Synthesis of Acyl Derivatives of Prolyl-leucinamides

Article abstract of DOI:10.1134/S1070428020010145

Synthetic routes to prolyl-leucinamide, N-benzyl(prolyl)leucinamide, and N-(prolyl-leucyl)morpholine were proposed. Treatment of these compounds with benzoyl chloride or acetyl chloride in the presence of triethylamine afforded the corresponding (N-acylpr

Full text of DOI:10.1134/S1070428020010145

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2020, Vol. 56, No. 1, pp. 82–89. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Organicheskoi Khimii, 2020, Vol. 56, No. 1, pp. 103–111.
Synthesis of Acyl Derivatives of Prolyl-leucinamides
V. A. Haidukevicha, D. V. Kievitskayaa, L. A. Popovaa, and V. A. Knizhnikova,*
a Institute of Physical Organic Chemistry, National Academy of Sciences of Belarus, Minsk, 220072 Belarus
*e-mail: knizh@ifoch.bas-net.by
Received July 23, 2019; revised November 22, 2019; accepted November 27, 2019
Abstract—Synthetic routes to prolyl-leucinamide, N-benzyl(prolyl)leucinamide, and N-(prolyl-leucyl)morpho-
line were proposed. Treatment of these compounds with benzoyl chloride or acetyl chloride in the presence of
triethylamine afforded the corresponding (N-acylprolyl)leucinamides. Acyl derivatives of N-benzyl(prolyl)-
leucinamide, and N-(prolyl-leucyl)morpholine were also synthesized by condensation of (N-benzoylprolyl)-
leucine or (N-acetylprolyl)leucine with benzylamine or morpholine in the presence of N,N′-dicyclohexyl-
carbodiimide.
Keywords: N-tert-butyloxycarbonylprolyl-leucine methyl ester, prolyl-leucinamide, benzylamine, morpholine,
acyl derivatives of prolyl-leucinamide.
DOI: 10.1134/S1070428020010145
Peptides are biologically active compounds. Medi-
cines with various therapeutic effects have been
designed on the basis of peptides and are widely used
in medical practice. There are published data [1–5]
according to which some peptide derivatives such as
amides, cyclic peptides, and acylpeptides also exhibit
high physiological activity and selectivity, so that they
can be used as drug substances and administered at
minimum doses to avoid side effects. However, only
a few examples of synthesis of acyl and amide
derivatives of peptides have been reported so far.
The goal of the present work was to develop methods
of synthesis of prolyl-leucinamides and their acyl
derivatives.
The starting compound was (N-tert-butoxycarbonyl-
prolyl)leucine methyl ester (1) which was prepared by
adding triethylamine to a cold (–15°C) mixture of
leucine methyl ester hydrochloride and mixed anhy-
dride obtained from N-tert-butoxycarbonylproline and
isobutyl chloroformate and subjected to further trans-
formations without isolation in the pure state. Treat-
ment of 1 with a 6 N solution of ammonia in ethanol
Scheme 1.
O
O
O
H
N
H
N
H
N
O
O
O
NH3, MeOH
HCl, dioxane
Boc
Boc
MeO
H2N
H2N
·HCl
NH
N
N
i-Pr
i-Pr
i-Pr
1
2
3
O
H
N
O
O
BzCl, Et3N
H2N
Ph
N
O
H
N
O
i-Pr
EtONa
5
H2N
NH
O
H
N
O
i-Pr
O
AcCl, Et3N
4
H2N
Me
N
i-Pr
6
82

SYNTHESIS OF ACYL DERIVATIVES OF PROLYL-LEUCINAMIDES
83
Scheme 2.
O
O
O
H
N
H
N
H
N
O
O
O
Ph
Ph
PhCH2NH2, DCC
HCl, dioxane
Boc
Boc
HO
N
H
N
H
N
N
NH ·HCl
i-Pr
i-Pr
i-Pr
7
9
O
H
N
O
Ph
EtONa
N
H
NH
i-Pr
11
O
O
O
H
N
H
N
H
N
O
O
O
NH
, DCC
O
HCl, dioxane
Boc
Boc
HO
N
N
·HCl
NH
N
N
i-Pr
i-Pr
i-Pr
O
O
8
10
O
H
N
O
EtONa
N
NH
i-Pr
O
12
gave (N-tert-butoxycarbonylprolyl)leucinamide 2. To
complete the ammonolysis process, the reaction mix-
ture was kept for 5 days at room temperature. The Boc
protecting group was removed from 2 by the action of
hydrogen chloride in dioxane, and the subsequent treat-
ment of hydrochloride 3 thus formed with an equimolar
amount of sodium ethoxide afforded prolyl-leucin-
amide 4 (Scheme 1). Amide 4 reacted with benzoyl
chloride and acetyl chloride in the presence of triethyl-
amine to produce N-benzoylprolyl and N-acetylprolyl
derivatives 5 and 6, respectively.
deprotected by treatment with a solution of hydrogen
chloride in dioxane, and hydrochlorides 9 and 10 were
converted to N-benzyl(prolyl)leucinamide 11 and
4-(prolyl-leucyl)morpholine 12 by the action of
an equimolar amount of sodium ethoxide (Scheme 2).
