Experimental
General
The melting points were determined on the Kofler block and are uncorrected. Optical rotations were measured in chloroform with a P3002 Krűss polarimeter and reported as follows: [α]
D25 (
c in g per 100 mL). NMR spectra were recorded at room temperature on a Varian Mercury
Plus 400 FT NMR spectrometer (
1H at 400.13 MHz and
13C at 100.6 MHz). Chemical shifts are referenced either to tetramethylsilane used as internal standard for
1H or to the solvent signal (
13C-NMR, δ CDCl
3=77.0).
13C-NMR multiplicities were determined by using a DEPT pulse sequence. Reactions were routinely monitored by TLC (Merck 60 F
254) and the products were visualized by UV light absorption at 254 nm or by spraying with Mo-reagent or KMnO
4-reagent. All reactions were performed under an atmosphere of nitrogen. Solvents were purified by standard procedures and distilled before use. Column chromatography was carried out on the glass columns using Kieselgel (0.035-0.070 mm) silica gel.
5-O-(tert-Butyldimethylsilyl)-1,2-O-isopropylidene-α-D-erythro-pentofuranosyl-3-ulose (
1) was prepared according to a published procedure [
4].
5-O-(tert-Butyldimethylsilyl)-3-C-(Z)-carboethoxymethylene-3-deoxy-1,2-O-isopropylidene-α-d-xylo-furanose (2) and its (E)-isomer (3)
(Carboethoxymethylene)triphenylphosphorane (7.84 g, 22.4 mmol) was added to a solution of ketone
1 [
4] (6.18 g, 20.4 mmol) in dry CH
2Cl
2 (80 mL). The reaction mixture was stirred at room temperature for 16 h. The solvent was removed under reduced pressure and the residue was purified by chromatography on silica gel (hexane-ethyl acetate, 13:1) to afford (
E)-
3 (0.65 g, 8.5%) and (
Z)-
2 (6.21 g, 82%) as colorless oils. Compound
3: [α]
D25 = +233.9 (
c 0.20);
1H-NMR: δ -0.01 (3H, s, CH
3), 0.02 (3H, s, CH
3), 0.86 (9H, s, 3 x CH
3), 1.30 (3H, t,
J =7.2 Hz, CH
3), 1.40 (3H, bs, CH
3), 1.43 (3H, bs, CH
3), 3.78 (1H, dd,
J5,5=10.4 Hz,
J5,4=2.2 Hz, H
5), 3.93 (1H, dd,
J5,5=10.4 Hz,
J5,4=1.6 Hz, H
5), 4.19 (2H, q,
J =7.2 Hz, CH
2O), 5.03 (1H, ddd,
J2,1=4.7 Hz,
J2,4=1.8 Hz,
J6,2=1.8 Hz, H
2), 5.57-5.59 (1H, m, H
4), 5.95 (1H, d,
J2,1=4.7 Hz, H
1), 6.13 (1H, dd,
J6,4=1.8 Hz,
J6,2=1.8 Hz, H
6);
13C-NMR: δ -5.7, -5.5, 14.2, 18.2, 25.9 (3 x C), 27.7, 27.8, 60.5, 65.8, 82.4, 82.6, 104.5, 113.2, 116.2, 160.8, 165.5; Anal. Calcd for C
18H
32O
6Si (372.54): C 58.03, H 8.66; found C 57.91, H 8.78. Compound
2: [α]
D25 = +131.3 (
c 0.20);
1H-NMR: δ 0.05 (3H, s, CH
3), 0.06 (3H, s, CH
3), 0.88 (9H, s, 3 x CH
3), 1.30 (3H, t,
J =7.1 Hz, CH
3), 1.43 (3H, bs, CH
3), 1.48 (3H, bs, CH
3), 3.74 (1H, dd,
J5,5=10.7 Hz,
J5,4=3.5 Hz, H
5), 3.79 (1H, dd,
J5,5=10.7 Hz,
J5,4=4.3 Hz, H
5), 4.25 (2H, q,
J =7.1 Hz, CH
2O), 4.84-4.87 (1H, m, H
4), 5.64-5.66 (1H, m, H
2), 5.91 (1H, d,
J1,2=4.1 Hz, H
1), 6.01 (1H, dd,
J6,2=1.7 Hz,
J6,4=1.7 Hz H
6);
13C-NMR: δ -5.6, -5.5, 14.1, 18.1, 25.7(3 x C), 27.2, 27.5, 60.5, 65.3, 78.8, 81.0, 105.4, 112.7, 116.5, 156.8, 164.9; Anal. Calcd for C
18H
32O
6Si (372.54): C 58.03, H 8.66; found C 58.15, H 8.55.
