Process for manufacturing (S)-3-hydroxy-1-(1H-indol-5-yl)-2-oxo-pyrrolidine-3-carboxylic acid 3,5-difluoro-benzylamide

Abstract

A process can be used for manufacturing (S)-3-hydroxy-1-(1H-indol-5-yl)-2-oxo-pyrrolidine-3-carboxylic acid 3,5-difluoro-benzylamide.

Claims

1: A process for manufacturing (S)-3-hydroxy-1-(1H-indol-5-yl)-2-oxo-pyrrolidine-3-carboxylic acid 3,5-difluoro-benzylamide, the process comprising: a) reacting 2-oxo-1-(1-(phenylsulfonyl)-H-indol-5-yl)pyrrolidine-3-carboxylic acid with 3,5-difluorobenzyl amine, to give 1-[1-(benzenesulfonyl)-1H-indol-5-yl]-N-[(3,5-difluorophenyl)methyl]-2-oxopyrrolidine-3-carboxamide, b) enantioselectively oxidizing the 1-[1-(benzenesulfonyl)-1H-indol-5-yl]-N-[(3,5-difluorophenyl)methyl]-2-oxopyrrolidine-3-carboxamide to give (3S)-1-[1-(benzenesulfonyl)-1H-indol-5-yl]-N-[(3,5-difiuorophenyl)methyl]-3-hydroxy-2-oxopyrrolidine-3-carboxamide, and c) subsequently cleaving off a phenylsulfonyl group from the (3S)-1-[1-(benzenesulfonyl)-1H-indol-5-yl]-N-[3,5-difluorophenyl)Methyl]-3-hydroxy-2-oxopyrrolidine-3-carboxamide, to give (S)-3-hydroxy-1-(1H-indol-5-yl)-2-oxo-pyrrolidine-3-carboxylic acid 3,5-difluoro-benzylamide.

2: The process according to claim 1, wherein a) is carried out presence of a base selected from the group consisting of triethylamine, diazabicycloundecen (DBU), and di-isopropylethylamine.

3: The process according to claim 1, wherein a) is carried out in dichloromethane.

4: The process according to claim 1, wherein a) is carried out in the presence of propanephosphonic acid anhydride.

5: The process according to claim 1, wherein b) is carried out in presence of an oxidizing reagent (+)-(2R,4aS,7S,8aR)-4H-4a, 7-methanooxazirino[3,2-i] [2,1] benzisothiazole, 8,8-dichlorotetrahydro-9,9-dimethyl-3,3-dioxide.

6: The process according to claim 1, wherein b) is carried out in presence of tetrahydrofuran (THF) or diethylether.

7: The process according to claim 1, wherein b) is carried out in presence of sodium-hexamethyldisilazane (NaHMDS).

8: The process according to claim 1, wherein c) is carried out in presence of NaOH.

9: An intermediate compound 1-[1-(benzenesulfonyl)-1H-indol-5-yl]-N-[(3,5-difluorophenyl)methyl]-2-oxopyrrolidine-3-carboxamide.

Description

EXAMPLES

Step-1: 3

[5-nitro-1-(phenylsulfonyl)-1H-indole]

[0037] ##STR00005##

Experimental Procedure

[0038] 5-nitro indole 1 (500 g, 3.08 mol) was dissolved in THF (5 L) and the mixture was cooled to 0° C. and stirred for 20 minutes. Sodium hydride (140 g, 3.5 mol) was added in portions and the mixture was stirred for additional 30 minutes at 15° C. Benzene sulphonyl chloride 2 (475 mL, 3.7 mol) was introduced through an additional funnel for 30 minutes under stirring. After completion of the addition the mixture was stirred for 4 hours. After completion of the reaction, the reaction mass was cooled to 0° C. and quenched with ice (3 L). Ethyl acetate (5 L) and water (2.5 L) were added. After phase separation the aqueous layer was re-extracted with ethyl acetate (5 L). The combined organic layer was dried over sodium sulphate and concentrated under reduced pressure at 55° C. Ethyl acetate/pet. ether (8%, 5 L) were added to the crude mass and the mixture was stirred for 20 min at room temperature. The product was filtered and washed with ethyl acetate and pet. ether mixture (5%, 2 L). The product was dried under vacuum to give 3 as a yellow solid.

[0039] Yield 890 g (95%).

