Synthesis of α,α-disubstituted 4-phosphonophenylalanine analogues as conformationally-constrained phosphotyrosyl mimetics

Article abstract of DOI:10.1016/j.tet.2004.02.005

Syntheses of N-Boc (S)-4-(diethylphosphono)-(α-methyl)phenylalanine [Boc-(α-Me)Phe(4-PO₃Et₂)-OH] (9) and N-Boc (S)-2-amino-6-(diethylphosphono)tetralin-2-carboxylic acid [Boc-Atc(6-PO ₃Et₂)-OH] (18) are reported

Full text of DOI:10.1016/j.tet.2004.02.005

Tetrahedron 60 (2004) 2971–2977
Synthesis of a,a-disubstituted 4-phosphonophenylalanine
analogues as conformationally-constrained
phosphotyrosyl mimeticsq
Shinya Oishi,a Sang-Uk Kang,a Hongpeng Liu,b Manchao Zhang,b Dajun Yang,b
Jeffrey R. Deschampsc and Terrence R. Burke, Jr.a
,
*
aLaboratory of Medicinal Chemistry, Center for Cancer Research, National Cancer Institute, National Institutes of Health,
NCI-Frederick, PO Box B, Bldg. 376 Boyles St., Frederick, MD 21702-1201, USA
bDepartment of Hematology/Oncology, University of Michigan Medical School, Ann Arbor, MI 48109, USA
cLaboratory for the Structure of Matter, Naval Research Laboratory, Washington, DC 20375, USA
Received 1 December 2003; revised 4 February 2004; accepted 4 February 2004
Abstract—Syntheses of N-Boc (S)-4-(diethylphosphono)-(a-methyl)phenylalanine [Boc-(a-Me)Phe(4-PO3Et2)-OH] (9) and N-Boc (S)-2-
amino-6-(diethylphosphono)tetralin-2-carboxylic acid [Boc-Atc(6-PO3Et2)-OH] (18) are reported as conformationally-constrained
phosphotyrosyl mimetics suitably protected for peptide synthesis. Both syntheses proceeded through chiral arylhalides that are converted
to arylphosphonates by palladium-catalyzed cross coupling with diethylphosphite. These amino acid analogues may be useful in the study of
cellular signal transduction processes.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
have been developed for this purpose. In the case of tyrosine
(Tyr, 1a), analogues have been reported that limit rotational
freedom either through the addition of substituents at the a-
or b-positions or through side chain inclusion in an
appended ring structure (Fig. 1).7 One example is
a-methyl-Tyr (2a), which is a member of the broader
class of a-methyl-containing amino acids known to promote
turn geometries.8 Another example is 2-amino-6-hydroxy-
tetralin-2-carboxylic acid (3a), which can induce turn
conformations similar to 2a as well as severely restrict x1
and x2 angles.9,10
The biological dependence of peptides on tertiary structure
has made restriction of conformational flexibility an
important component of peptide mimetic design.1–6
variety of non-proteinogenic constrained a-amino acids
A
The biological activities of proteins are also highly
influenced by post-translational modifications. This is
exemplified by the conversion of Tyr residues to phospho-
tyrosyl residues (pTyr, 1b) via protein-tyrosine kinases
(PTKs). In aberrant cellular signal transduction this process
can be critical to several diseases, including certain
cancers.11,12 Derivatives of pTyr such as a-methyl-pTyr
(2b) that include elements of conformational constraint can
be useful in the design of pTyr-dependent signaling
antagonists.13,14 This type of analogue is of limited use in
cellular systems where the phosphoryl ester bond is labile to
protein-tyrosine phosphatases (PTPs). Accordingly, the
development of PTP-stable phosphonate-based congeners
has been undertaken, as exemplified by 1c15,16 and (a-
methyl)-p-phosphonophenylalanine ((a-methyl)-Ppp, 2c).17
These compounds can retain much of the biological potency
of the parent phosphate-containing analogues.17,18 Although
Figure 1. Structures of pTyr and pTyr mimetics.
q Supplementary data associated with this article can be found in the online
version, at doi: 10.1016/j.tet.2004.02.005
Keywords: Enantioselective; Phosphotyrosyl mimetic; Conformational
constraint.
*
Corresponding author. Tel.: þ1-301-846-5906; fax: þ1-301-846-6033;
e-mail address: tburke@helix.nih.gov
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.02.005

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Scheme 1. (i) 4-Iodobenzyl bromide, KHMDS (86% yield); (ii) (EtO)2PHO, Et3N, Pd(PPh3)4 (74% yield); (iii) (a) H2, Pd·C, (b) Boc2O, Et3N (61% yield).
phosphonate-containing x1-constrained pTyr mimetics such
as 419 and 520 have been disclosed, to date the x1, x2-
restricted pTyr mimetic 3c has yet to be reported, in spite of
its potential usefulness. Work was therefore undertaken to
prepare 3c in its enantio-pure form, suitably protected for
incorporation into peptides using standard methodologies.
