References and Notes
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<A NAME="RG25106ST-7">7</A>
For examples of oxidation of 4-hydroxypipecolic acid derivatives with other oxidants,
see refs. 2c, 2g and 2j.
<A NAME="RG25106ST-8">8</A>
(2R,4S)-6: [α]D
24 6.45 (c = 0.93, CHCl3). 1H NMR (400 MHz): δ = 7.49-7.52 (m, 2 H, Ph), 7.28-7.34 (m, 2 H, Ph), 7.19-7.24 (m,
1 H, Ph), 4.01 (q, J = 6.9 Hz, 1 H, CHMe), 3.65 (s, 3 H, OCH3), 3.27 (dd, J = 2.8, 10.9 Hz, 1 H, 2-H), 2.44 (dt, J = 3.5, 11.4 Hz, 1 H, 6-H), 2.22 (d, J = 7.0 Hz, 2 H, CH
2CO2Me), 2.15 (dt, J = 2.5, 11.6 Hz, 1 H, 6-H), 1.92 (dm, J = 12.3 Hz, 1 H, 3-H), 1.76-1.88 (m, 1 H, 4-H), 1.43-1.57 (m, 2 H, 3-H, 5-H), 1.48
(s, 9 H, t-Bu), 1.32 (d, J = 6.9 Hz, 3 H, CHCH
3), 1.12 (dq, J = 3.8, 12.0 Hz, 1 H, 5-H). 13C NMR (100 MHz): δ = 173.1 (s, CO), 172.9 (s, CO), 143.4 (s, Ph), 127.9 (d, 2 × C,
Ph), 127.8 (d, 2 × C, Ph), 126.6 (d, Ph), 80.9 (s, t-Bu), 64.3 (d, C-2), 57.3 (d, CHMe), 51.5 (q, OCH3), 43.2 (t, C-6), 40.7 (t, CH2CO2Me), 36.2 (t, C-3), 32.6 (d, C-4), 31.6 (t, C-5), 28.0 (q, 3 × C, t-Bu), 9.0 (q, CHCH3).
(2R,4R)-6: [α]D
22 -0.55 (c = 1.02, CHCl3). 1H NMR (400 MHz): δ = 7.25-7.38 (m, 4 H, Ph), 7.17-7.23 (m, 1 H, Ph), 4.00 (q, J = 6.7 Hz, 1 H, CHMe), 3.86-3.91 (m, 1 H, 2-H), 3.65 (s, 3 H, OCH3), 2.86 (dt, J = 2.3, 12.1 Hz, 1 H, 6-H), 2.45 (dm, J = 11.7 Hz, 1 H, 6-H), 2.11-2.27 (m, 3 H, CH
2CO2Me, 3-H), 1.86-1.98 (m, 1 H, 4-H), 1.46-1.56 (m, 2 H, 3-H, 5-H), 1.51 (s, 9 H, t-Bu), 1.25 (d, J = 6.7 Hz, 3 H, CHCH
3), 1.11 (dq, J = 4.5, 12.4 Hz, 1 H, 5-H). 13C NMR (100 MHz): δ = 173.0 (s, CO), 172.9 (s, CO), 147.2 (s, Ph), 128.2 (d, 2 × C,
Ph), 127.0 (d, 2 × C, Ph), 126.6 (d, Ph), 80.6 (s, t-Bu), 61.7 (d, CHMe), 57.1 (d, C-2), 51.4 (q, OCH3), 45.5 (t, C-6), 41.2 (t, CH2CO2Me), 34.9 (t, C-3), 32.1 (t, C-5), 29.6 (d, C-4), 28.3 (q, 3 × C, t-Bu), 22.0 (q, CHCH3).
<A NAME="RG25106ST-9">9</A>
Sugg EE.
Griffin JF.
Portoghese PS.
J. Org. Chem.
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5032
<A NAME="RG25106ST-10">10</A>
The X-ray CIF file for this structure has been deposited at the Cambridge Crystallographic
Data Centre and allocated with the deposition number CCDC 607916. Copies of the data
can be obtained free of charge from CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (e-mail:
deposit@ccdc.cam.ac.uk; internet://www.ccdc.cam.ac.uk).
<A NAME="RG25106ST-11">11</A>
Esteves AP.
Rodrigues LM.
Silva ME.
Gupta S.
Oliveira-Campos AMF.
Machalicky O.
Mendonça AJ.
Tetrahedron
2005,
61:
8625
<A NAME="RG25106ST-12">12</A>
A slurry of diester (2S,4R)-6 (358 mg, 0.99 mmol) in THF (0.5 mL) was treated dropwise with an aq 1 M NaOH solution
(1.6 mL, 1.6 mmol). The mixture was stirred at r.t. for 3 h and concentrated. The
residue was dissolved in THF (1.0 mL) and NMM (0.109 mL, 0.99 mmol) and CDMT (174
mg, 0.99 mmol) were added. The reaction mixture was stirred at r.t. for 30 min and
then a solution of 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosylamine (321 mg, 0.99 mmol) in THF (1.3 mL) was added. The resulting
mixture was stirred at r.t. overnight, diluted with EtOAc, and washed sequentially
with H2O and brine. The separated organic layer was dried over Na2SO4, filtered, and concentrated. The residue was purified by column chromatography on
silica gel (eluent: PE-EtOAc = 2:3) to afford (2S,4R)-7 (423 mg, 63%) as a white solid.
