The design and synthesis of dansyl-containing cyclic pseudopeptides

Article abstract of DOI:10.1002/ejoc.200800248

Six cyclic pseudopeptides with the general formula cyclo-(LAA-D-Oxd) _n [where AA is an ?-amino acid, D-Oxd is trans-(4R,5S)-4- carboxy-5-methyloxazolidin-2-one and n = 3, 4] have been designed and efficiently synthesized in the liquid phase in good overall yields. The crucial step is the macrocyclization, which always occurs in satisfactory yields regardless of the cycle dimension and the nature of various functional groups in the side-chain. Moreover, a dansyl (dansyl = 5-dimethylamino-1- naphthylsulfonyl) unit was introduced into the side-chain with the aim of preparing a labelled cyclopeptide that can be easily located in a biological environment. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200800248

FULL PAPER
DOI: 10.1002/ejoc.200800248
The Design and Synthesis of Dansyl-Containing Cyclic Pseudopeptides
Gaetano Angelici,[a] Roger Tresanchez Carrera,[a] Gianlugi Luppi,[a] and
Claudia Tomasini*[a]
Keywords: Chiral pool / Chromophores / Coupling reactions / Cyclization / Peptides
Six cyclic pseudopeptides with the general formula cyclo-(
L
-
tional groups in the side-chain. Moreover, a dansyl (dansyl
= 5-dimethylamino-1-naphthylsulfonyl) unit was introduced
into the side-chain with the aim of preparing a labelled cy-
clopeptide that can be easily located in a biological environ-
ment.
AA- -Oxd)n [where AA is an α-amino acid, -Oxd is trans-
D
D
(4R,5S)-4-carboxy-5-methyloxazolidin-2-one and n = 3, 4]
have been designed and efficiently synthesized in the liquid
phase in good overall yields. The crucial step is the macrocy-
clization, which always occurs in satisfactory yields regard-
less of the cycle dimension and the nature of various func-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
(4R,5S)-4-carboxy-5-methyloxazolidin-2-one unit] as an
isoster for the -proline unit alternating with a generic -
amino acid (Figure 1). Indeed, cyclic ,-α-peptides are the
archetypical members of a growing class of organic tubular
macromolecular structures that have a plethora of promis-
ing potential applications,[6] so an efficient method for the
preparation of these compounds is highly desirable.
Introduction
Cyclic peptides have been extensively studied because
they provide ideal scaffolds for exploring structure–activity
relationships in ligand–receptor interactions[1] as cyclization
favours the mimicking of turns and the formation of intra-
molecular hydrogen bonds, and increases membrane perme-
ability by eliminating charged termini. Thus, many pharma-
cologically important natural products are constrained by
macrocyclization, from the cyclic non-ribosomal peptides
(NRP) tyrocidine A and cyclosporin to the polyketide (PK)
antibiotic erythromycin, and the hybrid peptide/polyketide
drugs rapamycin and epothilone.[2]
Furthermore several azole-based cyclic peptides have
been isolated from marine organisms, fungi and algae.
These molecules contain oxazole or triazole heterocyclic
moieties, display interesting antitumour and antidrug resis-
tance properties and are potential metal-ion chelators.[3]
Thus, heterocycle-containing cyclic pseudopeptides are
good candidates for mimicking the shape and pharmaco-
logical activity of these interesting natural products. For in-
stance, systematic studies on the complexes formed between
cyclic peptides and bivalent cations have been performed by
Blout and co-workers with cyclo-(-Pro-Gly)3 and cyclo-(-
Pro-Gly)4,[4] which are very flexible molecules.
Figure 1. General chemical structure of the cyclic pseudopeptides
reported in this study; X is a general side-chain.
The introduction of the Oxd moiety can be very useful
in the preparation of rigid cyclopeptides because, as we have
demonstrated, the Oxd moiety imparts rigidity to a pseudo-
peptide chain due to the presence of the oxazolidin-2-one
endocyclic carbonyls, which force the Oxd carbonyl groups
exclusively into the trans conformation.[5] This effect can be
seen by analysis of the CHα proton chemical shift of the
nearby amino acid, which is always very deshielded with a
chemical shift that is above 5 ppm, whereas the normal po-
sition is between 4 and 4.5 ppm (Figure 2).
Therefore the preparation of cyclic pseudopeptides with
the general formula cyclo-(-AA--Oxd)n (where AA is a
generic α-amino acid and n = 3, 4; Figure 1) was devised.
Our synthetic approach is quite general and is compatible
with macrocycles of different sizes (n = 3, 4) and with several
side-chains. Hence this general scaffold can be decorated
with different chemical functions simply by changing the
amino acid unit: as an example, we have prepared a cyclo-
hexapeptide that contains the fluorescent dansyl (dansyl =
As a part of a project directed towards the study of pseu-
dopeptides containing pseudoproline moieties,[5] we wish to
show here the synthesis of six cyclopeptides of different
shape, all containing the -Oxd unit [-Oxd = trans-
[a] Dipartimento di Chimica “G. Ciamician” – Alma Mater Stu-
diorum Università di Bologna,
Via Selmi 2, 40126 Bologna, Italy
Fax: +39-051-02099456
E-mail: claudia.tomasini@unibo.it
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Dansyl-Containing Cyclic Pseudopeptides
The pseudopeptide Boc-(-Ala--Oxd)4-OBn was fully
deprotected by hydrogenolysis with H2 in the presence of
Pd/C (10%) in methanol and then treated with trifluoro-
acetic acid (TFA) to obtain the amine 1a as its trifluoro-
acetic salt. The reactions afforded the desired compound
in 97% overall yield. Then the salt 1a was cyclized to the
corresponding cycle 2a. For this reaction several coupling
agents, such as O-(7-azabenzotriazol-1-yl)-N,N,NЈ,NЈ-
tetramethyluronium hexafluorophosphate (HATU),[10] O-
Figure 2. Preferred conformation for an -AA-D-Oxd unit with the
preferential trans conformation of the imide moiety, which ac-
counts for the anomalous chemical shift of the amino acid CHα
proton.
(benzotriazol-1-yl)-N,N,NЈ,NЈ-tetramethyluronium
fluorophosphate (HBTU) and O-(6-chlorobenzotriazol-1-
yl)-N,N,NЈ,NЈ-tetramethyluronium hexafluorophosphate
hexa-
(HCTU), were used in the presence of different bases, such
as triethylamine (TEA), diisopropylethylamine (DIEA) or
1,8-diazobicyclo[5.4.0]undec-7-ene (DBU), always using
1 equiv. of coupling agent and 3 equiv. of base. The solvent
of choice was dry acetonitrile, which is polar enough to
solubilize all the reagents. If wet acetonitrile was employed,
the reaction yield diminished. Among all the combinations
of coupling agents and bases tested, the best results were
obtained by employing HATU and TEA to give the desired
cyclo-(-Ala--Oxd)4 (2a).[11] Indeed, if HATU and DBU
were used, the reaction yield was poor due to the immediate
decomposition of the uronium agent. On the other hand, if
HCTU and TEA were employed, the reaction was very slow
and the yield poor due to their low reactivity. Finally, the
concentration of the reagents was studied, and the best con-
centration of pseudopeptide to avoid intermolecular coup-
lings was about 5 m (Table 1).
