Total and semi-syntheses of antimicrobial thuggacin derivatives

Article abstract of DOI:10.1002/chem.201405874

The total and semi-synthesis of 13 new macrolactones derived from thuggacin, which is a secondary metabolite from the myxobacterium Sorangium cellulosum, are reported. The thuggacins have attracted much attention due to their strong antibacterial activity, particularly towards Mycobacterium tuberculosis. This study focuses on 1) thuggacin derivatives that cannot equilibrate by transacylation between the three natural thuggacins A-C, 2) the roles of the thiazole ring, and 3) the hexyl side chain at C2. Semi-synthetic O-methylation at C17 suppressed the transacylations without a substantial loss of antibacterial activity. Exchanging the C17-C25 side chain for simplified hydrophobic chains led to complete loss of antibacterial activity. Exchange of the thiazole by an oxazole ring or removal of the hexyl side chain at C2 had no substantial effect on the biological properties.

Full text of DOI:10.1002/chem.201405874

DOI: 10.1002/chem.201405874
Full Paper
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Synthesis Design
Total and Semi-Syntheses of Antimicrobial Thuggacin Derivatives
Jana Franke,[a] Martin Bock,[a] Richard Dehn,[a] Jçrg Fohrer,[a] Santosh B. Mhaske,[a, b]
Antonella Migliorini,[a] Argyrios A. Kanakis,[a] Rolf Jansen,[c] Jennifer Herrmann,[d] Rolf Mꢀller,[d]
and Andreas Kirschning*[a]
Chem. Eur. J. 2015, 21, 1 – 14
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Abstract: The total and semi-synthesis of 13 new macro-
lactones derived from thuggacin, which is a secondary
metabolite from the myxobacterium Sorangium cellulosum,
are reported. The thuggacins have attracted much attention
due to their strong antibacterial activity, particularly towards
Mycobacterium tuberculosis. This study focuses on 1) thugga-
cin derivatives that cannot equilibrate by transacylation
between the three natural thuggacins A–C, 2) the roles of
the thiazole ring, and 3) the hexyl side chain at C2. Semi-syn-
thetic O-methylation at C17 suppressed the transacylations
without
a
substantial loss of antibacterial activity.
Exchanging the C17–C25 side chain for simplified hydro-
phobic chains led to complete loss of antibacterial activity.
Exchange of the thiazole by an oxazole ring or removal of
the hexyl side chain at C2 had no substantial effect on the
biological properties.
Introduction
In 2008, the isolation and structural elucidation of the
thuggacins A–C (1–3) and the total synthesis of thuggacin B
(2) were reported by Jansen et al.[1] and our group (Scheme
1).[2] In addition to reported partial syntheses,[3] Shibasaki and
co-workers recently disclosed a second successful synthesis of
thuggacin B (2).[4]
Compounds 1–3 are polyketide-derived natural products
produced by the myxobacterium Sorangium cellulosum. In
search of new thuggacin derivatives, Mꢀller and co-workers
found that the myxobacterium Chondromyces crocatus Cm c5
was also
a
source of thuggacin derivatives, namely,
thuggacin Cmc-A (4) and thuggacin Cmc-C (5).[5a]
The thuggacins exert strong antibiotic activity against
various bacteria, including Mycobacterium tuberculosis, by
targeting the bacterial respiratory chain.[6] The ability of M. tu-
berculosis to persist in host cells as a latent infection strongly
hampers the development of alternative antibiotics.[7,8]
Compound 1 features a 17-membered macrolactone ring and
compounds 2 and 3 both share the same structural features as
1, except for the ring size. In 2 the lactone is closed at O17 in-
stead of O16, and in 3 the position of macrocyclisation is at
Scheme 1. Thuggacins A–C (1–3), thuggacin Cmc-A (4), and thuggacin
Cmc-C (5) (stereochemistries of 4 and 5 have not been determined) and the
interconversion of 1–3 by transacylation.
[a] Dr. J. Franke, Dr. M. Bock, Dr. R. Dehn, Dr. J. Fohrer, Dr. S. B. Mhaske,
Dr. A. Migliorini, Dr. A. A. Kanakis, Prof. Dr. A. Kirschning
Institute of Organic Chemistry and Center of
Biomolecular Drug Research (BMWZ)
O18. From a pharmacological point of view, it is problematic
that the thuggacins are interconverted spontaneously by trans-
acylation towards an equilibrium (ratio of 1/2/3=1:2.1:2.7), so
that no single pharmaceutical entity is in hand when separate-
ly determining the biological efficacy of the constitutional
isomers.[1]
Leibniz Universitꢀt Hannover
Schneiderberg 1B, 30167 Hannover (Germany)
Fax: (+49)511-762-3011
E-mail: andreas.kirschning@oci.uni-hannover.de
[b] Dr. S. B. Mhaske
Typical structural elements of polyketide-based natural
products, including the thuggacins, incorporate one or more
heterocyclic oxazoles, oxazolines, thiazoles, or thiazolines.[5a]
These are formed by a non-ribosomal peptide module being
part of the polyketide synthase (PKS), which either accepts
serine or cysteine as extender units. Recently, we showed for
another metabolite from myxobacteria, noricumazole A, that
exchange of the oxazole for a thiazole moiety led to improved
pharmacological properties of noricumazole A as an anti-
hepatitis C virus (HCV) agent.[9] Based on these observations,
we disclose the preparation of new thuggacin derivatives by
utilising both semi-synthesis and a diverted total synthesis ap-
proach.[10,11] In detail, we address the following questions:
1) does the exchange of the thiazole for an oxazole moiety
Division of Organic Chemistry
CSIR-National Chemical Laboratory
Pune 411 008 (India)
[c] Dr. R. Jansen
Helmholtz Centre for Infection Research (HZI)
Microbial Drugs (MWIS), Inhoffenstraße 7
38124 Braunschweig (Germany)
[d] Dr. J. Herrmann, Prof. Dr. R. Mꢁller
Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS)
Helmholtz Centre for Infection Research
Microbial Natural Products (MINS) and Saarland University
Campus Building C2.3, 66123 Saarbrꢁcken (Germany)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201405874. It contains detailed descriptions
of all experimental procedures and analytical characterizations, as well as
containing copies of NMR spectra of new compounds.
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affect the biological potency, as observed in the case of the
noricumazoles; 2) what is the effect of the bulky, hydrophobic
character of the hexyl side chain; 3) is the oligohydroxydiene
chain at C16 relevant for the antibacterial properties of the
thuggacins; and finally 4) can one generate a constitutionally
stable thuggacin derivative that does not undergo transacyla-
tion reactions?
new 17-O-methyl thuggacin A 10 (28% yield over two steps).
This thuggacin derivative is constitutionally stable and cannot
equilibrate to the corresponding ring-expanded derivatives
related to 2 and 3, respectively. Indeed, we found that the
formation of new isomers was not detected upon standing in
methanol for 24 h at RT.
More semi-synthetic derivatives became available after
1 was subjected to NaIO4-mediated glycol cleavage, which
gave labile aldehyde 11 (Scheme 3). Reduction of the aldehyde
Herein, our total synthesis approaches are separated from
semi-synthetic ones, starting with
a description of our
semi-synthetic results and providing initial biological data on
new thuggacin derivatives.
Results and Discussions
Semi-synthesis
Although semi-synthesis is a rather classical approach to create
new natural product analogues,[10,11] it is still a challenge when
structurally complex molecules, such as the thuggacins, are
involved. When dealing with the unprotected multifunctional
thuggacins, five carbinol groups, an a,b-unsaturated ester, and
a highly substituted diene unit have to be taken into account;
thus, chemoselectivity is a key issue. Chemical stability also has
to be considered and substantial amounts of precious starting
material may be “destroyed” before the first useful transforma-
tions are achieved. Furthermore, the natural product is often
not available in large quantities.
We initiated our semi-synthetic program with the modifica-
tion of 1 because it was available after large-scale fermentation
of S. cellulosum. Compound 1 can be transformed into several
partially protected derivatives 6–9 by protecting the diols as
acetonides.[1] By changing the reaction conditions to the previ-
ously reported ones by using 2,2-dimethoxypropane as a sol-
vent, the preferred formation of bis-acetonide 6 was achieved
in 44% yield (Scheme 2).[12] This protected thuggacin derivative
is particularly important for further modifications because it
contains only one free hydroxyl group at C17, which, after
O-methylation[13] and removal of the cyclic acetals, provided
Scheme 3. Preparation of the macrocyclic cores of 12 and 13 by glycol
cleavage of 1, and the synthesis of esters 14a and 14b. DIC=diisopropyl-
carbodiimide, 4-DMAP=4-dimethylaminopyridine.
yielded alcohols 12 and 13 in a 1:4 ratio. This is another exam-
ple of facile transacylation of the thuggacins to preferentially
yield the larger macrolactone ring.
The major isomer 13 was transformed into hexanoate 14a
and sorbate 14b after 1,3-diol protection,[14] acylation, and
removal of the acetonide. These ester side chains were chosen
to mimic the lipophilic side chain of the thuggacins.
Additionally, aldehyde 11 can serve to introduce side chains
by Horner–Wadsworth–Emmons olefination under mild Masa-
Scheme 2. Semi-synthetic preparation of 17-O-methylthuggacin A (10).
p-TsOH=p-toluenesulfonic acid.
Scheme 4. Horner–Wadsworth–Emmons olefinations with aldehyde 11.
DIPEA=diisopropylethylamine.
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mune–Roush conditions[15] without the need for protecting the
1,3-diol moiety at C8 and C10 (Scheme 4). This protocol
provided alkenes 17 and 18 from phosphonates 15 and 16,
respectively.
The synthesis of benzoate 26 has been reported previously,[3]
and it was transformed into aldehyde 27 by standard function-
al-group manipulations (Scheme 6). The Stork–Zhao variant of
the Wittig olefination[16] terminated the synthesis of the
eastern fragment and gave vinyl iodide 28.
Total synthesis of new thuggacin derivatives 21 and 22
Several new thuggacin analogues were prepared by a total
synthesis strategy that was based, in part, on our first total
synthesis of 2. We planned to introduce two structural devia-
tions with respect to the parent compound. On the one hand,
we pursued removal of the hydrophobic n-hexyl side chain at
C2 and, on the other hand, we planned to exchange the thia-
zole with an oxazole ring. Our first-generation synthesis relied
on a Sonogashira–Hagihara coupling of eastern fragment 19
and western fragment 20, containing an (E)-configured vinyl
iodide (Scheme 5). The preparation of the vinyl iodide from the
Scheme 6. Synthesis of vinyl iodide 26 from advanced fragment 28.
Reagents and conditions: a) K2CO3, MeOH, RT, overnight (95%); b) N-methyl-
morpholine N-oxide (NMO), tetrapropylammonium perruthenate (TPAP),
CH2Cl2, RT, 30 min (90%); c) sodium hexamethyldisilazane (NaHMDS),
Ph3PCH2I2, THF, ꢀ858C (53%; E/Z=3:1; in some cases we encountered E/Z
ratios of up to 10:1, but reproducibility could not be achieved; see the
Supporting Information). TBS=tert-butyldimethylsilyl.
The synthesis of de-n-hexyl thuggacin started from the
commercially available protected l-cysteine derivative 29.[2b]
The acid was transformed into the corresponding aldehyde,
and Wittig olefination with ylide 33 gave ester 30 (Scheme 7).
Scheme 5. First-generation synthesis based on fragments 19 and 20,[3] and
a modified approach with fragments 23–25.
Scheme 7. Synthesis of the eastern fragment 32, which lacks the n-hexyl
substituent at C2. Reagents and conditions: a) NH(OMe)Me·HCl, 1-ethyl-3-(3-
dimethylaminopropyl)carbodiimide hydrochloride (EDCl·HCl), 4-DMAP, diiso-
propylethylamine (DIPEA) (87%); b) diisobutylaluminum hydride (DIBAL-H),
toluene, ꢀ788C (98%); c) 33, CHCl3, D (85%); d) trimethylsilyl trifluorome-
thanesulfonate (TMSOTf), 2,6-lutidine, CH2Cl2, 08C (97%); e) N,N,N’,N’-tetra-
methyl-O-(benzotriazol-1-yl)uronium tetrafluoroborate (TBTU), 1-hydroxy-
benzotriazole (HOBt), DIPEA, CH2Cl2 (85%); f) Hg(OAc)2, EtOH/EtOAc, NaBH4;
g) 34, benzene, Dean–Stark conditions; h) MnO2, CH2Cl2, (82% over three
steps); i) tetrabutylammonium fluoride (TBAF), THF; j) 2,2-dimethoxypropane
(2,2-DMP), camphorsulfonic acid (CSA) (87% over two steps). Trt=trityl.
corresponding alkene was achieved by a cross-metathesis reac-
tion with vinyltriethoxysilane followed by ipso-iododesilylation
(see bottom of Scheme 5). Eventually, we found that it was
difficult to reduce the disubstituted alkyne selectively formed
upon cross-coupling, and to create the Z alkene at C13–C14.
The principal novelty of our synthetic plan towards the syn-
theses of the de-n-hexyl derivative 21 and oxazole analogue
22 is the merging of the eastern half 23 with the western frag-
ments 24 and 25, respectively, by employing the Heck–Mizoro-
ki reaction instead of a Sonogashira–Hagihara cross-coupling
reaction. This new approach would reduce the number of
overall steps and additionally avoid problematic syn-selective
hydrogenation of an advanced alkyne intermediate.
After removal of the tert-butyloxycarbonyl (Boc) protecting
group, the resulting amine 30 was coupled with the known
carboxylic acid 31[2b] to give the amide by using the reagent
system of HOBt and TBTU. After removal of the trityl group,
the
molybdenum catalyst 34[17] enforced ring closure to give the
thiazoline derivative, which was oxidised to the desired
thiazole by using MnO2. Finally, the TBS protecting group for
the 1,3-diol had to be exchanged for the acetonide group be-
The total synthesis of both new thuggacin derivatives 21
and 22 requires the preparation of the (Z)-configured vinyl
iodide 28, which is well suited for the Heck–Mizoroki coupling.