The acylation of 11 and 12 with benzoyl chloride or
acetyl chloride in the presence of triethylamine gave
N-benzyl(N-benzoylprolyl)leucinamide 13, (N-acetyl-
prolyl)-N-benzylleucinamide 14, 4-(N-benzoylprolyl)-
leucyl)morpholine 15, and 4-[(N-acetylprolyl)leucyl]-
morpholine 16 (Scheme 3). Compounds 13–16 were
also synthesized independently starting from prolyl-
leucine which was obtained as described in [7].
Treatment of a solution of prolyl-leucine sodium salt
(prepared by reaction of prolyl-leucine with sodium
ethoxide) with benzoyl chloride or acetyl chloride
afforded N-acyl derivatives 17 and 18, respectively,
and the condensations of 17 and 18 with benzylamine
and morpholine in the presence of DCC produced
target N-substituted prolyl-leucinamides 13–16.
It should be noted that compound 1 failed to react
with morpholine or benzylamine at room temperature,
and the initial compound was recovered even after
three weeks. Therefore, as starting material for the
synthesis of N-substituted prolyl-leucinamides we used
(N-tert-butoxycarbonylprolyl)leucine which was pre-
pared according to the procedure developed by us
previously [6].
The condensations of (N-tert-butoxycarbonyl-
prolyl)leucine with benzylamine and morpholine in
the presence of N,N′-dicyclohexylcarbodiimide (DCC)
afforded N-benzyl(N-tert-butoxycarbonylprolyl)leucin-
amide 7 and 4-[(N-tert-butoxycarbonylprolyl)leucyl]-
morpholine 8, respectively. Compounds 7 and 8 were
The structure of the synthesized compounds was
confirmed by IR and NMR spectra and elemental
analyses. It should be noted that some signals in the
1H and 13C NMR spectra of compounds containing
a tert-butoxycarbonyl or acyl group were doubled,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020

HAIDUKEVICH et al.
84
Scheme 3.
O
O
H
N
H
N
O
O
O
O
Ph
Ph
BzCl, Et3N
AcCl, Et3N
11
N
H
Ph
N
H
Me
N
N
i-Pr
i-Pr
13
14
PhCH2NH2, DCC
PhCH2NH2, DCC
O
O
O
O
O
H
N
H
N
H
N
O
O
O
(1) EtONa
(2) BzCl
(1) EtONa
(2) AcCl
HO
Ph
N
HO
HO
Me
N
NH
i-Pr
i-Pr
i-Pr
17
18
NH
NH
, DCC
O
, DCC
O
O
O
O
O
H
N
H
N
O
O
BzCl, Et3N
AcCl, Et3N
12
N
Ph
N
Me
N
N
i-Pr
i-Pr
O
O
15
16
presumably due to the presence of stereoisomers.
Furthermore, hydrochlorides 3, 9, and 10 are extremely
hygroscopic, which made it difficult to obtain their
accurate elemental analyses.
chloride, the mixture was cooled to –15°C, and 13.66 g
(100 mmol) of isobutyl chloroformate was added drop-
wise. The mixture was stirred for 20 min at –15°C,
a suspension of 19.07 g (105 mmol) of leucine methyl
ester hydrochloride in 100 mL of methylene chloride,
cooled to –15°C, was added, and 10.63 g (105 mmol)
of cold triethylamine was added dropwise, maintaining
the temperature at –15±1°C. The mixture was then
stirred at –12±2°C for 3 h, allowed to slowly warm up
to room temperature, and left overnight. The mixture
was washed in succession with 0.8 N aqueous HCl
(3×100 mL), water (2×100 mL), a saturated solution of
sodium hydrogen carbonate (3×100 mL), and water
again (3×100 mL) and dried over sodium sulfate. The
resulting solution was filtered, the solvent was removed
under reduced pressure, and the residue was extracted
with diethyl ether. The extract was filtered and concen-
trated to a volume of 50 mL under reduced pressure.
The product was precipitated with 200 mL of cold
hexane, filtered off, washed with hexane, and dried
under reduced pressure. Yield 23.97 g (70%), mp 77–
78°C, [α]D20 = –75.3° (c = 3, MeOH); published data
[7]: mp 78–80°C, [α]D20 = –75.9° (c = 3, MeOH) [7].
IR spectrum, ν, cm–1: 1741, 1698, 1652 (C=O), 1560
EXPERIMENTAL
All reactions were carried out using anhydrous
organic solvents. Leucine methyl ester hydrochloride
[8] and N-tert-butoxycarbonylproline [9] were synthe-
sized by known methods. The IR spectra were recorded
in KBr on a Nicolet Protégé-460 spectrometer with
1
Fourier transform. The H and 13C NMR spectra were
measured with a Bruker Avance-500 spectrometer; the
chemical shifts were determined relative to the residual
proton and carbon signals of the deuterated solvent.
The optical rotations were measured on an ATAGO
AP-300 polarimeter.
tert-Butyl (2S)-2-{[(2S)-1-methoxy-4-methyl-1-
oxopentan-2-yl]carbamoyl}pyrrolidine-1-carbox-
ylate (1). Triethylamine, 10.12 g (100 mmol), was
added to a solution of 21.53 g (100 mmol) of N-tert-
butoxycarbonylproline in 250 mL of methylene
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020

SYNTHESIS OF ACYL DERIVATIVES OF PROLYL-LEUCINAMIDES
85
(δ NH). Found, %: C 59.81; H 8.98; N 8.05.