DANS
=
5-dimethylamino-1-naphthylsulfonyl) unit,[7]
which can be used to locate the molecule in a biological
environment.[8] Indeed, Kubik and co-workers recently
demonstrated that the production of a cyclic structure con-
taining fluorescent moieties allows the binding event of a
synthetic receptor to be combined with the change of an
easily measurable receptor property to produce a chemo-
sensor.[9]
Results and Discussion
The synthesis of cyclic pseudopeptides always requires
good reaction conditions to be found for the cyclization
step, so we have tested this reaction both for the formation
of cycles containing eight amino acid residues (24 atoms)
and also for smaller cycles containing six amino acid units
(18 atoms). The linear pseudopeptide preparations and the
cyclizations were performed in the liquid phase.
First we synthesized the two cyclic pseudopeptides that
contain eight amino acids units, 2a and 2b (Scheme 1). The
synthesis of the open chain Boc-(-Ala--Oxd)4-OBn (not
shown) has already been reported and was performed by
the addition of one -Ala--Oxd unit to the other.[5a] This
approach allowed us to halve the coupling steps for the
oligomer synthesis and is applicable to units containing any
sort of amino acid, including β-amino acids.
Table 1. Reaction yields of the cyclization reactions of H-(-Ala--
Oxd)4-OH·CF3CO2H (1a) performed for 45 min at room tempera-
ture in dry acetonitrile.
Entry Coupling reagent Base (3 equiv.) Conc. [m] % Yield
(1 equiv.)
1
2
3
4
5
6
7
8
HBTU
HBTU
HCTU
HATU
HATU
HATU
HATU
HATU
DBU
TEA
TEA
DBU
DBU
DIEA
TEA
TEA
10
10
10
10
5
5
10
5
10
–
5
–
10
24
32
40
Furthermore the purification step proved to be complex
because 2a is very polar and water-soluble. Therefore the
reaction mixture was concentrated to remove the volatiles
and the residue was washed with small amounts of acetoni-
trile, purified with preparative HPLC and finally obtained
in pure form in 40% yield. A similar approach allowed us
to prepare cyclo-(-Phe--Oxd)4 (2b) in which -alanine was
replaced by -phenylalanine in the pseudopeptide chain: the
cyclization step afforded the desired compound 2b, which
was insoluble in several solvents. Thus, it was purified sim-
ply by washing the mixture several times with acetonitrile.
A dilute solution of 2b was analyzed by HPLC, which
showed that the compound was pure and so its purification
by preparative HPLC could be avoided.
Scheme 1. Synthesis of 2a,b. Reagents and conditions: (i) H2, Pd/C
(10%), MeOH, room temp., 12 h; (ii) TFA (18 equiv.), dry CH2Cl2,
room temp., 4 h; (iii) HATU (1.1. equiv.), TEA (3 equiv.), dry
CH3CN, room temp., 45 min.
Then the formation of the cycle 4 containing 18 atoms
was tested by the cyclization of the salt [H-(-Ala--Oxd)3-
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G. Angelici, R. Tresanchez Carrera, G. Luppi, C. Tomasini
FULL PAPER
OH]+·CF3CO2 (3), which was obtained by deprotection of in 73% yield Boc--Lys(2Cl-Z)--Oxd-OBn (6), which was
Boc-(-Ala--Oxd)3-OBn following the previously reported then deprotected at the Cα amino group to give 7, which
protocol (Scheme 2). Also, in this case the cyclization step was then coupled with Boc-(-Ala--Oxd)2-OH.[5a] The lin-
required some attention and the best reaction conditions ear pseudopeptide Boc-(-Ala--Oxd)2--Lys(2Cl-Z)--
had to be found. The best coupling reagents again turned Oxd-OBn (8) was then deprotected at both ends to remove
out to be HATU and TEA in dry acetonitrile. The mixture the Boc and benzyl moieties. The hydrogenolysis step to
was stirred at room temperature for 45 min and then con- prepare the acid 9 required some attention as only the OBn
centrated. The residue was washed with small amounts of group was to be cleaved with the 2Cl-Z group left un-
acetonitrile, purified by preparative HPLC and finally ob- touched. The previously reported reaction conditions (H2
–
tained in pure form in 50% yield.
and 10% Pd/C in methanol) resulted in the cleavage of both
the OBn and 2Cl-Z groups. Thus, several reaction condi-
tions were checked, including the use of other palladium
catalysts such as PdO. The best results were obtained by
replacing the methanol with ethyl acetate and stopping the
reaction after 2 h: the more resistant 2Cl-Z group was un-
touched, whereas the OBn group was totally cleaved. The
cyclization was performed under the previously reported
conditions (HATU and TEA in dry acetonitrile at room
temperature) and the cycle 5a was obtained in pure form in
35% yield after purification by HPLC chromatography.
Then cyclo-[(-Ala--Oxd)2--Lys--Oxd] (5b) containing
the free lysine unit was prepared by hydrogenolysis of 5a
with H2 on 10% Pd/C in methanol without affecting any
other group of the cycle.
Scheme 2. Synthesis of 4. Reagents and conditions: (i) H2, Pd/C
(10%), MeOH, room temp., 12 h; (ii) TFA (18 equiv.), dry CH2Cl2,
room temp., 4 h; (ii) HATU (1.1. equiv.), TEA (3 equiv.), dry
CH3CN, room temp., 45 min.
By using the same approach, three additional cyclic pseu-
dopeptides were synthesized, replacing one -Ala unit with
an -Lys unit that has been further derivatized (Figure 3).
This variation was introduced with the aim of checking the
stability of this class of molecule both in the presence of a
polar moiety and in the presence of a large side-chain like
the dansyl (DANS) unit.
Scheme 3. Synthesis of 5b. Reagents and conditions: (i) HBTU
(1 equiv.), DBU (2 equiv.), dry CH3CN, room temp., 45 min; (ii)
TFA (18 equiv.), dry CH2Cl2, room temp., 3 h; (iii) HBTU
(1 equiv.), TEA (3 equiv.), dry CH3CN, room temp., 45 min; (iv)
H2, Pd/C (10%), AcOEt, room temp., 2 h; (v) TFA (18 equiv.) dry
CH2Cl2, room temp., 4 h; (vi) HATU (1 equiv.), TEA (3 equiv.),
room temp., 45 min; (vii) H2, Pd/C (10%), MeOH, room temp.,
12 h.
Figure 3. Chemical structure of the cyclic pseudopeptides 5a–c.
