Enantioselective Total Synthesis of the Putative Biosynthetic Intermediate Ambruticin J

Article abstract of DOI:10.1002/chem.202100975

The family of anti-fungal natural products known as the ambruticins are structurally distinguished by a pair of pyran rings adorning a divinylcyclopropane core. Previous characterization of their biosynthesis, including the expression of a genetically modified producing organism, revealed that the polyketide synthase pathway proceeds via a diol intermediate, known as ambruticin J. Herein, we report the first enantioselective total synthesis of the putative PKS product, ambruticin J, according to a triply convergent synthetic route featuring a Suzuki-Miyaura cross-coupling and a Julia-Kocienski olefination for fragment assembly. This synthesis takes advantage of synthetic methodology previously developed by our laboratory for the stereoselective generation of the trisubstituted cyclopropyl linchpin.

Full text of DOI:10.1002/chem.202100975

Accepted Article
Accepted Article
Title: Enantioselective Total Synthesis of the Putative Biosynthetic
Intermediate Ambruticin J
Authors: Richard Edmund Taylor, Kathryn Trentadue, Chia-Fu Chang,
and Ansel Nalin
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Link to VoR: https://doi.org/10.1002/chem.202100975
01/2020

10.1002/chem.202100975
Chemistry - A European Journal
RESEARCH ARTICLE
Enantioselective Total Synthesis of the Putative Biosynthetic
Intermediate Ambruticin J
Kathryn Trentadue[a], Chia-Fu Chang[b], Ansel Nalin[c], and Richard E. Taylor*[a]
[a]
[b]
[c]
K. Trentadue, Prof. R. Taylor, Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA E-mail: rtaylor@nd.edu
Current: Dr. C.-F. Chang, Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St, Cambridge, MA 02138, USA
Undergraduate research participant. Current: Dr. A. Nalin, College of Medicine, The Ohio State University, 370 W. 9th Avenue, Columbus, OH 43210
Supporting information for this article is given via a link at the end of the document.
Abstract: The family of anti-fungal natural products known as the
ambruticins are structurally distinguished by a pair of pyran rings
adorning a divinylcyclopropane core. Previous characterization of
their biosynthesis, including the expression of a genetically modified
producing organism, revealed that the polyketide synthase pathway
proceeds through a diol intermediate, known as ambruticin J. Here
we report the first enantioselective total synthesis of the putative
PKS product, ambruticin J, via a triply-convergent synthetic route
featuring a Suzuki-Miyaura cross-coupling and a Julia-Kocienski
olefination for fragment assembly. This synthesis takes advantage of
synthetic methodology, previously developed by our laboratory, for
the stereoselective generation of the trisubstituted cyclopropyl
linchpin.
The biosynthesis of these polyketides has been characterized by
Reeves et. al. via gene sequencing and knockout experiments
using wild-type and mutant S. cellulosum.[21] Fermentation of an
AmbJ--- mutant allowed isolation of an intermediate C3,C5 diol,
characterized as ambruticin J, 1 (Figure 2) and no other
ambruticins were observed. The enzyme AmbJ,
a flavin-
dependent monooxygenase, was proposed to be responsible for
conversion of ambruticin J to a second putative intermediate,
ambruticin F, 2, in which the stereochemical configuration at C5
is epimeric to isolated ambruticins. Thus, further post-PKS
modifications includes oxidation of C5 followed by divergent
functionalization to provide the known ambruticins. As AmbJ is a
flavin-dependent monooxygenase homologous to epoxidases
associated with polyether biosynthesis, including MonCI and
NanO, it is likely that the transformation of ambruticin J to
ambruticin F proceeds through epoxidation of the C6-C7 alkene
followed by 6-endo-tet ring formation via epoxide ring opening
by the C3 alcohol.[20–23] The mechanism of this cyclization step is
unclear and because the putative epoxide intermediate consists
of two three-membered rings in conjugation, degradative
pathways appear plausible which include cyclopropane
fragmentation. While the cyclization is likely spontaneous, it is
unknown if AmbJ plays any role in ensuring a productive
pathway towards the isolated ambruticins. Moreover, the role of
the C5-hydroxyl stereochemical configuration in the epoxidation
and cyclization steps as well as ambruticin’s biological activity is
unknown.