C17H30N2O5. Calculated, %: C 59.63; H 8.83; N 8.18.
ethanol was added with vigorous stirring to a solution
of sodium ethoxide prepared from 0.92 g (40 mmol) of
sodium and 20 mL of ethanol. The mixture was stirred
for 2 h and filtered, the solvent was removed from the
filtrate under reduced pressure, and the residue was
extracted with THF. The extract was filtered, and the
filtrate was evaporated under reduced pressure until
a solid began to precipitate. The product was precip-
itated with 150 mL of diethyl ether, filtered off, washed
with diethyl ether, and dried under reduced pressure.
Yield 8 g (88%), mp 148–150°C, [α]D20 = –58.7° (c = 2,
MeOH). IR spectrum, ν, cm–1: 1676, 1652 (C=O),
tert-Butyl (2S)-2-{[(2S)-1-amino-4-methyl-1-oxo-
pentan-2-yl]carbamoyl}pyrrolidine-1-carboxylate
(2). A solution of 22.65 g (65 mmol) of 1 in 100 mL of
a 6 N solution of ammonia in methanol was kept in
a hermetically closed flask for 5 days at room
temperature. The mixture was filtered, the solvent was
removed under reduced pressure, and the residue was
extracted with THF. The extract was filtered and con-
centrated until crystals began to separate, 100 mL of
diethyl ether–hexane (1:1) was added, the mixture was
kept for 12 h at 5°C, and the precipitate was filtered
off, washed with hexane, and dried under reduced
1
1516 (δ NH). H NMR spectrum (CD3OD), δ, ppm:
0.92 d (3H, J = 6.5 Hz), 0.95 d (3H, J = 6.5 Hz), 1.54–
1.67 m (3H), 1.68–1.80 m (3H), 2.08–2.16 m (1H),
2.90–3.01 m (2H), 3.66–3.72 m (1H), 4.38–4.43 m
(1H). 13C NMR spectrum, δC, ppm: 21.98, 23.52,
26.04, 26.98, 31.95, 42.44, 48.01, 52.45, 61.49, 176.95,
177.27. Found, %: C 58.27; H 9.43; N 18.61.
C11H21N3O2. Calculated, %: C 58.12; H 9.31; N 18.49.
pressure. Yield 18.30 g (86%), mp 157–159°C, [α]D20
=
–79.2° (c = 2, MeOH). IR spectrum, ν, cm–1: 1701,
1
1677, 1600 (C=O), 1549 (δ NH). H NMR spectrum
(CD3OD), δ, ppm: 0.87–0.98 m (6H), 1.41 s and 1.49 s
(9H), 1.52–1.74 m (3H), 1.82–2.0 m (3H), 2.14–2.21 m
(1H), 3.36–3.44 m (1H), 3.46–3.54 m (1H), 4.18–
4.24 m (1H), 4.38–4.47 m (1H). 13C NMR spectrum,
δC, ppm: 21.75, 22.09, 23.50, 23.64, 24.47, 25.47,
25.86, 25.91, 28.67, 28.73, 31.17, 32.45, 41.43, 42.29,
47.89, 48.21, 52.61, 61.39, 61.74, 81.35, 155.92,
156.73, 175.23, 175.37, 177.12, 177.52. Found, %:
C 58.92; H 8.73; N 12.66. C16H29N3O4. Calculated, %:
C 58.69; H 8.93; N 12.83.
(2S)-N-[(2S)-1-Amino-4-methyl-1-oxopentan-2-
yl]-1-benzoylpyrrolidine-2-carboxamide (5). Tri-
ethylamine, 1.62 g (16 mmol), was added to a solution
of 3.41 g (15 mmol) of amide 4 in 50 mL of THF, and
2.25 g (16 mmol) of benzoyl chloride was added drop-
wise with vigorous stirring. The mixture was stirred
for 2 h and concentrated to a volume of 20 mL, 100 mL
of hexane was added, and the precipitate was filtered
off, washed on a filter in succession with hexane
(2×15 mL) and water (2×20 mL), and dried under
reduced pressure at 45°C. The product was purified by
reprecipitation from THF with diethyl ether–hexane
(2S)-N-[(2S)-1-Amino-4-methyl-1-oxopentan-2-
yl]pyrrolidine-2-carboxamide hydrochloride (3).
Amide 2, 16.37 g (50 mmol), was dissolved in 70 mL
of dioxane, 50 mL of a 6.2 N solution of hydrogen
chloride in dioxane was added, and the mixture was
stirred for 2 h and concentrated to a volume of 50 mL
under reduced pressure. The product was precipitated
with 200 mL of diethyl ether, filtered off, washed twice
with diethyl ether, and dried under reduced pressure
at 45°C until constant weight. Yield 11.60 g (88%),
mp 145–148°C, [α]D20 = –74.7° (c = 2.6, MeOH).
IR spectrum, ν, cm–1: 1691, 1677 (C=O), 1549 (δNH).
1H NMR spectrum (D2O), δ, ppm: 0.78 d (3H, J =
6.5 Hz), 0.82 d (3H, J = 6.5 Hz), 1.42–1.50 m (1H),
1.52–1.63 m (2H), 1.87–2.02 m (3H), 2.33–2.45 m
(1H), 3.25–3.36 m (2H), 4.16–4.23 m (1H), 4.28–
4.35 m (1H). 13C NMR spectrum, δC, ppm: 20.78,
22.18, 23.74, 24.34, 29.82, 39.73, 46.56, 52.66, 59.48,
169.50, 176.89. Found, %: C 49.77; H 8.25; Cl 13.68;
N 15.69. C11H21N3O2·HCl. Calculated, %: C 50.09;
H 8.41; Cl 13.44; N 15.93.
