Topologically Chiral Covalent Assemblies of Molecular Knots with Linear, Branched, and Cyclic Architectures

Abstract

Selectively functionalized molecular knots (knotanes) of the amide-type have been used as building blocks in syntheses of higher covalent assemblies composed of up to four knotane units. Preparation of linear and branched tetraknotanes consisted of the consecutive selective removal of allyl groups followed by linking of the intermediate hydroxyknotanes with biphenyl-4,4'-disulfonyl chloride. Macrocyclic knotane oligomers involving two, three, and four knotane moieties were obtained by high-dilution cyclization of dihydroxyknotane and biphenyl-4,4'-disulfonyl chloride. Due to their relation with cyclophanes, the latter class of oligomeric knotanes was termed "knotanophanes". Chiral resolution analysis of new oligoknotanes has been attempted on chemically bonded Chiralpak AD stationary phases, however met severe difficulties due to their complex isomeric compositions, and in most cases a significant overlap of the isomer fractions was observed. In spite of the limits of presently available chiral stationary phases that allowed only partial resolution of the synthesized topologies, oligoknotanes have been shown to be of high fundamental interest due to their unprecedented chirality. The chirality descriptions of topologically chiral unsymmetrical dumbbell 4, and the linear tetraknotane 5 are analogous to the Fischer projections of erythrose/threose and hexaric acid, respectively, while the isomeric composition of the branched tetraknotane 8 is completely unique. Moreover, the linear and branched tetraknotanes are constitutional isomers. Chirality of knotanophanes represents, in turn, analogies to known cyclic forms of peptides or sugars with multiple stereogenic centers.