Development of a reliable synthetic scheme to isolate 2-hydroxy-2-benzodioxanylethoxy benzamides for the obtainment of fluorescent probles

Aiming at fighting antimicrobial resistance when acting on an innovative target, we developed a class of FtsZ inhibitors as promising new antimicrobials, which are structurally benzodioxane-benzamides. While characterizing the mechanism of action of this class of compounds, the need of a FtsZ fluorescent ligand to determine several biochemical data, such as confocal microscopy images of protein-ligand co-localization, arose. Therefore, starting from the structure of our strongest compound, which is able to interact and perturb both S. aureus and E. coli FtsZs, we decided to introduce an -OH group as an anchoring point for the preparation of both prodrugs and fluorescent probes, by inserting a proper dye (compound I-OH). This compound required the design of an ad hoc synthetic pathway, able to separate the two diastereomeric threo and erythro couples. A common intermediate of this synthesis is the epoxydic derivative (Scaffold A), obtained as a mixture of the two diastereomeric pairs, and soon chromatographied achieving the isolated diastereoisomers, which parallelly underwent ring opening, yielding to the final desired compounds (I-OH threo and I-OH erythro). After their isolation, each couple of enantiomers were linked to a proper fluorescent dye through a suitable spacer (Figure 1). With this work, we developed a synthetic scheme applicable to all the benzodioxane-benzamides FtsZ inhibitors, regardless the substitution of the benzodioxane moiety, to obtain hydroxylated derivatives.