Synthesis and precursor-directed biosynthesis of new hormaomycin analogues

Article abstract of DOI:10.1002/ejoc.200500856

Several new analogues of hormaomycin (1), a peptide lactone with interesting biological activities, were prepared by total synthesis or by precursor-directed biosynthesis. The new analogues 2a-c, 3a-c, O-MOM-1 and epi-O-MOM-1 as well as the model acyl tri

Full text of DOI:10.1002/ejoc.200500856

FULL PAPER
DOI: 10.1002/ejoc.200500856
Synthesis and Precursor-Directed Biosynthesis of New Hormaomycin
Analogues
Boris D. Zlatopolskiy,[a] Markus Radzom,[a] Axel Zeeck,*[a] and Armin de Meijere*[a]
Keywords: Natural products / Amino acids / Synthetic methods / Peptides / Biosynthesis
Several new analogues of hormaomycin (1), a peptide lac-
tone with interesting biological activities, were prepared by
total synthesis or by precursor-directed biosynthesis. The
new analogues 2a–c, 3a–c, O-MOM-1 and epi-O-MOM-1 as
well as the model acyl tripeptides 20a–c and 21a–e were
tested for their antibiotic activities to give new insights into
structure–activity relationships of this class of compounds. In
this context, an unexpected activity of 2c against C. albicans
was discovered. The precursors necessary for feeding experi-
ments, the amino acids 14a, 14b and 17, were prepared in
31, 48 and 55% yield over 4 and 3 steps, respectively. In ad-
dition, these studies provided some new information about
the biosynthetic route to furnish compound 1. They also sup-
port the notion that the combination of chemical and bio-
logical methods may provide a broad range of analogues of
an interesting biologically active natural product.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
Definitely the most commonly exploited way to com-
pounds with interesting biological activities is the design of
analogues of lead structures, which are frequently derived
from naturally occurring compounds. This can be achieved
either by conventional chemical synthesis or by precursor-
directed biosynthesis. If successful, this approach eventually
furnishes compounds with an enhanced biological activity
or even a totally changed activity pattern.[1]
Some time ago, we embarked on a project to develop a
total synthesis and to elucidate the biosynthesis of hormao-
mycin (1), a peptide lactone produced by Streptomyces
griseoflavus (strain W-384).[2,3] Besides challenging struc-
tural features, 1 exhibits quite an interesting spectrum of
biological activities, including a marked influence on the
secondary metabolite production of other streptomycetes,
an exceptionally selective inhibitory activity against coryne-
form bacteria[2] as well as an interesting antimalarial ac-
tivity.[4] Once our total synthesis of hormaomycin (1) had
been completed,[3b] we concentrated our efforts on the prep-
aration of new hormaomycin analogues as well as stripped-
down mimics, in order to determine its minimal structural
unit, which would still be biologically active. These studies
included precursor-directed biosynthetic approaches which,
at the same time, provided some clues about the biosynthe-
sis of 1 itself[5] (Figure 1).
Figure 1. Structures of hormaomycin (1) and its analogues 2a–c
and 3a–c.
As a first target, the total synthesis of an analogue con-
taining an (2S,1ЈR,2ЈR)-3-(2Ј-aminocyclopropyl)alanine [(3-
Acp)Ala] instead of the (2S,1ЈR,2ЈR)-3-(2Ј-nitrocyclopro-
pyl)alanine [(3-Ncp)Ala] moiety in the side chain was ad-
dressed. Feeding experiments with H-(3-Acp)Ala-OH had
shown that the latter was not incorporated, and thus such
an analogue could not be prepared by precursor-directed
biosynthesis.[5]
[a] Institut für Organische und Biomolekulare Chemie der Georg-
August-Universität Göttingen,
Because an initially attempted reduction of the N-Teoc-
protected (3-Ncp)Ala-OH 4[3b] or its methyl ester 5 failed,
the free amino acid 6 was hydrogenated over 10% Pd/C in
methanol according to the protocol of Larionov et al.[6] to
give the desired diamino acid. Without any purification, it
was acylated via the corresponding copper complex with Z-
Tammannstrasse 2, 37077 Göttingen, Germany
Fax: +49-551-399475
E-mail: Armin.deMeijere@chemie.uni-goettingen.de
azeeck@gwdg.de
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Eur. J. Org. Chem. 2006, 1525–1534
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B. D. Zlatopolskiy, M. Radzom, A. Zeeck, A. de Meijere
FULL PAPER
OSu to yield the Nω-Z-protected H-(3-Acp)Ala-OH 7 (52%
yield over two steps, Scheme 1).
Scheme 2. Synthesis of the O-MOM-protected hormaomycin ana-
logue 11. Reagents and conditions: a) anisole, TFA, 20 °C, 2 h. b)
Teoc-(2S,1ЈR,2ЈR)-(3-Acp)AlaOH (8), HATU, HOAt, DIEA,
TMP, CH2Cl2, 20 °C, 15 h. c) TFA, 20 °C, 1 h. d) 10, HATU,
HOAt, DIEA, TMP, CH2Cl2, 20 °C, 4 h. HATU = O-(7-azabenzo-
triazol-1-yl)-N,N,NЈ,NЈ-tetramethyluronium hexafluorophosphate,
HOAt = 7-aza-1-hydroxybenzotriazole, TMP = 2,4,6-trimethylpyr-
Scheme 1. Synthesis of the suitably protected diamino acid 8. Rea-
gents and conditions: a) H2, 10% Pd/C, MeOH, 20 °C, 16 h. b) H2,
