Conformationally assisted lactamizations for the synthesis of symmetrical and unsymmetrical bis-2,5-diketopiperazines

Article abstract of DOI:10.1021/jo401235k

Open-chain N-Cbz-protected-peptidoyl benzotriazolides are converted by a novel lactamization strategy using proline as a turn introducer into both symmetrical (5a-c and 11a-c) and unsymmetrical (19a-e) bis-2,5-diketopiperazines (bis-2,5-DKPs), previously recognized as difficult targets.

Full text of DOI:10.1021/jo401235k

Article
pubs.acs.org/joc
Conformationally Assisted Lactamizations for the Synthesis of
Symmetrical and Unsymmetrical Bis-2,5-diketopiperazines
Khanh Ha,‡ Iryna Lebedyeva,‡ Zhiliang Li,‡ Kristin Martin,‡ Byron Williams,‡ Eric Faby,‡
Amir Nasajpour,‡ Girinath G. Pillai,‡,§ Abdulrahman O. Al-Youbi,∥ and Alan R. Katritzky*,‡,∥
‡Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, United
States
§Institute of Chemistry, University of Tartu, Tartu 50411, Estonia
∥Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, 21589 Saudi Arabia
S
* Supporting Information
ABSTRACT: Open-chain N-Cbz-protected-peptidoyl benzo-
triazolides are converted by a novel lactamization strategy
using proline as a turn introducer into both symmetrical (5a−c
and 11a−c) and unsymmetrical (19a−e) bis-2,5-diketopiper-
azines (bis-2,5-DKPs), previously recognized as difficult
targets.
building blocks for metallo-supramolecular assemblies, metal−
organic polygons, and other metal−organic materials.14
Head-to-tail condensation between the N- and C-termini of
the corresponding linear peptides represents the most
straightforward synthesis for bis-2,5-DKPs.15,16 However,
head-to-tail condensation may require harsh conditions which
cause partial epimerization, other side reactions, and low yields.
Dimeric DKPs can also be obtained by radical dimeriza-
tion8,17,18 or direct modification of the N-alkylated DKP core
via carbanion chemistry,13,14 but these procedures are
challenging because multiple protection and deprotection
steps limit the methodology to specific peptide sequences.
As a part of our research program dedicated to the
development of innovative and efficient cyclization proce-
dures,19−21 we now report novel and versatile strategies for the
synthesis, from peptidoyl benzotriazolides containing proline as
a turn introducer, of both symmetrical and unsymmetrical bis-
2,5-DKPs by triethylamine-promoted lactamization (Figure 1).
Proline has high tendency to induce reverse turns in
polypeptides because it can accommodate both the cis and
the trans conformers of a tertiary Xaa-Pro amide bond (where
Xaa represents any l-α-amino-acid).22 It has therefore been
utilized to introduce reverse turns to achieve short end-to-end
distance in peptide chains.23
INTRODUCTION
■
2,5-Diketopiperazines (2,5-DKPs) occur in numerous natural
products, often as such, but also embedded in larger, more
complex molecular architectures in a variety of natural products
from fungi, bacteria, the plant kingdom, and mammals.1−3 2,5-
DPKs have the ability to bind to a wide range of receptors,
together with several characteristics attractive in scaffolds for
drug discovery.4 DKPs are small, conformationally constrained
heterocyclic molecules stable to proteolysis. Diversity can be
introduced at up to six positions and stereochemistry controlled
at up to four positions.1,5,6 Recent advances in solid-phase
methodology have increased their availability for combinatorial
drug discovery.5,7
In sharp contrast to numerous studies dedicated to the
synthesis and biological properties of DKPs, relatively few bis-
DKPs have been reported.1,8,9 They have, however, shown
considerable biological activity: (i) (+)-WIN 64821, from
Aspergillus flavus cultures is a potent competitive P antagonist
with submicromolar potency for both the human neurokinin 1
and the cholecystokinin B receptors;10 (ii) dimeric diketopiper-
azine (−)-ditryptophenaline alkaloids and (−)-N1-(2-
phenylethylene)ditryptophenaline inhibit the former recep-
tor;11 (iii) (+)-11,11′-dideoxyverticillin A is a tyrosine kinase
inhibitor with potent antitumor activity;11 (iv, v) naturally
occurring bis-DPKs chaetocin and chetomin are inhibitors of
HIF-1α-p300/CBP interaction, although the inhibition mech-
anism remains unclear12 (comparative analysis has shown that
bis-DKPs impact highly on the expression level of hypoxia-
inducible genes and have more genome-wide effects than
DPKs);13 (vi) X-ray crystallographic studies show that xylylene-
linked bis-2,5-DKPs obtained by direct C3 alkylation of the N-
substituted 2,5-DKP cores via carbanion chemistry can adopt
open and closed conformations, which enable them to serve as
RESULTS AND DISCUSSION
■
Synthesis of Symmetrical Bis-DPKs. Dimeric DKP 5a
was synthesized in four steps (Scheme 1): (i) Na,Na-bis-Cbz-L-
cystine (1a) was converted to benzotriazolide 2a in 86% yield;
(ii) reaction of l-Cbz-L-cystinyl benzotriazole 2a with D-proline,
according to our previously reported procedure,24−26 was
Received: June 7, 2013
Published: July 29, 2013
© 2013 American Chemical Society
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Figure 1. Ring construction strategy to form DKPs.
Scheme 1. Cyclization of Bis-Cbz-dipeptidoyl Benzotriazoles 4a−c
complete within 3 h at 20 °C and produced dipeptide dimer
bis-Cbz-L-Cys-D-Pro-OH 3a; (iii) the reaction of 3a with
BtS(O)Bt, generated in situ at −20 °C in dry THF, led without
epimerization to the Cbz N-protected dipeptidoyl benzotriazo-
lides 4a (82%); (iv) cyclization of 4a formed bis-(Cbz-L-Cys-D-
Pro) 5a (Scheme 1, Table 1).
signals), and was corroborated by 1H NMR data. Dimeric Cbz-
N-protected dipetidoyl benzotriazolide 4c has one typical
carbamate and four benzotriazolide proton signals with
chemical shifts ranging from δ 7.43 to 8.34 ppm. In sharp
contrast, the H NMR of bis-2,5-DKP 5c showed these peaks
were absent, which confirmed cyclization of the Cbz-protected
1
Optimum preparative conditions, coreagents, and solvents
for cyclization of 4a were examined: little reaction was observed
when compound 4a was treated under microwave irradiation in
acetonitrile without additive for 3 h, and conversion reached
just 10% after 18 h under reflux in acetonitrile. Addition of
triethylamine (2.2 equiv), however, gave the desired novel
cyclic bis-(Cbz-L-Cys-D-Pro) 5a in 76% yield (Scheme 1, Table
1). The presence of water (MeCN/H2O, 9: 1) in the reaction
mixture caused minimal (<5%) hydrolysis of 4a. No
epimerization of 5a was detected by HPLC. Thus, HPLC
analysis [chirobiotic T column (250 mm × 4.6 mm), detection
at 254 nm, flow rate 5 mL min−1, MeOH] showed a single
peak, retention time 12.0 min on 5a (see Supporting
Information), which confirmed the absence of diastereomers
in the lactamization product bis-2,5-DKP 5a. To study further
racemization-free evidence during Bt-mediated lactamization,
dimeric 2,5-DKP bis-(Cbz-L-Cys-D,L-Pro) 5b was synthesized
(Scheme 1, Table 1). HPLC analysis [chirobiotic T column
(250 mm −4.6 mm), detection at 230 nm, flow rate 0.25 mL/
min, MeOH] on 5a (single peak, retention time 19.0 min) and
5b (two equal peaks, retention times 18.9 and 20.6 min) which
suggest that product 5a should be enantiomerically pure (see
Supporting Information). Compounds 5a,b were characterized
N-terminus with the C-terminus (Scheme 1).
2D NMR Studies of Dimeric DKP 5a (bis-(Cbz-L-Cys-D-
1
Pro). 2D NMR spectra were recorded at 500 MHz for H and
125 MHz for 13C equipped with a three-channel, 5-mm,
indirect detection probe, with z-axis gradients. The chemical
1
shifts for H and 13C were referenced to the residual solvent
1
signal on the TMS scale. H and 13C chemical shifts were
assigned based on the 1H−1H, one-bond and long-range
1H−13C couplings, seen in the gDQCOSY, gHMQC, and
gHMBC spectra. The methylene protons in 5a were not
stereochemically assigned. Compound 5a was fully assigned
based on different 2D NMR experiments (Figure 2). The most
important correlations that confirm the successful cyclization
1
were seen in the H−13C gHMBC experiment. The gHMBC
(see the Supporting Information for more details) experiment
shows that the methine proton of Cbz-N-protected L-cystein at
5.04 ppm has a three-bond correlation with the carbonyl group
of the D-proline fragment at 167.7 ppm. This correlation
confirms the cyclic structure of 5a. There was no significant
correlation between methine protons 5.04 ppm and 4.39 ppm
in NOE experiment which suggests that the compound exists
exclusively in the trans-form (important correlations are
indicated with a single headed arrow in Figure 2).
1
by H and 13C NMR and HRMS (Table 1).
Turn-Introducer Effect of Proline on Cyclization To
Form Bis-DKPs. A prerequisite for facile cyclization is to bring
the Cbz-protected amino group into close proximity to the BtH
activated carbonyl group. In order to evaluate the role of
proline in cyclization, we analyzed the spatial distances between
relevant reaction centers b(N−C) in disulfides Cbz-Cys-Pro-Bt
4a and Cbz-Cys-Leu-Bt 4d. Computational analysis used
previously were employed27−30 for long-range acyl migration
A similar protocol was used to synthesize bis-2,5-DPK 5c bis-
(Cbz-D,L-Homo-Cys-D-Pro) (83%) by cyclization of its
precursor 4c (Scheme 1, Table 1). Compound 5c was purified
1
by semipreparative HPLC and fully characterized by H and
13C NMR spectroscopy, HRESI-MS, and analytical HPLC. 13C
NMR spectra indicated formation of desired lactamization
product 5c (appearance of two more upfield amide carbon
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Table 1. En Route to Symmetrical Bis-DKPs
The relevant energies and b(N−C) calculated for the
different preorganized structures were considered to prioritize
the conformers. Thus, the conformation with the shortest
geometrical distance between reaction centers b(N−C) affords
the preorganized structure through which cyclization was
expected to occur.
1
Figure 2. H and 13C chemical shift assignments of 5a.