[0040] .sup.1H NMR (400 MHz , DMSO-d.sub.6) δ 8.63-8.55 (m, 1H), 8.26-8.14 (m, 2H), 8.13-8.02 (m, 3H), 7.79-7.70 (m, 1H), 7.69-7.59 (m, 2H), 7.10 (d, J=3.7 Hz, 1H); Molecular Formula: C.sub.14H.sub.10N.sub.2O.sub.4S; HPLC purity: 99.92%; Expected LCMS Mass: 302.0; Observed: 161.2 (M-141).

Step-2: 4

1-(phenylsulfonyl)-1H-indol-5-amine

[0041] ##STR00006##

Experimental Procedure

[0042] Step-1 product 3 (500 g, 1.65 mol) was dissolved in ethanol (7 L). Iron powder was added (500 g, 8.95 mol) and the mixture was heated to 50° C. After 15 minutes, a solution of NH.sub.4Cl (1 kg, 18.69 mol) in water (3.1 L) was added to the reaction mixture through an additional funnel for 1 hour. The reaction mixture was heated to 80° C. for 2 hours. After completion of the reaction, the reaction mass was cooled to 40° C., filtered through celite and concentrated under reduced pressure at 50° C. Ethyl acetate and water (5 L each) were added and the layers were separated. The aq. layer was re-extracted with ethyl acetate (5 L). The combined organic layer was dried over sodium sulphate and concentrated under reduced pressure at 50° C. The reminder was suspended in ethyl acetate/pet. ether (5%, 5 L) and then cooled to room temperature. The product was filtered and washed with ethyl acetate/pet. ether (5%, 5 L). The product was dried under vacuum to give 4 as a brown solid.

[0043] Yield 400 g (89%).

[0044] .sup.1H NMR (300 MHz, DMSO-d.sub.6) δ 7.86 (d, J=7.5 Hz, 2H), 7.70-7.42 (m, 5H), 6.67-6.48 (m, 3H), 4.97 (s, 2H); Molecular Formula: C.sub.14H.sub.12N.sub.2O.sub.2S; HPLC purity: 97.25%; Expected LCMS Mass: 272.1; Observed: 273.0 (M+1).

Step-3: 5

2-oxo-1-(1-(phenylsulfonyl)-1H-indol-5-yl)pyrrolidine-3-carboxylic acid

[0045] ##STR00007##

Experimental Procedure

[0046] Step-2 product 4 (1.6 kg, 5.87 mol) and cyclopropyl meldrum acid (1.2 kg, 7.05 mol) were given into the reactor followed by acetonitrile (5.5 L) and DMF (1.9 L). The mixture was heated to 70° C. for 16 hours under nitrogen atmosphere. After completion of the reaction, the reaction mass was concentrated under reduced pressure at 50-55° C. The residue was cooled and treated with water and ethyl acetate (10 L each). After phase separation the organic layer was washed with brine (5 L), dried over sodium sulphate and concentrated under reduced pressure at 40-45° C. The obtained crude solid was washed with ethyl acetate/pet. ether (5%, 2 L) giving 5 as brown solid.

[0047] Yield: 1.8 kg (80%).

[0048] .sup.1H NMR (300 MHz, DMSO-d.sub.6) δ 12.80 (br.s., 1H), 8.02-7.85 (m, 3H), 7.85-7.74 (m, 2H), 7.71-7.47 (m, 4H), 6.84 (d, J=3.6 Hz, 1H), 3.94-3.76 (m, 2H), 3.57 (t, J=8.5 Hz, 1H), 2.37-2.20 (m, 2H); Molecular Formula: C.sub.19H.sub.16N.sub.2O.sub.5S; HPLC purity: 91.51%; Expected LCMS Mass: 384.08; Observed: 385.0 (M+1).

[0049] 5 is the starting point for both procedures, the racemic and the asymmetric syntheses.

Step-4: 6

3-hydroxy-2-oxo-1-(1-(phenylsulfonyl)-1H-indol-5-yl)pyrrolidine-3-carboxylic acid

[0050] ##STR00008##

Experimental Procedure

[0051] Step-3 product 5 (1.0 kg, 2.60 mol) was treated with DMF (8.5 L) and Magnesium monoperoxyphthalate hexahydrate 80% (1.9 kg, 3.84 mol). The mixture was heated to 60° C. for 2 hours under nitrogen atmosphere. After completion of the reaction, the reaction mass was concentrated under reduced pressure at 50-55° C. The residue was taken in water (5 L) and ethyl acetate (3 L) and stirred for 12 hours at room temperature. The product was filtered and washed with water and ethyl acetate (3 L each). The product was dried under vacuum at 65° C. to give 6 as off white solid.

