Synthesis of a new tyrosine analogue having χ1 and χ2 angles constrained to values observed for an SH2 domain-bound phosphotyrosyl residue

Article abstract of DOI:10.1021/jo9700787

Synthesis is reported of a new tricyclic amino acid, (±)-(rel-2S,3R)- 2-carboxy-1,2,3,4,5,6-hexahydro 8-hydroxy-1,5-methano-3-methyl-3-benzazocine (2), which contains within its structure the elements of a tyrosine moiety having χ₁ and χ₂ angles (168°and -95°, respectively) constrained to values observed for a phosphotyrosyl (pTyr) residue bound to the 56(lck) SH2 domain (χ₁ and χ₂ values of 163°and -94°, respectively). Additionally, the φ angle of N-acylated 2 correlates well with the angle of the SH2 domain-bound pTyr residue. Compound 2 represents a unique, highly constrained amino acid which may be of value in signal transduction studies.

Full text of DOI:10.1021/jo9700787

5428
J . Org. Chem. 1997, 62, 5428-5431
Syn th esis of a New Tyr osin e An a logu e Ha vin g ø1 a n d ø2 An gles
Con str a in ed to Va lu es Obser ved for a n SH2 Dom a in -Bou n d
P h osp h otyr osyl Resid u e
Bin Ye, Zhu-J un Yao, and Terrence R. Burke, J r.*,†
Laboratory of Medicinal Chemistry, Division of Basic Sciences, National Cancer Institute,
National Institutes of Health, Bethesda, Maryland 20892
Received J anuary 15, 1997X
Synthesis is reported of a new tricyclic amino acid, (()-(rel-2S,3R)-2-carboxy-1,2,3,4,5,6-hexahydro-
8-hydroxy-1,5-methano-3-methyl-3-benzazocine (2), which contains within its structure the elements
of a tyrosine moiety having ø1 and ø2 angles (168° and -95°, respectively) constrained to values
observed for a phosphotyrosyl (pTyr) residue bound to the 56lck SH2 domain (ø1 and ø2 values of
163° and -94°, respectively). Additionally, the φ angle of N-acylated 2 correlates well with the φ
angle of the SH2 domain-bound pTyr residue. Compound 2 represents a unique, highly constrained
amino acid which may be of value in signal transduction studies.
Phosphorylation of key tyrosyl residues in proteins by
protein-tyrosine kinases (PTKs) provides the “phospho-
tyrosyl pharmacophore” (pTyr) which is required for
recognition and binding by secondary signaling proteins
through their Src homology 2 (SH2) or phosphotyrosine
binding (PTB) domains. Such protein-protein associa-
tions subsequently establish the basis for further signal
transduction.1 Because of the central role played by pTyr
residues, its analogues have become important tools for
developing SH2 domain-binding antagonists.2 In order
to enhance binding affinities of flexible ligands, one useful
approach has been to reduce entropy penalties by con-
straining ligands to conformations approximating those
required for binding. A number of conformationally
restricted amino acids, including analogues of phenyl-
alanine3 and tyrosine,4 have been devised for these
purposes. In the case of SH2 domain ligands, the
availability of X-ray and solution structures of ligated
SH2 domains has provided a clear definition of relevant
binding geometries which would be required for the
preparation of conformationally constrained pTyr ana-
F igu r e 1. Comparison of p56lck-bound pTyr residue 1 with
the N-acetylated form of conformationally constrained tyrosyl
mimetic 2. The N-acyl group of 1 is held in the conformation
observed for the SH2 domain-bound Gln-pTyr amide bond,
while N-acetyl 2 represents an energy-minimized structure.
Shading of 2 and 3 is intended to highlight important
structural features.
† Author to whom correspondence should be addressed at Building
37, Room 5C06, National Institutes of Health, Bethesda, MD 20892.
Phone: (301) 496-3597. Fax: (301) 402-2275. E-mail: tburke@
helix.nih.gov.
X Abstract published in Advance ACS Abstracts, J uly 1, 1997.
(1) Panayotou, G.; Waterfield, M. D. Bioessays 1993, 15, 171-177.
(2) (a) Burke, T. R., J r.; Smyth, M. S.; Otaka, A.; Nomizu, M.; Roller,
P. P.; Wolf, G.; Case, R.; Shoelson, S. E. Biochemistry 1994, 33, 6490-
6494. (b) Gilmer, T.; Rodriquez, M.; J ordan, S.; Crosby, R.; Alligood,
K.; Green, M.; Kimery, M.; Wagner, C.; Kinder, D.; Charifson, P.;
Hassell, A. M.; Willard, D.; Luther, M.; Rusnak, D.; Sternbach, D. D.;
Mehrotra, M.; Peel, M.; Shampine, L.; Davis, R.; Robbins, J .; Patel, I.