A full conformational search considering both rotatable
bonds and the phenyl ring of the two related structures 4a,d
(Table 2) was implemented using the MMX force field, in
PCModel v. 9.3 software.37 The resultant conformers were
ranked in ascending order of b(N−C), and the best
preorganized structures, with the smallest b(N−C) values, are
shown in Figure 3. In addition, the spatial calculated distances
b(N−C), energies and heat of formation for the two structures
are shown in Table 2.
reactions including a full conformational search followed by
scoring the conformers based on energies and spatial distances
between relevant centers b(N−C). To justify the spatial
distance b(N−C), quantum chemical calculations were carried
out at DFT level of theory31,32 and/SV(P),33 def2-SV(P)34
basis sets using TURBOMOLE V5.9,35,36 a development of the
University of Karlsruhe and Forschungszentrum Karlsruhe
GmbH, 1989−2007, TURBOMOLE GmbH, since 2007;
available from http://www.turbomole.com.
We investigated the effect of the turn-introducer proline
moiety in 4a against 4d (leucine) in Figure 3 and Table 2. The
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Table 2. Geometrical Distances between (b(N−C)) in the Preorganized Structures
Figure 3. (A) Representation of 4a with proline. (B) Representation of 4d with leucine.
Scheme 2. Synthesis of Bis-benzotriazoles 10a−c
conformational analysis shows that the presence of proline in
the peptide chain brings the terminal protected amine and Bt−
activated carbonyl closer by 1.79−2.04 Å compared to the
system with leucine. In addition, the energy level of 4d lies
significantly higher than the energy level of 4a. These results
indicate that a reverse turn effect furnished by proline favors
intramolecular cyclization. Conformational analysis and quan-
tum chemical calculations showed that the spatial distance
between the terminal Cbz-protected amine and the CO group
b(N−C) is a central factor in controlling cyclization rate and
product yields.
Further Development of Bt Auxiliary Method for
Synthesis of Symmetrical Bis-2,5-DPKs. To broaden the
utility of our method, we applied the procedure to the
cyclization of open chain peptidoyl benzotriazolides 10a−c for
the synthesis of symmetrical dimeric DPKs 11a−c (Table 1,
entries 4−6) with aliphatic “mimetic” linkers (Scheme 2, Table
1). Bis-DKP derivative ICRF-159 with an aliphatic linker
between the DKP units showed unique preclinical properties:
chelation with divalent cations, potential amelioration of
anthracycline cardiac toxicity and possible antimetastatic
effects.38−40 Dicarboxylic acids: 3,3-dimethylglutaric and trans-
1,4-cyclohexanedicarboxylic acids were chosen as linker-
precusors for the DKPs units. To study the lactamization
reaction to form symmetrical bis-DKPs 11a−c, the starting
materials 10a−c were obtained in a six-step procedure starting
from commercially available bis-benzotriazolides 6a,b. The
symmetrical N-Cbz-protected tripeptide derivatives 7a,b were
prepared in yields of 72−78% by coupling bis-benzotriazolides
6a,b with Nα-Cbz-L-lysine, or N-Cbz-L-cysteine. Compounds
7a,b were then converted into N-(Cbz-α-aminoacyl)-
benzotriazoles 8a,b (78−83%) which were subsequently
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coupled with D-proline or L-proline to afford the side-chain
linked tetrapeptides 9a,c. Treatment of N-Cbz-tetrapeptides
9a−c with 8 equiv of BtH and 2 equiv of thionyl chloride in
tetrahydrofuran at −45 °C for 6 h gave N-protected α-
tetrapeptidoyl benzotriazolides 10a−c in yields of 68−88%
(Scheme 2).
Cyclization of bis-benzotriazolides 10a−c was carried out in
dry acetonitrile in the presence of 3.5 equiv of triethylamine.
The lactamization mixture was stirred at room temperature
until TLC revealed complete reaction. Open chain N-Cbz-
protected-peptidoyl benzotriazolides 10a−c were converted
into symmetrical bis-2,5-DKPs 11a−c in yields of 91%, 85%,
and 81% correspondingly by our cyclization strategy (Scheme
3, Table 1 entries 4−6).
precursors. Scheme 4 shows coupling reactions with side chain
functional groups in the linkers. Cbz-L-Asp-OH (12a) and Cbz-
L-Glu-OH (12b) were each converted into N-(Cbz-α-amino-
acyl)-benzotriazolides 13a,b (86% and 92% respectively).
Coupling of these benzotriazole derivatives 13a,b with
functional groups of the side chains in Cbz-N-protected-α-
aminoacids 14a−c in the presence of diisopropylethylamine
(for 15a,b) or triethylamine (for 15c−e) gave 15a−e (88−
93%) (Scheme 4).
Peptides 15a−e were converted into the corresponding
benzotriazolides 16a−e (68−78%, Scheme 5). Coupling 16a−e
with Cbz-protected L-proline or D-proline in acetonitrile−water
(3:1) in the presence of triethylamine provided peptides 17a−
e, which were subsequently treated with in situ generated
BtS(O)Bt to afford the peptide benzotriazolides 18a−e in 62−
72% yields. Cyclization of 18a−e occurred under conditions
similar to those used for the cyclization of 4a−c and gave the
desired bis-2,5-DPKs 19a−e in yields of 72−88% (Scheme 5,
Table 3). Samples 19a−e (Table 3) showed the advantage of
our base-assisted lactamization of open chain N-Cbz-protected
peptidoyl benzotriazolides for synthesis of DKPs derivatives
since direct lactamization of N-protected dipetides to form
DKPs using peptide coupling reagents often requires harsh
conditions,1,43,44 and the deprotection/cyclization strategy can
lead to extended procedures and lower yields.1,45
Scheme 3. Synthesis of Aliphatic “Mimetic” Linked Bis-2,5-
DKPs 11a−c
Synthesis of Unsymmetrical Bis-2,5-DKPs. Literature
examples of unsymmetrical bis-DPKs include compounds
endowed with antagonist and anticancer activity.1,41,42 We
therefore targeted bis-DKPs with unsymmetrical linkers to
broaden the scope of our methodology. Our strategy included
three key transformations: (i) preparation of unsymmetrical
linkers (15a−e) derived from amino dicarboxylic acids (12a,b)
to provide functional groups in one of the amino acid
constituents of the DKPs (Scheme 4); (ii) coupling of linkers
(15a−e) at both C-termini with a turn-introducer proline unit
as a second amino acid that forms a DPK unit forming
intermediates (17a−e) (Scheme 5); (iii) lactamization of
(17a−e) to form the designed bis-2,5-DKPs (19a−e). Cbz N-
protected L-aspartic and L-glutamic acids were chosen as linker-
CONCLUSION
■
In summary, we have developed novel, straightforward, and
versatile Bt-mediated cyclization for the synthesis of bis-2,5-
DKPs with both symmetrical and unsymmetrical linkers. The
methodology was utilized to ring-close a series of peptidoyl
benzotriazolides yielding a small library of bis-DKPs with novel
features, which could not be prepared efficiently using
previously reported methods. The approach described herein
should provide a convenient entry to the design and synthesis
of a variety of bis-DKPs with potential utility in drug discovery,
biological catalysis, and material chemistry. Our Bt-assisted
cyclization offers the following advantages: (i) lactamization at
room temperature; (ii) formation of bis-2,5-DKPs in good
Scheme 4. Preparation of 15a−e
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Scheme 5. Synthesis of Bis-DKPs 19a−e with Unsymmetrical Linkers
Table 3. En Route to Unsymmetrical Bis-DKPs 19a−e
yields with no detectable racemization; (iii) the use of
commercially available and inexpensive reagents, and (iv)
easy purification. Given that there are an increasing number of
studies involving the synthesis of symmetrical and unsym-
metrical DKPs to evaluate their biological activities, we believe
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reduced pressure, and the residue was dissolved in ethyl acetate. The
solution was washed with 4 N HCl (3 × 1.5 mL/1 mL of ethyl
acetate) and brine (1 mL/1 mL of ethyl acetate). Recrystallization
from ethyl acetate/hexanes yielded disulfide dipeptides 3a−c.
this new approach represents a significant development in the
field.
EXPERIMENTAL SECTION
■
Melting points were determined on a capillary point apparatus
equipped with a digital thermometer. H NMR and 13C NMR spectra
1
were recorded in CDCl3, DMSO-d6, acetone-d6, or CD3OD using a
300 or 500 MHz spectrometer (with TMS as an internal standard).
The following abbreviations are used to describe spin multiplicity: s =
singlet, d = doublet, t = triplet, q = quartet, m = multiplet, br s = broad
singlet, dd = doublet of doublets, ddd = doublet of doublets of
doublets, and dt = doublet of triplets. 3,3-DMG refers to 3,3 dimethyl
glutarate, and trans-1,4-CHD refers to trans-cyclohexane-1,4-dicarbox-
ylate. HPLC−MS analyses were performed on a reverse phase gradient
using 0.2% acetic acid in H2O/methanol as mobile phases; wavelength
=254 nm; mass spectrometry was done with electrospray ionization
(ESI), matrix-assisted laser desorption/ionization-time-of-flight
(MALDI-TOF) or atmospheric-pressure chemical ionization (APCI).
Ether refers to diethyl ether.
(Cbz-L-Cys-D-Pro-OH)2 (3a). White microcrystals, 2.22 g, 3.17
mmol, 75% yield. Mp: 78−80 °C. 1H NMR (DMSO-d6, 300 MHz): δ
1.78−1.96 (m, 6H), 2.08−2.18 (m, 2H), 2.85 (dd, J = 13.9, 9.9 Hz,
2H), 3.02 (dd, J = 13.7, 3.9 Hz, 2H), 3.56−3.68 (m, 4H), 4.24 (dd, J =
8.8, 3.8 Hz, 2H), 4.48−4.62 (m, 2H), 5.03 (br s, 4H), 7.28−7.51 (m,
10H), 7.78 (d, J = 8.2 Hz, 2H), 12.37 (br s, 2H). 13C NMR (CD3OD,
75 MHz): δ 26.0, 30.2, 40.7, 53.6, 60.7, 68.0, 129.0, 129.1, 129.6,
138.2, 158.6, 171.5, 175.3. HRMS (ESI): calcd for C32H37N4O10S2 [M
− H]− 701.1945, found 701.1959.
General Procedure for the Preparation of Bis-Benzotriazo-
lides 2a,b. A stirred solution of 1H-benzotriazole (BtH) (8 equiv) in
dry tetrahydrofuran (THF) (10 mL/1 g) was treated at 20 °C with
thionyl chloride (SOCl2) (2 equiv). After 20 min, a solution of (Cbz-L-
Cys-OH)2 (for 2a) or (Cbz-D,L-Homo-Cys-OH)2 (for 2b) (1 equiv)
in dry THF (10 mL/1 g) was added dropwise, and the resulting
solution was then stirred for 2 h at 20 °C. Upon completion, the
mixture was filtered, and THF was removed under reduced pressure.
