Chiral softballs: Synthesis and molecular recognition properties

Studies on the different congeners of the softball were undertaken to explo re structural variants for enantioselective encapsulation. Two different sp acer elements in the monomeric subunit render the dimeric softball chiral a lthough the monomer itself is achiral. The dimers represent capsules with d issymmetric cavities with volumes ranging from 190 to 390 Angstrom (3). The cavities are distorted spheres, and asymmetric guests, such as naturally o ccurring terpenes, generally prefer one enantiomer of the capsule to its mi rror image. The selectivities are moderate (up to 4:1). The complexation st udies show that the host capsules are flexible enough to arrange themselves comfortably around a guest but still maintain enough rigidity to be influe nced by the occupancy of a chiral guest. The enantiomeric capsules can inte rconvert (racemize) by dissociation and recombination of their subunits.