Synthesis and characterization of novel dipeptide mimetics with hydantoin moiety

Article abstract of DOI:10.1016/j.crci.2010.01.011

The synthesis of three novel 5,5-dimethylhydantoin derivatives 2-amino-N-(4,4-dimethyl-2,5-dioxoimidazolidin-1-yl)acetamide, 2-amino-N-(4,4-dimethyl-2,5-dioxoimidazol idin-1-yl)-3-phenylpropanamide, and 2-amino-4-methyl-N-(4,4-dimethyl-2,5-dioxoimidazol i

Full text of DOI:10.1016/j.crci.2010.01.011

C. R. Chimie 13 (2010) 1424–1428
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´
Full paper / Memoire
Synthesis and characterization of novel dipeptide mimetics with
hydantoin moiety
*
Petar T. Todorov , Emilia D. Naydenova
Department of Organic Chemistry, University of Chemical Technology and Metallurgy, BG-1756 Sofia, Bulgaria
A R T I C L E I N F O
A B S T R A C T
Article history:
The synthesis of three novel 5,5-dimethylhydantoin derivatives 2-amino-N-(4,4-
dimethyl-2,5-dioxoimidazolidin-1-yl)acetamide, 2-amino-N-(4,4-dimethyl-2,5-dioxoi-
midazol idin-1-yl)-3-phenylpropanamide, and 2-amino-4-methyl-N-(4,4-dimethyl-2,5-
dioxoimidazol idin-1-yl) pentanamide, is reported. The newly synthesized compounds
have been characterized by infrared (IR), MS, and NMR (1H and 13C) spectra.
Received 28 October 2009
Accepted after revision 27 January 2010
Available online 19 March 2010
Keywords:
´
ß 2010 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Hydantoins
5,5-Disubstituted hydantoins
Peptide synthesis
Amino acids
1. Introduction
phenytoin (Dilantin1, Epilan1), one of the important drugs
employed for the treatment of generalized convulsions, are
Hydantoin and its derivatives are biologically impor-
tant compounds of relevance to chemists, biologists and
pharmaceutical researchers. Over the last few decades,
there has been considerable interest in the synthesis and
characterization of hydantoin derivatives as an important
class of heterocyclic compounds. Hydantoin derivatives
that display interesting activities against a broad range of
biological targets have been identified [1]. Hydantoins,
substituted at C-5, are important medicinal compounds.
Numerous applications have been found for hydantoin
derivatives due to their antidepressant [2] and antiviral
activities [3], the inhibition of binding of HIV to
lymphocytes, [4] as well as their anticonvulsant and
cardiac anti-arrhythmic effects [5]. Epilepsy is a group of
chronic neurological disorders whose symptoms result
from a brain dysfunction or an abnormal discharge of
cerebral neurons. Drug therapy is the major treatment for
epilepsy, and among the major drugs used in its treatment
are the hydantoins [6]. The anticonvulsant properties of
responsible for the synthesis of many hydantoin analogs
[7]. In the chemical industry, various 5,5-disubstituted
hydantoins constitute the basis of a new generation of
weatherproof high-temperature stable epoxy resins.
Furthermore, hydantoin and hydantoin derivatives were
used as a monomer for the synthesis of condensation
polymers [8]. Hydantoin derivatives are synthetically
valuable, e.g. as precursors to
a-amino acid and pyruvic
acid derivatives [9–11]. The structural characteristics of
hydantoins and spirohydantoins are interesting in view of
the development of novel drugs [12], and for better
understanding the structure–activity relationship. As part
of our research, the synthesis and characterization of
series, new hydantoin-phosphonic acids and their analo-
gues have been described [13–15]. The main goal of this
study is synthesis of new hydantoin derivates as potential
biologically active compounds. Many derivatives of these
compounds have been synthesized and studied, but there
are no data about the influence of the amino group and
amino acids residue in the hydantoin ring on their
biological activity. Based on already existed papers and
our experience, we choose to synthesize some different
derivatives of 5,5-dimethylhydantoin by TBTU/DIEA
method.
* Corresponding author.
E-mail addresses: pepi_37@abv.bg (P.T. Todorov),
e_naydenova@abv.bg (E.D. Naydenova).
1631-0748/$ – see front matter ß 2010 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2010.01.011

P.T. Todorov, E.D. Naydenova / C. R. Chimie 13 (2010) 1424–1428
1425
Scheme 1. Synthesis of new hydantoin derivatives.
