Synthesis of dipeptides based on valine and threonine

Article abstract of DOI:10.1134/S1070428012100065

Val-Val, Val-Thr, and Thr-Val dipeptides were synthesized using trifluoroacetyl protecting group. The optical rotations of the products were similar to those of samples synthesized using Boc protection, which indicated the absence of racemization in the course of introduction and removal of trifluoroacetyl protection. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S1070428012100065

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2012, Vol. 48, No. 10, pp. 1297–1301. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © Yu.M. Sorokina, A.A. Sladkova, L.A. Popova, O.I. Shadyro, V.A. Knizhnikov, 2012, published in Zhurnal Organicheskoi Khimii,
2012, Vol. 48, No. 10, pp. 1302–1306.
Synthesis of Dipeptides Based on Valine and Threonine
Yu. M. Sorokinaa, A. A. Sladkovab, L. A. Popovaa, O. I. Shadyrob, and V. A. Knizhnikova
a Institute of Physical Organic Chemistry, National Academy of Sciences of Belarus,
ul. Surganova 13, Minsk, 220072 Belarus
e-mail: knizh@ifoch.bas-net.by
b Belarusian State University, Minsk, Belarus
Received March 3, 2012
Abstract— Val–Val, Val–Thr, and Thr–Val dipeptides were synthesized using trifluoroacetyl protecting group.
The optical rotations of the products were similar to those of samples synthesized using Boc protection, which
indicated the absence of racemization in the course of introduction and removal of trifluoroacetyl protection.
DOI: 10.1134/S1070428012100065
Hydroxy-containing amino acids and peptides
occupy a specific place among related compounds due
to diversity of radiation-induced reactions with their
participation. Water radiolysis products initiate consid-
erably more efficient deamination of threonine and
serine as compared to other amino acids [1]. Further-
more, di- and tripeptides having a hydroxy amino acid
residue at the C-terminus are known to be charac-
terized by higher radiochemical yields of the corre-
sponding amino acid amides, while dipeptides with
a hydroxy amino acid residue at the N-terminus
undergo deamination with a higher efficiency [2].
Decomposition of hydroxy-substituted peptides via
rupture of C–C bond by the action of UV or γ-irradia-
tion was not studied. Dipeptides based on valine and
threonine may be convenient model compounds for
studying the mechanism of radiation- and photo-
induced decomposition of carbon skeleton in hydroxy-
containing peptides. The goal of the present work was
to develop efficient procedures for the synthesis of
L-valyl–L-valine, L-valyl–L-threonine, and L-threonyl–
L-valine.
At present, carbamate type groups are used most
widely to protect amino groups in amino acids. Al-
though trifluoroacetyl protection has long been known,
it has not received wide application in peptide syn-
thesis because of possible racemization. Nevertheless,
facile introduction and removal of trifluoroacetyl pro-
tecting group makes its use quite promising provided
that racemization is impossible. In the present work we
synthesized L-valyl–L-valine, L-valyl–L-threonine, and
L-threonyl–L-valine using both trifluoroacetyl and tert-
butoxycarbonyl protecting groups and compared
optical rotations of the products, taking into account
that peptide synthesis with Boc-protected amino acids
is not accompanied by racemization.
N-Trifluoroacetyl derivatives of valine and threo-
nine I and II were synthesized by reaction of the
corresponding amino acid sodium salts with ethyl tri-
fluoroacetate (Scheme 1). Compounds I and II reacted
with valine and threonine methyl esters in tetrahydro-
furan in the presence of N,N′-dicyclohexylcarbodi-
imide (DCC) as condensing agent to give esters III–V
which were subjected to hydrolysis by the action of
aqueous sodium hydroxide; and subsequent acidifica-
tion afforded target dipeptides VI–VIII (Scheme 2).
An important problem in peptide synthesis is the
choice of an optimal combination of protecting groups.
Scheme 1.
