Synthesis and folding propensity of aliphatic oligoureas containing repeats of proline-type units

Article abstract of DOI:10.1021/jo5006075

The synthesis and conformational analysis of aliphatic oligoureas containing multiple adjacent N-alkylated units derived from proline (i.e., Pro^u) are reported. The insertion of trisubstituted ureas in the main chain of N,N′-linked oligourea fo

Full text of DOI:10.1021/jo5006075

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Article
Synthesis and Folding Propensity of Aliphatic
Oligoureas Containing Repeats of Proline-type Units
Juliette Fremaux, Brice Kauffmann, and Gilles Guichard
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/jo5006075 • Publication Date (Web): 08 May 2014
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Synthesis and Folding propensity of Aliphatic Oligoureas containing repeats of
proline-type Units
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Juliette Fremaux#,†, Brice Kauffmann‡ and Gilles Guichard*,†
†Université de Bordeaux, CNRS, IPB, UMR 5248, CBMN, Institut Européen de Chimie et de Biologie, 2
rue Robert Escarpit, 33607 Pessac, France*
‡
Université de Bordeaux, CNRS, UMR 3033, INSERM US001, Institut Européen de Chimie et de
Biologie, 2 rue Robert Escarpit, 33607 Pessac, France
E-mail : g.guichard@iecb.u-bordeaux.fr
ABSTRACT: The synthesis and conformational analysis of aliphatic oligoureas containing
multiple adjacent N-alkylated units derived from proline (i.e., Prou) is reported. The insertion of
tri-substituted ureas in the main chain of N,N’-linked oligourea foldamers locally impairs the
characteristic three centred-hydrogen bonding pattern associated with the formation of 2.5-helical
structures. Three series of oligomers have been studied : one series in which the Prou repeat is
flanked on both sides by canonical urea residues (e.g. oligomers 2-6), one series with canonical
residues on either side of the Prou repeat (oligomers 12 and 23), and one series consisting
exclusively of Prou residues (oligomers 25 and 26). Spectroscopic (NMR and electronic circular
dichroism) and X-ray diffraction studies reveal that the 2.5-helix formed by oligomers of N,N’-
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disubstituted ureas is robust enough to accommodate short oligopyrrolidine segments (Prou)n (n <
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7) which alone display no intrinsic folding propensity.
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INTRODUCTION
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The introduction of tertiary amides in the backbone of α-peptides, by locally decreasing the
hydrogen bond donor capability and populating both cis- and trans-amide bond conformers,
generally has dramatic consequences on the structure and dynamics of the peptide main chain. N-
methylation for exemple, is a well appreciated strategy to modulate the conformation but also the
potency and the membrane permeability of bioactive peptides.1-3 In proline containing peptides,
these effects are coupled with an increased conformational constraint imposed by the pyrrolidine
ring. With a φ angle in the range -60° ± 20°, proline is the most conformationally restricted of the
proteinogenic amino acids. As a result, proline tends to be excluded from α-helical and β-sheet
structures, though it is frequently found at their ends and also in transmembrane helices.4 A
remarkable feature is the propensity of proline repeats to adopt helical secondary structures to the
exclusion of hydrogen bonding such as the left-handed polyproline II (PPII) helix (with all
amides in trans conformation) which predominates in polar solvents and plays crucial role in
biological processes (e.g. protein-protein recognition, assembly of collagen triple helices5,6).
Electronic effects (ie nπ* interaction) have been shown to play a substantial role in the
stabilization of the PPII helical conformation.7,8 Synthetic proline-rich sequences that can adopt
PPII helical conformation have been developed as cell penetrating agents9 and as molecular ruler
(by enabling controlled inter-ligand distances).10,11,12
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Significant efforts have also been directed towards the elaboration of non natural peptidomimetic
tertiary amide oligomers that can form defined non-hydrogen bonded structures. These include
homooligomers of diversely substituted proline derivatives and analogues,13-16 homologated
proline residues,17-22 and N-alkyl glycines.23-26 Non canonical folded structures stabilized by H-
bonds have also been described for hybrid oligoamides made of alternating secondary and tertiary
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amides.27-29
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We have previously investigated30 the consequences of inserting N-(pyrrolidin-2-ylmethylamine)
units31 as proline analogues at discrete positions in the backbone of aliphatic N,N’-disubstituted
urea oligomers, a class of peptidomimetic helical foldamers.32-36 We found that despite the loss of
one H-bond donor site, the geometry of the canonical 2.5 helix of oligoureas is not significantly
impaired by the presence of multiple and non-adjacent pyrrolidine units. The tri-substituted urea
which is created at the pyrrolidine insertion site still has the ability to form intramolecular H-
bonds. In addition, the CO−N−Cβ−Cα angle (φ) values measured for pyrrolidine units (≈ −96°)
in the crystal structures of corresponding oligomers match the ϕ values in the structure of the
canonical 2.5-helix of oligoureas (i.e., φ ≈ −101°). However, our results also indicate that the
pyrrolidine unit is endowed with a lower 2.5-helix propensity compared to canonical units thus
suggesting that by changing the ratio of proline-type residues to canonical units, it may be
possible to tune the stability of the 2.5 helical structure. In the present work, we have explored
whether the helix geometry of aliphatic oligoureas may accommodate multiple adjacent
pyrrolidine residues. Oligomers containing 2 to 7 consecutive pyrrolidine units flanked by
canonical residues have been synthesized and characterised in solution and in solid state to
determine the extent to which these oligopyrrolidine segments can be enforced in the 2.5 helical
conformation. Furthermore, we have investigated new oligoureas consisting exclusively of
pyrrolidine units and trisubstituted ureas to evaluate the possibility for oligopyrrolidine-ureas to
adopt non canonical folding patterns.
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RESULTS AND DISCUSSION
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To evaluate the influence of multiple adjacent pyrrolidine residues on the 2.5-helix geometry of
oligoureas, we have prepared a series of oligomers derived from the previously described
heptamer 1 with one central pyrrolidine unit. The resulting oligomers 2-6 contain two to seven
consecutive pyrrolidine residues flanked by three canonical units with aliphatic side chains of
Ala, Val and Leu amino acid residues (See Figure 1).