Introduction
The ambruticin family of polyketide natural products, first
isolated from the myxobacterium Sorangium cellulosum in 1977,
display potentially useful biological properties, including
significant antifungal activity.[1–8] Studies of the mechanism of
action of these compounds suggest that the ambruticins
interfere with fungal osmoregulation by targeting the Hik1
kinase.[9,10] A recent study of the effect of ambruticin VS3 on soil
myxobacteria confirms an impact on a group III hybrid histidine
kinase (HHK) and provides an environmental advantage by
affecting the development of competitive myxobacterial
species.[11] Several studies using ambruticins and their
derivatives, in both in vitro and in vivo plant and murine models
of fungal infection, have shown therapeutic properties including
low toxicity and promising activity against fungal infections
including histoplasmosis and coccidiomycosis both intravenously
and orally administered.[2,9,10,12–14] Structurally, the ambruticins
consist of
a
trisubstituted divinylcyclopropane ring core
appended with two pyrans (Figure 1). Ambruticin congeners
vary in the C5 position, but it is the atypical trisubstituted
cyclopropane core and promising biological activity that have
made these molecules popular synthetic targets. The first total
synthesis of ambruticin S was completed in 1993 and several
additional successful strategies have been completed to date.[15–
20]
No other congener has been targeted by total or semi-
synthesis.
Figure 2. Post-PKS Epoxidation/Cyclization Mediated by AmbJ.
ambruticins R(C5)
H
H
H
H
H
-OH
-NH2
S
O
O
A
number of natural products contain substituted
VS5
VS4
VS3
VS1
HO2C
-NHCH3
-N(CH3)2
-N+(CH3)3
5
tetrahydropyran rings, including lasonolide A, the phorboxazoles,
cyanolide A, centrolobine, neopeltolide, zampanolide, and
dactylolide.[22] In addition, pyrans are among the most common
ring systems found in small molecule drugs.[23] Therefore,
strategies to efficiently and stereoselectively construct pyran
rings are of great synthetic interest and have the potential to
H
OH
R
Figure 1. The Structures of Natural Ambruticins.
1
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10.1002/chem.202100975
Chemistry - A European Journal
RESEARCH ARTICLE
boronic acid provided the desired vinyl iodide 3 in 67% yield
from alkyne 9 despite necessitating an additional step.
prove very useful in both natural product and medicinal
chemistry. Enzyme-catalyzed reactions may be especially
desirable, as they often provide the desired regio- and
stereoselectivity under relatively mild reaction conditions.[24–
26].Previous work by the Hahn lab has identified the enzyme
responsible for the biosynthetic formation of the dihydropyran
ring on the eastern side of the ambruticins. Exploration of the
dehydratase enzyme, AmbDH3, which catalyzed a dehydration-
oxa-Michael reaction, indicated a significant degree of substrate
flexibility.[27] However, no similar investigation has been
conducted into the possible scope and applications of the flavin-
dependent monooxygenase AmbJ. Therefore, to enable
exploration of this interesting post-PKS oxidation-cyclization and
the biocatalytic potential of AmbJ, we have developed a
synthetic route to the putative biosynthetic intermediate
ambruticin J.
Scheme 1. Preparation of Vinyl Iodide 3.
The C13-C24 divinyl pyran fragment of ambruticin J is identical
to that found in both the isolated ambruticins and jerangolides[43]
due to duplication within their PKS gene clusters.[21] Our
optimized route to this fragment is unique but borrows
significantly from previous independent efforts reported by
Hanessian and Lee (Scheme 2).[16,19] Dihydropyran 10 was
prepared using Hanessian’s route in 64% overall yield from (S)-
benzyl-glycidyl ether and highlighted by an electrophilic
cyclization. We then applied the strategy used by Lee to
stereoselectively generate the trisubstituted olefin, allowing us to
exploit the most advantageous portions of both Lee’s and
Hanessian’s routes. Specifically, benzyl deprotection with lithium
di-tert-butylbiphenyl complex afforded the desired free alcohol,
which then underwent Stark oxidation to give the carboxylic
acid.[44] The Weinreb amide 11 was then formed by amidation
and condensed with the organolithium generated from iodide 12,
to provide ketone 13 in 87% yield. Conversion of the ketone to a
vinyl triflate was carried out using Comins’ reagent, which
yielded exclusively the E-olefin.[45] The vinyl triflate then
underwent iron-mediated methylation using the conditions
developed by Fürstner to produce the desired tri-substituted
olefin 14 in 75% yield over two steps.[46,47] Benzyl deprotection
using identical conditions as before yielded unprotected alcohol,
which was then converted to the desired phenyl tetrazole
sulfone 4 in two steps using a Mitsonobu reaction followed by
oxidation with tetrapropylammonium perruthenate (TPAP).