R.; Kassel, D.; Burkhart, W.; Moyer, M.; Bradshaw, T.; Berman, J . J .
Biol. Chem. 1994, 269, 31711-31719. (c) Ye, B.; Akamatsu, M.;
Shoelson, S. E.; Wolf, G.; Giorgetti-Peraldi, S.; Yan, X.; Roller, P. P.;
Burke, T. R., J r. J . Med. Chem. 1995, 38, 4270-4275. (d) Shahripour,
A.; Plummer, M. S.; Lunney, E. A.; Para, K. S.; Stankovic, C. J .; Rubin,
J . R.; Humblet, C.; Fergus, J . H.; Marks, J . S.; Herrera, R.; Hubbel, S.
E.; Saltiel, A. R.; Sawyer, T. K. Bioorg. Med. Chem. Lett. 1996, 6, 1209-
1214.
logues.5 Utilizing the previously reported X-ray structure
of a pTyr-containing peptide bound to the p56lck SH2
domain,5b we have designed tricyclic methanobenzazocine
analogue 2, which contains within its structure a tyrosine
moiety having ø1 and ø2 torsion angles (168° and -95°,
respectively for the N-acylated form) closely approximat-
ing those of the SH2 domain-bound pTyr residue 1 (163°
and -94°, respectively, Figure 1). Additionally, as can
be seen from Figure 1, φ angles are also quite similar,
such that the N-acyl carbonyl groups are in close align-
ment. This carbonyl oxygen participates in hydrogen
bonding to the SH2 domain.5 Amino acid analogue 2 is
unusual in simultaneously constraining three torsion
angles to biologically relevant values displayed by the
(3) J osien, H.; Lavielle, S.; Brunissen, A.; Saffroy, M.; Torrens, Y.;
Beaujouan, J . C.; Glowinski, J .; Chassaing, G. J . Med. Chem. 1994,
37, 1586-1601.
(4) (a) J iao, D.; Russell, K. C.; Hruby, V. J . Tetrahedron 1993, 49,
3511-3520. (b) Mosberg, H. I.; Lomize, A. L.; Wang, C. G.; Kroona,
H.; Heyl, D. L.; Sobczykkojiro, K.; Ma, W. L.; Mousigian, C.; Porreca,
F. J . Med. Chem. 1994, 37, 4371-4383. (c) Obrecht, D.; Lehmann,
C.; Ruffieux, R.; Schonholzer, P.; Muller, K. Helv. Chim. Acta 1995,
78, 1567-1587. (d) Burke, T. R., J r.; Barchi, J . J ., J r.; George, C.;
Wolf, G.; Shoelson, S. E.; Yan, X. J . Med. Chem. 1995, 38, 1386-
1396.
(5) (a) Waksman, G.; Shoelson, S. E.; Pant, N.; Cowburn, D.;
Kuriyan, J . Cell 1993, 72, 779-790. (b) Eck, M. J .; Shoelson, S. E.;
Harrison, S. C. Nature 1993, 362, 87-91.
(6) Carruthers, W.; Williams, M. J . J . Chem. Soc., Chem. Commun.
1986, 1287-1288.
S0022-3263(97)00078-9 This article not subject to U.S. Copyright. Published 1997 by the American Chemical Society

Synthesis of a New Tyrosine Analogue
J . Org. Chem., Vol. 62, No. 16, 1997 5429
Sch em e 1a
Sch em e 2a
a
(a) MeNH2‚HCl, 36% CH2O, AcOH, reflux, overnight; 1 N
a
DMBz ) dimethoxybenzyl; (a) LDA, HMPA, THF, -78 °C, 1
NaOH, MeOH, room temperature, 2 h; (b) MeNH2, 1 N NaOH,
dioxane, room temperature, 1 h, 90%; (c) NH2NH2‚H2O, 88% KOH,
diethylene glycol, reflux, 14 h, 98%; (d) DIBAL-H, THF, -78 °C,
1 h, TMSCN, ZnCl2, CH2Cl2, room temperature, 2 h, 74%.
h; Eschenmoser’s salt, room temperature, overnight, 52%; (b)
DMBzNH2, 1 N NaOH, room temperature, 4 h; DBU, toluene,
reflux, overnight, 38%; (c) NH2NH2‚H2O, 88% KOH, diethylene
glycol, reflux, 5 h, 71%; (d) DIBAL-H, THF, -78 °C, 2 h, TMSCN,
ZnCl2, CH2Cl2, room temperature, 1.5 h, 78%; (e) TFA, anisole,
65 ( 5 °C, 3 h; MeOCOCl, Et3N, CH3CN, room temperature, 4 h,
93%; (f) 6 N HCl, reflux, 6 days, 88%.
parent on which it is modeled and may be of potential
value as a conformationally constrained tyrosine ana-
logue for signal transduction studies.
gave 10 in 74% yield as a single isomer, bearing the
desired relative stereochemistry as determined by X-ray
crystallography.11
Syn th esis
Surprisingly, attempted N-demethylation by a variety
of techniques failed, providing in each case recovered
starting 10. This potentially indicated severe steric
crowding which prevented reaction at the nitrogen center.
