Peptoids bearing tertiary amino residues in the n-alkyl side chains: synthesis of a potent inhibitor of Semaphorin 3A

Article abstract of DOI:10.1016/j.tet.2010.01.090

A study on the preparation of N-alkylglycines (peptoids) that contain tertiary amino residues on the N-alkyl side chains is reported. The appropriate combination of the submonomer strategy with N-alkylglycine monomer couplings depending upon the structure of the N-alkyl side chain that must be incorporated into the peptoid is determinant for the efficiency of the synthetic pathway. The application of this strategy to the preparation of SICHI, an N-alkyglycine trimer containing tertiary amino residues in the three N-alkyl branches, and that has been identified as a potent Semaphorin 3A inhibitor, is presented.

Full text of DOI:10.1016/j.tet.2010.01.090

Tetrahedron 66 (2010) 2444–2454
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Peptoids bearing tertiary amino residues in the n-alkyl side chains: synthesis of
a potent inhibitor of Semaphorin 3A
,
c
,
,e
Joaquim Messeguer a, Isabel Masip a, Marisol Montolio c, Jose Antonio del Rio b e, Eduardo Soriano d
,
,
Angel Messeguer a
*
a
´
Department of Chemical and Biomolecular Nanotechnology, Institut de Quımica Avançada de Catalunya (IQAC-CSIC), J. Girona 18, E-08034 Barcelona, Spain
b Institut de Bioenginyeria de Catalunya (IBEC). Parc Cientific de Barcelona, Barcelona, Spain
c CMBNN group, Department of cell Biology, Faculty of Biology University of Barcelona, Barcelona, Spain
d IRB Barcelona, Department of Cell Biology, University of Barcelona, Spain
e CIBERNED (ISCIII), Barcelona Science Park, Baldiri Reixac 10, E-08028 Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
A study on the preparation of N-alkylglycines (peptoids) that contain tertiary amino residues on the
N-alkyl side chains is reported. The appropriate combination of the submonomer strategy with
N-alkylglycine monomer couplings depending upon the structure of the N-alkyl side chain that must be
incorporated into the peptoid is determinant for the efficiency of the synthetic pathway. The application
of this strategy to the preparation of SICHI, an N-alkyglycine trimer containing tertiary amino residues in
the three N-alkyl branches, and that has been identified as a potent Semaphorin 3A inhibitor, is
presented.
Received 11 November 2009
Received in revised form
20 January 2010
Accepted 26 January 2010
Available online 10 February 2010
Dedicated to Professor Pelayo Camps on
occasion of his 65th anniversary
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Peptoids
N-Alkylglycine monomers
Solid-phase synthesis
Semaphorin inhibition
Axonal regeneration
1. Introduction
flexibility of these oligomers has led to their use for the disruption
of protein–protein,17–19 protein–nucleic acid and protein–mem-
Oligomers of N-substituted glycines, also known as peptoids, are
a family of non-natural molecules that are attractive for chemical
biology studies and also interesting as candidates for drug discov-
ery. These compounds exhibit higher stability towards proteolysis
than natural peptides and are also more bioavailable.1–3 From the
chemical point of view, peptoids have a modular scaffold amenable
to combinatorial strategies. As the synthesis of peptoids can be
easily automated, the split-and-mix format have been used to
prepare libraries that have allowed the identification of protein-
binding ligands,4–6 new antibacterial compounds7,8 and selective
toxin sequestrants.9 Peptoid libraries constructed under the posi-
tional scanning format have been also reported.10–13 The de-
velopment of peptoids as drug carriers,14,15 or in the case of cyclic
derivatives, as inhibitors of integrins, are applications of peptoids
recently described.16 Furthermore, the inherent conformational
brane interactions.20–22 Taken overall, the use of peptoid libraries
could lead to the identification of hit compounds bearing structures
that can be different from those previously identified towards the
same target and that are amenable of further manipulation in order
to increase activity and selectivity.23,24
In this context, it was reported that in the hippocampus Sem-
aphorin 3A causes strong chemorepulsion.25 Thus, embryonic ex-
plants of hippocampus cultured over 2–3 days in vitro give rise to
radial axons; in contrast, when explants are exposed to aggregates
of cells expressing Semaphorin 3A, fibres display strong chemo-
repulsion and grow at distal sites. Therefore, Semaphorin 3A in-
hibition could constitute a therapeutic target addressed to enhance
axonal regeneration. By using a simple functional assay, we
screened a mixture-based combinatorial library composed of tri-
mers of N-alkylglycines.10 This library was constructed following
the positional scanning format and the selection of diversity in-
cluded the use of primary amines bearing a tertiary amino moiety.
We deemed that the introduction of these amines would afford
peptoids containing additional protonable fragments, which could
* Corresponding author. Tel.: þ34 934006121.
E-mail address: angel.messeguer@iqac.csic.es (A. Messeguer).
0040-4020/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.01.090

J. Messeguer et al. / Tetrahedron 66 (2010) 2444–2454
2445
complement the activity and bioavailability of the library compo-
nents. The library was composed of 66 mixtures, each containing
484 molecules, giving rise to a total of 10.648 individual com-
pounds. The screening of this library using a Semaphorin 3A-in-
duced chemorepulsion assay in 3D hydrogel cultures and the
subsequent deconvolution procedure led to the identification of
three positives. Interestingly, all three peptoids contained addi-
tional tertiary amino residues in all three diversity positions. The
independent synthesis of these peptoids was thus required to
confirm their activity and then validate the deconvolution process.
However, the synthesis of these peptoids by using the conventional
submonomer procedure was troublesome (see below), although we
were able to isolate enough material to perform a second series of
in vitro assays. These experiments in vitro showed that peptoid 1
reversed Semaphorin 3A-induced chemorepulsion of hippocampal
axons most strongly. This compound was purified by preparative
reversed-phase high-performance liquid chromatography and re-
ferred to as Semaphorin-induced chemorepulsion inhibitor (SICHI,
Scheme 1). Nevertheless, a more efficient preparation procedure
was needed to fulfil the availability of this class of peptoids.
the solid-phase submonomer procedure.28,29 This method involves
an iterative acylation reaction with an -haloacetyl reagent that is
common to all backbone elongation processes, and an iterative
amination reaction employing the broad commercial availability of
primary amines (Scheme 2, lower pathway).
a
This last procedure has been the most employed for the prep-
aration of peptoid libraries under any format. However, its appli-
cation to the above peptoid hits did not afford the expected results.
We observed that in the second and third amination steps, exten-
sive side-reactions occurred leading to the formation of cyclic tet-
raalkylammonium compounds. Figure 1 shows a representative
HPLC profile of the crude reaction mixture of compound 1 syn-
thesised following the submonomer strategy. In spite of performing
the acylation steps at low temperature and short reaction times,
and then using a large excess of the corresponding primary amine,
yields in 1 were always lower than 8%. Although we took advantage
of this fact to design and construct a library of cyclic tetraalky-
lammonium derivatives,30 it was necessary to develop a general
approach for the preparation of peptoids like 1. It should be
remarked that in addition to our case, facts like the commercial
availability of primary amines bearing tertiary amino residues and
the occurrence of these molecular fragments in a wide variety of
bioactive compounds justify the interest of finding a reliable pro-
cedure for the synthesis of this class of N-alkylglycine oligomers.
We deemed that a mixed strategy involving the adequate com-
bination of synthetic steps derived from the use of the submonomer
method with the coupling of Fmoc protected N-alkylglycines could
fulfil the requirements for synthesising these peptoids (Scheme 3).
Thus, the submonomer method would be used in all steps with the
exception of those coming after the previous introduction of an N-
alkyl residue bearing an additional tertiary amino moiety. In these
cases, the use of the coupling with Fmoc protected N-alkylglycines
will be necessary to minimise side-reactions.
Scheme 1. Structure of SICHI, a peptoid identified from the deconvolution of a posi-
tional scanning library as a potent reversor of Semaphorin 3A-induced chemorepulsion
of hippocampal axons. It is worth noting that all three N-alkyl substituents contain
tertiary amino moieties.
The present contribution reports the study carried out to set up
a general synthetic methodology addressed to peptoids bearing
additional tertiary amino residues in the diversity positions. The
application of this study to an optimised synthesis of compound 1 is
also presented. The availability of SICHI confirmed its activity as
a potent inhibitor of Semaphorin 3A-induced chemorepulsion of
cortical axons.26
2.1. Preparation of N-protected-N-alkylglycine monomers
The use of this mixed strategy required the previous study of
different methods for the preparation of the protected N-alkylgly-
cine monomers in order to select the best one in terms of number of
steps, yields and compatibility with the presence of additional
tertiary amino moieties. The literature exam revealed contributions
carried out in solid phase, such as the reductive amination starting
2. Results and discussion
from
-haloacyl derivatives with primary amines.27,29 In addition, the
group of Liskamp reported a solution approach by reacting -hal-
a-oxoacids and primary amines, and the reaction between
Simon et al. reported the first solid-phase synthetic approach to
peptoids by using the standard strategy of peptide synthesis in-
volving the preparation of individual monomers of Fmoc protected
N-alkylglycines27 (Scheme 2, upper pathway). For the construction
of peptoid libraries, this strategy requires the independent syn-
thesis for each source of diversity. This drawback was overcome
when Zuckermann et al. reported the preparation of peptoids by
a
a
oesters with the corresponding primary amine.31,32 However, in all
cases the Fmoc group had been selected for the protection of the
glycine amino group, which could restrict the above desired
chemical compatibility. Furthermore, these studies did not report
examples of residues bearing an additional tertiary amino moiety.
R
N
O
Fmoc
Y
Fmoc
OH
N
R
deprotection
O
+ activation
X
(n + 1) cycles
Y
monomer
NH
R
O
resin
release
Y
O
Br
RNH2
Br
O
OH
Rn
N
+ activation
submonomer
O
N
Rn+1
YH
N
H
O
n
O
R
Scheme 2. Solid-phase synthesis of peptoids. Upper part: coupling of Fmoc protected N-alkylglycines. Lower part: coupling of submonomers:
amines. Y¼NH, O.
a-haloacetic acids and primary

2446
J. Messeguer et al. / Tetrahedron 66 (2010) 2444–2454
Figure 1. Reverse-phase HPLC–MS profile of the crude reaction mixture resulting from the synthesis of peptoid 1 (SICHI) following the submonomer strategy. The structures of side-
products 2 and 3 were confirmed by NMR and MS.
In our case, the three synthetic pathways envisaged for the
preparation of N-alkylglycine monomers, addressed preferentially to
the preparation of peptoid 1, are shown in Scheme 4A. The first
pathway was based on the work reported by the Liskamp group with
slight modifications.31 Thus, tert-butyl bromoacetate was allowed to
react with the corresponding primary amine followed by the acid
hydrolysis of the ester and the Fmoc protection of the amino group.
The tert-butyl ester was used instead of the reported ethyl ester to
avoid side-reactions, such as aminolysis or diketopiperazine forma-
tion during the work-up. This procedure was assayed using the
primary amines listed in Scheme 4B. It is worth of noting that the
three aliphatic amines listed are those present as diversity source in
peptoid 1. The overalkylation problems encountered in the first step
of this pathway, although they could be minimised, led to final 40%
overall yields of the protected N-alkylglycines.
The second pathway involved the use of Alloc (allyloxycarbonyl)
as protecting group. In this case, the reductive amination between
ethyl glyoxalate and the corresponding primary amine, followed by
reaction with Alloc-Cl and final saponification afforded the pro-
tected N-alkylglycines. While the overall yields for the glycines
bearing aromatic residues were around 65%, the isolation and pu-
rification problems of those bearing the tertiary amino group led to
isolated yields lower than 40%.
amino moieties (a–c in Scheme 4B) were within 70%. It should be
remarked that in the latter case a side-product originated from the
further N-alkylation of the tertiary amino moiety present in in-
termediate 10 by the
a-bromoester could be formed, thus difficulting
the purification procedures. In our case (amines a–c, Scheme 4B),
this side-product was formed in less than 10%, but complementary
assays employing less hindered primary amines, such as 2-(dime-
thylamino)ethyl amine or 3-(dimethyamino)propyl amine, showed
higher ratios of over alkylated products (results not shown).
2.2. Application of the mixed strategy to the synthesis of
peptoid 1 (SICHI)
Once the N-protected-N-alkylglycine monomers 6, 9 and 12
needed for the synthesis of 1 were available, a comparative study
was carried out to evaluate the monomer that could afford the best
results when used in the mixed strategy approach (Scheme 3).
Actually, and according to this strategy, the introduction of the first
diversity source (C-terminal), that is the 2-(1-methylpyrrolidin-2-
yl)ethylamino residue (cf. Scheme 1), could be carried out by using
the submonomer procedure since there was no risk for generation
of cyclic side-products. Therefore, the comparative study involved
the introduction of the second and N-terminal residues.
