Design and synthesis of fluorescent pilicides and curlicides: bioactive tools to study bacterial virulence mechanisms.
Bottom Line: To facilitate studies of the interaction between these compounds and the pili and curli assembly systems, fluorescent pilicides and curlicides have been synthesized.This was achieved by using a strategy based on structure-activity knowledge, in which key pilicide and curlicide substituents on the ring-fused dihydrothiazolo 2-pyridone central fragment were replaced by fluorophores.We created fluorescent pilicides and curlicides by introducing coumarin and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) fluorophores at two positions on the peptidomimetic pilicide and curlicide central fragment.
Affiliation: Department of Chemistry, Umeå University, 90187 Umeå, Sweden.Show MeSH
Related in: MedlinePlus
Mentions: Ring-fused 2-pyridones are peptidomimetics that can target protein–protein interactions in macromolecular assembly. We have previously shown that ring-fused dihydrothiazolo 2-pyridones (1) provide an excellent central fragment for design and synthesis of compounds that block the formation of pili and curli.10, 11, 14 Pilicides (2 a,b) are compounds that block pilus biogenesis (exemplified in UPEC), whereas curlicides (such as 3) prevent curli fiber biogenesis. Development of traceable pilicides and curlicides could potentially be obtained using a biomolecular labeling strategy, for example, by radiolabeling or by the introduction of a fluorescent label. In the latter case, a fluorescent probe is usually attached by using a linker to the biomolecule to avoid any interference with the biomolecular interactions. The low molecular weight of ligands such as the pilicides 2 a,b and curlicide 3, implies that this technique could change the overall molecular composition to a great extent and thereby potentially reduce the bioactivity of these compounds. An alternative approach would be to replace key substituents for bioactivity by a fluorophore. To increase the likelihood of succeeding by using this approach, and thus both retain the biological effect and gain fluorescent properties, the structure–activity knowledge on the central fragment could be used for both the choice of fluorophore and its positioning on the central fragment. One potential problem with this method is a higher probability for fluorescent quenching of the fluorophore due to its close proximity to the bioactive central fragment. Even so, exchange of one of the substituents on the peptidomimetic central fragment 1 to a fluorophore could render attractive compounds for uptake/distribution studies, development of competition-based assays, Förster resonance energy transfer (FRET) studies on binding interactions, and to specifically image conserved pili and curli assembly machineries in bacterial populations. Initial studies of the structure–activity relationships on the ring-fused dihydrothiazolo 2-pyridone central fragment have shown that the C7 and C8 positions are highly important for bioactivity and should preferably carry larger lipophilic substituents.10, 11, 15–17 Consequently, we have in the present study exchanged the substituents in the C7 and C8 positions on the central fragment 1 with coumarin (4) or BODIPY (5) fluorophores (Figure 1). The use of these particular fluorophores could be justified by their good (compound 4) to high (compound 5) quantum yields, absorption/emission wavelengths, lipophilicity, lack of net ionic charge, photostability, different emission colors and relatively small size.18–20
Affiliation: Department of Chemistry, Umeå University, 90187 Umeå, Sweden.