Synthesis of the first α-fluoro-phosphotyrosyl mimetic

Article abstract of DOI:10.1081/SCC-200034770

The diastereoselective preparation of (2S)-2-fluoro-4-[[bis(1,1- dimethylethoxy)phosphinyl]methyl] benzenepropanoic acid (5) is presented as new phosphotyrosyl (pTyr) mimetic suitably protected for incorporation into peptides. Synthesis of 5 utilized elec

Full text of DOI:10.1081/SCC-200034770

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Synthesis of the First
α‐Fluoro‐Phosphotyrosyl
Mimetic
Zhen‐Dan Shi a , Hongpeng Liu b , Manchao Zhang b
, Dajun Yang b & Terrence R. Burke Jr. a
a Laboratory of Medicinal Chemistry, Center for
Cancer Research , National Cancer Institute,
National Institutes of Health, NCI‐Frederick , P.O.
Box B, Bldg. 376 Boyles St., Frederick, Maryland,
20702‐1201, USA
b Department of Hematology/Oncology ,
University of Michigan Medical School , Ann Arbor,
Michigan, USA
Published online: 10 Jan 2011.
To cite this article: Zhen‐Dan Shi , Hongpeng Liu , Manchao Zhang , Dajun Yang &
Terrence R. Burke Jr. (2004) Synthesis of the First α‐Fluoro‐Phosphotyrosyl Mimetic,
Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 34:21, 3883-3889, DOI: 10.1081/SCC-200034770
To link to this article: http://dx.doi.org/10.1081/SCC-200034770
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 21, pp. 3883–3889, 2004
Synthesis of the First a-Fluoro-
Phosphotyrosyl Mimetic
Zhen-Dan Shi,1 Hongpeng Liu,2 Manchao Zhang,2
Dajun Yang,2 and Terrence R. Burke, Jr.1,
*
1Laboratory of Medicinal Chemistry, Center for Cancer Research,
National Cancer Institute, National Institutes of Health, NCI-Frederick,
Frederick, Maryland, USA
2Department of Hematology/Oncology, University of Michigan Medical
School, Ann Arbor, Michigan, USA
ABSTRACT
The diastereoselective preparation of (2S)-2-fluoro-4-[[bis(1,1-dimethyl-
ethoxy)phosphinyl]methyl] benzenepropanoic acid (5) is presented as
new phosphotyrosyl (pTyr) mimetic suitably protected for incorporation
into peptides. Synthesis of 5 utilized electrophilic fluorination under
chiral induction provided by the commercially available Evans auxiliary,
(S)-(þ)-4-phenyl-2-oxazolidinone. In order to demonstrate its synthetic
utility, analogue 5 was employed to prepare a signal transduction-directed
*
Correspondence: Terrence R. Burke, Jr., Laboratory of Medicinal Chemistry, Center
for Cancer Research, National Cancer Institute, National Institutes of Health, NCI-
Frederick, P.O. Box B, Bldg. 376 Boyles St., Frederick, MD 20702-1201, USA;
Fax: (301) 846-6033; E-mail: tburke@helix.nih.gov.
3883
DOI: 10.1081/SCC-200034770
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Shi et al.
tripeptide. The design considerations for this peptide and its preliminary
biological evaluation are included.
Key Words: Chiral induction; Enantioselective; Phosphotyrosyl mimetic;
Fluorination.
INTRODUCTION
Introduction of fluorine into biologically active molecules has proven to
be of widespread value as a means to modify pharmacological activity or to
probe physiological mechanisms of action.[1] In the area of cellular signal
transduction, phosphotyrosyl residues (pTyr, 1, Fig. 1) play central roles. To
date, fluorination of pTyr surrogates has been limited to the phenylphosphate
region of the amino acid side chain; either the phosphoryl-mimicking
component or to the aryl ring.[2] An example of the former is provided by
F2Pmp (2), wherein the pTyr phosphoryl ester oxygen has been replaced
with a difluoromethylene species.[3] This represents a fluorinated variant of
the widely used pTyr mimetic, phosphonomethyl phenylalanine (Pmp, 3).[4–6]
In theory, introduction of fluorine substituents at other side chain locations
could result in new and potentially useful analogues. Mimetic 4 is a fluorinated
des-amino Pmp analogue that can be derived from insertion of a fluorine atom
into the a-position of 3-[(4-phosphonomethyl)phenyl]proprionic acid. Con-
version of 4 into a more synthetically useful form yields the corresponding
bis-But phosphonic acid ester 5, which is suitably protected for incorporation
of 4 into peptides. Compounds 4 and 5 represent the first pTyr mimetics
bearing fluorine substituents outside the phenylphosphate region. The
purpose of the current report is to present the synthesis 5 as well as its first
application in a signal transduction-related study.
Figure 1. Structures of pTyr and pTyr mimetics.

