Rf = 0.34 (Etoac/Heptane 1/2, Ninhydrin Stain)

Chemistry

tert-Butyl (1S,4RS)-4-acetyl-N-(tert-butoxycarbonyl)pyroglutamate (17). To a solution of diisopropylamine (10.5 ml, 74.4 mmol) in dry THF (125 ml) at -78 °C was added n-BuLi (46.5 ml, 1.6 M, 74.4 mmol). tert-Butyl (S)-N-(tert-butoxycarbonyl)pyroglutamate (16,10.0 g, 34.8 mmol) was dissolved in THF (50 ml) and slowly added. The mixture was stirred at -78 °C for 10 min and then at -40 °C for 20 min. The mixture was cooled back to -78 °C. N-Acetylimidazole (4.66 g, 42.4 mmol) was dissolved in THF (100 ml) and added to the reaction mixture, which was slowly allowed to warm to -20 °C and then quenched with sat. aq. NH4Cl. The mixture was extracted with EtOAc (3 × 200 ml). The combined extracts were washed with water, dried over MgSO4, and the solvent was evaporated in vacuo. The residue was purified by column chromatography (EtOAc/heptane 1/2 to 1/1) yielding a yellowish oil of 17 (7.56 g, 66%) as » 1:1 mixture of diastereomers.

Rf = 0.34 (EtOAc/heptane 1/2, Ninhydrin stain)

1H NMR (300 MHz, CDCl3): δ 1.46-1.52 (m, 18 H), 1.89-1.99 (m, ½ H), 2.23-2.35 (m, ½ H), 2.67-2.99 (m, 1 H), 2.42 (s, 1½ H), 2.46 (s, 1½ H), 3.52 (dd, J = 3.0, 9.7 Hz, ½ H), 3.77 (t, J = 9.3 Hz, ½ H), 4.40-4.49 (m, 1 H).

tert-Butyl (S)-2-((tert-butoxycarbonyl)amino)-3-(3-hydroxy-5-methyl-1H-pyrazol-4-yl)propanoate (18). To a solution of 17 (1.94 g, 5.93 mmol) in CH3CN (35 ml) was added hydrazine hydrate (0.49 ml, 10.1 mmol). The solution was refluxed for 3½ hours and then cooled to r.t. The solvent was evaporated in vacuo and the residue was purified by column chromatography (10% MeOH in CH2Cl2) to give a colorless solid of 18 (1.73 g, 86%).

Rf = 0.27 (10% MeOH in CH2Cl2, Ninhydrin stain)

1H NMR (300 MHz, CDCl3): δ 1.32-1.43 (m, 18 H), 2.14 (m, 3 H), 2.63-2.83 (m, 2 H), 4.03-4.35 (m, 1 H), 6.63 (br s, 1 H), 8.45 (br s, 1 H).

13C NMR (75 MHz, CDCl3): δ 10.3, 10.6, 24.7, 25.1, 27.8, 28.3, 54.9, 57.4, 79.1, 80.2, 80.8, 81.4, 98.4, 142.8, 155.6, 156.6, 163.3, 163.8, 171.1, 171.8. (mixture of rotamers or tautomers; all peaks are listed).

(S)-tert-Butyl 2-((tert-butoxycarbonyl)amino)-3-(3-(2-ethoxy-2-oxoethoxy)-5-methyl-1H-pyrazol-4-yl)propanoate (19a). Compound 18 (750 mg, 2.20 mmol) was dissolved in DMF (20 ml). K2CO3 (860 mg, 6.23 mmol) was added, and the mixture was stirred at r.t. for 30 min. Ethyl bromoacetate (0.25 ml, 2.20 mmol) was added and stirring was continued for 3 hours. Water (50 ml) was added and the mixture was extracted with Et2O (4 × 50 ml). The combined extracts were washed with brine (50 ml), dried over MgSO4, and the solvent was removed in vacuo. The residue was purified by column chromatography (EtOAc/heptane 1/2 to 1/1) yielding a colorless oil of 19a (342 mg, 36%).

Rf = 0.30 (EtOAc/heptane 1/1, Ninhydrin stain)

1H NMR (300 MHz, CDCl3): δ 1.28 (t, J = 7.1 Hz, 3 H), 1.40 (s, 9 H), 1.41 (s, 9 H), 2.16 (s, 3 H), 2.75-2.87 (m, 2 H), 4.23 (q, J = 7.1 Hz, 2 H), 4.31 (m, 1 H), 4.70 (d, J = 16.0 Hz, 1 H), 4.79 (d, J = 16.0 Hz, 1 H), 5.55 (d, J = 8.2 Hz, 1 H).