Molybdenum-mediated oxidation conditions were also explored
but were found to be significantly lower yielding, potentially due
to the low solubility of the starting material. Characterization data
for both the unprotected alcohol and phenyl tetrazole sulfone 4
demonstrated excellent agreement with previous literature
characterizations of this compound.[16,48]
Results and Discussion
A desire for a convergent synthetic strategy for ambruticin J
inspires construction from three structural fragments such as
vinyl iodide 3, sulfone 4, and vinylcyclopropane linchpin 5
(Figure 3). This route also allows us to highlight synthetic
methodology previously developed in our lab which enables the
stereoselective and efficient creation of enantiomerically and
diastereomerically pure trisubstituted cyclopropanes from readily
available homoallylic alcohol precursors.[28–32] The vinyl iodide
and cyclopropane fragments would be coupled via a Suzuki-
Miyaura cross coupling.[33–35] and the final fragment would be
adjoined with a Julia-Kocienski olefination.[36]
Figure 3. Cyclopropyl Linchpin Strategy for the Total Synthesis of Ambruticin J.
Our total synthesis effort began with known dithiane 6, which
was prepared on a multi-gram scale in three steps from
propargyl alcohol (Scheme 1).[37] The lithiated dithiane was then
condensed with epoxide 7, which was also available on a multi-
gram scale in three steps from L-aspartic acid as previously
reported.[38] Application of this Corey-Seebach reaction yielded
dithiane 8 in 70% yield.[39] The dithiane group was hydrolyzed to
give the corresponding ketoalcohol in 83% yield using Nakata’s
conditions.[40] Stereoselective reduction with diisobutylaluminum
hydride generated the syn-diol in 81% yield with >20:1
diastereoselectivity. The relative stereochemistry of the diol was
confirmed by NMR analysis of an acetonide derivative, which
showed 13C NMR shifts characteristic of an acetal derived from a
syn diol.[41,42] The diol was protected with t-butyldimethylsilyl
triflate followed by selective removal of the trimethylsilyl group
with basic methanol to give terminal alkyne 9 in 83% yield over
two steps. Unfortunately, conversion of the alkyne to the E-iodo-
alkene proved more difficult than anticipated, with attempts at
using Schwartz reagent and N-iodosuccinimide proving
unsuccessful. However, exploitation of an intermediate vinyl
Scheme 2. Preparation of Pyran Fragment 4.