Synthesis of the First a-Fluoro-Phosphotyrosyl Mimetic
3885
RESULTS AND DISCUSSION
Enantioselective synthesis of a-fluoro phenylproprionic acid has been
reported by nucleophilic fluoride displacement of chiral a-sulfonates.[7]
However, a more attractive approach is the diastereoselective electrophilic
fluorination of an imide enolate derived from an appropriate Evans chiral
oxazolidinone auxiliary.[8] Such an approach has been used successfully to
prepare a-fluorocarboxylic acids in high enantiopurity.[9] For the synthesis
of 5, the requisite starting chiral imide 6 can be readily prepared from
commercially available (S)-(þ)-4-phenyl-2-oxazolidinone[10] in high yield
as previously reported.[11] Treatment of 6 with sodium bis(trimethylsilyl)
amide (NaHMDS) in THF at 2788C followed by reaction with N-fluorobeze-
nesulfonimide (7)[10] gave the (S)-a-fluoro analogue 8 in 73% yield without
any evidence of the diastereomeric (R)-fluoro analogue by 1H-NMR
or 19F-NMR (Sch. 1). To complete the synthesis, cleavage of the chiral
auxiliary was performed using lithium hydroxide in the presence of hydrogen
peroxide to give the desired final product 5 in 96% yield.
Protected analogue 5 represents the first a-fluoro-pTyr mimetic yet
reported. Analogue 5 was employed to introduce the a-fluoro-containing
pTyr mimetic 4 as a replacement for Pmp (2) in the naphthylpropylamide-
containing tripeptide 12, which has been reported previously to exhibit high
Grb2 SH2 domain-binding affinity.[12,13] As shown in Sch. 2, coupling of 5
with the naphthylpropylamide-containing dipeptide 9[13] gave protected 10
in 85% yield using 1-hydroxy-7-azabenzotriazole (HOAt) active ester
coupling.[14] TFA-mediated deprotection of 10 gave the desired a-fluoro-
containing tripeptide mimetic 11, which was purified by HPLC. No evidence
of epimerization at the a-fluoro center was evident from either the 1H-NMR or
the 19F-NMR spectra.
Scheme 1.

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Shi et al.
Scheme 2.
EXPERIMENTAL
Elemental analyses were obtained from Atlantic Microlab Inc., Norcross,
GA, and fast atom bombardment mass spectra (FAB-MS) were acquired with
a VG Analytical 7070E mass spectrometer under the control of a VG2035 data
system. Where indicated, FAB-MS matrixes used were glycerol or nitro-
benzoic acid. 1H-NMR and 19F-NMR data were obtained on a Varian 400 MHz
instrument and are reported in ppm relative to TMS or CFCl3, respectively,
and referenced to the solvent in which they were run. Solvent was removed
by rotary evaporation under reduced pressure, and anhydrous solvents were
obtained commercially and used without further drying.
Bis(1,1-dimethylethyl) [[4-[(2S)-2-fluoro-3-oxo-3-[(4S)-2-oxo-4-phenyl-
3-oxazolidinyl]propyl]phenyl]methyl]phosphonate (8). To a stirred solu-
tion of NaHMDS (8.28 mL, 8.28 mmol) was added dropwise a solution of
bis(1,1-dimethylethyl)
[[4-[3-oxo-3-[(4S)-2-oxo-4-phenyl-3-oxazolidinyl]
propyl]phenyl]methyl]phosphonate (6)[11] (3.77 g, 7.53 mmol) in THF
(40 mL) at 2788C. The solution was stirred at 2788C (0.5 h), N-fluoroben-
zenesulphonimide (7) (2.61 g, 8.28 mmol) in THF (25 mL) was added, and
the mixture was stirred for additional 2 h at 2788C. The mixture was then
warmed to room temperature and stirred overnight. The reaction was
quenched by the addition of ice-cooled saturated aqueous NH4Cl (150 mL),