13C NMR (75 MHz, CDCl3): δ 10.2, 14.2, 24.7, 27.9, 28.3, 54.5, 61.1, 65.0, 79.1, 81.3, 97.5, 139.1, 155.3, 161.0, 169.0, 171.1.

(S)-tert-Butyl 2-((tert-butoxycarbonyl)amino)-3-(3-(diethyl-phosphonomethoxy)-5-methyl-1H-pyrazol-4-yl)propanoate (19b). Compound 18 (2.00 g, 5.87 mmol) was dissolved in DMF (45 ml). K2CO3 (2.30 g, 16.7 mmol) was added and the mixture was heated to 60 °C for 30 min. Diethyl ((p-tosyloxy)methyl)phosphonate (1.89 g, 5.87 mmol) dissolved in DMF (5 ml) was added. The mixture was stirred at 60 °C overnight. Cold water (200 ml) and brine (20 ml) were added. The mixture was extracted with CH2Cl2 (10 × 150 ml). The combined extracts were dried over MgSO4 and the solvent was removed in vacuo. The residue was purified by flash chromatography (EtOAc to 6% MeOH in EtOAc) yielding a slightly yellow oil of 19b (870 mg, 30%).

Rf = 0.18 (EtOAc, Ninhydrin stain)

1H NMR (300 MHz, CDCl3): δ 1.35 (t, J = 7.1 Hz, 3 H), 1.36 (t, J = 7.1 Hz, 3 H), 1.40 (s, 18 H), 2.72 (d, J = 6.6 Hz, 2 H), 4.16-4.28 (m, 5 H), 4.55 (dd, J = 14.2, 8.3 Hz, 1 H), 4.62 (dd, J = 14.2, 8.1 Hz, 1 H), 5.21 (d, J = 8.2 Hz, 1 H).

13C NMR (75 MHz, CDCl3): δ 10.2, 16.4, 16.5, 24.9, 27.8, 28.3, 54.4, 60.7 (d, J = 168 Hz), 62.7, 62.8, 79.3, 81.3, 97.3, 139.0, 155.1, 161.1 (d, J = 10.4 Hz), 171.1.

(S)-tert-Butyl 2-((tert-butoxycarbonyl)amino)-3-(5-hydroxy-1,3-dimethyl-1H-pyrazol-4-yl)propanoate (20). Compound 17 (6.00 g, 18.4 mmol) was dissolved in CH3CN (150 ml) and methylhydrazine (1.20 ml, 22.1 mmol) was added. The mixture was refluxed for 4 hours. The solvent was removed in vacuo. The residue was purified by flash chromatography (2% to 10% MeOH in CH2Cl2) yielding a colorless foam of 20 (4.98 g, 77%).

Rf = 0.31 (10% MeOH in CH2Cl2, Ninhydrin stain)

1H NMR (300 MHz, CDCl3): δ 1.40 (s, 18 H), 2.15 (s, 3 H), 2.62-2.78 (m, 2 H), 3.38 (s, 3 H), 4.17 (br s, 1 H), 6.83 (br s, 1 H).

13C NMR (75 MHz, CDCl3): δ 10.9, 25.1, 28.0, 28.4, 30.8, 55.6, 79.1, 81.2, 99.4, 144.2, 155.7, 162.0, 171.3.

(S)-tert-Butyl 2-((tert-butoxycarbonyl)amino)-3-(3-(tert-butyldimethylsilyloxy)-5-methyl-1H-pyrazol-4-yl)propanoate (21). To a solution of 18 (1.50 g, 4.40 mmol) in CH2Cl2 (75 ml) were added triethylamine (1.86 ml, 13.4 mmol) and tert-butyldimethylsilylchloride (TBS-Cl) (0.94 g, 6.23 mmol). The mixture was stirred at r.t. for 4 hours. Et2O (75 ml) was added and the mixture was washed with brine (75 ml). The organic phase was dried over MgSO4 and the solvent was removed in vacuo. The residue was purified by column chromatography (EtOAc/Heptane 1:2) yielding a colorless oil of 21 (1.77 g, 88%).

