Total syntheses of the thiopeptides smythiamicin C and D

Article abstract of DOI:10.1002/chem.201002144

The thiopeptides amythiamicin C and D were synthesized by employing amide bond formation, a Stille cross-coupling reaction, and two Negishi cross-coupling reactions as key transformations. The central 2,3,6-trisubstituted pyridine ring of the target compounds was introduced as a 2,6-dibromo-3-iodopyridine, which was selectively metalated at the 3-position and connected to the complete Southern fragment of the amythiamicins by a Negishi cross-coupling. For the synthesis of amythiamicin C, this step was followed by a Negishi cross-coupling at C-6 of the pyridine core. Subsequent attachment of the Eastern fragment was achieved by amide bond formation and macrolactam ring closure by a Stille cross-coupling at C-2. The Eastern bithiazole fragment of the amythiamins was constructed also by regioselective metalation and cross-coupling reactions. The pivotal step involved the diastereoselective addition of 4-bromothiazole-2- magnesium bromide to a chiral sulfinyl imine. For the synthesis of amythiamicin D, the order of cross-coupling at C-6, amide bond formation, and cross-coupling at C-2 was changed. The amide bond formation to the Eastern fragment was performed first and it was subsequently attempted to close the macrolactam by an intramolecular regioselective Stille cross-coupling at C-2. Despite the low regioselectivity of this reaction it paved the way to the immediate completion of the amythiamicin D synthesis when followed by a Negishi cross-coupling at C-6 with 2-zincated methyl thiazole-5-carboxylate. Cross-coupling reactions paved the way to two short syntheses of amythiamicin C (1) and D (2; see scheme). In the former synthesis, the sequence A-C-B was followed to give access to the title compound 1. In the latter synthesis, the sequence C-B-A was probed and led successfully to amythiamicin D (2) in an extremely short, but less selective, synthetic sequence.

Full text of DOI:10.1002/chem.201002144

FULL PAPER
DOI: 10.1002/chem.201002144
Total Syntheses of the Thiopeptides Amythiamicin C and D
[
a]
Carolin Ammer and Thorsten Bach*
Abstract: The thiopeptides amythiami-
tachment of the Eastern fragment was
achieved by amide bond formation and
macrolactam ring closure by a Stille
cross-coupling at C-2. The Eastern bi-
thiazole fragment of the amythiamins
was constructed also by regioselective
metalation and cross-coupling reac-
tions. The pivotal step involved the dia-
stereoselective addition of 4-bromo-
of amythiamicin D, the order of cross-
coupling at C-6, amide bond formation,
and cross-coupling at C-2 was changed.
The amide bond formation to the East-
ern fragment was performed first and it
was subsequently attempted to close
the macrolactam by an intramolecular
regioselective Stille cross-coupling at
C-2. Despite the low regioselectivity of
this reaction it paved the way to the
immediate completion of the amythia-
micin D synthesis when followed by a
Negishi cross-coupling at C-6 with 2-
zincated methyl thiazole-5-carboxylate.
cin C and D were synthesized by em-
ploying amide bond formation, a Stille
cross-coupling reaction, and two Ne-
gishi cross-coupling reactions as key
transformations. The central 2,3,6-tri-
substituted pyridine ring of the target
compounds was introduced as a 2,6-di-
bromo-3-iodopyridine, which was selec-
tively metalated at the 3-position and
connected to the complete Southern
fragment of the amythiamicins by a
Negishi cross-coupling. For the synthe-
sis of amythiamicin C, this step was fol-
lowed by a Negishi cross-coupling at C-
thiazole-2-magnesium bromide to
a
chiral sulfinyl imine. For the synthesis
Keywords:
cross-coupling
antibiotics
macrocycles
·
·
·
natural products · total synthesis
6
of the pyridine core. Subsequent at-
Introduction
dine core surrounded by six thiazole moieties, five of which
form together with other amino acid fragments a macrolac-
tam ring connecting positions C-2 and C-3 of the pyridine
ring. The sixth thiazole ring G is bound by its carbon atom
C-2 (thiazole numbering) to carbon atom C-6 of the pyri-
dine (pyridine numbering). The amythiamicins differ in the
substituents R at the latter thiazole ring. In amythiamicin D
(4) the substituent is a plain methoxycarbonyl group. In
amythiamicin B (2) the substituent is a serine-prolinamide
dipeptide, the serine part of which is condensed to an oxazo-
Amythiamicins A (1), B (2), C (3), and D (4) were isolated
in 1994 by Takeuchi et al. from the fermentation broth of
[1]
Amycolatopsis sp. MI481-42F4. The microorganism was
found in soil samples collected in Nerima-ku, Tokyo
Japan). The amythiamicins belong to an increasing class of
complex naturally occurring, sulfur-containing macrocyclic
peptides called thiopeptides or thiazolyl peptides. The
structure of the amythiamicins was elucidated by chemical
degradation and NMR spectroscopic analysis. Degradation
studies were performed by hydrolysis of the individual amy-
thiamicins with 6n HCl. Subsequent esterification and N-
acetylation delivered the N-acetyl-O-methyl derivatives,
(
[2]
[1]
which were studied by NMR and UV/Vis spectroscopy.
Structurally, all amythiamicins exhibit a trisubstituted pyri-
[
a] Dr. C. Ammer, Prof. Dr. T. Bach
Lehrstuhl fꢀr Organische Chemie I
Technische Universitꢁt Mꢀnchen, Lichtenbergstr. 4
8
5747 Garching (Germany)
Fax : (+49)89-289-13315
E-mail: thorsten.bach@ch.tum.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201002144.
Chem. Eur. J. 2010, 16, 14083 – 14093
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
14083

line in amythiamicin A (1). Amythiamycin C (3) carries the
serine-prolinamide fragment as the serine ester with a dike-
topiperazine being formed between the proline and serine
amino acid fragments.
Biological interest in the amythiamicins stems from their
inhibition potential toward the bacterial elongation factor
[3]
EF-Tu. Proof for their antibacterial activity has been ob-
[4]
tained already in 1997 by a paper disc diffusion assay. In
addition, it was found that the plastid of P. falciparum, the
metabolism of which is closely related to a bacterium and
which is essential for survival of the malaria parasite, is in-
hibited by amythiamicins, most notably by amythiamicin A
Scheme 1. Key fragments 5–7 in the retrosynthetic analysis of amythiami-
cins C and D according to a regioselective cross-coupling protocol.
[5]
(
IC =10 nm). Inhibition of EF-Tu is a likely pathway for
50
the mode of action also in this case.
The first total synthesis of an amythiamicin, amythiamicin
coupling at C-6 (py C-6) and amide bond (amide) formation
by an intramolecular Stille cross-coupling (py C-2). Alterna-
tively, one could consider the amide bond formation to be
conducted first with a regioselective macrocyclization to
follow. Either way, a stannylated fragment, such as 6, would
be required for the synthesis of the amythiamicins. It exhib-
its an amino-substituted stereogenic center, which would be
possibly introduced through the previously unknown build-
ing block 7.
[6]
D (4), was achieved by Moody et al. in 2004. The key step
was a biomimetic hetero-Diels–Alder reaction of an enam-
ide and an azadiene, which was used for the construction of
the central pyridine ring. Nicolaou, Chen et al. reported in
[7]
2
008 the total syntheses of amythiamicins A–C (1–3) by
employing a key step earlier established for the construction
[8]
of the central pyridine core of thiostreptone and GE
[9]
2
270A. In this case, a hetero-Diels–Alder reaction oc-
curred as a 2-azadiene dimerization, which was induced by
thermolysis of an appropriate precursor. The formation of
the macrocylic ring was in both synthetic approaches to the
amythiamicins achieved by macrolactamization, either at the
amide bond connecting the glycine to thiazolecarboxylic
In this account we report on the total synthesis of amy-
thiamicins C (3) and D (4). The synthesis of amythiamicin C
(3) was accomplished by following the precedented bond-
formation sequence (py C-6, amide, py C-2), whereas in the
synthesis of amythiamicin D (4) the alternative sequence
(amide, py C-2, py C-6) was probed. An access to enantio-
merically pure compound 7 was established allowing its in-
stallation in the bithiazole core of compound 6. An im-
proved procedure for the preparation of 2,6-dibromo-3-io-
dopyridine was established and applied to the synthesis of
the key intermediate 5.
[6]
acid D or at the amide bond connecting the thiazole frag-
[7]
ments E and F. Other strategies and total syntheses of
[2,10,11]
thiopeptide antibiotics have been reviewed extensively.
The most notable recent achievement has been the synthesis
and stereochemical assignment of micrococcin P1 by Ciufo-
lini and Lefranc, in which the central pyridine ring was con-
[12]
structed by a Hantzsch synthesis.
Our own synthetic work in the area of thiopeptides was
triggered by methodology studies concerning the regioselec-
Results and Discussion
[13]
tivity of cross-coupling reactions on certain heterocycles,
specifically on pyridines and thiazoles. A strategy for the
Preparation of the Southern fragment and cross-coupling to
key intermediate 5: The Southern fragment of the amythia-
micins consists of three thiazole-containing fragments that
are connected by amide bonds. Bond disconnection at these
positions leads retrosynthetically to the three fragments 8,
11, and 13 depicted in Scheme 2. 2-Iodothiazole 13 contains
[14]
preparation of 2’,4-disubstituted 2,4’-bithiazoles
was im-
plemented in the total synthesis of cystothiazole E and the
[15]
formal syntheses of cystothiazoles A and C. The regiose-
lective assembly of 2,3,6-trisubstituted pyridines was first
probed in the synthesis of a degradation product of GE
2
270A, which served to establish the relative configuration
the iodine atom as a potential leaving group in the cross-
[16]
[17b]
of this thiopeptide,
and was later employed in its total
coupling event and has been previously prepared.
The
[17]
[18]
[19]
synthesis. In the latter synthesis, 2,6-dibromo-3-iodopyri-
dine had served as a central ring template to which the indi-
vidual parts of the thiopeptide were attached. Following this
strategy it was anticipated that a similar bond construction
was possible also for the synthesis of the amythiamicins
syntheses of compounds 8 and 11 are also precedented
and start from the respective amino acid derived building
blocks 10 and 12. Monobenzyl ester 10 is obtained in two
[20]
steps from aspartic acid.