2. Results and discussion
synthetic pathway for the preparation of the novel
compounds is given in the Scheme 1.
The synthesis and spectroscopic characteristics of many
hydantoin derivatives are given in the literature [16–20],
but no hydantoin consisting amino acid residue and
consequently, their spectroscopic data are published up
to now. In the present work, some different derivatives of
5,5-dimethylhydantoin were obtained in good yields by
TBTU (2-(1-OH-benzotriazole-1-yl)1,1,3,3-tetramethyl-
carbamide tetrafluoroborat)/DIEA (N,N-diiso propylethy-
lamine) method. To prepare the new hydantoin derivatives
(4a-4d and 5a-5c), we used, as a starting compound, 3-
amino-5,5-dimethylimidazolidine-2,4-dione (2), whose
synthesis was described in our previous work [15]. In
order to synthesize compounds 4a-4d, we decided to use
the corresponding protected amino acids, namely 3a-3d
(Boc-Gly-OH, Boc-L-Leu-OH, Z-L-Phe-OH, Z-Gly-OH).
Three novel dipeptides, 2-amino-N-(4,4-dimethyl-2,5-
dioxoimidazolidin-1-yl) acetamide (5a), 2-amino-N-(4,4-
dimethyl-2,5-dioxoimidazolidin-1-yl)-3-phenylpropana-
mide (5b), 2-amino-4-methyl-N-(4,4-dimethyl-2,5-diox-
oimidazolidin-1-yl)pentanamide (5c), were synthesized
by the deblocking of the Z-/Boc-group of the corresponding
protected dipeptides. The corresponding protected dipep-
tides with Boc-group 4a and 4b were deblocked by
Trifluoroacetic acid (TFA) for four hours at room tempera-
ture to obtain 5a and 5c, respectively. The corresponding
protected dipeptides with Z-group 4c and 4d were
deblocked by catalytic hydrogenolysis in the presence of
Pd/C for five hours to obtain 5a and 5b, respectively. The
The newly synthesized compounds were characterised
bymeltingpoints, thinlayer chromatography (TLC), infrared
(IR) and NMR spectroscopy, high performance liquid
chromatography (HPLC) and MS (see Experimental section).
The IR spectroscopy study confirms the structure of the
above-mentioned compounds. The IR spectra of hydantoin
derivatives 5a-5c showed two strong peaks between 3200
and 3300 cmꢀ1 that were assigned to the N-H of the imide
and amide groups. Absorption bands between 1780 and
1730 cmꢀ1 characterize the asymmetric and symmetric
stretching of the carbonyl groups of the hydantoin. In the
IR spectra of the compounds, 5a-5c absorption bands
between 1690 and 1630 cmꢀ1 (amide I) and 1580 and
1530 cmꢀ1 (amide II) are observed which are characteristic
peaks for amide groups.
The structures of all newly synthesized compounds
have also been confirmed by 1H- and 13C-NMR spectro-
scopies. The singlet of 1H-NMR spectra of compounds 4a
and 4b at 1.5 ppm can be assigned with the nine protons
from the tert-butyl group. The singlet at 3.8 ppm and the
triplet at 3.1 ppm for 4a and 4b, respectively, can be
assigned to the proton from CH-group connected to NH-
group. The signals of 1H-NMR spectra of compounds 4c and
4d at 4.7–4.8 ppm (singlet) can be assigned to the two
protons from CH2 of Z-group and 6.8–7.7 ppm (multiplet)
can be assigned with aromatic protons in Z-group. Signals
for NH2-group at 4.8–4.9 ppm were observed in 1H-NMR
spectra for all deblocked peptides 5a-5c.

1426
P.T. Todorov, E.D. Naydenova / C. R. Chimie 13 (2010) 1424–1428
Fig. 1. 13C-NMR spectrum of benzyl 1-(4,4-dimethyl-2,5-dioxoimidazolidin-1-ylcarbamoyl)-2-phenylethylcarbamate (4c).
