A convenient synthesis of N-fluorenylmethoxycarbonyl-N-methyl-L-Cysteine derivatives [Fmoc,Me-Cys(R)-OH]

Article abstract of DOI:10.1055/s-2002-33343

The synthesis of N-fluorenylmethoxycarbonyl-N,S-dimethyl-L-Cysteine (1) [Fmoc,Me-Cys(Me)-OH] and N-fluorenylmethoxycarbonyl-N-methyl-S-acetamidomethyl-L-Cysteine (2) [Fmoc,Me-Cys(Acm)-OH] is reported. The synthesis is characterized by a convenient two-step procedure from (R)-thiazolidine-4-carboxylic acid (3) via reduction and subsequent protection. Crystals of 1, which have been analyzed by single-crystal X-ray crystallography, are obtained after a simple crystallization at the end of the process, without purification of intermediates.

Full text of DOI:10.1055/s-2002-33343

SHORT PAPER
1499
A Convenient Synthesis of N-Fluorenylmethoxycarbonyl-N-Methyl-L-
Cysteine Derivatives [Fmoc,Me-Cys(R)-OH]
N
J
-Fluore
n
i
ylmeth
a
oxycarbony
-
l-
N
-
Met
F
hyl-
L
-
Cystein
e
e
D
erivativ
n
e
s
[Fmoc,M
e
g
-Cys(
R
)-OH
]
Liu, Xiao-Xia Tang, Biao Jiang*
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, P. R. China
Fax +86(21)64166128; E-mail: jiangb@pub.sioc.ac.cn
Received 18 March 2002; revised 1 May 2002
S
Abstract: The synthesis of N-fluorenylmethoxycarbonyl-N,S-dim-
ethyl-L-Cysteine (1) [Fmoc,Me-Cys(Me)-OH] and N-fluor-
HN
enylmethoxycarbonyl-N-methyl-S-acetamidomethyl-L-Cysteine
(
2) [Fmoc,Me-Cys(Acm)-OH] is reported. The synthesis is charac-
CO2H
terized by a convenient two-step procedure from (R)-thiazolidine-4-
carboxylic acid (3) via reduction and subsequent protection. Crys-
tals of 1, which have been analyzed by single-crystal X-ray crystal-
lography, are obtained after a simple crystallization at the end of the
process, without purification of intermediates.
3
c
a
Me
Me
Key words: amino acids, peptides, cysteine, protecting groups
–
+
–
+
Cl H N
Cl H N
2
2
SMe
SH
CO H
CO H
2
2
N-Methyl-amino acids are an important class of com-
pounds present in a wide variety of naturally occurring
peptides and depsipeptides with broad spectrum activities
4
5
b
d
1
such as antibiotic, antiviral and anticancer activities. In-
corporation of N-methyl-amino acids into key positions of
peptides and depsipeptides leads to an enhanced pro-
teolytic stability, a lipophilicity increase, and a secondary
Me
N
Me
N
Fmoc
SMe Fmoc
SAcm
2
structure domains’ stabilization. Therefore, they are
CO2H
CO2H
valuable building blocks for the synthesis of peptidomi-
metics. Consequently, quite a number of synthetic routes
1
2
3
Scheme Reagents and conditions: a) Na/NH , then MeBr, –40 °C,
to homochiral N-methyl-amino acids have been devel-
3
4
–6
then concd HCl; b) Fmoc-OSu/aq Na
7% from 3; c) Na/NH3, –40 °C, then concd HCl; d)
OH/H O, CF SO H/CF COOH (1:19), r.t., then Fmoc-
OSu/aq Na CO –dioxane, 0 °C r.t., 4 d, 41% from 3.
2 3
CO –dioxane, 0 °C r.t., 3 d,
oped.
5
For purposes of peptide synthesis, it is desirable to have MeCONHCH
the N-methyl-L-cysteine derivatives, N-fluorenylmeth-
oxycarbonyl-N,S-dimethyl-L-cysteine (1) [Fmoc,Me-
2
2
3
3
3
2
3
Cys-(Me)-OH] and N-fluorenylmethoxycarbonyl-N-me- The starting acid 3, which can be easily prepared from L-
8
thyl-S-acetamidomethyl-L-cysteine
(2)
[Fmoc,Me- cysteine hydrochloride in large quantities, was reduced
Cys(Acm)-OH]. As far as we know these two compounds with sodium in liquid ammonia4
,9,10
and methylated with
have not been described so far. However, both of them can MeBr in one pot to yield N,S-dimethyl-L-cysteine hydro-
be easily retrosynthesized to N-methyl-L-cysteine. The chloride (4). The amino acid 4 was protected as the fluo-
methods of choice for preparing N-methyl-L-cysteine in- renylmethoxycarbonyl (Fmoc) derivative with N-(9H-
clude Undheim’s procedure from the respective 4-carbox- fluoren-2-ylmethoxycarbonyloxy)succinimide
ythiazolinium derivative and Blondeau’s Na/NH3 OSu). Pure Fmoc,Me-Cys(Me)-OH (1) was obtained in
reduction process of (R)-thiazolidine-4-carboxylic acid modest yield after a simple crystallization (Scheme). For-
(Fmoc-
5
11
4
4
(
3), and the better one seems to be Blondeau’s. Enlight- tunately, crystals were obtained for an X-ray structure
ened by Albericio’s procedure of one-pot synthesis of analysis (Figure). In a similar way, the acid 3 was reduced
7
4,9,10
Fmoc-Cys(Acm)-OH, we succeeded in adapting with Na/NH3,
and treated following Albericio’s one-
7
Blondeau’s method to a two-step strategy for preparation pot protection procedure to obtain Fmoc,Me-Cys(Acm)-
of N-methyl-L-cysteine derivatives 1 and 2. Herein we re- OH (2) (Scheme).
