Conformational behavior of peptides containing residues of 3-azetidinesulfonic (3AzeS) and 4-piperidinemethanesulfonic (4PiMS) acids

Article abstract of DOI:10.1016/j.tetasy.2013.12.001

The conformational behavior of four model peptides containing residues of 3-azetidinesulfonic (3AzeS) and 4-piperidinemethane sulfonic (4PiMS) acids was studied in both a crystalline state and in solution using X-ray, NMR, and IR experiments. It was found that in the crystalline state, both of the models di- and tripeptides studied adopted extended conformations and demonstrated considerable conformational flexibility. In solution, it is likely that a flexible ensemble of conformations is adopted, including extended structures and more compact ones without persistent hydrogen bonds. One of the most interesting features of the peptides was the axial chirality observed due to the slow rotation around the amide bond formed by the endocyclic nitrogen atoms of the non-chiral 3AzeS and 4PiMS residues. It was shown for one of the derivatives that the configuration of the chiral axis had an impact on the conformation of the neighboring amino acid residue.

Full text of DOI:10.1016/j.tetasy.2013.12.001

Tetrahedron: Asymmetry 25 (2014) 229–237
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Conformational behavior of peptides containing residues of
3-azetidinesulfonic (3AzeS) and 4-piperidinemethanesulfonic
(4PiMS) acids
Oleksandr O. Grygorenko a, , Sergey Zhersh a,b, Bohdan V. Oliinyk a,b,c, Oleg V. Shishkin c,
⇑
Andrey A. Tolmachev a,b
a National Taras Shevchenko University of Kyiv, Volodymyrska Street 64, Kyiv 01601, Ukraine
b Enamine Ltd, Alexandra Matrosova Street 23, Kyiv 01103, Ukraine
c STC ‘Institute for Single Crystals’, National Academy of Sciences of Ukraine, Lenina ave. 60, 61001 Kharkiv, Ukraine
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 October 2013
Accepted 2 December 2013
The conformational behavior of four model peptides containing residues of 3-azetidinesulfonic (3AzeS)
and 4-piperidinemethane sulfonic (4PiMS) acids was studied in both a crystalline state and in solution
using X-ray, NMR, and IR experiments. It was found that in the crystalline state, both of the models
di- and tripeptides studied adopted extended conformations and demonstrated considerable conforma-
tional flexibility. In solution, it is likely that a flexible ensemble of conformations is adopted, including
extended structures and more compact ones without persistent hydrogen bonds. One of the most inter-
esting features of the peptides was the axial chirality observed due to the slow rotation around the amide
bond formed by the endocyclic nitrogen atoms of the non-chiral 3AzeS and 4PiMS residues. It was shown
for one of the derivatives that the configuration of the chiral axis had an impact on the conformation of
the neighboring amino acid residue.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
that the aminosulfonic acid residue 2 (2PyMS) is capable of induc-
ing folded structures when introduced into model peptides.13
The sulfonamide is one of the non-classical bioisosteres of pep-
tide bonds, introduced by Liskamp et al. nearly 20 years ago.1 As
the nearest analogues of a-amino acids, a-aminosulfonic acids, as
O
S
O
S
H2N
OH
N
H
OH
well as their derivatives have limited stability, while most of the
‘sulfopeptides’ studied to date are sulfonamido-b-peptides. In par-
ticular, the derivatives of the simplest b-aminosulfonic acid, tau-
rine 1 have been evaluated as potential tools for tumor imaging
and/or radionuclide therapy,2 chemotactic peptides,3 inhibitors of
leukocyte adhesion,4 PPI inhibitors,5 HIV-1 non-nucleoside reverse
transcriptase6 and factor Xa7 inhibitors, and scaffolds for MC4
pharmacophoric groups.8 (S)-2-Pyrrolidinemethanesulfonic acid 2
was used in the design of fibrillogenesis peptide inhibitors,9 mor-
phiceptin and endomorphin-2 analogues,10 as well as chiral ligands
for enantioselective catalysis.11
O
(Tau)
O
1
2 (2PyMS)
O
S
HN
O
S
OH
OH
O
HN
O
3
(3AzeS)
4
(4PiMS)
Herein, we report an experimental study on the conformational
properties of the model peptides containing residues of 3-azeti-
dinesulfonic acid 3 and 4-piperidine methanesulfonic acid 4, for
which we propose abbreviations ‘3AzeS’ and ‘4PiMS’, respectively.
To the best of our knowledge, both compounds have not been used
in the design of model peptides and peptidomimetics. Derivatives
of 3 and 4 suitable for peptide synthesis have been described by
our group elsewhere.14 It should be noted that both aminosulfonic
acids 3 and 4 have a common feature: while being conformation-
ally restricted, their molecules possess planes of symmetry and
Despite numerous reports on biological properties of sulfon-
amide peptides, little effort has been made to study their confor-
mational behavior. Most of the previous papers in this area have
dealt with taurine-derived peptides.12 Recently, we have reported
⇑
Corresponding author. Tel.: +380 44 239 33 15; fax: +380 44 573 26 43.
E-mail address: gregor@univ.kiev.ua (O.O. Grygorenko).
0957-4166/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetasy.2013.12.001

230
O. O. Grygorenko et al. / Tetrahedron: Asymmetry 25 (2014) 229–237
are thus non-chiral. It was shown previously in the case of a-amino
acids that peptides derived from such molecules demonstrate unu-
sual conformational behavior.15
2. Results and discussion
2.1. Synthesis
Four model peptides 5 (PhC(O)-3AzeS-Phe-NHiPr), 6 (PhC(O)-
4PiMS-Phe-NHiPr),
7
(PhC(O)-Ala-3AzeS-Phe-NHiPr), and
8
(PhC(O)-Ala-4PiMS-Phe-NHiPr) were prepared from sulfochlorides
9 and 10 using standard coupling procedures (Scheme 1). The reac-
DIPEA
+
Cbz-Xaa-Cl
H-Phe-NHiPr
Cbz-Xaa-Phe-NHiPr
57 - 63%
9
11
12
, Xaa = 3AzeS
, Xaa = 4PiMS
, Xaa = 3AzeS
, Xaa = 4PiMS
10
13
H2, Pd-C
100%
PhC(O)Cl
PhC(O)-Xaa-Phe-NHiPr
H-Xaa-Phe-NHiPr
Et3N
61 - 76%
5, Xaa = 3AzeS
6, Xaa = 4PiMS
14, Xaa = 3AzeS
15, Xaa = 4PiMS
Boc-Ala-OH
EDC, HOBt
Figure 1. ORTEP diagram of compound 5: (a) molecule A; (b) molecule B. Thermal
ellipsoids are shown at 20% probability level.
60 - 79%
1. HCl
PhC(O)-Ala-Xaa-Phe-NHiPr
Boc-Ala-Xaa-Phe-NHiPr
2. PhC(O)Cl
DIPEA
68 - 72%
7, Xaa = 3AzeS
8, Xaa = 4PiMS
16
17
, Xaa = 3AzeS
, Xaa = 4PiMS
Scheme 1. Synthesis of model peptides 5–8.
tion of 9 or 10 with (S)-phenylalanine isopropylamide 11 in the
presence of ethyl diisopropylamine (DIPEA) gave dipeptides 12
and 13 in 57% and 63% yields, respectively. Upon deprotection of
12 and 13 by catalytic hydrogenation, amines 14 and 15 were
obtained quantitatively. The reaction of 14 and 15 with benzoyl
chloride in the presence of triethylamine gave dipeptides 5 (76%)
and 6 (61%). Coupling of 14 and 15 with (S)-N-Boc-alanine in the
presence
of
1-ethyl-3-(3-dimethylaminopropyl)carbodiimide
(EDC) and 1-hydroxybenzotriazole (HOBt) gave 17 (60%) and 18
(79%). Their deprotection followed by benzoylation led to tripep-
tides 7 and 8 (72% and 68% yields, respectively).
2.2. Conformation: X-ray diffraction data
Crystals of 5 and 6 for the X-ray diffraction studies were
obtained by slow evaporation of their solutions in ethanol and
hexanes, respectively (in the case of 6, the same type of crystals
were obtained from several different solvents). Both 5 and 6 crys-
tallize in non-centrosymmetric space groups (P212121 for 5 and P21
for 6); this indicates the presence of single enantiomers in the crys-
tals. Compound 5 crystallizes as a 1:1 solvate with EtOH. The
asymmetric part of the unit cells contains two molecules (A and
B) of the dipeptide and two solvate molecules for 5, and two mol-
ecules of the dipeptide for 6 (Figs. 1 and 2). The molecules A and B
of 6 have similar conformations [the root-mean-square deviation
(RMSD)16 is 0.652 Å].