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Figure 1. Sequences of oligoureas 1-6 containing one to seven adjacent pyrrolidine residues
(shown in red)
Oligomers 2-6 ranging from 8-13 residues were synthesized by condensation of two (2-5) to three
(6) segments.30 Our approach involves the preparation of a first activated segment (7) containing
a terminal pyrrolidine residue terminated by a succinimidyl carbamate. The presence of an N-
alkylated residue (e.g. pyrrolidine) at the segment junction position is recommended to prevent a
possible intramolecular cyclization of the activated oligourea that would lead to the formation of
a heterocyclic biuret derivative.30,37
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The different segments were all synthesized stepwise from activated building blocks 8a-d.30,38,39
The segment condensation between activated oligourea 7 and oligomers 10-13 leading to
oligoureas 2-5 proceeded in good yields ranging from 56 to 80 % (Scheme 1).
Scheme 1. Synthesis of oligoureas 2-5a
aReaction conditions : (i) TFA, 45 min; (ii) 8d, DIEA, CH3CN; (iii) 7, DIEA, CH3CN
For the preparation of the longest oligomer 6, another activated segment of six pyrrolidine units
19 was prepared and coupled to the TFA salt derived from 9 prior to the final condensation with
7 (Scheme 2). The 12-mer 6 was thus readily obtained in good yields over the two segment
condensation steps (55 and 60% respectively)
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Scheme 2. Synthesis of oligourea 6a
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aReaction conditions : (i) TFA, 45 min; (ii) 8d, DIEA, CH3CN; (iii) H2, Pd/C, EtOH; (iv) DSC,
CH2Cl2; (v) 17, DIEA, CH3CN; (vi) 19 , DIEA, CH3CN; (vii) 7, DIEA, CH3CN;
We have next compared the folding propensity of oligomers 1-6 in solution, first using electronic
circular dichroism (ECD) in 2,2,2-trifluoroethanol (TFE). All spectra display a characteristic
ECD signature indicative of 2.5-helical folding with a positive maximum at 203 nm, zero
crossing at 193 nm and a weaker negative maximum at 188 nm (Figure 2). However, the per
residue molar ellipticity (PRME) value at 203 nm for the molecule 2 (2.3 x 104 deg cm2 dmol-1)
with two consecutive pyrrolidine units is significantly lower than in 1 (3.9 x 104 deg cm2 dmol-1)
which is indicative of a destabilization of the canonical helical structure. The absolute PRME
values further decrease gradually with the insertion of additional pyrrolidine residues (3-6), the
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signal of 6 becoming poorly defined below 193 nm. Overall these results point to diminished
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helical folding caused by additional adjacent proline type residues.
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Figure 2. ECD spectra of molecules 1-6 (TFE, 0.2 mM)
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These observations are supported by H NMR spectroscopy experiments. H NMR spectra of
molecules 2-6 were recorded in CD3OH at 3 mM. A lower solubility of oligomers is noticed upon
increasing the number of pyrrolidine units in the chain with 6 being hardly soluble in CD3OH.
1
The frequencies of H atoms were assigned using homonuclear DQF-COSY, TOCSY and
ROESY experiments (see Tables S1-S3 in supporting information). However, spin systems of
Prou residues in 3 and 5 could not be unequivocally resolved because of resonance overlaps and
peak broadening. The NMR spectra of 2 and 3 are very similar to that of 1 and display features
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typical of oligourea helices such as significant dispersion of urea NH signals (See Figs S3, S6 and
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S11 for illustration), high diastereotopicity of main chain CH2 protons (vide infra), and large
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vicinal coupling constants between NHs and CH protons of canonical residues.32,35,40 However,
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these characteristics progressively disappear in oligomers with more than three consecutive
pyrrolidine units. The signals broaden and the dispersion of NH signals decreases significantly in
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oligomer 4 and 5. The H NMR spectrum of 4 was poorly resolved precluding unambiguous
sequence assignment.
The anisochronicity values (Δδ) of main chain CH2 protons of acyclic/canonical residues at both
ends of the sequence were extracted from spectra of oligomers 2, 3 and 5 and compared to that of
1 (Figure 3). These values are sensitive to the number of pyrrolidine residues (n) in the sequence
and decreased rapidly when n > 2 to reach values below that generally observed for 2.5-helical
oligoureas in the case of 5. Only the Δδ values for the first two residues (Leuu1 and Alau2) are
moderately affected among all oligomers. Overall these data are in line with ECD results and
confirm that the introduction of multiple adjacent pyrrolidine residues in the central part of an
oligourea sequence significantly alter the 2.5-helical geometry in solution.
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Figure 3. Chemical shift differences Δδ (ppm) of main chain CH2 protons of canonical residues
in the sequence of oligomers 1, 2, 3 and 5
To determine which canonical segment in the sequence is the most efficient to induce helicity of
the Prou repeat, we have compared 3 with urea hexamers 12 and 23 (see scheme 3 for the
synthesis of 23) consisting of three contiguous pyrrolidine units linked to a canonical segment at
either end of the sequence.
Scheme 3. Synthesis of oligourea 23a
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aReaction conditions : (i) H2, Pd/C, EtOH; (ii) DSC, CH2Cl2; (iii) CH3NH2·HCl, DIEA, CH3CN;
(iv) TFA, 45 min; (v) 7, DIEA, CH3CN.
ECD experiments reveal that the PRME value measured for 12 at 203 nm is about the same as
that observed for 3 (Figure 4). This result suggests that three canonical residues at the start of the
sequence (residues 1-3) in 6-mer 12 are sufficient to promote the same level of helicity as
observed in 9-mer 3. The carbonyl groups of pyrrolidine units in 12 (residues 3-6) are believed to
be engaged in 12- and 14-H-bonded rings typical of 2.5-helices with urea NHs of canonical
residues. An additional 12-membered H-bonded ring may be formed between the first
trisubstituted urea (at the junction of residues 4 and 5) and the Boc carbonyl oxygen. In contrast,
the ECD spectrum recorded for 6-mer 23 gives a poor signature that can hardly be assigned to a
2.5 helical structure (Figure 4), thus indicating that a pyrrolidine unit repeat at the first three
positions (residues 1-3) is not compatible with a canonical helical arrangement .
