Asymmetric synthesis of 2-arylpiperazines

A Concise Synthetic Method for Constructing 3-Substituted Piperazine-2-Acetic Acid Esters from 1,2-Diamines

We report a short synthetic route for synthesizing 2,3-substituted piperazine acetic acid esters. Optically pure amino acids were efficiently converted into 1,2-diamines that could be utilized to deliver the title 2,3-substituted piperazines in five steps with a high enantiomeric purity. The novel route facilitated, for the first time, the synthesis of 3-phenyl substituted-2-piperazine acetic acid esters that were difficult to achieve using other methods; however, in this case, the products underwent racemization.

Practical and scalable synthesis of orthogonally protected-2-substituted chiral piperazines

A synthetic route to orthogonally protected, enantiomerically pure 2-substituted piperazines is described. Starting from α-amino acids, within four steps chiral 2-substituted piperazines are obtained. The key transformation involves an aza-Michael addition between an orthogonally bis-protected chiral 1,2-diamine and the in situ generated vinyl diphenyl sulfonium salt derived from 2-bromoethyl-diphenylsulfonium triflate. Further validation using different protecting groups as well as synthesis on multigram scale was performed. The method was also applied to the construction of chiral 1,4-diazepanes and 1,4-diazocanes. Additionally, the method was utilized in a formal synthesis of chiral mirtazapine.

Efficient one-pot synthesis of enantiomerically pure N-protected-α-substituted piperazines from readily available α-amino acids

A new pathway towards enantiomerically pure 3-substituted piperazines, bearing a benzyl protecting group, has been developed in good overall yields (83–92%), starting from commercially available N-protected amino acids.

Discovery of novel 2-(3-phenylpiperazin-1-yl)-pyrimidin-4-ones as glycogen synthase kinase-3β inhibitors

We herein describe the results of further evolution of glycogen synthase kinase (GSK)-3β inhibitors from our promising compounds containing a 2-phenylmorpholine moiety. Transformation of the morpholine moiety into a piperazine moiety resulted in potent GSK-3β inhibitors. SAR studies focused on the phenyl moiety revealed that a 4-fluoro-2-methoxy group afforded potent inhibitory activity toward GSK-3β. Based on docking studies, new hydrogen bonding between the nitrogen atom of the piperazine moiety and the oxygen atom of the main chain of Gln185 has been indicated, which may contribute to increased activity compared with that of the corresponding phenylmorpholine analogues. Effect of the stereochemistry of the phenylpiperazine moiety is also discussed.

Synthesis of Chiral Piperazines via Hydrogenation of Pyrazines Activated by Alkyl Halides

A facile method has been developed for the synthesis of chiral piperazines through Ir-catalyzed hydrogenation of pyrazines activated by alkyl halides, giving a wide range of chiral piperazines including 3-substituted as well as 2,3- and 3,5-disubstituted ones with up to 96% ee. The high enantioselectivity, easy scalability, and concise drug synthesis demonstrate the practical utility.