Recyclable Ligands for the Non‐Enzymatic Dynamic Kinetic Resolution of Challenging α‐Amino Acids

Abstract

Structurally simple and inexpensive chiral tridentate ligands were employed for substantially advancing the purely chemical dynamic kinetic resolution (DKR) of unprotected racemic tailor-made α-amino acids (TM-α-AAs), enabling the first DKR of TM-α-AAs bearing tertiary alkyl chains as well as multiple unprotected functional groups. Owing to the operationally convenient conditions, virtually complete stereoselectivity, and full recyclability of the source of chirality, this method should find wide applications for the preparation of TM-α-AAs, especially on large scale.

Which Stereoinductor Is Better for Asymmetric Functionalization of α‐Amino Acids in a Nickel(II) Coordination Environment? Experimental and DFT Considerations

“…( S , S )‐ III c : 1 H NMR (CDC1 3 ): δ =8.89 (d, J =2.0 Hz, 1 H), 8.18 (d, J =9.3 Hz, 1 H), 7.65 (dd, J =8.2, 2.0 Hz, 1 H), 7.60–7.51 (m, 2 H), 7.45–7.42 (m, 1 H), 7.41–7.37 (m, 3 H), 7.33–7.29 (m, 2 H), 7.18–7.14 (m, 2 H), 7.10 (dd, J =9.3, 2.6 Hz, 1 H), 6.76 (d, J =7.1 Hz, 1 H), 6.60 (d, J =2.6 Hz, 1 H), 4.27 (m, 1 H), 4.17 (d, J =12.5 Hz, 1 H), 3.21–3.10 (m, 3 H), 3.08 (d, J =12.5 Hz, 1 H), 2.81 (dd, J =13.8, 5.5 Hz, 1 H), 2.42–2.24 (m, 3 H), 1.95–1.87 (m, 1 H), 1.77–1.70 ppm (m, 1 H) …”

A Convergent Total Synthesis of the Death Cap Toxin α‐Amanitin

“…The synthesis of 6-hydroxytryptophan was not trivial and finally we decided for a dynamic kinetic resolution (DKR) route employing a chiral tridentate ligand. [24,25] Starting with 6-benzyloxyindol (9), alkylation using l-serine, Ac 2 O and AcOH (Scheme 2) was performed, which rendered racemic tryptophan 13. [26] After removal of the acetyl group the racemate was treated with the chiral ligand 16 and Ni-(NO 3 ) 2 ·6 H 2 O under basic conditions, which led to nickel(II) complex 14 with a diastereomeric ratio (dr) of 99 % (see Supporting Information).…”

Asymmetric Synthesis of 4,4‐(Difluoro)glutamic Acid via Chiral Ni(II)‐Complexes of Dehydroalanine Schiff Bases. Effect of the Chiral Ligands Structure on the Stereochemical Outcome

“…Our interest in studying the reaction of four different dehydroalanine complexes 12 a-d stems from the reports [28] that in the case of glycine complexes 10, a seemingly insignificant structural modifications with chlorine atoms or other halogen or alkyl substituents, results in a noticeable differences in the stereochemical outcome of their reactions with various electrophiles. In particular, it was shown [29] that 10 d provides for the most optimal parallel displaced type of aromatic interactions between o-amino-benzophenone and Pro N-benzyl rings controlling the stereochemical outcome.…”