N-tert-Butoxycarbonyl (Boc)-
protected valine (12) is commercially available or can be
[21]
(
Scheme 1). With compound 5 as a key intermediate it was
prepared from valine in one step.
planned to conduct subsequent reactions at the indicated
positions by cross-coupling at the pyridine core and by
amide bond formation.
In the synthesis of GE 2270A it was shown that macro-
lactam ring formation can be favorably achieved after cross-
The synthesis of valine-based thiazole 11 with a Hantzsch
thiazole reaction as a key step proceeded racemization-free
as proven by chiral HPLC analysis. However, it was found
in the Gabriel synthesis employed for the thiazole bond con-
struction from intermediate 9 that racemization was not
[17]
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Chem. Eur. J. 2010, 16, 14083 – 14093

Total Syntheses of the Thiopeptides Amythiamicin C and D
FULL PAPER
coupling. Earlier work had revealed that 2,6-dibromo-3-io-
dopyridine (17) is a superior precursor in the metalation
[17]
step relative to 2,3,6-tribromopyridine. Selective access to
this compound is best achieved from 3-aminopyridine (16,
[24]
Scheme 4). We found the bromination with N-bromosuc-
cinimide (NBS) to occur beneficially in acetonitrile relative
to tetrachloromethane providing 3-amino-2,6-dibromopyri-
dine in 58% yield. Subsequent iodo-de-amination turned
out to proceed smoothly and delivered pyridine 17 in 71%
yield (41% overall).
Scheme 2. The three building blocks 8, 11, and 13 required for the con-
struction of the Southern fragment of the amythiamicins and their key
precursors.
completely suppressed. A closer inspection of the reaction
conditions revealed that the quality of the Lawesson reagent
was critical to the success of the reaction. With commercial-
ly available reagent, which showed an acidic pH of 2, the
product was obtained in only 66% ee. Recrystallization of
the reagent from toluene increased the pH to 6 and the sub-
Scheme 4. Preparation of 2,6-dibromo-3-iodopyridine (17), its zincation,
and cross-coupling to iodothiazole 15.
[22]
sequent Gabriel reaction proceeded in 88% ee.
The assembly of the individual building blocks was per-
formed under typical peptide coupling conditions by em-
ploying N-(3-dimethylaminopropyl)-N’-ethyl-carbodiimide
hydrochloride (EDC) in the presence of 1-hydroxybenzo-
Reductive metalation of 3-iodopyridine 17 was performed
according to the Knochel protocol in N,N-dimethyl acet-
[25]
amide (DMA). Zincated iodide underwent a clean Negishi
[26]
cross-coupling reaction with iodide 15 at 458C in a solvent
mixture of THF/DMA by using [Pd (dba) ]/tfp (12 mol%
[23]
triazole (HOBt) as the reagent (Scheme 3). The substrates
and reagents were mixed at ꢀ108C and the mixture was
subsequently stirred at ambient temperature. Dipeptide 14
was deprotected at its N-terminus under acidic conditions
and the coupling to thiazole carboxylic acid 13 proceeded
smoothly under the conditions previously employed for the
ACHTUNGTRENNUNG
2
3
Pd) as the catalyst (dba=dibenzylidenacetone, tfp=tri ACHTUNGTRENNUNG( 2-
furyl)phosphane). The effectivity of the Negishi cross-cou-
pling reaction is undermined by the high yield achieved in
this reaction. Nonetheless, the process turned out to be
somewhat more capricious than previously conducted cross-
coupling reactions because starting material 15 and product
5 could not be separated by TLC. The reaction had to be
followed by analytical HPLC and the addition of zincated
pyridine was required in some instances to make the conver-
sion complete. Along the longest linear sequence starting
from known building block 8 diastereomerically pure prod-
uct 5 was obtained in four steps and an overall yield of
45%.
[17]
synthesis of 14.
Due to the incomplete enantiomeric
purity of asparagine-derived building block 8 (see above),
the target compound 15 was contaminated with minor
amounts of its epimer. A chromatographic separation of the
diastereomers could be achieved at this stage. The yield
given in Scheme 3 refers to diastereomerically pure product
15.
A pivotal step of our synthetic strategy towards the amy-
thiamicins was the connection of the complete Southern
fragment 15 to the central pyridine core by a Negishi cross-
Preparation of thiazole 7 and the complete bithiazole frag-
ment 6: Based on our previous experience with the genera-
tion of a 2-metalated thiazole 18 from 2,4-dibromothiazole
[27]
(
19) and based on the plan to set up the 2,4’-connectivity
in bithiazole building block 6 by regioselective cross-cou-
[16]
pling
possible chiral imine equivalents were considered,
which would give access to the enantiopure amine 7
(
Scheme 5). Since Grignard reagent 18 had been shown to
[27]
react nicely with nitriles
it was expected that it would
equally well add to the more electrophilic imines. In a semi-
nal report, oxime ether 20 was described by Moody et al. to
[28]
react with a 2-lithiated thiazole diastereoselectively. De-
spite the efficiency of this method, the reductive conditions
required for cleavage of the chiral auxiliary (Zn, HOAc)
were considered to be incompatible with the bromine atom
in the 4-position. The addition of Grignard reagents to
Scheme 3. Preparation of the trithiazole 15, the Southern fragment re-
quired for cross-coupling with the pyridine core of the amythiamicins.
[29]
chiral sulfinyl imines as described by Ellman et al. offered
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14085

T. Bach and C. Ammer
final solvent mixture. It is likely that the tight six-membered
[29]
transition state responsible for successful chirality transfer
is disfavored in coordinating ethereal solvents. Employing a
concentrated solution (c=2.5m) of the Grignard reagent in
diethyl ether with an eventual ratio of CH Cl /diethyl ether
2
2
2
7.5:1 in the reaction mixture, a d.r. of 85:15 was achieved.
Upon recrystallization from tert-butylmethyl ether and cy-
clohexane, the desired product 22 was obtained in a diaste-
reomerically pure form (d.r.>95:5). Cleavage of the auxili-
ary was achieved by treatment of sulfinyl amine 22 with
HCl in a mixture of methanol/dioxane delivering the hydro-
chloride of amine 7. The absolute configuration of the
amine was proven by N-Boc protection and debromination.
The resulting N-Boc protected (S)-configured amine is liter-
Scheme 5. Retrosynthetic consideration for the construction of product 7
and synthetic equivalents 19 and 20 for a chiral isobutyraldehyde imine.
a viable alternative approach. More specifically, it was envi-
sioned to convert thiazole 19 into the respective Grignard
reagent 18, which would then react with imine 21 in a dia-
stereoselective fashion. While our work was in progress a
[31]
ature known and was reported to be levorotatory.
The
[30]
publication appeared in which it was reported that a dia-
stereoselecitive addition of this kind is possible for related
selectively metalated heterocycles, but not referring to our
earlier work on the preparation and addition reactions of re-
agent 18.
compound we obtained was also levorotarory and showed a
specific rotation in accord with the literature data. The
result is in line with the earlier transition-state model for
[29]
the addition to chiral sulfinyl imines, such as 21.
Amine 7 was coupled with 9-fluorenylmethyloxycarbonyl
(Fmoc)-protected glycine (Fmoc-Gly-OH) by using bromo-
tri(pyrrolidino)phosphonium hexafluorophosphate (PyBrop)
Based on literature precedence, in which phenyl magnesi-
um bromide was added to imine 21 yielding the (S)-enantio-
meric amine predominantly (diastereomeric ratio d.r.
[32]
as the coupling reagent. For the further assembly of key
[29c]
[33]
89:11),
the (S)-configured sulfinyl amide was chosen as
intermediate 6, a regioselective Stille reaction with 2,4-di-
[14]
an auxiliary and condensed with isobutyric aldehyde to yield
imine 21. Grignard reagent 18 was generated from dibromo-
thiazole 19 by regioselective bromine–magnesium ex-
bromothiazole (19) was performed upon converting 4-bro-
mothiazole 23 to the respective stannane by a Pd-catalyzed
[34]
stannyl-debromination with hexamethylditin. For the stan-
nylation, a high temperature (1008C) and a short reaction
time (1.5 h) proved to be beneficial. The brominated dithia-
[27]
change
Scheme 6). Initial experiments were disappointing deliver-
ing the desired addition product 22 with a d.r. slightly above
0:50 irrespective of whether the Grignard reagent was pre-
and added to a solution of imine 21 in CH Cl
2 2
(
[35]
zole 24 was subjected to a second stannyl-debromination
providing building block 6 in a N-protected form. The over-
all yield for the transformation of isobutyraldehyde to com-
pound 6 was 47% over six reaction steps.
5
pared in THF or diethyl ether. It turned out that it was cru-
cial for a high selectivity to increase the concentration of
the Grignard reagent in the etheral solvent to as high a level
as possible and to maintain a large excess of CH Cl in the
Synthesis of amythiamicin D (4): After liberating the car-
boxylic acid of the Southern fragment 5 by saponification
and after N-Fmoc deprotection of the amine protecting
group in the Eastern fragment 6 (Scheme 6), the two frag-
ments were coupled with diphenylphosphoryl azide
2
2
[36]
(
DPPA) and Hꢀnigꢃs base in DMF (Scheme 7). By using
a slight excess of amine 25, the complete peptide backbone
6 of the amythiamicin macrolactam was assembled. Stille
2
cross-coupling reactions were attempted to connect the stan-
nylated bithiazole intramolecularly to the central dibromo-
pyridine core. Cylization reactions were indeed observed, if
the reaction was conducted under dilute conditions (c=
1
2
mm) in toluene. For the separation of the two regioisomers
7 and 28, the solvent system had to be carefully chosen and
the solid phase had to be mixed with potassium fluoride
[37]
(
10% w/w) to remove any tin impurities.
The constitution assignment of the two regioisomers was
[16]
based on earlier work, in which we had seen that related
1
2
,3-disubstituted 6-bromopyridines exhibit a strong H NMR
spectroscopic upfield shift for the protons at C-5 and C-4
relative to the competitively formed 3,6-disubstituted 2-bro-
mopyridines (e.g. d=7.61 vs. 8.33 ppm at C-5 and d=8.27
vs. 8.54 ppm at C-4). In the present case, one regioisomer
Scheme 6. Synthesis of the Eastern fragment 24 of the amythiamicins em-
ploying 2,4-dibromothiazole (19) as a key building block.
