Synthesis of the Deoxyaminosugar Forosamine via a Novel Domino-Knoevenagel-hetero-Diels-Alder Reaction L. F. Tietze*, N. Böhnke, S. Dietz
Institut für Organische und Biomolekulare Chemie der Georg-August-Universität Göttingen, Tammannstraße 2, D-37077 Göttingen, Germany E-mail:
[email protected] Supporting Information Table of Content General Methods:
S2
Experimental Procedures and Analytical Data
S3
1
S 12
H-NMR spectra
S1
General. Experimental methods: All solvents were distilled prior to use by common laboratory methods. All reagents purchased from commercial sources were used without further purification. Thin-layer chromatography was performed on precoated silica gel plates (SIL G/UV254, Macherey-Nagel GmbH & Co. KG). Silica gel 60 (0.032–0.064 mm) (Merck) was used for column chromatography. Vanillin in methanolic sulphuric acid was used as the staining reagent for TLC. 1H and
13
C NMR spectra were recorded with a Varian Mercury-300, Unity-
300 and Inova-500 spectrometer and a Bruker AMX-300 spectrometer in CDCl3; chemical shifts are given in δ (ppm) relative to tetramethylsilane (TMS), coupling constants J in Hertz. The multiplicities of first order were assigned as: s (singlet), d (doublet), t (triplet), q (quartet), dd (doublet of doublets), etc. Signals of higher orders were assigned as: m (multiplet) or mc (centred multiplet).IR spectra were recorded with a Bruker Vector 22 spectrometer. Liquids were gauged on NaCl plates and solids in a KBr matrix. UV spectra were recorded with a Perkin-Elmer Lambda 2 spectrometer. Mass-spectra were measured with a Finnigan MAT 95 and a Bruker Daltronik Apex IV. Optical Rotations were measured on a PerkinElmer 241 polarimeter in the solvent indicated.
S2
Advice: Due to the low molecular weight and the relatively high vapour pressure of the products it is recommended to remove the solvents carefully and to avoid too low pressures.
Nitroacetone (7) Nitromethane (5.00 mL, 36.5 mmol, 4.70 equiv.) was added dropwise to a solution of KOtBu (870 mg, 7.77 mmol, 1.00 equiv.) in abs. THF (20 mL) at rt. The mixture
O 1
was cooled to 0 °C and a solution of N-acetylimidazole (850 mg, 7.77 mmol,
NO2
1.00 Äq.) in THF (20 mL) was added over a period of 10 min. After stirring for 12 h
7
at rt the formed nitronate salt was filtered off, washed with Et2O (200 mL) and dissolved in H2O (200 mL). The aqueous solution was acidified with conc. HCl to pH 3 and extracted with CH2Cl2 (3 × 30 mL). The combined organic phases were dried over MgSO4 and concentrated to 60 mL at 30 °C under reduced pressure. Due to the danger of explosion of the nitronate salt and the product the compounds were always kept in solution or under supernatant. The yield (700 mg, 6.79 mmol, 87 %) was determined via an aliquot of 1 mL. 1H-NMR (300 MHz, CDCl3): δ = 2.33 (s, 3 H, CH3), 5.30 (s, 2 H, CH2).13C-NMR (75.5 MHz, CDCl3): δ = 27.38 (C-3), 83.67 (C-1), 193.65 (C-2). MS (EI, 70 eV): m/z (%) = 103.0 (17) [M + Na]+, 43.0 (100) [COCH3]+.
Domino Knoevenagel-hetero-Diels-Alder reaction: General procedure A mixture of the nitroacetone solution (5 mL), the alkyl vinyl ether (20 equiv.), and formaline solution (30 % in H2O, 2.0 equiv.) was heated to 80 °C for 3 h in a pressure flask. After cooling to rt the reaction mixture was washed with 5 % aq. NaHCO3 (10 mL) and the aqueous phase was extracted with CH2Cl2 (3 × 15 mL). The combined organic phases were dried over MgSO4 and the solvent was removed at rt under reduced pressure. The residue was purified by column chromatography (SiO2, n-pentane/ethyl acetate 9:1) to give the dihydropyrane as a colourless liquid and solids, respectively.
