title: Cryo-bioorganic chemistry: freezing effect on stereoselection of L- and DL-leucine cooligomerization in aqueous solution.
abstract: The chirality of L-/DL-leucine (50-50%) cooligomerization was investigated in liquid and frozen aqueous solutions. Cooligomerization was carried out by carbonyldiimidazole activation without initiator at an ambient (+ 22 degrees C) and frozen (- 18 degrees C) temperature, respectively. The separated samples obtained after different time intervals of treatment were completely hydrolyzed (HCl) and the diastereomeric L- and D-leucine derivates of Marfey's reagent (1-fluoro-2,4-dinitrophenyl-5-L-alanine amide) were then traced and evaluated by RP-HPLC analysis. After 9 days of oligomerization, the L-Leu content was slightly enhanced in the liquid (57%) and somewhat more enhanced in the frozen (64%) samples. After 17 days, however, the L-Leu content had decreased in the liquid (53%) and frozen (56%) conditions. These L-enantiomer amplifications indicate that an L-antipode is preferentially incorporated into the alpha-helical turn of the oligomer in the earlier stage of cooligomerization, while, later, the D-antipode is also incorporated. The role of ice in the improved stereoselection is discussed. This is the first recorded example of the effect of freezing on stereoselection.
authors: Department of Organic Chemistry, Eötvös Lorand University, Budapest, Hungary. vajda@szerves.chem.elte.hu
authors: T
authors: T
authors: Vajda
authors: M
authors: M
authors: Hollósi
mesh_terms: D002625:Chemistry, Organic; D002851:Chromatography, High Pressure Liquid; D005615:Freezing; D066298:In Vitro Techniques; D007930:Leucine / Q000737:chemistry*; D009842:Oligopeptides / Q000737:chemistry; D055601:Organic Chemistry Phenomena; D012996:Solutions; D013237:Stereoisomerism; D014867:Water
chemical_list: D009842:Oligopeptides; D012996:Solutions; D014867:Water; D007930:Leucine