Synthesis of the reported structure of piperazirum using a nitro-Mannich reaction as the key stereochemical determining step

Abstract

Piperazirum, isolated from Arum palaestinum Boiss, was originally assigned as r-3,c-5-diisobutyl-c-6-isopropylpiperazin-2-one. The reported structure was synthesised diastereoselectively using a key nitro-Mannich reaction to set up the C5/C6 relative stereochemistry. The structure was unambiguously assigned by single crystal X-ray diffraction but the spectroscopic data did not match those reported for the natural product. The structure of the natural product must therefore be revised.

Keywords

• alkaloid
• aza-Henry
• natural products
• nitro-Mannich
• piperazinone
• stereoselective synthesis