Long chain-substituted and triply functionalized molecular knots - Synthesis, topological chirality and monolayer formation

New topological chiral molecular knots (knotanes) 3a-6 of the amide type were substituted with long aliphatic side chains (butyloxy, hexyloxy, octenyloxy, decyloxy) and with p-bromobenzyloxy and oligoethylene glycol ether units, which resulted in improved solubility and enhanced potential for racemate separation. In consequence, the knotanes with longer substituted chains could be separated even on commercially available noncovalently bound chiral stationary phases. The (p-bromobenzyloxy)-knotane 6 and the octenyloxy-knotane 4 were synthesized with the intention of using their functional sidechains in further reactions, 6 being used in Suzuki-type reactions, while 4 was consequently allowed to react in the presence of Grubbs catalyst in metathesis reactions. The achieved solubility allowed us to test the abilities of the alkyl chain-substituted knotanes 3a-c and the (p-bromobenzyloxy)-knotane 6 to form Langmuir-Blodgett films. The assemblies were investigated on mica by AFM technique. A key point of focus was the (topological) chirality of the long chain-substituted knotanes. To address this point, the racemates were enantioseparated by HPLC on various chiral phases, and the obtained pure enantiomers were found to exhibit pronounced Cotton effects in their circular dichroism spectra. The absolute configurations of all new knots were derived by comparison with the unsubstituted knot.