An efficient and enantioselective synthesis of suitably protected β-[1-(4-malonyl)naphthyl]-L-alanine and β-[1-(4-malonylmethyl) naphthyl]-L-alanine: Novel fluorescent and non-hydrolysable phosphotyrosine mimetics

Article abstract of DOI:10.1002/ejoc.200500835

Molecular dynamics simulations based on the structure of the Grb7 SH2 domain in complex with the ErbB2 phosphorylated peptide pTyr1139 have suggested that β-[1-(4-malonyl)naphthyl]-L-alanine (L-mNal) may be accommodated in the pTyr binding pocket and offer additional beneficial interactions. Therefore, this compound and its analog β-[1-(4-malonylmethyl)naphthyl]-L-alanine (L-mmNal), which are new non-hydrolysable phosphotyrosine mimetics, have been prepared by the catalytic asymmetric hydrogenation of the corresponding prochiral enamides with excellent enantioselectivities. These compounds and their dehydro derivatives show interesting fluorescent properties. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejoc.200500835

FULL PAPER
DOI: 10.1002/ejoc.200500835
An Efficient and Enantioselective Synthesis of Suitably Protected β-[1-(4-
Malonyl)naphthyl]-
L
-alanine and β-[1-(4-Malonylmethyl)naphthyl]- -alanine:
L
Novel Fluorescent and Non-Hydrolysable Phosphotyrosine Mimetics
Huixiong Chen,[a] Jean-Philippe Luzy,[a] Nohad Gresh,[a] and Christiane Garbay*[a]
Keywords: Amino acids / Bioorganic chemistry / Enantioselectivity / Fluorescence
Molecular dynamics simulations based on the structure of the
Grb7 SH2 domain in complex with the ErbB2 phosphorylated
peptide pTyr1139 have suggested that β-[1-(4-malonyl)naph-
non-hydrolysable phosphotyrosine mimetics, have been pre-
pared by the catalytic asymmetric hydrogenation of the cor-
responding prochiral enamides with excellent enantio-
selectivities. These compounds and their dehydro derivatives
show interesting fluorescent properties.
thyl]-L-alanine (L-mNal) may be accommodated in the pTyr
binding pocket and offer additional beneficial interactions.
Therefore, this compound and its analog β-[1-(4-malo- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
nylmethyl)naphthyl]-
L-alanine (
L-mmNal), which are new
Germany, 2006)
13% more volume than the phosphate, although their inter-
action with the SH2 domain looks very similar and both
structures possess similar SH2 domain geometries. This
study has provided an impetus to further investigate the ef-
fect of modifying Pmf by β-[1-(4-malonyl)naphthyl]--ala-
nine (-mNal), in which the phenyl ring is replaced by a
naphthyl structure.
Introduction
Src homology-2 (SH2) domains and phosphotyrosine
binding (PTB) domains are the most prevalent phospho-
tyrosine-binding modules and have been shown to bind to
phosphorylated protein tyrosine kinases or other phosphor-
ylated proteins in response to external stimuli, such as the
binding of growth factors. These modules, which are a
promising therapeutic target, play an important role in sig-
nal transduction and have been the focus of drug discovery
efforts to develop novel inhibitors over recent years.[1]
A major challenge of SH2 domain inhibitors has been
the design of phosphotyrosine (pTyr) bioisosters that mimic
the complex hydrogen-binding network within the highly
positively charged pTyr-binding pocket. One of the ap-
proaches for developing metabolically stable pTyr mimetics
is the modification of the charged nature of a phosphate
group by replacement with a carboxylate, as exemplified by
para-malonylphenylalanine (Pmf), which has been reported
as being approximately equivalent to the phosphonate-
based pTyr mimetics in binding with the growth factor re-
ceptor-bound protein 2 (Grb2) SH2 domain.[2] Although
the structure of malonate as a phosphate bioisoster is chem-
ically distinct, molecular dynamics simulations based on the
NMR solution structure of the SH2 domain of growth fac-
tor receptor-bound protein 7 (Grb7), another adaptor pro-
tein, in a complex with the ErbB2 (epidermal growth factor
receptor family protein-2) phosphorylated peptide
pTyr1139[3] reveals that the malonate group occupies about
Molecular dynamic simulations performed in our labora-
tory indicate that this new pTyr mimetic can dock favorably
in the pTyr pocket of the Grb7 SH2 domain, with the onset
of an additional beneficial cation–π interaction between the
electron-rich naphthyl ring and the electron-deficient guani-
dinium moiety of an Arg residue. This type of interaction
has often been reported in proteins and protein com-
plexes.[4] Moreover, it has been observed in the crystal struc-
ture of Grb2 SH2 complexed with the 2-Abz-EpYINQ-
NH2 ligand, which has an anthranyl group attached to the
N-terminal end and is found stacked over an Arg residue.
