Synthesis of chiral pyrrolidine isostere inserted into pyrrole polyamide skeleton

Article abstract of DOI:10.1002/jccs.201100603

An efficient and general route towards the synthesis of a series of chiral pyrrolidine pyrrole polyamide distamycin analogues starting from (L)-hydroxyproline is described. The binding abilities of these chiral pyrrolidine containing molecules to calf thymus DNA were evaluated by duplex DNA melting temperature analysis. The results revealed that both the chirality at the pyrrolidine ring and the site of incorporation plays an important role for binding at the duplex DNA.

Full text of DOI:10.1002/jccs.201100603

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Synthesis of Chiral Pyrrolidine Isostere Inserted into Pyrrole Polyamide Skeleton
Chun-Yu Lin, Ya-Ting Yang and Chi Wi Ong*
Department of Chemistry, National Sun Yat Sen University, No. 70, Lienhai Rd., Kaohsiung 804, Taiwan, R.O.C.
(Received: Nov. 18, 2011; Accepted: Dec. 15, 2011; Published Online: Dec. 6, 2011; DOI: 10.1002/jccs.201100603)
An efficient and general route towards the synthesis of a series of chiral pyrrolidine pyrrole polyamide
distamycin analogues starting from (L)-hydroxyproline is described. The binding abilities of these chiral
pyrrolidine containing molecules to calf thymus DNA were evaluated by duplex DNA melting tempera-
ture analysis. The results revealed that both the chirality at the pyrrolidine ring and the site of incorpora-
tion plays an important role for binding at the duplex DNA.
Keywords: Polyamide; Pyrrole; Chiral pyrrolidine.
INTRODUCTION
Natural occurring DNA minor groove binding agents
to amide for the binding to the minor groove of DNA. On
the other hand, pyrrolidine with branching polyamine has
been reported to stabilize DNA duplexes and triplex
such as distamycin and netropsin (Fig. 1) possessing pyr-
role amide moieties have been found to bind favorably at
8
through strong electrostatic interaction.
9
Recently, Boger et al. has investigated the replace-
1
-3
the A and T rich region of DNA. One of the disadvan-
tages of netropsin and distamycin is their toxicity, and this
may be attributed to their extremely strong binding ability.
In the past, a vast number of minor grove binding agents
based on distamycin and netropsin have been synthesized
with the hope of achieving the following: (i) more site se-
lective by the incorporation of various heterocyclic ring
such as N-methylimidazole, thiazole, pyridine, thiophene,
ment of all three pyrrole rings with the saturated pyrroli-
dine ring system, while maintaining the amide bonds. In
this case, it was found that all pyrrolidine polyamide dista-
mycin analogues showed greatly less DNA binding ability
relative to distamycin. Furthermore, more basic nature of
the nitrogen atom in the pyrrolidine ring which can become
protonated readily was found to bind poorly to duplex
DNA. As such, the N-CBz pyrrolidine derivative has been
reported to be the more effective analogue for binding to
duplex DNA, although the binding is still weak as com-
pared to the pyrrole polyamide. On the other hand, (R,R)-
and (S,S)-trans-cyclohexane-1,2-diamine rings linked with
4
-6
triazole, furan and pyrazole and (ii) improving fit to com-
plement the DNA minor groove by controlling the curva-
7
ture of compound. Although, pyrrolidine ring is the satu-
rated isostere of the pyrrole ring, it has not been widely in-
corporated into distamycin model for studying the pre-
requisite of having exclusively flat heterocyclic ring linked
1
0
aliphatic spacer was found to bind to duplex DNA.
So far, there has been no report on the synthesis of mi-
nor groove DNA binding agents possessing a combination
of the pyrrole and pyrrolidine ring connected through an
amide bond. Such a combination might be advantages as it
maintain some of the rigidity of the aromatic moiety, while
allowing more conformationally variable structures through
the saturated pyrrolidine ring. A combination of two pyr-
role rings with one pyrrolidine ring was chosen because it
has been reported that a minimum of three pyrrole carbox-
amide units (3Py (1), Figure 2) are necessary for the onset
of DNAbinding, whereas two pyrrole caboxamide failed to
exhibit any detectable binding. The pyrrolidine ring that is
chiral at C-2 and C-4 hence can have two pairs of diastereo-
Fig. 1. Distamycin and netropsin.