O
O
O
(1) CF3COOEt
(2) HCl
H
EtONa
H2N
H2N
F3C
N
OH
ONa
OH
R
R
O
R
I, II
I, R = i-Pr; II, R = MeCH(OH).
1297

SOROKINA et al.
1298
Scheme 2.
O
O
O
H
R'
(1) NaOH, H2O
(2) H+
O
R'
H
DCC
F3C
N
H2N
F3C
N
OMe
H2N
OH
+
OH
OMe
N
N
H
H
O
R
R'
O
R
O
R
O
I, II
III–V
VI–VIII
III, VI, R = R′ = i-Pr; IV, VII, R = i-Pr, R′ = MeCH(OH); V, VIII, R = MeCH(OH), R′ = i-Pr.
Scheme 3.
O
O
O
R'
H
H
DCC
t-BuO
N
H2N
t-BuO
N
OMe
+
OH
OMe
N
H
O
R
R'
O
R
O
IX–XI
IX, R = R′ = i-Pr; X, R = i-Pr, R′ = MeCH(OH); XI, R = MeCH(OH), R′ = i-Pr.
Compounds VI–VIII were also synthesized using
Boc-protected amino acids. By condensation of N-tert-
butoxycarbonylvaline and N-tert-butoxycarbonylthre-
onine with valine and threonine methyl esters in the
presence of DCC we obtained N-Boc-Val–Val, N-Boc-
Val–Thr, and N-Boc-Thr–Val methyl esters (IX–XI)
(Scheme 3). Methyl esters IX and X were deprotected
using a solution of hydrogen chloride in methanol, and
hydrochlorides XII and XIII thus formed were con-
verted into dipeptides VI and VII by treatment with
aqueous sodium hydroxide, followed by acidification
(Scheme 4).
produced N-Boc-threonylvaline XIV which was
treated with a solution of HCl in dioxane to obtain
hydrochloride XV, and the latter was converted into
target dipeptide VIII by reaction with an equimolar
amount of sodium ethoxide (Scheme 5).
Samples of dipeptides VI–VIII obtained by the two
methods were characterized by almost similar optical
rotations, which indicated the absence of racemization
at all steps of synthesis of these dipeptides with the use
of trifluoroacetyl protecting group.
EXPERIMENTAL
Threonylvaline VIII was synthesized from methyl
ester XI following a different reaction sequence. Hy-
drolysis of the ester moiety in XI in aqueous sodium
hydroxide and subsequent acidification with citric acid
Commercial amino acids from Sigma and Aldrich
were used. N-tert-Butoxycarbonyl derivatives of valine
and threonine and valine and threonine methyl esters
Scheme 4.
O
R
O
R
(1) NaOH, H2O
(2) H+
O
R
H
HCl, MeOH
t-BuO
N
OMe
H2N
OMe
H2N
OH
N
N
N
H
H
H
O
Pr-i
IX, X
O
Pr-i
O
Pr-i
O
XII, XIII
VI, VII
VI, XII, R = i-Pr; VII, XIII, R = MeCH(OH).
Scheme 5.
O
Pr-i
O
Pr-i
OH
O
Pr-i
(1) NaOH, H2O
(2) Citric acid
H
H
N
HCl, dioxane
t-BuO
N
OMe
t-BuO
OH
OH
OH
N
N
H
Me
N
H
H
·HCl
O
O
O
O
NH2
O
Me
OH
Me
OH
XIV
XV
OH
O
Pr-i
EtONa
Me
N
H
NH2
O
VIII
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 10 2012

SYNTHESIS OF DIPEPTIDES BASED ON VALINE AND THREONINE
1299
were synthesized according to standard procedures [3].
Methanol and ethanol were purified by distillation over
calcium hydride. Diethyl ether, tetrahydrofuran, and
hexane were purified by distillation over metallic
sodium.
