Journal of Medicinal Chemistry
Article
immobilized on Wang resin (14′) was synthesized according to
procedure G2 using resin 5′. For 15′ to 22′, see Supporting Information.
N-(9-Fluorenylmethoxycarbonyl)-O-(c-alkyl or c-aryl-alkyl
chain)-L-tyrosine Immobilized on Wang Resin (23′ to 31′).
General procedure G3: To the resin 14′-22′ (loadings not calculated,
estimated at 4.5 mmol), in suspension in DCM (90 mL), was added 3.14
mL of diisopropylethylamine (4 equiv, 18 mmol). The mixture was
stirred for 15 min. A 3.5 g amount of Fmoc-Cl (3 equiv, 13.5 mmol), in
solution in 30 mL of DCM, was added to this suspension and the
reaction continued for 24 h at rt. The resin was filtered, rinsed with
DCM (3 × 100 mL), and dried in vacuo. N-(9-Fluorenylmethox-
ycarbonyl)-O-(cyclohexylmethyl)-L-tyrosine immobilized on Wang
resin (23′) was synthesized according to procedure G3 using resin
14′. For 24′ to 31′, see Supporting Information.
NMR (CDCl3) δ 1.52−1.93 (m, 4H), 3.32 (t, J = 6.8 Hz, 1H), 3.42 (t, J =
6.8 Hz, 1H), 3.55 (d, J = 5.4 Hz, 2H), 3.86−3.96 (m, 1H), 5.05 (s, 2H),
7.20−7.29 (m, 5H); 13C NMR (CDCl3) δ 24.53, 29.01, 47.82, 61.10,
67.00, 67.72, 128.43, 128.97, 129.04, 137.06, 157.48.
2-((2-((tert-Butyldimethylsilyl)oxy)ethyl)thio)ethanol (50′). A
5.8 mL (57.6 mmol) amount of 2,2′-thiodiethanol (49′) was dissolved
in dry THF containing 3.2 g (63.4 mmol) of NaH (60% in oil) and
stirred for 1.5 h under inert atmosphere. The solution was cooled to 0
°C, and 8.6 g (57.6 mmol) of tert-butyldimethylsilyl chloride was added
slowly. The mixture was stirred overnight at rt. A 10% K2CO3 solution
was then added, THF was evaporated, and diethyl ether was added and
extracted with water and brine. The organic phase was dried over
Na2SO4, and the solvent was evaporated under reduced pressure.
Purification by column chromatography on silica gel (eluted with
hexane/AcOEt: 8/2) afforded 8.1 g of 50′, as an almost colorless oil
(59%). 1H NMR (CDCl3) δ 0.86 (s, 6H), 0.91 (s, 9H), 2.68 (t, J = 6.5
Hz, 2H), 2.76 (t, J = 6.0 Hz, 2H), 2.88 (br s, 1H), 3.74 (t, J = 6.0 Hz, 2H),
3.79 (t, J = 6.75 Hz, 2H); 13C NMR (CDCl3) δ −5.3, 18.3, 25.9, 34.2,
35.8, 60.9, 63.4.
Benzyl 2-(((Benzyloxy)carbonyl)amino)-3-(4-(2-((2-((tert-
butyldimethylsilyl)oxy)ethyl)thio)ethoxy)phenyl)propanoate
(51′). A 4.1 g (17.4 mmol) amount of 50′ was dissolved in toluene and
cooled to 0 °C. A 8.8 g (1.2 equiv) amount of Z-Tyr-OBn dissolved in 10
mL of dry DMF was added together with 5.7 g (1.2 equiv) of PPh3. After
dissolution, DEAD (1.2 equiv) was added dropwise. The reaction was
then stirred overnight at rt. Sodium phosphate buffer (0.5 M, pH 7) was
added to the mixture, which was then extracted with AcOEt. The organic
phase was washed with a saturated solution of NH4Cl, water, and brine
and dried over Na2SO4, and the solvent was evaporated under reduced
pressure. Purification by column chromatography on silica gel (eluted
with hexane/AcOEt: 9/1 to 85/15) afforded 10.45 g of 51′ as a colorless
oil (96%). 1H NMR (CDCl3) δ 0.08 (s, 6H), 0.9 (s, 9H), 2.74 (t, J = 6.75
Hz, 2H), 2.92 (t, J = 6.75 Hz, 2H), 3.03 (d, J = 5.75 Hz, 2H), 3.81 (t, J =
7.0 Hz, 2H), 4.06 (t, J = 7.0 Hz, 2H), 4.65 (m, 1H), 5.11 (m, 4H), 5.27
(d, J = 8.25 Hz, 1H), 6.71 (d, J = 8.5 Hz, 2H), 6.89 (d, J = 8.5 Hz, 2H),
7.30 (m, 10H); 13C NMR (CDCl3) δ −5.2, 18.3, 25.9, 31.4, 34.9, 37.2,
54.9, 63.4, 66.9, 67.2, 67.7, 114.6, 127.7, 128.1, 128.2, 128.4, 128.5,
130.3, 135.1, 136.2, 155.6, 157.6, 171.4.