Figure 2. ORTEP diagram of compound 6: (a) molecule A; (b) molecule B. Thermal
ellipsoids are shown at 20% probability level.
To describe the conformation of the peptide backbone in the
molecules of 5 and 6, the commonly accepted torsion angles (
u,
) can be used (Fig. 3).17 However, in order to compare
Figure 3. Backbone and side chain torsion angles in the model dipeptide 5.
w
, hi, and
x
the conformational behavior of distinct peptide residues (e.g.,
b- and d-aminosulfonic acid), a unified approach based on ‘exit vec-
tors’ would be more convenient. This method was developed for
the CAVEAT program to compare molecular scaffolds;18 recently,
we have applied it in order to discuss the molecular geometry of
bicyclic conformationally restricted diamines and related mole-
cules.19 To describe the conformation of a peptide residue, two exit
vectors n1 and n2 can be introduced for the N- and S(C)-ends of the
fragment. The relative orientation of these vectors can be described
by the four parameters r, u1, u2, and h defined in Figure 4.

O. O. Grygorenko et al. / Tetrahedron: Asymmetry 25 (2014) 229–237
231
which can be characterized by the
x
i angle. Due to the high barrier
of rotation around the amide bond, two stereoisomers (‘rotamers’)
are possible in the case of N-acyl derivatives of 3Aze and 4PiMS
residues. However, this is not a classical cis-trans isomerism, which
is quite common for peptides. The rotamers of the simplest N-acyl
derivatives of 3Aze and 4PiMS residues are enantiomeric due to the
axial chirality of their molecules (Fig. 5). In the case of dipeptides 5
and 6, the rotamers become diastereomeric. For 5, they were ob-
served as two different molecules (A and B), whereas for 6, only
the (aS)-isomer was found in the solid state. Since the choice of
the main backbone in the 3Aze and 4PiMS residues is deliberate,
we have assigned large absolute values for the xi angle
[ꢀ171.3(3) to ꢀ174.8(4)°] for the (aS)-isomers (i.e., the molecule
Figure 4. Definition of the parameters r, u1, u2, and h.
For the model dipeptides 5 and 6, as well as for compound 18
(PhC(O)-2PyMS-Phe-NHiPr),13 the geometric parameters r, u1
,
u2,
and h discussed above are summarized in Table 1. The values of
the distance between nitrogen and sulfur atoms are largest for
the d-aminosulfonic acid derivative 6 (r = 5.580(3) ꢀ 5.625(3) Å).
Notably, in the case of 5, the values of r (3.313(4) ꢀ 3.419(4) Å)
are considerably smaller compared to that of 18 (4.053(2) Å),
although both compounds are derived from b-aminosulfonic acid
residues. This might be due to the lower value of the torsion angle
hi + 1 in the case of 5 [108.4(3) ꢀ 113.6(3)° vs 172.1(2)° for 18].
The relative mutual orientations of n1 and n2 vectors in mole-
cules A and B of 5 are almost enantiomorphic: h = 77(2)° for A
and ꢀ85(1)° for B. In addition to a twist of the 3AzeS residue
defined by these values, there is also a bent feature of this
molecular fragment, which is related mainly to the u2 angle
(61.8(2) – 63.4(2)°). The conformation of the 4PiMS residue of 6
is characterized by an almost antiperiplanar orientation of the n1
and n2 vectors (ꢀ150.4(4) to ꢀ164.3(4)°). Again, the bent shape
of the 4PiMS residue is defined mainly by the u2 angle (78.2(1)–
85.0(1)°). The mutual orientations of the n1 and n2 vectors in both
3AzeS and 4PiMS residues are completely different to that of the
2PyMS residue in the molecule of 18. In the latter case, a turn-
inducing conformation is observed,13 which is characterized by
large values of both u1 and u2 angles [72.2(2)° and 55.9(1)°,
respectively], as well as relatively low value of h [ꢀ37.9(2)°].
In our opinion, the most interesting conformational feature of
dipeptides 5 and 6 is related to the amide bonds formed by the
endocyclic nitrogen atoms of the aminosulfonic acid residues,
A of 5 and both molecules of 6), and the smaller ones [xi
25.0(9)°] for the (aR)-isomer (i.e., the molecule B of 5).
=
The difference in the configuration of the chiral axis in mole-
cules A and B of 5 has an impact on the conformation of the rest
of the molecule. As mentioned earlier, the values of the h angle
are nearly the same for the molecules A and B of 6, but have oppo-
site signs in the case of 5. Similar tendencies are observed for val-
ues of the xi + 1 angle. In the molecules of 6, the conformation of
the backbone observed around the sulfonamide bond is (ꢀ)-gauche
Ph
Ph
H
H
S
O
S
(aR)-rotamers
(aS)-rotamers
N
N
O
N
N
O
O
NH2
NH2
O
O
NH2
O
O
O
H
H
S
O
S
O
Ph
Ph
NH2
O
Figure 5. The axial chirality of rotamers of the simplest N-benzoyl derivatives of
3Aze and 4PiMS residues (the chiral axis is shown by red dotted line).
Table 1
Backbone and side chain parameters in the molecules of model dipeptides 5, 6, and 18a
Parametera
Definitionb
5, Molecule A
5, Molecule B
6, Molecule A
6, Molecule B
18
r, Å
u1
N1–S1
3.419(4)
9.0(3)
3.313(4)
15.1(3)
5.625(3)
26.9(2)
5.580(3)
27.8(2)
4.053(2)
72.2(2)
180 ꢀ \ðC4—N1—S1Þ 5
180 ꢀ \ðC6—N1—S1Þ 6
180 ꢀ \ðN2—S1—N1Þ
C4–N1–S1–N2 5
C6–N1–S1–N2 6
C5–C4–N1–C1 5
C7–C6–N1–C1 6c
C4–N1–C1–C2 5
C6–N1–C1–C2 6c
N1–C1–C2–S1 5c
C1–C2–S1–N2 5
u2
h
63.4(2)
77(2)
61.8(2)
ꢀ85(1)
78.2(1)
ꢀ164.3(4)
85.0(1)
ꢀ150.4(4)
55.9(1)
ꢀ37.9(2)
ꢀ174.8(3)
ꢀ67.7(3)
xi
ꢀ174.8(4)
25.0(9)
ꢀ172.1(3)
ꢀ172.5(3)
ui + 1
159.1(5)
161.7(5)
131.9(3)
130.6(3)
hi + 1
wi + 1
113.6(3)
61.3(4)
108.4(3)
ꢀ165.7(3)
—
—
172.1(2)
ꢀ159.2(2)
–65.0(3)
ꢀ54.6(3)
C3–C13–S1–N2 6c
C2–S1–N2–C11 5
C13–S1–N2–C14 6
S1–N2–C11–C12 5
S1–N2–C14–C15 6
N2–C11–C12–N3 5
N2–C14–C15–N3 6
N2A–C11–C16–C17 5
xi + 1
ui+2
wi+2
v1iþ2
xi+2
ui+3
73.5(4)
ꢀ79.5(4)
135.7(4)
178.3(4)
ꢀ91.5(4)
ꢀ105.7(4)
143.3(4)
ꢀ78.2(3)
ꢀ87.3(3)
ꢀ17.8(4)
ꢀ63.5(4)
ꢀ75.6(3)
ꢀ83.9(3)
ꢀ22.8(4)
ꢀ67.4(4)
80.0(2)
ꢀ88.8(3)
144.8(2)
ꢀ62.8(3)
ꢀ63.3(5)
N2–C14–C19–C20 6
C11–C12–N3–C13 5
C14–C15B–N3–C16 6
C12–N3–C13–C15 5
C15–N3–C16–C17 6
174.5(4)
176.8(4)
179.8(3)
178.8(3)
180.0(3)
ꢀ121.3(5)
ꢀ107.8(6)
ꢀ93.8(5)
ꢀ94.0(5)
ꢀ66.9(4)
a
b
c
All of the plane and torsion angles are given in degrees.
The definitions of all of the parameters are given for the dipeptides 5 and 6.