0.89 d (3H, CH3, J = 6.4 Hz), 0.94 d (3H, CH3, J =
6.4 Hz), 0.99 d (3H, CH3, J = 6.4 Hz), 2.08–2.19 m
(2H, CH), 3.73 s (3H, OCH3), 4.48–4.52 m (1H, CH),
4.56 t (1H, CH, J = 6.5 Hz). 13C NMR spectrum
(CDCl3), δC, ppm: 18.33, 18.83, 19.38, 19.43, 31.53,
32.08, 52.77, 58.21, 59.50, 116.48 q, 157.99 q, 170.83,
172.63. Found, %: C 47.99; H 6.64; N 8.43.
C13H21F3N2O4. Calculated, %: C 47.85; H 6.49; N 8.58.
The IR spectra were recorded in KBr on a Nicolet
Protégé-460 spectrometer with Fourier transform. The
NMR spectra were run at 20°C on Bruker Avance-400
and Tesla BS-567A spectrometers; the chemical shifts
were measured relative to the residual proton signal
of the corresponding deuterated solvent. The optical
rotations were measured on a Polamat A polarimeter
(DDR).
N-Trifluoroacetyl-L-valyl-L-threonine methyl
ester (IV). A solution of 18.32 g (86 mmol) of
compound I in 75 ml of THF was cooled to 0–5°C,
a solution of 17.72 g (86 mmol) of DCC in 75 ml of
THF was added, the mixture was stirred for 5 min, and
a solution of 11.44 g (86 mmol) of L-threonine methyl
ester in 100 ml of THF was added. The mixture was
stirred for 30 h, the precipitate was filtered off, the
solvent was removed from the filtrate under reduced
pressure, the residue was dried under reduced pressure
and extracted with methylene chloride, the extract was
filtered and evaporated under reduced pressure, and the
residue was washed with diethyl ether, dried under
reduced pressure, and purified by reprecipitation from
methylene chloride with hexane. Yield 18.35 g (65%),
mp 148–149°C, [α]D20 = –21.9 (c 3.0, MeOH). IR spec-
trum, ν, cm–1: 1731, 1709, 1655 (C=O), 1561 (NH).
1H NMR spectrum (CDCl3), δ, ppm: 1.01 d (3H, CH3,
J = 7 Hz), 1.03 d (3H, CH3, J = 7 Hz), 1.22 d (3H,
CH3, J = 6.5 Hz), 2.18–2.23 m (1H, CH), 3.80 s (3H,
CH3), 4.41–4.44 m (2H, CH), 4.61 d (1H, CH, J =
6.7 Hz). 13C NMR spectrum (CDCl3), δC, ppm: 18.61,
19.47, 20.66, 32.35, 53.39, 58.12, 59.48, 68.52,
170.79, 171.65. Found, %: C 43.95; H 5.94; N 8.41.
C12H19F3N2O5. Calculated, %: C 43.90; H 5.82; N 8.53.
N-Trifluoroacetyl-L-valine (I). L-Valine, 11.7 g
(100 mmol), was dissolved in a solution of sodium
methoxide prepared from 2.3 g (100 mmol) of sodium
and 100 ml of methanol, 21.3 g (150 mmol) of ethyl
trifluoroacetate was added dropwise, and the mixture
was stirred for 42 h, acidified with 21 ml of a 4.8 N
solution of hydrogen chloride in methanol, stirred for
2 h, and filtered. The filtrate was evaporated under
reduced pressure, the residue was extracted with di-
ethyl ether (3×100 ml), the extracts were filtered and
evaporated under reduced pressure, and the residue
was purified by reprecipitation from diethyl ether with
hexane. Yield 18.37 g (86%), [α]D20 = –15.3 (c = 3,
H2O); published data [4]: [α]D20 = –15.2. Found, %:
C 39.62; H 4.98; N 6.35. C7H10F3NO3. Calculated, %:
C 39.44; H 4.73; N 6.57.
N-Trifluoroacetyl-L-threonine (II) was synthe-
sized in a similar way from 11.9 g (100 mmol) of
L-threonine. Yield 17.2 g (80%), [α]D20 = –5.72 (c = 3,
MeOH); published data [5]: [α]D20 = –5.6. Found, %:
C 33.64; H 3.91; N 6.67. C6H8F3NO4. Calculated, %:
C 33.50; H 3.75; N 6.51.