N-(9-Fluorenylmethoxycarbonyl)-O-(c-alkyl or c-aryl-alkyl
chain)-L-tyrosine (32′ to 40′). General procedure G4 for resin
cleavage: The resin (23′−31′) was treated with 100 mL of TFA/DCM:
3/7 for 1 h at rt. The mixture was filtered, and the obtained organic layer
was washed with H2O (2 × 50 mL), dried over MgSO4, and evaporated.
The crude residue was applied to silica gel flash chromatography with
DCM and DCM/MeOH: 97/3 (flash chromatography condition 1:
FC1) or DCM and DCM/AcOH: 99/1 (flash chromatography
condition 2: FC2) as eluents to give compound 32′ to 40′ with yields
between 26% and 63%.
N-(9-Fluorenylmethoxycarbonyl)-O-(cyclohexylmethyl)-L-ty-
rosine (32′). Procedure G4 was applied to 23′, and the crude residue
was purified according to FC2 to yield 1.32 g of 32′ (59%) as a white
1
solid: Rf (DCM/AcOH: 99/1) = 0.47; mp 136−137 °C; H NMR
(CDCl3) δ 0.96−1.10 and 1.14−1.37 (2m, 6H), 1.63−1.91 (m, 5H),
3.11 (ddt, J = 14.0, 16.6, 5.8 Hz, 2H), 3.70 (d, J = 6.2 Hz, 2H), 4.21 (t, J =
7.1 Hz, 1H), 4.37 (dd, J = 9.8, 6.6 Hz, 1H), 4.45 (dd, J = 10.5, 7.1 Hz,
1H), 4.67 (dt, J = 6.0, 5.9 Hz, 1H), 5.17 (d, J = 8.1 Hz, 1H), 6.81 (d, J =
8.1 Hz, 2H), 7.04 (d, J = 8.1 Hz, 2H), 7.31 (t, J = 7.4 Hz, 2H), 7.41 (t, J =
7.4 Hz, 2H), 7.55 (t, J = 6.2 Hz, 2H), 7.76 (d, J = 7.3 Hz, 2H); 13C NMR
(CDCl3) δ 25.79, 26.50, 30.30, 36.38, 37.66, 47.10, 54.57, 66.99, 73.43,
114.63, 119.98, 125.03, 127.05, 127.72, 130.32, 141.26, 143.76, 155.72,
158.51, 175.78; ES/MS for C31H33NO5 (negative ionization):
Molecular wt calcd: 499.2, found: 499.1; tR (HPLC-A): 5.11 (94%).
For compounds 33′ to 40′, see Supporting Information.
2-Amino-3-(4-(2-((2-((tert-butyldimethylsilyl)oxy)ethyl)thio)-
ethoxy)phenyl)propanoic Acid (52′). A 10.45 g (16.8 mmol)
amount of 51′ was dissolved in 20 mL of MeOH and reduced overnight
with palladium black under 3.4 bar of H2. The slurry was filtered. The
catalyst was washed five times with MeOH, and the filtrate was
evaporated, yielding 6.62 g of compound 52′ (quantitative). ES/MS for
C19H33NO2SSi (positive ionization): Molecular wt calcd: 399.1, found:
399.1
4-Benzyloxy-1-butanol (44′). To sodium hydride (4.45 g, 111.2
mmol, 60% in mineral oil) in suspension in dry THF (200 mL), under
argon, cooled to 0 °C, was slowly added 50 g of 1,4-butanediol (41′) (5
equiv, 555 mmol). The reaction was stirred for 1 h. Benzyl bromide (13
mL, 111.2 mmol), in 200 mL of dry THF, was added dropwise, and the
reaction mixture was stirred an additional 5 h. After addition of 300 mL
of H2O, the solution was extracted twice with Et2O. The organic layer
was washed with water and brine and dried over MgSO4, and the solvent
was evaporated under reduced pressure. After purification by column
chromatography on silica gel (eluted with DCM and DCM/MeOH: 97/
3), 13.2 g (66%) of 44′ was obtained as a slightly yellow oil: Rf (DCM/
MeOH: 97/3) = 0.39; 1H NMR (CDCl3) δ 1.57−1.71 (m, 4H), 3.48 (t,
J = 6.1 Hz, 2H), 3.53 (s, 1H), 3.56 (t, J = 6.3 Hz, 2H), 4.49 (s, 2H), 7.24−
7.30 (m, 1H), 7.31−7.36 (m, 4H); 13C NMR (CDCl3) δ 26.33, 29.58,
62.10, 70.24, 72.86, 127.67, 128.35, 138.19. For compounds 45′ and 46′,
see Supporting Information.
