Ambidextrous α,γ-Hybrid Peptide Foldamers

Article abstract of DOI:10.1002/asia.201901411

Molecular chirality is ubiquitous in nature. The natural biopolymers, proteins and DNA, preferred a right-handed helical bias due to the inherent stereochemistry of the monomer building blocks. Here, we are reporting a rare co-existence of left- and right-handed helical conformations and helix-terminating property at the C-terminus within a single molecule of α,γ-hybrid peptide foldamers composed of achiral Aib (α-aminoisobutyric acid) and 3,3-dimethyl-substituted γ-amino acid (Adb; 4-amino-3,3-dimethylbutanoic acid). At the molecular level, the left- and right-handed helical screw sense of α,γ-hybrid peptides are representing a macroscopic tendril perversion. The pronounced helix-terminating behaviour of C-terminal Adb residues was further explored to design helix–Schellman loop mimetics and to study their conformations in solution and single crystals. The stereochemical constraints of dialkyl substitutions on γ-amino acids showed a marked impact on the folding behaviour of α,γ-hybrid peptides.

Full text of DOI:10.1002/asia.201901411

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Ambidextrous α,γ-Hybrid Peptide Foldamers
Authors: Rajkumar Misra, Gijo George, Abhijith Saseendran,
Srinivasarao Raghothama, and Hosahudya Gopi
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To be cited as: Chem. Asian J. 10.1002/asia.201901411
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Chemistry - An Asian Journal
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Ambidextrous α,-Hybrid Peptide Foldamers
[
a]
[b]
[a]
[b]
Rajkumar Misra, Gijo George, Abhijith Saseendran, Srinivasarao Raghothama,
[
a]
Hosahudya N. Gopi *
[a]Department of Chemistry, Indian Institute of Science Education and Research, Dr. Homi
Bhabha Road, Pashan, Pune-411 008, E-mail: hn.gopi@iiserpune.ac.in
[b]NMR Research Center, Indian Institute of Science, Bangalore-560012, India
ABSTRACT: Molecular chirality is ubiquitous in nature. The natural biopolymers, proteins
and DNA, preferred right-handed helical bias due to the inherent stereochemistry of monomer
building blocks. Here, we are reporting a rare co-existence of left and right-handed helical
conformations and helix terminating property at the C-terminus within a single molecule of
α,-hybrid peptide foldamers composed of achiral Aib (-aminoisobutyric acid) and 3,3-
dimethyl substituted -amino acid (Adb; 4-amino-3,3-dimethylbutanoic acid). The molecular
level left- and right-handed helical screw sense of α,-hybrid peptides are representing a
macroscopic tendril perversion. The pronounced helix terminating behaviour of C-terminal
Adb residues was further explored to design helix-Schellman loop mimetics and to study their
conformations in solution and single crystals. The stereochemical constraints of dialkyl
substitutions on -amino acids have showed a marked impact on the folding behaviour of α,-
hybrid peptides.
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INTRODUCTION
Helicity is the most common structural feature associated with many kinds of molecules
including biopolymers.[1] As proteins are exclusively built from L-amino acids, this
stereochemical bias is reflected in their strong preference to right-handed (P) helices over the
left-handed (M) helices. Nevertheless, a recent systematic survey of protein crystal structures
[2]
revealed the presence of short left-handed helices. Along with helices from chiral amino
acids, significant efforts have been made in the literature to build helices completely from
achiral amino acids such as Aib and its higher dialkyl substituted analogs.[3,4] Due to their
intrinsic conformational restriction, Aib residues invariably promote helical conformations.
This helix nucleating property of Aib has been widely explored to design - and 310-helices.
The helices constructed entirely from achiral Aib residues have shown to adopt both (P)-and
(M)-helices. These two helices are topologically equivalent enantiomers.
Compared to the limited set of -peptide helices, foldamers composed of unnatural β- and

