Solid-phase synthesis of oligourea peptidomimetics employing the Fmoc protection strategy

Article abstract of DOI:10.1021/jo010656q

A solid-phase-Fmoc-based-synthesis strategy is described for oligourea peptidomimetics as well as a convenient general synthesis approach for the preparation of the required building blocks 5a-j and 5k. These are suitable for use in peptide or robot synthesizers, which is illustrated by the synthesis of oligourea peptidomimetics of part of Leu-enkephalin (10) and a neurotensin derivative (17).

Full text of DOI:10.1021/jo010656q

8454
J . Org. Chem. 2001, 66, 8454-8462
Solid -P h a se Syn th esis of Oligou r ea P ep tid om im etics Em p loyin g
th e F m oc P r otection Str a tegy
Astrid Boeijen, J eroen van Ameijde, and Rob M. J . Liskamp*
Department of Medicinal Chemistry, Utrecht Institute for Pharmaceutical Sciences, Utrecht University,
P.O. Box 80082, NL-3508 TB Utrecht, The Netherlands
R.M.J .Liskamp@pharm.uu.nl
Received J une 26, 2001
A solid-phasesFmoc-basedssynthesis strategy is described for oligourea peptidomimetics as well
as a convenient general synthesis approach for the preparation of the required building blocks
5a -j and 5k . These are suitable for use in peptide or robot synthesizers, which is illustrated by
the synthesis of oligourea peptidomimetics of part of Leu-enkephalin (10) and a neurotensin
derivative (17).
In tr od u ction
ing blocks is just as important as the construction of the
oligomeric structure. Burgess et al.8 were the first to
describe a solid-phase synthesis of oligourea peptidomi-
metics, employing phthalimido-protected isocyanates as
monomers. Subsequently, Schultz and co-workers devel-
oped an elegant procedure using azido 4-nitrophenyl
carbamate monomers.9 Recently, we developed a proce-
dure for the solid-phase synthesis of oligoureas featuring
Boc-protected monomers.10 Boc-protected monomers were
also used for solution synthesis of oligoureas.11
However, none of the procedures mentioned above are
completely compatible with the solid-phase synthesis of
peptides using Fmoc-protected amino acids, which is
more often becoming the standard. Certainly, the Fmoc
protection strategy is very attractive, since Fmoc groups
can be removed using mildly basic conditions and their
cleavage monitored by UV.12,13 The latter is very impor-
tant for establishing the progress of a solid-phase syn-
thesis. Moreover, when using the Fmoc protection strat-
egy, acid-labile groups can be used for protection of the
side chains. As a consequence, final deprotection and
cleavage from the resin can be carried out under less
vigorous conditions than is the case using, e.g., the Boc
protection strategy.
Oligopeptidomimetics are interesting not only as “fol-
damers” 1 capable of folding into defined three-dimen-
sional structures similar to those of natural peptides,2
but also in view of noteworthy as well as promising
biological properties. Recent examples illustrate and
underline this perspective. Degrado et al. have published
the de novo design of antibacterial â-peptides.3 Wender
and Rothbard and their co-workers have shown that
peptoid peptidomimetics can serve as molecular trans-
porters by enabling or enhancing the cellular uptake of
agents.4 A third example is targeting RNA using oligo-
urea peptidomimetics.5
In the last years, we have spent considerable effort on
developing convenient and reliable syntheses for oligo-
peptidomimetics. This has resulted in the solid-phase
syntheses of peptoids using Fmoc-protected N-substituted
glycines6 and, more recently, in a practical solid-phase
synthesis of oligopeptidosulfonamide foldamers using
N-Fmoc-protected â-aminoethanesulfonyl chlorides.7 In
addition, we have been interested for quite some time in
developing a synthesis strategy for oligourea peptidomi-
metics. As is the case with the synthesis of other
oligopeptidomimetics, the synthesis of the required build-
Therefore, we describe in this paper a convenient
general method for the synthesis of Fmoc-protected urea
monomers, including examples having functional side
chains, as well as their incorporation into oligourea
peptidomimetics. Use of the Fmoc group also makes these
monomers fully compatible with usage of standard Fmoc-
protected amino acids or other Fmoc-protected building
blocks.7,14 Thus, urea-peptide hybrids can be synthe-
sized, but “mixed” peptidomimetics are accessible as well.
* To whom correspondence should be addressed. Fax: (+31)30-
2536655.
(1) The term “foldamer” was coined by Gellman: Borman, S. Chem.
Eng. News 1997 (J une 16), 32. Gellman, S. H. Acc. Chem. Res. 1998,
31, 173.
(2) See, e.g.: (a) Appella, H.; Christianson, L. A.; Klein, D. A.;
Richards, M. R.; Powell, D. R.; Gellman, S. H. J . Am. Chem. Soc. 1996,
118, 13071. (b) Seebach, D.; Ciceri, P.; Overhand, M.; J uan, B.; Rigo,
D.; Oberer, L.; Hommel, U.; Amstutz, R.; Widmer, H. Helv. Chim. Acta
1996, 79, 2043. (c) Seebach, D.; Matthews, J . L. Chem. Commun. 1997,
2015. (d) Appella, H.; Christianson, L. A.; Klein, D. A.; Richards, M.
R.; Powell, D. R.; Gellman, S. H. J . Am. Chem. Soc. 1999, 121, 7574.
(e) Wang, X.; Espinosa, J . F.; Gellman, S. H. J . Am. Chem. Soc. 2000,
122, 4821.
(8) Burgess, K.; Linthicum, S. S.; Shin, H. Angew. Chem., Int. Ed.
Eng. 1995, 34, 907-909. Burgess, K.; Ibarzo, J .; Linthicum, S. D.;
Russell, D. H.; Shin, H.; Shitankoon, A.; Totani, R.; Zhang, A. J . J .
Am. Chem. Soc 1997, 119, 1556-1564.
(9) Kim, J .-M.; Bi, Y.; Paikoff, S. J .; Schultz, P. G. Tetrahedron Lett.
1996, 37, 5305-5308.
(10) Boeijen, A.; Liskamp, R. M. J . Eur. J . Org. Chem. 1999, 2127-
2135.
(11) Guichard, G.; Semetey, V.; Didierjean, C.; Aubry, A.; Briand,
J . P.; Rodriguez, M. J . Org. Chem. 1999, 64, 8702-8705.
(12) Atherton, E.; Sheppard, R. C. In Solid-Phase Peptide Synthesis;
Rickwood, D., Hames, B. D., Eds.; IRL Press: Oxford, 1989.
(13) Chan, W. C., White, P. D., Eds. Fmoc Solid-Phase Peptide
Synthesis; Oxford University Press: Oxford, 2000.
(3) Hamuro, Y.; Schneider, J . P.; DeGrado, W. F. J . Am. Chem. Soc.
1999, 121, 12200-12201.
(4) Wender, P. A.; Mitchell, D. J .; Pattabiraman, K.; Pelkey, E. T.;
Steinman, L.; Rothbard, J . B. Proc. Natl. Acad. Sci. U.S.A. 2000, 97,
130003-13008.
(5) Tamilarasu, N.; Huq, I.; Rana, T. M. Bioorg. Med. Chem. Lett.
2001, 11, 505-507.
(6) Kruijtzer, J . A. W.; Hofmeyer, L. J . F.; Heerma, W.; Versluis,
C.; Liskamp, R. M. J . Chem. Eur. J . 1998, 4, 1570-1580.
(7) Monnee, M. C. F.; Marijne, M. F.; Brouwer, A. J .; Liskamp, R.
M. J . Tetrahedron Lett. 2000, 41, 7991-7995.
10.1021/jo010656q CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/17/2001

Solid-Phase Synthesis of Oligourea Peptidomimetics
J . Org. Chem., Vol. 66, No. 25, 2001 8455
Sch em e 1. Syn th esis of F m oc-P r otected Ur ea Mon om er s 5a -j
Sch em e 2. Syn th esis of F m oc-P r otected Glycin e Ur ea Mon om er 5k
A further advantage of this strategy is the ability to use
an earlier developed procedure.16 Subsequently, amine
7 was Fmoc-protected with Fmoc-OSu, after which the
Boc group in bisprotected amine 8 was removed with
HCl/ether. Finally, amine 4k was converted to carbamate
5k by reaction with 4-nitrophenyl carbamate, as was
described above.
these monomers on (commercial) automated (peptide)
synthesizers. Monitoring of the progress and validation
of the solid-phase synthesis is demonstrated by the solid-
phase synthesis of oligourea peptidomimetics of part of
Leu-enkephalin and a neurotensin derivative.
Au tom a ted Solid -P h a se Syn th esis of Ur ea Oligo-
m er s. Oligourea peptidomimetic 10 of the tetrapeptide
sequence Gly-Gly-Phe-Leu 9 (part of the endorphin Leu-
enkephalin) was chosen as a model compound to deter-
mine the appropriate procedures for automated synthesis
of oligourea peptidomimetics (Figure 1).
The synthesis was carried out on a commercial auto-
matic peptide synthesizer, and the urea oligomer was
prepared on Argogel Rink-N(H)-Fmoc (“Argogel S-Ram”)
resin (0.33 mmol/g, 0.73 g, 0.25 mmol) using the protocol
of the synthesizer for a 0.25 mmol scale. The general
procedure for the solid-phase synthesis of oligoureas
using Fmoc-protected monomers is depicted in Scheme
3. Prior to coupling of the first monomer, the Fmoc group
in resin 11 was removed with piperidine to afford 12.
In earlier investigations on the solid-phase synthesis
of oligoureas using Boc-protected monomers,10 it was
found that treatment of a resin-bound amine with 3 equiv
of a 4-nitrophenyl carbamate monomer and 3.5 equiv of
DiPEA for 3 h resulted in quantitative formation of the
desired urea compound. However, it was decided to follow
the standard synthesizer protocols as closely as pos-
sible: in each coupling step, the resin-bound amine (i.e.,
12 or 14) was treated with a solution of 4 equiv (1 mmol)
of urea monomer 5 and 8 equiv of DiPEA (2 mmol) in
NMP for 90 min (45 min when normal Fmoc-amino acids
are used). This corresponded to the number of equiva-
lents of an Fmoc-amino acid and DiPEA used in auto-
Resu lts a n d Discu ssion
P r ep a r a tion of Mon om er s. The required Fmoc-
protected monomers for the solid-phase synthesis of
oligourea peptidomimetics could be prepared in a rela-
tively straightforward manner (Scheme 1). First, an
Fmoc-protected amino acid (1) was converted into the
corresponding alcohol 2 according to Martinez et al.15
This alcohol was then transformed into the corresponding
azide 3 by a Mitsunobu reaction with hydrogen azide,
followed by reduction of the azide to amine 4 in the
presence of Pd on carbon. This amine was converted in
situ into its HCl salt by addition of chloroform to prevent
autocleavage of the Fmoc group. Initially, the crude HCl
salt 4 was directly converted to carbamate 5 with
4-nitrophenyl chloroformate using DiPEA as a base.
Later on, it became clear that HCl salt 4 was sufficiently
stable for isolation by precipitation prior to the prepara-
tion of carbamate 5. The Mitsunobu reaction step gave
appreciable variations in the yields, probably because of
difficulties in purifying the product. All reactions pro-
ceeded in satisfactory to good yields, and the end products
5a -j were stable white to yellow-white solids.
