ethyl 5-methyl-3-(nitromethyl)hexanoate

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 100 g of 5-methyl-3-nitromethyl-hexanoic acid ethyl ester (VIII, R1=ethyl) were added to an aqueous solution of EstB (500 mL cell extract; ˜5 g total protein concentration). At a temperature of 25° C. the pH was kept at 7.0 by continuous addition of 5M aqueous NaOH. After 55% conversion (corresponds to 50.6 mL of NaOH consumption) the reaction was stopped by addition of 100 mL of ethyl acetate. 100 mL of 5M aqueous NaOH were added and the layers were separated. The aqueous layer was washed once with 100 mL of ethyl acetate. The combined organic layers were concentrated under reduced pressure to give 43 g of (S)-5-methyl-3-nitromethyl-hexanoic acid ethyl ester (VIII, R1=ethyl; ee=98%). After 55% conversion (corresponds to 50.6 mL of NaOH consumption) the reaction was stopped by addition of 100 mL of ethyl acetate 100 mL of 5M aqueous NaOH were added the layers were separated The aqueous layer was washed once with 100 mL of ethyl acetate The combined organic layers were concentrated under reduced pressure

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 7.0 g of nitromethane and 3.3 mL of DBU (1,8-diazabicyclo[5.4.0]undece-7-en) were added to the DMSO solution of α,β-unsaturated ester VII. The reaction mixture was stirred until complete conversion was detected by GC. 20 mL of CH2Cl2 were added and the resulting mixture was washed with 2×20 mL of 1M aqueous H2SO4 and 1×20 mL of 0.5M aqueous NaHCO3. The organic layer was dried and the solvent was removed under reduced pressure. 3.6 g of γ-nitroester VIII were obtained (yield over two steps: 75%). the resulting mixture was washed with 2×20 mL of 1M aqueous H2SO4 and 1×20 mL of 0.5M aqueous NaHCO3 The organic layer was dried the solvent was removed under reduced pressure

Conditions: temp:150.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 10.0 g (34 mmol) of 2-(3-methyl-1-nitromethyl-butyl)-malonic acid diethyl ester (XII, R1=ethyl) were dissolved in 140 mL of DMSO. Water (10.4 mL) and solid NaCl (14.6 g) were added and the mixture was heated for 6 hours at 150° C. After complete conversion, the reaction mixture was cooled to 25° C. and 150 mL of methyl tert-butyl ether were added. 100 mL of water were added slowly. The heterogeneous mixture was stirred for 5 minutes prior to layer separation. The aqueous layer was washed once with 75 mL of methyl tert-butyl ether. The organic layers were combined and washed once with 50 mL of water. The combined organic layers were dried and the volatiles were removed under reduced pressure to give 7.0 g of 5-methyl-3-nitromethyl-hexanoic acid ethyl ester (VIII, R1=ethyl; 93% yield). After complete conversion, the reaction mixture was cooled to 25° C. to layer separation The aqueous layer was washed once with 75 mL of methyl tert-butyl ether washed once with 50 mL of water The combined organic layers were dried the volatiles were removed under reduced pressure

Conditions: temp:150.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 10.0 g (34 mmol) of 2-(3-methyl-1-nitromethyl-butyl)-malonic acid diethyl ester (XII, R1=ethyl) were dissolved in 140 mL of DMSO. Water (10.4 mL) and solid NaCl (14.6 g) were added and the mixture was heated for 6 hours at 150° C. After complete conversion, the reaction mixture was cooled to 25° C. and 150 mL of methyl tert-butyl ether were added. 100 mL of water were added slowly. The heterogeneous mixture was stirred for 5 minutes prior to layer separation. The aqueous layer was washed once with 75 mL of methyl tert-butyl ether. The organic layers were combined and washed once with 50 mL of water. The combined organic layers were dried and the volatiles were removed under reduced pressure to give 7.0 g of 5-methyl-3-nitromethyl-hexanoic acid ethyl ester (VIII, R1=ethyl; 93% yield). After complete conversion, the reaction mixture was cooled to 25° C. to layer separation The aqueous layer was washed once with 75 mL of methyl tert-butyl ether washed once with 50 mL of water The combined organic layers were dried the volatiles were removed under reduced pressure