-peptides uncovered various helical types with distinct intramolecular H-bonding pattern.[5,6]
Instructively, majority of β- and -peptides foldamers showed H-bonding between 14
residues, similar to the 310-helices. Moreover, foldamers composed of complete achiral β- and
-amino acids have not been scrutinized as those of corresponding chiral amino acids.
Nonetheless, Seebach and colleagues demonstrated a stair-like 8-helices[7] and uncommon
[8]
extended sheets from the oligomers of ,-dialkyl β-amino acids. In continuation, Balaram
and colleagues showed 9-helical(13, H-bonds) conformations from the oligomers of achiral
[
9]
3
,3-dialkyl substituted -amino acid gabapentin (gpn), and 12- helices (14, H-bonds) from
achiral hybrid peptides composed of Aib and gabapentin.[10]
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Figure 1. Chemical structure of Aib (-aminoisobutyric acid), Aic (4-aminoisocaproic acid,
doubly homologated Aib) and Adb (4-amino-3,3-dimethylbutanoic acid, present study).
In a sharp contrast to the 310-helices of Aib oligomers, the double homologated Aib (4,4-
dimethyl substituted -amino acid, Aic, Figure 1) oligomers have shown to adopt extended
sheet type conformations and to spontaneously self-aggregates into fibers.[11] Additionally, the
combination of Aic with helix inducing Aib in 1:1 alternating ,-hybrid peptides showed the
co-existence of 15/17- helices (15 H-bonds) and 12-helices(14 H-bonds) in single
crystals,[12] analogous to the - helix (15 H-bonds) and 310-helices(14 H-bonds) of -
peptides.
These remarkable structural features of hybrid peptides composed of 4,4-dimethyl -amino
acid, motivated us to examine the impact of dimethyl substitutions at the β-position on -
residues (4-amino-3,3-dimethyl butanoic acid, Adb, Figure 1) and their folding behavior in ,-
hybrid peptides. Herein, we are reporting a rare co-existence of left- and right- handed helical
screw sense and a remarkable helix terminating property at the C-terminus within a single
molecule of achiral ,-hybrid peptide foldamers composed of 1:1 alternating Aib and Adb
residues. The pronounced helix terminating behavior was further explored to design Schellman
loop mimetics.
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RESULTS AND DISCUSSION
The sequences of achiral ,-hybrid peptides (P1-P4) under investigation are shown Scheme
1
.
Scheme 1: Sequences of ,-hybrid peptides
The 3,3-dimethyl -amino acid was synthesized in excellent yield through the Michel addition
of nitromethane[13] to 2,2-dimethyl ethyl acrylate, and subsequent transformation of nitro into
amine by catalytic hydrogenation. The schematic representation of the 3, 3-dimethyl -amino
acid synthesis is shown in Scheme 2.
Scheme 2: Synthesis of N-Boc protected 3,3-dimethylbutanoic acid (Adb):
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All hybrid peptides were synthesized by solution phase chemistry using EDC/HOBt as
coupling agents and purified through reverse phase HPLC.
Figure 2: X-ray structure of peptides (a) P1 and (b) P2. The left- and right-handed helical
conformations are highlighted in yellow and cyan, respectively. The helix terminating C-
terminal Adb esters are highlighted in green. Top view of P1 and P2 are shown in (c) and (d),
respectively. The top views provide a clear distinction of left and right handed helical
conformations.
Initially, the octapeptide P1 was designed to understand whether this peptide can adopt
1
2- or 15/17- helix similar to its Aib/Aic analogues.[12] As crystal structures provide an useful
information on the folding properties of hybrid peptides, we attempted to grow X-ray quality
crystals of P1 in various solvent combinations. To facilitate the crystallization, we used
pentafluorobenzyl ester of Adb at the C-terminus. Single crystals of P1 obtained in aqueous
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MeOH solution yielded an interesting structure shown in Figure 2a. The local conformation of


β
β

Adb residues is described by the backbone torsion angles (N-C ), θ
1
(C -C ),  (C -C ) and
2


(C -C=O). The torsion angles of Adb residues are given in the Table 1. Notably, P1 adopted
an uncommon helix conformation with the co-existence of left- and right-handed helical screw
sense, along with a remarkable reversal of helix directionality at the C-terminus. Being an
achiral system, two molecules with opposite handedness are present in the asymmetric unit.
The structure adopted by the peptide P1 representing a phenomenon observed in macroscopic
“
tendril perversion”.[14] This type of opposite screw sense is a subject of interest, and the co-
existence of left- and right-handed helical screw sense is rather unusual in peptide foldamers.
Recently, Clayden and colleagues have demonstrated the tendril perversion at molecular level
by introducing amino acids opposite chirality at the N- and C-terminus of a helix composed of
achiralAib oligomers.[15] The crystal structure analysis of P1 reveals three interesting features;
the two N-terminus residues adopted a left-handed helix screw sense, while the middle five
residues adopted a right-handed helix screw sense, and finally the C-terminal Adb ester adopted
a left-handed conformation with reversal helix directionality. The hydrogen bond parameters
of P1 are tabulated in the Table S2. The N-terminus left-handed helix is stabilized by a weak
1
2-membered H-bond between Boc CO and Aib3NH (ii+3) as well as a nine membered H-
bond between the Aib 1CO andAib3 NH (ii+2).
Table 1: Torsion angles of Adb residues in the hybrid peptides P1, P2 and P4
o
o
o
o
Peptide
Residue
Adb(2)a
Adb(4)
Adb(6)
Adb(8)b
Adb(2)a

1
2

P1
114
-126
-126
99
-56
57
-76
55
90
-111
-112
169
97
52
63
59
176
-66
P2
125
-56
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Adb(4)
Adb(6)
Adb(8)b
Adba
-125
-133
106
59
54
65
-56
63
55
59
-115
-106
109
120
-42
177
-62
80
P4
126
Adbb
-106
a
b
Residues are part of left-handed helices. Residues are not part of a helix.
Interestingly, Adb4 NH is not participating in the canonical H-bonding, and this type of
non H-bonding partners have been observed at the junction of left- and right-handed helical
fusion.[15,16] The right-handed helix observed from the residues Aib3 to Aib7 is stabilized by
1
2-membered H-bonds (12-helix) between the residues i and i+3, which is the most stable helix
4
[17]
conformation observed in the ,-hybrid peptides composed of  -amino acids. In contrast

β
β

to the gauche (g) and extended (t) conformations along C -C and C -C bonds adopted by the
Aic residues in a 12-helix,[12] the Adb residues have adopted g, g conformations similar to 4-
residues.[16] The C-terminal Adb ester adopted a left-handed helix conformation with reversal
β

of helix direction. Instructively, the torsion variables  and  (C -C -C(O)’-O] adopted
2
extended conformation. In addition, the C-terminal twist is stabilized by a 15 membered C-