[0052] Yield: 700 g (67%).

[0053] Note: Moisture content of the step 4 product should be less than 0.5%.

[0054] .sup.1H NMR (400 MHz, DMSO-d.sub.6) δ 7.97-7.94 (m, 3H), 7.87 (s, 1H), 7.81 -7.80 (d, J=3.4 Hz, 1H), 7.73-7.66 (m, 2H), 7.60-7.56 (m, 2H), 7.16 (brs, 1H), 6.87 (d, J=3.4 Hz, 1H), 3.92 (q, J=8.4 Hz, 1H), 3.75 (t, J=8.7 Hz, 1H), 3.45-3.42 (m, 1H), 2.43-2.38 (m, 1H), 2.03-1.96 (m, 1H); Molecular Formula: C.sub.19H.sub.16N.sub.2O.sub.6S; HPLC purity: 96.12%; Expected LCMS Mass: 400.07; Observed: 401.0 (M+1).

Step-5: 7

3-acetoxy-2-oxo-1-(1-(phenylsulfonyl)-1H-indol-5-yl) pyrrolidine - 3-carboxylic acid

[0055] ##STR00009##

Experimental Procedure

[0056] Step-4 product 6 (1.0 kg, 2.5 mol) and DMF (8 L) were given into a reactor at room temperature and stirred for 10 minutes. Acetic anhydride (355 mL, 3.75 mol) was added slowly to the mass and the mixture was stirred for 12 hours. After completion of the reaction, the reaction mass was concentrated under reduced pressure at 50-55° C. The residue was cooled to 0° C., suspended with water (5 L) and stirred for overnight at room temperature. The precipitate was filtered, washed with water (3 L) and then suspended in acetone (3 L) for 1 hour. Filtration gave product 7 as white solid, which was dried under vacuum at 65° C.

[0057] Yield: 940 g (85%).

[0058] Note: Moisture content of the step 5 product should be less than 0.5%.

[0059] .sup.1H NMR (400 MHz, DMSO-d.sub.6) δ 7.98-7.89 (m, 3H), 7.86-7.77 (m, 2H), 7.73-7.62 (m, 2H), 7.60-7.51 (m, 2H), 6.85 (d, J=3.8 Hz, 1H), 3.98 (q, J=8.1 Hz, 1H), 3.72 (t, J=9.0 Hz, 1H), 2.79 (dd, J=7.3, 12.1 Hz, 1H), 2.22-2.09 (m, 1H), 2.01 (s, 3H); Molecular Formula: C.sub.21H.sub.18N.sub.2O.sub.7S; HPLC purity: 97.83%; Expected LCMS Mass: 442.08; Observed: 443.0 (M+1).

NB

[0060] Reaction mixture should be concentrated below 55° C. and evaporation should be complete within 2 hours. Higher temperature and prolong heating leads to de-carboxylation of the product.

Step-6: 8

3-((3,5-difluorobenzyl)carbamoyl)-2-oxo-1-(1-(phenylsulfonyl)-1H-indol-5-yl)pyrrolidin-3-yl acetate.

[0061] ##STR00010##

Experimental Procedure

[0062] Step-5 product 7 (1.0 kg, 2.26 mol) was dissolved in CH.sub.2Cl.sub.2 (10 L) at room temperature for 10 minutes and then cooled to 0° C. Triethyl amine (690 mL, 4.95 mol), 3,5-difluorobenzyl amine (405 g, 2.83 mol) and 2,4,6-tripropyl-[1,3,5,2,4,6]trioxatriphosphinane 2,4,6-trioxide (2.15 L, 3.38 mol) were added and the reaction mixture was stirred at room temperature for 2 hours. After completion of the reaction, the reaction mass was diluted with water (5 L) and stirred for 10 minutes. The aqueous layer was removed from the top. This aqueous washing was repeated 3 times. The organic layer was filtered and the precipitate was washed with CH.sub.2Cl.sub.2 (1 L) and acetone (0.5 L) to get 8 as off white solid.

[0063] Yield: 1.07 kg (83%).

