Synthesis of pseudoalanylalanine

Full text of DOI:10.1134/S1070363216120276

ISSN 1070-3632, Russian Journal of General Chemistry, 2016, Vol. 86, No. 12, pp. 2717–2720. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © A.V. Vinyukov, M.E. Dmitriev, V.V. Ragulin, 2016, published in Zhurnal Obshchei Khimii, 2016, Vol. 86, No. 12, pp. 2085–2088.
LETTERS
TO THE EDITOR
Synthesis of Pseudoalanylalanine
A. V. Vinyukov, M. E. Dmitriev, and V. V. Ragulin*
Institute of Physiologically Active Compounds, Russian Academy of Sciences,
Severnyi proezd 1, Chernogolovka, Moscow oblast, 142432 Russia
*
e-mail: rvalery@dio.ru
Received September 8, 2016
Keywords: pseudoalanylalanine, amidoalkylation, benzyl carbamate, acetaldehyde, acetyl chloride, acetic anhydride
DOI: 10.1134/S1070363216120276
Synthetic methodology for the preparation of
phosphinic peptide isosteres, based on the addition of
P,N-protected α-aminophosphonous acid silyl esters to
α-substituted acrylates according to Michael–Pudovik
reaction, makes it possible to obtain a wide series of
phosphinic pseudopeptides. However, it is not free
from some drawbacks related to the necessity of
introduction and subsequent removal of appropriate
protecting groups to the phosphorus and nitrogen
atoms of the α-aminophosphonous component [1–5].
We previously proposed and developed an alternative
approach implying the reverse order of the construc-
tion of target molecules [6–11], namely initial 1:1
addition of bis(trimethylsilyl) phosphonite generated in
situ to the corresponding α-substituted acrylates with
formation of phosphonous acids containing an amino
acid isostere fragment [7–9]. Amidoalkylation of the
latter with alkyl carbamates and carbonyl compounds
afforded phosphinic pseudopeptides (N-protected α-
aminophosphinic acids) that are phosphinic analogs of
the corresponding dipeptides in which the C(O)–NH
at room temperature seems to be optimal as regards
low-boiling aldehydes. In addition, an important
problem is search for efficient but mild conditions for
the amidoalkylation of phosphonous acids to minimize
decomposition of carboxylic acid ester fragments. The
proposed procedure ensured initial selective esterifica-
tion of the hydroxyphosphoryl fragment of phosphinic
acids like 2 and subsequent selective hydrolysis of the
carboxylic ester group to obtain the corresponding
pseudodipeptide block for peptide synthesis [2–5].
Herein we report amidoalkylation of phosphinic
acid 3 to acid 2 which may be regarded as N-protected
phosphinic pseudoalanylalanine ethyl ester, N-Cbz-Ala-
ψ[P(O)(OH)CH ]-Ala-OEt. The transformation 3→2
2
was accomplished in several ways with the use of
benzyl carbamate and acetaldehyde in acetic anhydride,
acetyl chloride, and a mixture of acetic anhydride with
acetyl chloride, as well as with acetaldehyde diethyl
acetal and N,N′-(ethane-1,1-diyl)bis(benzyl carbamate)
(
4) whose molecule is a combination of carbonyl and
amide components (Scheme 1).
peptide bond is replaced by a P(O)CH methylene-
2
phosphoryl moiety [10, 11].
In keeping with the mechanism proposed
previously for the amidoalkylation of PH compounds,
the phosphorus–carbon bond is formed via Arbuzov-
like reaction as a result of nucleophilic attack by the
P(III)OAc derivative on the positively charged carbon
atom of iminium ion (charged form of the Schiff base);
both these species are generated in situ from the initial
PH compound and N,N′-(alkane-1,1-diyl)bis(alkyl
carbamate), respectively [10, 11]. Bis-carbamates were
identified as stable intermediate products arising from
the reaction of aldehyde with alkyl carbamate and were
isolated from the reaction mixture [10]. Acetic
The present study continues further development of
the above methodology through the synthesis of
pseudoalanylalanine 1 which inhibits D-Ala-D-Ala
ligase (bacterial enzyme involved in the cell wall
biosynthesis) [12, 13]. Amino- and amidoalkylation of
PH compounds with acetaldehyde as carbonyl com-
ponent is usually complicated due to its high volatility.