Such a stacking interaction could account for the enhance-
ment of affinities of anthranyl-capped phosphopeptides for
different SH2 domains, such as Grb2, T-cell tyrosine kinase
(Lck), phospholipase Cγ (PLC-γ), and the p85 subunit of
phosphatidylinositol-3 (PI-3) kinase (p85).[5] In addition,
some compounds containing a naphthalene nucleus have
been reported to be attractive photoluminescent materials
due to their high efficiency and good thermal stability.[6,7]
The use of an amino acid as a fluorescent chromophore[7–9]
offers at least two advantages: first, peptides containing this
amino acid can be synthesized by solid-phase peptide syn-
thesis (SPPS), and second, since both ends of these peptides
are free, residues may be attached to improve solubility or
lability.[10] Thus, in this paper, we report the synthesis of -
mNal, -mmNal, and their dehydro derivatives, in which
the amino group is protected with widely used protecting
[a] Laboratoire de Pharmacochimie Moléculaire et Cellulaire,
INSERM U648, CNRS FRE 2718, Faculté de Médecine des
Saints-Pères, Université René Descartes,
75270 Paris Cedex 06, France
Fax: +33-1-4286-4082
E-mail: christiane.garbay@univ-paris5.fr
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H. Chen, J.-P. Luzy, N. Gresh, C. Garbay
FULL PAPER
groups such as Fmoc, Cbz, or Boc. These compounds could Towards this end, it was first necessary to prepare the key
be incorporated into peptides and may afford pharmacolog- aldehyde intermediates 6a and 6d, as outlined in Schemes 1
ically interesting alternatives to phosphonate-based pTyr and 2, respectively.
mimetics and also serve as a fluorescent probe for visualiz-
ing and studying biological processes or molecular interac-
tions.
Results and Discussion
Synthesis
The synthesis of unusual α-amino acids is of considerable
interest as they not only serve as building blocks for bioac-
tive peptides or peptidomimetics but also as starting points
for the preparation of drugs and natural products.[11,12] The
recent development in this field is linked to advances in se-
veral synthetic methodologies, including the building-block
approach,[13] and in the discovery of numerous chiral auxil-
iaries or ligands for the asymmetric synthesis. In particular,
asymmetric hydrogenation of the prochiral enamides using
the chiral complex RhI-(S,S)-Me-DuPHOS provides an ef-
ficient and attractive approach for the construction of α-
amino acids with high enantiomeric excesses.[14,15] Recently,
it has been reported that the preparation of 2-naphthylala-
nine from this type of precursors using a rhodium–methyl
BioPhoz-catalyzed asymmetric hydrogenation also shows
exceedingly high enantioselectivities.[16,17] The enhanced re-
activity of the enamide double bond has been attributed to
the ability of this group to chelate to the catalyst metal cen-
ter. This property is believed to be important for achieving
high enantioselectivity in rhodium-catalyzed hydrogena-
tions. Therefore, we have developed a procedure that takes
advantage of this feature to synthesize new -mNal and -
mmNal derivatives for use as phosphotyrosine mimetics.
Scheme 2. i) Di-tert-butyl malonate/TiCl4/pyridine; ii) NBS/diben-
zoyl peroxide; iii) DMSO/NaHCO3.
The synthesis of intermediate 6a starts by the simple
preparation of aldehyde 2 from commercially available 1-
bromo-4-methylnaphthalene. As illustrated in Scheme 1, the
para-methyl group of 1-bromo-4-methylnaphthalene was
brominated with N-bromosuccinimide to provide 1-
bromo-4-(bromomethyl)naphthalene (1), which was then
subjected to a Kornblum reaction.[18] This DMSO-based
oxidation led to 4-bromonaphthaldehyde (2) in excellent
yield. The aldehyde group of 2 was protected by treatment
with ethylene glycol in the presence of a catalytic amount
of p-toluenesulfonic acid (TosOH) to afford the (4-bromo-
naphthyl)dioxolane 3, which was used subsequently in fur-
ther transformation without purification. The palladium-
catalyzed arylation[19] of di-tert-butyl malonate with 3 was
successfully achieved in anhydrous dioxane at 70 °C over-
night, using tBu3P as ligand and tBuOK as base, to give a
malonyl intermediate, which immediately underwent acidic
hydrolysis to afford di-tert-butyl 2-(4-formylnaphthyl)-
malonate (6a). tBuOK was the most effective base for the
arylation as it gave significantly higher yields than reactions
run with K3PO4 or NaH. Use of these latter bases resulted
in very slow conversion or high levels of undesired side
products.
For the preparation of the vinylogue 6d, we synthesized
1-[2Ј,2Ј-bis(tert-butoxycarbonyl)vinyl]-4-methylnaphthalene
(4) from 4-methylnaphthaldehyde by a mild Knoevenagel
condensation,[20] as shown in Scheme 2. Thus, equal molar
equivalents of 4-methylnaphthaldehyde and di-tert-butyl
malonate were condensed in the presence of titanium tetra-
chloride and pyridine at 0 °C, followed by warming the re-
action mixture to room temperature for 3 h, to provide the
desired product 4 in quantitative yield. Then, we again
chose bromination of the para-methyl group of compound
4 followed by a Kornblum reaction to convert the methyl
Scheme 1. i) NBS/dibenzoyl peroxide; ii) DMSO/NaHCO3; iii) eth-
ylene glycol/TosOH; iv) di-tert-butyl malonate/[Pd2(dba)3]/P(tBu)3/
KOtBu; TosOH/THF.
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Novel Fluorescent and Non-Hydrolysable Phosphotyrosine Mimetics
FULL PAPER
Scheme 3. Asymmetric synthesis of N-protected β-[1-(4-malonyl)naphthyl]--alanine and β-[1-(4-malonylmethyl)naphthyl]--alanine and
their dehydroamino acid derivatives: i) 2-(Boc-amino)-2-dimethylphosphonylacetate or 2-(Cbz-amino)-2-dimethylphosphonyl-acetate/
TMG; ii) H2, 10 atm/[Rh(COD)2OTf]/(S,S)Me-DuPHOS; iii) Na2CO3/MeOH; iv) TFA/CH2Cl2; v) a, H2/Pd-C; b, FmocOSu/NaHCO3.
group into the aldehyde function. In this manner, 6d was tuted naphthyl--alanines 9c and 9e in good yield over the
obtained in good yield after purification by column two steps.
chromatography on silica gel.