port the convenient synthesis of compound 1 and 2 both
In summary, the first syntheses of the two N-methyl-L-
from (R)-thiazolidine-4-carboxylic acid (3) (Scheme).
cysteines, Fmoc,Me-Cys(Me)-OH (1) and Fmoc,Me-
Cys(Acm)-OH (2), were accomplished. By adaptation of
the stereoconservative Na/NH reduction procedure to a
two-step strategy, only with simple extraction purification
of the intermediates, we succeeded in synthesizing 1 and
3
Synthesis 2002, No. 11, Print: 22 08 2002.
Art Id.1437-210X,E;2002,0,11,1499,1501,ftx,en;F02202SS.pdf.
©
Georg Thieme Verlag Stuttgart · New York
2
conveniently.
ISSN 0039-7881

1
500
J.-F. Liu et al.
SHORT PAPER
IR: 3336, 1747, 1725, 1693, 1643, 1450, 1306, 1192, 1141, 759,
–
1
7
40 cm .
1H NMR: = 9.43 (br s, 1 H), 7.77 (d, J = 7.9 Hz, 2 H), 7.61 (d,
J = 7.3 Hz, 2 H), 7.41 (t, J = 7.6 Hz, 2 H), 7.31 (t, J = 7.6 Hz, 2 H),
4
1
2
.89 (dd, J = 10.4, 4.9 Hz, 1 H), 4.64–4.42 (m, 2 H), 4.32–4.21 (m,
H), 3.12 (dd, J = 14.0, 4.9 Hz, 1 H), 2.97 (s, 3 H), 2.88 (m, 1 H),
.14 (s, 3 H).
13C NMR:
20.1, 68.2, 58.1, 47.1, 33.1, 31.6, 15.5.
= 174.9, 157.2, 143.8, 141.4, 127.8, 127.2, 125.1,
1
+
+
MS-ESI: m/z = 372 [M + H] , 394 [M + Na] .
Anal. Calcd for C H NO S: C, 64.67; H, 5.70; N, 3.77; S, 8.63.
2
0
21
4
Found: C, 64.61; H, 5.88; N, 3.66; S, 8.64.
X-ray Crystallographic Data: Single crystals were grown from
CH Cl –hexane. Crystal system Monoclinic; Space group P2(1);
2
2
T = 293(2) K; a = 11.2621(11) Å, b = 6.4479(7) Å, c = 13.2810(14)
o
3
Å, = 90°, = 92.663(2) , = 90°, V = 963.38(17) Å , Z = 2;
3
D = 1.280 g/cm ; range for data collection 1.53 to 25.99°, Limiting
c
indices –12
h 13, –7 k 7, –16 l 16; Reflections collected:
5
333, Unique reflections: 3378 [R(int) = 0.0312]; Refinement
Figure X-ray crystal structure of 1
2
2
method: Full-matrix least-squares on F , Goodness-of-fit on F :
.777, Final R indices [I > 2(I)] R1 = 0.0385, wR2 = 0.0587 R indi-
ces (all data) R1 = 0.0639, wR2 = 0.0640, Largest diff. peak and
0
–
3
hole 0.190 and -0.136 e Å .
Flash chromatography was carried out using 300–400 mesh silica
gel. Melting points were recorded on WRS-1A apparatus and are
uncorrected. IR spectra were recorded on a Schimadzu 440-IR spec-
N-Fluorenylmethoxycarbonyl-N-methyl-S-acetamidomethyl-L-
cysteine (2)
1
13
trophotometer with KBr optics. H and C NMR spectra were re-
In a similar way to the above procedure, to refluxing liquid ammo-
nia (400 mL) (R)-thiazolidine-4-carboxylic acid (6.66 g, 50.0
mmol) and sodium (2.4 g, 104 mmol) were added successively in
small portions to keep the concentration of the acid at a low level.