N-Trifluoroacetyl-L-threonyl-L-valine methyl
ester (V) was synthesized in a similar way from
16.56 g (77 mmol) of N-trifluoroacetyl-L-threonine
(II) and 10.09 g (77 mmol) of L-valine methyl ester
using 15.86 g (77 mmol) of DCC. Yield 18.45 g
(73%), mp 106–108°C, [α]D20 = –6.8 (c = 2.0, MeOH).
IR spectrum, ν, cm–1: 1740, 1708, 1653 (C=O), 1553
(NH). 1H NMR spectrum (CDCl3), δ, ppm: 0.89 d (3H,
CH3, J = 7 Hz), 0.93 d (3H, CH3, J = 7 Hz), 1.18 d
(3H, CH3, J = 6.5 Hz), 2.19–2.22 m (1H, CH), 3.74 s
(3H, CH3), 4.22–4.31 m (1H, CH), 4.40–4.49 m (1H,
N-Trifluoroacetyl-L-valyl-L-valine methyl ester
(III). A solution of 12.14 g (57 mmol) of N-trifluoro-
acetyl-L-valine (I) in 25 ml of THF was cooled to 0–
5°C, a solution of 11.74 g (57 mmol) of DCC in 25 ml
of THF was added, the mixture was stirred for 5 min,
and a solution of 7.47 g (57 mmol) of L-valine methyl
ester in 25 ml of THF was added. The mixture was
stirred for 40 h, the precipitate was filtered off, the
filtrate was evaporated under reduced pressure, and the
residue was washed with hexane, dried under reduced
pressure, and reprecipitated from methylene chloride
with hexane. Yield 12.61 g (68%), mp 92–94°C,
[α]D20 = –55.6 (c = 3.0, MeOH). IR spectrum, ν, cm–1:
13
CH), 4.62 br.s (1H, CH). C NMR spectrum (CDCl3),
δC, ppm: 18.12, 18.30, 19.58, 31.20, 52.97, 58.04,
58.42, 67.28, 116.25 q, 158.29 q, 169.63, 172.72.
Found, %: C 44.05; H 5.63; N 8.32. C12H19F3N2O5.
Calculated, %: C 43.90; H 5.82; N 8.53.
1
1750, 1713, 1656 (C=O), 1557 (δNH). H NMR spec-
N-Boc-L-valyl-L-valine methyl ester (IX). A solu-
trum (CDCl3), δ, ppm: 0.85 d (3H, CH3, J = 6.5 Hz),
tion of 12.36 g (60 mmol) of DCC in 35 ml of THF
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 10 2012

SOROKINA et al.
1300
was added to a solution of 13.02 g (60 mmol) of
Boc-L-valine in 50 ml of THF, cooled to 0–5°C. The
mixture was stirred for 5 min, a solution of 7.86 g
(60 mmol) of L-valine methyl ester in 50 ml of THF
was added, and the mixture was stirred for 40 h. The
precipitate was filtered off, the solvent was removed
from the filtrate under reduced pressure, the residue
was washed with hexane, dried under reduced pres-
sure, and extracted with diethyl ether, the extract was
filtered and evaporated under reduced pressure, and
the residue was washed with hexane and dried under
reduced pressure. Yield 13.86 g (70%), mp 149–
150°C, [α]D20 = +8,2 (c = 3.0, THF). IR spectrum, ν,
6.06 g (70%), mp 186–188°C, [α]D20 = +13.3 (c = 3.0,
H2O). IR spectrum, ν, cm–1: 1665, 1585 (C=O), 1554
(NH). 1H NMR spectrum (D2O), δ, ppm: 0.86–0.93 d.d
(6H, CH3), 0.97–1.02 d.d (6H, CH3), 1.97–2.04 m (1H,
CH), 2.18–2.24 m (1H, CH), 3.84 d (1H, CH, J =
6 Hz), 4.0 d (1H, CH, J = 6.5 Hz). 13C NMR spectrum
(D2O), δC, ppm: 16.86, 17.69, 17.81, 18.81, 30.16,
30.30, 58.58, 61.57, 168.86, 177.99. Found, %:
C 55.68; H 9.54; N 12.73. C10H20N2O3. Calculated, %:
C 55.53; H 9.32; N 12.95.