Next, we performed the synthesis of differently protected
Optical and Fluorescence Spectroscopy
-mNal, -mmNal, and their dehydroamino acids, as illus-
trated in Scheme 3. A Horner–Emmons-type olefination[21]
of the compounds 6a and 6d proceeded smoothly with
methyl 2-(Boc-amino)-2-dimethylphosphonylacetate or
methyl 2-(Cbz-amino)-2-dimethylphosphonylacetate using
tetramethylguanidine (TMG) as base at –78 °C, followed by
allowing the solution to warm to room temperature, to af-
ford the (Z)-enamido esters 7a–b and 7d in good yields.
The configurational assignment of the dehydroamino ac-
ids was based on the NOE difference technique. These de-
rivatives with an (E) configuration have been reported to
display strong NOE crosspeaks between the olefinic CH
and NH protons;[22] in the case of 7a–b and 7d no such
effects were observed.
Asymmetric hydrogenation of 7a–b and 7d using Burk’s
catalytic RhI-(S,S)-Me-DuPHOS system[23] at 10 atm of H2
and 25 °C afforded the fully protected 4-substituted naph-
thyl--alaninate derivatives 8a–b and 8d in excellent yields.
The absolute configurations were assigned as (S) based on
the selectivity of the (S,S)-Me-DuPHOS ligand.[23]
Absorption and fluorescence emission, extinction coeffi-
cients, and fluorescence quantum yields (QY) were mea-
sured for some of the 4-substituted naphthyl--alanines and
their dehydro derivatives (Figure 1, Table 1). The optical
properties of the natural fluorescent amino acids Tyr and
Trp are also included in the table for comparison. As ob-
served in Table 1, the novel 4-substituted naphthyl--ala-
nines and their dehydro compounds have higher maximum
wavelength values of absorption and emission and display
higher quantum yields than Trp or Tyr, especially in the
case of dehydro compounds 7b and 7d, with values ranging
from 0.43 to 0.44 vs. 0.13 and 0.12 for Tyr and Trp, respec-
tively. As demonstrated in Figure 1, the emission spectra
were obtained in ethanol with excitation close to λmax (abs.)
for each compound. As expected, the emission band of 7b
Table 1. Spectral data for the 4-substituted naphthyl--alanines and
their dehydro derivatives.
In order to avoid partial hydrolysis of the di-tert-butyl
malonate, compounds 8a–b and 8d were treated under mild
conditions with Na2CO3 as base at room temperature over-
night to provide the desired acids 9a–b and 9d. Conversion
of 9b to 9B was achieved by TFA-mediated removal of the
di-tert-butyl malonate protection. Finally, Pd-catalyzed hy-
drogenolytic removal of the Cbz group from 9b and the Cbz
and vinyl moieties from 9d, followed by treatment with N-
Fmoc-succinimide in the presence of sodium hydrogencar-
Compd. λmax (abs) [nm][a] λmax (em) [nm][a] ε [cm–1 –1
]
QY[b]
Tyr
Trp
7b
274[24]
278[24]
383
303[24]
352[24]
434
1400[24]
5300[24]
15900
12900
2600
0.13[25]
0.12[25]
0.44
0.43
0.16
7d
408
431
9b
314
344
9B
9e
313
266
346
304
2900
4107
0.17
0.39
[a] Determined in ethanol. [b] Determined by using the compara-
tive method[26] and quinine sulfate in sulfuric acid (0.1 ) as a stan-
bonate in aqueous dioxane, afforded the N-Fmoc-4-substi- dard reference (QYS = 0.577).[27]
Eur. J. Org. Chem. 2006, 2329–2335
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H. Chen, J.-P. Luzy, N. Gresh, C. Garbay
FULL PAPER
Figure 1. Excitation and emission spectra of N-(benzyloxycarbonyl)-β-{1-[4-bis(tert-butoxycarbonyl)methyl]naphthyl}--alanine (9B) and
dehydroamino acids 7b and 7d.
Merk). Spots were visualized under UV light (254 nm). Flash
chromatography was performed with silica gel 60 (0.04–0.063 mm)
purchased from Carlo Erba-SDS. All chemicals were purchased
from Acros or Aldrich and used without further purification.
and 7d is shifted to longer wavelength. The maximum of
emission is at 431–434 nm. These characteristics make these
compounds potential new fluorophores for biological stud-
ies as they allow a good distinction from those of the natu-
ral fluorescent amino acids such as Tyr and Trp.