Therefore, the procedure proposed previously [10] for
the amidoalkylation of functionally substituted phos-
phonous acids in acetic anhydride under acid catalysis
2
717

2
718
VINYUKOV et all.
Scheme 1.
OH
P
OH
P
Me
MeCH(O)
а, AcCl
MeCH(OEt)
2
BnO
O
OEt
O
H
O
CbzNH +
2
2
+
е, Ac O (H )
N
H
2
O
Me
2
O
Me
+
OEt
b, Ac O (H )
2
3
c, Ac O −AcCl
2
MeCH(NHCbz)2
HCl
4
d, CF COOH, CH Cl
3
2
2
+
e, Ac O (H )
2
OH
P
Me
H N
OH
O
2
2
O
Me
1
anhydride and acetyl chloride are excellent acylating
agents capable of generating in situ nucleophilic P(III)OAc
species; acetic acid and hydrogen chloride are formed,
respectively, as by-products which catalyze the forma-
tion of bis-carbamates and subsequent generation of
acyliminium cation as electrophilic component [10, 11].
acetic anhydride under catalysis by p-toluenesulfonic
acid.
Thus, the optimal conditions for the synthesis of
phosphinic acid 2 by amidoalkylation of acid 3 include
the use of benzyl carbamate and acetaldehyde in acetic
anhydride in the presence of p-toluenesulfonic acid.
The two-component version involving bis-carbamate 4
provides better results, but it requires preliminary
preparation of N,N′-(ethane-1,1-diyl)bis(benzyl carba-
mate) (4).
3
1
Monitoring of the reaction progress by P NMR
spectroscopy revealed fairly fast amidoalkylation of
phosphinic acid 3 in acetyl chloride or its mixture with
acetic anhydride until complete disappearance of the
signal belonging to acid 3. However, partial dealkyla-
tion of the ester fragment of 2 was observed during the
reaction in acetyl chloride and (to a lesser extent) in
acetic anhydride–acetyl chloride mixture (3:1 by
volume), which probably lowers the yield of 2 and its
purity. Therefore, we tried procedures for the
amidoalkylation of 3 in acetic anhydride under milder
acid catalysis by p-toluenesulfonic acid. In this case,
we succeeded in avoiding undesirable dealkylation of
the carboxylic acid ester moiety, but the reaction was
appreciably slower. Nevertheless, the yield and purity
of target acid 2 remained fairly high.
2
-(Ethyloxycarbonyl)propylphosphonous acid (3)
was synthesized by reaction of ethyl methacrylate with
equiv of bis(trimethylsilyl) hypophosphite generated
3
in situ from ammonium hypophosphite according to
1
modified procedure [6–8]. Yield 73%. H NMR spec-
trum (CDCl containing a drop of CD OD), δ, ppm:
3
3
3
3
1
7
.19 d (3H, CH , J = 7.3 Hz), 1.24 t (3H, J
=
3
HH
HH
.3 Hz), 1.76 m and 2.14 m (1H each, PCH ), 2.82 m
2
3
(
1H, CHCO), 4.10 q (2H, CH O, J = 7.3 Hz), 6.50
2 HH
1
13
br.s (1H, POH), 7.12 d (1H, PH, J = 558.1 Hz). C
PH
NMR spectrum (CDCl containing a drop of CD OD),
3
3
3
δ , ppm: 14.0 (CH CH ), 18.5 d (CH CH, J = 10.7 Hz),
2.9 d (CH P, J = 94.7 Hz), 33.6 (CHCO), 61.0
C
3
2
3
PC
Considerably worse results were obtained with the
use of acetaldehyde diethyl acetal, which may be
rationalized assuming formation of ethyl acetate via
decomposition of acetaldehyde diethyl acetal into
1
3
2 PC
3
31
(
CH O), 174.9 d (C=O, J = 8.8 Hz). P NMR
2 PC
spectrum (CDCl containing a drop of CD OD): δ
3
3
P
3
4.7 ppm. Found, %: C 39.67; 39.52; H 7.57; 7.46.
acetaldehyde and ethanol in AcCl–Ac O and impaired
2
C H O P. Calculated, %: C 40.01; H 7.27.
