The entrapment of chiral guests with gated baskets: Can a kinetic discrimination of enantiomers be governed through gating- Article

Wang, BY, Stojanovic̈, S, Turner, DA et al. (2013). The entrapment of chiral guests with gated baskets: Can a kinetic discrimination of enantiomers be governed through gating- . CHEMISTRY-A EUROPEAN JOURNAL, 19(15), 4767-4775. 10.1002/chem.201204344

cited authors

  • Wang, BY; Stojanovic̈, S; Turner, DA; Young, TL; Hadad, CM; Badjic̈, JD

authors

abstract

  • The capacity of gated hosts for controlling a kinetic discrimination between stereoisomers is yet to be understood. To conduct corresponding studies, however, one needs to develop chiral, but modular and gated hosts. Accordingly, we used computational (RI-BP86/TZVP//RI-BP86/SV(P)) and experimental (NMR/CD/UV/Vis spectroscopy) methods to examine the transfer of chirality in gated baskets. We found that placing stereocenters of the same kind at the rim (R1=CH3, so-called bottom) and/or top amide positions (R2=sec-butyl) would direct the helical arrangement of the gates into a P or M propeller-like orientation. With the assistance of 1H NMR spectroscopy, we quantified the intrinsic (thermodynamic) and constrictive (kinetic) binding affinities of (R)- and (S)-1,2-dibromopropane 5 toward baskets (S3b/P)-2, (S3t/M)-3, and (S3bt/P)-4. Interestingly, each basket has a low (≤1.3 kcal mol-1), but comparable (de<10 %) affinity for entrapping enantiomeric (R/S)-5. In terms of the kinetics, basket (S3b/P)-2, with a set of S stereocenters at the bottom and P arrangement of the gates, would capture (R)-5 at a faster rate (kinR/kinS=2.0±0.2). Basket (S3t/M)-3, with a set of S centers at the top and M arrangement of the gates, however, trapped (S)-5 at a faster rate (kinR/kinS=0.30±0.05). In light of these findings, basket (S3bt/P)-4, with a set of S stereocenters installed at both top and bottom sites along with a P disposition of the gates, was found to have a lower ability to differentiate between enantiomeric (R/S)-5 (k inR/kinS=0.8). Evidently, the two sets of stereocenters in this "hybrid" host acted concurrently, each with the opposite effect on the entrapment kinetics. Gated baskets are hereby established to be a prototype for quantifying the kinetic discrimination of enantiomers through gating and elucidating the electronic/steric effects on the process. Falling into a trap: Controlling the rate at which two stereoisomeric compounds enter a host presents a challenge. Gated molecular baskets (see figure) are shown to be excellent prototypes for implementing a kinetic differentiation of guests. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

publication date

  • April 8, 2013

published in

Digital Object Identifier (DOI)

start page

  • 4767

end page

  • 4775

volume

  • 19

issue

  • 15