(1:1). Yield 3.63 g (73%), mp 132–134°C, [α]D20
=
–113.7° (c = 1.5, MeOH). IR spectrum, ν, cm–1: 1680,
1
1656, 1623 (C=O), 1543 (δ NH). H NMR spectrum
(CD3OD), δ, ppm: 0.8–1.0 m (6H), 1.17–1.30 m and
1.33–1.40 m (1H); 1.56–1.69 m, 1.70–1.91 m, and
1.92–2.07 m (5H); 2.25–2.36 m (1H); 3.49–3.58 m,
2.60–3.69 m, and 3.70–3.82 m (2H); 4.18–4.24 m,
4.44–4.52 m, and 4.57–4.63 m (2H); 7.38–7.82 m
(5H). 13C NMR spectrum, δC, ppm: 21.96, 23.65,
23.76, 25.46, 25.90, 26.36, 30.94, 33.23, 41.85, 42.07,
48.54, 51.72, 51.85, 52.91, 62.05, 63.37, 127.83,
128.33, 129.44, 131.07, 131.54, 137.32, 138.05,
172.14, 172.85, 174.48, 174.66, 177.10, 177.52.
Found, %: C 65.42; H 7.71; N 12.54. C18H25N3O3.
Calculated, %: C 65.23; H 7.60; N 12.68.
(2S)-1-Acetyl-N-[(2S)-1-amino-4-methyl-1-oxo-
pentan-2-yl]pyrrolidine-2-carboxamide (6) was syn-
thesized in a similar way from 3.41 g (15 mmol) of 4
and 1.26 g (16 mmol) of acetyl chloride using 1.62 g
(2S)-N-[(2S)-1-Amino-4-methyl-1-oxopentan-
2-yl]pyrrolidine-2-carboxamide (4). A solution of
10.55 g (40 mmol) of hydrochloride 3 in 75 mL of
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020

HAIDUKEVICH et al.
86
(16 mmol) of triethylamine. Yield 2.87 g (71%),
mp 163–166°C, [α]D20 = –98.3° (c = 1.5, MeOH). IR
spectrum, ν, cm–1: 1683, 1652, 1636 (C=O), 1544
mp 92–94°C, [α]D20 = –78.7° (c = 2, MeOH). IR spec-
trum, ν, cm–1: 1694, 1659, 1642 (C=O), 1543 (δNH).
1H NMR spectrum (CD3OD), δ, ppm: 0.90–0.99 m
(6H), 1.43 s and 1.45 s (9H), 1.47–1.53 m and 1.55–
1.64 m (2H), 1.67–1.78 m (1H), 1.80–1.99 m (3H),
2.09–2.28 m (1H), 3.34–3.42 m (1H), 3.44–3.59 m
(3H), 3.60–3.75 m (6H), 4.20–4.28 m (1H), 4.83–
4.91 m (1H). 13C NMR spectrum, δC, ppm: 21.99,
22.19, 23.58, 24.42, 25.37, 25.74, 25.83, 28.65, 28,72,
31.09, 32.42, 41.88, 42.02, 43.67, 47.31, 47.85, 48.16,
48.43, 61.06, 61.21, 67.67, 81.04, 81.24, 155.85,
156.20, 172.49, 174.75, 175.21. Found, %: C 60.55;
H 8.71; N 10.38. C20H35N3O5. Calculated, %: C 60.43;
H 8.87; N 10.57.
1
(δ NH). H NMR spectrum (CD3OD), δ, ppm: 0.90–
1.01 m (6H), 1.60–1.75 m (3H), 1.85–1.93 m and
1.95–2.06 m (3H), 2.12 s (3H), 2.17–2.28 m and 2.31–
2.39 m (1H); 3.45–3.53 m, 3.56–3.63 m, and 3.66–
3.72 m (2H); 4.36–4.43 m and 4.47–4.53 m (2H).
13C NMR spectrum, δC, ppm: 21.67, 22.16, 22.39,
23.53, 23.63, 23.85, 25.76, 25.94, 26.08, 31.03, 33.13,
41.45, 42.02, 48.09, 49.48, 52.67, 52.77, 61.59, 62.34,
172.32, 172.87, 174.22, 174.66, 177.08, 177.56.
Found, %: C 58.14; H 8.75; N 15.46. C13H23N3O3.
Calculated, %: C 57.97; H 8.61; N 15.60.