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Chem. Eur. J. 2010, 16, 14083 – 14093

Total Syntheses of the Thiopeptides Amythiamicin C and D
FULL PAPER
Scheme 8. Completion of the total synthesis of amythiamicin D (4).
the final thiazole to carbon atom C-6 of the pyridine core
were promising (Scheme 8). It was therefore initially consid-
ered to attach the complete Northern fragment of amythia-
micin C to bromopyridine 27 in a Negishi cross-coupling re-
action. The requisite bromo- and iodothiazoles 32 and 33
were readily accessible from the corresponding carboxylic
[38]
acids 30 and 13 by esterification with known alcohol 31.
mixture of EDC and N,N-dimethylaminopyridine
DMAP) turned out to be an excellent reagent combination
Scheme 7. Intramolecular Stille cross-coupling reaction employing 2,6-di-
bromopyridine 26 as the starting material.
A
(
to achieve this conversion in almost quantitative yields
(Scheme 9). Despite extensive experimental effort it was,
1
showed H NMR spectroscopic signals for these protons at
d=7.56 (C-5) and 7.82 ppm (C-4), whereas the other re-
gioiosmer displayed resonances at d=8.03 (C-5) and
8.55 ppm (C-4). Structure 28 was consequently assigned to
the latter regioisomer and—in agreement with its further
conversion into amythiamicin D (see below)—structure 27
to the former regiosiomer. A significant regioselectivity was
unfortunately not detected. Both regioisomers formed in
almost identical amounts but could be fully separated. The
desired regioisomer 27 was so obtained in 28% yield with
Scheme 9. Preparation of the Northern fragments 32 and 33 of amythia-
micin C.
[
Pd ACHTUNGTRENNUNG( PPh ) ] as the catalyst at 858C in toluene. Apparently,
3 4
the ring closure at C-2 to the naturally occurring macrolac-
tam, which was considered to be favorable by conformation-
al factors and due to a templating effect by the metal, com-
petes successfully with the sterically favored cross-coupling
reaction at C-6. It is, however, not able to dominate the re-
action course. Rather, both factors are perfectly balanced. A
beneficial aspect of the chosen sequence was the fact that
the last cross-coupling reaction proceeded smoothly provid-
ing the desired product amythiamicin D in 96% yield.
however, not possible to convert bromide 32 or iodide 33
into the respective zinc reagent. Decomposition was ob-
served under conditions of direct zincation and halogen–
metal exchange. In some instances, the amino alcohol 31
was recovered. N-Boc protection of the acidic NH group in
the diketopiperazine part of 32 and 33 did not improve the
stability of the substrates in the zincation step.
Insufficient separation of minor quantities of triphenyl-
phosphane oxide by flash chromatography forced us to use
semipreparative HPLC to obtain a pure sample of the natu-
ral product limiting the yield in the final step (Scheme 8) to
The instability of the complete Northern fragment of
amythiamicin C towards zincation made us return to a
[17]
better precedented
strategy for its preparation
(Scheme 10). To this end, dibromopyridine 5 was regioselec-
tively coupled with the 2-zincated tert-butyl thiazole-5-car-
boxylate (34). It was expected that intermediate 35 would
allow for the installation of the Eastern fragment 25 and
ring closure as well as—after tert-butyl deprotection—for at-
tachment of alcohol 31.
Indeed, after saponification of ethyl ester 35 to the free
carboxylic acid 36 the Eastern fragment 25 could be at-
tached by peptide coupling with DPPA and Hꢀnigꢃs base in
43%. Further optimization attempts to find an improved
method for the impurity removal were not possible due to
the limited material available.
Synthesis of amythiamicin C (3): Although the intramolecu-
lar cross-coupling reaction of dibromopyridine 26 was not
regioselective, the access to key intermediate 27 was rapid
(
Scheme 7) and the results regarding the cross-coupling of
Chem. Eur. J. 2010, 16, 14083 – 14093
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14087

T. Bach and C. Ammer
after work-up. In addition, some phosphane oxide impurities
were visible, which had apparently remained from the cross-
coupling step. For the sake of purity, we therefore decided
to run the reaction without major purification by starting
from intermediate 37 and attempted a purification step by
HPLC at the end of the three-step sequence. In the purifica-
tion procedure alcoholic solvents should be avoided because
the ester group of amythiamicin C (3) is labile towards
transesterification. Attempted HPLC purification on a re-
verse-phase column with MeOH/H O as the eluent led to
2
the isolation of amythiamicn D (4) but did not lead to any
recovery of 3. The fragility of product 3 did limit the yield,
with which it was eventually obtained along the three-step
procedure to 20%. Overall, however, the yield of amythia-
micn C (3) by starting from imine 21 is relatively high with
Scheme 10. Regioselective intermolecular Negishi cross-coupling of zinc
reagent 34 and 2,6-dibromopyridine 5 and subsequent saponification of
product 35.
5
.8% over a total of eleven linear steps.
The spectral data of synthetic amythiamicins C (3) and D
DMF. The macrolactam was formed by an intramolecular
Stille cross-coupling reaction at the 2-position of pyridine 37
in 79% yield. Subsequent functional-group transformations
included the hydrolysis of tert-butyl ester 38 and attachment
of the diketopiperazine 31 to the free acid 39. Whereas the
ester hydrolysis proceeded uneventfully, the esterification of
free acid 39 caused some purification problems
(4) matched the reported data perfectly (see the Experimen-
tal Section). The spectra of amythiamicin C (3) were record-
ed in CDCl3 instead of the previously used [D ]pyridine.
5
The former solvent allowed us to re-isolate the material
more readily and to employ it for biological tests. Assign-
ments are based on previously reported studies and on the
analogy of amythiamicins C (3) and D (4) in the macrolac-
tam core.
(
Scheme 11).
Alcohol 31 had to be used in excess (5 equiv) to achieve
quantitative conversion to amythiamicin C (3), but could
not be completely removed by column chromatography
Conclusion
In summary, two approaches were pursued for the synthesis
of amythiamicins, both of which rely on regioselective cross-
coupling reactions. In the first approach it was attempted to
differentiate the 2- and 6-position of a 3-substituted 2,6-di-
bromopyridine (substrate 26) by an intramolecular Stille
cross-coupling reaction. The reaction turned out to be possi-
ble but there was no significant regioselectivity. Cross-cou-
pling reactions were observed at both positions delivering
the two regioisomeric products 27 and 28 in moderate yield
(
56%). Nonetheless, intermediate 27 served as a very useful
intermediate for the synthesis of amythiamicin D (4) allow-
ing for its total synthesis in only ten steps with 4.5% yield
along the longest linear sequence. For amythiamicin C (3), a
second approach was taken, in which an intermolecular Ne-
gishi cross-coupling served to differentiate the 2- and 6-posi-
tion of a 3-substituted 2,6-dibromopyridine (substrate 5). By
this means the thiazole of the Northern fragment was selec-
tively installed at the 6-position. Subsequent attachment of
the Eastern fragment and an intramolecular Stille cross-cou-
pling delivered the desired product, amythiamicin C (3), in a
highly convergent fashion.
Experimental Section
General: All reactions involving water-sensitive chemicals were carried
out in flame-dried glassware with magnetic stirring under argon. THF, di-
Scheme 11. Completion of the total synthesis of amythiamicin C (3).
2 2 2
ethyl ether (Et O), and dichloromethane (CH Cl ) were purified by using
14088
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 14083 – 14093

Total Syntheses of the Thiopeptides Amythiamicin C and D
FULL PAPER
a SPS-800 solvent purification system (M. Braun). Diisopropylamine was
distilled over calcium hydride. All other chemicals were either commer-
cially available or prepared according to the cited references. TLC was
performed on silica-coated glass plates (silica gel 60 F254) with detection
C-5), 127.7 (d; A: C-5), 130.1 (s; A: C-3), 138.8 (s; A: C-2)*, 141.1 (d; A:
#
#
C-4), 141.3 (s; A: C-6)*, 141.9 (s; E: C-5) , 142.1 (s; E: C-4) , 146.3 (s; D:
C-4), 149.6 (s; F: C-4), 160.4 (s; F: CO), 161.4 (s; D: COO), 161.8 (s; F:
C-2), 162.1 (s; E: CO), 166.5 (s; E: C-2), 170.7 (s; D: C-2), 171.3 ppm (s;
by UV (254 nm) or KMnO
4
(0.5% in water) with subsequent heating.
E: CONHCH
3
); IR (ATR): n˜ =3785 (w; NH), 2346 (m), 1712 (m; CO),
Flash chromatography was performed on silica gel 60 (Merck, 230–400
mesh) with the indicated eluent. Common solvents for chromatography
1650 (s; CONH), 1549 (m), 1486 (s; CH), 1367 (m), 1331 (m), 1215 (m),
ꢀ
1
1163 (m), 1020 (w), 755 cm
(w); HRMS (ESI): m/z: calcd for
+
(
pentane (P), ethyl acetate (EtOAc), diethyl ether (Et
2
O), dichlorome-
28 2 7 5 3
C H30Br N O S
: 797.9837 [M+H] ; found: 797.9841.
thane, methanol (MeOH)) were distilled prior to use. HPLC analyses
were performed by using the stationary phases AD-RH Daicel, ODS-A
YMC, OD Daicel Chiracell, or AD-H Daicel Chirapak (analytical: 250ꢄ
(S)-N-[(S)-1-(4-Bromothiazole-2-yl)-2-methylpropyl]-2-methylpropan-2-
sulfinamide (22)
Imine 21:
8
A
suspension of (S)-tert-butylsulfinamide (1.00 g,
.25 mmol), isobutyraldehyde (828 mL, 654 mg, 9.07 mmol), and anhy-
drous cesium carbonate (5.91 g, 18.1 mmol) in CH Cl (16.5 mL) was
stirred for 16 h at 458C. The reaction mixture was filtered over a pad of
Celite, the filter cake was washed with CH Cl (2ꢄ5 mL), and the residue
purified by flash chromatography (3ꢄ15 cm, CH Cl ). The solvent was
4
.6 mm, 5 mm; semi-preparative: 250ꢄ20 mm, 5 mm) employing n-hexane/
[29]
i-propanol, methanol/water, or acetonitrile/water as eluents and UV-de-
tection at 208C. IR: JASCO IR-4100 (ATR). GCMS: Agilent 6890 in-
strument with Agilent N7873 mass detection, carrier gas: Helium
2
2
2
2
(
method: 608C, 3 min; 608C ! 3008C, 16 min; 3008C, 5 min). MS/
2
2
HRMS: Finnigan MAT 8200 (EI)/Finnigan MAT 95S (HR-EI)/Finnigan
removed under reduced pressure (400 mbar) to give imine 21, which was
used directly in the diastereoselective addition reaction.