1-[2Ј,2Ј-Bis(tert-butoxycarbonyl)vinyl]-4-methylnaphthalene (4): Ti-
tanium tetrachloride (0.7 mL, 6.3 mmol) in dry carbon tetrachlo-
ride (1.5 mL) was added dropwise to dry THF (12 mL) at 0 °C to
give a yellow precipitate. 4-Methylnaphthaldehyde (0.51 g, 3 mmol)
and di-tert-butyl malonate (0.65 g, 3 mmol) in dry THF (1.5 mL)
were added slowly, followed by pyridine (3.2 mL, 50 mmol) in dry
THF (1.5 mL). The reaction mixture was stirred at 0 °C for 1 h and
then at room temperature for 3 h. Water (10 mL) and ethyl acetate
(20 mL) were added and stirring was continued until the solid ma-
terial had dissolved. The organic layer was separated and washed
with brine and saturated NaHCO3, dried, and the solvents were
evaporated. The residue was then chromatographed on silica gel
(hexane/EtOAc = 4:1) to provide 1.1 g of the title compound in
Conclusion
We have developed a practical and efficient procedure for
the preparation of optically active and suitably protected -
mNal and -mmNal in high enantiomeric purity from com-
mercially available 1-bromo-4-methylnaphthalene and 4-
methylnaphthaldehyde. These compounds, and their dehy-
dro derivatives, show a promising fluorescence profile. Fur-
ther investigation of the Grb7 SH2 binding affinity of these
compounds as novel non-hydrolysable phosphotyrosine mi-
metics is in progress in our laboratory.
1
100% yield as a white solid. M.p. 124–125 °C. H NMR (CDCl3):
δ = 1.39 (s, 9 H, tBu), 1.58 (s, 9 H, tBu), 2.74 (s, 3 H, CH3), 7.32–
8.08 (m, 6 H, aromatic), 8.29 (s, 1 H, CH=) ppm. 13C NMR
(CDCl3): δ = 20.11, 28.22, 82.41, 125.06, 125.23, 126.33, 126.49,
126.73, 129.87, 131.92, 132.95, 137.22, 139.33, 163.87, 165.99 ppm.
HRMS (ESI): calcd. for C23H28NaO4 391.1885 [M + Na]+; found
391.1870.
Experimental Section
General: 1H and 13C NMR spectra were recorded with a Bruker
WMFT-250 MHz spectrometer. Chemical shifts are expressed in
parts per million (ppm) using TMS as internal standard. Mass
spectra were recorded with a Q-Tof1 spectrometer with Z-spray
source. Elemental analyses (C, H, N), performed at the Service de
Microanalyse, Pierre et Marie Curie Université, Paris, France, were
within 0.4% of the theoretical values. Optical rotations were mea-
sured with a Perkin–Elmer Model 141 polarimeter. Absorption and
emission spectra were measured with a Perkin–Elmer LB 50 Lumi-
nescence Spectrometer. Extinction coefficients and quantum yields
were determined with a Beckman DU640 spectrophotometer.
Melting points were determined with a Kofler apparatus and are
uncorrected. The purity of the compounds and reaction progress
were monitored by TLC on silica gel plates (60F254, 0.2 mm thick,
General Procedure for Bromination: A solution of the 1-substituted
4-methylnaphthalene (5.6 mmol), N-bromosuccinimide (6.1 mmol),
and benzoyl peroxide (0.2 mmol) in dry CCl4 (20 mL) was refluxed
under argon overnight, then cooled to room temperature, filtered,
and the filtrate concentrated to dryness. The residue was purified
by chromatography on silica gel (hexane/EtOAc = 9:1) to afford
the desired compound.
1-Bromo-4-(bromomethyl)naphthalene (1): Orange solid. Yield:
94%. M.p. 102–103 °C. 1H NMR (CDCl3): δ = 4.94 (s, 2 H, CH2),
7.39 (d, J = 8 Hz, 1 H, aromatic), 7.66 (d, J = 8 Hz, 1 H, aromatic),
7.70 (m, 2 H, aromatic), 8.15–8.32 (m, 2 H, aromatic) ppm. The
spectroscopic data were in accordance with the literature.[28]
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Novel Fluorescent and Non-Hydrolysable Phosphotyrosine Mimetics
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1-[2Ј,2Ј-Bis(tert-butoxycarbonyl)vinyl]-4-(bromomethyl)naphthalene
(5): Orange solid. Yield: 95%. M.p. 142–144 °C. 1H NMR (CDCl3):
δ = 1.3 (s, 9 H, tBu), 1.5 (s, 9 H, tBu), 4.98 (s, 2 H, CH2), 7.38–8.22
(m, 6 H, aromatic), 8.23 (s, 1 H, CH=) ppm. 13C NMR (CDCl3): δ
7.64–9.38 (m, 6 H, aromatic), 10.41 (s, 1 H, CHO) ppm. 13C NMR
(CDCl3): δ = 28.31, 57.22, 83.16, 123.77, 125.50, 126.02, 126.44,
128.63, 129.08, 130.11, 131.60, 136.40, 138.21, 167.37, 193.57 ppm.
HRMS (ESI): calcd. for C22H26NaO5 393.1678 [M + Na]+; found
= 28.56, 30.93, 82.45, 123.97, 124.93, 125.63, 126.13, 127.35, 393.1667.
127.65, 129.77, 131.82, 132.85, 132.31, 137.02, 159.87, 165.89 ppm.
General Procedure for Horner–Emmons-Type Olefination: TMG
HRMS (ESI): calcd. for C23H27BrNaO4 469.0990 [M + Na]+;
found 469.0976.
(0.16 mL, 1.3 mmol) was added to a solution of methyl 2-(Boc-
amino)-2-dimethylphosphonylacetate or methyl 2-(Cbz-amino)-2-
dimethylphosphonylacetate (1 mmol) in anhydrous THF (3 mL)
at –78 °C, and the mixture was stirred for 30 min. A solution of
the substituted naphthaldehyde derivative (1 mmol) in THF (1 mL)
was added, and the mixture was stirred at –78 °C for 1 h and at
room temperature for 6 h. The mixture was diluted with ethyl ace-
tate, washed with 10% citric acid and water, dried with Na2SO4,
and concentrated in vacuo. The residue was purified by flash
chromatography on silica gel (hexane/EtOAc = 4:1) to afford the
desired compound.
