An attempt to consider cooperativity in helical-sense preferences induced in fused macrocycles

Org Biomol Chem. 2023 Mar 22;21(12):2562-2569. doi: 10.1039/d3ob00171g.

Abstract

We synthesized bis and tris(macrocycle)s in which a two- or three-fold macrocycle was fused and each adopted twisted forms with M- or P-helicity. According to the sense of twisting in each element, diverse conformations can be generated in a molecule. We present two types of conformational preferences. One is the innate preference for a helical form with an identical sense of twisting throughout the entire molecule. The other is the helical-sense preference for a particular sense of twisting. We were interested in the relationship between Kn and (K1)n, where Kn is an equilibrium constant for the conformational interconversion between two helical forms (MM and PP, MMM and PPP) and n is the number of elements, since we considered that the relationship could be a metric to see the interinfluence among these macrocyclic elements in a single molecule. Through VT measurements in 1H NMR and CD spectroscopy, we attempted to quantify the helical-sense preferences induced in the fused macrocycles (n = 2 and 3) to compare Kn and (K1)n.