Journal of the American Chemical Society
Article
Notes
immediately preceding it. This information mirrored our study
on linear polyketide mimetics (Figure 4), which showed the
strongest sequestration of the fully elongated mimetic 32.
In this study, we have shown that selective replacement of
carbonyl groups with heteroatoms facilitates access to a diverse
class of polyketide mimetics that can be used to interrogate
polyketide biosynthetic enzymes. Inherent to this methodology,
these atom replacement mimetics can be chemoenzymatically
conjugated to ACP through the corresponding CoA analogs,
which provide the native scaffold to study these processes. While
no probe could ever exactly mimic the properties of natural
polyketone intermediates, this work demonstrates that mole-
cules that are much more polar than fatty acids14c or tricyclic
aromatics12 do associate with actACP, that longer chains
experience more residence time, and that cyclic intermediates
demonstrate the longest residence times. Our data, combined
with docking simulation of these probes (Figure S34), strongly
support that binding of both linear and cyclized polyketide
mimetics is not observed unless the mimetics are of sufficient
length. Taken together, these observations suggest that until the
polyketide has reached its terminal length, no preferential
sequestration by the actACP stabilizes the intermediate.
However, at full elongation, polyketide binding with the actACP
could facilitate release from the ketosynthase and assist transfer
to the KR for the first cyclization and reduction steps.15b
Binding of the first cyclized, reduced intermediate by the
actACP would then occur to facilitate release from the KR,
followed by delivery to the ARO/CYC.
In this study, the goal of these atom replacement mimetics
was to help understand the comparative binding and
stabilization of polyketone intermediates by ACPs. These
mimetics were not designed to serve as functional substrates
of PKS enzymes but instead to mimic the length, polarity, and
hydrophobicity found in natural intermediates. As with all
mimetics, the match was not perfect. In these examples, the C−
S bonds are considerably longer than those of their anticipated
ketides. The actual enol-keto states of natural polyketones
remain unknown, and the isoxazole moiety in part restricts
conformational freedom. These caveats aside, the establishment
of polyketide mimietics provides an excellent tool for inter-
rogating the iterative processes polyketide biosynthesis.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We thank Dr. X. Huang (UCSD), Dr. A. Mrse (UCSD), Dr. Y.
Su (UCSD), and Dr. P. Dennison (ICI) for assistance with
collection of NMR and MS data. We also thank Prof. C. A.
Townsend (Johns Hopkins), Prof. F. Ishikawa (UCSD), Prof. C.
D. Vanderwal (UCI), and Prof. A. R. Chamberlin (UCI) for
helpful advice. We also thank Prof. M. P. Crump for your advices
from full structural determinations as well as helpful discussions.
Funding was provided by National Institutes of Health
GM100305 and GM095970.
REFERENCES
■
(1) (a) Sadler, P. A.; Eschenmoser, A.; Scheinz, H.; Stork, G. Helv.
Chem. Acta 1957, 40, 2191. (b) Stork, G.; Burgstahler, A. W. J. Am.
Chem. Soc. 1955, 77, 5068. (c) Ruzicka, L.; Eschenmoser, A.; Heusser,
H. Experientia 1953, 9, 357. (d) Ruzicka, L. Experientia 1954, 50, 1.
(2) Abe, I.; Rohmer, M.; Prestwich, G. D. Chem. Rev. 1993, 93, 2189.
(3) (a) Johnson, W. S.; Semmelhack, M. F.; Sultanbawa, M. U.; Dolak,
L. A. J. Am. Chem. Soc. 1968, 90, 2994. (b) Schmidt, R.; Huesmann, P.
L.; Johnson, W. S. J. Am. Chem. Soc. 1980, 102, 5122.
(4) (a) Pichersky, E.; Noel, J. P.; Dudareva, N. Science 2006, 311, 808.
(b) Yoder, R. A.; Johnston, J. N. Chem. Rev. 2005, 105, 4730.
(c) Poralla, K. Chem. Biol. 2004, 11, 12. (d) Xu, R.; Fazio, G. C.;
Matsuda, S. P. Phytochemistry 2004, 65, 261.
(5) (a) Akey, D. L.; Gehret, J. J.; Khare, D.; Smith, J. L. Nat. Prod. Rep.
2012, 29, 1038. (b) Crawford, J. M.; Townsend, C. A. Nat. Rev.
Microbiol. 2010, 8, 870. (c) Khosla, C. J. Org. Chem. 2009, 74, 6416.
(d) Das, A.; Khosla, C. Acc. Chem. Res. 2009, 42, 631. (e) Bumpus, S.
