Efficient Synthesis of Symmetrical α,α-Disubstituted β-Amino Acids and α,α-Disubstituted Aldehydes via Dialkylation of Nucleophilic β-Alanine Equivalent

Synthesis of Unprotected Racemic Tryptophan Derivatives Using Gramine via Nickel(II) Complex

A chemical method for the preparation of nonprotected tryptophan via nickel(II) complexes under simple operating conditions was established. The carefully designed nickel(II) glycinates are inexpensive and can be quantitatively recovered releasing the target tryptophans in high yield. The method has a wide range of synthesis generality, allowing the preparation of various substituted tryptophans. Furthermore, the scalability of this method bodes well for its synthetic use as a general approach to biologically interesting tailor-made tryptophans and related compounds.

Modular synthesis of congested β2,2-amino acids via the merger of photocatalysis and oxidative functionalisations

A two-step protocol for the modular synthesis of β2- and α-quaternary β2,2-amino acid derivatives is reported. The key steps are a photocatalytic hydroalkylation reaction, followed by an oxidative functionalisation to access N-protected β-amino acids, esters, and amides. This strategy can be effectively scaled up via continuous-flow technology.

Chemical Resolution of C, N-Unprotected α-Substituted β-Amino Acids Using Stable and Recyclable Proline-Derived Chiral Ligands

We report the first purely chemical method for the resolution of C, N-unprotected racemic α-substituted β-amino acids (β²-AAs) using thermodynamically stable and recyclable chiral proline-derived ligands. The ligands and racemic β²-AAs along with Ni(II) could form a pair of Ni(II) complex diastereoisomers with a desirable diastereoselectivity (dr up to 91:9). Enantiomerically pure C, N-unprotected β²-AAs could be obtained by simple hydrolysis of an isolated favored Ni(II) complex. The method featured unique versatility compared with enzymatic approaches and characterized by its broad synthetic generality, good stereochemical outcome, and mild reaction conditions, thus making it a powerful supplement in the field of chemical resolution of β²-AAs.

Analysis of crystallographic structures of Ni(ii) complexes of α-amino acid Schiff bases: elucidation of the substituent effect on stereochemical preferences

This work disclosed the significance of a parallel displaced type of aromatic interactions between o-amino-benzophenone and N-benzyl rings in Ni(ii) complexes.

Efficient and scalable synthesis of α,α-disubstituted β-amino amides

A scalable synthesis of α,α-disubstituted β-amino amides comprising the chemoselective reduction of a nitrile group in presence of amides and aryl halides is described.

Preparation of conformationally restricted β(2,2)- and β(2,2,3)-amino esters and derivatives containing an all-carbon quaternary center

β-Amino acids are routinely incorporated into peptidic drugs to increase their stability and to incur conformational biases. However, the synthesis of highly substituted β-amino acids still represents a great challenge. A new approach to their preparation is reported involving a Vilsmeier-Haack reaction with nonaromatic carbon nucleophiles. The highly challenging preparation of contiguous tertiary and all-carbon quaternary centers was successfully used to generate several β(2,2,3)-amino esters, such as derivatives of homoproline, homoalanine, and homopipecolinic esters.

Diastereoselective three-component reactions of chiral nickel(II) glycinate for convenient synthesis of novel α-amino-β-substituted-γ,γ-disubstituted butyric acids

The convenient, high yielding and diastereoselective synthesis of α-amino-β-substituted-γ,γ-disubstituted butyric acid derivatives was carried out by a three-component tandem reaction of a chiral equivalent of nucleophilic glycine. The reaction was performed smoothly under mild conditions and enabled the construction of two or three adjacent chiral centers in one step, thus affording a novel and convenient route to α-amino-β-substituted-γ,γ-disubstituted butyric acid derivatives.