Highly Diastereoselective Metal-Free Catalytic Synthesis of Drug-Like Spiroimidazolidinone

Article abstract of DOI:10.1134/S107042801910021X

A four-step procedure has been developed for the synthesis of (S)-3-isopropyl-1-[(R)-1-phenylethyl)- 1,4-diazaspiro[4.5]decan-2-one with high diastereoselectivity (up to 95% de) from (S)-α-aminoisovaleric acid (L-valine). Quantum chemical computations of the synthesized compound have been performed using Gaussian 09 software package.

Full text of DOI:10.1134/S107042801910021X

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2019, Vol. 55, No. 10, pp. 1598–1603. © Pleiades Publishing, Ltd., 2019.
Highly Diastereoselective Metal-Free Catalytic Synthesis
of Drug-Like Spiroimidazolidinone
A. M. Jassema,* A. H. Raheemahb, W. A. Radhic, A. M. Alid, and H. A. Jabera
a Department of Chemistry, College of Education for Pure Sciences, Basrah University, Basrah, Iraq
*e-mail: ahmedmajeedhsskia@gmail.com
b Department of Chemistry, College of Science, Al-Mustansiriya University, Baghdad, Iraq
c Department of Chemistry, Polymer Research Center, Basrah University, Basrah, Iraq
d Department of Material Science, Polymer Research Center, Basrah University, Basrah, Iraq
Received May 24, 2019; revised June 25, 2019; accepted August 15, 2019
Abstract—A four-step procedure has been developed for the synthesis of (S)-3-isopropyl-1-[(R)-1-phenyl-
ethyl)-1,4-diazaspiro[4.5]decan-2-one with high diastereoselectivity (up to 95% de) from (S)-α-aminoisovaleric
acid (L-valine). Quantum chemical computations of the synthesized compound have been performed using
Gaussian 09 software package.
Keywords: spiroimidazolidinone, L-valine, catalysis, diastereoselectivity, DFT quantum chemical computa-
tions, B3LYP/6-31G(d).
DOI: 10.1134/S107042801910021X
The design and synthesis of cyclic amides are
a major perspective for the exploration and under-
standing of their applications [1]. Cyclic amides whose
active centers contain amino acids with primary amino
substructure are used as natural catalysts for the syn-
thesis of carbohydrates [2, 3]. Chiral α-amino acids
are fundamentally important structures in diverse ap-
plications [4]. A wide range of synthetic methods have
been developed over the last decades to provide access
to not only naturally occurring α-amino acids and their
enantiomers [5, 6] but also to unnatural amino acid
derivatives [7]. Amino acids and their derivatives such
as amides (peptides) are widely used as organo-
catalysts [8–15]. A cyclic amide moiety, particularly
imidazolidinone, is present in many biologically active
natural products and pharmaceutically important com-
pounds [16]. Examples are spiroimidazolones A [anta-
gonist of human glucagon receptor (hGCGR)] [17] and
B [BACE1 (β-secretase) inhibitor for the treatment of
Alzheimer’s disease] [18]. Diastereoisomeric imidazo-
lidinones have been studied as a core unit of many
pharmacological agents [19–22]. Chiral imidazolidi-
nones C [23] and D [24] are successfully used in
aminocatalysis, and imidazolidinone E is an analog of
Sanger and Marfey reagents for analysis of D- and
L-amino acids [25]. The imidazolidinone scaffold
offers many opportunities for tuning and modification
of steric requirements with regard to stereochemistry
of a catalytic system like F [26] which has been tested
as fragrance delivery system.
The construction of a quaternary stereogenic center
in imidazolidinones seems to be a challenging prob-
lem, which is evidenced by increased interest from
synthetic organic chemists over the last 10 years
[27, 28]. Asymmetric synthetic strategies ranging from
classical diastereoselective auxiliary-controlled meth-
ods to modern approaches involving enantioselective
catalysis have been reported. These methods include
allylic substitution [29], conjugate addition [30–32],
and nucleophilic allylation [33, 34].
