Modular Enzymatic Cascade Synthesis of Vitamin B5 and Its Derivatives

Abstract

Access to vitamin B₅ [(R)-pantothenic acid] and both diastereoisomers of α-methyl-substituted vitamin B₅ [(R)- and (S)-3-((R)-2,4-dihydroxy-3,3-dimethylbutanamido)-2-methylpropanoic acid] was achieved using a modular three-step biocatalytic cascade involving 3-methylaspartate ammonia lyase (MAL), aspartate-α-decarboxylase (ADC), β-methylaspartate-α-decarboxylase (CrpG) or glutamate decarboxylase (GAD), and pantothenate synthetase (PS) enzymes. Starting from simple non-chiral dicarboxylic acids (either fumaric acid or mesaconic acid), vitamin B₅ and both diastereoisomers of α-methyl-substituted vitamin B₅ , which are valuable precursors for promising antimicrobials against Plasmodium falciparum and multidrug-resistant Staphylococcus aureus, can be generated in good yields (up to 70 %) and excellent enantiopurity (>99 % ee). This newly developed cascade process may be tailored and used for the biocatalytic production of various vitamin B₅ derivatives by modifying the pantoyl or β-alanine moiety.

Keywords: biocatalysis; cascade reaction; enzymes; pantothenic acid.

Figure 1

Structures of vitamin B₅ and its α‐methyl‐substituted derivative.

Scheme 1

Proposed enzymatic cascade synthesis of vitamin B₅ and its derivatives.

Scheme 2

One‐pot, two‐step, enzymatic cascade reaction, involving MAL and CrpG, that fully converts mesaconate (1 b) to only (R)‐3 b. This is due to CrpG only acting on l‐erythro‐2 b and to the MAL‐mediated dynamic kinetic asymmetric transformation of the l‐threo‐2 b to the desired diastereomer.

Scheme 3

The one‐pot, two‐step, enzymatic cascade reaction that converts mesaconate (1 b) to only (S)‐3 b and relies on a diastereospecific mutant MAL (MAL‐H194A) and the newly discovered stereoselectivity of TkGAD towards l‐threo‐2 b.