The choice of C1 as the main backbone atom for the definition of xi angle was deliberate; the large absolute value of xi (close to 180°) was assigned to the (aS)-
i + 1, and hi + 1 angles followed this choice.
diastereoisomer. The definition of ui + 1, w

232
O. O. Grygorenko et al. / Tetrahedron: Asymmetry 25 (2014) 229–237
(-sc) [
x
i + 1 = ꢀ78.2(3) to ꢀ75.6(3)°]. In the case of 5, (+)-gauche
of chains are observed which differ in their direction; this is why
there are 2 ꢂ 2 ꢂ 2 = 8 molecules of 5 in the unit cell. The chains
are further held together via a number of weak intermolecular con-
tacts. The most important of them23 involve the benzoyl groups of
molecules A [H7A-H9A0 and H9A-H7A0, ( 0.5 + x, 0.5 ꢀ y, 1 ꢀ z),
H. . .H 2.263 Å] and ethanol B (H9A-O1SB0, (0.5 + x, 0.5 ꢀ y, 1 ꢀ z),
H. . .O 2.647 Å).
(+sc) and borderline (ꢀ)-anticlinal (ꢀac) conformations are ob-
served for the molecules A and B, respectively [ i + 1 = 73.5(4)
x
and ꢀ91.5(4)°]. Such absolute values of the torsion angle xi + 1
are typical for sulfonamide bonds;20 in particular, for the dipeptide
18,
x
i + 1 = 80.0(2)°.
The amide bond formed by the carboxylic group of the Phe res-
idue has a trans configuration for both 5 and 6 [
179.8(3)°].
x
i+2 = 174.5(4)°–
In the crystals of 6, the molecules are linked by hydrogen bonds
formed by the Phe NH and the benzoyl C@O of the next molecule
[for molecules A: N(2A)-H. . .O(1A)0, (1 ꢀ x, ꢀ0.5 + y, 1 ꢀ z), H. . .O
2.10 Å, N–H. . .O 173°; for molecules B: N(2B)-H. . .O(2B)0, (2 ꢀ x,
0.5 + y, 2 ꢀ z), H. . .O 2.02 Å, N–H. . .O 165°] (Fig. 7). It should be
noted that the iPrNH fragment is not involved in the hydrogen
The conformation of the Phe residue in the molecules of 5 cor-
responds to the b region of the Ramachandran plot [
= ꢀ79.5(4)°
to –105.7(4)°;
= 135.7(4)° to –143.3(4)°].21 Such a conformation
u
w
is typical for extended structures; it is not surprising, therefore,
that overall conformation of the peptide backbone in 5 can be de-
scribed as extended, with a small bulge observed in the sulfon-
amide region. Conversely in the case of 6, the conformation of
bonding. In addition, intermolecular C–H. . .p contacts are observed
between the isopropyl CH and benzoyl substituent of 6 [for mole-
cules A: C(16A)-H. . .C(9A)0, (x ꢀ 1, y ꢀ 1, z), H. . .C (
p) 2.84 Å, C–
the Phe residue is characteristic for the
dran plot [
= ꢀ87.3(3)° to ꢀ83.9(3)°,
a
region of the Ramachan-
H. . .C (
p
) 148°; for molecules B: C(16B)-H. . .C(9B)0, (x ꢀ 1, y + 1,
u
w
= ꢀ17.8(4)° to ꢀ22.8(4)°].
z), H. . .C (p) 2.85 Å, C–H. . .C (p) 154°]. All of these intermolecular
Although the overall conformation of the peptide backbone in 5
still remains extended, a pronounced twist is observed, which is
defined by the conformation of both the sulfonamide bond and
the Phe residue.
contacts result in the formation of two types of chains along the
b axis: one formed by the molecules A of 6 and another of B. Both
the chains have a helix-like configuration, with two molecules of 6
per helix turn.
The nitrogen atoms in the molecules of 5 and 6 have an almost
planar configuration. A slight pyramidalization is observed for the
azetidine nitrogen atom of 5 (the sum of the valent angles centered
at this atom is 355°).
Some differences are observed in the conformation of the side
chains of the amino acids in molecules of 5. In the molecule A of
5, the azetidine ring is planar within 0.01 Å deviation, whereas in
the molecule B, it adopts a flattened folded conformation, with a
puckering angle of 11°. The piperidine ring in the molecule of 6
is found in a chair conformation (the values of puckering parame-
ters: S = 1.12 ꢀ 1.14, h = 2.4°–2.7°,
w
= 2.9°–6.8°).22 The value of yjr
v1iþ2 angle [178.3(4)°] in molecule A of 5 corresponds to the anti-
periplanar orientation of phenyl and amino groups of the Phe res-
idue. For molecule B of 5 and both molecules of 6, the values of vi1þ2
angle [ꢀ63.3(5)°–67.4(4)°] are characteristic of a (ꢀ)-gauche (ꢀsc)
orientation of the corresponding fragments. Again, the distinct
conformations of 5 can be addressed in the configuration of the
chiral axis present in the molecules A and B.
Figure 6. Packing of the molecules of 5 in crystals viewed along a axis.
The elementary cell of 5 contains two molecules (A and B) and
two solvent molecules (EtOH, A and B). In the crystal lattice, the
molecules of 5 and EtOH are linked with a number of intermolec-
ular hydrogen bonds (Table 2), so that all of the NH and OH groups
are involved in hydrogen bonding. A short contact between the Phe
aCH of molecule B and the benzoyl fragment of the molecule A
from the neighboring elementary cell [C(11B)–H(11B). . .O(1A)0,
(2 ꢀ x, 0.5 + y, 1.5 ꢀ z), H. . .O 2.39 Å, C–H. . .O 140°] is also ob-
served. One ethanol molecule (A) acts as a bridge between mole-
cule A and molecule B of 5 from the neighboring elementary cell,
whereas the other one (ethanol B) is linked only to molecule B of
5. The repeating units of the elementary cell (molecule BꢁEtOH—
molecule A—EtOH) form chains along the b axis (Fig. 6). The neigh-
boring units in the chain are turned by 180°. Moreover, two types
Figure 7. Packing of the molecules of 6 in crystals viewed along a axis.
Table 2
Intermolecular hydrogen bonds in the crystal lattice of 5
Atoms
H-donor
H-acceptor
H. . .O, Å
X–H. . .O, deg
Symmetry operation
N(2A)–H(2NA)...O(1SA)
N(3A)–H(3NA)...O(4B)
N(2B)–H(2NB)...O(3A)
N(3B)–H(3NB)...O(1A)0
O(1SA)–H(1OA)...O(3B)0
O(1SB)–H(1OB)...O(1B)
Phe NH of molecule A
iPrNH of molecule A
Phe NH of molecule B
iPrNH of molecule B
OH of ethanol A
O of ethanol A
Phe C@O of molecule B
SO2 of molecule A
PhC@O of the next molecule A
SO2 of the next molecule B
PhC@O of the molecule B
2.06
2.09
2.07
2.03
2.13
1.97
151
175
173
166
155
166
2 ꢀ x, 0.5 + y, 1.5 ꢀ z
2 ꢀ x, ꢀ0.5 + y, 1.5 ꢀ z
OH of ethanol B

O. O. Grygorenko et al. / Tetrahedron: Asymmetry 25 (2014) 229–237
233
2.3. Conformation: solution studies
of the compound 6 also contained cross-peaks which are evident
for the gauche (and not trans) conformation of the sulfonamide
bond (Fig. 9), in particular, a strong correlation between the
signals corresponding to the CH2SO2 unit of the 4PiMS residue
The conformations of peptides 5–8 in solution were studied
using NMR and IR experiments. It was found that in CDCl3 as a sol-
vent, 5, 7, and 8 existed as two rotamers around the amide bonds,
showing two sets of signals in the 1H and 13C NMR spectra (the rot-
amer ratios ca. 1:1, 5 and 7, and 2:1 8). In the case of 6, a single set
of signals was present, although the signals corresponding to
piperidine CH2 units were significantly broadened in both the 1H
and 13C NMR spectra.
The addition of DMSO-d6 to CDCl3 solutions of 5–8 resulted in
remarkable changes of their NMR spectra. First, the overall appear-
ance of the spectra for 5, 7, and 8 changed, which was character-
ized by diminished differences between the signals of rotameric
pairs, an effect already observed at 5% v/v DMSO-d6. Moreover, in
the case of 8, the rotamer ratio reached a 1:1 value already at this
concentration of DMSO-d6. These data show that significant
changes occur to the conformation of the model peptides upon
addition of DMSO-d6 to their CDCl3 solutions.