Rf = 0.30 (EtOAc/Heptane 1:2, Ninhydrin stain)

1H NMR (300 MHz, CDCl3): δ 0.29 (s, 3 H), 0.30 (s, 3 H), 1.01 (s, 9 H), 1.39 (s, 9 H), 1.40 (s, 9 H), 2.17 (s, 3 H), 2.69 (d, J = 6.5 Hz, 2 H), 4.15 (m, 1 H), 5.46 (d, J = 7.7 Hz, 1 H).

13C NMR (75 MHz, CDCl3): δ -4.4, -4.3, 10.4, 18.1, 24.7, 25.9, 27.9, 28.4, 55.5, 79.2, 81.1, 99.6, 137.8, 155.4, 158.9, 171.5.

(S)-tert-Butyl 2-((tert-butoxycarbonyl)amino)-3-(5-(2-ethoxy-2-oxoethoxy)-1,3-dimethyl-1H-pyrazol-4-yl)propanoate (22a) and (S)-tert-butyl 2-((tert-butoxycarbonyl)amino)-3-(1-(2-ethoxy-2-oxoethyl)-2,5-dimethyl-3-oxo-2,3-dihydro-1H-pyrazol-4-yl)propanoate (32). Compound 20 (660 mg, 1.86 mmol) was dissolved in DMF (7 ml). K2CO3 (770 mg, 5.58 mmol) and ethyl bromoacetate (620 mg, 3.71 mmol) were added and the mixture was stirred at r.t. for 3 hours. Water (40 ml) was added and the mixture was extracted with Et2O (5 × 50 ml). The combined extracts were washed with brine (50 ml), dried over MgSO4, and the solvent was evaporated. The residue was purified by flash chromatography (EtOAc/heptane 1/1 to 1/0) yielding 22a (250 mg, 30%) and 32 (370 mg, 45%) as colorless oils.

22a:

Rf = 0.24 (EtOAc/heptane 1/1, Ninhydrin stain)

1H NMR (300 MHz, CDCl3): δ 1.30 (t, J = 7.1 Hz, 3 H), 1.39 (s, 9 H), 1.41 (s, 9 H), 2.14 (s, 3 H), 2.77 (d, J = 6.7 Hz, 2 H), 3.69 (s, 3 H), 4.20-4.34 (m, 3 H), 4.63 (d, J = 17 Hz, 1 H), 4.64 (d, J = 17 Hz, 1 H), 5.13 (d, J = 8.3 Hz, 1 H).

13C NMR (75 MHz, CDCl3): δ 12.7, 14.0, 26.2, 27.6, 28.1, 34.0, 54.0, 61.2, 69.8, 79.3, 81.6, 98.0, 146.0, 150.7, 154.7, 167.8, 170.7.

32:

Rf = 0.15 (EtOAc/heptane 1/1, Ninhydrin stain)

1H NMR (300 MHz, CDCl3): δ 1.24 (t, J = 7.1 Hz, 3 H), 1.41 (s, 9 H), 1.42 (s, 9 H), 2.12 (s, 3 H), 2.69 (dd, J = 14.5 Hz, 4.1 Hz, 1H), 2.79 (dd, J = 14.7 Hz, 4.1 Hz, 1H), 3.28 (s, 3 H), 4.07-4.24 (m, 3 H), 4.30 (s, 2H), 6.76 (br s, 1 H).

13C NMR (75 MHz, CDCl3): δ 10.0, 13.7, 24.6, 27.4, 27.9, 28.7, 46.9, 54.8, 61.3, 78.3, 80.4, 104.5, 149.4, 155.2, 166.0, 166.4, 170.7.

(S)-tert-Butyl 2-((tert-butoxycarbonyl)amino)-3-(5-(diethylphosphonomethoxy)-1,2-dimethyl-1H-pyrazol-4-yl)propanoate (22b). Compound 20 (1.50 g, 4.23 mmol) was dissolved in DMF (15 ml). K2CO3 (1.73 g, 12.5 mmol) and diethyl ((p-tosyloxy)methyl)phosphonate (2.73 g, 8.48 mmol) were added and the mixture was stirred at 50 °C for 20 hours. Cold water (75 ml) was added. The mixture was extracted with Et2O (6 × 100 ml). The combined extracts were dried over MgSO4 and the solvent was evaporated in vacuo. The residue was purified by flash chromatography (EtOAc) yielding a colorless oil of 22b (1.14 g, 53%).