5-O-(tert-Butyldimethylsilyl)-3-deoxy-3-C-(E)-(2-hydroxyethylidene)-1,2-O-isopropylidene-α-d-xylo-furanose (5)
LiAlH4 (0.045 g, 1.18 mmol) was added at 0 °C to a solution of (E)-3 (0.44 g, 1.18 mmol) in dry Et2O (7.2 mL). The reaction mixture was stirred at 0 °C for 15 min and then for 1.5 h at room temperature. The reaction was quenched by careful addition of water (0.3 mL) and the precipitate was removed by filtration. The filtrate was dried (Na2SO4) and concentrated under reduced pressure. Chromatography of the residue (hexane-ethyl acetate, 3:1) afforded 0.28 g (72 %) of allylic alcohol 5 as a white solid; m.p. 42 – 43 °C; [α]D25 = +79.6 (c 0.20); 1H-NMR: δ -0.01 (3H, s, CH3), 0.06 (3H, s, CH3), 0.88 (9H, s, 3 x CH3), 1.41 (3H, bs, CH3), 1.45 (3H, bs, CH3), 2.18-2.30 (1H, m, OH), 3.68 (1H, dd, J5,5=10.8 Hz, J5,4=4.0 Hz, H5), 3.72 (1H, dd, J5,5=10.8 Hz, J5,4=2.9 Hz, H5), 4.16-4.18 (2H, m, H7), 4.95-4.97 (1H, m, H2), 5.05-5.09 (1H, m, H4), 5.84 (1H, d, J2,1=4.4 Hz, H1), 5.99-6.04 (1H, m, H6); 13C-NMR: δ -5.6, -5.4, 18.3, 25.8 (3 x C), 27.6, 27.9, 60.1, 66.1, 80.2, 82.4, 104.5, 112.8, 126.6, 140.8; Anal. Calcd for C16H30O5Si (330.50): C 58.15, H 9.15; found C 58.25, H 9.05.
5-O-(tert-Butyldimethylsilyl)-3-deoxy-3-C-(Z)-(2-hydroxymethylidene)-1,2-O-isopropylidene-α-d-xylo-furanose (4)
To a solution of (Z)-2 (6.03 g, 16.2 mmol) in dry Et2O (100 mL) was added LiAlH4 (0.61 g, 16.2 mmol) at 0 °C. The reaction mixture was stirred for 15 min at 0 °C and then for 1 hour at room temperature. The reaction was quenched with water (4.2 mL) and the precipitate was removed by filtration. The filtrate was dried (Na2SO4) and concentrated under reduced pressure. Chromatography of the residue (hexane-ethyl acetate, 3:1) gave 5.14 g (96 %) of allylic alcohol 4 as a colorless oil; [α]D25= +136.3 (c 0.79); 1H-NMR: δ 0.04 (3H, s, CH3), 0.05 (3H, s, CH3), 0.88 (9H, s, 3 x CH3), 1.40 (3H, bs, CH3), 1.47 (3H, bs, CH3), 2.29-2.35 (1H, m, OH), 3.61 (1H, dd, J5,5=10.6 Hz, J5,4=3.4 Hz, H5), 3.74 (1H, dd, J5,5=10.6 Hz, J5,4=3.6 Hz, H5), 4.29 (1H, m, H7), 4.37 (1H, m, H7) 4.76-4.80 (1H, m, H4), 5.18-5.21 (1H, m, H2), 5.84 (1H, dddd, J7,6=6.3 Hz, J7,6=6.2 Hz, J6,2=1.9 Hz, J6,4=1.9 Hz, H6), 5.92 (1H, d, J2,1=4.5 Hz, H1); 13C-NMR: δ -5.5, -5.4, 18.2, 25.8 (3 x C), 27.5, 27.6, 60.3, 66.4, 79.1, 81.9, 105.5, 112.4, 125.9, 141.5; Anal. Calcd for C16H30O5Si (330.50): C 58.15, H 9.15; found C 58.03, H 9.25.