tert-Butyl (2S)-2-{[(2S)-1-(benzylamino)-4-
methyl-1-oxopentan-2-yl]carbamoyl}pyrrolidine-1-
carboxylate (7). A solution of 21.63 g (105 mmol) of
DCC in 200 mL of THF and 11.25 g (105 mmol) of
benzylamine were added in succession to a solution of
32.84 g (100 mmol) of (2S)-2-{[(2S)-1-(tert-butoxy-
carbonyl)pyrrolidine-2-carbonyl]amino}-4-methylpen-
tanoic acid. The mixture was stirred for 20 h, the
precipitate was filtered off, the solvent was removed
under reduced pressure, and the residue was washed
with cold hexane. The product was extracted with
diethyl ether, the extract was filtered and concentrated
to a volume of 50 mL under reduced pressure, 200 mL
of hexane was added, and the mixture was kept for
24 h at 3°C. The precipitate was filtered off, washed
with cold hexane, dried under reduced pressure, and
reprecipitated from diethyl ether with hexane. Yield
29.23 g (70%), mp 102–104°C, [α]D20 = –69.8° (c = 2,
MeOH). IR spectrum, ν, cm–1: 1700, 1643 (C=O),
(2S)-N-[(2S)-1-(Benzylamino)-4-methyl-1-oxo-
pentan-2-yl]pyrrolidine-2-carboxamide hydro-
chloride (9). Compound 7, 27.14 g (65 mmol), was
dispersed in 30 mL of dioxane, 50 mL of a 6.2 N so-
lution of hydrogen chloride in dioxane was added, and
the mixture was stirred for 2 h. The product was
precipitated by adding 250 mL of hexane, and the
precipitate was filtered off, washed twice with diethyl
ether, and dried under reduced pressure at 45°C until
constant weight. Yield 18.21 g (83%), [α]D20 = –42.4°
(c = 2, MeOH). IR spectrum, ν, cm–1: 1680, 1656
1
(C=O), 1549 (δNH). H NMR spectrum (CD3OD), δ,
ppm: 0.92 d (3H, J = 6.5 Hz), 0.96 d (3H, J = 6.5 Hz),
1.54–1.78 m (3H), 1.87–2.05 m (3H), 2.38–2.49 m
13
(1H), 3.31–3.43 m (2H), 4.30–4.48 m (4H). C NMR
spectrum, δC, ppm: 22.01, 23.32, 24.88, 25.79, 31.03,
41.75, 43.88, 48.41, 53.91, 60.78, 128.12, 128.36,
129.42, 139.77, 169.64, 174.18. Found, %: C 60.88;
H 8.17; Cl 10.26; N 11.69. C18H27N3O2·HCl. Calculat-
ed, %: C 61.09; H 7.97; Cl 10.02; N 11.87.
1
1555 (δ NH). H NMR spectrum (CDCl3), δ, ppm:
0.83–0.94 m (6H), 1.23 s and 1.37 s (9H), 1.48–1.70 m
(3H), 1.71–1.86 m (3H), 1.92–2.12 m (1H), 3.28–
3.45 m (2H), 4.06–4.27 m (1H), 4.29–4.58 m (3H),
7.17–7.30 m (5H). 13C NMR spectrum, δC, ppm: 21.68,
22.16, 23.02, 23.13, 24.67, 24.82, 25.14, 28.26, 31.14,
31.59, 40.64, 41.29, 43.32, 46.90, 47.25, 51.60, 51.91,
60.35, 60.86, 80.69, 127.15, 127.30, 127.59, 128.51,
138.03, 138.35, 154.53, 155.81, 172.07, 172.32, 173.0;
173.06. Found, %: C 66.34; H 8.65; N 9.87.
C23H35N3O4. Calculated, %: C 66.16; H 8.45; N 10.06.
(2S)-N-[(2S)-4-Methyl-1-(morpholin-4-yl)-1-oxo-
pentan-2-yl]pyrrolidine-2-carboxamide hydro-
chloride (10) was synthesized in a similar way from
28.84 g (65 mmol) of 8. Yield 18.66 g (86%), mp 168–
170°C, [α]D20 = –43.6° (c = 2, MeOH). IR spectrum, ν,
1
cm–1: 1683, 1635 (C=O), 1549 (δNH). H NMR spec-
trum (CD3OD), δ, ppm: 0.96 d (6H, J = 6.5 Hz), 1.44–
1.52 m (1H), 1.59–1.68 m (1H), 1.70–1.78 m (1H),
1.95–2.10 m (3H), 2.44–2.53 m (1H), 3.32–3.44 m
(2H), 3.45–3.52 m (1H), 3.52–3.59 m (1H), 3.60–
3.72 m (6H), 4.37–4.44 m (1H), 4.82–4.90 m (1H).
13C NMR spectrum, δC, ppm: 21.85, 23.55, 24.95,
25.87, 31.02, 41.44, 43.71, 47.21, 47.46, 49.39, 60.78,
67.62, 169.46, 172.15. Found, %: C 53.78; H 8.58;
Cl 10.83; N 12.24. C15H28ClN3O2. Calculated, %:
C 53.96; H 8.45; Cl 10.62; N 12.59.
tert-Butyl (2S)-2-{[(2S)-4-methyl-1-(morpholin-
4-yl)-1-oxopentan-2-yl]carbamoyl}pyrrolidine-1-
carboxylate (8) was synthesized in a similar way from
32.84 g (100 mmol) of (2S)-2-{[(2S)-1-(tert-butoxycar-
bonyl)pyrrolidine-2-carbonyl]amino}-4-methylpen-
tanoic acid and 9.15 g (105 mmol) of morpholine using
21.63 g (105 mmol) of DCC. Yield 28.62 g (72%),
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020

SYNTHESIS OF ACYL DERIVATIVES OF PROLYL-LEUCINAMIDES
87
(2S)-N-[(2S)-1-(Benzylamino)-4-methyl-1-oxo-
pentan-2-yl]pyrrolidine-2-carboxamide (11). A solu-
tion of 14.16 g (40 mmol) of hydrochloride 9 in
50 mL of ethanol was added with vigorous stirring to
a solution of sodium ethoxide prepared from 0.92 g
(40 mmol) of sodium and 20 mL of ethanol. The mix-
ture was stirred for 3 h and filtered, and the solvent was
removed from the filtrate under reduced pressure. The
residue was extracted with THF, the extract was filtered
and concentrated to a volume of 20 mL under reduced
pressure, 150 mL of hexane was added, and the precip-
itate was filtered off, washed with hexane, and dried
under reduced pressure. The product was purified by
reprecipitation from THF with hexane. Yield 9.27 g
(73%), mp 76–78°C, [α]D20 = –41.6° (c = 2, MeOH).
