Synthesis of L-2,3-trans-3,4-cis-Dihydroxyproline
J . Org. Chem., Vol. 64, No. 5, 1999 1557
The mixture was filtered through a plug of alumina in a
Pasteur pipet, washing well with absolute ethanol. The filtrate
and washings were concentrated. The residue was purified by
flash column chromatography, eluting with ethyl acetate, to
recover compound 6 (148 mg, 53%) and afford compound 7 as
a colorless oil (130 mg, 47%): TLC Rf ) 0.27 (ethyl acetate);
layer was dried (MgSO4) and concentrated. The colorless
residue was purified by flash column chromatography, eluting
with 2:1 hexanes-ethyl acetate, to give compound 10 as a
colorless oil (60 mg, 97%): TLC Rf ) 0.49 (2:1 hexanes-ethyl
1
acetate); [R]20 ) -22.8° (c 0.85, CHCl3); H NMR (200 MHz,
D
CDCl3) δ 1.34 (s, 3H), 1.49 (s, 3H), 3.58-3.74 (m, 1H), 3.98
(dd, J ) 12.4, 7.1 Hz, 1H), 4.20-4.48 (m, 2H), 4.59-4.61 (m,
2H), 4.64-4.73 (m, 1H), 4.76-4.80 (m, 2H), 5.22-5.38 (m, 2H),
5.78-6.19 (m, 1H), 7.29-7.43 (m, 4H), 7.53-7.62 (m, 2H),
7.62-7.77 (m, 2H); 13C NMR (50 MHz, CDCl3) δ 24.8, 26.8,
47.0, 52.2, 52.5, 66.1, 67.2, 78.4, 79.4, 82.3, 83.4, 112.6, 118.9,
119.9, 124.9, 125.1, 127.0, 127.6, 141.2, 155.1, 169.6; HRMS
(DCI) calcd for C26H28NO6 (M + H)+ 450.19166, obsd 450.19152.
F m oc-Hyp (OtBu )-OAll (10). Cesium carbonate (99 mg, 0.3
mmol, 0.5 equiv) was added to a suspension of Fmoc-Hyp(Ot-
Bu)-OH (250 mg, 0.6 mmol, 1.0 equiv) in dry methanol (2.5
mL). The resulting homogeneous solution was stirred at room
temperature under N2 for 2 h. The mixture was concentrated.
The residue was dissolved in DMF (2.5 mL) and treated with
allyl bromide (64 µL, 0.07 mmol, 1.2 equiv). The mixture was
stirred at room temperature under N2 for 15 h. The suspension
was partitioned between ethyl acetate (30 mL) and water (30
mL). The organic layer was washed with brine (30 mL), dried
over MgSO4, filtered, and concentrated. The residue was
purified by flash column chromatography, eluting with 2:1
hexanes-ethyl acetate, to give Fmoc-Hyp(OtBu)-OAll (10) as
[R]20 ) -34.3 o (c 1.35, CHCl3); 1H NMR (400 MHz, CDCl3) δ
D
1.25 (s, 3H), 1.34 (s, 3H), 3.29-3.41 (br m, 2H), 3.49-3.60 (br
m, 2H), 3.90 (d, J ) 12.9 Hz, 1H), 4.05 (d, J ) 8.6 Hz, 1H),
4.25 (t, J ) 6.8 Hz, 1H), 4.36 (dd, J ) 10.6, 7.2 Hz, 1H), 4.52
(dd, J ) 10.6, 6.6 Hz, 1H), 4.74 (t, J ) 5.1 Hz, 1H), 4.86 (d, J
) 5.8 Hz, 1H), 7.29-7.39 (m, 4H), 7.41-7.59 (m, 2H), 7.75 (d,
J ) 7.5 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 24.7, 26.8, 47.1,
52.1, 62.7, 65.1, 67.7, 70.5, 79.1, 81.8, 118.8, 119.9, 124.9, 125.0,
127.1, 127.7, 141.2, 141.3, 143.4, 143.7, 155.9; HRMS (CI) calcd
for C24H28NO6 (M + H)+ 426.1916, obsd 426.1910. Anal. Calcd
for C24H27NO6: C 67.75; H 6.40; N 3.29. Found: C 67.27; H
6.53; N 3.24.