Therefore, search for efficient methodologies for
the synthesis of imidazolidinone derivatives with
specific biological activities has been undertaken [35].
The developed methods for the synthesis of imidazoli-
dinones from chiral α-amino acids involve the use of
amidophosphane precatalysts [36, 37]. Different
reagents were utilized for the synthesis of disubstituted
chiral N-aryl and N-alkylamines (including α- and
β-amino acids) which can be further converted to
differently functionalized imidazolidinones. The direct
coupling reaction is one of the most common reactions
for C–C and C–N bond formation [38–40].
1598

HIGHLY DIASTEREOSELECTIVE METAL-FREE CATALYTIC SYNTHESIS
1599
Cl
Cl
N
Me
NH
N
Me
N
HN
N
O
N
O
HN
O
H
Me
O
N
N
N
NH
N
O
t-Bu
t-Bu
A
B
C
Me
O
Me
Me
Me
Me
N
H
NH
Me
O
N
HN
Me
O
Me
NH
N
O
F
Me
Me
NO2
O2N
D
E
F
Much effort has been devoted to the development
of highly asymmetric coupling reactions both in metal
[41] and metal-free catalytic conditions [42, 43]. The
coupling of different Boc-protected amino acids with
primary amines under controlled conditions provides
required intermediates [44] in high yields, and the Boc
protecting group can be directly removed to afford
chiral amines [45–48].
In this work, we focused on the synthesis of imid-
azolidinone heterocycle as a chiral auxiliary starting
from an amino acid (Scheme 1). For this purpose,
L-valine (1) was protected with Boc anhydride to
obtain chiral protected amino acid 2. Amino acid 2 was
coupled with chiral amine 3 to afford compound 4
which was deprotected by treatment with concentrated
aqueous HCl in methanol, and intermediate 5 thus
formed was cyclized with cyclohexanone (6) to desired
spiroimidazolidinone 7. The diastereoisomeric purity
of 7 was estimated at 95% de by chiral HPLC.
Chiral amino acid 1 (L-valine) was obtained from
imidazolidinone 7 under harsh acidic conditions
(110°C, 44 h) without loss of enantiomeric excess
(99% ee) (Scheme 2). (S)-2-Amino-3-methyl-N-[(S)-1-
phenylethyl]butanamide (5) can be generated in mod-
erate yield from imidazolidinone 7 through cleavage of
the N–C bond in the presence of 1 M aqueous HCl
under microwave irradiation for only 1 h at 100°C
(96% de).
Scheme 1.
Me
Ph
Me
(3)
H2N
O
Ph
(Boc)2O, aq. NaOH
THF/H2O
Et3N, CH2Cl2
ClC(O)OEt
COOH
NH2
COOH
NHBoc
NH
Me
Me
Me
Me
Me
Me
96%
80%
NHBoc
1
2
4
Ph
Me
O
Me
(6), DMF, reflux
O
O
Ph
N
MeOH/concd. aq. HCl
86%
NH
Me
Me
91%
Me
N
H
NH2
Me
5
7
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 10 2019

JASSEM et al.
1600
Scheme 2.
Ph
Me
Me
Concd. aq. HCl
AcOH, toluene, 110°C, 44 h
1 M HCl, AcOH
toluene, 100°C, 1 h, MW
O
N
COOH
NH2
O
Ph
Me
NH
Me
Me
65%, 99% ee
60%, 95% de
Me
N
H
Me
NH2
Me
1
7
5
The electronic structure of spiroimidazolidinone 7
was analyzed by quantum chemical calculations with
the help of Gaussian 09 software package. Geometry
optimization was carried out at the DFT level in the
B3LYP/6-31G(d) approximation. The energies of the
highest occupied molecular orbital (HOMO) and
lowest unoccupied molecular orbital (LUMO) and
molecular electrostatic potential (MEP) of 7 were
analyzed. The HOMO and LUMO surfaces are shown
in Fig. 1. The HOMO (EHOMO = –5.93 eV) is localized
mostly on the imidazolidinone heterocycle, while the
LUMO (ELUMO = –0.41 eV) is localized on the benzene
ring. The energy gap is 5.44 eV, which makes the
molecule more stable toward ionization.