To circumvent this obstacle, the nitrogen bearing a 2,4-
dimethoxybenzyl group (DMBz) was introduced, which
could be removed by chemical modification distal to the
nitrogen itself. Because of its acid lability, formation of
lactam 11 was done under basic conditions by treating
R,â-unsaturated keto ester 7 with 2,4-dimethoxybenzyl-
amine using DBU as a catalyst (refluxing toluene, 5 h,
38% yield) (Scheme 2). Keto ester 7, which had previ-
ously been obtained in low yield as a byproduct during
the synthesis of methylamine adduct 8, was prepared in
54% yield by treatment of 6 with Eschenmoser’s salt
(N,N-dimethylmethyleneammonium iodide), using LDA
as a base.12 Wolff-Kishner reduction of 11 afforded
lactam 12 (71% yield), with subsequent DIBAL-H reduc-
tion and treatment with TMSCN and ZnCl2 giving nitrile-
containing N-2,4-dimethoxybenzylated compound 13 (77%
yield).
Initial attempts at direct conversion of 13 to 2 by
simultaneous acid-catalyzed debenzylation, O-demethyl-
ation, and nitrile hydrolysis (6 N HCl, reflux) resulted
in loss of the nitrile group with formation of the corre-
sponding imine. Alternatively, treatment of 13 under
moderately alkaline conditions (NaOH, MeOH, reflux)13
gave no reaction, while harsher treatment (KOH, dieth-
ylene glycol, reflux)14 resulted in reductive displacement
of the nitrile to yield 14 (76% yield). The bulky benzyl
group was therefore replaced with a smaller carbamate
functionality, which both reduced steric crowding and
tied up the nitrogen lone electron pair, preventing its
We have previously reported the preparation of the
simplified, constrained, partial tyrosine analogue 3.4d In
relation to this structure, preparation of 2 would entail
selectively introducing the carboxyl functionality at
carbon “a” rather than carbon “b” while maintaining
proper relative stereochemistry at this center. In con-
trast to our previous synthesis of 3 where the amine-
containing ring was prepared in a one-pot manner by
Mannich-type condensation of methylamine and 2 equiv
of formaldehyde onto tetralone 4, our synthesis of 2
utilized a stepwise ring construction which introduced
oxygen functionality at the “a” carbon, which was sub-
sequently transformed into the desired carboxyl group.
The incipient oxygenated “a” carbon was first intro-
duced onto starting 6-methoxy-2-tetralone7 by car-
bomethoxylation to yield 5,8 which was then methylated
to yield 6. Methylation was required to prevent further
reaction at this center. While it was anticipated that
sequential Mannich reaction/intramolecular ring closure9
would yield the desired lactam 8, it was found that usual
Mannich conditions (MeNH2, HCHO, ACOH, reflux, 5 h)
gave only a 10% yield of desired 8 directly (Scheme 1). It
was necessary to treat the crude reaction product with
aqueous NaOH to obtain a 31% yield of lactam 8 along
with a 16% yield of highly unstable R,â-unsaturated keto
ester 7. Isolation of 7 and treatment with methylamine
(room temperature, 1 h) resulted in 1,4-Michael-type
addition,10 followed by intramolecular amidation to pro-
vide additional lactam 8 in 90% yield. The methanoben-
zazocine 11-oxo carbonyl was then removed via Wolff-
Kishner reduction (KOH, diethylene glycol, reflux, 4 h)4d
to provide 9 (98% yield). Sequential reduction of lactam
9 with DIBAL-H, followed by treatment with TMSCN in
the presence of ZnCl2 (room temperature, 1.5 h), then
(11) Relative configurations were confirmed by single-crystal X-ray
crystallography.
(7) Kidwell, R. L.; Darling, S. D. Tetrahedron Lett. 1966, 5, 531-
535.
(12) Marshall, J . A.; Flynn, G. A. J . Org. Chem. 1979, 44, 1391-
1397.
(8) Colvin, E. W.; Martin, J .; Parker, W.; Raphael, R. A.; Shroot,
B.; Doyle, M. J . Chem. Soc., Perkin Trans. 1 1972, 860-870.
(9) Tramontini, M. Synthesis 1973, 703.
(13) Ezzitouni, A.; Barchi, J . J .; Marquez, V. E. J . Chem. Soc., Chem.
Commun. 1995, 1345-1346.
(14) Christopfel, W. C.; Miller, L. L. J . Org. Chem. 1986, 51, 4169-
4175.