Efforts were also devoted to develop a new enantioselective
synthesis of orthogonally-protected 2c.
synthesis of racemic 2-amino-6-bromo-tetralin-2-carb-
oxylic acid methyl ester (12), which was obtained in classic
fashion23,24 from commercially available 6-bromo-2-tetra-
lone 10 through the intermediacy of spirohydantoin 11
(Scheme 2). Resolution of (^)-12 as the (L)-(þ)-mandelic
acid salt according to literature procedures23 provided the
ammonium salt 13 bearing the L-configuration as deter-
mined by single crystal X-ray crystallography. The optical
purity of 13 was verified by HPLC analysis of 14 using a
chiral stationary phase (ee .98%). Amino ester 13 was
converted in two steps to the N-Boc amino acid 15 (77%
yield), which represents a versatile intermediate for the
preparation of a variety of 6-substituted analogues using
cross-coupling chemistries. Transient protection of 15 as its
benzyl ester (16) allowed Pd(PPh3)4-mediated introduction
of the 6-(EtO)2PO-group, which provided the conformation-
ally-constrained pTyr mimetic 18 following hydrogenolytic
de-esterification.
1.1. Synthesis of N-Boc (S)-4-(diethylphosphono)-
(a-methyl)phenylalanine
The synthesis of (a-methyl)-Ppp (2c) in racemic form as the
diethyl phosphonate ester bearing N-Fmoc protection has
been achieved previously17 via a Schiff base approach.19 In
the current work, enantioselective synthesis of the (S)-N-
Boc variant of this compound (N-Boc (a-methyl)-
Ppp(OEt)2, 9) was accomplished using the 3-methyl-
substituted Williams oxazinone 621 in a protocol similar to
that used to prepare non-phosphorus-containing (a-methyl)-
pTyr mimetics (Scheme 1).14 Reaction of 6 with 4-iodo-
benzyl bromide in the presence of KHMDS afforded the
fully-protected (a-methyl)-(4-iodo)phenylalanine (7),22
which represents a potential common intermediate for
the enantioselective synthesis of a variety of 4-substituted
phenylalanines. While attempted Pd(PPh3)4-mediated
replacement of iodine using (ButO)2P(O)H failed, product
8 could be obtained in good yield using the sterically less
demanding (EtO)2P(O)H. Hydrogenolytic deprotection and
reaction with Boc anhydride provided the desired target
compound 9 in 39% overall yield.
1.3. Incorporation of pTyr mimetics 9 and 18 in Grb2
SH2 domain-directed peptides
In order to demonstrate the suitability of conformationally-
constrained pTyr mimetics 9 and 18 for peptide synthesis,
Grb2 SH2 domain-directed tripeptides 24 and 25 were
prepared, respectively (Scheme 3). This platform has been
used extensively to investigate a variety of pTyr mimetics,
including the x1-constrained analogue 5.20 Coupling of the
a,a-disubstituted residues with the sterically-crowded
amino group of dipeptide 1925 was achieved using
tetramethylfluoroformamidinium hexafluorophosphate
(TFFH).26 Final products 24 and 25 were obtained as their
ammonium salts following deprotection using trimethylsilyl
iodide (TMSI) and TFA.
1.2. Synthesis of N-Boc (S)-2-amino-6-(diethylphos-
phono)tetralin-2-carboxylic acid
The route to cyclic a,a-substituted analogue 18 involved the
Although the primary purpose in preparing peptides 24 and
Scheme 2. (i) KCN, (NH4)2CO3 (81% yield); (ii) (a) Ba(OH)2, (b) SOCl2, MeOH (54% yield); (iii) L-(þ)-mandelic acid (25% yield); (iv) Boc2O, Et3N (79%
yield); (v) LiOH (98% yield); (vi) BnBr, Pri2EtN (97% yield); (vii) (EtO)2PHO, Et3N, Pd(PPh3)4 (93% yield); (iii) (a) H2, Pd·C (99% yield).

S. Oishi et al. / Tetrahedron 60 (2004) 2971–2977
2973
Scheme 3. (i) 9 or 18, TFFH, Pri2EtN; (ii) (a) TFA, anisole, (b) ButO2CCOCl, Pr2i EtN; (iii) (a) TMSI, (b) TFA–H2O (95:5).