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cause the bulkiness of the TBS group hampered the cross-cou-
pling chemistry that we envisaged with respect to yield and re-
giocontrol (see Scheme 9 below). The whole sequence towards
the eastern fragment 32 proceeded with very good yields.
We first tested the Heck–Mizoroki coupling and macrocycli-
sation using the simpler vinyl iodide 35[18] (Scheme 8). Shang
et al. studied the cross-coupling of allylic ethers and esters,
isolated in a good yield of 53%. The final part of the synthesis
involved functional-group manipulations and macrolactone
formation. Firstly, the silyl protecting groups were removed
and the ethyl ester was saponificated to provide the corre-
sponding seco acid. Next, the Shiina protocol was applied for
macrolactonisation;[20] this yielded two macrolactones that
were analogous to 1 (cyclisation via carbinol at C16) and 2
(cyclisation via carbinol at C17). Finally, the acetals were
removed by using PPTS in methanol and, surprisingly, 2-de-n-
hexyl thuggacin C 38 was isolated in 55% yield as the only
product. Apparently, the absence of a substituent at C2 leads
to an equilibrium of transacylated products (see Scheme 1),
which favours the formation of the largest possible macrolac-
tone ring.
The preparation of the second thuggacin derivative 44b,
which contains an oxazole instead of the thiazole ring was
achieved by following the same synthetic approach as that
described for the de-n-hexyl thuggacin C derivative 38.
Starting from Boc-protected l-serine hydrochloride 39, the
methyl ester was transformed into the corresponding alde-
hyde. Wittig olefination under optimised conditions provided
the (E)-configured a-unsaturated ester 40 (Scheme 10). Amide
coupling with known carboxylic acid 31[3] yielded amide 41,
which was cyclised by DAST to form the oxazoline[21] and
aromatised to form the oxazole 42.
Scheme 8. Probing the Heck–Mizoroki reaction with model vinyl iodide 35
for the formation of simplified thuggacin derivative 36. Reagents and
conditions: a) Pd(OAc)2, AgOAc (50%); b) aqueous solution of KOH, ethanol
(quant); c) Et3N, 4-DMAP, 2,4,6-trichlorobenzoyl chloride (32%); d) MeOH,
p-TsOH, RT, 80%.
and obtained the best regiocontrol by employing a combina-
tion of Pd(OAc)2 and AgOAc.[19] When applying these condi-
tions to 32, the Heck–Mizoroki reaction provided the desired
product in 50% yield. After ester hydrolysis and desilylation,
Yamaguchi macrocyclisation and subsequent acetonide and
silyl deprotection led to simplified thuggacin derivative 36.
This compound was also esterified at C16, apparently because
of an excess of 2,4,6-trichlorobenzoyl chloride present in the
reaction mixture. Nevertheless, this short sequence proved the
validity of the Heck–Mizoroki coupling reaction and demon-
strated that the 18-membered macrolacton ring was preferred
over the 17-membered one because the latter ring must have
formed first (see also Scheme 3).
The western fragment 32 was coupled in the same manner
with vinyl iodide 28 (Scheme 9). Under the optimised
conditions, the coupling product 37, containing the complete
carbon backbone of the target thuggacin derivative, was
Scheme 10. Synthesis of western oxazole fragment 42 (corresponds to 25).
Reagents and conditions: a) para-methoxybenzyl (PMB) trichloroacetimidate,
CSA, CH2Cl2 (39%); b) DIBAL-H, toluene, ꢀ788C; c) 43, CHCl3, 658C (33%
over two steps); d) trifluoroacetic acid (TFA), CH2Cl2 (quant); e) i) 40, (COCl)2,
CH2Cl2, ii) 31, 4-DMAP (51%); f) i) diethylaminosulfur trifluoride (DAST),
CH2Cl2, ꢀ788C, ii) K2CO3, Na2CO3, Dean–Stark conditions (79%); g) MnO2,
CH2Cl2 (87%); h) TBAF, THF (75%); i) 2,2-DMP, CSA (95%).
With both fragments in hand, vinyl iodide 28 and oxazole
42 underwent a palladium-catalysed cross-coupling reaction to
give ester 43, which contained the desired E,Z-diene unit
(Scheme 11). Desilylation and ester hydrolysis gave the seco
acid, which was cyclised to give the macrolactone by using the
Shiina protocol. In [D6]methanol, we encountered the
formation of both macrolactones that resembled 1 and 2.
To our surprise, the diastereomeric mixture (1:1) of 24-
methoxy-20-desoxy oxazole thuggacin B 45a,b was isolated as
a major fraction after acetonide deprotection under mildly
acidic conditions (note: the pKa for PPTS is 5.21 in H2O). The
Scheme 9. Heck–Mizoroki reaction between fragments 28 and 32 and
completion of the total synthesis of de-n-hexyl thuggacin 38. Reagents and
conditions: a) Pd(OAc)2, AgOAc, N-methylpyrrolidone (NMP), 558C (53%);
b) TBAF, THF (92%); c) KOH (3m), EtOH; d) 2-methyl-6-nitrobenzoic
anhydride (MNBA), 4-DMAP, 4 ꢂ molecular sieves, toluene, 708C (56% over
two steps); e) pyridinium tosylate (PPTS), MeOH (72%).
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with implications for the biological activity of antillatoxin.[22]
Specifically, the diene unit in antillatoxin adopts two stable
conformers with different torsion angles. So far, no group has
reported on the chemical lability and reactivity of the terminal
diene unit in the thuggacins.
Both published thuggacin syntheses reported macrocyclisa-
tion via the carbinol at C17 to yield 2 as a major product and
1 as a minor by-product.[3,4] In the present study, we also
noted the presence of both macrocycles for the oxazole ana-
logues of the thuggacins. Finally, in the absence of the aliphat-
ic side chain at C2, the formation of thuggacin C derivative 38
is favoured because it is presumably the thermodynamically
more stable macrocycle.
Antibacterial activity
Assessment of the biological properties of new thuggacin de-
rivatives revealed insights into the types of structural elements
relevant for antimicrobial activity (minimum inhibitory
concentration (MIC) in mgmLꢀ1). Semi-synthetic thuggacin
derivatives 12–14, 17, and 18, modified or shortened in the
side chain (C17–C25), showed no antimicrobial activity against
several bacterial strains. In contrast, semi-synthetic 17-O-
methyl derivative 10 showed activity against M. tuberculosis
H37Rv at concentrations of 8 and 16 mgmLꢀ1; this demon-
strates that blocking of the hydroxy group at position 17 is
a feasible strategy to inhibit transacylation without significant
loss of activity.
Scheme 11. Heck–Mizoroki coupling between alkene 42 and vinyl iodide 28.
Reagents and conditions: a) Pd(OAc)2, AgOAc, NMP, 558C (50%); b) TBAF,
THF (quant.); c) KOH (3m), EtOH; d) MNBA, 4-DMAP, 4 ꢂ molecular sieves,
toluene, 708C (55% over two steps); e) PPTS, MeOH (44a=16%, 44b=8%,
45a,b=39%).
formation of the methoxy adduct can be rationalised if one as-
sumes protonation of the acetonide at C20, which activates
the diene system towards nucleophilic attack by methanol, as
depicted in Scheme 11.
In addition, the antimicrobial activity of oxazole thuggacin B
derivatives 44a/b and 45 and de-n-hexyl thuggacin 38 pre-
pared by total synthesis was evaluated against a small panel of
bacteria and compared with the natural product (1). A summa-
ry of the results is provided in Table 1. Thuggacin derivative 38
was the least active derivative among those tested, but still in-
hibited the growth of Corynebacterium and Micrococcus strains.
All oxazole derivatives exhibited pronounced activity against
the tested bacteria. The cis-configured isomer 44a appeared
to be slightly more active than the trans isomer 44b and 24-
methoxy-20-deoxyoxazole thuggacin B 45a,b. On average, the
biological activity of oxazole thuggacins was approximately re-
duced by one to two orders of magnitude relative to that of
natural product 1; this highlights the importance of the thia-
zole moiety in naturally occurring thuggacins.
Furthermore, the desired oxazole thuggacin B was isolated
and, unexpectedly, it formed as a mixture of two isomers,
44a,b, which was separable by HPLC. Structural analysis of
1
these two compounds turned out to be challenging. The H
and 13C NMR spectroscopy data only differ in the chemical
shifts (d) of atoms related to the diene unit (C21–C24). Nuclear
Overhauser contacts supported the premise that structural dif-
ferences were located in the diene unit (Scheme 12). Some of
these contacts observed would supposedly not occur if a truly
planar conformation of the diene system were present. Molec-
ular modelling experiments (see the Supporting Information)
were carried out with both stereoisomers 44a and 44b and re-
sults indicated that the Z configuration was thermodynamically
favoured by about 6.3 kJmolꢀ1, facilitating isomerisation under
acidic conditions.
All of these results provide an initial insight into the struc-
ture–activity relationships of the thuggacins. Major structural
changes in the side chain (C17–C25) are not tolerated, whereas
smaller deviations at the terminus, as found in thuggacin de-
rivatives 44b and 45a,b, do not result in a reduction of anti-
bacterial activity. One can speculate whether the polar part of
this side chain (C17–C20) is important for the anti-in-
We propose that the presence of the two methyl substitu-
ents at C21 and C23 force the conjugated diene out of plane.
In the total synthesis of the cyclic peptide antillatoxin, Inoue
et al. observed that side-chain modification led to dramatic
conformational changes in the shape of the twisted side chain
fective properties of the thuggacins. Secondly, the
lipophilic side chain at C2 modulates activity; its ab-
sence leads to a substantial loss in antibacterial prop-
erties. Thirdly, the thiazole ring is favoured over the
oxazole ring. Importantly, O-17 methyl derivative 10
provides several new insights. It is possible to sup-
Scheme 12. Key results collected from NOESY measurements observed in oxazole
thuggacin B 44a and in its C23–C24 cis isomer 44b.
press transacylation and create a constitutionally
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Table 1. Biological data for the thuggacin derivatives 1, 38, 44a, 44b, 45, and rifampicin (RIF).[a,b]
Indicator strain
1
38
32
32
32
>64
>64
44a
44b
45[c]
RIF[d]
Corynebacterium glutamicum DSM-20300
Micrococcus luteus GBF
M. luteus DSM-20030
Mycobacterium smegmatis mc2155ATCC-700084
Nocardia asteroides DSM-43757
0.025
0.006
8
16
32
1
0.25
32
64
64
4
0.5
32
64
64
8
4
16
32
64
0.001
0.04
0.01
8
0.5
[a] MIC values were determined in microbroth dilution assays in two independent experiments. [b] Strain M. tuberculosis H37Rv was not available for
evaluating this series of compounds. [c] Tested as a mixture of diasteromers, 45a,b. [d] RIF was used as a reference antibiotic.
stable derivative of 1 and this derivative still shows activity
against M. tuberculosis at a similar level to that of 1. Conse-
quently, we regard derivative 10 as one lead structure in anti-
biotic research.
carbon), d=doublet (methine), t=triplet (methylene), q=quartet
(methyl). For interpretation of carolacton derivative spectra, sup-
porting 1H–1H (COSY) and 1H–13C (phase-sensitive HSQC, HMBC)
correlation experiments were performed. High-resolution mass
spectra were obtained with a Micromass LCT instrument through
loop-mode injection from a Waters (Alliance 2695) HPLC system. Al-
ternatively, a Micromass Q-TOF in combination with a Waters
Aquity Ultraperformance LC system was employed. Ionisation was
achieved by ESI. Modes of ionisation, as well as calculated and
found mass are given. Analytical TLC was performed by using pre-
coated ALUGRAM SIL G/UV254 plates (Macherey–Nagel) and the
spots were visualised with UV light at l=254 nm or alternatively
by staining with solutions of permanganate or 4-methoxybenzalde-
hyde.[24] THF was distilled under nitrogen from sodium/benzophe-
none. Commercially available reagents were used as supplied.
Flash chromatography was performed with J.T. Baker brand silica
gel (40–60 mm, 60 ꢂ pores). Eluents used for flash chromatography
were distilled prior to use. Isolation of carolacton derivatives was
achieved by preparative HPLC by using a Merck Hitachi LaChrom
system (pump L-7150, interface D-7000, diode array detector L-
7450 (l=220–400 nm, preferred monitoring at l=230 nm)) with
the following column (abbreviation referred to in the experimental
part given in parentheses): Trentec Reprosil-Pur 120 C18 AQ 5 mm,
250ꢃ8 mm, with guard column, 40ꢃ8 mm (C18-SP). Operating
conditions and retention times (tR) are reported in the experimen-
tal part. Melting points were measured by using a SRS OptiMelt ap-
paratus. Optical rotations [a] were measured on a Polarimeter 341
(PerkinElmer) instrument at l=589 nm and are given in
Conclusion
We reported the semi-synthetic preparation of new macrocy-
clic thuggacin derivatives that were modified in the side chain
(C17–C25). This was achieved by oxidative cleavage and the
introduction of new side chains through O-acylation or olefina-
tion reactions. Alternatively, we were able to block O-17 with
a methyl group, thereby suppressing transacylation between
O-16 to O-18; this derivative showed activity towards M.
tuberculosis H37Rv at concentrations of 8 and 16 mgmLꢀ1.
Additionally, we prepared two new thuggacin derivatives by
total synthesis that either lacked the hexyl side chain at C-2 or
the thiazole ring was exchanged for an oxazole. Notably, the
Heck CꢀC coupling reaction served to merge the two major
fragments.
Evaluation of the antimicrobial activity revealed that
modifications of the side chain at C-16 were not tolerated.
When the hexyl side chain at C-2 was removed or the thiazole
ring was exchanged for an oxazole, the antibacterial properties
were retained, but with a substantial drop in activity.
10ꢀ1 8cm2 gꢀ1
.
The preparation and characterisation of thuggacin derivatives 6–9
were reported in Ref. [2].