Glycine derivative 5k (Scheme 2) was prepared via a
slightly different route. First, amine 7 was prepared by
mono-Boc protection of ethylenediamine (6), according to
(14) Brouwer, A. J .; Monnee, M.; Liskamp. R. M. J . Synthesis 2000,
1579-1584.
(15) Rodriguez, M.; Llinares, M.; Doulut, S.; Heitz, A.; Martinez, J .
Tetrahedron Lett. 1991, 32, 923-926.
(16) Kruijtzer, J . A. W.; Lefeber, D. J .; Liskamp, R. M. J . Tetrahe-
dron Lett. 1997, 38, 5335-5338.

8456 J . Org. Chem., Vol. 66, No. 25, 2001
Boeijen et al.
F igu r e 2. UV monitoring profile of the synthesis of resin-
bound urea tetramer 15. (i) Fmoc cleavage of resin 11 to yield
12; (ii) Fmoc cleavage after coupling of Fmoc-Leuu-pNP (5c);
(iii) Fmoc cleavage after coupling of Fmoc-Pheu-pNP (5e); (iv)
Fmoc cleavage after coupling of Fmoc-Glyu-pNP (5k ); (v) Fmoc
cleavage after coupling of Fmoc-Glyu-pNP (5k ).
F igu r e 1. Structure of peptide Ac-Gly-Gly-Phe-Leu-NH2 (9)
and the corresponding oligourea mimic Ac-Glyu-Glyu-Pheu-
Leuu-NH2 (10).
mated solid-phase peptide synthesis. After each coupling
step, the remaining free amino groups were acetylated
(capping) with a solution of Ac2O, HOBt, and DiPEA in
NMP followed by removal of the Fmoc group using
piperidine (deprotection). The coupling efficiencies were
monitored by measuring the UV absorption of the diben-
zofulvene-piperidine adduct, which has an absorption
maximum at 301 nm. As is evident from the monitoring
profile (Figure 2), the synthesis of the urea oligomer
proceeded smoothly.
After coupling of the last monomer and removal of the
Fmoc protecting group to give resin-bound urea oligomer
15 (n ) 4 Scheme 3), the amino terminus was acetylated,
after which the compound was cleaved from the resin by
treatment with TFA/TIS/H2O/EDT (92.5/2.5/2.5/2.5) for
3 h. After precipitation from 1/1 MTBE/hexanes, oligo-
urea mimic 10 was obtained in 53% yield and in high
purity.
preparation of the urea oligopeptidomimetic of a neuro-
tensin derivative 8-13 (16).
The tridecapeptide neurotensin (NT) displays a variety
of biological effects, the most important of which are
located in the central nervous system (CNS). NT plays
important roles in thermoregulation, as a modulator of
dopamine neurotransmission, and in the perception of
pain.17 The highly conserved 8-13 region (i.e., H-Arg-
Arg-Pro-Tyr-Ile-Leu-OH, 16, Figure 3) shows potency
similar to or greater than that of NT itself in a variety
of in vitro binding and functional assays.17,18
Because replacement of arginine with lysine in NT
8-13 does not result in a substantial loss in biological
activity, we aimed for the preparation of an oligourea
derivative, viz., 17, in which the arginines of 16 are
replaced by lysine urea residues.19 Furthermore, it was
decided to prepare an oligomer in which the leucine-13
residue is not replaced by a urea monomer, since it has
been shown that a free carboxyl terminus is essential for
the biological activity.
Having established the procedure for the solid-phase
synthesis of oligourea peptidomimetics, we chose as a
second example a more difficult sequence for transforma-
tion into the corresponding urea peptidomimetic, viz.,
Sch em e 3. Gen er a l P r oced u r e for th e Solid -P h a se Syn th esis of Oligou r ea P ep tid om im etics

Solid-Phase Synthesis of Oligourea Peptidomimetics
J . Org. Chem., Vol. 66, No. 25, 2001 8457
oped. The monomers are conveniently accessible starting
from Fmoc-protected amino acids and are prepared and
can be stored as the stable, solid 4-nitrophenyl carbamate
derivatives.
The preparation of oligoureas using Fmoc-protected
monomers has the advantage that the oligomers can be
prepared on resins with acid-labile linkers such as the
Rink and Wang linkers which are standard in (auto-
mated) solid-phase peptide synthesis. Moreover, when
Fmoc-protected monomers are used, the efficiency of the
coupling reactions can be monitored by measuring the
UV absorption of the dibenzofulvene-piperidine adduct
which is formed after cleavage of the Fmoc group. Finally
and most importantly, a procedure employing Fmoc-
protected monomers enables the preparation of urea
peptidomimetics on automated peptide synthesizers with-
out any major adjustments in the synthesis protocols,
since the Fmoc protecting group is the standard in
automated peptide synthesis today. Thus, libraries of all-
urea peptidomimetics, peptide-urea peptidomimetic hy-
brids and of mixed peptidomimetics are easily accessible,
thereby greatly enhancing the potential of these com-
pounds for combinatorial chemistry purposes.
Exp er im en ta l Section
Gen er a l P r oced u r es. Unless stated otherwise, the chemi-
cals were obtained from commercial sources and used without
further purification. Argogel S-RAM and Argogel Wang-OH
were purchased from Argonaut (Muttenz, Switzerland). All
protected amino acids were purchased from Advanced Chemtech
(Machelen, Belgium). THF, NMP, and DCM were purchased
from Biosolve (Valkenswaard, The Netherlands). THF was
distilled immediately from LiAlH4 prior to use. NMP and DCM
were stored on molecular sieves (4 Å). Hexanes had a boiling
range of 60-80 °C. DiPEA and TEA were distilled from
ninhydrin and KOH. Pyridine was distilled from KOH. Column
chromatography was perfomed on Merck Kieselgel 60 (40-63
µm). NMR spectra were obtained at 300.1 and 75.5 MHz for
F igu r e 3. Structure of neurotensin 8-13 (16) and the
corresponding urea peptidomimetics 17 and 18.
The synthesis of 17 was carried out on Argogel Wang-
OH, which after cleavage with TFA will result in the
formation of a carboxyl group. Prior to the automated
synthesis, the leucine residue was esterified to the
hydroxyl group of the resin using the procedure of
Sieber.20 After completion of the synthesis according to
Scheme 3 and cleavage from the resin, a byproduct was
formed: an acid-catalyzed cyclization reaction resulted
in formation of the corresponding hydantoin 18 (Figure
3). The estimated ratio of linear and cyclic product was
2/1 (according to the HPLC peak areas). The formation
of hydantoins had been observed earlier as a base-
catalyzed reaction in the synthesis of oligourea peptido-
mimetics using Boc-protected monomers.10 However, in
contrast to the procedure using Boc-protected monomers
where the hydantoins were the only products, here the
hydantoin is a byproduct which can in principle be
separated from the linear compound with preparative
HPLC.
1
1H and 13C, respectively. H NMR: CDCl3 as solvent, TMS as
internal standard; [D6]DMSO as solvent, δΗ ) 2.50. 13C
NMR: CDCl3 as solvent, δÌ ) 77.0; [D6]DMSO as solvent, δÌ
) 39.5. FAB MS was performed on a four-sector spectrometer.
Analytical HPLC was performed using an automated HPLC
instrument equipped with an analytical reversed-phase col-
umn (Alltech Adsorbosphere C8, 5 µm, 250 × 4.6 mm) and a
UV detector operating at 220 nm. Elution was effected using
an appropriate gradient from 0.1% TFA in water to 0.085%
TFA in acetonitrile/water (95/5, v/v), at a flow rate of 1 mL
min-1. Preparative HPLC was performed using an automated
HPLC instrument equipped with a preparative reversed-phase
column (Alltech Adsorbosphere C8, 10 µm, 250 × 22 mm) and
a UV detector operating at 220 nm. Elution was effected using
an appropriate gradient from 0.1% TFA in water to 0.085%
TFA in acetonitrile/water (95/5, v/v), at a flow rate of 11.5 mL
min-1
.
This procedure was also excellently suitable for the
preparation of urea peptidomimetic-peptide hybrids as
was applied to a positional urea scan of 16.21
F m oc-P r otected Am in o Alcoh ols 2. Gen er a l P r oce-
d u r e. Fmoc-protected amino alcohols 2 were prepared accord-
ing to Martinez et al.15 A solution of Fmoc-protected amino
acid 1 (25 mmol) in DME (50 mL) was cooled to -15 °C (ice/
salt bath) under a nitrogen atmosphere. NMM (25 mmol, 2.78
mL, 1 equiv) and ICF (25 mmol, 3.40 mL, 1 equiv) were added
successively in a dropwise manner. After 1 h, the reaction
mixture was filtered. The filtrate was cooled to -15 °C (ice/
salt bath), and a solution of NaBH4 (37.5 mmol, 1.42 g, 1.5
equiv) in H2O (12.5 mL) was added in one portion, followed
by H2O (625 mL). After precipitation of the product, the
suspension was filtered. The residue was washed with H2O
and hexanes, and dried in a vacuum desiccator to give alcohol
2 as a white solid.
Con clu sion s
A procedure for the synthesis of oligourea peptidomi-
metics using Fmoc-protected monomers has been devel-
(17) Wustrow, D. J . Drugs Future 1995, 20, 1023-1031.
(18) Carraway, L.; Leeman, S. E. In Peptides: Chemistry, Structure
and Biology; Walter, R., Meienhofer, J ., Eds.; Ann Arbor Sciences: Ann
Arbor, MI, 1975; pp 679-685.
(19) Granier, C.; van Rietschoten, J .; Kitabgi, P.; Poustis, C.;
Frechet, P. J . Biochem. 1982, 124, 117-124.
(20) Sieber, P. Tetrahedron Lett. 1987, 28, 6147-6150
(21) Data not shown: Boeijen, A. Thesis, Utrecht University, The
Netherlands, 2000.
F m oc-P r otected Ala n in e Alcoh ol 2a (R ) CH3). Yield:
7.45 g (25.0 mmol, 100%) of white solid. Mp: 120 °C. Rf (5%

8458 J . Org. Chem., Vol. 66, No. 25, 2001
Boeijen et al.
MeOH/DCM): 0.43. [R]D24 ) -0.58 (c ) 1.02, CHCl3). 1H NMR
(CDCl3): δ ) 1.16 (d, J ) 6.2 Hz, 3 H, CH3), 2.46 (br s, 1 H,
OH), 3.57 (br m, 2 H, CH2OH), 3.81 (m, 1 H, CHNH), 4.20 (t,
J ) 5.9 Hz, 1 H, Fmoc CH), 4.41 (d, J ) 5.9 Hz, 2 H, Fmoc
CH2), 5.03 (d, J ) 7.7 Hz, 1 H, NH), 7.25-7.42 (m, 4 H, Fmoc
Ar CH), 7.58 (d, 2 H, Fmoc Ar CH), 7.76 (d, 2 H, Fmoc Ar
CH). 13C NMR (CDCl3): δ ) 17.2 (CH3), 47.2 (Fmoc CH), 48.9
(CHNH), 66.6 (CH2OH, Fmoc CH2), 119.9, 124.9, 127.0, 127.6
(Fmoc Ar CH), 141.3, 143.8 (Fmoc Ar quat C), 156.5 [C(O)].
Anal. Calcd for C18H19NO3 (297.35): C, 72.71; H, 6.44; N, 4.71.
Found: C, 72.59; H, 6.48; N, 4.65. ES MS: m/z ) 320.1 [M +
Na]+.