25 was to verify the suitability of amino acid analogues 9
and 18 for peptide synthesis, once in hand, it was also of
interest to determine the Grb2 SH2 domain-binding potency
of these peptides. In an ELISA-based extracellular binding
assay, the unconstrained N a-oxalyl Pmp-containing variant
of 24 and 25 had previously been shown to exhibit low
nanomolar Grb2 SH2 domain-binding potency.25 Therefore,
it was surprising that in a similar ELISA-based Grb2 SH2
domain binding assay,27 peptides 24 and 25 displayed poor
affinity (IC50 .10 mM). This was reminiscent of a report
that conformational constraint of the pTyr-mimicking
residue is deleterious to SH2 domain-binding potency.20
However, it was in marked contrast to the findings of a
recent study employing a cyclopropane-based pTyr mimetic
that was equipotent to the unconstrained parent.28
trometer and are reported in ppm relative to TMS and
referenced to the solvent in which they were run. Fast atom
bombardment mass spectra (FABMS) were acquired with a
VG analytical 7070E mass spectrometer under the control of
a VG 2035 data system. HPLC separations were conducted
using a Cosmosil 5C18-ARII (20£250 mm) with a solvent
system of 0.1% aqueous NH3 (v/v, solvent A)/0.1% NH3
in MeCN (v/v, solvent B) or a CHIRALCEL OD
(10£250 mm) using hexanes (solvent C) and i-PrOH
(solvent D).
3.1.1. (3S,5S,6R)-4-(Benzyloxycarbonyl)-5,6-diphenyl-3-
(4-iodo)benzyl-3-methyl-2,3,5,6-tetrahydro-4H-1,4-oxa-
zin-2-one (7). To a stirred solution of 621 (2.00 g,
4.98 mmol) in dry THF (40 mL) was added a solution of
KHMDS in toluene (0.5 M, 12.0 mL, 6.0 mmol) at 278 8C
under argon. After 5 min, a solution of 4-iodobenzyl
bromide (1.84 g, 6.22 mmol) was added dropwise at
278 8C, and stirring was continued for 30 min, followed
by quenching with a saturated NH4Cl solution. The mixture
was extracted with EtOAc, and the extract was washed with
water and dried over MgSO4. Concentration under reduced
pressure followed by flash chromatography over silica gel
with n-hexanes–EtOAc (20:1) provided 7 as colorless
crystals (2.67 g, 86% yield): mp 98–100 8C; [a]2D1 þ156.0
(c 0.51, CHCl3); 1H NMR (400 MHz, CDCl3) d 2.01 (s, 3H),
3.08 (d, J¼13.2 Hz, 1H), 3.88 (m, 1H), 4.22 (d, J¼13.4 Hz,
1H), 5.01 (m, 1H), 5.10 (d, J¼12.2 Hz, 1H), 5.23 (d, J¼
12.2 Hz, 1H), 6.60–7.63 (m, 19H). 13C NMR (400 MHz,
CDCl3) d 25.3, 43.8, 59.9, 66.3, 67.6, 78.8, 93.1, 126.2,
128.1, 128.2, 128.6, 128.9, 132.0, 134.3, 135.6, 136.0,
136.3, 137.9, 153.5, 172.8. Anal. calcd for C32H28INO4: C,
62.24; H, 4.57; N, 2.27. Found: C, 62.30; H, 4.63; N, 2.26.
FABMS m/z 618 (MHþ).
2. Conclusions
Reported herein are the syntheses of two conformationally-
constrained pTyr mimetics in protected forms suitable for
incorporation into peptides using standard methodologies.
Chiral arylhalide intermediates in both approaches represent
potential starting points for the cross-coupling synthesis of
additional constrained phenylalanyl analogues.
3. Experimental
3.1. General synthetic
Reactions were carried out under argon in oven-dried
glassware using standard gas-tight syringes, cannulas and
septa. Anhydrous solvents were purchased from Aldrich
Chemical Corporation and used without further drying.
Melting points were measured using a MEL-TEMP II
apparatus and are uncorrected. Elemental analyses were
3.1.2. (3S,5S,6R)-4-(Benzyloxycarbonyl)-5,6-diphenyl-3-
(4-diethylphosphono)benzyl-3-methyl-2,3,5,6-tetrahy-
dro-4H-1,4-oxazin-2-one (8). A mixture of 7 (2.53 g,
4.09 mmol), diethyl phosphite (0.580 mL, 4.50 mmol),
1
obtained from Atlantic Microlab, Inc., Norcross, GA. H
NMR data were recorded on a Varian 400 MHz spec-

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S. Oishi et al. / Tetrahedron 60 (2004) 2971–2977
Et3N (0.627 mL, 4.50 mmol) and Pd(PPh3)4 (236 mg,
0.204 mmol) in dry toluene (5 mL) was stirred at reflux
for 6 h at 90 8C under argon. The whole was extracted with
EtOAc, and the extract was washed with H2O and brine, and
dried over MgSO4. Concentration under reduced pressure
followed by flash chromatography over silica gel with
n-hexanes–EtOAc (1:1) provided 8 as a colorless oil
(1.90 g, 74% yield): [a]2D2 þ189.9 (c 0.28, CHCl3); 1H
NMR (400 MHz, CDCl3) d 1.16 (t, J¼7.0 Hz, 3H), 1.27 (t,
J¼7.0 Hz, 3H), 1.57 (s, 9H), 2.02 (s, 3H), 3.17 (d, J¼
13.4 Hz, 1H), 3.80 (m, 1H), 3.83–4.16 (m, 4H), 4.37 (d,
J¼13.4 Hz, 1H), 5.02 (m, 1H), 5.14 (d, J¼12.3 Hz, 1H),
5.24 (d, J¼12.1 Hz, 1H), 6.64 (d, J¼7.2 Hz, 2H), 6.86 (d,
J¼6.8 Hz, 2H), 6.96–7.56 (m, 13H), 7.72 (m, 2H). 13C
NMR (400 MHz, CDCl3) d 16.2, 16.3, 5.4, 44.2, 59.6, 62.1,
62.2, 66.4, 67.7, 78.7, 125.8, 128.0, 128.1, 128.2, 128.4,
128.6, 128.8, 130.2, 132.2, 134.2, 135.4, 135.9, 141.3,
153.5, 172.6. FABMS m/z 628 (MHþ). Anal. calcd for
C36H38NO7P: C, 68.89; H, 6.10; N, 2.23. Found: C, 68.49;
H, 6.24; N, 2.41.