(10) Elz, S.; Heil, W. L. Bioorg. Med. Chem. Lett. 1995, 5, 667-672.

5430 J . Org. Chem., Vol. 62, No. 16, 1997
Ye et al.
temperature under argon were added 40% methylamine (39.5
mg, 0.51 mmol) and 1 N NaOH (0.51 mL, 0.51 mmol). The
reaction mixture was stirred (1 h) and then diluted with H2O
(5 mL), extracted with CHCl3 (3 × 20 mL), washed with brine
(2 × 5 mL), and dried (Na2SO4), and the solvent was removed
to provide crude 8. Silica gel chromatography (hexanes:EtOAc
2:8) afforded pure 8 (92 mg, 90%).
participation in intramolecular elimination of the nitrile
group. Although oxidative debenzylation worked well
(DDQ),15 ease of workup favored the use of TFA (65 °C,
3 h)16 to provide 15 in 92% yield. Subsequent treatment
with methyl chloroformate in the presence of Et3N gave
carbamate 16 in 85% overall yield from benzylamine 13.
Finally, treatment of 16 with 6 N HCl (reflux, 3 days),
followed by a propylene oxide quench,17 gave final target
2 in 87% yield.
(()-1,3-Dim eth yl-1,2,3,4,5,6-h exa h yd r o-1,5-m eth a n o-8-
m eth oxy-3-ben za zocin -2-on e (9). A mixture of 8 (292 mg,
1.1 mmol), NH2NH2‚H2O (450 mg, 9 mmol), and 88% KOH (381
mg, 6.8 mmol) in diethylene glycol (6 mL) was heated to reflux
(14 h). The reaction mixture was cooled to room temperature,
diluted with H2O (20 mL), extracted with EtOAc (3 × 50 mL),
washed with brine (2 × 5 mL), and dried (Na2SO4), and solvent
was removed to provide crude 9. Silica gel chromatography
(hexanes:EtOAc 3:7) afforded pure 9 (272 mg, 98%): 1H NMR
(250 M Hz, CDCl3) δ 7.39 (d, J ) 8.7 Hz, 1 H), 6.71 (dd, J )
8.7, 2.8 Hz, 1 H), 6.60 (d, J ) 2.8 Hz, 1 H), 3.74 (s, 3 H), 3.65
(dd, J ) 12.5, 6.7 Hz, 1 H), 3.25 (dd, J ) 17.6, 6.7 Hz, 1 H),
3.15 (d, J ) 12.5 Hz, 1 H), 2.79 (d, J ) 17.6 Hz, 1 H), 2.77 (s,
3 H), 2.56 (m, 1 H), 2.1 (dd, J ) 13.3, 3.5 Hz, 1 H), 1.97 (dd, J
) 13.3, 3.5 Hz, 1 H), 1.58 (s, 3 H); IR (film) 3420, 1651, 1031
cm-1; FABMS (m/z) 246 (M + H)+. Anal. Calcd (C15H19NO2):
C, 73.47; H, 7.76; N, 5.71. Found: C, 73.69; H, 7.86; N, 5.47.
(()-(r el-2S,3R)-2-Cyan o-1,3-dim eth yl-1,2,3,4,5,6-h exah y-
d r o-1,5-m eth a n o-8-m eth oxy-3-ben za zocin e (10). To a so-
lution of 9 (1.43 g, 5.82 mmol) in THF (15 mL) at -78 °C under
argon was added dropwise DIBAL-H, 1 M in hexanes (5.82
mL, 5.82 mmol), and the reaction mixture was stirred at -78
°C (1 h). The reaction mixture was quenched at -78 °C with
2 N NaOH (50 mL) and then warmed to room temperature
and extracted with CHCl3 (3 × 100 mL), washed with brine
(2 × 50 mL), and dried (Na2SO4), and the solvent was removed
to provide crude 10, which was placed under high vacuum (3
h). The material was taken up in CH2Cl2 (116 mL), and to
this solution at room temperature under argon was added
TMSCN (1.154 g, 11.6 mmol) followed by ZnCl2, 1 M in CH2Cl2
(5.82 mL, 5.82 mmol). The reaction mixture was stirred (2 h)
and then quenched with saturated aqueous NaHCO3 (30 mL),
extracted with CHCl3 (3 × 70 mL), washed with brine (2 × 50
mL), and dried (Na2SO4), and the solvent was removed to
provide crude 10. Purification by silica gel chromatography
afforded pure 10 as a crystalline solid (1.1 g, 74%): mp 105
Exp er im en ta l Section
Gen er a l Meth od s. 1H NMR data are reported in ppm
relative to TMS and referenced to the solvent in which they
were run. Solvent was removed by rotary evaporation under
reduced pressure and silica gel chromatography was performed
using Merck silica gel 60 with a particle size of 40-63 µm.