H···O H-bond between Aib6 CO and C H of Adb8 [C-H···O dist. 2.43Å and  C-H···O is
1
25]. The C-terminal helix reversal of P1 is representing a Schellman motif observed in
protein structures.[18] Schellman noted that helices in proteins are often terminated at the C-
terminal residue by adopting a left-handed conformation. It is pertinent to note that the helix
terminating residue is invariably achiral Gly and less frequently Asn. Similar type of helix
termination is often observed in synthetic -peptide helices containing C-terminal Aib
esters.[19] We speculated that the C-H···O H-bond observed at the C-terminus of P1 and the
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intermolecular head-to-tail H-bonds between the helices in the crystalpacking may be
responsible for the helix termination.[18f]
The unusual left- and right-handed helical screw sense along with the Schellman motif
type helix reversal motivated us to design peptide P2 and examine whether the observed
structure is unique to P1 or it can persist across other , -hybrid peptides of achiral Aib and
Adb. In P2, we chose to incorporate n-heptanol ester of Adb to assess if the helix reversal is
not due to the aromatic -staking as well as to verify whether the n-alkane can also fold back
towards the helix. Single crystals of P2 grown in aqueous methanol solution yielded the
structure shown in Figure 2b. Similar to P1, P2 adopted a rare helical conformation associated
with left- and right-handed helix screw sense. The first two residues adopted the left-handed
helix conformation, stabilized by a weak 12-membered H-bond between Boc CO and Aib3 NH
and a strong nine membered H-bond between Aib 1 CO and Aib3 NH. As observed earlier,
Adb4NH is not participating in the canonical intramolecular H-bonding. The H-bond
parameters are tabulated in the Table S4 (See ESI). Residues from Aib3 to Aib7 adopted a right-
handed 12-helix conformation with similar torsion variables as observed in P1 (Table 1). As
anticipated, the C-terminal Adb ester displayed a Schellman motif type helix terminating
property. Interestingly, the n-heptane chain fold back towards N-terminus of the helix. In
addition, the C-terminal helix reversal is stabilized by a 15 membered C-H···O H-bond

between Aib6 CO and C H of Adb8 [C-H···O dist. 2.49 Å and C-H···O is 149]. The
conformational analysis of n-heptanol ester reveals that C-C bonds with the exception of C1-
C2, other assumed antiperiplanar conformation. The C1-C2 and ester C-O bonds adopted
gauche and anticlinal conformations, respectively.
Inspired by the co-existence of opposite helix screw sense and helix terminating
property, we sought to investigate whether this property can be explored to design Schellman
loops. The helix-Schellman loop-helix structures are often found in proteins.[18] We hypothesize
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that instead of alkyl or aryl esters, if the C-terminal Adb is esterified with peptide alcohols it
may be possible to design Schellman loops. In this context, peptide P3 was designed (Scheme
1
). We chose Boc-Val-Val-ol (dipeptide alcohol) for the C-terminal esterification. As peptide
P3 did not yield X-ray quality single crystals, we subjected the peptide to 2D NMR analysis in
CDCl at room temperature (298K). The analysis of ROESY spectrum of P3 revealed strong
3
NHNH NOEs between Aib1Adb2, Aib5Adb6, Aib7Adb8 and Val9Val10, and
weak NHNH NOEs between Aib2Adb3 and Adb4Aib5. In addition, medium NOEs