b. Compound IX, 13.2 g (40 mmol), was added
under continuous stirring to 30 ml of a 3.5 N solution
of HCl in methanol. The mixture was stirred for 5 h
and evaporated under reduced pressure, and the residue
was washed with diethyl ether and dried under reduced
pressure. A solution of sodium ethoxide prepared from
0.92 g (40 mmol) of sodium and 70 ml of ethanol was
added to the residue, the mixture was stirred for 1 h,
and the precipitate was filtered off. A solution of 2 g
(50 mmol) of sodium hydroxide in 20 ml of water was
added dropwise to the filtrate, and the mixture was
stirred for 10 h and acidified with trifluoroacetic acid
to pH ~6. The solvent was removed under reduced
pressure, and the residue was washed with acetone and
diethyl ether, dried under reduced pressure, and repre-
cipitated from water with acetone. Yield 4.58 g (53%),
mp 187–188°C, [α]D20 = +13.5 (c = 3.5, H2O). Found,
%: C 55.62; H 9.43; N 12.81. C10H20N2O3. Calculated,
%: C 55.53; H 9.32; N 12.95.
1
cm–1: 1746, 1717, 1665 (C=O), 1545 (NH). H NMR
spectrum (CDCl3), δ, ppm: 0.83 br.s (6H, CH3),
0.92 br.s (6H, CH3), 1.37 s (9H, t-Bu), 1.90–2.20 m
(2H, CH), 3.61 s (3H, OCH3), 3.85–4.00 m (1H, CH),
4.35–4.50 m (1H, CH).
N-Boc-L-valyl-L-threonine methyl ester (X) was
synthesized in a similar way from 19.53 g (90 mmol)
of Boc-L-valine and 11.97 g (90 mmol) of threonine
methyl ester using 18.54 g (90 mmol) of DCC. Yield
19.44 g (65%), [α]D20 = –22.6 (c = 3.0, MeOH). IR
spectrum, ν, cm–1: 1745, 1715, 1683 (C=O), 1542
1
(NH). H NMR spectrum (CDCl3), δ, ppm: 0.90–
0.95 m (6H, CH3), 1.15 d (3H, CH3, J = 6.5 Hz), 1.38 s
(9H, t-Bu), 1.98–2.06 m (1H, CH), 3.71 s (3H, OCH3),
3.92–3.96 m (1H, CH), 4.29–4.34 m (1H, CH), 4.55–
4.60 m (1H, CH). Found, %: C 54.36; H 8.74; N 8.63.
C15H28N2O6. Calculated, %: C 54.20; H 8.49; N 8.43.
L-Valyl-L-threonine (VII). a. A solution of 3.6 g
(90 mmol) of sodium hydroxide in 20 ml of water was
added dropwise to a solution of 13.13 g (40 mmol) of
N-trifluoroacetyl-L-valyl-L-threonine methyl ester (IV)
in 40 ml of ethanol. The mixture was stirred for 20 h
and acidified with trifluoroacetic acid to pH ~6. The
solvent was removed under reduced pressure, and the
residue was washed with acetone and diethyl ether,
dried under reduced pressure, and reprecipitated from
water with acetone. Yield 4.63 g (53%), mp 158–
159°C, [α]D20 = +16.5 (c = 4.0, H2O). IR spectrum, ν,
N-Boc-L-threonyl-L-valine methyl ester (XI) was
synthesized from 13.14 g (60 mmol) of Boc-L-threo-
nine and 7.86 g (60 mmol) of valine methyl ester using
12.36 g (60 mmol) of DCC. Yield 15.96 g (80%),
mp 71.5–73°C, [α]D20 = –18.0 (c = 3.0, MeOH). IR
spectrum, ν, cm–1: 1740, 1716, 1681 (C=O), 1525
1
(NH). H NMR spectrum (CDCl3), δ, ppm: 0.81–
0.86 m (6H, CH3), 1.11 d (3H, CH3, J = 6.5 Hz), 1.35 s
(9H, t-Bu), 2.06–2.14 m (1H, CH), 3.72 s (3H, CH3),
4.05–4.10 m (1H, CH), 4.18–4.24 m (1H, CH), 4.38–
4.43 m (1H, CH). Found, %: C 54.32; H 8.61; N 8.27.