5-O-(tert-Butyldimethylsilyl)-3-deoxy-1,2-O-isopropylidene-3-C-(E)-(2-thiocyanatoethylidene)-α-d-xylofuranose (7)
To a solution of (E)-5 (0.23 g, 0.70 mmol) in dry CH2Cl2 (1.7 mL) were added Et3N (0.15 mL, 1.04 mmol) and CH3SO2Cl (0.07 mL, 0.83 mmol) at 0 °C. The reaction mixture was stirred at 0 °C for 15 min and then at room temperature for 45 min. The solvent was evaporated under reduced pressure. The residue was diluted with diethyl ether (3 mL) and the solid was removed by filtration. Evaporation of the solvent under reduced pressure afforded crude mesylate which was used directly in the next reaction without any further purification. To a solution of crude mesylate (0.27 g, 0.66 mmol) in CH3CN (3 mL), KSCN (0.08 g, 0.82 mmol) was added. After stirring for 3 h at room temperature under a nitrogen atmosphere, the solvent was evaporated. The residue was diluted with diethyl ether (3 mL) and the solid was removed by filtration. The evaporation of the solvent under reduced pressure and chromatography of the residue (hexane-ethyl acetate, 7:1) afforded 0.18 g (70% from 5) of pure thiocyanate 7 as a colorless oil; [α]D25 = +164.3 (c 0.21); 1H-NMR: δ 0.05 (3H, s, CH3), 0.06 (3H, s, CH3), 0.88 (9H, s, 3 x CH3), 1.42 (3H, bs, CH3), 1.47 (3H, bs, CH3), 3.61-3.67 (2H, m, H7, H5), 3.74 (1H, dd, J5,5=10.6 Hz, J5,4=3.8 Hz, H5), 3.80 (1H, dd, J7,7= 13.0 Hz, J7,6= 8.8 Hz, H7), 4.98-5.03 (2H, m, H2, H4), 5.89 (1H, d, J2,1=4.4 Hz, H1), 5.95 (1H, dddd, J7,6= 8.8 Hz, J7,6=7.6 Hz, J6,4=1.8 Hz, J6,2=1.8 Hz, H6); 13C-NMR: δ -5.5, -5.4, 18.2, 25.8 (3 x C), 27.7, 27.9, 32.5, 66.3, 80.3, 81.9, 105.0, 111.4, 113.2, 119.4, 147.0; Anal. Calcd for C17H29NO4SSi (371.57): C 54.95, H 7.87, N 3.77, S 8.63; found C 54.83, H 7.77, N 3.85, S 8.50.
5-O-(tert-Butyldimethylsilyl)-3-deoxy-1,2-O-isopropylidene-3-C-(Z)-(2-thiocyanatoethylidene)-α-d-xylofuranose (6)
Et3N (3.18 mL, 22.9 mmol) and CH3SO2Cl (1.42 mL, 18.3 mmol) were added at 0 °C to a solution of (Z)-4 (5.05 g, 15.3 mmol) in dry CH2Cl2 (36 mL). The reaction mixture was stirred for 15 min at 0 °C and then for 45 min at room temperature. The solvent was evaporated under reduced pressure. The residue was diluted with diethyl ether (60 mL) and the solid was removed by filtration. Evaporation of the solvent under reduced pressure afforded crude mesylate which was used directly in the next reaction without further purification. To a solution of crude mesylate (5.99 g, 14.7 mmol) in CH3CN (55 mL), KSCN (1.78 g, 18.3 mmol) was added. After stirring for 5 h at room temperature the solvent was evaporated. The residue was diluted with diethyl ether (60 mL) and the solid was removed by fitration. The evaporation of the solvent at reduced pressure and chromatography of the residue (hexane-ethyl acetate, 7:1) gave 4.13 g (73% from 4) of pure thiocyanate 6 as a white solid; m.p. 58 – 60 °C; [α]D25 = +159.3 (c 0.34); 1H NMR: δ 0.06 (3H, s, CH3), 0.07 (3H, s, CH3), 0.89 (9H, s, 3 x CH3), 1.41 (3H, bs, CH3), 1.46 (3H, bs, CH3), 3.66 (1H, dd, J5,5=10.5 Hz, J5,4=3.2 Hz, H5), 3.74 (1H, dd, J5,5=10.5 Hz, J5,4=4.1 Hz, H5), 3.75 (1H, ddd, J7,7=13.1 Hz, J7,6=7.5 Hz, J7,2=1.2 Hz, H7), 3.95 (1H, dd, J7,7= 13.1 Hz, J7,6= 8.5 Hz, H7), 4.79-4.82 (1H, m, H4), 5.13-5.15 (1H, m, H2), 5.79-5.85 (1H, m, H6), 5.92 (1H, d, J2,1= 4.5 Hz, H1); 13C-NMR: δ -5.5, -5.4, 18.2, 25.9 (3 x C), 27.6, 27.9, 32.3, 66.3, 78.9, 81.7, 105.6, 111.7, 113.0, 119.0, 146.8; Anal. Calcd for C17H29NO4SSi (371.57): C 54.95, H 7.87, N 3.77, S 8.63; found C 54.86, H 7.95, N 3.85, S 8.55.