To introduce a free lysine unit into the cyclic pseudopep-
tide, the side-chain of the lysine was initially protected with
the 2-chlorobenzyloxycarbonyl (2-chlorobenzyloxycarbonyl
Finally, the cyclic pseudopeptide cyclo-[(-Ala--Oxd)2-
= 2Cl-Z) group (Scheme 3). This compound is commer- -Lys(DANS)--Oxd] (5c) was prepared by a similar strat-
cially available and was coupled with -Oxd-OBn to obtain egy. In this case the dansyl group could be introduced into
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Eur. J. Org. Chem. 2008, 3552–3558

Dansyl-Containing Cyclic Pseudopeptides
the Boc--Lys-OH unit or into the cycle 5b. We chose to
introduce the dansyl unit at the beginning of the synthesis
as it could be used to locate the products in the reaction
mixtures. Thus, Boc--Lys-OH was treated with dansyl
chloride in the presence of a base. To obtain the desired
Boc--Lys(DANS)-OH (8) in a satisfactory yield, several re-
action conditions were tested and are reported in Table 2.
The best results were obtained with DBU (4 equiv.) in
dichloromethane.[12] Any attempt to further increase the
yield by using more equivalents of base or a longer reaction
time failed.
Conclusions
Six cyclic pseudopeptides, two containing eight amino
acid units and four containing six amino acid units, were
prepared in the liquid phase in good overall yields. The cy-
clization step required some attention and the best reaction
conditions were found using HATU and TEA as reagents
in a 5 m solution of dry acetonitrile at room temperature.
All the pseudopeptides contained an alternating sequence
of -amino acid and -Oxd, a proline analogue that imparts
rigidity to the cyclic system. We have demonstrated that this
synthetic method is compatible with different side-chains
and cycle sizes so that it can be used to synthesize several
molecules of the cyclo-(-AA--Oxd)n (n = 3, 4) series in
good overall yields.
Table 2. Reaction yields for the reactions of Boc--Lys-OH with
dansyl chloride for 16 h at room temperature.
Entry
Equiv. of base
Solvent
% Yield
1
2
3
4
5
DIEA (4)/DMAP (0.5)
DIEA (4)/DMAP (0.5)
DBU (4)
DBU (4)
DBU (4)
CH2Cl2
DMF
CH2Cl2
DMF
–
21
73
40
63
Experimental Section
General: Routine NMR spectra were recorded with spectrometers
at 400, 300 or 200 MHz (1H NMR) and 100, 75 or 50 MHz (13C
NMR). Chemical shifts are reported in δ values relative to the sol-
CH3CN
1
vent peak of CHCl3, set at δ = 7.27 ppm. High quality H NMR
spectra were recorded with a Varian Inova 600 spectrometer. Mea-
surements were carried out in CDCl3, CD3OD, [D6]acetonitrile or
D2O. Proton signals were assigned by COSY spectra. Infrared spec-
tra were recorded with an FTIR spectrometer. High quality infra-
red spectra (64 scans) were obtained at 2 cm–1 resolution using a
1 mm NaCl solution cell. All spectra were obtained in 3 m solu-
tions in dry CH2Cl2 at 297 K. All compounds were dried in vacuo
and all the sample preparations were performed under nitrogen.
Melting points were determined in open capillaries and are uncor-
rected. Purification of the six cyclic pseudopeptides 2a, 2b, 4, 5a, 5b
and 5c was accomplished on an Agilent 1100 liquid chromatograph
equipped with a variable-wavelength UV detector (deuterium lamp
190–600 nm) using a Zorbax Eclipse XDB-C18 PrepHT column
(21.2ϫ150 mm, 7 µm) (Agilent Technologies). Acetonitrile
CHROMASOLV® for HPLC was purchased from Riedel-de Haën
and was used as the eluting solvent (mixed with water).
Then the cyclic pseudopeptide 5c was prepared following
the same reaction protocol as used for the preparation of
5a (Scheme 4). All the reactions were performed with good-
to-excellent yields and the final compound was purified by
HPLC chromatography (from 100% H2O to 100% CH3CN
in 5 min).
General Method for the Hydrogenolysis: 10% palladium on char-
coal (10 mg) was added to a stirred solution of Boc-(L-AA--
Oxd)n-OBn (0.10 mmol) in methanol (10 mL). The mixture was
stirred under hydrogen for 12 h. Then the catalyst was filtered
through a Celite pad and the mixture was concentrated. The prod-
uct was obtained in pure form without any further purification.
General Method for the Hydrolysis of Boc-(L-AA-D-Oxd)n-OH
Compounds: A solution of Boc-(-AA--Oxd)3-OBn (0.1 mmol)
and TFA (18 mmol, 1.39 mL) in dry dichloromethane (10 mL) was
stirred for 4 h at room temperature, the volatiles were removed un-
der reduced pressure and the product was obtained in pure form
without any further purification.
General Method for the Cyclization of the Pseudopeptides: HATU
(0.38 mmol, 144 mg) and then TEA (1.2 mmol, 0.16 mL) were
added to a stirred solution of H-(-AA--Oxd)n-OH·CF3CO2H
(0.38 mmol) in dry acetonitrile (80 mL, solution 5 m) under an
inert atmosphere at room temperature. The solution was stirred for
45 min under an inert atmosphere and then acetonitrile was re-
moved under reduced pressure. The crude was washed with small
portions of acetonitrile (2ϫ2 mL) to remove all byproducts. The
desired cycle was obtained as a white solid after HPLC chromatog-
raphy (H2O/acetonitrile, 80:20Ǟ70:30 as eluent).
Scheme 4. Synthesis of 5c. Reagents and conditions: (i) HBTU
(1 equiv.), DBU (2 equiv.), dry CH3CN, room temp., 3 h; (ii) TFA
(18 equiv.), dry CH2Cl2, room temp., 3 h; (iii) HATU (1 equiv.),
TEA (3 equiv.), dry CH3CN, room temp., 2 h; (iv) H2, Pd/C (10%),
MeOH, room temp., 2 h; (v) TFA (18 equiv.), dry CH2Cl2, room
temp., 3 h; (vi) HATU (1 equiv.), TEA (3 equiv.), room temp.,
45 min.
Eur. J. Org. Chem. 2008, 3552–3558
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G. Angelici, R. Tresanchez Carrera, G. Luppi, C. Tomasini
FULL PAPER
H-(L-Ala-D
-Oxd)4-OH·CF3CO2H (1a): Yield 97% (90 mg). 1H 5.23 [m, 4 H, OCH2Ph, OCH2(2Cl-Z)], 5.44 (br. s, 1 H, NH), 7.28–
NMR (CD3OD, 200 MHz): δ = 1.41–1.65 (m, 24 H, 8 Me), 4.63– 7.40 (m, 9 H, Ph) ppm. 13C NMR (CDCl3, 100 MHz): δ = 21.3,
5.10 (m, 8 H, 4 CHN, 4 CHO), 5.60–5.90 (m, 4 H, 4 CHN- 22.7, 28.4, 29.0, 33.0, 40.8, 53.1, 62.2, 63.8, 64.1, 68.2, 73.9, 80.1,
Ala) ppm.
