Nor-seco-cucurbit[10]uril exhibits homotropic allosterism.

The condensation of glycoluril and formaldehyde in concentrated HCl at 50 degrees C delivers nor-seco-cucurbit[10]uril (ns-CB [10]). 1H NMR and X-ray crystallographic evidence indicates that the two cavities of ns-CB[10] accommodate guests that are typically bound within CB[6] or CB[7]. Several interesting types of selectivity are possible within these ternary complexes-top/center isomerism, diastereoselective complexation of chiral (but racemic) guest pairs, and guest size controlled homotropic allosterism.