Dedicated to the memory of Professor Yung-Son Hon (1955–2011).
*
Corresponding author. E-mail: cong@mail.nsysu.edu.tw
436
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CHEMICAL SOCIETY
Chiral Pyrrolidine Isostere
Scheme I
Reagents and conditions: (i) a. SOCl
2
, MeOH b. Boc
N, DCM, 4 hr,
, DMF, 80 C, 3 hr. 80%; (iv) CBr , Ph P, DCM,
, DMF, 80 C, 3 hr. 81%.
2 3
O, Et N,
Fig. 2. Distamycin analogs bispyrrole-pyrrolidine.
DCM, rt. overnight, two steps 90%; (ii) MsCl, Et
3
o
rt. 85%; (iii) NaN
3
4
3
o
mers (cis 2S,4S, 2R,4R and trans 2S,4R, 2R,4S). Herein we
report the synthesis of two of the four possible stereoiso-
mers (cis 2S,4S and trans 2S,4R) of chiral pyrrolidine ring
inserted onto different site of the bispyrrole amide, namely
PySSPy (2), PySRPy (3), 2PySS (4) and 2PySR (5) (Fig.
overnight, rt. 73%; (v) NaN
3
1
from pyrrole-2-carboxylic acid 12 in the presence of
2
Et N, provided the pyrrole-pyrrolidine ester 15a and 15b
3
respectively. The ester group in 15a and 15b was hydro-
lyzed to the acid, followed by activation to the mix anhy-
dride 17a and 17b; and was subsequently coupled with the
N-dimethylpropylamine pyrrole 19 (prepared from the re-
duction of nitro pyrrole 18 according to a published proce-
2
), and evaluate their binding ability to duplex DNA.
RESULTS AND DISCUSSION
In order to synthesize the four different combinations
of pyrrolidine-pyrrole polyamides, PySSPy (2), PySRPy
1
3
dure ) to give PySSPy (2) and PyRSPy (3) respectively.
The synthesis of the 2PySS (4) and 2PySR (5) began
with the coupling of the individual chiral amino-pyrroli-
dine 13a and 13b with 4-nitro-pyrrole-2-acyl trichloride 20
to give 21a and 21b respectively, as shown in Scheme III.
(
3), 2PySS (4) and 2PySR (5) are derived from the appro-
priate chiral (cis 2S,4S) and (trans 2S,4R) 4-aminopyrroli-
dine-2-carboxylic acid. These were synthesized according
to Scheme I starting from commercially available (L)-4-hy-
11
droxyproline, 6. Esterfication of 6, followed by protect-
ing the amine group as the N-Boc provided the common in-
termediate 7. The mesylation of hydroxyl group in 7 gave
2
Reduction of the nitro group in 21a and 21b with H -Pd/C
in methanol gave the corresponding amines. This was trans-
formed to the desired (2S,4S)-22a and (2S,4R)-22b-bis-
pyrrole-pyrrolidine ester by coupling with pyrrole-2-car-
bonyl chloride 14. Hydrolysis of ester group in 22a and
22b to the acid 23a and 23b was effect by treatment with
aqueous NaOH. Activation of the acid to the anhydride,
followed by coupling with N,N-dimethylpropylamine gave
2PySS (4) and 2PyRS (5), respectively.
8
, which in the presence of sodium azide in DMF at 80 °C
gave the inversion (2S,4S)-cis-azide 10. On the other hand,
the retention of configuration of azide at C-4 was achieved
by conversion of the hydroxy group in 7 to the bromide 9,
followed by displacement with sodium azide give the dou-
ble inversion product, or the total retention of configura-
tion to afford (2S,4R)-trans-azide 11.
