Solid-phase synthesis of biaryl cyclic peptides containing a 3-aryltyrosine

Article abstract of DOI:10.1002/ejoc.201200832

A concise and efficient solid-phase synthesis of biaryl cyclic peptides containing a Phe-Tyr or a Tyr-Tyr linkage has been accomplished. The key steps include a Miyaura borylation of a resin-bound 3-iodotyrosine and a microwave-assisted Suzuki-Miyaura reaction for the formation of the macrocycle. First, the feasibility of the solid-phase Miyaura borylation of a 3-iodotyrosyltripeptide was established. Then, the Suzuki-Miyaura reaction was applied to the cross-coupling of linear 3-boronotyrosine-containing peptidyl resins with iodobenzene and with halogenated aromatic amino acids. Finally, this methodology was extended to the synthesis of biaryl cyclic peptides through the preparation of a linear peptidyl resin containing both the required boronate and halogenated derivatives, followed by a microwave-assisted Suzuki-Miyaura macrocyclization.

Full text of DOI:10.1002/ejoc.201200832

Job/Unit: O20832
/KAP1
Date: 13-09-12 17:00:18
Pages: 9
FULL PAPER
DOI: 10.1002/ejoc.201200832
Solid-Phase Synthesis of Biaryl Cyclic Peptides Containing a 3-Aryltyrosine
Ana Afonso,[a] Olaf Cussó,[a] Lidia Feliu,*[a] and Marta Planas*[a]
Keywords: Synthetic methods / Solid-phase synthesis / Microwave chemistry / Cyclization / Cross-coupling / Macrocycles /
Peptides / Biaryls / Boronates
A concise and efficient solid-phase synthesis of biaryl cyclic
peptides containing a Phe–Tyr or a Tyr–Tyr linkage has been
accomplished. The key steps include a Miyaura borylation of
a resin-bound 3-iodotyrosine and a microwave-assisted Su-
zuki–Miyaura reaction for the formation of the macrocycle.
First, the feasibility of the solid-phase Miyaura borylation of
a 3-iodotyrosyltripeptide was established. Then, the Suzuki–
Miyaura reaction was applied to the cross-coupling of linear
3-boronotyrosine-containing peptidyl resins with iodo-
benzene and with halogenated aromatic amino acids. Finally,
this methodology was extended to the synthesis of biaryl
cyclic peptides through the preparation of a linear peptidyl
resin containing both the required boronate and halogenated
derivatives, followed by
Miyaura macrocyclization.
a microwave-assisted Suzuki–
the solid support avoids the synthesis and purification of
the amino acid boronate in solution. Therefore, this strategy
is amenable to the preparation of biaryl cyclic peptides in a
flexible and convergent manner under mild conditions.
We envisioned that this methodology could be extended
to the formation of biaryl linkages involving a tyrosine resi-
due. This would represent an efficient strategy for the syn-
thesis of natural biaryl cyclic peptides bearing an aryltyros-
ine, such as biphenomycins, RP-66453, or glycopeptide an-
tibiotics, and the strategy could be extended to allow the
preparation of analogues. In this paper, we report the re-
sults from our work in this area, in which we studied the
effectiveness of the solid-phase Miyaura borylation of 3-
iodotyrosine peptides and of the Suzuki–Miyaura macrocy-
clization of conveniently functionalized linear peptidyl res-
ins.
Introduction
Biaryl cyclic peptides have been subject to the attention
of synthetic chemists during the last few years due to their
interesting biological activity.[1] Biaryl compounds have
been mainly prepared in solution using a Suzuki–Miyaura
cross-coupling reaction for the formation of the biaryl link-
age.[2] The solid-phase synthesis of biaryl peptides has
scarcely been reported, being limited to linear sequences
and involving the coupling of a polymer-bound halogenated
aromatic amino acid with an arylboron in solution.[3]
We have described the solid-phase synthesis of biaryl cy-
clic peptides containing an arylphenylalanine residue.[4] All
the key steps of this approach were performed on a solid
support and entail (i) Miyaura borylation of a 4-iodophen-
ylalanine peptide; (ii) chain elongation to afford a linear
peptide containing both the boronate and the halogenated
amino acid derivative, and (iii) Suzuki–Miyaura macrocycli-
zation for the formation of the aryl–aryl bond. Recently,
James et al. reported a complementary study for the synthe-
sis of arylphenylalanine-containing cyclic peptides, but they
prepared the corresponding boronophenylalanine derivative
in solution.[5] In our methodology, both borylation and
macrocyclization are performed on the solid support, and
therefore it benefits from the advantages inherent to solid-
phase synthesis. In particular, performing the borylation on
Results and Discussion
Solid-Phase Synthesis of Boronotyrosines
Miyaura borylation of a 3-iodotyrosine residue on solid
support was investigated using Boc-Tyr(3-BPin,SEM)-Leu-
Leu-Rink-MBHA (1a; Boc = tert-butyloxycarbonyl; SEM
= 2-(trimethylsilyl)ethoxymethyl; BPin = pinacolboranyl)
and Boc-Tyr(3-BPin,Me)-Leu-Leu-Rink-MBHA (1b) as
model systems (Scheme 1). SEM and methyl protecting
groups served to ensure the stability of the hydroxy func-
tionality under the reaction conditions. Thus, we prepared
the required halogenated resins Boc-Tyr(3-I,SEM)-Leu-
Leu-Rink-MBHA (2a) and Boc-Tyr(3-I,Me)-Leu-Leu-
Rink-MBHA (2b) by coupling Boc-Tyr(3-I,SEM)-OH or
Boc-Tyr(3-I,Me)-OH[3d] to H-Leu-Leu-Rink-MBHA. This
dipeptidyl resin was constructed from Fmoc-Rink-MBHA
[a] Laboratori d’Innovació en Processos i Productes de Síntesi
Orgànica (LIPPSO), Departament de Química, Universitat de
Girona,
Campus Montilivi, 17071 Girona, Spain
Fax: +34-972-418150
E-mail: marta.planas@udg.edu
lidia.feliu@udg.edu
Homepage: http://www.lippso.com
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201200832.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1

Job/Unit: O20832
/KAP1
Date: 13-09-12 17:00:18
Pages: 9
A. Afonso, O. Cussó, L. Feliu, M. Planas
FULL PAPER
Scheme 1. Solid-phase Miyaura borylation of a 3-iodotyrosyltripeptide.
following an Fmoc/tBu strategy by sequential coupling and Pd2(dba)3 (0.2 equiv.), P(o-tolyl)3 (0.4 equiv.), and KF
deprotection steps using standard protocols. Treatment of (4 equiv.) in DME/EtOH/H2O (9:9:2; DME = 1,2-dimeth-
an aliquot of the resulting resins 2a and 2b with TFA/TIS/ oxyethane) under microwave irradiation at 120 °C for
H2O (95:2.5:2.5; TFA = trifluoroacetic acid; TIS = triiso- 30 min. Acidolytic cleavage of the resulting resins with
propylsilane) for 2 h at room temperature gave H-Tyr(3-I)- TFA/TIS/H2O (95:2.5:2.5) gave the corresponding biaryl
Leu-Leu-NH2 and H-Tyr(3-I,Me)-Leu-Leu-NH2 in 97 and tripeptides 6a and 6b in 80 and 92% purity, respectively.
92% purity, respectively. These compounds were charac- These compounds were purified by column chromatog-
terized by mass spectrometry.
raphy, and were obtained in 34 and 38% yield, respectively.