On the other hand, remarkable shifts to a higher field were ob-
served for the signals corresponding to all of the Phe and iPr NH
protons of 5–7 (by 0.63–1.15 ppm at 10% v/v DMSO-d6), as well
as the Ala NH proton of 7 (by 0.36 ppm) (Fig. 8). Therefore, these
protons are unlikely to be involved in any intramolecular hydrogen
bonding, although such conclusions should be made carefully due
to the effects discussed in the above paragraph. Interpretation of
the data for the NH protons of 8 was complicated, since the chem-
ical shift of their signal depended on the concentration of DMSO-d6
in non-monotonic manner.
and Phe
aCH proton. Analogous (although weak) correlations,
which can be used as proof for the gauche conformation of the
corresponding sulfonamide bond, were found in NOESY spectrum
of 5.
The IR spectra of the model dipeptides in CHCl3 showed three
bands in the NH stretching region (in the case of 8, the band at
ꢃ3380 cmꢀ1 was not seen clearly), which can be assigned to free
and hydrogen-bonded C(O)NH and SO2NH (Table 3). It is note-
worthy that the relative intensities of the bands observed at
ꢃ3370 cmꢀ1 and ꢃ3160 cmꢀ1 were only slightly diminished upon
dilution of the solutions (Fig. 10). Moreover, almost no changes in
the overall appearance of the IR spectra occurred. This is contrary
to the behavior of the corresponding 2PyMS derivatives studied
previously.13 These data indicate that the conformational behav-
ior and aggregation of the model peptides 5–8 are slightly differ-
ent in the concentration range studied, which can be rationalized
by a tendency to adopt extended conformations under these
conditions.
In the amide I (ꢃ1650 cmꢀ1) and
m
(SO2) regions (ꢃ1300 cmꢀ1
and ꢃ1150 cmꢀ1) of the IR spectra, multiple bands are observed
for the model peptides 6, 7, and 8, a feature which can be assigned
to their conformational flexibility in solution. In the case of 5, the
existence of several conformations (which is obvious from NMR
data) could not be resolved by IR spectroscopy.
NOESY spectra of the compounds 5–8 in CDCl3 were poor
with non-trivial and informative correlations, partially due to
signal overlap in some cases. In particular, no significant interre-
sidual cross-peaks were observed, which can be used as a proof
of extended conformations for the model peptides studied in the
solution, although a flexible ensemble of conformations is more
likely. Evidence for a trans-conformation was obtained for the
amide bonds formed by the following nitrogen atoms: NHiPr of
6, Ala NH and NHiPr of 7, and Ala NH of 8. The NOESY spectrum
O
O
Ph
N
H
N
O
Strong NOE
Weak NOE
S
N
H
O
Ph
Figure 9. Significant correlations observed in the NOESY spectrum of 6 (CDCl3
solution).
8
8
8
8
δ, p. p. m.
δ, p. p. m.
δ, p. p. m.
δ, p. p. m.
7.5
7.5
7.5
7.5
7
7
6.5
6
7
6.5
6
7
6.5
6.5
NHPhe
NHiPr
NHAla
NHPhe
NHiPr
NHPhe
NHiPr
NHPhe
NHiPr
6
6
NHPhe
5.5
5.5
5.5
5.5
0
5
10
15
20
0
5
10
15
20
0
10
20
0
10
20
% v/v DMSO-d6
% v/v DMSO-d6
% v/v DMSO-d6
% v/v DMSO-d6
(a)
(b)
(c)
(d)
Figure 8. Chemical shift dependence of the NH resonances of 5 (a), 6 (b), 7 (c), and 8 (d) as a function of DMSO-d6 concentration (% v/v) in CDCl3. Peptide concentration 14 g/L
(ca. 30 mM). Weighted average values of the chemical shifts were considered when two rotamers were observed.

234
O. O. Grygorenko et al. / Tetrahedron: Asymmetry 25 (2014) 229–237
Table 3
Main absorption bands in IR spectra of 5–8 (CHCl3, peptide concentration 18 g/L (ca. 35 mM))
Bands, cmꢀ1
Assignmenta
5
6
7
8
3423
3350
3169
1673
1636
3422
3371
3160
1676
1673
1667
1624
1620
1615
1602
1341
1333
1324
1150
1132
3424
3368
3163
1670
1666
1657
1649
1644
3422
m
m
m
(NH) free C(O)NH
(NH) hydrogen-bonded C(O)NH and free SO2NH
(NH) hydrogen-bonded SO2NH
ꢃ3380 (sh)
3157
1671
1667
1659
1649
1636
1633
Amide I
1343
1152
1342
1327
1307
1150
1339
1336
1322
1159
1146
1143
m
as(SO2)
s(SO2)
m
a
The band assignment was carried out by using the literature data for analogous systems.13
Figure 10. NH stretching region of IR spectra of 5 (a), 6 (b), 7 (c), and 8 (d) (CHCl3).
to the methods reported in the literature. All other starting mate-
3. Conclusions
rials were purchased from Acros, Merck, Fluka, and UkrOrgSyntez.
Analytical TLC was performed using Polychrom SI F254 plates. Col-
umn chromatography was performed using Kieselgel Merck 60
(230–400 mesh) as the stationary phase. 1H, 13C, and all 2D NMR
spectra were recorded on a Bruker 170 Avance 500 spectrometer
(at 499.9 MHz for Protons and 124.9 MHz for Carbon-13). Chemical
shifts are reported in ppm downfield from TMS (1H, 13C) as an
internal standard. IR spectra were obtained on a Perkin Elmer BX
Although being non-chiral, the residues of 3-azetidinesulfonic
(3AzeS) and 4-piperidinemethane sulfonic (4PiMS) acids possess
an element of asymmetry in their peptide derivatives: a chiral axis
appears due to the slow rotation around amide bond formed by
the endocyclic nitrogen atoms. As it was shown for a model dipep-
tide derived from 3AzeS, the configuration of this chiral axis had a
strong influence on the conformation of the rest of the molecule.
So far, 3AzeS and 4PiMS residues were not capable of inducing
turn-like structures in the peptides; instead, extended conforma-
tions were found for the corresponding derivatives in crystals. It
should be noted however that in the crystalline state, a number of
intermolecular hydrogen bonds and other weak contacts were ob-
served between the different peptide molecules, which may play a
key role in determining and stabilizing the observed extended struc-
ture. Considerable conformational heterogeneity was also observed
for the the model peptides both in a crystalline state and in solution.
II FT-IR spectrometer. m
max (cmꢀ1) values in IR spectra are given
for the main absorption bands. Elemental analyses were performed
at the Laboratory of Organic Analysis, Department of Chemistry,
Kyiv National Taras Shevchenko University. Mass spectra were re-
corded on an Agilent 1100 LCMSD SL instrument.
4.2. Cbz-3AzeS-Phe-NHiPr 12
Amine 11 (7.84 g, 38 mmol) was dissolved in CH2Cl2 (100 mL),
and then DIPEA (5.01 g, 50 mmol) was added. The mixture was
cooled to 0 °C, and compound 5 (11.0 g, 38 mmol) in CH2Cl2
(100 mL) was added dropwise with stirring. The resulting mixture
was stirred at 0 °C for 30 min and then at rt for 1 h, then washed
with saturated aq NaHCO3 (100 mL), 1 M aq KHSO4 (100 mL), brine
(100 mL), dried over Na2SO4 and evaporated in vacuo. The residue
was purified by column chromatography (CH2Cl2–MeOH (39:1) as
4. Experimental
4.1. General
The solvents were purified according to the standard proce-
14
dures. Compounds 9,14 10,
and 1124 were prepared according

O. O. Grygorenko et al. / Tetrahedron: Asymmetry 25 (2014) 229–237
235
eluent) to give 12. Yield 10.0 g (57%). White amorphous solid. Mp
was cooled to 0 °C, and benzoyl chloride (0.51 g, 3.7 mmol) was
added dropwise. The resulting mixture was stirred at rt for 2 h,
then washed with 1 M aq KHSO4 (15 mL), brine (15 mL), dried over
Na2SO4, and evaporated in vacuo. The residue was purified by col-
umn chromatography (Hexanes–EtOAc (60:40) as eluent) to give 5.
Yield 1.20 g (76%). White solid. Mp 102–103 °C (EtOH).