General Procedure for the Kornblum Reaction: NaHCO3
(10.5 mmol) was added to a stirred solution of the 1-substituted 4-
(bromomethyl)naphthalene (5.27 mmol) in DMSO (15 mL) and the
reaction mixture was stirred at 95 °C for 3 h. Subsequently, the re-
action mixture was cooled to room temperature, diluted with water
(45 mL), and extracted twice with ethyl acetate (50 mL). The or-
ganic layer was dried with Na2SO4 and concentrated in vacuo.
4-Bromonaphthaldehyde (2): Isolated as a white solid after purifica-
tion by flash chromatography on silica gel (hexane/EtOAc = 8:1).
1
Yield: 91.3%. M.p. 120–122 °C. H NMR (CDCl3): δ = 7.68–7.88
Methyl (Z)-2-(tert-Butoxycarbonylamino)-3-[4-bis(tert-butoxycar-
bonyl)methyl]naphthylacrylate (7a): Isolated as a white solidified
foam from 4 and methyl 2-(Boc-amino)-2-dimethylphosphonylacet-
ate. Yield: 90%. Rf = 0.19 (hexane/EtOAc = 4:1). 1H NMR
(CDCl3): δ = 1.45 (s, 27 H, tBu), 3.95 (s, 3 H, CH3), 5.29 (s, 1 H,
CH), 6.14 (s, 1 H, CH=), 7.55–8.05 (m, 7 H, NH, aromatic) ppm.
13C NMR (CDCl3): δ = 28.19, 28.35, 52.20, 57.65, 78.38, 82.81,
122.72, 122.98, 124.48, 124.84, 125.71, 125.87, 126.42, 126.64,
130.89, 132.60, 133.98, 134.20, 154.38, 161.84, 172.09 ppm. HRMS
(ESI): calcd. for C30H39NNaO8 564.2573 [M + Na]+; found
564.2592.
(m, 2 H, aromatic), 7.81 (d, J = 8 Hz, 1 H, aromatic), 7.98 (d, J =
8 Hz, 1 H, aromatic), 8.37 (d, J = 8 Hz, 1 H, aromatic), 10.41 (s, 1
H, CHO) ppm. The spectroscopic data are in accordance with
those in the literature.[29]
4-[2Ј,2Ј-Bis(tert-butoxycarbonyl)vinyl]naphthaldehyde (6d): Isolated
as a white solid after flash chromatography (hexane/EtOAc = 4:1).
Yield: 85%. M.p. 124–125 °C. 1H NMR (CDCl3): δ = 1.31 (s, 9 H,
tBu), 1.58 (s, 9 H, tBu), 7.44–9.3 (m, 6 H, aromatic), 8.22 (s, 1 H,
CH=), 10.44 (s, 1 H, CHO) ppm. 13C NMR (CDCl3): δ = 28.41,
83.36, 122.95, 125.13, 126.12, 127.43, 127.65, 127.89, 129.18,
130.31, 133.60, 135.98, 139.31, 157.87, 164.98, 193.27 ppm. HRMS
(ESI): calcd. for C23H26NaO5 405.1678 [M + Na]+; found 405.1657.
Methyl
(Z)-2-(Benzyloxycarbonylamino)-3-[4-bis(tert-butoxycar-
bonyl)methyl]naphthylacrylate (7b): Isolated as a white solidified
foam from 4 and methyl 2-(Cbz-amino)-2-dimethylphosphonyla-
cetate. Yield: 85%. Rf = 0.2 (hexane/EtOAc = 4:1). 1H NMR
(CDCl3): δ = 1.45 (s, 18 H, tBu), 3.91 (s, 3 H, CH3), 5.03 (s, 2 H,
CH2), 5.28 (s, 1 H, CH), 6.31 (s, 1 H, CH=), 7.28–8.02 (m, 12 H,
NH, aromatic) ppm. 13C NMR (CDCl3): δ = 28.30, 51.21, 57.52,
65.98, 82.82, 122.70, 122.94, 124.41, 124.82, 125.67, 125.78, 126.40,
126.62, 127.41, 127.87, 129.45, 130.86, 132.57, 133.95, 134.30,
141.42, 154.58, 161.74, 172.01 ppm. HRMS (ESI): calcd. for
C33H37KNO8 614.2156 [M + K]+; found 614.2159.
(4-Bromonaphthyl)dioxolane 3: p-Toluenesulfonic acid (4 mg,
0.02 mmol) and ethylene glycol (0.36 g, 5.8 mmol) were added to a
stirred solution of 2 (0.47 g, 2 mmol) in dry toluene (6 mL) under
argon and the reaction mixture was refluxed in a Dean–Stark appa-
ratus for 16 h. The reaction mixture was cooled to room tempera-
ture and extracted with saturated NaHCO3 (3 mL) and then brine
(3 mL). The organic layer was dried with Na2SO4 and concentrated
in vacuo to give 3 (0.59 g) in 100% yield as a viscous, oil which
was used without further purification. Rf = 0.3 (hexane/EtOAc =
1
8:1). H NMR (CDCl3): δ = 4.20 (s, 4 H, CH2-CH2), 6.48 (s, 1 H,
CH), 7.29–8.35 (m, 6 H, aromatic) ppm. 13C NMR (CDCl3): δ =
65.75, 102.12, 124.30, 124.86, 127.32, 127.52, 128.2, 129.64, 132.48,
132.60, 133.72 ppm. HRMS (ESI): calcd. for C13H11BrNaO2
300.9840 [M + Na]+; found 300.9840.
