Complete structure of the mycolactones [10]

Full text of DOI:10.1021/ja011824z

J. Am. Chem. Soc. 2001, 123, 10117-10118
Complete Structure of the Mycolactones
10117
Steve Fidanze,† Fengbin Song,† Magali Szlosek-Pinaud,†
P. L. C. Small,‡ and Yoshito Kishi*,†
Department of Chemistry and Chemical Biology
HarVard UniVersity, Cambridge, Massachusetts 02138
Department of Microbiology, UniVersity of Tennessee
KnoxVille, Tennessee 37996
Figure 1. I (Z-∆4′,5′), mycolactone A; II (E-∆4′,5′), mycolactone B.
ReceiVed July 27, 2001
The mycolactones were isolated in 1999 by Small and
co-workers1 from Mycobacterium ulcerans, the causative pathogen
of Buruli ulcer. This disease is characterized by the formation of
large, painless, necrotic ulcers and the lack of an acute inflam-
matory response. Evidence from animal studies suggests that the
mycolactones are directly responsible for the observed pathology,
and they have attracted considerable attention for their highly
potent apoptotic activity as well as for being the first examples
of polyketide macrolides to be isolated from a human pathogen.
The gross structure of these natural products was elucidated
through 2D NMR experiments.2 Via a combined approach
employing both an NMR database and the preparation of model
compounds, we recently established the relative and absolute
configuration of the mycolactone core structure (Figure 1).3
Extending the newly developed universal NMR database concept
in chiral solvents4 to a proton NMR database, we report the
complete structure of the mycolactones in this Communication.
In our view, the universal NMR database approach5 is ideally
suited to address the relative stereochemistry at C12′, C13′, and
C15′.6 Thus, we have chosen the diastereomers 1a-d to create
the NMR database to elucidate the relative stereochemistry of
the fatty acid portion of the mycolactones. In practice, all four
Figure 2. Difference in carbon chemical shifts (A) and proton chemical
shifts (B) between 1a-d and mycolactone B in acetone-d6. The x and y
axes represent carbon or proton number and ∆δ (δ1a-d - δmycolactone B in
ppm), respectively.
conjugated systems. Therefore, the protons and carbons within
these conjugated systems were not included for the NMR profile
comparison. As anticipated, the C8′-C11′ carbons and their
attached protons exhibited significant chemical shift differences.7,8
Interestingly, however, these differences were approximately in
the same magnitude for all 1a-d, suggesting the suitability of
the model diastereomers 1a-d for the present study.9
diastereomers 1a-d were synthesized from D-glyceraldehyde
acetonide in an optically active form. The details of the synthesis
and stereochemistry assignment of 1a-d are included in the
Supporting Information.
Obviously, the fatty acid portion of the mycolactones and the
diastereomers 1a-d are structurally different, particularly in their
The 13C NMR profiles in acetone-d6 of each of 1a-d were
compared with those reported for the corresponding portion of
the mycolactones2 (Figure 2A). Through this comparison, it
became evident that the C13′/C15′ relative stereochemistry of the
mycolactones is syn. The 13C NMR profiles of 1a and 1b were
very similar, although 1a appeared to represent the 13C NMR
profile of the mycolactones slightly better than 1b. As noticed
† Harvard University.
‡ University of Tennessee.
(1) (a) George, K. M.; Chatterjee, D.; Gunawardana, G.; Welty, D.;
Hayman, J.; Lee, R.; Small, P. L. C. Science 1999, 283, 854. (b) George, K.
M.; Pascopella, L.; Welty, D. M.; Small, P. L. C. Infect. Immun. 2000, 68,
877. (c) Rohr, J. Angew. Chem., Int. Ed. 2000, 39, 2847.
(2) Gunawardana, G.; Chatterjee, D.; George, K. M.; Brennan, P.; Whittern,
D.; Small, P. L. C. J. Am. Chem. Soc. 1999, 121, 6092.
1
previously,10 the 13C and H NMR spectra are complementary
(3) Benowitz, A. B.; Fidanze, S.; Small, P. L. C.; Kishi, Y. J. Am. Chem.