between Aib3NHC HAdb2, Aib5NHC HAdb4, Aib7NHC HAdb6, and strong




Aib3NHC HAdb2, Aib5NHC HAdb4, Aib7NHC HAdb6, and Val9NHC H Val10,

and a weak NOE between Val9NHC HAdb8 were also observed. Further, the DMSO
titration studies suggested that except the N-terminusAib1 and Adb 2 NHs, no pronounced
chemical shift variation is observed in other amideNHs. It is fairly surprising that the amide
NHs of Val-Val residues are also not exposed to solvent, indicating their involvement in the
intramolecular H-bonding. Using unambiguous NHNH and other NOEs, the solution
structure of P3 was generated and the superposition of ten lowest energy minimized structures
is shown in Figure 3. Instructively, the peptide adopted a continuous right-handed 12-helix
conformation up to Aib7. The C-terminal Adb adopted a left-handed helical conformation.
Intriguingly, the Val9 and Val10 NHs are involved in the bifurcated H-bonds with Aib7CO. The
average torsion values of NMR derived structures are given in the Table S8. Overall, the
structure of P3 resembling a helix-Schellman loop conformation observed in the protein
structures.[17]
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Figure 3: Solution NMR structures of peptide P3 (a) and (b), and X-ray structure of P4 (c).
To realize the helix-Schellman loop type conformation of ,-hybrid peptides in single
crystals and to support the solution structure of P3, we synthesized several ,-hybrid peptides
from hexa to octapeptides composed of achiral amino acids with Boc-Val-Val-ol ester of C-
terminal Adb. Among all the peptides synthesized, the hexapeptide P4 (Scheme 1) composed
of alternating Ac
6
c (1-aminocyclohexane-1-carboxylic acid) and Adb yielded X-ray quality
. The X-ray structure of P4 is shown in Figure 3c. The first three
crystals in aprotic CHCl
3
residues of P4 adopted a right handed 12-helix conformation, while the C-terminal Adb4
adopted a left-handed helical conformation. The torsion angles of Adb residues are given in the
Table 1. Structural analyses revealed that the C-terminus Boc-Val-Val dipeptide ester adopted
a semi-extended type conformation. Notably, the carbonyl of Ac c3 is participated in three-
6
center H-bonds with amide NHs of Val5 (24) and Val6 (14) involving 12 and 15 membered
pseudocycles, respectively. Interestingly, the concavity induced at the site of bifurcated H-
bonds is occupied by the solvent CHCl . The crystal structure of P4 is mimicking helix-
3
Schellman loops in protein structures, and in complete agreement with the solution structure
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of P3. Moreover, the helix terminating property of Adb esters is found to be persistent across
the Aib/Adb hybrid peptide foldamers.
CONCLUSION
In summary, we have demonstrated the unique folding properties of achiral ,-hybrid
peptides composed of Aib and Adb. The two octapeptides (P1 and P2) have shown to adopt
helical conformations with opposite chirality, along with the helix terminating property at the
C-terminal Adb esters. Accommodation of three different structural features in a single peptide
foldamer is unprecedented. The Schellman motif type helix reversal is consistent across the
hybrid peptides studied. The stabilization of the Val-Val dipeptide through three center H-bonds
resembling the Schellman loops in protein structures. The study further reveals that the position
of dialkyl substitutions on -amino acids has a major impact on the folding properties of -
peptide foldamers and also induces fragility into the 12-helix conformations of ,-hybrid
peptides. More importantly, the role of protic solvents in the induction of opposite chirality
within the helix cannot be ruled out. Overall, the simple chemistry of amino acid synthesis and
the unique structural properties of ,-hybrid peptides presented here can be further explored
to design novel foldamers.
EXPERIMENTAL SECTION
All amino acids, ethyl 3,3-dimethylacrylate,nitro methane, Pd/C, TFA, EDC, HOBt, DIEPA,
were commercially available. DCM, DMF, ethyl acetate and pet-ether (60-80 °C) were distilled
prior to use. Column chromatography was performed on silica gel (120-200 mesh).Final
peptides were purified on reverse phase HPLC (C18 column, MeOH/H
2
O 70:30-95:5 as
gradient with flow rate 2.5 mL/min). H NMR and CNMR spectra were recorded on 400 MHz
and on 100 MHz respectively, using residual solvent signal as internal standards (CDCl ).
1
13
3
Chemical shifts (δ) reported in parts per million (ppm) and coupling constants (J) reported in
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Hz. Mass spectra were recorded using MALDITOF/TOF and HRMS Electron Spray Ionization
ESI).
(
