Towards large tubular helices based on the polymerization of tri(benzamide)s

Herein we present the synthesis and polycondensation of mono- and di-N-protected,bis-substituted tri(benzamide)s with the aim tocreate large, tubular helices. We synthesized 2,4-dimethoxy and2,5-bis-TEGylated aminobenzoic acid derivatives as bent and linear monomers and introduced p-methoxybenzyl (PMB) amide protecting groups to the oligobenzamide backbone. An iterative coupling strategy allowed for sequence control, giving rise to oligomers consisting of one bent and two linear monomers. The resulting meta-para-para-linkedaromatictrimers carried either one or two PMB-protecting groups. With high organosolubility and flexibility, this synthetic strategy generated suitable precursors for subsequent polycondensation reactions. After polymerization, treatment with acid triggered the cleavage of the N-protecting groups. We hypothesize that the hydrogen bonding pattern generated along the polyaramide backbone could lead to the formation of a helical polymer. A drastic change in hydrodynamic volume was observed by gel permeation chromatography and dissolution in a chiral solvent lead to the observation of a circular dichroism signal for this polymer. The results of the polycondensations of N-protected oligobenzamides are reported herein. The formation of macrocycles as well as polymers could also be observed, giving a highly interestinginsight into the underlying mechanism of the polycondensation of flexible, oligobenzamide-based oligomers.