Soc. 2001, 123, 5128.
(7) The 1H and 13C NMR profiles including these nuclei are included in
the Supporting Information.
(4) (a) Kobayashi, Y.; Hayashi, N.; Tan, C.-H.; Kishi, Y. Org. Lett. 2001,
3, 2245. (b) Hayashi, N.; Kobayashi, Y.; Kishi, Y. Org. Lett. 2001, 3, 2249.
(c) Kobayashi, Y.; Hayashi, N.; Kishi, Y. Org. Lett. 2001, 3, 2253.
(5) (a) Kobayashi, Y.; Lee, J.; Tezuka, K.; Kishi, Y. Org. Lett. 1999, 1,
2177. (b) Lee, J.; Kobayashi, Y.; Tezuka, K.; Kishi, Y. Org. Lett. 1999, 1,
2181. (c) Kobayashi, Y.; Tan, C.-H.; Kishi, Y. HelV. Chim. Acta 2000, 83,
2562. (d) Kobayashi, Y.; Tan, C.-H.; Kishi, Y. Angew. Chem., Int. Ed. 2000,
39, 4279. (e) Tan, C.-H.; Kobayashi, Y.; Kishi, Y. Angew. Chem., Int. Ed.
2000, 39, 4282. (f) Kobayashi, Y.; Tan, C.-H.; Kishi, Y. J. Am. Chem. Soc.
2001, 123, 2076.
(8) For this purpose, we initially synthesized the four diastereomers of
(Me)2CdCHCH(OH)CH(OH)CH2CH(OH)Me and created the NMR databases.
The 1H and 13C NMR profiles were found to be very similar to those reported
in Figure 2.
(9) Gurjar and Cherian recently reported a synthesis of the protected form
of the fatty acid portion of mycolactones: Gurjar, M. K.; Cherian, J.
Heterocycles 2001, 55, 1095. Although the stereochemistry at C12′, C13′,
and C15′ does not correspond to the one determined in this work, it is worth
noting that the C11′ proton chemical shift difference between 1a (this paper)
and 3 or 4 (the referenced paper) is approximately the same as that between
1a (this paper) and mycolactone A or B.
(6) For the numbering adopted in this paper, see the structures in Figure 1.
10.1021/ja011824z CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/19/2001

10118 J. Am. Chem. Soc., Vol. 123, No. 41, 2001
Communications to the Editor
established through COSY experiments.12 The 1H chemical shifts
thus obtained were compared with those of 1a-d. Interestingly,
1
the H NMR profile difference between 1a and 1b became far
more pronounced in (R)- and (S)-DMBA than in acetone-d6,11,13
confirming the C12′/C13′/C15′ relative configuration of the
1
mycolactones. The H chemical shift differences (∆δ ) δR -
δS) for the relevant protons of the mycolactones were opposite
in sign to those observed for 1a (Figure 3B), establishing that
the C12′/C13′/C15′ absolute configuration of the mycolactones
corresponds to the antipode of 1a derived from D-glyceraldehyde
acetonide. Combined with the previous conclusion on the relative
and absolute configuration of the core portion,3 the current work
allows us to establish the complete structure of the mycolactones
A and B as shown in Figure 1.
It is worth adding that we were able unambiguously to make
the chemical shift assignment in (R)- and (S)-DMBA, and we
determined the chemical shift differences (∆δ ) δR - δS) for
the H17 (∆δ ) -0.009) and H19 (∆δ ) 0.006) protons present
1
in the core portion of the mycolactones. This H NMR profile
Figure 3. Difference in proton chemical shifts of 1a-d (A), mycolactone
A (B, I), and mycolactone B (B, II) between (R)- and (S)-DMBA-d13.