The borylation was first attempted under the conditions They were characterized by NMR spectroscopy and mass
previously described for the preparation of resin-bound spectrometry.
phenylalanine boronates.[6] Resins 2a and 2b were treated
with bis(pinacolato)diboron (B2Pin2) (4 equiv.), PdCl2-
(dppf) (0.18 equiv.), 1,1Ј-bis(diphenylphosphanyl)ferrocene
(dppf; 0.09 equiv.), and KOAc (6 equiv.), in DMSO at 80 °C
for 24 h (Scheme 1). In both cases, acidolytic cleavage of the
resulting resins gave the corresponding borylated products
with low purities. Moreover, mass spectrometry analysis of
the crude reaction mixtures resulting from 2a and 2b
showed the presence of H-Tyr-Leu-Leu-NH2 (5a) and H-
Tyr(Me)-Leu-Leu-NH2 (5b) as the respective major prod-
ucts. These tripeptides resulted from protodeborylation of
resins 1 or deiodination of resins 2. Since the formation of
Scheme 2. Solid-phase arylation of resins 1a and 1b with PhI.
such by-products has been reported to increase in the pres-
Bearing in mind our aim of preparing biaryl cyclic pept-
ence of transition metals, such as palladium, and with long
ides, we then studied the feasibility of the arylation of a
heating times,[7] the borylation was attempted with a shorter
boronopeptidyl resin with a halogenated aromatic amino
reaction time. Carrying out the reaction for 8 h, the amount
acid. In particular, Boc-Tyr(3-BPin,SEM)-Leu-Leu-Rink-
of 5a and 5b was reduced to less than 10%, and the corre-
MBHA (1a) was treated with the methyl ester derivatives
sponding boronopeptides (i.e., 3a+4a and 3b+4b) were ob-
tained in 60 and 78% purity, respectively. As previously re-
ported, peptide boronic acids 4a and 4b could be formed
Boc-Phe(4-I)-OMe[9] and Boc-Tyr(3-I,SEM)-OMe[3d] under
the conditions described above (Scheme 3). After arylation
and hydrolysis of the methyl ester with LiOH in THF, the
resulting biaryl peptidyl resins were cleaved with TFA/TIS/
by hydrolysis of the pinacol ester functionality of the corre-
sponding boronate during HPLC analysis.[7,8]
H2O. HPLC and ESI-MS analysis of the crude reaction
mixtures showed the presence of the expected biaryl tetra-
peptides (i.e., 6c and 6d), in 64 and 61% purity, respectively,
together with a small amount of the protodeborylated prod-
Arylation of Resin-Bound Boronotyrosine-Containing
Peptides
uct, H-Tyr-Leu-Leu-NH2 (5a, 8–9%). Purification of these
With resin-bound tyrosine boronates 1a and 1b in hand, crude reaction mixtures by column chromatography gave
we attempted their arylation with iodobenzene by a Su- the corresponding biaryl peptides (i.e., 6c and 6d) in 44 and
zuki–Miyaura cross-coupling (Scheme 2).[4,6] Thus, resins 55% yield, respectively. These products were fully charac-
1
1a and 1b were treated with iodobenzene (5 equiv.), terized by mass spectrometry, and H and 13C NMR spec-
2
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O20832
/KAP1
Date: 13-09-12 17:00:18
Pages: 9
Solid-Phase Synthesis of Biaryl Cyclic Peptides
troscopy. Moreover, 2D COSY, HSQC and HMBC experi- to overcome the instability of Fmoc under the Miyaura bor-
ments were carried out to completely assign all the proton ylation conditions. Next, the boronate was formed using
and carbon signals. The NMR spectra showed the presence the conditions described above, which led to Tr-Lys(Boc)-
of a single stereoisomer, revealing that no epimerization oc- Lys(Boc)-Leu-Tyr(3-BPin,R)-Leu-Leu-Rink-MBHA (R =
curred during the borylation and Suzuki–Miyaura cross- Me or SEM). Trityl group removal and coupling of the cor-
coupling steps.
responding 4-iodophenylalanine or 3-iodotyrosine deriva-
tive gave peptidyl resins 7a–d. Acidolytic cleavage of an ali-
quot of these resins yielded the expected borylated peptides
in purities ranging from 30–62%. The cleaved peptides were
characterized by HRMS.
Scheme 3. Solid-phase arylation of resin 1a with halogenated aro-
matic amino acids.
Synthesis of Biaryl Cyclic Peptides
To achieve our final goal, we set out to examine the syn-
thesis of biaryl cyclic peptides with the aim of achieving
ring closure by solid-phase formation of the aryl–aryl bond
under the conditions of the Suzuki–Miyaura cross-cou-
pling. This approach involved the preparation of linear
Scheme 4. Synthesis of linear peptidyl resins 7a–d.
Cyclization of resins 7a–d by Suzuki–Miyaura cross-cou-
peptidyl resins containing the required boronate and haloge- pling was attempted using Pd2(dba)3, P(o-tolyl)3, and KF
nated amino acid derivatives, followed by macrocyclization. in DME/EtOH/H2O under microwave irradiation at 120 °C
Thus, we prepared the peptidyl resins Boc-AA(I)-Lys(Boc)- for 30 min. After cleavage, HPLC and ESI-MS analysis of
Lys(Boc)-Leu-Tyr(3-BPin,R)-Leu-Leu-Rink-MBHA (7a–d) the crude reaction mixtures showed that only resin 7b had
where AA(I) corresponds to Phe(4-I), Tyr(3-I,Me) or Tyr(3- cyclized to form the expected biaryl cyclic peptide 8b, and
I,SEM), and R is Me or SEM (Scheme 4). Since in previous in low purity (Ͻ10%). In all reactions a major product de-
studies we had observed that the boronate functionality de- rived from the simultaneous protodeborylation and dehalo-
composed into the phenolic compound after several Fmoc genation of the corresponding linear precursor was ob-
removal and coupling steps,[4] we decided to form the served. In order to improve these results, the macrocycliza-
boronate in the last steps of the synthesis. Therefore, we tion was tested using SPhos instead of P(o-tolyl)3.[10] Under
first prepared Fmoc-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-I,R)- these conditions, biaryl cyclic peptides 8b and 8d were
Leu-Leu-Rink-MBHA (R = Me or SEM) starting from res- formed in 47 and 33% purity, respectively (Scheme 5).
ins Boc-Tyr(3-I,SEM)-Leu-Leu-Rink-MBHA (2a) and Boc- These compounds were purified by column chromatog-
Tyr(3-I,Me)-Leu-Leu-Rink-MBHA (2b). After Boc removal raphy and were obtained in 16 and 22% yield, respectively.
by treatment with trimethylsilyl triflate (TMSOTf) and 2,6- 8b and 8d were characterized by mass spectrometry and 1H
lutidine in CH2Cl2 for 1 h, the peptidyl chain was elon- NMR spectroscopy, and the data were consistent with the
gated. Then we replaced the Fmoc group by a trityl group formation of the biaryl bond. In the case of 8b, only one
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3

Job/Unit: O20832
/KAP1
Date: 13-09-12 17:00:18
Pages: 9
A. Afonso, O. Cussó, L. Feliu, M. Planas
FULL PAPER
Flash chromatography purifications were performed on C18 re-
verse-phase silica gel 100 (not end-capped; 230–400 mesh, Fluka).
