A one-step synthesis of Nα-Fmoc-4-O-[O′,O″-di- tert-butyl-2-(2-fluoromalonyl)]-L-tyrosine from commercially available starting material

Article abstract of DOI:10.1016/j.tetlet.2004.09.163

A one-step high yield synthesis from commercially available starting material is reported for the novel phosphotyrosyl mimetic, N^α- Fmoc-4-O-[O′,O″-di-tert-butyl-2-(2-fluoromalonyl)]-l-tyrosine. The conditions employed for this transformation may also be applicable for the direct electrophilic fluorination of other N^α-Fmoc-protected amino acids.

Full text of DOI:10.1016/j.tetlet.2004.09.163

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 8611–8613
A one-step synthesis of
N -Fmoc-4-O-[O ,O -di-tert-butyl-2-(2-fluoromalonyl)]-L-tyrosine
from commercially available startingmaterial
a
0
00
Sang Uk Kang and Terrence R. Burke, Jr.*
Laboratory of Medicinal Chemistry, Center for Cancer Research, National Cancer Institute, National Institutes of Health,
Frederick, MD 21702, USA
Received 8 July 2004; revised 23 September 2004; accepted 28 September 2004
Abstract—A one-step high yield synthesis from commercially available starting material is reported for the novel phosphotyrosyl
0
a
00
mimetic, N -Fmoc-4-O-[O ,O -di-tert-butyl-2-(2-fluoromalonyl)]-L-tyrosine. The conditions employed for this transformation
may also be applicable for the direct electrophilic fluorination of other N -Fmoc-protected amino acids.
Published by Elsevier Ltd.
a
1
0–17
1. Introduction
phosphatases (PTPs).
In further work based on
molecular modelling studies, the corresponding fluoro-
O-malonyl-tyrosine (FOMT, 3) was prepared and
shown to exhibit 10-fold higher affinity than OMT when
incorporated in place of pTyr in a PTP 1B-directed sub-
Central roles played by phosphotyrosyl (pTyr) residues
1) in signal transduction associated with diseases such
as diabetes and cancers, have made the development
(
1
–3
18
of pTyr mimetics an important area of study. Among
a large number of analogues reported to date, O-malon-
strate peptide. Subsequently, the X-ray crystal struc-
ture of a low-nanomolar affinity FOMT-containing
4
19
yl-tyrosine (OMT, 2, Fig. 1) has found application
in signalling antagonists directed against Src homology
peptide bound to the PTP 1B protein clarified the
manner in which the FOMT residue interacts within
5
–8
20
2
(
(SH2) domains,
9
phosphotyrosine binding domains
PTBs) and more particularly, against protein–tyrosine
the PTP catalytic site. More recentuses of FOMT in
peptides directed against other PTPs, including the
1
6
17
Yersinia pestis YopH and purple acid phosphatases,
have continued to validate the utility of FOMT. How-
ever, unlike OMT, which is commercially avialable in
O
O
1
a
0 00
R
O
O
O
O
its N -Fmoc-4-O-(O ,O -di-tert-butyl)-L-tyrosine form
21
O
OH
a
t
[
sponding protected FOMT analogue, N -Fmoc-4-O-
N -Fmoc ( BuO) -OMT-OH, 4], to date the corre-
2
1
(
HO) P
N
R
O
N
2
a
2
O
H
H
R
X
0 00
[O ,O -di-tert-butyl-2-(2-fluoromalonyl)]-L-tyrosine,
1
2
R
R
X
a
t
[
N -Fmoc ( BuO) -FOMT-OH, 5] has been available
2
1
pTyr Residue
2
OMT
FOMT
H
H
H
H
H
F
18
only by multi-step synthesis. In lightof ht is, work
reported herein was undertaken to effect a direct conver-
sion of commercially available protected-OMT 4 to the
desired FOMT analogue 5.
3
4
t
t
Bu
Fmoc
H
5
Bu
Fmoc
F
Figure 1. Structures of pTyr and malonyl-based mimetics.
The original preparation of 5 employed electrophilic
fluorination of the N -Fmoc ( BuO) -OMT methyl ester
a
t
2
6
ing 8. This procedure was noteworthy by its mainte-
, followed by LiOH-catalyzed hydrolysis of the result-
Keywords: OMT; FOMT; Phosphotyrosyl mimetic; Amino acid ana-
logue; Electrophilic flourination.
a
*
Corresponding author. Tel.: +1 301 846 5906; fax: +1 301 846
033; e-mail: tburke@helix.nih.gov
nance of base-labile N -Fmoc-protection in the
1
presence of two strongly alkaline reagents. The choice
8
6
0040-4039/$ - see front matter Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2004.09.163