(a)
The molecular electrostatic potential (MEP) map
[49–51] of 7 was constructed for the most stable
conformer at the same level of theory [DFT B3LYP/
6-31G(d)]. Figure 2 shows two negative regions, one
of which is near the carbonyl oxygen atom and the
other is near the NH nitrogen atom. These two regions
are nucleophilic, and they tend to form hydrogen
bonds by accepting hydrogen atoms from nearest
donor counterparts. Out of these, electrostatic potential
shows positive regions. Thus, there are many regions
that can be involved in interactions with various
targets.
(b)
In summary, a novel drug-like imidazolidinone has
been synthesized from a chiral amino acid (L-valine)
and (S)-(–)-α-methylbenzylamine in a good yield
(91%) with high diastereoselectivity (up to 95% de).
Quantum chemical calculations, including molecular
orbital and electrostatic potential map analysis, have
been performed to elucidate features of its probable
binding to specific sites (biological targets) of proteins,
nucleic acids, receptors, and enzymes.
Fig. 1. (a) HOMO and (b) LUMO structures of imidazoli-
dinone 7.
EXPERIMENTAL
All solvents and starting materials were purchased
from Sigma–Aldrich. All reactions were carried out in
1
a nitrogen atmosphere. The H and 13C NMR spectra
were recorded at room temperature on a Bruker
AV-400 spectrometer at 400 and 100.5 Hz, respec-
tively, using chloroform-d as solvent and reference
(δ 7.26 ppm, δC 77.16 ppm). The melting points were
measured in capillary tubes with a Gallenkamp melting
point apparatus and are uncorrected. The high-resolu-
tion mass spectra (electrospray ionization) were re-
Fig. 2. MEP map of imidazolidinone 7 molecule; negative
region is shown in red, and positive, in yellow.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 10 2019

HIGHLY DIASTEREOSELECTIVE METAL-FREE CATALYTIC SYNTHESIS
1601
corded using a Waters Micromass LCT instrument.
The IR spectra were recorded in the range 4000–
700 cm–1 on a Perkin Elmer Paragon 100 FTIR spec-
trophotometer. Microwave-assisted reactions were ac-
complished using a Smith CreatorTM EXP reactor and
Smith process vialsTM (Sheffield, UK). The products
were purified by flash column chromatography on
silica gel 60 (230–400 mesh). HPLC analyses were
carried out using an Alltima C18 column (4.6 mm×
250 mm, 3 μm); 5–95% MeCN/0.1% aqueous TFA
(10 min), then hold 6 min; UV detection at λ 256 nm;
room temperature. The optical rotations were meas-
ured at λ 589 nm. Analytical TLC was performed
using plates precoated with silica gel 60 UV 254 nm;
spots were visualized by treatment with aqueous potas-
sium permanganate and under UV light.
Yield 3.2 g (80%), white solid, mp 133–136°C, [α]D20 =
+27.4° (c = 1, CHCl3). IR spectrum, ν, cm–1: 3352 s
(N–H), 3062 (C–Harom), 2932 (C–H), 2861 (C–H),
1
1685 s (C=O), 1604 (C=Carom). H NMR spectrum, δ,
ppm: 0.91 d (3H, CH3, J = 6.6 Hz), 0.96 d (3H, CH3,
J = 6.6 Hz), 1.40 s (9H, t-Bu), 1.48 d (3H, CH3, J =
6.8 Hz), 2.10–2.15 m (1H, CH), 4.42 d (1H, CH, J =
4.3 Hz), 5.04–5.11 m (1H, CH), 7.22–7.33 m (5H, Ph).
13C NMR spectrum, δC, ppm: 19.4, 21.9, 28.3 (3C),
30.5, 50.8, 63.3, 79.2, 125.7, 127.3, 128.6, 142.9,
155.9, 170.6. Mass spectrum: m/z 321.2178 [M + H]+.