Methyl (Z)-2-(Benzyloxycarbonylamino)-3-{4-[2Ј,2Ј-bis(tert-butoxy-
carbonyl)vinyl]}naphthylacrylate (7d): Isolated as a white solidified
foam from 10 and methyl 2-(Cbz-amino)-2-dimethylphosphonyla-
cetate. Yield: 81%. Rf = 0.24 (hexane/EtOAc = 4:1). 1H NMR
(CDCl3): δ = 1.34 (s, 9 H, tBu), 1.58 (s, 9 H, tBu), 3.92 (s, 3 H,
CH3), 4.99 (s, 2 H, CH2), 5.28 (s, 1 H, CH), 6.38 (s, 1 H, CH=),
7.21–8.07 (m, 12 H, NH, aromatic), 8.25 (s, 1 H, CH=) ppm. 13C
NMR (CDCl3): δ = 28.31, 52.42, 66.06, 82.68, 122.74, 124.41,
125.98, 126.44, 126.60, 127.21, 127.67, 129.25, 129.96, 131.81,
134.95, 141.32, 152.48, 155.78, 161.70, 172.05 ppm. HRMS (ESI):
calcd. for C34H37NNaO8 610.2417 [M + Na]+; found 610.2408.
Di-tert-butyl 2-(4-Formylnaphthyl)malonate (6a): KOtBu (255 mg,
2.1 mmol), [Pd2(dba)3] (22.6 mg, 0.024 mmol), and P(tBu)3
(15.3 mg, 0.076 mmol) were added to a solution of di-tert-butyl ma-
lonate (590 mg, 2 mmol) and the (4-bromonaphthyl)dioxolane 3
(449 mg, 2.1 mmol) in dioxane (6 mL) and the heterogeneous reac-
tion mixture was stirred at 70 °C overnight. The mixture was fil-
tered through a plug of Celite and concentrated in vacuo to
furnish the corresponding {4-[2Ј,2Ј-bis(tert-butoxycarbonyl)methyl]-
naphthyl}dioxolane, which was used without further purification.
p-Toluenesulfonic acid (12 mg, 0.06 mmol) was added to a solution
of the above product in THF (11 mL) and water (1.2 mL) under
argon. The reaction mixture was stirred at 36 °C for 12 h, cooled
to room temperature, diluted with water (20 mL), and extracted
twice with ethyl acetate (30 mL). The organic layer was dried with
Na2SO4 and concentrated in vacuo. The residue was then chro-
matographed on silica gel to provide 0.75 g of the title compound
General Procedure for Asymmetric Hydrogenation: A reaction vessel
for a Parr hydrogenation apparatus was charged with the substi-
tuted naphthylacrylate derivative (1 mmol) and bis(1,5-cyclooc-
tadiene)rhodium trifluoromethanesulfonate (8.5 mg). The vessel
was evacuated and filled with argon three times before degassed
methanol (20–25 mL) and a solution of (S,S)-Me-DuPHOS (1 mg)
in degassed methanol were added. The vessel was connected to the
Parr apparatus and shaken under hydrogen (10 atm) for 1 d. The
reaction mixture was concentrated in vacuo and the residue puri-
fied by flash chromatography on silica gel (hexane/EtOAc = 3:1)
to provide the desired compound.
1
in 75% yield as a viscous oil. Rf = 0.38 (hexane/EtOAc = 5:1). H
NMR (CDCl3): δ = 4.20 (s, 4 H, CH2-CH2), 5.33 (s, 1 H, CH),
Eur. J. Org. Chem. 2006, 2329–2335
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2333

H. Chen, J.-P. Luzy, N. Gresh, C. Garbay
FULL PAPER
Methyl N-(tert-Butoxycarbonyl)-β-{1-[4-bis(tert-butoxycarbonyl)-
1
M.p. 93–94 °C. [α]2D0 = –10.1 (c = 1, CHCl3). H NMR (CDCl3): δ
methyl]naphthyl}-
foam (94%). Rf = 0.19 (hexane/EtOAc = 4:1). H NMR (CDCl3):
δ = 1.45 (s, 27 H, tBu), 3.51–3.62 (m, 2 H, CH2β), 3.63 (s, 3 H,
L
-alaninate (8a): Isolated as a white solidified
= 1.34 (s, 9 H, tBu), 1.60 (s, 9 H, tBu), 3.47–3.79 (m, 2 H, CH2β),
4.79–4.82 (m, 1 H, CHα), 5.09 (s, 2 H, CH2), 5.27 (d, J = 8 Hz, 1
H, NH), 7.27–8.06 (m, 11 H, aromatic), 8.24 (s, 1 H, CH) ppm.
1
CH3), 4.60–4.80 (m, 1 H, CHα), 5.05 (d, J = 8 Hz, 1 H, NH), 5.28 13C NMR (CDCl3): δ = 28.40, 35.28, 56.92, 66.12, 82.81, 125.06,
(s, 1 H, CH), 7.29–8.17 (m, 6 H, aromatic) ppm. 13C NMR 125.25, 125.43, 126.33, 126.46, 126.71, 127.22, 127.84, 129.13,
(CDCl3): δ = 28.19, 28.30, 35.12, 52.40, 55.71, 57.64, 78.28, 82.83, 129.88, 131.82, 132.93, 137.22, 139.68, 141.42, 155.98, 156.31,
120.97, 124.38, 125.54, 130.29, 132.62, 133.52, 156.28, 168.54,
172.19 ppm. HRMS (ESI): calcd. for C30H41NaNO8 566.2730 [M
+ Na]+; found 566.2692.