NMR spectroscopy: All NMR studies were carried out by using either 400 or 600 MHz
spectrometer. Resonance assignments were obtained by TOCSY and ROESY analysis. All
two-dimensional data were collected in phase-sensitive mode by using the time-proportional
phase incrementation (TPPI) method. Sets of 1024 and 512 data points were used in the t2 and
t1 dimensions, respectively. For TOCSY and ROESY analysis, 32 and 72 transients were
collected, respectively. A spectral width of 6007 Hz was used in both dimensions. A spin-lock
time of 200 and 250 ms were used to obtain ROESY spectra. Zero-filling was carried out to
finally yield a data set of 2 K × 1 K. A shifted square-sine-bell window was used before
processing.
Molecular Dynamics (MD): Structure calculation was done using a simulated annealing
protocol in vacuum using DESMOND and OPLS 2005 force field with NOE and dihedral
constraints. A fully extended peptide molecule (all backbone dihedral angles were kept to be
1
80˚) was kept in orthorhombic simulation cell of dimensions 40.96*66.43*32.40 Å. Upper
limit for distance was kept at 3 Å and 4 Å for strong and medium NOEs. All the lower distance
limits were taken to be 1.8 Å. 1 Kcal/Mol force constant was used for all the constraints. NOE
potentials (appropriate for treating ambiguous NOE assignments) used are having the
following form,
2
E
E
E
E
NOE = fc* (lower - d) , if d <lower;
NOE = 0, if lower <= d <= upper;
2
NOE = fc* (upper - d) , if upper <d <= upper + sigma;
NOE = fc* (a + beta * (d - upper) + c / (d - upper)), if d >upper + sigma;
where d is the distance and fc is the force constant.
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Values of sigma and beta used in the calculation are 0.5 and 1.5 respectively. The values a and
c are determined automatically such that potential is continuous and differential everywhere.
Before production run simulation, a default NVT relaxation was done as implemented in
DESMOND. NVT ensemble was used for the production run simulation. Berendsen thermostat
with a relaxation time of 1 ps was used. A RESPA integrator was used in which for all the
bonded interactions and near non-bonded interactions a time step of 1 fs was used and far non-
bonded interaction time step of 3 fs was used. A cut-off of 9 Å was used for short range
electrostatic interactions. A smooth particle mesh ewald method was used for treating long
range electrostatic interactions. Simulated annealing was done in 6 stages. First stage consist
simulation for 30 ps at 10 K. In the second stage, temperature was linearly increased to 100 K
till 100 ps. In the third stage, temperature was linearly increased to 300 K till 200 ps. In the
fourth stage, temperature was linearly increased to 400 K till 300 ps. In the fifth stage,
temperature was maintained at 400 k till 500 ps. In the sixth stage, temperature was linearly
decreased to 300 K till 1000 ps and maintained at 300 k till 1200 ps. 20 minimum energy
structures were taken from the trajectory between 1000 ps and 1200 ps. The lowest energy
structure from the trajectory between 1000 ps and 1200 ps was taken and minimized using a
steepest descent method using a convergence gradient threshold of 0.05 kcal/mol/Å.
Synthesis of N-Boc protected3,3-dimethylbutanoic acid (Adb):
Ethyl 3,3-dimethylacrylate (6.4 g, 50 mmol) was dissolved in neat nitro methane (13.5 ml, 250
mmol, 5 molequivalents) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, 11.2 mL, 75 mmol,
1
.5 molequivalents) were added. The mixture was heated at 60 °C overnight, and the
nitromethane was evaporated under reduced pressure. Ethyl acetate and 1MHCl were added to
the resulting residue, and the organic phase was separated. The acidic aqueous layer was
washed twice with ethyl acetate, the combined organic phase was dried over Na
2
SO , and the
4
solvent was evaporated under reduced pressure. The product, 3,3-dimethyl-4-nitro-butyric acid
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ethyl ester was collected (7.56 g, 80 % yield) as colorless oil. The suspension of activated Pd/C
(
20% by weight) and 3,3-dimethyl-4-nitro-butyric acid ethyl ester (3.78 g, 20 mmol) in MeOH
40 mL) and acetic acid(5mL) was stirred at room temperature in the presence of hydrogen.
(
After completion of the reaction (TLC, ~36 hrs), Pd/C was filtered through the bed of celite
and the filtrate was evaporated to dryness under vacuum to get gummy 4,4-dimethyl-2-
pyrrolidinone (2.14 g, 95 % yield) as oil. The amide NH group of 4,4-dimethyl-2-pyrrolidinone
was further protected with Boc group and then hydrolyzed using NaOH (2.0 M) in MeOH to
get final product N-Boc protected 3,3-dimethylbutanoic acid (3.21 g, 80 % yield in two step)
