Arylation of phe and tyr side chains of unprotected peptides by a Suzuki-Miyaura reaction in water

Article abstract of DOI:10.1021/ol801009z

(Chemical Equation Presented) An efficient arylation in water of tyrosine and phenylalanine side chains from unprotected iodopeptides is accomplished by using Suzuki-Miyaura cross-coupling processes. The method is compatible with the hydrophilic and thermolabile nature of biologically active peptides. Also of interest, the arylated tyrosine peptides can be accessed in one-pot mode starting from native peptides.

Full text of DOI:10.1021/ol801009z

ORGANIC
LETTERS
2008
Vol. 10, No. 15
3243-3245
Arylation of Phe and Tyr Side Chains of
Unprotected Peptides by a
Suzuki-Miyaura Reaction in Water
Maria Vilaro´, Gemma Arsequell, Gregorio Valencia,* Alfredo Ballesteros, and
Jose´ Barluenga*
Instituto de InVestigacions Quimicas y Ambientales de Barcelona,
Jordi Girona 18-26 E08034, Barcelona, Spain, and Instituto UniVersitario de Qu´ımica
Organometa´lica “Enrique Moles” Unidad Asociada al C.S.I.C., UniVersidad de
OViedo, Julia´n ClaVer´ıa, 8; 33006 OViedo, Spain
barluenga@unioVi.es
Received May 2, 2008
ABSTRACT
An efficient arylation in water of tyrosine and phenylalanine side chains from unprotected iodopeptides is accomplished by using Suzuki-Miyaura
cross-coupling processes. The method is compatible with the hydrophilic and thermolabile nature of biologically active peptides. Also of
interest, the arylated tyrosine peptides can be accessed in one-pot mode starting from native peptides.
Aromatic amino acids like Phe and Tyr are important
structural elements in many native peptide pharmacophores.1
However, the study of their biological roles is limited by
the shortage of available aromatic amino acid building blocks
that can be used for the standard synthesis of peptides.2
An alternative could be to selectively modify Phe and Tyr
chains in already preformed peptides through conventional
organicchemistryreactions.Amongthem,theSuzuki-Miyaura
cross-coupling3 of halogenated Phe4 and Tyr residues with
organoboron derivatives could be an appealing entry into
discrete libraries of peptides. The Suzuki-Miyaura reaction
is known for both protected and unprotected Phe and Tyr
amino acid derivatives5 and also for protected small hydro-
phobic peptides containing them either in solution6 or in
solid-phase.7 However, these procedures require the use of
(3) (a) Suzuki, A. In Metal-Catalyzed Cross-Coupling Reactions;
Diederich, F.,; Stang, P. J., Eds.; Wiley-VCH: New York, 1998. (b) Miyaura,
N.; Suzuki, A. Chem. ReV. 1995, 95, 2457–2483. (c) Miyaura, N. Cross-
Coupling Reaction; Springer: Berlin, 2002. (d) Negishi, E. In Handbook of
Organopalladium Chemistry for Organic Synthesis; Wiley Interscience: New
York, 2002. (e) Beletskaya, I. P.; Cheprakov, A. V. In Handbook of
Organopalladium Chemistry for Organic Synthesis; Negishi, E; Ed.; Wiley-
Interscience: New York, 2002, Vol. 2, pp 2957-3006.
(4) 40. For Sonogashira cross-coupling reactions in 4-iodo-Phe peptides
see: Dibowski, H; Schmidtchen, F. P. Angew. Chem., Int. Ed. 1998, 37,
476–478.
(5) Gong, Y; He, W. Org. Lett. 2002, 4, 3803–3805.
(1) (a) Sewald, N.; Jakubke, H. D. Peptides: Chemistry and Biology;
Wiley-VCH: Weinheim, Germany, 2002. (b) Handbook of Biologically
ActiVe Peptides; Kastin, A., Ed.; Academic Press: New York, 2006.
(2) (a) Burk, M. J.; Lee, J. R.; Martinez, J. P. J. Am. Chem. Soc. 1994,
116, 10847–10848. (b) Berezowska, I.; Chung, N. N.; Lemieux, C.; Wilkes,
B. C; Schiller, P. W. J. Med. Chem. 2007, 50, 1414–1417. (c) Agnes, R. S.;
Lee, Y. S.; Davis, P.; Ma, S. W.; Badghisi, H.; Porreca, F.; Lai, J.; Hruby,
V. J. J. Med. Chem. 2006, 49, 2868–2875.
(6) (a) Kotha, S.; Lahiri, K. Biopolymers 2003, 69, 517–528. (b) Basse,
N.; Piguel, S.; Papapostolou, D.; Ferrier-Berthelot, A.; Richy, N.; Pagano,
M.; Sarthou, P.; Sobczak-The´pot, J.; Reboud-Ravaux, M.; Vidal, J. J. Med.