The residue was dissolved by dichloromethane (CH2Cl2 50 mL/1 g of
1a,b) and washed successively with HCl (4 N, 2 × 1 mL/1 mL
CH2Cl2), aq Na2CO3 (10%, 2 × 1 mL/1 mL CH2Cl2), and brine (1
mL/1 mL). The organic layer was dried over magnesium sulfate
(MgSO4), filtered, and evaporated to give the crude product. The solid
was recrystallized from CH2Cl2/hexanes to yield bis-benzotriazolides
2a,b.
(Cbz-L-Cys-D,L-Pro-OH)2 (3b). White microcrystals, 1.54 g, 2.20
mmol, 78% yield. Mp: 68−72 °C. 1H and 13C NMR were identical to
those for 3a.
(Cbz-D,L-Homo-Cys-D-Pro-OH)2 (3c). Sticky gel, 0.77 g, 1.05 mmol,
1
78% yield. H NMR (DMSO-d6, 300 MHz): δ 1.80−2.00 (m. 8H),
2.02−2.24 (m, 4H), 2.62−2.82 (m, 4H), 3.64 (br s, 4H), 4.144.27 (m,
2H), 5.01 (t, J = 3.4 Hz, 2H), 5.04 (br s, 4H), 7.24−7.40 (m, 10H),
7.81 (d, J = 8.3 Hz, 2H). 13C NMR (CD3OD, 75 MHz): δ 26.0, 30.2,
32.2, 35.6, 53.0, 54.1, 67.8, 127.2, 128.9, 129.1, 129.5, 138.1, 158.7,
174.2. HRMS (ESI): calcd for C34H41N4O10S2 [M − H]− 729.2259,
found 729.2268.
(Cbz-L-Cys-Bt)2 (2a). White microcrystals, 3.82 g, 5.38 mmol, 86%
yield. Mp: 105−108 °C.46 1H NMR (CDCl3, 300 MHz): δ 3.20−3.37
(m, 2H), 3.38−3.50 (m, 2H), 5.11 (br s, 4H), 5.91 (d, J = 7.2 Hz, 2H),
5.97−6.07 (m, 2H), 7.26−7.38 (m, 10H), 7.51 (t, J = 7.3 Hz, 2H),
7.65 (t, J = 7.2 Hz, 2H), 8.05 (d, J = 8.2 Hz, 2H), 8.19 (d, J = 8.2 Hz,
2H). 13C NMR (CDCl3, 75 MHz): δ 41.0, 54.3, 67.7, 114.5, 120.6,
126.9, 128.4, 128.7, 131.2, 136.1, 146.2, 155.9, 169.4. Anal. Calcd for
C34H30N8O6S2: C, 57.45; H, 4.25; N, 15.76. Found: C, 57.66; H, 4.09;
N, 15.40.
General Procedure for the Preparation of Disulfide
Dipeptidoyl Benzotriazolides 4a−c. A stirred solution of BtH (8
equiv) in dry tetrahydrofuran (THF) (15 mL/1 g) was treated at −20
°C with SOCl2 (1 equiv). After 20 min, a solution of 3a−c (1 equiv) in
dry THF (15 mL/1 g 3a−c) was added dropwise, and the resulting
solutions were then stirred for 1.5 h at −20 °C. The ice bath was then
removed, and the reaction mixture was stirred for an additional 1.5 h at
room temperature. The mixture was filtered, and THF was removed
under reduced pressure. The residue was dissolved CH2Cl2 (100 mL/1
g 3a−c) and washed successively with HCl (4 N, 2 × 0.7 mL/1 mL of
CH2Cl2), Na2CO3 10 wt % in water (2 × 1 mL/1 mL of CH2Cl2), and
brine (1 × 30 mL). The organic layer was dried over magnesium
sulfate, filtered, and evaporated. The crude product was then
recrystallized from CH2Cl2/hexanes to yield disulfide dipeptidoyl
benzotriazolides 4a−c.
(Cbz-D,L-Homo-Cys-Bt)2 (2b). White microcrystals, 1.86 g, 2.5
1
mmol, 68% yield; mp 98−104 °C. H NMR (CDCl3, 300 MHz): δ
2.21−2.32 (m, 2H), 2.48−2.62 (m, 2H), 2.85−2.96 (m, 4H), 5.15 (br
s, 4H), 5.87−5.95 (m, 2H), 6.00−6.13 (m, 2H), 7.16 (br s, 2H), 7.28−
7.42 (m, 8H), 7.50−7.57 (m, 2H), 7.66−7.70 (m, 2H), 8.09−8.15 (m,
2H), 8.26 (t, J = 7.6 Hz, 2H). 13C NMR (CDCl3, 75 MHz): δ 33.1,
34.7, 54.2, 67.6, 114.5, 120.6, 126.8, 128.5, 128.7, 131.1, 131.3, 136.1,
146.2, 156.3, 171.3. HRMS (ESI): calcd for C36H34N8O6S2Na [M +
Na]+ 761.1935, found 761.1949.
General Procedure for the Preparation of Disulfide
Dipeptides 3a−c. Disulfide dipeptide benzotriazolides 2a,b (1
equiv) were each suspended in acetonitrile/water (3:1) (25 mL/1
g), and a solution of D-proline or D,L-proline (2 equiv) in water (10
mL/1 g of proline) containing triethylamine (2−2.2 equiv) was added
slowly. The mixtures were stirred at 20 °C for 15 h until TLC revealed
consumption of the starting materials. The solvent was removed under
(Cbz-L-Cys-D-Pro-Bt)2 (4a). White microcrystals, 1.58 g, 1.75 mmol,
1
82% yield. Mp: 119−124 °C. H NMR (DMSO-d6, 300 MHz): δ
2.02−2.26 (m, 6H), 2.38−2.47 (m, 2H), 2.89 (dd, J = 13.7, 8.8 Hz,
2H), 3.14 (dd, J = 13.7, 5.1 Hz, 2H), 3.74−3.95 (m, 4H), 4.72−4.82
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(m, 2H), 5.09 (br s, 4H), 5.68−5.78 (m, 2H), 7.28−7.42 (m, 10H),
7.64 (dt, J = 8.3, 1.2 Hz, 2H), 7.81 (dt, J = 8.3, 1.1 Hz, 2H), 7.84 (d, J
= 8.6 Hz, 2H), 8.22 (d, J = 8.3 Hz, 2H), 8.29 (d, J = 8.3 Hz, 2H). 13C
NMR (CDCl3, 75 MHz): δ 25.2, 29.9, 41.2, 48.0, 52.1, 60.0, 67.3,
114.7, 120.4, 126.6, 128.2, 128.3, 128.7, 130.7, 131.3, 136.3, 146.2,
155.9, 169.0, 170.3. HRMS (ESI): calcd for C44H44N10O8S2Na [M +
Na]+ 927.2677, found 927.2681.
2H), 3.44−3.58 (m, 4H), 4.54−4.60 (m, 2H), 5.005.06 (m, 2H),
5.26−5.36 (m, 4H), 7.24−7.48 (m, 10H). 13C NMR (CDCl3, 75
MHz): 22.9, 29.4, 31.8, 31.8, 34.2, 45.8, 59.7, 60.5, 69.7, 128.4, 128.6,
128.8, 128.9, 134.8, 152.3, 152.4, 164.7, 167.5. HRMS (ESI): calcd for
C32H34N4O8S2Na [M + Na]+ 689.1710, found 689.1724.
Bis[cyclo-(Cbz-D,L-Homo-Cys-D-Pro)] (5c). White microcrystals,
1
0.29 g, 0.42 mmol 83% yield. Mp: 85−86 °C. H NMR (CDCl3,
300 MHz): δ 1.86−2.24 (m, 10H), 2.35−2.48 (m, 2H), 2.64−2.78 (m,
4H), 3.48−3.59 (m, 4H), 4.26 (t, J = 7.6 Hz, 2H), 4.85 (t, J = 7.7 Hz,
2H), 5.29 (br s, 4H), 7.26−7.44 (m, 10H). 13C NMR (CDCl3, 75
MHz): δ 23.1, 29.6, 32.0, 34.4, 46.0, 59.9, 60.7, 69.8, 128.8, 129.0,
129.1, 135.0, 152.5, 164.9, 167.7. HRMS (ESI): calcd for
C34H38N4O8S2Na [M + Na]+ 717.2023, found 717.2034.
(Cbz-L-Cys-D,L-Pro-Bt)2 (4b). White microcrystals, 1.09 g, 1.21
1
mmol, 85% yield. Mp: 111−114 °C. H and 13C NMR were identical
to those of 4a.
General Procedure for the S- and N-Acylations of 6a,b for
Preparation of Compounds 7a,b. Bis-benzotriazolides 6a,b (1
equiv) were each suspended in acetonitrile/water (3:1) (20 mL/1 g)
(for S-and N-acylations), and a solution of Cbz-L-Cys-OH (2−2.1
equiv) or Cbz-L-Lys-OH (2−2.1 equiv) in water (10 mL/1 g)
containing triethylamine (2.2 equiv) was added slowly. The mixtures
were stirred at 20 °C for 16−72 h until the TLC revealed consumption
of the starting materials. The solvent was removed under reduced
pressure, and the residue was dissolved in ethyl acetate (30 mL/1 g of
6a,b). The organic layer was washed with 4 N HCl (3 × 1 mL/1 mL of
ethyl acetate) and evaporated, and the products were recrystallized
from ethyl acetate/hexanes to yield 7a,b.
(Cbz-D,L-Homo-Cys-D-Pro-Bt)2 (4c). White microcrystals, 5.32 g, 5.7
mmol 91% yield. Mp: 83−84 °C. 1H NMR (DMSO-d6, 300 MHz): δ
1.78−2.00 (m, 4H), 2.01−2.26 (m, 8H), 2.66−2.86 (m, 4H), 3.49−
4.29 (m, 4H), 4.34−4.74 (m, 2H), 5.03 (br s, 4H), 5.21−5.32 (m,
1H), 5.60−5.80 (m, 1H), 7.24−7.46 (m, 12H), 7.56−7.84 (m, 4H),
8.14−8.24 (m, 2H), 8.26−8.34 (m, 2H). 13C NMR (CDCl3, 75 MHz):
δ 25.2, 25.5, 29.9, 32.4, 34.1, 47.9, 51.5, 59.9, 67.2, 114.6, 120.4, 126.4,
126.6, 128.3, 128.7, 128.9, 130.8, 136.3, 146.1, 156.3, 170.2. HRMS
(ESI): calcd for C46H48N10O8S2Na [M + Na]+ 955.2990, found
955.2996.