After the addition of ammonium chloride, the solution was allowed
to evaporate to dryness. The residue was dissolved in as little water
as possible and acidified with concd aq HCl to pH 2. Evaporation of
the water gave a solid residue. Extraction with EtOH (3 40 mL)
followed by evaporation of the solvent afforded N-methyl-L-cys-
teine hydrochloride (5). The solid was used in the following reac-
tion without further purification.
corded on 300 spectrometer in CDCl using TMS as an internal
standard. Mass spectra were recorded on an Applied Biosystems
Mariner time-of-flight mass spectrometer.
3
N-Fluorenylmethoxycarbonyl-N,S-dimethyl-L-cysteine (1)
(
R)-Thiazolidine-4-carboxylic acid (3) (5.33 g, 40.0 mmol) and so-
dium (1.9 g, 83 mmol) were added successively in small portions to
a refluxing liquid ammonia (300 mL). To keep the concentration of
the acid at a low level, small pieces of sodium were added following
the addition of every portion (100–200 mg) of acid 3 till a persistent
blue color appeared. When all the acid had been added, the blue col-
or was discharged with ammonium chloride. To the solution, bro-
momethane (2.5 mL, 45 mmol) was added. The mixture was stirred
for 2.5 h, and then the solution was allowed to evaporate to dryness.
The residue was dissolved in as little water as possible and acidified
with concd aq HCl to pH 2. Evaporation of the water gave a solid
residue. Extraction with EtOH (3 30 mL) followed by evaporation
of the solvent afforded N,S-dimethyl-L-cysteine hydrochloride (4).
The solid was used in the following reaction without further purifi-
cation.
Yield: 7.04 g (82.0%); white solid; mp 127–128 °C.
N-Methyl-L-cysteine hydrochloride (5) (7.04 g, 41.0 mmol) and N-
hydroxymethylacetamide (4.75 g, 53.3 mmol) were dissolved in
H O (20 mL). The mixture was cooled in an ice-water bath and tri-
fluoromethanesulfonic acid–TFA (1:19; 72 mL) was added. After 3
h stirring under argon, TLC indicated that all the N-methyl-l-cys-
teine has reacted. The solvent was removed by rotary evaporation,
including chasing with Et O (4 50 mL) to give a pale yellow oil.
The oil was dissolved in a 10% aq Na CO , and the resulting solu-
2
2
2
3
tion was brought to pH 10 by adding more 10% aq Na CO . The so-
Yield: 5.80 g (78.0%); white solid, mp 119–120 °C.
2
3
lution was cooled with ice-water bath and Fmoc-OSu (13.5 g, 40.0
mmol) in dioxane (140 mL) was added. After 2 h of stirring, the
mixture was allowed to react at r.t. for 4 more days and kept at pH
N,S-Dimethyl-L-cysteine hydrochloride (4) (5.80 g, 31.2 mmol)
was dissolved in a 10% aq Na CO , and the resulting solution was
2
3
brought to pH 10 by adding 10% aq Na CO . The solution was
2
3
9–10. The mixture was then diluted with H O (500 mL), washed
2
cooled in ice-water bath and Fmoc-OSu (10.0 g, 29.6 mmol) in di-
oxane (100 mL) was added. After 2 h, the mixture was allowed to
warm to r.t. for 3 days and kept at pH 9–10. The mixture was then
with Et O (2 150 mL), acidified with concd aq HCl to pH 2, and
2
extracted with EtOAc (3 200 mL). The combined organic layers
were dried (Na SO ). After concentration, flash chromatography
2
4
diluted with water (300 mL), and extracted with Et O (2 80 mL).
2
(
CH Cl –MeOH, 10:1 gradient as eluent) afforded the title com-
2 2
The aqueous layer was acidified with concd aq HCl to pH 2, and ex-
tracted with EtOAc (3 200 mL). The combined organic layers
were dried (Na SO ) and after filtration the solvent was removed.
pound 2.
Yield 8.75 g (49.8%; 41% yield over two steps from initial acid 3);
2
4
2
0
white foam; [ ]D
–60.4° (c 1.05, CHCl3).
Product 1 was recrystallized by dissolving in hot CH Cl , adding
hexane to incipient turbidity and placing in a refrigerator for two
days to give 1.
2
2
–
1
IR: 3318, 1703, 1547, 1450, 1402, 1318, 1181, 1137, 759, 740 cm .
1H NMR: = 9.13 (br s, 2 H), 7.75 (d, J = 7.5 Hz, 2 H), 7.59 (d,
J = 7.2 Hz, 2 H), 7.39 (t, J = 7.3 Hz, 2 H), 7.30 (t, J = 7.3 Hz, 2 H),
4.95 (d, J = 8.4 Hz, 1 H), 4.53–4.39 (m, 3 H), 4.29–4.21 (m, 2 H),
Yield: 8.48 g (73.2%, 57% yield over two steps from initial acid 3);
2
0
colorless crystals; mp 105–107 °C; [ ]D –53.2° (c 1.08, CHCl3).