F m oc-P r otected Tyr osin e Alcoh ol 2f (R ) CH2C6H4-
OtBu ). Yield: 10.7 g (23.9 mmol, 95%) of white solid. Mp:
114-115 °C. Rf (5% MeOH/DCM): 0.43. [R]D ) -18.5 (c )
24
1.02, CHCl3). 1H NMR (CDCl3): δ ) 1.22 [s, 9 H, (CH3)3], 2.22
(d, J ) 6.9 Hz, 1 H, OH), 2.87 (d, J ) 6.2 Hz, 2H, CH2C6H5),
3.57 (m, 2 H, CH2OH), 3.89 (m, 1 H, CHNH), 4.18 (t, J ) 6.6
Hz, 1 H, Fmoc CH), 4.40 (m, 2 H, Fmoc CH2), 5.96 (br s, 1 H,
NH), 6.89-7.08 (m, 4 H, C6H4), 7.25-7.42 (m, 4 H, 4 · Fmoc
Ar CH), 7.55 (m, 2 H, Fmoc Ar CH), 7.75 (d, 2 H, J ) 7.3 Hz,
Fmoc Ar CH). 13C NMR (CDCl3): δ ) 28.7 [(CH3)3], 36.5
(CH2C6H5), 47.2 (Fmoc CH), 54.1 (CHNH), 63.8 (CH2OH), 66.6
(Fmoc CH2), 78.3 [C(CH3)3], 120.0 (Fmoc Ar CH), 124.3
(CH2C6H4), 125.0, 127.1, 127.8 (Fmoc Ar CH), 129.7 (C6H4),
132.4 (C6H4 quat C), 141.4, 144.0 (Fmoc Ar quat C), 154.2
(C6H4 quat C), 156.4 [C(O)]. Anal. Calcd for C28H31NO3
(445.56): C, 75.48; H, 7.01; N, 3.14. Found: C, 75.36; H, 7.05;
N, 3.06. ES MS: m/z ) 468.2 [M + Na]+.
F m oc-P r otected Va lin e Alcoh ol 2b [R ) CH(CH3)2].
Yield: 7.15 g (22.0 mmol, 88%) of white solid. Mp: 107-108
24
°C. Rf (5% MeOH/DCM): 0.44. [R]D ) -18.4 (c ) 1.02,
1
CHCl3). H NMR (CDCl3): δ ) 0.93 [t, 6 H, (CH3)2], 1.84 [m,
1 H, CH(CH3)2], 2.37 (br s, 1 H, OH), 3.55 (br m, 2 H, CH2-
OH), 3.81 (m, 1 H, CHNH), 4.21 (t, J ) 6.6 Hz, 1 H, Fmoc
CH), 4.43 (m, 2 H, Fmoc CH2), 5.03 (d, J ) 8.0 Hz, 1 H, NH),
7.26-7.42 (m, 4 H, Fmoc Ar CH), 7.58 (d, 2 H, Fmoc Ar CH),
7.76 (d, 2 H, Fmoc Ar CH). 13C NMR (CDCl3): δ ) 18.6 (CH3),
19.5 (CH3), 29.1 [CH(CH3)2], 47.3 (Fmoc CH), 58.5 (CHNH),
63.6 (CH2OH), 66.5 (Fmoc CH2), 119.9, 124.9, 127.0, 127.6
(Fmoc Ar CH), 141.3, 143.8 (Fmoc Ar quat C), 157.0 [C(O)].
Anal. Calcd for C20H23NO3 (325.41): C, 74.31; H, 7.12; N, 4.30.
Found: C, 73.74; H, 7.18; N, 4.20. ES MS: m/z ) 348.2 [M +
Na]+.
F m oc-P r otected Ser in e Alcoh ol 2g (R ) CH2OtBu ).
Yield: 8.3 g (22.4 mmol, 90%) of white solid. Mp: 97-98 °C.
24
Rf (5% MeOH/DCM): 0.46. [R]D ) +12.3 (c ) 1.02, CHCl3).
1H NMR (CDCl3): δ ) 1.19 [s, 9 H, (CH3)3], 3.30-3.85 (m, 4
H, OH, CH2OH, CHNH), 4.22 (t, J ) 6.4 Hz, 1 H, Fmoc CH),
4.41 (m, 2 H, Fmoc CH2), 5.75 (d, J ) 7.7 Hz, 1 H, NH), 7.28-
7.45 (m, 4 H, Fmoc Ar CH), 7.58 (d, 2 H, Fmoc Ar CH), 7.76
(d, 2 H, Fmoc Ar CH). 13C NMR (CDCl3): δ ) 27.0 [(CH3)3],
46.7 (Fmoc CH), 51.8 (CHNH), 62.1 (CH2OtBu), 63.1 (CH2OH),
66.5 (Fmoc CH2), 73.3 [C(CH3)3], 119.7, 124.8, 126.7, 127.3
(Fmoc Ar CH), 140.9, 143.6 (Fmoc Ar quat C), 156.2 [C(O)].
Anal. Calcd for C22H27NO4 (369.46): C, 71.52; H, 7.37; N, 3.79.
Found: C, 71.36; H, 7.30; N, 3.78. ES MS: m/z ) 392.2 [M +
Na]+.
F m oc-P r otected Leu cin e Alcoh ol 2c [R ) CH2CH-
(CH3)2]. Yield: 7.99 g (23.7 mmol, 95%) of white solid. Mp:
24
112-113 °C. Rf (5% MeOH/DCM): 0.45. [R]D ) -20.8 (c )
1
1.01, CHCl3). H NMR (CDCl3): δ ) 0.93 [d, J ) 5.2 Hz, 6 H,
F m oc-P r otected Asp a r tic Alcoh ol 2h (R ) CH2C(O)-
(CH3)2], 1.33 [m, 2 H, CH2CH(CH3)2], 1.63 [m, 1 H, CH(CH3)2],
2.80 (br s, 1 H, OH), 3.55 (br m, 2 H, CH2OH), 3.77 (m, 1 H,
CHNH), 4.19 (t, J ) 6.6 Hz, 1 H, Fmoc CH), 4.41 (m, 2 H,
Fmoc CH2), 5.07 (d, J ) 8.8 Hz, 1 H, NH), 7.27-7.41 (m, 4 H,
Fmoc Ar CH), 7.58 (d, 2 H, Fmoc Ar CH), 7.75 (d, 2 H, Fmoc
Ar CH). 13C NMR (CDCl3): δ ) 22.0 (CH3), 23.0 (CH3), 24.6
[CH(CH3)2], 40.3 [CH2CH(CH3)2], 47.2 (Fmoc CH), 51.2 (CHNH),
65.5 (CH2OH), 66.4 (Fmoc CH2), 119.8, 124.9, 126.9, 127.6
(Fmoc Ar CH), 141.2, 143.8 (Fmoc Ar quat C), 156.7 [C(O)].
Anal. Calcd for C21H25NO3 (339.43): C, 74.31; H, 7.42; N, 4.13.
Found: C, 74.21; H, 7.54; N, 4.04. ES MS: m/z ) 362.2 [M +
Na]+.
OtBu ). Yield: 9.25 g (23.3 mmol, 93%) of white solid. Mp: 89-
24
90 °C. Rf (5% MeOH/DCM): 0.47. [R]D ) +1.89 (c ) 1.03,
1
CHCl3). H NMR (CDCl3): δ ) 1.44 [s, 9 H, (CH3)3], 2.55 (br
d, 2 H, CH2C(O)OtBu), 2.90 (br s, 1 H, OH), 3.67 (d, J ) 4.4
Hz, 2 H, CH2OH), 4.04 (br s, 1 H, CHNH), 4.20 (t, J ) 6.6 Hz,
1 H, Fmoc CH), 4.38 (d, J ) 6.5 Hz, 2 H, Fmoc CH2), 5.67 (d,
J ) 8.4 Hz, 1 H, NH), 7.27-7.41 (m, 4 H, Fmoc Ar CH), 7.58
(d, 2 H, Fmoc Ar CH), 7.75 (d, 2 H, Fmoc Ar CH). 13C NMR
(CDCl3): δ ) 27.9 [(CH3)3], 37.2 [CH2C(O)OtBu], 47.0 (Fmoc
CH), 49.9 (CHNH), 64.1 (CH2OH), 66.7 (Fmoc CH2), 81.3
[C(CH3)3], 119.9, 124.9, 126.9, 127.6 (Fmoc Ar CH), 141.1, 143.7
(Fmoc Ar quat C), 156.2 [C(O)NH], 170.9 [C(O)OtBu]. Anal.
Calcd for C23H27NO5 (397.47): C, 69.50; H, 6.85; N, 3.52.
Found: C, 69.63; H, 6.84; N, 3.44. ES MS: m/z ) 420.2 [M +
Na]+.
F m oc-P r ot ect ed Isoleu cin e Alcoh ol 2d [R ) CH -
(CH2CH3)(CH3)]. Yield: 8.23 g (24.3 mmol, 95%) of white
24
solid. Mp: 114-115 °C. Rf (5% MeOH/DCM): 0.45. [R]D
)
1
-20.0 (c ) 1.02, CHCl3). H NMR (CDCl3): δ ) 0.91 (m, 6 H,
2 × CH3), 1.13 [m, 1 H, CH(CH2CH3)(CH3)], 1.53 [m, 2 H, CH-
(CH2CH3)(CH3)], 2.11 (t, J ) 5.5 Hz, 1 H, OH), 3.64 (br m, 3
H, CH2OH + CHNH), 4.21 (t, J ) 6.6 Hz, 1 H, Fmoc CH),
4.44 (m, 2 H, Fmoc CH2), 4.91 (d, J ) 8.8 Hz, 1 H, NH), 7.25-
7.42 (m, 4 H, Fmoc Ar CH), 7.59 (d, 2 H, Fmoc Ar CH), 7.76
(d, 2 H, Fmoc Ar CH). 13C NMR (CDCl3): δ ) 11.3 (CH3), 15.5
(CH3), 25.4 [CH(CH2CH3)(CH3)], 35.8 [CH(CH2CH3)(CH3)], 47.3
(Fmoc CH), 57.3 (CHNH), 63.3 (CH2OH), 66.5 (Fmoc CH2),
119.9, 125.0, 127.0, 127.6 (Fmoc Ar CH), 141.3, 143.8 (Fmoc
Ar quat C), 157.0 [C(O)]. Anal. Calcd for C21H25NO3 (339.43):
C, 74.31; H, 7.42; N, 4.13. Found: C, 74.22; H, 7.52; N, 4.08.
ES MS: m/z ) 362.2 [M + Na]+.