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Figure 4. ECD spectra of 1, 3, 12 and 23 recorded in TFE at 0.2 mM
We obtained single crystal of 2 and 3 suitable for X-ray diffraction (XRD) analysis and solved
their structure in the P21 and C2 space groups respectively (The crystal structure of 2 contains
two independent molecules in the asymmetric unit) (Table 1). XRD analysis revealed that both
molecules adopt a helical structure in the crystal with an overall geometry close to the canonical
helix of oligoureas (Figure 5). Though the centre part of 3 tends to be slightly bent, the mean
backbone torsion angles for each pyrrolidine residues are similar to those measured for 1 (CCDC
836810) and match well values generally found in 2.5-helical structures of oligoureas (
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Table ).30,33,34
Table 1. X-Ray cristallographic data of oligoureas 2 and 3
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7
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9
Compound
2
-
3
-
CCDC code
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12
13
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19
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C55.5 H101 N18 O11
1196.54
monoclinic
P21
C58 H109 N19 O11
1248.64
Monoclinic
C2
Formula
M
Crystal system
Space group
10.379(2)
33.918(7)
19.627(4)
90
18.609(4)
20.000(4)
21.577(4)
90
a/Å
b/Å
c/Å
α/°
99.06(3)
90
107.06(3)
90
β/°
γ/°
V/Å3
6823(2)
293(2)
7677(3)
213(2)
T /K
4
4
Z
ρ/g cm–1
1.165
1.080
-
0.1x0.01x0.01
1.54178
0.621
size (mm)
1.54178
0.675
λ/ Å
μ/mm-1
15187
5332
Independent reflections
measured reflections
parameters/restraints
R1, wR2
15187
-
1558/2
0.0514/0.1337
1.036
794/1
0.0832/0.2188
1.053
goodness of fit
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Figure 5. Comparison of X-Ray diffraction structures (side- and top views) of oligoureas (a) 130
(CCDC 836810), (b) 2 and (c) 3. Pyrrolidine units are coloured in red.
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Table 2. Dihedral angles measured for each pyrrolidine type residues in 1, 2 and 3. (The P1
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6
position corresponds to the terminal residue (Leuu) coupled to methyl amine).
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θ1
θ2
Cmpd
1
Res.
φ
P4
P4
P5
P4
P5
P6
-104,3°
-97,1°
-100,3°
-95,1°
-98,6°
-90,2°
58,7°
45,9°
66,6°
50,3°
54,2°
68,9°
91,2°
86,3°
74,1°
93,2°
73,3°
87,9°
2
3
All possible intramolecular 12- and 14-membered H-bonded rings involving disubstituted urea
NHs are formed in the three crystal structures. However, differences are observed for 3 in the H-
bond network at the trisubstituted urea positions. At these positions involving pyrrolidine units,
only 12-membered pseudorings between the remaining secondary amide (N’(i)) and C=O at
position i+2 (O(i+2)) can be formed. In the structures of 1 and 2, the N’(i) positions of
tribustituted ureas (N’5 in 1 and both N’5 and N’6 in 2) are all within a hydrogen-bonded
distance to the corresponding carbonyl oxygens at i+2 positions (D(N···O) = 2.9-3.1 Å) (Figure
6a). Though two of these interactions closing 12-membered H-bonded rings are conserved in the
structure of 3 (D(N’7···O9) = 3.0 Å and D(N’6···O8) = 2.9 Å), the distance between O7 and
amide N’5 is much higher (D(N···O) = 4.3 Å) (Figure 6b). This reorganisation may be due to a
steric repulsion between the two pyrrolidine rings of residues at P4 and P6. This observation
further supports the conclusion drawn from solution studies indicating that the destabilization of
the helical structure is largely amplified in 3 compared to 1 and 2.
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Figure 6 : Hydrogen bond details at the pyrrolidine positions in a) molecule 2 and b) molecule 3.
Main chain N’5 and O7 atoms are within a H-bond distance in 2 (D(N···O) = 3.14 Å) but not in 3
(D(N···O) > 4 Å).
To investigate whether oligomers built exclusively from N-(pyrrolidin-2-ylmethyl)ureido units
can adopt a specific secondary structure, we have prepared two oligoureas containing six and
nine pyrrolidine units (Scheme 4). Successive condensation steps using the activated segment 17
containing three pyrrolidine residues on a trimeric segment 24 afforded 25 and 26 in 40 and 48 %
yield respectively.
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Scheme 4. Synthesis of oligoureas 25 and 26 containing 6 and 9 pyrrolidine residues.
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aReaction conditions : (i) CH3NH2·HCl, DIEA, CH3CN; (ii) TFA, 45 min; (iii) 17, DIEA, DMF.
Oligoureas 25 and 26 exhibited poor ECD spectra in TFE, which reflects the absence of a well-
1
defined folded conformation (Figure 7). These observations are confirmed by H NMR analysis
α
in CD3OH at 3 mM. The NHs signals are broad and poorly dispersed and CH2 protons of the
main chain are all overlapped between 3.0 and 3.5 ppm. These features indicate a lack of
conformational homogeneity that may result from the presence of rapidly interconverting
populations with various ratios of urea cis-trans isomers41 and / or from interchain aggregation
even at the low concentrations used for ECD measurements. It remains to be seen whether longer
oligomers of pyrrolidine units could eventually adopt preferential conformations.
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Figure 7. ECD spectra of 1, 25 and 26 recorded in TFE at 0.2 mM
CONCLUSION
We have shown previously that the helix conformation of aliphatic N,N’-linked oligoureas
tolerates the insertion of one or multiple non adjacent trisubstituted ureas such as those formed by
insertion of pyrrolidine (Prou) units. This approach has been exploited to prepare long helical
segments by fragment condensation.30 We have now extended this work to oligoureas containing
Prou repeats. ECD and NMR studies suggest that in solution the helix propensity of oligoureas
decreases with the length of the repeat. Helices with (Prou)2 and (Prou)3 have been characterized
by X-ray diffraction and reveal little deviation compared to canonical 2.5-helices. Oligomers
consisting exclusively of pyrrolidine units, i.e. (Prou)6 and (Prou)9 have also been studied but do
not show evidence of a dominant folded structure. The absence of defined secondary structure
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elements could be due to several factors such as insufficient chain length to stabilize folded
populations, uncontrolled urea cis-trans isomerization and/ or aggregation. The introduction of
hydroxypyrrolidine derivatives (Hypu) or more constrained pyrrolidine type units with 3-
aminopyrrolidine skeleton for example could be considered in future studies to modulate cis-
trans isomerisation and possibly promote main chain organization and folding of N-alkyl-N,N’-
linked oligoureas into well-defined secondary structures.
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EXPERIMENTAL SECTION
Activated monomers 8 (a R = iBu; b R = Me; c R = iPr)38 and 8d30, oligomers 130, 730 and 934
were prepared using previously described procedures.
