Diisopropylethylamine → (2S)-2-[[(4-methoxy-2,3,6-trimethylphenyl)sulfonyl]amino]-3-phenylpropanoic acid

Participants

Reaction Steps

To a solution of 0.5 g of L-phenylalanine t-butyl ester hydrochloride in 4 mL of N,N-dimethylformamide were added 0.67 g of 4-methoxy-2,3,6-trimethylphenylsulfonylchloride and 0.96 mL of N,N-diisopropylethylamine. After stirring for 2 hours at room temperature the reaction mixture was concentrated and the residue dissolved in ethyl acetate. The ethyl acetate solution was washed with aqueous potassium hydrogensulfate (5%), water, aqueous sodium hydrogencarbonate (5%) and brine, dried over magnesium sulfate and concentrated. The residue was dissolved in 16 mL of dichloromethane and 4 mL of trifluoroacetic acid was added. After stirring for 2 h at room temperature the reaction mixture was concentrated. Dichloromethane and aqueous sodium hydrogencarbonate (5%) were added to the residue (the mixture was basic), the aqueous layer separated and washed with dichloromethane. The aqueous layer was made acid (pH 2) using 2 N hydrochloric acid and several times extracted with dichloromethane. The combined dichloromethane layers were washed with brine, dried over magnesium sulfate and concentrated to give 0.65 g of (2S)-2-[[(4-methoxy-2,3,6-trimethylphenyl)sulfonyl]amino]-3-phenylpropanoic acid. This acid (80 mg) was coupled with deprotected 5a (75 mg) according to the procedure described for 5c to afford compound 55 (55 mg) as a mixture of diastereomers (1:1). 1H-NMR 400 MHz (CD3OD) δ: 1.25-1.67 (6H, m), 1.97 and 1.99 (3H, 2× s), 2.12 and 2.17 (3H, 2× s), 2.45-3.54 (8H, m), 2.49 (3H, s), 3.81 and 3.85 (3H, 2× s), 3.82-3.92 (1H, m), 5.13-5.28 (1H, m), 6.61 (1H, s), 6.84-7.07 (5H, m), 7.17-7.21 (1H, m), 7.50-7.56 (1H, m), 7.65-7.69 (1H, m), 7.76-7.82 (1H, m), 8.30-8.35 (1H, m).

Provenance & Evidence