Journal of the American Chemical Society
Communication
weaker interaction might diminish the deprotonation ability of
ACKNOWLEDGMENTS
This work is supported by Fonds der Chemischen Industrie
Frankfurt/Main, Germany); German Science Foundation
DFG, Bad Godesberg, Germany); The National Natural
Science Foundation of China (No. 20802066); The Zhejiang
Qianjiang talent plan (No. 2011R10023); and K. P. Chao High-
Tech Foundation of Zhejiang University. We appreciate David
Cane (Brown University, USA) for critical reading of the
manuscript. We also thank the staff members of Shanghai
Synchrotron Radiation Facility (SSRF) and of beamline X06DA
at the Swiss Light Source (Paul Scherrer Institute).
■
Glu309 for 1, which likely represents the first step of the
3
a,4b
PSR.
Second, if the ligand complex of 1 was superimposed
(
(
3a
with the native STR1-secologanin (2) complex, the gap
between the amine and the aldehyde group of 2 should be 2.3
Å. The actual distance in both superimposed native complexes
was, however, much shorter (0.92 Å), which would favor Schiff
base formation between tryptamine and 2 compared to the
3
a
amine 1. In addition, the indole part of the tryptamine
analogue 1 lies nearly perpendicular to the aromatic rings of
Tyr151 and Phe226, resulting therefore in a decrease in π−π
interactions. This arrangement would make the indole portion
of 1 more flexible, in contrast to the sandwich-like structure in
the STR1 complex with tryptamine, a conformation resulting in
optimum orientation of the amino group for the Pictet−
Spengler condensation.
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̈
(
̈
̈
(
̈
(
6
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AUTHOR INFORMATION
Author Contributions
‡
These authors contributed equally.
1
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dx.doi.org/10.1021/ja211524d | J. Am. Chem.Soc. 2012, 134, 1498−1500