NCA
(1b) gave lower conversions (Table 1, entries 6, 7, 9, and 10),
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Phe OMe (aspartame).
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We have studied the coupling of urethane-protected
a-amino acid N-carboxyanhydride (UNCA) derivatives 1
with a-amino acids, amides, or esters, while keeping in mind
that all of these compounds have to remain in the solid state
under the ball-milling conditions[9] (Scheme 1). UNCAs are
except when coupling with HCl·H Ala OMe (2c; Table 1,
entry 8). Excellent conversions and yields were achieved with
Boc Phe NCA (1c; Table 1, entries 12–14), except for the
reaction with HCl·H Phe OMe (Table 1, entry 15). Recov-
ery of the product from the reaction vessel was less efficient in
some cases and resulted in inferior yields (Table 1, entries 12
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[*] Dr. V. Declerck,[+] P. Nun, Prof. J. Martinez, Dr. F. Lamaty
Institut des Biomolꢀcules Max Mousseron (IBMM)
UMR 5247 CNRS-UM1-UM2, Universitꢀ Montpellier II
Place Eugꢁne Bataillon, 34095 Montpellier Cedex 5 (France)
Fax: (+33)4-6714-4866
E-mail: frederic.lamaty@univ-montp2.fr
[+] Current address:
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and 14). An amino ester, AcOH·H Gly OtBu was also tested
and gave satisfying results (Table 1, entry 16). By contrast, the
free amino acid did not react. It is worth noting that better
results were obtained with freshly prepared starting materials.
By reaching the maximum capacity of the ball-mill used in
this study, up to 500 mg of dipeptides could be prepared. The
reaction mixture was recovered directly from the milling jar,
washed with water to remove the inorganic salts, and dried to
provide the clean dipeptide. In the case of an incomplete
reaction, maybe due to the physicochemical state of the
reaction mixture (Table 1, entry 15), addition of water to the
reaction mixture resulted in the opening of the UNCA.
Laboratoire de Synthꢁse Organique et Mꢀthodologie (LSOM)
ICMMO UMR 8182, Universitꢀ Paris-Sud 11
15 Rue Georges Clemenceau, 91405 Orsay Cedex (France)
[**] We thank the MENRT, the CNRS, and the Fondation d’Enterprise
EADS for financial support.
Supporting information for this article is available on the WWW
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Insoluble in water, the protected dipeptide Boc Phe Phe
9318
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2009, 48, 9318 –9321