IR spectrum, ν, cm–1: 1656, 1637 (C=O), 1547 (δNH).
1H NMR spectrum (CD3OD), δ, ppm: 0.91 d (3H, J =
6.0 Hz), 0.94 d (3H, J = 6.0 Hz), 1.54–1.79 m (6H),
2.04–2.12 m (1H), 2.86–2.96 m (2H), 3.62–2.68 m
(1H), 4.35 q (2H, J = 14 Hz), 4.43–4.48 m (1H), 7.20–
7.31 m (5H). 13C NMR spectrum, δC, ppm: 22.10,
23.42, 26.01, 27.01, 31.98, 42.39, 43.94, 48.01, 52.87,
61.45, 128.12, 128.37, 129.45, 139.73, 174.43, 177.09.
Found, %: C 68.25; H 8.74; N 13.08. C18H27N3O2.
Calculated, %: C 68.11; H 8.57; N 13.24.
room temperature. The products were purified by
reprecipitation from THF with hexane.
(2S)-1-Benzoyl-N-[(2S)-1-(benzylamino)-4-
methyl-1-oxopentan-2-yl]pyrrolidine-2-carbox-
amide (13) was synthesized from 3.17 g of amide 11
and 1.55 g of benzoyl chloride in the presence of 1.11 g
of triethylamine. Yield 2.87 g (68%), mp 58–61°C,
[α]D20 = –137.1° (c = 2, MeOH). IR spectrum, ν, cm–1:
1703, 1654, 1620 (C=O), 1545 (δNH). 1H NMR spec-
trum (CD3OD), δ, ppm: 0.80 d (J = 6.5 Hz), 0.85 d (J =
6.5 Hz), 0.93 d (J = 6.5 Hz), and 0.96 d (J = 6.5 Hz)
(6H); 1.25–1.40 m (1H), 1.61–1.86 m (3H), 1.88–
1.99 m (2H), 2.17–2.32 m (1H), 3.46–3.53 m and
3.59–3.79 m (2H), 4.19–4.59 m (4H); 7.18–7.29 m,
7.34–7.49 m, and 7.55 d (J = 8.2 Hz) (10H). 13C NMR
spectrum, δC, ppm: 22.01, 22.09, 23.40, 23.49, 23.67,
25.43, 25.89, 26.31, 30.91, 33.16, 41.65, 41.85, 43.88,
43.95, 48.47, 51.65, 52.97, 53.37, 62.02, 63.29, 127.75,
128.10, 128.31, 128.43, 129.38, 129.43, 130.59,
130.97, 131.49, 133.55, 137.25, 138.03, 139.79,
139.82, 172.01, 172.77, 174.12, 174.28, 174.46,
174.51. Found, %: C 71.41; H 7.58; N 9.74.
C25H31N3O3. Calculated, %: C 71.23; H 7.41; N 9.97.
(2S)-1-Acetyl-N-[(2S)-1-(benzylamino)-4-methyl-
1-oxopentan-2-yl]pyrrolidine-2-carboxamide (14)
was synthesized from 3.17 g of amide 11 and 0.86 g of
acetyl chloride in the presence of 1.11 g of triethyl-
amine. Yield 2.52 g (70%), mp 69–72°C, [α]D20 = –87.6°
(c = 2, MeOH). IR spectrum, ν, cm–1: 1687, 1659, 1621
(2S)-N-[(2S)-4-Methyl-1-(morpholin-4-yl)-1-oxo-
pentan-2-yl]pyrrolidine-2-carboxamide (12) was
synthesized in a similar way from 13.35 g (40 mmol)
of hydrochloride 10 using 0.92 g (40 mmol) of sodium.
Yield 8.92 g (75%), mp 90–93°C, [α]D20 = –62.8° (c = 2,
MeOH). IR spectrum, ν, cm–1: 1660, 1632 (C=O),
1
(C=O), 1549 (δNH). H NMR spectrum (CD3OD), δ,
ppm: 0.90–0.97 m (6H); 1.53–1.78 m, 1.88–1.93 m,
1.94–2.03 m, 1.97 s, 2.06, and 2.11–2.29 m (10H);
3.42–3.66 m (2H), 4.29–4.54 m (4H), 7.18–7.32 m
(5H). 13C NMR spectrum, δC, ppm: 21.87, 22.16,
22.36, 23.41, 23.51, 23.61, 23.77, 25.69, 25.89, 25.99,
30.93, 33.08, 41.40, 41.86, 43.90, 47.97, 49.38, 53.13,
53.30, 61.42, 62.19, 128.06, 128.13, 128.32, 128.38,
129.39, 129.46, 139.87, 172.26, 172.72, 174.19,
174.28, 174.54, 174.68. Found, %: C 67.04; H 8.35;
N 11.46. C20H29N3O3. Calculated, %: C 66.83;
H 8.13; N 11.69.