The x and y axes represent proton number and ∆δ (δR - δS in ppm),
respectively. Asterisk indicates these peaks are hidden underneath the
solvent peak.
matched with that of 2 [H17 (∆δ ) -0.007) and H19 (∆δ )
0.011)], thereby showing that the absolute configuration of the
core portion of the mycolactones corresponds to that of 2. This
for this type of comparison. Indeed, the 1H NMR profile difference
between 1a and 1b was more pronounced (Figure 2B), ensuring
that the C12′/C13′/C15′ relative configuration of the mycolactones
is syn/syn, cf. 1a.
With this information in hand, we then attempted to establish
the absolute configuration of the mycolactones through deriva-
tizations and/or degradations, coupled with spectroscopic and/or
chromatographic analyses, but without success. The difficulties
encountered were primarily due to the very limited availability
of the mycolactones. Under this circumstance, we recognized the
appealing potential that the universal NMR database concept in
chiral solvents offers.4 To demonstrate the reliability and useful-
assignment is consistent with the previous conclusion,3 which
further validates the reliability of the universal 1H NMR database
approach in chiral solvents.
In summary, using the universal NMR database approach in
achiral and chiral solvents, the relative and absolute configuration
of the fatty acid portion of the mycolactones has been elucidated
without degradation/derivatization. Combined with the previous
conclusion on the core portion, this work allows us to establish
the complete structure of mycolactones A and B as shown in
Figure 1. This work also represents a new and important extension
of the universal NMR database concept in chiral solvents to proton
NMR databases.
ness of this approach, we have focused on comparison of the 13
C
NMR profiles. For this work, however, because of the very limited
availability of the natural products, it was necessary to extend
this approach to the proton NMR databases.
1
The H NMR profiles of 1a-d in (R)- and (S)-N,R-dimethyl-
benzylamines (PhCH(Me)NHMe, DMBA) were studied, illustrat-
ing two important aspects. First, each diastereomer exhibited, at
the first approximation, an almost identical NMR profile in both
(R)- and (S)-DMBA, but a distinct and differing NMR profile
from each other, demonstrating that the 1H NMR database in (R)-
and/or (S)-DMBA can be used for predicting the relatiVe
configuration of the structural motif represented by 1a-d.11
Second, each diastereomer exhibited a small but definitive
difference between the chemical shifts recorded in (R)- and (S)-
DMBA, demonstrating that the NMR database in (R)- and/or (S)-
DMBA can be used for predicting the absolute configuration of
the structural motif represented by 1a-d (Figure 3A).
Acknowledgment. We are grateful to the National Institutes of Health
for generous financial support (CA 22215). M.S.-P. gratefully acknowl-
edges a postdoctoral fellowship from Association Franc¸aise pour la
Recherche The´rapeutique (AFRT).
Supporting Information Available: Complete experimental details
for the synthesis and stereochemical assignment of 1a-d, raw data of
1H and 13C NMR chemical shifts, 1H and 13C NMR comparisons, and 1H
NMR spectra of 1a-d and mycolactones (PDF). This material is available
free of charge via the Internet at http://pubs.acs.org.
JA011824Z
(12) The 1H NMR spectra of the mycolactones in (R)- and (S)-DMBA were
recorded by a Varian Inova 600 MHz spectrometer. The mycolactones are
known to exist as a 3:2 mixture of Z-∆4′,5′- and E-∆4′,5′-isomers. The
chemical shifts of Z-∆4′,5′- and E-∆4′,5′-isomers, i.e., mycolactones A and
B, were used for preparation of the graphs I and II in Figure 3B.
(13) This is a general phenomenon observed for a system containing an
olefinic group, cf., sCHdCHCH(OH)CH(Me)CHdCHs: Hayashi, N.;
Kobayashi, Y.; Kishi, Y., unpublished results.
1
The H NMR spectra of the mycolactones were recorded in
(R)- and (S)-DMBA, and the chemical shift assignment was
(10) Zheng, W.; DeMattei, J. A.; Wu, J.-P.; Duan, J. J.-W.; Cook, L. R.;
Oinuma, H.; Kishi, Y. J. Am. Chem. Soc. 1996, 118, 7946. Also see ref 5.
(11) The graphs in (R)- and (S)-DMBA, corresponding to the graphs shown
in Figure 2B, are included in the Supporting Information.