A design principle has been devised for the construction of sterol-pol
yamine conjugates that function as synthetic ionophores. For feasibili
ty studies, a prototype (1) was synthesized from 3 beta-hydroxybisnor-
5-cholenic acid via sequential activation of its carboxylic acid moiet
y, condensation with spermine, and sulfation of the 3 beta-hydroxyl gr
oup. Closely related analogues were also prepared in which the termina
l amine group was acetylated (2), the 3 beta-hydroxyl group was left u
nsulfated (3), and each of the two remaining secondary amines was repl
aced with oxygen atoms (4). Incorporation of each conjugate into egg p
hosphatidylglycerol-based vesicles showed that 1 functions as an ionop
hore by discharging a pH difference across the vesicle membrane, but t
hat 2, 3, and 4 do not. A kinetic analysis of the ionophoric activity
of 1 has provided evidence that the majority of the conjugate exists a
s membrane-bound monomer and that dimers are the active species that a
re responsible for ion transport. Comparative experiments have also sh
own that 1 exhibits greater activity in negatively charged phospholipi
d membranes relative to ones that are electrically neutral. The implic
ations of these findings, with regard to the design of new classes of
antibacterial agents, are briefly discussed.