General Procedure for the Cyclization of Disulfide
Dipeptidoyl Benzotriazolides 4a−c to Form Symmetrical Bis-
DKPs 5a−c. A solution of disulfide dipeptidoyl bentrotriazolides 4a−c
(1 equiv) and triethylamine (2.2 equiv) in dry acetonitrile (15 mL/1
g) was stirred at room temperature until the TLC revealed completion
of the reaction. The mixture was then concentrated under vacuum and
the residue was dissolved in ethyl acetate. The organic layer was
washed with 4 N HCl (3 × 1 mL/1 mL of ethyl acetate) and Na2CO3
10 wt % in water (3 × 1 mL/1 mL of ethyl acetate), and purified by
column chromatography (hexanes/ethyl acetate gradient) to give the
corresponding symmetrical bis-DKPs 5a−c.
3,3-DMG-(Cbz-L-Lys-OH)2 (7a). Sticky gel, 5.36 g, 7.83 mmol, 72%
yield. H NMR (CD3OD, 300 MHz): δ 1.08 (s, 6H), 1.36−1.61 (m,
1
8H), 1.64−1.75 (m, 2H), 1.80−1.92 (m, 2H), 2.25 (s, 2H), 2.35 (s,
2H), 3.18 (t, J = 6.8 Hz, 2H), 3.26 (t, J = 6.8 Hz, 2H), 4.09−4.17 (m,
2H), 5.09 (s, 4H), 7.27−7.38 (m, 10H). 13C NMR (CD3OD, 75
MHz): δ 24.4, 28.7, 30.0, 32.5, 34.1, 40.2, 47.0, 55.3, 67.7, 128.9, 129.1,
129.6, 138.2, 158.7, 174.4, 176.0. HRMS (ESI): calcd for C35H47N4O10
[M − H]− 683.3287, found 683.3293.
trans-1,4-CHD-(Cbz-L-Cys-OH)2 (7b). Sticky gel, 1.51 g, 2.33 mmol,
1
78% yield. H NMR (CD3OD, 300 MHz): δ 1.52−1.75 (m, 4H),
Bis[cyclo-(Cbz-L-Cys-D-Pro)] (5a). White microcrystals, 0.51 g, 0.76
mmol, 76% yield. Mp: 116−120 °C. H NMR (CDCl3, 300 MHz): δ
1.78−2.06 (m, 4H), 2.40−2.68 (m, 2H), 3.13 (dd, J = 13.7, 8.9 Hz,
2H), 3.50 (dd, J = 13.8, 4.5 Hz, 2H), 4.36 (dd, J = 8.6 Hz, 4.4 Hz, 2H),
5.18−5.01 (m, 4H), 7.21−7.41 (m, 10H). 13C NMR (CDCl3, 75
MHz): δ 26.2, 30.6, 49.3, 53.7, 67.4, 128.3, 128.3, 128.7, 136.1, 156.2,
1
1.86−1.94 (m, 2H), 1.97−2.11 (m, 4H), 2.38−2.46 (m, 2H), 3.23 (d, J
= 6.1 Hz, 2H), 3.42−3.63 (m, 6H), 4.39 (dd, J = 9.1, 6.9 Hz, 2H), 5.04
(dd, J = 5.8, 5.8 Hz, 2H), 5.27 (d, J = 7.5 Hz, 2H), 5.31 (d, J = 7.5 Hz,
2H), 7.31−7.41 (m, 10H). 13C NMR (CDCl3, 75 MHz): δ 22.5, 29.7,
40.6, 45.8, 60.0, 60.7, 69.7, 128.6, 128.9, 134.7, 152.1, 163.1, 167.3.
HRMS (ESI): calcd for C32H34N4O8S2Na [M + Na]+ 689.1710, found
689.1731.
1
173.8, 201.6. Compound 7b was characterized by H and 13C NMR.
General Procedure for the Preparation of Bis-benzotriazo-
lides 8a,b. A stirred solution of BtH (8 equiv) in dry THF (10 mL/1
g) was treated at 20 °C by SOCl2 (2 equiv). After 20 min, a solution of
7a,b (1 equiv) in dry THF (15 mL/1 g) was added dropwise at −20
°C, and each resulting solution was stirred for 2 h at −20 °C. The ice
bath was removed, and each reaction mixture was stirred for an
additional 2 h at room temperature. The mixtures were filtered, and
THF was removed under reduced pressure. Each residue was dissolved
in ethyl acetate (50 mL/1 g of 7a,b) and washed successively with HCl
(4 N, 2 × 1.5 mL/1 mL of ethyl acetate), Na2CO3 10 wt % in water (2
× 1.5 mL/1 mL of ethyl acetate), and brine (1 × 1 mL/1 mL of ethyl
acetate). The organic layers were dried over sodium sulfate, filtered,
evaporated, and recrystallized from CH2Cl2/hexane to give the
corresponding bis-benzotriazolides 7a,b.
Bis[cyclo-(Cbz-L-Cys-D,L-Pro)] (5b). Isolated as mixture of diaster-
eomers. White microcrystals, 0.43 g, 0.65 mmol, 78% yield. Mp: 96−
101 °C. 1H NMR (CD3OD, 300 MHz): δ 1.90−2.14 (m, 6H), 2.34−
2.42 (m, 1H), 3.12 (dd, J = 8.7, 3.6 Hz, 2H), 3.18 (dd, J = 8.7, 4.5 Hz,
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trans-1,4-CHD-(Cbz-L-Cys-L-Pro-OH)2 (9c). Sticky gel, 0.93 g, 1.11
1
mmol, 75% yield. H and 13C NMR were identical to 9b.
3,3-DMG-(Cbz-L-Lys-Bt)2 (8a). Sticky gel, 1.01 g, 1.14 mmol, 78%
yield. 1H NMR (DMSO-d6, 300 MHz): δ 1.12 (s, 6H), 1.34−1.50 (m,
8H), 1.79−1.96 (m, 4H), 2.25 (s, 4H), 2.92−3.06 (m, 4H), 5.03 (br s,
4H), 5.28−5.52 (m, 2H), 7.28−7.38 (m, 10H), 7.53−7.66 (m, 2H),
7.74−7.81 (m, 2H), 7.85−7.92 (m, 2H), 8.16−8.29 (m, 4H). 13C
NMR (CDCl3, 75 MHz): δ 24.5, 28.5, 29.1, 29.8, 30.9, 32.6, 34.1, 44.4,
69.4, 114.6, 120.1, 125.9, 126.3, 127.7, 128.5, 130.5, 131.1, 138.9,
146.1, 156.5, 170.9, 172.4. HRMS (ESI): calcd for C47H54N10O8Na [M
+ Na]+ 909.4018, found 909.4038.
General Procedure for the Preparation of Cyclization
Precursors 10a−c. A stirred solution of BtH (8 equiv) in dry
THF (10 mL/1 g) was treated at 0 °C with SOCl2 (2 equiv). After 20
min, the reaction mixture was cooled to −45 °C in acetone/dry ice
bath and a solution of 9a−c (1 equiv) in dry THF (15 mL/1 g) was
added dropwise. The resulting solution was stirred for 6 h at −45.0 °C,
after which THF was removed under reduced pressure. The residue
was dissolved by ethyl acetate (20 mL/1 g of 9a−c) and washed with
brine (2 × 1.5 mL/1 mL), HCl (4 N, 2 × 1 mL/1 mL ethyl acetate),
and Na2CO3 10 wt % in water (2 × 1 mL/1 mL ethyl acetate). The
organic layer was dried over sodium sulfate, filtered, and evaporated.
The residue was recrystallized with CH2Cl2/hexane to yield
compounds 10a−c.
trans-1,4-CHD-(Cbz-L-Cys-Bt)2 (8b). Sticky gel, 0.70 g, 0.83 mmol,
83% yield. 1H NMR (CDCl3, 300 MHz): δ 1.38−1.83 (m, 8H), 2.42−
2.58 (m, 2H), 3.51 (dd, J = 14.6, 4.7 Hz, 2H), 3.76 (dd, J = 14.6, 5.3
Hz, 2H), 5.08−5.17 (m, 4H), 5.87−6.20 (m, 4H), 7.20−7.42 (m,
10H), 7.51 (t, J = 7.8 Hz, 2H), 7.64 (t, J = 7.8 Hz, 2H), 8.11−8.24 (m,
4H). 13C NMR (CDCl3, 75 MHz): δ 25.7, 26.2, 31.3, 49.1, 54.2, 67.4,
114.3, 120.4, 126.6, 128.2, 128.2, 128.5, 130.9, 131.0, 146.1, 155.6,
168.8, 200.9. HRMS (ESI): calcd for C42H40N8O8S2Na [M + Na]+
871.2303, found 871.2322.
General Procedure for the Coupling of 8a,b with Proline to
Prepare Compounds 9a−c. Bis-benzotriazolides 8a,b (1 equiv)
were each suspended in acetonitrile/water (3:1) (15 mL/1 g), and a
solution of D- or L-proline (2−2.1 equiv) in water (10 mL/1 g)
containing triethylamine (2−2.2 equiv) was added slowly. The
mixtures were stirred at 20 °C for up to 16 h until the TLC revealed
consumption of the starting materials. The solvent was removed under
reduced pressure and the residue dissolved in ethyl acetate (30 mL/1 g
of 8a,b). The organic layer was washed with 4 N HCl (3 × 1 mL/1 mL
of ethyl acetate) and Na2CO3 10 wt % in water (3 × 1 mL/1 mL of
ethyl acetate), and purified by column chromatography (ethyl acetate/
hexanes gradient) to yield compounds 9a−c.
3,3-DMG-(Cbz-L-Lys-D-Pro-Bt)2 (10a). Sticky gel, 1.67 g, 1.55 mmol,
68% yield. 1H NMR (CDCl3, 300 MHz): δ 1.07 (br s, 6H), 1.14−1.31
(m, 6H), 1.33−1.87 (m, 10H), 2.10−2.31 (m, 4H), 2.50 (br s, 4H),
3.26 (br s, 2H), 3.52−3.58 (m, 1H), 3.68−3.85 (m, 4H), 3.90−4.08
(m, 1H), 4.56−4.70 (m, 2H), 5.03−5.18 (m, 4H), 5.51−5.67 (m, 2H),
5.68−5.82 (m, 2H), 5.88−5.98 (m, 2H), 7.27−7.42 (m, 10H), 7.52 (t,
J = 7.2 Hz, 2H), 7.66 (t, J = 7.7 Hz, 2H), 8.13 (d, J = 8.1 Hz, 2H), 8.27
(d, J = 8.4 Hz, 2H). 13C NMR (CDCl3, 75 MHz): δ 22.3, 25.2, 27.9,
28.9, 29.3, 29.8, 32.3, 39.0, 46.6, 47.7, 52.5, 59.8, 67.1, 114.7, 120.4,
126.5, 128.1, 128.7, 130.7, 131.4, 136.6, 146.2, 156.0, 170.3, 170.7,
172.2. HRMS (ESI): calcd for C57H68N12O10Na [M + Na]+
1103.5074, found 1103.5096.