rac-2-Ethoxy-6-methyl-5-nitro-3,4-dihydro-2H-pyrane (rac-3a) Nitroacetone (7) (120 mL of the solution in CH2Cl2, 13.7 mmol), formaldehyde
(30 %
in
H2O,
2.04 mL,
13.4 M,
27.4 mmol,
O
1 2
O
8 7
2.00 equiv.), and ethyl vinyl ether (26.3 mL, 0.27 mol, 20 equiv.) were O2N reacted according to the general procedure to give the product (0.96 g,
3a
5.13 mmol, 37 %) as a white solid. TLC: Rf = 0.50 (n-pentane/ethyl acetate 15:1), staining with vanilline/sulphuric acid: yellow. mp: 50.1 °C. IR (KBr): ∼ ν = 2979 cm-1, 2898, 2872, S3
1623, 1487, 1479, 1453, 1430, 1375, 1360, 1311, 1252, 1222, 1198, 1156, 1132, 1117, 1090, 1056, 1003, 965, 937, 900, 875, 848. UV (MeCN): λmax (lg ε) = 225.0 nm (3.416), 301.5 (3.924). 1H-NMR (300 MHz, CDCl3): δ = 1.23 (t, J = 7.2 Hz, 3 H, 8-H3), 1.80–1.91 (m, 1 H, 3-Ha), 1.98–2.08 (m, 1 H, 3-Hb), 2.44 (t, J = 1.4 Hz, 3 H, 6-CH3), 2.72 (tq, J = 5.6, 1.5 Hz, 2 H, 4-H2), 3.65 (dq, J = 9.6, 7.2 Hz, 1 H, 7-Ha), 3.86 (dq, J = 9.6, 7.2 Hz, 1 H, 7-Hb), 5.15 (dd, J = 7.2, 3.5 Hz, 1 H, 2-H).
13
C-NMR (75.5 MHz, CDCl3): δ = 14.97 (C-8), 18.46 (C-3),
21.58 (6-CH3), 25.69 (C-4), 64.82 (C-7), 98.32 (C-2), 129.24 (C-5), 162.51 (C-6). MS (EI): m/z (%) = 187.2 (5) [M]+, 72.1 (38) [C4H8O]+, 142.1 (10) [M–OCH2CH3]+, 43.0 (100) [COCH3]+. HRMS (EI) Found: 187.0845 [M+H]+ C8H13NO4 requires 187.0845.
rac-2-n-Butoxy-6-methyl-5-nitro-3,4-dihydro-2H-pyrane (rac-3b) Nitroacetone (7) (5.0 mL of the solution in CH2Cl2, 0.62 mmol),
O
1 2
formaldehyde (30 % in H2O, 93 µL, 13.4 M, 1.24 mmol, 2.00 equiv.), and n-butyl vinyl ether (1.6 mL, 12.4 mol,
O
10
7
O2N
20 equiv.) were reacted according to the general procedure to
3b
give the product (35.8 mg, 0.166 mmol, 27 %) as a colourless oil. TLC: Rf = 0.74 (npentane/ethyl acetate 1:1), staining with vanilline/sulphuric acid: yellowish-red. IR (NaCl): ∼ ν = 2960 cm-1, 2936, 2874, 1636, 1492, 1377, 1323, 1252, 1127, 1091, 1000, 852. UV (MeCN): λmax (lg ε) = 227.0 nm (0.402), 301.5 (0.813). 1H-NMR (300 MHz, CDCl3): δ = 0.91 (t, J = 7.4 Hz, 3 H, 10-H3), 1.35 (mc, 2 H, 9-H2), 1.56 (mc, 2 H, 8-H2), 1.78–1.91 (m, 1 H, 3Ha), 1.98–2.09 (mc, 1 H, 3-Hb), 2.44 (t, J = 1.4 Hz, 3 H, 6-CH3), 2.72 (mc, 2 H, 4-H2), 3.58 (ddd, J = 9.6, 6.5, 6.5 Hz, 1 H, 7-Ha), 3.80 (ddd, J = 9.6, 6.6, 6.6 Hz, 1 H, 7-Hb), 5.14 (dd, J = 3.5, 2.8 Hz, 1 H, 2-H).
