Biomedical Engineering Reference
In-Depth Information
R
2
O
OH
O
OH
OH
1. Fmoc-amino
dimethyl acetate
HCl, TMSCl
2. Piperidine, DMF
O
X
R
2
XH
X = S, NR
2'
N
H
O
H
O
R
1
O
R
1
O
Si
Si
i
-Pr
i
-Pr
i
-Pr
i
-Pr
123
124
HN R
3
NH
2
n
n
R
2
O
O
O
O
O
O
R
2
X
X
N
H
O
H
O
HF
ยท
Py
Electrophile
R
1
R
1
O
O
Si
Si
i
-Pr
i
-Pr
i
-Pr
i
-Pr
126
125
(
n
= 0, 1)
H
2
N
H
2
N
HN R
3
n
R
2
O
O
O
O
O
O
S
X
S
O
O
R
1
HO
HO
N
HO
N
127
128
129
SCHEME 15.11
with uretupamine, only a few genes repressed by Ure2p were upregulated in the wild-
type strain, whereas others remained unchanged. Uretupamine had no effect on the
expression levels of these genes on an isogenic strain lacking
URE2,
suggesting a high
specificity of the small molecule for its cellular target. Prior to this study, Ure2p had
been shown to repress the transcription factors Gln3p and Nil1p, the latter being
upregulated upon removal of glucose nutrient. Strains lacking
NIL1
were not respon-
sive to the small molecule, whereas strains lacking
GLN3
were equally affected,
demonstrating that uretupamine inhibits the Nil1p Ure2p-mediated repression func-
tion, but not its Gln3p counterpart. Additional experiments established a functional
relationship between the level of glucose, Ure2p phosphorylation status, and the level
of endogenous Nil1p, showing that Ure2p is a glucose-responsive element. These
results highlight the advantages offered by small molecules over the sole
URE2
knockout by providing a means to modulate selectively a subset of Ure2p functions.
This early example of a reverse genetic approach demonstrates that a small molecule
can induce a phenotype and lead to the identification of key players providing a clear
understanding of unanticipated cell circuitry, for instance, the involvement of Ure2p in
glucose signaling. It also emphasizes the power of diversity-oriented synthesis
associated with unbiased high-throughput screening technologies to discover small
molecule modulators, in particular in the case of an understudied biological target for
which very little or no structural information is available.
15.6.2. Secramine
In a conceptually similar approach, Shair and coworkers developed a small molecule
library inspired by the polycyclic structure of galanthamine (highlighted in gray in
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