F m oc-P r otected Lysin e Alcoh ol 2i [R ) (CH2)4N(H)-
Boc]. Yield: 10.9 g (24.0 mmol, 96%) of white solid. Mp: 130-
24
131 °C. Rf (5% MeOH/DCM): 0.33. [R]D ) -8.05 (c ) 1.02,
1
CHCl3). H NMR (CDCl3): δ ) 1.43 [m, 15 H, (CH3)3 + CH2-
(CH2)3NHBoc], 2.50 (br s, 1 H, OH), 3.07 [m, 2 H, CH2(CH2)3-
NHBoc], 3.62 (br m, 2 H, CH2OH + CHNH), 4.19 (t, J ) 6.9
Hz, 1 H, Fmoc CH), 4.39 (d, J ) 6.9 Hz, 2 H, Fmoc CH2), 4.66
(br m, 1 H, NHBoc), 5.22 (d, J ) 7.0 Hz, 1 H, NHFmoc), 7.26-
7.41 (m, 4 H, Fmoc Ar CH), 7.58 (d, 2 H, Fmoc Ar CH), 7.75
(d, 2 H, Fmoc Ar CH). 13C NMR (CDCl3): δ ) 22.5, 29.9, 30.4
[CH2(CH2)3NHBoc], 28.3 [(CH3)3], 39.6 [CH2(CH2)3], 47.2 (Fmoc
CH), 52.9 (CHNH), 64.5 (CH2OH), 66.5 (Fmoc CH2), 79.2
[C(CH3)3], 119.9, 125.0, 127.0, 127.6 (Fmoc Ar CH), 141.2, 143.9
(Fmoc Ar quat C), 156.4 [C(O)], 156.7 [C(O)]. Anal. Calcd for
F m oc-P r otected P h en yla la n in e Alcoh ol 2e (R ) CH2C6-
H5). Yield: 8.70 g (23.3 mmol, 95%) of white solid. Mp: 129-
C
26H34N2O5 (454.57): C, 68.70; H, 7.54; N, 6.16. Found: C,
24
68.59; H, 7.44; N, 6.08. ES MS: m/z ) 477.2 [M + Na]+.
F m oc-P r otected P r olin e Alcoh ol 2j. Proline alcohol 2j
did not precipitate from the reaction mixture as a solid after
the addition of water, but as an oil. Therefore, the DME was
removed in vacuo, whereupon the residual water phase was
extracted with DCM (2×). The DCM layers were combined and
washed with water (3×) and brine. The organic phase was
dried (Na2SO4), filtered, and concentrated in vacuo. The
residue was crystallized from EtOAc/hexanes. Yield: 2.58 g
(8.0 mmol, 80%) of white crystals starting from 10 mmol of
130 °C. Rf (5% MeOH/DCM): 0.44. [R]D ) -23.2 (c ) 1.02,
1
CHCl3). H NMR (CDCl3): δ ) 2.07 (s, 1 H, OH), 2.87 (d, J )
6.2 Hz, 2 H, CH2C6H5), 3.64 (m, 2 H, CH2OH), 3.96 (m, 1 H,
CHNH), 4.18 (t, J ) 6.6 Hz, 1 H, Fmoc CH), 4.40 (m, 2 H,
Fmoc CH2), 5.96 (br s, 1 H, NH), 7.10-7.42 (m, 9 H, C6H5 + 4
× Fmoc Ar CH), 7.55 (m, 2 H, Fmoc Ar CH), 7.76 (d, 2 H, J )
7.3 Hz, Fmoc Ar CH). 13C NMR (CDCl3): δ ) 37.3 (CH2C6H5),
47.2 (Fmoc CH), 54.1 (CHNH), 64.0 (CH2OH), 66.6 (Fmoc CH2),
120.0, 125.0 (Fmoc Ar CH), 126.7 (CH2C6H5), 127.0, 127.7
(Fmoc Ar CH), 128.6, 129.2 (C6H5), 137.5 (C6H5 quat C), 141.3,
24
143.9 (Fmoc Ar quat C), 156.4 [C(O)]. Anal. Calcd for C24H23
-
Fmoc-Pro-OH. Mp: 89-90 °C. Rf (5% MeOH/DCM): 0.46. [R]D
1
NO3 (373.45): C, 77.19; H, 6.21; N, 3.75. Found: C, 76.89; H,
) -30.3 (c ) 1.02, CHCl3). H NMR (CDCl3): δ ) 1.21-2.07
6.32; N, 3.68. ES MS: m/z ) 396.2 [M + Na]+.
(m, 4 H, CHCH2CH2CH2), 3.20-3.67 (m, 4 H, CHCH2-

Solid-Phase Synthesis of Oligourea Peptidomimetics
J . Org. Chem., Vol. 66, No. 25, 2001 8459
CH2CH2N + CH2OH), 4.00 (m, 1 H, CHN), 4.19 (m, 2 H, Fmoc
CH + OH), 4.41 (m, 2 H, Fmoc CH2), 7.26-7.43 (m, 4 H, Fmoc
Ar CH), 7.60 (d, 2 H, Fmoc Ar CH), 7.77 (d, 2 H, Fmoc Ar
CH). 13C NMR (CDCl3): δ ) 24.1 (CH2), 28.6 (CH2), 47.3 (Fmoc
CH), 47.3 (CH2N), 60.8 (CHN), 67.0 (CH2OH), 67.5 (Fmoc CH2),
120.0, 125.0, 127.0, 127.7 (Fmoc Ar CH), 141.3, 143.9 (Fmoc
Ar quat C), 157.1 [C(O)]. Anal. Calcd for C20H21NO3 (323.39):
C, 74.28; H, 6.54; N, 4.33. Found: C, 74.17; H, 6.55; N, 4.26.
ES MS: m/z ) 346.2 [M + Na]+.
F m oc-P r otected Azid es 3. Gen er a l P r oced u r e. Under
a nitrogen atmosphere, DEAD (10 mmol, 1.55 mL, 1 equiv)
was added dropwise to a cooled (0 °C) solution of PPh3 (10
mmol, 2.63 g) in THF (30 mL). Subsequently, a 1.5 M solution
of HN3 in benzene22 (10 mmol, 6.62 mL, 1 equiv) was added
dropwise, whereupon Fmoc-protected amino alcohol 13 (10
mmol, 1 equiv) was added in one portion. The reaction mixture
was stirred overnight at room temperature, and was concen-
trated in vacuo. After column chromatography, azide 7 was
obtained as a white solid.
Fmoc CH), 4.45 (d, J ) 6.9 Hz, 2 H, Fmoc CH2), 4.77 (d, J )
9.2 Hz, 1 H, NH), 7.24-7.43 (m, 4 H, Fmoc Ar CH), 7.59 (d, 2
H, Fmoc Ar CH), 7.76 (d, 2 H, Fmoc Ar CH). 13C NMR
(CDCl3): δ ) 11.2 (CH3), 15.5 (CH3), 25.2 [CH(CH2CH3)(CH3)],
36.2 [CH(CH2CH3)(CH3)], 47.3 (Fmoc CH), 52.9 (CH2N3), 54.9
(CHNH), 66.6 (Fmoc CH2), 120.0, 125.0, 127.0, 127.6 (Fmoc
Ar CH), 141.3, 143.8 (Fmoc Ar quat C), 156.0 [C(O)]. Anal.
Calcd for C21H24N4O2 (364.44): C, 69.21; H, 6.64; N, 15.37.
Found: C, 69.30; H, 6.72; N, 15.24. ES MS: m/z ) 387.2 [M +
Na]+.
F m oc-P r otected P h en yla la n in e Azid e 3e. Yield: 2.80
g (8.0 mmol, 80%) of white solid obtained from 2e after column
chromatography (EtOAc/hexanes, 1/8). Mp: 81-82 °C. Rf
(EtOAc/hexanes, 1/4.5): 0.31. [R]D24 ) -14.5 (c ) 1.01, CHCl3).
1H NMR (CDCl3): δ ) 2.87 (m, 2 H, CH2C6H5), 3.39 (m, 2 H,
CH2N3), 4.02 (m, 1 H, CHNH), 4.19 (t, J ) 6.6 Hz, 1 H, Fmoc
CH), 4.39 (m, 2 H, Fmoc CH2), 4.87 (br d, J ) 8.1 Hz, 1 H,
NH), 7.20-7.43 (m, 9 H, C6H5 + 4 × Fmoc Ar CH), 7.55 (m, 2
H, Fmoc Ar CH), 7.76 (d, 2 H, J ) 7.3 Hz, Fmoc Ar CH). 13C
NMR (CDCl3): δ ) 37.9 (CH2C6H5), 47.2 (Fmoc CH), 51.9
(CHNH), 53.0 (CH2N3), 66.7 (Fmoc CH2), 120.1, 125.1 (Fmoc
Ar CH), 127.0 (C6H5), 127.1, 127.8 (Fmoc Ar CH), 128.8, 129.3
(C6H5), 136.9 (C6H5 quat C), 141.4, 143.9 (Fmoc Ar quat C),
156.4 [C(O)]. Anal. Calcd for C24H22N4O2 (398.46): C, 72.34;
H, 5.56; N, 14.06. Found: C, 72.31; H, 5.68; N, 14.07. ES MS:
m/z ) 421.2 [M + Na]+.
F m oc-P r otected Tyr osin e Azid e 3f. Yield: 8.21 g (17.4
mmol, 87%) of white solid obtained from 20 mmol of 2f after
column chromatography (EtOAc/hexanes, 1/6). Mp: 84-85 °C.
Rf (EtOAc/hexanes, 1/5): 0.27. [R]D24 ) -6.1 (c ) 1.01, CHCl3).
1H NMR (CDCl3): δ ) 1.33 [s, 9 H, (CH3)3], 2.80 (m, 2 H,
CH2C6H5), 3.40 (m, 2 H, CH2N3), 4.00 (m, 1 H, CHNH), 4.20
(t, J ) 7.0 Hz, 1 H, Fmoc CH), 4.40 (d, J ) 7.0 Hz, 2 H, Fmoc
CH2), 4.92 (d, J ) 8.1 Hz, 1 H, NH), 6.91-7.08 (m, 4 H, C6H4),
7.26-7.43 (m, 4 H, 4 × Fmoc Ar CH), 7.57 (m, 2 H, Fmoc Ar
CH), 7.76 (d, 2 H, J ) 7.3 Hz, Fmoc Ar CH). 13C NMR
(CDCl3): δ ) 28.8 [(CH3)3], 37.3 (CH2C6H5), 47.2 (Fmoc CH),
51.9 (CHNH), 53.0 (CH2N3), 66.7 (Fmoc CH2), 78.4 [C(CH3)3],
120.0 (Fmoc Ar CH), 124.3 (C6H4), 125.0, 127.0, 127.7 (Fmoc
Ar CH), 129.6 (C6H4), 131.5 (C6H4 quat C), 141.3, 143.8 (Fmoc
Ar quat C), 154.2 (C6H4 quat C), 155.6 [C(O)]. Anal. Calcd for
C28H30N4O3 (470.57): C, 71.47; H, 6.43; N, 11.91. Found: C,
71.33; H, 6.48; N, 11.69. ES MS: m/z ) 493.2 [M + Na]+.
F m oc-P r otected Ala n in e Azid e 3a . Yield: 2.98 g (9.8
mmol, 98%) of white solid obtained from 2a after column
chromatography (EtOAc/hexanes, 1/5). Mp: 109-110 °C. Rf
24
(EtOAc/hexanes, 1/5): 0.27. [R]D ) -10.3 (c ) 0.96, CHCl3).
