An efficient and practical N-methylation of amino acid derivatives

Organic Letters

Volumn 5, Issue 2, 2003, Pages 125-128

  Prashad, Mahavir ^a   Har, Denis ^a   Hu, Bin ^a   Kim, Hong Yong ^a   Repic, Oljan ^a   Blacklock, Thomas J ^a  

^a NOVARTIS INSTITUTES FOR BIOMEDICAL RESEARCH   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

AMINO ACID DERIVATIVE; DIMETHYL SULFATE; SODIUM DERIVATIVE; SODIUM HYDROXIDE; WATER; AMINO ACID; SULFATE;

ARTICLE; CATALYSIS; CHEMICAL REACTION; METHYLATION; CHEMISTRY; SYNTHESIS;

AMINO ACIDS; METHYLATION; SODIUM HYDROXIDE; SULFURIC ACID ESTERS; WATER;

EID: 0038003837     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol0268440     Document Type: Article

References (31)

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24. Pure sodium hydride is not as reactive as sodium hydroxide, perhaps due to lower solubility in tetrahydrofuran.
25. Typical Procedure. To a suspension of sodium hydride (60% dispersion in mineral oil; 10.0 mmol) in tetrahydrofuran (12 mL) was added a solution of the substrate (5.0 mmol) and water (1.0 mmol) in tetrahydrofuran (10 mL) dropwise over a period of 20 min while maintaining an internal temperature of 17-20 °C. The mixture was stirred at the same temperature for 10 min, and dimethyl sulfate (9.0 mmol) was added over a period of 20 min while maintaining an internal temperature of 17-20 °C. The stirring was continued at the same temperature for the specified time in Table 1, and the reaction was monitored by HPLC. The reaction mixture was quenched with 30% ammonium hydroxide (6 mL) over a period of 10 min while maintaining an internal temperature of 17-20 °C, and the stirring was continued for an additional 1 h (to ensure complete destruction of dimethyl sulfate as monitored by GC). The mixture was diluted with toluene (20 mL) and water (10 mL). The organic layer was separated, washed with water (10 mL), and concentrated under reduced pressure, and the crude product was purified by silica gel chromatography. (The procedure with powdered sodium hydroxide was similar except no water was used.)
26. Chiral purity was determined on a Waters HPLC system using a Chiralcel OD column (4.6 x 250 mm) and a mixture of hexane/ethanol/TFA (100:2:0.2 v/v/v) as the mobile phase (isocratic at a flow rate of 1 mL/min and UV detector at 210 nm) at 40 °C. The retention times for 1a(RS), 1a(RR), 1a(SS), and 1a(SR) were 19.3, 23.0, 25.4, and 36.4 min, respectively.
27. All the compounds gave satisfactory spectral data.
28. Determined by derivatizing the amino acid (obtained from deprotecting the BOC group) with 2,3,4,6-tetra-o-acetyl-β-D-glucopyranosyl isothiocyanate (GITC), using a Waters Symmetry C-18 column (4.6 x 150 mm) and a mixture of acetonitrile (40%) and water (60%, contaning 0.1% TFA) as the mobile phase (isocratic at a flow rate of 1.5 mL/min and UV detector at 254 nm).
29. Enantiomeric enrichment by recrystallizations is known. For example: (a) Jacques, J. Collet, A.; Wilen, S. H. In Enantiomers, Racemates, and Resolution; Wiley-Interscience Publication: New York, 1981; pp 369-377. (b) Shieh, W.; Carlson, J. A. J. Org. Chem. 1994, 59, 5463-5465. (c) Prashad, M.; Har, D.; Chen, L.; Kim, H. Y.; Repic, O.; Blacklock, T. J. J. Org. Chem. 2002, 67, 6612-6617.
30. Enantiomeric enrichment by recrystallizations is known. For example: (a) Jacques, J. Collet, A.; Wilen, S. H. In Enantiomers, Racemates, and Resolution; Wiley-Interscience Publication: New York, 1981; pp 369-377. (b) Shieh, W.; Carlson, J. A. J. Org. Chem. 1994, 59, 5463-5465. (c) Prashad, M.; Har, D.; Chen, L.; Kim, H. Y.; Repic, O.; Blacklock, T. J. J. Org. Chem. 2002, 67, 6612-6617.
31. Enantiomeric enrichment by recrystallizations is known. For example: (a) Jacques, J. Collet, A.; Wilen, S. H. In Enantiomers, Racemates, and Resolution; Wiley-Interscience Publication: New York, 1981; pp 369-377. (b) Shieh, W.; Carlson, J. A. J. Org. Chem. 1994, 59, 5463-5465. (c) Prashad, M.; Har, D.; Chen, L.; Kim, H. Y.; Repic, O.; Blacklock, T. J. J. Org. Chem. 2002, 67, 6612-6617.