The Entrapment of Chiral Guests with Gated Baskets: Can a Kinetic Discrimination of Enantiomers Be Governed through Gating?

摘要: The capacity of gated hosts for controlling a kinetic discrimination between stereoisomers is yet to be understood. To conduct corresponding studies, however, one needs develop chiral, but modular and hosts. Accordingly, we used computational (RI-BP86/TZVP//RI-BP86/SV(P)) experimental (NMR/CD/UV/Vis spectroscopy) methods examine the transfer chirality in baskets. We found that placing stereocenters same kind at rim (R(1) =CH3, so-called bottom) and/or top amide positions (R(2) =sec-butyl) would direct helical arrangement gates into P or M propeller-like orientation. With assistance (1)H NMR spectroscopy, quantified intrinsic (thermodynamic) constrictive (kinetic) binding affinities (R)- (S)-1,2-dibromopropane 5 toward baskets (S3b/P)-2, (S3t/M)-3, (S3bt/P)-4. Interestingly, each basket has low ( ≤1.3 kcal mol(-1)), comparable (de<10%) affinity entrapping enantiomeric (R/S)-5. In terms kinetics, with set S bottom gates, capture (R)-5 faster rate (kin(R)/kin(S) =2.0±0.2). Basket centers trapped (S)-5 =0.30±0.05). light these findings, (S3bt/P)-4, installed both sites along disposition was have lower ability differentiate (R/S)-5 =0.8). Evidently, two sets this "hybrid" host acted concurrently, opposite effect on entrapment kinetics. Gated are hereby established prototype quantifying enantiomers through gating elucidating electronic/steric effects process.