Anhydrous solvents were obtained commercially and used
without further drying. Preparative HPLC were conducted
using a Vydac preparative C18 peptide and protein column.
Energy minimization of N-acetyl 2 was achieved with the
CAChe mechanics program (version 3.9) using augmented
MM2 parameters in a conjugate gradient method with con-
vergence at 0.001 kcal/mol.
(()-3,4-Dih yd r o-1-ca r bom eth oxy-6-m eth oxy-1-m eth yl-
2(1H)-n a p h th a len -2-on e (6). A mixture of (()-3,4-dihydro-
1-carbomethoxy-6-methoxy-2(1H)-naphthalen-2-one (5)18 (17.8
g, 76.1 mmol), potassium carbonate (52.5 g, 381 mmol), and
iodomethane (13 g, 91.2 mmol) in acetone (500 mL) was heated
to reflux (3 h). The reaction mixture was cooled to room
temperature and filtered and the filter cake washed with ether.
The combined filtrate was taken to dryness and then diluted
with EtOAc (200 mL), washed with brine (3 × 30 mL), and
dried (MgSO4), and the solvent was removed to provide crude
6. Purification by silica gel chromatography (hexanes:EtOAc
4:1) afforded pure 6 (12.3 g, 65%) as a syrup: 1H NMR (250
MHz, CDCl3) δ 7.15 (d, J ) 8.6 Hz, 1 H), 6.81 (dd, J ) 8.6, 2.6
Hz, 1 H), 6.73 (d, J ) 2.6 Hz, 1 H), 3.8 (s, 3 H), 3.61 (s, 3 H),
3.2-2.54 (m, 4 H), 1.67 (s, 3 H); IR (film) 3020, 1715, 1504,
1216 cm-1; FABMS (m/z) 249 (M + H)+. Anal. Calcd
(C14H16O4): C, 67.73; H, 6.5. Found: C, 67.88; H, 6.57.
(()-3,4-Dih yd r o-1-ca r bom eth oxy-6-m eth oxy-1-m eth yl-
3-m et h ylen e-2(1H )-n a p h t h a len -2-on e (7) a n d (()-1,3-
Dim eth yl-1,2,3,4,5,6-h exa h yd r o-1,5-m eth a n o-8-m eth oxy-
3-ben za zocin e-2,11-d ion e (8). A mixture of 6 (1.176 g, 4.78
mmol), MeNH2‚HCl (355 mg, 5.26 mmol), and aqueous 37%
(CH2O)n (158 mg) in AcOH (10 mL) was heated to reflux (3 h).
The reaction mixture was cooled to room temperature and
AcOH reduced in volume nearly to dryness. To the resulting
residue was added 1 N NaOH (to pH 12-13), the reaction
mixture was stirred (1 h) and then extracted with CHCl3 (3 ×
50 mL), washed with brine (2 × 20 mL), and dried (MgSO4),
and the solvent was removed to provide crude product contain-
ing a mixture of 7 and 8. Purification by silica gel chroma-
tography (hexanes:EtOAc gradient from 20% to 90%) afforded
7 (198 mg, 16%) and 8 (387 mg, 31%). 7: 1H NMR (250 MHz,
DMSO-d6) δ 7.19 (d, J ) 9.0 Hz, 1 H), 6.89 (s, 1 H), 6.86 (m,
1 H), 6.08 (s, 1H), 5.63 (d, J ) 1.3 Hz, 1H), 3.87 (d, J ) 17.8
Hz, 1 H), 3.76 (s, 3 H), 3.74 (d, J ) 17.8 Hz, 1 H), 3.60 (s, 3 H),
1
°C; H NMR (250 M Hz, CDCl3) δ 7.16 (d, J ) 8.6 Hz, 1 H),
6.67 (dd, J ) 8.6, 2.6 Hz, 1 H), 6.6 (d, J ) 2.6 Hz, 1 H), 3.76
(s, 3 H), 3.32 (s, 1 H), 3.13 (dd, J ) 17.6, 6.9 Hz, 1 H), 2.77 (d,
J ) 17.6 Hz, 1 H), 2.69 (d, J ) 11.8 Hz, 1 H), 2.57 (dd, J )
11.8, 2.5 Hz, 1 H), 2.19 (s, 3 H), 2.06 (d, J ) 13.8 Hz, 1 H),
1.85 (dd, J ) 12.3, 2.3 Hz, 1 H), 1.69 (d, J ) 12.3 Hz, 1 H), 1.5
(s, 3 H); IR (CHCl3) 2922, 2364, 1544, 1134 cm-1; FABMS (m/
z) 257 (M + H)+. Anal. Calcd (C16H20N2O): C, 74.97; H, 7.86;
N, 10.93. Found: C, 74.68; H, 7.88; N, 10.66.