Experimental Section
General
All reactions were performed in oven-dried glassware under an at-
mosphere of nitrogen gas, unless otherwise stated. H NMR spectra
Antimicrobial testing
1
were recorded at 400 MHz with a BRUKER Avance-400 spectro-
meter or at 500 MHz with a Bruker DRX-500 spectrometer at room
temperature. 13C NMR spectra were recorded at 100 MHz with
a Bruker Avance-400 spectrometer and at 125 MHz with a Bruker
DRX-500 spectrometer. Chemical shift values of 1H and 13C NMR
spectra are reported in ppm relative to the (residual undeuterated)
All microorganisms were obtained from the German Collection of
Microorganisms and Cell Cultures (Deutsche Sammlung fꢀr Mik-
roorganismen und Zellkulturen, DSMZ) and the American Type Cul-
ture Collection (ATCC) or were part of our internal strain collection.
MIC values were determined in microdilution assays. Nocardia and
Mycobacterium strains were maintained in M7H9 medium (Difco
Middlebrook 7H9 broth supplemented with BBL Middlebrook ADC
enrichment and 2 mLLꢀ1 glycerol) and Micrococcus and Corynebac-
terium spp. were grown in Mꢀller-Hinton broth (0.2% beef infusion
solids, 1.75% casein hydrolysate, 0.15% starch, pH 7.4). Overnight
cultures were diluted in the respective growth medium to achieve
a final inoculum of about 106 cfumLꢀ1 (cfu=colony-forming unit).
Serial dilutions of thuggacins were prepared in sterile 96-well
plates. The cell suspension was added and microorganisms were
grown for 18 h on a microplate shaker at 308C. Growth inhibition
was assessed by visual inspection and given MIC values were the
1
solvent signal as an internal standard.[23] Multiplicities for H NMR
signals are described by using the following abbreviations: s=sin-
glet, d=doublet, t=triplet, q=quartet, m=multiplet; where ap-
propriate, with the addition of br=broad or p=pseudo. Coupling
constants (J) are stated in Hertz (Hz) and were determined after
Gaussian multiplication. Multiplicities for 13C NMR spectroscopy
signals refer to the resonances as they would appear in the
non-proton-decoupled spectra and were elucidated by using
phase-sensitive HSQC experiments. Multiplicities are reported by
using the following abbreviations: s=singlet (due to quaternary
Chem. Eur. J. 2015, 21, 1 – 14
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7
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lowest concentration of antibiotic at which there was no visible
growth.
1H; 26-Ha), 2.37–2.31 (m, 1H; 15-Ha), 2.05 (m, 1H; 19-H), 1.80 (ddd,
J=15.1, 9.5, 4.0 Hz, 1H; 9-Hb), 1.75 (s, 3H; 21-Me), 1.71 (s, 3H; 23-
Me), 1.62 (d, J=7.1 Hz, 3H; 25-Me), 1.57 (d, J=6.7 Hz, 3H; 7-Me),
1.48–1.39 (m, 2H; 27-H), 1.38–1.24 (m, 6H; 28-H, 29-H, 30-H), 0.93
(d, J=6.7 Hz, 3H; 19-Me), 0.88 (t, J=6.7 Hz, 3H; 31-H), 0.77 ppm
(ddd, J=15.1, 3.2, 1.2 Hz, 1H; 9-Ha); 13C NMR (100 MHz, CD3OD):
d=173.1 (C6), 168.4 (C1), 151.2 (C4), 135.9, 134.4, 133.6 (C2, C21,
C23), 137.6 (C11), 135.0 (C3), 132.7 (C13), 131.2 (C22), 128.9 (C14),
127.4 (C12), 124.7 (C24), 119.7 (C5), 84.4 (C17), 81.0 (C20), 78.1 (C8),
74.1, 73.9 (C16, C18), 71.8 (C10), 60.8 (OMe), 32.9, 30.9, 23.7, (C28,
C29, C30), 44.9 (C7), 40.8 (C9), 38.6 (C19), 30.3 (C15), 29.3 (C27),
28.2 (C26), 17.9 (7-Me), 16.9 (23-Me), 14.9 (21-Me), 14.4 (31-Me),
13.7 (25-Me), 8.3 ppm (19-Me); HRMS (ESI): m/z calcd for
C36H55NO6NaS [M+Na]: 668.3597; found: 668.3599.
Aldehyde 27 and alcohol 41 were prepared according to the pro-
cedure reported by Bock et al.[2] (Iodomethyl)triphenylphosphoni-
um iodide (S8) was prepared according to the procedure reported
by Menche et al.[25]
Preparation of acetonides
6 and 7: Compound 1 (10 mg,
15.8 mmol, 1 equiv) was dissolved in 2,2-dimethoxypropane
(0.8 mL) and was treated with a few crystals of p-TsOH (ꢁ20 mol%
mol). The reaction mixture was stirred for 1 h and terminated by
addition of phosphate buffer (pH 7). After extraction with dichloro-
methane, the combined organic phases were dried over MgSO4, fil-
tered, and the filtrate was concentrated under reduced pressure.
The residue was purified by reversed-phase (RP) HPLC (RP18,
MeOH/H2O, 70% MeOH to 100% over 60 min) to yield acetonides
Preparation of alcohols 12 and 13: A solution of 1 (12 mg,
19 mmol, 1 equiv) in THF (0.1 mL) was treated with NaIO4 (20 mg,
95 mmol, 5 equiv, 1m in water) and stirred for 40 min. The reaction
was terminated by the addition of brine, and was extracted with
ethyl acetate. The combined organic phases were dried over
MgSO4, filtered, and the filtrate was evaporated. The residue (thug-
gacin derivative 11) was dissolved in a mixture of CH2Cl2/MeOH
(3:1, 2 mL) and treated with NaBH4 (2 mg, 57 mmol, 3 equiv) for
1 h. After the addition of ethyl acetate, the solvent was removed
under reduced pressure and the residue was purified by RP-HPLC
(RP18, MeOH/H2O, 40% MeOH to 100% over 60 min) to yield triols
13 (4.4 mg, 9.8 mmol, 51%) and 12 (1.3 mg, 2.9 mmol, 15%).
1
6 (5 mg, 7.0 mmol, 44%) and 7 (1.9 mg, 2.7 mmol, 17%). 6: H NMR
(400 MHz, CD3OD): d=7.82 (s, 1H; 3-H), 7.62 (s, 1H; 5-H), 6.15 (dd,
J=15.0, 11.3 Hz, 1H; 12-H), 5.98–5.87 (m, 2H; 13-H, 22-H), 5.47
(ddd, J=11.3, 11.3, 6.1 Hz, 1H; 14-H), 5.37–5.26 (m, 2H; 11-H, 24-
H), 5.08–5.02 (m, 1H; 16-H), 4.25 (s, 1H; 20-H), 4.20–4.14 (m, 1H; 8-
H), 3.95 (dd, J=8.2, 2.0 Hz, 1H; 18-H), 3.73 (dd, J=8.2, 1.7 Hz, 1H;
17-H), 3.52 (dq, J=6.8, 4.1 Hz, 1H; 7-H), 3.07–3.00 (m, 1H; 10-H),
2.97–2.86 (m, 1H; 15-Hb), 2.78–2.63 (m, 2H; 26-H), 2.38–2.25 (m,
1H; 9-Hb), 2.23–2.15 (m, 1H; 15-Ha), 2.11–2.02 (m, 1H; 19-H), 1.78–
1.73 (m, 1H; 9-Ha), 1.71 (s, 3H; Me-21), 1.68 (d, J=6.8 Hz, 3H; 25-
Me), 1.65 (s, 3H; Me-23), 1.48 (s, 3H; Me-acetonide C18–C20), 1.46
(s, 3H; Me-acetonide C18–C20), 1.44 (d, J=7.2 Hz, 3H; 7-Me), 1.38
(s, 3H; Me-acetonide C8–C10), 1.57–1.24 (m, 8H; 27-H, 28-H, 29-H,
30-H), 1.20 (s, 3H; Me-acetonide C8–C10), 0.89 (t, J=7.0 Hz, 3H;
31-H), 0.80 ppm (d, J=6.6 Hz, 3H; 19-Me); HRMS (ESI): m/z calcd
for C41H62N O7S [M+H]: 712.4247; found: 712.4247. 7: 1H NMR
(400 MHz, CD3OD): d=7.56, 7.60 (s, 2H; 3-H, 5-H), 6.16 (dd, J=
14.8, 11.3 Hz, 1H; 12-H), 5.95 (dd, J=10.9, 10.9 Hz, 1H; 13-H), 5.83
(s, 1H; 22-H), 5.45 (ddd, J=11.1, 11.1, 6.5 Hz, 1H; 14-H), 5.38–5.29
(m, 2H; 11-H, 24-H), 4.99–4.93 (m, 1H; 16-H), 4.18–4.12 (m, 1H; 8-
H), 4.00 (dd, J=9.0, 2.2 Hz, 1H; 17-H), 3.89–3.83 (m, 2H; 18-H, 20-
H), 3.58–3.50 (m, 1H; 7-H), 3.22–3.15 (m, 1H; 10-H), 2.82–2.60 (m,
3H; 15-Hb, 26-H), 2.31–2.21 (m, 2H; 15-Ha, 9-Hb), 1.94–1.82 (m, 1H;
19-H), 1.69, 1.70 (s, 6H; 21-Me, 23-Me), 1.60 (d, J=6.8 Hz, 3H; 25-
Me), 1.44 (d, J=7.2 Hz, 3H; 7-Me), 1.41 (s, 6H; Me-acetonide C17–
C18), 1.39 (s, 3H; Me-acetonide C8–C10), 1.78–1.24 (m, 10H; 9-Ha,
27-H, 28-H, 29-H, 30-H), 1.23 (s, 3H; Me-acetonide C8–C10), 1.09 (d,
J=6.8 Hz, 3H; 19-Me), 0.89 ppm (t, J=7.0 Hz, 3H; 31-H); HRMS
(ESI): m/z calcd for C41H62N O7S [M+H]: 712.4247; found: 712.4249.
1
Data for 13: H NMR (400 MHz, CD3OD): d=7.98 (s, 1H; 3-H), 7.62
(s, 1H; 5-H), 6.64 (dd, J=15.4, 11.1 Hz, 1H; 12-H), 6.11 (dd, J=11.1,
11.1 Hz, 1H; 13-H), 5.75 (dd, J=15.4, 6.3 Hz, 1H; 11-H), 5.69–5.60
(m, 1H; 14-H), 4.70–4.63 (m, 1H; 10-H), 4.31 (dd, J=10.4, 3.2 Hz,
1H; 17-Hb), 4.01 (dd, J=10.4, 7.3 Hz, 1H; 17-Ha), 3.95–3.88 (m, 1H;
16-H), 3.84–3.79 (m, 1H; 8-H), 3.53–3.45 (m, 1H; 7-H), 2.75–2.60 (m,
3H; 15-Hb, 26-H), 2.56–2.48 (m, 1H; 15-Ha), 1.93 (ddd, J=14.7, 10.4,
3.4 Hz, 1H; 9-Hb), 1.83 (ddd, J=14.7, 5.9, 2.7 Hz, 1H; 9-Ha), 1.52 (d,
J=7.0 Hz, 3H; 7-Me), 1.58–1.27 (m, 8H; 27-H, 28-H, 29-H, 30-H),
0.90 ppm (t, J=7.0 Hz, 3H; 31-H); 13C NMR (100 MHz, CD3OD): d=
173.1 (C6), 168.9 (C1), 151.6 (C4), 138.0, 134.2, 134.0, 131.1, 128.5,
126.4, 119.9, 75.2 (C2, C3, C5, C11, C12, C13, C14), 70.2, 69.7, 67.7,
44.7 (C8, C10, C16, C17), 39.9 (C7), 32.8, 30.4, 29.1, 28.7, 23.6, 18.2,
14.4 ppm (C9, C15, C26, C27, C28, C29, C30, C31, Me-7).
1
Data for 12: H NMR (400 MHz, CD3OD): d=7.99 (s, 1H; 3-H), 7.61
(s, 1H; 5-H), 6.69 (dd, J=15.0, 11.3 Hz, 1H; 12-H), 5.98 (dd, J=11.0,
11.0 Hz, 1H; 13-H), 5.49 (dd, J=15.0, 9.3 Hz, 1H; 11-H), 5.40 (ddd,
J=11.5, 11.3, 5.5 Hz, 1H; 14-H), 5.14–5.08 (m, 1H; 10-H), 4.91–4.84
(m, 1H; 16-H), 3.73–3.69 (m, 2H; 17-H), 3.69–3.63 (m, 1H; 8-H),
3.60–3.50 (m, 1H; 7-H), 2.94–2.83 (m, 1H; 15-Hb), 2.65–2.57 (m, 1H;
26-Hb), 2.49–2.40 (m, 1H; 26-Ha), 2.28 (ddd, J=14.3, 5.5, 5.5 Hz, 1H;
15-Ha), 1.83 (ddd, J=15.0, 9.5, 3.8 Hz, 1H; 9-Hb), 1.57 (d, J=7.0 Hz,
3H; 7-Me), 1.50–1.24 (m, 8H; 27-H, 28-H, 29-H, 30-H), 0.89 (t, J=
7.0 Hz, 3H; 31-H), 0.82 ppm (ddd, J=15.0, 3.3, 1.5 Hz, 1H; 9-Ha);
13C NMR (100 MHz, CD3OD): d=173.1 (C6), 168.9 (C1), 138.0, 134.2,
134.0, 131.1, 128.5, 126.4, 119.9 (C2, C3, C5, C11, C12, C13, C14),
151.6 (C4), 75.2, 70.2, 69.7, 67.7 (C8, C10, C16, C17), 44.7 (C7), 39.9,
32.8, 30.4, 29.1, 28.7, 23.6, 18.2, 14.4 ppm (C9, C15, C26, C27, C28,
C29, C30, C31, Me-7); HRMS (ESI): m/z calcd for C24H35N O5NaS
[M+Na]: 472.2134; found: 472.2137.