The three pyrrole carboxamide 3Py (1), is known to
be the minimum backbone necessary for the onset of DNA
duplexes stabilization, although much less than that of
distamycin. Here, the comparative thermal stabilization of
calf-thymus (CT) duplex with 3Py (1) and the pyrrolidyl
containing analogues PySSPy (2), PyRSPy (3), 2PySS (4),
and 2PyRS (5) were determined under identical conditions
of buffer and pH by UV absorbance-temperature plot and
the melting data summarized in Table 1. Almost all of the
We next examine the systematic incorporation of the
chiral pyrrolidine into the distamycin analogues at different
sites. The introduction of the pyrrolidine ring between two
pyrrole amide ring was first examined and is shown in
Scheme II. Accordingly, reduction of the azide 10 and 11
using Pd/C in methanol gave the chiral amino-pyrrolidine
(
2S,4S)-13a and (2S,4R)-13b respectively. The coupling of
3a and 13b with pyrrol-2-carbonyl chloride 14, prepared
1
J. Chin. Chem. Soc. 2012, 59, 436-442
© 2012 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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437

Article
Lin et al.
Scheme II
o
o
Reagents and conditions: (i) H
2
, Pd/C, MeOH; (ii) SOCl
5a: 72% , 15b: 75%; (iv) NaOH, MeOH/H O, 4 hr. rt.; (v) N-methylmorpholine, isopropyl chloroformate, Et
N, DMF, rt. overnight, two steps from 16, 2: 40%, 3: 41%.
2
, THF, 0 C, 30 min then rt 1 hour (iii) Et
3
N, DCM, 0 C, overnight, three steps
1
2
3
N, DCM; (vi) H , Pd/C,
2
MeOH; (vii) Et
3
Scheme III
Reagents and conditions: (i) Et
3
2
N, DCM, overnight, rt. 21a: 80% , 21b: 80%; (ii) H , Pd/C, MeOH then 14, DCM, rt. overnight, 22a:
6
0%, 22b: 55%; (iii) NaOH, MeOH/H O, rt. 4hr.; (iv) N-methylmorpholine, isopropyl chloroformate then N,N-dimethylpropylamine,
2
DCM, rt. overnight, two steps 4: 50%, 5: 46%.
tested pyrrolidine-pyrrole polyamides stabilized the CT-
DNA double helix, but to a different extent as shown by the
increasing melting temperature effects (DTm > 0, Table 1).
Among the four pyrrolidine-pyrrole diastereomers synthe-
sized, the 2PySS (4) cis-isomer appeared to be best in stabi-
lizing the duplex (DTm = 2.9 °C) and superior to that of 3Py
1.0 °C). An important observation is the relatively weak
binding for the 2PySR (5) and PySRPy (3) trans-isomers.
The results suggest that the degree of stabilization is de-
pendent on the stereochemistry at the C-2 and C-4-position
of the pyrrolidine ring, and the site at which it was incorpo-
rated with the bis-pyrrole units.
(
1) (DTm = 1.7 °C), followed by cis-PySSPy (2) (DTm =
In summary, we have described an efficient synthesis
438
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JOURNAL OF THE CHINESE
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Chiral Pyrrolidine Isostere
Table 1. Melting temperature with calf thymus DNA (2.77 mM)
and compound (50 mM)
was maintained for 30 min, then the reaction mixture was
allowed to warm up to room temperature for one hour. The
mixture was concentrated in vacuo to obtain acryl chloride
Compound
3Py(1) PySSPy(2) PySRPy(3) 2PySS(4) 2PySR(5)
1.7 1.0 0.2 2.9 0.1
1
4.
DTm (°C)
In another flask, a suspension of 5% Pd-C (150 mg)
and 10 (1.5 g, 5.5 mmole) in methanol (10 mL) was stirred
for four hours under 1 atm of H at room temperature. The
of a new class of distamycin analogues by incorporating
conformationally flexible chiral pyrrolidine isostere into
the pyrrole polyamide backbone. Preliminary binding stud-
ies with C-T DNA showed an interesting stereochemical
requirement at the C-2 and C-4 position of pyrrolidine ring
for good binding. The site of incorporating the pyrrolidine
ring also plays an important role. The newly synthesized
distamycin analog 2PySS (4) showed substantially im-
prove DNA duplex stabilization over that of 3Py (1). Our
results will add to an expanding library of methodology for
the design of small molecules for DNA binding.
