Chemoenzymatic Hydroxymethylation of Carboxylic Acids by Tandem Stereodivergent Biocatalytic Aldol Reaction and Chemical Decarboxylation

Abstract

Chiral 2-substituted 3-hydroxycarboxylic acid derivatives are valuable building blocks for the preparation of naturally occurring and synthetic biologically active molecules. Current methodologies for the preparation of these compounds are still limited for large-scale production due to the high costs, limited microbial strains, low yields, difficult downstream processing, and limited range of structures. We report an effective chemoenzymatic method for the synthesis of enantiomerically pure 2-substituted 3-hydroxycarboxylic esters. The strategy comprises: (i) a stereoselective aldol addition of 2-oxoacids to methanal catalyzed by two enantiocomplementary 2-oxoacid aldolases, (ii) oxidative decarboxylation, and (iii) esterification. Compounds with S-configuration were obtained in 69–80% isolated yields (94–99% ee), and the R enantiomers in 57–88% (88–98% ee), using a substrate concentration range of 0.1–1.0 M. The method developed offers a versatile alternative route to this important class of chiral building blocks and highlights the exciting opportunities available for using natural enzymes with minimal active site modification.

Chemoenzymatic Production of Enantiocomplementary 2‐Substituted 3‐Hydroxycarboxylic Acids from l‐α‐Amino Acids

“…Ramification in position 3 ( 1 a and 1 e rendering 2 a and 2 e , respectively) was tolerated by all KPHMT catalysts (Table 2, entries 1–3 and 16–18), whereas with MBP‐YfaU catalysts only negligible aldol was formed (Table 2, entries 4–5 and 19–20). The shortest amino acid 1 b was not accepted by Pma LAAD in accordance with the literature, [8a] even though the 2‐oxoacid 2 b is known to be a well‐accepted substrate by both MBP‐YfaU and KPHMT [9b] . The highest overall conversions were achieved employing unbranched aliphatic α‐amino acids 1 d , 1 g and 1 h , reaching almost complete conversion to the aldol product in some cases (Table 2, entries 14, 15, 26, 28, 30, 33 and 35).…”

“…For the stereoselective aldol addition, MBP‐YfaU, KPHMT and variants thereof, offer a wide acceptance toward diverse 2‐oxoacids [9b,13] . Thus, wild‐type MBP‐YfaU and variant W23V, supplied with Ni 2+ as metal cofactor, [14] were selected for the ( S )‐selective aldol reaction, while wild‐type KPHMT and variants I202A and I212A supplied with Co 2+ were the biocatalysts of choice for the preparation of the ( R )‐aldol products [9b] …”

“…Hence, the substrate panel was tested under the established optimized conditions with wild‐type MBP‐YfaU, MBP‐YfaU‐W23V, wild‐type KPHMT, KPHMT‐I202A and KPHMT‐I212A catalysts (Table 2), which successfully probed activity on several intermediates 2 [9b] …”

“…In a previous work we developed an effective chemoenzymatic method for the synthesis of enantiomerically pure 2‐substituted 3‐hydroxycarboxylic esters [9b] . The key step was an enzymatic stereoselective aldol addition of chemically synthetized 2‐oxoacids to formaldehyde catalyzed by two enantiocomplementary Type II 2‐oxoacid aldolases, 2‐keto‐3‐deoxy‐ l ‐rhamnonate aldolase (YfaU, EC 4.1.2.53) fused with maltose binding protein from E. coli (MBP) (MBP‐YfaU), and 3‐methyl‐2‐oxobutanoate hydroxymethyltransferase (KPHMT, EC 2.1.2.11) and variants thereof.…”

Zirconium@guanine@MCM‐41 nanoparticles: An efficient heterogeneous mesoporous nanocatalyst for one‐pot, multi‐component tandem Knoevenagel condensation–Michael addition–cyclization Reactions

“…[8,[12][13][14] The major advantages of multicomponent reactions are one-pot synthesis, high atom economy and time-saving without isolation of intermediates or generating byproducts. [14][15][16][17][18][19] In particular, Phenazines and chromenes have attracted increasing attention in drug discovery and medicinal chemistry which can be synthesized by a one-pot two-steps procedure. [8,[18][19][20] These compounds have been reported as biological active species which involve anticancer, antifungal, antiplasmodial, antimalarial, antibacterial, cancer chemopreventive, antiparasitic and antichagasagen activities.…”