Potassium Hydroxide → HCID 54549299, compound

Participants

Reaction Steps

At the same time, an elegant asymmetric glycine enolate reaction was developed by Evans and Weber for the synthesis of MeBmt and other chiral amino acids. [See Evans, D. A. and Weber, A. E., J. Am. Chem. Soc. 108:6757 (1986)]. The approach was also applied to prepare MeLeu(OH) [see FIG. 6]. In the reaction sequence, the chiral glycine synthon isothiocyanate was obtained from corresponding chloroacetate and followed by azide replacement in 56% yield. The isothiocyanate chiral auxiliary was condensed with isobutyraldehyde under stannous triflate mediated aldol reaction (-78° C. for 4 h) to give the aldol adduct in 63% yield (>90% e.e). Transesterification with a solution of magnesium methoxide in methanol at room temperature for 3 min gave the methyl ester in 78-82% yield. The yield of the bis-methylation was low, 52% as compared to 76% of Evans in MeBmt synthesis. Two epimers are usually obtained in a ratio of 1:5, which was not found by Evans for the MeBmt synthesis. The 1H NMR spectra of the epimers were compared as shown in Table 4 and FIG. 7. Hydrolysis of the desired trans-oxazolidinone with 2N KOH under reflux gave the pure β-hydroxy-N-methylleucine (see 1H NMR spectra in FIG. 8) after chromatographic purification over Sephadex LH-20.

Provenance & Evidence