127.1, 128.5, 128.8, 129.3, 129.7, 134.8, 151.4, 156.5, 167.7,
173.5 ppm. C30H36ClN3O9 (617.21): calcd. C 58.30, H 5.87, N 6.80;
found C 58.26, H 5.85, N 6.82.
cyclo-( -Ala-D-Oxd)4 (2a): Yield 40% (120 mg); m.p. 165 °C. [α]D
L
= –86.9 (c = 0.4, CH Cl ). IR (CH Cl , 3 m): ν = 3385, 1784,
˜
2
2
2
2
1709, 1660 cm–1. H NMR (CD3CN, 600 MHz): δ = 1.43 (d, J =
1
1
CF3COO–·+H3N-
L-Lys(2Cl-Z)-D-Oxd-OBn (7): A solution of Boc-
1
7.2 Hz, 12 H, 4 Me-Ala), 1.49 (d, J = 6.0 Hz, 12 H, 4 Me-Oxd),
-Lys(2Cl-Z)--Oxd-OBn (6) (0.50 mmol, 316 mg) and TFA
(9 mmol, 0.67 mL) in dry dichloromethane (8 mL) was stirred for
3 h at room temperature, then the volatiles were removed under
reduced pressure and the product was obtained pure in 98% yield
(93 mg) without any further purification. 1H NMR (CDCl3,
300 MHz): δ = 1.46–1.70 (m, 7 H, 2 CH2-Lys, CH3-Oxd), 2.05 (br.
1
1
3.91 (d, J = 6.0 Hz, 4 H, 4 CHN), 4.44 (dq, J = 7.2 Hz, 4 H, 4
1
CHO), 4.56 (dq, J = 6.0 Hz, 4 H, 4 CHN-Ala), 7.17 (br. s, 4 H, 4
NH) ppm. 13C NMR (CD3CN, 75 MHz): δ = 17.5, 20.9, 29.4, 30.2,
30.4, 30.9, 29.9, 49.6, 63.0, 63.5, 64.0, 75.9, 76.2, 153.0, 169.0,
173.3 ppm. C32H40N8O16 (792.26): calcd. C 48.48, H 5.09, N 14.14;
found C 48.52, H 5.11, N 14.16.
1
s, 2 H, CH2-Lys), 3.24 (br. s, 2 H, CH2-Lys), 4.56 (d, J = 3.6 Hz,
1 H, CHN-Oxd), 4.65 (m, 1 H, CHO-Oxd), 5.16–5.34 [m, 6 H,
CHN-Lys, OCH2Ph, OCH2(2Cl-Z), NH], 7.29–7.43 (m, 9 H, Ph),
8.1 (br. s, 1 H, COOH) ppm.
H-(L-Phe-D-Oxd)4-OH·CF3CO2H (1b): Yield 97% (108 mg); m.p.
215 °C. [α]D = +43.6 (c = 0.1, MeOH). 1H NMR (CDCl3,
200 MHz): δ = 1.10–1.63 (m, 12 H, 4 Me), 2.81–3.43 (m, 8 H, 4
CH2Ph), 4.01–4.83 (m, 8 H 4 CHO, 4 CHN), 5.60–6.53 (m, 4 H, 4
CHN-CH2Ph), 7.18–7.61 (m, 20 H, 4 Ph) ppm.
Boc-(L-Ala-D-Oxd)2-L-Lys(2Cl-Z)-D-Oxd-OBn (8): A mixture of
CF3COO–·+H3N-[-Lys(2Cl-Z)--Oxd]-OBn (7) (0.50 mmol) and
cyclo-(L-Phe-D-Oxd)4 (2b): Yield 40% (67 mg); m.p. 230 °C. [α]D
=
TEA (1.5 mmol, 0.41 mL) in dry acetonitrile (5 mL) was added to
–73.2 (c = 0.1, MeOH). IR (CH Cl , 3 m): ν = 3309, 1775, 1726, a stirred solution of Boc-(L-Ala--Oxd)2-OH (0.50 mmol, 257 mg)
˜
2
2
1661 cm–1. 1H NMR ([D6]DMSO, 300 MHz): δ = 1.43 (m, 12 H, 4
Me), 2.70–3.81 (m, 12 H, 4 CH2Ph, 4 CHN), 4.40–4.60 (m, 4 H, 4
and HBTU (0.50 mmol, 190 mg) in dry acetonitrile (10 mL) under
an inert atmosphere at room temperature. The solution was stirred
CHO), 5.60 (m, 1 H, CHNCH2Ph), 5.78–6.11 (m, 3 H, 3 for 45 min under an inert atmosphere, then acetonitrile was re-
CHNCH2Ph), 7.07–7.40 (m, 20 H, 4 Ph), 8.38–8.65 (m, 4 H, 4
NH) ppm. 13C NMR ([D6]DMSO, 75 MHz): δ = 23.3, 37.4, 46.3,
87.6, 95.9, 126.8, 128.9, 153.3, 154.5, 156.1, 164.2, 166.7 ppm.
C56H56N8O16 (1096.38): calcd. C 61.31, H 5.14, N 10.21; found C
61.35, H 5.16, N 10.23.
H-(L-Ala-D
-Oxd)3-OH·CF3CO2H (3): Yield 97% (70 mg). 1H
NMR (CD3OD, 200 MHz): δ = 1.41–1.65 (m, 18 H, 3 CH3-Ala, 3
CH3-Oxd), 4.63–5.10 (m, 6 H 3 CHN-Oxd, 3 CHO-Oxd), 5.60–
5.90 (m, 3 H, 3 CHN-Ala) ppm.
moved under reduced pressure and replaced with ethyl acetate
(30 mL). The mixture was washed with brine (30 mL), aqueous
HCl (3ϫ20 mL) and NaHCO3 5% (20 mL), and then dried with
Na2SO4, then ethyl acetate was eliminated under reduced pressure.
The product was obtained in pure form after flash chromatography
(eluent: cyclohexane/ethyl acetate, 8:2) in 63% yield (0.32 g). M.p.
