Oligosaccharides based antibacterial drug conjugates

Abstract

Gram negative bacteria are intrinsically resistant to antibiotics, as their outer membrane constitutes a permeability barrier that limits the number of antibiotics available for an effective treatment. There is also a lack of sensitive methods to diagnose infection in the early stages. The limited pipeline of new antibiotics demands novel ways to translocate antibiotics into gram negative bacteria. One possible strategy to improve bacterial penetration is to exploit the specific active transport machinery of bacteria to achieve facilitated transport of antibiotics, also referred to as Trojan horse strategy.

In recent years maltodextrins conjugates modified at the anomeric end have been used in the Trojan horse strategy to detect and treat bacterial infection. However, it is also reported that blocking the reducing end of maltodextrin by residues larger than methyl groups are not transported by the maltodextrin receptor. This thesis deals with the synthesis and investigation of conjugates with modification at the non-reducing end of maltodextrins. The conjugates can accommodate a fluorophore or an antibiotic for detection and treatment of infection, respectively. The critical structural requirements in the maltodextrin based conjugate design for an efficient uptake have been investigated. A systematic series of fluorescent conjugates with varying critical parameters including chain length of maltodextrins, linker types, site of modification and type of fluorophore have been synthesized. The uptake efficiencies of the conjugates have been studied using growth recovery assays, confocal microscopy and flow cytometry. The validation of intracellular uptake of conjugates was performed using a fluorogen activating protein (FAP)-based approach. Finally, maltodextrin-ampicillin conjugates were synthesized and tested for antibacterial activity in E. coli and K.oxytoca