13
C-NMR (75.5 MHz, CDCl3): δ = 13.69 (C-10), 18.40 (C-3), 19.08
(C-9), 21.56 (6-CH3), 25.66 (C-4), 31.43 (C-8), 69.00 (C-7), 98.47 (C-2), 129.25 (C-5), 162.50 (C-6). MS (EI): m/z (%) = 215.1 (6) [M]+, 142.0 (20) [M–OC4H9]+. HRMS (ESI) Found: 238.1049 [M+Na]+ C10H17NO4 requires 238.1050.
rac-2-iso-Butoxy-6-methyl-5-nitro-3,4-dihydro-2H-pyrane (rac-3c) Nitroacetone (7) (5.0 mL of the solution in CH2Cl2, 0.62 mmol), formaldehyde (30 % in H2O, 93 µL, 13.4 M, 1.24 mmol, 2.00 equiv.),
O
and iso-butyl vinyl ether (1.6 mL, 12.4 mol, 20 equiv.) were reacted O N 2 according to the general procedure to give the product (42.5 mg,
3c
1 2
O 7
0.197 mmol, 33 %) as a colourless oil. TLC: Rf = 0.74 (n-pentane/ethyl acetate 1:1), staining S4
with vanilline/sulphuric acid: yellowish-red. IR (NaCl): ∼ ν = 2959 cm-1, 2874, 1637, 1493, 1474, 1324, 1252, 997. UV (MeCN): λmax (lg ε) = 225.5 nm (0.368), 301.5 (0.777). 1H-NMR (300 MHz, CDCl3): δ = 0.86–0.92 (m, 6 H, CH(CH3)2), 1.78–1.91 (m, 2 H, CH(CH3)2, 3-Ha), 2.00–2.10 (m, 1 H, 3-Hb), 2.43 (t, J = 1.5 Hz, 3 H, 6-CH3), 2.73 (mc, 2 H, 4-H2), 3.53 (dd, J = 9.3, 6.6 Hz, 1 H, 2-H).
13
7-Ha), 3.56 (dd, J = 9.3, 6.5 Hz, 1 H, 7-Hb), 5.13 (dd, J = 3.4, 2.6 Hz, 1 H,
C-NMR (75.5 MHz, CDCl3): δ = 18.36 (C-3), 19.05 (CH(CH3)2), 21.55 (6-CH3),
25.62 (C-4), 28.34 (CH(CH3)2), 75.78 (C-7), 98.50 (C-2), 129.27 (C-5), 162.47 (C-6). MS (EI): m/z (%) = 215.1 (4) [M]+, 200.1 (1) [M – CH3]+, 142.0 (16) [M–OC4H9]+. HRMS (ESI) Found: 238.1050 [M+Na]+ C10H17NO4 requires 238.1050.
rac-2-iso-Propoxy-6-methyl-5-nitro-3,4-dihydro-2H-pyrane (rac-3d) Nitroacetone (7) (5.0 mL of the solution in CH2Cl2, 0.65 mmol), formaldehyde (30 % in H2O, 97 µL, 13.4 M, 1.29 mmol, 2.00 equiv.),
O
1 2
O
and iso-propyl vinyl ether (1.49 mL, 13.0 mol, 20 equiv.) were reacted O2N according to the general procedure to give the product (29.9 mg,
3d
0.149 mmol, 23 %) as a colourless oil. TLC: Rf = 0.73 (n-pentane/ethyl acetate 1:1), staining with vanilline/sulphuric acid: yellow. IR (NaCl): ∼ ν = 2974 cm-1, 2873, 2857, 1697, 1371, 1324, 1277, 1107, 1085, 986. UV (MeCN): λmax (lg ε) = 227.0 nm (0.697), 301.0 (0.249). 1HNMR (300 MHz, CDCl3): δ = 1.18 (d, J = 2.4 Hz, 3 H, CH(CH3ACH3B)2), 1.20 (d, J = 2.4 Hz, 3 H, CH(CH3ACH3B)2), 1.80–1.91 (m, 1 H, 3-Ha), 1.97–2.04 (m, 1 H, 3-Hb), 2.43 (t, J = 1.4 Hz, 3 H, 6-CH3), 2.72 (mc, 2 H, 4-H2), 4.02 (sept, J = 6.2 Hz, 1 H, OCH(CH3)2), 5.24 (dd, J = 3.7, 2.7 Hz, 1 H, 2-H).
13
C-NMR (75.5 MHz, CDCl3): δ = 18.53 (C-3), 21.71 (6-CH3),
21.80*, 23.24* (CH(CH3)2), 26.07 (C-4), 71.33 (OCH(CH3)2), 96.87 (C-2), 129.16 (C-5), 162.70 (C-6). MS (EI): m/z (%) = 201.1 (4) [M]+, 142.0 (20) [M–OCH(CH3)2]+. HRMS (EI) Found: 201.100 [M]+ C9H15NO4 requires 201.100.
