Synthese von 4‐Oxo‐L‐prolin‐ und cis‐4‐Hydroxy‐L‐prolin‐Derivaten aus L‐Asparaginsäure**

Abstract

Mit Hexafluoraceton als Schutzgruppenreagens und ausgehend von L‐Asparaginsäure ist die Diazocarbonylverbindung 1 erhältlich, aus der Rh‐katalysiert das bicyclische Prolinderivat 2 entsteht. Wegen dessen konkaver Form gelingt die Bildung neuer Chiralitätszentren mit hoher Stereoselektivität, und 4‐Oxo‐L‐Prolin, in 5‐Stellung substituiertes 4‐Oxo‐L‐Prolin und cis‐4‐Hydroxy‐L‐Prolin 3 sowie weitere Derivate sind sehr einfach zugänglich. R = H, CO2Et.

Effects of Zeolitic Parameters and Irradiation on the Retention Properties of Silver Zeolites Exposed to Molecular Iodine

“…Despite hundreds structural types of zeolites exist, most of academic and industrial studies have focused on Ag/X and Ag/MOR types. 9,12,[19][20][21] These latter materials are also those sold for iodine retention (FCVS and fuel reprocessing applications) by commercial suppliers (for instance under the trademark Ionex 22 ). Recently, we examined during systematic studies the respective influences of the zeolite framework type, the Si/Al ratio, the silver content and its speciation in the case of methyl iodide retention by silver-exchanged zeolites.…”

Hexafluoroacetone as Protecting and Activating Reagent: New Routes to Amino, Hydroxy, and Mercapto Acids and Their Application for Peptide and Glyco- and Depsipeptide Modification

“…The diazoketone derived from HFA[Asp(Cl)] and ethyl diazoacetate when treated with dirhodium tetraacetate forms a cyclic enol, which tautomerizes during purification to give the ketone. The trans-stereoisomer is formed exclusively. , The stereoselectivity can be explained by the concave shape of the bicyclic HFA-prolines. Thus, substituents such as the ethyl carboxylate prefer the exo position to avoid steric strain, giving the trans -dicarboxylate (Scheme ).…”

“…Reduction of the 4-oxo group with Na[BH 3 CN] proceeds stereoselectively because the hydride transfer occurs preferentially from the Re face (de = 88%). Subsequent cleavage of the lactone and reduction of the ethyl carboxylate in the 5-position provides efficient access to bulgecinine [( 2S, 4 S ,5 R )-4-hydroxy-5-hydroxymethylproline] (Scheme ). , Bulgecinine is the aglycone of bulgecines, a class of glycopeptide antibiotics attracting growing interest due to their synergistic effect on the antibacterial activities of β-lactams. −

44

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“…The trans-stereoisomer is formed exclusively. 120,121 The stereoselectivity can be explained by the concave shape of the bicyclic HFA-prolines. Thus, substituents such as the ethyl carboxylate prefer the exo position to avoid steric strain, giving the trans-dicarboxylate (Scheme 43).…”

“…Subsequent cleavage of the lactone and reduction of the ethyl carboxylate in the 5-position provides efficient access to bulgecinine [(2S,4S,5R)-4-hydroxy-5-hydroxymethylproline] (Scheme 44). 120,121 Bulgecinine is the aglycone of bulgecines, a class of glycopeptide antibiotics attracting growing interest due to their synergistic effect on the antibacterial activities of β-lactams. [122][123][124]…”