C15H28N2O6. Calculated, %: C 54.20; H 8.49; N 8.43.
1
cm–1: 1667, 1582 (C=O), 1525 (NH). H NMR spec-
trum (D2O), δ, ppm: 1.01 d (3H, CH3, J = 7 Hz), 1.03 d
(3H, CH3, J = 7 Hz), 1.19 d (3H, CH3, J = 6 Hz), 2.19–
2.26 m (1H, CH), 3.89 d (1H, CH, J = 6 Hz), 4.11–
L-Valyl-L-valine (VI). a. A solution of 3.6 g
(90 mmol) of sodium hydroxide in 20 ml of water was
added dropwise to a solution of 13.05 g (40 mmol) of
ester III in 40 ml of ethanol, and the mixture was
stirred for 5 h and acidified with 5.7 g (50 mmol) of
trifluoroacetic acid. The mixture was stirred for 1 h
and evaporated under reduced pressure, and the residue
was washed with acetone, dried under reduced pres-
sure, and reprecipitated from water with acetone. Yield
13
4.16 m (2H, CH). C NMR spectrum (D2O), δC, ppm:
16.86, 17.83, 19.40, 30.10, 58.72, 61.28, 67.82,
169.16, 176.14. Found, %: C 49.69; H 8.54; N 12.75.
C9H18N2O4. Calculated, %: C 49.53; H 8.31; N 12.84.
b. Ester X, 18.28 g (55 mmol), was added under
vigorous stirring to 35 ml of a 3.4 N solution of HCl in
methanol, the mixture was stirred for 7 h, the solvent
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 10 2012

SYNTHESIS OF DIPEPTIDES BASED ON VALINE AND THREONINE
1301
was removed under reduced pressure, and the residue
was washed with diethyl ether and dried under reduced
pressure. The dry residue was dissolved in 30 ml of
ethanol, a solution of 4.4 g (110 mmol) of sodium
hydroxide in 30 ml of water was added dropwise, and
the mixture was stirred for 15 h and acidified with
hydrochloric acid to pH ~6. The solvent was removed
under reduced pressure, the residue was washed with
acetone, dried under reduced pressure, and extracted
with anhydrous ethanol (2×50 ml), the extract was
filtered, the filtrate was evaporated under reduced
pressure, and the residue was washed in succession
with acetone and diethyl ether, and reprecipitated from
water with acetone. Yield 5.4 g (45%), mp 157–158°C,
[α]D20 = +16.6 (c = 3.0, H2O). Found, %: C 49.40;
H 8.18; N 12.61. C9H18N2O4. Calculated, %: C 49.53;
H 8.31; N 12.84.