Detailed spectroscopic data for all other hydantoin
the starting compound 2, which is a proof that the new
compound 4c is obtained. These data from the NMR and
MS spectra confirm the structure of the compound 4c.
derivatives are presented in the Experimental section. As
an example, we present here the 13C-NMR and MS spectra
of compound benzyl 1-(4,4-dimethyl-2,5-dioxoimidazoli-
din-1-ylcarbamoyl)-2-phenylethyl carbamate (4c) (Fig. 1
and Fig. 2). The 13C-NMR spectrum of compound 4c,
recorded in CD3OD solution, exhibits the four signals of
carbon atom for C = O group, 155.16 (14C = O), 158.19
(2C = O), 173.11 (4C = O), 176.74 (5C = O) ppm. The signals
in the diapason at 127–138 ppm in the 13C-NMR spectrum
can be assigned to the carbon atoms of both aromatic
systems (Fig. 1). In the 1H-NMR spectrum of this structure,
there are signals at 4.40 ppm (triplet) that can be assigned
to the CH proton, and the multiplet at 6.80-7.70 that can be
assigned to the protons of two aromatic systems.
Additionally in the same NMR spectrum, there is no signal
at 4.8 ppm for the protons of the NH2 group characterizing
3. Conclusion
In this article, the synthesis and characterization of new
hydantoin derivatives, prepared by reacting of 3-amino-
5,5-dimethylimidazolidine-2,4-dione (2) and the corre-
sponding protected amino acids (3a-3d) by TBTU/DIEA
method, are described. After removing the Z-/Boc-group
from the protected dipeptides, compounds (5a-5c) were
obtained in good yields. The molecular structure of all
compounds was studied by means of spectral methods.
Further studies for the preparation and application of
dipeptide derivatives with hydantoin moiety are currently
in progress.
4. Experimental section
The protected amino acids were purchased from
IrisBiotech (Germany). All other reagents and solvents
were analytical or HPLC grade and were bought from
Merck (Germany). The IR spectra were recorded in KBr
pellets with a Perkin-Elmer Model 1600 Series FTIR
instrument. Melting points (mp) were determined on a
Koffler microscope and were uncorrected. Optical rota-
tions were measured with a Perkin-Elmer 341 polarimeter.
Fig. 2. MS spectrum of compound 4c.

P.T. Todorov, E.D. Naydenova / C. R. Chimie 13 (2010) 1424–1428
1427
The purity of the products was checked by TLC on pre-
coated plates of Silica gel 60 F254 (on recoated plates,
Merck – Germany) using as mobile phase a 9:1 mixture of
chloroform and methanol. Spots on TLS chromatograms
were detected by chlorine/o-tolidine reaction and ninhi-
drine. The 1H and 13C-NMR spectra were obtained with a
Bruker DRX 400 spectrometer at 400.13 and 100.61 MHz,
respectively. 13C-NMR spectra were fully 1H decoupled. All
21.06 (CH3), 22.50 (CH), 24.05 (CH3), 28.30 (CH3), 40.50
(CH2), 50.16 (CH-N), 61.07 (-C-), 79.50 (-C-), 148.20
(2C = O), 154.08 (C = O), 163.84 (4C = O), 168.90 (C = O); IR
(KBr, cmꢀ1): 3312, 2962, 2872, 1770, 1740, 1695, 1519,
1166; ESI-MS: [M + 1] = 357.2; RP-HPLC: Rt 6.50 min.
4.5. Benzyl 1-(4,4-dimethyl-2,5-dioxoimidazolidin-1-
ylcarbamoyl)-2-phenylethyl carbamate: 4c
chemical shifts were reported as
d values (ppm) relative to
internal tetramethylsilane. The crude peptides were
purified on a reversed-phase HPLC C18 column: flow
1 ml/min, H2O/CH3CN/0.1% TFA gradient 0 ! 100% 20 min.
The peptide purity was checked by electrospray ionization
mass spectrometry.
White solid, 86.0% yield; Rf = 0.68; mp 145–147 8C; 1H-
NMR (400.13 MHz, CD3OD):
d (ppm): 1.70 (s, 6H, CH3),
3.15 (d, 2H, CH-CH2-Ar), 4.40 (t, 1H, CH-CH2), 4.81 (s, 2H, O-
CH2-Ar), 6.80-7.70 (m, 10H, Ar), 8.80 (s, 1H, NH-CO);
13C{1H} NMR (100.61 MHz, CD3OD):
d (ppm): 25.03 (CH3),
39.18 (CH2-Ar), 56.25 (CH), 58.90 (-C-), 67.59 (O-CH2-Ar),
127-138 (C-Ar), 155.16 (C = O), 158.19 (2C = O), 173.11
(4C = O), 176.74 (C = O); IR (KBr, cmꢀ1): 3300, 3063, 2981,
1790, 1740, 1695, 1521, 1258; ESI-MS: [M + 1] = 424.5; RP-
HPLC: Rt 8.33 min.