3
.23 (d, J = 14.3 Hz, 1 H), 2.92 (s, 3 H), 2.80 (m, 1 H), 1.99 (s, 3 H).
Synthesis 2002, No. 11, 1499–1501 ISSN 0039-7881 © Thieme Stuttgart · New York

SHORT PAPER
N-Fluorenylmethoxycarbonyl-N-Methyl-L-Cysteine Derivatives [Fmoc,Me-Cys(R)-OH]
1501
13C NMR:
25.4, 120.3, 68.3, 59.1, 54.2, 47.3, 37.1, 31.2, 25.7.
= 172.6, 172.0, 157.8, 144.0, 141.5, 128.0, 127.4,
(5) Undheim, K.; Eidem, A. Acta Chem. Scand. 1970, 24, 3129.
(6) (a) Burger, K.; Spengler, J. Eur. J. Org. Chem. 2000, 199.
(b) Spengler, J.; Burger, K. Synthesis 1998, 67. (c) Yang,
L.; Chiu, K. Tetrahedron Lett. 1997, 38, 7307. (d) Myers,
A. G.; Gleason, J. L.; Yoon, T.; Kung, D. W. J. Am. Chem.
Soc. 1997, 119, 656. (e) Dorrow, R. L.; Gingrich, D. E.
Tetrahedron Lett. 1999, 40, 467. (f) Freidinger, R. M.;
Hinkle, J. S.; Perlow, D. S.; Arison, B. H. J. Org. Chem.
1
+
+
MS-ESI: m/z = 429 [M + H] , 451 [M + Na] .
+
HRMS-ESI: (m/z) [M + H] calcd for C H N O S, 429.1484.
2
2
25
2
5
+
Found, 429.1486. [M + Na] calcd for C H N O NaS, 451.1304.
2
2
24
2
5
Found, 451.1293.
1
983, 48, 77. (g) Cheung, S. T.; Benoiton, N. L. Can. J.
References
Chem. 1977, 55, 906.
(
7) Albericio, F.; Grandas, A.; Porta, A.; Pedroso, E.; Giralt, E.
Synthesis 1987, 271.
8) Ratner, S.; Clarke, H. T. J. Am. Chem. Soc. 1937, 59, 200.
9) It was reported that the sodium in liquid ammonia reduction
(
1) (a) Li, W. R.; Jouillie, M. M. Steroselective Synthesis, In
Studies in Natural Products Chemistry, Part F, Vol. 10;
Attaur-Rahman, Elsevier: Amsterdam, 1992, 241.
(
(
(
1
b) Ramanjulu, I. M.; Ding, X.; Joullie, M. M. J. Org. Chem.
997, 62, 4961. (c) Pettit, G. R.; Kamano, Y.; Herald, C. L.;
4
,10
of l-thiazolidine-4-carboxylic acid gave dimeric product.
4
By keeping a low concentration of the acid or adding one
Fuji, Y.; Kizu, H.; Boyd, M. R.; Boettner, F. E.; Doubek, D.
L.; Schmidt, J. M.; Chapuis, J.; Michel, C. Tetrahedron
1
1
0
molecular portion of water, dimerization was avoided.
However, from our three parallel experiments following (1)
low concentration procedure, (2) water addition treatment,
and (3) addition of one molecular portion of water and
keeping the low concentration of the acid, the best result was
obtained from the low concentration procedure.
993, 49, 9151.
2) Ovchinnikov, Y. A.; Ivanov, V. T. Tetrahedron 1975, 31,
177.
3) For reviews, see: (a) Gante, J. Angew. Chem., Int. Ed. Engl.
994, 33, 1699. (b) Giannis, A.; Kolter, T. Angew. Chem.,
(
(
2
1
(
10) Yamashiro, D.; Aanning, H. L.; Branda, L. A.; Cash, W. D.;
Int. Ed. Engl. 1993, 32, 1244. (c) Balkenhohl, F.; Busche-
Hünnefeld, C.; Lansky, A.; Zechel, C. Angew. Chem., Int.
Ed. Engl. 1996, 35, 2288.
Murti, V. V. S.; Vigneaud, V. J. Am. Chem. Soc. 1968, 90,
4141.
(
11) Milton, R. C. deL.; Becker, E.; Milton, S. C. F.; Baxter, J. E.
(4) Blondeau, P.; Berse, C.; Gravel, D. Can. J. Chem. 1967, 45,
J.; Elsworth, J. F. Int. J. Peptide Protein Res. 1987, 30, 431.
49.
Synthesis 2002, No. 11, 1499–1501 ISSN 0039-7881 © Thieme Stuttgart · New York