naphthalenecarboxylate (12). A suspension of 11
(21.5 g, 72.9 mmol) and Ba(OH)2 in H2O (750 mL) was
stirred at reflux for 36 h. The mixture was acidified with 6 N
H2SO4, and filtered and the filter pad was washed with
MeOH repeatedly. The combined filtrate was concentrated
under reduced pressure to yield a suspension, which was
adjusted to pH 6.0 with NH4OH and the resulting solid
was collected by filtration to provide the crude amino acid
(18.7 g, 95%). A mixture of amino acid (17.7 g) and SOCl2
(14.3 mL, 197 mmol) in MeOH (350 mL) was stirred at
reflux for 3 h. After filtration, the filtrate was concentrated
under reduced pressure to give the methyl ester as an HCl
salt. This was neutralized with excess NaHCO3 in toluene–
H2O (5:9, 840 mL) and the organic phase was separated and
dried over Na2SO4. Concentration under reduced pressure
followed by flash chromatography over silica gel with
n-hexanes–EtOAc (1:1) gave 12 as a pale yellow oil
(10.7 g, 57% yield): 1H NMR (400 MHz, CDCl3) d 1.62 (s,
2H), 1.87 (m, 1H), 2.12 (ddd, J¼13.4, 9.6, 6.1 Hz, 1H), 2.68
(d, J¼16.5 Hz, 1H), 2.78 (dt, J¼17.2, 5.5 Hz, 1H), 2.98
(m, 1H), 3.21 (d, J¼16.4 Hz, 1H), 3.74 (s, 3H), 6.94 (d,
J¼8.0 Hz, 1H), 7.20–7.28 (m, 2H). 13C NMR (400 MHz,
CDCl3) d 25.3, 31.6, 38.8, 52.4, 56.2, 119.6, 129.0, 130.9,
131.4, 132.7, 137.1, 177.0. FABMS m/z 284 (MHþ). Anal.
calcd for C12H14BrNO2; C: 50.72; H: 4.97; N: 4.93. Found:
C, 50.90; H, 5.00; N, 4.93.
3.1.3. (2S)-2-(tert-Butyloxycarbonyl)amino-3-(4-diethyl-
phosphono)phenylpropionic acid [Boc-(a-Me)Phe(4-
PO3Et2)-OH] (9). Oxazinone 8 (4.70 g, 7.48 mmol) was
treated using Pd·C (10%, 1.0 g) in THF–EtOH (1:1,
300 mL) under H2. After filtration through Celite, the
solution was concentrated under reduced pressure to yield
the amino acid. This was taken up in DMF–H2O (4:1,
25 mL) and reacted with Boc2O (2.45 g, 11.23 mmol) and
Et3N (3.13 mL, 22.4 mmol) at 0 8C and with stirring for 4
days at room temperature. The mixture was acidified with
saturated citric acid solution and extracted with EtOAc. The
extract was washed with H2O and brine, and dried over
MgSO4. Concentration under reduced pressure followed by
flash chromatography over silica gel using CH2Cl2–MeOH
(10:1) provided 9 as colorless gum (1.92 g, 61% yield):
[a]2D2 þ22.0 (c 0.95, CHCl3); 1H NMR (400 MHz, CDCl3) d
1.31 (m, 6H), 1.45 (s, 9H), 1.74 (s, 3H), 3.28 (d, J¼13.3 Hz,
1H), 3.69 (m, 1H), 4.00–4.25 (m, 4H), 5.56 (s, 1H), 7.35
(dd, J¼8.2, 4.2 Hz, 2H), 7.66 (dd, J¼13.3, 8.0 Hz, 2H). 13C
NMR (400 MHz, CDCl3) d 16.1, 16.2, 24.2, 28.4, 41.1,
60.4, 62.5, 62.7, 79.1, 124.2, 126.1, 130.2, 131.5, 142.8,
154.3, 175.3. FABMS m/z 416 (MHþ). Anal. calcd for
C19H30NO7P: C, 54.93; H, 7.28; N, 3.37. Found: C, 55.24;
H, 7.42; N, 3.22.