All compounds were analyzed under standard analytical HPLC
conditions with a Dionex liquid chromatography instrument or
with an Agilent Technologies 1200 Series HPLC instrument. Detec-
tion was performed at 220 nm. Method A: Analysis was carried out
using the Dionex instrument with a Kromasil 100 C18 (250 mmϫ
4.6 mm, 3.5 μm) column with a 2–100% B linear gradient over
28 min at a flow rate of 1 mL/min. Method B: Analysis was carried
out using the Dionex instrument with a Kromasil 100 C18
(40 mmϫ 4.6 mm, 3.5 μm) column with a 2–100% B linear gradi-
ent over 7 min at a flow rate of 1 mL/min. Method C: Analysis was
carried out using the Agilent instrument with a Kromasil 100 C18
(250 mmϫ 4.6 mm, 3.5 μm) column with a 2–100% B linear gradi-
ent over 28 min at a flow rate of 1 mL/min. Method D: Analysis
was carried out using the Agilent instrument with a Kromasil 100
C18 (40 mmϫ 4.6 mm, 3.5 μm) column with a 2–100% B linear
gradient over 10 min at a flow rate of 1 mL/min. Solvent A was
0.1% aqueous TFA, and solvent B was 0.1% TFA in CH3CN. ESI-
MS analyses were performed with an Esquire 6000 ESI ion-trap
LCMS (Bruker Daltonics) instrument equipped with an electro-
spray ion source. The instrument was operated in the positive
(ESI+) ion mode. Samples (5 μL) were introduced into the mass
spectrometer ion source directly through an HPLC autosampler.
The mobile phase (80:20 CH3CN/H2O at a flow rate of 100 μL/
min) was delivered by a 1100 Series HPLC pump (Agilent). Nitro-
gen was used as both the drying and nebulizing gas. HRMS were
recorded under ESI conditions with a Bruker MicroTof-Q instru-
ment using a hybrid quadrupole time-of-flight mass spectrometer
(University of Zaragoza). Samples were introduced into the mass
spectrometer ion source directly through a 1100 Series Agilent
HPLC autosampler, and were externally calibrated using sodium
formate. The instrument was operated in the positive (ESI+) ion
steroisomer was observed. NMR analysis of 8d indicated
the presence of two conformers, which was confirmed by
1
performing further H NMR experiments at high tempera-
ture in [D6]DMSO. As expected, raising the temperature
resulted in the coalescence of the proton signals.
1
mode. H and 13C NMR spectra were measured with Bruker 300
or 400 MHz NMR spectrometers. Chemical shifts are reported as δ
values (ppm), directly referenced to the solvent signal. Microwave-
assisted reactions were performed with an Ethos SEL labstation
microwave (Milestone) equipped with a dual magnetron (1600 W).
The time, temperature, and power were controlled with the Easy-
Control software. The temperature was monitored through the
ATC-400FO Automatic Fiber Optic Temperature Control System
immersed in a standard Milestone reference vessel. This equipment
regulates the power to achieve and maintain the selected tempera-
ture. Microwave-assisted reactions were also performed with a sin-
gle mode Discover S-Class labstation microwave (CEM) (0–300 W).
The time, temperature, and power were controlled with the Synergy
software. The temperature was monitored through an infrared sen-
sor in the floor of the cavity.
Scheme 5. Synthesis of biaryl cyclic peptides 8b and 8d.
Conclusions
We have developed a convenient strategy for the modifi-
cation of tyrosine peptides through solid-phase borylation
and subsequent arylation. This methodology can be consid-
ered to be a useful approach for the synthesis of linear and
cyclic 3-aryltyrosine-containing peptides. Moreover, this
work constitutes the first example of a solid-phase intramo-
lecular Suzuki–Miyaura cross-coupling for the formation of
biaryl cyclic peptides containing a Tyr–Tyr linkage. We ex-
pect that this approach will find applications in the synthe-
sis of natural products or biaryl-containing analogues.
Boc-Tyr(3-I,SEM)-Leu-Leu-Rink-MBHA (2a): This peptidyl resin
was synthesized manually by the solid-phase method using stan-
dard Fmoc chemistry. Fmoc-Rink-MBHA resin (0.56 mmol/g) was
used as solid support. Fmoc-Leu-OH (4 equiv.) and Boc-Tyr(3-
I,SEM)-OH[3d] were coupled using ethyl cyanoglyoxylate 2-oxime
(3 equiv.) and N,NЈ-diisopropylcarbodiimide (DIPCDI) (3 equiv.)
in DMF at room temperature for 3 h. The completion of the reac-
tions was checked by the Kaiser test.[11] Fmoc group removal was
achieved with piperidine/DMF (3:7, 2+8 min). After each coupling
and deprotection step, the resin was washed with DMF (6ϫ 1 min),
and CH2Cl2 (3ϫ 1 min), and air-dried. An aliquot of Boc-Tyr(3-
I,SEM)-Leu-Leu-Rink-MBHA (2a) was cleaved with TFA/H2O/tri-
isopropylsilane (TIS) (95:2.5:2.5) whilst stirring for 2 h at room
temperature. Following TFA evaporation and Et2O extraction, the
crude peptide was dissolved in H2O/CH3CN, lyophilized, analyzed
Experimental Section
General Methods: Commercially available reagents were used
throughout without purification. Solvents were purified and dried
by passing them through an activated alumina purification system
(MBraun SPS-800), or by conventional distillation techniques.
4
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O20832
/KAP1
Date: 13-09-12 17:00:18
Pages: 9
Solid-Phase Synthesis of Biaryl Cyclic Peptides
by HPLC and characterized by MS. H-Tyr(3-I)-Leu-Leu-NH2 was
obtained in 97% purity. tR = 6.49 min (Method B). MS (ESI): m/z
= 533.0 [M + H]+, 555.0 [M + Na]+.
Pd2(dba)3 (0.2 equiv.), P(o-tolyl)3 (0.4 equiv.), and KF (4 equiv.).
Thoroughly degassed DME/EtOH/H2O (9:9:2, 1ϫ 1.5 mL) was
then added under nitrogen. The reaction mixture was heated at
120 °C under microwave irradiation for 30 min. After this time, the
resin was washed with DMF (6ϫ 1 min), EtOH (6ϫ 1 min),
CH2Cl2 (6ϫ 1 min), and Et2O (3ϫ 1 min). An aliquot of the re-
sulting biaryl peptidyl resin was cleaved with TFA/H2O/TIS
(95:2.5:2.5) whilst being stirred for 2 h at room temperature. Fol-
lowing TFA evaporation and Et2O extraction, the crude peptide
was dissolved in H2O/CH3CN, lyophilized, and analyzed by HPLC.
When necessary, the rest of the biaryl peptidyl resin was hydrolyzed
by treatment with LiOH (5 equiv.) in THF/H2O (7:1) at room tem-
perature for 24 h. After the reaction was finished, the solvent was
removed and the resin was washed with DMF (3ϫ 1 min), MeOH
(2ϫ 1 min), H2O (2ϫ 1 min), DMF (3ϫ 1 min), and CH2Cl2 (3ϫ
1 min). The resulting biaryl peptide was released from the solid
support by treatment with TFA/H2O/TIS (95:2.5:2.5) with stirring
for 2 h at room temperature. Following TFA evaporation and Et2O
extraction, the crude peptide was dissolved in H2O/CH3CN, lyophi-
lized, analyzed by HPLC, and purified by reverse-phase column
chromatography. Biaryl peptides were characterized by MS and
NMR spectroscopy.