In pathway III the 2-nitrobenzenesulfonyl (Ns) was employed as
protecting group. Thus, reaction of 2-nitrobenzenesulfonyl chloride
with the corresponding primary amine followed by the attack of the
activated amino moiety to tert-butyl bromoacetate and final acid
hydrolysis gave the Ns-protected N-alkylglycine. In this case, the
protecting group was introduced first. We anticipated that the re-
action product would exhibit a better nucleophilic reactivity against
the bromoester and a higher lipophilic character for facilitating the
HPLC or TLC monitoring and the purification procedures. High
overall conversion yields were observed for the N-protected N-
alkylglycines in the three-step procedure. Isolated yields for those
monomers containing aromatic amino residues (d and e in Scheme
4B) were within 55% whereas for those bearing additional tertiary
2.2.1. Use of Fmoc protected N-alkylglycine monomers. Compound
6a (Scheme 4) was coupled to the intermediate attached to the
solid phase containing a free secondary amine (cf. Scheme 3) in the
presence of 2-(7-aza-1H-benzotriazole-1-yl)-1,1,3,3-tetramethy-
luronium hexafluorophosphate (HATU) and diisopropylethylamine
(DIEA). After deprotection of the Fmoc group, a similar coupling
was carried out using compound 6c. After the release from the
resin, purification of the crude reaction mixture by semipreparative
HPLC afforded peptoid 1 in 45% yield (98% purity by HPLC).
2.2.2. Use of Alloc protected N-alkylglycine monomers. In this case,
compound 9a (Scheme 4) was coupled to the intermediate attached

J. Messeguer et al. / Tetrahedron 66 (2010) 2444–2454
2447
to the solid phase containing a free secondary amine in the pres-
ence of N,N0-diisopropylcarbodiimide (DIC). After deprotection of
the Alloc group with a Pd(PPh3)4/PhSiH3 mixture, a similar coupling
was carried out using compound 9c. After releasing the new Alloc
protecting group and then the peptoid from the resin, purification
of the crude reaction mixture by semipreparative HPLC afforded
peptoid 1 in 43% yield (98% purity by HPLC).
2.2.3. Use of Ns-protected N-alkylglycine monomers. In this case,
compound 12a (Scheme 4) was allowed to react with the in-
termediate attached to the solid phase containing a free secondary
amine, in the presence of DIC. However, the MS analysis of an ali-
quote after the release from the resin showed that the absence of the
expected amide. Therefore we performed an additional study to
optimise the reaction conditions of this amidation reaction, which
led to select the use of HATU/DIEA in DMF (see Supplementary data).
After deprotection of the Ns group with a PhSH/DBU mixture,
a similar coupling was carried out using compound 12c. After re-
leasing the new Ns protecting group and then the peptoid from the
resin, purification of the crude reaction mixture by semipreparative
HPLC afforded peptoid 1 in 29% yield (98% purity by HPLC).
2.2.4. Discussion. As shown in Scheme 5, the appropriate combi-
nation of the submonomer and monomer strategies makes possible
the solid phase preparation of peptoids containing diversity sources
with additional tertiary amino residues. Thus, the introduction of
the first diversity source should be carried out with the sub-
monomer strategy. Then, the question arises: does the amine al-
ready introduced as diversity source contain an additional tertiary
amino residue? If not, the route 1 involving the submonomer
strategy should be used for introducing the second diversity source.
However, if the answer is yes, route 2 should be followed using the
pertinent protected N-alkylglycine monomer. By this combined
strategy, the synthesis of the N-alkylglycine oligomer would be
continued up to the introduction of the last diversity source. Finally,
release from the resin would be carried out (route 3). Moreover and
according to our experience in related peptoid syntheses,12 the use
of microwave activation can accelerate the reaction times in most of
the steps involved in this mixed strategy.
On the other hand, the selection of the required N-protected-N-
alkylglycine monomer would depend on different factors. First, the
protecting group should be compatible with the reaction conditions
of the peptoid synthesis. Concerning the Fmoc protected monomers
6, the concomitant dialkylation reactions produced in the first step
of their preparation leads to tedious and inefficient purification
procedures. With respect to the Alloc protected monomers 9, al-
though their syntheses do not involve overalkylation problems and
the Alloc group is stable under acid and mild base conditions, these
compounds are the less convenient for most applications: the first
and third reaction steps require tedious purification procedures and
Alloc release require the use of the palladium catalyst and oxygen-
free reaction conditions. According to our experience, when
primary amines such as those present in peptoid 1 need to be used,
Ns-protected N-alkylglycine monomers 12 constitute the best
choice. All three reactions involved in the preparation of these
monomers take place with high conversion yields, the protecting
group is stable under both acid and base conditions and its release
can be carried out under mild conditions and using readily available
reagents. Actually, the overall yield of monomers 12 was higher than
that obtained with compounds 6 or 9.
Scheme 3. Mixed strategy for the synthesis of peptoids bearing tertiary amino groups
in the N-alkyl side chains. Initially the submonomer strategy (A) is applied and then
the monomer strategy (B) is used in those cases where the formation of cyclic side-
products is anticipated (i.e., after the incorporation of a primary amine bearing an
additional tertiary amino residue). PG: protecting group; n¼1 or 2 depending upon the
amine selected.
In summary, we think that the use of this mixed strategy com-
bined with the appropriate selection of the N-protected N-alkyl-
glycine monomers for those steps where they will be required,
widens the synthetic possibilities for the chemical diversity that
can be inserted into N-alkylglycine oligomers. In our case, prepa-
ration of peptoids containing diversity sources with additional
Scheme 4. A: The three pathways explored for the preparation of N-protected-N-al-
kylglycine monomers. The amino protecting groups selected were: Fmoc (pathway I),
Alloc (pathway II) and 2-nitrobenzenesulfonyl (Ns) (pathway III). B: The primary amines
selected for this study.

2448
J. Messeguer et al. / Tetrahedron 66 (2010) 2444–2454
Scheme 5. Summary of the different strategies developed for the synthesis of peptoids on solid phase.
tertiary amino groups, such as SICHI (1), has been conducted with
satisfactory overall yields and purities, which would facilitate the
availability of this compound and related analogues for further
biological studies. In addition, our results can be of extended in-
terest since there is a wide commercial offer of primary amines
bearing additional tertiary amino groups that can be used for the
synthesis of peptoids and related peptidomimetics, and these
fragments are frequently present in bioactive compounds.
was treated with a solution of bromoacetic acid (146 mg, 5 equiv)
and DIC (162 L, 5 equiv) in 2:1 CH2Cl2/DMF (5 mL). The reaction
m
mixture was stirred for 30 min at room temperature. The resin was
filtered and the reaction was repeated under the same conditions.
Afterwards, the resin was drained and washed with DMF (3ꢁ5 mL),
isopropyl alcohol (3ꢁ5 mL) and CH2Cl2 (3ꢁ5 mL). A solution of 2-
(10-methyl-20-pyrrolidinyl)ethylamine (152
mL, 5 equiv) and trie-
thylamine (146 mL, 5 equiv) in 5 mL of DMF was added to the resin
and the suspension was stirred for 3 h at room temperature. The
supernatant was removed and the reaction was repeated under the
same conditions. Then, the resin was filtered and washed with DMF
(3ꢁ5 mL), isopropyl alcohol (3ꢁ5 mL) and CH2Cl2 (3ꢁ5 mL). Af-
terwards, the resin was treated with a solution of chloracetyl
3. Experimental section
3.1. General
Solvents, amines and other reagents were purchased from
commercial suppliers and used without further purification. An-
hydrous MgSO4 was used to dry organic solutions. The IR spectra
were registered with a Bomen Michelson Series MB120 apparatus
and absorptions are given in cmꢀ1. The NMR spectra were recorded
on a Varian Inova 500 apparatus (1H NMR, 500 MHz), and Unity
300 apparatus (1H NMR, 300 MHz). Spectra were taken in neu-
tralised CDCl3 solutions unless otherwise indicated. Chemical shifts
chloride (85
m
L, 5 equiv) in 5 ml of CH2Cl2 at ꢀ78 ꢂC for 5 min. The
resin was drained and washed with CH2Cl2 (3ꢁ5 mL), isopropyl
alcohol (3ꢁ5 mL) and DMF (3ꢁ5 mL). Then, a solution of 2-(1-
pyrrolidinyl)ethylamine (530 mL, 20 equiv) and triethylamine
(146 mL, 5 equiv) in 5 mL of DMF was added to the resin and the
suspension was stirred for 3 h at room temperature. The resin was
filtered and the reaction was repeated (16 h at the same tempera-
ture). The supernatant was removed and the residue was drained
and washed with DMF (3ꢁ5 mL), isopropyl alcohol (3ꢁ5 mL) and
CH2Cl2 (3ꢁ5 mL). The last two steps were repeated using N,N-
(d) are given in parts per million relative to tetramethylsilane (1H,
0.0 ppm). The RP-HPLC analyses were performed with a Hewlett
Packard Series 1100 (UV detector 1315A) modular system using
diethylethylendiamine instead of triethylamine (589 mL, 20 equiv).
a reverse-phase Kromasil 100 C8 (25ꢁ0.46 cm, 5
m
m) column, with
The cleavage was carried out by treatment with a mixture of
60:40:2 TFA/CH2Cl2/water (5 mL) for 30 min at room temperature.
The crude reaction mixture was filtered, the filtrates were pooled
and the solvent was removed by evaporation under reduced pres-
sure to obtain 85 mg of the desired compound after lyophilisation
(10% purity). The product was purified by semipreparative RP-HPLC
using aqueous acetonitrile gradient (8% yield, 98% purity).
CH3CN/buffer ammonium formate (20 mM, pH¼5.0) mixtures at
1 mL/min as mobile phase and monitoring at 220 nm. Semi-
preparative RP-HPLC was performed with a Waters (Milford, MA,
USA) system using a Kromasil 100 C8 (250ꢁ20 cm, 5
mm) column,
with CH3CN/H2O mixtures containing 0.1% TFA at 10 mL/min as
mobile phase. The GC analyses were performed in a Hewlett
Packard 5890 Series II (FID detector) system using an SPB-5 capil-
lary column. High resolution mass spectra (HRMS-FAB) were car-
ried out at the Mass Spectrometry Service of the University of
Santiago de Compostela (Spain) and at the Mass Spectrometry
Service of the IQAC. Elemental analyses were carried out at the
IQAC Microanalysis Service.
Compound (1): 1H NMR (500 MHz, CD3OD):
d 4.38 (s, 2H,
COCH2N), 4.25 (s, 2H, COCH2N), 3.87 (2H, NCH2CH2NCO), 3.86 (s,
2H, COCH2N), 3.78 (2H, 2ꢁꢁNCH2CH2), 3.68 (1H, NCH2CH2CH2CH),
3.66 (1H, NCH2CH2CH), 3.54 (2H, NCH2CH2NH), 3.42 (1H,
NCH2CH2CH), 3.40 (2H, NCH2CH2NCO), 3.36 (2H, NCH2CH2NH), 3.33
(4H, 2ꢁNCH2CH3), 3.27 (1H, NCH2CH2CH2CH), 3.15 (1H,
NCH2CH2CH2CH), 3.15 (2H, 2ꢁNCH2CH2), 2.93 (s, 3H, NCH3),
2.46 (1H, NCH2CH2CH2CH), 2.20 (1H, NCH2CH2CH), 2.15 (4H,
3.2. Submonomer strategy
2ꢁNCH2CH2),
2.13
(2H,
NCH2CH2CH2CH),
1.85
(1H,
3.2.1. N-({Carbamoylmethyl-[2-(1-methylpyrrolidin-2-yl)-
ethyl]carbamoyl}methyl)-2-(2-diethylaminoethylamino)-N-(2-pyrro-
lidin-1-ylethyl)acetamide (1). A mixture of 300 g of Fmoc-Rink-
Amide AM Polystyrene Resin (0.7 mmol/g resin, 0.21 mmol) and
3 mL of 20% piperidine in DMF was stirred at room temperature for
30 min. The resin was filtered and washed with DMF (3ꢁ5 mL),
isopropyl alcohol (3ꢁ5 mL) and CH2Cl2 (3ꢁ5 mL). Then, the resin
NCH2CH2CH2CH), 1.80 (1H, NCH2CH2CH), 1.37 (t, J¼7 Hz, 6H,
2ꢁNCH2CH3). 13C NMR (125 MHz, CD3OD):
d 172.4 (CO), 171.7 (CO),
170.9 (CO), 68.3 (NCH2CH2CH2CH), 57.2 (NCH2CH2CH2CH), 55.7
(2ꢁNCH2CH2), 53.8 (NCH2CH2NCO), 50.6 (COCH2N), 50.3 (COCH2N),
49.5 (COCH2N), 48.8 (2ꢁNCH2CH3), 47.1 (NCH2CH2NH), 46.6
(NCH2CH2CH), 45.1 (NCH2CH2NCO), 43.4 (NCH2CH2NH), 39.9
(NCH3), 30.5 (NCH2CH2CH2CH), 29.7 (NCH2CH2CH), 24.1

J. Messeguer et al. / Tetrahedron 66 (2010) 2444–2454
2449
(2ꢁNCH2CH2), 22.5 (NCH2CH2CH2CH), 9.0 (2ꢁNCH2CH3). HRMS
(MþH)þ calcd for C25H50N7O34, 496.3975; found, 496.3966.
