Direct Synthesis of α-Amino Acid Derivatives by Hydrative Amination of Alkynes

Negishi-coupling-enabled synthesis of α-heteroaryl-α-amino acid building blocks for DNA-encoded chemical library applications

Amino acids are vital motifs in the domain of biochemistry, serving as the foundational unit for peptides and proteins, while also holding a crucial function in many biological processes. Due to their bifunctional character, they have been also used for combinatorial chemistry purposes, such as the preparation of DNA-encoded chemical libraries. We developed a practical synthesis for α-heteroaryl-α-amino acids starting from an array of small heteroaromatic halides. The reaction sequence utilizes a photochemically enhanced Negishi cross-coupling as a key step, followed by oximation and reduction. The prepared amino esters were validated for on-DNA reactivity via a reverse amidation-hydrolysis-reverse amidation protocol.

Integrating Au Catalysis and Engineered Amine Dehydrogenase for the Chemoenzymatic Synthesis of Chiral Aliphatic Amines

Direct synthesis of aliphatic amines from alkynes is highly desirable due to its atom economy and high stereoselectivity but still challenging, especially for the long-chain members. Here, a combination of Au-catalyzed alkyne hydration and amine dehydrogenase-catalyzed (AmDH) reductive amination was constructed, enabling sequential conversion of alkynes into chiral amines in aqueous solutions, particularly for the synthesis of long-chain aliphatic amines on a large scale. The production of chiral aliphatic amines with more than 6 carbons reached 36-60 g/L. A suitable biocatalyst [PtAmDH (A113G/T134G/V294A)], obtained by data mining and active site engineering, enabled the transformation of previously inactive long-chain ketones at high concentrations. Computational analysis revealed that the broader substrate scope and tolerance with the high substrate concentrations resulted from the additive effects of mutations introduced to the three gatekeeper residues 113, 134, and 294.

Enantioselective Formal 1,2-Diamination of Ketenes with Iminosulfinamides: Asymmetric Synthesis of Unnatural α,α-Disubstituted α-Amino Acid Derivatives

A method was developed for the enantioselective formal 1,2-diamination of disubstituted ketenes using iminosulfinamides as nitrogen sources. The protocol involves the addition of lithium iminosulfinamides to ketenes to form N-iminosulfinyl amide metalloenolates. These metalloenolates then undergo a [2,3]-sigmatropic rearrangement to yield unnatural α,α-disubstituted α-amino acid derivatives with high enantiopurity. The chirality present at the sulfur atom in the iminosulfinamides is effectively transferred to α carbon of the resulting products, facilitating the highly enantioselective amination of ketenes.

Acid-Catalyzed Highly Enantioselective Synthesis of α-Amino Acid Derivatives from Sulfinamides and Alkynes

An enantioselective difunctionalization of activated alkynes using chiral sulfinamide reagents is developed. It is an atom and chirality transfer process that allows for the modular synthesis of optically active α-amino acid derivatives under mild conditions. The reaction proceeds through an acid-catalyzed [2,3]-sigmatropic rearrangement mechanism with predictable stereochemistry and a broad scope.

Sulfonium Rearrangements Enable the Direct Preparation of Sulfenyl Imidinium Salts

Sulfenyl imidinium salts are a virtually unexplored class of intermediates in organic chemistry. Herein, we demonstrate how sulfonium rearrangements can be deployed to access these versatile synthetic intermediates, bearing three contiguous (and congested) stereogenic centers, with high levels of selectivity. The synthetic value of the scaffold was unraveled by selective transformations into a range of building blocks, including 1,4-dicarbonyl derivatives and sulfonolactones.

Synthesis of Polypeptides and Poly(α-hydroxy esters) from Aldehydes Using Strecker Synthesis

This report presents a versatile approach for the synthesis of new polypeptide and polyester-based biomaterials. The well-established Strecker reaction was utilized, with hexanal serving as the model aldehyde, to synthesize α-amino and α-hydroxy acids as monomer units for the polymer system. Following the formation of the corresponding amino and hydroxy acid monomers, they were subsequently converted to N-carboxy and O-carboxy-anhydrides. The resultant cyclic anhydride molecules were then polymerized via ring-opening polymerization to yield the corresponding polypeptides and polyesters. This report establishes a straightforward methodology for the synthesis of new polypeptide and poly(a-hydroxy acid)-based biomaterials, thereby expanding the existing library of polymers for various biomedical applications.

Free Amino Group Transfer via α-Amination of Native Carbonyls

We report herein a straightforward transfer of a free amino group (NH2 ) from a commercially available nitrogen source to unfunctionalized, native carbonyls (amides and ketones) resulting in direct α-amination. Primary α-amino carbonyls are readily produced under mild conditions, further enabling diverse in situ functionalization reactions-including peptide coupling and Pictet-Spengler cyclization-that capitalize on the presence of the unprotected primary amine.