P r ep a r a t ion of Com p ou n d 7 Usin g E sch en m oser ’s
Sa lt. To a solution of 6 (12 g, 48.4 mmol) in THF (300 mL)
containing HMPA (20 mL) at -78 °C under argon was
dropwise added LDA, 2 M in THF (29 mL, 58.1 mmol), and
the reaction mixture stirred at -78 °C (1 h). To this was added
Eschenmoser’s salt (N,N-dimethylmethyleneammonium io-
dide) (17.9 g, 97 mmol) quickly in one portion, the dry ice-
acetone bath was then removed, and the reaction mixture was
allowed to come to room temperature (overnight). The reaction
mixture was quenched with 1 N HCl (70 mL), diluted with
brine (150 mL), extracted with EtOAc (2 × 200 mL), washed
with brine (2 × 100 mL), and dried (Na2SO4), and the solvent
was removed to provide crude 7. Purification by silica gel
chromatography (hexanes:EtOAc; 8:2) afforded pure 7 (6.6 g,
52%). (See also above.)
1.63 (s, 3 H); IR (film) 2953, 1733, 1661, 1615, 1505, 873 cm-1
.
8: 1H NMR (250 MHz, CDCl3)δ 7.3 (d, J ) 8.7 Hz, 1 H), 6.8
(dd, J ) 8.7, 2.6 Hz, 1 H), 6.62 (d, J ) 2.6 Hz, 1 H), 3.76 (s, 3
H), 3.67-3.49 (m, 3 H), 3.28 (m, 2 H), 2.85 (s, 3 H), 1.65 (s, 3
H); IR (film) 2987, 1715, 1655, 1029 cm-1; FABMS (m/z) 260
(M + H)+. Anal. Calcd (C15H17NO3‚1/4H2O): C, 68.31; H, 6.64;
N, 5.31. Found: C, 68.62; H, 7.04: N, 4.94.
Con ver sion of Com p ou n d 7 to Com p ou n d 8. To a
solution of 7 (102 mg, 0.39 mmol) in dioxane (1 mL) at room
(()-1-(2,4-Dim eth oxyben zyl)-1,2,3,4,5,6-h exa h yd r o-1,5-
m e t h a n o-8-m e t h oxy-3-m e t h yl-3-b e n za zocin e -2,11-d i-
on e (11). To a solution of 7 (400 mg, 1.54 mmol) in dioxane
(8 mL) at room temperature under argon was added 2,4-
dimethoxybenzylamine, prepared by the reaction of 2,4-
dimethoxybenzylamine hydrochloride (344 mg, 1.7 mmol) with
1 N NaOH (1.7 mL, 1.7 mmol). The reaction mixture was
stirred (4 h) and then diluted with brine, extracted with CHCl3
(3 × 50 mL), washed with brine (2 × 5 mL), and dried
(15) Matteson, D. S.; Kandil, A. A. J . Org. Chem. 1987, 52, 5121-
5124.
(16) Buckle, D. R.; Rockell, C. J . M. J . Chem. Soc., Perkin Trans. 1
1982, 627-630.
(17) Langolis, N.; Rojas, A. Tetrahedron 1993, 49, 77-82.
(18) Colvin, E. W.; Martin, J .; Parker, W.; Raphael, R. A.; Shroot,
B.; Doyle, M. J . Chem. Soc., Perkin Trans. 1 1972, 860-870.

Synthesis of a New Tyrosine Analogue
J . Org. Chem., Vol. 62, No. 16, 1997 5431
(Na2SO4), and the solvent was removed to provide crude 11.
This was dried under high vacuum (4 h) and then dissolved
in toluene (80 mL) containing DBU (23 mg) and stirred at
reflux (overnight). The reaction mixture was concentrated and
then purified by silica gel chromatography (hexanes:EtOAc 7:3)
to afford pure 11 (232 mg, 38%): 1H NMR (250 M Hz, CDCl3)
δ 7.34 (d, J ) 8.8 Hz, 1 H), 6.81 (dd, J ) 8.8, 6.1 Hz, 1 H), 6.7
(d, J ) 8.4 Hz, 1 H), 6.58 (d, J ) 2.5 Hz, 1 H), 6.35 (d, J ) 2.3
Hz, 1 H), 6.28 (dd, J ) 8.3, 2.5 Hz, 1 H); 4.62 (d, J ) 14.7 Hz,
1 H), 4.3 (d, J ) 14.7 Hz, 1 H), 3.77 (s, 3 H), 3.75 (s, 3 H), 3.62
(s, 3 H), 3.59-3.4 (m, 3 H), 3.2-3.0 (m, 2 H), 11.48 (s, 3 H); IR
(C24H28N2O3‚1/4H2O): C, 72.64; H, 7.19; N, 7.06. Found: C,
72.63; H, 7.39; N, 6.94.