Main impurities detected:
2970–2779, 1735 (CO), 1457, 1389–1348 (C(CH3)3), 1225, 1152.
HRMS (MþH)þ calcd for C13H27N2O2, 243.2073; found, 243.2066.
3.3.1.1.3. tert-Butyl (N0,N0-diethylethylenediamino)acetate (4c).
3-Carbamoylmethyl-6-methyl-4-oxooctahydropyrrolo[1,2-d]-
Bp 78–80 ꢂC (0.3 Torr). 1H NMR (500 MHz, CDCl3):
d 3.27 (s, 2H,
[1,4]diazepin-6-ium trifluoroacetate (2): 1H NMR (500 MHz,
COCH2NH), 2.61 (t, J¼6 Hz, 2H, CH2CH2NH), 2.50 (t, J¼6 Hz, 2H,
CH2CH2NH), 2.48 (q, J¼7.2 Hz, 4H, 2ꢁCH3CH2N), 2.06 (br s, 1H, NH),
1.42 (s, 9H, 3ꢁCH3), 0.97 (t, J¼7.2 Hz, 6H, CH3CH2N). 13C NMR
CD3OD):
d
4.81 (s, 1H, COCH2Nþ), 4.45 (s, 1H, COCH2N), 4.11 (1H,
CH2CH2N), 4.03–3.92 (1H, NCH2CH2CH2CH), 3.96 (s, 1H, COCH2N),
3.84–3.78 (1H, NCH2CH2CH2CH), 3.80 (s, 1H, COCH2Nþ), 3.71–3.64
(1H, NCH2CH2CH2CH), 3.46–3.40 (1H, CH2CH2N), 3.34 (s, 3H, NCH3),
2.74–2.66 (1H, CH2CH2N), 2.38–2.33 (2H, NCH2CH2CH2CH), 2.30–
2.16 (2H, NCH2CH2CH2CH), 2.12 (1H, CH2CH2N). 13C NMR (125 MHz,
(125 MHz, CDCl3):
d 171.6 (CO), 80.8 (C(CH3)3), 52.6 (CH2CH2NH),
51.0 (COCH2NH), 47.2 (CH2CH2NH), 46.9 (2ꢁCH3CH2N), 28.0
(3ꢁꢁCH3), 11.6 (2ꢁCH3CH2N). IR (film),
n: 3335 (NH), 2974–2809,
1736 (CO), 1453, 1390–1365 (C(CH3)3), 1229, 1155. HRMS (MþH)þ
calcd for C12H27N2O2, 231.2073; found, 231.2065.
CD3OD):
d 171.9 (CO), 165.8 (CO), 75.4 (NCH2CH2CH2CH), 70.2
(NCH2CH2CH2CH), 61.1 (COCH2Nþ), 51.9 (COCH2N), 48.9 (NCH3), 45.0
(CH2CH2N), 26.7 (CH2CH2N), 26.0 (NCH2CH2CH2CH), 19.5
(NCH2CH2CH2CH). HRMS (M)þ calcd for C11H20N3Oþ2 , 226.1550;
found, 226.1556.
3.3.1.1.4. tert-Butyl phenethylaminoacetate (4d). Bp 107–110 ꢂC
(0.5 Torr). 1H NMR (500 MHz, CDCl3):
d 7.29 (2H, Har), 7.21 (3H, Har),
3.31 (s, 2H, COCH2NH), 2.85 (2H, CH2CH2NH), 2.82 (2H, CH2CH2NH),
1.70 (br s, 1H, NH), 1.44 (s, 9H, 3ꢁCH3). 13C NMR (125 MHz, CDCl3):
8-({Carbamoylmethyl-[2-(1-methylpyrrolidin-2-yl)ethyl]carba-
d
171.5 (CO), 139.7 (Car), 128.6 (2ꢁCHar), 128.4 (2ꢁCHar), 126.1
moyl}methyl)-7-oxo-8-aza-5-azonia-spiro[4.5]decane
trifluoro-
(CHar), 81.1 (C(CH3)3), 51.6 (COCH2NH), 50.7 (CH2CH2NH), 36.5
acetate (3): 1H NMR (500 MHz, CD3OD):
d
4.34 (s, 2H, COCH2N),
(CH2CH2NH), 28.0 (3ꢁCH3). IR (film),
n: 3330 (NH), 3092–2814,1735
4.31 (s, 2H, COCH2N), 4.23 (s, 2H, COCH2Nþ), 3.89 (2H, NCH2CH2Nþ),
3.80–3.73 (4H, 2ꢁCH2CH2Nþ), 3.76–3.74 (2H, NCH2CH2Nþ), 3.72–
3.69 (1H, NCH2CH2CH), 3.69–3.62 (1H, NCH2CH2CH2CH), 3.46–3.38
(1H, NCH2CH2CH), 3.33 (1H, NCH2CH2CH2CH), 3.17–3.09 (1H,
NCH2CH2CH2CH), 2.90 (s, 3H, NCH3), 2.45 (1H, CH2CH2CH2CH),
2.38–2.34 (1H, NCH2CH2CH), 2.30 (4H, 2ꢁCH2CH2Nþ), 2.24–2.12
(1H, NCH2CH2CH2CH), 1.94–1.87 (1H NCH2CH2CH), 1.86–1.78 (1H,
NCH2CH2CH2CH), 1.77–1.70 (1H, NCH2CH2CH2CH). 13C NMR
(CO), 1459, 1393–1350 (C(CH3)3), 1228, 1155. HRMS (MþH)þ calcd
for C14H22NO2, 236.1651; found, 236.1643.
3.3.1.1.5. tert-Butyl
2-((2,4-dichlorophenyl)ethylamino)acetate
7.33 (s,
(4e). Bp 145–147 ꢂC (0.8 Torr). 1H NMR (500 MHz, CDCl3):
d
1H, Har), 7.16 (2H, Har), 3.30 (s, 2H, COCH2NH), 2.86 (2H,
CH2CH2NH), 2.84 (2H, CH2CH2NH), 1.68 (br s, 1H, NH), 1.43 (s, 9H,
3ꢁCH3). 13C NMR (125 MHz, CDCl3):
d 171.5 (CO), 136.0 (Car), 134.6
(Car), 132.5 (Car), 131.5 (CHar), 129.2 (CHar), 127.0 (CHar), 81.2
(125 MHz, CD3OD):
d
172.6 (CO), 170.0 (CO), 162.9 (CO), 68.3
(C(CH3)3), 51.5 (COCH2NH), 48.6 (CH2CH2NH), 33.6 (CH2CH2NH),
(NCH2CH2CH2CH), 64.7 (2ꢁCH2CH2Nþ), 61.3 (COCH2Nþ), 57.2
(NCH2CH2CH2CH), 56.1 (NCH2CH2Nþ), 50.0 (COCH2N), 48.7
(COCH2N), 46.3 (NCH2CH2CH), 44.5 (NCH2CH2Nþ), 40.1 (NCH3), 30.7
(NCH2CH2CH), 30.5 (NCH2CH2CH2CH), 29.9 (NCH2CH2CH2CH), 22.4
(2ꢁCH2CH2Nþ). HRMS (M)þ calcd for C19H34N5O3þ, 380.2656; found,
380.2665.
28.0 (3ꢁCH3). IR (film),
n: 3328 (NH), 3091–2817, 1731 (CO), 1473,
1388–1346 (C(CH3)3), 1224, 1152. HRMS (MþH)þ calcd for
C14H20Cl2NO2, 304.0871; found, 304.0866.
3.3.1.2. General procedure for tert-butyl esters hydrolysis
(5a-e). To a solution of the corresponding N-substituted tert-butyl
aminoacetate (4a–e) (9 mmol) in 20 mL of CH2Cl2, 20 mL of TFA
were added. After stirring for 3 h at room temperature, the solvent
was evaporated to dryness to obtain the desired acid quantitatively.
3.3. Mixed strategy
3.3.1. Pathway I: via Fmoc protected monomers 6.
3.3.1.1. General procedure for N-substituted tert-butyl amino-
acetates (4a–e). To a solution of the appropriate amine (25.8 mmol)
and triethylamine (7.2 mL, 2 equiv) in 25 mL of THF, tert-butyl
bromoacetate (3.8 mL,1 equiv) was added at 0 ꢂC. Then the mixture
was allowed to react for 30 min at room temperature. The solvent
was evaporated to dryness and the residue obtained was treated
with water and extracted with CH2Cl2. The organic layer was
washed with brine, dried and filtered. The solvent was eliminated
and the residue was distilled under vacuum to yield the desired
product in 50% yields in all cases.
3.3.1.3. General procedure for Fmoc protection (6a–e). To a solu-
tion of the corresponding N-substituted glycine (5a–e) (9 mmol) in
water adjusted to pH: 9–9.5 with triethylamine, a solution of
FmocOsu (3 g, 3 equiv) in 25 mL of acetonitrile was added. The
mixture was allowed to react for 4 h at room temperature (HPLC
monitoring). Then, the mixture was acidified with HCl and the
solvent concentrated at reduced pressure. The residue was
extracted with ethyl acetate and the joined organic fractions were
dried. The solvent was removed under reduced pressure and the
desired products were obtained (yield >90%, purity >85%).
3.3.1.1.1. tert-Butyl (2-pyrrolidin-1-ylethylamino)acetate (4a). Bp
3.3.1.3.1. [(90-Fluorenylmethoxycarbonyl)-(2-pyrrolidin-1-ylethy-
81–84 ꢂC (0.3 Torr). 1H NMR (500 MHz, CDCl3):
d
3.27 (s, 2H,
l)amino]acetic acid (6a). 1H NMR (500 MHz, CDCl3):
d 7.75 (d,
COCH2NH), 2.68 (t, J¼5.7 Hz, 2H, CH2CH2NH), 2.55 (t, J¼5.7 Hz, 2H,
J¼7.5 Hz, 2H, 2ꢁHar), 7.53 (d, J¼7.5 Hz, 2H, 2ꢁHar), 7.42–7.29 (4H,
4ꢁHar), 4.37 (d, J¼6.5 Hz, 2H, CHCH2O), 4.20 (t, J¼6.5 Hz, 1H,
CHCH2O), 4.08 (s, 2H, COCH2N), 3.72 (t, J¼6 Hz, 2H, NCH2CH2NCO),
3.41–3.36 (4H, 2ꢁCH2CH2N), 2.93 (br s, 2H, NCH2CH2NCO), 2.06 (br
CH2CH2NH), 2.47 (4H, 2ꢁCH2CH2N), 2.19 (br s, 1H, NH), 1.73 (4H,
CH2CH2N), 1.43 (s, 9H, 3ꢁCH3). 13C NMR (125 MHz, CDCl3):
d 171.7
(CO), 80.9 (C(CH3)3), 56.0 (CH2CH2NH), 54.1 (COCH2NH), 51.7
(2ꢁCH2CH2N), 48.0 (CH2CH2NH), 28.0 (3ꢁCH3), 23.4 (2ꢁCH2CH2N).
s, 4H, 2ꢁCH2CH2N). 13C NMR (125 MHz, CDCl3):
d 172.8 (CO), 156.3
IR (film),
n
: 3336 (NH), 2970–2792, 1738 (CO), 1459, 1396–1355
(CO), 143.5 (2ꢁCar), 141.2 (2ꢁCar), 127.8 (2ꢁCHar), 127.1 (2ꢁCHar),
125.0 (2ꢁCHar), 120.0 (2ꢁCHar), 68.5 (CHCH2O), 54.3 (2ꢁCH2CH2N),
52.8 (COCH2N), 50.2 (CHCH2O), 46.9 (NCH2CH2NCO), 45.2
(NCH2CH2NCO), 23.1 (2ꢁCH2CH2N). HRMS (MþH)þ calcd for
C23H27N2O4, 395.1971; found, 395.1979.
(C(CH3)3), 1236, 1159. HRMS (MþH)þ calcd for C12H25N2O2,
229.1916; found, 229.1920.