6
13
4
conditions for the generation in situ of the above
reaction intermediates. The two-component version of
amidoalkylation of phosphinic acid 3 with pre-
liminarily prepared biscarbamate 4 in methylene
chloride in the presence of an equimolar amount of
trifluoroacetic anhydride afforded a lower yield of 2
than that obtained in the three-component version in
N,N′-(Ethane-1,2-diyl)bis(benzyl carbamate) (4)
was synthesized by reaction of acetaldehyde diethyl
acetal with 2 equiv of benzyl carbamate in acetic
anhydride according to the procedure described in
[14]. Yield 77%, mp 206–207°C; published data [14]:
1
mp 203–204°C. H NMR spectrum (DMSO-d
), δ,
6
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

SYNTHESIS OF PSEUDOALANYLALANINE
2719
3
31
ppm: 1.23 d (3H, CH , J = 6.6 Hz), 5.00 br.s (4H,
monitored by P NMR. The product was isolated as
3
HH
CH O), 5.14 m (1H, CHN), 7.34 m (10H, Ph), 7.61 d
described above in a. Yield 2.5 g (70%), mp 117–118°C.
2
3
13
(
2H, NH, J = 5.0 Hz). C NMR spectrum (DMSO-
HH
c. Preliminarily cooled acetaldehyde, 0.7 mL
d ), δ , ppm: 21.2 (CH ), 56.1 (CHN), 65.2 (CH O);
6
C
3
2
(
1
12.5 mmol), was added in portions to a mixture of
.8 g (10 mmol) of anhydrous phosphonous acid 3 and
1
27.6, 127.7, 127.8, 128.4, 137.1 (Carom); 154.6 (C=O).
{
1-[(Benzyloxycarbonyl)amino]ethyl}(3-ethoxy-2-
1.5 g (10 mmol) of benzyl carbamate in 12 mL of
acetic anhydride under stirring at room temperature.
Cold acetyl chloride, 4 mL, was then added, and the
mixture was stirred at room temperature until the
reaction was complete ( P NMR). The product was
isolated as described above in a. Yield 2.0 g (56%), mp
113–115°C.
methyl-3-oxopropyl)phosphinic acid (2). a. A mix-
ture of 3.6 g (20 mmol) of preliminarily dried
phosphonous acid 3 and 3.0 g (20 mmol) of benzyl
carbamate in 25 mL of acetyl chloride was cooled to 5°C,
and 1.4 mL (25 mmol) of acetaldehyde was added. The
mixture spontaneously warmed up and was stirred
until it cooled down and then for several hours at room
temperature. When the reaction was complete (accord-
3
1
d. Trifluoroacetic anhydride, 2.1 g (10 mmol), was
added with stirring to a cold solution of 1.8 g
31
ing to the P NMR data), the mixture was poured into
0 mL of an ice–water mixture and evaporated under
(10 mmol) of preliminarily dried phosphonous acid 3 and
7
3
.3 g (10 mmol) of N,N′-(ethane-1,1-diyl)bis(benzyl
reduced pressure. The residue was treated with 70 mL
of a saturated solution of sodium hydrogen carbonate
and extracted with diethyl ether (2×10 mL). The
aqueous phase was carefully acidified to pH ~2 and
extracted with chloroform (3×10 mL) or ethyl acetate.
The organic extract was dried over magnesium sulfate
and evaporated under reduced pressure. The residue
crystallized either spontaneously or after treatment
carbamate) (4) in 15 mL in of anhydrous methylene
chloride. The mixture was stirred at room temperature
31
until the reaction was complete ( P) and evaporated
under reduced pressure, and the residue was treated
with a mixture of 30 mL of a saturated solution of
sodium hydrogen carbonate and 30 mL of diethyl ether.