146 °C. [α]D = +15.6 (c = 0.5, CH Cl ). IR (CH Cl , 3 m): ν =
˜
2
2
2
2
3440, 3356, 2930, 2848, 1790, 1721 cm–1. 1H NMR (CDCl3,
300 MHz): δ = 1.30–1.60 (m, 28 H, tBu, 2 CH3-Ala, 3 CH3-Oxd,
2 CH2-Lys) 1.79 (m, 2 H, CH2-Lys), 3.25 (m, 2 H, CH2-Lys), 4.49
1
(d, 1J = 5.7 Hz, 1 H, CHN-Oxd), 4.54 (d, J = 5.4 Hz, 1 H, CHN-
cyclo-(L-Ala-D-Oxd)3 (4): Yield 50% (110 mg); m.p. 271 °C (de-
comp.). [α]D = –55 (c = 0.03, MeOH). IR (CH Cl , 3 m): ν =
˜
2
2
Oxd), 4.60–4.80 (m, 7 H, CHN-Oxd, 3 CHO-Oxd, CHN-Lys, 2
CHN-Ala), 5.18–5.35 [m, 5 H, OCH2Ph, OCH2(2Cl-Z), NH], 5.80
(br. s, 1 H, NH), 7.26–7.48 (m, 9 H, Ph) ppm. 13C NMR (CDCl3,
75 MHz): δ = 14.1, 15.8, 17.0, 21.0, 21.1, 22.2, 28.3, 29.1, 30.0,
31.2, 40.5, 49.3, 49.4, 51.7, 61.8, 62.3, 62.9, 63.6, 68.06, 73.88,
74.61, 75.2, 80.5, 126.8, 128.3, 128.5, 128.7, 129.1, 129.4, 129.5,
134.6, 134.7, 151.3, 151.6, 151.7, 156.3, 167.0, 167.4, 167.8, 171.8,
172.3, 174.4 ppm. C46H56ClN7O17 (1014.43): calcd. C 54.46, H
5.56, N 9.67; found C 54.48, H 5.56, N 9.66.
3440, 3284, 1789, 1662 cm–1. H NMR ([D6]DMSO, 300 MHz): δ
1
= 1.29 (d, J = 7.2 Hz, 9 H, 3 CH3-Ala), 1.38 (d, 1J = 6.6 Hz, 9 H,
1
1
1
3 CH3-Oxd), 4.53 (d, J = 3.0 Hz, 3 H, 3 CHN-Oxd), 4.64 (dq, J
= 9.3 Hz, 3 H, 3 CHO-Oxd), 5.28 (dq, 1J = 6.0, 6.9 Hz, 1 H, 3
CHN-Ala), 8.76 (d, 1J = 7.5 Hz, 3 H, 3 NH) ppm. 13C NMR ([D6]-
DMSO, 100 MHz): δ = 16.7, 19.0, 20.7, 30.9, 45.8, 47.4, 61.2, 74.6,
78.7, 79.1, 79.6, 152.4, 167.6, 171.4 ppm. C24H30N6O12 (594.19):
calcd. C 48.48, H 5.09, N 14.14; found C 48.45, H 5.03, N 14.19.
Boc-L-Lys(2Cl-Z)-D-Oxd-OBn (6): HBTU (1.25 mmol, 474 mg),
Boc-(L-Ala-D-Oxd)2-L-Lys(2Cl-Z)-D-Oxd-OH (9): 10% palladium
then -Oxd-OBn (1.25 mmol, 294 mg) and finally DBU (2.5 mmol,
0.37 mL) were added to a stirred solution of a commercial sample
of Boc--Lys(2Cl-Z)-OH (1.25 mmol, 520 mg) in dry acetonitrile
(10 mL) under an inert atmosphere. The solution was stirred for
45 min under an inert atmosphere and then acetonitrile was re-
moved under reduced pressure and replaced with ethyl acetate
(30 mL). The mixture was washed with brine (30 mL), aqueous
HCl (3ϫ20 mL) and 5% NaHCO3 (20 mL), and then dried with
Na2SO4, then ethyl acetate was eliminated under reduced pressure.
The product was obtained in pure form after flash chromatography
(eluent: cyclohexane/ethyl acetate 8.2) in 73% yield (0.56 g).
on charcoal (10 mg) was added to a stirred solution of Boc-(L-Ala-
-Oxd)2--Lys(2Cl-Z)--Oxd-OBn (8) (0.10 mmol, 103 mg) in ethyl
acetate (5 mL). The mixture was stirred under hydrogen for 2 h.
Then the catalyst was filtered through a Celite pad and the mixture
was concentrated. The product 6 was obtained in pure form in 98%
yield (91 mg) without any further purification. M.p. 144 °C. [α]D
=
–8.98 (c = 0.5, CH Cl ). IR (Nujol): ν = 2956, 1793, 1713, 1677,
˜
2
2
1536, 1296, 1259, 1213 cm–1. 1H NMR (CDCl3, 300 MHz): δ =
1.26–1.60 (m, 28 H, tBu, 2 CH3-Ala, 3 CH3-Oxd, 2 CH2-Lys), 1.80
(m, 2 H, CH2-Lys), 3.24 (br. s, 2 H, CH2-Lys), 4.47–4.80 (m, 9 H,
3 CHN-Oxd, 3 CHO-Oxd, CHN-Lys, 2 CHN-Ala), 5.20–5.34 [m,
3 H, OCH2(2Cl-Z), NH], 5.7 (br. s, 1 H, NH), 7.25–7.40 (m, 4 H,
Ph) ppm. 13C NMR (CDCl3, 75 MHz): δ = 19.5, 21.4, 22.4, 24.5,
28.6, 30.0, 39.0, 40.8, 49.6, 60.7, 62.1, 64.0, 68.4, 72.7, 127.2, 128.6,
M.p. 98 °C. [α]D = +13 (c = 0.03, MeOH). IR (CH Cl , 3 m): ν
˜
2
2
= 3686, 3439, 2927, 2853, 1793, 1757, 1714, 1605, 1507 cm–1. 1H
NMR (CDCl3, 200 MHz): δ = 1.45 (m, 13 H, tBu, 2 CH2-Lys),
1.55 (d, 1J = 6.2 Hz, 3 H, CH3-Oxd), 1.79 (br. s, 2 H, CH2-Lys), 129.0, 129.5, 133.6, 134.4, 152.0, 156.9, 167.4, 168.3, 172.7 ppm.
1
3.23 (m, 2 H, CH2-Lys), 4.47 (d, J = 4 Hz, 1 H, CHN-Oxd), 4.58
C39H50ClN7O17 (924.3): calcd. C 50.68, H 5.45, N 10.61; found C
50.66, H 5.42, N 10.57.