3.3.1.1.2. tert-Butyl [2-(1-methylpyrrolidin-2-yl)ethylamino]ace-
tate (4b). Bp 90–93 ꢂC (0.3 Torr). 1H NMR (500 MHz, CDCl3):
d 3.21
(s, 2H, COCH2NH), 2.97 (m, 1H, CH), 2.55 (2H, CH2CH2NH), 2.23 (s,
3H, CH3N), 2.09–1.93 (3H, NH–CH2CH2N), 1.92–1.73 (2H, CH2CHN),
1.39 (br s, 11H, CH2CH2NH and 3ꢁCH3). 13C NMR (125 MHz, CDCl3):
3.3.1.3.2. [(90-Fluorenylmethoxycarbonyl)-(2-(1-methyl-
pyrrolidin-2-yl)ethyl)amino]acetic acid (6b). 1H NMR (500 MHz,
CDCl3):
d
7.73 (d, J¼7.5 Hz, 2H, 2ꢁHar), 7.52 (d, J¼7.5 Hz, 2H, 2ꢁHar),
d
171.6 (CO), 80.9 (C(CH3)3), 64.2 (CH), 57.0 (COCH2NH), 51.7
7.39–7.28 (4H, 4ꢁHar), 4.36 (d, J¼6.3 Hz, CHCH2O), 4.18 (t, J¼6.3 Hz,
1H, CHCH2O), 4.07 (s, 2H, COCH2N), 3.74 (1H, NCH2CH2CH2CH), 3.70
(1H, CHCH2CH2N), 3.30 (1H, NCH2CH2CH2CH), 3.10 (1H,
(CH2CH2N), 46.8 (CH2CH2NH), 40.3 (NCH3), 33.8 (CH2CH2NH), 30.5
(CH2CHN), 28.0 (3ꢁCH3), 21.7 (CH2CH2N). IR (film), : 3337 (NH),
n

2450
J. Messeguer et al. / Tetrahedron 66 (2010) 2444–2454
CHCH2CH2N), 2.84 (1H, NCH2CH2CH2CH), 2.79 (s, 3H, CH3), 2.49
(1H, NCH2CH2CH2CH), 2.20 (1H, CHCH2CH2N), 2.05 (1H,
NCH2CH2CH2CH), 1.87 (1H, NCH2CH2CH2CH), 1.86–1.74 (2H, 1H,
NCH2CH2CH2CHþ1H of CHCH2CH2N). 13C NMR (125 MHz, CDCl3):
Afterwards, the resin was treated with a mixture of acid 6a
(252 mg, 2 equiv), HATU (240 mg, 2 equiv) and DIEA (220 L,
m
4 equiv) in 5 mL of DMF. The reaction mixture was stirred for 1 h at
room temperature. The resin was drained and washed with DMF
(3ꢁ5 mL), isopropyl alcohol (3ꢁ5 mL) and CH2Cl2 (3ꢁ5 mL),
deprotected from the Fmoc group, and coupled to acid 6c as de-
scribed above. Then, Fmoc group was eliminated again with 5 mL of
20% piperidine in DMF. After washing, the cleavage step was carried
out bytreatment with a mixtureof 60:40:2 TFA/CH2Cl2/water(5 mL)
for 30 min at room temperature. The crude reaction mixture was
filtered, the filtrates were pooled and the solvent was removed by
evaporation under reduced pressure to obtain 110 mg of the desired
compound after lyophilisation (85% purity). The product was puri-
fied by semipreparative RP-HPLC using an aqueous acetonitrile
gradient to obtain 70 mg of 1 (45% yield, 98% purity).
d
172.0 (CO),156.5 (CO),143.5 (2ꢁCar), 141.2 (2ꢁCar), 127.8 (2ꢁCHar),
127.1 (2ꢁCHar), 124.9 (2ꢁCHar), 120.0 (2ꢁCHar), 68.0 (CHCH2O), 67.4
(NCH2CH2CH2CH), 56.3 (NCH2CH2CH2CH), 49.4 (COCH2N), 47.0
(CHCH2O), 46.2 (CHCH2CH2N), 40.0 (CH3), 29.6 (NCH2CH2CH2CH),
29.4 (CHCH2CH2N), 21.6 (NCH2CH2CH2CH). HRMS (MþH)þ calcd for
C24H29N2O4, 409.2127; found, 409.2126.
3.3.1.3.3. [(2-Diethylaminoethyl)-(90-fluorenylmethox-
ycarbonyl)amino]acetic acid (6c). 1H NMR (500 MHz, CDCl3):
d 7.75
(d, J¼7.5 Hz, 2H, 2ꢁHar), 7.53 (d, J¼7.5 Hz, 2H, 2ꢁHar), 7.44–7.30
(4H, 4ꢁHar), 4.39 (d, J¼7 Hz, 2H, CHCH2O), 4.20 (t, J¼7 Hz, 1H,
CHCH2O), 4.11 (s, 2H, COCH2N), 3.38 (br s, 2H, NCH2CH2NCO), 3.23–
3.14 (4H, 2ꢁCH3CH2N), 2.73 (br s, 2H, NCH2CH2NCO), 1.30 (t,
J¼7.5 Hz, 6H, 2ꢁCH3CH2N). 13C NMR (125 MHz, CDCl3):
d
173.5 (CO),
3.3.2. Pathway II: via Alloc protected monomers 9. 3.3.2.1. General
procedure for N-substituted ethyl aminoacetates (7a–e). To a solu-
tion of the appropriate amine (50 mmol) in 100 mL of ethanol, ethyl
glyoxylate (50% in toluene) (10.4 mL, 1.05 equiv) was added and the
mixture was allowed to react for 1 h at room temperature. Then,
156.3 (CO), 143.4 (2ꢁCar), 141.2 (2ꢁCar), 127.8 (2ꢁCHar), 127.2
(2ꢁCHar), 124.9 (2ꢁCHar), 120.0 (2ꢁCHar), 68.6 (CHCH2O), 50.4
(CHCH2O), 50.1 (COCH2N), 47.3 (NCH2CH2NCO), 47.1 (2ꢁCH3CH2N),
44.4 (NCH2CH2NCO), 8.4 (2ꢁCH3CH2N). HRMS (MþH)þ calcd for
C23H29N2O4, 397.2127; found, 397.2137.
NaBH3CN (3.96 g, 1.2 equiv) and 100 mL of acetic acid in 15 mL of
3.3.1.3.4. [(2-Phenethyl)-(90-fluorenylmethoxycarbonyl)amino]-
ethanol were added to the mixture and reaction was prolonged for
2 h. The solvent was evaporated to dryness and the residue obtained
was treated with 10% NaOH, saturated with NaCl and extracted with
AcOEt (polar amines) or tBuOMe (apolar amines). The organic layer
was dried and filtered. The solvent was eliminated to obtain the
desired compound 7 (purity >90%, yields 60–85%).
acetic acid (6d). 1H NMR (500 MHz, CDCl3):
d
7.73 (d, J¼7.6 Hz, 2H,
2ꢁHar), 7.58 (d, J¼7.2 Hz, 2H, 2ꢁHar), 7.40–7.14 (8H, 8ꢁHar), 6.95 (d,
J¼7.2 Hz, 1H, Har), 4.57 (d, J¼5.6 Hz, CHCH2O), 4.20 (1H, CHCH2O),
3.84 (s, 2H, COCH2N), 3.33 (t, J¼7.2 Hz, 2H, CH2CH2N), 2.56 (t,
J¼7.2 Hz, 2H, CH2CH2N). 13C NMR (125 MHz, CDCl3):
d 174.6 (CO),
156.5 (CO), 143.7 (2ꢁCar), 141.4 (2ꢁCar), 138.5 (Car), 128.7 (2ꢁCHar),
128.5 (2ꢁCHar), 127.7 (2ꢁCHar), 127.1 (2ꢁCHar), 126.4 (CHar), 124.7
(2ꢁCHar), 120.0 (2ꢁCHar), 67.2 (CHCH2O), 50.2 (COCH2N), 49.4
(CH2CH2N), 47.2 (CHCH2O), 34.7 (CH2CH2N). Elemental analysis for
C25H23NO4: calcd C, 74.79; H, 5.77; N, 3.49. Found: C, 74.75; H, 5.85;
N, 3.43.
3.3.2.1.1. Ethyl (2-pyrrolidin-1-ylethylamino)acetate (7a). 1H
NMR (300 MHz, CDCl3):
d
4.19 (q, J¼7.2 Hz, 2H, CH3CH2O), 3.43 (s,
2H, COCH2NH), 2.74 (t, J¼6.3 Hz, 2H, CH2CH2NH), 2.60 (t, J¼6.3 Hz,
2H, CH2CH2NH), 2.51 (4H, 2ꢁCH2CH2N), 2.14 (br s,1H, NH),1.77 (4H,
2ꢁCH2CH2N), 1.28 (t, J¼7.2 Hz, 3H, CH3CH2O). 13C NMR (75 MHz,
CDCl3):
d
172.5 (CO), 60.5 (CH3CH2O), 55.9 (2ꢁCH2CH2N), 54.1
3.3.1.3.5. [(2-(2,4-Dichlorophenyl)ethyl)-(90-fluorenylmethox-
(CH2CH2NH), 50.9 (COCH2NH), 48.0 (CH2CH2NH), 23.4
(2ꢁCH2CH2N), 14.1 (CH3CH2O). HRMS (MþH)þ calcd for
C10H21N2O2, 201.1603; found, 201.1598.
ycarbonyl)amino]acetic acid (6e). 1H NMR (500 MHz, CDCl3):
d 7.73
(d, J¼7.6 Hz, 2H, 2ꢁHar), 7.58 (d, J¼7.6 Hz, 2H, 2ꢁHar), 7.40–7.25
(5H, 5ꢁHar), 7.12 (1H, Har), 6.68 (d, J¼7.6 Hz, 1H, Har), 4.61 (d,
J¼5.2 Hz, 2H, CHCH2O), 4.21 (1H, CHCH2O), 3.86 (s, 2H, COCH2N),
3.3.2.1.2. Ethyl (N0,N0-diethylethylenediamino)acetate (7c). 1H
NMR (500 MHz, CDCl3):
d
4.17 (q, J¼7.2 Hz, 2H, CH3CH2O), 3.40 (s,
3.26 (t, J¼7.2 Hz, 2H, CH2CH2N), 2.60 (t, J¼7.2 Hz, 2H, CH2CH2N). 13
C
2H, COCH2NH), 2.66 (t, J¼6.3 Hz, 2H, CH2CH2NH), 2.55 (t, J¼6.3 Hz,
2H, CH2CH2NH), 2.52 (q, J¼7 Hz, 4H, 2ꢁCH3CH2N), 2.15 (br s, 1H,
NH), 1.28 (t, J¼7.2 Hz, 3H, CH3CH2O), 1.02 (t, J¼7 Hz, 6H,
NMR (125 MHz, CDCl3):
d
174.7 (CO), 156.3 (CO), 143.7 (2ꢁCar), 141.3
(2ꢁCar), 134.7 (Car), 134.4 (Car), 133.0 (Car), 131.8 (CHar), 129.3 (CHar),
127.7 (2ꢁCHar), 127.1 (2ꢁCHar), 127.0 (CHar), 124.6 (2ꢁCHar), 120.0
(2ꢁCHar), 67.0 (CHCH2O), 49.5 (COCH2N), 48.0 (CH2CH2N), 47.2
(CHCH2O), 31.8 (CH2CH2N). Elemental analysis for C25H21Cl2NO4:
calcd C, 63.84; H, 4.50; Cl,15.08; N, 2.98. Found: C, 63.80; H, 4.51; Cl,
15.02; N, 2.93.
2ꢁCH3CH2N). 13C NMR (125 MHz, CDCl3):
d 172.5 (CO), 60.6
(CH3CH2O), 52.5 (CH2CH2NH), 51.0 (COCH2NH), 47.0 (CH2CH2NH),
46.8 (2ꢁCH3CH2N), 14.8 (CH3CH2O), 11.6 (2ꢁCH3CH2N). HRMS
(MþH)þ calcd for C10H23N2O2, 203.1760; found, 203.1755.
3.3.2.1.3. Ethyl phenethylaminoacetate (7d). 1H NMR (300 MHz,
CDCl3):
d
7.32–7.17 (5H, Har), 4.17 (q, J¼7.2 Hz, 2H, CH3CH2O), 3.41 (s,
3.3.1.4. Application to the synthesis of peptoid 1. A mixture of
400 g of Fmoc-Rink-Amide AM Polystyrene Resin (0.79 mmol/g
resin, 0.32 mmol) and 3 mL of 20% piperidine in DMF was stirred at
room temperature for 30 min. The resin was filtered and washed
with DMF (3ꢁ5 mL), isopropyl alcohol (3ꢁ5 mL) and CH2Cl2
(3ꢁ5 mL). Then, the resin was treated with a solution of bromo-
2H, COCH2NH), 2.87 (t, J¼6.3 Hz, 2H, CH2CH2NH), 2.81 (t, J¼6.3 Hz,
2H, CH2CH2NH), 1.65 (br s, 1H, NH), 1.26 (t, J¼7.2 Hz, 3H, CH3CH2O).