3,3-DMG-(Cbz-L-Lys-D-Pro-OH)2 (9a). Sticky gel, 1.67 g, 1.89 mmol,
84% yield. H NMR (CD3OD, 300 MHz): δ 1.03 (s, 6H), 1.28−1.40
trans-1,4-CHD-(Cbz-L-Cys-D-Pro-Bt)2 (10b). Sticky gel, 0.72 g, 0.85
mmol, 85% yield. H NMR (DMSO-d6, 300 MHz): δ 1.79−1.52 (m,
1
1
(m, 4H), 1.45−1.59 (m, 4H), 1.60−1.77 (m, 4H), 1.78−2.12 (m, 5H),
2.13−2.31 (m, 3H), 2.52 (s, 4H), 3.14−3.25 (m, 1H), 3.41−3.55 (m,
1H), 3.58−3.69 (m, 1H), 3.68−3.77 (m, 4H), 3.80−3.87 (m, 1H),
4.00−4.22 (m, 2H), 4.31−4.53 (m, 2H), 5.03−5.15 (m, 4H),7.28−
7.37 (m, 10H). 13C NMR (CD3OD, 75 MHz): δ 24.0, 24.4, 25.8, 27.8,
28.5, 30.1, 32.2, 40.0, 47.0, 54.0, 55.3, 60.8, 67.8, 127.2, 128.9, 129.5,
140.1, 158.2, 174.2, 175.4, 176.0. HRMS (ESI): calcd for C45H61N6O12
[M − H]− 877.4342, found 877.4361.
5H), 2.05−2.78 (m, 5H), 2.06−2.31 (m, 6H), 2.47−2.71 (m, 2H),
3.30 (dd, J = 14.1, 4.2 Hz, 2H), 3.38 (dd, J = 13.5, 6.6 Hz, 2H), 3.64−
4.09 (m, 4H), 4.84−4.80 (m, 2H), 5.03−5.18 (m, 4H), 5.70 (dd, J =
14.2 Hz, 8.0 Hz, 2H), 5.84 (dd, J = 8.4 Hz, 3.9 Hz, 2H), 7.26−7.42 (m,
10H), 7.46−7.56 (m, 2H), 7.59−7.69 (m, 2H), 8.12 (d, J = 8.4 Hz,
2H), 8.25 (d, J = 8.4 Hz, 2H). 13C NMR (CDCl3, 75 MHz): δ 25.1,
26.1, 29.7, 31.2, 47.6, 49.3, 51.8, 59.8, 66.9, 114.5, 120.2, 126.4, 127.9,
128.0, 128.5, 130.5, 131.2, 136.4, 146.0, 155.8, 168.4, 170.0, 201.6.
HRMS (ESI): calcd for C52H54N10O10S2Na [M + Na]+ 1065.3358,
found 1065.3372.
trans-1,4-CHD-(Cbz-L-Cys-D-Pro-OH)2 (9b). Sticky gel, 0.99 g, 1.18
1
mmol, 80% yield. H NMR (DMSO-d6, 300 MHz): δ 1.30−1.99 (m,
14H), 2.01−2.23 (m, 2H), 2.58−2.74 (m, 2H), 2.91 (dd, J = 13.3, 9.3
Hz, 2H) 3.18 (dd, J = 13.7, 5.0 Hz, 2H), 3.51−3.72 (m, 4H), 4.19 (dd,
J = 9.1, 3.7 Hz, 2H), 4.41−4.54 (m, 1H), 4.95−5.12 (m, 5H), 7.23−
7.42 (m, 10H), 7.60−7.76 (m, 2H), 12.45 (br s, 2H). 13C NMR
(DMSO-d6, 75 MHz): δ 24.0, 25.4, 28.4, 29.8, 46.2, 48.2, 51.2, 58.4,
65.2, 127.2, 127.4, 127.9, 136.6, 155.4, 156.6, 167.7, 171.4, 172.6,
trans-1,4-CHD-(Cbz-L-Cys-L-Pro-Bt)2 (10c). Sticky gel, 0.78 g, 0.92
1
mmol, 88% yield. H and 13C NMR were identical to those of 10b.
General Procedure for the Cyclization of Precursor 10a−c
To Form Symmetrical DKPs 11a−c. A solution of 10a−c (1 equiv)
and triethylamine (2−2.2 equiv) in dry acetonitrile (100 mL) was
stirred for 48−84 h until TLC revealed cyclization was complete. Each
mixture was concentrated under vacuum, and the residue was
1
200.6, 201.2. Compound 9b was characterized by H and 13C NMR.
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dissolved in ethyl acetate (20 mL/1 g of 11a−c). The organic layer
was washed with 4 N HCl (3 × 1 mL/1 mL ethyl acetate) and
Na2CO3 10 wt % in water (3 × 1 mL/1 mL ethyl acetate) and purified
by column chromatography (CH2Cl2/hexanes gradient) to give the
corresponding symmetrical bis-DKPs 11a−c.
8.07−8.26 (m, 4H). 13C NMR (CDCl3, 75 MHz): δ 27.5, 31.9, 54.3,
67.7, 114.5, 120.4, 120.7, 126.5, 126.9, 128.4, 128.7, 130.7, 131.1,
131.2, 136.0, 146.3, 156.1, 171.1, 171.3. Anal. Calcd for C25H21N7O4:
C, 62.11; H, 4.38; N, 20.28. Found: C, 62.15; H, 4.26; N, 20.56.
Synthesis of Compounds 15a−e. Compounds 15a−e were
prepared by O-acylation (for 15a,b) of 13a,b by Cbz-L-Ser-OH (2−2.1
equiv) in acetonitrile (10 mL/1 g) containing diisopropylamine
(DIPEA) (6.5 equiv) or S-acylation (for 15c,d) of 13a,b by Cbz-L-Cys-
OH (2−2.1 equiv) in water (10 mL/1 g) containing triethylamine (2.2
equiv) or N-acylation (for 15e) of of 13a by Cbz-L-Lys-OH (2−2.1
equiv) in water (10 mL/1 g) containing triethylamine (2.2 equiv)
according to the method for preparation of 7a,b.
3,3-DMG-cyclo-(Cbz-L-Lys-D-Pro)]2 (11a). Sticky gel, 0.35 g, 0.42
1
mmol, 91% yield. H NMR (CD3OD, 300 MHz): δ 0.98 (br s, 6H),
1.22−1.34 (m, 8H), 1.42−1.63 (m, 6H), 1.78−2.00 (m, 4H), 2.13−
2.24 (m, 1H), 2.28−2.37 (m, 1H), 2.47 (br s, 4H), 3.07−3.19 (m,
1H), 3.37−3.52 (m, 2H), 3.54−3.61 (m, 1H), 3.62−3.73 (m, 3H),
3.73−3.83 (m, 1H), 4.02−4.38 (m, 2H), 4.40−4.82 (m, 2H), 4.99−
5.27 (m, 4H), 7.21−7.36 (m, 8H), 7.37−7.44 (m, 2H) . 13C NMR
(CDCl3, 75 MHz): δ 22.8, 24.8, 27.8, 29.4, 29.9, 31.4, 38.6, 46.5, 52.5,
59.6, 61.5, 67.1, 69.9, 128.1, 128.7, 129.0, 134.9, 156.1, 165.3, 167.9,
172.3. HRMS (ESI): calcd C45H58N6O10Na [M + Na]+ 865.4107,
found 865.4125.
Cbz-L-Asp-(Cbz-L-Ser-OH)-Cbz-L-Ser-OH (15a). Sticky gel, 5.32 g,
7.50 mmol, 88% yield. 1H NMR (CD3OD, 300 MHz): δ 2.79 (dd, J =
16.9, 7.0 Hz, 1H), 2.87 (dd, J = 16.9, 7.0 Hz, 1H), 3.79 (ddd, J = 18.0,
11.4, 4.5 Hz, 1H), 4.26−4.42 (m, 2H), 4.45−4.63 (m, 4H), 5.07 (br s,
6H), 7.26−7.40 (m, 15H). 13C NMR (CD3OD, 75 MHz): δ 37.2,
51.9, 54.6, 57.8, 63.2, 65.6, 66.0, 68.0, 68.1, 127.2, 128.9, 129.1, 129.3,
129.5, 137.9, 138.0, 158.4, 158.5, 171.7, 172.0, 172.4, 172.6. Anal.
Calcd for C34H35N3O14: C, 57.54; H, 4.97; N, 5.92. Found: C, 57.37;
H, 5.02; N, 5.96.
trans-1,4-CHD-[cyclo-(Cbz-L-Cys-D-Pro)]2 (11b). Sticky gel, 0.85 g,
1
1.05 mmol, 85% yield. H NMR (CD3OD, 300 MHz): δ 1.49−1.67
(m, 3H), 1.74−2.12 (m, 12H), 2.34−2.46 (m, 2H), 2.50−2.58 (m,
1H), 3.34−3.59 (m, 8H), 4.66 (dd, J = 8.0, 8.0 Hz, 2H), 4.95 (dd, J =
7.1, 7.1 Hz, 2H), 5.22−5.36 (m, 4H), 7.22−7.45 (m, 10H). 13C NMR
(CD3OD, 75 MHz): δ 23.5, 27.2, 27.4, 30.3, 46.9, 50.0, 61.3, 61.7,
70.4, 129.6, 129.7, 129.8, 136.7, 153.6, 165.4, 169.0, 202.3. HRMS
(ESI): calcd for C40H44N4O10S2Na [M + Na]+ 827.2391, found
827.2371.
Cbz-L-Glu-(Cbz-L-Ser-OH)-Cbz-L-Ser-OH (15b). Sticky gel, 5.51 g,
7.62 mmol, 92% yield. H NMR (DMSO-d6, 300 MHz): δ 1.93−2.04
1
(m, 1H), 2.21−2.40 (m, 2H), 2.42−2.47 (m, 1H), 3.66 (d, J = 4.8 Hz,
1H), 4.00−4.12 (m, 1H), 4.20 (dd, J = 10.5, 6.9 Hz, 1H), 4.31−4.42
(m, 2H), 4.48 (dd, J = 10.8, 4.5 Hz, 1H), 4.70 (dd, J = 9.8, 2.6 Hz,
1H), 4.99−5.07 (m, 4H), 5.15−5.26 (m, 2H), 7.24−7.46 (m, 15H),
7.62−7.80 (m, 2H), 7.91 (br s, 1H). 13C NMR (DMSO-d6, 75 MHz):
δ 20.9, 30.6, 52.7, 56.6, 58.3, 61.3, 64.0, 65.4, 65.7, 67.3, 127.5, 127.7,
128.1, 128.3, 135.4, 136.8, 150.5, 156.0, 170.5, 170.9, 172.0, 172.8.