8612
S. U. Kang, T. R. Burke, Jr. / Tetrahedron Letters 45 (2004) 8611–8613
O
O
t
BuO
O
O
t
NFSI, NaHMDS
THF, 89%
BuO
t
BuO
O
O
OR
OR
Fmoc
t
BuO
N
N
H
Fmoc
H
F
O
O
4
R = H
5
7
R = H
R = Me
6
R = Me
Scheme 1. Approaches towards electrophilic flourination leading to FOMT analogues.
of methyl ester 6 as the fluorination substrate was predi-
cated on its availability as an intermediate in the syn-
2. Experimental
a
t
thesis of N -Fmoc ( BuO) -OMT-OH (4). A similar
a
t
2.1. Synthesis of N -Fmoc ( BuO) -FOMT-OH (5)
2
2
approach starting from commercially available 4 would
require a three-step protocol of esterification to 6 fol-
lowed by electrophilic flourination to 7, then demethyl-
ation to 5 (Scheme 1). Given the cost of starting 4
a
t
To a stirred solution of N -Fmoc ( BuO) -OMT-OH
21
2
(500mg, 0.81mmol) in anhydrous THF (10mL) at
ꢀ78°C under argon was added NaHMDS (1.7mL,
1.70mmol) dropwise. After stirring at ꢀ78°C (15min)
a solution of NFSI (307mg, 0.97mmol) in THF (5mL)
was added dropwise and the mixture was stirred at
ꢀ78°C (1h). The reaction was quenched (2.5mL of
2
1
(
approximately $1800/g), circumvention of such a mul-
ti-step scenario by elimination of the carboxylic acid
protection/deprotection would be desirable. Indeed, it
was found that treatment of 4 with N-fluorobenzenesulf-
onimide (NFSI) in the presence of slightly greater than 2
equiv of sodium bis(trimethylsilyl)amide (NaHMDS) at
carefully controlled temperature, followed by quenching
with 1N HCl provided the desired 5 cleanly in 89%
1N HCl at ꢀ78°C) then subjected to extraction (H O/
2
EtOAc). The organic extract was dried (MgSO ) and
4
purified by silica gel flash column chromatography
(CH Cl :MeOH, 20:1 followed by CH Cl :MeOH,
10:1 then CH Cl :MeOH, 5:1) to provide N -Fmoc
2 2
2
2
2
2
a
(
Scheme 1).
t
22 1
(
BuO) -FOMT-OH (460mg, 89% yield) as an oil.
2
H
The enantiomeric purity of 5 was determined by cou-
pling with (±)-a-methylbenzylamine [(±)-8] and with
R-(+)-a-methylbenzylamine [(±)-8] to yield the corre-
NMR (CDCl ) d 8.92 (1H, br s), 7.75 (2H, d,
3
J = 7.4Hz), 7.54 (2H, d, J = 7.2Hz), 7.39 (2H, t,
J = 7.2Hz), 7.30 (2H, t, J = 7.3Hz), 7.11 (2H, d, J =
8.0Hz), 7.04 (2H, d, J = 8.2Hz), 5.21 (1H, d, J =
7.4Hz), 4.62 (m, 1H), 4.48–4.35 (2H, m), 4.18 (1H, t,
sponding diastereomeric amides 9 and 10, respectively
1
Scheme 2). Comparison of H NMR of 9 and 10 in
(
1
3
CDCl indicated a clearly resolved multiplet in 9 at d
J = 6.4Hz), 3.17–3.02 (2H, m), 1.39 (18H, s).
C
3
7
.03–6.98 corresponding to the five benzylamide five
NMR (400 MHz, CDCl ) d 175.6, 161.4, 161.0, 155.8,
3
aryl protons of the (S,S) diastereomer, which were
absentin 10. In benzene-d6 better resolution was
achieved for several diastereomeric protons, including
those arising from certain aryl protons, the amide pro-
ton and the methyl protons. Within the limits of detec-
tion, no enantiomeric contamination of 5 was evidient.
152.7, 143.6. 141.3, 132.3, 130.3, 127.8, 127.1, 125.0,
120.2, 120.0, 105.2, 102.8, 84.6, 67.0, 54.6, 47.1, 37.5,
27.5.
2.2. Enantiomeric purity determination for 5: synthesis of
amides 9 and 10
a
The facile and directconversion of 4 to 5 makes N -
Fmoc ( BuO) -FOMT-OH readily available for use in
To a solution of 5 (30mg, 0.047mmol) in anhydrous
DMF (0.4mL) was added EDCIÆHCl (8mg,
0.061mmol) followed by HOAt(0.5M in DMF,
0.1mL, 0.047mmol). The mixture was stirred for
10min at room temperature, then either (±)-a-methyl-
benzylamine [(±)-8] or R-(+)-a-methylbenzylamine
t
2
signal transduction-related studies. Of equal impor-
tance, the conditions reported herein may also be appli-
cable for the direct electrophilic fluorination of other
a
N -Fmoc-protected amino acids.
[
(+)-8] (8mg, 0.066mmol) was added dropwise. The
mixture was stirred overnight then purified directly by
column chromatography to yield the corresponding
amides 9 (7.9mg, 23% yield) and 10 (6.4mg, 18% yield).
O
Me
Me
t
BuO
t
BuO
O
O
N
H
H N
2
N
+
For 9: FABMS m/z 739 (MH ); H NMR (CDCl , a
1
H
Fmoc
3
F
(
+)-8
mixture of two diasteromers) d 7. 76 (4H, d, J =
7.0Hz, overlapping), 7.54 (4H, m, overlapping), 7.40
(4H, t, J = 7.4 Hz, overlapping), 7.33–7.21 (10H, m,
overlapping), 7.17–7.12 (7H, m, overlapping), 7.03–
6.98 (5H, m, (S,S)), 5.81 (1H, br s), 5.76 (1H, br s),
5.35 (2H, br s, overlapping), 4.99 (2H, m, overla-
pping), 4.41 (4H, m, overlapping), 4.29 (2H, m, overlap-
ping), 4.18 (2H, m, overlapping), 3.10–2.92 (4H, m,
overlapping), 1.41 (39H, m), 1.30 (3H, broad doublet,
J = 5.1Hz (S,R)).
–
O
9
5
HOAt, EDC.HCl, DMF
O
Me
Me
t
BuO
t
BuO
O
O
N
H
H N
2
N
H
Fmoc
F
R-(+)-8
O
1
0
Scheme 2. Determination of enantiomeric purity.