Rf = 0.20 (EtOAc, Ninhydrin stain)

1H NMR (300 MHz, CDCl3): δ 1.37 (t, J = 7.0 Hz, 6 H), 1.41 (s, 18 H), 2.17 (s, 3 H), 2.76 (d, J = 6.9 Hz, 2 H), 3.67 (s, 3 H), 4.16-4.46 (m, 7 H), 5.21 (d, J = 8.3 Hz, 1 H).

13C NMR (75 MHz, CDCl3): δ 12.8, 16.4, 16.5, 26.3, 27.9, 28.3, 34.0, 54.2, 62.8, 62.9, 67.6 (d, J = 166 Hz), 79.5, 81.9, 98.6, 146.2, 151.5 (d, J = 10.7), 154.9, 170.9.

(S)-tert-Butyl 2-((tert-butoxycarbonyl)amino)-3-(3-(tert-butyldimethylsilyloxy)-1,5-dimethyl-1H-pyrazol-4-yl)propanoate (23). Sodium hydride (165 mg, 60% in mineral oil, 4.13 mmol) was suspended in dry DMF (30 ml) and cooled to -50 °C. 21 (1.65 g, 3.63 mmol) dissolved in DMF (30 ml) was added and the mixture was stirred for 10 min. Methyl iodide (560 mg, 3.94 mmol) dissolved in DMF was added. The mixture was allowed to stir at r.t. for 1 hour. Water (350 ml) was added and extracted with Et2O (5 × 300 ml). The combined organic phases were washed with brine (200 ml), dried over MgSO4, and the solvent was removed in vacuo. The residue was purified by column chromatography (EtOAc/Heptane 1:3) yielding a colorless oil of 23 (1.32 g, 77%).

Rf = 0.42 (EtOAc/Heptane 1:2, Ninhydrin stain)

1H NMR (300 MHz, CDCl3): δ 0.27 (s, 3 H), 0.29 (s, 3 H), 1.00 (s, 9 H), 1.39 (s, 9 H), 1.40 (s, 9 H), 2.10 (s, 3 H), 2.65 (d, J = 6.3 Hz, 2 H), 3.55 (s, 3H), 4.08 (m, 1 H), 5.52 (d, J = 7.4 Hz, 1 H).

13C NMR (75 MHz, CDCl3): δ -4.5, -4.4, 9.9, 18.0, 24.9, 25.9, 27.9, 28.3, 35.6, 55.8, 79.0, 80.9, 99.5, 136.9, 155.4, 157.2, 171.4.

(S)-tert-Butyl 2-((tert-butoxycarbonyl)amino)-3-(3-(tert-butyldimethylsilyloxy)-1-ethyl-5-methyl-1H-pyrazol-4-yl)propanoate (24). Sodium hydride (728 mg, 60 % in mineral oil, 16.8 mmol) in dry DMF (35 ml) was cooled to -50 °C. 21 (7.28 g, 16.0 mmol) dissolved in dry DMF (35 ml) was added. The mixture was stirred for 10 min at -50 °C. Ethyl bromide (1.22 ml, 16.3 mmol) was added and the mixture was stirred for 1 hour at r.t. Water (600 ml) was added and the mixture was extracted with Et2O (4 × 500 ml). The combined extracts were washed with brine, dried over MgSO4, and the solvent removed in vacuo. The residue was purified by column chromatography (EtOAc/petroleum ether 1:4) yielding 24 (5.49 g, 68%) as a viscous colorless oil.

1H NMR (300 MHz, CDCl3): δ 0.26 (s, 3 H), 0.29 (s, 3 H), 1.00 (s, 9 H), 1.28 (t, J = 7.1 Hz, 3 H), 1.37 (s, 9 H), 1.40 (s, 9 H), 2.10 (s, 3 H), 2.59-2.74 (m, 2 H), 3.84 (q, J = 7.1 Hz, 2 H), 4.10 (m, 1 H), 5.61 (d, J = 7.5 Hz, 1 H).

13C NMR (75 MHz, CDCl3): δ -4.6, -4.5, 9.5, 15.2, 17.9, 24.8, 25.9, 27.7, 28.2, 43.0, 55.6, 78.8, 80.6, 99.1, 135.8, 155.2, 157.1, 171.3.

