Synthesis of Phosphinic Analogue of Alanylleucine

Article abstract of DOI:10.1134/S1070363220040313

Abstract: The amidoalkylation reactions of a phosphonous acid containing a structural isostere of leucine in acetyl chloride and(or) acetic anhydride were studied under conditions of acid catalysis. A two-component method for the synthesis of a phosphinic

Full text of DOI:10.1134/S1070363220040313

ISSN 1070-3632, Russian Journal of General Chemistry, 2020, Vol. 90, No. 4, pp. 753–756. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Obshchei Khimii, 2020, Vol. 90, No. 4, pp. 645–649.
LETTERS
TO THE EDITOR
Synthesis of Phosphinic Analogue of Alanylleucine
S. R. Golovasha, O. S. Grigorkevichb, G. S. Tsebrikovac, M. E. Dmitrieva, and V. V. Ragulina,*
a Institute of Physiologically Active Substances of the Russian Academy of Sciences, Chernogolovka, 142432 Russia
b V.V. Zakusov Research Institute of Pharmacology of the Russian Academy of Sciences, Moscow, 125315 Russia
c A.N. Frumkin Institute of Physical Chemistry and Electrochemistry of the Russian Academy of Sciences,
Moscow, 119071 Russia
*e-mail: rvalery@dio.ru
Received September 27, 2019; revised September 27, 2019; accepted October 5, 2019
Abstract—The amidoalkylation reactions of a phosphonous acid containing a structural isostere of leucine in
acetyl chloride and(or) acetic anhydride were studied under conditions of acid catalysis. Atwo-component method
for the synthesis of a phosphinic analogue of alanylleucine using ethylidenebis(benzylcarbamate) was proposed.
Keywords: pseudo-alanylleucine, matrix metalloproteinases (MMPs), zinc metalloproteinase inhibitors, amido-
alkylation, phosphinic structural isosteres
DOI: 10.1134/S1070363220040313
Phosphinic structural analogues of natural peptides
are included in promising radiopharmaceuticals as
ligand components [1]. They are also inhibitors of
matrix metalloproteinases (MMPs), which are a family
of zinc-containing endoproteases involved into various
biological processes [2, 3]. Metalloproteinases of types
2 and 9 (MMP-2 and MMP-9), called gelatinases,
play an important role in post-infarction myocardial
remodeling [4]. Undesirable activity of gelatinases, which
manifests itself in a negative effect on the tissues of the
cardiovascular system, can be reduced or eliminated using
inhibitors containing function that chelates zinc cation
[5, 6]. Effective inhibitors of zinc-metalloproteinases are
phosphinic pseudopeptides, structural isosteres of peptides
in the molecule of which two amino acid components of
the dipeptide are linked by a zinc chelating phosphinic
fragment [2, 7]. In this case, methylenephosphorylic
CH2P(O)(OH) fragment imitates a natural peptide bond
with a tetra-coordinated carbon atom in the transition
state of peptide hydrolysis (Scheme 1).
We have proposed a shorter synthesis with the reverse
construction of the desired pseudopeptide 3 molecule.
It consists in the initial addition of the in situ generated
hypophosphite 4 to the corresponding α-R2-substituted
acrylates 2 with the formation of phosphonous acids
5 containing a structural isostere fragment of the
corresponding amino acid, which is determined by the
corresponding substituent (R2) in the α-position of the
acrylic system [10–13].Amidoalkylation of phosphonous
acids 5 using alkyl carbamates 6 and the corresponding
carbonyl compounds 7 leads to target pseudopeptides 3
(Scheme 2) [11–13].
This work is a further development of the pre-
viously proposed methodology for the synthesis of
phosphoisosteres of peptides from hypophosphites
[10–13] and is devoted to the synthesis of pseudoalanyl-
ψ[P(O)(OH)CH2]-leucine 8, which is a promising type
Scheme 1.
Awidely used approach to the phosphinic modification
of the peptide bond is the synthesis of the N,P-protected
derivative 1, the phosphorous isoster of the corresponding
amino acid, developed by Ciba-Geigy company [8, 9]
with its subsequent conversion to the silylic ether of the
PIII-phosphonous analog of the amino acid and addition to
corresponding α-substituted acrylates 2 (Scheme 2) [2, 7].
753

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GOLOVASH et al.
Scheme 2.
Scheme 3.
9 matrix-zinc metalloproteinase (MMP-9) inhibitor [14]
(Scheme 3).
In this regard, we have studied the amidoalkylation of
acid 9 in acetic anhydride under milder acid catalysis using
p-toluenesulfonic acid. The side process of dealkylation
of ester fragments in this case is absent, however, the
amidoalkylation reaction proceeds noticeably slower.
A high yield of target acid 11 was achieved using a
two-component version of amidoalkylation using
ethylidenebis(benzylcarbamate) 10, which combines
carbonyl and carbamate components in the molecule,
since this avoids side processes involving acetaldehyde.
The process of amidoalkylation of phosphonous acid 9
containing structural leucine isostere was performed using
benzyl carbamate and acetic aldehyde in acetyl chloride
and (or) acetic anhydride as a three-component carbamate
version of the Kabachnik–Fields reaction [11–13] for the
synthesis of phosphinic acid 11, which is ethyl ester of
N-protected phosphinic pseudoalanylleucine N-Cbz-Ala-
ψ[P(O)(OH)CH2]-Leu-OEt. As an alternative method,
a two-component synthesis was performed by reaction
of the phosphonous component 9 with pre-synthesized
N,N'-ethylidenebis(benzylcarbamate) 10 [12].
The reaction progress was monitored using 31P
NMR spectroscopy by the ratio of the intensities of
the signals of phosphinic acid 11 (δP ~55 ppm) and the
starting phosphonous component 9 (δP ~32–33 ppm)
in the spectrum of the reaction mixture. It was found
that the process of amidoalkylation of phosphonous
acid 9 proceeds rather quickly in acetyl chloride or in a
mixture with acetic anhydride. However, in this case, side
processes occur, associated with partial dealkylation of the
ester fragment of acid 11 during the amidoalkylation of
phosphonous acid 9. Side reactions with the participation
of acetaldehyde and the formation of phosphorus-free
compounds are also observed. This leads to the fact that
phosphonous component 9 is partially remains unchanged
in the reaction mixture.
Ethylidenebis(benzylcarbamate) 10 was previously
synthesized in accordance with our previously proposed
procedure [12]. The synthesis of phosphonous acid 9
was carried out in accordance with the modified method
proposed by us earlier [11]. In this case, it was also possible
to isolate the product of double addition, phosphinic acid
9a. Synthesis of ethyl ester of α-isobutylacrylic acid was
carried out in accordance with a previously published
procedure [15].
2-(Ethoxycarbonyl)-4-methylamylphosphonic
acid (9). Yield 81%, oily substance. 1H NMR spectrum
(CCl4–CD3OD), δ, ppm: 0.97–1.05 br. t (3H, CH3), 1.35 d
(6H, CH3, 3JНH = 7.0 Hz), 1.48 m (1H, CH), 1.65 m (2Н,
СН2СН),2.10m(2H,СН2Р),2.83m[1Н,СНС(O)],4.17m
1
(2Н, CH2O), 7.05 d (1H, PH, JPH = 560.0 Hz),
12.68 br. s (1Н, РООН). 31Р NMR spectrum (CCl4–
CD3OD): δР 31.1 ppm. Mass spectrum (ESI), m/z: 223.4
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 4 2020

SYNTHESIS OF PHOSPHINIC ANALOGUE OF ALANYLLEUCINE
755
[М + Н]+ (caculated for C9H19O4P: 223.2). Found Р, %:
13.63, 13.43. C9H19O4P. Calculated Р, %: 13.94.
p-toluenesulfonic acid. The reaction mixture was stirred
at room temperature, monitoring the reaction progress by
31P NMR. Upon completion of the reaction, the mixture
was filtered, the filtrate was treated similarly to procedure
a. Yield 3.3 g (83%), mp 80–81°С, Rf ~ 0.20–0.35
(CHCl3 : EtOH = 5 : 1) (two spots due to the presence
of diastereomers). 1H NMR spectrum (CDCl3), δ, ppm:
Bis[2-(ethoxycarbonyl)-4-methylamyl]phosphinic
acid (9a) was obtained as a pale yellow oily substance.
1H NMR spectrum (CCl4–CD3OD), δ, ppm: 0.85–0.95 m
(6H, CH3), 1.25–1.35 m (12H, CH3), 1.43 m (2H, CH),
1.60 m (4Н, СН2СН), 2.05 m (4H, СН2Р), 2.76 m [2Н,
2СНС(O)], 4.12 m (4Н, CH2O). 31Р NMR spectrum
(CCl4–CD3OD): δP 47.1 ppm. Found, %: C 56.95, 57.05;
H 9.45, 9.50; P 8.33, 8.21. C18H35O6P. Calculated, % C:
57.13; H 9.32; P 8.18.
0.84 d (3Н, СН3, 3JHH = 6.4 Hz), 0.88 d (3Н, СН3, 3JHH
=
7.5 Hz), 1.21 t (3Н, СН3, 3JHH = 7.0 Hz), 1.34 d. d (3Н,
CH3CH, 3JHH = 6.5, 3JPH = 14.5 Hz), 1.45–1.80 m (4Н,
РСН2 + СНСН2СН), 2.00–2.27 m (1Н, СНСН3), 2.70–
2.92 m [1Н, CHC(O)], 3.90–4.05 m (1Н, PCHN), 4.11 q
2-(Ethyloxycarbonyl)-4-methylamyl-1-(N-
benzyloxycarbonyl)aminoethylphosphinic acid (11).
a. To a mixture of 4.4 g (20 mmol) of pre-dried
phosphonous acid 9 and 3.0 g (20 mmol) of benzyl
carbamate in 25 mL of acetyl chloride, cooled to 5°С,
was added in portions 1.4 mL(25 mmol) of acetaldehyde.
The resulting mixture was stirred at room temperature
for several hours, then poured into 70 mL of ice water
and evaporated in vacuum at a bath temperature of not
higher than 35°C. The residue was treated with 70 mL
of saturated sodium bicarbonate solution. The aqueous
phase was washed with diethyl ether (2 × 10 mL),
carefully acidified with a solution of 1 N HCl to pH ~
2 and then extracted with chloroform (3 × 10 mL) or
ethyl acetate. The combined organic extract was dried
with magnesium sulfate and evaporated in vacuum. The
residue was chromatographed on silica gel [eluent—
chloroform, chloroform–isopropanol (5–7%)]. The
eluate was evaporated in vacuum, the residue crystallized
spontaneously, and also after treatment with diethyl or
petroleum ether (40/70). Phosphinic acid 11 was isolated
after additional crystallization from petroleum ether. Yield
4.1 g (51%), mp. 74–77°C.
3
(2H, CH2O, JHH = 7.0 Hz), 5.10 br. s (2H, OCH2Ph),
5.38 br. d (1Н, NH, 3JHH = 8.6 Hz), 6.50 br. s (1Н, РООН),
7.33 s (5Н, Ph). 13C NMR spectrum (CDCl3), δС, ppm:
13.84* (hereafter, an asterisk indicates the signal of a
minor diastereomer), 14.05, 20.88*, 21.84, 22.32*, 22.67,
25.06*, 25.73, 28.67 d (1JPC = 95.1 Hz), 28.96* d (1JPC
91.6 Hz), 37.12, 43.17* d (3JPC = 8.8 Hz), 43.37 d (3JPC
11.1 Hz), 45.10* d (1JPC = 103.5 Hz), 45.85 d (1JPC
=
=
=
104.3 Hz), 60.71, 67.04, 127.97, 128.09, 128.44, 136.18,
155.86 d (3JPC = 5.0 Hz), 175.1. 31P NMR spectrum
(CDCl3), δР, ppm: 54.7*, 55.0. Mass spectrum (ESI),
m/z: 400.5 [М + Н]+ (caculated for C19H30NO6P: 400.4).
Found, %: C 56.68, 56.92; H 7.78, 7.87. C19H30NO6P.
Calculated, %: C 57.13; H 7.57.
2-(Hydroxycarbonyl)-4-methylamyl-1-amino-
ethylphosphinic acid (pseudo-alanylleucine) (8).
Phosphinic acid 11 (1.1 g, 2.8 mmol) was boiled in 15 mL
of 6 N HCl for 17 h. The cooled solution was treated with
chloroform (2 × 5 mL). The aqueous phase was evaporated
in vacuum and the residue was chromatographed on
cation exchange resin (eluent—water, then 0.5 N HCl).
The ninhydrin-positive eluate was evaporated in vacuum.
The residue (~ 0.6 g) was dissolved in 5.5 mL of aqueous
alcohol (~ 1 : 10), treated with 0.5 mL (7 mmol) of
propylene oxide, and 0.4 g (62%) of aminophosphinic
acid 8 was isolated.Amino acid 8 is a crystalline powder,
sparingly soluble in water; therefore, the spectral data
are given below in an acidic and alkaline medium; in the
latter case, the presence of diastereomers manifests to a
greater extent. Yield 62%, mp 197–199°С (decomp.). 1H
NMR spectrum (D2O–DCl, pH = 1), δ, ppm: 0.48 d (3Н,
b.Amidoalkylation of phosphonous acid 9 in a mixture
of acetyl chloride and acetic anhydride allowed to isolate
the target product 11 with a yield of 58%, mp 77–78°С.
c. The synthesis in the medium of acetic anhydride
with the addition of p-toluenesulfonic acid (3 mol %)
made it possible to obtain acid 11 with a yield of 71%,
mp 78–80°C.
The two-component synthesis was carried out using
pre-synthesized N,N'-ethylidenebis(benzylcarbamate)
10 [12] also using p-toluenesulfonic acid (3 mol %).
To a stirred mixture of 2.2 g (10 mmol) of anhydrous
phosphonous acid 9 and 3.3 g (10 mmol) of N,N'-
ethylidenebis(benzylcarbamate) 10 in 20 mL of
acetic anhydride was added 0.05 g (0.3 mmol) of
СН3СHC, 3JHH = 5.9 Hz), 0.52 d (3Н, СН3СHC, 3JHH
6.5 Hz), 1.08 d. d (3H, СН3СHP, JPH = 14.7, JHH
=
=
3
3
7.1 Hz), 1.14–1.32 m [3Н, СH2CH(CH3)2], 1.56–1.74 m
(1H, РСН2), 1.78–1.98 m (1H, РСН2), 2.35–2.57 m [1Н,
CHC(O)], 3.10–3.30 m (1H, CHN). 1H NMR spectrum
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 4 2020

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GOLOVASH et al.
(D2O–NaOD, pH ~9), δ, ppm: 0.78 d (3Н, СН3СHC,
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FUNDING
This work was performed as part of the governmental task
of the Institute of Physiologically Active Substances of the
Russian Academy of Sciences for 2019 (topic no. 00902019-
008) with partial financial support from the Presidium of the
RussianAcademy of Sciences no. 14P, the Russian Foundation
for Basic Research (grants no. 18-03-00959, 18-03-01123)
and the Russian Science Foundation (grant no. 19-13-00294,
chromatographic, spectral and elemental analysis).
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CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
https://doi.org/10.1055/s-1979-28537
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