(()-(r el-2S,3R)-1-Ca r boxym eth oxy-2-cya n o-1,2,3,4,5,6-
h exa h yd r o-1,5-m eth a n o-8-m eth oxy-3-m eth yl-3-ben za zo-
cin e (16). A mixture of 13 (140 mg) and anisole (0.5 mL) in
TFA (6 mL) was heated to 65 ( 5 °C (3 h) and then cooled to
room temperature and TFA removed under vacuum. The
resulting residue was diluted with CHCl3 (10 mL), treated with
saturated aqueous NaHCO3 (5 mL), extracted with CHCl3 (3
× 20 mL), washed with brine (2 × 5 mL), and dried (Na2SO4),
and the solvent was removed. The resulting residue was
purified by silica gel chromatography (hexanes:EtOAc 8:2) to
afford intermediate amine 15 (77.2 mg, 91%). This residue
(72.7 mg, 0.31 mmol) was reacted with methyl chloroformate
(148 mg, 1.57 mmol) in the presence of Et3N (162 mg, 1.57
mmol) in acetonitrile (6.3 mL) at 0 °C. After addition of
reagents at 0 °C, the reaction mixture was warmed to room
temperature and stirred (4 h). The reaction mixture was
quenched with saturated aqueous NaHCO3 (5 mL), extracted
with CHCl3 (3 × 20 mL), washed with brine (2 × 5 mL), and
dried (Na2SO4), and the solvent was removed to provide crude
16. Purification by silica gel chromatography (hexanes:EtOAc
8:2) afforded pure 16 (84 mg, 93%): 1H NMR (250 MHz, CDCl3)
δ 7.22 (m, 1 H), 6.69 (dd, J ) 8.7, 2.9 Hz, 1 H), 6.56 (brs, 1 H),
4.82 (brs, 0.4 H), 4.63 (brs, 0.6 H), 4.27-4.03 (m, 1 H), 3.74
(s, 3 H), 3.52 (s, 1.2 H), 3.33 (s, 1.8 H), 3.25 (m, 1H), 3.11 (brd,
J ) 16.3 Hz, 1 H), 2.78 (m, 1 H), 2.23 (m, 1 H), 2.05 (d, J )
15.1 Hz, 1 H), 1.82 (d, J ) 15.1 Hz, 1 H), 1.54 (s, 3 H); IR
(film) 2952, 1738, 1651, 1155, 931 cm-1
.
Anal. Calcd
(C23H25NO5‚1/2H2O): C, 68.32; H, 6.94; N, 3.47. Found: C,
68.26; H, 6.62; N, 3.38.
(()-1-(2,4-Dim eth oxyben zyl)-1,2,3,4,5,6-h exa h yd r o-1,5-
m eth a n o-8-m eth oxy-3-m eth yl-3-ben za zocin -2-on e (12). A
mixture of 11 (870 mg, 2.2 mmol), NH2NH2‚H2O (890 mg, 17.6
mmol), and 88% KOH (739 mg, 13.2 mmol) in diethylene glycol
(6 mL) was heated to reflux (5 h) and then cooled to room
temperature. The reaction mixture was diluted with H2O (20
mL), extracted with EtOAc (3 × 50 mL), washed with brine (2
× 5 mL), and dried (Na2SO4), and the solvent was removed to
provide crude 12. Purification by silica gel chromatography
(hexanes:EtOAc 3:7) afforded pure 12 (582 mg, 71%): 1H NMR
(250 MHz, CDCl3) δ 7.44 (d, J ) 8.6 Hz, 1 H), 6.73 (brd, J )
8.4 Hz, 1 H), 6.6 (brs, 1 H), 6.55 (d, J ) 8.4 Hz, 1 H), 6.34 (brs,
1 H), 6.23 (d, J ) 8.3 Hz, 1 H), 4.6 (d, J ) 14.8 Hz, 1 H), 4.18
(d, J ) 14.8 Hz, 1 H), 3.76 (s, 3 H), 3.73 (s, 3 H), 3.62 (s, 3 H),
3.6 (m, 1H), 3.21 (dd, J ) 17.6, 6.5 Hz, 1 H), 3.06 (d, J ) 12.5
Hz, 1 H), 2.66 (d, J ) 17.6 Hz, 1 H), 2.49 (m, 1 H), 2.11 (d, J
) 13.4 Hz, 1 H), 1.98 (d, J ) 13.4 Hz, 1 H), 1.64 (s, 3 H); IR
(film), 2931, 1675, 1208, 935 cm-1; FABMS (m/z) 382 (M +
H)+. Anal. Calcd (C23H27NO4): C, 72.42; H, 7.13; N, 3.67.
Found: C, 72.48; H, 7.21; N, 3.72.
