Dansyl chloride → tert-butyl N-[(2S)-4-methyl-1-oxopentan-2-yl]carbamate

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Reaction Conditions

Reaction Steps

This material (130 mg, 0.562 mmol) was dissolved in ethyl acetate (2 ml). The solution was cooled to 0° C., saturated with HCl (g) and stirred 15 min. Evaporation of the solvent in vacuo gave an oil which was repeatedly evaporated in vacuo with ethyl acetate until a white solid precipitated. Filtration gave leucine-HCl (75 mg) which was dried in vacuo at room temperature. This hydrochloride (10 μg, 0.06 μmol) in 100 μl of 0.2 M sodium bicarbonate buffer, pH 9.0, was treated with 100 μl of a 0.02 M solution of 5-dimethylaminonaphthalene-1-sulfonyl chloride in acetone. The mixture was stirred at 37° C. for 30 min and quenched with 0.1 ml of formic acid. The mixture was evaporated to dryness under a stream of nitrogen and the residue dissolved in methanol (0.5 ml). The solution (10 μl) was analyzed by HPLC using as the mobile phase a solution of arginine (5 mM), copper sulfate.5H2O (2.5 mM) and ammonium acetate (5 mM) in glass distilled water, adjusted to pH 7.8 with NH4OH. Fluorescence at 520 nm was monitored with excitation at 340 nm. Samples were run in duplicate, and authentic samples of D- and L-leucine were used as controls. The observed L- to D-ratios along with measured optical rotations of the leucine HCl samples are summarized below.

Provenance & Evidence