Ammonium Chloride → (6R)-2,6-Dimethylnon-2-ene

To (S)-citronellyl bromide (50 g, 0.228 mol) in THF (800 mL) at 0° C. was added LiCi (4.3 g) followed by CuCl2 (6.8 g). After 30 minutes methylmagnesium chloride (152 mL of a 3 M solution in THF, Aldrich) was added and the solution warmed to room temperature. After 10 hours the solution was cooled to 0° C. and a saturated aqueous solution of ammonium chloride carefully added. The resultant two layers were separated and the aqueous phase extracted with ether. The combined organic phases were dried (MgSO4) and concentrated to give (R)-2,6-dimethyl-non-2-ene. 32.6 9; 93%. Used without further purification. 1H NMR (400 MHz; CDCl3) δ 5.1 (m, 1H), 1.95 (m, 2H), 1.62 (s, 3H), 1.6 (s, 3H), 1.3 (m, 4H), 1.2 (m, 2H), 0.8 (s, 6H);13C NMR (100 MHz; CDCl3) δ 131.13, 125.28, 39.50, 37.35, 32.35, 25.92, 25.77, 20.31, 19.74, 17.81, 14.60. (R)-4-Methyl-heptanoic acid. To (R)-2,6-dimethyl-non-2-ene (20 g, 0.13 mol) in acetone (433 mL) was added a solution of CrO3 (39 g, 0.39 mol) in H2SO4 (33 mL)/H2O (146 mL) over 50 minutes. After 6 hours a further amount of CrO3 (26 g, 0.26 mol) in H2SO4 (22 mL)/H2O (100 mL) was added. After 12 hours the solution was diluted with brine and the solution extracted with ether. The combined organic phases were dried (MgSO4) and concentrated. Flash chromatography (gradient of 6:1 to 2:1 hexane/EtOAc) gave (R)-4-methyl-heptanoic acid as an oil. 12.1 g; 65%. MS, m/z (relative intensity): 143 [M−H, 100%]; 1H NMR (400 MHz; CDCl3) δ2.35 (m, 2H), 1.6 (m, 1H), 1.4 (m, 1H), 1.3 (m, 4H), 1.1 (m, 1H), 0.85 (s, 6H). (4R,5S)-4-Methyl-3-((R)-4-methyl-heptanoyl)-5-phenyl-oxazolidin-2-one. To (R)-4-methyl-heptanoic acid (19 g, 0.132 mol) and triethylamine (49.9 g, 0.494 mol) in THF (500 mL) at 0° C. was added trimethylacetylchloride (20 g, 0.17 mol). After 1 hour LiCl (7.1 g, 0.17 mol) was added followed by (4R,5S)-(+)-4-methyl-5-phenyl-2-oxazolidinone) 3 (30 g, 0.17 mol). The mixture was warmed to room temperature and after 16 hours the filtrate was removed by filtration and the solution concentrated under reduced pressure. Flash chromatography (7:1 hexane/EtOAc) gave (4R,5S)-4-methyl-3-((R)-4-methyl-heptanoyl)-5-phenyl-oxazolidin-2-one as an oil. 31.5 g; 79%. [α]D=+5.5 (c 1 in CHCl3). MS, m/z (relative intensity): 304 [M+H, 100%]; 1H NMR (400 MHz, CDCl3) δ7.4-7.2 (m, 5H), 5.6 (d, J=7.32 Hz, 1H), 4.75 (m, 1H), 2.96 (m, 1H), 2.86 (m, 1H), 1.62 (m, 1H), 1.43 (m, 1H), 1.25 (m, 4H), 1.12 (m, 1H), 0.85 (m, 9H); 13C NMR (100 MHz; CDCl3) 8173.70, 153.23, 133.81, 133.59, 128.92, 128.88, 128.92, 128.88, 125.83, 79.12, 54.93, 39.24, 33.66, 32.32, 31.47, 27.18, 26.52, 20.25, 19.57, 14.75, 14.52. (3S,5R)-5Methyl-3-((4R,5S)-4-methyl-2-oxo-5-phenyl-oxazolidine-3-carbonyl)-octanoic acid tert-butyl ester. To (4R,5S)-4-methyl-3-((R)-4-methyl-heptanoyl)-5-phenyl-oxazolidin-2-one (12.1 g, 0.04 mol) in THF (200 ml) at −50° C. was added sodium bis(trimethylsilyl)amide (48 mL of a 1 M solution in THF). After 30 min t-butylbromoaceate (15.6 