Synthesis of 17-O-methyl thuggacin A derivative 10: A catalytic
amount of p-TsOH (~20 mol%) was added to a solution of thugga-
cin derivative S1 (2.5 mg, 3.6 mmol, 1 equiv; for the preparation of
S1 see the Supporting Information) in MeOH (0.1 mL) and the mix-
ture was stirred for 2 h at room temperature. The reaction was ter-
minated by addition of a saturated bicarbonate solution and ex-
tracted with CH2Cl2. The combined organic phases were dried over
MgSO4, filtered, and the filtrate was concentrated under reduced
pressure. The residue was purified by RP-HPLC chromatography
(RP18, MeOH/H2O, 70% MeOH to 100% over 60 min) to yield 17-O-
methyl thuggacin A derivative 10 (2 mg, 3.1 mmol, 87%). 1H NMR
(400 MHz, CD3OD): d=7.95 (s, 1H; 3-H), 7.63 (s, 1H; 5-H), 6.62 (dd,
J=14.7, 11.1 Hz, 1H; 12-H), 5.99–5.91 (m, 2H; 13-H, 22-H), 5.46 (dd,
J=15.1, 9.5 Hz, 1H; 11-H), 5.40–5.30 (m, 2H; 10-H, 16-H), 5.13–5.04
(m, 2H; 10-H, 16-H), 4.07 (d, J=6.0 Hz, 1H; 20-H), 3.78 (dd, J=6.7,
2.8 Hz, 1H; 18-H), 3.67–3.63 (m, 1H; 8-H), 3.61 (s, 3H; OMe), 3.59–
3.51 (m, 1H; 7-H), 3.44 (dd, J=6.7, 3.6 Hz, 1H; 17-H), 2.98–2.89 (m,
1H; 15-Hb), 2.61 (ddd, J=13.1, 7.5, 7.5 Hz, 1H; 26-Hb), 2.45–2.38 (m,
Synthesis of thuggacin B derivatives 14a and 14b: Triol 13
(3.6 mg, 8 mmol, 1 equiv) was dissolved in 2,2-dimethoxypropane
(0.4 mL) and treated with p-TsOH (ꢁ20% mol) and the reaction
mixture was stirred for 1 h. The reaction was terminated by the ad-
dition of phosphate buffer (pH 7), and was extracted with dichloro-
methane. The combined organic phases were dried over MgSO4,
filtered, and the filtrate was concentrated under reduced pressure.
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The residue was purified by RP-HPLC (RP18, MeOH/H2O, 50%
MeOH to 100% over 60 min) to yield acetonide S4 (1.7 mg,
3.5 mmol, 43%) and the by-product S5 (0.8 mg, 1.4 mmol, 18%).
Data for S4 and S5 are to be found in the Supporting Information.
DIC (2 equiv) was added by means of a syringe to a solution of
acetonide S4 (1 equiv) and the acid (2 equiv) in dry CH2Cl2. After
stirring for 1 h, 4-DMAP (0.2 equiv) was added. The reaction mix-
ture was stirred for another 3 h at room temperature. Then the sol-
vent was removed under reduced pressure and the residue (S6
and S7; see Supporting Information for data) was directly purified
by RP-HPLC (RP18, MeOH/H2O, 60% MeOH to 100% over 60 min).
A catalytic amount of p-TsOH (ꢁ20 mol%) was added to a solution
of alcohol S6 (1 equiv) in MeOH (ꢁ0.1m) and the mixture was
stirred for 1 h at room temperature. The reaction was terminated
by the addition of a saturated solution of bicarbonate and the mix-
ture was extracted with CH2Cl2. The combined organic phases
were dried over MgSO4, filtered, and the filtrate was concentrated
under reduced pressure. The residue was purified by RP-HPLC
(RP18, MeOH/H2O, 60% MeOH to 100% over 60 min).
28.6 mmol, 4 equiv), and finally aldehyde 11 dissolved in acetoni-
trile were added to a stirred suspension of LiCl (1.2 mg, 28.6 mmol,
4 equiv) in dry acetonitrile (0.2 mL) under a nitrogen atmosphere.
After 3 h, the reaction was terminated by the addition of an aque-
ous solution of bicarbonate, and was extracted with ethyl acetate.
The combined organic phases were dried over MgSO4, filtered, and
the filtrate was evaporated under reduced pressure. The resulting
residue was purified by RP-HPLC (RP18, MeOH/H2O, 50% MeOH to
100% over 60 min).
Data for thuggacin A derivative 17a: Scale: 15 mmol, E isomer:
1
3.7 mg, 7.2 mmol, 48% over two steps; H NMR (400 MHz, CD3OD):
d=8.04 (s, 1H; 3-H), 7.67 (s, 1H; 5-H), 7.01 (dd, J=15.8, 4.8 Hz, 1H;
17-H), 6.70 (dd, J=15.0, 11.3 Hz, 1H; 12-H), 6.05 (dd, J=11.0,
11.0 Hz, 1H; 13-H),5.98 (dd, J=15.6, 1.5 Hz, 1H; 18-H), 5.56 (dd, J=
15.0, 9.3 Hz, 1H; 11-H), 5.44 (J=11.5, 11.3, 5.5 Hz, 1H; 14-H), 5.40–
5.34 (m, 1H; 16-H), 5.14–5.08 (m, 1H; 10-H), 4.20 (q, J=7.3 Hz, 2H;
CO2CH2CH3), 3.75–3.68 (m, 1H; 8-H), 3.57–3.47 (m, 1H; 7-H), 2.86
(ddd, J=14.0, 11.0, 11.0 Hz, 1H; 15-Hb), 2.67–2.58 (m, 1H; 26-Hb),
2.54–2.45 (m, 1H; 26-Ha), 2.42–2.35 (m, 1H; 15-Ha), 1.88 (ddd, J=
14.8, 9.5, 3.5 Hz, 1H; 9-Hb), 1.57 (d, J=7.0 Hz, 3H; 7-Me), 1.52–1.41
(m, 2H; 27-H), 1.39–1.23 (m, 9H; 28-H, 29-H, 30-H, CO2CH2CH3),
0.95–0.85 ppm (m, 4H; 31-H, 9-Ha); 13C NMR (100 MHz, CD3OD): d=
173.4 (C6), 168.1 (C1), 167.5 (CO2CH2CH3), 151.0 (C4), 147.1, 138.4,
134.9, 133.4, 133.1, 127.6, 127.0, 122.1, 120.0, (C2, C3, C5, C11, C12,
C13, C14, C17, C18), 77.7, 73.8, 71.8 (C8, C10, C16), 61.8
(CO2CH2CH3), 44.9 40.9, 34.6, 32.9, 30.2, 29.1, 28.1, 23.6, 17.9, 14.5,
14.4 ppm (CO2CH2CH3, Me-7, C7, C9, C15, C26, C27, C28, C29, C30,
C31); HRMS (ESI): m/z calcd for C28H39NO6NaS [M+Na]: 540.2396;
found: 540.2390.
Data for ester 14a: Scale: 1.4 mmol, yield: 0.73 mg, 1.34 mmol, 96%;
1H NMR (400 MHz, CD3OD): d=8.00 (s, 1H; 3-H), 7.67 (s, 1H; 5-H),
6.65 (dd, J=15.3, 11.0 Hz, 1H; 12-H), 6.07 (dd, J=11.0, 11.0 Hz, 1H;
13-H), 5.75 (dd, J=15.3, 6.5 Hz, 1H; 11-H), 5.39 (m, 1H; 14-H), 5.18
(m, 1H; 16-H), 4.82–4.76 (m, 1H; 10-H), 4.67 (dd, J=11.8, 4.3 Hz,
1H; 17-Hb), 4.12 (dd, J=11.8, 2.0 Hz, 1H; 17-Ha), 3.79–3.73 (m, 1H;
8-H), 3.57–3.49 (m, 1H; 7-H), 3.34–3.16 (m, 1H; 15-Hb), 2.72–2.59
(m, 2H; 19-H), 2.42–2.33 (m, 1H; 15-Ha), 2.20 (dd, J=7.3, 7.3 Hz,
2H; 26-H), 1.90 (ddd, J=14.8, 10.8, 3.5 Hz, 1H; 9-Hb), 1.75 (ddd, J=
14.8, 5.8, 2.5 Hz, 1H; 9-Ha), 1.55 (d, J=7.0 Hz, 3H; 7-Me), 1.60–1.19
(m, 14H; 27-H, 28-H, 29-H, 30-H, 20-H, 21-H, 22-H), 0.90 (t, J=
7.0 Hz, 3H; 31-H), 0.83 ppm (t, J=7.0 Hz, 3H; 23-H); 13C NMR
(100 MHz, CD3OD): d=174.6 (C18), 173.6 (C6), 169.2 (C1), 151.5
(C4), 138.6 134.3, 133.9, 131.7, 127.7, 126.0, 120.3 (C2, C3, C5, C11,
C12, C13, C14), 75.7, 72.0, 70.5, 65.1, (C8, C10, C16, C17), 44.6, 35.2,
32.8, 32.3, 30.5, 30.4, 29.1, 28.8, 25.7, 23.6, 23.3, 18.2, 14.4,
14.2 ppm (Me-7, C7, C9, C15, C26, C27, C28, C29, C30, C31, C19,
C20, C21, C22, C23); HRMS (ESI): m/z calcd for C30H45NO6NaS
[M+Na]: 570.2865; found: 570.2861.
Data for thuggacin A derivative 17b: Scale: 15 mmol, Z isomer:
1
1.47 mg, 2.9 mmol, 19% over two steps; H NMR (400 MHz, CD3OD):
d=8.03 (s, 1H; 3-H), 7.37 (s, 1H; 5-H), 6.73 (dd, J=15.3, 11.3 Hz,
1H; 12-H), 6.31 (dd, J=11.5, 7.3 Hz, 1H; 17-H), 6.12–6.02 (m, 2H;
13-H, 16-H), 5.91 (dd, J=11.5, 1.5 Hz, 1H; 18-H), 5.57 (dd, J=14.8,
9.3 Hz, 1H; 11-H), 5.53–5.46 (m, 1H; 14-H), 5.17–5.10 (m, 1H; 10-H),
4.23 (q, J=7.3 Hz, 2H; CO2CH2CH3), 3.71 (ddd, J=9.5, 3.5, 3.5 Hz,
1H; 8-H), 3.57–3.49 (m, 1H; 7-H), 3.02–2.91 (m, 1H; 15-Hb), 2.63–
2.54 (m, 1H; 26-Hb), 2.51–2.43 (m, 1H; 26-Ha), 2.32–2.25 (m, 1H;
15-Ha), 1.87 (ddd, J=14.8, 9.5, 3.5 Hz, 1H; 9-Hb), 1.57 (d, J=7.0 Hz,
3H; 7-Me), 1.50–1.40 (m, 2H; 27-H), 1.39–1.25 (m, 9H; 28-H, 29-H,
30-H, CO2CH2CH3), 0.90 (ddd, J=14.8, 3.3, 1.5 Hz, 1H; 9-Ha),
0.88 ppm (t, J=7.0 Hz, 3H; 31-H); 13C NMR (100 MHz, CD3OD): d=
173.3 (C6), 168.6 (C1), 167.1 (CO2CH2CH3), 151.1 (C4), 149.6, 138.2,
134.8, 133.2, 133.0, 128.0, 127.2, 121.2, 119.9, (C2, C3, C5, C11, C12,
C13, C14, C17, C18) 77.7, 73.4, 71.9 (C8, C10, C16), 61.6
(CO2CH2CH3), 44.8, 40.8, 34.8, 32.8, 30.3, 29.1, 28.1, 23.6, 17.9, 14.5,
14.4 ppm (CO2CH2CH3, Me-7, C7, C9, C15, C26, C27, C28, C29, C30,
C31); HRMS (ESI): m/z calcd for C28H39N O6NaS [M+Na]: 540.2396;
found: 540.2396.
Data for ester 14b: Scale: 3 mmol, yield: 0.73 mg, 1.35 mmol, 45%;
1H NMR (100 MHz, CD3OD): d=8.01 (s, 1H; 3-H), 7.67 (s, 1H; 5-H),
7.12 (dd, J=15.2, 11.0 Hz, 1H; 13-H), 6.66 (dd, J=15.2, 11.0 Hz, 1H;
12-H), 6.23–6.14 (m, 1H; 21-H), 6.07 (dd, J=11.0, 11.0 Hz, 1H; 13-
H), 5.97 (dq, J=14.7, 7.0 Hz, 1H; 22-H), 5.74 (dd, J=15.2, 6.5 Hz,
1H; 11-H), 5.67 (d, J=15.2 Hz, 1H; 19-H), 5.41 (ddd, J=10.9, 10.9,
4.9 Hz, 1H; 14-H), 5.26–5.18 (m, 1H; 16-H), 4.79 (m, 1H; 10-H), 4.67
(dd, J=11.8, 4.4 Hz, 1H; 17-Hb), 4.17 (dd, J=11.6, 1.9 Hz, 1H; 17-
Ha), 3.80–3.73 (m, 1H; 8-H), 3.58–3.49 (m, 1H; 7-H), 3.38–3.17 (m,
1H; 15-Hb), 2.72–2.58 (m, 2H; 26-H), 2.47–2.38 (m, 1H; 15-Ha),
1.95–1.84 (m, 1H; 9-Hb), 1.79 (d, J=6.7 Hz, 3H; 23-H), 1.73 (ddd,
J=14.7, 5.6, 2.6 Hz, 1H; 9-Ha), 1.56 (d, J=7.0 Hz, 3H; 7-Me), 1.58–
1.27 (m, 8H; 27-H, 28-H, 29-H, 30-H), 0.90 ppm (t, J=7.0 Hz, 3H;
31-H); 13C NMR (100 MHz, CD3OD): d=173.6 (C6), 169.1 (C1), 167.9
(C18), 151.5 (C4), 147.1 141.1, 138.5, 134.4, 133.8, 131.7, 131.0,
127.7, 126.0, 120.4, 119.4, (C2, C3, C5, C11, C12, C13, C14, C19, C20,
C21, C22), 75.6, 72.0, 70.4, 65.2, (C8, C10, C16, C17), 44.7, 39.8, 32.9,
30.7, 30.5, 29.0, 28.8, 23.7, 18.7, 18.2, 14.4 ppm (Me-7, C7, C9, C15,
C26, C27, C28, C29, C30, C31, C23); HRMS (ESI): m/z calcd for
C30H41N O6NaS [M+Na]: 566.2552; found: 566.2552.