3.1.6. (S)-2-Amino-1,2,3,4-tetrahydro-6-bromo-2-
naphthalenecarboxylic acid methyl ester (S)-mandelic
acid salt (13). To a solution of amino ester 12 (10.4 g,
36.8 mmol) in Et2O–MeOH (3:1, 150 mL) was added
L-(þ)-mandelic acid (5.55 g, 36.5 mmol). Repeated recrys-
talization from Et2O–MeOH (3:1) provided salt 13 as
colorless crystals (4.07 g, 25% yield): mp 138–140 8C;
Anal. calcd for C20H22BrNO5: C, 55.06; H, 5.08; N, 3.21.
Found: C, 54.77; H, 5.08; N, 3.21.
3.1.7. Methyl (S)-2-(tert-butyloxycarbonyl)amino-
1,2,3,4-tetrahydro-6-bromo-2-naphthalenecarboxylate
(14). To a stirred suspension of 13 (50 mg, 0.114 mmol) in
CHCl3 (0.160 mL) were added Boc2O (55 mg, 0.252 mmol)
and Et3N (0.070 mL, 0.504 mmol) at 0 8C, and stirring was
continued for 2 days at room temperature. The mixture was
extracted with EtOAc, and the extract was successively
washed with 5% citric acid solution, brine, 5% NaHCO3
solution and brine, and dried over MgSO4. Concentration
under reduced pressure followed by flash chromatography
over silica gel with n-hexanes–EtOAc (7:1) provided 14 as
colorless crystals (35 mg, 79% yield): mp 115–117 8C;
[a]2D1 þ30.6 (c 0.68, CHCl3). Enantiomeric purity, deter-
mined by HPLC analysis using a CHIRALCEL column
3.1.4. 30,40-Dihydro-60-bromo-spiro[imidazolidine-
4,20(10H)-naphthalene]-2,5-dione (11).
A mixture of
6-bromo-2-tetralone 10 (20.3 g, 90.2 mmol), KCN
(7.63 mL, 117 mmol), (NH4)2CO3 (78.0 g, 811 mmol) in
50% aqueous EtOH (540 mL) was stirred at reflux for 1 h.
After evaporation of EtOH, the suspension was filtrated to
provide 11 as brown powder (21.7 g, 81% yield): mp 285–
1
(isocratic, 10% D in C), was .98%. H NMR (400 MHz,
CDCl3) d 1.41 (s, 9H), 2.10 (m, 1H), 2.46 (m, 1H), 2.82 (dd,
J¼8.3, 4.8 Hz, 2H), 2.92 (d, J¼16.8 Hz, 1H), 3.22 (d, J¼
16.7 Hz, 1H), 3.76 (s, 3H), 4.72 (s, 1H), 6.92 (d, J¼8.0 Hz,
1H), 7.23–7.29 (m, 2H). 13C NMR (400 MHz, CDCl3) d
25.1, 28.2, 37.6, 52.5, 57.6, 120.0, 129.2, 130.9, 131.4,
131.6, 137.2, 154.9, 174.2. FABMS m/z 384 (MHþ). Anal.
calcd for C17H22BrNO4: C, 53.14; H, 5.77; N, 3.65. Found:
C, 53.27; H, 5.78; N, 3.70.
1
287 8C (decomp.); H NMR (400 MHz, DMSO-d6) d 1.80
(m, 1H), 1.92 (m, 1H), 2.75 (d, J¼17.0 Hz, 1H), 2.90 (m,
2H), 3.04 (d, J¼17.3 Hz, 1H), 7.05 (d, J¼8.0 Hz, 1H), 7.30
(dd, J¼8.0, 2.2 Hz, 1H), 7.35 (d, J¼2.2 Hz, 1H). 13C NMR
(400 MHz, CDCl3) d 24.5, 29.5, 36.3, 60.3, 118.8, 128.5,
130.9, 131.0, 132.1, 137.7, 156.2, 177.9. FABMS m/z 295
(MHþ). Anal. calcd for C12H11BrN2O2: C, 48.84; H, 3.76;
N, 9.49. Found: C, 49.27; H, 3.79; N, 9.20.