g, 0.08 mol) was added. The solution was stirred for 4 hours at −50° C. and then warmed to room temperature. After 16 hours a saturated aqueous solution of ammonium chloride was added and the two layers separated. The aqueous phase was extracted with ether and the combined organic phases dried (MgSO4) and concentrated. Flash chromatography (9:1 hexane/EtOAc) gave (3S,5R)-5-methyl-3-((4R,5S)4-methyl-2-oxo-5-phenyl-oxazolidine-3-carbonyl)-octanoic acid tert-butyl ester as a white solid 12 g; 72%. [α]D=+30.2 (c 1 in CHCl3). 13C NMR (100 MHz; CDCl3) δ 176.47, 171.24, 152.72, 133.63, 128.87, 125.86, 80.85, 78.88, 55.34, 39.98, 38.77, 38.15, 37.58, 30.60, 28.23, 20.38, 20.13, 14.50, 14.28. (S)-2-(R)-2-Methyl-pentyl)-succinic acid 4-tert-butyl ester. To (3S,5R)-5-methyl-3-((4R,5S)-4-methyl-2-oxo-5-phenyl-oxazolidine-3-carbonyl)-octanoic acid tert-butyl ester (10.8 g, 0.025 mol) in H2O (73 mL) and THF (244 mL) at 0° C. was added a premixed solution of LiOH (51.2 mL of a 0.8 M solution) and H2O2 (14.6 mL of a 30% solution). After 4 hours a further 12.8 mL LiOH (0.8 M solution) and 3.65 mL of H2O2 (30% solution) was added. After 30 minutes sodium bisulfite (7 g), sodium sulfite (13 9), and water (60 mL) was added followed by hexane (100 mL) and ether (100 mL). The two layers were separated and the aqueous layer extracted with ether. The combined organic phases were concentrated to an oil that was dissolved in heptane (300 mL). The resultant solid was filtered off and the filtrate dried (MgSO4) and concentrated to afford (S)-2-((R)-2-methyl-pentyl)-succinic acid 4-tert-butyl ester (6 g, 93%) which was used immediately without further purification. MS, m/z (relative intensity): 257 [M+H, 100%]. (3S,5R-3-Benzyoxycarbonylamino-5-methyl-octanoic acid, tert-butyl ester. A solution of (S)-2-((R)-2-methyl-pentyl)-succinic acid 4-tert-butyl ester (6.0 g, 23.22 mmol) and triethylamine (3.64 mL, 26.19 mmol) in toluene (200 mL) was treated with diphenylphosphoryl azide (5.0 mL, 23.22 mL) and stirred at room temperature for 0.5 hours. After the reaction mixture was then heated at reflux for 3 h and cooled briefly, benzyl alcohol was added (7.2 mL, 69.7 mmol) and the solution heated for another 3 h. After the reaction mixture was allowed to cool, it was diluted with ethyl ether (200 mL) and the combined organic layer was washed successively with saturated NaHCO3 and brine and dried (Na2SO4). The concentrated organic component was purified by chromatography (MPLC) eluting with 8:1 hexanes:ethyl acetate to provide (3S,5R)-3-benzyoxycarbonylamino-5-methyl-octanoic acid, tert-butyl ester (6.4 g, 75.8%). MS: M+1: 364.2, 308.2. 1HNMR (400 MHz, CDCl3) δ 0.83 (t, 3H, J=6.59 Hz), 0.87 (d, 3H, J=6.59 Hz), 1.08-1.34 (m, 6H), 1.39 (s, 9H), 1.41-1.52 (m, 2H), 2.39 (m, 2H), 4.02 (m, 1H), 5.05 (s, 2H), 5.09 (m, 1H), and 7.24-7.32 (m, 5H) ppm. (3S,5R)-3-Amino-5-methyl-octanoic acid, tert-butyl ester. A solution of (3S,5R)-3-benzyoxycarbonylamino-5-methyl-octanoic acid, tert-butyl ester (2.14 g, 5.88 mmol) in THF (50 mL) was treated with Pd/C (0.2 g) and H2 at 50 psi for 2 hours. The reaction mixture was then filtered and concentrated to an oil in vacuo to give (3S,5R)-3-amino-5-methyl-octanoic acid, tert-butyl ester in quantitative yield. MS: M+1: 230.2, 174.1. 