Data for thuggacin A derivative 18: Scale: 15 mmol, yield: 4.4 mg,
1
9 mmol, 60% over two steps; H NMR (400 MHz, CD3OD): d=8.05
(s, 1H; 3-H), 7.66 (s, 1H; 5-H), 6.96 (dd, J=16.0, 4.8 Hz, 1H; 17-H),
6.70 (dd, J=15.0, 11.3 Hz, 1H; 12-H), 6.21 (dd, J=16.0, 1.5 Hz, 1H;
18-H), 6.05 (dd, J=11.0, 11.0 Hz, 1H; 13-H), 5.56 (dd, J=14.8,
9.2 Hz, 1H; 11-H), 5.49–5.37 (m, 2H; 14-H, 16-H), 5.14–5.07 (m, 1H;
10-H), 3.71 (ddd, J=9.5, 3.5, 3.5 Hz, 1H; 8-H), 3.57–3.48 (m, 1H; 7-
H), 2.94–2.83 (m, 1H; 15-Hb), 2.66–2.57 (m, 1H; 26-Hb), 2.53–2.44
(m, 1H; 26-Ha), 2.41–2.391 (m, 1H; 15-Ha), 2.30 (s, 3H; CH3CO), 1.88
(ddd, J=14.8, 9.3, 3.7 Hz, 1H; 9-Hb), 1.57 (d, J=7.0 Hz, 3H; 7-Me),
1.51–1.42 (m, 2H; 27-H), 1.39–1.25 (m, 6H; 28-H, 29-H, 30-H), 0.95–
0.85 ppm (m, 4H; 31-H, 9-Ha); 13C NMR (100 MHz, CD3OD): d=
200.6 (CH3C=O), 173.3 (C6), 168.1 (C1), 151.0 (C4), 146.6, 138.4,
135.0, 133.5, 133.1, 130.7, 127.6, 127.0, 120.0 (C2, C3, C5, C11, C12,
Preparation of thuggacin A derivatives 17 and 18: Compound
1 (6.4 mg, 10 mmol, 1 equiv) was treated with NaIO4 as described
above. Aldehyde 11 (3.2 mg, 7.2 mmol, 1 equiv) was used without
further purification for the following Horner–Wadsworth–Emmons
olefination. Phosphonates 15 or 16 (4 equiv), DIPEA (3.7 mg,
Chem. Eur. J. 2015, 21, 1 – 14
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C13, C14, C17, C18), 77.7, 73.9, 71.8 (C8, C10, C16), 44.9, 40.9, 34.6,
32.8, 30.2, 29.1, 28.2, 27.1, 23.6, 17.9, 14.4 ppm (CH3C=O, Me-7, C7,
C9, C15, C26, C27, C28, C29, C30, C31); HRMS (ESI): m/z calcd for
C27H37N O5NaS [M+Na]: 510.2290; found: 540.2284.
of bis-TBS-ether S14 (65 mg, 0.12 mmol, 1 equiv; for the prepara-
tion of S14 see the Supporting Information) in THF (1 mL) at 08C
and the resulting mixture was stirred at RT overnight. The reaction
was terminated by the addition of a saturated aqueous solution of
NH4Cl, and water was added. After extraction with CH2Cl2, the com-
bined organic layers were dried over Na2SO4, concentrated under
reduced pressure, and vacuum dried to give diol S15. HRMS (ESI):
m/z calcd for C15H21NO4SNa [M+Na]+: 334.1089; found: 334.1091.
Crude diol S15 was dissolved in CH2Cl2 (2 mL), and subsequently
2,2-dimethoxypropane (0.5 mL) and CSA (1 mg) were added. The
reaction mixture was stirred at room temperature for 30 min. Di-
ethyl ether, a saturated aqueous solution of NaHCO3, and water
were added. The layers were separated and the aqueous layer was
extracted with diethyl ether. The combined organic extracts were
dried over Na2SO4 and concentrated under reduced pressure. Pu-
rification by flash chromatography (petroleum ether/ethyl ace-
tate=9:1) gave acetonide 32 as a colourless oil (37 mg, 0.11 mmol,
87% over two steps). ½aꢂ2D0 = +56.38 (c=0.6, CH2Cl2); 1H NMR
(400 MHz, CDCl3): d=7.58 (d, J=15.5 Hz, 1H; H3), 7.32 (s, 1H; H5),
6.73 (d, J=15.5 Hz, 1H; H2), 5.83 (ddd, J=17.0, 10.5, 6.0 Hz, 1H;
H11), 5.18 (d, J=17.0 Hz, 1H; H12a), 5.10 (d, J=10.5 Hz, 1H; H12b),
4.26 (dt, J=6.0, 5.7 Hz, 1H; H10), 4.25 (q, J=7.2 Hz, 2H; HEt), 4.10
(dt, J=9.3, 6.5 Hz, 1H; H8), 3.28 (dq, J=6.9, 6.5 Hz, 1H; H7), 1.80
(ddd, J=13.1, 9.3, 5.7 Hz, 1H; H9a), 1.64 (ddd, J=13.1, 9.3, 6.0 Hz,
1H; H9b), 1.43 (d, J=6.9 Hz, 3H; H7-Me), 1.41 (s, 3H; acetonide), 1.40
(s, 3H; acetonide), 1.32 ppm (t, J=7.2 Hz, 3H; HEt); 13C NMR
(101 MHz, CDCl3): d=173.3 (q, C6), 167.3 (q, C1), 150.8 (q, C4), 138.3
(t, C11), 136.4 (t, C3), 121.2 (t, C2), 120.4 (t, C5), 115.3 (s, C12), 100.8 (q,
acetonide), 69.1 (t, C8), 68.1 (t, C10), 60.4 (s, CEt), 43.5 (t, C7), 34.7 (s,
C9), 25.3 (p, acetonide), 24.6 (p, acetonide), 16.5 (p, C7-Me), 14.3 ppm
(p, CEt); HRMS (ESI): m/z calcd for C18H25NO4SNa [M+Na]+:
374.1402; found: 374.1409.
Synthesis of (5S,6S)-5-[(Z)-3-iodoallyl]-2,2,3,3,8,8,9,9-octamethyl-
6-[(4R,5S,6S)-2,2,5-trimethyl-6-{(2E,4E)-4-methylhexa-2,4-dien-2-
yl}-1,3-dioxan-4-yl]-4,7-dioxa-3,8-disiladecane (28): A 2m solution
of NaHMDS (34 mL, 0.068 mmol, 2.5 equiv) in THF was slowly
added to a suspension of ylide S8 (29 mg, 0.054 mmol, 2 equiv) in
THF (0.5 mL) at room temperature. After stirring for 1 min, the so-
lution was cooled to ꢀ858C and stirred for another 5 min followed
by the addition of a cold (ꢀ858C) solution of aldehyde 27 (15 mg,
0.027 mmol, 1 equiv) in THF (0.5 mL). The reaction mixture was
stirred at the same temperature for 10 min and gradually warmed
to ꢀ708C until complete consumption of aldehyde 27 was deter-
mined by TLC. The reaction was terminated by the addition of
a 1:1 mixture of a saturated aqueous solution of bicarbonate and
Na2S2O3. After warming to room temperature, the organic phase
was extracted with diethyl ether. The combined organic extracts
were dried over Na2SO4, filtered, and the filtrate was concentrated
under reduced pressure. Purification by flash chromatography (pe-
troleum ether/ethyl acetate=100:1) yielded vinyl iodide 28 as
a colourless oil (9.7 mg, 0.014 mmol, 53%, E/Z=3:1). ½aꢂ2D0 =ꢀ10.38
1
(c=1.5, EtOAc); H NMR (500 MHz, C6D6): d=6.45 (s, 1H; H10), 6.09
(dt, J=7.3, 6.9 Hz, 1H; H2), 5.99 (d, J=7.3 Hz, 1H; H1), 5.49 (q, J=
6.7 Hz, 1H; H12), 4.41 (s, 1H; H8), 4.18 (d, J=8.5 Hz, 1H; H6), 3.99
(dt, J=6.9, 1.5 Hz, 1H; H4), 3.76 (d, J=8.5 Hz, 1H; H5), 2.65–2.54
(m, 2H; H3), 2.07–2.00 (m, 1H; H7), 1.78 (s, 3H; H11-Me), 1.73 (s, 3H;
H9-Me), 1.61 (d, J=6.7 Hz, 3H; H13), 1.59 (s, 3H; acetonide), 1.46 (s,
3H; acetonide), 1.07 (s, 9H; TBS), 1.05 (d, J=6.7 Hz, 3H; H7-Me), 0.98
(s, 9H; TBS), 0.23 (s, 3H; TBS), 0.19 (s, 3H; TBS), 0.15 ppm (s, 6H;
TBS); 13C NMR (101 MHz, C6D6): d=138.2 (t, C2), 133.7 (q, C11), 131.8
(q, C9), 128.9 (t, C10), 123.6 (t, C12), 99.6 (q, acetonide), 85.0 (t, C1),
76.2 (t, C8), 75.1 (t, C6), 74.7 (t, C5), 72.8 (t, C4), 39.0 (s, C3), 31.9 (t,
C7), 30.2 (p, acetonide), 26.4 (p, TBS), 26.2 (p, TBS), 19.7 (p, aceto-
nide), 18.8 (q, TBS), 18.4 (q, TBS), 17.1 (p, C11-Me), 15.4 (p, C9-Me), 13.8
(p, C13), 6.6 (p, C7-Me), ꢀ3.3 (p, TBS), ꢀ3.6 (p, TBS), ꢀ3.8 (p, TBS),
ꢀ4.4 ppm (p, TBS); HRMS (ESI): m/z calcd for C31H59O4WSi2Na
[M+Na]+: 701.2894; found: 701.2893.
Synthesis of (S,Z)-1-[(tert-butyldimethylsilyl)oxy]-5-iodopent-4-
en-2-yl acetate (35): BH3·SMe2 (0.13 mL, 1.45 mmol, 1.45 equiv)
was added to a solution of cyclohexene (0.3 mL, 2.96 mmol,
2.96 equiv) in THF (7 mL) at 08C. After stirring for 1.5 h at RT, io-
doalkyne S17 (328 mg, 1.00 mmol, 1.00 equiv; for the preparation
of S17 see the Supporting Information) in THF (2 mL) was added
and the reaction mixture was stirred for 3 h before HOAc (0.1 mL)
was added. After an additional 30 min of stirring, the reaction was
terminated by the addition of an aqueous solution of NaHCO3. The
aqueous layer was extracted with diethyl ether and the combined
organic extracts were washed with brine and dried over MgSO4.
Purification by flash column chromatography (petroleum ether/
ethyl acetate=50:1) yielded iodoalkene 35 (237 mg; 0.62 mmol,
62%) as a colourless oil. Rf =0.29 (petroleum ether/ethyl acetate=
20:1); ½aꢂ2D0 =12.5 (c=92.7, CDCl3); 1H NMR (400 MHz, CDCl3): d=
6.34 (ddd, J=7.3, 1.5, 1.5 Hz, 1H), 6.23 (ddd, J=7.3, 7.2, 7.2 Hz,
1H), 5.02 (dddd, J=7.0, 5.4, 5.3, 5.2, 1H), 3.70 (dd, J=10.9, 5.4 Hz,
1H), 3.67 (dd, J=10.9, 5.2 Hz, 1H), 2.53–2.40 (m, 2H), 2.05 (s, 3),
0.89 (s, 9H), 0.05 ppm (s); 13C NMR (100 MHz, CDCl3): d=170.5 (q),
136.5 (t), 85.0 (t), 72.8 (t), 63.8 (s),36.2 (s), 25.8 (p), 21.1 (p), 18.2 (q),
ꢀ5.4 (p), ꢀ5.4 ppm (p).
Synthesis of macrolactone 36: A 3m aqueous solution of KOH
(1 mL) at 08C was added to the solution of diene S19 (15.5 mg,
0.026 mmol, 1 equiv; for the preparation of S19 see the Supporting
Information) in ethanol (2 mL) and the reaction mixture was stirred
overnight at room temperature. The reaction was terminated by
adding a saturated aqueous solution of NH4Cl. Ethyl acetate was
added to the reaction mixture and the two layers were separated.
The aqueous layer was extracted with ethyl acetate. The combined
organic extracts were dried over Na2SO4 and concentrated under
reduced pressure to yield the acid S20 (14.5 mg crude weight;
Synthesis of (R,E)-ethyl 4-amino-5-(tritylthio)pent-2-enoate (30):
2,6-Lutidine (0.5 mL, 4.56 mmol, 4 equiv) and TMSOTf (0.4 mL,
2.28 mmol, 2 equiv) were sequentially added to a solution of carba-
mate S10 (590 mg, 1.14 mmol, 1 equiv; for preparation of S10 see
the Supporting Information) in CH2Cl2 (5 mL) at 08C. The reaction
mixture was stirred for 14 h at room temperature. The reaction
was quenched by the addition of methanol (5 mL) and water was
added. After extraction with CH2Cl2, the combined organic extracts
were dried over Na2SO4 and concentrated under reduced pressure.
Purification by flash chromatography (petroleum ether/EtOAc
10:1!1:1) gave amine 30 as colourless oil (463 mg, 1.11 mmol,
1
97%). ½aꢂ2D0 = +17.08 (c=1.9, CH2Cl2); H NMR (400 MHz, CDCl3) d=
7.41–7.44 (m, 5H; -Trt), 7.21–7.32 (m, 10H; -Trt), 6.61 (dd, J=15.7,
6.5 Hz, 1H; H3), 5.75 (d, J=15.7 Hz, 1H; H2), 4.13 (q, J=7.1 Hz, 2H;
HEt), 2.77–2.85 (m, 1H; H4), 2.65 (brs, 2H; -NH2), 2.52 (dd, J=13.4,
8.0 Hz, 1H; H5a), 2.46 (dd, J=13.4, 5.5 Hz, 1H; H5b), 1.25 ppm (t, J=
7.2 Hz, 3H; HEt); 13C NMR (101 MHz, CDCl3) d=166.2 (q, C1), 148.0
(t, C3), 144.5 (q, Trt), 129.6 (t, Trt), 128.0 (t, Trt), 126.9 (t, Trt), 121.8
(t, C2), 67.1 (q, Trt), 60.5 (s, CEt), 51.8 (t, C4), 38.3 (s, C5), 14.2 ppm (p,
CEt); HRMS (ESI): m/z calcd for C26H27NO2SNa [M+Na]+: 440.1660;
found: 440.1678.