61–64 °C. ½a D
ꢄ
¼ ꢀ4:8 (c 1.84, MeOH). MS (CI, m/z): 460 (MH+),
416 (MH+–CO2). Anal. Calcd for C23H29N3O5S: C, 60.11; H, 6.36;
N, 9.14; S, 6.98. Found C, 60.47; H, 5.98; N, 9.35, S, 6.72. 1H NMR
(500 MHz, CDCl3) d 7.40–7.25 (m, 8H), 7.22 (d, J = 7.4 Hz, 2H),
5.84 (s, 1H), 5.76 (d, J = 8.2 Hz, 1H), 5.07 (s, 2H), 4.18–4.11 (m,
1H), 4.11–4.05 (m, 1H), 4.05–3.93 (m, 3H), 3.86 (s, 1H), 3.50 (s,
1H), 3.07 (s, 1H), 3.01–2.91 (m, 1H), 1.11 (d, J = 6.0 Hz, 3H), 1.03
(d, J = 6.1 Hz, 3H). 13C NMR (126 MHz, CDCl3) d 169.5, 156.0,
136.3, 136.1, 129.4, 129.0, 128.5, 128.2, 128.0, 127.5, 67.1, 59.1,
50.8, 49.7, 41.9, 39.7, 22.4, 22.3.
½
aꢄD
¼ þ22:4 (c 0.24, MeOH). MS (CI, m/z): 430 (MH+). Anal. Calcd.
for C22H27N3O4SꢁC2H5OH: C, 60.61; H, 6.99; N, 8.83; S, 6.74. Found:
C, 60.92; H, 7.35; N, 8.61; S, 6.27. 1H NMR (500 MHz, CDCl3) d 7.55
(d, J = 7.1 Hz, 2H, 20-CH of PhCO), 7.48 (t, J = 7.1 Hz, 1H, 40-CH of
PhCO), 7.40 (t, J = 7.1 Hz, 2H, 30-CH of PhCO), 7.35–7.17 (m, 5H,
C6H5CH2), 6.42 (br s, 0.5H, NH of Phe), 6.32 (br s, 1H, NH of Phe
and NHiPr), 6.29 (br s, 0.5H, NHiPr), 4.37–4.27 (m, 2H, CH2 of
3AzeS), 4.27–4.20 (m, 0.5H, CH2 of 3AzeS), 4.20–4.14 (m, 0.5H,
4.3. Cbz-4PiMS-Phe-NHiPr 13
Compound 13 was prepared from sulfochloride 11 analogously
CH2 of 3AzeS), 4.10 (br s, 1H, aCH of Phe), 4.07–4.02 (m, 0.5H,
to 12. Yield 11.6 g (63%). White solid. Mp 75–76 °. ½a D
ꢄ
¼ þ5:3 (c
CH2 of 3AzeS), 4.02-3.90 (m, 0.5H, CH2 of 3AzeS, and 1H, CH of
iPr), 3.64 (br s, 0.5H, CH of 3AzeS), 3.48 (br s, 0.5H, CH of 3AzeS),
3.20–3.12 (m, 0.5H, CH2 of Phe), 3.12–3.04 (m, 0.5H, CH2 of Phe),
2.98–2.86 (m, 1H, CH2 of Phe), 1.08 (d, J = 6.4 Hz, 3H, CH3), 1.02
(d, J = 6.5 Hz, 3H, CH3). 13C NMR (126 MHz, CDCl3) d 170.6 (C@O),
169.8 (C@O), 136.7 and 136.5 (10-C of PhCO), 132.1 (10-C of PhCH2),
131.6 (40-CH of PhCO), 129.5 (CH of Ph), 128.9 (CH of Ph), 128.6 (CH
1.03, MeOH). MS (CI, m/z): 502 (MH+). Anal. Calcd for C26H35N3O5S:
C, 62.25; H, 7.03; N, 8.38; S, 6.39. Found: C, 61.87; H, 7.09; N, 8.21;
S, 6.48. 1H NMR (500 MHz, CDCl3) d 7.52–7.29 (m, 7H), 7.29–7.20
(m, 3H), 6.08–5.80 (m, 1H), 5.66–5.30 (m, 1H), 5.12 (s, 2H), 4.10
(s, 2H), 4.04–3.91 (m, 2H), 3.21–3.11 (m, 1H), 3.04–2.93 (m, 1H),
2.75 (s, 2H), 2.53–2.37 (m, 2H), 2.03–1.87 (m, 1H), 1.83–1.65 (m,
2H), 1.12 (d, J = 6.0 Hz, 3H), 1.12–1.04 (m, 2H), 1.04 (d, J = 6.1 Hz,
3H). 13C NMR (126 MHz, cdcl3) d 169.6, 155.1, 136.7, 136.6,
129.6, 128.9, 128.5, 128.0, 127.8, 127.4, 67.1, 59.0, 58.6, 43.6,
41.8, 39.4, 31.7, 31.5, 22.5, 22.3.
of Ph), 127.8 (CH of Ph), 127.3 (CH of Ph), 59.4 and 59.2 (aCH of
Phe), 54.2 and 54.1 (CH2 of 3AzeS), 50.4 and 50.2 (CH2 of 3AzeS),
49.9 (CH of 3AzeS), 41.9 (CH of iPr), 39.63 and 39.55 (CH2 of
Phe), 22.4 (CH3), 22.3 (CH3).
4.4. H-3AzeS-Phe-NHiPr 14
4.7. PhC(O)-4PiMS-Phe-NHiPr 6
Compound 12 (10.0 g, 21.8 mmol) was dissolved in MeOH
(150 mL), and then 10% Pd–C (1 g) was added. A slow steam of
hydrogen was bubbled through the mixture at rt with stirring until
the starting material disappeared (monitored by TLC). The catalyst
was filtered off, and the filtrate was evaporated to dryness to give
14 as a white amorphous solid. The product was pure enough to be
used in the next steps without any additional purification. An ana-
lytical sample was prepared by column chromatography (Hex-
anes–EtOAc (2 : 3) as eluent). Yield 7.08 g (100%). White solid.
Compound 6 was prepared from 15 analogously to 5. Yield
1.20 g (61%). White solid. Mp 98–99 °C. ½aꢄD ¼ þ21:1 (c 0.28,
MeOH). MS (CI, m/z): 472 (MH+). Anal. Calcd for C25H33N3O4S: C,
63.67; H, 7.05; N, 8.91; S, 6.80. Found: C, 63.29; H, 7.26; N, 9.03;
S, 6.65. 1H NMR (500 MHz, CDCl3) d 7.44–7.39 (m, 3H, CH of Ph),
7.38–7.34 (m, 2H, CH of Ph), 7.34–7.29 (m, 2H, CH of Ph), 7.27–
7.21 (m, 3H, CH of Ph), 6.11 (br s, 1H, NHiPr), 5.64 (br s, 1H, NH
of Phe), 4.63 (br s, 1H, 2- or 6-CHH of 4PiMS), 4.06–3.93 (m, 2H,
CH of iPr and
aCH of Phe), 3.68 (br s, 1H, 2- or 6-CHH of 4PiMS),
Mp 94–95 °C. ½a D
ꢄ
¼ þ8:1 (c 0.84, MeOH). MS (CI, m/z): 326
3.15 (dd, J = 13.6, 5.9 Hz, 1H, CHH of Phe), 3.03-2.89 (br s, 1H, 2-
or 6-CHH of 4PiMS), 2.94 (dd, J = 13.5, 8.7 Hz, 1H, CHH of Phe),
2.75 (br s, 1H, 2- or 6-CHH of 4PiMS), 2.53–2.45 (m, 1H, CHHSO2
of 4PiMS), 2.41 (dd, J = 14.0, 6.2 Hz, 1H, CHHSO2 of 4PiMS), 2.06–
1.96 (m, 1H, CH of 4PiMS), 1.79 (br s, 2H, 3- and/or 5-CH2 of
4PiMS), 1.20 (br s, 2H, 3- and/or 5-CH2 of 4PiMS), 1.08 (d,
J = 6.5 Hz, 3H, CH3), 1.02 (d, J = 6.5 Hz, 3H, CH3). 13C NMR
(126 MHz, CDCl3) d 170.3 (C@O), 169.6 (C@O), 136.8 (10-C of Ph),
135.9 (10-C of Ph), 129.7 (CH of Ph), 129.6 (CH of Ph), 128.9 (CH
of Ph), 128.5 (CH of Ph), 127.4 (CH of Ph), 126.8 (CH of Ph), 59.0
(MH+). Anal. Calcd for C15H23N3O3S: C, 55.36; H, 7.12; N, 12.91;
S, 9.85. Found: C, 55.14; H, 7.40; N, 13.11; S, 9.66. 1H NMR
(500 MHz, CDCl3) d 7.40–7.12 (m, 6H), 6.54 (d, J = 7.2 Hz, 1H),
4.19 (br s, 1H), 4.08 (t, J = 6.9 Hz, 1H), 4.04–3.91 (m, 1H), 3.83–
3.69 (m, 3H), 3.67 (s, 1H), 3.55 (s, 1H), 3.11–2.98 (m, 2H), 1.11
(d, J = 6.4 Hz, 3H), 1.04 (d, J = 6.5 Hz, 3H). 13C NMR (126 MHz,
CDCl3) d 170.0, 136.5, 129.6, 128.8, 127.3, 59.0, 54.8, 48.0, 47.8,
41.8, 39.5, 22.4, 22.3.