Boc-Tyr(3-I,Me)-Leu-Leu-Rink-MBHA (2b): This peptidyl resin
was synthesized manually by the solid-phase method using stan-
dard Fmoc chemistry. Fmoc-Rink-MBHA resin (0.56 mmol/g) was
used as solid support. Fmoc-Leu-OH (4 equiv.) and Boc-Tyr(3-
I,Me)-OH[3d] were coupled using ethyl cyanoglyoxylate 2-oxime
(3 equiv.) and DIPCDI (3 equiv.) in DMF at room temperature for
3 h. The completion of the reactions was checked by the Kaiser
test.[11] Fmoc group removal was achieved with piperidine/DMF
(3:7, 2+8 min). After each coupling and deprotection step, the
resin was washed with DMF (6ϫ 1 min), and CH2Cl2 (3ϫ 1 min),
and air-dried. An aliquot of Boc-Tyr(3-I,Me)-Leu-Leu-Rink-
MBHA (2b) was cleaved with TFA/H2O/TIS (95:2.5:2.5) whilst stir-
ring for 2 h at room temperature. Following TFA evaporation and
Et2O extraction, the crude peptide was dissolved in H2O/CH3CN,
lyophilized, analyzed by HPLC and characterized by MS. H-Tyr(3-
I,Me)-Leu-Leu-NH2 was obtained in 92% purity. tR = 6.86 min
(Method B). MS (ESI): m/z = 547.0 [M + H]+, 569.0 [M + Na]+,
585.0 [M + K]+.
General Method for the Borylation of Linear Peptidyl Resins 2a and
2b by a Miyaura Reaction: A 25 mL round-bottomed flask was
charged with the appropriate iodopeptidyl resin, bis(pinacolato)di-
boron (B2Pin2) (4 equiv.), PdCl2(dppf) (0.18 equiv.), and 1,1Ј-
Biaryl Linear Peptide 6a: Starting from resin Boc-Tyr(3-BPin,SEM)-
Leu-Leu-Rink-MBHA (1a, 100 mg), the Suzuki–Miyaura reaction
was performed following the General Procedure using 4-iodo-
benzene as the aryl halide. After the reaction was finished, acido-
lytic cleavage of an aliquot of the biaryl peptidyl resin gave 6a in
80% purity. Elution with H2O/MeOH/TFA (80:20:0.2) yielded pure
6a (7.5 mg, 34% yield). tR = 3.09 min (Method D). 1H NMR
(400 MHz, CD3OD): δ = 0.92–0.99 [m, 12 H, 4ϫ CH3(δ)-Leu],
1.53–1.74 [m, 6 H, 2 CH(γ)-Leu, 2 CH2(β)-Leu], 2.88–2.94 [m, 1
H, CH2(β)-Tyr], 3.25–3.34 [m, 1 H, CH2(β)-Tyr], 4.08 [dd, J = 4.4,
9.2 Hz, 1 H, CH(α)-Tyr], 4.41 [dd, J = 5.6, 10.0 Hz, 1 H, CH(α)-
Leu], 4.48 [dd, J = 6.4, 9.2 Hz, 1 H, CH(α)-Leu], 6.90 [d, J =
8.2 Hz, 1 H, CHarom-5], 7.10 [dd, J = 2.2, 8.2 Hz, 1 H, 6-Harom],
7.26 [d, J = 2.2 Hz, 1 H, 2-Harom], 7.29 [tt, J = 1.4, 8.4 Hz, 1 H,
4Ј-Harom], 7.39 [t, J = 8.4 Hz, 2 H, 3Ј-Harom, 5Ј-Harom], 7.58 [dt, J
= 1.4, 8.4 Hz, 2 H, 2Ј-Harom, 6Ј-Harom] ppm. 13C NMR (100 MHz,
CD3OD): δ = 21.96, 22.06, 23.42, 23.47 [4 CH3(δ)-Leu], 25.85,
25.91 [2 CH(γ)-Leu], 37.97 [CH2(β)-Tyr], 41.88, 42.21 [2 CH2(β)-
Leu], 52.79, 53.41 [2 CH(α)-Leu], 55.79 [CH(α)-Tyr], 117.68
bis(diphenylphosphanyl)ferrocene (dppf) (0.09 equiv.).
A thor-
oughly sonicated solution of KOAc (6 equiv.) in degassed anhy-
drous DMSO (20 mL/mg of resin) was then added, and the mixture
was heated at 80 °C for 8 h. Then, the resin was washed with
DMSO (6ϫ 1 min), MeOH (6ϫ 1 min), CH2Cl2 (6ϫ 1 min), and
Et2O (3ϫ 1 min). An aliquot of the resulting boronopeptidyl resin
was cleaved with TFA/H2O/TIS (95:2.5:2.5) whilst being stirred for
2 h at room temperature. Following TFA evaporation and Et2O
extraction, the crude peptide was dissolved in H2O/CH3CN, lyophi-
lized, analyzed by HPLC, and characterized by MS.
Boc-Tyr(3-BPin,SEM)-Leu-Leu-Rink-MBHA (1a): This peptidyl
resin was prepared starting from Boc-Tyr(3-I,SEM)-Leu-Leu-
Rink-MBHA (2a, 600 mg) following the General Method for solid-
phase Miyaura borylation. Acidolytic cleavage of an aliquot of this
peptidyl resin gave H-Tyr(3-BPin)-Leu-Leu-NH2 (3a, 23% purity)
and H-Tyr[3-B(OH)2]-Leu-Leu-NH2 (4a, 37% purity), resulting
from partial hydrolysis of the pinacol boronate during HPLC
[CHarom-5], 126.51 [Carom-1], 127.89 [CHarom-4Ј], 129.02 [CHarom
-
3Ј, CHarom-5Ј], 130.42 [CHarom-2Ј, CHarom-6Ј], 130.48 [CHarom-6],
130.54 [Carom-3], 132.83 [CHarom-2], 139.86 [Carom-1Ј], 155.24 [Ca-
rom-4], 169.88 [CO-Tyr], 174.10, 177.21 [2 CO-Leu] ppm. MS (ESI):
m/z = 483.1 [M + H]+. HRMS (ESI): calcd. for C27H39N4O4
483.2966; found 483.2978; calcd. for C27H38N4NaO4 505.2785;
found 505.2797.
analysis. tR
= 6.11 min (boronic acid), 7.12 min (boronate)
(Method B). HRMS (ESI): calcd. for C21H36BN4O6 451.2726;
found 451.2729; calcd. for C27H46BN4O6 533.3510; found
533.3511.
Boc-Tyr(3-BPin,Me)-Leu-Leu-Rink-MBHA (1b): This peptidyl
resin was prepared starting from Boc-Tyr(3-I,Me)-Leu-Leu-Rink-
MBHA (2b, 380 mg) following the General Method for solid-phase
Miyaura borylation. Acidolytic cleavage of an aliquot of this pepti-
dyl resin gave H-Tyr(3-BPin,Me)-Leu-Leu-NH2 (3b, 29% purity)
and H-Tyr[3-B(OH)2,Me]-Leu-Leu-NH2 (4b, 49% purity), re-
sulting from partial hydrolysis of the pinacol boronate during
HPLC analysis. tR = 6.28 min (boronic acid), 7.06 min (boronate)
(Method B). MS (ESI): m/z = 465.2 [MB(OH)2 + H]+, 547.3 [MBPin
+ H]+. HRMS (ESI): calcd. for C22H38BN4O6 465.2879; found
465.2897; calcd. for C28H48BN4O6 547.3666; found 547.3683; calcd.
for C28H47BN4NaO6 569.3486; found 569.3485.