Synthesis of (E)-ethyl 3-{2-[(R)-1-{(4S,6S)-2,2-dimethyl-6-vinyl-1,3-
dioxan-4-yl}ethyl]thiazol-4-yl} acrylate (32): A solution of TBAF
(95 mg, 0.30 mmol, 2.5 equiv) in THF (1 mL) was added to a solution
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HRMS (ESI): m/z calcd for C21H28NO6S [MꢀH]ꢀ: 422.1637; found:
422.1635), which was used in the next step without further purifi-
cation. Et3N (65 mL, 0.47 mmol, 20 equiv) and 2,4,6-trichlorobenzoyl
chloride (55 mL, 0.35 mmol, 15 equiv) were added to a solution of
crude acid S20 (10 mg, 0.024 mmol, 1 equiv) in THF (2 mL) at room
temperature. The reaction mixture was stirred overnight and dilut-
ed with toluene (2 mL). The diluted reaction mixture was added to
a solution of 4-DMAP (115 mg, 0.94 mmol, 40 equiv) in toluene
(15 mL) by means of a syringe pump over a period of 2 h at room
temperature. The reaction mixture was stirred for 12 h before it
was hydrolysed with a saturated aqueous solution of NH4Cl. The re-
sulting mixture was extracted with EtOAc (3ꢃ20 mL), and the com-
bined organic layers were dried over Na2SO4 and concentrated in
vacuo. Flash column chromatography on silica gel (petroleum
ether/ethyl acetate=10:1) afforded an inseparable mixture of mac-
rocycles and other side products (dimer/trimer etc.) as a colourless
oil. This crude material was further treated with p-TsOH (0.5 mg) in
methanol (1 mL) at 08C for 5 min. The reaction was terminated by
the addition of phosphate buffer (pH 7) and the solution was ex-
tracted with CH2Cl2 (5ꢃ), dried over Na2SO4, and concentrated
under reduced pressure. Thuggacin B derivative 36 (1.2 mg,
0.0021 mmol, 8.2% over three steps) was separated from other
H7-Me), 1.19 (s, 9H; TBS), 1.14 (d, J=6.8 Hz, 3H; H19-Me), 1.10 (t, J=
7.1 Hz, 3H; HEt), 1.09 (s, 9H; TBS), 0.35 (s, 3H; TBS), 0.31 (s, 3H;
TBS), 0.24 ppm (s, 6H; 2ꢃTBS); 13C NMR (101 MHz, CDCl3): d=
173.0 (q, C6), 167.0 (q, C1), 151.5 (q, C4), 136.8 (t, C3), 134.8 (t, C11),
133.8 (q, C23), 131.8 (q, C21), 130.4 (t, C13), 128.9 (t, C22), 128.4 (t, C14),
124.9 (t, C12), 123.6 (t, C24), 121.4 (t, C5), 121.3 (t, C2), 101.0 (q, aceto-
nide), 99.6 (q, acetonide), 76.3 (t, C20), 75.0 (t, C18), 74.5 (t, C17), 74.5
(t, C16), 69.5 (t, C8), 67.3 (t, C10), 60.4 (s, CEt), 43.8 (t, C7), 35.8 (s, C9),
32.1 (s, C15), 32.1 (t, C19), 30.3 (p, acetonide), 26.5 (p, TBS), 26.2 (p,
TBS), 25.3 (p, acetonide), 24.8 (p, acetonide), 19.8 (p, acetonide),
18.9 (q, TBS), 18.4 (q, TBS), 17.1 (p, C23-Me), 16.5 (p, C7-Me), 15.4 (p,
C21-Me), 14.3 (p, CEt), 13.8 (p, C25), 6.6 (p, C19-Me) ꢀ3.8 (p, TBS),
ꢀ4.5 ppm (p, TBS); HRMS (ESI): m/z calcd for C49H83NO8Si2SNa
[M+Na]+: 924.5276; found: 924.5261.
Synthesis of 2-deshexyl thuggacin C (38): Bis-acetonide S23
(0.7 mg, 1.11 mmol, 1 equiv; for the preparation of S23 see the Sup-
porting Information) was dissolved in MeOH (1 mL) and treated
with PPTS (17 mg, 0.0676 mmol, 65 equiv); stirring was continued
at RT for 14 d. The reaction mixture was concentrated under re-
duced pressure and the residue was dissolved in MeOH and puri-
fied by RP-HPLC (ISIS; time: 80 min; H2O/MeOH=60:40!0:100 in
80 min; tr(38)=31 min). 2-Deshexylthuggacin C 38 (0.5 mg,
0.8 mmol, 72%) was obtained as a colourless oil. ½aꢂ2D0 = +158 (c=
1
side products by HPLC. H NMR (500 MHz, CD3OD): d=7.67 (s, 1H),
7.61 (s, 2H), 7.60 (d, J=15.31 Hz, 1H), 7.03 (d, J=15.44 Hz, 1H),
6.67 (dd, J=11.04, 15.18 Hz, 1H), 6.16 (t, J=10.98 Hz), 5.79 (dd, J=
6.71, 15.25 Hz), 5.62–5.48 (m, 2H; 17-H), 4.85–4.75 (m, 1H), 4.52
(dd, J=4.27, 11.29 Hz, 1H), 4.29 (dd, J=6.65, 11.17 Hz, 1H), 3.83
(ddd, J=2.70, 5.90, 8.47 Hz, 1H), 3.58–3.47 (m, 1H), 3.12–3.01 (m,
1H), 2.69–2.59 (m, 1H), 2.02 (ddd, J=3.14, 11.17, 14.49 Hz, 1H),
1.65 (ddd, J=2.13, 6.21, 14.68 Hz, 1H), 1.55 ppm (d, J=6.90 Hz,
3H); 13C NMR (125 MHz, CD3OD): d=175.61, 168.61, 165.40, 153.12,
139.92, 138.99, 138.61, 134.40, 134.11, 133.62, 130.26, 126.90,
126.52, 123.30, 123.15, 76.21, 75.12, 70.97, 64.22, 45.85, 49.30,
30.61, 18.78 ppm; HRMS (ESI): m/z calcd for C25H24NO6SCl3Na
[M+Na]+: 594.0288; found: 594.0283.
1
0.2, MeOH); H NMR (500 MHz, MeOD): d=7.72 (s, 1H; H5), 7.64 (d,
J=15.5 Hz, 1H; H3), 6.96 (d, J=15.5 Hz, 1H; H2), 6.42 (dd, J=15.2,
11.5 Hz, 1H; H12), 6.03 (dd, J=11.5, 11.0 Hz, 1H; H13), 5.96 (s, 1H;
H22), 5.61 (dd, J=15.2, 8.3 Hz, 1H; H11), 5.51–5.45 (m, 1H; H14), 5.44
(q, J=6.9 Hz, 1H; H24), 5.14 (ddd, J=11.0, 8.3, 2.6 Hz, 1H; H10), 5.08
(dd, J=5.0, 3.5 Hz, 1H; H18), 4.05 (ddd, J=9.1, 6.7, 5.1 Hz, 1H; H16),
3.89 (dd, J=6.7, 5.0 Hz, 1H; H17), 3.80 (d, J=7.4 Hz, 1H; H20), 3.65–
3.62 (m, 2H; H7, H8), 2.50–2.47 (m, 1H; H15), 2.10 (ddq, J=7.4, 7.1,
3.5 Hz, 1H; H19), 1.88–1.79 (m, 2H; H9), 1.81 (s, 3H; H21-Me), 1.76 (s,
3H; H23-Me), 1.69 (d, J=6.9 Hz, 3H; H25), 1.57–1.53 (m, 3H; H7-Me),
1.17 ppm (d, J=7.1 Hz, 3H; H19-Me); 13C NMR (101 MHz, MeOD): d=
176.3 (q, C6), 168.1 (q, C1), 151.9 (q, C4), 138.3 (t, C11), 138.3 (t, C3),
134.1 (q, C23), 133.5 (q, C21), 133.3 (t, C22), 131.4 (t, C13), 130.7 (t, C14),
126.4 (t, C12), 126.0 (t, C24), 123.6 (t, C5), 121.3 (t, C2), 92.9 (t, C20),
83.3 (t, C17), 82.1 (t, C18), 77.2 (t, C8), 72.5 (t, C16), 71.5 (t, C10), 46.9 (t,
C19), 44.9 (t, C7), 39.6 (s, C9), 31.1 (s, C15), 16.7 (p, C23-Me), 16.0 (p, C21-
Me), 18.6 (p, C7-Me), 13.0 (p, C25), 11.8 ppm (p, C19-Me); HRMS (ESI): m/z
calcd for C29H40NO6S [M+HꢀH2O]+: 630.2576; found: 630.2579; m/
z calcd for C29H38NO5S [M+Hꢀ2H2O]+: 612.2471; found: 612.2469.
Synthesis of compound 41: The acid 31 (25 mg, 0.062 mmol,
1 eq.) was dissolved in CH2Cl2 (1 mL). The solution was cooled to
08C and oxalyl chloride was added. The reaction mixture was
stirred for 90 min and the solvent was removed under reduced
pressure. A solution of amine 40 (15 mg, 0.062 mmol, 1 eq.) and
DMAP (7.5 mg, 0.062 mmol, 1 eq.) in CHCl3 (1 mL) was added at
08C to a solution of acid chloride in CH2Cl2 (1 mL). After stirring for
40 min, brine was added. After phase separation, the aqueous
phase was extracted with CH2Cl2. The combined extracts were col-
lected, dried over MgSO4, concentrated and dried in vacuo. Flash
column chromatographic purification (petroleum ether/ethyl ace-
tate=10:1) over silica gel provided amide 41 as a colourless oil (20
mg, 0.032 mmol, 51%). ½aꢂ2D0 =ꢀ21.88 (c=0.6 CH2Cl2); 1H NMR
(400 MHz, CDCl3): d=6.87 (d, J=6.5 Hz, NH), 6.49 (1H, d, J=9.9 Hz,
H3), 5.75 (1H, ddd, J=7.5, 10.0, 17.1 Hz, H11), 5.09 (1H, d, J=
17.1 Hz, H12b), 5.01 (1H, d, J=10.0 Hz, H12a), 4.72-4.81 (1H, m, H4),
4.09-4.23 (3H, m, HEt, H10), 3.95 (1H, ddd, J=2.3, 2.6, 8.1 Hz, H8),
3.67 (2H, dd, J=3.7, 3.9 Hz, H5), 2.98 (1H, t, J=3.9 Hz, OH), 2.55
(1H, dq, J=3.1, 7.2 Hz, H7), 2.30-2.38 (2H, m, hexyl), 1.66 (1H, ddd,
J=2.3, 9.4, 14.2 Hz, H9b), 1.37 (1H, ddd, J=3.1, 8.1, 14.2 Hz, H9a),
1.28 (t, J=7.2 Hz, HEt), 1.22-1.33 (8H, m, Hhexyl), 1.07 (3H, d, J=
Synthesis of (E)-ethyl 3-{2-[(R)-1-{(4S,6S)-6-[(1E,3Z,6S,7S)-6,7-bis-
{(tert-butyldimethylsilyl)oxy}-7-{(4R,5S,6S)-2,2,5-trimethyl-6-
[(2E,4E)-4-methylhexa-2,4-dien-2-yl]-1,3-dioxan-4-yl}hepta-1,3-
dien-1-yl]-2,2-dimethyl-1,3-dioxan-4-yl}ethyl]thiazol-4-yl}acrylate
(37): A solution of vinyl iodide 28 (24 mg, 0.035 mmol, 1 equiv)
and alkene 32 (19 mg, 0.053 mmol, 1.5 equiv) in degassed NMP
(0.5 mL) was added to a reaction mixture containing powdered
AgOAc (4.13 mg, 0.035 mmol, 1 equiv), Pd(OAc)2 (0.79 mg,
0.0035 mmol, 0.1 equiv), and degassed NMP (0.5 mL). After stirring
the reaction mixture at RT for 10 min, it was gradually heated to
558C and stirred overnight at the same temperature. The reaction
mixture was cooled to room temperature and directly purified by
flash column chromatography on silica gel (petroleum ether/ethyl
acetate=9:1) to give diene 37 as
a colourless oil (17 mg,
0.019 mmol, 53%). ½aꢂD20 =ꢀ29.48 (c=0.8, EtOAc); 1H NMR
(400 MHz, CDCl3): d=7.87 (d, J=15.3 Hz, 1H; H3), 7.33 (d, J=
15.4 Hz, 1H; H2), 6.86 (dd, J=15.5, 11.5 Hz, 1H; H12), 6.62 (s, 1H;
H5), 6.54 (s, 1H; H22), 6.19 (dd, J=11.5, 11.0 Hz, 1H; H13), 5.64–5.73
(m, 1H; H14), 5.68 (dd, J=15.5, 5.3 Hz, 1H; H11), 5.59 (q, J=6.9 Hz,
1H; H24), 4.48 (s, 1H; H20), 4.41 (ddd, J=9.5, 5.3, 5.0 Hz, 1H; H10),
4.29 (dd, J=8.7, 2.0 Hz, 1H; H18), 4.19 (ddd, J=9.1, 6.5, 6.2 Hz, 1H;
H8), 4.18 (q, J=7.1 Hz, 2H; HEt), 4.04 (dt, J=6.5, 6.5, 2.0 Hz, 1H;
H16), 3.95 (dd, J=8.7, 2.0 Hz, 1H; H17), 3.23 (dq, J=7.0, 6.5 Hz, 1H;
H7), 2.83 (ddd, J=14.0, 7.0, 6.5 Hz, 1H; H15a), 2.75 (ddd, J=14.0, 7.5,
6.5 Hz, 1H; H15b), 2.09–2.17 (m, 1H; H19), 1.89 (s, 3H; H21-Me), 1.83 (s,
3H; H23-Me), 1.77 (ddd, J=13.0, 9.5, 6.2 Hz, 1H; H9a), 1.71 (s, 3H; ace-
tonide), 1.69 (d, J=6.9 Hz, 3H; H25), 1.56–1.67 (m, 1H; H9b), 1.55 (s,
3H; acetonide), 1.50 (s, 6H; 2ꢃacetonides), 1.44 (d, J=7.0 Hz, 3H;
Chem. Eur. J. 2015, 21, 1 – 14
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7.2 Hz, H7-Me), 0.91 (9H, s, TBS), 0.87 (3H, t, J=6.1 Hz, Hhexyl), 0.86
(9H, s, TBS), 0.13 (6H, s, 2ꢃTBS), 0.04 (3H, s, TBS), 0.02 (3H, s, TBS)
ppm; 13C NMR (CDCl3, 100 MHz, CDCl3=77.0 ppm): d=174.6 (q,
C6), 167.1 (q, C1), 141.7 (t, C11), 136.7 (q, C2), 135.3 (t, C3), 114.8 (s,
C12), 72.0 (t, C10), 71.9 (t, C8), 66.4 (s, C5), 66.4 (s, C5), 60.7 (s, Et), 50.7
(t, C4), 45.8 (t, C7), 42.0 (s, C9), 31.5 (s, hexyl), 29.5 (s, hexyl), 29.3 (s,
hexyl), 27.5 (s, hexyl), 25.9 (p, TBS), 25.8 (p, TBS), 22.6 (s, hexyl),
18.1 (q, TBS), 17.9 (q, TBS), 14.2 (p, hexyl), 14.1 (p, Et), 12.4 (p, 7-
Me), ꢀ3.1 (p, TBS), ꢀ4.3 (p, TBS), ꢀ4.4 (p, TBS), ꢀ4.5 ppm (p, TBS);
HRMS (ESI): m/z calculated for C33H66NO6Si2 [M+H]+: 628.4429,
found: 628.4446.
