Synthesis of phenanthridine-based calix[4]arene glycoconjugate and physicochemical characterization of its complexation reactions with alkali metal cations

Sintetiziran je fluorescentni glikokonjugat kaliks[4]arena (L) koji na donjem obodu posjeduje dvije fenantridinske i dvije glikozilirane amidne skupine. Detaljno je istražen afinitet tog spoja prema kationima alkalijskih metala u metanolu te su određene konstante stabilnosti nastalih kompleksa i ostali termodinamički parametri reakcija kompleksiranja. Vezanje kationa proučavano je spektrofotometrijski, fluorimetrijski, mikrokalorimetrijski te spektroskopijom NMR. Sinteza je provedena u nekoliko koraka počevši od 2-aminobifenila iz kojeg je sintetizirana fenantridinska podjedinica, koja je u sljedećem koraku vezana na p-tert-butilkaliks[4]aren. U idućoj je reakciji na preostale dvije, nesupstituirane fenolne podjedinice vezan tercijarni amid prilikom čega je formirano efikasno mjesto za vezanje kationa. Uslijedila je bakrom katalizirana reakcija alkina i azida kojom su uvedene glukozne skupine. Priređeni derivat kaliks[4]arena pokazuje značajan afinitet prema kationima alkalijskih metala u metanolu, a konstante stabilnosti kompleksa ML+ smanjuju se u nizu Na+ > K+ > Li+ > Rb+, dok je vezanje Cs+ preslabo da bi se moglo kvantitativno okarakterizirati. Reakcije kompleksiranja svih kationa s ligandom entalpijski su kontrolirane, s nepovoljnim entropijskim doprinosom standardnoj reakcijskoj Gibbsovoj energiji.The fluorescent calix[4]arene glycoconjugate (L) bearing two phenanthridine and two glycosylated tertiary-amide moieties at the lower rim was synthesized. The affinity of this compound towards alkali metal cations in methanol was thoroughly studied and the stability constants of the complexes formed as well as other thermodynamic parameters of complexation reactions were determined. Cation binding was investigated by means of spectrophotometry, fluorimetry, microcalorimetry, and 1H NMR spectroscopy. The synthesis was carried out through several reactions starting from 2-aminobiphenyl from which phenanthridine subunit was synthesized and then bound to p-tert-butylcalix[4]arene. In the next step, tertiary amide was introduced on the remaining, unsubstituted phenolic groups which resulted in the formation of the efficient cation-binding site. Cooper-catalyzed alkyne-azide cycloaddition followed, and in this step glucose groups were introduced. The prepared calix[4]arene derivative exhibited significant affinity towards alkali metal cations in methanol. The decrease of the ML+ complex stability constants was observed in a series: Na+ > K+ > Li+ > Rb+, whereas binding of Cs+ was too weak to be quantitatively characterized. Complexation reactions of all cations with L were enthalpy driven, with unfavorable entropic contribution to the standard reaction Gibbs energy