[0064] .sup.1H NMR (400 MHz, DMSO-d.sub.6) δ 8.99 (t, J=6.2 Hz, 1H), 7.97 (d, J=8.1 Hz, 3H), 7.83 (dd, J=2.8, 5.2 Hz, 2H), 7.72-7.63 (m, 2H), 7.62-7.53 (m, 2H), 7.06 (t, J=9.4 Hz, 1H), 6.93 (d, J=7.0 Hz, 2H), 6.87 (d, J=3.5 Hz, 1H), 4.33 (dq, J=6.0, 16.1 Hz, 2H), 3.99-3.83 (m, 2H), 2.88 (ddd, J=2.6, 7.9, 13.2 Hz, 1H), 2.43-2.28 (m, 1H), 2.18 (s, 3H); Molecular Formula: C.sub.28H.sub.23F.sub.2N.sub.3O.sub.6S; HPLC purity: 99.88%; Expected LCMS Mass: 567.13; Observed: 568.0 (M+1).

[0065] Step-7: 9

N-(3,5-difluorobenzyl)-3-hydroxy-1-(1H-indol-5-yl)-2-oxopyrrolidine-3-carboxamide

[0066] ##STR00011##

Experimental Procedure

[0067] Step-6 product 8 (1.2 kg, 2.11 mol) was dissolved in ethanol (5 L) and THF (10 L) and stirred at room temperature for 10 minutes. Sodium hydroxide (422 g, 10.55 mol) was added and stirred for 2 hours at 50° C. After completion of the reaction, the reaction mass was concentrated under reduced pressure at 45° C. The residue was dissolved in ethyl acetate (10 L) and water (5 L). After phase separation the organic layer was washed with water (2×5 L) and brine (5 L). The organic layer was dried over sodium sulphate, filtered and concentrated under reduced pressure at 45-50° C. CH.sub.2Cl.sub.2 (1 L) was added to the reminder and the precipitate was filtered and washed with CH.sub.2Cl.sub.2 (1.0 L) to give 9 as off white solid.

[0068] Yield: 700 g (86%).

[0069] .sup.1H NMR (400 MHz, DMSO-d.sub.6) δ 11.12 (br.s., 1H), 8.69 (t, J=6.4 Hz, 1H), 7.70 (s, 1H), 7.46-7.32 (m, 3H), 7.12-6.94 (m, 3H), 6.69 (s, 1H), 6.47-6.38 (m, 1H), 4.41 (dd, J=6.9, 16.0 Hz, 1H), 4.25 (dd, J=5.9, 15.8 Hz, 1H), 3.94-3.81 (m, 2H), 2.66-2.54 (m, 1H), 2.13 (td, J=7.6, 13.0 Hz, 1H); Molecular Formula: C.sub.20H.sub.17F.sub.2N.sub.3O.sub.3; HPLC purity: 98.11%; Expected LCMS Mass: 385.12; Observed: 386.0 (M+1).

SFC Separation:

[0070] Isomers of 9 (5.20 Kg) were separated via SFC purification.

SFC Method:

[0071] Column: Lux Amylose-2 (250×30) mm, 5 micron
Mobile phase: CO.sub.2: MeOH (60:40)
Flow rate: 200 g/min
Run time: 10 min (cycle time)
Loading per injection: 700 mg

TABLE-US-00001 Quantity Output Quantity S-9 Mixture of R-9 input 9 (Fraction 1) fraction 1 & 2 (Fraction 2) 5.20 Kg 1.93 Kg 0.60 Kg 1.80 Kg (37%)

[0072] Fraction 1 (S-9): .sup.1H NMR (400 MHz, DMSO-d.sub.6) δ 11.12 (br.s., 1H), 8.69 (t, J=6.4 Hz, 1H), 7.70 (s, 1H), 7.46-7.32 (m, 3H), 7.12-6.94 (m, 3H), 6.69 (s, 1H), 6.47-6.38 (m, 1H), 4.41 (dd, J=6.9, 16.0 Hz, 1H), 4.25 (dd, J=5.9, 15.8 Hz, 1H), 3.94-3.81 (m, 2H), 2.66-2.54 (m, 1H), 2.13 (td, J=7.6, 13.0 Hz, 1H); Molecular Formula: C.sub.20H.sub.17F.sub.2N.sub.3O.sub.3; HPLC purity: 99.46%; Chiral HPLC purity: 100%; Expected LCMS Mass: 385.12; Observed: 386.0 (M+1); SOR: +14.69.