The resulting two-phase system was filtered from benzyl
carbamate, the aqueous phase was carefully acidified
to pH ~1–2 and extracted with chloroform and/or ethyl
acetate (3×30 mL), and the extracts were combined
with the organic phase, dried over magnesium sulfate,
and evaporated under reduced pressure. The residue
crystallized spontaneously or after treatment with
diethyl ether. Yield 1.6 g (45%), mp 114–115°C.
with diethyl ether or petroleum ether (40–70°C). Yield
1
4
(
1
.4 g (62%), mp 112–115°C. H NMR spectrum
3
CDCl ), δ, ppm : 1.22 t (3H, CH , J = 7.5 Hz),
3 3 HH
3
.24 d (3H, CH , J
= 7.0 Hz), 1.34 d.d (3H,
CH CH, J = 7.5, J = 14.9 Hz), 1.76 m and 2.24
3
HH
3
3
3
HH
PH
m (1H each, PCH ), 2.85 m [1H, CHC(O)], 4.02 m
2
3
(
1H, CHN), 4.11 q (2H, CH O, J = 7.5 Hz), 5.11
br.s (2H, OCH Ph), 5.38 d (1H, NH, J = 7.5 Hz),
.33 m (5H, Ph), 9.72 br.s (1H, POH). C NMR spec-
trum (DMSO-d ), δ , ppm: 13.9 d ( J = 13.8 Hz),
2 HH
3
e. p-Toluenesulfonic acid, 0.03 g (0.2 mmol), was
added with stirring to a mixture of 1.8 g (10 mmol) of
anhydrous phosphonous acid 3 and 3.3 g (10 mmol) of
bis-carbamate 4 in 20 mL of acetic anhydride. The
mixture was stirred at room temperature until the
2
HH
1
3
7
3
6
C
PC
2
2
1
(
(
8.6 d ( J = 7.0 Hz), 18.8* d ( J = 8.1 Hz), 29.3 d
PC PC
1
1
JPC = 88.6 Hz), 29.4* d ( J = 88.2 Hz), 33.4, 45.7 d
JPC = 105.8 Hz), 46.0* d ( J = 105.8 Hz), 60.1,
PC
3
1
1
1
reaction was complete ( P NMR) and evaporated
under reduced pressure, and the residue was treated as
described above in d. Yield 2.8 g (78%), mp 116–118°C.
PC
6
(
5.6, 127.7 (2C), 127.8, 128.4 (2C), 137.1, 155.8 d
3
3
31
JPC = 3.7 Hz), 175.1 d ( J = 9.5 Hz). P NMR spec-
PC
trum (CDCl ), δ , ppm: 53.6,* 55.0. Hereinafter, signals
f. A solution of 1.8 g (10 mmol) of phosphonous
acid 3 and 1.5 g (10 mmol) of benzyl carbamate in a
mixture of 15 mL of acetic anhydride and 5 mL of
acetyl chloride was cooled to 5°C, and 1.6 mL
3
P
of the minor diastereoisomer are marked with an asterisk.
Found, %: C 53.68, 53.57; H 6.79, 6.87; P 8.53, 8.43.
C H NO P. Calculated, %: C 53.78; H 6.77; P 8.67.
1
6
24
6
(
11 mmol) of acetaldehyde diethyl acetal was slowly
b. p-Toluenesulfonic acid, 0.03 g (0.2 mmol), was
added with stirring at room temperature to a mixture of
.8 g (10 mmol) of acid 3 and 1.5 g (10 mmol) of
benzyl carbamate in 15 mL of acetic anhydride, 0.7 mL
12.5 mmol) of preliminarily cooled acetaldehyde was
added dropwise. The mixture was stirred at room
temperature until the reaction was complete ( P NMR)
and was then treated as described above in a. Yield
1
3
1
1
.1 g (31%), mp 108–111°C.