Synthesis of the vinylcyclopropane linchpin was highlighted by
application of methodology previously developed in our
laboratory. Our efforts combined well-established asymmetric,
aldehyde allylation reactions with subsequent olefin metathesis
chemistry to access allylsilane homoallylic alcohols as
2
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10.1002/chem.202100975
Chemistry - A European Journal
RESEARCH ARTICLE
cyclization substrates. In the current application, we eliminated
one step by taking advantage of Hall’s “double allylation”
reagent (Scheme 3) which was shown to condense with
aldehydes with up to 99:1 enantiomeric ratios. Allylboronate 15
was synthesized in four steps from commercially available
starting materials according to literature precedent.[49] This
reagent was then used for the allylation of aldehyde 16, which
was synthesized in 92% yield by ozonolysis from the
corresponding symmetrical alkene. The homoallylic alcohol 17
was obtained in 63% yield as a single diastereomer. Crucially,
this reaction was found to scale well, allowing multi-gram scale
reactions to be conducted without notable loss of yield. The
homoallylic alcohol was then treated with our standard
conditions, triflic anhydride, triethylsilane, and 2,6-lutidine to give
cyclopropane 18 in 87% yield.[30] As we noted previously, only a
single stereoisomeric cyclopropane was observed. This reaction
was also carried out at large scale and maintained both yield
and selectivity, enabling large scale production of the
cyclopropyl linchpin of our convergent strategy. Ozonolysis of
the vinylcyclopropane gave the intermediate aldehyde in 72%
yield, and reaction with Ohira-Bestmann reagent produced the
alkyne in 81% yield.[50–52] Removal of the silyl ether protecting
group with tetrabutylammonium fluoride (TBAF) gave
unprotected alcohol in quantitative yield. This cyclopropylalkyne
then underwent conversion to the pinacol boronic ester with
Schwartz reagent, freshly distilled pinacolborane, and
triethylamine to provide the linchpin 5 in 60% yield for the
desired E-alkene.[53]
Previous characterization of the target had suggested that the
divinylcyclopropane is potentially unstable and may be
especially sensitive to acidic conditions, leading to some
concern over the final oxidation step. Therefore, we took
advantage of the 1,3,5-triol intermediate and generated lactone
21 directly using TEMPO/BAIB with sodium bicarbonate as a
buffer (Scheme 5). This allowed for selective oxidation of the
primary alcohol under mild conditions and avoided issues
related to selectivity of the oxidation and instability of the
compound to harsher conditions. Methanolysis of the resulting
lactone gave the methyl ester in 50% yield (with 37% of the
lactone starting material being recovered and the remaining 13%
being lost to degradation pathways). While ester saponification
under
a number of conditions provided an intermediate
carboxylate, the acidification necessary to isolate ambruticin J
was accompanied by degradation. We were eventually able to
isolate characterizable quantities of ambruticin J using either
potassium trimethylsilanoate or potassium carbonate in aqueous
methanol.
Scheme 5. Completion of the Total Synthesis of Ambruticin J, 1
Unfortunately, an authentic sample of ambruticin J was not
available as a comparative standard. Comparison of the carbon
and proton NMR data of our synthetic ambruticin J to the data
reported by Reeves et al. was further complicated because the
literature data was limited to an NMR peak list.[21] However,
spectral data shows excellent agreement with that reported with
a single exception. Agreement between the proton NMR data is
excellent, with deviations of 0.04 ppm or less, with the exception
of a single proton with a deviation of 0.1 ppm. This deviation is
almost certainly due to issues assigning overlapping complex
resonances; the peak with the deviation of 0.1 ppm (belonging to
proton 4b), overlaps with H4a, H23b, and H27. The overlapping
signals also made determination of coupling constants difficult in
some instances, leading to minor variations in reported J-values.
Reeves also reported difficulty in obtaining a pure sample of
ambruticin J, so overlapping impurity peaks may have also
confounded J-value assignments. We speculate that this may
have also confounded 13C NMR assignments, as discussed
below.
Scheme 3. Preparation of Tri-Substituted Cyclopropyl Linchpin 5.
With all three fragments in hand, we proceeded with the
sequential fragment coupling reactions (Scheme 4). Vinyl iodide
3 and vinyl pinacol boronic ester 5 were combined under Suzuki
coupling conditions using thallium carbonate as
a base,
providing desired (E,E)-diene in 86% yield. The resultant primary
alcohol was then oxidized to an aldehyde using Dess-Martin
periodinane, providing aldehyde 19 in excellent yield. Finally,
Julia-Kocienski olefination was performed to add the final
fragment, yielding the desired E-olefin and providing the linear
skeleton of ambruticin J, 20.