[0073] Fraction 2 (R-9): .sup.1H NMR (400 MHz, DMSO-d.sub.6) δ 11.12 (br.s., 1H), 8.69 (t, J=6.3 Hz, 1H), 7.73-7.68 (m, 1H), 7.45-7.31 (m, 3H), 7.11-6.94 (m, 3H), 6.69 (s, 1H), 6.46-6.38 (m, 1H), 4.41 (dd, J=6.7, 15.8 Hz, 1H), 4.25 (dd, J=5.9, 15.8 Hz, 1H), 3.94-3.79 (m, 2H), 2.66-2.56 (m, 1H), 2.13 (td, J=7.6, 13.0 Hz, 1H); Molecular Formula: C.sub.20H.sub.17F.sub.2N.sub.3O.sub.3; HPLC purity: 97.20%; Chiral HPLC purity: 98.17%; Expected LCMS Mass: 385.12; Observed: 386.2 (M+1); SOR: −13.49.

[0074] Mixture of fraction (1 & 2): HPLC purity: 98.90%; Chiral HPLC purity: 32.99% (fraction 1) & 67.01 (fraction 2).

[0075] Yield optimization can be achieved by inversion of the chiral centre. The invented procedure is outlined.

Step 8: 10

(R)-3-((3,5-difluorobenzyl)carbamoyl)-1-(1H-indol-5-yl)-2-oxopyrrolidin-3-yl methanesulfonate

[0076] ##STR00012##

Experimental Procedure

[0077] To an ice cooled solution of R-9 (200 g, 0.52 mol) in dry CH.sub.2Cl.sub.2 (2 L), was added Et.sub.3N (252 ml, 1.81 mol) followed by drop wise addition of Mesyl chloride (80.4 ml, 1.03 mol). The reaction mixture was stirred at the same temperature for another 2 hours. After completion, reaction mixture was washed with water (1.5 L), 5% Citric acid (1 L) and saturated aqueous solution of NaHCO.sub.3 (1×5 L). The combined organic extracts were washed with brine (1 L), dried over Na.sub.2SO.sub.4, filtered and concentrated under vacuum yielded 10 (260 g). The crude product was directly taken for next step without further purification.

[0078] Molecular Formula: C.sub.21H.sub.19F.sub.2N.sub.3O.sub.5S; HPLC purity: 81.76%; Expected LCMS Mass: 463.10; Observed: 464.0 (M+1).

Step 9: 11

(S)-3-((3,5-difluorobenzyl)carbamoyl)-1-(1H-indol-5-yl)-2-oxopyrrolidin-3-yl acetate

[0079] ##STR00013##

Experimental Procedure

[0080] To a solution of cesium acetate (214 g, 1.12 mol) in dry DMF (1.2 L) at 100° C. was added a solution of 10 (260 g, 0.560 mol) in DMF (1.0 L) dropwise over 20 minutes through an addition funnel. The heating was continued for another 1.5 hours. After completion, the reaction mass was concentrated under vacuum. The crude mass was dissolved in ethyl acetate (2 L) and washed with water (2×2 L). The combined organic extracts were washed with brine (1 L), dried over Na.sub.2SO.sub.4, filtered and concentrated under vacuum to yield 11 (250 g). The crude product was directly taken for next step without further purification.

[0081] Molecular Formula: C.sub.22H.sub.19F.sub.2N.sub.3O.sub.4; HPLC purity: 45.64%; Expected LCMS Mass 427.13; Observed: 428.3 (M+1).

Step 10: S-9

(S)-N-(3,5-difluorobenzyl)-3-hydroxy-1-(1H-indol-5-yl)-2-oxopyrrolidine-3-carboxamide

[0082] ##STR00014##

Experimental Procedure

[0083] To an ice cooled solution of the crude 11 (250 g 0.52 mol) in methanol (2.5 L) was added NaOH pellets (63 g, 1.56 mol). The reaction mixture was stirred at RT for 2 hours. After completion, methanol was concentrated under vacuum at <55° C. The crude mass was dissolved in ethyl acetate (2 L) and washed with water (3×2 L). The combined organic extracts were washed with brine (1 L), dried over Na.sub.2SO.sub.4, filtered and concentrated under vacuum. It was passed through a wash column (Silica 60-120) and nonpolar impurities ware removed using 30-40% ethyl acetate/pet. ether. The product was eluted with 3-5% MeOH/CH.sub.2Cl.sub.2. The isolated product was dissolved in minimum amount of ethyl acetate and kept in cold room for 16 hours. The solid formed was filtered through a Büchner funnel, washed with ethyl acetate (3×100 ml) to give S-9 (56 g, 28% in three steps) as off white solid.

