Chemistry Reference
In-Depth Information
40
000
N
HN
+
N
N
30
000
H
2
N
NH
2
N
N
PA 6
+
20
000
N
H
2
N
NH
2
1
m/z
=
661
10
000
100
200
300
400
500
600
m/z
Figure 7.15
DIOSmass spectrumof the
in situ
Click chemistry experiment of tacrine fragment
TZ2
, phenanthridinium fragment
PA6
targeting AChE. Unreacted
TZ2
is detected with low
sensitivity under these conditions (independent measurements confirmed). Reproduced with
permission from Lewis, W.G., Green, L.G., Grynszpan, F., Radic, Z., Carlier, P.R., Taylor, P.,
Finn, M.G. and Sharpless, K.B., Click chemistry
in situ
: acetylcholinesterase as a reaction ves-
sel for the selective assembly of a femtomolar inhibitor from an array of building blocks.
Angewandte Chemie, International Edition
2002,
41
, 1053-1057; Supporting Information.
Copyright Wiley-VCHVerlag GmbH.
analysis to accommodate better the low product conversion rates of fragments to triazoles
and also to enable the capability to evaluate complex multi-fragment libraries rather than
only binary fragment combinations. Follow-up work also targeting AChE delivered the
breakthrough advance in screening performance by using selected ion monitoring mass
spectrometry (SIM-MS), in which the mass spectrometer is set to scan over a very small
m
/
z
range (typically 1 Da) rather than a broad
m
/
z
range. This narrow mass range permits
greater specificity of the analysis as only compounds with the selected mass of interest are
detected. The SIM mode also increases the sensitivity of detection of the triazole molecule
by decreasing the contribution of other components to the recorded MS signal. In addition,
SIM-MS was coupled with HPLC, which allowed the triazole products to be characterized
by both their mass and their retention time. The retention time is of special significance
for this application as it permits the
syn-
/
anti-
regioisomer assignment of the Click triazoles
formed, which are identical by mass analysis but typically have different retention times.
The other key advantage of the HPLC-SIM-MS technique is that it allowed the analysis
of
in situ
Click chemistry performed with multi-fragment mixtures that consisted of the
target and up to 11 fragments. Additionally, chromatographic removal of the molecules that
may otherwise obscure the mass spectrum of the triazole product allowed a decrease in the