1H NMR (CDCl3): δ ) 1.16 (d, J ) 6.6 Hz, 3 H, CH3), 3.39 (br
m, 2 H, CH2N3), 3.93 (m, 1 H, CHNH), 4.22 (t, J ) 6.6 Hz, 1
H, Fmoc CH), 4.41 (m, 2 H, Fmoc CH2), 4.84 (d, J ) 8.1 Hz, 1
H, NH), 7.25-7.42 (m, 4 H, Fmoc Ar CH), 7.58 (d, 2 H, Fmoc
Ar CH), 7.76 (d, 2 H, Fmoc Ar CH). 13C NMR (CDCl3): δ )
18.2 (CH3), 46.6 (CHNH), 47.2 (Fmoc Ar CH), 55.8 (CH2N3),
66.6 (Fmoc CH2), 119.9, 124.9, 127.0, 127.7 (Fmoc Ar CH),
141.3, 143.8 (Fmoc Ar quat C), 155.5 [C(O)]. Anal. Calcd for
C
18H18N4O2 (422.47): C, 67.07; H, 5.63; N, 17.38. Found: C,
67.19; H, 5.70; N, 17.33. ES MS: m/z ) 345.1 [M + Na]+.
F m oc-P r otected Va lin e Azid e 3b. Yield: 2.80 g (8.0
mmol, 80%) of white solid obtained from 2b after column
chromatography (EtOAc/hexanes, 1/6). Mp: 109 °C. Rf (EtOAc/
hexanes, 1/5): 0.34. [R]D24 ) -26.4 (c ) 1.03, CHCl3). 1H NMR
(CDCl3): δ ) 0.95 [t, 6 H, (CH3)2], 1.82 [m, 1 H, CH(CH3)2],
3.55 (d, J ) 4.8 Hz, 2 H, CH2N3), 3.60 (m, 1 H, CHNH), 4.24
(t, J ) 7.0 Hz, 1 H, Fmoc CH), 4.46 (d, J ) 7.0 Hz, 2 H, Fmoc
CH2), 4.92 (d, J ) 9.2 Hz, 1 H, NH), 7.30-7.44 (m, 4 H, Fmoc
Ar CH), 7.61 (d, 2 H, Fmoc Ar CH), 7.77 (d, 2 H, Fmoc Ar
CH). 13C NMR (CDCl3): δ ) 18.4 (CH3), 19.3 (CH3), 29.6 [CH-
(CH3)2], 47.2 (Fmoc CH), 52.9 (CH2N3), 56.1 (CHNH), 66.5
(Fmoc CH2), 119.9, 124.9, 126.9, 127.6 (Fmoc Ar CH), 141.2,
143.7 (Fmoc Ar quat C), 156.0 [C(O)]. Anal. Calcd for
F m oc-P r otected Ser in e Azid e 3g. Yield: 2.86 g (7.3
mmol, 73%) of colorless oil, which solidified upon standing,
obtained from 2g after column chromatography (EtOAc/
C
20H22N4O2 (350.42): C, 68.55; H, 6.33; N, 15.99. Found: C,
24
hexanes, 1/6). Mp: 83 °C. Rf (EtOAc/hexanes, 1/4): 0.36. [R]D
68.63; H, 6.39; N, 16.08. ES MS: m/z ) 373.1 [M + Na]+.
F m oc-P r otected Leu cin e Azid e 3c. Yield: 3.17 g (8.8
mmol, 88%) of white solid obtained from 2c after column
chromatography (EtOAc/hexanes, 1/9). Mp: 85 °C. Rf (EtOAc/
hexanes, 1/5): 0.51. [R]D24 ) -26.4 (c ) 1.03, CHCl3). 1H NMR
(CDCl3): δ ) 0.91 [d, J ) 6.2 Hz, 6 H, (CH3)2], 1.35 [m, 2 H,
CH2CH(CH3)2], 1.60 [m, 1 H, CH(CH3)2], 3.55 (br m, 2 H,
CH2N3), 3.86 (m, 1 H, CHNH), 4.21 (t, J ) 6.6 Hz, 1 H, Fmoc
CH), 4.43 (d, J ) 6.6 Hz, 2 H, Fmoc CH2), 4.72 (d, J ) 8.8 Hz,
1 H, NH), 7.24-7.42 (m, 4 H, Fmoc Ar CH), 7.58 (d, 2 H, Fmoc
Ar CH), 7.75 (d, 2 H, Fmoc Ar CH). 13C NMR (CDCl3): δ )
21.9 (CH3), 22.8 (CH3), 24.6 [CH(CH3)2], 41.2 [CH2CH(CH3)2],
47.2 (Fmoc CH), 49.0 (CHNH), 55.1 (CH2N3), 66.5 (Fmoc CH2),
120.0, 125.1, 127.1, 127.7 (Fmoc Ar CH), 141.4, 143.9 (Fmoc
Ar quat C), 155.9 [C(O)]. Anal. Calcd for C21H24N4O2 (364.45):
C, 69.21; H, 6.64; N, 15.37. Found: C, 69.29; H, 6.66; N, 15.33.
ES MS: m/z ) 387.2 [M + Na]+.
) +1.32 (c ) 1.02, CHCl3). 1H NMR (CDCl3): δ ) 1.19 [s, 9 H,
(CH3)3], 3.36-3.52 (m, 4 H, CH2N3 + CH2O), 3.90 (br s, 1 H,
CHNH), 4.22 (t, J ) 6.6 Hz, 1 H, Fmoc CH), 4.42 (m, 2 H,
Fmoc CH2), 5.13 (d, J ) 8.8 Hz, 1 H, NH), 7.26-7.43 (m, 4 H,
Fmoc Ar CH), 7.59 (d, 2 H, Fmoc Ar CH), 7.77 (d, 2 H, Fmoc
Ar CH). 13C NMR (CDCl3): δ ) 27.4 [(CH3)3], 47.2 (Fmoc CH),
50.6 (CHNH), 51.4 (CH2N3), 60.4 (CH2OtBu), 66.8 (Fmoc CH2),
73.4 [C(CH3)3], 119.7, 124.8, 126.7, 127.3 (Fmoc Ar CH), 140.9,
143.6 (Fmoc Ar quat C), 156.2 [C(O)NH]. Anal. Calcd for
C
22H26N4O3 (394.47): C, 66.99; H, 6.64; N, 14.20. Found: C,
67.16; H, 6.63; N, 14.22. ES MS: m/z ) 417.2 [M + Na]+.
F m oc-P r otected Asp a r tic Azid e 3h . Yield: 4.20 g (10.0
mmol, 100%) of white solid obtained from 2h after column
chromatography (EtOAc/hexanes, 1/6). Mp: 88-89 °C. Rf
24
(EtOAc/hexanes, 1/4): 0.34. [R]D ) -1.68 (c ) 1.01, CHCl3).
1H NMR (CDCl3): δ ) 1.46 [s, 9 H, (CH3)3], 2.54 (d, J ) 5.8
Hz, 2 H, CH2C(O)OtBu), 3.51 (m, 2 H, CH2N3), 4.16 (br s, 1 H,
CHNH), 4.22 (m, 1 H, Fmoc CH), 4.40 (m, 2 H, Fmoc CH2),
5.42 (d, J ) 8.8 Hz, 1 H, NH), 7.26-7.43 (m, 4 H, Fmoc Ar
CH), 7.59 (m, 2 H, Fmoc Ar CH), 7.77 (d, 2 H, Fmoc Ar CH).
13C NMR (CDCl3): δ ) 28.0 [(CH3)3], 37.3 [CH2C(O)OtBu], 47.2
(Fmoc CH), 47.9 (CHNH), 53.7 (CH2N3), 66.9 (Fmoc CH2), 81.7
[C(CH3)3], 120.0, 125.0 127.0, 127.7 (Fmoc Ar CH), 141.3, 143.8
(Fmoc Ar quat C), 155.6 [C(O)NH], 170.2 [C(O)OtBu]. Anal.
Calcd for C23H26N4O4 (422.40): C, 65.39; H, 6.20; N, 13.26.
Found: C, 65.47: H, 6.31; N, 13.29. ES MS: m/z ) 445.2 [M
+ Na]+.
F m oc-P r otected Isoleu cin e Azid e 3d . Yield: 2.80 g (8.0
mmol, 80%) of white solid obtained from 2d after column
chromatography (EtOAc/hexanes, 1/8). Mp: 111 °C. Rf (EtOAc/
hexanes, 1/5): 0.50. [R]D24 ) -24.6 (c ) 0.99, CHCl3). 1H NMR
(CDCl3): δ ) 0.92 (m, 6 H, 2 × CH3), 1.13 [m, 1 H, CH(CH2-
CH3)(CH3)], 1.52 [m, 2 H, CH(CH2CH3)(CH3)], 3.54 (br m, 2
H, CH2N3), 3.62 (m, 1 H, CHNH), 4.23 (t, J ) 6.9 Hz, 1 H,
(22) Wolff, H. In Organic Reactions; Adams, R., Bachmann, W. E.,
Fieser, L. F., J ohnson, J . R., Snyder, H. R., Eds.; J ohn Wiley & Sons:
New York, 1947; Vol. 3, p 327.

8460 J . Org. Chem., Vol. 66, No. 25, 2001
Boeijen et al.
F m oc-P r otected Lysin e Azid e 3i. Yield: 4.17 g (8.7
mmol, 87%) of white solid obtained from 2i after column
chromatography (EtOAc/hexanes, 1/3). Mp: 97-98 °C. Rf
CH(CH3)2], 3.37 (m, 2 H, CH2NH), 4.20 (t, J ) 6.6 Hz, 1 H,
Fmoc CH), 4.40 (m, 2 H, Fmoc CH2), 6.42 (d, J ) 9.5 Hz, 1 H,
NH), 7.19-7.36 (m, 7 H, 4 × Fmoc Ar CH + 2 × C6H4NO2 +
NH), 7.63 (m, 2 H, Fmoc Ar CH), 7.77 (d, 2 H, Fmoc Ar CH),
8.14 (d, 2 H, C6H4NO2). 13C NMR (CDCl3): δ ) 18.1 (CH3),
19.3 (CH3), 30.5 [CH(CH3)2], 44.3 (CH2NH), 47.3 (Fmoc CH),
56.8 (CHNH), 66.8 (Fmoc CH2), 120.0 (Fmoc Ar CH), 121.8,
124.9 (C6H4NO2), 125.0, 127.1, 127.8 (Fmoc Ar CH), 141.3,
143.7 (Fmoc Ar quat C), 144.7, 153.7 (quat C6H4NO2), 155.8
[Fmoc C(O)], 157.2 [C(O)OC6H4NO2]. Anal. Calcd for C27H27N3O6
(489.53): C, 66.25; H, 5.56; N, 8.58. Found: C, 66.03; H, 5.62;
N, 8.40. ES MS: m/z ) 512.2 [M + Na]+.
F m oc-P r ot ect ed Act iva t ed Leu cin e Mon om er 5c.
Yield: 2.10 g (4.2 mmol, 83%) of white solid. Mp: >144-146
°C dec. Rf (EtOAc/hexanes, 1/1): 0.67. [R]D24 ) -18.7 (c ) 0.48,
dioxane). 1H NMR ([D8]THF): δ ) 0.93 [m, 6 H, (CH3)2], 1.27-
1.40 [m, 3 H, CH2CH(CH3)2], 3.20 (br m, 2 H, CH2NH), 3.84
(m, 1 H, CHNH), 4.19 (t, J ) 7.0 Hz, 1 H, Fmoc CH), 4.34 (m,
2 H, Fmoc CH2), 6.44 (d, J ) 9.1 Hz, 1 H, CHNH), 7.20-7.36
(m, 5 H, 2 × C6H4NO2 + 2 × Fmoc Ar CH + CH2NH), 7.63 (m,
2 H, Fmoc Ar CH), 7.77 (d, 2 H, Fmoc Ar CH), 8.13 (d, 2 H,
Fmoc Ar CH), 8.13 (d, 2 H, C6H4NO2). 13C NMR (CDCl3): δ
22.0 (CH3), 23.0 (CH3), 24.8 [CH(CH3)2], 41.7 [CH2CH(CH3)2],
46.8 (CH2NH), 47.3 (Fmoc CH), 49.8 (CHNH), 66.7 (Fmoc CH2),
120.0 (Fmoc Ar CH), 121.8, 124.9 (C6H4NO2), 125.0, 127.1,
127.8 (Fmoc Ar CH), 141.3, 143.7 (Fmoc Ar quat C), 144.7,
153.6 (quat C6H4NO2), 155.8 [Fmoc C(O)], 156.9 [C(O)OC6H4-
NO2]. Anal. Calcd for C28H29N3O6 (503.55): C, 66.79; H, 5.80;
N, 8.34. Found: C, 66.62; H, 6.01; N, 8.30. ES MS: m/z ) 526.2
[M + Na]+.
