This paper describes the design and synthesis of a series of conjugate
s derived from cholic acid, spermidine, and 5-(dimethylamino)-1-naphth
alenesulfonyl (dansyl), which effectively shield the dansyl moiety fro
m water. Direct coupling of cholic acid to both terminal amino groups
of spermidine, and attachment of the environmentally-sensitive dansyl
moiety to the remaining secondary amine, yields a ''molecular umbrella
'' (Ia) whose fluorescent properties (lambda(max) and emission intensi
ty) reflect a nonpolar microenvironment in water and one that is relat
ively polar in intermediate dimethoxyethane/water mixtures. Comparison
of Ia with analogous ''single-walled'' (II) and ''no-walled'' (III) u
mbrellas further indicates that a minimum of two walls is necessary in
order to have ''umbrella-like'' properties. Examination of the fluore
scent properties of a related double-walled umbrella, bearing a flexib
le (2-hydroxyethyl)-carbamate moiety at the C-3 position of the sterol
(Ib), reveals that ''umbrella-like'' properties are present even when
facial amphiphilicity is not rigorously maintained; however, the mole
cule's ability to shield the fluorophore, as judged by its relative em
ission intensity, is diminished. ''Methyl-capping'' of the (2-hydroxye
thyl)carbamate (i.e., Ic) enhances the umbrella's ability to provide a
hydrophobic shelter in water. A tetra-walled analogue of Ia, bearing
four cholic acid units (i.e., IV), has been synthesized and its dansyl
group found to have reduced exposure toward water. The potential util
ity of molecular umbrellas in the area of drug delivery is briefly dis
cussed.