S5
rac-(2R,5S,6R)-2-Ethoxy-6-methyl-5-nitrotetrahydropyrane
(rac-10)
and
rac-(2R,5R,6R)-2-ethoxy-6-methyl-5-nitrotetrahydropyrane (rac-11) A solution of dihydropyrane rac-3a (960 mg, 5.13 mmol) in abs. Et2O (50 mL) was added dropwise to a solution of NaB(OCH3)3H
O2N
8 7
10 O2 N O1
for 18 h. After stirring for further 2 h at –15 °C (TLC control) the reaction was quenched by addition of a acetic acid/urea-mixture
O
2
(1.64 g, 12.8 mmol, 2.5 equiv.) in abs. Et2O (85 mL) and abs. THF (70 mL) at –78 °C. The mixture was warmed to –35 °C and stirred
O1
2
O
8 7
11
(30 mL of a solution of 10 g glacial acetic acid and 8 g urea in 40 mL H2O). The mixture was warmed to rt, saturated with NaCl, the phases were separated and the aq. phase was extracted with Et2O (2 × 30 mL). The combined organic phases were washed with sat. NaHCO3 (100 mL) and dried over Na2SO4. After removal of the solvent under reduced pressure the residue was purified by column chromatography (SiO2, n-pentane/ethyl acetate 9:1) to give rac-10 (507 mg, 2.68 mmol, 52 %) as a colourless oil and rac-11 (224 mg, 1.18 mmol, 23 %) as a white solid. rac-10 TLC: Rf = 0.88 (n-pentane/ethyl acetate 1:1), staining with vanilline/sulphuric acid: red. IR (NaCl): ∼ ν = 2979 cm-1, 2935, 2879, 2810, 1547, 1460, 1446, 1417, 1379, 1337, 1324, 1272, 1220, 1203, 1178, 1158, 1133, 1117, 1081, 1063, 1042, 1012, 990, 944, 925, 898. UV (MeCN): λmax (lg ε) = 200.4 nm (4.723), 279.0 (2.924). 1H-NMR (300 MHz, CDCl3): δ = 1.24 (t, J = 7.2 Hz, 3 H, 8-H3), 1.30 (d, J = 5.9 Hz, 3 H, 6-CH3), 1.61 (ddd, J = 13.7, 9.8, 4.8 Hz, 1 H, 3-Hax), 2.00 (ddd, J = 13.7, 4.4, 2.5 Hz, 1 H, 3-Heq), 2.23 (ddd, J = 13.5, 9.3, 4.4 Hz, 1 H, 4-Hax), 2.46 (ddd, J = 13.5, 4.8, 4.5 Hz, 1 H, 4-Heq), 3.55 (dq, J = 9.2, 7.3 Hz, 1 H, 7-Ha), 3.88–4.01 (m, 2 H, 7-Hb, 6-H), 4.25 (ddd, J = 11.5, 9.3, 4.5 Hz, 5-H), 4.57 (dd, J = 9.8, 2.5 Hz, 1 H, 2-H).
13
C-NMR (75.6 MHz, CDCl3): δ = 14.99 (C-8),
18.01 (6-CH3), 27.74 (C-3), 29.40 (C-4), 64.60 (C-7), 72.37 (C-6), 86.81 (C-5), 100.91 (C-2). MS (DCI): m/z = 224.1 (24) [M+NH3+NH4]+, 207.1 (100) [M+NH4]+, 178.1 (82) [M–CH2CH3+NH3]+. HRMS (ESI) Found: 212.0895 [M+Na]+ C8H15NO4 requires 212.0893. rac-11 TLC: Rf = 0.63 (n-pentane/ethyl acetate 1:1) staining with vanilline/sulphuric acid: red. IR (KBr): ∼ ν = 2974 cm-1, 2942, 2882, 2812, 1537, 1468, 1442, 1416, 1383, 1350, 1327, 1319, 1301, 1269, 1220, 1172, 1149, 1129, 1106, 1092, 1076, 1056, 1044, 1027, 959, 922, 912, 900, 868. UV (MeCN): λmax (lg ε) = 199.5 nm (3.702). 1H-NMR (300 MHz, CDCl3):
δ = 1.24 (t, J = 7.1 Hz, 3 H, 8-H3), 1.36 (d, J = 6.5 Hz, 3 H, 6-CH3), 1.75 (ddd, J = 13.1, 3.4, 2.8 Hz, 1 H, 3-Heq), 1.89–2.04 (mc, 1 H, 4-Hax), 2.21 (ddd, J = 13.1, 9.0, 4.4 Hz, 1 H, 3-Hax), S6
2.45 (dddd, J = 14.8, 5.1, 4.4, 3.4 Hz, 1 H, 4-Heq), 3.52 (dq, J = 9.3, 7.1 Hz, 1 H, 7-Ha), 3.90– 4.03 (m, 2 H, 7-Hb, 6-H), 4.47 (ddd, J = 5.0, 4.7, 3.2 Hz, 1 H, 5-H), 4.54 (dd, J = 9.0, 2.8 Hz, 1 H,
2-H).