Synthesis of peptides P1-P5:
All peptides were synthesized through conventional solution phase methods using fragment
condensation strategy. The Boc group was used for the N-terminal protection and the C-
terminus was protected as a benzyl ester. Couplings were carried out using N-Ethyl-N′-(3-
dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 1-hydroxybenzotriazole
(HOBt). The N-terminal protecting groups was removed with trifluoroacetic acid C-terminal
benzyl group was deprotected by catalytic hydrogenation. The octapeptide acid(Aib-Adp)
4
–
COOH was further reacted with pentafluorobenzyl bromide and heptyl bromide in presence
of potsiumcarbonate and DMF as solvent to obtain compound P1and P2. For compound
P3(Aib-Adb)
case of P4, the tetrapeptide acid, Boc-(Ac
presence of DCC and DMAP. Finally, all the peptides were purified by RP-HPLC using
MeOH/H O gradient system.
4
–COOH was reacted with Boc-Val-Valol in presence of DCC and DMAP. In
6
c-Adb) -COOH was coupled with Boc-Val-Valol in
2
2
Structural data of the compound1and peptides:
Compound 1:
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1H NMR (400 MHz, DMSO-d
) δ 11.94 (s, 1H), 6.86 – 6.55 (t, 1H), 2.86 (d, J = 6.4 Hz, 2H),
6
1
3
2
1
.06 (s, 2H), 1.37 (s, J = 1.2 Hz, 9H), 0.89 (s, 6H). C NMR (101 MHz, DMSO) δ 173.53,
56.54, 77.89, 50.55, 44.05, 34.82, 28.70, 25.07. HR-MS m/z calculated value for C11
H21NO
4
+
is [M+Na] 254.1368 and observed 254.1370
PeptideP1:
1HNMR (600 MHz, Chloroform-d) δ 8.17 (s, 1H), 8.03 (s, 1H), 7.80 (t, J = 6.5 Hz, 1H), 7.71
s, 1H), 7.61 (t, J = 6.5 Hz, 1H), 7.59 – 7.49 (m, 1H), 6.55 (t, J = 6.2 Hz, 1H), 5.16 (s, 2H),
.98 (s, 1H), 3.27 – 3.04 (m, 8H), 2.33 (s, 2H), 2.06 (d, J = 11.3 Hz, 6H), 1.56 – 1.36 (m, 33H),
(
4
1
1
7
2
1
3
.11 – 0.92 (m, 24H). C NMR (151 MHz, CDCl ) δ 175.65, 175.38, 175.23, 171.50, 171.21,
3
71.17, 171.01, 154.99, 146.21, 144.56, 137.94, 136.33, 130.77, 128.58, 80.10, 77.37, 77.16,
6.95, 56.76, 56.48, 52.57, 49.30, 48.08, 47.61, 39.79, 38.17, 35.30, 35.17, 35.04, 29.40, 28.24,
6.83, 26.67, 26.53, 25.15, 24.99, 24.83.MALDITOF/TOF- m/zcalcd.forC52
H
83
F
5
N
8
O
11
+
[
M+Na] 1113.59, obsrvd. 1113.76
PeptideP2:
1HNMR (400 MHz, Chloroform-d) δ 8.15 (s, 1H), 8.06 (s, 1H), 7.76 – 7.68 (m, 2H), 7.63 (t, J
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Chemistry - An Asian Journal
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=
6.5 Hz, 1H), 7.53 (d, J = 7.7 Hz, 1H), 6.59 (t, J = 6.1 Hz, 1H), 5.06 (s, 1H), 4.03 (t, J = 6.8
Hz, 2H), 3.25 – 3.08 (m, 8H), 2.28 (s, 2H), 2.11 – 2.00 (m, 6H), 1.69 (s, 5H), 1.50 – 1.43 (m,
1
3
2
7H), 1.35 – 1.21 (m, 9H), 1.04 (dd, J = 12.3, 6.5 Hz, 24H), 0.90 – 0.83 (m, 3H). C NMR
(
151 MHz, CDCl ) δ 176.01, 175.64, 174.98, 172.83, 171.77, 171.49, 171.22, 155.15, 81.17,
3
7
3
2
7.37, 77.16, 76.95, 64.44, 57.46, 57.12, 57.01, 49.61, 48.60, 48.45, 47.98, 44.82, 44.67, 44.42,
5.54, 35.46, 35.35, 31.86, 29.05, 28.79, 28.51, 27.25, 27.01, 26.89, 26.07, 25.64, 25.54, 25.45,
+
2.71, 14.20.MALDITOF/TOF- m/zcalcd.forC52
H
96
N
8
O
11 [M+Na] 1031.70, obsrvd. 1031.85.
Peptide P3:
1H NMR (600 MHz, Chloroform-d) δ 8.21 (d, J = 9.8 Hz, 2H), 7.90 (t, J = 6.5 Hz, 1H), 7.75
s, 1H), 7.70 (t, J = 6.6 Hz, 1H), 7.59 (s, 1H), 7.54 (d, J = 9.3 Hz, 1H), 6.59 (t, J = 6.4 Hz, 1H),
(
5
1
5
1
6
3
2
.53 (d, J = 9.2 Hz, 1H), 5.06 (d, J = 15.7 Hz, 1H), 4.19 (d, J = 2.8 Hz, 2H), 4.03 – 3.96 (m,
H), 3.90 (tt, J = 9.2, 3.2 Hz, 1H), 3.29 – 3.09 (m, 10H), 2.15 – 2.05 (m, 9H), 1.57 – 1.41 (m,
1
3
7H), 1.11 – 0.99 (m, 32H), 0.98 – 0.90 (m, 15H). C NMR (151 MHz, CDCl ) δ 175.98,
3
75.71, 175.42, 174.69, 172.14, 171.91, 171.87, 171.34, 171.05, 155.84, 154.98, 81.19, 79.13,
4.11, 60.23, 57.38, 56.99, 56.86, 53.80, 48.37, 48.28, 47.80, 44.68, 44.46, 44.28, 43.29, 35.37,
5.35, 35.24, 34.98, 31.31, 30.94, 28.98, 28.36, 27.11, 26.98, 26.88, 26.73, 26.30, 25.96, 25.59,
5.48, 25.35, 25.12, 19.65, 19.53, 17.97.MALDITOF/TOF- m/zcalcd.forC60
H
110
N
10
O
14
+
[
M+Na] 1217.81, obsrvd. 1217.99
Peptide P4:
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Chemistry - An Asian Journal
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1H NMR (400 MHz, Chloroform-d) δ 7.68 (s, 1H), 7.49 (d, J = 9.0 Hz, 2H), 6.87 (d, J = 7.7
Hz, 1H), 5.38 (d, J = 9.2 Hz, 1H), 4.87 (s, 1H), 4.25 (d, J = 10.7 Hz, 1H), 4.11 (d, J = 7.4 Hz,
1
H), 3.98 (t, J = 8.2 Hz, 1H), 3.87 (td, J = 9.2, 4.8 Hz, 1H), 3.54 – 3.41 (m, 1H), 3.27 – 3.06
(m, 2H), 3.01 (d, J = 14.2 Hz, 1H), 2.30 (dd, J = 31.5, 14.5 Hz, 2H), 2.20 – 2.00 (m, 4H), 1.99
1
3
–
1.72 (m, 9H), 1.72 – 1.54 (m, 7H), 1.50 – 1.20 (m, 22H), 1.11 – 0.84 (m, 25H). C NMR
(126 MHz, CDCl
3
) δ 175.54, 175.37, 172.01, 156.97, 155.97, 154.89, 80.67, 79.41, 77.41,