L-2,3-tr a n s-3,4-cis-N-F lu or en ylm et h oxyca r b on yl-3,4-
d ih yd r oxy-3,4-O-isop r op ylid en e-p r olin e (9). Diol 7 (122
mg, 0.28 mmol, 1 equiv) was dissolved in ethanol-water (5:2
ratio, 4.5 mL). Sodium periodate (166 mg, 0.78 mmol, 2.7
equiv) was added, resulting in a cloudy suspension which was
stirred at room temperature for 15 min. The mixture was
filtered and concentrated. The crude aldehyde was dissolved
in tert-butyl alcohol (4.5 mL) and cyclohexene (0.3 mL). A
solution of sodium chlorite (313 mg, 2.87 mmol, 10 equiv) and
potassium dihydrogen phosphate (390 mg, 2.87 mmol, 10
equiv) in water (4 mL) was added dropwise to the aldehyde
mixture. The resulting biphasic reaction mixture was stirred
at room temperature under an atmosphere of N2 for 12 h. The
reaction mixture was concentrated, and the residue was
partitioned between ethyl acetate (50 mL) and water (10 mL).
The organic layer was dried (MgSO4) and concentrated. The
residue was purified by flash column chromatography, eluting
with 9:1 CH2Cl2-MeOH. This afforded L-2,3-trans-3,4-cis-N-
fluorenylmethoxycarbonyl-3,4-dihydroxy-3,4-O-isopropylidene-
proline (9) as a colorless solid (96 mg, 82%): TLC Rf ) 0.21
a colorless oil (252 mg, 92%): TLC Rf ) 0.33 (2:1 hexanes-
1
ethyl acetate); [R]20 ) -27.4° (c 0.90, CHCl3); H NMR (200
D
MHz, DMSO-d6) δ 1.11 (s, 9H), 1.93-2.19 (m, 2H), 3.12-3.34
(m, 1H), 3.53 (dd, J ) 10.6, 5.5 Hz, 1H), 4.15-4.36 (m, 5H),
4.51-4.60 (m, 2H), 5.16-5.36 (m 2H), 5.78-5.99 (m, 1H),
7.28-7.45 (m, 4H), 7.57-7.65 (m, 1H), 7.80-7.89 (m, 3H); 13
C
NMR (50 MHz, DMSO-d6) (mixture of rotamers) δ 27.9, 37.3
& 38.2, 46.4, 53.4 & 53.8, 57.1 & 57.5, 64.7 & 65.0, 66.6 &
66.7, 68.0, 68.9, 73.6, 117.6 & 117.9, 120.0, 124.9, 127.0, 127.6,
132.2, 140.7, 143.4 & 143.7, 153.5 & 153.9, 171.5; HRMS (CI)
calcd for C27H32NO5 (M + H)+ 450.22806, obsd 450.22802.
Dip ep tid e 11. Diethylamine (1 mL) was added to a solution
of Fmoc-Hyp(OtBu)-OAll (10) (58 mg, 0.1 mmol, 1.0 equiv) in
acetonitrile (1 mL), and the mixture was stirred at room
temperature under N2 for 30 min. The mixture was concen-
trated, and the residue was redissolved in acetonitrile (2 mL)
and concentrated again. A solution of compound 9 (50 mg, 0.1
mmol. 1.0 equiv) in dry CH2Cl2 (1.5 mL) was added to the
residue. Diisopropylethylamine (56 µL, 0.3 mmol, 2.5 equiv)
was added, followed by BroP reagent (55 mg, 0.1 mmol, 1.0
equiv). The resulting solution was stirred at room temperature
under N2 for 5 d. The mixture was concentrated, and the brown
residue was purified by flash column chromatography, eluting
with 2:1 hexanes-ethyl acetate, to give dipeptide 11 as a
colorless oil (80 mg, 75%): Rf ) 0.26 (2:1 hexanes-ethyl
acetate); HPLC tR ) 11.34 min (85% MeCN in H2O; 0.05%
(9:1 CH2Cl2-methanol); [R]20 ) -47.7° (c 0.85, CHCl3); 1H
D
NMR (200 MHz, DMSO-d6, 343 K) δ 1.27 (s, 3H), 1.37 (s, 3H),
3.45-3.70 (m, 4H), 4.20-4.38 (m, 4H), 4.70-4.85 (m, 2H),
7.26-7.41 (m, 4H), 7.61 (d, J ) 7.2 Hz, 2H), 7.83 (d, J ) 7.2
Hz, 2H); 13C NMR (50 MHz, CDCl3) δ 24.6, 26.7, 46.7, 52.3,
67.5, 68.2, 78.9, 82.1, 111.6, 119.8, 125.1, 127.0, 127.6, 141.1,
143.6, 156.7, 177.2; HRMS (CI) calcd for C23H24NO6 (M + H)+
410.1603, obsd 410.1608. Anal. Calcd for C23H23NO6: C 67.47;
H 5.66; N 3.42. Found: C 67.41; H 5.62; N 3.65.