13
C-NMR (75.6 MHz, CDCl3): δ = 14.98 (C-8), 17.44 (6-CH3), 25.03 (C-3),
25.82 (C-4), 64.23 (C-7), 70.95 (C-6), 81.89 (C-5), 101.35 (C-2). MS (ESI): m/z = 228.0 [M+K]+, 212.0 [M+Na]+. HRMS (ESI) Found: 212.0893 [M+Na]+
228.0633 [M+K]+,
C8H15NO4 requires 212.0893, 228.0634.
Isomerisation of (rac-11) (rac-10) KHMDS (153 µl, 0.5 M in toluene, 76.6 µmol, 5 mol%) was added dropwise to a solution of rac-11 (290 mg, 1.53 mmol) in abs. THF (30 mL) at rt and stirred for 2 d. The reaction was quenched by addition of 5% NaHCO3 (10 mL) and the aq. phase was extracted with ethyl acetate (3 × 20 mL). The combined organic phases were washed with brine (20 mL) and dried over MgSO4. After removal of the solvent under reduced pressure the residue was purified by column chromatography (SiO2, n-pentane/ethyl acetate 9:1) to give rac-10 (220 mg, 1.16 mmol, 76 %) as a colourless oil and rac-11 (53.8 mg, 0.28 mmol, 19 %) as a white solid.
rac-β-Ethyl-N,N-desdimethylforosamine (rac-12) Raney®-Nickel (1.0 mL, 50% slurry in H2O, Acros) was washed under an argon atmosphere with water (1 × 5 mL) and MeOH (2 × 5 mL) whereupon a solution of the nitro compound rac-10 (100 mg,
6
H 2N
O
O 1
8 7
12
0.53 mmol) in MeOH (20 mL) was added. The mixture was stirred at rt for 3 h under a hydrogen atmosphere, filtered and the residue was washed thoroughly with MeOH (80 mL). The filtrate was concentrated under reduced pressure and the residue was purified by column chromatography (SiO2, CH2Cl2/MeOH 7:1, 0.5 % NEt3) to give the product (67.9 mg, 0.43 mmol, 81 %) as a colourless, malodorous oil. TLC: Rf = 0.31 (CH2Cl2/MeOH 7:1), staining with vanilline/sulphuric acid: red. IR (NaCl): ∼ ν = 3362 cm-1, 2975, 2932, 2866, 1604, 1555, 1455, 1378, 1317, 1166, 1075, 982, 916, 887. 1H-NMR (300 MHz, CDCl3): δ = 1.23 (t, J = 7.1 Hz, 3 H, 8-H3), 1.30 (d, J = 6.1 Hz, 3 H, 6-H ), 1.34–1.48 (m, 1 H, 3-Hax), 1.58 (ddd, J = 13.2, 9.5, 4.0 Hz, 1 H, 2-Hax), 1.80–1.90 (mc, 1 H, 2-Heq), 1.93–2.05 (mc, 1 H, 3-Heq), 2.45– 2.60 (m, 3 H, 4-H, NH2), 3.23 (dq, J = 9.2, 6.1 Hz, 1 H, 5-H), 3.52 (dq, J = 9.4, 7.1 Hz, 1 H, 7-Ha), 3.94 (dq, J = 9.4, 7.1 Hz, 1 H, 7-Hb), 4.44 (dd, J = 9.2, 1.9 Hz, 1 H, 1-H).