Chem. 2007, 50, 2842–2850. (c) Bois-Choussy, M.; Cristeua, P.; Zhu, J.
Angew. Chem., Int. Ed. 2003, 42, 4238–4241. (d) Le´pine, R.; Zhu, J. Org.
Lett. 2005, 14, 2981–2984. (e) Espun˜a, G.; Arsequell, G.; Valencia, G.;
Barluenga, J.; Alvarez-Gutie´rrez, J. M.; Ballesteros, A.; Gonza´lez, J. M.
Angew. Chem., Int. Ed. 2004, 43, 325–329.
10.1021/ol801009z CCC: $40.75
Published on Web 07/04/2008
2008 American Chemical Society

organic solvents (i.e., dioxane and toluene) and temperatures
higher that 80 °C. Owing that these conditions are incompat-
ible with the hydrophilic nature and thermal lability of the
vast majority of native peptides, we have settled to study
the feasibility of these reactions in water and low tempera-
tures as to make the Suzuki-Miyaura reaction amenable to
the majority of biologically active peptides.
Table 1. Pd-Catalyzed Suzuki-Miyaura Reaction on
Iodophenylalanine Peptides in Water
Previously, Pd-catalyzed cross-coupling reactions other
than Suzuki type on iodophenylalanine peptides in aqueous
media have been scarcely reported.4,8 A report on a Suzuki
reaction on iodopeptides in glycerol/water mixtures is
known.9 However, the Suzuki-Miyaura cross coupling in
neat water is restricted to the preparation of biaryls,10
nucleoside, and nucleotide derivatives.11 Here, we report
successful results on the Suzuki-Miyaura reaction in fully
aqueous media at room or moderate temperature of unpro-
tected, biologically active peptides.
conversion
% (h)b
entry
peptidea
Ar BF3K
1
2
3
4
5
6
7
8
1a: H-Tyr-Gly-Gly-4-iodo-
Phe-Leu-OH
1b: H-Gly-Gly-4-iodo-
Phe-Leu-OH
1c: For-Met-Leu-4-iodo-
Phe-OH
1d: H-Tyr-Gly-Gly-4-iodo-
Phe-Met-OH
1e: H-Tyr-D-Ala-4-iodo-
Phe-Gly-Tyr-Pro-Ser-NH2
1f: H-Met-Glu-His-4-iodo-
Phe-Arg-Trp-Gly-OH
2a
2b
2a
2b
2a
2b
2a
2b
2a
2b
2a
2b
3a
3b
3c
3d
3e
3f
3g
3h
3i
26 (24)
98 (24)
92 (3)
84 (3)
100 (3)
100 (3)
52 (24)
90 (3)
82 (24)
76 (3)
Using the iodinated derivative: H-Tyr-Gly-Gly-4-iodo-Phe-
Leu-OH, 1a, of the opioid peptide Leu enkephalin12 as a
model compound, a screening for suitable Suzuki-Miyaura
reaction conditions in water has been conducted. The reaction
conditions that furnished nearly quantitative conversions after
24 h at 50 °C were 5 mol % Pd from a Pd(OAc)2/TPPTS
(1:3)13 (TPPTS ) P(m-C6H4SO3Na)3) catalytic mixture, 2.5
equiv of potassium 2,4-difluorophenyltrifluoroborate and 3
equiv with respect to the boron compound of K3PO4 in neat
degassed water. Alternatively, similar reaction performance
could be observed at room temperature but after longer times
and 10 mol % of catalyst.14
9
10
11
12
3j
3k
3l
15 (24)
24 (24)
a Reaction conditions: peptide (1 equiv), potassium 2,4-difluorophenyl
trifluoroborate (2a) or potassium 4-methoxyphenyltrifluoroborate (2b) (2.5
equiv), K3PO4 (3 equiv with respect to the boron compound), Pd(OAc)2/
TPPTS (1:3) [5 mol% Pd] in degassed water (1 mL) at 50 °C. b Conversions
were calculated at specific time (h) shown in brackets.
conversions are either obtained with activated (4-methoxy)
or deactivated (2,4-difluoro) substitutions.
These conditions were further applied to a series of Phe-
iodinated derivatives of bioactive peptides. Results of Table
1 show that the reaction performance is difficult to rationalize
in terms of the nucleophilic character induced by electronic
contributions of the aryl rings of these reagents and high
Three out of twelve reactions (entries 1, 11, and 12)
presented low conversions probably indicating that not only
the size of the peptide is critical (chemotactic peptide 1c,
entries 5, and 6 vs enkephalins 1a and 1d, entries 1, 2, 7,
and 8) but that the amino acid sequence is also playing a
role (dermorphin 1e, entries 9 and 10 vs ACTH 4-10 1f,
entries 11 and 12).