13C NMR (75 MHz, CDCl3):
d
172.3 (CO), 139.6 (Car), 128.6 (2ꢁCHar),
128.4 (2ꢁCHar), 126.2 (Car), 60.6 (CH3CH2O), 50.8 (COCH2NH), 50.7
(CH2CH2NH), 36.4 (CH2CH2NH), 14.1 (CH3CH2O). HRMS (MþH)þ
calcd for C12H18NO2, 208.1338; found, 208.1335.
acetic acid (146 mg, 5 equiv) and DIC (162
mL, 5 equiv) in 2:1
3.3.2.1.4. Ethyl 2-((2,4-dichlorophenyl)ethylamino)acetate (7e). 1H
CH2Cl2/DMF (5 mL). The reaction mixture was stirred for 30 min at
room temperature. The resin was filtered and the reaction was re-
peated under the same conditions. Afterwards, the resin was
drained and washed with DMF (3ꢁ5 mL), isopropyl alcohol
(3ꢁ5 mL) and CH2Cl2 (3ꢁ5 mL). A solution of 2-(1-methyl-2-pyr-
NMR (500 MHz, CDCl3):
d
7.35 (1H, Har), 7.20–7.13 (2H, 2ꢁHar), 4.17
(q, J¼7.2 Hz, 2H, CH3CH2O), 3.42 (s, 2H, COCH2NH), 2.87 (2H,
CH2CH2NH), 2.83 (2H, CH2CH2NH), 2.43 (br s, 1H, NH), 1.25 (t,
J¼7.2 Hz, 3H, CH3CH2O). 13C NMR (125 MHz, CDCl3):
d 172.2 (CO),
135.8 (Car), 134.7 (Car), 132.6 (Car), 131.7 (CHar), 129.4 (CHar), 127.2
(CHar), 60.8 (CH3CH2O), 50.7 (COCH2NH), 48.7 (CH2CH2NH), 33.4
(CH2CH2NH),14.2 (CH3CH2O). HRMS (MþH)þ calcd for C12H16Cl2NO2,
276.0558; found, 276.0554.
rolidinyl)ethylamine (152 mL, 5 equiv) and triethylamine (146 mL,
5 equiv) in 5 mL of DMF was added to the resin and the suspension
was stirred for 3 h at room temperature. The supernatant was re-
moved and the reaction was repeated under the same conditions.
Then, the resin was filtered and washed with DMF (3ꢁ5 mL), iso-
propyl alcohol (3ꢁ5 mL) and CH2Cl2 (3ꢁ5 mL).
3.3.2.2. General procedure for Alloc protection (8a–e). To a sus-
pension of the corresponding N-substituted ethyl aminoacetate

J. Messeguer et al. / Tetrahedron 66 (2010) 2444–2454
2451
(7a–e) (10 mmol), K2CO3 (2.07 mL, 1.5 equiv) in 30 ml of CH2Cl2,
cooled down to 5 ꢂC, allyl chloroformate was added slowly
(1.27 mL, 1.2 equiv). After stirring at this temperature for 1 h, the
crude reaction mixture was filtered and the solvent was evaporated
to dryness to obtain the desired allyl carbamate 8 with yields higher
than 90% in all cases.
3 h at 80 ꢂC the crude reaction mixture was acidified with con-
centrated HCl and the solvent was evaporated to dryness. Then, for
compounds 8a–c, the crude was redissolved in 15 mL of water and
lyophilised. The residue obtained was treated with CHCl3, sonicated
and filtered to obtain the desired acids 9a–c as solids (yields 70–
75%). For compounds 8d and 8e the crude was redissolved in 30 mL
of water, and extracted with BuOMe. The organic layer was dried
and filtered. The solvent was eliminated to obtain the acids 9d and
9e as oils (yields 78–86%).
t
3.3.2.2.1. Ethyl [allyloxycarbonyl-(2-pyrrolidin-1-ylethyl)amino]-
acetate (8a). 1H NMR (300 MHz, CDCl3):
d
5.91 (m, 1H,
OCH2CH]CH2), 5.34–5.15 (2H, OCH2CH]CH2), 4.62 (d, J¼5.4 Hz,
2H, OCH2CH]CH2), 4.18 (q, J¼7.2 Hz, 2H, CH3CH2O), 4.06 (s, 2H,
COCH2N), 3.49 (t, J¼6.9 Hz, 2H, CH2CH2NCO), 2.66 (t, J¼6.9 Hz, 2H,
CH2CH2NCO), 2.52 (4H, 2ꢁCH2CH2N), 1.76 (4H, 2ꢁCH2CH2N), 1.27 (t,
3.3.2.3.1. [Allyloxycarbonyl-(2-pyrrolidin-1-ylethyl)amino]acetic
acid$HCl (9a). 1H NMR (300 MHz, CDCl3):
d 10.84 (br s,1H, OH), 5.89
(1H, OCH2CH]CH2), 5.31–5.17 (2H, OCH2CH]CH2), 4.57 (d, J¼6 Hz,
2H, OCH2CH]CH2), 4.18 (s, 2H, COCH2N), 3.82 (4H, 2ꢁCH2CH2N),
3.47 (br s, 2H, CH2CH2NCO), 3.03 (br s, 2H, CH2CH2NCO), 2.11 (4H,
J¼7.2 Hz, 3H, CH3CH2O). 13C NMR (75 MHz, CDCl3):
d 169.8 (CO),
155.7 (CO), 132.7 (OCH2CH]CH2), 117.3 (OCH2CH]CH2), 66.3
(OCH2CH]CH2), 61.0 (CH3CH2O), 54.5 (CH2CH2NCO), 54.1
(2ꢁCH2CH2N), 49.5 (COCH2N), 47.5 (CH2CH2NCO), 23.4
2ꢁCH2CH2N). 13C NMR (75 MHz, CDCl3):
d 171.8 (CO), 155.7 (CO),
132.2 (OCH2CH]CH2), 117.2 (OCH2CH]CH2), 66.7 (OCH2CH]CH2),
54.1 (2ꢁCH2CH2N), 52.5 (COCH2N), 49.9 (CH2CH2NCO), 45.2
(CH2CH2NCO), 23.4 (2ꢁCH2CH2N). HRMS (MþH)þ calcd for
C12H21N2O4, 257.1501; found, 257.1494.
(2ꢁCH2CH2N), 14.1 (CH3CH2O). IR (film),
n: 2968–2793, 1746 (CO),
1702 (CO), 1466, 1410, 1365, 1214, 1150. Elemental analysis for
C14H24N2O4: calcd C, 59.13; H, 8.51; N, 9.85. Found: C, 59.21; H,
8.53; N, 9.69.
3.3.2.3.2. (Allyloxycarbonyl-(2-diethylaminoethyl)amino)acetic
3.3.2.2.2. Ethyl (allyloxycarbonyl-(2-diethylaminoethyl)amino)-
acid$HCl (9c). 1H NMR (300 MHz, CDCl3):
d 10.65 (br s, 1H, OH),
acetate (8c). 1H NMR (300 MHz, CDCl3):
d
5.88 (m, 1H,
5.87 (m, 1H, OCH2CH]CH2), 5.35–5.16 (2H, OCH2CH]CH2), 4.58 (d,
J¼5.4 Hz, 2H, OCH2CH]CH2), 4.07 (s, 2H, COCH2N), 3.76 (d,
J¼6.3 Hz, 2H, CH2CH2NCO), 3.34 (d, J¼6.3 Hz, 2H, CH2CH2NCO), 3.17
(q, J¼7.2 Hz, 4H, 2ꢁCH3CH2N), 1.34 (t, J¼7.2 Hz, 6H, 2ꢁCH3CH2N).
OCH2CH]CH2), 5.32–5.14 (2H, OCH2CH]CH2), 4.59 (d, J¼5 Hz, 2H,
OCH2CH]CH2), 4.17 (q, J¼7.2 Hz, 2H, CH3CH2O), 4.07 (s, 2H,
COCH2N), 3.40 (t, J¼7.5 Hz, 2H, CH2CH2NCO), 2.59 (t, J¼7.5 Hz, 2H,
CH2CH2NCO), 2.50 (q, J¼7.5 Hz, 4H, 2ꢁCH3CH2N), 1.25 (t, J¼7.2 Hz,
3H, CH3CH2O), 1.01 (t, J¼7.5 Hz, 6H, 2ꢁCH3CH2N). 13C NMR
13C NMR (75 MHz, CDCl3):
d 173.9 (CO), 156.1 (CO), 132.2
(OCH2CH]CH2), 117.5 (OCH2CH]CH2), 66.4 (OCH2CH]CH2), 51.6
(COCH2N), 49.4 (CH2CH2NCO), 46.8 (2ꢁCH3CH2N), 44.8
(CH2CH2NCO), 8.5 (2ꢁCH3CH2N). HRMS (MþH)þ calcd for
C12H23N2O4, 259.1658; found, 259.1664.
(75 MHz, CDCl3):
d 169.9 (CO), 155.8 (CO), 132.0 (OCH2CH]CH2),
117.7 (OCH2CH]CH2), 66.6 (OCH2CH]CH2), 61.5 (CH3CH2O), 51.5
(CH2CH2NCO), 49.8 (COCH2N), 47.3 (2ꢁCH3CH2N), 47.0
(CH2CH2NCO), 14.1 (CH3CH2O), 11.8 (2ꢁCH3CH2N). IR (film),
n
:
3.3.2.3.3. (Allyloxycarbonyl-(2-phenethyl)amino)acetic acid (9d).
2973–2803,1751 (CO),1706 (CO),1466,1410,1375,1295,1240,1200,
1170, 1125. Elemental analysis for C14H26N2O4: calcd C, 58.72; H,
9.15; N, 9.78. Found C, 58.67; H, 9.14; N, 9.67.
1H NMR (300 MHz, CDCl3):
d 10.01 (br s, 1H, OH), 7.30–7.13 (5H,
5ꢁHar), 5.88 (m, 1H, OCH2CH]CH2), 5.33–5.17 (2H, OCH2CH]CH2),
4.54 (d, J¼5.6 Hz, 2H, OCH2CH]CH2), 3.90 (s, 2H, COCH2N), 3.56 (t,
3.3.2.2.3. Ethyl
(allyloxycarbonyl-(2-phenethyl)amino)acetate
7.31–7.15 (5H, 5ꢁHar), 5.90 (m,
J¼7.2 Hz, 2H, CH2CH2NCO), 2.88 (t, J¼7.2 Hz, 2H, CH2CH2NCO). 13
C
(8d). 1H NMR (300 MHz, CDCl3):
d
NMR (75 MHz, CDCl3): d 173.2 (CO), 156.3 (CO), 139.0 (Car), 132.7
1H, OCH2CH]CH2), 5.34–5.17 (2H, OCH2CH]CH2), 4.59 (d,
J¼5.2 Hz, 2H, OCH2CH]CH2), 4.17 (q, J¼7.2, 2H, CH3CH2O), 3.89 (s,
2H, COCH2N), 3.55 (t, J¼7.4 Hz, 2H, CH2CH2N), 2.86 (t, J¼7.4 Hz, 2H,
CH2CH2N), 1.25 (t, J¼7.2 Hz, 3H, CH3CH2O). 13C NMR (75 MHz,
(OCH2CH]CH2), 128.6 (2ꢁCHar), 128.3 (2ꢁCHar), 126.6 (CHar), 117.6
(OCH2CH]CH2), 66.9 (OCH2CH]CH2), 51.1 (COCH2N), 49.6
(CH2CH2NCO), 35.3 (CH2CH2NCO). Elemental analysis for
C14H17NO4: calcd C, 63.87; H, 6.51; N, 5.32. Found: C, 63.96; H, 6.54;
N, 5.26.
CDCl3):
d 169.7 (CO), 156.2 (CO), 138.8 (Car), 132.7 (OCH2CH]CH2),
128.7 (2ꢁCHar), 128.5 (2ꢁCHar), 126.5 (CHar), 117.4 (OCH2CH]CH2),
3.3.2.3.4. [Allyloxycarbonyl-(2-(2,4-dichlorophenyl)ethyl)amino]-
66.3 (OCH2CH]CH2), 61.2 (CH3CH2O), 50.0 (COCH2N), 49.5
acetic acid (9e). 1H NMR (300 MHz, CDCl3):
d 9.95 (br s, 1H, OH),
(CH2CH2N), 35.0 (CH2CH2N), 14.1 (CH3CH2O). IR (film),
n
: 3090–
7.35 (s, 1H, Har), 7.17–7.10 (2H, 2ꢁHar), 5.85 (m, 1H,
OCH2CH]CH2), 5.30–5.16 (2H, OCH2CH]CH2), 4.52 (d, J¼6 Hz,
2H, OCH2CH]CH2), 3.95 (s, 2H, COCH2N), 3.53 (t, J¼7.2 Hz, 2H,
CH2CH2NCO), 2.95 (t, J¼7.2 Hz, 2H, CH2CH2NCO). 13C NMR
2877, 1748 (CO), 1703 (CO), 1526, 1472, 1410, 1370, 1237, 1192, 1174,
1126, 1028, 988, 952, 930, 770, 748, 699. Elemental analysis for
C16H21NO4: calcd C, 65.96; H, 7.27; N, 4.81. Found: C, 65.85; H, 7.24;
N, 4.90.