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: In Synthesis 1989, 953 a synthesis of rac.-Pregabalin, starting from (E)-5-methyl-hex-2-enoic acid ethyl ester, which was converted with nitromethane into 5-methyl-3-nitromethyl-hexanoic acid ethyl ester, has been reported. Subsequent catalytic hydrogenation followed by saponification leads to rac.-Pregabalin. Recently an enzymatic hydrolysis of this racemic nitro ester was carried out (Tetrahedron Asymmetry 2008, 19, 945). With enzyme Novozyme 435 enantiomerically enriched (S)-5-methyl-3-nitromethyl-hexanoic acid could be obtained in a good selectivity if the conversion was stopped at 30%. In Synthesis 1989, 953 a synthesis of rac

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 100 g of 5-methyl-3-nitromethyl-hexanoic acid ethyl ester (VIII, R1=ethyl) were added to an aqueous solution of EstB (500 mL cell extract; ˜5 g total protein concentration). At a temperature of 25° C. the pH was kept at 7.0 by continuous addition of 5M aqueous NaOH. After 55% conversion (corresponds to 50.6 mL of NaOH consumption) the reaction was stopped by addition of 100 mL of ethyl acetate. 100 mL of 5M aqueous NaOH were added and the layers were separated. The aqueous layer was washed once with 100 mL of ethyl acetate. The combined organic layers were concentrated under reduced pressure to give 43 g of (S)-5-methyl-3-nitromethyl-hexanoic acid ethyl ester (VIII, R1=ethyl; ee=98%). After 55% conversion (corresponds to 50.6 mL of NaOH consumption) the reaction was stopped by addition of 100 mL of ethyl acetate 100 mL of 5M aqueous NaOH were added the layers were separated The aqueous layer was washed once with 100 mL of ethyl acetate The combined organic layers were concentrated under reduced pressure

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 7.0 g of nitromethane and 3.3 mL of DBU (1,8-diazabicyclo[5.4.0]undece-7-en) were added to the DMSO solution of α,β-unsaturated ester VII. The reaction mixture was stirred until complete conversion was detected by GC. 20 mL of CH2Cl2 were added and the resulting mixture was washed with 2×20 mL of 1M aqueous H2SO4 and 1×20 mL of 0.5M aqueous NaHCO3. The organic layer was dried and the solvent was removed under reduced pressure. 3.6 g of γ-nitroester VIII were obtained (yield over two steps: 75%). the resulting mixture was washed with 2×20 mL of 1M aqueous H2SO4 and 1×20 mL of 0.5M aqueous NaHCO3 The organic layer was dried the solvent was removed under reduced pressure

Conditions: temp:150.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 10.0 g (34 mmol) of 2-(3-methyl-1-nitromethyl-butyl)-malonic acid diethyl ester (XII, R1=ethyl) were dissolved in 140 mL of DMSO. Water (10.4 mL) and solid NaCl (14.6 g) were added and the mixture was heated for 6 hours at 150° C. After complete conversion, the reaction mixture was cooled to 25° C. and 150 mL of methyl tert-butyl ether were added. 100 mL of water were added slowly. The heterogeneous mixture was stirred for 5 minutes prior to layer separation. The aqueous layer was washed once with 75 mL of methyl tert-butyl ether. The organic layers were combined and washed once with 50 mL of water. The combined organic layers were dried and the volatiles were removed under reduced pressure to give 7.0 g of 5-methyl-3-nitromethyl-hexanoic acid ethyl ester (VIII, R1=ethyl; 93% yield). After complete conversion, the reaction mixture was cooled to 25° C. to layer separation The aqueous layer was washed once with 75 mL of methyl tert-butyl ether washed once with 50 mL of water The combined organic layers were dried the volatiles were removed under reduced pressure