The carbon NMR data shows deviations of 0.1 ppm or less for
all peaks with the exception of the peak belonging to C16, which
shows a deviation of 6.6 ppm. In an effort to alleviate this
ambiguity, we obtained one- and two-dimensional NMR data for
for the triol 23 and methyl ester 22 (Figure 4). Reeves reported
that the C16 13C resonance for isolated ambruticin J was found
at 124.3 ppm. However, synthetic ambruticin J carboxylic acid 1,
synthetic ambruticin J methyl ester 22, and synthetic triol
intermediate 23 all have no peak in this region and instead have
a peak at 130.9 ppm. The proton NMR signals were assigned
using COSY data obtained for the triol and methyl
ester intermediates, confirming Reeves’ assignments of all
proton peaks, including the peak at 5.25 ppm which belongs to
H16. HSQC data for the triol showed a strong correlation
between the proton peak at 5.25 ppm and the carbon peak at
130.9 ppm, confirming our assignment for C16 in ambruticin J.
The HSQC data for the ambruticin J methyl ester also identified
four other carbon peaks which were incorrectly assigned in the
literature data. While COSY data supports the assignments of all
Scheme 4. Preparation of Protected syn-3,5-Diol Fragment 20.
Completion of the synthesis of ambruticin J required only
desilylation and terminal oxidation. Global deprotection of the
silyl groups using TBAF yielded the expected triol intermediate.
3
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10.1002/chem.202100975
Chemistry - A European Journal
RESEARCH ARTICLE
protons, HSQC indicates that the C3 and C5 carbon signals
were previously interchanged in Reeves’ assignments, as well
as the C4 and C12 carbon resonances. Seeking further
evidence for our assignment of the signal at 130.9 ppm as C16,
we also found literature proton and carbon data obtained for the
natural product ambruticin VS3[54]. Assignments in this data set
closely matched the eastern half of our synthetic ambruticin J
and identified C16 at 130.7 ppm. The sum of this analysis
confirms our assignment of the carbon NMR data for ambruticin
Keywords: !"!#$%&$%'()*+*,-$."(/0).-.*+*1"2$,'!/)&-'*+*
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[1]
[2]
F. Hahn, F. N. Guth, Nat. Prod. Rep. 2020, 37, 1300-1315.
S. M. Ringel, R. C. Greenough, S. Roemer, D. Connor, A. L.
Gutt, B. Blair, G. Kanter, M. V. Strandtmann, J. Antibiot.
(Tokyo) 1977, 30, 371–375.
J
and the total synthesis of this putative biosynthetic
intermediate.
[3]
L. F. Shubitz, J. N. Galgiani, Z.-Q. Tian, Z. Zhong, P.
Timmermans, L. Katz, Antimicrob. Agents Chemother. 2006, 50,
3467–3469.
H
H
H
O
[4]
[5]
D. T. Connor, R. C. Greenough, M. Von Strandtmann, J. Org.
Chem. 1977, 42, 3664–3669.
D. T. Connor, M. Von Strandtmann, J. Org. Chem. 1978, 43,
4606–4607.
R
16
OH OH
H
H
R = -CH2OH, 23
R = -CO2CH3, 22
R = -CO2H, ambruticin J, 1
[6]
[7]
G. Just, P. Potvin, Can. J. Chem. 1980, 58, 2173–2177.
N. J. Barnes, A. H. Davidson, L. R. Hughes, G. Procter, V.
Rajcoomar, Tetrahedron Lett. 1981, 22, 1751–1754.
V. Michelet, J.-P. Genet, Curr. Org. Chem. 2005, 9, 405.
H
H
H
H
H
O
O
HO2C
[8]
16
H
H
[9] A. Dongo, N. Bataillé-Simoneau, C. Campion, T. Guillemette, B.
Hamon, B. Iacomi-Vasilescu, L. Katz, P. Simoneau, Appl.
Environ. Microbiol. 2009, 75, 127–134.
OH
N(CH3)2
ambruticin VS3
1H-16
(ppm)
13C-16
(ppm)
[10] L. Vetcher, H. G. Menzella, T. Kudo, T. Motoyama, L. Katz,
Antimicrob. Agents Chemother. 2007, 51, 3734–3736.
[11] F. J. Marcos-Torres, C. Volz, R. Müller, Nat. Commun. 2020, 11,
5563.
Natural and synthetic
ambruticin structures
isolated ambruticin J, 1
synthetic ambruticin J, 1
5.25
5.26
124.3
130.9
intermediate triol, 23
5.25
5.25
5.30
130.9
130.9
130.7
[12] S. Shadomy, C. J. Utz, S. White, Antimicrob. Agents Chemother.
