New 1,3-diarylureas linked by CC Suzuki coupling to the methyl 3-aminothieno[3,2-b]pyridine-2-carboxylate moiety: Synthesis and fluorescence studies in solution and in lipid membranes

New six fluorescent 1,3-diarylureas linked by CC Suzuki coupling to the 6-position of the methyl 3-aminothieno[3,2-b]pyridine-2-carboxylate moiety were prepared by reaction of the amino groups on the ortho or meta positions relative to the CC bond of the Suzuki coupling products, with different para-substituted arylisocyanates (H, OMe, CN), in high to excellent yields. The fluorescence properties of the 1,3-diarylureas in solution and in lipid membranes of egg yolk phosphatidylcholine (Egg-PC), dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylglycerol (DPPG) or dioctadecyldimethylammonium bromide (DODAB), with or without cholesterol (Ch), were studied. The six 1,3-diarylureas have reasonable fluorescence quantum yields in several solvents (0.02 ≤ ΦF ≤ 0.69) and present a moderately solvent sensitive emission, but are not fluorescent in alcohols and water. The compounds bearing the arylurea moiety in the meta position relative to the CC bond, especially with the OMe and CN substituents, present the better solvatochromic properties.Incorporation of the six compounds in lipid membranes indicates that all the compounds are deeply located in the hydrophobic region of the lipid bilayers, feeling the transition between the rigid gel phase and fluid phases.

► Six new 1,3-diarylurea derivatives in the thieno[3,2-b]pyridine series were synthesized. ► The fluorescence properties of the new compounds were studied in solution and in lipid membranes. ► The compounds were incorporated in lipid membranes of DPPC, DPPG, egg lecithin and DODAB. ► These compounds are useful to monitor changes in fluidity of lipid membranes.