F m oc-P r otected Activa ted Isoleu cin e Mon om er 5d .
Yield: 2.00 g (4.0 mmol, 80%). Mp: >138-140 °C dec. Rf
(EtOAc/hexanes, 1/1): 0.63. [R]D24 ) -18.3 (c ) 0.55, dioxane).
1H NMR ([D8]THF): δ ) 0.94 (m, 6 H, 2 × CH3), 1.18 [m, 1 H,
CH(CH2CH3)(CH3)], 1.55 [m, 2 H, CH(CH2CH3)(CH3)], 3.30 (br
m, 2 H, CH2NH), 3.68 (m, 1 H, CHNH), 4.20 (t, J ) 6.6 Hz, 1
H, Fmoc CH), 4.28-4.45 (m, 2 H, Fmoc CH2), 6.46 (d, J ) 9.1
Hz, 1 H, CHNH), 7.20-7.36 (m, 7 H, 4 × Fmoc Ar CH + C6H4-
NO2 + CH2NH), 7.64 (m, 2 H, Fmoc Ar CH), 7.78 (d, 2 H, Fmoc
Ar CH), 8.13 (d, 2 H, C6H4NO2). 13C NMR ([D8]THF): δ ) 11.5
(CH3), 15.7 (CH3), 26.0 [CH(CH2CH3)(CH3)], 37.8 [CH(CH2-
CH3)(CH3)], 43.7 (CH2NH), 48.3 (Fmoc CH), 56.3 (CHNH),
120.5 (Fmoc Ar CH), 122.5, 125.4 (C6H4NO2), 125.8, 127.6,
128.1 (Fmoc Ar CH), 142.2, 144.3 (Fmoc Ar quat C), 144.7,
153.6 (quat C6H4NO2), 156.3 [Fmoc C(O)], 157.3 [C(O)OC6H4-
NO2]. Anal. Calcd for C28H29N3O6 (503.55): C, 66.79; H, 5.80;
N, 8.34. Found: C, 66.87; H, 5.73; N, 8.26. ES MS: m/z ) 526.3
[M + Na]+.
24
(EtOAc/hexanes, 1/3): 0.33. [R]D ) -16.4 (c ) 0.99, CHCl3).
1H NMR (CDCl3): δ ) 1.43 [m, 15 H, (CH3)3 + CH2(CH2)3-
NHBoc], 3.10 [m, 2 H, CH2(CH2)3NHBoc], 3.39 (br m, 2 H,
CH2N3), 3.75 (br m, 1 H, CHNH), 4.20 (t, J ) 6.9 Hz, 1 H,
Fmoc CH), 4.39 (m, 2 H, Fmoc CH2), 4.59 (br m, 1 H, NHBoc),
5.00 (d, J ) 8.1 Hz, 1 H, NHFmoc), 7.25-7.41 (m, 4 H, Fmoc
Ar CH), 7.59 (d, 2 H, Fmoc Ar CH), 7.75 (d, 2 H, Fmoc Ar
CH). 13C NMR (CDCl3): δ ) 22.8, 29.7, 31.6 (CH2(CH2)3-
NHBoc), 28.4 [(CH3)3], 40.0 [CH2(CH2)3], 47.2 (Fmoc CH), 50.7
(CHNH), 54.7 (CH2N3), 66.6 (Fmoc CH2), 79.1 [C(CH3)3], 119.9,
125.0, 127.0, 127.6 (Fmoc Ar CH), 141.2, 143.8 (Fmoc Ar quat
C), 155.9 [C(O)], 156.0 [C(O)]. ES MS: m/z ) 502.3 [M + Na]+.
F m oc-P r otected P r olin e Azid e 3j. Yield: 3.20 g (9.2
mmol, 92%) of colorless oil, which solidified upon standing,
obtained from 2j after column chromatography (EtOAc/hex-
24
anes, 1/6). Mp: 64-65 °C. Rf (EtOAc/hexanes, 1/5): 0.26. [R]D
) -32.8 (c ) 1.09, CHCl3). The NMR spectrum indicates the
presence of two conformers. H NMR (CDCl3): δ ) 1.68-2.03
1
(m, 4 H, CHCH2CH2CH2N), 2.71-2.89 (m, 1 H, CH2N), 3.34-
3.63 (m, 3.5 H, CH2N3 + 1 × CH2 N + 0.5 × CHN), 4.03 (m,
0.5 H, CHN), 4.25 (t, 1 H, Fmoc CH), 4.32-4.49 (m, 1 H, Fmoc
CH2), 4.59-4.71 (m, 1 H, Fmoc CH2), 7.30-7.44 (m, 4 H, Fmoc
Ar CH), 7.56-7.62 (m, 2 H, Fmoc Ar CH), 7.78 (d, 2 H, Fmoc
Ar CH). 13C NMR (CDCl3): δ ) 22.8, 23.9 (CHCH2CH2CH2
f
N), 28.4, 29.1 (CHCH2CH2CH2N), 46.9, 46.9 (CH2N), 47.3
(Fmoc CH), 52.6 (CH2N3), 56.0, 57.0 (CHN), 66.3, 67.1 (Fmoc
CH2), 119.9, 119.9, 124.4, 124.5, 127.0, 127.0 127.6 (Fmoc Ar
CH), 141.3, 141.3, 143.9, 144.0 (Fmoc Ar quat C), 154.9, 155.0
[C(O)]. Anal. Calcd for C20H20N4O2 (348.40): C, 68.95; H, 5.79;
N, 16.08. Found: C, 69.07; H, 5.88; N, 15.97. ES MS: m/z )
371.2 [M + Na]+.
F m oc-P r otected Activa ted Mon om er s 5. Gen er a l P r o-
ced u r e. Azide 3 (5.0 mmol) was dissolved in THF (50 mL),
and CHCl3 (1.0 mL) was added. To this solution, a catalytic
amount of 10% palladium on carbon (100 mg) was added. The
resulting mixture was stirred overnight at room temperature
under a hydrogen atmosphere. Then, water (4.0 mL) was
added to redissolve precipitated material. Subsequently, the
reaction mixture was filtered over Celite, and the solvents were
evaporated. The resulting HCl salt 4 was dried in vacuo over
P2O5. Then, DCM (40 mL) and 4-nitrophenyl chloroformate
(5.5 mmol, 1.11 g, 1.1 equiv) were added. The resulting
suspension was cooled to 0 °C with an ice bath, and a solution
of DiPEA (10 mmol, 1.74 mL, 2 equiv) in DCM (10 mL) was
added dropwise. After being stirred for 30 min, the reaction
mixture was allowed to warm to room temperature, and
stirring was continued for another 2 h. The reaction mixture
was then washed with 1 N KHSO4 (3×), water, and brine. The
organic fraction was dried on Na2SO4, and the solvents were
removed in vacuo. Subsequent precipitation from DCM/hex-
anes gave monomer 5 as a white to yellow-white solid.
F m oc-P r otected Activa ted Ala n in e Mon om er 5a .
Yield: 1.67 g (3.7 mmol, 75%) of white solid obtained after
trituration with 2-propanol and Et2O. Mp: >161-163 °C dec.
F m oc-P r ot ect ed Act iva t ed P h en yla la n in e Mon om er
5e. Yield: 2.69 g (3.5 mmol, 69%) of white solid. Mp: >166-
168 °C dec. Rf (EtOAc/hexanes, 1/1): 0.53. [R]D24 ) -10.1 (c )
1
0.50, dioxane). H NMR ([D8]THF): δ ) 2.84 (d, J ) 7.0 Hz, 2
H, CH2C6H5), 3.30 (m, 2 H, CH2NH), 4.01 (m, 1 H, CHNH),
4.16 (t, J ) 7.0 Hz, 1 H, Fmoc CH), 4.31 (m, 2 H, Fmoc CH2),
6.57 (d, J ) 8.5 Hz, 1 H, CHNH), 7.05-7.36 (m, 12 H, 4 ×
Fmoc Ar CH + 2 × C6H4NO2 + C6H5 + CH2NH), 7.57 (m, 2 H,
Fmoc Ar CH), 7.77 (d, 2 H, Fmoc Ar CH), 8.16 (d, 2 H, C6H4-
NO2). 13C NMR (CDCl3): δ ) 38.9 (CH2C6H5), 45.3 (CH2NH),
47.2 (Fmoc CH), 52.7 (CHNH), 66.7 (Fmoc CH2), 120.0 (Fmoc
Ar CH), 121.9, 125.1 (C6H4NO2) 125.1 (Fmoc Ar CH), 127.0
(CH2C6H5), 127.1, 127.8 (Fmoc Ar CH), 128.8, 129.1 (CH2C6H5),
136.9 (C6H5 quat C), 141.3, 143.7 (Fmoc Ar quat C), 144.4,
153.7 (quat C6H4NO2), 155.7 [Fmoc C(O)], 156.3 [C(O)OC6H4-
NO2]. Anal. Calcd for C31H27N3O6 (537.57): C, 69.26; H, 5.06;
N, 7.82. Found: C, 69.20; H, 5.12; N, 7.76. ES MS: m/z ) 560.2
[M + Na]+.
24
Rf (EtOAc/hexanes, 1/1): 0.35. [R]D ) +7.64 (c ) 0.25,
dioxane). 1H NMR ([D8]THF): δ ) 1.15 (d, J ) 6.6 Hz, 3 H,
CH3), 3.23 (br m, 2 H, CH2NH), 3.84 (m, 1 H, CHNH), 4.19 (t,
J ) 6.6 Hz, 1 H, Fmoc CH), 4.35 (m, 2 H, Fmoc CH2), 6.51 (d,
J ) 8.4 Hz, 1 H, NH), 7.21-7.37 (m, 7 H, 4 × Fmoc Ar CH +
2 · C6H4NO2 + NH), 7.62 (d, 2 H, Fmoc Ar CH), 7.77 (d, 2 H,
Fmoc Ar CH), 8.16 (d, 2 H, C6H4NO2). 13C NMR (D8[THF]): δ
) 18.4 (CH3), 47.3 (CH2NH), 48.0 (Fmoc CH), 48.4 (CHNH),
66.8 (Fmoc CH2), 120.6 (Fmoc Ar CH), 122.6, 125.5 (C6H4NO2),
125.9, 127.7, 128.3 (Fmoc Ar CH), 142.3 (Fmoc Ar quat C),
145.3, 154.4 (C6H4NO2 quat C), 156.9 [Fmoc C(O)], 157.7 [C(O)-
OC6H4NO2]. Anal. Calcd for C25H23N3O6 (461.47): C, 65.07;
H, 5.02; N, 9.11. Found: C, 65.15; H, 5.04; N, 8.98. ES MS:
m/z ) 484.2 [M + Na]+.