Urea formation: General procedure
Boc‐protected oligourea (1.0 eq) was dissolved in TFA (3 ml / g) and stirred for 45 min. The
reaction mixture was then concentrated under reduced pressure and the resulting residue was
coevaporated three times with cyclohexane. The crude product was then dissolved in CH3CN (5
ml / g). DIEA (3.0 eq) was then added and the mixture was cooled to 0°C prior to the dropwise
addition of the following carbamate, 11a-d, dissolved in CH3CN. After completion of the
reaction, the reaction mixture was evaporated, dissolved in EtOAc and treated with saturated
NaHCO3 aqueous solution, 1M KHSO4 aqueous solution and brine. The organic layer was then
dried over Na2SO4 and evaporated. Flash column chromatography (CH2Cl2-MeOH (v/v), 90:10)
over silica gel gave the desired compound as a white product.
Boc-Prou-Valu-Alau-Leuu-NHMe (10). 10 was prepared from 8d (0.064 g, 0.189 mmol) and 9
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(0.100 g, 0.199 mmol) as described in the general procedure (0.090 g, 72 %). H NMR:
(300MHz, CD3OH) δ = 6.43-6.29 (m, 2H, NH), 6.23-5.98 (m, 4H, NH), 5.92 (s, 1H, NH), 5.80
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(d, J = 9.7 Hz, 1H, NH), 4.09-3.94 (m, 1H, CHN), 3.94-3.74 (m, 2H, CHN), 3.72-3.31 (m, 5H,
CHN-CH2N), 3.20-2.82 (m, 2H, CH2N), 2.73 (d, J = 4.5 Hz, 3H, CH3N), 2.64-2.30 (m, 4H,
CH2N), 2.03-1.81 (m, 4H, CH2), 1.82-1.60 (m, 2H,CH), 1.50 (s, 9H, CH3), 1.34-1.20 (m, 2H,
CH2), 1.04 (d, J = 6.8 Hz, 3H, CH3), 0.98-0.89 (m, 12H, CH3). ESI-MS (MW 627.82): m/z 628.3
[M + H]+, 650.4 [M + Na]+, 1277.1 [2M + Na]+, C18 RP-HPLC (A : 0.1% TFA in H2O, B: 0.1%
TFA in MeOH, 50-100% B, 1 ml/min, 5 min): tR= 5.62 min.
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Boc-Valu-Alau-Leuu-Prou-Prou-Valu-Alau-Leuu-NHMe (2). 2 was prepared from 7 (0.021 g,
0.030 mmol) and 10 (0.020 g, 0.032 mmol) as described in the general procedure. (0.020 g, 56
%).1H NMR : (300MHz, CD3OH) δ = 6.73 (3, 1H, NH), 6.57 (m, 1H, NH), 6.52 (d, J = 9.8 Hz,
1H, NH), 6.43 (m, 2H, NH), 6.35 (m, 2H, NH), 6.23 (m, 1H, NH), 6.13-5.96 (m, 4H, NH), 5.92-
5.85 (m, 2H, NH), 5.82 (m, 1H, NH), 4.34-4.12 (m, 1H, CHN), 4.09-3.83 (m, 4H, CHN), 3.70-
3.39 (m, 15H, CHN-CH2N), 3.05-2.95 (m, 1H, CH2N), 2.88-2.74 (m, 3H, CH2N), 2.73 (d, J = 4.6
Hz, 3H, CH3N), 2.65-2.33 (m, 4H, CH2N), 2.09-1.83 (m, 6H, CH2), 1.81-1.56 (m, 6H, CH-CH2),
1.48 (s, 9H, Boc), 1.34-1.22 (m, 4H, CH2), 1.13-1.02 (m, 6H, CH3), 0.99-0.85 (m, 24H, CH3).
ESI-MS (Mw 1124.47) : m/z 585.0 [M+2Na]2+ , 1146.8 [M+Na]+, C18 RP-HPLC (A : 0.1% TFA
in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1 ml/min, 5 min): tR= 6.46 min.
Boc-Prou-Prou-Valu-Alau-Leuu-NHMe (11). 11 was prepared from 8d (0.217 g, 0.030 mmol)
and 10 (0.280 g, 0.032 mmol) as described in the general procedure. (0.320 g, 70 %).1H NMR :
(300MHz, CD3CN) δ = 6.85 (m, 1H, NH), 6.26 (m, 1H, NH), 6.14 (d, J = 8.6 Hz, 1H, NH), 6.11
(d, J = 9.8 Hz, 1H, NH), 6.04 (m, 1H, NH), 5.74 (d, J = 9.7 Hz, 1H, NH), 5.67 (d, J = 10.8 Hz,
1H, NH), 5.62 (m, 1H, NH), 5.22 (d, J = 10.3 Hz, 1H, NH), 4.29-4.15 (m, 2H, CHN), 4.08-3.92
(m, 1H, CHN), 3.91-3.77 (m, 1H, CHN), 6.68-3.48 (m, 5H, CHN, CH2N), 3.46-3.13 (m, 5H,
CH2N), 2.77-2.68 (m, 1H, CH2N), 2.65 (d, J = 4.7 Hz, 3H, CH3N), 2.55-2.30 (m, 3H, CH2N),
2.12-2.25 (m, 1H, CH2N), 2.07-1.50 (m, 10H, CH, CH2), 1.47 (s, 9H, Boc), 1.21-1.12 (m, 2H,
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CH2), 0.98 (d, J = 6.9 Hz, 3H, CH3), 0.92 (d, J = 6.5 Hz, 3H, CH3), 0.90 (d, J = 6.7 Hz, 3H, CH3),
0.85 (d, J = 6.7 Hz, 3H, CH3), 0.81 (d, J = 6.8 Hz, 3H, CH3). ESI-MS (MW 753.98) : m/z 776.5
[M+Na]+, C18 RP-HPLC (A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1 ml/min,
5 min): tR= 5.86 min.