B.; Kelleher, N. L. Curr. Opin. Chem. Biol. 2008, 12, 475.
(6) (a) Korman, T. P.; Hill, J. A.; Vu, T. N.; Tsai, S. C. Biochemistry
2004, 43, 14529. (b) Rudd, B. A.; Hopwood, D. A. J. Gen. Microbiol.
́
1979, 114, 35. (c) Fernandez-Moreno, M. A.; Martínez, E.; Caballero, J.
L.; Ichinose, K.; Hopwood, D. A.; Malpartida, F. J. Biol. Chem. 1994,
269, 24854.
(7) (a) Crump, M. P.; Crosby, J.; Dempsey, C. E.; Parkinson, J. A.;
Murray, M.; Hopwood, D. A.; Simpson, T. J. Biochemistry 1997, 36,
6000. (b) Revill, W. P.; Bibb, M. J.; Hopwood, D. A. J. Bacteriol. 1996,
178, 5660.
(8) (a) Teufel, R.; Miyanaga, A.; Michaudel, Q.; Stull, F.; Louie, G.;
Noel, J. P.; Baran, P. S.; Palfey, B.; Moore, B. S. Nature 2013, 503, 552.
(b) Ames, B. D.; Lee, M. Y.; Moody, C.; Zhang, W.; Tang, Y.; Tsai, S.
C. Biochemistry 2011, 50, 8392. (b1) Tsai, S. C.; Lu, H.; Cane, D. E.;
Khosla, C.; Stroud, R. M. Biochemistry 2002, 41, 12598. (c) Pan, H.;
Tsai, S. C.; Meadows, E. S.; Miercke, L. J.; Keatinge-Clay, A. T.;
O’Connell, J.; Khosla, C.; Stroud, R. M. Structure 2002, 10, 1559.
Finally, the involvement of the ACP in these pathways adds
significant complexity when compared to non-templated
biosynthetic pathways, and the creation of new tools to
understand this role merits special attention. Most critically,
this study defines new methods of atom replacement that can be
used to rapidly assemble both linear and cyclic polyketide
mimetics for structural and functional applications. Studies on
the protein−protein interactions of these species are ongoing.
́
(9) (a) Fouche, M.; Rooney, L.; Barrett, A. G. M. J. Org. Chem. 2012,
77, 3060. (b) Calo, F.; Richardson, J.; Barrett, A. G. M. Org. Lett. 2009,
11, 4910. (c) Navarro, I.; Basset, J. F.; Hebbe, S.; Major, S. M.; Werner,
T.; Howsham, C.; Brackow, J.; Barrett, A. G. M. J. Am. Chem. Soc. 2008,
̈
130, 10293. (d) Harris, T. M.; Murray, T. P.; Harris, C. M.; Gumulka,
M. J. Chem. Soc. Chem. Comm. 1974, 10, 362. (e) Harris, T. M.; Harris,
C. M. Tetrahedron 1977, 33, 2159.
(10) (a) Worthington, A. S.; Burkart, M. D. Org. Biomol. Chem. 2006,
4, 44. (b) Kosa, N. M.; Haushalter, R. W.; Smith, A. R.; Burkart, M. D.
Nat. Methods 2012, 9, 981.
(11) (a) La Clair, J. J.; Foley, T. L.; Schegg, T. R.; Regan, C. M.;
Burkart, M. D. Chem. Biol. 2004, 11, 195. (b) Meier, J. L.; Burkart, M.
D. Methods Enzymol. 2009, 458, 219. (c) Foley, T. L.; Burkart, M. D.
Curr. Opin. Chem. Biol. 2007, 11, 12.
(12) Haushalter, R. W.; Filipp, F. V.; Ko, K. S.; Yu, R.; Opella, S. J.;
Burkart, M. D. ACS Chem. Biol. 2011, 6, 413.
(13) (a) Stork, G.; Hagedorn, A. A., III J. Am. Chem. Soc. 1978, 100,
3609. (b) Stork, G.; La Clair, J. J.; Spargo, P.; Nargund, R. P.; Totah, N.
J. Am. Chem. Soc. 1996, 118, 5304. (c) Wright, P. M.; Myers, A. G.
ASSOCIATED CONTENT
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* Supporting Information
Copies of spectral data, synthetic methods, and experimental
procedures. This material is available free of charge via the
AUTHOR INFORMATION
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Corresponding Authors
Author Contributions
§G.S. and H.R. contributed equally.
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dx.doi.org/10.1021/ja5064857 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX