Efficient peptide coupling method of conjugated carboxylic acids with methyl ester amino acids hydrochloride. Application to the synthesis of Fa-Met, an important enzymatic substrate

Article abstract of DOI:10.1016/j.tetlet.2004.11.082

Benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate reagent (BOP) serves as an efficient and versatile coupling reagent for the coupling of conjugated carboxylic acid with methyl ester amino acids hydrochloride allowing the synthesis of various substituted amino acid derivatives in high chemical yields of up to 90%. The usefulness of this method is illustrated in the synthesis of Fa-Met, an important enzymatic substrate.

Full text of DOI:10.1016/j.tetlet.2004.11.082

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 217–220
Efficient peptide coupling method of conjugated carboxylic
acids with methyl ester amino acids hydrochloride. Application
to the synthesis of Fa-Met, an important enzymatic substrate
Jean Michel Brunel,* Chanaz Salmi and Yves Letourneux
`
Laboratoire Synthese et Etude de Substances Naturelles a Activites Biologiques (SESNAB), IMRN INRA 1111,
Faculte des Sciences et Techniques de St Jerome, Universite Paul Cezanne, Avenue Escadrille Normandie Niemen,
`
´
´
´ ˆ
´
´
´
13397 Marseille cedex 20, France
Received 28 September 2004; revised 8 November 2004; accepted 15 November 2004
Available online 30 November 2004
Dedicated to the memory of A. Mingot deceased on September 19, 2004
Abstract—Benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate reagent (BOP) serves as an efficient and ver-
satile coupling reagent for the coupling of conjugated carboxylic acid with methyl ester amino acids hydrochloride allowing the syn-
thesis of various substituted amino acid derivatives in high chemical yields of up to 90%. The usefulness of this method is illustrated
in the synthesis of Fa-Met, an important enzymatic substrate.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Substituted furan-amino acid derivatives have been re-
ported to possess biological and pharmacological activi-
ties.1 Two major methods of synthesis have been
described to date. The first method involves the reaction
of 2-furylacryloylchloride with appropriate amino acids
leading to the expected compounds in moderate yields.2
In our hands, formation of numerous by-products have
been also noticed and the purity of the products ob-
tained is less than 80% due to difficulties of purification.
The second interesting method introduced by Blumberg
and Vallee in 1975 involves the synthesis of N-hydroxy-
succinimide esters of aliphatic and aromatic amino
acids. Nevertheless, in this case the authors mentioned
that the products are obtained in low yields.3 Thus,
the synthesis of such compounds remains an interesting
challenge and in this context, peptide coupling reactions,
which have been significantly advanced in accord with
the development of new peptide coupling reagents in or-
ganic syntheses could constitute an interesting
alternative.4,5
In this letter, we report an efficient and general method
for the synthesis of various substituted amino acid deriva-
tives and its application to the total synthesis of Fa-Met,
an important enzymatic substrate.
For our optimization studies, we chose to focus on the
coupling of 3-(2-furyl)acrylic acid with methionine
methyl ester hydrochloride, as our test reaction, under
various experimental conditions (Table 1).
The standard coupling method using a dicyclohexylcar-
bodiimide (DCC)/additive method produces generally
peptides in good yields but in this case no conversion
was observed whatever the applied experimental condi-
tions (entries 1–5). Similar negative results were encoun-
tered using more sophisticated coupling reagents such
as O-benzotriazol-1-yl-N,N,N0,N0-tetramethyluronium
hexafluoro phosphate (HBtU).6 Introduced in 1975
by Castro et al., benzotriazol-1-yloxytris(dimethyl-
amino)phosphonium hexafluorophosphate reagent
(BOP)7 and its parent derivatives have been widely ap-
plied in organic synthesis.8 BOP is a nonhygroscopic
crystalline compound easily prepared in large quantities
and which led to the expected coupling product 3 in 75%
isolated yield at room temperature in CH2Cl2 in the
presence of 3equiv of diisopropylethylamine (Table 1,
Keywords: Peptides; Coupling; Amino acids; BOP; Fa-MET.
*
Corresponding author. Tel.: +33 04 91 28 85 50; fax: +33 04 91 28 84
40; e-mail: bruneljm@yahoo.fr
0040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.11.082

218
J. M. Brunel et al. / Tetrahedron Letters 46 (2005) 217–220
Table 1. Coupling of 3-(2-furyl)acrylic acid 1 with methionine methyl ester hydrochloride 2 under various experimental conditions
-
Cl
+
NH3
H
OH
MeO
S
N
Me
base
O
1
Me
S
O
+
O
O
2
3
O
COOMe
coupling reagent
1 equiv.
1 equiv.
Entrya
Coupling agent
Baseb
Solvent
Yield (%)
1
2
3
4
5
6
7
8
9
DCC/DMAP
DCC
—
EtN(i-Pr)2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
DMF
<2
<2
<2
<5
<5
<5
<5
75
DCC/HOBt
DCC/HOAt
DCC/HOAt
HBtU
—
—
—
—
CH2Cl2
DMF
HBtU
BOP
BOP
—
EtN(i-Pr)2
—
CH2Cl2
CH2Cl2
27
a Reactions performed at room temperature.
b Reactions performed using 3 equiv of EtN(i-Pr)2.
entry 8).9 This method was then successfully applied to
the coupling of conjugated carboxylic acids with numer-
ous methyl ester amino acids hydrochloride as illus-
trated in Table 2.
dioxane for 12 h at room temperature. In all cases, the
products were obtained in excellent isolated yields vary-
ing from 80% to 92% (Table 3).11
Table 3. Synthesis of substituted amino acid derivatives 13–20
In all cases, adducts 3 and 5–12 were obtained in excel-
lent yields varying from 31% to 90% depending on the
nature of the considered amino acid derivatives. It is
noteworthy that replacement of 3-(2-furyl)acrylic acid
by trans-cinnamic acid led to the formation of the ex-
pected coupling products in yields above 80% (Table
2, entries 8 and 9). Moreover, no detectable racemiza-
tion of the amino acid moiety has been noticed whatever
the considered substrate.10
H
N
H
N
R'
R'
R
R
Dioxane
COOH
O
COOMe
O
NaOH 1M (1.1 equiv.)
20°C, 12 h
5-12
13-20
Entry
Compound
Product
Isolated yield (%)
1
2
3
4
5
6
7
8
5
13
14
15
16
17
18
19
20
84
89
80
80
88
81
92
89
6
7
8
As previously mentioned, substituted amino acid deriva-
tives possess biological activities and their synthesis
could be envisioned through removal of the methyl ester
moiety. This reaction was easily performed by hydroly-
sis of compounds 5–13 with a 1 M NaOH solution in
9
10
11
12
Table 2. Synthesis of substituted amino acid methyl ester derivatives 3, 5–12
-
Cl
+
NH3
H
N
R'
COOMe
R
R
OH
MeO
BOP (1 equiv.)
R'
1 equiv.
4 R = Ph
+
O
O
O
EtN(i-Pr)2 (3 equiv.)
1 equiv.
CH2Cl2, 20°C, 12 h
3, 5-12
1 R =
O
Entry
Acid derivative
R0
Product
Yield (%)a
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
4
4
MeSCH2CH2
H
i-Pr
3
75
69
73
89
90
59
31
86
83
5
6
i-Bu
MeO2CCH2
PhCH2
7
8
9
p-HOPhCH2
MeSCH2CH2
i-Pr
10
11
12
a Isolated yield.

J. M. Brunel et al. / Tetrahedron Letters 46 (2005) 217–220
219
-
Cl
+
NH3
H
OH
MeO
+
S
N
Me
BOP (1 equiv.)