[0084] Dried solid was milled in a pin mill (rpm 6000, 30 min) to obtain final API.

[0085] .sup.1H NMR (400 MHz, DMSO-d.sub.6) δ 11.12 (br.s., 1H), 8.69 (t, J=6.4 Hz, 1H), 7.70 (s, 1H), 7.46-7.32 (m, 3H), 7.12-6.94 (m, 3H), 6.69 (s, 1H), 6.47-6.38 (m, 1H), 4.41 (dd, J=6.9, 16.0 Hz, 1H), 4.25 (dd, J=5.9, 15.8 Hz, 1H), 3.94-3.81 (m, 2H), 2.66-2.54 (m, 1H), 2.13 (td, J=7.6, 13.0 Hz, 1H); Molecular Formula: C.sub.20H.sub.17F.sub.2N.sub.3O.sub.3; HPLC purity: 98.72%; Chiral HPLC purity: 98.68%; (ee: 97.36%); Expected LCMS Mass: 385.12; Observed: 386.2 (M+1).

TABLE-US-00002   Particle size: <18 μm. SOR: +13.62. MP: 195.3-198.9° C. MC: 0.21% RESIDUAL SOLVENTS: Methanol ------------ 17 ppm Ethanol ------------ ND ACN ------------ ND CH.sub.2Cl.sub.2 ------------ ND Ethyl acetate -------- 75 ppm THF ------------- 206 ppm n-Heptane ----------- 47 ppm

Step-4C: 12

1-[1-(benzenesulfonyl)-1H-indol-5-yl]-N-[(3,5-difluorophenyl)methyl]-2-oxopyrrolidine-3-carboxamide

[0086] ##STR00015##

Experimental Procedure

[0087] To an ice cooled solution of 5 (750 g, 1.95 mol) in CH.sub.2Cl.sub.2 (7 L), Et.sub.3N (600 mL, 4.29 mol) was added followed by 3,5-difluorobenzyl amine (363 g, 2.53 mol). T.sub.3P (Propanephosphonic acid anhydride) (1.86 L (50% EA [ethyl acetate] solution), 3.0 mol) was added dropwise into the reaction mixture slowly and the reaction mixture was stirred at RT for 2 h. After completion of the reaction, the reaction mass was quenched with water (3 L) and stirred for 10 minutes. The organic layer was separated and washed with 10% NaHCO.sub.3 solution (2 L) followed by water wash (3 L×3). The organic phase was finally washed with brine (3 L), dried over anhydrous sodium sulfate and concentrated to get the crude product as light brown solid. It was made slurry with minimum amount of ethyl acetate (1.5 L) and filtered. The cake was washed with ice cold ethyl acetate (1 L×2) to get the pure product as off white solid with HPLC >99%. Amount obtained: 720 g; Yield: 72%;

[0088] .sup.1H-NMR (400 MHz, DMSO-d.sub.6): δ 8.82 (t, J=5.60 Hz, 1H), 7.99-7.94 (m, 3H), 7.83 (d, J=2.80 Hz, 2H), 7.71-7.67 (m, 2H), 7.61-7.57 (m, 2H), 7.12-7.05 (m, 3H), 6.87 (d, J=3.60 Hz, 1H), 4.49 (dd, J=6.80, 16.20 Hz, 1H), 4.27 (dd, J=5.20, 16.00 Hz, 1H), 3.90-3.85 (m, 2H), 3.63 (t, J=8.80 Hz, 1H), 2.40-2.27 (m, 2H).

Step C5: 13

(3S)-1-[1-(benzenesulfonyl)-1H-indol-5-yl]-N-[(3,5-difluorophenyl)methyl]-3-hydroxy-2-oxopyrrolidine-3-carboxamide