13
C-NMR
(75.6 MHz, CDCl3): δ = 14.99 (C-8), 18.27 (C-6), 30.79, 30.83 (C-2, C-3), 52.73 (C-4), 64.07
S7
(C-7), 76.30 (C-5), 101.24 (C-1). MS (ESI): m/z = 160.1 [M]+. HRMS (ESI) Found: 160.1333 [M+H]+ C8H17NO2 requires 160.1332.
rac-β β-Ethyl-forosamine (rac-14) Formaldehyde (30 % in H2O, 0.18 mL) and palladium (10 % on charcoal, 98 mg, 92.3 µmol, 14 mol%) were added to a solution of
6
O
N
O 1
amine rac-12 (104 mg, 0.65 mmol) in MeOH (10 mL) and the
8 7
14
mixture was stirred at rt for 14 h under an hydrogen atmosphere. The reaction mixture was filtered through Celite®, the filter pad thoroughly washed with MeOH (80 mL), and the filtrate was concentrated under reduced pressure. Purification of the residue by column chromatography (SiO2, CH2Cl2/MeOH 9:1, 1 % NEt3) gave the product (89.3 mg, 0.48 mmol, 73 %) as a colourless oil. TLC: Rf = 0.60 (CH2Cl2/MeOH 7:1), staining with vanilline/sulphuric acid: red. IR (NaCl): ∼ ν = 2972 cm-1, 2934, 2864, 2826, 2781, 2617, 1453, 1410, 1377, 1355, 1320, 1290, 1271, 1224, 1207, 1192, 1168, 1129, 1097, 1073, 1040, 989, 905, 892. 1H-NMR (300 MHz, CDCl3): δ = 1.23 (t, J = 7.0 Hz, 3 H, 8-H3), 1.30 (d, J = 5.9 Hz, 3 H, 6-H3), 1.38–1.58 (m, 2 H, 3-H2), 1.79–1.97 (m, 2 H, 2-H2), 2.19–2.27 (m, 1 H, 4-H), 2.23 (s, 6 H, N(CH3)2), 3.44–3.56 (m, 2 H, 5-H, 7-Ha), 3.93 (dq, J = 7.0, 9.7 Hz, 1 H, 7Hb), 4.39 (mc, 1 H, 1-H). 13C-NMR (75.6 MHz, CDCl3): δ = 15.10 (C-8), 18.15 (C-6), 18.89 (C-3), 31.15 (C-2), 40.63 (N(CH3)2), 64.03 (C-4), 64.97 (C-7), 73.60 (C-5), 101.47 (C-1). MS (EI): m/z (%) = 188.0 (100) [M+H]+, 142.2 (14) [M–OCH2CH3]+. HRMS (ESI) Found: 188.1645 [M+H]+ C10H21NO2 requires 188.1645.
rac-Forosamine (rac-2) A solution of the ethyl glycoside rac-14 (167 mg, 0.893 mmol) in 1 M aq. H2SO4 (25 mL) was stirred at rt for 14 h after which the reaction mixture was neutralised with Ba(OH)2·8 H2O (7.9 g). The suspension was diluted
6
N
O
1
OH 2
with EtOH (75 mL), centrifuged (10 min at 1500 U/min), and decanted from the precipitate. The process was repeated two more times. The combined supernatants were concentrated under reduced pressure and the residue was purified by column chromatography (SiO2, CH2Cl2/MeOH 9:1, 0.5 % NEt3) to give the free sugar (115 mg, 0.725 mmol, 81 %) as a colourless oil. TLC: Rf = 0.28 (CH2Cl2/MeOH 7:2), staining with vanilline/sulphuric acid: red. IR (NaCl): ∼ ν = 3383 cm-1, 2936, 2869, 2827, 1454, 1129, 1087, 1066, 1037, 989. 1HS8
NMR (300 MHz, CDCl3): δ = 1.24 (d, J = 6.3 Hz, 3 H, 6-H3α), 1.31 (d, J = 6.3 Hz, 3 H, 6-H3β), 1.42–1.53, 1.62–2.06 (m, 4 H + 4 H, 2-H2α, 2-H2β, 3-H2α, 3-H2β), 2.18–2.32 (m, 1 H + 1 H, 4-Hα, 4-Hβ), 2.24 (s, 6 H, N(CH3)2β), 2.27 (s, 6 H, N(CH3)2α), 3.57 (dq, J = 9.5, 6.2 Hz, 1 H, 5-Hβ), 3.96 (sbr, 1 H + 1 H, OHα, OHβ), 4.09 (dq, J = 9.2, 6.3 Hz, 1 H, 5-Hα), 4.72 (dd, J = 9.0, 2.1 Hz, 1 H, 1-Hβ), 5.21 (dd, J = 3.0, 2.1 Hz, 1 H, 1-Hα).
