7,15,23-Tri-tert-butyl-25,26,27-trihydroxy-2,3,10,11,18,19-hexahomo-3,11,19-trioxacalixarene (1H3) was tri-O-alkylated with alkyl halides (RX: R=Me, Et, n-Pr, and n-Bu) in the presence of various bases and the products (1R3) were analyzed by HPLC and 1H NMR spectroscopy. It was found that (i) ring inversion which occurs through the oxygen-through-the-annulus rotation is allowed for 1Me3, 1Et3, and 1Pr3 whereas it is inhibited for 1Bu3, (ii) the cone/partial-cone equilibrium in 1Et3 and 1Pr3 is predominantly inclined to partial-cone, indicating the thermodynamic stability of partial-cone conformers, and (iii) in the product distribution of 1Bu3 partial-cone is yielded in preference for cone, indicating the kinetic preference for partial-cone. From the analysis of the reaction intermediates the possible reaction routes to cone- and partial-cone-1Bu3 are discussed. 1R3 showed the selectivity toward K+ among alkali metal cations and the cone conformers had the extractability (Ex%) higher than the partial-cone conformers. Cone-1R3 showed the high affinity for BuNH3+ because of (averaged) C3 symmetry common to both cone-1R3 host and BuNH3+ guest.
All Science Journal Classification (ASJC) codes
- Drug Discovery
- Organic Chemistry