(()-(r el -2S ,3R )-2-C y a n o -1-(2,4-d im e t h o x y b e n zy l)-
1,2,3,4,5,6-h exa h yd r o-1,5-m eth a n o-8-m eth oxy-3-m eth yl-
3-ben za zocin e (13). To a solution of 12 (115 mg, 0.3 mmol)
in THF (1 mL) at -78 °C under argon was added dropwise
DIBAL-H, 1 M in hexane (0.45 mL, 0.45 mmol), and the
reaction mixture was stirred at -78 °C (2 h). The reaction
mixture was quenched at -78 °C with 2 N NaOH (10 mL) and
then allowed to warm to room temperature. The mixture was
extracted with CHCl3 (3 × 30 mL), washed with brine (10 mL),
and dried (Na2SO4), and the solvent was removed to provide
crude product, which was dried under high vacuum (3 h). The
residue was dissolved in CH2Cl2 (6 mL), and to this solution
was added at room temperature under argon, TMSCN (60 mg,
11.6 mmol) followed by ZnCl2, 1 M in CH2Cl2 (0.33 mL, 0.33
mmol). The reaction mixture was stirred (1.5 h) and then
quenched with saturated aqueous NaHCO3 (10 mL), extracted
with CHCl3 (3 × 20 mL), washed with brine (2 × 50 mL), and
dried (Na2SO4), and the solvent was removed. Purification by
silica gel chromatography afforded pure 13 as a white crystal-
line solid (92 mg, 78%): mp 98 °C; 1H NMR (250 M Hz, CDCl3)
δ 7.04 (d, J ) 9.34 Hz, 1 H), 6.67-6.65 (m, 2 H), 6.31-6.27
(m, 2 H), 6.14 (dd, J ) 8.4, 2.3 Hz, 1 H), 3.79 (s, 3 H), 3.73 (s,
3 H), 3.55 (s, 3 H), 3.5 (d, J ) 17.6 Hz, 1 H), 3.44 (d, J ) 17.6
Hz, 1 H), 3.26 (brs, 1 H), 3.12 (dd, J ) 17.4, 6.7 Hz, 1 H), 2.85-
2.7 (m, 3 H), 2.19 (m, 1 H), 1.93 (dd, J ) 13.1, 2.1 Hz, 1 H),
1.75 (brd, J ) 13.1 Hz, 1 H), 1.45 (s, 3 H); IR (CHCl3) 2920,
2218, 1612, 933 cm-1; FABMS (m/z) 392 (M + H)+. Anal. Calcd
(CHCl3) 2923, 1684, 2200 (weak), 1216 cm-1
. Anal. Calcd
(C17H20N2O3): C, 67.98; H, 6.71; N, 9.33. Found: C, 67.72; H,
6.90; N, 9.05.
(()-(r el-2S,3R)-2-Ca r b oxy-1,2,3,4,5,6-h exa h yd r o-8-h y-
d r oxy-1,5- m eth a n o-3-m eth yl-3-ben za zocin e (2). A sus-
pension of compound 16 (51 mg) in 6 N HCl (6 mL) was heated
to reflux (3 days). The reaction mixture was cooled to room
temperature, and the main portion of 6 N HCl was removed
under vacuum. The resulting solid was treated with propylene
oxide (1 mL) in EtOH (3 mL) and then taken to dryness. The
1
resulting residue was shown by H NMR to be relatively pure
2. Further purification by HPLC (solvent A ) 0.05% TFA in
H2O, solvent B ) 0.5% TFA in acetonitrile; linear gradient 0%
B to 100% B over 30 min) provided target 2 as a solid (38 mg,
88%): mp 64 °C; 1H NMR (250 MHz, D2O) δ 7.39 (d, J ) 8.67
Hz, 1 H), 6.83 (dd, J ) 8.67, 2.4 Hz, 1 H), 6.72 (d, J ) 2.4 Hz,
1 H), 4.0 (dd, J ) 12.7, 4 Hz, 1 H), 3.83 (brs, 1 H), 3.27-3.18
(m, 2 H), 2.81 (d, J ) 18 Hz, 1 H), 2.5 (m, 1 H), 2.05 (d, J )
13.6 Hz, 1 H), 1.76 (d, J ) 13.6 Hz, 1 H), 1.51 (s, 3 H);
IR 3700-2400, 2960, 1716, 1501, 1024 cm-1; FABMS (m/z)
360 (M + TFA-)-, 246 (M - H)-. Anal. Calcd (C14H17NO3‚
CF3CO2H‚9/4H2O): C, 47.82; H, 5.6; N, 3.49. Found: C, 47.79;
H, 5.77; N, 3.42.
Ack n ow led gm en t. Appreciation is expressed to Dr.
Clifford George of the Naval Research Laboratory,
Washington, DC, for X-ray crystallographic analysis and
to Ms. Pamela Russ and Dr. J ames Kelley of the LMC
for mass spectral analysis.
J O9700787