3.14 (dd, J ) 14.8, 4.8 Hz, 1H), 3.72 (dd, J ) 8.0, 4.8 Hz, 1H),
6.82 (d, J ) 8.4 Hz, 1H), 7.35 (dd, J ) 8.4, 2.0 Hz, 1H), 7.71 (d,
J ) 2.0 Hz, 1H); MS (FAB) m/z 246.0 (Na salt), 223.9 [M + H]+,
207.0, 178.0, 158.9, 115.0. These data correspond to those
previously reported for this compound.20,21
Exp er im en ta l Section
N-ter t-Bu t yloxyca r b on yl-3-t r im et h ylsilylet h yn yl-L-t y-
r osin e Meth yl Ester . N-tert-Butyloxycarbonyl-3-iodo-L-tyrosine
methyl ester (1.0 g, 2.4 mmol), Cl2(Ph3P)2Pd (170 mg, 0.24
mmol), and CuI (20 mg, 0.11 mmol) were added to an oven-dried
flask containing a magnetic stir bar and fitted with a rubber
septum and nitrogen inlet. The solids were dried under high
vacuum for 30 min with constant stirring under ambient
temperature. Freshly distilled anhyd Et3N (50 mL) was added
via an oven-dried nitrogen-flushed syringe and the resulting
yellow solution was stirred for 5 min. Ethynyltrimethylsilane
(490 mg, 5.0 mmol, 710 µL) was added via an oven-dried
nitrogen-flushed syringe causing an immediate precipitation of
a fine white solid from a pale green solution. Within 10 min,
the reaction mixture became a thick slurry and was vigorously
stirred for 4 h at ambient temperature. The mixture was fil-
tered and the solids were washed with ether. The filtrate and
ether wash were combined and evaporated under reduced
pressure. The resulting residue was purified by silica gel
chromatography (hexanes:ethyl acetate, 70:30 v/v) to yield
N-tert-butyloxycarbonyl-3-trimethylsilylethynyl-L-tyrosine meth-
yl ester (310 mg, 96%) as a yellow oil. IR (thin film) 3500, 3400,
2150, 1750, 1700, 1250 cm-1; 1H NMR (400 MHz, CD3OD) δ 0.25
(s, 9H), 1.37 (s, 9H), 2.74 (dd, J ) 14.0, 8.8 Hz, 1H), 2.95 (dd, J
) 14.0, 5.4 Hz, 1H), 3.67 (s, 3H), 4.25 (dd, J ) 8.8, 5.4 Hz, 1H),
6.72 (d, J ) 8.3 Hz, 1H), 6.99 (dd, J ) 8.3, 2.0 Hz, 1H), 7.14 (d,
J ) 2.0 Hz, 1H); 13C NMR (100 MHz, CD3OD) δ 0.01, 28.4, 32.1,
37.3, 51.8, 54.3, 100.2, 100.9, 109.7, 115.0, 127.7, 131.6, 132.8,
154.6, 156.8, 171.9; MS (EI) m/z 391.2 (M+), 335.1, 318.1, 274.1,
259.0, 201.7.
3-Iod o-L-tyr osin a to-bicyclon on ylbor on (5). 3-Iodo-L-ty-
rosine (1) (1.00 g, 3.26 mmol) was suspended in anhyd THF (5
mL) and vigorously stirred for 5 min. A solution of 9-BBN in
THF (0.5 M, 9.0 mL) was added via syringe and the resulting
suspension was stirred under N2 at ambient temperature until
all materials had dissolved (12 h).11 The product was precipitated
by addition of cyclohexane, filtered, and recrystallized from
CH3CN-water to yield 3-iodo-L-tyrosinato-bicyclononylboron (5)
(1.2 g, 86%) as a white powder; mp (browned from 235 to 240
°C) 241 °C dec; IR (thin film) 3420, 2917, 2840, 2530, 2362, 1684,
1419, 1363, 1288, 1213 cm-1; 1H NMR (400 MHz, CD3OD) δ 0.23
(s, 1H), 0.54 (s, 1H), 1.79 (m, 12H), 2.95 (dd, J ) 14.7, 7.8 Hz,
1H), 3.15 (dd, J ) 14.7, 5.0 Hz, 1H), 3.90 (dd, J ) 7.8, 5.0 Hz,
1H), 4.62 (s, 1H), 6.80 (d, J ) 8.3 Hz, 1H), 7.15 (dd, J ) 8.3, 2.0
Hz, 1H), 7.70 (d, J ) 2.0 Hz, 1H); 13C NMR (100 MHz, CD3OD)
δ 23.1, 23.7, 25.1, 25.6, 32.3, 32.5, 32.6, 32.7, 36.7, 37.0, 57.5,
116.0, 129.8, 131.5, 141.0, 157.4, 173.7, 176.4; MS (FAB) m/z
428 [M + H]+, 262, 85; HRMS (FAB) calcd for C17H24NO3BI [M
+ H]+ 428.0894, found 428.0883.