O
1
Me
S
O
O
O
2
3
O
COOMe
EtN(i-Pr)2 (3 equiv.)
1 equiv.
1 equiv.
75% yield
CH2Cl2, 20°C, 12 h
H
N
S
Me
Dioxane
O
O
COOH
NaOH 1M (1.1 equiv.)
20°C, 12 h
Fa-Met 82% yield
21
Scheme 1. Synthesis of Fa-Met 21.
B. Tetrahedron Lett. 1979, 20, 3321–3322; (d) Le-Nguyen,
D.; Heitz, A.; Castro, B. J. Chem. Soc. Perkin Trans. 1
1987, 1915–1919.
Efficiency of this methodology is illustrated in Scheme 1
dealing with the synthesis of Fa-Met 21 in 62% overall
yield, an important synthetic substrate for enzymatic
studies allowing, due to its structure, the determination
of acylases activities.12
8. (a) Taunton, J.; Collins, J. L.; Schreiber, S. L. J. Am.
Chem. Soc. 1996, 118, 10412–10422; (b) Wipf, P.; Ven-
katraman, S. J. Org. Chem. 1995, 60, 7224–7229; (c)
Ward, D. E.; Gai, Y.; Lazny, R.; Pedras, M. S. C. J. Org.
Chem. 2001, 66, 7832–7840; (d) Jing, W.; Sui, Z.; Macie-
lag, M. J.; Walsh, S. P.; Fiordeliso, J. J.; Lanter, J. C.;
Guan, J.; Qiu, Y.; Kraft, P.; Bhattacharjee, S.; Craig, E.;
Haynes-Johnson, D.; John, T. M. J. Med. Chem. 2003, 46,
441–444; (e) Andrus, M. B.; Li, W.; Keyes, R. F. J. Org.
Chem. 1997, 62, 5542–5549.
9. General procedure (Table 2, entry 1): In a 50 mL two
necked round flask were placed at room temperature
under argon methionine methyl ester hydrochloride
(630 mg, 3.8 · 10ꢀ3 mol) and 3-(2-furyl)acrylic acid
(531 mg, 3.85 · 10ꢀ3 mol) in anhydrous CH2Cl2 (30 mL).
The mixture was placed under stirring and cooled to 0 ꢁC.
Diisopropylethylamine (1.49 g, 1.41 · 10ꢀ2 mol) was
slowly added, followed by the addition of the coupling
reagent (BOP) (1.8 g, 4.23 · 10ꢀ3 mol) dissolved in 5 mL
of anhydrous CH2Cl2. The reaction was stirred for 12 h at
20 ꢁC. Ethyl acetate (50 mL) was added to the reaction
mixture and the organic layer was successively washed
with a 1 N HCl solution (2 · 35 mL), a 20% NaHCO3
solution (2 · 30 mL) and brine. The organic layer was
dried over MgSO4 and concentrated in vacuo. The crude
residue was purified by chromatography on a silica gel
column using EtOAc/petroleum ether as eluent (1:1)
affording the expected coupling product 3 in 75% yield.
Compound 3, white solid; mp: 103 ꢁC; 1H NMR (CDCl3):
d = 7.39–6.34 (m, 6H), 4.86–4.79 (m, 1H), 3.73 (s, 3H),
2.54–2.49 (m, 2H), 2.22–1.95 (m, 5H). 13C (CDCl3):
d = 172.50, 165.60, 151.06, 144.07, 128.47, 117.62,
114.01, 112.06, 52.44, 51.61, 31.69, 29.91, 15.33.
In summary, we have determined that BOP serves as an
efficient and versatile coupling peptide reagent for cou-
pling of conjugated carboxylic acid with methyl ester
amino acids hydrochloride allowing the synthesis of var-
ious substituted amino acid derivatives. Usefulness of
this method has been illustrated in the synthesis of
Fa-Met 21 and further applications will be reported in
due course.
