Add time:08/18/2019         Source:sciencedirect.com

3-Triphenylphosphonio-2,5-piperazinediones were effectively synthesized from homochiral valine or proline via Boc-Val-Gly-OMe, Boc-Pro-Gly-OMe or Cbz-Pro-Gly-OMe. Retention of configuration of the primary stereogenic center of the valine and proline moieties was observed. Diastereoselective nucleophilic substitution of the triphenylphosphonium group in 2,5-piperazinediones with S-, N-, P- and C-nucleophiles was observed. The configuration of the substitution products was assigned either by their hydrolysis and decarboxylation or based on the analysis of the H–C(3)–N–H coupling constants of 3-substituted-2,5-piperazinediones derived from proline. The trans-stereoselectivity was predominant in reactions of 3-triphenylphosphonio-1,6-trimethylene-2,5-piperazinediones with the nucleophiles investigated. The stereodifferentiating ability of the proline moiety is much stronger than that of the valine unit and allowed nucleophilic α-functionalization of the glycine moiety with good to excellent diastereoselectivity.

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