3-Tr im et h ylsilylet h yn yl-L-t yr osin a t o-b icyclon on ylb o-
r on (6). 3-Iodo-L-tyrosinato-bicyclononylboron (5) (210 mg, 490
µmol), Cl2(Ph3P)2Pd (8.4 mg, 12 µmol), and CuI (3.2 mg, 17 µmol)
were added to an oven-dried flask containing a magnetic stir
bar and fitted with a rubber septum and nitrogen inlet. The
solids were dried under high vacuum for 30 min with constant
stirring. Freshly distilled anhyd THF (45 mL) and Et3N (58 mg,
570 µmol, 80 µL) were added via an oven-dried nitrogen-flushed
syringe and the resulting yellow solution was stirred for 5 min.
Ethynyltrimethylsilane (98 mg, 1.0 mmol, 150 mL) was added
via an oven-dried nitrogen-flushed syringe, and the reaction
mixture was vigorously stirred for 4 h under ambient conditions.
The mixture was filtered and the solids were washed with THF.
The filtrate was purified by silica gel chromatography (hexanes:
ethyl acetate 50:50 v/v) to yield 3-trimethylsilylethynyl-L-tyro-
sinato-bicyclononylboron (6) (194 mg, 99%); mp 108-122 °C. IR
N-ter t-Bu tyloxycar bon yl-3-eth yn yl-L-tyr osin e Meth yl Es-
ter . Solid KF (45 mg, 0.77 mmol) was added to a solution of
N-tert-butyloxycarbonyl-3-trimethylsilylethynyl-L-tyrosine meth-
yl ester (280 mg, 0.71 mmol) in DMF (reagent grade, 15 mL)
and stirred at ambient temperature for 4 h. The solution was
diluted with water (100 mL) and extracted with diethyl ether
(3 × 50 mL). The combined ether layers were washed with water
(3 × 50 mL) and saturated aqueous NaCl (50 mL), dried over
anh MgSO4, filtered, and evaporated under reduced pressure
to yield N-tert-butyloxycarbonyl-3-ethynyl-L-tyrosine methyl
ester (180 mg, 79%) as a pale yellow oil IR (thin film) 3287, 2231,
(thin film) 3504, 2843, 2690, 2658, 2148, 1708, 1492 cm-1 1H
;
NMR (400 MHz, CD3OD) δ 0.14 (s, 9H), 0.23 (s, 1H), 0.48 (s,
1H), 1.79 (m, 12H), 2.98 (dd, J ) 14.7, 8.0 Hz, 1H), 3.12 (dd, J
) 14.7, 4.9 Hz, 1H), 3.86 (dd, J ) 8.0, 4.9 Hz, 1H), 5.12 (br s,
1H), 6.33 (br s, 1H), 6.75 (d, J ) 8.4 Hz, 1H), 7.8 (dd, J )
8.4, 2.1 Hz, 1H), 7.25 (d, J ) 2.1 Hz, 1H); 13C NMR (100
MHz, CD3OD) δ -1.2, 35.0, 56.3, 97.4, 101.1, 110.6, 115.4, 126.8,
130.8, 134.0, 157.5, 171.5; MS (FAB) m/z 398.3 [M + H]+, 232.2,
203.2.
3-Eth yn yl-L-tyr osin a to-bicyclon on ylbor on (7). 3-Trim-
ethylsilylethynyl-L-tyrosinato-bicyclononylboron (6) (194 mg,
0.52 mmol) was dissolved in DMF (10 mL), treated with KF (28
mg, 0.47 mmol), and stirred at ambient temperature for 2 h.
The reaction was quenched with 1 M KHSO4 (2 mL), which led
to precipitation of the product (7) (120 mg, 78%) as a white solid.