Biaryl Linear Peptide 6b: Starting from resin Boc-Tyr(3-BPin,Me)-
Leu-Leu-Rink-MBHA (1b, 150 mg), the Suzuki–Miyaura reaction
was performed following the General Procedure using 4-iodo-
benzene as the aryl halide. After the reaction was finished, acido-
lytic cleavage of an aliquot of the biaryl peptidyl resin gave 6b in
92% purity. Elution with H2O/MeOH/TFA (60:40:0.2) yielded pure
6b (12.5 mg, 38% yield). tR = 7.31 min (Method B). 1H NMR
(400 MHz, CD3OD): δ = 0.92–0.99 [m, 12 H, 4 CH3(δ)-Leu], 1.53–
1.75 [m, 6 H, 2 CH(γ)-Leu, 2 CH2(β)-Leu], 2.95 [dd, J = 9.2,
14.4 Hz, 1 H, CH2(β)-Tyr], 3.25–3.34 [m, 1 H, CH2(β)-Tyr], 3.80
[s, 3 H, OCH3], 4.12 [dd, J = 4.4, 9.2 Hz, 1 H, CH(α)-Tyr], 4.41
[dd, J = 5.2, 9.6 Hz, 1 H, CH(α)-Leu], 4.48 [dd, J = 6.4, 8.4 Hz, 1
H, CH(α)-Leu], 7.06 [d, J = 8.2 Hz, 1 H, 5-Harom], 7.26 [dd, J =
2.4, 8.2 Hz, 1 H, 6-Harom], 7.28–7.32 [m, 2 H, 2-Harom, 4Ј-Harom],
7.38 [t, J = 8 Hz, 2 H, 3Ј-Harom, 5Ј-Harom], 7.51 [dt, J = 1.6, 8.4 Hz,
General Method for the Arylation of Linear Peptides by a Solid-
Phase Suzuki–Miyaura Reaction: A 5 mL quartz vial was charged
with the appropriate boronopeptidyl resin, the aryl halide or halo-
genated aromatic amino acid conveniently protected (5 equiv.),
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5

Job/Unit: O20832
/KAP1
Date: 13-09-12 17:00:18
Pages: 9
A. Afonso, O. Cussó, L. Feliu, M. Planas
FULL PAPER
2 H, 2Ј-Harom, 6Ј-Harom] ppm. 13C NMR (75 MHz, CD3OD): δ = 133.56 [Carom], 155.20 [Carom-2Ј, Carom-4], 170.10, 174.45 [CO]
21.95, 22.08, 23.44, 23.49 [4 CH3(δ)-Leu], 25.86, 25.91 [2 CH(γ)-
Leu], 37.92 [CH2(β)-Tyr], 41.90, 42.22 [2 CH2(β)-Leu], 52.76, 53.36
ppm. MS (ESI): m/z = 586.3 [M + H]+. HRMS (ESI): calcd. for
C30H44N5O7 586.3235; found 586.3220.
[2 CH(α)-Leu], 55.73 [CH(α)-Tyr], 56.13 [OCH3], 113.18 [CHarom
-
General Method for the Synthesis of 3-Iodotyrosylpeptidyl Resins:
Peptidyl resins were synthesized manually by the solid-phase
method using standard Fmoc chemistry. Fmoc-Rink-MBHA resin
(0.56 mmol/g) was used as solid support. Couplings of the corre-
sponding amino acids Fmoc-Leu-OH, Boc-Tyr(3-I,Me)-OH,[3d]
Boc-Tyr(3-I,SEM)-OH,[3d] or Fmoc-Lys(Boc)-OH (4 equiv.) were
performed using ethyl cyanoglyoxylate 2-oxime (4 equiv.) and
DIPCDI (4 equiv.) in DMF at room temperature for 1 h. The com-
pletion of the reactions was monitored by the Kaiser test.[11] Fmoc
group removal was achieved with piperidine/DMF (3:7, 2ϫ
10 min). The Boc group of the tyrosine residue was removed by
treatment with trimethylsilyl triflate (TMSOTf; 1 m in CH2Cl2) and
2,6-lutidine (1.5 m in CH2Cl2) at room temperature (2ϫ 30 min).[12]
After each coupling and deprotection step, the resin was washed
with DMF (6ϫ 1 min) and CH2Cl2 (3ϫ 1 min) and air-dried. Once
the peptide sequence was complete, the N-terminal Fmoc group
was removed and the trityl group was introduced using TrCl
(10 equiv.) and N,NЈ-diisopropylethylamine (DIEA) (10 equiv.) in
DMF at room temperature for 3 h. Then, the resin was washed
with DMF (6ϫ 1 min) and CH2Cl2 (3ϫ 1 min) and air-dried. An
aliquot of the resulting peptidyl resin was cleaved with TFA/H2O/
TIS (95:2.5:2.5) whilst being stirred for 2 h at room temperature.
Following TFA evaporation and Et2O extraction, the crude peptide
was dissolved in H2O/CH3CN, lyophilized, analyzed by HPLC, and
characterized by MS.
5], 127.63 [Carom-1], 128.04 [CHarom-4Ј], 128.94 [CHarom-3Ј,
CHarom-5Ј], 130.58 [CHarom-2Ј, CHarom-6Ј], 130.76 [CHarom-6],
132.65 [Carom-3], 132.83 [CHarom-2], 139.74 [Carom-1Ј], 157.65 [Ca-
rom-4], 169.77 [CO-Tyr], 174.12, 177.20 [2 CO-Leu] ppm. MS (ESI):
m/z = 497.2 [M + H]+. HRMS (ESI): calcd. for C28H41N4O4
497.3122; found 497.3118.
Biaryl Linear Peptide 6c: Starting from resin Boc-Tyr(3-BPin,SEM)-
Leu-Leu-Rink-MBHA (1a, 120 mg), the Suzuki–Miyaura reaction
was performed following the General Procedure using Boc-Phe(4-
I)-OMe[9] as the aryl halide. After the reaction was finished, acido-
lytic cleavage of an aliquot of the biaryl peptidyl resin gave the
corresponding methyl ester in 70% purity. tR = 6.17 min (Method
B). MS (ESI): m/z = 584.3 [M + H]+.
After hydrolysis, crude biaryl peptide 6c was obtained in 64% pu-
rity. Elution first with H2O/MeOH/TFA (90:10:0.2) in reverse
phase, and then with CH2Cl2/MeOH/AcOH (5:3:1) in normal
phase yielded pure 6c (14.4 mg, 44% yield). tR = 6.04 min (Method
B). 1H NMR (400 MHz, CD3OD): δ = 0.89–0.95 [m, 12 H, 4
CH3(δ)-Leu], 1.54–1.70 [m, 6 H, 2 CH(γ)-Leu, 2ϫ CH2(β)-Leu],
2.80–2.93 [m, 1 H, CH2(β)], 3.13–3.19 [m, 1 H, CH2(β)], 3.19–3.30
[m, 2 H, CH2(β)], 4.01–4.11 [m, 2 H, CH(α)-Tyr, CH(α)-Phe], 4.34–
4.45 [m, 2 H, 2 CH(α)-Leu], 6.86 [d, J = 8.0 Hz, 1 H, 5-Harom],
7.06–7.09 [m, 1 H, 6-Harom], 7.22 [d, J = 1.6 Hz, 1 H, 2-Harom],
7.31 [d, J = 8.0 Hz, 2 H, 3Ј-Harom, 5Ј-Harom], 7.57 [d, J = 8.0 Hz,
2 H, 2Ј-Harom, 6Ј-Harom] ppm. 13C NMR (100 MHz, CD3OD): δ =
20.51, 20.59, 21.97, 22.06 [4 CH3(δ)-Leu], 24.40, 24.48 [2 CH(γ)-
Leu], 35.87, 36.46 [CH2(β)-Phe, CH2(β)-Tyr], 40.40, 40.73 [2
CH2(β)-Leu], 52.08 [CH(α)-Leu], 54.25 [CH(α)-Phe, CH(α)-Tyr],
116.12 [CHarom-5], 125.17 [Carom-1], 128.42 [Carom-3], 128.75
[CHarom-3Ј, CHarom-5Ј], 129.33 [Carom-4Ј], 129.74 [CHarom-2Ј,
Tr-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-I,SEM)-Leu-Leu-Rink-MBHA:
This peptidyl resin was prepared following the General Method for
the synthesis of 3-iodotyrosylpeptidyl resins. Acidolytic cleavage of
an aliquot of this peptidyl resin gave H-Lys-Lys-Leu-Tyr(3-I)-Leu-
Leu-NH2 in 68% purity. tR = 17.86 min (Method A). MS (ESI):
m/z = 902.4 [M + H]+.