4.5. H-4PiMS-Phe-NHiPr 15
(aCH of Phe), 58.5 (CH2SO2 of 4PiMS), 47.2 and 41.8 (br s, 2- and
6-CH2 of 4PiMS), 41.7 (CH of iPr), 39.5 (CH2 of Phe), 32.0 (CH of
4PiMS), 31.6 (br s, 2C, 3- and 5-CH2 of 4PiMS), 22.4 (CH3), 22.3
(CH3).
Compound 15 was prepared from 13 analogously to 14. Yield
8.54 g (%). White amorphous solid. Mp 80–81 °C. ½aꢄD ¼ þ6:4 (c
1.84, MeOH). MS (CI, m/z): 368 (MH+). Anal. Calcd for C18H29N3O3S:
C, 58.83; H, 7.95; N, 11.43; S, 8.72. Found: C, 58.89; H, 8.36; N,
11.08; S, 8.51. 1H NMR (500 MHz, CDCl3) d 7.35–7.28 (m, 2H),
7.28–7.18 (m, 4H), 6.16 (s, 1H), 4.06 (br s, 1H), 3.99 (s, 2H), 3.16–
3.07 (m, 1H), 3.18–3.07 (m, 1H), 3.07–2.89 (m, 3H), 2.57 (m, 1H),
2.50–2.35 (m, 2H), 1.88 (s, 1H), 1.74 (m, 2H), 1.20–1.05 (m, 2H),
1.08 (d, J = 26.9 Hz, 3H), 1.02 (d, J = 6.4 Hz, 3H). 13C NMR
(126 MHz, CDCl3) d 169.9, 136.8, 129.6, 128.8, 127.3, 59.2, 59.0,
45.7, 41.7, 39.4, 32.3, 31.8, 22.5, 22.3.
4.8. Boc-Ala-3AzeS-Phe-NHiPr 16
Compound 14 (2.00 g, 6.1 mmol), HOBt (0.88 g, 6.5 mmol), and
DIPEA (1.81 g, 14 mmol) were dissolved in DMF (100 mL). The mix-
ture was cooled to ꢀ10 °C, and EDCꢁHCl (1.24 g, 6.5 mmol) was
added. The resulting mixture was stirred at ꢀ10 °C for 1 h, then
warmed to rt over 2 h, poured into H2O (250 mL), and extracted
with EtOAc (2 ꢂ 100 mL). The combined organic extracts were
washed with 1 M aq KHSO4 (50 mL), saturated aq NaHCO3
(50 mL), brine (50 mL), dried over Na2SO4 and evaporated in vacuo
to give 16. Yield 1.80 g (60%). White solid. Mp 87–88 °C.
4.6. PhC(O)-3AzeS-Phe-NHiPr 5
Compound 14 (1.20 g, 3.7 mmol) was dissolved in CH2Cl2
(100 mL), and DIPEA (0.57 g, 4.4 mmol) was added. The mixture
½
a D
ꢄ
¼ ꢀ8:1 (c 0.21, MeOH). MS (CI, m/z): 397 (MH+–CO2–C4H8).
Anal. Calcd for C23H36N4O6S: C, 55.63; H, 7.31; N, 11.28; S, 6.46.

236
O. O. Grygorenko et al. / Tetrahedron: Asymmetry 25 (2014) 229–237
Found: C, 55.38; H, 7.03; N, 11.00; S, 6.53. 1H NMR (500 MHz,
CDCl3) d 7.38–7.33 (m, 2H), 7.33–7.29 (m, 1H), 7.27–7.21 (m,
2H), 6.26–6.20 (m, 0.5H), 6.17–6.11 (m, 0.5H), 6.07–6.02 (m,
0.5H), 5.99–5.95 (m, 0.5H), 5.41 (d, J = 7.2 Hz, 0.5H), 5.23 (d,
J = 8.0 Hz, 0.5H), 4.39 (s, 0.5H), 4.29–4.16 (m, 1.5H), 4.15–4.08
(m, 1.5H), 4.08–3.93 (m, 3H), 3.81 (t, J = 9.6 Hz, 0.5H), 3.55–3.44
(m, 1H), 3.14–3.06 (m, 1H), 2.99–2.94 (m, 1H), 2.02 (s, 1H), 1.44
(s, 9H), 1.26 (d, J = 6.5 Hz, 1.5H), 1.25 (d, J = 6.3 Hz, 1.5H), 1.13 (d,
J = 3.6 Hz, 1.5H), 1.12 (d, J = 3.7 Hz, 1.5H), 1.04 (d, J = 5.8 Hz,
1.5H), 1.03 (d, J = 6.1 Hz, 1.5H). 13C NMR (126 MHz, CDCl3) d
172.6, 169.7 and 169.6, 155.1 and 155.0, 136.6 and 136.4, 129.5,
128.9, 127.5 and 127.4, 79.8, 59.3 and 59.2, 51.7 and 51.6, 49.8
and 49.6, 49.5, 45.8 and 45.5, 41.9, 39.7 and 39.5, 28.3, 22.7,
22.3, 18.5, 18.1.
3AzeS), 3.15–3.06 (m, 1H, CHH of Phe), 2.99–2.87 (m, 1H, CHH of
Phe), 1.39 (d, J = 6.2 Hz, 3H, CH3 of Ala), 1.11 (d, J = 6.5 Hz, 1.5H,
CH3 of iPr), 1.07 (d, J = 6.5 Hz, 1.5H, CH3 of iPr), 1.03 (d, J = 5.7 Hz,
1.5H, CH3 of iPr), 1.01 (d, J = 5.7 Hz, 1.5H, CH3 of iPr). 13C NMR
(126 MHz, CDCl3) d 172.3 and 172.1 (C@O), 169.7 and 169.4
(C@O), 166.8 (C@O), 136.7 and 136.4 (10-C of Ph), 133.8 and
133.7 (10-C of Ph), 131.8 and 131.7 (CH of Ph), 129.5 and 129.4
(CH of Ph), 129.0 and 128.9 (CH of Ph), 128.6 and 128.5 (CH of
Ph), 127.5 and 127.4 (CH of Ph), 127.2 and 127.1 (20-CH of PhCO),
59.4 and 59.2 (
and 49.72 (CH2 of 3AzeS), 49.66 and 49.5 (CH of 3AzeS), 45.0 and
44.9 ( CH of Ala), 41.9 and 41.8 (CH of iPr), 39.7 and 39.5 (CH2
aCH of Phe), 51.9 and 51.8 (CH2 of 3AzeS), 49.9
a
of Phe), 22.44 and 22.37 (CH3 of iPr), 22.3 (CH3 of iPr), 18.2 and
18.0 (CH3 of Ala).
4.9. Boc-Ala-4PiMS-Phe-NHiPr 17
4.11. PhC(O)-Ala-4PiMS-Phe-NHiPr 8
Compound 6 was prepared from 15 analogously to 5. Yield
Compound 8 was prepared from 17 analogously to 7. Yield
2.30 g (79%). White solid. Mp 105–106 °C. ½a D
ꢄ
¼ þ6:1 (c 0.8,
1.03 g (68%). White solid. Mp 119–120 °C. ½aꢄD ¼ þ45:2 (c 0.21,
MeOH). MS (CI, m/z): 439 (MH+–CO2–C4H8); negative mode: 537
(MꢀH+). Anal. Calcd for C26H42N4O6S: C, 57.97; H, 7.86; N, 10.40;
S, 5.95. Found: C26H42N4O6S C, 57.82; H, 7.76; N, 10.17; S, 5.94.