1978, 14, 95–98.
[13] P. Knauth, H. Reichenbach, J. Antibiot. (Tokyo) 2000, 53, 1182–
1190.
ambruticin J methyl ester, 22
isolated ambruticin VS3
[14] J. Wesolowski, R. Y. A. Hassan, K. Reinhardt, S. Hodde, U.
Bilitewski, J. Appl. Microbiol. 2010, 108, 462.
[15] S. M. Berberich, R. J. Cherney, J. Colucci, C. Courillon, L. S.
Geraci, T. A. Kirkland, M. A. Marx, M. F. Schneider, S. F.
Martin, Tetrahedron 2003, 59, 6819–6832.
Figure 4. NMR Correlation between Ambruticin Structures.
Conclusion
[16] S. Hanessian, T. Focken, X. Mi, R. Oza, B. Chen, D. Ritson, R.
Beaudegnies, J. Org. Chem. 2010, 75, 5601–5618.
[17] A. S. Kende, J. S. Mendoza, Y. Fujii, Tetrahedron 1993, 49,
8015–8038.
[18] T. A. Kirkland, J. Colucci, L. S. Geraci, M. A. Marx, M.
Schneider, D. E. Kaelin, S. F. Martin, J. Am. Chem. Soc. 2001,
123, 12432–12433.
[19] E. Lee, S. J. Choi, H. Kim, H. O. Han, Y. K. Kim, S. J. Min, S.
H. Son, S. M. Lim, W. S. Jang, Angew. Chem. Int. Ed. 2002, 41,
176–178.
[20] P. Liu, E. N. Jacobsen, J. Am. Chem. Soc. 2001, 123, 10772–
10773.
[21] B. Julien, Z.-Q. Tian, R. Reid, C. D. Reeves, Chem. Biol. 2006,
13, 1277–1286.
[22] N. Mad Nasir, K. Ermanis, P. A. Clarke, Org. Biomol. Chem.
2014, 12, 3323–3335.
[23] R. D. Taylor, M. MacCoss, A. D. G. Lawson, J. Med. Chem.
2014, 57, 5845–5859.
In summary, we have completed the first total synthesis of
ambruticin J,
a putative biosynthetic intermediate in the
biosynthesis of the ambruticin family of natural products. We
synthesized this compound via a triply convergent synthetic
route relying on a Suzuki-Miyaura coupling and a Julia-Kocienski
olefination for fragment assembly to a vinylcyclopropane core.
The synthesis of this strategic linchpin was highlighted by
application of our cyclopropanation methodology. Through total
synthesis we have confirmed the structural assignment of
ambruticin J and corrected an assignment within the existing
literature NMR data for this compound. This synthesis also
provides access to ambruticin J and congeners and sets the
stage for biochemical studies of the enzyme AmbJ and its role in
the epoxidation and cyclization process that eventually leads to
the isolated ambruticins.
[24] S. Friedrich, F. Hahn, Tetrahedron 2015, 71, 1473–1508.
[25] M. T. Reetz, J. Am. Chem. Soc. 2013, 135, 12480–12496.
[26] N. J. Turner, E. O’Reilly, Nat. Chem. Biol. 2013, 9, 285–288.
[27] T. Hollmann, G. Berkhan, L. Wagner, K. H. Sung, S. Kolb, H.
Geise, F. Hahn, ACS Catal. 2020, DOI
10.1021/acscatal.9b05071.
[28] R. E. Taylor, M. K. Ameriks, M. J. LaMarche, Tetrahedron Lett.
1997, 38, 2057–2060.
Acknowledgements
We acknowledge the preliminary efforts of Dr. Coura Diene and
Dr. Matt Wilson for setting the foundation of this project.
Financial support by Notre Dame's Chemistry-Biochemistry-
Biology
Interface
Program,
an
NIH
training
grant
[29] R. E. Taylor, M. J. Schmitt, H. Yuan, Org. Lett. 2000, 2, 601–
603.
[30] R. E. Taylor, F. C. Engelhardt, M. J. Schmitt, H. Yuan, J. Am.
Chem. Soc. 2001, 123, 2964–2969.
