Steric effects on the isomer equilibrium of amides N-terminal to proline can be explored with 5-alkylprolines having bulky 5-position substituents. Enantiopure 5-tert-butylprolines were thus synthesized from glutamic acid via an acylation/diastereoselective reductive amination sequence. Double deprotonation of γ-methyl N-(PhF) glutamate (2) with LiN (SiMe3) 2 and C-acylation with pivaloyl chloride provided β-keto ester 3, which upon γ-ester hydrolysis ...
![(2S,4S)-6-FLUORO-2,5-DIOXO-2,3-DIHYDROSPIRO[CHROMENE-4,4-IMIDAZOLIDINE]-2-CARBOXAMIDE Structure](https://image.chemsrc.com/caspic/199/185142-15-8.png)