1H NMR (500 MHz, CDCl3) d 7.36–7.30 (m, 2H), 7.30–7.23 (m,
3H), 6.02 (d, J = 7.1 Hz, 0.5H), 5.95 (d, J = 7.2 Hz, 0.5H), 5.77 (br s,
0.5H), 5.64 (br s, 0.5H), 5.64 (d, J = 7.5 Hz, 0.5H), 5.56 (d,
J = 7.6 Hz, 0.5H), 4.63–4.55 (m, 1H), 4.48 (t, J = 15.0 Hz, 1H), 4.05–
3.93 (m, 2H), 3.85 (d, J = 12.8 Hz, 0.5H), 3.79 (d, J = 14.0 Hz, 0.5H),
3.23–3.12 (m, 1H), 3.05–2.90 (m, 2H), 2.56 (t, J = 12.6 Hz, 1H),
2.49 (dd, J = 14.0, 5.4 Hz, 0.5H), 2.42 (dd, J = 14.0, 6.7 Hz, 0.5H),
2.36 (dd, J = 14.0, 7.5 Hz, 0.5H), 2.29 (dd, J = 13.9, 5.2 Hz, 0.5H),
2.03–1.91 (m, 1.5H), 1.86 (d, J = 12.0 Hz, 0.5H), 1.72 (br s, 1H),
1.45 (s, 4.5H), 1.43 (s, 4.5H), 1.28 (d, J = 5.6 Hz, 1.5H), 1.27 (d,
J = 5.6 Hz, 1.5H), 1.11 (d, J = 6.5 Hz, 3H), 1.08–1.00 (m, 5H). 13C
NMR (126 MHz, CDCl3) d 171.0 and 170.8, 169.6, 155.1, 137.0
and 136.8, 129.63 and 129.58, 128.9, 127.4, 79.5, 59.2 and 59.1,
58.3, 46.2 and 46.1, 45.1 and 44.8, 42.0 and 41.7, 41.8, 39.4 and
39.2, 32.1 and 31.9, 31.8 and 31.8, 31.4 and 31.3, 28.41 and
28.38, 22.5, 22.3, 19.74 and 19.31.
MeOH). MS (CI, m/z): 543 (MH+). Anal. Calcd for C28H38N4O5S: C,
61.97; H, 7.06; N, 10.32; S, 5.91. Found: C, 61.64; H, 7.10; N,
10.41; S, 6.08. 1H NMR (500 MHz, CDCl3) d, major rotamer (mole
fraction 3): 7.85 (d, J = 7.5 Hz, 2H, 20-CH of PhCO), 7.61 (d,
2
J = 6.7 Hz, 1H, NH of Ala), 7.53 (t, J = 7.3 Hz, 1H, 40-CH of PhCO),
7.45 (t, J = 7.8 Hz, 2H, 30-CH of PhCO), 7.37–7.21 (m, 5H, CH of
PhCH2), 6.44 (d, J = 8.6 Hz, 1H, NH of Phe), 6.29 (d, J = 7.8 Hz, 1H,
NHiPr), 5.12–5.03 (m, 1H,
or 6-CH2 of 4PiMS), 4.07–3.99 (m, 2H, CH of iPr and 2- or 6-CH2
of 4PiMS), 3.98–3.94 (m, 1H, CH of Phe), 3.31 (dd, J = 13.7,
aCH of Ala), 4.54 (d, J = 12.9 Hz, 1H, 2-
a
4.9 Hz, 1H, CHH of Phe), 3.01 (d, J = 10.6 Hz, 1H, 2- or 6-CH2 of
4PiMS), 3.00–2.92 (m, 1H, CHH of Phe), 2.61 (d, J = 12.1 Hz, 1H,
2- or 6-CH2 of 4PiMS), 2.21 (dd, J = 13.7, 8.5 Hz, 1H, CHHSO2 of
4PiMS), 2.12 (dd, J = 13.8, 3.3 Hz, 1H, CHHSO2 of 4PiMS), 2.07–
1.94 (m, 2H, 3- or 5-CH2 of 4PiMS and CH of PiMS), 1.60 (d,
J = 12.8 Hz, 1H, 3- or 5-CH2 of 4PiMS), 1.41 (d, J = 6.3 Hz, 3H, CH3
of Ala), 1.09 (d, J = 7.5 Hz, 3H, CH3 of iPr), 1.18–1.04 (m, 1H, 3- or
5-CH2 of 4PiMS), 1.08 (d, J = 7.5 Hz, 3H, CH3 of iPr), 1.03–0.92 (m,
1
1H, 3- or 5-CH2 of 4PiMS); minor rotamer (mole fraction 3):
7.82 (d, J = 7.6 Hz, 2H, 20-CH of PhCO), 7.53 (t, J = 7.3 Hz, 2H, 30-
CH of PhCO), 7.45 (t, J = 7.8 Hz, 1H, 40-CH of PhCO), 7.43 (d,
J = 8.2 Hz, 1H, NH of Ala), 7.37–7.21 (m, 5H, CH of PhCH2), 5.98
(d, J = 7.7 Hz, 1H, NHiPr), 5.68 (d, J = 8.4 Hz, 1H, NH of Phe), 5.12–
4.10. PhC(O)-Ala-3AzeS-Phe-NHiPr 7
Compound 16 (1.80 g, 3.60 mmol) was dissolved in 10% HCl in
dioxane (50 mL). The resulting mixture was stirred for 2 h and
evaporated to dryness. Next, CH2Cl2 (50 mL) and DIPEA (0.65 g,
5.0 mmol) were added to the residue, and the mixture was stirred
for 30 min, then cooled to ꢀ10 °C, and benzoyl chloride (0.46 g,
3.1 mmol) was added dropwise. The mixture was warmed to rt
upon stirring over 1 h, then poured into H2O (200 mL). The organic
phase was separated, washed with 1 M KHSO4 (50 mL), brine
(50 mL), dried over Na2SO4, and evaporated in vacuo. The residue
was purified by column chromatography (Hexanes–EtOAc
(50:50) to give 7. Yield 1.30 g (72%). White solid. Mp 107–108 °C.
5.03 (m, 1H,
aCH of Ala), 4.49 (d, J = 13.3 Hz, 1H, 2- or 6-CH2 of
4PiMS), 4.07–3.99 (m, 2H, CH of iPr and
a
CH of Phe), 3.90 (d,
J = 13.3 Hz, 1H, 2- or 6-CH2 of 4PiMS), 3.18 (dd, J = 13.6, 6.1 Hz,
1H, CHH of Phe), 3.07 (d, J = 12.8 Hz, 1H, 2- or 6-CH2 of 4PiMS),
3.02–2.94 (m, 1H, CHH of Phe), 2.63 (d, J = 11.8 Hz, 1H, 2- or 6-
CH2 of 4PiMS), 2.52 (dd, J = 14.0, 5.5 Hz, 1H, CHHSO2 of 4PiMS),
2.46 (dd, J = 13.9, 6.7 Hz, 1H, CHHSO2 of 4PiMS), 2.07–1.94 (m,
2H, 3- or 5-CH2 of 4PiMS and CH of PiMS), 1.74 (d, J = 13.3 Hz,
1H, 3- or 5-CH2 of 4PiMS), 1.42 (d, J = 5.5 Hz, 3H, CH3 of Ala),
1.11 (d, J = 7.8 Hz, 3H, CH3 of iPr), 1.05 (d, J = 6.6 Hz, 3H, CH3 of
iPr), 1.18–1.04 (m, 1H, 3- or 5-CH2 of 4PiMS), 1.11–1.01 (m, 1H,
3- or 5-CH2 of 4PiMS). 13C NMR (126 MHz, CDCl3) d, major rotamer:
170.5 (C@O), 169.8 (C@O), 166.3 (C@O), 137.5 (10-C of Ph), 133.9
(10-C of Ph), 131.8 (40-CH of PhCO), 129.8 (CH of PhCH2), 128.8
(CH of PhCH2), 128.6 (30-CH of PhCO), 127.2 (CH of PhCH2), 127.0
½
aꢄD
¼ þ44:8 (c 0.19, MeOH). MS (CI, m/z): 501 (MH+). Anal. Calcd
for C25H32N4O5S: C, 59.98; H, 6.44; N, 11.19; S, 6.40. Found: C,
60.17; H, 6.34; N, 11.45; S, 6.69. 1H NMR (500 MHz, CDCl3) d
7.81 (d, J = 7.3 Hz, 2H, 20-CH of PhCO), 7.54–7.47 (m, 1H, CH of
Ph), 7.46–7.38 (m, 2H, CH of Ph), 7.37–7.31 (m, 2H, CH of Ph),
7.31–7.26 (m, 1H, CH of Ph, and 0.5H, NH of Ala), 7.26–7.20 (m,
2H, CH of Ph), 7.09 (d, J = 7.3 Hz, 0.5H, NH of Ala), 6.42 (d,
J = 8.3 Hz, 0.5H, NH of Phe), 6.23 (d, J = 8.3 Hz, 0.5H, NH of Phe),
6.08 (d, J = 7.0 Hz, 0.5H, NHiPr), 5.97 (d, J = 7.4 Hz, 0.5H, NHiPr),
(20-CH of PhCO), 59.6 (
CH of Ala), 45.0 (2- or 6-CH2 of 4PiMS), 42.2 (2- or 6-CH2 of
aCH of Phe), 58.1 (CH2SO2 of 4PiMS), 45.9
(a
4PiMS), 41.7 (CH of iPr), 38.9 (CH2 of Phe), 32.0 (3- or 5-CH2 of
4PiMS), 31.8 (CH of 4PiMS), 31.5 (3- or 5-CH2 of 4PiMS), 22.5
(CH3 of iPr), 22.4 (CH3 of iPr), 19.1 (CH3 of Ala); minor rotamer:
170.8 (C@O), 169.6 (C@O), 166.3 (C@O), 136.9 (10-C of Ph), 134.1
(10-C of Ph), 131.6 (40-CH of PhCO), 129.6 (CH of PhCH2), 128.9
(CH of PhCH2), 128.5 (30-CH of PhCO), 127.4 (CH of PhCH2), 127.0
4.75–4.67 (m, 0.5H,
aCH of Ala), 4.67–4.60 (m, 0.5H, aCH of Ala),
4.43 (dd, J = 9.8, 5.2 Hz, 0.5H, CH2 of 3AzeS), 4.32–4.23 (m, 1H,
CH2 of 3AzeS), 4.18–4.11 (m, 1H, CH2 of 3AzeS), 4.11–4.01 (m,
2H, CH2 of 3AzeS and
aCH of Phe), 4.01–3.92 (m, 1H, CH of iPr),
3.82 (t, J = 9.6 Hz, 0.5H, CH2 of 3AzeS), 3.55–3.43 (m, 1H, CH of
(20-CH of PhCO), 59.1 (
aCH of Phe), 58.3 (CH2SO2 of 4PiMS), 45.6