7
3
2
7.16, 76.91, 64.15, 60.46, 60.28, 59.54, 53.86, 49.36, 48.32, 48.09, 45.05, 43.36, 35.40, 35.07,
4.07, 32.76, 32.35, 31.92, 31.70, 31.42, 29.82, 29.29, 28.50, 26.83, 26.61, 25.76, 25.51, 25.22,
5.08, 21.77, 21.45, 19.68, 19.53, 18.32.MALDITOF/TOF- m/zcalcd.forC46
H
82
N
6
O
10
+
[
M+Na] 901.75, obsrvd. 901.75
Crystallographic Information of Peptides:
Crystal structure analysis of (P1): Crystals of peptide were grown by slow evaporation from
a solution of aqueous methanol. A single crystal (0.24 × 0.09 × 0.12 mm) was mounted on loop
with a small amount of the paraffin oil. The X-ray data were collected at 100K temperature on
a Bruker APEX(II) DUO CCD diffractometer using Mo K
α
radiation (λ = 0.71073 Ǻ), ω-scans
(2θ = 56.804), for a total of 15327 independent reflections. Space group P-1, a = 12.4211(17),
3
b = 14.978(2), c = 18.010(2), α = 86.938(3),β = 72.999(3), = 73.465(3),V = 3070.1(7)Ǻ ,
triclinic, Z = 2 for chemical formula C53 12, with one molecule in asymmetric unit;
H
86
F
5
8
N O
-3
-1
ρcalcd = 1.214 gcm , μ = 0.096 mm , F(000) = 1280, The structure was obtained by direct
1
methods using SHELXS-97. The final R value was 0.0611 (wR2 = 0.1421) 4923 observed
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Chemistry - An Asian Journal
10.1002/asia.201901411
reflections (F
0
≥ 4σ(|F
0
|)) and 558 variables, S = 0.895.The largest difference peak and hole
3
were 0.474 and -0.506eǺ , respectively
Crystal structure analysis of (P2): Crystals of peptide were grown by slow evaporation from
a solution of aqueous methanol. A single crystal (0.34 × 0.06 × 0.18 mm) was mounted on loop
with a small amount of the paraffin oil. The X-ray data were collected at 100K temperature on
a Bruker APEX(II) DUO CCD diffractometer using Mo K
α
radiation (λ = 0.71073 Ǻ), ω-scans
(2θ = 57.728), for a total of 16084 independent reflections. Space group P-1, a = 13.932(10), b
3
=
14.137(10), c = 17.651(14), α = 103.854(18),β =100.946(19),= 108.442(17),V = 3066(4)Ǻ ,
triclinic, Z = 2 for chemical formula C53
H
93
N O
8
12, with one molecule in asymmetric unit;
-3
-1
ρcalcd = 1.120 gcm , μ = 0.079 mm , F(000) = 1342, The structure was obtained by direct
1
methods using SHELXS-97. The final R value was 0.1173 (wR2 = 0.0.2192) 5639 observed
reflections (F
0
≥ 4σ(|F
0
|)) and 679 variables, S = 1.128.The largest difference peak and hole
3
were 0.295 and -0.445 Ǻ , respectively
Crystal structure analysis of (P4): Crystals of peptide were grown by slow evaporation from
a solution of chloroform. A single crystal (0.31 × 0.04 × 0.20 mm) was mounted on loop with
a small amount of the paraffin oil. The X-ray data were collected at 100K temperature on a
Bruker APEX(II) DUO CCD diffractometer using Mo K
α
radiation (λ = 0.71073 Ǻ), ω-scans
(2θ = 57.14), for a total of 15677 independent reflections. Space group P 21, a = 11.261(3), b
3
=
20.461(5), c = 14.368(4), =108.903(6),V = 3132.1(14)Ǻ , monoclinic, Z = 2 for chemical
-3
formula C47
H85 Cl
3
N
6
O
13, with one molecule in asymmetric unit; ρcalcd = 1.112gcm , μ =
-1
1
0
.202mm , F(000) = 4599, The structure was obtained by direct methods using SHELXS-97.
The final R value was 0.1173 (wR2 = 0.0.2310) 6854 observed reflections (F
0
≥ 4σ(|F
0
|)) and
6
37variables, S = 1.212.The largest difference peak and hole were 0.846and -0.436Ǻ3,
respectively
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Chemistry - An Asian Journal
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Acknowledgements
R. M is thankful to CSIR for fellowship. HNG thank IISER-Pune for financial support.
Keywords: achiral peptides • foldamers • tendril perversion • 310-helix • Schellman motif
REFERENCES
[
1] a) P. Cintas, Angew. Chem. Int. Ed. 2002, 41, 1139–1145; b) M. Rickhaus, M. Mayor.
M. Juríěka, Chem. Soc. Rev., 2016, 45, 1542-1556; d) Y. Wang, J. Xu, Y. Wang, H.
Chen, Chem. Soc. Rev., 2013, 42, 2930–2962.
[2] M. Novotny, G. J. Kleywegt, J. Mol. Biol., 2005, 347, 231–241.
[
3] a) S. Aravinda, N. Shamala, P. Balaram, Chem. Biodiversity, 2008, 5, 1238-1262; b) J.
Venkatraman, S. C. Shankaramma, P. Balaram, Chem. Rev., 2001, 101, 3131-3152; c)
I. L. Karle, P. Balaram, Biochemistry, 1990, 29, 6747-6756; d) C. Toniolo, M. Crisma,
F. Formaggio, C. Peggion, Biopolymers, 2001, 60, 396-419; e) B. A. F. LeBailly, J.
Clayden, Chem. Commun., 2016, 52, 4852-4863; f) M. Crisma, M. De Zotti, F.
Formaggio, C. Peggion, A. Moretto, C. Toniolo, J. Pept. Sci., 2015, 21, 148–177.
[4] a) J. Clayden, A. Castellanos, J. Solá, G. A. Morris, Angew. Chem. Int. Ed., 2009, 48,
5
962-5965; b) J. Solá, G. A. Morris, J. Clayden, J. Am. Chem. Soc., 2011, 133, 3712 –