1
1514 (δ NH). H NMR spectrum (CD3OD), δ, ppm:
0.94 d (3H, J = 6.5 Hz), 0.95 d (3H, J = 6.5 Hz), 1.44–
1.52 m (1H), 1.55–1.68 m (2H), 1.69–1.79 m (3H),
2.08–2.16 m (1H), 2.89–2.98 m (2H), 3.43–3.52 m
(1H), 3.61–3.72 m (6H), 4.70–4.80 m (1H), 4.85–
4.92 m (1H). 13C NMR spectrum, δC, ppm: 22.08,
23.61, 25.98, 27.06, 32.09, 42.20, 43.65, 47.29, 48.05,
48.18, 61.42, 67.64, 172.45, 176.81. Found, %:
C 60.72; H 9.24; N 14.02. C15H27N3O2. Calculated, %:
C 60.58; H 9.15; N 14.13.
General procedure for the synthesis of acyl
derivatives of N-substituted prolyl-leucinamides 13–
16. a. Amide 11 or 12, 10 mmol, was dissolved in
100 mL of THF, 1.11 g (11 mmol) of triethylamine was
added, and 11 mmol of benzoyl chloride or acetyl
chloride was then added. The mixture was stirred for
3 h and concentrated to a volume of 15 mL, 100 mL of
hexane was added, and the precipitate was filtered off,
washed in succession with hexane (2×20 mL) and
water (2×20 mL), and dried under reduced pressure at
(2S)-1-Benzoyl-N-[(2S)-4-methyl-1-(morpholin-
4-yl)-1-oxopentan-2-yl]pyrrolidine-2-carboxamide
(15) was synthesized from 2.97 g of amide 12 and
1.55 g of benzoyl chloride in the presence of 1.11 g
of triethylamine. Yield 2.89 g (72%), mp 157–159°C,
[α]D20 = –118.8° (c = 2, MeOH). IR spectrum, ν, cm–1:
1685, 1643, 1600 (C=O), 1553 (δNH). 1H NMR spec-
trum (CD3OD), δ, ppm: 0.82–0.85 m and 0.95–0.99 m
(6H); 1.08–1.38 m, 1.47–1.54 m, 1.62–1.72 m, 1.77–
1.88 m, 1.91–2.05 m, and 2.23–2.36 m (7H); 3.38–
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020

HAIDUKEVICH et al.
88
3.53 m (2H), 3.54–3.75 m (8H); 4.45–4.50 m, 4.56–
4.65 m, and 4.89–4.95 m (2H); 7.33–7.48 m and 7.58–
7.63 m (5H). 13C NMR spectrum, δC, ppm: 21.83,
22.14, 23.56, 23.63, 25.42, 25.72, 26.29, 30.95, 33.16,
41.33, 41.91, 43.67, 47.19, 47.32, 48.64, 51.63, 61.52,
63.22, 67.66, 127.82, 128.19, 129.41, 130.97, 131.41,
137.44, 138.07, 171.83, 172.34, 172.60, 172.76,
173.94, 174.07. Found, %: C 65.88; H 7.62; N 10.36.
C22H31N3O4. Calculated, %: C 65.81; H 7.78; N 10.47.
extract was filtered and concentrated to a volume of
30 mL under reduced pressure, 100 mL of hexane was
added, and the precipitate was filtered off, washed with
hexane, and dried under reduced pressure. The product
was reprecipitated from THF with diethyl ether–hexane
(1:3). Yield 13.62 g (82%), mp 176–178°C, [α]D20
=
–109.3° (c = 2, MeOH). IR spectrum, ν, cm–1: 1744,
1
1671, 1619 (C=O), 1557 (δ NH). H NMR spectrum
(CD3OD), δ, ppm: 0.85–0.98 m (6H), 1.20–1.29 m and
1.37–1.50 m (1H); 1.62–1.71 m, 1.79–1.90 m, and
1.93–2.10 m (5H); 2.24–2.35 m (1H); 3.45–3.51 m,
3.58–3.64 m, 3.67–3.73 m, and 3.74–3.80 m (2H);
4.20–4.24 m, 4.43–4.50 m, and 4.60–4.68 m (2H);
(2S)-1-Acetyl-N-[(2S)-4-methyl-1-(morpholin-4-
yl)-1-oxopentan-2-yl]pyrrolidine-2-carboxamide
(16) was synthesized from 2.97 g of amide 12 and
0.86 g of acetyl chloride in the presence of 1.11 g of
triethylamine. Yield 2.41 g (71%), mp 115–117°C,
[α]D20 = –77.3° (c = 2, MeOH). IR spectrum, ν, cm–1:
13
7.36–7.49 m (4H), 7.58 d (1H, J = 9.5 Hz). C NMR
spectrum, δC, ppm: 21.62, 21.92, 23.48, 23.60, 25.49,
25.84, 26.22, 30.85, 33.02, 41.08, 41.62, 48.47, 51.64,
51.75, 52.13, 61.47, 63.46, 127.79, 128.16, 129.42,
129.47, 130.99, 131.41, 137.41, 137.47, 171.87,
172.89, 174.38, 174.63, 175.47, 175.83. Found, %:
C 65.25; H 7.41; N 8.26. C18H24N2O4. Calculated, %:
C 65.04; H 7.28; N 8.43.
1
1644 br (C=O), 1557 (δ NH). H NMR spectrum
(CD3OD), δ, ppm: 0.89–0.98 m (6H), 1.40–1.51 m
(1H), 1.55–1.76 m (2H), 1.81–1.90 m (1H), 1.92 s and
2.08 s (3H), 1.94–2.05 m (2H), 2.14–2.22 m and 2.29–
2.37 m (1H), 3.43–3.69 m (10H), 4.39–4.48 m (1H),
4.85–4.95 m (1H). 13C NMR spectrum, δC, ppm: 22.33,
22.42, 23.76, 23.81, 24.03, 25.89, 25.92, 26.38, 31.16,
33.30, 42.16, 43.90, 47.53, 48.77, 49.03, 49.56, 60.97,
62.34, 67.88, 172.28, 172.45, 172.61, 172.74, 174.21,
174.38. Found, %: C 60.29; H 8.68; N 12.16.
C17H29N3O4. Calculated, %: C 60.15; H 8.61; N 12.38.