3.1.8. (S)-2-(tert-Butyloxycarbonyl)amino-1,2,3,4-tetra-
hydro-6-bromo-2-naphthalenecarboxylic acid (15). To a
3.1.5. Methyl 2-amino-1,2,3,4-tetrahydro-6-bromo-2-

S. Oishi et al. / Tetrahedron 60 (2004) 2971–2977
2975
stirred solution of amino ester 14 (2.00 g, 5.20 mmol), in
THF (25 mL) was added 1 N LiOH (15.6 mL, 15.6 mmol)
at 0 8C, and stirring was continued overnight at room
temperature. The mixture was acidified with saturated citric
acid solution, concentrated under reduced pressure and
extracted with EtOAc. The extract was washed with H2O
and brine, and dried over MgSO4. Concentration and
recrystalization from Et2O–MeOH (5:1) gave 15 as color-
less crystals (1.90 g, 98% yield): mp 183–185 8C; [a]D22
þ22.8 (c 0.49, CHCl3); 1H NMR (400 MHz, CDCl3) d
1.42 (s, 9H), 2.10 (ddd, J¼13.6, 10.5, 6.8 Hz, 1H), 2.53
(m, 1H), 2.84 (m, 2H), 2.94 (d, J¼17.1 Hz, 1H), 3.31
(d, J¼16.8 Hz, 1H), 4.79 (br, 1H), 6.95 (d, J¼8.0 Hz, 1H),
7.27 (m, 2H). 13C NMR (400 MHz, CDCl3) d 24.6, 28.1,
56.6, 77.9, 118.3, 128.2, 130.5, 131.3, 133.5, 137.7,
155.0,175.4. FABMS m/z 370 (MHþ). Anal. calcd for
C16H20BrNO4; C, 51.90; H, 5.44; N, 3.78. Found: C, 51.90;
H, 5.47; N, 3.66.
300 mg) in EtOAc (100 mL) under an H2 atmosphere.
After filtration through Celite and concentration under
reduced pressure, purification by flash chromatography over
silica gel with CH2Cl2–MeOH (10:1) provided 18 as a
colorless powder (1.51 g, 99% yield): mp 75–77 8C; [a]D22
þ7.19 (c 0.67, CHCl3); 1H NMR (400 MHz, CDCl3) d 1.33
(t, J¼7.0 Hz, 6H), 1.42 (s, 9H), 2.14 (m, 1H), 2.51 (m, 1H),
2.91 (m, 2H), 3.07 (d, J¼17.3 Hz, 1H), 3.43 (d, J¼17.3 Hz,
1H), 4.13 (m, 4H), 4.87 (br, 1H), 7.17 (dd, J¼7.8, 4.1 Hz,
1H), 7.53 (dd, J¼12.9, 7.8 Hz, 1H), 7.59 (d, J¼14.1 Hz,
1H). 13C NMR (400 MHz, CDCl3) d 16.3, 25.1, 28.2, 37.8,
57.6, 62.3, 80.6, 124.7, 126.6, 129.1, 129.6, 132.4, 135.4,
138.0, 155.6, 177.0. FABMS m/z 428 (MHþ). Anal. calcd
for C20H30NO7P: C, 56.20; H, 7.07; N, 3.28. Found: C,
56.07; H, 7.10; N, 3.22.
3.1.12. Boc-(a-Me)Phe(4-PO3Et2)-Ac6c-Asn-(CH2)3-(1-
naphthyl) (20). To a stirred solution of 9 (215 mg,
0.518 mmol) in dry DMF (2 mL) was added TFFH
(136 mg, 0.518 mmol) at room temperature. After 10 min,
amine 1925 (200 mg, 0.471 mmol) and Pr2i EtN (0.180 mL,
1.03 mmol) were added to the above mixture at room
temperature, and stirring was continued for 24 h at 50 8C.
The mixture was extracted with EtOAc, and the extract was
washed successively with saturated citric acid solution,
brine, saturated NaHCO3 solution and brine, and dried over
Na2SO4. Concentration followed by flash chromatography
over silica gel with CH2Cl2–MeOH (100:0 to 10:1) gave 20
as colorless semisolid (282 mg, 71% yield): 1H NMR
(400 MHz, CDCl3) d 1.20–1.53 (m, 21H), 1.58–1.77 (m,
3H), 1.82 (m, 1H), 1.90–2.11 (m, 4H), 2.17 (m, 1H), 2.65
(dd, J¼15.3, 5.1 Hz, 1H), 2.90 (d, J¼13.6 Hz, 1H), 3.04 (dd,
J¼15.3, 5.6 Hz, 1H), 3.12 (m, 2H), 3.35 (m, 1H), 3.41 (m,
1H), 3.51 (d, J¼13.6 Hz, 1H), 4.14 (m, 4H), 4.66 (s, 1H),
4.71 (m, 1H), 5.35 (br, 1H), 6.22 (br, 1H), 7.04 (m, 3H),
7.34 (m, 2H), 7.43 (m, 2H), 7.53 (t, J¼5.6 Hz, 1H), 7.66
(m, 3H), 7.79 (m, 1H), 7.85 (d, J¼8.3 Hz, 1H), 7.93 (d,
J¼8.3 Hz, 1H). FABMS m/z 822 (MHþ). Anal. calcd for
C43H60N5O9P·0.5H2O: C, 62.15; H, 7.40; N, 8.43. Found:
C, 62.00; H, 7.38; N, 8.37.