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Boc-Valu-Alau-Leuu-Prou-Prou-Prou-Valu-Alau-Leuu-NHMe (3). 3 was prepared from 7 (0.027
g, 0.038 mmol) and 11 (0.030 g, 0.040 mmol) as described in the general procedure. (0.030 g, 60
%).1H NMR: (300MHz, CD3OH) δ = 6.68 (m, 2H, NH), 6.51 (m, 1H, NH), 6.45 (d, J = 9.9 Hz,
1H, NH), 6.42-6.14 (m, 5H, NH), 6.08 (d, J = 9.2 Hz, 1H, NH), 6.01-5.81 (m, 6H, NH), 4.21-4.10
(m, 1H, CHN), 4.08-3.97 (m, 2H, CHN), 3.95-3.81 (m, 3H, CHN), 3.68-3.17 (m, 19H, CHN-
CH2N), 3.17-3.02 (m, 2H, CH2N), 3.01-2.79 (m, 3H, CH2N), 2.73 (d, J = 4.6 Hz, 3H, CH3N),
2.70 (m, 1H, CH2N), 2.65-2.49 (m, 1H, CH2N), 2.49-2.34 (m, 1H, CH2N), 2.11-1.90 (m, 12H,
CH2) 1.79-1.60 (m, 4H, CH), 1.47 (s, 9H, Boc), 1.33-1.22 (m, 4H, CH2), 1.13-1.02 (m, 6H, CH3),
0.99-0.84 (m ; 24H, CH3). ESI-MS (MW 1250.62): m/z 1250.6 [M+H]+, 1276.9 [M+Na]+, C18
RP-HPLC (A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1 ml/min, 5 min): tR=
6.27 min.
Boc-Prou-Prou-Prou-Valu-Alau-Leuu-NHMe (12). 12 was prepared from 8d (0.135 g, 0.397
mmol) and 11 (0.300 g, 0.397 mmol) as described in the general procedure. (0.260 g, 75 %).1H
NMR : (300MHz, CD3OH) δ = 6.69 (m, 1H, NH), 6.56 (m, 1H, NH), 6.46-6.15 (m, 5H, NH),
6.10 (d, J = 8.8 Hz, 1H, NH), 6.05-5.88 (m, 2H, NH), 4.29-3.81 (m, 5H, CHN), 3.68-3.50 (m, 5H,
CHN-CH2N), 3.44-3.23 (m, 8H, CH2N), 3.22-3.03 (m, 3H, CH2N), 2.81-2.74 (m, 1H, CH2N),
2.73 (d, J = 4.7 Hz, 3H, CH3), 2.66-2.51 (m, 1H, CH2N), 2.51-2.38 (m, 1H, CH2N), 2.12-1.81
(m, 12H, CH2), 1.79-1.59 (m, 2H, CH), 1.50 (s, 9H, Boc), 1.34-1.21 (m, 2H, CH2), 1.06 (d, J =
6.8 Hz, 3H, CH3), 0.97-0.86 (m, 12H, CH3). ESI-MS (MW 880.13): m/z 902.6 [M+Na]+, C18 RP-
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Boc-Valu-Alau-Leuu-Prou-Prou-Prou-Prou-Valu-Alau-Leuu-NHMe (4). 4 was prepared from 7
(0.102 g, 0.143 mmol) and 12 (0.120 g, 0.136 mmol) as described in the general procedure.
(0.140 g, 82 %).1H NMR : (300MHz, DMSO) δ = 6.88 (m, 1H, NH), 6.79 (m, 1H, NH), 6.57 (d,
J = 9.1 Hz, 1H, NH), 6.42 (m, 1H, NH), 6.20 (m, 1H, NH), 6.10-5.71 (m, 12H, NH), 3.96-3.46
(m, 10H, CHN), 3.26-2.55 (m, 28H, CH2N), 2.55 (d, 3H, CH3N), 1.93-1.72 (m, 16H, CH2), 1.70-
1.52 (m, 4H, CH), 1.39 (s, 9H, Boc), 1.18-1.07 (m, 4H, CH2), 0.99-0.91 (m, 6H, CH3), 0.90-0.75
(m, 24H, CH3). ESI-MS (MW 1376.78): m/z 689.0 [M+2H]2+ , 1398.8 [M+Na]+ , C18 RP-HPLC
(A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1 ml/min, 5 min): tR= 6.29 min.
Boc-Prou-Prou-Prou-Prou-Valu-Alau-Leuu-NHMe (13). 13 was prepared from 8d (0.049 g,
0.143 mmol) and 12 (0.120 g, 0.136 mmol) as described in the general procedure. (0.104 g, 76
%).1H NMR : (300MHz, CD3CN) δ = 6.87 (m, 1H, NH), 6.53-6.40 (m, 2H, NH), 6.32 (m, 1H,
NH), 6.27-6.14 (m, 2H, NH), 6.08 (m, 1H, NH), 5.99 (m, 1H, NH), 5.89-5.69 (m, 3H, NH), 4.46-
4.32 (m, 1H, CHN), 4.30-4.12 (m, 2H, CHN), 4.10-3.93 (m, 2H, CHN), 3.90-3.77 (m, 2H, CHN),
3.67-3.49 (m, 5H, CH2N), 3.47-3.12 (m, 11H, CH2N), 3.11-2.81 (m, 2H, CH2N), 2.78-2.70 (m,
1H, CH2N), 2.66 (d, J = 4.7 Hz, 3H, CH3N), 2.60-2.30 (m, 3H, CH2N), 2.13-1.77 (m, 13H, CH2),
1.75-1.50 (m, 5H, CH-CH2), 1.48 (s, 9H, Boc), 1.25-1.15 (m, 2H, CH2), 1.00 (d, J = 6.8 Hz, 3H,
CH3), 0.93 (d, J = 6.5 Hz, 3H, CH3), 0.92 (d, J = 6.7 Hz, 3H, CH3), 0.87 (d, J = 6.7 Hz, 3H,
CH3), 0.82 (d, J = 6.7 Hz, 3H, CH3). ESI-MS (MW 1006.31): m/z 503.8 [M+2H]2+ , 1006.4
[M+H]+, C18 RP-HPLC (A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1 ml/min, 5
min): tR= 6.01 min.