4.1. 3-Amino-5,5-dimethylimidazolidine-2,4-dione: 2
This compound was prepared according to the proce-
dure described by us [15].
4.2. General procedure for preparation by the TBTU/DIEA
4.6. Benzyl (4,4-dimethyl-2,5-dioxoimidazolidin-1-
(compounds 4a-4d)
ylcarbamoyl)methylcarbamate: 4d
3-Amino-5,5-dimethylimidazolidine-2,4-dione
2
White solid, 79.0% yield; Rf = 0.65; mp 165–166 8C; 1H-
(0.50 g, 1.00 mol), and the corresponding Boc-Gly-OH 3a
(0.74 g, 1.20 mol), Boc-L-Leu-OH 3b (0.63 g, 1.20 mol), Z-L-
Phe-OH 3c (0.76 g, 1.20 mol), and respectively, Z-Gly-OH
3d (0.88 g, 1.20 mol) were dissolved in Dimethylforma-
mide (DMF) (4 ml). Then (1.20 mol) of TBTU (2-(1-OH-
benzotriazole-1-yl)1,1,3,3-tetramethyl-carbamide tetra-
fluoroborat), (1.20 mol) HOBt (1-hydroxy benzotriazole)
NMR (400.13 MHz, CD3OD): d (ppm): 1.71 (s, 6H, CH3),
3.80 (s, 2H, CH2-NH), 4.75 (s, 2H, O-CH2-Ar), 6.85-7.72 (m,
5H, Ar), 6.92 (s, 1H, NH), 8.15 (s, 1H, N-NH-CO); 13C{1H}
NMR (100.61 MHz, CD3OD):
d (ppm): 22.45 (CH3), 42.10
(CH2-N), 60.59 (O-CH2-Ar), 65.60 (-C-), 126-137 (C-Ar),
151.20 (2C = O), 155.17 (C = O), 164.08 (4C = O), 172.00
(C = O); IR (KBr, cmꢀ1): 3310, 3072, 2977, 1785, 1744, 1682,
1530, 1260; ESI-MS: [M + 1] = 335.2; RP-HPLC: Rt 6.65 min.
and (1.20 mol,
r=0.76) of DIEA (N,N-diisopropylethyla-
mine) were added. The reaction mixture was stirred at
room temperature for 24 hours. After the end of the
reaction, 10 ml water was added and the product was
extracted by ethyl acetate (3 ꢁ 10 ml). The organic layer
was washed with 5% NaHCO3 (3 ꢁ 10 ml), and water to pH
6–7 and dried over Na2SO4. The solvent was removed in
vacuo and the crystallized product was purified by
precipitation in ethyl acetate/petroleum ether.
4.7. General procedure for deblocking of Boc-group.
Obtaining of compounds 5a and 5c
The corresponding protected dipeptides 4a and 4b
(1.00 mol) were dissolved in 10.00 mol TFA. The reaction
mixture was stirred for four hours at room temperature.
The end of the reaction was monitored by TLC. The excess
of the solvent was removed in vacuo and the crystallized
product was washed with cold diethyl ether.
4.3. Tert-butyl (4,4-dimethyl-2,5-dioxoimidazolidin-1-
ylcarbamoyl) methylcarbamate: 4a
4.8. 2-Amino-N-(4,4-dimethyl-2,5-dioxoimidazolidin-1-
1
White solid, 80.5% yield; Rf = 0.55; mp 135–137 8C; H-
yl)acetamide: 5a
NMR (400.13 MHz, CD3OD):
(s, 6H, CH3), 3.83(s, 2H, CH2-NH),6.80(s, 1H,NH), 7.95(s,1H,
N-NH-CO); 13C{1H} NMR (100.61 MHz, CD3OD):
(ppm):
21.90 (CH3), 28.65 (CH3), 52.10 (CH-N), 62.00 (-C-), 77.50 (-
C-), 150.20 (2C = O), 156.07 (C = O), 165.04 (4C = O), 171.10
(C = O); IR (KBr, cmꢀ1): 3314, 2980, 1793, 1750, 1682, 1530,
1157; ESI-MS: [M + 1] = 301.2; RP-HPLC: Rt 5.80 min.
