2.1. Synthesis Description
General Experimental Details. NMR spectra were recorded with a Bruker Avance II 400 MHz and 1H NMR spectra were assigned using 2D methods. Chemical shifts are given in ppm downfield from the signal for Me4Si, with reference to residual C6D6 (1H NMR 7.16, 13C NMR 128.06) or D2O (1H NMR 4.79). Reactions were monitored by TLC using alumina plates coated with silica gel and visualized either by using UV light or by charring with para-anisaldehyde. Preparative chromatography was performed with silica gel (35–70 μm, 60 Å) or Biotage Isolera One SNAP columns. Dichloromethane and toluene were dried on an mBraun solvent dispense system, benzyl alcohol, triethylamine, and phosphorous trichloride were distilled prior to use, and pyridine (extra dry) and all other reagents were used as supplied from the manufacturer. NMR spectra of compounds 3, 4, 8, 9, and 10 are provided in the Supplementary Material available online at http://dx.doi.org/10.1155/2016/3475235.
1,6-Dideoxy-1,6-diphosphoramidate Mannitol (
3
). Compound 9 (95 mg, 0.09 mmol) was dissolved in EtOAc/EtOH/H2O (3 : 5 : 2, 4 mL) and Pd/C (10%, 66 mg) was added and the mixture was hydrogenolysed at atmospheric pressure. After 4 h the mixture was filtered through Celite and concentrated down to approximately 1 mL, H2O (20 mL) was added, and the mixture was lyophilized to give 3 (27 mg, 89%). αD21 +19 (c 0.5, D2O), 1H NMR (D2O): δ 3.93 (bs, 2H), 3.78 (bs, 2H), 3.40 (bs, 2H), 3.06 (bs, 2H). 13C NMR (D2O): δ 70.5 (CH), 66.9 (CH), 42.5 (CH2). 31P NMR (D2O): δ 0.02. HRMS (ESI) calcd. for C6H17N2O10P2 (M)−: 339.0358, found: 339.0382.
1,6-Dideoxy-1,6-dimethansulfonamide Mannitol (
4
). Compound 10 (55 mg, 0.08 mmol) was dissolved in EtOAc/EtOH/H2O (3 : 5 : 2, 3.3 mL) and Pd/C (10%, 100 mg) was added and the mixture was hydrogenolysed at atmospheric pressure. After 3 h Pd/C (10%, 50 mg) was added and the mixture was hydrogenolysed at atmospheric pressure for another 18 h. The mixture was filtered through Celite and concentrated down to approximately 1 mL, H2O (20 mL) was added, and the mixture was lyophilized to give 4 (26 mg, 99%). αD21 +21 (c 0.4, D2O), 1H NMR (D2O): δ 3.73–3.80 (m, 4H, H-2, H-3, H-4, H-5), 3.47 (dd, 2H, J 13.5, 2.2 Hz, H-1, H-6), 3.20 (dd, 2H, J 13.5, 6.2 Hz, H-1′, H-6′), 3.09 (s, 6H, SCH3). 13C NMR (D2O): δ 69.7, 69.3, 45.7, 38.9. HRMS (ESI) calcd. for C8H20N2O8S2Na (M+Na)+: 359.0559, found: 359.0586.
1,6-Di-O-trityl Mannitol (
6
). Mannitol (5) (5.05 g, 27.57 mmol) was coevaporated from pyridine two times and then suspended in pyridine (95 mL) and stirred at r.t. under nitrogen. Trityl chloride (18.55 g, 66.55 mmol) was added followed by AgNO3 (12.20 g, 71.84 mmol). After 18 h CH2Cl2 was added and the mixture was washed twice with NaHCO3 (sat. aq.). The aqueous phase was extracted once with CH2Cl2 and the combined organic phase was dried (MgSO4), concentrated, and coevaporated from toluene. The residue was purified by chromatography (Biotage Isolera One, SNAP 50 g, EtOAc 0–100% in heptane; the material was split into four equal parts before chromatography and the clean fractions were pooled) to give 6 (11.17 g, 61%). Spectral data was in agreement with previously published data [20].
2,3,4,5-Tetra-O-benzyl Mannitol (
7
). Compound 6 (11.06 g, 16.58 mmol) was dissolved in THF (100 mL) and stirred at r.t. under argon. Benzyl bromide (9 mL, 75.67 mmol) was added followed by NaH (60% suspension in oil, 4.03 g, and 100.75 mmol). After 18 h the mixture was filtered through Celite, eluting with Et2O and then washed once with H2O, dried (MgSO4), and concentrated to give 1,6-di-O-trityl-2,3,4,5-tetra-O-benzyl mannitol that was used in the next step without further purification. 1,6-Di-O-trityl-2,3,4,5-tetra-O-benzyl mannitol was dissolved in n-BuOH/CH2Cl2 (1 : 1, 230 mL) and trifluoroacetic acid (23 mL, 135 mmol) was added and the mixture was stirred at r.t. After 18 h the mixture was poured into NaHCO3 (sat. aq., 250 mL) and stirred for 5 min. The phases were separated and the organic phase was concentrated down. The residue was purified by chromatography (CH2Cl2 followed by pentane/EtOAc 1 : 1) to give 7 (6.87 g, 76% over two steps). Spectral data was in agreement with previously published data [21].