(75 MHz, CDCl3):
d 172.9 (CO), 156.7 (CO), 135.6 (Car), 135.0 (Car),
3.3.2.2.4. Ethyl
[allyloxycarbonyl-(2-(2,4-dichlorophenyl)ethyl)-
7.36 (s, 1H, Har),
133.6 (Car), 132.8 (OCH2CH¼CH2), 132.2 (CHar), 130.0 (CHar), 127.9
(CHar), 117.5 (OCH2CH]CH2), 67.3 (OCH2CH]CH2), 50.0
(COCH2N), 49.6 (CH2CH2NCO), 32.9 (CH2CH2NCO). Elemental
analysis for C14H15Cl2NO4: calcd C, 50.62; H, 4.55; Cl, 21.35; N,
4.22. Found: C, 50.74; H, 4.60; Cl, 21.28; N, 4.13.
amino]acetate (8e). 1H NMR (300 MHz, CDCl3):
d
7.19–7.14 (2H, 2ꢁHar), 5.87 (m, 1H, OCH2CH]CH2), 5.32–5.17 (2H,
OCH2CH]CH2), 4.56 (2H, OCH2CH]CH2), 4.19 (q, J¼7.2 Hz, 2H,
CH3CH2O), 3.94 (s, 2H, COCH2N), 3.54 (t, J¼7.2 Hz, 2H, CH2CH2N),
3.00 (t, J¼7.2 Hz, 2H, CH2CH2N), 1.26 (t, J¼7.2 Hz, 3H, CH3CH2O). 13
C
NMR (75 MHz, CDCl3):
d
169.6 (CO), 156.1 (CO), 135.0 (Car),134.7 (Car),
3.3.2.4. Application to the synthesis of 1. A mixture of 600 g of
Fmoc-Rink-Amide AM Polystyrene Resin (0,70 mmol/g resin,
0.42 mmol) and 3 mL of 20% piperidine in DMF was stirred for
30 min at room temperature. The resin was filtered and washed
with DMF (3ꢁ5 mL), isopropyl alcohol (3ꢁ5 mL) and CH2Cl2
(3ꢁ5 mL). Then, the resin was treated with a solution of bromo-
133.0 (Car), 132.6 (OCH2CH]CH2), 131.8 (CHar), 129.3 (CHar), 127.2
(CHar), 117.7 (OCH2CH]CH2), 66.5 (OCH2CH]CH2), 61.2 (CH3CH2O),
49.5 (COCH2N), 48.0 (CH2CH2N), 31.3 (CH2CH2N), 14.1 (CH3CH2O). IR
(film), n: 3090–2877, 1748 (CO), 1708 (CO), 1521, 1472, 1410, 1379,
1237, 1197, 1179, 1099, 1050, 1028, 988, 956, 930, 863, 823, 770. El-
emental analysis for C16H19Cl2NO4: calcd C, 53.35; H, 5.32; Cl, 19.68;
N, 3.89. Found: C, 53.44; H, 5.40; Cl, 19.86; N, 3.92
acetic acid (290 mg, 5 equiv) and DIC (320 mL, 5 equiv) in 2:1
CH2Cl2/DMF (5 mL). The reaction mixture was stirred for 30 min at
room temperature. The resin was filtered and the reaction was re-
peated under the same conditions. Afterwards, the resin was
drained and washed with DMF (3ꢁ5 mL), isopropyl alcohol
(3ꢁ5 mL) and CH2Cl2 (3ꢁ5 mL). A solution of 2-(1-methyl-2-
3.3.2.3. General procedure for esters hydrolysis (9a–e). To
a solution of the corresponding allyl carbamate (8a–e) (6 mmol) in
30 mL of dioxane, 5 mL of 4 N NaOH was added. After stirring for

2452
J. Messeguer et al. / Tetrahedron 66 (2010) 2444–2454
pyrrolidinyl)ethylamine (305
m
L, 5 equiv) and triethylamine
0.90 (t, J¼7.2 Hz, 6H, 2ꢁCH3CH2N). 13C NMR (125 MHz, CDCl3):
(146
mL, 5 equiv) in 5 mL of DMF was added to the resin and the
d 148.0 (Car),133.5 (CHar),133.3 (Car),132.5 (CHar),131.1 (CHar),125.2
suspension was stirred for 3 h at room temperature. The superna-
tant was removed and the reaction was repeated under the same
conditions. Then, the resin was filtered and washed with DMF
(3ꢁ5 mL), isopropyl alcohol (3ꢁ5 mL) and CH2Cl2 (3ꢁ5 mL).
Afterwards, the resin was treated with a mixture of acid 7a
(CHar), 51.0 (CH2CH2NH), 46.2 (2ꢁCH3CH2N), 41.1 (CH2CH2NH), 11.5
(2ꢁCH3CH2N). IR (film),
n: 3330 (NH), 3096 (CAr–H), 2972–2817 (C–
H), 1593 (NH), 1541 (NO2), 1350 (SO2), 1169 (SO2). HRMS (MþH)þ
calcd for C12H20N3O4S, 302.1175; found, 302.1170.
3.3.3.1.4. 2-Nitro-N-phenethyl-benzenesulfonamide
(10d). 1H
(268 mg, 2.5 equiv) and DIC (320
m
L, 52 equiv) in 2:1 CH2Cl2/DMF
NMR (500 MHz, CDCl3): 8.09 (1H, Har), 7.82 (1H, Har), 7.72 (2H,
2ꢁHar), 7.24 (2H, 2ꢁHar), 7.19 (1H, Har), 7.08 (d, J¼7.5 Hz, 2H,
2ꢁHar), 5.34 (br s, 1H, NH), 3.39 (br s, 2H, CH2CH2NH), 2.84 (t,
(5 mL). The reaction mixture was stirred for 3 h at room tempera-
ture. The resin was drained and washed with DMF (3ꢁ5 mL), iso-
propyl alcohol (3ꢁ5 mL) and CH2Cl2 (3ꢁ5 mL). Then, the resin was
treated with tetrakis(triphenylphosphine)palladium(0) (48 mg,
J¼7 Hz, 2H, CH2CH2NH). 13C NMR (125 MHz, CDCl3):
d 147.8 (Car),
133.7 (Car), 133.5 (CHar), 132.8 (CHar), 130.9 (CHar), 128.7 (2ꢁCHar),
0.1 equiv) and phenylsilane (518 mL, 10 equiv) in anhydrous CH2Cl2
128.6 (2ꢁCHar), 126.9 (CHar), 125.4 (CHar), 45.0 (CH2CH2NH), 35.9
for 30 min at room temperature under an argon atmosphere. This
procedure was repeated. The supernatant was removed and the
residue was drained and washed with CH2Cl2 (3ꢁ3 mL), isopropyl
alcohol (3ꢁ3 mL) and DMF (3ꢁ3 mL). The resin was coupled to acid
7c and the allyl group deprotected as described above. After
washing, the cleavage step was carried out by treatment with
a mixture of 60:40:2 TFA/CH2Cl2/water (5 mL) for 30 min at room
temperature. The crude reaction mixture was filtered, the filtrates
were pooled and the solvent was removed by evaporation under
reduced pressure to obtain 158 mg of the desired compound after
lyophilisation.(84% purity) The product was purified by semi-
preparative RP-HPLC using an aqueous acetonitrile gradient to
obtain 88 mg of 1 (43% yield, 98% purity).
(CH2CH2NH). IR (KBr), n: 3297 (NH), 3090–3029 (CAr–H), 2950–
2825 (C–H), 1593 (NH), 1536 (NO2), 1360 (SO2), 1164 (SO2). HRMS
(MþH)þ calcd for C14H15N2O4S, 307.0753; found, 307.0744.
3. 3. 3.1. 5. N-[2-(2, 4-Dichlorophenyl)ethyl]-2-nitro-
benzenesulfonamide (10e). 1H NMR (500 MHz, CDCl3): 8.05 (dd,
J1¼7 Hz, J2¼2 Hz, 1H, Har), 7.83 (dd, J1¼7 Hz, J2¼2 Hz, 1H, HAr), 7.71
(2H, 2ꢁHAr), 7.26 (s, 1H, HAr), 7.11 (2H, 2ꢁHar), 5.40 (t, J¼5.5 Hz, 1H,
NH), 3.43 (2H, CH2CH2NH), 2.95 (t, J¼7 Hz, 2H, CH2CH2NH). 13C
NMR (125 MHz, CDCl3):
d 147.7 (Car), 136.5 (Car), 135.9 (Car), 134.6
(Car),133.7 (Car),133.5 (CHar),132.9 (CHar),132.0 (CHar),130.7 (CHar),
129.4 (CHar), 127.2 (CHar), 125.4 (CHar), 43.0 (CH2CH2NH), 33.5
(CH2CH2NH). IR (KBr), n: 3343 (NH), 3089 (CAr–H), 2942–2886 (C–
H), 1591 (NH), 1538 (NO2), 1335 (SO2), 1160 (SO2). HRMS (MþH)þ
calcd for C14H13Cl2N2O4S, 374.9973; found, 374.9979.
3.3.3. Pathway III: via nosyl protected monomers 12. 3.3.3.1. Gen-
eral procedure for N-substituted 2-nitrobenzensulfonamides (10a–
e). To a solution of the appropriate amine (20 mmol) and trie-
thylamine (2.7 mL, 1 equiv) in 50 ml of CH2Cl2, 2-nitro-
benzenesulfonyl chloride (4.4 g, 1 equiv) was added at 0 ꢂC and the
mixture was allowed to react for 1 h at room temperature. For
amines a–c the crude reaction mixture was washed with 0.5 N HCl
and water. The joined organic layers were dried, filtered and con-
centrated to give the desired compound 10a–c (yield >90%). For
amines d and e the solvent was eliminated under reduced pressure
and the residue was recrystallised from CH2Cl2/hexane to obtain
10d and 10e as solids (yield 75%).
3.3.3.2. General procedure for Ns-protected N-substituted tert-
butyl aminoacetates (11a–e). To a solution of the appropriate
nosylamine 10a–e (10 mmol) and K2CO3 (2.7 g, 2 equiv) in 50 ml of
DMF, tert-butyl bromoacetate (1.1 mL, 1 equiv) was added and the
mixture was allowed to react for 2 h at room temperature. Salts
were filtered and the solvent was evaporated to dryness. For
amines a–c the residue obtained was treated with 1 N NaOH and
extracted with CH2Cl2. The organic layers were dried, filtered and
concentrated to give the desired compounds 11a–c (yield 86–90%)
as brownish oils. For amines d and e the residue obtained was
treated with a 1:1 tBuOMe/water mixture, and extracted with
tBuOMe. The joined organic layers were dried, filtered and con-
centrated to give the expected compounds 11d and 11e (yield
>90%) as yellow oils.
3.3.3.1.1. 2-Nitro-N-(2-pyrrolidin-1-ylethyl)benzenesulfonamide
(10a). 1H NMR (500 MHz, CDCl3):
d 8.15 (1H, Har), 7.86 (1H, Har),
7.74 (2H, 2ꢁHar), 5.00 (br s, 1H, NH), 3.20 (t, J¼6 Hz, 2H,
NCH2CH2NH), 2.68 (t, J¼6 Hz, 2H, NCH2CH2NH), 2.48 (t, J¼7 Hz, 4H,
2ꢁCH2CH2N), 1.74 (4H, 2ꢁCH2CH2N). 13C NMR (125 MHz, CDCl3):
3.3.3.2.1. tert-butyl [(2-nitrobenzenesulfonyl)-(2-pyrrolidin-1-
ylethyl)amino]acetate (11a). 1H NMR (500 MHz, CDCl3):
d 8.10
d
147.2 (Car),133.5 (CHar),133.3 (Car),132.6 (CHar), 131.2 (CHar),125.2
(1H, Har), 7.68 (2H, 2ꢁHar), 7.61 (1H, Har), 4.23 (s, 2H, COCH2N), 3.53
(t, J¼7 Hz, 2H, NCH2CH2NSO2), 2.68 (t, J¼7 Hz, 2H, NCH2CH2NSO2),
2.47 (4H, 2ꢁCH2CH2N), 1.73 (4H, 2ꢁCH2CH2N), 1.37 (s, 9H, 3ꢁCH3).
(CHar), 53.7 (NCH2CH2NH), 53.4 (2ꢁCH2CH2N), 41.7 (NCH2CH2NH),
23.4 (2ꢁCH2CH2N). IR (film),
n
: 3326 (NH), 3096 (CAr–H), 2965–
2802 (C–H), 1676 (NH), 1541 (NO2), 1346 (SO2), 1169 (SO2). HRMS
(MþH)þ calcd for C12H18N3O4S, 300.1018; found, 300.1011.
3.3.3.1.2. N-[2-(1-Methylpyrrolidin-2-yl)ethyl]-2-nitro-
13C NMR (125 MHz, CDCl3):
d 167.9 (CO), 147.9 (Car), 133.6 (Car),
133.3 (CHar), 131.6 (CHar), 130.8 (CHar), 124.0 (CHar), 82.1 (C(CH3)3),
54.7 (COCH2N), 54.0 (2ꢁCH2CH2N), 49.3 (NCH2CH2NSO2), 46.8
benzenesulfonamide (10b). 1H NMR (500 MHz, CDCl3):
d
8.11 (1H,
(NCH2CH2NSO2), 27.8 (3ꢁCH3), 23.4 (2ꢁCH2CH2N). IR (film),
n:
Har), 7.83 (1H, Har), 7.73 (2H, 2ꢁHar), 3.23 (1H, CH2CH2NH), 3.16 (1H,
CH2CH2NH), 3.10 (1H, NCH2CH2CH2CH), 2.43 (1H, NCH2CH2CH2CH),
2.32 (s, 3H, NCH3), 2.14 (1H, NCH2CH2CH2CH), 1,84 (2H, CH2CH2NH),
1.65 (2H, NCH2CH2CH2CH), 1.65–1.40 (2H, NCH2CH2CH2CH). 13C
3107–3087 (CAr–H), 2975–2796 (C–H), 1740 (CO), 1543 (NO2), 1371
(NO2), 1352 (SO2),1158 (SO2). HRMS (MþH)þ calcd for C18H28N3O6S,
414.1699; found, 414.1691.