1H; H19), 1.79 (s, 3H; H21-Me), 1.75 (s, 3H; H23-Me), 1.72–1.83 (m, 1H;
H9a), 1.65 (ddd, J=9.6, 6.4, 6.4 Hz, 1H; H9b), 1.61 (d, J=6.7 Hz, 3H;
H25), 1.59 (s, 3H; acetonide), 1.59–1.37 (m, 8H; Hb-e), 1.46 (s, 3H;
acetonide), 1.41 (s, 3H; acetonide), 1.37 (s, 3H; acetonide), 1.36 (d,
J=7.2 Hz, 3H; H7-Me), 1.09 (s, 9H; TBS), 1.04 (d, J=6.9 Hz, 3H; H19-
Me), 1.03 (t, J=7.2 Hz, 3H; HEt), 1.00 (s, 9H; TBS), 0.25 (s, 3H; TBS),
0.21 (s, 3H; TBS), 0.16 (s, 3H; TBS), 0.15 ppm (s, 3H; TBS); 13C NMR
(101 MHz, C6D6): d=168.0 (q, C1), 165.8 (q, C6), 139.4 (q, C4), 138.3
(q, C2), 134.8 (t, C3), 134.8 (t, C11), 133.8 (q, C21), 131.8 (q, C23), 130.4
(t, C13), 128.9 (t, C22), 127.9 (t, C14), 126.3 (t, C5), 124.9 (t, C12), 123.6
(t, C24), 100.9 (q, acetonide), 99.6 (q, acetonide), 76.3 (t, C20), 75.0 (t,
C18), 74.5 (t, C17), 74.5 (t, C16), 69.0 (t, C8), 67.2 (t, C10), 60.7 (s, CEt),
39.7 (t, C7), 36.8 (s, C9), 32.2 (s, C15), 32.1 (t, C19), 30.3 (s, Cb-e), 30.0
(p, acetonide), 29.7 (s, Cb-e), 28.4 (s, Ca), 26.5 (p, TBS), 26.2 (p, TBS),
25.2 (p, acetonide), 24.7 (p, acetonide), 23.1 (s, Cb-e), 19.8 (p, aceto-
nide), 18.9 (q, TBS), 18.4 (q, TBS), 17.1 (p, C23-Me), 15.4 (s, Cb-e), 14.9
(p, C21-Me), 14.4 (p, C7-Me), 14.4 (p, CEt), 14.4 (p, Cf), 13.8 (p, C25), 6.6
(p, C19-Me), ꢀ3.2 (p, TBS), ꢀ3.8 (p, TBS), ꢀ4.4 ppm (p, TBS); HRMS
(ESI): m/z calcd for C55H95NO9Si2Na [M+Na]+: 992.6443; found:
992.6436.
Synthesis of (E)-ethyl 2-{[2-{(R)-1-[(4S,6S)-2,2-dimethyl-6-vinyl-
1,3-dioxan-4-yl]ethyl}oxazol-4-yl]methylene}octanoate (42): 2,2-
Dimethoxypropane (0.5 mL) and CSA (1 mg) were added to a solu-
tion of diol S26 (86 mg, 0.23 mmol, 1 equiv; for the preparation of
S26 see the Supporting Information) in DMF (2.5 mL), and the mix-
ture was stirred at room temperature for 2 h. Diethyl ether, a satu-
rated aqueous solution of NaHCO3, and water were added to the
reaction mixture and the layers were separated. The aqueous layer
was extracted with diethyl ether. The combined organic extracts
were dried over Na2SO4 and concentrated under reduced pressure.
Purification by flash column chromatography on silica gel (petrole-
um ether/ethyl acetate=5:1) gave acetonide 42 as a colourless oil
(90 mg, 0.22 mmol, 95%). ½aꢂ2D0 =ꢀ40.48 (c=1.2, EtOAc); 1H NMR
(400 MHz, C6D6): d=7.62 (s, 1H; H5), 7.02 (s, 1H; H3), 5.80 (ddd, J=
17.0, 10.7, 5.6 Hz, 1H; H11), 5.17 (d, J=17.0 Hz, 1H; H12a), 4.95 (d,
J=10.7 Hz, 1H; H12b), 4.30–4.20 (m, 1H; H10), 4.17–4.06 (m, 1H; H8),
4.10 (q, J=7.1 Hz, 2H; HEt), 3.19 (t, J=7.6 Hz, 2H; Ha), 2.95 (dq, J=
7.2, 7.0 Hz, 1H; H7), 1.81–1.70 (m, 3H; H9a, Hb-e), 1.61 (ddd, J=13.0,
9.2, 6.2 Hz, 1H; H9b), 1.56–1.25 (m, 6H; Hb-e), 1.34 (s, 3H; acetonide),
1.33 (d, J=7.2 Hz, 3H; H7-Me) 1.31 (s, 3H; acetonide), 1.02 (t, J=
7.1 Hz, 3H; HEt), 0.89 ppm (t, J=7.0 Hz, 3H; Hf); 13C NMR (101 MHz,
C6D6): d=168.6 (q, C1), 166.4 (q, C6), 140.0 (t, C11), 139.7 (t, C3),
138.8 (q, C4), 135.3 (q, C2), 126.8 (t, C5), 114.7 (s, C12), 101.4 (q, aceto-
nide), 69.4 (t, C8), 68.5 (t, C10), 61.2 (s, CEt), 40.2 (t, C7), 36.6 (s, C9),
32.8 (s, Ca-e), 30.6 (s, Ca-e), 30.3 (s, Ca-e), 28.9 (s, Ca-e), 25.9 (p, aceto-
nide), 25.2 (p, acetonide), 23.7 (s, Ca-e), 15.4 (p, CEt), 14.9 ppm (p,
Cf); HRMS (ESI): m/z calcd for C24H37NO5Na [M+Na]+: 442.2569;
found: 442.2570.
Synthesis of oxazole thuggacin
B (44b): Bis-acetonide S29
(2.8 mg, 4.0 mmol, 1 equiv; for the preparation of S29 see the Sup-
porting Information) was dissolved in MeOH (1 mL), treated with
PPTS (61 mg, 0.24 mmol, 60 equiv), and stirred at RT for 48 h. The
reaction mixture was concentrated under reduced pressure and
the residue was dissolved in MeOH and purified by RP-HPLC (ISIS;
time: 80 min; H2O/MeOH=60:40!0:100 in 80 min; tr(44b)=
29 min; tr(44a)=30 min; tr(45)=31 min). Oxazoles 44b (0.2 mg,
0.3 mmol, 8%), 44a (0.4 mg, 0.6 mmol, 16%), and 45 (1.0 mg,
1.6 mmol, 39%) were obtained as colourless oils.
1
Data for 44b: H NMR (500 MHz, C6D6): d=8.03 (s, 1H; H3), 7.28 (s,
1H; H5), 6.45 (dd, J=14.9, 11.1 Hz, 1H; H12), 6.24 (s, 1H; H22), 6.05
(dd, J=11.1, 11.0 Hz, 1H; H13), 5.52 (dd, J=14.9, 7.7 Hz, 1H; H11),
5.49 (q, J=6.8 Hz, 1H; H24), 5.10 (ddd, J=11.5, 11.0, 4.1 Hz, 1H;
H14), 5.03 (dd, J=5.2, 1.0 Hz, 1H; H17), 4.37 (s, 1H; H20), 4.26 (ddd,
J=5.2, 3.6, 3.5 Hz, 1H; H18), 4.15–4.10 (m, 1H; H10), 3.84–3.80 (m,
1H; H8), 3.62–3.58 (m, 1H; H16), 3.26 (d, J=5.6 Hz, 1H; -OH), 3.22
(d, J=3.6 Hz, 1H; -OH), 3.07 (dq, J=7.1, 6.8 Hz, 1H; H7), 2.84 (ddd,
J=13.0, 9.4, 6.2 Hz, 1H; Ha), 2.78 (ddd, J=13.9, 11.6, 11.5 Hz, 1H;
H15a), 2.51 (ddd, J=13.0, 9.3, 6.2 Hz, 1H; Ha), 2.11 (ddq, J=7.0, 6.8,
3.5 Hz, 1H; H19), 2.07 (d, J=2.4 Hz, 1H; -OH), 1.94 (d, J=3.7 Hz,
1H; -OH), 1.85 (ddd, J=9.8, 5.7, 5.3 Hz, 1H; H9a), 1.83 (s, 3H; H23-Me),
1.83–1.80 (m, 1H; H9b), 1.76–1.71 (m, 1H; H15b), 1.71 (s, 3H; H21-Me),
1.61 (d, J=6.8 Hz, 3H; H25), 1.66–1.55 (m, 2H; Hb), 1.38–1.18 (m,
6H; Hc-e), 1.23 (d, J=6.8 Hz, 3H; H19-Me), 1.22 (d, J=6.8 Hz, 3H; H7-
Me), 0.86 ppm (t, J=7.0 Hz, 3H; Hf); 13C NMR (101 MHz, C6D6): d=
169.2 (q, C1), 166.3 (q, C6), 137.7 (q, C4), 137.5 (t, C11), 135.3 (q, C21),
134.8 (q, C2), 133.9 (q, C23), 132.4 (t, C13), 131.1 (t, C3), 129.9 (t, C22),
126.7 (t, C14), 124.8 (t, C12), 123.7 (t, C24), 79.1 (t, C20), 78.0 (t, C17),
75.4 (t, C18), 73.1 (t, C8), 71.7 (t, C16), 70.8 (t, C10), 39.5 (t, C7), 38.0 (s,
C9), 37.7 (t, C19), 32.4 (s, C15), 31.6 (s, Cd), 29.5 (s, Cc), 28.6 (s, Ca), 27.9
(s, Cb), 22.7 (s, Ce), 14.9 (p, C7-Me), 14.4 (p, C21-Me), 13.6 (p, Cf),
7.0 ppm (p, C19-Me); HRMS (ESI): m/z calcd for C35H53NO8Na
[M+Na]+: 638.3669; found: 638.3657. Due to the small amount ob-
tained, it was not possible to record 13C NMR spectra. Therefore,
the chemical shifts of the carbon atoms were assigned by 2D spec-
tral analysis (HMBC, HSQC). The signals of the quaternary carbon
atom at C5, as well as the primary ones C23-Me and C25, could
not be unequivocally assigned.
