Controlled Expansion of a Molecular Cavity in a Steroid Host Compound

Expansion of a molecular cavity is described by using elongation of the side chain of a bile acid
host compound. Bishomocholic acid (2), which has a side chain that is longer by two methylene unit than
cholic acid (1), includes many organic substances at 1:1 host:guest ratios. X-ray crystallographic studies revealed
that 2 has two types of open host frameworks:  a bilayer type and a crossing type. Both of them are isostructural
to those of 1, indicating that they are robust against the elongation of the side chain. In the former type, the
increment of the width of the host channel corresponds to that of the length of the molecular structures. Larger
aromatic guest components such as 1-methylnaphthalene and 1-tetralone, are included in 2, but not in 1.