5-O-(tert-Butyldimethylsilyl)-3-deoxy-1,2-O-isopropylidene-3-isothiocyanato-3-C-vinyl-α-d-xylo-furanose (8)
A solution of (E)-7 (0.10 g, 0.27 mmol) in dry heptane (1 mL) was heated at 90 °C for 16 h. The solvent was evaporated under reduced pressure and chromatography of the residue on silica gel (hexane-ethyl acetate, 13:1) afforded 0.07 g (70%) of isothiocyanate 8. Alternatively, a solution of (Z)-6 (1.0 g, 2.69 mmol) in dry heptane (5.8 mL) was heated at 90 °C for 16 h under a nitrogen atmosphere. The solvent was evaporated under reduced pressure and the chromatography of the residue (hexane-ethyl acetate, 13:1) gave 0.82 g (82%) of isothiocyanate 8 as a colorless oil; [α]D25 = +49.8 (c 0.22); 1H-NMR: δ 0.06 (3H, s, CH3), 0.07 (3H, s, CH3), 0.88 (9H, s, 3 x CH3), 1.33 (3H, bs, CH3), 1.56 (3H, bs, CH3), 3.78 (1H, dd, J5,5=11.1 Hz, J5,4=5.5 Hz, H5), 3.86 (1H, dd, J5,5=11.1 Hz, J5,4=5.8 Hz, H5), 4.19 (1H, dd, J5,4=5.8 Hz, J5,4=5.5 Hz, H4), 4.50 (1H, d, J2,1=3.5 Hz, H2), 5.39 (1H, d, J7cis,6=10.6 Hz, H7cis), 5.56 (1H, d, J7trans,6=17.0 Hz, H7trans), 5.93 (1H, dd, J7trans,6=17.0 Hz, J7cis,6=10.6 Hz, H6), 5.96 (1H, d, J2,1=3.5 Hz, H1); 13C-NMR: δ -5.5, -5.4, 18.3, 25.8 (3 x C), 26.5, 26.7, 61.1, 74.9, 82.7, 87.9, 104.3, 113.1, 118.0, 130.7, 138.2; Anal. Calcd for C17H29NO4SSi (371.57): C 54.95, H 7.87, N 3.77, S 8.63; found C 54.82, H 7.98, N 3.68, S 8.71.
5-O-(tert-Butyldimethylsilyl)-3-deoxy-1,2-O-isopropylidene-3-methoxythiocarbonylamino-3-C-vinyl-α-d-xylofuranose (9)
To a solution of isothiocyanate 8 (0.58 g, 1.56 mmol) in dry methanol (15.5 mL) was added sodium methoxide (0.093 g, 1.72 mmol). The reaction mixture was stirred at room temperature for 4 h. The solvent was evaporated under reduced pressure and the residue was partitioned between CH2Cl2 (20 mL) and water (5 mL). The organic layer was dried (Na2SO4) and the solvent evaporated under reduced pressure. Chromatography of the residue (hexane–ethyl acetate, 11:1) afforded 0.60 g (95%) of compound 9 as a colorless oil; [α]D25 = +62.1 (c 0.49); 1H-NMR: δ 0.17 (3H, s, CH3), 0.18 (3H, s, CH3), 0.97 (9H, s, 3 x CH3), 1.35 (3H, bs, CH3), 1.52 (3H, bs, CH3), 3.71 (1H, dd, J5,4=3.0 Hz, J5,4=0.8 Hz, H4), 3.97-4.04 (2H, m, H5), 4.01 (3H, s, CH3O), 4.81 (1H, d, J2,1=3.7 Hz, H2), 5.29 (1H, dd, J7trans,6=17.5 Hz, J7trans,7cis=0.8 Hz, H7trans), 5.33 (1H, dd, J7cis,6=10.9 Hz, J7trans,7cis=0.8 Hz, H7cis), 5.92 (1H, d, J2,1=3.7 Hz, H1), 6.01 (1H, dd, J7trans,6=17.5 Hz, J7cis,6=10.9 Hz, H6), 9.37 (1H, bs, NH); 13C-NMR: δ -5.6, -5.3, 18.5, 26.0 (3 x C), 26.4, 26.7, 57.9, 59.1, 71.6, 78.6., 83.7, 104.5, 112.2, 117.0, 131.9, 191.3; Anal. Calcd for C18H33NO5SSi (403.62): C 53.57, H 8.24, N 3.47, S 7.94; found C 53.80, H 8.38, N 3.66, S 7.70.