Synthesis of the First a-Fluoro-Phosphotyrosyl Mimetic
3887
extracted with CH2Cl2, washed with brine, and dried (Na2SO4). Evaporation
provided a residue, which was purified by silica gel flash chromatography
1
to provide 8 (2.85 g, 73% yield). H-NMR (CDCl3) d 7.34–7.20 (m, 9H),
6.04 (ddd, 1H, J ¼ 3.7 Hz and 8.8 Hz and 49.4 Hz), 5.29 (dd, 1H,
J ¼ 4.2 Hz and 9.0 Hz), 4.65 (t, 1H, J ¼ 8.8 Hz), 4.31 (dd, 1H, J ¼ 3.3 Hz
and 8.5 Hz), 3.19 (m, 1H), 3.04 (m, 1H), 2.98 (d, 2H, J ¼ 21.5 Hz), 1.39
(s, 18H); 19F-NMR (CFCl3) 2190.4; FABMS (þVe) m/z 520 [MHþ];
Anal. Calcd for C27H35FNO6P: C, 62.41; H, 6.80; N, 2.70. Found: C, 62.64;
H, 6.87; N, 2.72.
(2S)-2-Fluoro-4-[[bis(1,1-dimethylethoxy)phosphinyl]methyl] benzene-
propanoic acid (5). To a solution of 8 (636 mg, 1.22 mmol) in THF-H2O
(v : v, 3 : 1) (18 mL) was added via syringe a solution of aqueous 30% H2O2
(0.62 mL, 6.1 mmol) at 08C over 2 minutes. This was followed by the addition
of LiOH (102 mg, 1.44 mmol) in H2O (2.5 mL). After stirring at 08C for 1.5 h,
the solution was raised to room temperature and stirring was continued (3 h).
To the mixture was added sodium sulfite (964 mg, 6.1 mmol) in H2O (5 mL)
followed by 2 N HCl (30 mL). Evaporation of solvent in vacuo provided a
residue that was washed using CH2Cl2 to remove Evans auxiliary. The
aqueous layer was then extracted (EtOAc) and the combined organic extracts
were washed with brine, dried (Na2SO4), and taken to dryness to provide 5
1
(440 mg, 96% yield). H-NMR (CDCl3) d 7.20–7.11 (m, 5H), 5.12 (dt, 1H,
J ¼ 5.0, J ¼ 48.6 Hz), 3.30–3.11 (m, 2H), 2.87 (d, 2H, J ¼ 21.5 Hz), 1.30
(s, 18H); 19F-NMR (CFCl3) 2189.5; FABMS (2Ve) m/z 373 [M-H].
[[4-[3-[[1-[[[(1S)-3-amino-1-[[[3-(1-naphthalenyl)propyl]amino]carbo-
nyl]-3-oxopropyl]amino]carbonyl]cyclohexyl]amino]-3-[(2S)-2-fluoro]
oxopropyl]phenyl]methyl] bis(1,1-dimethylethyl) phosphonate (10). To a
solution of 5 (63 mg, 0.169 mmol) and (2S)-2-amino-N1-[3-(1-naphthalenyl)-
propyl]butanediamide (9)[13,15] (65.3 mg, 0.154 mmol) in DMF (4 mL) was
.
added HOAt (0.40 mL, 0.20 mmol) and EDCI HCl (38.4 mg, 0.20 mmol) at
08C. The solution was stirred at 08C (1.5 h) and then at room temperature
(24 h). The crude reaction mixture was evaporated in vacuo, and the residue
was purified by silica gel flash chromatogaphy to provide 10 (103 mg, 86%
yield). 1H-NMR (CDCl3) d 8.02 (d, 1H, J ¼ 8.8 Hz), 7.79 (d, 1H, J ¼ 8.0 Hz),
7.65 (t, 1H, J ¼ 4.8 Hz), 7.53–7.01 (m, 9H), 7.00 (d, 1H, J ¼ 8.0 Hz), 6.59
(d, 1H, J ¼ 5.5 Hz), 5.98 (brs, 1H), 5.02 (ddd, 1H, J ¼ 3.7 Hz and 7.4 Hz and
49.4 Hz), 4.67 (m, 1H), 3.41 (m, 1H), 3.30 (m, 1H), 3.19–2.83 (m, 7H), 2.42
(dd, 1H, J ¼ 5.2 Hz and 15.2 Hz), 2.07–1.47 (m, 10H), 1.38 (s, 18H), 1.29–
1.19 (m, 2H); 19F-NMR (CFCl3) 2188.1; FABMS (þVe) m/z 781 [M þ H].
([[4-[3-[[1-[[[(1S)-3-Amino-1-[[[3-(1-naphthalenyl)propyl]amino]car-
bonyl]-3-oxopropyl]amino]carbonyl]cyclohexyl]amino]-3-[(2S)-2-fluoro]
oxopropyl]phenyl]methyl]phosphonic acid (11). A solution of 11 (103 mg,
0.132 mmol) in a mixture of TFA-TES-H2O (v : v, 3.7 : 0.1 : 0.2) (4 mL) was