3.1.9. Benzyl (S)-2-(tert-butyloxycarbonyl)amino-1,2,3,4-
tetrahydro-6-bromo-2-naphthalenecarboxylate (16). To
a stirred solution of 15 (1.88 g, 5.07 mmol) in DMF
(5.5 mL) were added BnBr (0.664 mL, 5.58 mmol) and
Pri2EtN (1.06 mL, 6.09 mmol) at 0 8C and stirring was
continued for 24 h at room temperature. The mixture was
extracted with EtOAc, and the extract was washed with
saturated citric acid solution, H2O, 5% NaHCO3 solution
and brine, and dried over Na2SO4. Concentration under
reduced pressure followed by flash chromatography over
silica gel with n-hexane–EtOAc (7:1) provided 16 as
colorless crystals (2.27 g, 97% yield): mp 89–91 8C; [a]D22
þ16.9 (c 0.92, CHCl3); 1H NMR (400 MHz, CDCl3) d 1.37
(s, 9H), 2.12 (ddd, J¼13.6, 9.7, 7.5 Hz, 1H), 2.46 (m, 1H),
2.79 (m, 2H), 2.92 (d, J¼16.5 Hz, 1H), 3.26 (d, J¼16.6 Hz,
1H), 4.75 (br, 1H), 5.18 (s, 2H), 6.91 (d, J¼8.0 Hz, 1H),
7.21–7.27 (m, 2H), 7.29–7.38 (m, 5H). 13C NMR
(400 MHz, CDCl3) d 25.1, 28.2, 37.6, 57.7, 67.2, 120.0,
128.1, 128.2, 128.5, 129.2, 130.9, 131.5, 135.6, 137.2,
149.1, 154.8, 173.5. FABMS m/z 460 (MHþ). Anal. calcd
for C23H26BrNO4: C, 60.01; H, 5.69; N, 3.04. Found: C,
59.64; H, 5.70; N, 2.92.
3.1.13. Boc-Atc(6-PO3Et2)-Ac6c-Asn-(CH2)3-(1-naph-
thyl) (21). Using a procedure similar to that described for
the preparation of peptide 20 from 19, coupling of 18
(200 mg, 0.471 mmol) with 19 provided 21 as a colorless
semisolid (282 mg, 71% yield): 1H NMR (400 MHz,
CDCl3) d 1.21–1.43 (m, 18H), 1.52–1.84 (m, 5H), 1.85–
2.09 (m, 5H), 2.22 (m, 1H), 2.39 (m, 1H), 2.57–2.91 (m,
5H), 3.08 (m, 2H), 3.25 (d, J¼17.0 Hz, 1H), 3.34 (m, 2H),
4.13 (m, 4H), 4.79 (dt, J¼8.2, 5.8 Hz, 1H), 4.81 (s, 1H), 5.35
(br, 1H), 6.36 (br, 1H), 7.02 (dd, J¼7.8, 4.1 Hz, 1H), 7.20
(br, 1H), 7.30 (m, 2H), 7.40 (m, 2H), 7.50 (dd, J¼17.9,
7.5 Hz, 1H), 7.55 (m, 2H), 7.64 (m, 1H), 7.80 (m, 2H), 8.01
(d, J¼8.3 Hz, 1H). FABMS m/z 834 (MHþ). Anal. calcd for
C44H60N5O9P·H2O: C, 62.03; H, 7.34; N, 8.22. Found: C,
62.29; H, 7.30; N, 8.32.
3.1.10. (S)-2-(tert-Butyloxycarbonyl)amino-1,2,3,4-tetra-
hydro-6-(diethylphosphono)-2-naphthalenecarboxylic
acid benzyl ester (17). Treatment of 16 (2.21 g, 4.80 mmol)
with diethyl phosphite using a procedure similar to that
described for the preparation 8 from 7, gave 17 as a colorless
1
oil (1.91 g, 93% yield): [a]2D2 þ9.30 (c 1.13, CHCl3); H
NMR (400 MHz, CDCl3) d 1.33 (t, J¼7.0 Hz, 6H), 1.38 (s,
9H), 2.15 (ddd, J¼13.6, 9.2, 7.3 Hz, 1H), 2.45 (m, 1H), 2.86
(m, 2H), 3.04 (d, J¼17.3 Hz, 1H), 3.40 (d, J¼17.0 Hz, 1H),
4.11 (m, 4H), 4.79 (s, 1H), 5.19 (s, 2H), 7.15 (dd, J¼7.8,
4.3 Hz, 1H), 7.28–7.38 (m, 5H), 7.49–7.60 (m, 2H). 13C
NMR (400 MHz, CDCl3) d 16.3, 25.1, 28.2, 28.9,
38.0, 57.7, 62.0, 67.2, 125.2, 127.1, 128.1, 128.2, 128.5,
129.1, 129.5, 132.4, 135.3, 135.6, 137.7, 154.8, 173.5.
HR-FABMS m/z calcd for C27H37NO7P (MHþ) 518.2308,
found: 518.2264.
