Biocatalytic Oxidative Cascade for the Conversion of Fatty Acids into α‐Ketoacids via Internal H₂O₂ Recycling

Abstract

The functionalization of bio‐based chemicals is essential to allow valorization of natural carbon sources. An atom‐efficient biocatalytic oxidative cascade was developed for the conversion of saturated fatty acids to α‐ketoacids. Employment of P450 monooxygenase in the peroxygenase mode for regioselective α‐hydroxylation of fatty acids combined with enantioselective oxidation by α‐hydroxyacid oxidase(s) resulted in internal recycling of the oxidant H2O2, thus minimizing degradation of ketoacid product and maximizing biocatalyst lifetime. The O2‐dependent cascade relies on catalytic amounts of H2O2 and releases water as sole by‐product. Octanoic acid was converted under mild conditions in aqueous buffer to 2‐oxooctanoic acid in a simultaneous one‐pot two‐step cascade in up to >99 % conversion without accumulation of hydroxyacid intermediate. Scale‐up allowed isolation of final product in 91 % yield and the cascade was applied to fatty acids of various chain lengths (C6:0 to C10:0).

Regioselective Biocatalytic Hydroxylation of Fatty Acids by Cytochrome P450s

“…Therefore, peroxygenases have high potential; however, since elevated H 2 O 2 -concentrations are harmful for both, the enzyme and its heme-cofactor [58][59][60], stable variants [59,61] and variants rescuing the heme-cofactor are highly desired. Furthermore, alternative in situ H 2 O 2 -production methods [69,133] or feeding of low amounts of H 2 O 2 may be exploited.…”

“…Recently, a cascade was reported, that allowed the conversion of fatty acids to α-ketoacids in a one pot fashion by combining SPα and α-hydroxyacid oxidase via an internal H 2 O 2 recycling. Here C6:0, C7:0, C8:0 and C10:0 were demonstrated to be substrates for SPα [69]. Myristic acid (C14:0) was postulated to be the natural substrate of SPα and is hydroxylated stereo-, and regioselectively to produce (S)-2-hydroxymyristic acid (94% e.e.…”

“…2), mainly at the α-position. Shorter fatty acids (C6:0, C7:0 and C10:0) are hydroxylated in α-position as demonstrated in a one pot cascade combining CLA and α-hydroxyacid oxidase to produce α-ketoacids [69]. Although substrate binding was demonstrated via a spin-shift, methyl esters were reported to be non-substrates [63].…”

Preparative Asymmetric Synthesis of Canonical and Non‐canonical α‐amino Acids Through Formal Enantioselective Biocatalytic Amination of Carboxylic Acids

“…[3] Saturated fatty acids (FAs) are promising feedstocks [4] since they are available in large quantities, from organic waste or fermentative processes and, in particular short chain FAs (C6:0-C8:0), do not compete with food. [7] a-HAs can be further oxidized into a-keto-acids [8] to serve as precursors for a-amino acid (a-AAs). [5] The a-carbon has rarely been targeted for chemical/biological hydroxylation, [6] although selective a-functionalization affords versatile a-hydroxy acids (a-HAs; 1 b-13 b; Scheme 1), e. g., for the production of biodegradable polyesters (PLA derivatives), pharmaceuticals, antimicrobial agents and natural products.…”

“…50% yield; Scheme 1 B). [6,8,19] Herein, we show the development of a three-step linear biocascade for the atom-efficient formal asymmetric a-amination of saturated FAs into enantiopure l-a-AAs in one-pot, on preparative scale, using mild reaction conditions, renewable feedstocks, reagents and catalysts (Scheme 2). [17] Still, many of these routes are based on petroleum-derived feedstocks such as benzenes, olefins, aldehydes or a-HAs (Scheme 2).…”