O. O. Grygorenko et al. / Tetrahedron: Asymmetry 25 (2014) 229–237
237
2. Yim, C.-B.; Dijkgraaf, I.; Merkx, R.; Versluis, C.; Eek, A.; Mulder, G. E.; Rijkers, D.
T. S.; Boerman, O. C.; Liskamp, R. M. J. J. Med. Chem. 2010, 53, 3944–3953.
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(aCH of Ala), 44.8 (2- or 6-CH2 of 4PiMS), 41.8 (2- or 6-CH2 of
4PiMS), 41.8 (CH of iPr), 39.5 (CH2 of Phe), 31.9 (3- or 5-CH2 of
4PiMS), 31.8 (CH of 4PiMS), 31.3 (3- or 5-CH2 of 4PiMS), 22.5
(CH3 of iPr), 22.3 (CH3 of iPr), 19.5 (CH3 of Ala).
4.12. X-ray diffraction studies
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Crystals of 5ꢁC2H5OH and 6 for X-ray diffraction studies were
obtained by slow evaporation of their solution in EtOH and hex-
anes, respectively. It should be noted that for 6, the same type of
crystals was obtained from several other solvents, including EtOH.
The crystals of 5ꢁC2H5OH (C22H27N3O4SꢁC2H5OH) are ortho-
rhombic. At 293 K, 0 a = 9.5196(4) Å, b = 20.119(1) Å, c = 27.744
(1) Å, V = 5313.6(4) ÅA3, Mr = 475.59, Z = 8, space group P212121,
6. Piscitelli, F.; Coluccia, A.; Brancale, A.; La Regina, G.; Sansone, A.; Giordano, C.;
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P.; Kleanthous, S.; Mason, A. M.; Mordaunt, J. E.; Patel, C.; Pateman, A. J.; Senger,
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dcalcd = 1.189 g/cm3, ) = 0.158 mmꢀ1, F(000) = 2032.
l(MoKa
The crystals of 6 (C25H33N3O4S) are monoclinic. At 293 K,
a = 8.4812(4) Å, b = 13.3697(3) Å, c = 22.4426(9) Å, b = 100.115
(4)°, V = 2505.2(2) Å3, Mr = 471.60, Z = 4, space group P21,
dcalcd = 1.250 g/cm3, ) = 0.164 mmꢀ1, F(000) = 1008.
l(MoKa
Intensities of 55463 reflections (15496 independent,
Rint = 0.175) for 5 and 24,585 reflections (11,011 independent,
Rint = 0.049) for 6 were measured on an Xcalibur 3 diffractometer
(graphite monochromated MoKa radiation, CCD-detector, x scan-
ning, 2Hmax = 60°).
The structures were solved by direct method using the SHELXTL
package.25 The positions of the hydrogen atoms were located from
electron density difference maps and refined using riding model
with Uiso = nUeq (n = 1.5 for methyl groups and 1.2 for other hydro-
gen atoms), except for the atoms of 5 involved in the intermolecu-
lar hydrogen bonds which were refined in isotropic approximation.
In the case of 6, restrictions were imposed on the bond lengths in
the isopropyl substituents and EtOH molecules (CC 1.54 Å, CO
1.43 Å). Full-matrix least-squares refinement against F2 in aniso-
tropic approximation for non-hydrogen atoms was converged to
wR2 = 0.138 for 10,900 reflections (R1 = 0.058 for 6119 reflections
13. Grygorenko, O. O.; Zhersh, S.; Oliinyk, B. V.; Shishkin, O. V.; Tolmachev, A. A.
Org. Biomol. Chem. 2013, 11, 975–983.
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Synthesis 2011, 3669–3674.
15. (a) Montelione, G. T.; Hughes, P.; Clardy, J.; Scheraga, H. A. J. Am. Chem. Soc.
1986, 108, 6765–6773; (b) Avenoza, A.; Busto, J. H.; Peregrina, J. M.; Rodríguez,
F. J. Org. Chem. 2002, 67, 4241–4249.
16. Molecule overlay and calculation of RMSD values were performed using VMD
for WIN32, version 1.9 Humphrey, W.; Dalke, A.; Schulten, K. J. Mol. Graphics
1996, 14, 33–38.
with F > 4r(F), S = 0.941) in the case of 5, and wR2 = 0.178 for
17. Chatterjee, S.; Roy, R. S.; Balaram, P. J. R. Soc. Interface 2007, 4, 587–606.
18. Lauri, G.; Bartlett, P. A. J. Comp. Aided Mol. Des. 1994, 8, 51–66.
19. (a) Grygorenko, O. O.; Prytulyak, R.; Volochnyuk, D. M.; Kudrya, V.;
Khavryuchenko, O. V.; Komarov, I. V. Mol. Divers. 2012, 16, 477–487; (b)
Yarmolchuk, V. S.; Mukan, I. L.; Grygorenko, O. O.; Tolmachev, A. A.; Shishkina,
S. V.; Shishkin, O. V.; Komarov, I. V. J. Org. Chem. 2011, 76, 7010–7016; (c)
Radchenko, D. S.; Pavlenko, S. O.; Grygorenko, O. O.; Volochnyuk, D. M.;
Shishkina, S. V.; Shishkin, O. V.; Komarov, I. V. J. Org. Chem. 2010, 75, 5941–
5952.
15,413 reflections (R1 = 0.082 for 4608 reflections with F > 4
S = 0.852) in the case of 6.
r(F),
Final atomic coordinates, geometrical parameters and crystallo-
graphic data have been deposited with the Cambridge Crystallo-
graphic Data Centre, 11 Union Road, Cambridge, CB2 1EZ, UK (E-
mail: deposit@ccdc.cam.ac.uk; fax: +44 1223 336033) and are
available on request quoting the deposition numbers 967,608 for
5 and 967,609 for 6.
20. (a) Kalman, A.; Parkanyi, L.; Kucsman, Á. Acta Crystallogr. Sect. B 1980, 36,
1440–1443; (b) Brameld, K. A.; Kuhn, B.; Reuter, D. C.; Stahl, M. J. Chem. Inf.
Model. 2008, 48, 1–24.
21. Hollingsworth, S. A.; Karplus, P. A. Biomol. Concepts 2010, 1, 271–283.
22. Zefirov, N. S.; Palyulin, V. A.; Dashevskaya, E. E. J. Phys. Org. Chem. 1990, 3, 147–
154.
23. Intermolecular contacts between the atoms with an interatomic distance of at
least 0.05 Å less than the sum of their van der Waals radii.
Acknowledgments
The authors thank Dr. Valeriya Makhankova for her invaluable
help with the manuscript preparation and Mr. Vitaliy Polovinko
for NMR experiments.
24. Baldauf, C.; Günther, R.; Hofmann, H.-J. J. Mol. Struct. (Theochem) 2004, 675, 19–
28.
25. Sheldrick, G. M. Acta Crystallogr. Sect. A 2008, A64, 112–122.
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