(dq, 1J = 4.4, 6.5 Hz, 1 H, CHO-Oxd), 5.01 (br. s, 1 H, CHN-Lys),
3556
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 3552–3558

Dansyl-Containing Cyclic Pseudopeptides
cyclo-[( -Ala- -Oxd)2- -Lys-(2Cl-Z)- -Oxd] (5a): Prepared ac-
L
D
L
D
acetate, 7:3) in 52% yield (228 mg). M.p. 77 °C. [α]D = +12 (c =
cording to the General Method for the Cyclization of the Pseudo-
peptides. Yield 35% (107 mg); m.p. 230 °C. [α]D = +20 (c = 0.3,
0.2, CH Cl ). IR (CH Cl , 3 m): ν = 3436, 3387, 1793, 1752,
˜
2
2
1
2
2
1708 cm–1. H NMR (CDCl3, 300 MHz): δ = 1.46 (m, 15 H, tBu,
1
CH Cl ). IR (CH Cl , 3 m): ν = 3407, 3322, 3198, 1787, 1713, 3 CH2-Lys), 1.53 (d, J = 6.6 Hz, 3 H, CH3-Oxd), 2.95 (m, 8 H, 2
˜
2
2
2
2
1364, 1224 cm–1. 1H NMR (CD3CN, 300 MHz): δ = 1.30–1.61 (m,
CH3-DANS, CH2-NH-Lys), 4.45 (d, 1J = 3.9 Hz, 1 H, CHN-Oxd),
28 H, tBu, 2 CH3-Ala, 3 CH3-Oxd, 2 CH2-Lys), 1.79 (m, 2 H, CH2-
4.54 (m, 1 H, CHO-Oxd), 4.91 (br. s, 1 H, NHSO2), 5.22 (s, 2 H,
Lys), 3.17 (m, 2 H, CH2-Lys), 4.42 (m, 2 H, 2 CHN-Oxd), 4.45 (d, OCH2Ph), 5.35 (m, 1 H, CHN-Lys), 7.21 (d, 1J = 7.8 Hz, 1 H,
1J = 3.6 Hz, 1 H, CHN-Oxd), 4.60–4.80 (m, 5 H, 3 CHO-Oxd, 2
DANS-H), 7.30–7.40 (m, 5 H, Ph), 7.56 (m, 2 H, 2 DANS-H), 8.23
CHN-Ala), 5.20 [s, 2 H, OCH2(2Cl-Z)], 5.46 (m, 2 H, CHN-Lys, (d, 1J = 7.2 Hz, 1 H, DANS-H), 8.32 (d, 1J = 8.1 Hz, 1 H, DANS-
NH), 5.81 (br. s, 1 H, NH), 7.30–7.54 (m, 4 H, Ph) ppm. 13C NMR H), 8.58 (d, J = 8.1 Hz, 1 H, DANS-H) ppm. 13C NMR (CDCl3,
1
(CD3CN, 75 MHz): δ = 16.8, 20.02, 29.2, 40.5, 48.1, 52.0, 62.3,
63.4, 75.0, 75.2, 100.2, 127.5, 129.6, 167.7, 172.0 ppm.
C34H40ClN7O14 (806.17): calcd. C 50.65, H 5.00, N 12.16; found C
50.68, H 5.04, N 12.17.
50 MHz): δ = 12.7, 21.1, 22.1, 28.3, 42.8, 45.4, 68.0, 73.8, 80.7,
82.7, 90.3, 91.7, 97.1, 115.2, 1 23.2, 128.3, 128.7, 129.5, 134.8,
151.0, 173.1, 198.0, 216.7 ppm. C35H44N4O9S (696.81): calcd. C
60.33, H 6.36, N 8.04; found C 60.35, H 6.32, N 8.01.
cyclo-[(
coal (2 mg) was added to a stirred solution of cyclo-[(L-Ala--
Oxd)2--Lys-(2Cl-Z)--Oxd] (5a) (0.020 mmol, 17 mg) in methanol (4.57 mmol, 0.34 mL) in dry dichloromethane (10 mL) was stirred
L-Ala-D-Oxd)2-L-Lys-D-Oxd] (5b): 10% palladium on char-
CF3COO–·+H3N-
Boc--Lys(DANS)--Oxd-OBn (11) (0.25 mmol, 177 mg) and TFA
L-Lys(DANS)-D-Oxd-OBn (12): A solution of
(10 mL). The mixture was stirred under hydrogen for 12 h. Then
the catalyst was filtered through a Celite pad and the mixture was
concentrated. The product 1b was obtained in pure form in 98%
for 3 h at room temperature, then the volatiles were removed under
reduced pressure and the product was obtained in pure form in
98% yield (143 mg) without any further purification. 1H NMR
(CDCl3, 300 MHz): δ = 1.50 (s, 6 H, 3 CH2 Lys), 1.54 (d, 1J =
yield (13 mg) without any further purification. M.p. 205 °C. [α]D
=
–120 (c = 0.4, CH Cl ). IR (CH Cl , 3.0 m): ν = 3682, 3623, 3401, 6.3 Hz, 3 H, CH3 Oxd), 3.0 (br. s, 2 H, CH2-NH-Lys), 3.46 (s, 6
˜
2
2
2
2
1798, 1781, 1670 cm–1. 1H NMR ([D6]DMSO, 400 MHz): δ = 0.76 H, 2 CH3-DANS), 4.30–4.80 (m, 3 H, CHN-Oxd, CHO-Oxd,
(d, 1J = 6.4 Hz, 3 H, CH3-Ala), 0.90 (d, 1J = 6.8 Hz, 3 H, CH3- NHSO2), 5.22 (m, 1 H, CHN Lys), 5.33 (s, 2 H, OCH2Ph), 7.39
Ala), 1.12–1.25 (m, 4 H, 2 CH2-Lys), 1.28–1.57 (m, 9 H, 3 CH3- (m, 5 H, Ph), 7.80 (m, 2 H, DANS-H), 8.40 (m, 1 H, DANS-H),
Oxd) 1.74 (m, 2 H, CH2-Lys), 3.12 (m, 2 H, CH2NH2), 3.68 (m, 2 8.50 (d, 1J = 9 Hz, 1 H, DANS-H), 8.63 (d, 1J = 8.7 Hz, 1 H,
H, CHN-Oxd), 3.90–4.09 (m, 4 H, CHN-Oxd, 3 CHO-Oxd), 4.48– DANS-H), 8.91 (m, 1 H, DANS-H) ppm.
1
4.59 (m, 2 H, 2 CHN-Ala), 5.21 (m, 1 H, CHN-Lys), 7.48 (d, J =
Boc-(L-Ala-D-Oxd)2-L-Lys-(DANS)-D-Oxd-OBn (13): A mixture of
5.7 Hz, 1 H, NH-Lys), 8.85 (d, 1J = 5.1 Hz, 1 H, NH-Ala), 8.95
(d, 1J = 5.7 Hz, 1 H, NH-Ala) ppm. 13C NMR ([D6]DMSO,
100 MHz): δ = 14.7, 17.5, 18.7, 26.1, 29.2, 31.4, 47.1, 58.0, 59.8,
61.0, 75.5, 84.2, 101.2, 117.6, 128.2, 145.1, 173.2 ppm.
C27H37N7O12 (651.62): calcd. C 49.77, H 5.72, N 15.05; found C
49.74, H 5.74, N 15.03.