2
reaction was then filtered and the Pd-C catalyst wash fur-
ther with methanol. The methanol filtrate was concentrated
in vacuo to obtain amine 13 and used in situ.
To amine 13 prepared in situ was added a solution of
o
(30 mL) at 0 C and stirred for 12 hours. The
14 in CH
2
Cl
2
reaction was quenched by the drop-wise addition of
NaHCO3 (aq) (30 mL) and the organic layer separated,.
4
washed with brine, and dried over MgSO . The organic
layer was concentrated to give the crude product and puri-
fied by column chromatography using EtOAc/Hexane
1
1/1) to obtain the product 1.4 g, 72% yield. H-NMR (500
(
EXPERIMENTAL
3
MHz, CDCl ): d 7.125-7.271 (m, 1H), 6.67 (s, 1H), 6.58-
General
6.63 (bs, 1H), 6.04 (bs, 1H), 4.74 (m, 1H), 4.27-4.37 (m,
1H), 3.90 and 3.89 (diastereomer, m, 3H), 3.75 and 3.90
(diastereomer, s, 3H), 3.49-3.63 (m, 2H), 2.42-2.51 (m,
Reactions were carried out under nitrogen in oven-
dried glassware. Tetrahydrofuran was distilled over so-
1
13
dium. H and C NMR spectra were recorded by 200 MHz
13
1H), 1.95-2.00 (m, 1H), 1.39-1.42 (m, 9H); C-NMR (125
and 500 MHz spectrometer using CDCl
spectra were obtained by ESI FT-MS.
3
as solvent. Mass
3
MHz, CDCl ): d 174.97 and 175.08 (diastereomer),
160.87, 153.36 and 154.11 (diastereomer), 127.97, 125.21,
112.13, 107.22, 80.46, 57.75 and 57.64 (diastereomer),
53.02 and 53.67 (diastereomer), 52.37 and 52.60 (diaster-
eomer), 47.16 and 48.12 (diastereomer), 35.70 and 36.74
(diastereomer), 36.59, 28.09 and 28.19 (diastereomer);
DNA melting temperature (Tm) measurement
The experiments were conducted with a Pharmacia
Biotect Ultrospec 4000 UV/Visible Spectrophotometer
with a temperature controller in 3 mL quartz cuvettes with a
Teflon cap. The absorbance of the DNA–compound com-
plex was monitored at 260 nm as a function of temperature
and DNAwithout compound was used as a control. Cuvettes
were mounted in a thermal block and the solution tempera-
tures were monitored with a heating rate of 0.5 °C/min. The
concentration of DNA was determined by measuring the
absorbance at 260 nm. A ratio of approximately 2:1 com-
pound/DNA (50 mM: 27.7 mM) was used in the studies.
The compounds were dissolved in DMSO and kept below
25 3 5
HRMS (m/z, ESI): Calcd for C17H N O Na: 374.1692,
found, 374.1689.
(2S,4S)-tert-butyl-2-(5-(3-(dimethylamino)propylcar-
bamoyl)-1-methyl-1H-pyrrol-3-ylcarbamoyl)-4-(1-
methyl-1H-pyrrole-2-carboxamido)pyrrolidine-1-car-
boxylate (2)
2
To a solution of 15 (1 g, 2.7 mmole) in MeOH/H O
(1/1) 30 mL, sodium hydroxide was added (230 mg, 5.7
mmole) and stir for four hours at rt. The solution was acidi-
fied to pH~5 with 10% aqueous HCl and the reaction mix-
1
% at the final concentration in the cuvettes. All the bind-
ing experiments were carried out in an aqueous solution of
0% 1X PBS buffer (pH: 6.8) at 25 °C.
Synthesis
2S,4S)-1-tert-butyl-2-methyl-4-(1-methyl-1H-pyrrole-
ture was extracted with CH
2
Cl
2
. The organic layers were
1
combined, dried over MgSO
4
, filtered, and concentrated to
obtain crude acid compound 16a.
(
To a solution of 16a in DMF (15 mL) was added
4-methylmorpholine (600 mg, 5.9 mmole) and stirred for
20 min, followed by isopropyl chloroformate (430 mg, 3.5
mmole) and reacted for half an hour to obtain anhydride
17a.
