Chemistry Reference
In-Depth Information
Figure 4.4
1
H 1D relaxation filter spectra of part of the aromatic region (left) and the aliphatic
region (right) for a cocktail containing 10 compounds in the absence (top) and presence (bot-
tom) of A-FABP. The two doublet signals at 6.64 and 6.98 ppm and the two triplets at 2.25
and 2.62 ppm in the reference spectrum (top) originate from BVT.1960 (structure shown to
the right). These signals disappear when A-FABP is present in the sample, as pointed out by
the arrows. The signals from the nonbinding compounds in the mixture remain unaffected.
The spinlock time in this experiment was 400 ms. Adapted with permission from van Dongen
et al
.,
J. Am. Chem. Soc
.,
124
, 11874. Copyright 2002 American Chemical Society.
intolerability, in some cases even leading to death.
[
125
]
The potencies of the highest ranked
NMR hits were therefore measured and compared betweenA-FABP and H-FABP using the
fluorescence polarization assay. BVT.1960 gave an IC
50
value of 0.59 mM for A-FABP and
it was shown to be at least 25 times selective over H-FABP (IC
50
=
30 mM). This selectivity
is remarkable for such a small compound with a molecular weight of only 166 g mol
−
1
.
The amino acid sequences of A-FABP and H-FABP are 65% identical
[
126
]
with only a
few substitutions in the ligand-binding pocket. With the structure of the complex between
A-FABP and BVT.1960 at hand, a comparison of the amino acid sequences of the two
proteins reveals that the selectivity of BVT.1960 against H-FABP can be attributed to the
effect of Val115-Leu and Cys117-Leu substitutions (illustrated in Figure 4.5). Presumably,
the additional bulkiness introduced by these substitutions hampers the beneficial van der
Waals interactions experienced by one of the flanks of BVT.1960.
Because of the
>
25 times selectivity for A-FABP over H-FABP and the availability of a
structure of a ligand-target complex, the BVT.1960 scaffold was chosen as a starting point
for testing of compound analogues. Based on the structure of the ligand-target complex,
it can be concluded that there should be room for extension of BVT.1960 on the opposite
side to the one interacting with Val115 and Cys117 (Figure 4.5). Substructure searches in