C18H29N2O3. Calculated: M + H 321.2180.
(S)-2-Amino-3-methyl-N-[(S)-1-phenylethyl]-
butanamide (5). A solution of 2.5 g (12.5 mmol) of
carbamate 4 in 15 mL of methanol was cooled to 0°C,
1.3 mL (11.7 mmol) of 10 N aqueous HCl was added
dropwise, and the mixture was stirred for 4 h at room
temperature. The mixture was then evaporated under
reduced pressure, and the residue was neutralized with
aqueous NaHCO3 and extracted with ethyl acetate. The
ethyl acetate layer was dried over anhydrous MgSO4
and concentrated under reduced pressure, and the
crude product was purified by column chromatography
(ethyl acetate–petroleum ether, 4:6; Rf 0.4). Yield
2.1 g (86%), gummy material, [α]D20 = –115.4° (c = 1,
CHCl3). IR spectrum, ν, cm–1: 3353 s (N–H), 3085
(C–Harom), 3062 (C–Harom), 2978 (C–H), 2881 (C–H),
(S)-2-[(tert-Butoxycarbonyl)amino]-3-methyl-
butanoic acid (2) [52–54]. An aqueous solution of
2.5 g (63.8 mmol) of sodium hydroxide was added to
a solution of 2.5 g (21.2 mmol) of (S)-α-aminoiso-
valeric acid (1) in 50 mL of THF, and 5.1 g
(23.4 mmol) of Boc anhydride was then added. The
mixture was stirred for 14 h at room temperature,
acidified with 1 N aqueous HCl, and extracted with
ethyl acetate (3×25 mL). The combined organic ex-
tracts were dried over anhydrous MgSO4 and evapo-
rated under reduced pressure. Yield 4.4 g (96%), oily
mate-rial, [α]D20 = –9.6° (c = 1, DMF). IR spectrum, ν,
cm–1: 3446–3289 br (O–H), 2936 (C–H), 2861 (C–H),
1715 s (C=O). 1H NMR spectrum, δ, ppm: 0.96 d (3H,
CH3, J = 6.8 Hz), 1.00 d (3H, CH3, J = 6.8 Hz), 1.45 s
(9H, t-Bu), 2.18–2.21 m (1H, CH), 4.24–4.27 m (1H,
CH), 8.10 br.s (1H, NH). 13C NMR spectrum, δC, ppm:
19.0, 28.3 (3C), 31.2, 58.4, 80.0, 155.8, 176.6. Mass
spectrum: m/z 218.3436 [M + H]+. C10H19NO4. Cal-
culated: M + H 218.3440.
1
1686 (C=O), 1614 (C=Carom). H NMR spectrum, δ,
ppm: 0.87 d (3H, CH3, J = 7.0 Hz), 1.01 d (3H, CH3,
J = 7.0 Hz), 1.31 br.s (2H, NH2), 1.51 d (3H, CH3
J = 6.8 Hz), 2.35 d.d (1H, CH, J = 6.9, 3.7 Hz), 3.24 d
(1H, CH, J = 3.7 Hz), 5.16 d.t (1H, CH, J = 15.2,
6.9 Hz), 7.27–7.29 m (1H, Harom), 7.33–7.36 m (2H,
H
arom), 7.37 m (2H, Harom), 7.36 d (1H, NH,
J = 5.5 Hz). 13C NMR spectrum, δC, ppm: 15.9, 19.7,
22.1, 30.8, 48.1, 60.0, 126.2 (Carom), 127.2 (CHarom),
128.6 (CHarom), 143.4, 173.3. Mass spectrum:
m/z 221.1654 [M + H]+. C13H21N2O. Calculated:
M + H 221.1667.
tert-Butyl ((S)-3-methyl-1-oxo-1-{[(S)-1-phenyl-
ethyl]amino}butan-2-yl)carbamate 4 [55, 56].