(2S,4R)-7: [α]D
27 -32.65 (c = 0.525, CHCl3). 1H NMR (400 MHz): δ = 7.23-7.34 (m, 3 H, Ph), 7.14-7.19 (m, 2 H, Ph), 6.18 (d, J = 9.3 Hz, 1 H, NH), 5.28 (t, J = 9.5 Hz, 1 H, 3′-H), 5.19 (t, J = 9.4 Hz, 1 H, 1′-H), 5.04 (t, J = 9.7 Hz, 1 H, 4′-H), 4.87 (t, J = 9.6 Hz, 1 H, 2′-H), 4.29 (dd, J = 4.2, 12.5 Hz, 1 H, 6′-H), 4.04 (dd, J = 2.0, 12.5 Hz, 1 H, 6′-H), 3.97 (q, J = 7.0 Hz, 1 H, CHMe), 3.78 (ddd, J = 2.0, 4.2, 10.1 Hz, 1 H, 5′-H), 3.00 (dm, J = 11.4 Hz, 1 H, 6-H), 2.77 (dd, J = 2.9, 11.2 Hz, 1 H, 2-H), 2.07 (A part of an ABX system, J = 6.7, 14.6 Hz, 1 H, CHHCON), 2.06 (s, 3 H, CH3CO), 2.02 (s, 3 H, CH3CO), 2.00 (s, 3 H, CH3CO), 1.99 (s, 3 H, CH3CO), 1.96 (B part of an ABX system, J = 7.0, 14.6 Hz, 1 H, CHHCON), 1.79 (dm, J = 12.4 Hz, 1 H, 3-H), 1.71 (tm, J = 11.5 Hz, 1 H, 6-H), 1.50-1.60 (m, 2 H, 4-H, 5-H), 1.53 (s, 9 H, t-Bu), 1.48 (d, J = 7.0 Hz, 3 H, CHCH
3), 1.36 (q, J = 11.8 Hz, 1 H, 3-H), 1.19-1.30 (m, 1 H, 5-H). 13C NMR (100 MHz): δ = 173.1 (s, CO), 171.6 (s, CO), 171.0 (s, CO), 170.6 (s, CO), 169.8
(s, CO), 169.5 (s, CO), 137.7 (s, Ph), 128.9 (d, 2 × C, Ph), 127.7 (d, 2 × C, Ph),
127.2 (d, Ph), 80.9 (s, t-Bu), 78.0 (d, C-1′), 73.5 (d, C-5′), 72.6 (d, C-3′), 70.5 (d, C-2′), 68.1 (d, C-4′),
64.5 (d, C-2), 61.6 (t, C-6′), 59.4 (d, CHMe), 43.8 (t, C-6), 43.2 (t, CH2CON), 36.3 (t, C-3), 32.6 (d, C-4), 31.3 (t, C-5), 28.1 (q, 3 × C, t-Bu), 20.7 (q, CH3CO), 20.6 (q, CH3CO), 20.5 (q, 2 × C, CH3CO), 18.5 (q, CH3CH).
<A NAME="RG25106ST-13">13</A>
A solution of (2S,4R)-7 (105 mg, 0.155 mmol) in MeOH (1.6 mL) and AcOH (18 µL, 0.310 mmol) was hydrogenated
in the presence of 10% Pd/C (9 mg) at r.t. and atmospheric pressure overnight. The
reaction mixture was filtered through cotton wool and concentrated. The residue was
dissolved in the minimum amount of TFA at 0 °C and the mixture was stirred at r.t.
for 2.5 h and then concentrated. The residue was dissolved in anhyd MeOH (217 µL)
and treated sequentially with DIPEA (67 µL, 0.386 mmol) and Boc2O (28.1 mg, 0.129 mmol) at 0 °C. The reaction mixture was stirred at r.t. overnight,
and then concentrated. The residue was dissolved in a mixture of EtOAc and CH2Cl2 (1:1, 2.8 mL), treated with 5% aq KHSO4 solution (1 mL) and stirred at r.t. for 1 h. After the organic layer was separated,
the aqueous layer was extracted with EtOAc (3 × 1.4 mL). The combined organic phases
were washed with brine, dried over Na2SO4, filtered, and concentrated. The crude product was purified by column chromatography
on silica gel (eluent: CH2Cl2-MeOH, 10:1) to afford (2S,4R)-8 (32.4 mg, 34%) as a white solid. Molecular mass determinations by electrospray ionization
mass spectrometry (ESI-MS) was used to identify the N-protected amino acid (2S,4R)-8. MS (ESI): m/z = 639.3 [M + Na+].