CHarom-6Ј], 130.22 [CHarom-6], 131.24 [CHarom-2], 138.05 [Carom
-
Tr-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-I,Me)-Leu-Leu-Rink-MBHA:
This peptidyl resin was prepared following the General Method for
the synthesis of 3-iodotyrosylpeptidyl resins. Acidolytic cleavage of
an aliquot of this peptidyl resin gave H-Lys-Lys-Leu-Tyr(3-I,Me)-
Leu-Leu-NH2 in 73% purity. tR = 18.94 min (Method A).
1Ј], 153.80 [Carom-4], 168.49, 170.30, 173.04 [4 CO] ppm. MS (ESI):
m/z = 570.3 [M + H]+. HRMS (ESI): calcd. for C30H44N5O6
570.3286; found 570.3277.
Biaryl Linear Peptide 6d: Starting from resin Boc-Tyr(3-BPin,SEM)-
Leu-Leu-Rink-MBHA (1a, 120 mg), the Suzuki–Miyaura reaction
was performed following the General Procedure using Boc-Tyr(3-
I,SEM)-OMe[3d] as the aryl halide. After the reaction was finished,
acidolytic cleavage of an aliquot of the biaryl peptidyl resin gave
the corresponding methyl ester in 61% purity. tR = 6.08 min
(Method B). MS (ESI): m/z = 600.3 [M + H]+.
General Method for Miyaura Borylation of the Above Hexapeptidyl
Resins: A 25 mL round-bottomed flask was charged with the corre-
sponding
3-iodotyrosylpeptidyl
resin,
B2Pin2
(4 equiv.),
PdCl2(dppf) (0.18 equiv.), and dppf (0.09 equiv.). A thoroughly
sonicated solution of KOAc (6 equiv.) in degassed anhydrous
DMSO (20 mL/mg of resin) was then added, and the mixture was
heated at 80 °C for 8 h. Then, the resin was washed with DMSO
(6ϫ 1 min), MeOH (6ϫ 1 min), CH2Cl2 (6ϫ 1 min), and Et2O
(3ϫ 1 min). An aliquot of the resulting boronopeptidyl resin was
cleaved with TFA/H2O/TIS (95:2.5:2.5) whilst being stirred for 2 h
at room temperature. Following TFA evaporation and Et2O extrac-
tion, the crude peptide was dissolved in H2O/CH3CN, lyophilized,
analyzed by HPLC, and characterized by MS.
After hydrolysis, crude biaryl peptide 6d was obtained in 61% pu-
rity. Elution first with H2O/MeOH/TFA (90:10:0.2) in reverse
phase, and then with CH2Cl2/MeOH/AcOH (5:3:1) in normal
phase yielded pure 6d (12.8 mg, 55% yield). tR = 5.96 min (Method
B). 1H NMR (400 MHz, CD3OD): δ = 0.92–0.98 [m, 12 H, 4
CH3(δ)-Leu], 1.55–1.75 [m, 6 H, 2 CH(γ)-Leu, 2 CH2(β)-Leu],
2.89–2.95 [m, 1 H, CH2(β)-Tyr], 3.11 [dd, J = 8.4, 14.8 Hz, 1 H,
CH2(β)-Tyr], 3.25–3.37 [m, 2 H, CH2(β)-Tyr], 4.10 [dd, J = 4.4,
Tr-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-BPin,SEM)-Leu-Leu-Rink-MBHA:
9.2 Hz, 1 H, CH(α)-Tyr], 4.18–4.21 [m, 1 H, CH(α)-Tyr], 4.39 [dd, This peptidyl resin was prepared starting from Tr-Lys(Boc)-Lys-
J = 5.2, 10.0 Hz, 1 H, CH(α)-Leu], 4.47 [t, J = 7.6 Hz, 1 H, CH(α)- (Boc)-Leu-Tyr(3-I,SEM)-Leu-Leu-Rink-MBHA following the Ge-
Leu], 6.93 [dd, J = 5.2, 8.8 Hz, 2 H, 3Ј-Harom, 5-Harom], 7.15–7.18 neral Method for solid-phase Miyaura borylation. Acidolytic cleav-
[m, 4 H, 2-Harom, 6-Harom, 4Ј-Harom, 6Ј-Harom] ppm. 13C NMR age of an aliquot of this resin gave H-Lys-Lys-Leu-Tyr(3-BPin)-
(100 MHz, CD3OD): δ = 21.95, 22.05, 23.41, 23.52 [4 CH3(δ)-Leu],
Leu-Leu-NH2 (27% purity) and H-Lys-Lys-Leu-Tyr[3-B(OH)2]-
25.85, 25.94 [2 CH(γ)-Leu], 36.57, 37.86 [2 CH2(β)-Tyr], 41.86, Leu-Leu-NH2 (33% purity), resulting from partial hydrolysis of the
42.20 [2 CH2(β)-Leu], 52.86, 53.44 [CH(α)-Leu], 55.82 [2 CH(α)-
Tyr], 117.50, 117.57 [CHarom-5, CHarom-3Ј], 126.85, 127.43, 127.48
pinacol boronate during HPLC analysis. tR = 16.80 (boronic acid),
20.53 (boronate) (Method A). MS (ESI): m/z = 820.5 [MB(OH)2
+
[Carom], 131.65 [CHarom-2, CHarom-6, CHarom-4Ј, CHarom-6Ј], H]+, 902.4 [MBPin + H]+.
6
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O20832
/KAP1
Date: 13-09-12 17:00:18
Pages: 9
Solid-Phase Synthesis of Biaryl Cyclic Peptides
Tr-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-BPin,Me)-Leu-Leu-Rink-MBHA:
This peptidyl resin was prepared starting from Tr-Lys(Boc)-Lys-
(Boc)-Leu-Tyr(3-I,Me)-Leu-Leu-Rink-MBHA following the Gene-
ral Method for solid-phase Miyaura borylation. Acidolytic cleavage
of an aliquot of this peptidyl resin gave H-Lys-Lys-Leu-Tyr[3-
B(OH)2,Me]-Leu-Leu-NH2 (41% purity), resulting from hydrolysis
of the pinacol boronate during HPLC analysis. tR = 17.17 (boronic
acid) (Method A). MS (ESI): m/z = 834.5 [MB(OH)2 + H]+, 856.5
[MB(OH)2 + Na]+, 916.5 [MBPin + H]+, 938.4 [MBPin + Na]+.
(boronic acid) (Method A). MS (ESI): m/z = 1137.3 [MB(OH)2 +
H]+, 1219.1 [MBPin + H]+.