[31] R. E. Taylor, C. A. Risatti, F. C. Engelhardt, M. J. Schmitt, Org.
Lett. 2003, 5, 1377–1379.
(T32GM075762), and the National Institute of General Medical
Sciences are gratefully acknowledged (GM084922). We would
also like to thank Dr. Evgenii Kovrigin (Director; Magnetic
Resonance Research Center, Notre Dame) for assisting with the
2D NMR experiments.
4
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Chemistry - A European Journal
RESEARCH ARTICLE
[32] C. A. Risatti, R. E. Taylor, Angew. Chem. Int. Ed. 2004, 43,
6671–6672.
[33] A. Suzuki, J. Organomet. Chem. 1999, 576, 147–168.
[34] S. A. Frank, H. Chen, R. K. Kunz, M. J. Schnaderbeck, W. R.
Roush, Org. Lett. 2000, 2, 2691–2694.
[35] J. Uenishi, J. M. Beau, R. W. Armstrong, Y. Kishi, J. Am. Chem.
Soc. 1987, 109, 4756–4758.
[36] P. J. Kocienski, A. Bell, P. R. Blakemore, Synlett 2000, 2000,
365–366.
[37] N. H. Andersen, A. D. Denniston, D. A. McCrae, J. Org. Chem.
1982, 47, 1145–1146.
[38] J. Frick, Synthesis 1992, 7, 621–623.
[39] D. Seebach, E. J. Corey, J. Org. Chem. 1975, 40, 231–237.
[40] T. Ichige, A. Miyake, N. Kanoh, M. Nakata, Synlett 2004, 2004,
1686–1690.
[41] S. D. Rychnovsky, D. J. Skalitzky, Tetrahedron Lett. 1990, 31,
945–948.
[42] D. A. Evans, D. L. Rieger, J. R. Gage, Tetrahedron Lett. 1990,
31, 7099–7100.
[43] K. Gerth, P. Washausen, G. Höfle, H. Irschik, H. Reichenbach, J.
Antibiot. (Tokyo) 1996, 49, 71–75.
[44] A.-K. C. Schmidt, C. B. W. Stark, Org. Lett. 2011, 13, 4164–
4167.
[45] D. L. Comins, A. Dehghani, Tetrahedron Lett. 1992, 33, 6299–
6302.
[46] A. Fürstner, A. Leitner, M. Méndez, H. Krause, J. Am. Chem.
Soc. 2002, 124, 13856–13863.
[47] B. Scheiper, M. Bonnekessel, H. Krause, A. Fürstner, J. Org.
Chem. 2004, 69, 3943–3949.
[48] J. Pospíšil, I. E. Markó, J. Am. Chem. Soc. 2007, 129, 3516–
3517.
[49] F. Peng, D. G. Hall, J. Am. Chem. Soc. 2007, 129, 3070–3071.
[50] S. Ohira, Synth. Commun. 1989, 19, 561–564.
[51] G. J. Roth, B. Liepold, S. G. Müller, H. J. Bestmann, Synthesis
2004, 2004, 59–62.
[52] S. Müller, B. Liepold, G. J. Roth, H. J. Bestmann, Synlett 1996,
1996, 521–522.
[53] Y. D. Wang, G. Kimball, A. S. Prashad, Y. Wang, Tetrahedron
Lett. 2005, 46, 8777–8780.
[54] G. Höfle, H. Steinmetz, K. Gerth, H. Reichenbach, Liebigs Ann.
Chem. 1991, 1991, 941–945.
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10.1002/chem.202100975
Chemistry - A European Journal
RESEARCH ARTICLE
Entry for the Table of Contents
The first total synthesis of a putative intermediate in the biosynthesis of the ambruticins has been prepared by a convergent synthetic
route that takes advantage of a trisubstituted cyclopropyl linchpin. The stereochemical assignment has been confirmed while
previously reported, incorrect spectral data, has been updated. Access to this material will enable studies of the post-PKS processing
that leads to isolated ambruticin structures and garner greater understanding of the evolution of their structures and potent anti-fungal
activity.
Institute and/or researcher Twitter usernames: @UNDresearch, @retaylor61
6
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