1
LCQ classic (ESI)/Thermo Finnigan LTQ FT (HRMS-ESI). H and
1
3
C NMR spectra: Bruker AV-250, Bruker AV-360, Bruker AV-500,
Bruker AV-600 recorded at 303 K. Chemical shifts are reported relative
Diastereoselective addition: A solution of isopropylmagnesiumbromide
(
4.8 mL, 3.45m in diethyl ether) was added slowly to a stirred solution of
1
3
to tetramethylsilane. The multiplicities of the C NMR signal were deter-
mined by DEPT experiments, assignments are based on COSY, HMBC,
and HMQC experiments. H or C NMR spectroscopic signals are usual-
ly assigned by using significant short sections of the molecular formula.
Heteroaromatic and aromatic signals are assigned by using the respective
atom numbers according to IUPAC rules and the letters A–F as depicted
in the schemes. The symbols , *, , and denote interconvertible assign-
ments. Optical rotations were measured by using a Perkin–Elmer 241
MC Polarimeter. Elemental analyses were carried out on a Elementar
Vario EL in the Department Chemie at the Technische Universitꢁt Mꢀn-
chen.
[39]
2
,4-dibromothiazole (18) (4.01 g, 16.5 mmol) in diethyl ether (1.8 mL).
After stirring for 30 min at 08C, the Grignard reagent solution was added
to a stirred solution of sulfinyl imine 21 (8.25 mmol) in CH Cl (50 mL)
1
13
2
2
at ꢀ488C. After 2 h at ꢀ488C, the reaction mixture was allowed to reach
room temperature over a period of 12 h. The reaction was quenched by
adding saturated NH
aqueous layer was extracted with ethyl acetate (2ꢄ50 mL) and the com-
bined organic layers were dried with Na SO . After filtration, the solvent
4
Cl solution (50 mL) and ethyl acetate (50 mL). The
#
§
~
2
4
was removed under reduced pressure. The crude product was purified by
flash chromatography (P/EtOAc 1:1!1:2) to yield (2.50 g, 7.36 mmol,
8
9%, 70% de) N-[(1-(4-bromothiazole-2-yl)-2-methylpropyl]-2-methyl-
Ethyl-(S,S)-2-{1-[(2-{1-[(2-(2,6-dibromopyridine-3-yl)thiazole-4-carbonyl)-
amino]-2-methylcarbamoyl-ethyl}-5-methylthiazole-4-carbonyl)amino]-2-
methylpropyl}thiazole-4-carboxylate (5)
propan-2-sulfinamide as a mixture of two diastereoisomers. Single recrys-
tallisation (tert-butyl methyl ether/cyclohexane) yielded 2.02 g
(5.97 mmol, 72%, >95% de) of the major diastereoisomer 22. M.p.
Zincation: DMA (0.76 mL) and 1,2-dibromoethane (7.13 mL, 15 mg, 87.7
mmol) were added to a flame-dried flask charged with zinc dust (53 mg,
918C; R
f
=0.24 (P/EtOAc 1:1; UV); [a]
D
=+35.4 (c=1.1 in CHCl
3
);
),
3 3
) ), 2.24–2.33 (m,
1
3
H NMR (CDCl
3
, 360 MHz): d=0.94 (d, J=8.3 Hz, 3H; CH
0.96 (d, J=8.3 Hz, 3H; CH(CH ), 1.27 (s, 9H; C(CH
), 4.16 (d, J=8.1 Hz, 1H; NH), 4.39 (dd, J=8.1, 5.8 Hz,
3 2
ACHTUNGTRENNUNG( CH )
3
0
.817 mmol). The zinc suspension was shortly heated with a heat gun
A
H
U
G
R
N
U
G
3
)
2
A
H
U
G
R
N
U
G
3
3
until evolution of ethylene occurred and then allowed to reach ambient
temperature. This procedure was repeated three times. TMSCl (23.8 mL,
1H; CH
1H; CHNH), 7.16 ppm (s, 1H; H-5); C NMR (CDCl
7.9 (q; CH(CH ), 19.3 (q; CH(CH ), 22.8 (s; C(CH
(CH ), 56.7 (s; C(CH ), 63.5 (d; CHNH), 116.8 (d; C-5), 124.8 (s; C-
3 2
ACHTUNGRTNNGE(U CH )
1
3
3
, 90 MHz): d=
3 3
) ), 35.0 (d; CH-
1
A
H
U
G
R
N
U
G
3
)
2
A
H
U
G
R
N
U
G
3
)
2
A
H
U
G
E
N
N
2
0 mg, 0.186 mmol) was added neat and the reaction mixture was stirred
A
H
U
G
R
N
N
3
)
2
A
H
U
G
R
N
U
G
3 3
)
for 5 min. 2,6-Dibromo-3-iodopyridine (17) (99 mg, 0.272 mmol) dis-
solved in THF (0.47 mL) was added. The stirring was continued for
+
4
), 172.5 ppm (s; C-2); MS (EI, 70 eV): m/z: (%): 307 (1) [MꢀS] , 295
+
+
(
(
1) [MꢀC
2
H
H
6
+
N] , 284 (24) [MꢀC
4 7
H ] , 221 (82), 206 (34), 191 (8), 57
3
0 min at 258C, then the zinc dust was allowed to settle (30 min).
Negishi cross-coupling: The supernatant liquid containing the zincated
dibromopyridine was added to solution of trithiazole 15 (47 mg,
] (3.7 mg, 4.08 mmol, 6 mol%), and tfp (47 mg,
8.0 mmol, 12 mol%) in THF (0.51 mL). The reaction mixture was stirred
+
100) [C
4
9 2 3
], 41 (32) [C H N ]; elemental analysis calcd (%) for
11 2 2
C H19BrN OS (339.32): C 38.94, H 5.64, N 8.26; found: C 39.23, H 5.58,
N 8.16.
a
6
6
2 3
8.0 mmol), [Pd ACHTUNGTRENNUNG( dba)
2-[(1S)-1-({[2-(2,6-Dibromopyridine-3-yl)-thiazole-4-yl]carbonyl}amino)-
3-(methylamino)-3-oxopropyl]-5-methyl-N-((1S)-2-methyl-1-{4-[4-({(1S)-
2-methyl-1-[4-(trimethylstannyl)-2,4’-bithiazole-2’-yl]propyl}amino)-2-
at room temperature (12–24 h) until full conversion was achieved (moni-
tored by HPLC). After quenching with saturated aq. NH Cl (4 mL), the
aqueous layer was extracted with EtOAc (3ꢄ5 mL). The combined or-
ganic layers were dried (Na SO ) and concentrated in vacuo. The crude
product was purified by flash chromatography (EtOAc) to yield the de-
sired product 5 (43 mg, 53.8 mmol, 79%) as a grey solid. M.p. 1138C; R
4
oxo-ethylamino]-thiazole-2-yl}propyl)thiazole-4-carboxamide (26)
Saponification: Aqueous lithium hydroxide solution (1m; 0.5 mL,
0.500 mmol) was added to a solution of the ethyl ester 5 (40 mg,
50.0 mmol) in tBuOH (0.5 mL) and THF (0.5 mL) at room temperature.
The reaction mixture was stirred at room temperature for 2 h, concen-
2
4
f
=
2
D
0
1
0
3
6
2
.36 (EtOAc; UV); [a] =ꢀ22.1 (c=1.0 in CHCl
3 3
); H NMR (CDCl ,
3
3
60 MHz): d=0.98 (d, J=6.5 Hz, 3H; D: CH
A
H
U
G
R
N
N
(CH
3
)
2
), 1.01 (d, J=
CH ), 2.35–
), 2.60 (d, J=4.7 Hz, 3H; E: NHCH ), 2.73
), 2.94 (dd, J=14.8, J=4.9 Hz, 1H; E:
trated in vacuo, and the crude solid was dissolved in H
aqueous layer was acidified with aq. HCl (2m) to pH 1 and extracted
with CH Cl (2ꢄ4 mL) and EtOAc (2ꢄ4 mL). The combined organic ex-
tracts were dried (Na SO ) and concentrated in vacuo to yield the free
2
O (3 mL). The
3
.8 Hz, 3H; D: CH
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(CH
3
)
2
), 1.41 (t, J=7.2 Hz, 3H; D: OCH
2
3
3
.44 (m, 1H; D: CH
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(CH
3
)
2
3
2
2
2
3
(
s, 3H; E: C5-CH
3
2
4
2
3
CHHCONHCH
CHHCONHCH
9
3
),
3.33
(dd,
J=14.8,
J=4.3 Hz,
1H;
E:
carboxylic acid (36 mg, 46.7 mmol, 93%) as a colorless solid.
3
3
3
), 4.41 (q, J=7.2 Hz, 2H; D: OCH
2
CH ), 5.32 (dd, J=
.0, 8.6 Hz, 1H; D: CH), 5.82 (ddd, J=8.6, 4.9, 4.3 Hz, 1H; E: CH), 6.85
), 7.60 (d, J=8.3 Hz, 1H; A: H-5), 8.11
s, 1H; D: H-5), 8.36 (s, 1H; F: H-5), 8.52 (d, J=8.3 Hz, 1H; A: H-4),
3
Peptide coupling: Free carboxylic acid (17 mg, 22.0 mmol) and amine 25
(13 mg, 28.3 mmol) were dissolved in DMF (2 mL) and cooled to 08C.