13
C-NMR (125.7 MHz,
CDCl3): δ = 14.42 (C-3α), 18.20 (C-3β), 18.96 (C-6β), 19.00 (C-6α), 30.05*, 32.67* (C-2α, C2β), 40.65 (N(CH3)2β), 40.72 (N(CH3)2α), 64.78 (C-4β), 65.51 (C-4α), 66.91 (C-5α), 73.99 (C5β), 90.99 (C-1α), 96.04 (C-1β). MS (ESI): m/z = 160.1 [M + H]+, 192.0 [M+MeOH+H]+. HRMS (ESI) Found: 160.1332 [M+H]+ C16H23NO4 requires 160.1332.
(rac)-Ethyl-N,N-desdimethyl-N-benzyloxycarbonyl-β-forosamin (13) To a solution of amine rac-12 (242 mg, 1.52 mmol) in CH2Cl2 (5 mL) a sat. K2CO3-sol. (5 mL) was added, the mixture was stirred at r.t. for 1 h, CbZ-Cl (1.04 g, 6.08 mmol, 0.87 mL) was
6
Cbz N H
O
O 1
8 7
13
added and stirring was continued for 12 h. The mixture was diluted with CH2Cl2 (50 mL), washed with water (20 mL), the aqueous layer was extracted with CH2Cl2 (2 × 20 mL), dried over Na2SO4 and the solvent removed under reduced pressure. The residue was purified by column chromatography (SiO2, n-pentane: ethyl acetate 3:1) to give the product as a white solid (425 mg, 1.49 mmol, 95 %). TLC: Rf = 0.20 (PE/EE 16:5), staining with vanilline/sulphuric acid: orange. IR (NaCl): ν~ = 3299 cm-1, 3067, 3041, 2972, 2944, 2894, 2860, 2813, 1687, 1609, 1589, 1548, 1500, 1454, 1423, 1377, 1349, 1321, 1303, 1253, 1161, 1134, 1105, 1070, 1046, 986, 918, 907, 887. UV (MeCN) : λ max (lg ε ) = 205.0 nm (3.942), 251.5 (2.351), 257.0 (2.413), 263.0 (2.339), 267.0 (2.217). 1H-NMR (300 MHz, C2D2Cl4, 100 °C): δ H = 1.23 (t, J = 7.2 Hz, 3 H, 8-H3), 1.30 (d, J = 5.8 Hz, 3 H, 6-H3), 1.34–1.50 (m, 1 H, 3-Hax), 1.62 (dddd, J = 13.1, 9.1, 8.4, 4.5 Hz, 1 H, 2-Hax), 1.85 (ddd, J = 13.3, 5.8, 3.6 Hz, 1 H, 2-Heq), 2.11 (ddd, J = 13.3, 4.5, 3.6 Hz, 1 H, 3-Heq), 3.28–3.41 (m, 2 H, 4-H, 5-H), 3.55 (dq, J = 9.7, 7.2 Hz, 1 H, 7-Ha), 3.87 (dq, J = 9.7, 7.2 Hz 1 H, 7-Hb), 4.43 (dd, J = 9.2, 2.3 Hz, 1 H, 1-H), 4.44–4.56 (m, 1 H, NH), 5.13 (s, 2 H, CH2Ar), 7.30–7.40 (m, 5 H, 5 × Ar-
H). 13C-NMR (75 MHz, C2D2Cl4, 100 °C): δ C = 14.92 (C-8), 18.40 (C-2), 26.90 (C-6), 30.44 (C-3), 52.42 (CH2Ar), 63.63 (C-7), 66.44 (C-4), 74.77 (C-5), 100.87 (C-1), 127.53 (C-Ar), 127.75 (C-Ar), 128.22 (C-Ar), 136.51 (Cquart-Ar), 155.51 (COOBn). MS (ESI, MeOH):
m/z = 332.1 [M+K]+, 316.1 [M+Na]+.HRMS (ESI) Found: 316.1520 [M+Na]+, 332.1257 [M+K]+ C16H23NO4 requires 316.1519, 332.1258.
S9
Separation of the enantiomers of 13 (rac)-13 (400 mg, 1.36 mmol) was dissolved in CH2Cl2 (10 mL) and 400 µL of this solution (16.0 mg, 60.0 µmol of the racemic mixture) were repeatedly injected into a preparative HPLC-System (column: Chiralpak IA, 250 × 20 mm, particle size: 5 µm, mobile phase
n-hexane/ethyl acetate 9:1, flow: 18 mL/min, pressure: 10.1 Mpa). Fractionate collection of the eluate (UV-detektor: λ = 261 nm) afforded the enantiomers (+)-13a und (–)-13b.
analytical data for (+)-13a HPLC (preparative)
tR :
21.7
HPLC (analytical)
column:
Chiralpak IA
eluate:
n-hexane/ethyl acetate 8:2
flow:
0.8 mL/min
tR :
10.1, 99 % ee.
