6654
S. Mukherjee et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6651–6655
Scheme 5. Synthesis of 29, an alkyne-tagged and azide-appended derivative of 534F6.
agents to modify their protein targets.11 In addition, we
incorporated terminal alkyne substituents as chemical
tags that would allow us to separate the modified target
from the cellular lysate (Scheme 3).12
agarose in hopes of pulling down the protein target
from a cell lysate of E. coli.
In summary, we have discovered a new compound
(534F6) that appears to inhibit bacterial cell division
without inhibiting FtsZ as the primary target. Initial at-
tempts to prepare alkyne tagged photoaffinity reagents
have revealed regions of the molecule that are not suit-
able for structural variation. We are currently examining
a variety of alternative approaches for identifying the
target of this compound.
We initially explored the possibility of incorporating a
benzophenone group in the para position of the N-ben-
zyl substituent. The requisite 4-formyl benzophenone
(18) was prepared using the palladium coupling reported
by Goossen.13 Reductive amination of 18 yielded 19.
This compound’s weak activity (MIC > 80 lM)
prompted us to explore other options for installing a
photoreactive group (Scheme 4).
Acknowledgments
Our next compound was designed to use an aryl azide as
the photoreactive group. 21a was prepared by reductive
amination of 20. This compound was converted to sul-
fonamide 22a, which was carried on to alkyne 23a. Sul-
fonamidopyrrolidine 23a exhibited an MIC of <12 lM,
indicating that the presence of the alkyne did not affect
the activity. Encouraged by this result, we proceeded
with the synthesis of 23b by a parallel synthetic route.
This synthesis was enabled by the ligand- and copper-
free Sonagashira reaction reported by Verkade,14 which
avoids reduction and cycloaddition of the aryl azide.
Compound 23b exhibited an MIC of >40 lM, confirm-
ing the necessity of a lipophilic group at this site for
activity. The activity of 23a established the viability of
an alkyne on sulfonamide portion of the molecule
(Scheme 5).
J.T.S. thanks the National Institute for Allergy and
Infectious Disease (NIAID, RO3 AI062905) and the
Broad Institute Scientific Planning and Allocation of
Resources Committee (SPARC) for funding of this
research. D.R.C. acknowledges DARPA, the Charles
A. Dana Foundation, and the National Institute of
General Medical Sciences (NIGMS; RO1 GM068025)
for research support. The Hudson-Alpha Institute for
Biotechnology is acknowledged for support of S.M. as
a visiting scientist. The Harvard College Research
Program (HCRP) is acknowledged for a fellowship to
T.M. We thank Profs. Marc Kirschner and Tim Mitch-
ison (Harvard Medical School) for insightful discus-
sions. A portion of this work was conducted in Prof.
Kirschner’s Laboratory. This project has been funded
in part with Federal funds from the NCI’s Initiative
for Chemical Genetics, NIH, under Contract No.
N01-CO-12400. The content of this publication does
not necessarily reflect the views or policies of the
Department of Health and Human Services, nor does
mention of trade names, commercial products or organi-
zations imply endorsement by the U.S. Government.
The activities of 23a and 23b encouraged us to explore
the possibility of a hybrid of these two compounds
with 534F6. Sulfonamide 25 was prepared in two steps
from N-Boc-(R)-3-aminopyrrolidine (20). The Boc
group was removed and the 3-nitro-4-isopropoxy ben-
zyl group was installed by reductive amination.15 The
nitro group was reduced to the corresponding aniline,
which was then diazotized and displaced with azide.
After deprotection with TBAF, compound 29 was
examined for antimicrobial activity and found to have
an MIC of >64 lM. Although installation of the al-
kyne on the sulfonamide only slightly lowered the
activity of 23a relative to 5a, it is apparent that the
combined effect of the ortho azide and the alkyne
greatly diminishes the activity of 29. We are currently
preparing an affinity matrix with 23a using ‘clickable’
References and notes
1. Walsh, C. Nat. Rev. Microbiol. 2003, 1, 65.
2. Walsh, C. Antibiotics: Actions, Origins, Resistance; ASM
Press: Washington DC, 2003.
3. (a) Romberg, L.; Levin, P. A. Ann. Rev. Microbiol 2003,
57, 125; (b) Margolin, W. Nat. Rev. Mol. Cell Biol. 2005,
6, 862; (c) Dajkovic, A.; Lutkenhaus, J. J. Mol. Microbiol.
Biotechnol. 2006, 11, 140.