Optically Active Dioxatetraazamacrocycles: Chemoenzymatic Syntheses and Applications in Chiral Anion Recognition

✍ Scribed by Ignacio Alfonso; Francisca Rebolledo; Vicente Gotor

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 240 KB
• Volume: 6
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/1521-3765(20000915)6:18<3331::aid-chem3331>3.0.co;2-8

✦ Synopsis

Two new C2 and D2 symmetrical dioxatetraaza 18-membered macrocycles [(R,R)-1 and (S,S,S,S)-2] are efficiently synthesized in enantiomerically pure forms by a chemoenzymatic method starting from (+/-)-trans-cyclohexane-1,2-diamine. The protonation constants and the binding constants with different chiral dicarboxylates are determined in aqueous solution by means of pH-metric titrations. The triprotonated form of (S,S,S,S)-2 shows moderate enantioselectivity with malate and tartrate anions (deltadeltaG=0.62 and 0.66 kcal mol(-1), respectively), being the strongest binding observed in both cases with the L enantiomer. Good enantiomeric discrimination is obtained with tetraprotonated (R,R)-1 and N-acetyl aspartate, the complex with the D-enantiomer being 0.92 kcalmol(-1) more stable than its diastereomeric counterpart. Despite the lack of enantioselectivity of tri- and tetraprotonated (R,R)-1 for the tartrate anion, a very good diastereopreference for meso-tartrate is found. All these experimental results allow us to propose a model for the host-guest structure based on coulombic interactions and hydrogen bonds.