(S)-tert-butyl 2-((tert-butoxycarbonyl)amino)-3-(1-benzyl-3-(tert-butyldimethylsilyloxy)-5-methyl-1H-pyrazol-4-yl)propanoate (25). Sodium hydride (380 mg, 60% in mineral oil, 8.77 mmol) in dry DMF (15 ml) was cooled to -50 °C. 21 (3.80 g, 8.35 mmo1) dissolved in dry DMF (15 ml) was added. The mixture was stirred for 10 min at -50 °C. Benzyl bromide (1.0 ml, 8.36 mmol) was added and the mixture was stirred for l hour at r.t. Water (200 ml) was added and the mixture was extracted with Et2O (5 × 200 ml). The combined extracts were washed with brine, dried over MgSO4, and the solvent was removed in vacuo. The residue was purified by column chromatography (EtOAc/petroleum ether 1:3) yielding 25 (2.80 g, 62%) as a viscous colorless oil.

1H NMR (300 MHz, CDCl3): δ 0.28 (s, 3 H), 0.30 (s, 3 H), 1.01 (s, 9 H), 1.34 (s, 9 H), 1.40 (s, 9 H), 2.04 (s, 3 H), 2.60-2.75 (m, 2 H), 4.12 (q, J = ca. 7 Hz, 1 H), 5.03 (s, 2 H), 5.61 (d, J = 7.6 Hz, 1 H), 7.02-7.30 (m, 5 H).

13C NMR (75 MHz, CDCl3): δ -4.4, -4.2, 10.0, 18.2, 25.1, 26.0, 27.8, 27.9, 28.4, 52.5, 55.7, 79.1, 81.0, 100.4, 126.7, 127.2, 128.4, 128.5, 137.1, 137.5, 155.4, 157.6, 171.4.

(S)-tert-Butyl 2-((tert-butoxycarbonyl)amino)-3-(3-hydroxy-1,5-dimethyl-1H-pyrazol-4-yl)propanoate (26). Compound 23 (1.10 g, 2.35 mmol) was dissolved in DMF (20 ml). Potassium fluoride (500 mg, 8.62 mmol) was added and the mixture was stirred at r.t. for 48 hours. Water (250 ml) was added and the mixture was extracted with Et2O (4 × 250 ml). The combined extracts were washed with brine (150 ml), dried over MgSO4, and the solvent was removed in vacuo. The residue was purified by column chromatography (EtOAc) yielding a colorless oil of 26 (750 mg, 90%).

Rf = 0.33 (EtOAc, Ninhydrin stain)

1H NMR (300 MHz, CDCl3): δ 1.40 (s, 9 H), 1.41 (s, 9H), 2.12 (s, 3 H), 2.74 (dd, J = 5, 14 Hz, 1 H), 2.79 (dd, J = 6, 14 Hz, 1 H), 3.57 (s, 3 H), 4.24 (m, 1 H), 5.79 (d, J = 7.5 Hz, 1 H).

13C NMR (75 MHz, CDCl3): δ 9.8, 25.1, 27.9, 28.4, 34.9, 55.1, 79.1, 81.3, 97.5, 138.6, 155.4, 159.5, 171.1.

(S)-tert-Butyl 2-((tert-butoxycarbonyl)amino)-3-(1-ethyl-3-hydroxy-5-methyl-1H-pyrazol-4-yl)propanoate (27). Compound 24 (5.49 g, 11.4 mmol) was dissolved in DMF (100 ml). KF (2.50 g, 43.0 mmol) was added, and the mixture was stirred at r.t. for 3 days. Water (500 ml) was added, and the mixture was extracted with Et2O (5 × 400 ml). The extracts were washed with brine, dried over MgSO4, and the solvent was evaporated. The residue was purified by column chromatography (EtOAc/petroleum ether 1/1 to 1/0) yielding a colorless viscous oil of 27 (3.71 g, 88%).

1H NMR (300 MHz, CDCl3): δ 1.33 (t, J = 7.2 Hz, 3 H), 1.38 (s, 9 H), 1.41 (s, 9 H), 2.12 (s, 3 H), 2.72 (dd, J = 4.7, 14.5 Hz, 1 H), 2.80 (dd, J = 6.8, 14.7 Hz, 1 H), 3.86 (q, J = 7.2 Hz, 2 H), 4.24 (q, J = ca. 6 Hz, 1 H), 5.91 (d, J = 7.8 Hz, 1 H).