715; c) J. Solà, M. Helliwell, J. Clayden, Biopolymers, 2011, 95, 62-69; d) R. A.
3
Brown, T. Marcelli, M. De Poli, J. Solá, J. Clayden, Angew. Chem., Int. Ed., 2012, 51,
1
4
4
395–1399; e) T. Boddaert, J. Solá, M. Helliwell, J. Clayden, Chem. Commun., 2012,
8, 3397–3399; f) J. Solá, M. Helliwell, J. Clayden, J. Am. Chem. Soc., 2010, 132,
548–4549.
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201901411
[
5] a) D. Seebach, A. K. Beck, D. J. Bierbaum, Chem. Biodiversity 2004, 1, 111-1239; b)
W. S. Horne, S. H. Gellman, Acc. Chem. Res., 2008, 41, 1399-1408; c) R. P. Cheng, S.
H. Gellman, W. F. DeGrado, Chem. Rev., 2001, 101, 3219-3232; d) F. Fülöp, T. A.
Martinek, G. K. Tóth, Chem. Soc. Rev., 2006, 35, 323-334; e) G. Guichard, I. Huc,
Chem. Commun., 2011, 47, 5933-594; f) P. G. Vasudev, S. Chatterjee, N. Shamala, P.
Balaram, Chem. Rev., 2011, 111, 657-687; g) T. A. Martinek, F. Fülöp, Chem. Soc.
Rev., 2012, 41, 687-702; h) F. Bouillère, S. Thétiot-Laurent, C. Kouklovsky, V. Alezra,
Amino Acids, 2011, 41, 687-707.
[6] a) S. Shin, M. Lee, I. A. Guzei, Y. K. Kang, S. H. Choi, J. Am. Chem. Soc., 2016, 138,
13390-13395; b) K. Basuroy, B. Dinesh, M. B. M. Reddy, S. Chandrappa, S.
Raghothama, N. Shamala, P. Balaram, Org. Lett., 2013, 15 , 4866–4869.
7] S. Abele, P. Seiler, D. Seebach, Helv. Chim. Acta, 1999, 82, 1559–1571.
[
[
8] D. Seebach, T. Sifferlen, D. J. Bierbaum, M. Rueping, B. Jaun, B. Schweizer, J.
Schaefer, A. K. Mehta, R. D. O’ Connor, B. H. Meier, M. Ernst, A. Glättli, Helv. Chim.
Acta, 2002, 85, 2877 -2917.
[9] P. G. Vasudev, N. Shamala, K. Ananda, P. Balaram, Angew. Chem. Int. Ed., 2005, 44,
4972–4975.
[10] S. Chatterjee, P. G. Vasudev, S. Ragothama, C. Ramakrishna, N. Shamala, P.
Balaram, J. Am. Chem. Soc., 2009, 131, 5956- 5965.
[11] S. V. Jadhav, H. N. Gopi, Chem. Commun., 2013, 49, 9179-9181.
[12] R. Misra, A. Saseendran, G. George, K. Veeresh, K. M. P. Raja, S. Raghothama, H.-
J Hofmann, H. N. Gopi, Chem. Eur. J 2017, 23, 3764.
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201901411
[
[
[
13] M. G. Kumar, S. M. Mali, H. N. Gopi, Org. Biomol. Chem., 2013, 11, 803–813.
14] A. Goriely, M. Tabor, Phys. Rev. Lett., 1998, 80, 1564–1567.
15] M. Tomsett, I. Maffucci, B. A. F. Le Bailly, L. Byrne, S. M. Bijvoets, M. G. Lizio, J.
Raftery, C. P. Butts, S. J. Webb, A. Contini, J. Clayden, Chem. Sci., 2017, 8, 3007-
3
018.
16] A. Banerjee, S. Raghothama, I. L. Karle, P. Balaram Biopolymers, 1996, 39, 279–
85.
[
2
[
17] a) C. Baldauf, R. Günther H.-J. Hofmann, J. Org. Chem., 2006, 71, 1200-1208; b) C.
Baldauf, R. Genther, H.-J. Hofmann, Biopolymers 2005, 80, 675; c) S. V. Jadhav, A.
Bandyopadhyay, H. N. Gopi, Org. Biomol. Chem., 2013, 11, 509-514; d) B. F. Fisher,
S. H. Gellman, J. Am. Chem. Soc., 2016, 138, 10766-10769. e) C. Bonnel, B. Legrand,
M. Simon, J. Martinez, J.-L. Bantignies, Y.K. Kang, E. Wenger, F. Hoh, N. Masurier,
L. T. Maillard, Chem. Eur. J. 2017, 23, 17584 – 17591.f) S. Shankar, N. A. Wani, U. P.
Singh, R. Rai ChemistrySelect, 2016, 1, 3675 – 3678
[18] Schellman, In Protein Folding; Jaenicke, R., Ed.; Elsevier/North-Holland
Biochemical Press: Amsterdam, 1980, 53-61.
[19] a) S. Aravinda, N. Shamala, A. Bandyopadhyay, P. Balaram J. Am. Chem.
Soc., 2003, 125, 15065–15075; b) S. J. Pike, J. Raftery, S. J. Webb, J. Clayden, Org.
Biomol. Chem., 2014, 12, 4124-4131; c) N. Ousaka, Y. Inai J. Am. Chem. Soc., 2006
,
128, 14736–14737; d) N. E. Shepherd, H. N. Hoang, G. Abbenante, D. P. Fairlie J. Am.
Chem. Soc., 2009, 131, 15877–15886; e) V. Maurizot, C. Dolain, Y. Leydet, J. M.
Léger, P. Guionneau, I. Huc J. Am. Chem. Soc., 2004, 126, 10049–10052; f) S.
Aravinda, N. Shamala, A. Pramanik, C. Das, P. Balaram Biochem. Biophys. Res.
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201901411
Commun., 273, 933–936; g) I. L. Karle Biopolymers peptide science. 2001, 60, 351–
3
65; h) A. Banerjee, S. Raghothama, I. L. Karle, P. Balaram Biopolymers, 1996, 39,
79–285; i) S. Datta, N. Shamala, A. Banerjee, A. Pramanik, S. Bhattacharjya, P.
2
Balaram J. Am. Chem. Soc., 1997, 119, 9246-9251. j) S.-I, Sakurai, S. Ohsawa, K.
Nagai, K. Okoshi, J. Kumaki, E, Yashima, Angew. Chem. Int. Ed. 2007, 46, 7605 –
7608. k) S, Lifson, C. E. Felder, M. M. Green, Macromolecules 1992, 25, 4142-4148.
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Table of Contents
We are reporting the co-existence of left- and right-handed helical screw sense along with
the C-terminal helix terminating property within the single molecule of new achiral ,-
hybrid peptide foldamers. The molecular level left- and right–handed helix
conformation representing the macroscopic tendril perversion
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