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.
Some functional food components may help maintain homeostasis by promoting balanced gut microbiota. Here, we explore the possible complementary effects of d-fagomine and ω-3 polyunsaturated fatty acids (ω-3 PUFAs) eicosapentaenoic acid/docosahexaenoic acid (EPA/DHA 1:1) on putatively beneficial gut bacterial strains. Male Sprague–Dawley rats were supplemented with d-fagomine, ω-3 PUFAs, or both, for 23 weeks. Bacterial subgroups were evaluated in fecal DNA by quantitative real-time polymerase chain reaction (qRT-PCR) and short-chain fatty acids were determined by gas chromatography. We found that the populations of the genus Prevotella remained stable over time in animals supplemented with d-fagomine, independently of ω-3 PUFA supplementation. Animals in these groups gained less weight than controls and rats given only ω-3 PUFAs. d-Fagomine supplementation together with ω-3 PUFAs maintained the relative populations of Bacteroides. ω-3 PUFAs alone or combined with d-fagomine reduced the amount of acetic acid and total short-chain fatty acids in feces. The plasma levels of pro-inflammatory arachidonic acid derived metabolites, triglycerides and cholesterol were lower in both groups supplemented with ω-3 PUFAs. The d-fagomine and ω-3 PUFAs combination provided the functional benefits of each supplement. Notably, it helped stabilize populations of Prevotella in the rat intestinal tract while reducing weight gain and providing the anti-inflammatory and cardiovascular benefits of ω-3 PUFAs.
The congested nature of quaternary carbons hinders their preparation, most notably when stereocontrol is required. Here we report a biocatalytic method for the creation of quaternary carbon centers with broad substrate scope, leading to different compound classes bearing this structural feature. The key step comprises the aldol addition of 3,3-disubstituted 2-oxoacids to aldehydes catalyzed by metal dependent 3-methyl-2-oxobutanoate hydroxymethyltransferase from E. coli (KPHMT) and variants thereof. The 3,3,3-trisubstituted 2-oxoacids thus produced were converted into 2-oxolactones and 3-hydroxy acids and directly to ulosonic acid derivatives, all bearing gem-dialkyl, gem-cycloalkyl, and spirocyclic quaternary centers. In addition, some of these reactions use a single enantiomer from racemic nucleophiles to afford stereopure quaternary carbons. The notable substrate tolerance and stereocontrol of these enzymes are indicative of their potential for the synthesis of structurally intricate molecules.
A two‐enzyme cascade reaction plus in situ oxidative decarboxylation for the transformation of readily available canonical and non‐canonical l‐α‐amino acids into 2‐substituted 3‐hydroxycarboxylic acid derivatives is described. The biocatalytic cascade consisted of an oxidative deamination of l‐α‐amino acids by an l‐α‐amino acid deaminase from Cosenzaea myxofaciens, rendering 2‐oxoacid intermediates, with an ensuing aldol addition reaction to formaldehyde, catalyzed by metal‐dependent (R)‐ or (S)‐selective carboligases namely 2‐oxo‐3‐deoxy‐l‐rhamnonate aldolase (YfaU) and ketopantoate hydroxymethyltransferase (KPHMT), respectively, furnishing 3‐substituted 4‐hydroxy‐2‐oxoacids. The overall substrate conversion was optimized by balancing biocatalyst loading and amino acid and formaldehyde concentrations, yielding 36–98% aldol adduct formation and 91–98% ee for each enantiomer. Subsequent in situ follow‐up chemistry via hydrogen peroxide‐driven oxidative decarboxylation afforded the corresponding 2‐substituted 3‐hydroxycarboxylic acid derivatives.
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