References and notes
1. (a) El Naggar, A. M.; Abd El Rahman, M. O.; Makhlouf,
A. A. Roczniki Chemii 1976, 50, 2175–2179; (b) El Naggar,
A. M.; Ahmed, F. S. M.; Abd El Salam, A. M.; El Gazzar,
M. A. Pol. J. Chem. 1982, 56, 1279–1285; (c) Dubois, R.
J.; Lin, C. C. L.; Michel, B. L. J. Pharm. Sci. 1975, 64,
825–829; (d) Ayalp, A. Pak. J. Pharm. Sci. 1990, 3, 21–27.
2. (a) El Naggar, A. M.; Ahmed, F. S. M.; Abd El Salam, A.
M.; El Shami, M. S. Egypt. J. Chem. 1983, 26, 75–81; (b)
Giardina, T.; Biagini, A.; DalleOre, F.; Ferre, E.; Reynier,
M.; Puigserver, A. Biochimie 1997, 79, 265–273.
3. (a) Blumberg, S.; Vallee, B. L. Biochemistry 1975, 14,
2410–2419; (b) Kunugi, S.; Tanabe, K.; Yamashita, K.;
Morikawa, Y.; Ito, T.; Kondoh, T.; Hirata, K.; Nomura,
A. Bull. Chem. Soc. Jpn. 1989, 62, 514–518, and references
cited therein.
4. In 1992, Schreiber et al. have reported the synthesis of
similar vinylogous polypeptides but under his experimen-
tal conditions no conversion has occurred in our hands
Hagihara, M.; Anthony, N. J.; Stout, T. J.; Clardy, J.;
Schreiber, S. L. J. Am. Chem. Soc. 1992, 114, 6568–6570.
5. (a) Bodanszky, M.; Bodanszky, A. In The Practice of
Peptide Synthesis; Hafner, K., Rees, C., Trost, B. M.,
Compound 5, white solid; mp: 134 ꢁC; 1H NMR (CDCl3):
d = 7.47–7.28 (m, 2H), 6.58–6.37 (m, 3H), 6.20 (s, 1H),
4.19 (d, 2H), 3.80 (s, 3H). 13C (CDCl3): d = 170.89, 166.23,
151.51, 144.58, 129.07, 117.79, 114.59, 112.57, 52.84,
41.88.
Compound 6, white solid; mp: 146 ꢁC; 1H NMR (CDCl3):
d = 7.61–6.23 (m, 6H), 4.74–4.70 (m, 1H), 3.77 (s, 3H),
2.25–2.21 (m, 1H), 0.99–0.94 (m, 6H). 13C (CDCl3):
d = 173.03, 166.05, 151.62, 144.48, 128.89, 118.33,
114.36, 112.53, 57.58, 52.56, 31.95, 19.32, 18.27.
´
Lehn, J. M., vonRagueSchleyer, P., Zahradnik, R., Eds.;
Springer-Verlag: Berlin, 1984; (b) Han, S. Y.; Kim, Y. A.
Tetrahedron 2004, 60, 2447–2467.
6. (a) Dourtoglou, V.; Ziegler, J. C.; Gross, B. Tetrahedron
Lett. 1978, 19, 1269–1272; (b) Dourtoglou, V.; Ziegler, J.
C.; Gross, B. Synthesis 1984, 572–574.
7. (a) Castro, B.; Dormoy, J. R.; Evin, G.; Selve, C.
Tetrahedron Lett. 1975, 16, 1219–1222; (b) Castro, B.;
Dormoy, J. R.; Dourtoglou, B.; Evi, G.; Selve, C.; Ziebler,
J. C. Synthesis 1976, 751–752; (c) Dormoy, J. R.; Castro,
Compound 7, white solid; mp: 100 ꢁC; 1H NMR (CDCl3):
d = 7.41–7.36 (m, 2H), 6.55–6.36 (m, 4H), 4.90–4.75 (m,
1H), 3.73 (s, 3H), 1.72–1.58 (m, 3H), 0.95–0.90 (m, 6H).
