Serine Hydroxymethyl Transferase from Streptococcus thermophilusand L‐Threonine Aldolase from Escherichia colias Stereocomplementary Biocatalysts for the Synthesis of β‐Hydroxy‐α,ω‐diamino Acid Derivatives

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‐erythrodiastereomers in 34–60 % conversion, whereas LTA gave L‐threodiastereomers 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 °C SHMT has high synthetic activity but negligible retroaldol activity on L‐threonine. Thus, the kinetic L‐erythroisomer 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‐γ‐amino‐β‐hydroxy‐α‐amino acid derivatives with potassium hydroxide (1m) resulted in the spontaneous formation of 2‐oxazolidinone derivatives of the β‐hydroxyl and γ‐amino groups in quantitative yield. This reaction might be useful for further chemical manipulations of the products.