Synthesis of (E)-ethyl 2-{[2-{(R)-1-[(4S,6S)-6-{(1E,3Z,6S,7S)-6,7-
bis[(tert-butyldimethylsilyl)oxy]-7-[(4R,5S,6S)-2,2,5-trimethyl-6-
{(2E,4E)-4-methylhexa-2,4-dien-2-yl}-1,3-dioxan-4-yl]hepta-1,3-
dien-1-yl}-2,2-dimethyl-1,3-dioxan-4-yl]ethyl}oxazol-4-yl]methy-
lene}octanoate (43):
A solution of vinyl iodide 28 (33 mg,
0.049 mmol, 1 equiv) and alkene 42 (25 mg, 0.058 mmol, 1.2 equiv)
in degassed NMP (0.5 mL) was added to a reaction mixture com-
posed of powdered AgOAc (5.68 mg, 0.049 mmol, 1 equiv),
Pd(OAc)2 (1.1 mg, 0.0049 mmol, 0.1 equiv), and degassed NMP
(0.5 mL). The reaction mixture was stirred at RT for 10 min and
then gradually heated to 558C. The flask was left stirring overnight
at this temperature before it was cooled to room temperature and
directly purified by flash column chromatography on silica gel (pe-
troleum ether/ethyl acetate=18:1) to give diene 43 as a colourless
oil (23 mg, 0.024 mmol, 50%). ½aꢂ2D0 =ꢀ31.88 (c=1.0, EtOAc);
1H NMR (400 MHz, C6D6): d=7.66 (s, 1H; H5), 7.07 (s, 1H; H3), 6.79
(dd, J=15.3, 11.2 Hz, 1H; H12), 6.44 (s, 1H; H22), 6.11 (dd, J=11.2,
10.5 Hz, 1H; H13), 5.64 (dd, J=15.3, 5.5 Hz, 1H; H11), 5.63–5.57 (m,
1H; H14), 5.48 (q, J=6.7 Hz, 1H; H24), 4.39 (s, 1H; H20), 4.43–4.34 (m,
1H; H10), 4.20 (dd, J=8.7, 1.5 Hz, 1H; H18), 4.17 (ddd, J=8.9, 7.5,
6.4 Hz, 1H; H8), 4.11 (q, J=7.2 Hz, 2H; HEt), 3.96 (dt, J=6.9, 1.8 Hz,
1H; H16), 3.85 (dd, J=8.7, 1.8 Hz, 1H; H17), 3.20 (t, J=7.8 Hz, 1H;
Ha), 2.98 (dq, J=7.5, 7.2 Hz, 1H; H7), 2.75 (ddd, J=14.0, 6.9, 6.9 Hz,
1H; H15a), 2.66 (ddd, J=14.0, 7.3, 6.9 Hz, 1H; H15b), 2.07–2.01 (m,
1
Data for Z-oxazole thuggacin B (44a): H NMR (500 MHz, C6D6): d=
8.04 (s, 1H; H3), 7.29 (s, 1H; H5), 6.45 (dd, J=15.1, 11.1 Hz, 1H; H12),
6.21 (s, 1H; H22), 6.05 (dd, J=11.1, 11.0 Hz, 1H; H13), 5.52 (dd, J=
15.1, 7.7 Hz, 1H; H11), 5.35 (q, J=6.8 Hz, 1H; H24), 5.11 (ddd, J=
&
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ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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11.3, 11.0, 3.9 Hz, 1H; H14), 5.01 (dd, J=4.6, 1.0 Hz, 1H; H17), 4.43 (s,
1H; H20), 4.26 (ddd, J=4.6, 3.5, 3.5 Hz, 1H; H18), 4.14–4.09 (m, 1H;
H10), 3.84–3.79 (m, 1H; H8), 3.57–3.62 (m, 1H; H16), 3.34 (d, J=
3.5 Hz, 1H; -OH), 3.26 (d, J=5.4 Hz, 1H; -OH), 3.07 (dq, J=7.2,
7.0 Hz, 1H; H7), 2.84 (ddd, J=13.1, 9.2, 6.3 Hz, 1H; Ha), 2.78 (ddd,
J=14.0, 11.6, 11.3 Hz, 1H; H15a), 2.51 (ddd, J=J=13.1, 9.2, 6.0 Hz,
1H; Ha), 2.26 (d, J=2.6 Hz, 1H; -OH), 2.11 (ddq, J=6.7, 3.5, 3.5 Hz,
1H; H19), 1.99 (d, J=3.8 Hz, 1H; -OH), 1.84 (ddd, J=15.2, 10.2,
5.0 Hz, 1H; H9a), 1.81 (s, 3H; H23-Me), 1.77–1.71 (m2H;, H9b, H15b),
1.64 (s, 3H; H21-Me), 1.60 (d, J=6.8 Hz, 3H; H25), 1.64–1.57 (m, 2H;
Hb), 1.37–1.20 (m, 6H; Hc-e), 1.22 (d, J=7.0 Hz, 3H; H7-Me), 1.21 (d,
J=6.7 Hz, 3H; H19-Me), 0.87 ppm (t, J=6.9 Hz, 3H; Hf); 13C NMR
(101 MHz, C6D6): d=169.0 (q, C1), 166.0 (q, C6), 137.8 (t, C11), 137.8
(q, C4), 137.5 (q, C21), 136.5 (t, C5), 134.8 (q, C2), 134.0 (q, C23), 132.2
(t, C13), 131.0 (t, C3), 127.1 (t, C14), 125.4 (t, C22), 124.9 (t, C12), 121.9
(t, C24), 78.8 (t, C20), 78.2 (t, C17), 76.4 (t, C18), 73.6 (t, C8), 72.4 (t, C16),
71.3 (t, C10), 40.0 (t, C7), 38.3 (s, C9), 38.2 (t, C19), 32.8 (s, C15), 32.0 (s,
Cd), 29.8 (s, Cc), 29.2 (s, Ca), 28.3 (s, Cb), 24.3 (p, C23-Me), 23.0 (s, Ce),
15.4 (p, C21-Me), 15.4 (p, C25), 15.2 (p, C7-Me), 14.3 (p, Cf), 7.1 ppm (p,
C19-Me); HRMS (ESI): m/z calcd for C35H53NO8Na [M+Na]+: 638.3669;
found: 638.3657.
Keywords: antibiotics · lactones · natural products · synthesis
design · total synthesis
[1] H. Steinmetz, H. Irschik, B. Kunze, H. Reichenbach, G. Hçfle, R. Jansen,
Chem. Eur. J. 2007, 13, 5822–5832.
[2] a) M. Bock, R. Mꢀller, K. Buntin, A. Kirschning, Angew. Chem. Int. Ed.
2008, 47, 2308–2311; Angew. Chem. 2008, 120, 2341–2344; b) M. Bock,
R. Dehn, A. Kirschning, Angew. Chem. Int. Ed. 2008, 47, 9134–9137;
Angew. Chem. 2008, 120, 9274–9277.
[3] a) G. A. Zarate-Ruiz, R. M. de Figueiredo, G. Niel, J.-M. Campagn, Synlett
2012, 219–222; b) S. Tang, Z. Xu, T. Ye, Tetrahedron: Asymmetry 2009,
20, 2027–2032.
[4] A. Matsuzawa, C. R. Opie, N. Kumagai, M. Shibasaki, Chem. Eur. J. 2014,
20, 68–71.
[5] a) K. Buntin, H. Irschik, K. J. Weissman, E. Luxenburger, H. Blçcker, R.
Mꢀller, Chem. Biol. 2010, 17, 342–356; b) R. Jansen, B. Kunze, H. Irschik
EP2089025 B1 (published December 26th, 2012).
[6] H. Irschik, H. Reichenbach, G. Hçfle, R. Jansen, J. Antibiot. 2007, 60,
733–738.
Data for 24-methoxy-20-deshydroxyoxazole thuggacin B (45a,b):
1H NMR (500 MHz, MeOD): d=8.18 (s, 1H; H3), 7.91 (s, 1H; H5), 6.16
(dd, J=15.0, 11.6 Hz, 1H; H12), 6.04 (dd, J=11.6, 10.3 Hz, 1H; H13),
5.87 (s, 1H; H22), 5.56 (dd, J=15.0, 7.5 Hz, 1H; H11), 5.50 (ddd, J=
10.3, 10.5, 6.2 Hz, 1H; H14), 5.30 (d, J=9.6 Hz, 1H; H20), 5.02 (ddd,
J=6.3, 4.1, 2.4 Hz, 1H; H17), 3.92–3.85 (m, 3H; H18,H16, H8), 3.70 (q,
J=6.2 Hz, 1H; H24), 3.33–3.32 (m, 1H; H10), 3.19 (s, 3H; -OMe), 3.17
(dd, J=13.5, 7.1 Hz, 1H; H7), 2.77 (ddq, J=9.6, 6.8, 6.6 Hz, 1H; H19),
2.71 (ddd, J=13.2, 8.7, 6.4 Hz, 1H; Ha), 2.59 (ddd, J=14.2, 11.0,
10.5 Hz, 1H; H15a), 2.47 (ddd, J=13.2, 8.7, 6.4 Hz, 1H; Ha), 2.16 (dd,
J=14.2, 6.2 Hz, 1H; H15b), 1.86 (ddd, J=14.7, 8.3, 6.5 Hz, 1H; H9a),
1.76 (s, 3H; H21-Me), 1.73–1.72 (s, 3H; H23-Me), 1.66 (ddd, J=14.7, 4.9,
4.8 Hz, 1H; H9b), 1.60–1.32 (m, 8H; Hb-e), 1.41 (d, J=7.1 Hz, 3H;
H7-Me), 1.22 (d, J=6.2 Hz, 3H; H25), 1.11–1.09 (m, 3H; H19-Me),
0.91 ppm (t, J=6.9 Hz, 3H; Hf); 13C NMR (101 MHz, MeOD): d=
169.0 (q, C1), 167.6 (q, C6), 139.3 (t, C4), 137.3 (t, C11), 137.2 (q, C5),
136.5 (q, C23), 135.6 (q, C2), 134.1 (t, C20), 133.6 (q, C21), 132.6 (t, C22),
131.6 (t, C3), 131.2 (t, C13), 129.9 (t, C14), 127.4 (t, C12), 84.8 (t, C24),
78.2 (t, C17), 75.8 (t, C18), 73.4 (t, C8), 73.4 (t, C16), 70.0 (t, C10), 56.0
(p, -OMe), 41.9 (t, C7), 41.7 (s, C9), 36.7 (t, C19), 33.1 (s, C15), 32.9 (s,
Cd), 30.5 (s, Cc), 29.7 (s, Ca), 28.9 (s, Cb), 23.7 (s, Ce), 20.4 (p, C25), 17.6
(p, C23-Me), 16.4 (p, C19-Me), 16.3 (p, C7-Me), 14.4 (p, Cf), 12.2 ppm (p,
C21-Me); HRMS (ESI): m/z calcd for C36H55NO8Na [M+Na]+: 652.3825;
found: 652.3831.
[7] a) D. McKinney, Nat. Med. 2000, 6, 1330–1333; b) E. L. Corbett, C. J.
Watt, N. Walker, D. Maher, B. G. Williams, M. C. Raviglione, C. Dye, Arch.
Intern. Med. 2003, 163, 1009–1021.
[8] R. J. O’Brien, P. P. Nunn, Am. J. Respir. Crit. Care Med. 2001, 163, 1055–
1058.
[9] J. Barbier, J. Wegner, S. Benson, T. Pietschmann, J. Gentzsch, C. Zeilinger,
A. Kirschning, Chem. Eur. J. 2012, 18, 9083–9090.
[10] F. von Nussbaum, M. Brands, B. Hinzen, S. Weigand, D. Hꢄbich, Angew.
Chem. Int. Ed. 2006, 45, 5072–129; Angew. Chem. 2006, 118, 5194–
5254.
[11] a) A. M. Szpilman, E. M. Carreira, Angew. Chem. Int. Ed. 2010, 49, 9592–
9628; Angew. Chem. 2010, 122, 9786–9823; b) R. M. Wilson, S. J. Dani-
shefsky, J. Org. Chem. 2006, 71, 8329–8351.
[12] The mild Brønsted acid proved to be more suitable than CSA, which we
used in our previous studies (see ref. [2]).
[13] O-Methylation also provided two additional by-products, which could
be separated from the desired 17-O-methyl derivative by HPLC; see the
Supporting Information.
[14] Notably, all transformations involving acetonide formation and aceto-
nide cleavage under acidic conditions in alcoholic solvents (e.g., MeOH)
also yield open-chain esters in minor amounts, as exemplified for com-
pound 9.
[15] M. A. Blanchette, W. Choy, J. T. Davis, A. P. Essenfeld, S. Masamune, W. R.
Roush, T. Sakai, Tetrahedron Lett. 1984, 25, 2183–2186.
[16] G. Stork, K. Zhao, Tetrahedron Lett. 1989, 30, 2173–2174.
[17] A. Sakakura, R. Kondo, S. Umemura, K. Ishihara, Adv. Synth. Catal. 2007,
349, 1641–1646.
[18] R. Dehn, Diploma Thesis, Leibniz Universitꢄt Hannover, 2006.
[19] X. Shang, Y. Xiong, Y. Zhang, L. Zhang, Z. Liu, Synlett 2012, 259–262.
[20] I. Shiina, M. Kubota, R. Ibuka, Tetrahedron Lett. 2002, 43, 7535–7539.
[21] G. Burrell, J. M. Evans, G. E. Jones, G. Stemp, Tetrahedron Lett. 1990, 31,
3649–3652.
[22] K. Okura, S. Matsuoka, R. Goto, M. Inoue, Angew. Chem. Int. Ed. 2010,
49, 329–332; Angew. Chem. 2010, 122, 339–342.
[23] H. E. Gottlieb, V. Kotlyar, A. Nudelman, J. Org. Chem. 1997, 62, 7512–
7515.
[24] J. Leonard, B. Lygo, G. Procter, Praxis in der organischen Chemie, VCH,
Weinheim, 1996.
[25] P. Li, J. Li, F. Arikan, W. Ahlbrecht, M. Dieckmann, D. Menche, J. Org.
Chem. 2010, 75, 2429–2444.
Acknowledgements
The work was funded by graduate scholarships for R.D.
provided by the Stiftung Stipendien-Fonds des Verbandes der
Chemischen Industrie. In addition, S.B.M. and A.M. thank the
Alexander-von-Humboldt Foundation for postdoc scholarships.
Finally, an Evonik Industries scholarship for J.F. is gratefully ac-
knowledged. This work was supported by the computer cluster
funded by the Leibniz Universitꢄt Hannover, the Lower Saxony
Ministry of Science and Culture (MWK), and the German Re-
search Association (DFG). We thank Prof. Dr. Franz Bange (Med-
ical High School Hannover, MHH) for conducting biological
assays.
Received: October 29, 2014
Published online on && &&, 0000
Chem. Eur. J. 2015, 21, 1 – 14
www.chemeurj.org
13
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
FULL PAPER
Working hand in hand: Semi- and total
syntheses provide new derivatives of
thuggacins (see scheme), which are sec-
ondary metabolites from myxobacteria
that show good activity against Myco-
bacterium tuberculosis. O-Methylation at
C17 provided the first constitutionally
stable thuggacin A derivative that
retained the biological profile of
the thuggacins.
&
Synthesis Design
J. Franke, M. Bock, R. Dehn, J. Fohrer,
S. B. Mhaske, A. Migliorini, A. A. Kanakis,
R. Jansen, J. Herrmann, R. Mꢁller,
A. Kirschning*
&& – &&
Total and Semi-Syntheses of
Antimicrobial Thuggacin Derivatives
Synthesis Design
In their Full Paper on page && ff., A. Kirschning report the
semi-synthetic preparation of new macrocyclic thuggacin
derivatives that were modified in the side chain (C17–C25).
Evaluation of the antimicrobial activity revealed that
modifications of the side chain at C-16 were not tolerated.
When the hexyl side chain at C-2 was removed or the
thiazole ring was exchanged for an oxazole, the
antibacterial properties were retained, but with a substantial
drop in activity.
&
&
Chem. Eur. J. 2015, 21, 1 – 14
www.chemeurj.org
14
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!