F m oc-P r ot ect ed Act iva t ed Tyr osin e Mon om er 5f.
Yield: 3.38 g (5.5 mmol, 60%) of white solid obtained from 9.2
mmol of 7g. Mp: >142-143 °C dec. Rf (EtOAc/hexanes, 1/1):
24
1
0.54. [R]D ) -6.2 (c ) 0.49, dioxane). H NMR ([D8]THF): δ
) 1.27 [s, 9 H, (CH3)3], 2.79 (d, J ) 7.0 Hz, 2 H, CH2C6H4),
3.35 (m, 2 H, CH2NH), 3.96 (m, 1 H, CHNH), 4.16 (t, J ) 6.6
Hz, 1 H, Fmoc CH), 4.32 (m, 2 H, Fmoc CH2), 6.58 (d, J ) 8.4
Hz, 1 H, CHNH), 6.86 (d, 2 H, 2 × CH2C6H4), 7.12 (d, 2 H, 2
× CH2C6H4), 7.20-7.36 (m, 7 H, 4 × Fmoc Ar CH + 2 × C6H4-
F m oc-P r otected Activa ted Va lin e Mon om er 5b. Yield:
1.49 g (3.1 mmol, 64%) of white solid. Mp: >144-145 °C dec.
24
Rf (EtOAc/hexanes, 1/1): 0.56. [R]D ) -36.3 (c ) 0.25,
dioxane). 1H NMR ([D8]THF): δ ) 0.95 [m, 7 H, (CH3)2
+

Solid-Phase Synthesis of Oligourea Peptidomimetics
J . Org. Chem., Vol. 66, No. 25, 2001 8461
NO2 + CH2NH), 7.59 (m, 2 H, 2 × Fmoc Ar CH), 7.77 (d, 2 H,
Fmoc Ar CH), 8.16 (d, 2 H, C6H4NO2). 13C NMR (CDCl3): δ )
28.8 [(CH3)3], 38.1 (CH2C6H4), 47.2 (Fmoc CH), 52.7 (CHNH),
66.7 (Fmoc CH2), 67.1 (CH2NH), 78.4 [C(CH3)3], 120.0 (Fmoc
Ar CH), 121.9 (C6H4NO2), 124.3 (CH2C6H4), 124.9 (C6H4NO2),
125.0, 127.0, 127.7 (Fmoc Ar CH), 129.5 (CH2C6H4), 131.3
(CH2C6H4 quat C), 141.3, 143.7 (Fmoc Ar quat C), 144.7, 153.7
(C6H4NO2 quat C), 154.3 (CH2C6H4 quat C), 155.7 [Fmoc C(O)],
156.6 [C(O)OC6H4NO2]. Anal. Calcd for C35H35N3O7 (609.67):
C, 68.95; H, 5.79; N, 6.89. Found: C, 68.42; H, 5.58; N, 6.45.
ES MS: m/z ) 610.3 [M + H]+.
(Fmoc Ar quat C), 144.6, 153.4 (quat C6H4NO2), 156.1 [Fmoc
C(O)], 156.9 [C(O)OC6H4NO2]. Anal. Calcd for C27H25N3O6
(487.51): C, 66.52; H, 5.17; N, 8.62. Found: C, 66.40; H, 5.16;
N, 8.55. ES MS: m/z ) 488.2 [M + H]+.
Bisp r otected Am in e 8. Mono-Boc-protected ethylenedi-
amine (7)16 (7.70 g, 50 mmol) was dissolved in water (50 mL).
The pH was adjusted to 9-9.5 using 1 N NaOH. Subsequently,
a solution of Fmoc-OSu (16.9 g, 50 mmol) in acetonitrile (100
mL) was added in one portion. The product, which precipitated
from the reaction mixture, was collected by filtration. The
residue was washed with water and acetonitrile, redissolved
in CHCl3 and MeOH, and coevaporated with toluene. The
residue was dried in a vacuum desiccator over P2O5 to give
the product (16.2 g, 42 mmol, 84%) as a white solid. Mp: 155-
156 °C. Rf (5% MeOH/DCM): 0.66. 1H NMR (CDCl3): δ ) 1.43
[s, 9 H, C(CH3)3], 3.27 (br s, 4 H, 2 × CH2NH), 4.19 (t, 1 H,
Fmoc CH), 4.39 (d, 2 H, Fmoc CH2), 4.85 (br s, 1 H, NH), 5.26
(br s, 1 H, NH), 7.25-7.41 (m, 4 H, Fmoc Ar CH), 7.58 (d, 2 H,
Fmoc Ar CH), 7.75 (d, 2 H, Fmoc Ar CH). 13C NMR (CDCl3):
δ ) 28.3 [(CH3)3], 40.6 (CH2NH), 41.6 (CH2NH), 47.2 (Fmoc
CH), 66.7 (Fmoc CH2), 79.6 [C(CH3)3], 120.0, 125.0, 127.0, 127.7
(Fmoc Ar CH), 141.3, 143.9 (Fmoc Ar quat C), 156.6 [C(O)],
156.8 [C(O)]. Anal. Calcd for C22H26N2O4 (382.46): C, 69.09;
H, 6.85; N, 7.32. Found: C, 68.93; H, 6.76; N, 7.26. ES MS:
m/z ) 383.2 [M + H]+.
F m oc-P r otected Eth ylen ed ia m in e Hyd r och lor id e Sa lt
(4k ). A solution of bisprotected amine 8 (15.2 g, 40 mmol) in
CHCl3 (200 mL) was cooled to 0 °C. A saturated solution of
HCl in ether (50 mL) was added dropwise, and the solution
was allowed to warm to room temperature. A white precipitate
was formed, which was collected by filtration. The residue was
recrystallized from MeOH/ether/hexanes and dried in a vacuum
desiccator over P2O5 to give product 4k as a white solid (10.5
g, 33 mmol, 82%). 1H NMR (D6[DMSO]): δ ) 2.80 (t, 2 H, CH2-
NH3), 3.22 (q, 2 H, CH2NHFmoc), 4.22 (t, J ) 5.9 Hz, 1 H,
Fmoc CH), 4.31 (d, J ) 5.9 Hz, 2 H, Fmoc CH2), 7.29-7.48
(m, 5 H, 4 × Fmoc Ar CH + NHFmoc), 7.67 (d, 2 H, Fmoc Ar
CH), 7.87 (d, 2 H, Fmoc Ar CH), 7.97 (br s, 3 H, NH3). 13C
NMR ([D6]DMSO): δ ) 38.3 (CH2), 38.8 (CH2), 46.9 (Fmoc CH),
65.9 (Fmoc CH2), 120.4, 125.5, 127.3, 127.9 (Fmoc Ar CH),
141.0, 144.1 (Fmoc Ar quat C), 156.5 [C(O)]. ES MS: m/z )
283.2 [M + H]+.
F m oc-P r otected Activa ted Ser in e Mon om er 5g. Yield:
2.19 g (3.6 mmol, 73%) of white solid. Mp: >140-142 °C dec.
24
Rf (EtOAc/hexanes, 1/1): 0.57. [R]D ) +4.35 (c ) 0.49,
dioxane). 1H NMR ([D8]THF): δ ) 1.19 [s, 9 H, (CH3)3], 3.30-
3.50 (m, 4 H, CH2C6H4 + CH2NH), 3.87 (m, 1 H, CHNH), 4.20
(t, J ) 6.6 Hz, 1 H, Fmoc CH), 4.32 (m, 2 H, Fmoc CH2), 6.47
(d, J ) 8.8 Hz, 1 H, CHNH), 7.21-7.40 (m, 7 H, 4 · Fmoc Ar
CH + 2 × C6H4NO2 + CH2NH), 7.63 (d, 2 H, 2 × Fmoc Ar
CH), 7.77 (d, 2 H, 2 · Fmoc Ar CH), 8.16 (d, 2 H, 2 × C6H4-
NO2). 13C NMR (CDCl3): δ ) 27.4 [(CH3)3], 44.4 (CH2NH), 47.2
(Fmoc CH), 50.6 (CHNH), 62.4 (CH2OtBu), 66.9 (Fmoc CH2),
73.6 [C(CH3)3], 120.0 (Fmoc Ar CH), 121.9, 124.9 (C6H4NO2),
125.0, 127.0, 127.7 (Fmoc Ar CH), 141.3, 143.7 (Fmoc Ar quat
C), 144.6, 153.5 (quat C6H4NO2), 155.9 [Fmoc C(O)], 156.7
[C(O)OC6H4NO2]. Anal. Calcd for C29H31N3O7 (533.58): C,
65.28; H, 5.86; N, 7.88. Found: C, 65.20; H, 5.85; N, 7.93. ES
MS: m/z ) 556.2 [M + Na]+.
F m oc-P r otected Activa ted Asp a r tic Acid Mon om er 5h .
Yield: 1.30 g (2.5 mmol, 49%) of white solid. Mp: >146-148
°C dec. Rf (EtOAc/hexanes, 1/1): 0.64. [R]D24 ) -19.4 (c ) 0.53,
1
dioxane). H NMR ([D8]THF): δ ) 1.42 [s, 9 H, (CH3)3], 2.45
[m, 2 H, CH2C(O)OtBu], 3.31 (m, 2 H, CH2NH), 4.23 (m, 4 H,
Fmoc CH + Fmoc CH2 + CHNH), 6.61 (m, 1 H, NH), 7.21-
7.36 (m, 7 H, 4 × Fmoc Ar CH + 2 × C6H4NO2 + CH2NH),
7.65 (m, 2 H, 2 × Fmoc Ar CH), 8.09 (d, 2 H, 2 × Fmoc Ar
CH), 8.16 (d, 2 H, C6H4NO2). 13C NMR (CDCl3): δ ) 28.0
[(CH3)3], 37.8 (CH2C(O)OtBu), 45.0 (CH2NH), 47.2 (Fmoc CH),
48.5 (CHNH), 67.0 (Fmoc CH2), 81.9 [C(CH3)3], 120.0 (Fmoc
Ar CH), 121.9, 125.1 (C6H4NO2), 125.1, 127.0, 127.8 (Fmoc Ar
CH), 141.3, 143.6 (Fmoc Ar quat C), 144.7, 153.6 (C6H4NO2
quat C), 155.7 [C(O)], 156.5 [C(O)], 170.2 [C(O)OtBu]. ES MS:
m/z ) 584.3 [M + Na]+.
F m oc-P r otected Activa ted Glycin e Mon om er 5k . A
suspension of Fmoc-protected ethylenediamine hydrochloride
(4k ) (3.18 g, 10 mmol) and 4-nitrophenyl chloroformate (2.22
g, 11 mmol) in CHCl3 (75 mL) was cooled to 0 °C. A solution
of DiPEA (2.48 mL, 20 mmol) in CHCl3 (25 mL) was added
dropwise. The reactants slowly dissolved. When the product
started to precipitate, the reaction mixture was allowed to
warm to room temperature. After 2 h, the product was
collected by filtration, washed with CHCl3 and ether, and dried
in a vacuum desiccator over P2O5 to give product 5k as a white
solid (4.2 g, 9.5 mmol, 95%). Mp: >174-175 °C dec. Rf (EtOAc/
F m oc-P r otected Activa ted Lysin e Mon om er 5i. Yield:
2.19 g (3.6 mmol, 73%) of white solid. Mp: >148-150 °C dec.