S. U. Kang, T. R. Burke, Jr. / Tetrahedron Letters 45 (2004) 8611–8613
8613
1
H NMR (C D , a mixture of two diasteromers) d 7.49
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(
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doublet, (S,R)), 6.61 (broad doublet, (S,S)), 5.53 (2H,
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272.
. Giorgetti-Peraldi, S.; Ottinger, E.; Wolf, G.; Ye, B.;
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(4H, m, overlapping), 1.17 (36H, s, overlapping), 1.01
(3H, d, J = 6.6Hz, (S,S)), 0.97 (3H, d, J = 6.8Hz,
(S,R)).
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Roller, P. P.; Burke, T. R., Jr. Biochem. Biophys. Res.
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+
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1
1
1
1
1. Akamatsu, M.; Roller, P. P.; Chen, L.; Zhang, Z. Y.; Ye,
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(S,R)) d 7.76 (2H, d, J = 7.3Hz), 7.54 (2H, d,
J = 7.3Hz), 7.40 (2H, t, J = 7.3Hz), 7.33–7.21 (6H, m),
1
63.
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7
4
.17–7.12 (5H, m), 5.76 (1H, br s), 5.33 (1H, br s),
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Z.-Y.; Burke, T. R., Jr. Bioorg. Med. Chem. Lett. 2000, 10,
9
23–927.
J = 6.3Hz), 3.10 (1H, m), 2.94 (1H, m), 1.42 (19H, s),
.30 (3H, d, J = 6.1Hz).
3. Bleasdale, J. E.; Ogg, D.; Palazuk, B. J.; Jacob, C. S.;
Swanson, M. L.; Wang, X.-Y.; Thompson, D. P.;
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C. W.; Heijbel, A.; Bergdahl, K.; Bannow, C. A.; Smith,
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1
H NMR (C D ) d 7.49 (2H, d, J = 7.4Hz), 7.32 (2H,
6
6
m), 7.17–6.88 (11H, m), 6.72 (2H, broad doublet), 5.45
(
1 H, br s), 4.99 (2H, m), 4.28 (2H, broad doublet),
5
642–5654.
4
2
.12 (1H, m), 3.88 (1 H, broad triplet), 2.75 (1H, m),
.63 (1H, m), 1.18 (9H, s), 1.17 (9 H, s), 0.97 (3H, d,
1
1
4. Larsen, S. D.; Barf, T.; Liljebris, C.; May, P. D.; Ogg, D.;
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6
22.
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Acknowledgements
9
75.
Appreciation is expressed to Drs. James Kelley and
Christopher Lai of the LMC for mass spectral analysis.
1
1
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. Burke, T. R., Jr.; Yao, Z.-J.; Smyth, M. S.; Ye, B. Curr.
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. Burke, T. R., Jr.; Yao, Z.-J.; Liu, D.-G.; Voigt, J.; Gao, Y.
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. Burke, T. R.; Lee, K. Acc. Chem. Res. 2003, 36, 426–433.
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21. Available from Bachem. Corp. as catalogue number B-
2825.
4
736.
5
. Ye, B.; Akamatsu, M.; Shoelson, S. E.; Wolf, G.;
Giorgetti-Peraldi, S.; Yan, X.; Roller, P. P.; Burke, T.
R., Jr. J. Med. Chem. 1995, 38, 4270–4275.
6
. Yao, Z. J.; King, C. R.; Cao, T.; Kelley, J.; Milne, G. W.
A.; Voigt, J. H.; Burke, T. R., Jr. J. Med. Chem. 1999, 42,
22. Less than 4% unfluorinated starting material was evi-
denced by the presence of a singlet in the H NMR at d
4.95.
2
5–35.