(2S)-2-{[(2S)-1-Acetylpyrrolidine-2-carbonyl]-
amino}-4-methylpentanoic acid (18) was synthesized
in a similar way from 11.41 g (50 mmol) of prolyl-
leucine and 3.93 g (50 mmol) of acetyl chloride using
1.15 g (50 mmol) of sodium. Yield 10.81 g (80%),
mp 150–152°C, [α]D20 = –77.9° (c = 2, MeOH). IR spec-
trum, ν, cm–1: 1737, 1663, 1599 (C=O), 1558 (δNH).
1H NMR spectrum (CD3OD), δ, ppm: 0.91–0.97 m
(6H); 1.58–1.70 m, 1.72–1.82 m, 1.85–1.97 m, 1.98 s,
2.0–2.07 m, 2.08 s, 2.10–2.21 m, and 2.30–2.38 m
(10H); 3.44–3.51 m and 3.52–3.70 m (2H), 4.37–
4.50 m (2H). 13C NMR spectrum, δC, ppm: 21.55,
21.91, 22.17, 22.21, 23.51, 23.81, 25.61, 25.84,
26.20, 30.86, 33.04, 41.28, 41.79, 48.02, 49.37, 52.29,
52.34, 60.94, 62.51, 172.13, 172.48, 174.31, 174.49,
175.99, 176.27. Found, %: C 57.92; H 8.43; N 10.14.
C13H22N2O4. Calculated, %: C 57.76; H 8.20; N 10.36.
b. Compound 17 or 18, 20 mmol, was dissolved in
100 mL of THF, a solution of 4.12 g (20 mmol) of
DCC in 50 mL of THF was added, the mixture was
stirred for 15 min, and 22 mmol of benzylamine or
morpholine was added. The mixture was stirred for
24 h and filtered, the filtrate was concentrated to
a volume of 30 mL under reduced pressure, 150 mL of
hexane was added, and precipitate was filtered off,
washed first with hexane and then with water, and
dried under reduced pressure. The product was purified
by reprecipitation from THF with hexane. The IR and
NMR spectra of the isolated compounds were identical
to those given above. Yield: 13, 6.15 g (73%); 14,
5.18 g (72%); 15, 6.02 g (75%); 16, 4.75 g (70%).
CONFLICT OF INTEREST
The authors declare the absence of conflict of interest.
REFERENCES
(2S)-2-{[(2S)-1-Benzoylpyrrolidine-2-carbonyl]-
amino}-4-methylpentanoic acid (17). Prolyl-leucine,
11.41 g (50 mmol), was added to a solution of sodium
ethoxide prepared from 1.15 g (50 mmol) of sodium
and 150 mL of ethanol. The mixture was stirred until
the mixture became homogeneous, and 7.03 g
(50 mmol) of benzoyl chloride was added dropwise.
The mixture was stirred for 48 h and filtered, the
solvent was removed from the filtrate under reduced
pressure, and the residue was extracted with THF. The
1. Kim, K., Kim, N.J., Kim, S.Y., Kim, I.H., Kim, K.S., and
Lee, G.R., Infect. Immun., 2015, vol. 83, p. 1150.
https://doi.org/10.1128/IAI.02878-14
2. Salaga, M., Binienda, A., Draczkowski, P., Kosson, P.,
Kordek, R., Jozwiak, K., and Fichna, J., Peptides, 2018,
vol. 108, p. 34.
https://doi.org/10.1016/j.peptides.2018.08.011
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020

SYNTHESIS OF ACYL DERIVATIVES OF PROLYL-LEUCINAMIDES
89
3. Borthwick, A.D., Chem. Rev., 2012, vol. 112, p. 3641.
7. Yushkin, D.V., Bartashevich, V.A., Zubreichuk, Z.P.,
Murashova, M.Yu., Popova, L.A., and Knizhnikov, V.A.,
Vestsi Nats. Akad. Navuk Belarusi, Ser. Khim. Navuk,
2014, no. 4, p. 56.
https://doi.org/10.1021/cr200398y
4. de Carvalho, M.P. and Abraham, W.R., Curr. Med. Chem.,
2012, vol. 19, p. 3564.
https://doi.org/10.2174/092986712801323243
5. Pan, W. and Kastin, A.J., Peptides, 2007, vol. 28, p. 2411.
8. Li, J.A. and Sha, Y., Molecules, 2008, vol. 13, p. 1111.
https://doi.org/10.3390/molecules13051111
https://doi.org/10.1016/j.peptides.2007.10.006
9. Ragnarsson, U., Karlsson, S.M., Sandberg, B.E., and
Larsson, L.-E., Org. Synth., 1973, vol. 53, p. 25.
https://doi.org/10.15227/orgsyn.053.0025
6. Gordashnikova, E.I., Gaidukevich, V.A., Popova, L.A.,
and Knizhnikov, V.A., Vestsi Nats. Akad. Navuk Belarusi,
Ser. Khim. Navuk, 2016, no. 2, p. 50.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 1 2020