24
Rf (EtOAc/hexanes, 1/1): 0.25. [R]D ) -10.9 (c ) 0.51,
dioxane). 1H NMR ([D8]THF): δ ) 1.40 [m, 15 H, (CH3)3
+
CH2(CH2)3NHBoc], 3.03 [m, 2 H, CH2(CH2)3NHBoc], 3.24 (br
m, 2H, CH2NH), 3.74 (br m, 1 H, CHNH), 4.19 (t, J ) 6.9 Hz,
1 H, Fmoc CH), 4.34 (m, 2 H, Fmoc CH2), 6.01 (br m, 1 H,
NHBoc), 6.46 (d, J ) 8.8 Hz, 1 H, NHFmoc), 7.21-7.37 (m, 7
H, 4 × Fmoc Ar CH + 2 × C6H4NO2 + NH), 7.64 (m, 2 H,
Fmoc Ar CH), 7.77 (d, 2 H, Fmoc Ar CH), 8.15 (d, 2 H, C6H4-
NO2). 13C NMR (CDCl3): δ ) 22.5, 29.9, 31.6 (CH2(CH2)3-
NHBoc), 28.4 [(CH3)3], 39.6 [CH2(CH2)3], 45.8 (CH2NH), 47.2
(Fmoc CH), 51.6 (CHNH), 66.7 (Fmoc CH2), 79.3 [C(CH3)3],
120.0 (Fmoc Ar CH), 121.8, 125.0 (C6H4NO2), 125.0, 127.0,
127.7 (Fmoc Ar CH), 141.3, 143.8 (Fmoc Ar quat C), 144.6,
153.8 (C6H4NO2 quat C), 155.8 [C(O)], 156.3 [C(O)], 156.9
[C(O)]. Anal. Calcd for C33H38N4O8 (618.67): C, 64.07; H, 6.19;
N, 9.06. Found: C, 64.15; H, 6.11; N, 8.88. ES MS: m/z ) 619.3
[M + H]+
1
hexanes, 1/1): 0.20. H NMR ([D8]THF): δ ) 3.27 (br s, 4 H,
2 × CH2NH), 4.19 (t, 1 H, Fmoc CH), 4.38 (m, 2 H, Fmoc CH2),
6.73 (br s, 1 H, NH), 7.24-7.35 (m, 7 H, 4 × Fmoc Ar CH + 2
× C6H4NO2 + NH), 7.63 (d, 2 H, Fmoc Ar CH), 7.78 (d, 2 H,
Fmoc Ar CH), 8.20 (d, 2 H, C6H4NO2). 13C NMR ([D8]THF): δ
) 41.3 (CH2NH), 42.2 (CH2NH), 48.4 (Fmoc CH), 120.6 (Fmoc
Ar CH), 122.7, 125.6 (C6H4NO2), 125.9, 127.7, 128.3 (Fmoc Ar
CH), 142.3, 145.4 (Fmoc Ar quat C), 145.4, 154.2 (C6H4NO2
quat C), 157.5 [C(O)], 157.6 [C(O)]. ES MS: m/z ) 448.2 [M +
H]+.
Au tom a ted P r ep a r a tion of Resin -Bou n d Ur ea Tet-
r a m er 10. Resin-bound tetraurea peptidomimetic 10 was
prepared using an automated ABI 433A peptide synthesizer
using slightly altered ABI Fastmoc 0.25 mmol protocols.
Although the deprotection, washing, and acetylation modules
were left unchanged, a few modifications were introduced into
the coupling module. The coupling time was 90 min instead
of 20 min, and since no coupling reagent was required for the
couplings of the urea monomers, the coupling reagent flask
was filled with NMP instead of a solution of HBTU and HOBt
in NMP.
F m oc-P r otected Activa ted P r olin e Mon om er 5j.
Yield: 2.08 g (4.3 mmol, 86%) of white solid. Mp: >134-136
°C dec. Rf (EtOAc/hexanes, 1/1): 0.40. [R]D24 ) -44.0 (c ) 0.55,
1
dioxane). H NMR (CDCl3): δ ) 1.58-2.10 (m, 4 H, CHCH2-
CH2CH2 + CHCH2CH2CH2), 3.22-3.51 (m, 4 H, CHCH2-
CH2CH2 + CH2NH), 4.10 (m, 1 H, CHN), 4.24 (t, J ) 7.0 Hz,
1 H, Fmoc CH), 4.45 (d, J ) 7.3 Hz, 2 H, Fmoc CH2), 6.79 (s,
1 H, CH2NH), 7.25-7.44 (m, 6 H, 4 × Fmoc Ar CH + 2 × C6H4-
NO2), 7.60 (d, 2 H, Fmoc Ar CH), 7.77 (d, 2 H, Fmoc Ar CH),
8.19 (d, 2 H, C6H4NO2). 13C NMR (CDCl3): δ ) 24.0 (CH2),
29.5 (CH2), 46.9 (CH2NH), 47.0 (CH2N), 47.3 (Fmoc CH), 60.8
(CHN), 67.6 (Fmoc CH2), 120.0 (Fmoc Ar CH), 121.9, 125.0
(C6H4NO2), 125.0, 127.0, 127.8 (Fmoc Ar CH), 141.3, 143.8

8462 J . Org. Chem., Vol. 66, No. 25, 2001
Boeijen et al.
The apparatus was mounted with a reaction vessel filled
with Argogel Rink-NH-Fmoc resin (0.74 g, 0.34 mmol/g, 0.25
mmol), and with four cartridges loaded with 1 mmol of leucine
urea monomer 5c, phenylalanine urea monomer 5e, glycine
urea monomer 5k , and glycine urea monomer 5k , respectively.
The resin was preswelled with DCM (6×) and NMP (5×) and
treated twice with 20% piperidine in NMP (3.6 and 7 min) to
effect cleavage of the Fmoc group. After removal of the
piperidine, the resin was washed with NMP (5×). Subse-
quently, the activated leucine urea monomer 5c (1.0 mmol, 4
equiv) in the cartridge was dissolved in NMP (4 mL). To this
solution was added 1 mL of 2 M DiPEA in NMP (2.0 mmol, 8
equiv), whereupon the resulting mixture was transferred into
the reaction vessel, where an additional amount of NMP
(approximately 5 mL) was added. After the resulting mixture
was vortexed for 90 min, the reaction vessel was drained, and
the resin was washed with NMP (4×). The resin was then
treated for 10 min with a capping solution (a solution of acetic
anhydride (0.5 M), DiPEA (0.125 M), HOBt (0.015 M), and a
catalytic amount of DMAP in NMP) to acetylate any unreacted
amino groups.
To complete the synthesis of immobilized tetramer 10, the
resin was subjected to similar deprotection, coupling, and
capping cycles with the remaining three urea monomers (5e,
5k (twice), respectively). The deprotection and coupling cycles
were followed by monitoring the absorption of the dibenzo-
fulvene-piperidine adduct at 301 nm (Figure 2). The loading
was determined by Fmoc cleavage from a resin sample, and
was 0.282 mmol/g, corresponding to an overall yield of 83%
over eight steps. Finally, the Fmoc group was removed with
piperidine to obtain resin-bound oligourea peptidomimetic 15.
Clea va ge of Ur ea Tetr a m er 10 fr om th e Resin . Resin-
bound urea tetramer 15 (0.355 g, 0.282 mmol/g, 0.10 mmol)
was washed with NMP (5×). The amino terminus was acety-
lated by treatment with 5 mL of capping solution (vide supra).
After 15 min, the solution was drained, and the resin was
washed with NMP (6×) and DCM (5×) and dried in vacuo over
P2O5. Tetramer 10 was then cleaved from the solid support
by shaking of the resin (0.355 g, 0.288 mmol/g, 0.10 mmol)
with 5 mL of TFA/H2O/TIS/EDT (92.5/2.5/2.5/2.5) for 3 h.
Subsequently, the resin was filtered and washed with 2 mL
of TFA. The filtrate was concentrated in vacuo to a volume of
approximately 1 mL and extruded into 40 mL of cold MTBE/
hexanes (1/1). A white fluffy precipitate was formed, which
was collected by centrifugation (3500 rpm, 5 min). The
supernatant was decanted, after which the residue was
resuspended in 40 mL of MTBE/hexanes (1/1) and centrifuged
again. This was repeated twice. Finally, the residue was
purified by preparative HPLC to give 29 mg (0.053 mmol, 53%)
of tetramer 10 after lyophilization. Exact mass: 550.349 [M
+ H]+ (calcd 550.347). HPLC: >99% pure. 1H NMR ([D6]-
DMSO): δ ) 0.83 [m, 6H, (CH3)2], 1.14 [t, 2H, CH2CH(CH3)2],
1.58 [m, 1H, CH(CH3)2], 1.78 (s, 3H, C(O)CH3), 2.64 (m, 4H,
ArCH2 + CH2NAc), 2.8-3.2 (m, 10H, 5 × CH2NHC(O)NH),
3.4-4.0 (m, 8H, 2 × CHNH + NHC(O)NH2 + H2O), 5.7-6.1
(m, 6H, 3 × NHC(O)NH), 7.21 (m, 5H, ArH), 7.89 (br s, NHAc).
P r ep a r a tion of Resin -Bou n d Neu r oten sin Der iva tive
17. Resin-bound neurotensin derivative 17 was prepared
analogously to 10. First, Argogel S-OH (0.38 mmol/g) was
coupled with Fmoc-Leu-OH using the procedure of Sieber.20
The loading was determined by Fmoc cleavage from a resin
sample, and was 0.33 mmol/g. Next, isoleucine monomer 5d ,
tyrosine monomer 5f, proline monomer 5j, and lysine monomer
5i (twice) were coupled, respectively. After removal of the Fmoc
group, cleavage from the resin was carried out as was
described above for urea tetramer 10 to yield a mixture of the
desired oligourea peptidomimetic 17 along with hydantoin 18
in a 2/1 ratio (according to HPLC). Total yield: 105 mg (0.116
mmol, 46%). Exact mass: 906.625 [M + H]+ (calcd 906.625
for the linear oligomer 17) and 888.614 [M + H]+ (calcd
888.615 for the hydantoin 18).
1H NMR (D2O) (17): δ ) 0.86 (m, 13H), 1.07 (m, 1H), 1.3-
1.9 (m, 20H), 2.42 (m, 1H), 2.7-3.0 (m, 3H), 3.0-3.4 (m, 10H),
3.4-4.0 (m, 9H), 4.05 (m, 1H), 5.4 (s, 3H), 6.77 (d, J ) 8.2 Hz,
2H), 7.09 (m, 2H).
Ack n ow led gm en t. Financial support by Solvay
Pharmaceuticals and the Ministry of Economic Affairs
is gratefully acknowledged. We thank Dr G. M. Visser,
Prof. Dr. C. Kruse, and especially Dr. J . A. J . den Hartog
for useful discussions and their interest in this research.
C. Versluis is thanked for performing the MS analyses.
We highly appreciate the efforts of S. Hendriks and H.
B. Albada with respect to optimizing the reproducibility
of the Mitsunobu reaction.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
compounds 10 and 17. This material is available free of charge
via the Internet at http://pubs.acs.org.
J O010656Q