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Boc-Valu-Alau-Leuu-Prou-Prou-Prou-Prou-Prou-Valu-Alau-Leuu-NHMe (5). 5 was prepared
from 7 (0.074 g, 0.104 mmol) and 13 (0.100 g, 0.099 mmol) as described in the general
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procedure. (0.090 g, 60 %).1H NMR : (300MHz, DMSO) δ = 7.0-6.75 (m, 2H, NH), 6.56 (d, J =
8.9 Hz, 1H, NH), 6.41 (m, 1H, NH), 6.20 (m, 1H, NH), 6.09-5.72 (m, 13H, NH), 4.18-3.72 (m,
6H, CHN), 3.63-3.30 (m, 31H, CHN-CH2N), 3.30-2.75 (m, 6H, CH2N), 2.72 (d, 3H, CH3N),
2.11-1.71 (m, 20H, CH2), 1.69-1.50 (m , 4H, CH), 1.39 (s, 9H, Boc), 1.29-1.16 (m, 4H, CH2),
0.99-0.90 (m, 6H, CH3), 0.90-0.74 (m, 24H, CH3). ESI-MS (MW 1502.94) : m/z 771.8 [M+K]2+,
1524.8 [M+Na]+, C18 RP-HPLC (A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1
ml/min, 5 min): tR= 6.34 min.
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Boc-Prou-2-Azidomethyl-pyrrolidine (15). 15 was prepared from 8d (0.729 g, 2.137 mmol) and
14 (0.509 g, 2.25 mmol) as described in the general procedure. (0.710 g, 89 %).1H NMR:
(300MHz, CDCl3) δ = 6.38 (s, 1H, NH), 4.16-4.01 (m, 2H, CHN), 3.56-3.11 (m, 8H, CH2N),
2.11-1.78 (m, 8H, CH2), 1.49 (s, 9H, Boc). ESI-MS (MW 352.43) : m/z 353.0 [M+H]+, 726.9
[2M+Na]+, C18 RP-HPLC (A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1 ml/min,
5 min): tR= 5.40 min.
Boc-Prou-Prou-2-Azidomethyl-pyrrolidine (16). 16 was prepared from 8d (0.609 g, 1.78 mmol)
and 15 (0.662 g, 1.87 mmol) as described in the general procedure. (0.665 g, 74 %).1H NMR :
(300MHz, CDCl3) δ = 6.91 (s, 1H, NH), 6.54 (s, 1H, NH), 4.28-4.15 (m, 1H, CHN), 4.16-4.03
(m, 2H, CHN), 3.54-3.08 (m, 12H, CH2N), 2.10-1.83 (m, 10H, CH2), 1.83-1.64 (m, 2H, CH2),
1.49 (s, 9H, Boc). ESI-MS (MW 478.59): m/z 501.3 [M+Na]+ , 979.0 [2M+Na]+, C18 RP-HPLC
(A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1 ml/min, 5 min): tR= 5.62 min.
Boc-Prou-Prou-Prou-OSu (17). 16 (0.640 g, 0.418 mmol) was dissolved in ethanol. Pd/C 10%
(0.060 g) was introduced under Ar atmosphere. The reaction mixture was put under vacuum then
flushed with H2 (three times) and the mixture was finally stirred at room temperature under H2
for 12h. Pd/C was then removed by microfiltration, washed with EtOH and the solvent was then
completely evaporated under vacuum. Disuccinimidyl carbonate (0.410 g, 1.62 mmol) was
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suspended in dry CH2Cl2 (10 mL) and the amine (0.610 g, 1.35 mmol) was added portionwise.
The reaction mixture was stirred at room temperature under N2 atmosphere for 4h. After 4h
stirring a white precipitate was formed (HOSu). CH2Cl2 was added and the precipitate was
filtered and washed with CH2Cl2. Organic phase was washed with a 1M KHSO4 aqueous
solution and water, dried over Na2SO4, and concentrated under reduced pressure. 1mL of CH2Cl2
was added to the residue and the product 17 was precipitated as a white solid by adding Et2O
(0.770 g, 96%). 1H NMR : (300MHz, CDCl3) δ = 8.23 (s, 1H, NH), 7.08 (s, 1H, NH), 6.63 (s, 1H,
NH), 4.33-4.19 (m, 1H, CHN), 4.18-4.02 (m, 2H, CHN), 3.55-3.03 (m, 12H, CH2N), 2.82 (s, 4H,
CH2), 2.10-1.80 (m, 10H, CH2), 1.79-1.65 (m, 2H, CH2), 1.49 (s, 9H, Boc). ESI-MS (MW
593.67) : m/z 594.1 [M+H]+.
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Boc-Prou-Prou-Prou-Prou-Prou-2-Azidomethyl-pyrrolidine (18). 18 was prepared from 17
(0.053 g, 0.089 mmol) and III.16 (0.045 g, 0.094 mmol) as described in the general procedure.
(0.060 g, 75 %).1H NMR : (300MHz, CDCl3) δ = 7.29-7.06 (m, 4H, NH), 6.63 (s, 1H, NH), 4.32-
4.01 (m, 6H, CHN), 3.61-3.02 (m, 24H, CH2N), 2.15-1.83 (m, 20H, CH2), 1.80-1.67 (m, 4H,
CH2), 1.50 (s, 9H, Boc). ESI-MS (MW 857.06) : m/z 857.2 [M+H]+, 879.3 [M+Na]+, C18 RP-
HPLC (A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1 ml/min, 5 min): tR= 6.07
min.
Boc-Prou-Prou-Prou-Prou-Prou-Prou-OSu (19). 18 (0.630 g, 0.740 mmol) was dissolved in
ethanol. Pd/C 10% (0.060 g) was introduced under Ar atmosphere. The reaction mixture was put
under vacuum then flushed with H2 (three times) and the mixture was finally stirred at room
temperature under H2 for 12h. Pd/C was then removed by microfiltration, washed with EtOH and
the solvent was then completely evaporated under vacuum. Disuccinimidyl carbonate (0.225 g,
0.880 mmol) was suspended in dry CH2Cl2 (10 mL) and the amine (0.610 g, 0.734 mmol) was
added portionwise. The reaction mixture was stirred at room temperature under N2 atmosphere
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for 4h. After 4h stirring a white precipitate was formed (HOSu). CH2Cl2 was added and the
precipitate was filtered and washed with CH2Cl2. Organic phase was washed with a 1M KHSO4
aqueous solution and water, dried over Na2SO4, and concentrated under reduced pressure. 1mL of
CH2Cl2 was added to the residue and the product 19 was precipitated as a white solid after
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addition of Et2O (0.690 g, 97%). H NMR : (300MHz, CDCl3) δ = 8.31 (s, 1H, NH), 7.31-7.22
(m, 3H, NH), 7.18 (s, 1H, NH), 6.63 (s, 1H, NH), 4.28-4.03 (m, 6H, CHN), 3.53-3.05 (m, 24H,
CH2N), 2.83 (s, 4H, CH2), 2.11-1.84 (m, 20H, CH2), 1.81-1.66 (m, 4H, CH2), 1.48 (s, 9H, Boc).