HRMS (ESI): calcd for C35H36N3O14 [M − H]− 722.2192, found
722.2181.
trans-1,4-CHD-[cyclo-(Cbz-L-Cys-L-Pro)]2 (11c). Sticky gel, 0.61 g,
0.75 mmol, 81% yield. 1H NMR (CDCl3, 300 MHz): δ 1.82−2.20 (m,
12H), 2.42−2.65 (m, 6H), 3.32−3.43 (m, 2H), 3.46−3.63 (m, 6H),
4.56 (dd, J = 5.7, 4.2 Hz, 2H), 4.98 (t, J = 4.4 Hz, 2H), 5.27−5.36 (m,
4H), 7.28−7.46 (m, 10H). 13C NMR (CDCl3, 75 MHz): 22.7, 26.1,
26.3, 29.2, 29.4, 45.8, 59.9, 60.4, 69.6, 128.6, 128.7, 128.8, 134.8, 152.2,
163.3, 167.2, 200.7. HRMS (ESI): calcd for C40H44N4O10S2Na [M +
Na]+ 827.2391, found 827.2398.
Cbz-L-Asp-(Cbz-L-Cys-OH)-Cbz-L-Cys-OH (15c). Sticky gel, 1.38 g,
1
1.86 mmol, 90% yield. H NMR (DMSO-d6, 300 MHz): δ 2.84−3.19
Preparation of Compounds 13a,b. The compounds were
prepared according to the method for preparation of 2a,b.
(m, 6H), 4.02−4.19 (m, 2H), 4.42−4.68 (m, 1H), 5.03 (br s, 4H),
5.07 (br s, 2H), 7.22−7.41 (m, 15H), 7.75 (d, J = 9.0 Hz, 2H), 8.18 (t,
J = 9.0 Hz, 1H). 13C NMR (CD3OD, 75 MHz): δ 27.1, 31.8, 45.9,
54.9, 59.2, 67.9, 128.9, 129.1, 129.6, 138.2, 158.5, 165.0, 173.4, 196.7.
HRMS (ESI): calcd for C34H34N3O12S2 [M − H]− 740.1578, found
740.1594.
Cbz-L-Asp-(Bt)-Bt (13a). White microcrystals, 1.51 g, 3.22 mmol,
86% yield. Mp: 140−143 °C.47 1H NMR (CDCl3, 300 MHz): δ 4.35−
4.54 (m, 2H), 5.13 (br s, 2H), 6.08−6.13 (m, 1H), 6.19−6.26 (m,
1H), 7.26−7.36 (m, 5H), 7.46−7.71 (m, 4H), 8.07−8.19 (m, 3H),
8.26 (d, J = 8.5 Hz, 1H).
Cbz-L-Glu-(Cbz-L-Cys-OH)-Cbz-L-Cys-OH (15d). Sticky gel, 9.65 g,
12.78 mmol, 90% yield. H NMR (CDCl3, 300 MHz): δ 1.94−2.08
1
(m, 1H), 2.14−2.49 (m, 2H), 2.50−2.71 (m, 1H), 3.05−3.38 (m, 3H),
3.43−3.58 (m, 1H), 4.47−4.80 (m, 3H), 4.99−5.26 (m, 6H), 5.56 (d, J
= 9.0 Hz, 1H), 5.87 (d, J = 9.0 Hz, 1H), 7.23−7.40 (m, 14H), 7.53 (br
s, 2H). 13C NMR (CDCl3, 75 MHz): δ 22.5, 30.8, 53.3, 65.3, 67.5,
68.8, 128.3, 128.4, 128.7, 134.8, 136.0, 150.8, 156.2, 173.1, 173.7,
198.3. HRMS (ESI): calcd for C35H36N3O12S2 [M − H]− 754.1735,
found 754.1716.
Cbz-L-Glu-(Bt)-Bt (13b). White microcrystals, 6.33 g, 13.09 mmol,
92% yield. Mp: 150−152 °C.47 1H NMR (CDCl3, 300 MHz): δ 2.47−
2.61 (m, 1H), 2.73−2.87 (m, 1H), 3.72 (t, J = 7.1 Hz, 2H), 5.10 (br s,
2H), 5.80−6.04 (m, 2H), 7.20−7.38 (m, 5H), 7.45−7.71 (m, 4H),
8519
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Article
Cbz-L-Glu-(Cbz-L-Cys-Bt)-Cbz-L-Cys-Bt (16d). Sticky gel, 0.93 g,
1
0.97 mmol, 68% yield. H NMR (CD3OD, 300 MHz): δ 1.92−2.04
(m, 1H), 2.28−2.50 (m, 1H), 2.51−2.81 (m, 2H), 3.47−3.70 (m, 4H),
4.18−4.46 (m, 1H), 5.075.17 (m, 5H), 5.195.29 (m, 1H), 5.88−5.99
(m, 2H), 7.27−7.40 (m, 15H), 7.57−7.69 (m, 2H), 7.71−7.85 (m,
2H), 8.15−8.22 (m, 2H), 8.23−8.28 (m, 2H). 13C NMR (CDCl3, 75
MHz): δ 22.6, 27.5, 30.7, 31.6, 39.3, 54.0, 60.0, 65.1, 67.5, 68.7, 114.3,
114.4, 120.4, 120.5, 125.9, 126.7, 126.9, 128.2, 128.6, 131.0, 136.0,
146.0, 155.8, 168.6, 168.9, 197.9, 198.5. HRMS (ESI): calcd for
C47H43N9O10S2Na [M + Na]+ 980.2466, found 980.2482.
Cbz-L-Asp-(Cbz-L-Lys-OH)-Cbz-L-Lys-OH (15e). Sticky gel, 6.27g,
7.92 mmol, 93% yield. H NMR (CD3OD, 300 MHz): δ 1.37−1.45
1
(m, 5H), 1.57−1.72 (m, 5H), 1.80−1.90 (m, 2H), 2.64 (dd, J = 5.7,
5.7 Hz, 1H), 2.67 (dd, J = 5.6, 5.6 Hz, 1H), 3.00 (dd, J = 10.7, 5.6 Hz,
1H), 3.52 (t, J = 3.9 Hz, 3H), 4.111−4.15 (m, 2H), 4.32−4.39 (m,
1H), 5.06 (s, 2H), 5.08 (s, 4H), 7.25−7.31 (m, 3H), 7.32−7.38 (m,
12H). 13C NMR (CD3OD, 75 MHz): δ 23.8, 27.9, 29.7, 32.1, 36.1,
39.4, 51.1, 51.2, 55.1, 67.6, 67.9, 68.0, 128.7, 128.9, 129.1, 129.4, 137.8,
138.1, 158.1, 158.6, 175.8, 176.9, 178.3. Anal. Calcd for C40H49N5O12:
C, 60.67; H, 6.24; N, 8.84. Found: C, 60.61; H, 6.27; N, 9.11.
Preparation of Compounds 16a−e. The compounds were
prepared according to the method for preparation of 8a,b.
Cbz-L-Asp-(Cbz-L-Lys-Bt)-Cbz-L-Lys-Bt (16e). Sticky gel, 1.86 g, 1.87
mmol 74% yield. 1H NMR (CDCl3, 300 MHz): δ 1.44−1.71 (m, 7H),
1.72−1.83 (m, 1H), 1.85−1.98 (m, 2H), 2.05−2.16 (m, 2H), 2.70−
2.88 (m, 1H), 2.99−3.06 (m, 2H), 3.51−3.62 (m, 3H), 4.21−4.32 (m,
1H), 5.04−5.13 (m, 7H), 5.64−5.77 (m, 3H), 5.79−5.85 (m, 1H),
6.00 (br s, 1H), 7.10 (br s, 1H), 7.26−7.38 (m, 15H), 7.52 (t, J = 4.7
Hz, 2H), 7.66 (t, J = 4.4 Hz, 2H), 8.12 (d, J = 5.1 Hz, 2H), 8.25 (d, J =
4.8 Hz, 2H). 13C NMR (CDCl3, 75 MHz): δ 22.3, 26.6, 32.1, 35.6,
38.3, 50.1, 54.5, 67.2, 114.4, 120.3, 126.5, 128.1, 128.2, 128.3, 128.5,
130.8, 131.1, 135.8, 136.1, 145.9, 156.0, 156.3, 171.7, 174.6, 176.1.
HRMS (ESI): calcd for C52H55N11O10Na [M + Na]+ 1016.4026, found
1016.4033.
Cbz-L-Asp-(Cbz-L-Ser-Bt)-Cbz-L-Ser-Bt (16a). White microcrystals,
1.86 g, 2.5 mmol, 68%. Mp: 80−83 °C. 1H NMR (CDCl3, 300 MHz):
δ 2.76 (dd, J = 17.0, 4.4 Hz, 1H), 2.87 (dd, J = 17.4, 4.5 Hz, 1H),
4.50−4.59 (m, 2H), 4.65−4.73 (m, 1H), 4.77−4.96 (m, 2H), 5.02−
5.17 (m, 6H), 5.79−5.90 (m, 1H), 5.94−6.60 (m, 2H), 6.24 (t, J =
10.2 Hz, 2H), 7.20−7.37 (m, 15H), 7.43−7.59 (m, 4H), 8.05−8.14
(m, 4H). 13C NMR (DMSO−d6, 75 MHz): δ 35.5, 50.1, 53.6, 63.1,
63.6, 65.7, 66.11, 113.9, 120.22, 126.8, 127.7, 127.9, 128.4, 130.6,
130.9, 131.2, 136.5, 136.6, 136.8, 145.3, 155.7, 156.1, 168.4, 168.5,
169.5, 170.3. HRMS (ESI): calcd for C46H41N9O12Na [M + Na]+
934.2767, found 934.2756.
Preparation of Compounds 17a−e. The compounds were
prepared according to the method for preparation of 9a−c.
Cbz-L-Asp-(Cbz-L-Ser-L-Pro-OH)-Cbz-L-Ser-L-Pro-OH (17a). White
microcrystals, 3.69 g, 4.08 mmol, 92% yield; sticky gel. 1H NMR
(DMSO-d6, 300 MHz): δ 1.62−1.94 (m, 6H), 1.98−2.20 (m, 2H),
2.72 (dd, J = 16.5, 8.0 Hz, 1H), 2.84 (dd, J = 16.8, 4.7 Hz, 1H), 3.56−
3.66 (m, 3H), 3.93−4.05 (m, 2H), 4.22−4.27 (m, 2H), 4.30−4.37 (m,
2H), 4.44−4.53 (m, 2H), 4.57−4.65 (m, 2H), 4.93−5.06 (m, 6H),
7.24−7.37 (m, 15H), 7.71 (d, J = 8.3 Hz, 1H), 7.80 (t, J = 7.6 Hz, 2H).