58.88, 61.49, 66.67, 168.21, 178.03. Found, %:
C 49.67; H 8.53; N 12.66. C9H18N2O4. Calculated, %:
C 49.53; H 8.31; N 12.84
b. A solution of 2.0 g (50 mmol) of sodium hydrox-
ide in 30 ml of water was added dropwise to a solution
of 13.3 g (40 mmol) of N-Boc-L-threonyl-L-valine
methyl ester (XI) in 50 ml of ethanol, and the mixture
was stirred for 15 h and acidified with citric acid to
pH ~6. The solvent was removed under reduced
pressure, the residue was extracted with ethyl acetate
(4×50 ml), the combined extracts were washed with
a saturated solution of sodium chloride, dried over
sodium sulfate, filtered, and evaporated, and the resi-
due was reprecipitated from diethyl ether with hexane,
dried under reduced pressure, and dissolved in 40 ml
of a 3.5 N solution of HCl in dioxane. The mixture was
stirred for 7 h, the solvent was removed under reduced
pressure, and the residue was washed with diethyl
ether and dried under reduced pressure. A 7.64-g
portion of the product was dissolved in 50 ml ethanol,
a solution of sodium ethoxide prepared from 0.69 g
(30 mmol) of sodium and 50 ml of ethanol was added
dropwise, the mixture was stirred for 2 h and filtered,
the solvent was removed under reduced pressure, and
the residue was reprecipitated from ethanol with
diethyl ether. Yield 5.23 g (60%), mp 153–156°C,
[α]D20 = –10.7 (c = 2.0, H2O). Found, %: C 49.78;
H 8.47; N 12.69. C9H18N2O4. Calculated, %: C 49.53;
H 8.31; N 12.84.
L-Threonyl-L-valine (VIII). a. A solution of 3.6 g
(90 mmol) of sodium hydroxide in 30 ml of water was
added dropwise to a solution of 13.13 g (40 mmol) of
N-trifluoroacetyl-L-threonyl-L-valine methyl ester (V)
in 35 ml of ethanol, the mixture was stirred for 28 h,
1.14 g (10 mmol) of trifluoroacetic acid was added, the
mixture was stirred for 1 h and filtered, and solvent
was removed from the filtrate under reduced pressure.
The residue was washed with acetone and diethyl
ether, dried under reduced pressure, and dissolved in
35 ml of water. The solution was acidified with hydro-
chloric acid to pH ~6 and evaporated under reduced
pressure, the residue was extracted with anhydrous
ethanol (2×50 ml), and the combined extracts were
filtered and concentrated to a volume of 15 ml. Diethyl
ether, 100 ml, was added, and the precipitate was
filtered off, washed with diethyl ether, dried under
reduced pressure, and reprecipitated from ethanol with
diethyl ether. Yield 3.93 g (45%), mp 152–154°C,
[α]D20 = –10.8 (c = 2.0, H2O). IR spectrum, ν, cm–1:
REFERENCES
1. Shadyro, O.I., Sosnovskaya, A.A., and Vrublevskaya, O.N.,
Khim. Vys. Energ., 1999, vol. 33, no. 2, p. 94.
2. Shadyro, O.I., Sosnovskaya, A.A., and Vrublevskaya, O.N.,
J. Radiat. Biol., 2003, vol. 79, no. 4, p. 269.
3. Gershkovich, A.A. and Kibirev, V.K., Sintez peptidov.
Reagenty i metody (Synthesis of Peptides. Reagents and
Methods), Kiev: Naukova Dumka, 1987.
1
1674, 1580 (C=O), 1539 (NH). H NMR spectrum
(D2O), δ, ppm: 0.89 d (3H, CH3, J = 7 Hz), 0.92 d (3H,
CH3, J = 7 Hz), 1.29 d (3H, CH3, J = 6.5 Hz), 2.05–
2.15 m (1H, CH), 3.86 d (1H, CH, J = 6 Hz), 4.04 d
(1H, CH, J = 6 Hz), 4.10–4.18 m (1H, CH). 13C NMR
spectrum (D2O), δC, ppm: 17.53, 18.77, 18.86, 30.27,
4. Curphey, T.J., J. Org. Chem., 1979, vol. 44, p. 2885.
5. Cherevin, M.S., Gulevich, T.G., Yurashevich, N.Ya., Zub-
reichuk, Z.P., and Knizhnikov, V.A., Vestsi Nats. Akad.
Navuk Belarusi, Ser. Khim. Navuk, 2008, no. 2, p. 55.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 10 2012