3.3.3.2.2. tert-Butyl [[2-(1-methylpyrrolidin-2-yl)ethyl]-(2-nitro-
NMR (125 MHz, CDCl3): d 148.0 (Car), 133.7 (Car), 133.2 (CHar), 132.4
benzenesulfonyl)amino] acetate (11b). 1H NMR (500 MHz, CDCl3):
(CHar), 130.8 (CHar), 125.0 (CHar), 64.2 (NCH2CH2CH2CH), 56.8
(NCH2CH2CH2CH), 40.5 (NCH3), 40.3 (CH2CH2NH), 28.8
(CH2CH2NH), 28.2 (NCH2CH2CH2CH), 22.6 (NCH2CH2CH2CH). IR
d
8.09 (1H, Har), 7.69 (2H, 2ꢁHar), 7.61 (1H, Har), 4.18 (s, 2H,
COCH2N), 3.44 (t, J¼7.3 Hz, 2H, CH2CH2NSO2), 3.05 (t, J¼7 Hz, 1H,
NCH2CH2CH2CH), 2.26 (s, 3H, NCH3), 2.14 (2H, NCH2CH2CH2CH),
1,94 (2H, CH2CH2NSO2), 1.70 (2H, NCH2CH2CH2CH), 1.50–1.40 (2H,
NCH2CH2CH2CH), 1.38 (s, 9H, 3ꢁCH3). 13C NMR (125 MHz, CDCl3):
(film), n: 3346 (NH), 3097–3024 (CAr–H), 2970–2800 (C–H), 1671
(NH), 1538 (NO2), 1338 (SO2), 1162 (SO2). HRMS (MþH)þ calcd for
C13H20N3O4S, 314.1175; found, 314.1172.
d
167.6 (CO), 147.9 (Car), 133.5 (Car), 133.4 (CHar), 131.6 (CHar), 130.8
3.3.3.1.3. N-(2-Diethylaminoethyl)-2-nitrobenzenesulfonamide
(CHar), 124.0 (CHar), 82.3 (C(CH3)3), 63.4 (NCH2CH2CH2CH), 57.0
(NCH2CH2CH2CH), 48.3 (COCH2N), 45.6 (CH2CH2NSO2), 40.3 (NCH3),
31.5 (NCH2CH2CH2CH), 30.3 (CH2CH2NSO2), 27.9 (3ꢁCH3), 21.9
(10c). 1H NMR (500 MHz, CDCl3):
d 8.14 (1H, Har), 7.87 (1H, Har),
7.75 (2H, 2ꢁHar), 5.02 (br s, 1H, NH), 3.09 (t, J¼6 Hz, NCH2CH2NH),
2.55 (t, J¼6 Hz, NCH2CH2NH), 2.39 (q, J¼7.2 Hz, 4H, 2ꢁCH3CH2N),
(NCH2CH2CH2CH). IR (film), n: 3097–3073 (CAr–H), 2972–2780 (C–

J. Messeguer et al. / Tetrahedron 66 (2010) 2444–2454
2453
H), 1744 (CO), 1544 (NO2), 1371 (NO2), 1351 (SO2), 1160 (SO2). HRMS
(MþH)þ calcd for C19H30N3O6S, 428.1855; found, 428.1842.
3.3.3.2.3. tert-Butyl [(2-diethylaminoethyl)-(2-nitrobenzene-
d 172.4 (CO), 149.6 (Car), 135.6 (CHar), 133.3 (CHar), 133.2 (Car), 131.6
(CHar), 125.5 (CHar), 68.0 (NCH2CH2CH2CH), 57.3 (NCH2CH2CH2CH),
50.0 (COCH2N), 47.9 (CH2CH2NSO2), 40.1 (NCH3), 30.7
(NCH2CH2CH2CH), 30.3 (CH2CH2NSO2), 22.5 (NCH2CH2CH2CH).
HRMS (MþH)þ calcd for C15H22N3O6S, 372.1229; found, 372.1237.
3.3.3.3.3. [(2-Diethylaminoethyl)-(2-nitrobenzenesulfonyl)-
sulfonyl)amino]acetate (11c). 1H NMR (500 MHz, CDCl3):
d 8.09
(1H, Har), 7.68 (2H, 2ꢁHar), 7.60 (1H, Har), 4.23 (s, 2H, COCH2N), 3.47
(t, J¼6.8 Hz, 2H, NCH2CH2NSO2), 2.63 (t, J¼6.8 Hz, 2H,
NCH2CH2NSO2), 2.48 (q, J¼7.2 Hz, 4H, 2ꢁCH3CH2N), 1.37 (s, 9H,
3ꢁCH3), 0.98 (t, J¼7.2 Hz, 6H, 2ꢁCH3CH2N). 13C NMR (125 MHz,
amino]acetic acid (12c). 1H NMR (500 MHz, D2O):
d
7.96 (d, J¼7.5 Hz,
Har), 7.82–7.76 (3H, 3ꢁHar), 4.24 (s, 2H, COCH2N), 3.77 (t, J¼6.5 Hz,
2H, NCH2CH2NSO2), 3.38 (t, J¼6.5 Hz, 2H, NCH2CH2NSO2), 3.24 (4H,
2ꢁCH3CH2N), 1.24 (t, J¼7 Hz, 6H, 2ꢁCH3CH2N). 13C NMR (125 MHz,
CDCl3):
d 168.0 (CO), 147.9 (Car), 133.6 (Car), 133.3 (CHar), 131.6
(CHar), 130.7 (CHar), 124.0 (CHar), 82.0 (C(CH3)3), 52.2 (COCH2N),
49.5 (NCH2CH2NSO2), 47.2 (2ꢁCH3CH2N), 46.2 (NCH2CH2NSO2),
D2O):
d 172.9 (CO), 147.5 (Car), 135.6 (CHar), 133.2 (CHar), 130.2 (Car),
27.8 (3ꢁCH3), 11.8 (2ꢁCH3CH2N). IR (film),
n
: 3094–3074 (CAr–H),
130.1 (CHar), 125.2 (CHar), 52.2 (COCH2N), 50.1 (NCH2CH2NSO2), 46.5
(2ꢁCH3CH2N), 45.7 (NCH2CH2NSO2), 8.0 (2ꢁCH3CH2N). HRMS
(MþH)þ calcd for C14H22N3O6S, 360.1229; found, 360.1222.
3.3.3.3.4. [(2-Nitrobenzenesulfonyl)-(2-phenethyl)amino]acetic
2979–2812 (C–H), 1742 (CO), 1543 (NO2), 1369 (NO2), 1353 (SO2),
1155 (SO2). HRMS (MþH)þ calcd for C18H30N3O6S, 416.1855; found,
416.1850.
3.3.3.2.4. tert-Butyl [(2-nitrobenzenesulfonyl)-(2-phen-
acid (12d). 1H NMR (500 MHz, CDCl3)H NMR:
d
8.00 (dd, J1¼7.5 Hz,
ethyl)amino]acetate (11d). 1H NMR (500 MHz, CDCl3):
d
8.04 (1H,
J2¼2 Hz, 1H, Har), 7.65 (2H, 2ꢁHar), 7.59 (dd, J1¼7.5 Hz, J2¼1.5 Hz,
1H, Har), 7.23 (2H, 2ꢁHar), 7.17 (2H, 2ꢁHar), 7.13 (d, J¼7 Hz, 1H, Har),
4.15 (s, 2H, COCH2N), 3.61 (t, J¼7.5 Hz, 2H, CH2CH2NSO2), 2.86 (t,
Har), 7.65 (2H, 2ꢁHar), 7.58 (1H, Har), 7.26 (2H, 2ꢁHar), 7.20 (1H, Har),
7.16 (2H, 2ꢁHar), 4.05 (s, 2H, COCH2N), 3.63 (t, J¼7.6 Hz, 2H,
CH2CH2NSO2), 2.89 (t, J¼7.6 Hz, 2H, CH2CH2NSO2), 1.37 (s, 9H,
J¼7.5 Hz, 2H, CH2CH2NSO2). 13C NMR (125 MHz, CDCl3):
d 173.6
3ꢁCH3). 13C NMR (125 MHz, CDCl3):
d
167.7 (CO), 147.8 (Car), 137.8
(CO), 147.7 (Car), 137.6 (Car), 133.7 (CHar), 133.0 (Car), 131.8 (CHar),
130.8 (CHar), 128.7 (2ꢁCHar), 128.6 (2ꢁCHar), 126.8 (CHar), 124.3
(CHar), 50.1 (COCH2N), 48.1 (CH2CH2NSO2), 34.7 (CH2CH2NSO2).
HRMS (MþH)þ calcd for C16H17N2O6S, 365.0807; found, 365.0799.
3.3.3.3.5. [(2-(2,4-Dichlorophenyl)ethyl)-(2-nitrobenzene-
(Car), 133.5 (Car), 133.3 (CHar), 131.7 (CHar), 130.8 (CHar), 128.7
(2ꢁCHar), 128.6 (2ꢁCHar), 126.7 (CHar), 124.0 (CHar), 82.3 (C(CH3)3),
50.0 (COCH2N), 49.0 (CH2CH2NSO2), 34.8 (CH2CH2NSO2), 27.9
(3ꢁCH3). IR (film),
n: 3095–3004 (CAr–H), 2984–2876 (C–H), 1740
(CO), 1545 (NO2), 1366 (NO2), 1350 (SO2), 1159 (SO2). HRMS (MþH)þ
sulfonyl)amino]acetic acid (12e). 1H NMR (500 MHz, CDCl3):
d 8.00
calcd for C20H25N2O6S, 421.1433; found, 421.1441.
(dd, J1¼8 Hz, J2¼1 Hz,1H, Har), 7.72–7.60 (3H, 3ꢁHar), 7.23 (s,1H, Har),
7.13 (d, J¼8 Hz, 1H, Har), 7.07 (d, J¼8 Hz, 1H, Har), 4.25 (s, 2H,
COCH2N), 3.62 (t, J¼7.5 Hz, 2H, CH2CH2NSO2), 2.97 (t, J¼7.5 Hz, 2H,
3.3.3.2.5. tert-butyl [(2-(2,4-dichlorophenyl)ethyl)-(2-nitrobenz-
enesulfonyl)amino]acetate (11e). 1H NMR (500 MHz, CDCl3):
d 8.03
(d, J¼7.4 Hz, 1H, Har), 7.65 (2H, 2ꢁHar), 7.58 (d, J¼7.4 Hz, 1H, Har),
7.26 (s, 1H, Har), 7.15 (d, J¼8 Hz, 2H, 2ꢁHar), 7.09 (d, J¼8 Hz, 2H,
2ꢁHar), 4.11 (s, 2H, COCH2N), 3.61 (t, J¼7.4 Hz, 2H, CH2CH2NSO2),
2.98 (t, J¼7.4 Hz, 2H, CH2CH2NSO2), 1.40 (s, 9H, 3ꢁCH3). 13C NMR
CH2CH2NSO2). 13C NMR (125 MHz, CDCl3):
d 174.1 (CO), 147.5 (Car),
134.4 (Car), 133.8 (CHar), 133.7 (Car), 133.4 (Car), 132.9 (Car), 132.1
(CHar), 131.9 (CHar), 130.9 (CHar), 129.3 (CHar), 127.3 (CHar), 124.4
(CHar), 48.0 (COCH2N), 47.8 (CH2CH2NSO2), 31.8 (CH2CH2NSO2).
HRMS (MþH)þ calcd for C16H15Cl2N2O6S, 433.0028; found, 433.0019.
(125 MHz, CDCl3):
d 167.6 (CO), 147.7 (Car), 139.2 (Car), 134.5 (Car),
133.9 (Car), 133.4 (CHar), 133.3 (Car), 132.1 (CHar), 131.7 (CHar), 130.9
(CHar), 129.3 (CHar), 127.3 (CHar), 124.1 (CHar), 82.5 (C(CH3)3), 48.8
(COCH2N), 47.7 (CH2CH2NSO2), 31.9 (CH2CH2NSO2), 27.9 (3ꢁCH3). IR
3.3.3.4. Application to the synthesis of 1. A mixture of 100 g of
Fmoc-Rink-Amide AM Polystyrene Resin (0.79 mmol/g resin,
0.08 mmol) and 3 mL of 20% piperidine in DMF was stirred for
30 min at room temperature. The resin was filtered and washed
with DMF (3ꢁ3 mL), isopropyl alcohol (3ꢁ3 mL) and CH2Cl2
(3ꢁ3 mL). Then, the resin was treated with a solution of chloracetic
(film), n: 3094–3008 (CAr–H), 2984–2870 (C–H), 1743 (CO), 1541
(NO2), 1368 (NO2), 1351 (SO2), 1167 (SO2). HRMS (MþH)þ calcd for
C20H23Cl2N2O6S, 489.0654; found, 489.0643.