[0089] ##STR00016##

Experimental Procedure

[0090] A suspension of 12 (500 g, 0.98 mol) in dry THF (7.5 L) was cooled to −68° C. (inside temperature). NaHMDS solution (1078 mL, 1M in THF, 1.078 mol) was added drop wise over a period of 1.5 h while maintaining the same temperature range. After the complete addition, the reaction mixture temperature was allowed to rise to −55° C. in another 1 h and then recooled to −68° C. inside. To the yellow reaction mixture was added a solution of ((+)-(2R, 4aS, 7S, 8aR)-4H-4a, 7-methanooxazirino[3,2-i] [2,1] benzisothiazole, 8,8-dichlorotetrahydro-9,9-dimethyl-3,3-dioxide (365 g, 1.22 mol) in THF (1.1 L) dropwise over a period of 1.3 h at the same temperature. The reaction mass was allowed to come to −25° C. in another 1.5 h. After the complete conversion the system was quenched at −15° C. with ice/water (2 L). Ethyl acetate (5 L) was added to the reaction mixture, the organic layer was separated and washed with water (3 L). The aqueous layer was saturated with NaCl and re-extracted with ethyl acetate (1 L). The combined organic layer was finally washed with brine, dried over Na.sub.2SO.sub.4 and concentrated to get the crude product which was purified by column chromatography (SiO.sub.2 230-400 mesh). The product eluted in 50-60% ethyl acetate and was obtained as off-white solid.

[0091] Amount obtained: 375 g; Yield: 73%.

[0092] .sup.1H NMR (500 MHz, DMSO-d.sub.6) ppm=8.67 (t, J=6.4, 1H), 7.98-7.92 (m, 3H), 7.86 (d, J=2.2, 1H), 7.82 (d, J=3.7, 1H), 7.75-7.65 (m, 2H), 7.61-7.55 (m, 2H), 7.05 (tt, J=9.3, 2.4, 1H), 7.01-6.93 (m, 2H), 6.89 - 6.84 (m, 1H), 6.72 (s, 1H), 4.39 (dd, J=15.8, 6.8, 1H), 4.25 (dd, J=15.8, 6.0, 1H), 3.90-3.83 (m, 2H), 2.65-2.54 (m, 1H), 2.17-2.09 (m, 1H). LCMS system A: H2O+0.05% HCOOH|system B: MeCN+0.04% HCOOH; T: 30° C.|Flow:2.4 ml/min|Column: Chromolith RP-18e 100-3|MS:85-800 amu. Gradient: 4%-->100% (B) 0-->2.8 min|100% (B) 2.8-3.3 min. retention time: 2.376 min (M+H.sup.+): 526.1.

[0093] Note: Average chiral purity achieved in this step was 85% and the maximum was 87%. It is important that any washing of crude will result in a considerable reduction in the chiral purity.

Structure of Davis Oxaziridine

[0094] ##STR00017##

Step C6: S-9

(S)-3-Hydroxy-1-(1H-indol-5-yl)-2-oxo-pyrrolidine-3-carboxylic acid 3,5-difluoro-benzylamide

[0095] ##STR00018##

Experimental Procedure

[0096] Sodium hydroxide pellets (140 g, 3.56 mol) were added to a stirred suspension of 12 (375 g, 0.71 mol) in ethanol/THF mixture (3 L/1 L) at RT. The reaction mixture was heated at 50° C. for 2 h. After the complete conversion the reaction mixture was concentrated to get the crude mass. Water (4 L) was added and stirred for 1 h at RT. The solid formed was filtered through a Buchner funnel, neutralized by washing with 1.5 N HCl followed by water (1 L×3). The residue was finally washed with ether (2 L) to get the crude product. The chiral purity of the compound was checked at this stage and found to be 95.5%. To increase the chiral purity the solid was dissolved in minimum amount of THF/ethyl acetate (9:1) and heated to reflux at 60° C. for 30 min. The solution was filtered through a Büchner funnel and the clear filtrate was ice cooled for 2-3 h and the solid formed was filtered. The filtrate was ice cooled again for 2 h and the solid was separately filtered. Chiral purity of each solid was checked and all the fractions were mixed with ee >98.7% and finally purified by column chromatography (SiO.sub.2 230-400 mesh) using DCM/MeOH as the eluent. The pure product was eluted with 2% methanol, concentrated under reduced pressure to get the desired S-9 as off white solid. The product was dried at 60° C. for 12 h

[0097] Amount obtained: 140 g; Yield: 51%.

[0098] Note 01: If the chiral purity of the crude S-9 was >97%, the mass was treated with minimum volume of ethyl acetate/THF (3V, 9:1), stirred for 30 min at RT and filtered to give desired chiral purity >98.7%

[0099] Note 02: The main aqueous layer collected was acidified with 2N HCl and the solid formed was filtered. The cake was neutralized by washing with water and finally washed with cold ethyl acetate to give remaining compound with chiral purity of 60%.