3.1.14. tert-ButO-(CO)2-(a-Me)Phe(4-PO3Et2)-Ac6c-
Asn-(CH2)3-(1-naphthyl) (22). Protected peptide 20
(93 mg, 0.113 mmol) was treated with TFA-anisole (10:1,
5.5 mL) for 2 h at room temperature then the reaction
mixture was concentrated and dissolved in dry DMF
(1 mL). To this were added tert-butyl oxalyl chloride
3.1.11. (S)-2-(tert-Butyloxycarbonyl)amino-1,2,3,4-tetra-
hydro-6-(diethylphosphono)-2-naphthalenecarboxylic
acid [Boc-Atc(6-PO3Et2)-OH] (18). Benzyl ester 17
(1.84 g, 3.55 mmol) was treated using Pd·C (10%,

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S. Oishi et al. / Tetrahedron 60 (2004) 2971–2977
(24 mg, 0.169 mmol) and Pri2EtN (0.059 mL, 0.339 mmol)
at 0 8C, and stirring was continued for 2 h at 50 8C. The
mixture was extracted with EtOAc, and the extract was
washed successively with saturated citric acid solution,
brine, saturated NaHCO3 solution and brine, and dried over
Na2SO4. Concentration followed by flash chromatography
over silica gel with CH2Cl2–MeOH (100:0 to 10:1) gave 20
as colorless semisolid (56 g, 58% yield): 1H NMR
(400 MHz, CDCl3) d 1.18–1.45 (m, 12H), 1.49 (s, 9H),
1.56–1.82 (m, 5H), 1.99 (m, 3H), 2.29 (m, 1H), 2.71 (dd,
J¼14.6, 5.3 Hz, 1H), 2.82 (dd, J¼14.6, 6.3 Hz, 1H), 3.03 (d,
J¼13.6 Hz, 1H), 3.11 (m, 2H), 3.34 (m, 2H), 3.46 (d,
J¼13.4 Hz, 1H), 4.12 (m, 4H), 4.65 (m, 1H), 5.65 (br, 1H),
6.89 (br, 1H), 7.23 (dd, J¼8.0, 3.6 Hz, 2H), 7.28 (s, 1H),
7.32–7.38 (m, 2H). 7.40–7.50 (m, 3H), 7.52 (m, 1H), 7.66
(dd, J¼6.5, 2.6 Hz, 1H), 7.70–7.84 (m, 4H), 8.04 (d,
J¼8.0 Hz, 1H). FABMS m/z 850 (MHþ). Anal. calcd for
C44H60N5O10P·H2O: C, 60.89; H, 7.20; N, 8.07. Found: C,
61.11; H, 7.03; N, 8.09.
2.84–3.34 (m, 7H), 4.25 (m, 1H), 6.66 (s, 1H), 7.06 (m, 1H),
7.30–7.54 (m, 7H), 7.74 (m, 1H), 7.82 (d, J¼7.3 Hz, 1H),
7.86–7.96 (m, 2H), 8.09 (m, 1H), 8.26 (br, 1H). FABMS
m/z 748 [(M2H)2].
4. Supplementary Material
Single crystal X-ray crystallographic data for salt 13,
including a thermal ellipsoid plot at the 50% confidence
interval and tables of atomic coordinates and parameters are
provided (10 pages). Supplementary material can be found
in the online version of this paper.
Acknowledgements
Appreciation is expressed to Dr. James Kelley of the LMC
for mass spectral analysis. Gratitude is also expressed to the
Japan Society for the Promotion of Science for Research
Abroad for Postdoctoral Fellowship funding of S.O. Work
was supported in part by the Office of Naval Research
(ONR) and the National Institute on Drug Abuse (NIDA)
(for J.R.D.) and by the Susan G. Komen Breast Cancer
Foundation (for M.Z. and D.Y.).
3.1.15. tert-BuO-(CO)2-Atc(6-PO3Et2)-Ac6c-Asn-(CH2)3-
(1-naphthyl) (23). Using a procedure similar to that
described for the preparation of peptide 22 from 20,
coupling of 21 (265 mg, 0.317 mmol) with tert-butyl oxalyl
chloride gave 23 as colorless semisolid (183 mg, 66%
yield): 1H NMR (400 MHz, CDCl3) d 0.83 (m, 2H), 1.14 (m,
1H), 1.33 (m, 6H), 1.36–1.62 (m, 12H), 1.65 (m, 2H), 1.86–
2.06 (m, 3H), 2.24 (m, 3H), 2.78 (m, 4H), 3.10 (m, 3H), 3.23
(m, 1H), 3.37 (m, 1H), 3.61 (d, J¼17.3 Hz, 1H), 4.11 (m,
4H), 4.66 (m, 1H), 5.52 (br, 1H), 6.74 (br, 1H), 6.93 (s, 1H),
7.20 (dd, J¼4.3, 3.9 Hz, 1H), 7.35 (m, 3H), 7.44 (m, 3H),
7.60 (m, 3H), 7.68 (dd, J¼7.0, 2.2 Hz, 1H), 7.82 (m, 1H),
8.04 (d, J¼8.2 Hz, 1H). FABMS m/z 862 (MHþ). Anal.
calcd for C45H60N5O10P·H2O: C, 61.42; H, 7.10; N, 7.96.
Found: C, 61.58; H, 7.13; N, 7.90.
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