CF3COO–·+H3N--Lys(DANS)--Oxd-OBn (0.25 mmol) and TEA
(1.9 mmol, 0.15 mL) in dry acetonitrile (15 mL) was added to a
stirred solution of Boc-(-Ala--Oxd)2-OH (0.25 mmol, 129 mg)
and HATU (0.25 mmol, 95 mg) in dry acetonitrile (10 mL) under
an inert atmosphere at room temperature. The solution was stirred
for 2 h under an inert atmosphere, then acetonitrile was removed
Boc-L-Lys(DANS)-OH (10): Dansyl chloride (1.8 mmol, 493 mg) under reduced pressure and replaced with ethyl acetate (30 mL).
was added to a stirred solution of Boc--Lys-OH (1.8 mmol,
450 mg) and DBU (7.2 mmol, 1.1 mL) in dry dichloromethane .
The mixture was stirred for 16 h at room temperature, then the
volatiles were removed under reduced pressure and 1  HCl was
added to the residue to obtain pH = 3. The aqueous mixture was
extracted with dichloromethane (3ϫ30 mL) and then the com-
bined organic layers were dried with Na2SO4 and removed under
reduced pressure. The product 10 was obtained in pure form with-
out any further purification in 73% yield (0.63 mg). 1H NMR
(CDCl3, 300 MHz): δ = 1.26–1.54 (m, 13 H, tBu, 2 CH2-Lys), 1.80
(br. s, 2 H, CH2-Lys), 2.95–3.26 (m, 8 H, 2 CH3-DANS, CH2-NH-
The mixture was washed with brine (30 mL), aqueous HCl
(3ϫ20 mL) and 5% NaHCO3 (20 mL), and then dried with
Na2SO4, then ethyl acetate was eliminated under reduced pressure.
The product was obtained in pure form after flash chromatography
(eluent: cyclohexane/ethyl acetate, 8:2) in 40% yield (109 mg). M.p.
126 °C. [α]D = +0.62 (c = 0.7, CH Cl ). IR (CH Cl , 2.9 m): ν =
˜
2
2
2
2
3442, 3359, 2988, 2931, 1790, 1720, 1691 cm–1. 1H NMR (CD3CN,
400 MHz): δ = 1.31 (m, 6 H, 2 CH3-Ala), 1.40 (m, 18 H, 3 CH2-
Lys, tBu, CH3--Oxd), 1.46 (d, 1J = 6.4 Hz, 3 H, CH3-D-Oxd),
1.50 (d, 1J = 6.4 Hz, 3 H, CH3--Oxd), 2.90 (m, 2 H, CH2-NH-
Lys), 2.95 (s, 6 H, 2 CH3-DANS), 4.39 (d, 1J = 4.4 Hz, 1 H, CHN-
1
1
Lys), 4.05 (br. s, 1 H, NHSO2), 5.01 (m, 1 H, CHN-Lys), 7.42 (br. Oxd), 4.43 (d, J = 4.38 Hz, 1 H, CHN-Oxd), 4.54 (d, J = 4 Hz,
1
s, 1 H, NH), 7.54 (m, 2 H, DANS-H), 8.25 (d, J = 7.1 Hz, 1 H, 1 H, CHN-Oxd), 4.56–4.74 (m, 3 H, CHO-Oxd), 5.14–5.29 (m, 4
1
DANS-H), 8.31 (d, J = 6.7 Hz, 1 H, DANS-H), 8.54 (br. s, 1 H, H, 2 CHN-Ala, OCH2Ph), 5.48 (m, 1 H, CHN-Lys), 6.0 (br. s, 1
DANS-H), 8.70 (br. s, 1 H, DANS-H) ppm.
H, NHSO2), 7.40 (m, 5 H, Ph), 7.47 (m, 1 H, NH-Lys), 7.66 (m, 2
H, DANS-H), 8.20 (d, J = 7.2 Hz, 1 H, DANS-H), 8.39 (m, 1 H,
1
Boc- -Lys(DANS)- -Oxd-OBn (11): A mixture of -Oxd-OBn
L
D
DANS-H), 8.55 (d, 1J = 8.4 Hz, 1 H, DANS-H), 8.72 (d, 1J = 4 Hz,
1 H, DANS-H) ppm. 13C NMR (CD3CN, 75 MHz): δ = 20.3, 22.4,
27.9, 28.6, 38.2, 42.8, 45.4, 48.8, 61.8, 62.9, 68.0, 74.6, 75.3, 116.4,
120.8, 124.4, 128.5, 128.5, 128.8, 129.3, 129.6, 135.6, 136.1, 152.2,
152.5, 168.0, 168.4, 172.0, 172.4, 174.1 ppm. C51H64N8O17S
(1093.16): calcd. C 56.03, H 5.90, N 10.25; found C 56.01, H 5.92,
N 10.28.
(0.63 mmol, 263 mg) and DBU (1.26 mmol 0.19 mL) in dry aceto-
nitrile (10 mL) was added to a stirred solution of Boc--Lys-
(DANS)-OH (0.63 mmol, 304 mg) and HBTU (0.63 mmol.
239 mg) in dry acetonitrile (10 mL) under an inert atmosphere at
room temperature. The solution was stirred for 3 h under an inert
atmosphere and then acetonitrile was removed under reduced pres-
sure and replaced with ethyl acetate (30 mL). The mixture was
washed with brine (30 mL), aqueous HCl (3ϫ20 mL) and 5%
NaHCO3 (20 mL), and then dried with Na2SO4, then ethyl acetate
was eliminated under reduced pressure. The product was obtained
in pure form after flash chromatography (eluent: cyclohexane/ethyl
Boc-(
cording to the General Method for the Hydrogenolysis. Yield 98%
(98 mg from 0.1 mmol of starting material); m.p. 162 °C. [α]D
–5.73 (c = 0.7, CH Cl ). IR (Nujol): ν = 3363, 2721, 2672, 2365,
L-Ala-D-Oxd)2-L-Lys(DANS)-D-Oxd-OH (14): Prepared ac-
=
˜
2
2
Eur. J. Org. Chem. 2008, 3552–3558
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3557

G. Angelici, R. Tresanchez Carrera, G. Luppi, C. Tomasini
FULL PAPER
2365, 2333, 1789, 1679, 1548 cm–1. H NMR (CD3CN, 400 MHz):
δ = 1.20–1.70 (m, 30 H, 2 CH3-Ala, 3 CH2-Lys, tBu, 3 CH3-Oxd),
2.50–3.40 (m, 8 H, CH2-NH-Lys, 2 CH3-DANS), 4.39–4.73 (m, 6
H, 3 CHN-Oxd, 3 CHO-Oxd), 5.26 (m, 2 H, 2 CHN-Ala), 5.43 (m,
2 H, CHN-Lys, NH), 5.88–5.98 (br. s, 1 H, NHSO2), 7.28 (d, J =
6.8 Hz, 1 H, DANS-H), 7.61 (m, 2 H, 2 DANS-H), 8.18 (d, J =
1
[2] a) D. E. Cane, C. T. Walsh, C. Khosla, Science 1998, 282, 63–
68; b) M. A. Marahiel, T. Stachelhaus, H. D. Mootz, Chem.
Rev. 1997, 97, 2651–2674.