2
-carboxamido)pyrrolidine-1,2-dicarboxylate (15a)
To a cooled (0 °C) solution of 12 (870 mg, 7 mmole)
in dry THF (30 mL) in a 100 mL flask was added thionyl
chloride (3.3 g, 27.7 mmole) and the temperature (0 °C)
J. Chin. Chem. Soc. 2012, 59, 436-442
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439

Article
Lin et al.
o
To the anhydride 17a in DMF (15 mL) at 0 C was
added a solution of compound 19 in DMF (5 mL) and then
left to warm to room temperature overnight. The solvent
was evaporated in vacuo and purified by column chroma-
(2S,4S)-1-tert-butyl-2-methyl-4-(4-amino-1-methyl-1H-
pyrrole-2-carboxamido)pyrrolidine-1,2-dicarboxylate
(21a)
13a was dissolved in CH
of compound 20 in CH Cl (10 mL) was added with stirring
overnight. The reaction mixture was added NaHCO solu-
tion and the orgaic layer seperated and further extracted
with CH Cl . The organic layers were combined and washed
with NaHCO3 (aq) (15 mL ´ 3) and brine, dried over MgSO
2 2
Cl (10 mL) and a solution
tography on silica gel with CH
2
Cl
2
/MeOH/NH
4
OH (90/10/
2
2
1
) to obtain the product, 588 mg, 40% yield. H-NMR (500
3
3
3
MHz, CDCl ): d 9.53 (m, 1H), 8.13 (m, 1H), 7.89 (m, 1H),
7
6
3
2
.11 (s, 1H), 6.74 (m, 1H), 6.68 (s, 1H), 6.38 (m, 1H),
2
2
.06-6.07 (m, 1H), 4.60 (m, 1H), 3.94 (s, 3H), 3.91 (s, 3H),
.51-3.89 (m, 2H), 3.42-3.46 (m, 2H), 2.43-2.46 (m, 2H),
1
.29 (m, 6H), 1.69-1.72 (m, 2H), 1.46 (m, 9H); C-NMR
4
,
filtered, and concentrated in vacuo to obtain crude 16. Puri-
3
fication by column chromatography on silica gel with
(
125 MHz, CDCl
3
): d 169.28, 161.58, 156.60, 127.82,
EtOAc/Hexane (1/1) gave product 21a, 1.2 g, 80% yield.
1
1
8
3
5
25.47, 123.91, 121.12, 118.30, 112.45, 107.18, 102.65,
1.31, 59.77, 59.12, 55.21, 48.96, 45.38, 39.58, 36.73,
3
H-NMR (500 MHz, CDCl ): d 7.53-7.59 (m, 1H), 7.51 (s,
1H), 7.09 (m, 1H), 4.64 (m, 1H), 4.23-4.32 (m, 1H), 3.89
(s, 3H), 3.72 (s, 3H), 3.44-3.62 (m, 2H), 1.93-2.50 (m, 2H),
42 7 5
6.62, 28.32; HRMS (m/z, ESI): Calcd for C27H N O :
1
3
44.3247, found, 544.3251.
3
1.32-1.36 (m, 9H); C-NMR (125 MHz, CDCl ): d
(
2S,4R)-1-tert-butyl-2-methyl-4-(1-methyl-1H-pyrrole-
-carboxamido)pyrrolidine-1,2-dicarboxylate (15b)
Compound 11 and 14 were prepared in 75% yield by
175.00-175.07, 159.38, 153.20 and 153.91 (diastereomer),
134.64, 126.68, 125.82, 107.22, 80.50, 57.46 and 57.55
(diastereomer), 52.58, 53.12, 52.46 and 52.67 (diastereo-
mer), 47.49 and 48.39 (diastereomer), 37.63, 35.15 and
36.05 (diastereomer), 27.91 and 28.03 (diastereomer);
2
1
the same procedure as that described for 15a, 15b. H-
NMR (500 MHz, CDCl ): d 6.72 (s, 1H), 6.53 (s, 1H), 6.07
bs, 1H), 5.9-5.96 (m, 1H), 4.63-4.69 (m, 1H), 4.31-4.45
m, 1H), 3.92 (s, 3H), 3.82-3.90 (m, 1H), 3.74 (s, 3H), 3.3-
.46 (m, 1H), d 2.16-2.32 (m, 2H), 1.42-1.45 (m, 9H);
3
(
(
24 4 7
HRMS (m/z, ESI): Calcd for C17H N O Na: 419.1543,
found, 419.1547.