1H NMR (400 MHz, CD3OD) δ 0.24 (s, 1H), 0.52 (s, 1H), 1.58
(m, 12H), 2.95 (dd, J ) 14.8, 7.6 Hz, 1H), 3.14 (dd, J ) 14.8, 5.2
Hz, 1H), 3.91 (dd, J ) 7.6, 5.2 Hz, 1H), 5.17 (br s, 1H), 6.43 (br
s, 1H), 6.80 (d, J ) 8.4 Hz), 7.14 (dd, J ) 8.4, 2.0 Hz, 1H), 7.31
(d, J ) 2.0 Hz, 1H); 13C NMR (100 MHz, CD3OD) δ 25.1, 25.6,
31.7, 32.2, 32.5, 32.6, 36.4, 37.0, 57.8, 80.7, 82.9, 111.2, 116.9,
128.3, 132.3, 135.8, 176.6.
1
2106, 1750, 1700 cm-1; H NMR (400 MHz, CD3OD) δ 0.20 (s,
9H), 1.37 (s, 9H), 2.75 (dd, J ) 13.6, 8.8 Hz, 1H), 2.96 (dd, J )
13.6, 5.6 Hz, 1H), 4.25 (dd, J ) 8.8, 5.6 Hz, 1H), 6.72 (d, J ) 8.4
Hz, 1H), 6.99 (dd, J ) 8.4, 2.0 Hz, 1H), 7.12 (d, J ) 2.0 Hz, 1H);
13C NMR (100 MHz, CD3OD) δ 28.4, 32.1, 37.3, 51.8, 79.2, 100.2,
109.7, 115.0, 127.7, 131.6, 132.6, 154.6, 156.8, 171.9.
N-ter t-Bu tyloxyca r bon yl-3-eth yn yl-L-tyr osin e (3). A solu-
tion of R-chymotrypsin (8.0 mg, 410 units, bovine pancreas) in
aq NH4OAc (2 mL, 0.5 M, pH 6.0) was added to a solution of
N-tert-butyloxycarbonyl-3-ethynyl-L-tyrosine methyl ester (180
mg, 0.56 mmol) in DMF (2 mL) with stirring at ambient
temperature for 12 h.19 The solution was diluted with water (10
mL) and extracted with EtOAc (3 × 10 mL). The combined
EtOAc layers were washed with water (3 × 10 mL) and
saturated aqueous NaCl (10 mL), dried over anhyd MgSO4,
filtered, and evaporated under reduced pressure to yield N-tert-
butyloxycarbonyl-3-ethynyltyrosine (3) (100 mg, 60%) as an
amorphous solid. IR (thin film) 3285, 2977, 2932, 2150, 1670,
1595, 1508, 1418 cm-1;1H NMR (400 MHz, CD3OD) δ 1.39 (s,
9H), 2.80 (m, 1H), 3.03 (m, 1H), 3.52 (s, 1H), 4.10 (m, 1H), 6.70
(d, J ) 8.4 Hz, 1H), 7.06 (dd, J ) 8.4, 2.0 Hz, 1H), 7.19 (d, J )
2.0 Hz, 1H).
3-Eth yn yl-L-tyr osin e (8). 3-Ethynyl-L-tyrosinato-bicyclononyl-
boron (7) (120 mg, 0.40 mmol) was dissolved in a minimum
amount of MeOH (100 µL), diluted with CHCl3 (5 mL), and
stirred at ambient temperature for 3 h. The precipitated product
was filtered, dissolved in 0.1 M aq NH3, and loaded onto Dowex-1
anion-exchange resin (1 mL). The resin was then washed with
water and the product was eluted with 1.0 M AcOH and
lyophilized to yield 3-ethynyl-L-tyrosine (8) (49 mg, 62%) as a
3-Acetyl-L-tyr osin e (4). A solution of N-tert-butyloxycarbo-
nyl-3-ethynyl-L-tyrosine (5.0 mg, 16 mmol) in 10% TFA in
CH2Cl2 (1.0 mL) was stirred at ambient temperature for 1 h.
The mixture was diluted with water (5 mL) and extracted with
CH2Cl2 (3 × 5 mL), and the aqueous layer was evaporated to
1
yield crude 3-acetyl-L-tyrosine (4) (2.9 mg, 79%). H NMR (400
MHz, CD3OD) δ 2.55 (s, 3H), 2.96 (dd, J ) 14.8, 8.0 Hz, 1H),
(20) Boger, D. L.; Yohannes, D. J . Org. Chem. 1987, 52, 5283-5286.
(21) Ranganathan, S.; Tamilarasu, N. Tetrahedron Lett. 1994, 35,
447-450.
(19) Walton, E.; Rodin, J . O.; Stammer, C. H. J . Org. Chem. 1962,
27, 2255-2257.
J . Org. Chem, Vol. 68, No. 4, 2003 1565