5-O-(tert-Butyldimethylsilyl)-3-deoxy-1,2-O-isopropylidene-3-methoxycarbonylamino-3-C-vinyl-α-d-xylofuranose (10)
To a solution of 9 (0.56 g, 1.39 mmol) in CH3CN (13.5 mL) was added mesitylnitrile oxide (0.25 g, 1.53 mmol). The reaction mixture was stirred at room temperature for 23 h, acetonitrile was evaporated under reduce pressure. Chromatography of residue (hexane-ethyl acetate, 9:1) gave 0.50 g (93%) of 10 as a white crystals; m.p. 103 − 106 oC; [α]D25= +69.5 (c 0.28); 1H-NMR: δ 0.11 (3H, s, CH3), 0.12 (3H, s, CH3), 0.92 (9H, s, 3 x CH3), 1.33 (3H, bs, CH3), 1.52 (3H, bs, CH3), 3.62 (3H, s, CH3O), 3.79 (1H, m, H4), 3.94 (1H, d, J5,5=12.4 Hz, H5), 4.06 (1H, dd, J5,5=12.4 Hz, J5,4=3.0 Hz, H5), 5.07 (1H, d, J2,1=3.5 Hz, H2), 5.32 (1H, d, J7trans,6=17.5 Hz, H7trans), 5.37 (1H, d, J7cis,6=10.8 Hz, H7cis), 5.88 (1H, d, J2,1=3.5 Hz, H1), 6.08 (1H, dd, J7trans,6=17.5 Hz, J7cis,6=10.8 Hz, H6), 7.57 (1H, bs, NH); 13C-NMR: δ -5.7, -5.5, 18.2, 25.7 (3 x C), 26.3, 26.8, 51.8, 59.4, 68.6, 78.7., 83.4, 104.5, 112.1, 116.6, 132.6, 155.8; Anal. Calcd for C18H33NO6Si (387.55): C 55.79, H 8.58, N 3.61; found C 55.58, H 8.27, N 3.42.
5-O-(tert-Butyldimethylsilyl)-3-deoxy-1,2-O-isopropylidene-3-methoxycarbonylamino-α-d-xylo-furanose 3-C-carbaldehyde (11)
To a solution of 10 (0.30 g, 0.77 mmol) in 2:2:3 CCl4/CH3CN/H2O (8.5 mL) were added sodium periodate (0.68 g, 3.16 mmol) and ruthenium trichloride hydrate (4.2 mg, 2.5 mol %). The reaction mixture was stirred at room temperature for 20 h, then extracted with CH2Cl2 (3 x 20 mL). The combined organic layers were dried (Na2SO4) and concentrated under reduced pressure. The residue was purified by chromatography (hexane–ethyl acetate, 7:1) to afford 0.21 g (70%) of compound 11 as a colorless oil; [α]D25 = +69.3 (c 0.29); 1H-NMR: δ 0.09 (3H, s, CH3), 0.10 (3H, s, CH3), 0.90 (9H, s, 3 x CH3), 1.35 (3H, bs, CH3), 1.56 (3H, bs, CH3), 3.67 (3H, s, CH3O), 3.92 (1H, dd, J5,5=12.1 Hz, J5,4=1.8 Hz, H5), 4.01 (1H, dd, J5,5=12.1 Hz, J5,4=4.2 Hz, H5), 4.27 (1H, dd, J5,4=4.2 Hz, J5,4=1.8 Hz, H4) 5.12 (1H, d, J2,1=3.6 Hz, H2), 5.99 (1H, d, J2,1=3.6 Hz, H1), 7.31 (1H, bs, NH), 9.91 (1H, s, CHO); 13C-NMR: δ -5.7, -5.6, 18.1, 25.7 (3 x C), 26.3, 26.7, 52.4, 60.3, 71.8, 76.2, 84.4, 105.3, 113.3, 156.5, 197.4; Anal. Calcd for C17H31NO7Si (389.53): C 52.42, H 8.02, N 3.60; found C 52.27, H 8.27, N 3.42.
