Substrate spectrum of mandelate racemase

The Substrate Spectrum of Mandelate Racemase: Minimum Structural Requirements for Substrates and Substrate Model

“…A similar rate-enhancing effect by a p-Br substituent was observed for the corresponding mandeloamides (27) and (28). For the fluoro analogue (2), the electron-withdrawing effect is cancelled out by the well-known "back-donation" effect of F. [30] The ability of heterocycles to stabilize the a-carbanion intermediate is nicely paralleled with their ability for resonance stabilization through their aromaticity (expressed as the resonance energy): Whereas furan analogues (13) and (14) (resonance energy of furan ca.…”

“…Although first hints on the relaxed substrate specificity of mandelate racemase were published quite early, [14] it was the availability of this enzyme by fermentation [13] that facilitated the exploration of its substrate tolerance considerably. [15,28] Moreover, molecular modeling showed that the hydrophobic binding pocket within the active site (which accommodates the phenyl moiety of the natural substrate, mandelate, see Fig. 1) shows a Ref.…”

Deracemisation of Mandelic Acid to Optically Pure Non‐Natural L‐Phenylglycine via a Redox‐Neutral Biocatalytic Cascade

“…As a further challenge our aim was to start from racemic mandelic acid and to convert the racemate to the optically pure l-amino acid, thus performing a deracemisation. For this purpose mandelate racemase [24] as a third enzyme was employed in an extended system (Scheme 2) for the interconversion/racemisation of mandelic acid. Mandelate racemase has been shown to racemise a broad spectrum of substituted mandelic acid derivatives as well as heteroaromatic analogues.…”

“…Mandelate racemase has been shown to racemise a broad spectrum of substituted mandelic acid derivatives as well as heteroaromatic analogues. [24,25] The racemase was required since d-mandelate dehydrogenase is a highly stereoselective enzyme exclusively transforming d-mandelic acid and leaving the l-enantiomer untouched. Fortunately, mandelate racemase racemises only the a-hydroxy acid 1 but not the corresponding amino acid 3.…”

“…Fortunately, mandelate racemase racemises only the a-hydroxy acid 1 but not the corresponding amino acid 3. [24] Consequently, racemic mandelic acid was transformed in the presence of mandelate racemase, d-MDH and various AADHs at a substrate concentration of 5 g L À1 (Table 2, entries 1-10) on an analytical scale to yield l-phenylglycine l-3 in up to 86% conversion (entry 1). Performing the redox-neutral cascade at a 10-fold larger scale led to 94% conversion of l-3 (entry 11).…”