2-((((9H-Fluoren-9-yl)methoxy)carbonyl)amino)-3-(4-(2-((2-
((tert-butyldimethylsilyl)oxy)ethyl)thio)ethoxy)phenyl)-
propanoic Acid (53′). Compound 52′, dissolved in 50 mL of DMF,
was added to 5.9 g (17.5 mmol) of Fmoc N-hydroxysuccinimide ester in
a mixture of 750 mL of CH3CN, 370 mL of H2O, and 5.3 g of NaHCO3
and stirred overnight at rt. The solution was concentrated and extracted
with AcOEt. The organic layer was washed with 10% citric acid, a
saturated solution of NH4Cl, water, and brine and dried over Na2SO4,
and the solvent was evaporated under reduced pressure. Purification by
column chromatography on silica gel (eluted with DCM/AcOH: 99.5/
0.5 to DCM/MeOH/AcOH: 95/5/0.5) afforded 8 g of 53′ as a colorless
oil (78%). 1H NMR (CDCl3) δ 0.09 (s, 6H), 0.9 (s, 9H), 2.74 (t, J = 6.75
Hz, 2H), 2.92 (t, J = 6.75 Hz, 2H), 3.09 (m, 2H), 3.81 (t, J = 6.75 Hz,
2H), 4.08 (t, J = 6.75 Hz, 2H), 4.19 (t, J = 6.85 Hz, 1H), 4.41 (m, 2H),
4.65 (m, 1H), 5.28 (t, J = 10.5 Hz, 1H), 6.80 (d, J = 8.5 Hz, 2H), 7.05 (d,
J = 8.5 Hz, 2H), 7.16−7.43 (m, 4H), 7.53−7.58 (m, 2H), 7.76 (d, J = 7.5
Hz, 2H), 8.94 (br s, 1H); 13C NMR (CDCl3) δ −5.2, 18.4, 26.0, 31.5,
34.9, 36.9, 47.2, 54.8, 63.5, 67.1, 67.8, 114.8, 120.1, 125.2, 127.2, 127.8,
128.2, 130.5, 141.4, 143.8, 155.9, 157.8, 176.2. ES/MS for
C34H43NO6SSi (positive ionization): Molecular wt calcd: 622.2,
found: 622.2
N-Cbz-(S)-(+)-2-Pyrrolidinemethanol (48′). To 9 g of (−)-Cbz-L-
proline (47′) (36.1 mmol) in DME (55 mL) was added 4-
methylmorpholine (1.1 equiv, 39.7 mmol). The reaction mixture was
cooled to −15 °C, and isobutyl chloroformate (1.3 equiv, 46.9 mmol)
was added slowly. After 20 min of stirring at this temperature, the white
precipitate was quickly filtered off and washed with DME. To the
obtained solution, cooled again to −15 °C, was added sodium
borohydride (1.5 equiv, 54.2 mmol), in 23 mL of water, and the
reaction mixture stirred during 1 h, allowing it to warm to rt. After
addition of 65 mL of water and evaporation of DME under reduced
pressure, the solution was extracted twice with AcOEt. The organic layer
was washed with 1 N aqueous KHSO4 solution, 1 N aqueous NaHCO3
solution, and finally brine. It was dried over MgSO4, and the solvent was
evaporated under reduced pressure. A 7.4 g (87%) amount of 48′ was
2-((((9H-Fluoren-9-yl)methoxy)carbonyl)amino)-3-(4-(2-((2-
((tert-butyldimethylsilyl)oxy)ethylsulfinyl)ethoxy)phenyl)-
propanoic Acid (54′). A 1.24 g (2 mmol) amount of 53′ was dissolved
1
obtained as a colorless thick oil: Rf (DCM/MeOH: 95/5) = 0.55; H
K
dx.doi.org/10.1021/jm4002988 | J. Med. Chem. XXXX, XXX, XXX−XXX