Diisopropylethylamine (13.5 mL, 10 mg, 81.5 mmol) and DPPA (8.6 mL,
11 mg, 39.7 mmol) were consecutively added to this mixture. The reaction
mixture was allowed to reach room temperature over 16 h and was then
partitioned between ethyl acetate (10 mL) and saturated aq. NH Cl
(10 mL). The aqueous layer was extracted with ethyl acetate (2ꢄ10 mL)
and the combined organic extracts were dried (Na SO ) and concentrated
in vacuo. Purification by flash chromatography (EtOAc) gave product 26
3
3
3
(
(
8
q, J=4.7 Hz, 1H; E: NHCH
3
3
3
3
.58 (d, J=9.0 Hz, 1H; D: NH), 9.48 ppm (d, J=8.6 Hz, 1H; E: NH);
1
3
C NMR (CDCl
OCH CH ), 18.1 (q; D: CH
NHCH ), 34.5 (d; D: CH(CH
3
,
90 MHz): d=12.5 (q; E: C5-CH
(CH ), 19.1 (q; D: CH(CH
), 38.5 (t; E: CH CONHCH
CH ), 126.2 (d; F: C-5), 127.4 (d; D:
3
), 14.3 (q; D:
), 26.1 (q; E:
), 48.5 (d; E:
4
2
3
A
H
U
G
E
N
N
3
)
2
A
H
U
G
R
N
U
G
3
)
2
3
A
H
U
G
R
N
U
G
3
)
2
2
3
2
4
CH), 56.1 (d; D: CH), 61.6 (t; OCH
2
3
Chem. Eur. J. 2010, 16, 14083 – 14093
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14089

T. Bach and C. Ammer
2
D
0
(
ꢀ
25 mg, 20.6 mmol, 93%) as a yellow oil. R
f
=0.32 (EtOAc; UV); [a]
=
A
H
N
T
E
N
N
3
3
3
)
)
)
2
2
2
), 18.6 (q; D: CH
), 26.4 (q; E: NHCH
), 42.1 (t; E: CH CONHCH
A
H
N
T
E
N
N
(CH
3
)
2
), 19.3 (q; D: CH ), 19.6 (q; C: CH-
), 33.2 (d; C: CH(CH ), 34.3 (d; D: CH-
2
), 43.6 (t; Gly: CH ), 47.2 (d; E: CH),
A
H
U
T
E
N
N
(CH
3
)
2
1
35.7 (c=0.45 in CH
Sn(CH ), 0.94–0.99 (m, 12H; D: CH
m, 2H; D: CH(CH , C: CH(CH
NHCH ), 2.73 (s, 3H; E: C5-CH ), 2.93 (dd, J=16.0, J=5.0 Hz, 1H; E:
2
Cl
2
); H NMR (CDCl
(CH
), 2.63 (d, J=4.5 Hz, 3H; E:
3
, 500 MHz): d=0.37 (s, 9H;
A
H
N
T
E
N
G
3
A
T
N
R
N
N
3 2
)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
)
3
A
H
U
G
R
N
U
G
3
)
2
, C: CH(CH ), 2.29–2.39
A
H
U
T
N
U
G
3
)
2
A
H
U
T
E
N
G
2
3
3
(
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
)
2
A
H
U
G
R
N
U
G
3
)
2
56.1 (d; D: CH), 56.3 (d; C: CH), 119.0 (d; C: C-5), 119.9 (d; A: C-5),
120.4 (d; B: C-5), 122.8 (d; D: C-5), 126.1 (d; F: C-5), 129.4 (s; A: C-3),
139.8 (d; A: C-4), 140.0 (s; A: C-2)*, 141.8 (s; E: C-5) , 142.9 (s; E: C-
4) , 148.9 (s; C: C-4), 149.3 (s; F: C-4), 150.0 (s; D: C-4), 153.3 (s; B: C-
4), 153.9 (s; A: C-6)*, 160.1 (s; F: CO)’, 161.5 (s; Gly: CO) , 162.1 (s; C:
C-2), 162.3 (s; B: C-2), 163.1 (s; F: C-2)’, 163.8 (s; E: C-2) , 168.6 (s; D:
CO) , 169.4 (s; E: CONHCH
2); HRMS (ESI): m/z: calcd for C38
2
3
3
3
2
3
#
CHHCONHCH
CHHCONHCH
(
3
),
3.25
(dd,
J=16.0,
J=4.0 Hz,
1H;
E:
2
3
#
3
), 4.13 (dd, J=16.5, J=4.5 Hz, 1H; Gly: CH
2
), 4.51
2
3
3
~
dd, J=16.5, J=7.0 Hz, 1H; Gly: CH
2
), 5.17 (dd, J=8.2, 6.0 Hz, 1H;
D: CH), 5.33 (dd, J=9.0, 6.0 Hz, 1H; C: CH), 5.73–5.79 (m, 1H; E:
), 7.31 (d, J=8.2 Hz, 1H; D:
NH), 7.35 (s, 1H; C: H-5), 7.61 (d, J=8.2 Hz, 1H; A: H-5), 7.90 (s, 1H;
3
§
3
3
~
§
CH), 6.83 (q, J=4.5 Hz, 1H; E: NHCH
3
3
) , 170.0 (s; E: CO), 174.2 ppm (s; D: C-
3
+
H
38BrN11NaO
5
S
5
: 990.0742 [M+Na] ;
B: H-5), 8.08 (s, 1H; D: H-5), 8.15 (brs, 1H; C: NH), 8.22–8.24 (m, 1H;
Gly: NH), 8.34 (s, 1H; F: H-5), 8.52 (d, J=8.2 Hz, 1H; A: H-4),
found: 990.0747.
3
Ethyl-(S,S)-2-{1-[(2-{1-[(2-{2-bromo-6-(4-tert-butoxycarbonyl-thiazole-2-
yl)pyridine-3-yl}thiazole-4-carbonyl)amino]-2-methylcarbamoyl-ethyl}-5-
methylthiazole-4-carbonyl)amino]-2-methylpropyl}thiazole-4-carboxylate
(35)
3
13
9
.65 ppm (d, J=9.0 Hz, 1H; E: NH); C NMR (CDCl
8.83 (q; Sn(CH ), 12.6 (q; E: C5-CH ), 17.9 (q; C: CH
q; D: CH(CH ), 19.2 (q; D: CH(CH ), 19.2 (q; C: CH
q; E: NHCH ), 33.6 (d; C: CH(CH ), 34.5 (d; D: CH(CH
CONHCH ), 43.2 (t; Gly: CH ), 48.4 (d; E: CH), 55.6 (d; D:
3
, 90 MHz): d=
(CH ), 18.1
(CH ), 26.1
), 38.3 (t;
ꢀ
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
)
3
3
A
H
U
T
E
N
N
3 2
)
)
3 2
(
(
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
)
2
A
H
U
G
R
N
U
G
3
)
2
A
H
U
G
E
N
N
3
A
H
N
T
E
N
N
3
)
2
A
T
N
T
E
N
N
3 2
)
Zincation: DMA (0.61 mL) and 1,2-dibromoethane (6.1 mL, 15 mg,
E: CH
2
3
2
8
0.8 mmol) were added to a flame-dried flask charged with zinc dust
41 mg, 0.625 mmol). The zinc suspension was shortly heated with a heat
gun until evolution of ethylene occurred and was then allowed to reach
CH), 56.8 (d; C: CH), 115.3 (d; C: C-5), 123.6 (d; D: C-5), 126.1 (d; F:
C-5), 126.3 (d; B: C-5), 127.8 (d; A: C-5), 129.0 (s; E: C-5), 130.1 (s; A:
C-3), 138.8 (s; A: C-2), 141.2 (d; A: C-4), 141.2 (s; A: C-6), 142.1 (s; E:
C-4), 148.9 (s; D: C-4), 149.7 (s; F: C-4), 149.8 (s; C: C-4), 160.5 (s; F:
CO), 161.3 (s; B: C-2), 161.4 (s; D: CO)*, 161.9 (s; F: C-2), 162.1 (s; E:
CO), 163.0 (s; B: C-4), 166.8 (s; E: C-2), 169.1 (s; Gly: CO)*, 169.9 (s;
(
258C. This procedure was repeated three times. TMSCl (16.7 mL, 14 mg,
0.131 mmol) was added neat and the reaction mixture was stirred for
5 min. tert-Butyl 2-iodothiazole-4-carboxylate (62 mg, 0.200 mmol) was
added. Stirring was continued for 45 min at 258C, then the zinc dust was
allowed to settle (30 min).
C: C-2), 170.5 (s; D: C-2), 171.3 ppm (s; E: CONHCH
3
); IR (ATR): n˜ =
3
1
C
297 (w; NH), 2961 (w; NH), 1654 (s; CONH), 1537 (s), 1490 (m; CH),
Negishi cross-coupling: The supernatant liquid containing the zinc organ-
ꢀ
1
406 (w; CH), 1070 (w), 773 cm (w); HRMS (ESI): m/z: calcd for
yl 34 was transferred to
.50 mmol, 30 mol%). Pyridine
1.5 mL) were added to this mixture, which was then stirred at 458C for
.5 h. The reaction mixture was partitioned between saturated aq. NH Cl
6 mL) and EtOAc (3ꢄ6 mL). The combined extracts were dried
Na SO ) and concentrated in vacuo. Purification by flash chromatogra-
a
flask containing [PdCl
2 3 2
ACHTUNGTRNENG(U PPh ) ] (5.3 mg,
1
20
+
41
H
48Br
2
N
11
O
5
S
5
Sn: 1211.9832 [M+H] ; found: 1211.9817.
7
(
3
5
(19.7 mg, 25.0 mmol) and DMA
Regiosiomeric macrocycles 27 and 28 by an intramoleculaur Stille cross-
coupling reaction: Stannane 26 (18 mg, 16.5 mmol) and tetrakis(triphenyl-
phosphane)palladium(0) (4.2 mg, 3.63 mmol, 22 mol%) were dissolved in
degassed toluene (16.5 mL) and stirred until full conversion (45 h) was
achieved at 858C. The reaction mixture was concentrated in vacuo. Flash
4
(
(
2
4
phy (P/EtOAc 1:1!0:1) afforded a yellow solid containing the desired
pyridine 35 (11 mg, 12.2 mmol, 49%, yellow solid) together with triphe-
nylphosphane oxide. Separation of the oxidated ligand from compound
chromatography (10% KF in silica, EtOAc!CH
2
Cl
6:4!94:6!92:8!90:10) yielded regioisomers 27 (4.0 mg, 4.13 mmol,
8%) and 28 (4.0 mg, 4.13 mmol, 28%).
