a. Synthesis of 2-(3-bromophenyl)[1,3]dioxolane: 870 g (4.56 mol) of 3-bromobenzaldehyde, 2.6 L (45.6 mol) of 1,2-ethylene glycol, and 87 g (0.46 mol) of p-toluenesulfonic acid were dissolved in 4 L of toluene. The reaction mixture was refluxed for 5 h. After cooling to ambient temperature, 30.1 L of aqueous 1N sodium hydroxide was added. The mixture was filtered through diatomaceous earth and the organic phase was washed with 2 L of water. After evaporation of the solvent, 1060 g of 2-(3-bromophenyl)[1,3]dioxolane was obtained in quantitative yield.
b. Synthesis of 3-boronic acid-benzaldehyde: The reaction was carried out according to a similar method to that used for the preparation of tert-butyl (3-boronic acid-phenyl)methylcarbamate (Example LD) using 819 g (3.57 mol) of 2-(3-bromophenyl)[1,3]dioxolane and 355 g of unpurified dioxolane.
c. Synthesis of ethyl (S)-2- tert-butoxycarbonylamino-3-(3'-formyl-biphenyl-4-yl)propanoate: following a similar method to that used for the preparation of (S)-2- tert-butoxycarbonylamino-3-[3'-(tert-butoxycarbonylmethylamino)biphenyl-4-yl]propanoate (Example LE), 173 g (391 mmol) of ethyl (S)-2-tert-butoxycarbonyl amino-3-(4-trifluoromethanesulfonyloxyphenyl)propionate and 82 g (547 mmol) 3-boronic acid-benzaldehyde to give 95.7 g of coupling product in 61% yield.
d. Synthesis of ethyl (S)-2-(tert-butoxycarbonylamino)-3-(3'-methylaminomethylbiphenyl-4-yl)propionate: To a 200 mL methanol solution of 25 g (63.0 mmol) of ethyl (S)-2-(tert-butoxycarbonylamino)-3-(3'-formylbiphenyl-4-yl)propionate was added 21.2 g (314 mmol) of methanamine hydrochloride. After stirring at ambient temperature for 30 minutes, 6.0 g (95.4 mmol) of sodium cyanoborohydride was added in one batch. The reaction mixture was stirred for 16 hours and the solvent was evaporated. The residue was dissolved in ethyl acetate, the organic phase was washed with water, dried over magnesium sulfate and concentrated. The crude product was purified by silica gel column chromatography, eluting first with heptane/ethyl acetate and then with a methanol/ethyl acetate mixture to give 10 g of the target amine in 38% yield.
e. Synthesis of ethyl (S)-3-{3'-[(benzoylmethylamino)methyl]biphenyl-4-yl}-2-tert-butoxycarbonylaminopropionate: to 10 g (24.3 mmol) of ethyl (S)-2- tert-butoxycarbonylamino-3-(3'-methylaminomethylbiphenyl-4-yl) propionate and 10.1 mL (72.6 mmol) of triethylamine in 100 mL of tetrahydrofuran solution was added 4.2 mL (36.3 mmol) benzoyl chloride. The reaction mixture was stirred for 3 h. The reaction was hydrolyzed, extracted with ethyl acetate, dried over magnesium sulfate and concentrated. The residue was purified by silica gel column chromatography, eluting with a 3/2 heptane/ethyl acetate mixture to give 8.0 g of target amide in 64% yield.
f. Synthesis of ethyl (S)-2-amino-3-{3'-[(benzoylmethylamino)methyl]biphenyl-4-yl}propionate: 8.0 g (15.5 mmol) of ethyl (S)-3-{3'-[(benzoylmethylamino)methyl]biphenyl-4-yl}-2-tert-butyloxycarbonyl aminopropionate was dissolved in 70 mL of methylene chloride, and 12 mL ( 157 mmol) trifluoroacetic acid. The reaction mixture was stirred for 16 hours, then adjusted to pH 9 with sodium carbonate, extracted with dichloromethane, dried over magnesium sulfate and concentrated. The residue was purified by silica gel column chromatography, eluting with a 1/1 heptane/ethyl acetate mixture to give 5.2 g of the target amine in 82% yield.
g. Synthesis of ethyl (S)-3-{3'-[(benzoylmethylamino)methyl]biphenyl-4-yl}-2-(2-benzoylphenylamino)propanoate: according to a similar method for the preparation of ethyl (S)-2-(2-benzoylphenylamino)-3-(3'-methylamino biphenyl-4-yl)propanoate (Example LG), 3.8 g (9.13 mmol) of ethyl (S)-2-(2-benzoylphenylamino)-3-(3'-methylamino biphenyl-4-yl)propanoate were used, using 3.8 g (9.13 mmol) of Ethyl (S)-2-amino-3-{3'-[(benzoylmethylamino)methyl]biphenyl-4-yl} propionate to afford the target product in 24% yield. Melting point: 55°C.
