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Optically Active Dioxatetraazamacrocycles: Chemoenzymatic Syntheses and Applications in Chiral Anion Recognition
Author(s) -
Alfonso Ignacio,
Rebolledo Francisca,
Gotor Vicente
Publication year - 2000
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20000915)6:18<3331::aid-chem3331>3.0.co;2-8
Subject(s) - chemistry , tartrate , enantiomer , protonation , diastereomer , stereochemistry , aqueous solution , titration , medicinal chemistry , ion , organic chemistry
Two new C 2 and D 2 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 (ΔΔ G =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 kcal mol −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.