165.89, 176.14 ppm. HRMS (ESI): calcd. for C33H37NNaO8
598.2417 [M + Na]+; found 598.2321.
N-(Benzyloxycarbonyl)-β-[1-(4-malonyl)naphthyl]-L-alanine (9B):
Methyl
methyl]naphthyl}-
N-(Benzyloxycarbonyl)-β-{1-[4-bis(tert-butoxycarbonyl)-
-alaninate (8b): Isolated as a white solidified
Compound 9b (56.3 mg, 0.1 mmol) was dissolved in dichlorometh-
ane (1 mL), TFA (1 mL) was added at 0 °C, and the mixture stirred
at the same temperature for 30 min and then at room temperature
for 2 h. After solvent removal, the residue was precipitated by ad-
dition of diethyl ether to give 42.9 mg of the title compound in
95% yield as a white solid. M.p. 97–99 °C. [α]2D0 = –10.8 (c = 1,
L
1
foam (93%). Rf = 0.2 (hexane/EtOAc = 4:1). H NMR (CDCl3): δ
= 1.49 (s, 9 H, tBu), 1.59 (s, 9 H, tBu), 3.40–3.70 (m, 4 H, CH3,
CH2β), 4.70–4.82 (m, 1 H, CHα), 5.11 (s, 2 H, CH2), 5.28 (s, 1 H,
CH), 5.33 (d, J = 8 Hz, 1 H, NH), 7.29–8.13 (m, 11 H, aromatic)
ppm. 13C NMR (CDCl3): δ = 28.35, 35.12, 51.24, 56.85, 57.54,
65.94, 82.87, 120.63, 124.19, 125.51, 127.28, 127.89, 129.17, 130.28,
132.56, 133.48, 141.50, 156.27, 168.84, 172.16 ppm. HRMS (ESI):
calcd. for C33H39NaNO8 600.2573 [M + Na]+; found 600.2491.
1
CHCl3). H NMR (CDCl3): δ = 3.37–3.79 (m, 2 H, CH2β), 4.70–
4.90 (m, 1 H, CHα), 5.10 (s, 2 H, CH2), 5.28 (s, 1 H, CH), 5.30 (d,
J = 8 Hz, 1 H, NH), 7.29–8.15 (m, 11 H, aromatic) ppm. 13C NMR
(CDCl3): δ = 35.16, 56.95, 61.12, 65.96, 120.51, 124.18, 125.49,
127.35, 127.89, 129.12, 130.27, 132.53, 133.45, 141.50, 156.31,
171.34, 176.32 ppm. HRMS (ESI): calcd. for C24H21NNaO8
474.1165 [M + Na]+; found 474.1278.
Methyl N-(Benzyloxycarbonyl)-β-(1-{4-[2Ј,2Ј-bis(tert-butoxycarb-
onyl)]vinyl}naphthyl)-L-alaninate (8d): Isolated as a white solidified
1
foam (90%). Rf = 0.21 (hexane/EtOAc = 4:1). H NMR (CDCl3):
δ = 1.34 (s, 9 H, tBu), 1.59 (s, 9 H, tBu), 3.52–3.62 (m, 2 H, CH2β),
3.62 (s, 3 H, CH3), 4.79–4.82 (m, 1 H, CHα), 5.11 (s, 2 H, CH2),
5.30 (d, J = 8 Hz, 1 H, NH), 7.17–8.14 (m, 11 H, aromatic), 8.25
(s, 1 H, CH=) ppm. 13C NMR (CDCl3): δ = 28.36, 35.38, 52.49,
55.32, 66.08, 82.71, 125.01, 125.14, 125.33, 126.13, 126.26, 126.41,
127.20, 127.74, 129.03, 129.98, 131.86, 132.97, 137.12, 139.68,
141.40, 155.78, 156.61, 166.82, 177.34 ppm. HRMS (ESI): calcd.
for C34H39NaNO8 612.2573 [M + Na]+, found 612.2496.
General Procedure for Hydrogenation and Fmoc Protection: A solu-
tion of the N-(benzyloxycarbonyl)-4-substituted naphthylalanine
(1 mmol) in methanol (10 mL) was hydrogenated in the presence of
10% Pd black (10%) under 1 atm of H2 at room temperature for
4 h. The catalyst was removed by filtration and the combined or-
ganic layers were concentrated to give a white powder sufficiently
pure for further use. A mixture of the above product, Fmoc-OSu
(1.02 mmol), and NaHCO3 (3 mmol) in dioxane/water (1:1; 16 mL)
was stirred at room temperature overnight, then cooled, acidified
with 1  HCl, and extracted twice with ethyl acetate (2×20 mL).
The combined extracts were washed with brine, dried with Na2SO4,
concentrated, and purified by silica gel chromatography (CH2Cl2/
MeOH = 10:1) to provide the desired compound.