General Method for the Cyclization by a Solid-Phase Suzuki–Mi-
yaura Reaction – Synthesis of Biaryl Cyclic Peptides 8b and 8d: A
5 mL quartz vial was charged with the linear precursor incorporat-
ing the borono and iodo functionalities, Pd2(dba)3 (0.2 equiv.),
SPhos (0.4 equiv.), and KF (4 equiv.). Thoroughly degassed DME/
EtOH/H2O (9:9:2, 1–1.9 mL) was then added under nitrogen. The
reaction mixture was heated at 120 °C under microwave irradiation
for 30 min. After this time, the resin was washed with DMF (6ϫ
1 min), EtOH (6ϫ 1 min), CH2Cl2 (6ϫ 1 min), and Et2O (3ϫ
1 min). The resulting biaryl cyclic peptidyl resin was cleaved with
TFA/H2O/TIS (95:2.5:2.5) whilst being stirred for 2 h at room tem-
perature. Following TFA evaporation and Et2O extraction, the
crude peptide was dissolved in H2O/CH3CN, lyophilized, analyzed
by HPLC, and purified by reverse-phase column chromatography.
Biaryl cyclic peptides were characterized by MS and NMR spec-
troscopy.
General Method for the Synthesis of the Linear Precursors 7a–d:
The corresponding boronopeptidyl resin was treated with TFA/
H2O/CH2Cl2 (0.2:1:98.8, 2ϫ 1 min, 1ϫ 20 min), and then washed
with DMF (3 ϫ 1 min), DIEA/CH2Cl2 (1:19) (3 ϫ 1 min), and
DMF (3 ϫ 1 min). The corresponding halogenated amino acid
Boc-Phe(4-I)-OH,[9] Boc-Tyr(3-I,Me)-OH[3d] or Boc-Tyr(3-I,SEM)-
OH[3d] was coupled using ethyl cyanoglyoxylate 2-oxime (3 equiv.),
DIPCDI (3 equiv.) in DMF at room temperature for 3 h. The resin
was washed with DMF (6ϫ 1 min) and CH2Cl2 (3ϫ 1 min) and
air-dried. The completion of the reaction was monitored by the
Kaiser test.[11] An aliquot of the resulting peptidyl resin was cleaved
with TFA/H2O/TIS (95:2.5:2.5) whilst being stirred for 2 h at room
temperature. Following TFA evaporation and Et2O extraction, the
crude peptide was dissolved in H2O/CH3CN, lyophilized, analyzed
by HPLC, and characterized by MS.
Biaryl Cyclic Peptide 8b: Starting from resin Boc-Phe(4-I)-Lys-
(Boc)-Lys(Boc)-Leu-Tyr(3-BPin,Me)-Leu-Leu-Rink-MBHA (7b,
134 mg), Suzuki–Miyaura cyclization followed by acidolytic cleav-
age gave biaryl cyclic peptide 8b (47% purity). Elution with H2O/
MeOH/TFA (60:40:0.2) yielded pure 8b (6.9 mg, 16% yield). tR
=
6.51 min (Method B). 1H NMR (300 MHz, CD3OD): δ = 0.87–
0.97 [m, 18 H, 6 CH3(δ)-Leu], 1.29–1.72 [m, 21 H, 3 CH(γ)-Leu, 3
CH2(β)-Leu, 2 CH2(β)-Lys, 2 CH2(γ)-Lys, 2 CH2(δ)-Lys], 2.81–2.91
[m, 4 H, 2 CH2(ε)-Lys], 3.06–3.18 [m, 4 H, CH2(β)-Tyr, CH2(β)-
Phe], 3.79 [s, 3 H, OCH3], 4.22–4.56 [m, 7 H, CH(α)-Tyr, CH(α)-
Phe, 3 CH(α)-Leu, 2 CH(α)-Lys], 6.99 [d, J = 8.7 Hz, 1 H, 5-Harom],
7.16 [dd, J = 1.6, 8.7 Hz, 1 H, 6-Harom], 7.32 [d, J = 8.1 Hz, 2 H,
3Ј-Harom, 5Ј-Harom], 7.44 [d, J = 1.6 Hz, 1 H, 2-Harom], 7.65 [d, J
= 8.1 Hz, 2 H, 2Ј-Harom, 6Ј-Harom], 7.78–8.03 (m, 4 H, NH) ppm.
MS (ESI): m/z = 468.3 [M + 2H]2+, 935.7 [M + H]+.
Boc-Phe(4-I)-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-BPin,SEM)-Leu-Leu-
Rink-MBHA (7a): This peptidyl resin was prepared starting from
Tr-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-BPin,SEM)-Leu-Leu-Rink-
MBHA following the General Method using Boc-Phe(4-I)-OH as
halogenated amino acid. Acidolytic cleavage of an aliquot of the
resulting peptidyl resin gave H-Phe(4-I)-Lys-Lys-Leu-Tyr[3-B-
(OH)2]-Leu-Leu-NH2 (30% purity), resulting from hydrolysis of
the pinacol boronate during HPLC analysis. tR = 15.11 min
(Method C). MS (ESI): m/z = 1093.3 [MB(OH)2 + H]+, 1175.1
[MBPin + H]+.
Biaryl Cyclic Peptide 8d: Starting from resin Boc-Tyr(3-I,Me)-Lys-
(Boc)-Lys(Boc)-Leu-Tyr(3-BPin,Me)-Leu-Leu-Rink-MBHA (7d,
123 mg), Suzuki–Miyaura cyclization followed by acidolytic cleav-
age gave biaryl cyclic peptide 8d (33% purity). Elution with H2O/
Boc-Phe(4-I)-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-BPin,Me)-Leu-Leu-
Rink-MBHA (7b): This peptidyl resin was prepared starting from
Tr-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-BPin,Me)-Leu-Leu-Rink-MBHA
following the General Method using Boc-Phe(4-I)-OH as haloge-
nated amino acid. Acidolytic cleavage of an aliquot of the resulting
peptidyl resin gave H-Phe(4-I)-Lys-Lys-Leu-Tyr[3-B(OH)2,Me]-
Leu-Leu-NH2 (51% purity), resulting from hydrolysis of the pin-
acol boronate during HPLC analysis. tR = 15.41 min (Method C).
MS (ESI): m/z = 1107.4 [MB(OH)2 + H]+, 1189.3 [MBPin + H]+.
MeOH/TFA (60:40:0.2) yielded pure 8d (9 mg, 22% yield). tR
=
6.59 min (Method B). 1H NMR (300 MHz, CD3OD): δ = 0.86–
0.98 [m, 18 H, 6 CH3(δ)-Leu], 1.29–1.81 [m, 21 H, 3 CH(γ)-Leu, 3
CH2(β)-Leu, 2 CH2(β)-Lys, 2 CH2(γ)-Lys, 2 CH2(δ)-Lys], 2.70–2.92
[m, 4 H, 2 CH2(ε)-Lys], 3.07–3.23 [m, 4 H, 2 CH2(β)-Tyr], 3.73 [s,
2.6 H, OCH3], 3.74 [s, 0.4 H, OCH3], 3.77 [s, 2.6 H, OCH3], 3.79
[s, 0.4 H, OCH3], 4.15–4.50 [m, 7 H, 2 CH(α)-Tyr, 3 CH(α)-Leu, 2
CH(α)-Lys], 6.88–7.07 [m, 2 H, 3Ј-Harom, 5-Harom], 7.11–7.33 [m, 3
H, 2-Harom, 4Ј-Harom, 6-Harom], 7.75 [s, 1 H, 6Ј-Harom], 7.82–8.19
[m, 1 H, NH] ppm. MS (ESI): m/z = 965.7 [M + H]+, 987.7 [M +
Na]+.
