Add time:07/17/2019         Source:sciencedirect.com

Conversion of the easily accessible racemic bis(amino acid)s cis- and trans-2a into the (S)-enantiomers via the corresponding Schiff bases with (1S,2S,5S)-2-hydroxy-3-pinanone is described. Condensation of the N-Boc-protected bis(amino acid)s with esters of the corresponding axially chiral amino acids (R)- and (S)-1b afforded tetraspiro-substituted bis(dioxopiperazine)s 7 representing a rare case of primary helical topology. Absolute configuration of the products was assigned by NMR and CD spectra and confirmed by X-ray analysis of the Schiff base (S)-cis-3.

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