13C NMR (CD3OD, 75 MHz): δ 25.8, 30.1, 37.1, 51.8, 53.1, 60.6, 64.9,
65.2, 68.0, 115.7, 127.2, 128.7, 128.9, 129.1, 129.5, 138.0, 140.0, 158.3,
169.8, 171.8, 172.2, 175.2. HRMS (ESI): calcd for C44H48N5O16 [M −
H]− 902.3091, found 902.3099.
Cbz-L-Glu-(Cbz-L-Ser-Bt)-Cbz-L-Ser-Bt (16b). White microcrystals,
1.86 g, 2.5 mmol, 68% yield. Mp: 71−75 °C. H NMR (CDCl3, 300
1
MHz): δ 1.97−2.13 (m, 1H), 2.22−2.37 (m, 1H), 2.39−2.66 (m, 2H),
4.44 (dd, J = 12.3, 5.1 Hz, 1H), 4.66 (dd, J = 9.3, 2.9 Hz, 1H), 4.68
(dd, J = 9.3, 2.3 Hz, 1H), 4.78−4.86 (m, 2H), 5.04−5.20 (m, 4H),
5.21−5.34 (m, 2H), 5.81 (d, J = 7.5 Hz, 1H), 5.94−6.08 (m, 2H),
6.09−6.19 (m, 1H), 6.39−6.52 (m, 1H), 7.28−7.42 (m, 15H), 7.48−
7.60 (m, 2H), 7.61−7.70 (m, 2H), 8.09−8.32 (m, 4H). 13C NMR
(CDCl3, 75 MHz): δ 21.8, 21.9, 31.2, 54.9, 58.8, 59.0, 65.3, 67.8, 69.0,
114.4, 115.1, 120.7, 126.3, 127.1, 128.4, 128.5, 128.7, 131.1, 131.3,
135.0, 136.0, 138.7, 146.2, 151.5, 156.1, 168.0, 170.8, 172.7, 173.6.
HRMS (ESI): calcd for C47H43N9O12Na [M + Na]+ 948.2923, found
948.2938.
Cbz-L-Glu-(Cbz-L-Ser-D-Pro-OH)-Cbz-L-Ser-D-Pro-OH (17b). Sticky
1
gel, 0.81 g, 0.89 mmol, 82% yield. H NMR (CD3OD, 300 MHz): δ
1.78−2.10 (m, 6H), 2.10−2.32 (m, 3H), 2.34−2.46 (m, 2H), 2.48−
2.62 (m, 1H), 3.41−3.78 (m, 1H), 3.57−3.75 (m, 2H), 4.03−4.18 (m,
1H), 4.18−4.46 (m, 3H), 4.48−4.60 (m, 1H), 4.62−4.73 (m, 2H),
4.76−4.89 (m, 1H), 5.04−5.11 (m, 4H), 5.12−5.30 (m, 2H), 7.23−
7.38 (m, 15H). 13C NMR (CD3OD, 75 MHz): δ 22.8, 26.2, 30.7, 32.3,
53.1, 60.7, 61.1, 66.0, 68.4, 69.8, 116.1, 127.6, 129.4, 129.5, 129.7,
130.0, 130.1, 137.1, 138.5, 140.5, 152.6, 158.6, 169.7, 173.0, 175.7,
176.4. HRMS (ESI): calcd for C45H50N5O16 [M − H]− 916.3247,
found 916.3266.
Cbz-L-Asp-(Cbz-L-Cys-Bt)-Cbz-L-Cys-Bt (16c). Sticky gel, 0.99 g,
1.05 mmol, 78% yield. 1H NMR (CDCl3, 300 MHz): δ 3.25−3.71 (m,
4H), 3.76−4.00 (m, 2H), 4.50−4.96 (m, 1H), 5.15 (br s, 6H), 5.40−
5.80 (m, 2H), 5.80−6.20 (m, 3H), 7.24−7.40 (m, 15H), 7.42−7.59
(m, 3H), 7.60−7.78 (m, 1H), 7.85−8.28 (m, 4H). 13C NMR (CDCl3,
75 MHz): δ 31.6, 36.7, 45.2, 53.4, 54.2, 57.4, 67.9, 115.1, 120.6, 126.3,
126.9, 128.3, 128.8, 131.2, 136.0, 138.8, 146.2, 155.9, 168.9, 196.6.
HRMS (ESI): calcd for C46H41N9O10S2Na [M + Na]+ 966.2310, found
966.2304.
Cbz-L-Asp-(Cbz-L-Cys-L-Pro-OH)-Cbz-L-Cys-L-Pro-OH (17c). Sticky
gel, 0.89 g, 0.95 mmol, 86% yield. 1H NMR (DMSO-d6, 300 MHz): δ
1.50−2.02 (m, 5H), 2.02−2.35 (m, 2H), 2.62−3.20 (m, 7H), 3.48−
8520
dx.doi.org/10.1021/jo401235k | J. Org. Chem. 2013, 78, 8510−8523

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3.73 (m, 3H), 3.95−4.14 (m, 1H), 4.14−4.29 (m, 2H), 4.39−4.74 (m,
2H), 4.93−5.18 (m, 7H), 7.25−7.42 (m, 15H), 7.73 (d, J = 8.1 Hz,
2H), 7.80−8.21 (m, 1H). 13C NMR (CD3OD, 300 MHz): δ 25.8,
30.4, 31.9, 45.9, 53.2, 54.9, 59.2, 60.8, 68.0, 128.9, 129.1, 129.6, 138.2,
158.2, 158.5, 170.6, 173.5, 175.4, 196.7. HRMS (ESI): calcd for
C44H48N5O14S2 [M − H]− 934.2634, found 934.2649.
59.8, 60.1, 64.8, 67.4, 68.7, 67.0, 69.9, 114.6, 115.2, 120.5, 125.9, 126.7,
128.2, 128.3, 128.5, 128.7, 128.9, 130.8, 134.6, 135.0, 136.3, 146.2,
151.3, 152.2, 156.0, 162.2, 167.3, 170.6, 172.9. HRMS (ESI): calcd for
C57H57N11O14Na [M + Na]+ 1142.3979, found 1142.3995.
Cbz-L-Asp-(Cbz-L-Cys-L-Pro-Bt)-Cbz-L-Cys-L-Pro-Bt (18c). Sticky
1
gel, 1.60 g, 1.40 mmol, 67% yield. H NMR (CDCl3, 300 MHz): δ
1.89−2.32 (m, 8H), 2.40−2.72 (m, 2H), 2.78−3.45 (m, 4H), 3.48−
3.82 (m, 3H), 3.82−4.08 (m, 2H), 4.34−4.94 (m, 2H), 4.95−5.28 (m,
6H), 5.46−5.78 (m, 1H), 5.78−5.98 (m, 2H), 5.98−6.12 (m, 1H),
6.18−6.50 (m, 1H), 7.15−7.44 (m, 15H), 7.50−7.62 (m, 2H), 7.62−
7.74 (m, 2H), 8.08−8.20 (m, 2H), 8.20−8.32 (m, 2H). 13C NMR
(CDCl3, 75 MHz): δ 24.9, 28.6, 29.6, 31.3, 40.6, 44.7, 47.6, 51.5, 51.9,
57.4, 59.5, 59.8, 67.1, 67.3, 114.3, 114.8, 120.1, 120.2, 125.7, 126.3,
126.5, 127.9, 130.5, 130.9, 131.0, 135.9, 136.1, 138.5, 145.8, 155.9,
168.7, 169.7, 195.9, 199.5. HRMS (ESI): calcd for C56H55N11O12S2Na
[M + Na]+ 1160.3365, found 1160.3355.
Cbz-L-Glu-(Cbz-L-Cys-D-Pro-OH)-Cbz-L-Cys-D-Pro-OH (17d). Sticky
gel, 0.81 g, 0.89 mmol, 82% yield. H NMR (CD3OD, 300 MHz): δ
1
1.75−2.06 (m, 8H), 2.12−2.31 (m, 3H), 2.32−2.74 (m, 3H), 2.99−
3.18 (m, 2H), 3.31−3.62 (m, 2H), 3.63−3.78 (m, 2H), 4.24−4.48 (m,
3H), 4.54−4.74 (m, 1H), 5.02−5.12 (m, 5H), 5.13−5.26 (m, 2H),
7.23−7.48 (m, 15H). 13C NMR (CD3OD, 75 MHz): δ 23.4, 25.8,
30.4, 31.7, 32.1, 40.7, 48.0, 52.8, 53.4, 60.8, 61.7 66.8, 68.0, 69.5, 128.9,
129.2, 129.3 129.4, 129.6, 136.6, 138.2, 152.1, 158.3, 158.4, 170.4,
170.7, 175.4, 176.1, 200.4. HRMS (ESI): calcd for C45H50N5O14S2 [M
− H]− 948.2790, found 948.2772.
Cbz-L-Glu-(Cbz-L-Cys-D-Pro-Bt)-Cbz-L-Cys-D-Pro-Bt (18d). White
microcrystals, 1.50 g, 1.3 mmol 62% yield. Mp: 93−98 °C. H NMR
Cbz-L-Asp-(Cbz-L-Lys-D-Pro-OH)-Cbz-L-Lys-D-Pro-OH (17e). Sticky
gel, 0.77 g, 1.53 mmol, 76% yield. H NMR (CD3OD, 300 MHz): δ
1
1
(CDCl3, 300 MHz): δ 1.80−2.09 (m, 1H), 2.10−2.34 (m, 6H),
2.362.78 (m, 5H), 3.10−3.40 (m, 3H), 3.40−3.65 (m, 2H), 3.88−4.44
(m, 3H), 4.77 (dd, J = 9.5, 2.3 Hz, 1H), 4.78−4.94 (m, 1H), 4.98−
5.16 (m, 5H), 5.20−5.38 (m, 2H), 5.73 (d, J = 9 Hz, 2H), 5.76−5.88
(m, 3H), 7.33−7.45 (m, 15H), 7.46−7.55 (m, 2H), 7.60−7.68 (m,
2H), 8.00−8.15 (m, 2H), 8.20−8.26 (m, 2H). 13C NMR (CDCl3, 75
MHz): δ 22.6, 25.2, 29.9, 31.0, 31.7, 47.7, 51.3, 60.0, 60.3, 65.3, 67.2,
68.7, 114.6, 120.4, 125.8, 126.6, 128.3, 128.7, 130.8, 131.3, 135.1,
136.3, 146.1, 151.1, 155.9, 168.0, 170.1, 173.2, 199.0. HRMS (ESI):
calcd for C57H57N11O12S2Na [M + Na]+ 1174.3522, found 1174.3541.