=0.20 (CH Cl /MeOH 95:5; UV); H NMR (CDCl
60 MHz): d=0.89 (d, J=7.2 Hz, 3H; D: CH
2
/MeOH 98:2!
9
2
3
2
5 was performed by reverse-phase HPLC (RP, ODS-A, MeCN/H O
1
ꢀ1
20
Regioisomer 27: R
f
2
2
3
,
10:90, 7 mLmin ). M.p. 1358C; R
f
=0.36 (EtOAc; UV); [a] =ꢀ25.5
D
3
3
1
3
3
6
1
A
H
U
G
R
N
U
G
3
)
2
), 0.95 (d, J=
(CH ), 1.01–
), 1.13 (d, J=6.8 Hz, 3H; C: CH-
), 2.07–2.13 (m, 1H; D: CH(CH ), 2.26–2.31 (m, 1H; C: CH-
), 2.63 (d, J=4.9 Hz, 3H; E: NHCH ), 2.67 (s, 3H; E: C5-CH ),
), 3.86 (dd, J=17.3, J=3.4 Hz,
(c=0.45 in CHCl
3H; D: CH(CH
7.2 Hz, 3H; D: OCH
D: CH(CH ), 2.64 (d, J=4.7 Hz, 3H; E: NHCH
CH ), 3.02 (dd, J=14.8, J=5.8 Hz, 1H; E: CHHCONHCH
3
3
); H NMR (CDCl
3
, 360 MHz): d=0.98 (d, J=6.8 Hz,
3
3
3
.8 Hz, 3H; C: CH
.11 (m, 1H; E: CHHCONHCH
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(CH
3
)
2
A
H
U
G
R
N
N
3
)
2
A
H
U
G
R
N
U
G
3
)
2
), 1.01 (d, J=6.8 Hz, 3H; D: CH
A
H
U
G
R
N
U
G
3 2
) ), 1.41 (t, J=
3
3
2
CH ), 1.63 (s, 9H; G: C(CH )
3
A
H
U
G
R
N
U
G
3 3
3
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(CH
3
)
)
2
2
A
H
U
G
R
N
U
G
3
)
2
A
H
U
G
R
N
U
G
3
)
2
3
3
2
3
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(CH
3
3
3
3
2
3
2
3
3
2
1
.68–2.74 (m, 1H; E: CHHCONHCH
H; Gly: CHH), 4.94–5.23 (m, 2H; C: CH, Gly: CHH), 5.24 (dd, J=8.1,
3
J=14.8, J=4.3 Hz, 1H; E: CHHCONHCH
3
3
3
D: OCH
E: CH), 6.82 (q, J=4.7 Hz, 1H; E: NHCH
(s, 1H; G: H-5), 8.38 (s, 1H; F: H-5), 8.39 (d, J=8.3 Hz, 1H; A: H-5),
2 3
CH
3
3
3
J=4.7 Hz, 1H; D: CH), 5.39–5.44 (m, 1H; E: CH), 6.20 (d, J=6.1 Hz,
3
), 8.13 (s, 1H; D: H-5), 8.20
3
3
3
1
1
7
H; C: NH), 6.73 (q, J=4.9 Hz, 1H; E: NHCH
3
), 7.17 (t, J=3.4 Hz,
3
3
3
H; Gly: NH), 7.20 (s, 1H; C: H-5), 7.56 (d, J=8.0 Hz, 1H; A: H-5),
8.64 (d, J=8.6 Hz, 1H; D: NH), 8.74 (d, J=8.3 Hz, 1H; A: H-4),
3
3
13
.82 (d, J=8.0 Hz, 1H; A: H-4), 8.11 (s, 1H; D: H-5), 8.16 (s, 1H; B: H-
9.39 ppm (d, J=9.0 Hz, 1H; E: NH); C NMR (CDCl
12.5 (q; E: C5-CH ), 14.3 (q; D: OCH CH ), 18.0 (q; D: CH
(q; D: CH(CH ), 26.2 (q; E: NHCH ), 28.2 (q; G: C(CH
D: CH(CH ), 38.7 (t; E: CH CONHCH ), 48.5 (d; E: CH), 56.3 (d; D:
CH), 61.6 (t; OCH CH ), 82.4 (s; G: C(CH ), 119.3 (d; A: C-5), 126.1
d; F: C-5), 127.3 (d; D: C-5), 129.7 (d; G: C-5), 131.6 (s; A: C-3), 139.5
3
, 90 MHz): d=
(CH ), 19.1
), 34.5 (d;
3
5
), 8.35 (s, 1H; F: H-5), 8.78 (d, J=8.1 Hz, 1H; D: NH), 8.93 ppm (d,
3
2
3
A
H
U
G
R
N
U
G
3 2
)
3
J=9.0 Hz, 1H; E: NH); HRMS (ESI): m/z: calcd for
A
H
U
G
R
N
N
3
)
2
3
A
H
U
G
R
N
U
G
3 3
)
+
C
38
H
38BrN11NaO
5
S
5
: 990.0742 [M+Na] ; found: 990.0747.
A
H
U
G
R
N
N
3
)
2
2
3
2
D
0
2
3
A
H
U
G
R
N
U
G
3 3
)
Regioisomer 28: R
0
1
f
=0.18 (CH
2
Cl
2
/MeOH 95:5; UV); [a] =ꢀ9.6 (c=
(
3
.44 in CHCl ); IR (ATR): n˜ =3675 (w; NH), 1652 (s; CONH), 1536 (s),
495 (s, CH), 1347 (w), 1252 (w), 1074 (m), 734 (s), 693 cm (w);
#
ꢀ
1
(s; A: C-2), 140.7 (d; A: C-4), 141.9 (s; A: C-6), 142.2 (s; E: C-5) , 146.4
(s; D: C-4), 149.8 (s; E: C-4) , 150.2 (s; F: C-4), 151.3 (s; G: C-4), 160.2
(s; G: COO), 160.5 (s; F: CO), 161.4 (s; D: COO), 162.1 (s; E: CO),
162.3 (s; F: C-2), 166.5 (s; G: C-2), 166.6 (s; E: C-2), 170.7 (s; D: C-2),
#
1
3
H NMR (CDCl
3
, 360 MHz): d=0.97 (d, J=7.9 Hz, 3H; CH
A
H
U
G
R
N
U
G
3
)
3
)
3
)
2
2
2
),
),
),
3
3
1
1
2
.05 (d, J=6.8 Hz, 3H; CH
A
H
U
G
R
N
G
3
)
2
), 1.09 (d, J=6.8 Hz, 3H; CH
), 2.28–2.34 (m, 1H; D: CHACHTGNUTRENNUNG
ACHTUNGTRENNUNG
3
A
H
N
T
E
N
N
3
)
2
1
71.0 ppm (s; E: CONHCH
3
); IR (ATR): n˜ =2355 (m), 1719 (m; CO),
A
H
U
G
R
N
U
G
3
)
2
3
, E: C5-
2
3
1668 (s; CONH), 1530 (s), 1476 (m; CH), 1338 (w), 1232 (m), 1159 (m),
1068 (w), 1020 (w), 749 cm
CH
3
3
ꢀ
1
2
3
2
3
(w); HRMS (ESI): m/z: calcd for
+
J=15.1, J=5.4 Hz, 1H; E: CHHCONHCH
3
), 3.97 (dd, J=17.1, J=
2
3
C
36
H
39BrN
8
NaO : 925.0906 [M+Na] ; found: 925.0914.
7 4
S
5
5
.0 Hz, 1H; Gly: CHH), 4.49 (dd, J=17.1, J=7.6 Hz, 1H; Gly: CHH),
.28 (dd, J=8.5, 7.2 Hz, 1H; D: CH), 5.40 (dd, J=9.2, 8.6 Hz, 1H; C:
CH), 5.91–5.95 (m, 1H; E: CH), 6.05 (q, J=4.7 Hz, 1H; E: NHCH
.49 (d, J=8.5 Hz, 1H; D: NH), 7.67 (s, 1H; C: H-5), 7.73–7.76 (m, 1H;
Gly: NH), 7.97 (s, 1H; D: H-5), 8.03 (d, J=8.3 Hz, 1H; A: H-5), 8.05
d, J=9.2 Hz, 1H; C: NH), 8.26 (s, 1H; B: H-5), 8.35 (s, 1H; F: H-5),
.32 (d, J=9.0 Hz, 1H; E: NH), 8.55 ppm (d, J=8.3 Hz, 1H; A: H-4);
3
3
tert-Butyl-2-{2-bromo-3-[4-({[(1S)-3-(methylamino)-1-(5-methyl-4-{[((1S)-
2-methyl-1-{4-[4-({(1S)-2-methyl-1-[4-(trimethylstannyl)-2,4’-bithiazole-2’-
yl]propyl}amino)-2-oxo-ethylamino]thiazole-2-yl}propyl)amino]carbo-
nyl}thiazole-2-yl)-3-oxopropyl]amino}carbonyl)thiazole-2-yl]pyridine-6-
yl}thiazole-4-carboxylate (37)
3
3
),
3
7
3
3
(
3
3
8
Saponification: Aqueous lithium hydroxide solution (1m, 99.6 mL,
99.6 mmol) was added to a solution of the ethyl ester 35 (9.0 mg,
1
3
C NMR (CDCl
3
3
, 90 MHz): d=12.7 (q; E: C5-CH ), 17.5 (q; C: CH-
14090
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 14083 – 14093

Total Syntheses of the Thiopeptides Amythiamicin C and D
FULL PAPER
2
0
9
.96 mmol) in tBuOH (199 mL) and THF (99.6 mL) at room temperature.