[α ]20D
= + 20.5 (c 1.0 in MeOH)
analytical data for (–)-13b HPLC (preparative)
tR :
26.4
HPLC (analytical)
column:
Chiralpak IA
eluate:
n-hexane/ethyl acetate 8:2
flow:
0.8 mL/min
tR :
11.4, 95 % ee.
[α ]20D
= – 18.3 (c 1.0 in MeOH).
Ethyl-β-D-forosamin (14a) and Ethyl-β-L-forosamin (14b) Formaldehyde (30 % in H2O, 0.55 mL) and palladium (50 % on charcoal, 200 mg) were added to a solution of carbamate 13a/13b (100 mg, 0.34 mmol) in MeOH (10 mL) and were shaken under an H2-atmosphere (3 bar) at r.t. for 4 h. The reaction mixture was filtered through Celite®, the residue washed thoroughly with MeOH (80 mL), and the filtrate was concentrated under reduced pressure (p ≥ 120 mbar). Purification of the residue by column chromatography (SiO2, CH2Cl2/MeOH 7:1) gave the product (51.0 mg, 0.27 mmol, 79 %) as a colourless oil. [α ]D = + 19.4 (c 1.0 in MeOH) 14a. [α ]D = – 18.3 (c 1.0 in MeOH) 14b. 20
D-(+)-forosamine
20
(2a)
A solution of ethyl glycoside 14b (12.4 mg, 66.2 µmol) in 1 M aq. H2SO4 (2 mL) was stirred at rt for 17 h after which the reaction mixture was neutralised with Ba(OH)2·8 H2O (0.63 g). S10
The suspension was diluted with EtOH (20 mL), centrifuged (10 min at 1500 U/min) and decanted from the precipitate. The process was repeated two more times. The combined supernatants were concentrated under reduced pressure and the residue was purified by column chromatography (SiO2, CH2Cl2/MeOH 9:1, 0.5 % NEt3) to give the free sugar (7.9 mg, 49.6 µmol, 75 %) as a colouless oil. [α ]D = + 68.0 (c 1.0 in MeOH) 20
L-(–)-forosamine
(2b)
A solution of ethyl glycoside 14a (14.2 mg, 75.8 µmol) in 1 M aq. H2SO4 (2 mL) was stirred at rt for 20 h after which the reaction mixture was neutralised with Ba(OH)2·8 H2O (0.63 g). The suspension was diluted with EtOH (20 mL), centrifuged (10 min at 1500 U/min) and decanted from the precipitate. The process was repeated two more times. The combined supernatants were concentrated under reduced pressure and the residue was purified by column chromatography (SiO2, CH2Cl2/MeOH 9:1, 0.5 % NEt3) to give the free sugar (11.0 mg, 69.1 µmol, 91 %) as a colouless oil. [α ]D = – 75.0 (c 1.0 in MeOH) 20
S11
6.0
5.8
5.6
5.4
2.33 1. 52
5.30 1. 00
6.2
5.2
5.0
4.8
4.6
4.4
4.2
4.0
3.8 3.6 f1 (ppm)
S12
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
5.2
5.0
4.8
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2
3.0 f1 (ppm)
S13
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
5.0
4.5
4.0
3.5
3.0 f1 (ppm)
S14
2.5
2.0
1.5
1.0
0.5
5.6
5.4
5.2
5.0
4.8
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2 3.0 f1 (ppm)
S15
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
5.4
5.2
5.0
4.8
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2 f1 (ppm)
S16
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2
3.0
2.8 2.6 f1 (ppm)
S17
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
4.5
4.0
3.5
3.0
2.5 f1 (ppm)
S18
2.0
1.5
1.0
0.5
4.4
4.2
4.0
3.8
3.6
3.4
3.2
3.0
2.8 2.6 f1 (ppm)
S19
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0 f1 (ppm)
S20
3.5
3.0
2.5
2.0
1.5
1.0
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2
3.0
2.8 2.6 f1 (ppm)
S21
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
5.0
4.5
4.0
3.5
3.0 f1 (ppm)
S22
2.5
2.0
1.5
1.0
0.5
