shortest linker. The RBA of this bivalent conjugate is seven
times higher than that of the monovalent raloxifen–oligo-
ethyleneglycol conjugate Ral3. Again, a docking study
illustrated the potential of the simultaneous binding of the
raloxifene units to the consensus binding pocket and an
adjacent hydrophobic site (Figure 3b,d).
second hydrophobic binding site near the consensus ligand
binding pocket of ER-a. This assumption is supported by
docking studies and binding experiments, in which raloxifene
was linked through short spacers to a second raloxifene or a
hydrophobic group such as pyrene. The DNA-controlled
ligand presentation should facilitate the spatial screening of
receptors because this method involves the synthesis of only
two ODN–ligand conjugates rather than the synthesis of a
multitude of differently covalently conjugated dimers. This
may accelerate the identification of high-affinity binders of
structurally not characterized target proteins for biological
and medicinal applications.
Additional experiments with compounds in which the
raloxifene units were conjugated to hydrophobic groups such
as pyrene suggested that the hydrophobic site can be occupied
by “non-SERMs” (Table S4 in the Supporting Information,
Ral-Pyr). In contrast, conjugates Ral27, Ral210, and Ral213, in
which the raloxifene units were connected by flexible and
long spacers, were found to bind with an affinity that only
slightly surpassed the affinity of the monovalent conjugates
Ral3 and Ral5. This result is in agreement with earlier studies
on flexibly linked SERM conjugates.[17b,d] As a control, we
conducted experiments with raloxifene dimers in which
single-stranded bivalent oligonucleotides served as flexible
linkers. A previous study showed that the binding of
bivalently modified DNA single strands to bivalent receptors
should—in principle—lead to higher binding affinities than
those expected for the binding of monovalent oligonucleotide
conjugates.[8b,23] However, we observed that the bivalent
single strands had a lower ER affinity than the monovalent
single strands (Table S4 in the Supporting Information),
which is in agreement with the results obtained with flexibly
bridged ligand dimers.[17b,d]
Received: March 7, 2011
Revised: May 2, 2011
Published online: July 26, 2011
Keywords: click chemistry · drug discovery · multivalency ·
.
receptors · steroid hormones
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Angew. Chem. Int. Ed. 2011, 50, 8592 –8596
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