5-O-(tert-Butyldimethylsilyl)-3-deoxy-1,2-O-isopropylidene-3-methoxycarbonylamino-α-d-xylo-furanose 3-C-carboxylic acid (12)
A solution of NaClO2 (0.23 g, 2.54 mmol) and NaH2PO4 (0.285 g, 1.83 mmol) in water (1.55 mL) was added dropwise to the solution of aldehyde 11 (0.107 g, 0.275 mmol) in 4:4:1 acetonitrile/tert-butyl alcohol/2-methyl-2-butene (6.2 mL) at 0 oC over 5 min and then stirred at the same temperature for 25 min. The reaction mixture was poured into brine (8 mL) and extracted with ethyl acetate (3 x 10 mL). The combined organic layers were dried (Na2SO4) and concentrated under reduced pressure. The residue was purified by chromatography (1:2 hexane–ethyl acetate) to give 0.082 g (74%) of carboxylic acid 12 as a colorless oil; [α]D25 = +45.4 (c 0.57); 1H-NMR: δ 0.11 (3H, s, CH3), 0.12 (3H, s, CH3), 0.91 (9H, s, 3 x CH3), 1.35 (3H, bs, CH3), 1.53 (3H, bs, CH3), 3.76 (3H, s, CH3O), 4.22 (2H, m, H5), 4.42 (1H, m, H4), 5.04 (1H, d, J2,1=3.9 Hz, H2), 5.95 (1H, d, J2,1=3.9 Hz, H1), 8.30 (1H, bs, NH); 13C-NMR: δ -5.7, -5.6, 18.2, 25.6 (3 x C), 26.3, 26.5, 53.4, 61.0, 70.6, 76.8, 82.1, 104.3, 113.2, 159.5, 167.6; Anal. Calcd for C17H31NO8Si (405.52): C 50.35, H 7.71, N 3.45; found C 50.17, H 7.53, N 3.20.
5-O-[(tert-Butyldimethylsilyl)-3-deoxy-1,2-O-isopropylidene-3-methoxycarbonylamino-α-d-xylo-furanosyl-3-C-carbonyl]glycine methyl ester (13)
To a solution of glycine methyl ester hydrochloride (11 mg, 0.0886 mmol) in dry dichloromethane (0.5 mL) was added Et3N (0.041 mL, 0.30 mmol). The suspension was cooled to 0 oC. Then, a solution of aminoacid 12 (24 mg, 0.059 mmol) in dry CH2Cl2 (0.3 mL) and DCC (24.4 mg, 0.12 mmol) were added. The reaction mixture was stirred at 0 oC for 1 h and then at room temperature for 18 h. Dichloromethane (3 mL) was added and solution was washed with ice water (0.5 mL). The organic layer was dried (Na2SO4) and concentrated under reduced pressure. The residue was purified by chromatography (2:1 hexane–ethyl acetate) to afford 22 mg (78%) of dipeptide 13 as a colorless oil; [α]D25 = +35.1 (c 0.14); 1H-NMR: δ 0.11 (3H, s, CH3), 0.12 (3H, s, CH3), 0.91 (9H, s, 3 x CH3), 1.37 (3H, bs, CH3), 1.58 (3H, bs, CH3), 3.67 (3H, s, CH3O), 3.75 (3H, s, CH3O), 4.01 (1H, dd, J=18.4 Hz, JCH2,NH= 4.7 Hz, CH2NH), 4.13 (1H, dd, J5,5=12.4 Hz, J5,4=2.8 Hz, H5), 4.18 (1H, m, H5), 4.19 (1H, dd, J=18.4 Hz, JCH2,NH= 5.7 Hz, CH2NH), 4.25 (1H, m, H4), 5.15 (1H, d, J2,1=3.6 Hz, H2), 5.92 (1H, d, J2,1=3.6 Hz, H1), 7.93 (1H, bs, NH), 8.28 (1H, dd, JCH2,NH= 5.7 Hz, JCH2,NH= 4.7 Hz, NH); 13C-NMR: δ -5.7, -5.6, 18.2, 25.7 (3 x C), 26.5, 26.8, 41.5, 52.2, 52.3, 61.0, 69.7, 78.2, 82.6, 104.9, 113.1, 157.2, 168.3, 170.1; Anal. Calcd for C20H36N2O9Si (476.60): C 50.40, H 7.61, N 5.88; found C 50.22, H 7.49, N 5.61.