13C (CDCl3): d = 174.25, 166.17, 151.61, 144.46, 128.88,
118.19, 114.34, 112.50, 52.71, 51.27, 42.03, 25.26, 23.20,
22.30.

220
J. M. Brunel et al. / Tetrahedron Letters 46 (2005) 217–220
Compound 8, white solid; mp: 152 ꢁC; 1H NMR (CDCl3):
2H). 13C (D2O): d = 177.14, 168.82, 151.11, 145.50, 128.59,
117.60, 115.16, 112.81, 43.80.
Compound 14, white solid; mp: 210 ꢁC; H NMR (D2O):
d = 7.60–6.51 (m, 5H), 4.23 (d, J = 6.0 Hz, 1H), 3.75–3.55
(m, 1H), 2.30–2.10 (m, 1H), 0.98–0.93 (m, 6H). 13C
(D2O): d = 178.93, 168.60, 151.15, 145.37, 128.56, 117.65,
115.09, 112.81, 61.24, 30.92, 19.25, 17.65.
d = 7.40–6.37 (m, 6H), 5.03–4.95 (m, 1H), 3.73 (s, 3H),
3.65 (s, 3H), 3.06–2.89 (m, 2H). 13C (CDCl3): d = 171.99,
171.69, 166.17, 151.49, 144.64, 129.12, 117.93, 114.62,
112.56, 53.21, 52.42, 49.10, 36.55.
1
Compound 9, white solid; mp: 109 ꢁC; 1H NMR (CDCl3):
d = 7.45–7.04 (m, 7H), 6.58–6.24 (m, 3H), 6.19 (s, 1H),
3.76 (s, 3H), 3.23–2.85 (m, 3H). 13C (CDCl3): d = 172.47,
165.72, 151.53, 144.58, 136.21, 129.72, 129.00, 127.55,
117.98, 114.61, 112.59, 53.74, 52.79, 38.31.
Compound 15, white solid; mp: 215 ꢁC; 1H NMR
(DMSO): d = 8.14–6.5 (m, 6H), 4.35–4.27 (m, 1H), 3.75
(s, 1H), 1.61–1.45 (m, 3H), 0.86–0.84 (m, 6H). 13C
(DMSO): d = 165.08, 152.03, 145.41, 126.54, 121.20,
114.06, 113.15, 53.14, 42.62, 25.36, 24.06, 22.70.
Compound 10, white solid; mp: 90 ꢁC; 1H NMR (CDCl3):
d = 7.46–6.29 (m, 10H), 6.14–6.11 (d, 1H), 5.01 (m, 1H),
3.76 (s, 3H), 3.21–3.05 (m, 2H). 13C (CDCl3): d = 172.59,
165.84, 155.53, 155.05, 151.47, 147.34, 144.64, 130.81,
129.18, 127.81, 117.88, 115.97, 114.74, 112.62, 53.89,
52.83, 37.60.
1
Compound 16, white solid; mp: 230 ꢁC; H NMR (D2O):
d = 7.63–6.47 (m, 6H), 4.68–4.63 (m, 1H), 2.90–2.73 (m,
2H). 13C (D2O): d = 177.67, 177.06, 168.43, 151.13, 145.45,
128.78, 117.50, 115.23, 112.83, 52.28, 38.36.
Compound 11, white solid; mp: 137 ꢁC; 1H NMR
(CDCl3): d = 7.66–6.48 (m, 5H), 4.91–4.88 (m, 1H), 3.76
(s, 3H), 2.59–2.54 (m, 2H), 2.30–2.02 (m, 6H). 13C
(CDCl3): d = 173.16, 166.28, 142.31, 135.00, 130.23,
129.19, 128.29, 120.35, 53.00, 52.11, 32.11, 30.43, 15.84.