Triethylamine, 2.8 mL (20.1 mmol), was added under
nitrogen to a cold solution of 4.0 g (18.4 mmol) of acid
2 in 75 mL of methylene chloride. Ethyl chloro-
formate, 1.9 mL (20.1 mmol), was then slowly added,
the mixture was stirred for 1 h at room temperature,
2.4 mL (18.4 mmol) of of (S)-(–)-α-methylbenzyl-
amine was added, and the mixture was additionally
stirred for 2 h at room temperature. The organic layer
was washed with aqueous NaHCO3 and brine, ex-
tracted with ethyl acetate, dried over anhydrous
Na2SO4, and evaporated under reduced pressure. The
crude compound was purified by column chromatog-
raphy (ethyl acetate–petroleum ether, 4:6; Rf 0.2).
(3S)-1-[(R)-1-Phenylethyl]-3-(propan-2-yl)-1,4-
diazaspiro[4.5]decan-2-one (7). A mixture of 2.2 g
(10.0 mmol) of 5 and 1.0 mL of cyclohexanone (6) in
15.0 mL of DMF was refluxed for 5 h. The mixture
was concentrated on a rotary evaporator, and the
residue was treated thrice with 10 mL of isopropyl al-
cohol, followed by evaporation, to remove DMF com-
pletely. The product was purified by flash chromatog-
raphy on silica gel (ethyl acetate–petroleum ether, 4:6;
Rf 0.3). Yield 2.0 g (91%), viscous oil. IR spectrum, ν,
cm–1: 3351 s (N–H), 3062 (C–Harom), 3028 (C–Harom),
2932 (C–H), 2861 (C–H), 1685 (C=O), 1638
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 10 2019

JASSEM et al.
1602
(C=Carom). 13C NMR spectrum, δC, ppm: 0.95 d (3H,
CH3, J = 6.8 Hz), 1.05 d (3H, CH3, J = 6.9 Hz), 1.78–
1.55 m (10H, CH2) 1.85 d (3H, CH3, J = 3.6 Hz), 2.20–
2.16 m (1H, CH) 3.45 d (1H, CH, J = 3.7 Hz), 4.42 d.d
(1H, CH, J = 14.2, 7.1 Hz), 7.23 t (1H, Harom, J =
7.3 Hz), 7.31 t (2H, Harom, J = 7.4 Hz), 7.45 d (2H,
10. Samanta, S., Liu, J., Dodda, R., and Zhao, C.-G., Org.
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H
arom, J = 8.4 Hz). 13C NMR spectrum, δC, ppm: 16.9,
12. He, L., Jiang, J., Tang, Z., Cui, X., Mi, A.-Q.,
Jiang, Y.-Z., and Gong, L.-Z., Tetrahedron: Asymmetry,
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19.2, 19.7, 23.1 (2C), 24.9, 37.7, 52.4 (2C, CH2), 62.5
(CH), 78.6, 126.8, 128.2, 142.7 (CH), 178.4. Mass
spectrum: m/z 301.2274 [M + H]+. C19H28N2O. Cal-
culated: M + H 301.2276.
FUNDING
This work was financially supported by the Ministry of
Higher Education and Scientific Research (Iraq).
https://doi.org/10.1021/ja0510156
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ACKNOWLEDGMENTS
The authors gratefully acknowledge Sheffield University
1
(UK) for recording IR, H and 13C NMR, and high-resolu-
tion mass spectra.
https://doi.org/10.1021/ja001133n
CONFLICT OF INTERESTS
The authors declare no conflict of interests.
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 55 No. 10 2019