3
1
(2S,4S)-1-tert-butyl-2-methyl-4-(1-methyl-4-(1-methyl-
1H-pyrrole-2-carboxamido)-1H-pyrrole-2-arboxamido)
pyrrolidine-1,2-dicarboxylate (22a)
3
C-NMR (125 MHz, CDCl
diastereomer), 161.64, 153.65 and 154.3 (diastereomer),
28.28, 125.04, 111.87, 107.25, 80.55, 57.85 and 57.51
diastereomer), 52.3 and 52.1, 52.05 and 51.49 (diaster-
eomer), 48.168 and 47.76 (diastereomer), 37.01 and 35.82
diastereomer), 36.7, 28.3 and 28.21; HRMS (m/z, ESI):
Calcd for C17 Na: 374.1692, found, 374.1689.
2S,4R)-tert-butyl-2-(5-(3-(dimethylamino)propylcar-
3
): d 172.97 and 172.63
(
1
Compound 12 and 21a were prepared using the same
procedure as that described for 15a, 22a. Purifiication by
column chromatography on silica gel with EtOAc/Hexane
(
1
(
(1/1) gave product 22a, 1.2 g, 60% yield. H-NMR (500
H
25
N
3
O
5
3
MHz, CDCl ): d 8.42 (m, 1H), 8.06 (m, 1H), 7.33 (m, 1H),
(
6.87-6.88 (m, 1H), 6.70 (m, 1H), 6.33 (s, 1H), 6.07-6.08
(m, 1H), 6.06-6.07 (m, 1H), 4.64-4.72 (m, 1H), 4.27-4.36
(m, 1H), 3.92 (s, 3H), 3.86 (s, 3H), 3.70 (s, 3H), 3.47-3.65
(m, 2H), 2.43-2.49 (m, 2H), 1.96-2.06 (m, 2H), 1.42 (m,
bamoyl)-1-methyl-1H-pyrrol-3-ylcarbamoyl)-4-(1-
methyl-1H-pyrrole-2-carboxamido)pyrrolidine-1-car-
boxylate (3)
1
3
Compound 2, 3 are prepared in 41% yield by the same
1
procedure as that described for 15b and 19. H-NMR (500
3
9H); C-NMR (125 MHz, CDCl ): d 174.85 and 175.02
(diastereomer), 160.81, 159.23 and 159.26 (diastereomer),
153.57 and 154.14, 128.16 and 128.22 (diastereomer),
125.32 and 125.40 (diastereomer), 122.24 and 122.45
(diastereomer), 121.50 and 121.60 (diastereomer), 119.45
and 119.58 (diastereomer), 111.95 and 112.15 (diastereo-
mer), 107.18 and 107.21, 102.85 and 103.26 (diastereo-
mer), 80.53 and 80.61 (diastereomer), 57.58 and 57.77
(diastereomer), 52.38 and 53.29 (diastereomer), 52.56 and
52.65 (diastereomer), 47.47 and 48.22 (diastereomer),
36.76, 36.61, 35.62, 28.15 and 28.20 (diastereomer);
MHz, CDCl
3
): d 9.13 (m, 1H, pro-CONH), 7.72 (m, 1H),
7
6
4
2
1
.12 (m, 1H), 6.71 (s, 1H), 6.57-6.58 (m, 1H), 6.50 (s, 1H),
.10-6.11 (m, 1H), 6.05-6.06 (m, 1H), 4.59-4.63 (m, 1H),
.28-4.47 (m, 1H), 3.90 (s, 3H), 3.87 (s, 3H), 3.7-3.84 (m,
H), 3.42-3.46 (m, 2H), 2.63 (m, 2H), 2.42 (m, 6H),
1
3
.81-1.83 (m, 2H), 1.43 (m, 9H); C-NMR (125 MHz,
): d 161.84, 161.82, 128.23, 125.11, 123.42, 121.13,
18.63, 111.99, 107.23, 103.17, 81.04, 66.88, 57.97, 55.38,
2.34, 44.66, 38.29, 36.96, 36.55, 28.33; HRMS (m/z,
: 544.3247, found, 544.3245.