Compound 12, white solid; mp: 130 ꢁC; 1H NMR
(DMSO): d = 7.69–7.38 (m, 6H), 6.53–6.47 (d, 1H), 6.21
(s, 1H), 4.78–4.73 (m, 1H), 3.78 (s, 3H), 2.30–2.21 (m, 1H),
1.02–0.96 (m, 6H). 13C (DMSO): d = 173.09, 166.11,
142.20, 135.09, 130.20, 129.22, 128.27, 120.57, 57.56,
52.62, 31.97, 19.36, 18.30.
Compound 17, White solid; mp: 206 ꢁC; 1H NMR
(DMSO): d = 7.97–6.51 (m, 10H), 4.35–4.31 (m, 1H),
3.44 (s, 2H), 3.08–2.74 (m, 2H). 13C (DMSO): d = 164.18,
155.67, 151.37, 144.66, 130.25, 129.43, 125.65, 120.69,
114.87, 113.30, 112.48, 56.07, 47.24.
Compound 18, white solid; mp: 212 ꢁC; 1H NMR
(DMSO): d = 7.51 (m, 3 H), 7.26–6.19 (m, 9H), 5.06 (m,
1H), 3.36–3.11 (m, 2H). 13C (DMSO): d = 177.01, 165.09,
154.70, 150.31, 145.02, 129.15, 128.80, 121.52, 120.48,
112.10, 111.03, 55.15, 37.20.
Compound 19, white solid; mp: 220 ꢁC; 1H NMR
(DMSO): d = 8.07–6.90 (m, 7H), 4.48–4.27 (m, 1H),
3.52–3.12 (m, 6H), 2.01 (s, 3H). 13C (DMSO):
d = 165.18, 157.63, 139.02, 135.99, 129.73, 128.37,
123.89, 54.38, 48.71, 33.61, 15.55.
10. No detectable racemization was noticed by comparison of
optical rotations of our products with authentic samples
purchased from Sigma.
11. General procedure (Table 3, entry 1): In a 25 mL two
necked round flask was placed compound 5 (75 mg,
3.8 · 10ꢀ4 mol) at room temperature under argon in
anhydrous dioxane (5 mL). NaOH (0.38 mL, 1 M) solu-
tion was added and the mixture stirred at room temper-
ature for 12 h. HCl (0.38 mL, 1 M) solution was then
added and stirring was maintained for 2 h. The reaction
mixture was concentrated in vacuo and the crude residue
was purified by chromatography on a silica gel column
using EtOAc/MeOH as eluent (1:0–1:1) affording the
expected product 13 in 84% yield as a white solid.
Compound 13, white solid; mp: 245 ꢁC; 1H NMR
(D2O): d = 7.61–7.30 (m, 2H), 6.76–6.46 (m, 3H), 3.87 (s,
Compound 20, white solid; mp: 206 ꢁC; 1H NMR
(DMSO): d = 7.75–6.95 (m, 7H), 4.09–4.05 (m, 1H),
3.65–3.20 (m, 1H), 2.20–2.08 (m, 1H), 0.85–0.82 (m,
6H). 13C (DMSO): d = 173.34, 164.37, 140.57, 136.30,
128.90, 128.88, 128.41, 113.41, 58.07, 31.09, 20.03, 18.03.
Compound 21, white solid; mp: 182 ꢁC; 1H NMR
(CDCl3): d = 11.0 (s, 1H), 7.60–7.21 (m, 3H), 6.49–6.24
(m, 3H), 4.59 (s, 1H), 2.50–1.95 (m, 7H). 13C (CDCl3):
d = 177.57, 166.93, 151.21, 144.03, 128.17, 118.24, 113.94,
112.04, 53.46, 31.35, 30.52, 15.24.
12. Durand, A.; Giardina, T.; Villard, C.; Roussel, A.;
Puigserver, A.; Perrier, J. Biochimie 2003, 85, 953–962.