Asymmetric azidohydroxylation of styrene derivatives mediated by a biomimetic styrene monooxygenase enzymatic cascade

Strategies for Accessing cis-1-Amino-2-Indanol

cis-1-amino-2-indanol is an important building block in many areas of chemistry. Indeed, this molecule is currently used as skeleton in many ligands (BOX, PyBOX…), catalysts and chiral auxiliaries. Moreover, it has been incorporated in numerous bioactive structures. The major issues during its synthesis are the control of cis-selectivity, for which various strategies have been devised, and the enantioselectivity of the reaction. This review highlights the various methodologies implemented over the last few decades to access cis-1-amino-2-indanol in racemic and enantioselective manners. In addition, the various substitution patterns on the aromatic ring and their preparations are listed.

Synthesis of Chiral Sulfoxides by A Cyclic Oxidation-Reduction Multi-Enzymatic Cascade Biocatalysis

Optically pure sulfoxides are valuable organosulfur compounds extensively employed in medicinal and organic synthesis. In this study, we present a biocatalytic oxidation-reduction cascade system designed for the preparation of enantiopure sulfoxides. The system involves the cooperation of a low-enantioselective chimeric oxidase SMO (styrene monooxygenase) with a high-enantioselective reductase MsrA (methionine sulfoxide reductase A), facilitating "non-selective oxidation and selective reduction" cycles for prochiral sulfide oxidation. The regeneration of requisite cofactors for MsrA and SMO was achieved via a cascade catalysis process involving three auxiliary enzymes, sustained by cost-effective D-glucose. Under the optimal reaction conditions, a series of heteroaryl alkyl, aryl alkyl and dialkyl sulfoxides in R configuration were synthesized through this "one-pot, one step" cascade reaction. The obtained compounds exhibited high yields of >90 % and demonstrated enantiomeric excess (ee) values exceeding 90 %. This study represents an unconventional and efficient biocatalytic way in utilizing the low-enantioselective oxidase for the synthesis of enantiopure sulfoxides.

Enzymatic Oxy- and Amino-Functionalization in Biocatalytic Cascade Synthesis: Recent Advances and Future Perspectives

Biocatalytic cascades are a powerful tool for building complex molecules containing oxygen and nitrogen functionalities. Moreover, the combination of multiple enzymes in one pot offers the possibility to minimize downstream processing and waste production. In this review, we illustrate various recent efforts in the development of multi-step syntheses involving C-O and C-N bond-forming enzymes to produce high value-added compounds, such as pharmaceuticals and polymer precursors. Both in vitro and in vivo examples are discussed, revealing the respective advantages and drawbacks. The use of engineered enzymes to boost the cascades outcome is also addressed and current co-substrate and cofactor recycling strategies are presented, highlighting the importance of atom economy. Finally, tools to overcome current challenges for multi-enzymatic oxy- and amino-functionalization reactions are discussed, including flow systems with immobilized biocatalysts and cascades in confined nanomaterials.

Metal-Catalyst-Free One-Pot Aqueous Synthesis of trans-1,2-Diols from Electron-Deficient α,β-Unsaturated Amides via Epoxidation Using Oxone as a Dual Role Reagent

In organic synthesis, incorporating two functional groups into the carbon-carbon double bond of α,β-unsaturated amides is challenging due to the electron-deficient nature of the olefin moiety. Although a few examples of dihydroxylation of α,β-unsaturated amides have been demonstrated, producing cis-1,2-diols using either highly toxic OsO4 or other specialized metal reagents in organic solvents, they are limited to several specific amides. We describe herein a general and one-pot direct synthesis of trans-1,2-diols from electron-deficient α,β-unsaturated amides through dihydroxylation using oxone as a dual-role reagent in water. This reaction does not require any metal catalyst and produces non-hazardous and nontoxic K2 SO4 as the sole byproduct. Moreover, epoxidation products could also be selectively formed by adjusting the reaction conditions. By the strategy, the intermediates of Mcl-1 inhibitor and antiallergic bioactive molecule can be synthesized in one pot. The gram-scale synthesis of trans-1,2-diol which is isolated and purified by recrystallization further shows the potential applications of this new reaction in organic synthesis.

Two (Chemo)-Enzymatic Cascades for the Production of Opposite Enantiomers of Chiral Azidoalcohols

Multi-step cascade reactions have gained increasing attention in the biocatalysis field in recent years. In particular, multi-enzymatic cascades can achieve high molecular complexity without workup of reaction intermediates thanks to the enzymes’ intrinsic selectivity; and where enzymes fall short, organo- or metal catalysts can further expand the range of possible synthetic routes. Here, we present two enantiocomplementary (chemo)-enzymatic cascades composed of either a styrene monooxygenase (StyAB) or the Shi epoxidation catalyst for enantioselective alkene epoxidation in the first step, coupled with a halohydrin dehalogenase (HHDH)-catalysed regioselective epoxide ring opening in the second step for the synthesis of chiral aliphatic non-terminal azidoalcohols. Through the controlled formation of two new stereocenters, corresponding azidoalcohol products could be obtained with high regioselectivity and excellent enantioselectivity (99% ee) in the StyAB-HHDH cascade, while product enantiomeric excesses in the Shi-HHDH cascade ranged between 56 and 61%.