3.3.3.3. General procedure for esters hydrolysis (12a–e). To a so-
lution of the corresponding nosyl substituted aminoacetate (11a–e)
(7 mmol) in 30 mL of CH2Cl2, 30 mL of TFA was added. The mixture
was stirred for 3 h at room temperature and the solvent was
evaporated to dryness to give the desired acid. For compounds
d and e, the residue obtained was recrystallised from CH2Cl2/hex-
ane (yield 75–85%)
acid (38 mg, 5 equiv) and DIC (61 mL, 5 equiv) in 2:1 CH2Cl2/DMF
(3 mL). The reaction mixture was stirred for 30 min at room tem-
perature. The resin was filtered and the reaction was repeated
under the same conditions. Afterwards, the resin was drained and
washed with DMF (3ꢁ3 mL), isopropyl alcohol (3ꢁ3 mL) and
CH2Cl2 (3ꢁ3 mL). A solution of 2-(1-methyl-2-pyrrolidinyl)ethyl-
amine (58 mL, 5 equiv) and triethylamine (28 mL, 5 equiv) in 3 mL of
3.3.3.3.1. [(2-Nitrobenzenesulfonyl)-(2-pyrrolidin-1-ylethyl)ami-
DMF was added to the resin and the suspension was stirred for 3 h
at room temperature. The supernatant was removed and the re-
action was repeated under the same conditions. Then, the resin was
filtered and washed with DMF (3ꢁ3 mL), isopropyl alcohol
(3ꢁ3 mL) and CH2Cl2 (3ꢁ3 mL). The resin was treated with a mix-
ture of acid 12a (84 mg, 3 equiv), HATU (150 mg, 5 equiv) and DIEA
no]acetic acid (12a). 1H NMR (500 MHz, D2O):
d 8.03 (1H, Har),
7.90–7.85 (3H, 3ꢁHar), 4.31 (s, 2H, COCH2N), 3.85 (t, J¼6 Hz, 2H,
NCH2CH2NSO2), 3.79 (2H, CH2CH2N), 3.51 (t, J¼6 Hz, 2H,
NCH2CH2NSO2), 3.18 (2H, CH2CH2N), 2.17 (2H, 2ꢁCH2CH2N), 2.05
(2H, 2ꢁCH2CH2N). 13C NMR (125 MHz, D2O):
d 173.0 (CO), 147.5
(Car),135.5 (CHar),133.3 (CHar),130.3 (Car),130.0 (CHar),125.2 (CHar),
54.8 (2ꢁCH2CH2N), 52.9 (COCH2N), 49.4 (NCH2CH2NSO2), 46.2
(NCH2CH2NSO2), 22.9 (2ꢁCH2CH2N). HRMS (MþH)þ calcd for
C14H20N3O6S, 358.1073; found, 358.1067.
(68 mL, 3 equiv) in DMF (1.5 mL). The reaction mixture was stirred
for 1.5 h at room temperature. The resin was filtered and the re-
action was repeated at the same conditions The resin was drained
and washed with DMF (3ꢁ3 mL), isopropyl alcohol (3ꢁ3 mL) and
3.3.3.3.2. [[2-(1-Methylpyrrolidin-2-yl)ethyl]-(2-nitrobenzene-
CH2Cl2 (3ꢁ3 mL), treated with a solution of thiophenol (40
m
m
L,
L,
sulfonyl)amino]acetic acid (12b). 1H NMR (500 MHz, CD3OD):
d
8.07
0.1 equiv) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, 60
(dd, J1¼7.5 Hz, J2¼2 Hz, 1H, Har), 7.82 (2H, Har), 7.77 (dd, J1¼7.5 Hz,
J2¼2 Hz, 1H, Har), 4.22 (s, 2H, COCH2N), 3.67 (1H, NCH2CH2CH2CH),
3.57 (2H, CH2CH2NSO2), 3.45 (1H, NCH2CH2CH2CH), 3.16 (1H,
NCH2CH2CH2CH), 2.94 (s, 3H, NCH3), 2.49 (1H, CH2CH2NSO2), 2.32
(1H, NCH2CH2CH2CH), 2.16–2.02 (2H, NCH2CH2CH2CH),1.79 (2H, 1H
CH2CH2NSO2 and 1H NCH2CH2CH2CH). 13C NMR (125 MHz, CD3OD):
5 equiv) in 1.5 mL of DMF, and the mixture was allowed to react for
30 min at room temperature. The supernatant was removed and
the residue was drained and washed with DMF (3ꢁ3 mL), isopropyl
alcohol (3ꢁ3 mL) and CH2Cl2 (3ꢁ3 mL). The resin was coupled to
acid 12c, and the nosyl group deprotected as described above. After
washing, the cleavage step was carried out by treatment with

2454
J. Messeguer et al. / Tetrahedron 66 (2010) 2444–2454
10. Humet, M.; Carbonell, T.; Masip, I.; Sa´nchez-Baeza, F.; Mora, P.; Canto´n, E.;
a mixture of 60:40:2 TFA/CH2Cl2/water (3 mL) for 30 min at room
temperature. The crude reaction mixture was filtered, the filtrates
were pooled and the solvent was removed by evaporation under
reduced pressure to give 34 mg of the desired compound after
lyophilisation. The product was purified by semipreparative RP-
HPLC using aqueous acetonitrile gradient to obtain 11.3 mg of 1
(29% yield, 98% purity).
´
´
Gobernado, M.; Abad, C.; Perez-Paya, E.; Messeguer, A. J. Comb. Chem. 2003, 5,
597–605.
´
´
´
11. Masip, I.; Cortes, N.; Abad, M. J.; Guardiola, M.; Perez-Paya, E.; Ferragut, J.;
Ferrer-Montiel, A.; Messeguer, A. Bioorg. Med. Chem. 2005, 13, 1929–1936.
12. Messeguer, J.; Corte´s, N.; Garcı´a-Sanz, N.; Navarro-Vendrell, G.; Ferrer-Montiel,
A.; Messeguer, A. J. Comb. Chem. 2008, 10, 974–980.
13. Kruijtzer, J. A.; Nijenhuis, W. A.; Wanders, N.; Gispen, W. H.; Liskamp, R. M.;
Adan,
R. A. J. Med. Chem. 2005, 48, 4224–4230.
14. Wender, P. A.; Mitchell, D. J.; Pattabiraman, K.; Pelkey, E. T.; Steinman, L.;
Rothbard, J. B. T. Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 13003–13008.
15. Schro¨der, T.; Niemeier, N.; Afonin, S.; Ulrich, A. S.; Krug, H. F.; Bra¨se, S. J. Med.
Chem. 2008, 51, 376–379.
Acknowledgements
16. Vercillo, O. E.; Rade, C. K. Z.; Wessjohann, L. A. Org. Lett. 2008, 10, 205–208.
17. Hara, T.; Durrell, S. R.; Myers, M. C.; Appella, D. H. J. Am. Chem. Soc. 2006, 128,
1995–2004.
18. Lim, H. S.; Archer, C. T.; Kodadek, T. J. Am. Chem. Soc. 2007, 129, 7750–7751.
19. Wrenn, S. J.; Weisinger, R. M.; Halpin, D. R.; Harbury, P. B. J. Am. Chem. Soc. 2007,
129, 13137–13143.
20. Daelemans, D.; Schols, D.; Witvrouw, M.; Pannecouque, C.; Hatse, S.; Van
Dooren, S.; Hamy, F.; Klimkait, T.; De Clercq, E.; Vandamme, A.-M. Mol. Phar-
macol. 2000, 57, 116–124.
Financial support from Ministry of Science and Innovation
(Grant CTQ 2005-00995 and SAF2008-00048 to A.M.), MICINN,
Instituto Carlos Tercero and Generalitat de Catalunya (SGR2009-
366, to J.A.D.R.), Fundacio Marato TV3 and Spanish Ministry of
Education and Science (SAF2005-0171 and BFU2008-3980 to E.S.).
Supplementary data
21. Hamy, F.; Felder, E. R.; Heizmann, G.; Lazdins, J.; Aboul-ela, F.; Varani, G.; Karn,
J.; Klimkait, T. Proc. Natl. Acad. Sci. U.S.A. 1997, 94, 3548–3553.
22. Murphy, J. E.; Uno, T.; Hamer, J. D.; Cohen, F. E.; Dwarki, V.; Zuckermann, R. N.
Proc. Natl. Acad. Sci. U.S.A. 1998, 95, 1517–1522.
23. Malet, G.; Martı´n, A.; Orza´ez, M.; Vicent, M. J.; Masip, I.; Sanclimens, G.; Min-
garro, I.; Ferrer-Montiel, A.; Messeguer, A.; Fearnhead, H. O.; Pe´rez-Paya´, E. Cell
Death Differ. 2006, 13, 1523–1532.
Study of the reaction conditions for the coupling of Ns-protected
N-alkylglycines with primary amines containing an additional ter-
tiary amino residue. Supplementary data associated with this article
can be found in the online version, at doi:10.1016/j.tet.2010.01.090.
24. Lim, H.-S.; Archer, C. T.; Kim, Y.-C.; Hutchens, T.; Kodadek, T. Chem. Commun.
2008, 1064–1066.
References and notes
25. Che´dotal, A.; Del Rio, J. A.; Ruiz, M.; He, Z.; Borrell, V.; de Castro, F.; Ezan, F.;
Goodman, C. S.; Tessier-Lavigne, M.; Sotelo, C.; Soriano, E. Development 1998,
125, 4313–4323.
26. Montolio, M.; Messeguer, J.; Masip, I.; Guijarro, P.; Del Rio, J. A.; Messeguer, A.;
Soriano, E. Chem. Biol. 2009, 16, 691–701.
27. Simon, R. J.; Kania, R.; Zuckermann, R. N.; Hueber, V. D.; Jewell, D. A.; Banville,
S.; Ng, S.; Wang, L.; Rosenberf, S.; Marlowe, C. K.; Spellmeyer, D. C.; Tan, R.;
Frankel, A. D.; Santi, D. V.; Cohen, F. E.; Bartlett, P. A. Proc. Natl. Acad. Sci. U.S.A.
1992, 89, 9367–9371.
28. Zuckermann, R. N.; Kerr, J. M.; Kent, S. B. H.; Moos, W. H. J. Am. Chem. Soc. 1992,
114, 10646–10647.
1. Miller, S. M.; Simon, R. J.; Ng, S.; Zuckermann, R. N.; Kerr, J. M.; Moss, W. H.
Bioorg. Med. Chem. Lett. 1994, 4, 2657–2662.
2. Yoo, B.; Kirshenbaum, K. Curr. Opin. Chem. Biol. 2008, 12, 714–721.
3. Fowler, S. A.; Blackwell, H. E. Org. Biomol. Chem. 2009, 7, 1508–1524.
4. Udugamasooriya, A. D.; Dineen, S. P.; Brekken, R. A.; Kodadek, T. J. Am. Chem.
Soc. 2008, 130, 5744–5752.
5. Lee, B. C.; Zuckermann, R. N.; Dill, K. A. J. Am. Chem. Soc. 2008, 130, 8847–8855.
6. Ruijtenbeek, R.; Kruijtzer, J. A.; van de Wiel, W.; Fisher, M. J. E.; Flu¨ck, M.;
Redegeld, F. A. M.; Liskamp, R. M. J.; Nijkamp, F. P. ChemBioChem 2001, 2,171–179.
7. Goodson, B.; Ehrhardt, A.; Ng, S.; Nuss, J.; Johnson, K.; Giedlin, M.; Yamamoto,
R.; Moos, W. H.; Krebber, A.; Ladner, M.; Giacona, M. B.; Vitt, C.; Winter, J.
Antimicrob. Agents Chemother. 1999, 43, 1429–1434.
29. Figliozzi, G. M.; Goldsmith, R.; Ng, S.; Banville, S. C.; Zuckermann, R. N. Methods
Enzymol. 1996, 267, 437–447.
´
´
´
30. Masip, I.; Ferrandiz-Huertas, C.; Garcıa-Martınez, C.; Ferragut, J. A.; Ferrer-
Montiel, A.; Messeguer, A. J. Comb. Chem. 2004, 6, 135–141.
8. Ng, S.; Goodson, B.; Ehrhard, A.; Moos, W. H.; Siani, M.; Winter, J. Bioorg. Med.
Chem. 1999, 7, 1781–1785.
9. Simpson, L. S.; Burdine, L.; Dutta, A. K.; Feranchak, A. P.; Kodadek, T. J. Am. Chem.
Soc. 2009, 131, 5760–5762.
31. Kruijtzer, J. A. W.; Liskamp, R. M. J. Tetrahedron Lett. 1995, 36, 6969–6972.
32. Kruijtzer, J. A.; Hofmeyer, L. J. F.; Heerma, W.; Versluis, C.; Liskamp, R. M. J.
Chem.dEur. J. 1998, 4, 1570–1580.