(7) Doan, N. D.; Bourgault, S.; Le´tourneau, M.; Fournier, A. J. Comb.
Chem. 2008, 10, 44–51.
(8) (a) Kodama, K.; Fukuzawa, S.; Nakayama, H.; Sakamoto, K.;
Kigawa, T.; Yabuki, T.; Matsuda, N.; Shirouzu, M.; Takio, K.; Yokoyama,
S.; Tachibana, K. Chembiochem. 2007, 8, 232–238. (b) Hoffmanns, U.;
Metzler-Nolte, N. Bioconjug. Chem. 2006, 17, 204–213.
Next, we studied the application of this protocol to the
coupling of doubly halogenated Tyr residues in peptides
4a-4f (see Table 2). The 4-methoxyphenyltrifluoroborate
2a furnishes the desired doubly cross-coupling reaction in
good to high conversion (entries 1, 3, 7). However, when
the arylborate contains an arene substituted by electron-
withdrawing groups (see compound 2b), low conversions
are always obtained for the target bisarylation reaction of
the peptide. Variable amounts of the corresponding starting
material as well as of the products derived from the
monocoupling process were always present in the crude
reaction mixtures. Significantly, when the related bromine-
containing peptide 4c (entries 5, 6) is used no coupling
reaction was observed under the same reaction conditions.
Same experimental conditions have been tested on 1a, 1b,
and 4b at 50-100 mg scale of the peptide. A standard work-
up procedure to isolate the modified peptides has been
established. From pure samples, full spectroscopic charac-
terization of the arylated peptides, as well as the quantifica-
tion of the yields was obtained. The results were consistent
(9) Ojidaa, A.; Tsutsumia, H.; Kasagia, N.; Hamachi, I. Tetrahedron
Lett. 2005, 19, 3301–3305.
(10) (a) Bumagin, N. A.; More, P. G.; Beletskaya, I. P. J. Organomet.
Chem. 1989, 371–397. (b) Bumagin, N. A.; Bykov, V. V.; Beletskaya, I. P.
IzVest. Akad. Nauk. SSSR, Ser. Khim. 1989, 2394. (c) Bumagin, N. A.;
Bykov, V. V. Tetrahedron 1997, 53, 14437–14450. (d) Dupusi, C.; Adiey,
K.; Michelet, V.; Savignac, M.; Genet, J. P. Tetrahedron Lett. 2001, 42,
6523–6526.
(11) (a) Collier, A.; Wagner, G. Org. Biomol. Chem. 2006, 4, 4526–
4532. (b) Capek, P.; Pohl, R.; Hocek, M. Org. Biomol. Chem. 2006, 4,
2278–2284. (c) Western, E. C.; Daft, J. R.; Johnson, E. M.; Gannett, P. M.;
Shaughnessy, K. H. J. Org. Chem. 2003, 68, 6767–6774.
(12) (a) Hughes, J.; Smith, T. W.; Kosterlitz, H. W.; Fothergill, L. A.;
Morgan, B. A.; Morris, H. R. Nature 1975, 258, 577–579. (b) Zadina, J. E.;
Hackler, L.; Ge, L. J.; Kastin, A. J. Nature 1997, 386, 499–502.
(13) This combination has been previously used in the coupling of
several biaryls and nucleosides and nucleotides in mixtures of water and
different organic solvents: Casalnuovo, A. L.; Calabrese, J. C. J. Am. Chem.
Soc. 1990, 112, 4324–4330.
(14) Different Pd sources [Pd(OAc)2, Pd(NO3)2, and Na2PdCl4] have
been assayed either alone or in combination with water soluble sulfonated
phosphine ligands (TPPTS, TPPMS, TPPDS, TXPTS) and Buchwald-type
sulfonated phosphine : Anderson, K. W.; Buchwald, S. L. Angew. Chem.,
Int. Ed. 2005, 44, 61736177. A set of inorganic bases (Na2CO3, K2CO3,
Cs2CO3, K3PO4 and Na3PO4) have also been tested at either room
temperature or 50 °C, see the Supporting Information.
3244
Org. Lett., Vol. 10, No. 15, 2008

Table 2. Pd-Catalyzed Suzuki-Miyaura Reaction with Different
[3,5-Dihalo-Tyr]-Containing Peptides in Water: Influence of the
Potassium Aryltrifluoroborate Reagent
Scheme 1. One-Pot, Sequential Iodination/Suzuki-Miyaura
Cross-Coupling Reactions in Water of Leu-enkephalin
H-Tyr-Gly-Gly-Phe-Leu-OH) with IPy2BF4 followed by
coupling with potassium 4-methoxyphenyl trifluoroborate
under Suzuki conditions (Scheme 1). After the addition of
IPy2BF4 (2.5 equiv) a quick and quantitative conversion to
the diiodo analogue 4b was evidenced by HPLC. Subsequent
addition of the Suzuki reagents gave the disubstituted
analogue 6c in 60% conversion after 20 h at 50 °C. By a
second addition of fresh Pd catalyst, this result could be
improved up to 80%, which is in good agreement with the
one previously obtained from pure samples of 4b (92%, see
Table 2, entry 3).