d (ppm): 1.55 (s, 9H, CH3), 1.71
White solid, 78.5% yield; mp 142–144 8C; 1H-NMR
d
(400.13 MHz, CD3OD):
2H, CH2-NH2), 4.8 (s, 2H, NH2), 6.7 (s, 1H, NH), 7.92 (s, 1H,
N-NH-CO); 13C{1H} NMR (100.61 MHz, CD3OD):
(ppm):
d (ppm): 1.69 (s, 6H, CH3), 3.73 (s,
d
25.01 (CH3), 40.38 (CH2), 59.03 (-C-), 154.92 (2C = O),
167.14 (4C = O), 176.63 (C = O); IR (KBr, cmꢀ1): 3300, 2982,
1773, 1736, 1681 and 1625 (amide I), 1575 and 1532
(amide II); ESI-MS: [M + 1] = 201.2; RP-HPLC: Rt 5.80 min.
4.4. Tert-butyl 1-(4,4-dimethyl-2,5-dioxoimidazolidin-1-
ylcarbamoyl)-3-methylbutyl carbamate: 4b
4.9. 2-Amino-4-methyl-N-(4,4-dimethyl-2,5-
White solid, 80.5% yield; Rf = 0.60; mp 115–118 8C; 1H-
dioxoimidazolidin-1-yl)pentanamide: 5c
NMR (400.13 MHz, CD3OD):
1.24 (m, 1H, CH), 1.54 (s, 9H, CH3), 1.69 (s, 6H, CH3), 1.82 (t,
d (ppm): 1.11 (d, 6H, CH3-CH),
White solid, 70.2% yield; mp 135–136 8C; 1H-NMR
2H, CH2), 3.13 (t, 1H, CH-NH), 6.71 (s, 1H, NH), 8.60 (s, 1H,
(400.13 MHz, CD3OD):
(m, 1H, CH), 1.71 (s, 6H, CH3), 1.80 (t, 2H, CH2), 3.13 (t, 1H,
d (ppm): 1.01 (d, 6H, CH3-CH), 1.21
N-NH-CO); 13C{1H} NMR (100.61 MHz, CD3OD):
d (ppm):

1428
P.T. Todorov, E.D. Naydenova / C. R. Chimie 13 (2010) 1424–1428
CH-NH2), 4.90 (s, 2H, NH2), 6.90 (s, 1H, NH), 8.62 (s, 1H, N-
NH-CO); 13C{1H} NMR (100.61 MHz, CD3OD):
(ppm):
Acknowledgement
d
22.00 (CH3), 23.50 (CH), 23.85 (CH3), 40.50 (CH2), 49.66
(CH-N), 60.11 (-C-), 148.20 (2C = O), 163.84 (4C = O), 168.90
(C = O); IR (KBr, cmꢀ1): 3315, 2960, 2881, 1772, 1732, 1678
and 1639 (amide I), 1575 and 1541 (amide II); ESI-MS:
[M + 1] = 257.3; RP-HPLC: Rt 5.78 min.
We gratefully acknowledge the financial support by
Bulgarian National Fund of Scientific Research and the
University of Chemical Technology and Metallurgy – Sofia
– contract 10646.
References
4.10. General procedure for deblocking of Z-group by
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White solid, 75.0% yield; mp 175–177 8C; [a 20
(c0.1, MeOH);1H-NMR(400.13 MHz,CD3OD):
(ppm):1.68
] D = + 59.4
d
(s, 6H, CH3), 3.20 (d, 2H, CH-CH2-Ar), 4.46 (t, 1H, CH-NH2),
4.87 (s, 2H, NH2), 6.75 - 7.81 (m, 5H, Ar), 7.90 (s, 1H, N-NH-
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d (ppm): 25.10
(CH3), 39.22 (CH2-Ar), 57.05 (CH), 59.00 (-C-), 127-138 (C-
Ar), 158.19 (2C = O), 173.11 (4C = O), 176.74 (C = O); IR (KBr,
cmꢀ1): 3305, 2985, 2890, 1774, 1741, 1681 and 1636
(amideI), 1580and 1533(amideII);ESI-MS:[M + 1] = 291.2;
RP-HPLC: Rt 7.50 min.
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