CDCl
3
1
5
+
ESI): Calcd for C27
H
42
N
7
O
5
LRMS (m/z, ESI): 496 (M+Na ); HRMS (m/z, ESI): Calcd
440
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Chiral Pyrrolidine Isostere
for C23
H
31
N
5
O
6
Na: 496.2172, found, 496.2173.
24 4 7
for C17H N O Na: 419.1543, found, 419.1547.
(
2S,4S)-tert-butyl-2-(3-(dimethylamino)propylcarba-
(2S,4R)-1-tert-butyl-2-methyl-4-(1-methyl-4-(1-methyl-
1H-pyrrole-2-carboxamido)-1H-pyrrole-2-carboxami-
do)pyrrolidine-1,2-dicarboxylate (22b)
moyl)-4-(1-methyl-4-(1-methyl-1H-pyrrole-2-carbox-
amido)-1H-pyrrole-2-carboxamido)pyrrolidine-1-car-
boxylate (4)
Compound 12 was synthesized from 23b in 55%,
To a solution of 22a (500 mg, 1 mmole) in MeOH/
yield by the same procedure as that described for 22a, 22b.
1
H
2
O (1/1) (30 mL), sodium hydroxide was added (230 mg
.7 mmole) and stir for four hours at rt. The solution was
acidified to pH~5 with 10% aqueous HCl and the reaction
mixture was extracted with CH Cl . The organic layers
were combined, dried over MgSO , filtered, and concen-
trated in vacuo to obtain crude 23a.
To a solution of 23a in CH Cl
-methylmorpholine (600 mg, 5.9 mmole) for 20 min, fol-
3
H-NMR (500 MHz, CDCl ): d 7.62 (m, 1H), 7.11 (s, 1H),
5
6.76 (s, 1H), 6.87-6.88 (m, 1H), 6.70 (m, 1H), 6.33 (s, 1H),
6.64-6.66 (m, 1H), 6.62 (s, 1H), 6.11-6.12 (m, 2H), 4.64-
4.66 (m, 1H), 4.33-4.34 (m, 1H), 3.97 (s, 3H), 3.89 (s, 3H),
3.84 (m, 2H), 3.74 (s, 3H), 2.31 (m, 2H), 1.42-1.46 (m,
2
2
4
1
3
3
9H); C-NMR (125 MHz, CDCl ): d 173.09 and 172.78
2
2
(15 mL) was added
(diastereomer), 161.4, 159.38, 154.33 and 153.69 (diaster-
eomer), 128.50, 125.34, 122.8, 121.45 and 121.37
(diastereomer), 119.13, 111.87, 107.4, 103.9, 80.61, 57.87
and 57.55 (diastereomer), 52.37 and 52.22 (diastereomer),
52.04 and 51.5 (diastereomer), 48.26 and 47.79 (diastereo-
mer), 36.98, 36.82 and 36.66 (diastereomer), 35.86, 28.36
4
lowed by isopropyl chloroformate (430 mg, 3.5 mmole)
and stirred for a further half hour to obtain the anhydride.
o
To the anhydride in DMF (15 mL) at 0 C was added
N,N-dimethylpropylamine (204 mg, 2 mmole) and then left
to warm to room temperature overnight. The solvent was
evaporated and purified by column chromatography on sil-
and 28.25 (diastereomer); LRMS (m/z, ESI): 496 (M+
+
Na ); HRMS (m/z, ESI): Calcd for C23
H
31
N
5
O
6
Na:
ica gel with CH
product, 270 mg, 50% yield. H-NMR (500 MHz, CDCl
d 8.72 (m, 1H), 8.31 (m, 1H), 7.91 (m, 1H), 7.40 (s, 1H),
2
Cl
2
/MeOH/NH
4
OH (90/10/3) to obtain the
496.2172, found, 496.2176.