(
then added in portions, and the mixture was stirred at
room temperature. The progress of the reaction was
2-(Hydroxycarbonyl)propyl-1-aminoethylphos-
phinic acid (1, pseudoalanylalanine) was syn-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

2
720
VINYUKOV et all.
thesized by hydrolysis of acid 2 in 6 N HCl under
reflux. The product was isolated by chromatography
on a cation exchanger (using water and 0.3 N aqueous
HCl as eluents), followed by crystallization from
acetone. Yield 68%, mp 127–134°C (foaming with
3. Georgiadis, D., Dive, V., and Yiotakis, A., J. Org.
Chem., 2001, vol. 66, no. 20, p. 6604. doi 10.1021/
jo0156363
4. Yiotakis, A., Georgiadis, D., Matziari, M., Makaritis, A.,
and Dive, V., Curr. Org. Chem., 2004, vol. 8, p. 1135.
doi 10.2174/ 1385272043370177
1
liberation of water), 218–221°C (decomp.). H NMR
3
5
. Mucha, A., Molecules, 2012, vol. 17, p. 13530. doi
0.3390/molecules171113530
spectrum (D O), δ, ppm: 1.20 d (3H, CH CHC, J
=
=
2
3
HH
3
3
1
7
7
.3 Hz), 1.32 d.d (3H, CH CHP, J = 13.4, J
3 PH
HH
.3 Hz), 1.50–1.75 m and 1.92–2.14 m (1H each,
6. Kurdyumova, N.R., Ragulin, V.V., and Tsvetkov, E.N.,
Mendeleev Commun., 1997, no. 2, p. 69. doi 10.1070/
MC1997v007n02ABEH000721
PCH ), 2.65–2.85 m [1H, CHC(O)], 3.12–3.28 m (1H,
2
1
3
CHN). C NMR spectrum (D O), δ , ppm: 11.9 d
2
C
3
2
2
7
. Kurdyumova, N.R., Rozhko, L.F., Ragulin, V.V., and
Tsvetkov, E.N., Russ. J. Gen. Chem., 1997, vol. 67,
no. 12, p. 1852.
(
JPC = 8.1 Hz), 18.0 d ( J = 5.9 Hz), 18.2* d ( J
=
=
PC
PC
1
1
7
9
.3 Hz), 29.7* d ( J = 94.4 Hz), 29.8 d ( J
PC PC
1
5.1 Hz), 33.3 d and 45.4* d ( J = 93.6 Hz), 45.5 d
JPC = 95.1 Hz), 179.5 d ( J 6.6 Hz), 180.5* d ( J
.5 Hz). P NMR spectrum: in D O: δ 35.2 ppm; in
PC
1
3
3
8
. Ragulin, V.V., Rozhko, L.F., Saratovskikh, I.V., and
Zefirov, N.S., JPN Patent Appl. no. 2000-018568, 2000;
Chem. Abstr., 2001, no. 552806; Ragulin, V.V.,
Rozhko, L.F., Saratovskikh, I.V., and Zefirov, N.S., JPN
Patent Appl. no. 2000-018581, 2000; Chem. Abstr.,
(
=
PC
PC
31
9
2 P
D O/DCl: δ 45.1 ppm Found, %: C 28.65, 28.56; H
2
P
7
.02, 7.11; P 11.94, 12.13. C H NO P·HCl·H O. Cal-
6 14 4 2
culated, %: C 28.87; H 6.86; P 12.41.
2
001, no. 574226.
1
31
13
The H, P, and C NMR spectra were recorded on
a Bruker DPX-200 spectrometer with Fourier trans-
form. Ion exchange chromatography was performed
9. Rozhko, L.F. and Ragulin, V.V., Amino Acids, 2005,
vol. 29, p. 139. doi 10.1007/s00726-005-0194-9
10. Dmitriev, M.E. and Ragulin, V.V., Tetrahedron Lett.,
2010, vol. 51, no. 19, p. 2613. doi 10.1016/
j.tetlet.2010.03.020
+
using KUICT (H ) cation exchanger. The melting
points were measured on a Boetius PHMK melting
point apparatus.
11. Dmitriev, M.E. and Ragulin, V.V., Tetrahedron Lett.,
2
012, vol. 53, no. 13, p. 1634. doi 10.1016/
ACKNOWLEDGMENTS
j.tetlet.2012.01.094
1
2. Parsons, W.H., Patchett, A.A., Bull, H.G., Schoen, W.R.,
Taub, D., Davidson, J., Combs, P.L., Springer, J.P.,
Gadebusch, H., Weissberger, B., Valiant, M.E., Mellin, T.N.,
and Busch, R.D., J. Med. Chem., 1988, vol. 31, p. 1772.
doi 10.1021/jm00117a017
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 15-03-06062).
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016