3888
Shi et al.
stirred at room temperature (1 h). The solvent was evaporated in vacuo and the
residue was purified by HPLC using a Waters Prep LC4000 system having
photodiode array detection and binary solvent systems as indicated, where
A ¼ 0.1% aqueous TFA and B ¼ 0.1% TFA in acetonitrile. Columns used
were either a Vydac C18 (10 mm) Peptide and Protein column (20 mm
diameter ꢀ 250 mm long with a flow of 10 mL/min for preparative work or
a 4.6 mm diameter ꢀ 250 mm long with a flow of 1.0 mL/min for analytical
work). A linear gradient from 10% B to 70% B over 10 minutes provided
product retention times of 22.5 minutes on the preparative column and 12.7
minutes on the analytical column. Following liophilization, product 11 was
obtained as a white solid (54 mg, 62% yield: 95% purity by HPLC).
1H-NMR (CDCl3) d 8.16 (s, 1H), 8.03 (m, 1H), 7.82 (dd, 1H, J ¼ 2.7 Hz
and 6.6 Hz), 7.68 (t, 1H, J ¼ 4.6 Hz), 7.46–7.40 (m, 2H), 7.35–7.31
(m, 1H), 7.07 (dd, 2H, J ¼ 2.2 Hz and 8.2 Hz), 7.00–6.98 (m, 2H), 6.87
(s, 1H), 5.08 (ddd, 1H, J ¼ 2.9 Hz and 9.8 Hz and 49.4 Hz), 4.34 (m, 1H),
3.96 (t, 1H, J ¼ 6.5 Hz), 3.12–3.08 (m, 3H), 2.98 (t, 2H, J ¼ 7.8 Hz), 2.87
(m, 1H), 2.84 (d, 2H, J ¼ 21.3 Hz), 2.59 (dd, 1H, J ¼ 6.7 Hz, J ¼ 16.0 Hz),
1.95–1.17 (m, 12H); 19F-NMR (CFCl3) 2188.2; FABMS (þVe) m/z 667
.
[M-H]. Anal. Calcd for C41H46N4O10 2.5H2O: C, 57.22; H, 6.59; N, 7.85.
Found: C, 57.01; H, 5.91; N, 7.63.
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Received in the USA June 25, 2004