Serine hydroxymethyl transferase from Streptococcus thermophilus and L-threonine aldolase from Escherichia coli as stereocomplementary biocatalysts for the synthesis of beta-hydroxy-alpha,omega-diamino acid derivatives

Abstract

A novel serine hydroxymethyl transferase from Streptococcus thermophilus (SHMT) and a L-threonine aldolase from Escherichia coli (LTA) were used as stereocomplementary biocatalysts for the aldol addition of glycine to N-Cbz amino aldehydes and benzyloxyacetaldehyde (Cbz=benzyloxycarbonyl). Both threonine aldolases were classified as low-specific L-allo-threonine aldolases, and by manipulating reaction parameters, such as temperature, glycine concentration, and reaction media, SHMT yielded exclusively L-erythro diastereomers in 34-60 % conversion, whereas LTA gave L-threo diastereomers in 30:70 to 16:84 diastereomeric ratios and with 40-68 % conversion to product. SHMT is among the most stereoselective L-threonine aldolases described. This is due, among other things, to its activity-temperature dependence: at 4 degrees C SHMT has high synthetic activity but negligible retroaldol activity on L-threonine. Thus, the kinetic L-erythro isomer was largely favored and the reactions were virtually irreversible, highly stereoselective, and in turn, gave excellent conversion. It was also found that treatment of the prepared N-Cbz-gamma-amino-beta-hydroxy-alpha-amino acid derivatives with potassium hydroxide (1 m) resulted in the spontaneous formation of 2-oxazolidinone derivatives of the beta-hydroxyl and gamma-amino groups in quantitative yield. This reaction might be useful for further chemical manipulations of the products.