Synthesis and properties of two PRODAN-based fluorescent models of cholesterol

The syntheses and photophysical properties of 1-(5-methylhexyl)-2,3,7,8-tetrahydro-1H-naphtho[2,1-e]indol-9(6H)-one (7a) and 1-(5-methylhexyl)-2,3,8,9-tetrahydro-1H-naphtho[2,1-e]indol-6(7H)-one (7b) are reported. They are prepared in eight steps from the corresponding bromonaphthylamines. These fluorescent compounds have PRODAN-like cores, and they are structurally similar to cholesterol. Compound 7a is the first reported PRODAN derivative where both the amino and carbonyl groups are constrained to be coplanar with the naphthalene core. Comparing the photophysical behavior of these compounds with related compounds indicates that locking the amino group in a five-membered ring enhances their desirable properties as solvent polarity sensors.

Figure optionsDownload as PowerPoint slideHighlights
► Two cholesterol models bearing a PRODAN chromophore are prepared.
► The fluorescence of both is solvatochromic and similar to structurally related compounds with freely rotating dimethylamino groups.
► The photophysical properties of both are ideal for studying interactions with biological structures.