ESI-MS (MW 972.14) (in MeOH the methlyl ester is formed Mw 888): m/z 889.2 [M+H]+, 911.4
[M+Na]+, C18 RP-HPLC (A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1 ml/min,
5 min): tR= 5.68 min.
Boc-Prou-Prou-Prou-Prou-Prou-Prou-Valu-Alau-Leuu-NHMe (20). 20 was prepared from 19
(0.020 g, 0.020 mmol) and 9 (0.011 g, 0.020 mmol) as described in the general procedure. (0.015
g, 55 %). 1H NMR : (300MHz, CD3CN) δ = 6.87 (m, 1H, NH), 6.65 (m, 1H, NH), 6.43 (m, 1H,
NH), 6.52-6.38 (m, 2H, NH), 6.35-6.14 (m, 4H, NH), 6.12-5.99 (m, 1H, NH), 5.90-5.79 (m, 2H,
NH), 5.76 (m, 1H, NH), 4.43-4.31 (m, 1H, CHN), 4.28-4.18 (m, 1H, CHN), 4.14-3.71 (m, 6H,
CHN), 3.70-3.49 (m, 4H, CHN-CH2N), 3.74-3.07 (m, 20H, CH2N), 3.05-2.82 (m, 3H, CH2N),
2.66 (d, J = 4.7 Hz, 3H, CH3N), 2.57-2.27 (m, 4H, CH2N), 1.97-1.73 (m, 24H, CH2), 1.71-1.54
(m, 2H, CH), 1.47 (s, 9H, Boc), 1.27-1.09 (m, 2H, CH2), 1.00 (d, J = 6.8 Hz, 3H, CH3), 0.94-0.77
(m, 12H, CH3). ESI-MS (MW 1258.60) : m/z 652.1 [M+2Na]2+, 1280.8 [M+Na]+, C18 RP-HPLC
(A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1 ml/min, 5 min): tR= 6.13 min.
Boc-Valu-Alau-Leuu-Prou-Prou-Prou-Prou-Prou-Prou-Prou-Valu-Alau-Leuu-NHMe (6). 6 was
prepared from 7 (0.008 g, 0.011 mmol) and 20 (0.015 g, 0.011 mmol) as described in the general
procedure. (0.013 g, 60 %).1H NMR : (300MHz, CD3CN) δ = 6.84 (m, 1H, NH), 6.41 (m, 1H,
NH), 6.30 (m, 2H, NH), 6.23-6.13 (m, 2H, NH), 6.11-5.95 (m, 3H, NH), 5.89-5.79 (m, 4H, NH),
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5.77-5.48 (m, 8H, NH), 4.41-4.31 (m, 1H, CHN), 4.27-4.13 (m, 1H, CHN), 4.10-3.75 (m, 6H,
CHN), 3.70-3.13 (m, 20H, CHN-CH2N), 3.10-2.73 (m, 10H, CH2N), 2.67 (d, J = 4.6 Hz, 3H,
CH3N), 2.62-2.08 (m, 15H, CH2N), 1.94-1.54 (m, 32H, CH-CH2), 1.44 (s, 9H, Boc), 1.33-1.09
(m, 4H, CH2), 1.08-0.99 (m, 6H, CH3), 0.93-0.78 (m, 24H, CH3). ESI-MS (MW 1798.27) : m/z
900.0 [M+2H]2+, C18 RP-HPLC (A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1
ml/min, 5 min): tR= 6.43 min.
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Boc-Prou-Prou-OSu (21). 15 (0.120 g, 0.306 mmol) was solubilized in ethanol. Pd/C 10% was
introduced under Ar. The reaction mixture was put under vacuum then flushed with H2 (three
times) and the mixture was finally stirred at room temperature under H2 atmosphere for 12h.
Pd/C was then removed by microfiltration, washed with EtOH and the solvent was then
completely evaporated under vacuum. Disuccinimidyl carbonate (0.094 g, 0.367 mmol) was
suspended in dry CH2Cl2 (8mL) and the amine (0.100 g, 0.306 mmol) was added portionwise.
The reaction mixture was stirred at room temperature under N2 for 4h. After 4h stirring a white
precipitate was formed (HOSu). CH2Cl2 was added and the precipitate was filtered off and
washed with CH2Cl2. The organic layers were combined, washed with a 1M KHSO4 aqueous
solution and water, dried over Na2SO4, and concentrated under reduced pressure. 1mL of CH2Cl2
was added to the residue and the product 24 was precipitated as a white solid after addition of
Et2O (0.130 g, 90%). 1H NMR : (300MHz, CDCl3) δ = 8.14 (s, 1H, NH), 6.53 (s, 1H, NH), 4.27-
4.06 (m, 2H, CHN), 3.48-3.30 (m, 5H, CH2N), 3.29-3.11 (m, 3H, CH2N), 2.83 (s, 4H, CH2),
2.10-1.69 (m, 8H, CH2), 1.47 (s, 9H, Boc). ESI-MS (MW 476.52) : m/z 490.1 [M+Na]+, 956.8
[2M+Na]+
Boc-Prou-Prou-NHMe (22). Methylamine hydrochloride (0.188 g, 0.280 mmol) was dissolved in
CH3CN. DIPEA (0.14 ml, 0.830 mmol) was then added and the mixture was cooled to 0°C prior
to the dropwise addition of 21 (0.130 g, 0.280 mmol), dissolved in CH3CN. After completion, the
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reaction mixture was evaporated, dissolved in EtOAc and treated with saturated NaHCO3
aqueous solution, 1M KHSO4 aqueous solution and brine. The organic layer was then dried over
Na2SO4 and evaporated. Flash column chromatography (CH2Cl2-MeOH (v/v), 95:5) over silica
gel gave 22 (0.090 g, 84%). 1H NMR : (300MHz, CD3OH) δ = 6.64 (m, 1H, NH), 6.33 (m, 1H,
NH), 6.04 (m, 1H, NH), 4.07-3.81 (m, 2H, CHN), 3.49-3.04 (m, 8H, CH2N), 2.73 (d, J = 4.6 Hz,
3H, CH3N), 2.08-1.72 (m, 8H, CH2), 1.49 (m, 9H, Boc). ESI-MS (MW 383.49) : m/z 384.0
[M+H]+ , 406.1 [M+Na]+ , 788.8 [2M+Na]+, C18 RP-HPLC (A : 0.1% TFA in H2O, B: 0.1% TFA
in MeOH, 50-100% B, 1 ml/min, 5 min): tR= 4.20 min.