General Procedure for Saponification: A solution of the 4-substi-
tuted naphthyl--alaninate (1 mmol) in methanol (64 mL) at 0 °C
was treated with a 1  Na2CO3 aqueous solution (16 mL). The re-
action was complete after 16 h at room temperature (TLC monitor-
ing) and the reaction mixture was neutralized with 1  HCl. The
mixture obtained after solvent removal was extracted with dichlo-
romethane. The organic layer was dried with Na2SO4 and concen-
trated in vacuo and the residue purified by flash chromatography
on silica gel (CH2Cl2/MeOH = 9:1) to give the desired compound.
N-Fmoc-β-{1-[4-bis(tert-butoxycarbonyl)methyl]naphthyl}-
L-alanine
(9c): Isolated as a white solid (92%). M.p. 125–128 °C. [α]2D0
=
–15.2 (c = 1, CHCl3). 1H NMR (CDCl3): δ = 1.49 (s, 18 H, 2×tBu),
3.51–3.76 (m, 2 H, CH2β), 4.21–4.40 (m, 3 H, CH2-CH), 4.80–4.83
(m, 1 H, CHα), 5.27 (s, 1 H, CH), 5.39 (d, J = 8 Hz, 1 H, NH),
7.31–8.19 (s, 14 H, aromatic) ppm. 13C NMR (CDCl3): δ = 28.30,
35.08, 47.10, 56.82, 57.56, 67.48, 82.87, 120.31, 124.12, 125.58,
126.65, 127.49, 128.07, 128.70, 130.23, 132.56, 133.44, 141.65,
144.21, 156.41, 168.26, 176.16 ppm. HRMS (ESI): calcd. for
C39H41NNaO8 674.2730 [M + Na]+; found 674.2836.
N-(tert-Butoxycarbonyl)-β-{1-[4-bis(tert-butoxycarbonyl)methyl]-
naphthyl}-L-alanine (9a): Isolated as a white solid (87.8%). M.p.
90–92 °C. [α]2D0 = –8.5 (c = 1, CHCl3). 1H NMR (CDCl3): δ = 1.50
(s, 27 H, tBu), 3.30–3.90 (m, 2 H, CH2β), 4.67–4.75 (m, 1 H, CHα),
5.03 (d, J = 8 Hz, 1 H, NH), 5.27 (s, 1 H, CH), 7.37–8.32 (m, 6 H,
aromatic) ppm. 13C NMR (CDCl3): δ = 28.21, 28.32, 35.16, 56.95,
57.62, 78.24, 82.85, 120.77, 124.34, 125.52, 130.27, 132.58, 133.42,
156. 23, 168. 34, 176.16 ppm. HRMS (ESI): calcd. for
C29H39NNaO8 552.2573 [M + Na]+; found 552.2489.
N-Fmoc-β-(1-{4-[2Ј,2Ј-bis(tert-butoxycarbonyl)]ethyl}naphthyl)-L-
alanine (9e): Isolated as a white solid (90%). M.p. 126–128 °C.
[α]2D0 = –11.3 (c = 1, CHCl3). 1H NMR (CDCl3): δ = 1.42 (s, 18 H,
2×tBu), 3.30–3.39 [m, 5 H, CH2β, CH2, CH(CO2tBu)2], 4.10–4.50
(m, 3 H, CH2-CH), 4.70–4.80 (m, 1 H, CHα), 5.30 (d, J = 8 Hz, 1
H, NH), 7.34–8.24 (m, 14 H, aromatic) ppm. 13C NMR (CDCl3):
δ = 28.42, 31.10, 35.05, 47.08, 53.25, 56.80, 67.48, 82.85, 120.51,
124.22, 125.68, 126.63, 127.59, 128.17, 128.75, 132.68, 133.55,
141.68, 144.31, 156.45, 166.64, 176.05 ppm. HRMS (ESI): calcd.
for C40H43NNaO8 688.2886 [M + Na]+; found 688.2929.
N-(Benzyloxycarbonyl)-β-{1-[4-bis(tert-butoxycarbonyl)methyl]-
naphthyl}-L-alanine (9b): Isolated as a white solid (85%). M.p. 94–
96 °C. [α]2D0 = –10.5 (c = 1, CHCl3). H NMR (CDCl3): δ = 1.50
(s, 18 H, tBu), 3.37–3.78 (m, 2 H, CH2β), 4.70–4.90 (m, 1 H, CHα),
5.10 (s, 2 H, CH2), 5.26 (s, 1 H, CH), 5.30 (d, J = 8 Hz, 1 H, NH),
7.29–8.15 (m, 11 H, aromatic) ppm. 13C NMR (CDCl3): δ = 28.32,
35.18, 56.85, 57.58, 65.98, 82.83, 120.57, 124.14, 125.56, 127.32,
127.87, 129.14, 130.25, 132.59, 133.46, 141.52, 156.34, 168.54,
176.36 ppm. HRMS (ESI): calcd. for C32H37NaNO8 586.2417 [M
+ Na]+; found 586.2325.
1
Acknowledgments
N-(Benzyloxycarbonyl)-β-(1-{4-[2Ј,2Ј-bis(tert-butoxycarbonyl)- We thank the Ligue Nationale contre le Cancer (Comité de Paris)
vinyl]}naphthyl)-
L
-alanine (9d): Isolated as a white solid (90 %).
for financial support.
2334
www.eurjoc.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 2329–2335

Novel Fluorescent and Non-Hydrolysable Phosphotyrosine Mimetics
FULL PAPER
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Received: October 24, 2005
Published Online: March 16, 2006
Eur. J. Org. Chem. 2006, 2329–2335
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2335