Abstract
Especially in the case of a chelating binding mode, it is necessary to find the optimal linker. The results obtained led to the conclusion that, despite the difficulties encountered during the design of a rigid linker, a fixed geometry could bring an enhancement in the affinity and a higher selectivity.
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The lectin LecA from Pseudomonas aeruginosa is an extremely interesting target, not only because of its biological relevance but also for its suitability to study the chelating multivalency effect. Furthermore, the affinity for LecA showed to be dependent on the geometry of the multivalent system and it seemed to be an optimal target to investigate the role of a rigid linker. This thesis covers the design and the synthesis of new rigid spacers used to form divalent systems. The spacer designs were based on a triazole-glucose repeating unit or on phenylene-ethynylene repeating unit. The inhibitors obtained were tested with LecA to evaluate a correlation between rigidity and affinity. The first spacer taken into account was based on a triazole-glucose repeating unit and in Chapter 2 the attempts to synthesize a suitable building block were described. The ideal building block required reproducible and high-yielding reactions. The successfully synthesized building block was used in Chapter 3 to synthesize rigid spacers. The strategy was based on the reiteration of three reactions: copper alkyne-azide cycloaddition (CuAAC) and introduction of the azide moiety via a triflate. The spacers synthesized were characterized by a different number of units, ranging from 2 to 4. The galactoside ligands coupled to the spacers exhibited different degrees of freedom. Furthermore, a PEG-based divalent system was synthesized as a flexible reference to compare with the rigid systems. The divalent inhibitors obtained were evaluated with lectin LecA. In Chapter 4 a different spacer design is described. The repeating unit was based, this time, on a phenylene-ethynylene moiety. The syntheses of the building blocks is described. The strategy consisted of alternating Sonogashira reactions and silyl-protecting group removal. The spacers obtained contained two to five phenylene-ethynylene unit. The three-unit spacer was coupled to a galactoside ligand and its potency as a LecA inhibitor was determined. In the last chapter, Chapter 5, a new and faster strategy to build rigid spacers based on the triazole-glucose unit is described. To increase the solubility of the protected spacer a new building block containing a silyl group was synthesized. The three different length spacers, from two to four units, were coupled with galactose ligands with different aglycon chains. Their inhibitiory potencies were tested with LecA and, for some compounds, also the Kd values were determined by ITC in selected cases.
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