Boc-Tyr(3-I,SEM)-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-BPin,SEM)-Leu-
Leu-Rink-MBHA (7c): This peptidyl resin was prepared starting
from Tr-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-BPin,SEM)-Leu-Leu-Rink-
MBHA following the General Method using Boc-Tyr(3-I,SEM)-
OH as halogenated amino acid. Acidolytic cleavage of an aliquot
of the resulting peptidyl resin gave H-Tyr(3-I)-Lys-Lys-Leu-Tyr(3-
BPin)-Leu-Leu-NH2 (26 % purity) and H-Tyr(3-I)-Lys-Lys-Leu-
Tyr[3-B(OH)2]-Leu-Leu-NH2 (36% purity), resulting from partial
Supporting Information (see footnote on the first page of this arti-
cle): Copies of HPLC chromatograms and mass spectra of com-
1
pounds. Copies of H and 13C NMR spectra of 6a–d, 8b, and 8d.
hydrolysis of the pinacol boronate during HPLC analysis. tR
=
17.69 min (boronic acid), 20.88 (boronate) (Method A). MS (ESI):
m/z = 1109.3 [MB(OH)2 + H]+, 1191.3 [MBPin + H]+.
Acknowledgments
Boc-Tyr(3-I,Me)-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-BPin,Me)-Leu-
Leu-Rink-MBHA (7d): This peptidyl resin was prepared starting
from Tr-Lys(Boc)-Lys(Boc)-Leu-Tyr(3-BPin,Me)-Leu-Leu-Rink-
MBHA following the General Method using Boc-Tyr(3-I,Me)-OH
as halogenated amino acid. Acidolytic cleavage of an aliquot of
the resulting peptidyl resin gave H-Tyr(3-I,Me)-Lys-Lys-Leu-Tyr[3-
B(OH)2,Me]-Leu-Leu-NH2 (45% purity), resulting from hydrolysis
of the pinacol boronate during HPLC analysis. tR = 18.94 min
A. A. thanks the Ministerio de Ciencia e Innovación (MICINN)
of Spain for a predoctoral fellowship. This work was supported by
grant AGL2009-13255-C02-02/AGR from MICINN. We are also
grateful to the Serveis Tècnics de Recerca of the University of Gi-
rona.
[1] L. Feliu, M. Planas, Int. J. Pept. Res. Ther. 2005, 11, 53–97.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
7

Job/Unit: O20832
/KAP1
Date: 13-09-12 17:00:18
Pages: 9
A. Afonso, O. Cussó, L. Feliu, M. Planas
FULL PAPER
[2] a) A.-C. Carbonnelle, J. Zhu, Org. Lett. 2000, 2, 3477–3480; b)
M. Bois-Choussy, P. Cristau, J. Zhu, Angew. Chem. 2003, 115,
4370–4373; Angew. Chem. Int. Ed. 2003, 42, 4238–4241; c) S.
Kotha, K. Lahiri, Biopolymers 2003, 69, 517–528; d) J. C. Yob-
urn, D. L. Van Vranken, Org. Lett. 2003, 5, 2817–2820; e) R.
Lépine, J. Zhu, Org. Lett. 2005, 7, 2981–2984; f) S. Kotha, K.
Lahiri, Eur. J. Org. Chem. 2007, 1221–1236; g) T. C. Roberts,
P. A. Smith, R. T. Cirz, F. E. Romesberg, J. Am. Chem. Soc.
2007, 129, 15830–15838; h) J. Dufour, L. Neuville, J. Zhu, Syn-
lett 2008, 2355–2359; i) H. Waldmann, Y.-P. He, H. Tan, L.
Arve, H.-D. Arndt, Chem. Commun. 2008, 5562–5564; j) V.
Böhrsch, C. P. R. Hackenberger, ChemCatChem 2010, 2, 243–
245; k) Z. Wang, M. Bois-Choussy, Y. Jia, J. Zhu, Angew.
Chem. 2010, 122, 2062–2066; Angew. Chem. Int. Ed. 2010, 49,
[4] A. Afonso, L. Feliu, M. Planas, Tetrahedron 2011, 67, 2238–
2245.
[5] F.-M. Meyer, J. C. Collins, B. Borin, J. Bradow, S. Liras, C.
Limberakis, A. M. Mathiowetz, L. Philippe, D. Price, K. Song,
K. James, J. Org. Chem. 2012, 77, 3099–3114.
[6] A. Afonso, C. Rosés, M. Planas, L. Feliu, Eur. J. Org. Chem.
2010, 1461–1468.
[7] a) N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457–2483; b)
S. Kotha, K. Lahiri, D. Kashinath, Tetrahedron 2002, 58, 9633–
9695; c) D. G. Hall Boronic acids vol 1–2, Wiley–VCH Verlag,
Weinheim, 2011.
[8] a) M. J. Schulz, S. J. Coats, D. J. Hlasta, Org. Lett. 2004, 6,
3265–3268; b) D. Duran, N. Wu, B. Mao, J. Xu, J. Liq. Chro-
matogr. Relat. Technol. 2006, 29, 661–672.
2018–2022; l) M. Berwe, W. Jöntgen, J. Krüger, Y. Cancho- [9] H. Lei, M. S. Stakes, K. Herath, J. Lee, A. W. Shwabacher, J.
Grande, T. Lampe, M. Michels, H. Paulsen, S. Raddatz, S. Wei-
gand, Org. Process Res. Dev. 2011, 15, 1348–1357.
Org. Chem. 1994, 59, 4206–4210.
[10] M. Prieto, S. Mayor, P. Lloyd-Williams, E. Giralt, J. Org.
Chem. 2009, 74, 9202–9205.
[11] E. Kaiser, R. L. Colescott, C. D. Bossinger, P. Cook, Anal. Bio-
chem. 1970, 34, 595–598.
[3] a) T. E. Nielsen, S. Le Quement, M. Meldal, Tetrahedron Lett.
2005, 46, 7959–7962; b) B. E. Haug, W. Stensen, J. S. Svendsen,
Bioorg. Med. Chem. Lett. 2007, 17, 2361–2364; c) N.-D. Doan,
S. Bourgault, M. Létourneau, A. Fournier, J. Comb. Chem.
2008, 10, 44–51; d) V. Cerezo, M. Amblard, J. Martinez, P.
Verdié, M. Planas, L. Feliu, Tetrahedron 2008, 64, 10538–
10545.
[12] A. J. Zhang, D. H. Russell, J. P. Zhu, K. Burguess, Tetrahedron
Lett. 1998, 39, 7439–7442.
Received: June 21, 2012
Published Online: ᭿
8
www.eurjoc.org
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O20832
/KAP1
Date: 13-09-12 17:00:18
Pages: 9
Solid-Phase Synthesis of Biaryl Cyclic Peptides
Biaryl Cyclic Peptides
A. Afonso, O. Cussó, L. Feliu,*
M. Planas* ....................................... 1–9
Solid-Phase Synthesis of Biaryl Cyclic
Peptides Containing a 3-Aryltyrosine
Keywords: Synthetic methods / Solid-phase
synthesis / Microwave chemistry / Cycli-
zation / Cross-coupling / Macrocycles /
Peptides / Biaryls / Boronates
Biaryl cyclic peptides containing a Phe–Tyr
or a Tyr–Tyr linkage have been synthesized
by solid-phase Miyaura borylation and mi-
crowave-assisted Suzuki–Miyaura macro-
cyclization.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
9