1HNMR (400 MHz, CDCl3) δ 0.85-0.86 (overlapping t and d, 6H), 1.13-1.40 (m, 6H), 1.44 (s, 9H), 1.60 (m, 1H), 2.31 (dd, 1H, J=7.81 and 15.86 Hz), 2.38(dd, 1H, J=5.13 and 15.86 Hz), 3.31(m, 1H), and 3.45(brs, 2H) ppm. (3S,5R)-3-Amino-5-methyl-octanoic acid hydrochloride. A slurry of (3S,5R)-amino-5-methyl-octanoic acid, tert-butyl ester (2.59 g, 11.3 mmol) in 6N HCl (100 mL) was heated under reflux 18 hours, cooled, and filtered over Celite. The filtrate was concentrated in vacuo to 25 mL and the resulting crystals were collected and dried to provide (3S,5R)-3-amino-5-methyl-octanoic acid hydrochloride, mp 142.5-142.7° C. (1.2 g, 50.56%). A second crop (0.91 g) was obtained from the filtrate. Anal. Calc'd for C9H19NO2.HCl: C, 51.55; H, 9.61, N, 6.68, Cl: 16.91. Found: C, 51.69; H: 9.72, N, 6.56, Cl: 16.63. MS: M+1: 174.1. 1HNMR (CD3OD) δ 0.89 (t, 3H, J=7.32 Hz), 0.92 (d, 3H, J=6.35 Hz), 1.12-1.18 (m, 1H), 1.25-1.35 (m, 2H), 1.35-1.42 (m, 2H), 1.54-1.64 (m, 2H), 2.50 (dd, 1H, J=7.81 and 17.33 Hz), 2.65 (dd, 1H, J=4.64 and 17.32 Hz), and 3.52 (m, 1H) ppm. (3S,5R)-3-Amino-5-methyl-octanoic acid hydrochloride acid salt. 5.3 g of 2S-(2R-methyl-pentyl)-succinic acid-4-tert-butyl ester contained in 30 mL methyltertbutyl ether is reacted at room temperature with 3.5 mL triethylamine followed by 6.4 g of diphenylphosphoryl azide. After allowing the reaction to exotherm to 45° C. and stirring for at least 4 hours, the reaction mixture is allowed to cool to room temperature and stand while the phases separated. The lower layer is discarded and the upper layer is washed with water, followed by dilute aqueous HCl. The upper layer is then combined with 10 mL of 6 N aqueous HCl, and stirred at 45-65° C. The reaction mixture is concentrated by vacuum distillation to about 10-14 mL and allowed to crystallize while cooling to about 5° C. After collecting the product by filtration, the product is washed with toluene and reslurried in toluene. The product is dried by heating under vacuum resulting in 2.9 g (67%) of white crystalline product. The product may be recrystallized from aqueous HCl. mp 137° C., HNMR (400 MHz, D6 DMSO) delta 0.84-0.88 (overlapping d and t, 6H), 1.03-1.13 (m, 1H), 1.16-1.37 (m, 4H), 1.57-1.68 (m, 2H), 2.55 (dd, 1H, J=7, 17 Hz), 2.67 (dd, 1H, J=6, 17 Hz), 3.40 (m, 1H), 8.1 (br s, 3H), 12.8 (brs, 1H).

1. temperatureAfter 10 hours the solution was cooled to 0° C.
2. customThe resultant two layers were separated
3. extractionthe aqueous phase extracted with ether
4. dry with materialThe combined organic phases were dried (MgSO4)
5. concentrationconcentrated

ORD record

ord-16ff4685b0d74a758e7462fdc300adde

Source dataset

uspto-grants-2009_04

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US07517909B2