1,6-Azido-1,6-dideoxy-2,3,4,5-tetra-O-benzyl Mannitol (
8
). Compound 7 (1.37 g, 2.53 mmol) was dissolved in dry pyridine (4 mL) and tosyl chloride (1.22 g, 6.39 mmol) was added. The mixture was stirred for 18 h at r.t. under N2. H2O was added and the mixture was extracted twice with CH2Cl2 and the combined organic phase was washed twice with H2O, dried (MgSO4), concentrated, and coevaporated from toluene twice to give 2,3,4,5-tetra-O-benzyl-1,2-tosyl mannitol. This material was dissolved in DMSO (3 mL) and NaN3 (650 mg, 10.0 mmol) was added. The mixture was heated to 100°C for 18 h followed by 150°C for another 18 h. The reaction was allowed to cool before brine was added. The mixture was extracted thrice with ether, dried (MgSO4), concentrated, and coevaporated from toluene. The residue was purified by chromatography (Biotage Isolera One, SNAP 50 g, EtOAc 5–95% in heptane) to give 8 (774 mg, 60%) as a yellow oil. IR (ATR) υ 2096 cm−1 (N3), αD24 +100 (c 0.5, Benzene), 1H NMR (C6D6): δ 7.26–7.29 (m, 8H, ArH), 7.14–7.19 (m, 8H, ArH), 7.06–7.12 (m, 4H, ArH), 4.64, 4.49 (ABq, 2H each, J 11.5 Hz, PhCH2), 4.38, 4.18 (ABq, 2H each, J 11.5 Hz, PhCH2), 3.87–3.89 (m, 2H, H-3, H-4), 3.64–3.68 (m, 2H, H-2, H-5), 3.37, 3.25 (dABq, 2H each, J 13.4, 5.3, 2.8 Hz, H-1, H-1′, H-6, H-6′). 13C NMR (C6D6): δ 138.8, 138.2, 128.2, 128.1, 128.00, 127.96, 79.9, 79.2, 74.6, 72.2, 50.9. HRMS (ESI) calcd. for C34H36N6O4Na (M+Na)+: 615.2696, found: 615.2687.
1,6-Dideoxy-1,6-di-(di-benzyl-phosphoramidate)-2,3,4,5-tetra-O-benzyl Mannitol (
9
). Compound 8 (94 mg, 0.16 mmol) was dissolved in dry toluene (4 mL) and stirred at r.t. under N2. Tribenzyl phosphite [22] (560 mg, 1.59 mmol) dissolved in dry toluene (2 mL) was added and the mixture was heated to 90°C. After 18 h the mixture was allowed to cool down and then concentrated. The residue was purified by chromatography (SiO2, heptane/EtOAc 1 : 4) to give 9 (103 mg, 61%) as a clear oil. αD21 +19 (c 0.6, C6D6), 1H NMR (C6D6): δ 6.96–7.40 (m, 40H, ArH), 5.00 (d, 4H, J 7.8 Hz, PhCH2), 4.97 (d, 4H, J 7.9 Hz, PhCH2), 4.79, 4.71 (ABq, 2H each, J 11.3 Hz, PhCH2), 4.46, 4.39 (ABq, 2H each, J 11.6 Hz, PhCH2), 4.00–4.04 (m, 2H, H-3, H-4), 3.82–3.87 (m, 2H, H-2, H-5), 3.38–3.47 (m, 4H, H-1, H-1′, H-6, H-6′), 3.28–3.37 (m, 2H, NH). 13C NMR (C6D6): δ 139.4, 138.9, 137.5, 137.4, 128.7, 128.2, 127.94, 127.91, 127.7, 80.6, 80.5, 79.5, 74.7, 72.0, 68.2, 68.1, 41.6. 31P NMR (C6D6): δ 23.9. HRMS (ESI) calcd. for C62H67N2O10P2 (M+H)+: 1061.4271, found: 1061.4294.
1,6-Dideoxy-1,6-dimethansulfonamide-2,3,4,5-tetra-O-benzyl Mannitol (
10
). Compound 8 (117 mg, 0.20 mmol) was dissolved in dry toluene (4 mL) and PPh3 on polystyrene (280 mg, 3.1 mmol/g, 0.87 mmol) was added and the mixture was stirred at 60°C for 18 h. The mixture was allowed to cool and mesyl chloride (0.10 mL, 1.29 mmol) was added. The mixture was stirred at r.t. under N2 for 90 min and then Na2CO3 (3 mL, sat. aq.) was added. This mixture was stirred at r.t. for an additional 18 h before the solid support was filtered and washed with EtOAc. The organic phase was washed twice with H2O and the aqueous phase was extracted once with EtOAc. The combined organic phase was dried (MgSO4) and concentrated. The residue was purified by chromatography (Biotage Isolera One, SNAP 25 g, EtOAc 5–95% in heptane) to give 10 (774 mg, 60%) as a clear oil. αD23 +26 (c 0.9, C6H6), 1H NMR (C6D6): δ 7.41–7.43 (m, 4H, ArH), 7.27–7.29 (m, 4H, ArH) 7.15–7.22 (m, 8H, ArH), 7.05–7.12 (m, 4H, ArH), 4.80, 4.71 (ABq, 2H each, J 11.3 Hz, PhCH2), 4.60 (t, 2H, J 6.2 Hz, NH), 4.42, 4.38 (ABq, 2H each, J 11.6 Hz, PhCH2), 3.92–3.93 (m, 2H, H-3, H-4), 3.74–3.79 (m, 2H, H-2, H-5), 3.26–3.39 (m, 4H, H-1, H-1′, H-6, H-6′), 2.26 (s, 6H, SCH3). 13C NMR (C6D6): δ 138.9, 138.4, 128.9, 128.8, 128.6, 128.4, 79.9, 79.5, 74.8, 72.4, 43.2, 39.6. HRMS (ESI) calcd. for C36H45N2O8S2 (M+H)+: 697.2617, found: 697.2624.