1
3
):
(2S,4S)-tert-butyl-2-(3-(dimethylamino)propylcarba-
moyl)-4-(1-methyl-4-(1-methyl-1H-pyrrole-2-carbox-
amido)-1H-pyrrole-2-carboxamido)pyrrolidine-1-car-
boxylate (5)
7
4
3
6
9
1
1
5
.01 (s, 1H), 6.80 (m, 1H), 6.70 (s, 1H), 6.07-6.08 (m, 1H),
.64 (m, 1H), 4.34-4.36 (m, 1H), 3.95 (s, 3H), 3.90 (s, 3H),
.45 (m, 2H), 3.38-3.63 (m, 2H), 2.87 (m, 2H), 2.60 (m,
H), d 2.18-2.29 (m, 2H), d 1.85-1.94 (m, 2H), d 1.43 (m,
Compound 5 was prepared in 46% yield by the same
1
procedure as that described for 4. H-NMR (500 MHz,
1
3
H); C-NMR (125 MHz, CDCl
3
): d 174.03, 161.04,
CDCl ): d 8.32-8.33 (m, 1H), 8.08 (m, 1H), 7.83 (m, 1H),
3
59.366, 155.49, 128.09, 125.54, 122.60, 121.95, 119.27,
12.65, 107.26, 103.72, 80.70, 66.74, 59.48, 54.96 and
5.91, 55.29, 50.57, 48.43, 44.02, 36.57; HRMS (m/z,
7.40 (s, 1H), 6.77 (s, 1H), 6.74 (s, 1H), 6.6 (s, 1H), 6.11-
6.12 (m, 1H), 4.58-4.59 (m, 1H), 4.40-4.42 (m, 1H), 3.97
(s, 3H), 3.92 (s, 3H), 3.5-3.54 (m, 2H), 3.32-3.46 (m, 2H),
2.2-2.47 (m, 2H), 2.28 (s, 6H), 2.2-2.34 (m, 2H), 1.7-1.77
ESI): Calcd for C27
2S,4R)-1-tert-butyl-2-methyl4-(1-methyl-4-nitro-1H-
pyrrole-2-carboxamido)pyrrolidine-1,2-dicarboxylate
21b)
42 7 5
H N O : 544.3247, found, 544.3244.
1
(m, 2H), 1.43 (m, 9H); C-NMR (125 MHz, CDCl ): d
3
(
3
173.04, 161.10, 159.166, 156.02, 128.16, 125.6, 122.75,
(
121.65, 119.10, 111.94, 107.29, 103.32, 80.94, 66.74,
Compound 11 was obtained in 80% by the same pro-
5
9.60, 56.85, 55.2, 48.72, 45.11, 38.13, 36.80 and 36.62
diastereomer), 32.29, 28.33, 26.61; HRMS (m/z, ESI):
Calcd for C27 : 544.3247, found, 544.3244.
1
cedure as that described for 21a, 21b.. H-NMR (500 MHz,
CDCl ): d 7.56 (s, 1H), 7.17 (s, 1H), 7.09 (m, 1H), 4.64 (m,
H), 4.35-4.46 (m, 1H), 3.98 (s, 3H), 3.82 (m, 2H), 3.75 (s,
(
3
42 7 5
H N O
1
3
1
3
H), 2.33 (m, 2H), 1.42-1.46 (m, 9H); C-NMR (125
): d 172.88 and 172.61 (diastereomer),
60.20, 153.73, 134.87, 126.90 and 126.773 (diastereo-
mer), 125.67, 107.51, 80.89 and 80.77 (diastereomer),
7.77 and 57.52 (diastereomer), 52.43 and 52.28 (diaster-
eomer), 51.84 and 51.37 (diastereomer), 48.56 and 48.16
diastereomer), 37.96, 36.78 and 35.6 (diastereomer),
ACKNOWLEDGEMENTS
MHz, CDCl
3
We thank the National Sciences Council of Taiwan
for the financial support.
1
5
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© 2012 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J. Chin. Chem. Soc. 2012, 59, 436-442