Biomedical Engineering Reference
In-Depth Information
involving very few fundamental organic reactions and the absence of column
chromatography. Even though the preparation of each building block may be seen
as a limiting parameter, unprecedented structural diversity was obtained from simple
oligomers in a straightforward manner. It was represented by acyclic and cyclic
structures containing 5-15-membered rings, including isolated, fused, and bridged
carba-, oxa-, and azacycles. Chemical processes were designed to create different
molecular scaffolds as opposed to an overall large number of structurally similar small
molecules. Of particular importance will be the preparation of related analogues for
each of the molecular frameworks created, in order to maximize the probability of
identifying lead molecules in biological screens. This step has been elegantly
anticipated in the forward synthetic planning by an ingenious preimplementation
of residual functional groups that could be used postcyclization to incorporate
additional functionalities. This includes a variety of orthogonal nucleophiles such
as alcohols and amines, electrophilic centers such as lactones, and apolar reactive
elements such as conjugated dienes poised for additional cycloadditions.
15.6. BIOLOGICALLY ACTIVE SMALL MOLECULES
OBTAINED FROM DOS
15.6.1. Uretupamine
Ure2p is an important yeast protein that represses a number of genes involved in the
qualitycontrol of nitrogennutrients. Theabsenceof structural informationprevents the
rational design ofmolecular probes that could potentially interact andmodulateUre2p
functions to study the processes occurring downstream. Schreiber and coworkers
realized a tour de force by combiningdiversity-oriented synthesis andhigh-throughput
screening to discover a small molecule inhibitor of Ure2p [56,57]. A small molecule
library was designed on the basis that the cyclic nature of a dioxane corewould restrict
the conformational freedom of the molecule and potentially enhance its affinity for a
given biological target. In order to avoid tedious purification, dioxane precursors
were first loaded onto beads to afford the resin derivatized epoxy alcohols
123
(Scheme 15.11). The silylated linker was chosen for the mild conditions required to
release the small molecule prior to its biological evaluation. A set of nucleophilic
amines and thiolswere reactedwith the terminal epoxidemoietyof
, resulting in the
introduction of diverse side appendages with concomitant formation of a secondary
alcohol. The resulting diols
123
were then reacted with Fmoc-aminodimethyl acetals
and deprotected in the presence of piperidine to afford dioxanes
124
125
. Finally, the
resulting amines were reacted with diverse electrophiles to provide
126
, which were
subjected toaHF
in individual stocksolutions.
The library containing 3780 compounds, adapted in microarray format, was screened
with a fluorescently labeled Ure2p. Eight small molecules based on a 1,3-dioxane
scaffoldwith lowmicromolar affinities forUre2pwere identified.Areportergeneassay
confirmed that one member, uretupamine A (
Py treatment yieldingpureproducts
127
), showed cellular activity at micro-
molar concentrations consistent with
in vitro K
d
measurement. Further postscreening
chemical modifications led to the more potent uretupamine B
128
129
. Upon incubation
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