1.22−1.52 (m, 6H), 1.53−1.80 (m, 7H), 1.82−1.94 (m, 2H), 1.95−
2.08 (m, 3H), 2.16−2.32 (m, 2H), 2.63 (dd, J = 5.9, 5.9 Hz, 1H), 2.66
(dd, J = 5.7, 5.7 Hz, 1H), 3.00 (dd, J = 10.8, 5.4 Hz, 1H), 3.08−3.19
(m, 1H), 3.46−3.55 (m, 4H), 3.56−3.67 (m, 1H), 3.78−3.85 (m, 1H),
4.32−4.42 (m, 3H), 4.43−4.48 (m, 1H), 5.05−5.10 (m, 7H), 7.27−
7.40 (m, 15H). 13C NMR (CDCl3, 75 MHz): δ 21.8, 22.8, 24.7, 26.9,
28.8, 31.6, 35.6, 28.4, 47.3, 50.0, 52.2, 53.6, 59.5, 66.9, 67.2, 76.8, 77.3,
77.7, 136.0, 136.3, 156.2, 156.5, 171.5, 174.0, 175.0, 176.5. HRMS
(ESI): calcd for C50H62N7O14 [M − H]− 984.4349, found 984.4362.
Preparation of Compounds 18a−e. The compounds were
prepared according to the method for preparation of 10a−c.
Cbz-L-Asp-(Cbz-L-Lys-D-Pro-Bt)-Cbz-L-Lys-D-Pro-Bt (18e). Sticky
gel, 0.83 g, 0.70 mmol, 69% yield. H NMR (CDCl3, 300 MHz): δ
1
Cbz-L-Asp-(Cbz-L-Ser-L-Pro-Bt)-Cbz-L-Ser-L-Pro-Bt (18a). Sticky gel,
0.44 g, 0.40 mmol, 72% yield. H NMR (DMSO-d6, 300 MHz): δ
1
1.28−1.42 (m, 5H), 1.56−1.64 (m, 5H), 1.64−1.84 (m, 5H), 2.12−
2.26 (m, 5H), 2.50−2.66 (m, 2H), 3.03 (dd, J = 10.8, 5.4 Hz, 2H),
3.50−3.66 (m, 3H), 3.68−3.74 (m, 2H), 3.92−3.98 (m, 1H), 4.36−
4.48 (m, 2H), 4.55−4.61 (m, 1H), 5.03−5.13 (m, 7H), 5.60−5.68 (m,
2H), 5.92 (dd, J = 5.4, 2.1 Hz, 2H), 5.98 (d, J = 3.0 Hz, 1H), 7.27−
7.36 (m, 17H), 7.48−7.54 (m, 2H), 7.65 (t, J = 4.4 Hz, 2H), 8.11−
8.14 (m, 2H), 8.22−8.27 (m, 2H). 13C NMR (CDCl3, 75 MHz): δ
21.8, 21.9, 25.1, 26.9, 29.7, 32.4, 35.9, 38.5, 47.6, 50.1, 52.1, 59.7, 67.0,
67.4, 114.7, 120.4, 126.6, 127.9, 128.1, 128.2, 128.3, 128.4, 128.7,
130.7, 131.3, 136.4, 146.1, 156.2, 156.3, 170.3, 170.7, 174.7, 176.1.
HRMS (ESI): calcd for C62H69N13O12Na [M + Na]+ 1210.5081, found
1210.5099.
1.64−1.98 (m, 2H), 1.98−2.30 (m, 6H), 2.68−2.96 (m, 2H), 3.72−
3.90 (m, 3H), 3.95−4.17 (m, 2H), 4.28−4.58, (m, 4H), 4.64−4.80 (m,
2H), 5.02 (br s, 6H), 5.68−5.84 (m, 2H), 7.24−7.42 (m, 15H), 7.56−
7.68 (m, 3H), 7.68−7.85 (m, 4H), 8.08−8.30 (m, 4H). 13C NMR
(CDCl3, 75 MHz): δ 25.3, 29.8, 36.7, 47.9, 50.9, 51.8, 60.1, 67.3,
114.5, 120.3, 126.5, 127.7, 128.2, 128.6, 130.8, 131.2, 136.3, 146.0,
156.2, 167.6, 169.9, 170.4. HRMS (ESI): calcd for C56H55N11O14Na
[M + Na]+ 1128.3828, found 1128.3845.
Preparation of Unsymmetrical bis-DKPs 19a−e. The com-
pounds were prepared according to the method for preparation of
11a−c.
Cbz-L-Glu-(Cbz-L-Ser-D-Pro-Bt)-Cbz-L-Ser-D-Pro-Bt (18b). White
microcrystals, 1.24 g, 1.11 mmol 68% yield. Mp: 85−89 °C. 1H
NMR (CDCl3, 300 MHz): δ 1.88−2.10 (m, 6H), 2.14−2.23 (m, 2H),
2.28−2.48 (m, 2H), 2.48−2.76 (m, 2H), 3.45−3.68 (m, 3H), 3.82−
3.94 (m, 1H), 4.19−4.42 (m, 3H), 4.48−4.66 (m, 3H), 4.92−5.08 (m,
2H), 5.12−5.17 (m, 1H), 5.20−5.35 (m, 4H), 5.74 (d, J = 8.2 Hz,
2H), 5.86−5.93 (m, 3H), 7.28−7.40 (m, 15H), 7.50−7.56 (m, 2H),
7.64−7.70 (m, 2H), 8.13−8.16 (m, 2H), 8.2−8.27 (m, 2H). 13C NMR
(CDCl3, 75 MHz): δ 21.9, 22.3, 25.2, 29.6, 29.9, 31.2, 45.8, 52.1, 58.8,
Cbz-L-Asp-[cyclo-(Cbz-L-Ser-L-Pro)]-cyclo-(Cbz-L-Ser-L-Pro) (19a).
1
Sticky gel, 0.56 g, 0.65 mmol, 72% yield. H NMR (DMSO-d6, 300
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Article
MHz): δ 1.69−1.98 (m, 6H), 2.02−2.24 (m, 2H), 2.54−2.78 (m, 2H),
3.54−3.62 (m, 4H), 3.68−4.06 (m, 2H), 4.23−4.80 (m, 6H), 4.82−
4.92 (m, 1H), 4.94−5.06 (m, 4H), 5.20−5.29 (m, 2H), 7.24−7.43 (m,
15H), 7.68−7.70 (m, 1H). 13C NMR (CDCl3, 75 MHz): δ 22.4, 22.8,
29.6, 31.8, 36.1, 45.8, 50.3, 60.0, 64.0, 65.2, 66.0, 67.3, 67.5, 69.8,
128.3, 128.5, 128.7, 128.8, 134.6, 136.0, 152.2, 156.0, 162.5, 167.3,
170.3. HRMS (ESI): calcd for C44H45N5O14Na [M + Na]+ 890.2855,
found 890.2828.
22.6, 22.7, 26.3, 29.2, 30.4, 36.1, 38.1, 45.8, 50.0, 59.4, 60.8, 67.4, 69.4,
128.3, 128.5, 128.7, 128.8, 134.8, 136.1, 152.1, 156.3, 165.1, 167.6,
174.9, 176.5. HRMS (MALDI-TOF): calcd for C50H59N7O12Na [M +
Na]+ 972.4114, found 972.4115.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C spectra of all novel compounds listed in the
Experimental Section. This material is available free of charge
via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: katritzky@chem.ufl.edu.
■
Cbz-L-Glu-[cyclo-(Cbz-L-Ser-D-Pro)]-cyclo-(Cbz-L-Ser-D-Pro) (19b).
White microcrystals, 178.4 mg, 0.20 mmol, 88% yield. Mp: 70−72
1
°C. H NMR (CD3OD, 300 MHz): δ 1.91−2.10 (m, 6H), 2.26−2.45
Notes
(m, 4H), 2.46−2.60 (m, 2H), 3.41−3.62 (m, 4H), 4.364.44 (m, 2H),
4.49 (dd, J = 12.0, 4.5 Hz, 2H), 4.57 (dd, J = 11.7, 4.2 Hz, 2H), 4.73
(dd, J = 9.5, 2.9 Hz, 1H),5.01 (t, J = 4.2 Hz, 2H), 5.13−5.30 (m, 2H),
5.31 (br s, 4H), 7.28−7.39 (m, 12H), 7.43−7.47 (m, 3H). 13C NMR
(CD3OD, 75 MHz): δ 22.6, 23.2, 26.7, 27.1, 30.4, 32.0, 44.4, 46.9,
60.3, 61.1, 61.6, 66.1, 68.0, 69.6, 70.5, 129.0, 129.2, 129.5, 129.6, 129.7,
136.6, 136.7, 152.5, 153.5, 164.2, 168.9, 172.3, 175.6. HRMS (ESI):
calcd for C45H47N5O14Na [M + Na]+ 904.3012, found 904.3021.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the University of Florida and the Kenan Foundation
for financial support. This paper was also funded in part by
generous support from King Abdulaziz University, under Grant
No. D-006/431. The authors, therefore, acknowledge the
technical and financial support of KAU. Part of the work
presented was supported by the EU European Regional
Development Fund through the Center of Excellence in
Chemical Biology, Estonia, and by targeted financing from the
Estonian Ministry of Education and Research
(SF0140031As09). G.G.P. thanks Chemaxon Kft., Hungary,
for the academic license for MarvinBeans and thanks Prof. Mati
Karelson for permitting access to Turbomole package,
COSMOlogic, GmbH at University of Tartu, Estonia. We are
grateful to Dr. C. D. Hall, Mrs. Galyna Vakulenko, and Mr. Z.
Wang for helpful discussions, to Dr. M. C. A. Dancel
(University of Florida, Mass Spectrometry Services) for
HRMS analysis, and to Dr. Hendrik Luesch (University of
Florida, Department of Medicinal Chemistry) for helpful NMR
discussions.
Cbz-L-Asp-[cyclo-(Cbz-L-Ser-L-Pro)]-cyclo-(Cbz-L-Ser-L-Pro) (19c).
1
Sticky gel, 0.69 g, 0.76 mmol, 76% yield. H NMR (DMSO-d6, 300
MHz): δ 1.72−2.04 (m, 8H), 2.18−2.24 (m, 2H), 3.21−3.30 (m, 2H),
3.38−3.42 (m, 6H), 4.60 (dd, J = 9.8, 5.6 Hz, 2H), 4.76−4.83 (m,
1H), 4.91 (t, J = 4.4 Hz, 1H), 4.98−5.12 (m, 3H), 5.20−5.34 (m, 4H),
7.22−7.51 (m, 16H). 13C NMR (DMSO-d6, 75 MHz): δ 22.2, 28.6,
29.4, 37.9, 45.3, 59.0, 59.5, 65.6, 66.0, 68.4, 127.7, 127.9, 128.2, 135.2,
136.6, 136.9, 151.7, 151.9, 155.8, 162.3, 162.4, 166.9, 167.3, 199.6,
199.9. HRMS (ESI): calcd for C44H45N5O12S2Na [M + Na]+
922.2398, found 922.2382.
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