6
The low affinities, typical of interactions
between fragments and their targets,
require fragments to be at high
concentrations which HTS assays
can't handle. Screening methods
for FBDD then must use biophysical
techniques, as these can offer a broader
sensitivity range. They also provide
Recipe for a
successful
fragment
library
Fragments must be highly soluble at the high concentrations needed, yet mustn't
be prone to interference that leads to false positives at such levels. For this reason,
good fragment library design is critical. A well-designed, diverse fragment library
will have about a thousand-fold fewer constituents than a typical HTS library, which
contains about 1000 to 10,000 species. In order to ensure that the library covers a
large chemical space, good practice in library design involves following the four
components of the "rule of three":
1
Molecular
weight less than
300 Da
2
Fewer than three
H-bond donors/
acceptors
3
Fewer than three
rotatable bonds
fragments bind to their target proteins
with relatively low affinity
10
. This is
an extremely important point when
choosing a screening method, as
one must look for one that has the
sensitivity to detect hits or binding
interactions with K
d
values in the range
of high micromolar to millimolar range
7
.
complementary data on biochemical
and cellular activity as well as info
on aggregation, solubility, and cell
permeability
21, 11
.
4
cLogP (measure of
hydrophilicity) ≤ 3
4