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Boc-Valu-Alau-Leuu-Prou-Prou-Prou-NHMe (23). 23 was prepared from 7 (0.053 g, 0.074
mmol) and 22 (0.030 g, 0.078 mmol) as described in the general procedure. (0.035 g, 51 %).1H
NMR : (300MHz, CD3OH) δ = 7.15 (m, 1H, NH), 6.96 (m, 1H, NH), 6.76 (m, 1H, NH), 6.62-
6.50 (m, 2H, NH), 6.23-5.93 (m, 5H, NH), 4.15-3.79 (m, 5H, CHN), 3.76-3.62 (m, 1H, CHN),
3.61-3.06 (m, 16H, CH2N), 2.94-2.78 (m, 2H, CH2N), 2.75 (d, J = 4.6 Hz, 3H, CH3N), 2.09-1.80
(m, 12H, CH2), 1.78-1.62 (m, 2H, CH), 1.47 (s, 9H, Boc), 1.37-1.26 (m, 2H, CH2), 1.08 (d, J =
6.6 Hz, 3H, CH3), 0.96-0.92 (m, 12H, CH3). ESI-MS (MW 880.13) : m/z 463.0 [M+2Na]2+,
902.6 [M+Na]+, C18 RP-HPLC (A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1
ml/min, 5 min): tR= 5.64 min
Boc-Prou-Prou-Prou-NHMe (24). Methylamine hydrochloride (0.044 g, 0.65 mmol) was
dissolved in CH3CN. DIPEA (0.3 ml, 0.151 mmol) was then added and the mixture was cooled
down to 0°C prior to the dropwise addition of 17 (0.350 g, 0.590 mmol), dissolved in CH3CN.
After completion, the reaction mixture was evaporated, dissolved in EtOAc and treated with
saturated NaHCO3 aqueous solution, 1M KHSO4 aqueous solution and brine. The organic layer
was then dried over Na2SO4 and evaporated. Flash column chromatography (CH2Cl2-MeOH
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(v/v), 95:5) over silica gel gave 21 (0.268 g, 90%). H NMR : (300MHz, CD3CN) δ = 6.61 (m,
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1H, NH), 6.33 (m, 1H, NH), 2.74 (m, 1H, NH), 5.37 (m, 1H, NH), 4.02-3.74 (m, 3H, CHN),
3.41-3.11 (m, 10H, CH2N), 3.08-2.82 (m, 2H, CH2N), 2.67 (d, J = 4.7 Hz, 3H, CH3N), 2.00-1.71
(m, 12H, CH2), 1.47 (s, 9H, Boc). ESI-MS (MW 509.64): m/z 510.3 [M+H]+, 532.3 [M+Na]+,
C18 RP-HPLC (A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-100% B, 1 ml/min, 5 min):
tR= 4.78 min.
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Boc-Prou-Prou-Prou-Prou-Prou-Prou-NHMe, (25). 25 was prepared from 17 (0.110 g, 0.186
mmol) and 22 (0.100 g, 0.196 mmol) as described in the general procedure. (0.070 g, 40 %).1H
NMR : (300MHz, CD3OH) δ = 7.06-6.89 (m, 4H, NH), 6.75 (s, 1H, NH), 6.33 (s, 1H, NH), 6.05
(s, 1H, NH), 4.06-3.79 (m, 6H, CHN), 3.49-3.18 (m, 18H, CH2N), 3.13-2.97 (m, 6H, CH2N),
2.73 (d, J = 4.0 Hz, 3H, CH3N), 2.10-1.77 (m, 24H, CH2), 1.48 (s, 9H, Boc). ESI-MS (MW
888.11): m/z 910.6 [M+Na]+, C18 RP-HPLC (A : 0.1% TFA in H2O, B: 0.1% TFA in MeOH, 50-
100% B, 1 ml/min, 5 min): tR= 6.47min.
Boc-Prou-Prou-Prou-Prou-Prou-Prou-Prou-Prou-Prou-NHMe, (26). 26 was prepared from 17
(0.040 g, 0.067 mmol) and 25 (0.060 g, 0.067 mmol) as described in the general procedure.
(0.041 g, 48 %).1H NMR : (300MHz, CD3OH) δ = 7.11-6.84 (m, 7H, NH), 6.76 (s, 1H, NH),
6.30 (s, 1H, NH), 6.06 (s, 1H, NH), 4.08-3.79 (m, 9H, CHN), 3.53-3.18 (m, 27H, CH2N), 3.17-
2.97 (m, 9H, CH2N), 2.73 (d, J = 4.1 Hz, 3H, CH3N), 2.10-1.75 (m, 36H, CH2), 1.48 (s, 9H, Boc).
ESI-MS (MW 1266.58): m/z 1266.5 [M+H]+, C18 RP-HPLC (A : 0.1% TFA in H2O, B: 0.1%
TFA in MeOH, 50-100% B, 1 ml/min, 5 min): tR= 6.98 min.
ASSOCIATED CONTENT
*S Supporting Information
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General methods, copies of 1H NMR spectra, HPLC profiles and ESI-MS spectra for compounds
2-6, 10-13, and 15-26, tables of 1H chemical shifts of compounds 2,3 and 5 and ORTEP drawings
of structures of 2 and 3. This material is available free of charge via the Internet at
http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding author
*E-mail : g.guichard@iecb.u-bordeaux.fr
Present Address
# (J.F.) UREkA Sàrl, 2 rue Robert Escarpit, 33607 Pessac, France
Notes
The authors declare no competing financial interest.
ACKOWLEDGMENTS
This work was supported in part by the Centre National de la Recherche Scientifique (CNRS),
the Université de Bordeaux and the Region Aquitaine. We thank Nathalie Trouche and
Christophe Pardin for some early work on (Prou) repeats and Axelle Grelard for assistance with
NMR measurements. The crystallographic data were collected at the IECB X-ray facility
(UMS3033, CNRS and Université de Bordeaux, US001 INSERM).
REFERENCES
(1)
(2)
Chatterjee, J.; Rechenmacher, F.; Kessler, H. Angew. Chem. Int. Ed. 2013, 52,
Chatterjee, J.; Gilon, C.; Hoffman, A.; Kessler, H. Acc. Chem. Res. 2008, 41,
254.
1331.
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