L-2,3-tr a n s-3,4-cis-3,4-Dih yd r oxyp r olin e (1). Trifluoro-
acetic acid (0.5 mL) was added to a solution of compound 9
(30 mg, 0.07 mmol) in CH2Cl2 (0.5 mL). The orange solution
was stirred at room temperature under N2 overnight. The
reaction mixture was concentrated, dissolved in Tesser’s base
(1 mL), and stirred at room temperature for 1 h. The reaction
mixture was concentrated, and the residue was purified by
ion exchange chromatography (Dowex H+), eluting with 0.5
M NH4OH. The fractions which gave a positive ninhydrin test
were lyophilized to give 1 as a colorless solid (8 mg, 74%): TLC
Rf ) 0.34 (6:4:1 CHCl3-methanol-H2O); [R]20D ) +5.9° (c 0.35,
H2O) [lit.7 +7.5° (c 0.16, H2O)]; 1H NMR (400 MHz, D2O, DSS
as internal reference) δ 3.30 (dd, J ) 12.4, 4.4 Hz, 1H), 3.55
(dd, J ) 12.4, 4.9 Hz, 1H), 3.97 (d, J ) 4.9 Hz, 1H), 4.37 (m,
2H); 13C NMR (100 MHz, D2O) δ 51.1, 67.2, 72.8, 76.9, 175.3;
HRMS (FAB) calcd for C5H10NO4 (M + H)+ 148.06098, obsd
148.06349.
L-2,3-tr a n s-3,4-cis-N-F lu or en ylm et h oxyca r b on yl-3,4-
d ih yd r oxy-3,4-O-isop r op yl-id en ep r olin e Allyl Ester (13).
Cesium carbonate (23 mg, 0.07 mmol, 0.5 equiv) was added to
a suspension of acid 9 (57 mg, 0.13 mmol, 1.0 equiv) in dry
methanol (1 mL). The reaction mixture was stirred at room
temperature under N2 for 2 h. The solvent was removed to
give a colorless residue, which was dissolved in DMF (1 mL)
and treated with allyl bromide (14 µL, 0.17 mmol, 1.2 equiv).
The mixture was stirred at room temperature under N2 for
14 h. The suspension was diluted with ethyl acetate (30 mL)
and washed with water (20 mL) and brine (20 mL). The organic
TFA); [R]20 ) -28.7° (c 0.60, CHCl3); 1H NMR (200 MHz,
D
CDCl3) (mixture of rotamers) δ 1.11 (s, 3H), 1.18 (s, 6H), 1.32
(s, 1H), 1.35 (s, 2H), 1.47 (s, 1H), 1.51 (s, 2H), 2.06-2.35 (m,
2H), 2.49 (br, 1H), 3.29 (dd, J ) 10.1, 5.6 Hz, 0.25H), 3.68 (dd,
J ) 10.1, 5.6 Hz, 0.75H), 3.78-4.00 (m, 3H), 4.22-4.89 (m,
10H), 5.22-5.38 (m, 2H), 5.76-5.97 (m, 1H), 7.25-7.42 (m,
4H), 7.51-7.63 (m, 2H), 7.76 (d, J ) 7.8 Hz, 2H); 13C NMR
(CDCl3, 50 MHz) (mixture of rotamers) δ 24.9, 26.9, 28.2, 36.6
& 36.7, 47.0 & 47.2, 52.9 & 53.1, 53.3, 57.5, 65.3 & 65.4, 65.8,
67.2 & 67.7, 69.4, 74.2, 78.9 & 80.0, 82.3 & 83.3, 112.4 & 112.5,
118.6 & 118.7, 119.9, 124.7, 124.8, 125.2, 127.0, 127.6, 131.6,
141.2, 143.8, 143.9, 144.0, 154.5 & 155.2, 168.6 & 168.9, 171.6
& 171.7; HRMS (FAB+) calcd for C35H43N2O8 (M + H)+
619.30194, obsd 619.30190.
Dip ep tid e 12. Trifluoroacetic acid (0.5 mL) was added to a
solution of dipeptide 11 (13 mg, 0.02 mmol) in dichloromethane
(0.5 mL). The orange solution was stirred at room temperature
under N2 for 23 h and then concentrated. The residue was
purified by RP-HPLC (70-95% MeCN in H2O over 30 min) to
give, after lyophilization, dipeptide 12 as a colorless solid (5
mg, 46%): Rf 0.47 (9:1 CH2Cl2-MeOH); HPLC tR ) 4.89 min
(70-95% MeCN in H2O over 30 min); [R]20 ) -34.9° (c 0.30,
D
1
CH3OH); H NMR (400 MHz, CD3OD) (mixture of rotamers)