[3] For some recent references, see: a) J. P. Michael, G. Pattenden,
Angew. Chem. Int. Ed. Engl. 1993, 32, 1–23; b) A. Bertram, G.
Pattenden, Nat. Prod. Rep. 2007, 24, 18–30; c) A. Bertram, N.
Maulucci, O. M. New, S. M. M. Nor, G. Pattenden, Org. Bi-
omol. Chem. 2007, 5, 1541–1553; d) Y. Hamada, T. Shioiri,
Chem. Rev. 2005, 105, 4441–4482; e) B. S. Davidson, Chem.
Rev. 1993, 93, 1771–1791; f) P. Wipf, Chem. Rev. 1995, 95,
2115–2134.
[4] a) C. M. Deber, E. R. Blout, J. Am. Chem. Soc. 1974, 96, 7566–
7568; b) V. Madison, C. M. Deber, E. R. Blout, J. Am. Chem.
Soc. 1977, 99, 4788–4798; c) V. Madison, M. Atreyi, C. M. De-
ber, E. R. Blout, J. Am. Chem. Soc. 1974, 96, 6725–6734; d)
C. M. Deber, V. Madison, E. R. Blout, Acc. Chem. Res. 1976,
9, 106–113.
[5] a) C. Tomasini, G. Luppi, M. Monari, J. Am. Chem. Soc. 2006,
128, 2410–2420; b) F. Bernardi, M. Garavelli, M. Scatizzi, C.
Tomasini, V. Trigari, M. Crisma, F. Formaggio, C. Peggion, C.
Toniolo, Chem. Eur. J. 2002, 8, 2516–2525; c) C. Tomasini, V.
Trigari, S. Lucarini, F. Bernardi, M. Garavelli, C. Peggion, F.
Formaggio, C. Toniolo, Eur. J. Org. Chem. 2003, 259–267.
1
1
6.8 Hz, 1 H, DANS-H), 8.29 (d, 1J = 8.4 Hz, 1 H, DANS-H), 8.56
(d, 1J = 8.4 Hz, 1 H, DANS-H) ppm. 13C NMR (CD3CN,
75 MHz): δ = 17.3, 20.1, 20.5, 22.4, 27.8, 38.1, 42.7, 45.0, 48.6, 48.8,
62.6, 75.5, 115.6, 117.6, 119.3, 123.7, 128.4, 129.2, 135.8, 152.1,
155.9 ppm. C44H58N8O17S (1002.36): calcd. C 52.69, H 5.83, N
11.17; found C 52.73, H 5.88, N 11.20.
CF3COO–·+H3N-(
L-Ala-D-Oxd)2-L-Lys(DANS)-D-Oxd-OH (15):
Prepared according to the General Method for the Hydrolysis
of Boc-(-AA--Oxd)n-OH Compounds. Yield 97% (99 mg). 1H
NMR (CD3CN, 300 MHz): δ = 1.20–1.70 (m, 21 H, 2 CH3-Ala, 3
CH2-Lys, 3 CH3-Oxd), 2.90 (m, 2 H, CH2-NH-Lys), 3.25 (m, 6 H,
2 CH3-DANS), 4.25–4.70 (m, 6 H, 3 CHN-Oxd, 3 CHO-Oxd),
5.26–5.50 (m, 3 H, 2 CHN-Ala, CHN-Lys), 6.10 (br. s, 1 H,
NHSO2), 7.80 (m, 3 H, DANS-H), 8.30 (m, 1 H, DANS-H), 8.50
(m, 1 H, DANS-H), 8.60 (m, 1 H, DANS-H) ppm.
[6]
W. S. Horne, N. Ashkenasy, M. R. Ghadiri, Chem. Eur. J. 2005,
11, 1137–1144, and all the references therein.
cyclo-[(L-Ala-D-Oxd)2-L-Lys(DANS)-D-Oxd] (5c): Prepared accord-
ing to the General Method for the Cyclization of the Pseudopep-
tides. Yield 40% (35 mg from 0.1 mmol of starting material); m.p.
[7]
a) L. Wang, P. G. Schultz, Angew. Chem. Int. Ed. 2005, 44, 34–
66; b) D. Summerer, S. Chen, N. Wu, A. Deiters, J. W. Chin,
P. G. Schultz, Proc. Natl. Acad. Sci. 2006, 103, 9785–9789; c)
S. A. Fleming, J. A. Pincock, Mol. Supramol. Photochem. 1999,
211–281; d) G. Lu, K. Burgess, Bioorg. Med. Chem. Lett. 2006,
16, 3902–3905.
204 °C. [α]D = –0.30 (c = 0.7, CH Cl ). IR (CH Cl , 1.5 m): ν =
˜
2
2
2
2
3680, 3594, 1789, 1712, 1671, 1602 cm–1. 1H NMR ([D6]acetone,
300 MHz): δ = 1.25–1.70 (m, 21 H, 2 CH3-Ala, 3 CH2-Lys, 3 CH3-
Oxd), 2.90 (m, 8 H, CH2-NH-Lys, 2 CH3-DANS), 4.57–4.78 (m, 3
H, 3 CHN-Oxd), 4.80–4.95 (m, 3 H, 3 CHO-Oxd), 5.59 (m, 3 H,
2 CHN-Ala, CHN-Lys), 6.80 (m, 1 H, NHSO2), 7.31 (d, 1J =
[8] a) E. Kimura, S. Aoki, E. Kikuta, T. Koike, Proc. Natl. Acad.
Sci. 2003, 100, 3731–3736; b) Y. K. Reshetnyak, O. A. Andreev,
U. Lehnert, D. M. Engelman, Proc. Natl. Acad. Sci. 2006, 103,
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1
6.9 Hz, 1 H, DANS-H), 7.64 (m, 2 H, 2 DANS-H), 8.25 (d, J =
7.2 Hz, 1 H, DANS-H), 8.42 (d, 1J = 8.7 Hz, 1 H, DANS-H), 8.60
(d, 1J = 8.7 Hz, 1 H, DANS-H) ppm. 13C NMR (D6]acetone,
75 MHz): δ = 17.3, 20.1, 22.6, 42.8, 45.0, 48.3, 52.0, 62.2, 74.5,
75.3, 115.5, 119.7, 123.6, 128.1, 129.0, 129.9, 130.1, 136.6, 152.2,
152.4 ppm. C39H48N8O14S (884.91): calcd. C 52.93, H 5.47, N
12.66; found C 52.90, H 5.44, N 12.68.
Acknowledgments
We. thank the Ministero dell’Università e della Ricerca Scientifica
(PRIN 2006 “Sintesi, attività biologica e applicazioni diagnostiche
di ligandi delle integrine α-v-β-3, α-4-β-1 e α-4-β-7”) and the Uni-
versity of Bologna (Funds for Selected Topics) for financial sup-
port.
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Received: March 5, 2008
Published Online: June 3, 2008
3558
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Eur. J. Org. Chem. 2008, 3552–3558