In conclusion, using biologically active peptides, iodinated
at Phe and Tyr residues, a new aqueous Suzuki-Miyaura
cross-coupling procedure is described. The method can also
be applied to native, noniodinated Tyr-containing peptides
by simply performing a previous IPy2BF4 mediated iodination
step. Both iodination and cross-coupling can be fashioned
in one-pot mode. The reactions proceed with quantitative
conversions after short reaction times and the products can
be purified in high yields. The resulting arylated peptides
open the way to new structure-activity relationship studies
of peptides and other water soluble aromatic substrates.
conversion
(%)b
entry
peptidea
Ar-BF3K mono
di
1
2
3
4
5
6
7
8
9
4a: Ac-Phe-3,5-diiodo-
Tyr-OH
2a
2b
2a
2b
2a
2b
2a
2b
2a
2b
5a
6a 92
5b 10 6b
5c 6c 92
5d 25 6d 28
8
4b: H-3,5-diiodo-Tyr-
Gly-Gly-Phe-Leu-OH
4c: H-3,5-dibromo-Tyr-
Gly-Gly-Phe-Leu-OH
4d: H-3,5-diiodo-Tyr-
Gly-Gly-Phe-Met-OH
4f: H-3,5-diiodo-Tyr-D-
5f 17 6f 83
5g 23 6g 73
5h
8 6h 40
10 Ala-Phe-Gly-Tyr-Pro-Ser-NH2
5i 25 6i 12
a Reaction conditions: peptide (1 equiv), potassium 2,4-difluorophe-
nyltrifluoroborate 2a or potassium 4-methoxyphenyl-trifluoroborate 2b (5
equiv), K3PO4 (3 equiv with respect to the boron compound), Pd(OAc)2/
TPPTS (1:3) [10 mol % Pd] in degassed water (1 mL) at 50 °C.
b Conversions were calculated at 24 h of reaction time.
with those previously obtained using a smaller scale of
peptide, rendering yields in the range of 56-98%. Besides,
the evolution of the reactions of 1a with 2b and 4b with 2a
were monitored by HPLC.15
The feasibility of a one-pot, sequential iodination/cross-
coupling process was also tested. On the basis of our previous
Acknowledgment. This work was supported by the
Ministerio de Educacio´n y Ciencia of Spain (CTQ 2004-
08077-C02-01; CTQ2007-61048). Dedicated to Professor
Angel Gutie´rrez-Ravelo.
16
work on aromatic iodination of biomolecules in water,
the iodinating reagent bis(pyridine)iodonium tetrafluoroborate
(IPy2BF4)17 was used for the initial screening.18As a model,
we have studied the reaction of Leu-enkephalin (Leu-Enk:
Supporting Information Available: Experimental pro-
cedures and characterization data for the new peptides 3a,
3b, 3c, and 6c. This material is available free of charge via
the Internet at http://pubs.acs.org.
(15) For experimental data, see the accompanying Supporting Informa-
tion.
OL801009Z
(16) For recent representative work, see: Espun˜a, G.; Andreu, D.;
Barluenga, J.; Pe´rez, X.; Planas, A; Arsequell, G.; Valencia, G. Biochemistry
2006, 45, 5957–5963.
(18) (a) Arsequell, G.; Espun˜a, G.; Valencia, G.; Barluenga, J.; Pe´rez
Carlo´n, R.; Gonza´lez, J. M. Tetrahedron Lett. 1998, 39, 7393–7396. (b)
Arsequell, G.; Espun˜a, G.; Valencia, G.; Barluenga, J.; Pe´rez Carlo´n, R.;
Gonza´lez, J. M. Tetrahedron Lett. 1999, 40, 7279–7282. (c) Espun˜a, G.;
Arsequell, G.; Valencia, G.; Barluenga, J.; Pe´rez, R.; Gonza´lez, J. M. Chem.
Commun. 2000, 1307–1308.
(17) (a) Barluenga, J.; Gonza´lez, J. M. In Current Trends in Organic
Synthesis; Scolastico, C., ; Nicotra, F., Eds.; Academic/Plenum Publishers:
New York, 1999; pp 145-151. (b) Barluenga, J. Pure Appl. Chem. 1999,
71, 431–436.
Org. Lett., Vol. 10, No. 15, 2008
3245