The reaction mixture was stirred at room temperature for 1 h, concen-
trated in vacuo, and the crude solid was dissolved in H O (3 mL). The
aqueous layer was acidified with aqueous citric acid (10%) to pH 3 and
extracted with CH Cl (2ꢄ4 mL) and EtOAc (2ꢄ4 mL). The combined
organic extracts were dried (Na SO ) and concentrated in vacuo to yield
f
D
three steps) as a colorless solid. R =0.43 (EtOAc/MeOH 3:1); [a] =
1
+114.0 (c=0.18 in MeOH); H NMR (CDCl
3
, 600 MHz): d=0.89 (d,
3
3
2
J=6.6 Hz, 3H; D: CH
A
H
U
G
R
N
U
G
3
2
ACHTUNGTRENNUNG
3 2
3
3 2
1.00 (d, J=7.2 Hz, 3H; C: CH ACHTUNGRTNEUNG( CH ) ), 1.06–1.09 (m, 1H; E:
CHHCONHCH ), 1.15 (d, J=6.6 Hz, 3H; C: CH ACHTUNRTGENNUNG( CH ) ), 1.91–1.98 (m,
3 3 2
3
2
2
2
4
2 3 2 2 2
1H; G: H -7’), 2.07–2.18 (m, 3H; C: CH ACHUTNTGNERNUG( CH ) , G: H -7’/H -8’), 2.28–
3
the free carboxylic acid (8.5 mg, 9.70 mmol, 99%) as a yellow solid.
2.31 (m, 1H; D: CH
A
H
U
G
R
N
N
(CH )), 2.40–2.44 (m, 1H; G: H -8’), 2.65 (d, J=
3
2
2
3
4
.8 Hz, 3H; E: NHCH
3
), 2.66 (s, 3H; E: C5-CH
3
), 2.72 (dd, J=16.8, J=
-6’), 3.65–3.70
-6’), 3.89 (dd, J=17.4, J=3.0 Hz, 1H; Gly: CHH), 4.18
t, J=8.4 Hz, 1H; G: H-8a’), 4.55–4.61 (m, 2H; G: H-3’, G: CH OCO),
Peptide coupling: Free carboxylic acid (7.5 mg, 8.56 mmol) and amine 24
3
3 2
.0 Hz, 1H; E: CHHCONHCH ), 3.58–3.62 (m, 1H; G: H
(
5.0 mg, 10.9 mmol) were dissolved in DMF (1 mL) and cooled to 08C.
Diisopropylethylamine (6.1 mL, 4.7 mg, 36.7 mmol) and DPPA (3.9 mL,
.9 mg, 17.9 mmol) were consecutively added to this mixture. The reaction
mixture was allowed to reach room temperature over 16 h and then
quenched with saturated aqueous NH Cl (10 mL). The aqueous layer was
extracted with CH Cl (3ꢄ10 mL) and the combined organic extracts
were dried (Na SO ) and concentrated in vacuo. Purification by flash
chromatography (EtOAc) gave the bromopyridine 37 (7.7 mg, 6.83 mmol,
2
3
(
(
m, 1H; G: H
2
3
4
2
2
3
4.98–5.02 (m, 2H; Gly: CHH, C: CH), 5.19 (dd, J=11.4, J=2.4 Hz,
2
OCO), 5.25 (dd, J=10.2, 7.8 Hz, 1H; D: CH), 5.41–5.43 (m,
1H; E: CH), 6.31 (d, J=6.0 Hz, 1H; C: NH), 6.55 (s, 1H; G: NH-2’),
6.78 (q, J=4.8 Hz, 1H; E: NHCH ), 7.26 (s, 1H; C: H-5), 7.78–7.90 (m,
3
1H; Gly: NH), 8.12 (d, J=7.8 Hz, 1H; A: H-4), 8.12 (s, 1H; D: H-5),
8.24 (s, 1H; B: H-5), 8.35 (d, J=7.8 Hz, 1H; A: H-5), 8.36 (s, 1H; G: H-
5), 8.40 (s, 1H; F: H-5), 8.79 (d, J=7.8 Hz, 1H; D: NH), 8.95 ppm (d,
3
1H; G: CH
4
3
2
2
3
2
4
3
2
D
0
3
6
5%) as a yellow oil. R
f
=0.29 (EtOAc; UV); [a] =ꢀ34.0 (c=0.60 in
1
3
CHCl
1
2
NHCH
CHHCONHCH
CHHCONHCH
3
); H NMR (CDCl
.00 (m, 12H; D: CH(CH
.39 (m, 2H; D: CH(CH
), 2.74 (s, 3H; E: C5-CH
3
, 360 MHz): d=0.37 (s, 9H; Sn
A
H
U
G
R
N
U
G
3
)
3
), 0.94–
), 2.31–
3
13
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
)
2
, C: CH
, C: CH
), 2.99 (dd, J=15.8, J=5.0 Hz, 1H; E:
A
H
U
G
R
N
U
G
3
)
2
), 1.63 (s, 9H; C
A
H
U
G
R
N
U
G
3
)
3
J=9.0 Hz, 1H; E: NH); C NMR (CDCl
C5-CH ), 18.1 (q; D: CH(CH ), 18.4 (q; D: CH
(CH ), 19.2 (q; C: CH(CH ), 22.6 (t; G: C-7’), 26.3 (q; E: NHCH
28.4 (t; G: C-8’), 33.4 (d; C: CH(CH ), 34.7 (d; D: CH(CH ), 38.4 (t;
E: CH CONHCH ), 41.5 (t; Gly: CH ), 45.6 (t; G: C-6’), 48.3 (d; E:
3
, 150 MHz): d=12.3 (q; E:
(CH ), 19.2 (q; C: CH-
),
3
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
)
2
A
H
U
G
R
N
U
G
3
)
2
3
A
H
U
G
R
N
U
G
3
)
2
A
H
U
G
R
N
U
3 2
)
2
3
A
H
U
G
R
N
U
G
3
)
2
A
H
U
G
R
N
U
G
3
)
2
3
3
3
2
3
),
3.26
(dd,
J=15.8,
J=4.3 Hz,
1H;
E:
A
H
U
G
R
N
U
G
3
)
2
A
H
U
G
R
N
U
3 2
)
3
2
3
3
), 4.15 (dd, J=16.6, J=4.3 Hz, 1H; Gly: CH
2
), 4.53
2
3
2
2
3
3
(
dd, J=16.6, J=6.5 Hz, 1H; Gly: CH
2
), 5.19 (dd, J=9.0, 8.6 Hz, 1H;
CH), 54.8 (d; G: C-3’), 56.2 (d; D: CH), 59.1 (d; G: C-8a’), 59.4 (d; C:
CH), 64.3 (t; G: C-9’), 114.3 (d; C: C-5), 118.7 (d; A: C-5), 123.2 (d; B:
C-5), 123.9 (d; D: C-5), 125.2 (d; F: C-5), 127.9 (s; A: C-3), 131.5 (s; G:
C-5), 140.4 (d; A: C-4), 140.5 (d; E: C-5), 142.1 (s; E: C-4), 147.2 (s; G:
C-4), 148.4 (s; D: C-4), 148.8 (s; C: C-4), 150.3 (s; A: C-2), 150.3 (s; F:
C-4), 150.4 (s; A: C-6), 154.4 (s; B: C-4), 160.0 (s; B: C-2), 161.2 (s; F:
CO), 161.3 (s; D: CO), 161.3 (s; G: CO), 162.0 (s; E: CO), 162.7 (s; G:
C-4’), 164.8 (s; F: C-2), 167.6 (s; E: C-2), 168.6 (s; D: C-2), 169.1 (s; G:
3
3
D: CH), 5.32 (dd, J=9.0, J=6.1 Hz, 1H; C: CH), 5.75–5.79 (m, 1H; E:
CH), 6.78 (q, J=4.7 Hz, 1H; E: NHCH
1
1
3
3
), 7.24 (d, 1H; NH), 7.36 (s,
H; C: H-5), 7.90 (s, 1H; B: H-5), 8.08 (s, 1H; D: H-5), 8.08–8.13 (m,
H; NH), 8.19–8.22 (m, 1H; Gly: NH), 8.21 (s, 1H; G: H-5), 8.35 (s, 1H;
3
3
F: H-5), 8.38 (d, J=7.9 Hz, 1H; A: H-5), 8.75 (d, J=7.9 Hz, 1H; A: H-
3
13
4
), 9.62 ppm (d, J=8.6 Hz, 1H; E: NH); C NMR (CDCl
(CH ), 12.7 (q; E: C5-CH ), 17.9 (q; C: CH
(CH ), 19.2 (q; D: CH(CH ), 19.2 (q; C: CH
6.1 (q; E: NHCH ), 28.2 (q; G: C(CH ), 33.6 (d; C: CH(CH
(CH ), 38.3 (t; E: CH CONHCH ), 43.0 (t; Gly: CH
d; E: CH), 55.5 (d; D: CH), 56.8 (d; C: CH), 82.4 (s; G: C(CH
3
, 90 MHz):
d=ꢀ8.80 (q; Sn
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
)
3
3
A
T
N
T
E
U
G
3
)
)
2
),
),
1
2
8.1 (q; D: CH
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
)
2
A
H
U
G
R
N
U
G
3
)
2
A
H
U
G
R
N
U
G
3
2
3
C-2), 169.3 (s; Gly: CO), 169.4 (s; G: C-1’), 169.6 (s; E: CONHCH ),
3
A
H
U
G
E
N
N
3
)
3
A
H
U
G
E
N
N
3
)
2
), 34.4
), 48.3
172.7 ppm (s, C: C-2); HRMS (ESI): m/z: calcd for C50
1205.2107 [M+Na] ; found: 1205.2108.
H
50
N
14NaO
9
S
6
:
+
(
(
(
(
(
(
(
(
(
d; D: CH
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
)
2
2
3
2
A
H
U
G
R
N
U
G
3
)
3
), 115.3
Amythiamicin D (4)
d; C: C-5), 119.3 (d; A: C-5), 123.6 (d; D: C-5), 126.1 (d; F: C-5), 126.3
d; B: C-5), 129.8 (d; G: C-5), 131.5 (s; A: C-3), 139.4 (s; A: C-2), 140.7
d; A: C-4), 141.9 (s; A: C-6), 142.1 (s; E: C-5), 148.9 (s; D: C-4), 149.5
s; C: C-4), 149.7 (s; E: C-4), 150.0 (s; F: C-4), 151.2 (s; G: C-4), 160.3
s; G: CO), 160.5 (s; F: CO), 161.2 (s; B: C-2), 161.3 (s; D: CO)*, 162.0
s; E: CO), 162.2 (s; F: C-2), 163.0 (s; B: C-4), 166.6 (s; G: C-2), 166.8
s; E: C-2), 169.0 (s; Gly: CO)*, 169.9 (s; C: C-2), 170.4 (s; D: C-2),
Zincation: DMA (0.51 mL) and 1,2-dibromoethane (3.6 mL, 0.77 mg,
.08 mmol) were added to a flame-dried flask charged with zinc dust
24 mg, 124 mmol). The zinc suspension was shortly heated with a heat
gun until evolution of ethylene occurred and then allowed to reach 258C.
This procedure was repeated three times. TMSCl (10.2 mL, 8.7 mg,
9.8 mmol) was added neat and the reaction mixture was stirred for
min. Methyl 2-iodothiazole-4-carboxylate (33 mg, 124 mmol) was added.
The stirring was continued for 1 h at 258C, then the zinc dust was allowed
4
(
7
5
1
71.1 ppm (s; E: CONHCH
3
); IR (ATR): n˜ =3675 (w; NH), 2375 (s;
NH), 2348 (s), 1825 (w), 1681 (m; CONH), 1668 (m; CONH), 1652 (m;
to settle (30 min).
ꢀ
1
CONH), 1540 (s), 1226 (w; CꢀO), 768 (m), 756 cm (s); HRMS (ESI):
1
20
+
Negishi cross-coupling: The supernatant liquid (0.25 mL) containing the
m/z: calcd for
339.0902.
Amythiamicin C (3)
Stille macrocyclization: Stannane 37 (13 mg, 9.87 mmol) and [Pd
C
49
H
57BrN12NaO
7
S
6
Sn: 1339.0900 [M+Na] ; found:
zinc organyl 29 was added to a flask containing [PdCl
.24 mmol, 30 mol%) and macrocycle 27 (3.9 mg, 4.02 mmol) in THF
0.14 mL). The reaction mixture was stirred at 458C for 24 h. The reac-
tion mixture was partitioned between H O (5 mL) and EtOAc (3ꢄ
0 mL). The combined organic layers were dried (Na SO ) and concen-
trated in vacuo. Purification by flash chromatography (CH Cl /MeOH
2 3 2
ACHTUNGTRNENG(U PPh ) ] (0.9 mg,
1
1
(
A
H
U
G
R
N
U
G
3 4
) ]
2
(
(
1
2
4
2
2
mixture was concentrated in vacuo. Flash chromatography (EtOAc!
CH Cl
/MeOH 98:2!90/10) yielded macrolide 38 (8.4 mg, 7.83 mmol,
9%) as a pale-yellow solid together with triphenylphosphane oxide.
1
00:0!94:6) afforded amythiamicin D (4) (4.0 mg, 3.88 mmol, 96%) to-
2
2
gether with triphenylphosphane oxide. Separation of the oxidated ligand
from the natural product was performed by reverse-phase HPLC (RP,
7
ꢀ
1
Deprotection of tert-butyl ester 38: Trifluoroacetic acid (0.29 mL) was
added at room temperature to a stirred solution of the macrocyle 38
ODS-A, MeCN/H O 20:80!100:0, 50 min, 15 mLmin ) yielding amy-
2
thiamicin D (4) (1.7 mg, 1.65 mmol, 43%) as a colorless solid. R =0.30
f
2
0
1
(
8.2 mg, 7.73 mmol) in CH
2
Cl
2
(1.6 mL). After 8 h, the reaction mixture
(CH Cl /MeOH 95:5); [a] =+170.0 (c=0.15 in MeOH); H NMR
2
2
D
3
was concentrated in vacuo and then azetroped with toluene (2ꢄ5 mL) to
give the corresponding acid 39 as a colorless solid. This material was
used in the subsequent ester coupling without further purification.
(
CDCl
J=6.5 Hz, 3H; C: CH
.07 (m, 1H; E: CHHCONHCH
3
, 500 MHz): d=0.89 (d, J=7.0 Hz, 3H; D: CH
A
H
U
G
R
N
N
3
)
2
), 0.96 (d,
(CH ),
), 1.14 (d, J=6.5 Hz, 3H; C: CH-
), 2.08–2.14 (m, 1H; C: CH(CH ), 2.25–2.33 (m, 1H; D: CH-
), 2.65 (d, J=4.5 Hz, 3H; E: NHCH ), 2.66 (s, 3H; E: C5-CH ),
3
3
A
H
U
G
R
N
U
G
3
)
2
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3 2
)
3
1
3
Ester coupling: Acid 39, diketopiperazine 31 (7.1 mg, 38.7 mmol), and
DMAP (1.4 mg, 11.6 mmol) were dissolved in CH
for 15 min. EDC (1.8 mg, 9.28 mmol) and CH Cl
and the reaction mixture was stirred for 24 h. Purification by flash chro-
A
H
U
G
R
N
U
G
3
)
)
2
2
A
H
U
G
R
N
N
3 2
)
3
2
Cl
2
(0.8 mL) and stirred
A
H
N
R
N
G
3
3
3
2
3
2
2
2
(0.8 mL) were added
2.73 (dd, J=14.0, J=3.5 Hz, 1H; E: CHHCONHCH
3
17.5, J=3.0 Hz, 1H; Gly: CHH), 4.02 (s, 3H; G: OCH
3
), 3.89 (dd, J=
), 4.98–5.03 (m,
2H; Gly: CHH, C: CH), 5.25 (dd, J=8.0, 4.5 Hz, 1H; D: CH), 5.41–5.43
3
3
matography (EtOAc/MeOH 100:0!2:1) yielded amythiamicin C (3)
3
3
(
15 mg) together with diketopiperazine 31. Further purification by re-
(m, 1H; E: CH), 6.31 (d, J=6.0 Hz, 1H; C: NH), 6.76 (q, J=4.5 Hz,
3
), 7.25 (s, 1H; C: H-5), 7.77 (dd, J=9.5, J=3.0 Hz, 1H;
Gly: NH), 8.12 (s, 1H; D: H-5), 8.13 (d, J=8.0 Hz, 1H; A: H-4), 8.24 (s,
2
3
verse-phase HPLC (RP, ODS-A, MeCN/H
1
2
O
20:80!100:0, 50 min,
1H; E: NHCH
ꢀ
1
3
5 mLmin ) gave amythiamicin C (3) (2.4 mg, 2.03 mmol, 20% over
Chem. Eur. J. 2010, 16, 14083 – 14093
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14091

T. Bach and C. Ammer
3
1
8
9
H; B: H-5), 8.35 (s, 1H; G: H-5), 8.37 (s, 1H; F: H-5), 8.38 (d, J=
[9] a) K. C. Nicolaou, B. Zou, D. H. Dethe, D. B. Li, Chen, Angew.
Chem. 2006, 118, 7950–7956; Angew. Chem. Int. Ed. 2006, 45, 7786–
7792; b) K. C. Nicolaou, D. H. Dethe, G. Y. C. Leung, B. Zou, D. Y.-
K. Chen, Chem. Asian J. 2008, 3, 413–429.
[10] K. C. Nicolaou, J. S. Chen, D. J. Edmonds, A. A. Estrada, Angew.
Chem. 2009, 121, 670–732; Angew. Chem. Int. Ed. 2009, 48, 660–
719.
3
3
.0 Hz, 1H; A: H-5), 8.79 (d, J=8.0 Hz, 1H; D: NH), 8.95 ppm (d, J=
1
3
.0 Hz, 1H; E: NH); C NMR (CDCl
), 18.0 (q; D: CH(CH ), 18.3 (q; D: CH
), 19.2 (q; C: CH(CH ), 26.2 (q; E: NHCH
), 34.7 (d; D: CH(CH ), 38.4 (t; E: CH
), 48.3 (d; E: CH), 52.6 (q; G: OCH ), 56.2 (d; D: CH), 59.4 (d;
3
, 150 MHz): d=12.3 (q; E: C5-
CH
(CH
(CH
3
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
)
2
A
H
U
G
R
N
U
(CH
3
)
2
), 19.2 (q; C: CH-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
)
)
2
2
A
H
U
G
R
N
U
G
3
)
2
3
), 33.4 (d; C: CH-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
A
H
U
G
R
N
U
G
3
)
2
2 3
CONHCH ), 41.4 (t;
Gly: CH
2
3
C: CH), 114.3 (d; C: C-5), 118.6 (d; A: C-5), 123.2 (d; B: C-5), 123.9 (d;
D: C-5), 125.2 (d; F: C-5), 127.7 (s; A: C-3), 130.4 (d; G: C-5), 140.3 (d;
A: C-4), 140.5 (s; E: C-5), 142.1 (s; E: C-4), 148.2 (s; G: C-4), 148.3 (s;
D: C-4), 148.8 (s; C: C-4), 150.3 (s; A: C-3), 150.3 (s; F: C-4), 150.5 (s;
A: C-6), 154.5 (s; B: C-4), 160.0 (s; B: C-2), 161.2 (s; F: CO), 161.4 (s;
D: CO), 161.8 (s; G: CO), 162.0 (s; E: CO), 164.9 (s; F: C-2), 167.6 (s;
E: C-2), 168.6 (s; D: C-2), 169.1 (s; G: C-2), 169.1 (s; Gly: CO), 169.6 (s;
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3
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+
C
43
H
42
N
12NaO
7
S
6
: 1053.1521 [M+Na] ; found: 1053.1523.
1
025–1026; k) C.-g. Shin, K. Okumura, M. Shigekuni, Y. Nakamura,
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Acknowledgements
This project was supported by the Deutsche Forschungsgemeinschaft (Ba
372-11). We thank Wacker Chemie (Munich), and Umicore (Hanau) for
the donation of chemicals.
1
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D
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14092
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 14083 – 14093

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Received: July 27, 2010
Published online: October 19, 2010
Chem. Eur. J. 2010, 16, 14083 – 14093
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14093