10% Pd/C, EtOAc, 20 °C, 2 h. c) Zn/AcOH, 20 °C, 3 h. d) NiCl2,
NaBH4, MeOH/THF, 20 °C, 2 h. e) CuSO4, NaHCO3, H2O, 20 °C,
10 min, then Z-OSu, acetone, 20 °C, 1.5 h. f) disodium ethylenedi-
aminetetraacetate (Trilon B), H2O, reflux, 10 min. g) Teoc-OSu,
NaHCO3, acetone/H2O (1:1), 20 °C, 16 h. h) H2, 10% Pd/C,
MeOH, 20 °C, 2.5 h. i) Npys-Cl, Et3N, DMF, 0 Ǟ 20 °C, 15 h.
Teoc-OSu = 2-(trimethylsilyl)ethyl N-hydroxysuccinimidyl carbon-
ate, Z-OSu = benzyl N-hydroxysuccinimidyl carbonate, Npys-Cl =
3-nitro-2-pyridinesulfenyl chloride.
idine, DIEA
oxymethyl.
= N,N-diisopropylethylamine, MOM = meth-
the hormaomycin synthetase would accept amino acid sub-
strates without a cyclopropyl group, and the importance of
the two cyclopropyl fragments in hormaomycin (1) for its
biological activities remained open. Therefore, feeding ex-
periments with nitro-substituted amino acids devoid of a
cyclopropyl moiety, e.g. 14a, 14b, 17 and 18, were carried
The latter was first Nα-protected with Teoc-OSu and out.
then, after hydrogenolytic removal of the Z-group, treated
These precursors were prepared as follows (Scheme 3).
with 3-nitro-2-pyridinesulfenyl chloride (NpysCl) to give The Nα-Boc-Nω-Z-protected ornithines 12a and lysines 12b
the orthogonally bisprotected derivative 8 in 29% yield over were converted into the corresponding tert-butyl esters,
three steps.
Boc-Orn-OtBu and Boc-Lys-OtBu,[11] according to a proto-
The Npys group, which was proposed for amino group col of Chevallet et al.[12] These diamino esters, after removal
protection by Matsueda et al.,[7] is stable towards trifluoro- of the Z-group, were oxidized to the α-amino ω-nitro amino
acetic acid, but easily removed with highly diluted (0.1– esters 13a and 13b, respectively, with m-chloroperbenzoic
0.2 ) HCl in organic solvents. It has been reported that it acid (MCPBA) in refluxing 1,2-dichloroethane following a
can also be cleaved off under nearly neutral conditions with protocol of Gilbert et al.[13] Final deprotection with TFA
triphenylphosphane and a proton source, as well as under or HCl in EtOAc gave the desired 5-nitronorvalines, (S)-
essentially neutral conditions with thiols such as 2-pyri- 14a and (R)-14a, and 6-nitronorleucines, (S)-14b and rac-
dinethiol N-oxide or 2-mercaptobenzothiazole. This there- 14b, as hydrochlorides in 31, 44, 48 and 42% yields, respec-
fore appeared to be the group of choice for protection of tively, over four steps.[14,15]
the ω-amino function of (3-Acp)Ala units taking into ac-
5-Nitro-4-thianorvaline (17) was prepared in 55% yield
count the limitations imposed on the deprotection condi- over three steps, starting from the N,O-protected cysteine
tions by other sensitive moieties in the hormaomycin mole- 15. The latter was chlorinated at the sulfur atom with
cule (Scheme 2).[8]
SO2Cl2 to give an unstable sulfenyl chloride, which was im-
After removal of the MeZ group from the lactone 9,[3b] mediately treated with potassium methylnitronate to furnish
was acylated with the orthogonally bisprotected diamino the protected amino acid 16. The ester was hydrolyzed un-
acid 8 (Scheme 2). After removal of the Teoc group, the der basic conditions with strict exclusion of oxygen, and
resulting intermediate product was in turn coupled with the subsequently the Boc group was removed by treatment with
O-MOM-protected Chpca 10[9] to give the O-MOM-pro- hydrochloric acid to furnish compound 17. 2Ј-Nitrophenyl-
tected hormaomycin analogue 11 in 54% yield over four alanine (18), a phenyl analogue of H-(3-Ncp)Ala-OH, was
steps. The latter was treated first with MgBr2·Et2O and prepared according to a published procedure.[16]
EtSH in CH2Cl2, and then with PPh3 and Py·HCl.[10] Al-
Feeding of 5-nitronorvaline (S)-14a to growing cultures
though the reaction mixture, according to TLC, contained of Streptomyces griseoflavus (strain W-384) was successful
two compounds sensitive to Ehrlich’s reagent, attempted and, according to ESI-MS spectra of the isolated crude
separation by exclusion chromatography did not provide product, gave a mixture of hormaomycin (1) and the ana-
any compound containing a pyrrole fragment.
logues 2a–c. This indicates that the cyclopropyl ring in H-
Cyclopropylalanines with electron-withdrawing substitu- (3-Ncp)Ala-OH is not essential for the recognition of the
ents (like NO2, CO2Me) in the cyclopropyl fragment have amino acid by the hormaomycin synthetase.[17] The mixture
already been shown to be acceptable substrates for the hor- was separated by HPLC to give the pure analogue 2c with
maomycin synthetase.[3b] However, the question whether two, and one of the analogues with one nitronorvaline
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Synthesis and Precursor-Directed Biosynthesis of New Hormaomycin Analogues
FULL PAPER
Chpca(MOM)-OH (10) to give, after removal of the MOM
group, the tripeptide ester 21a (73%).
Scheme 3. Syntheses of nitro amino acids 14a,b and 17. Reagents
and conditions: a) tBuBr, K2CO3, TEBAC, DMA, 55 °C, 24 h. b)
H2, 10% Pd/C, EtOAc, 20 °C, 3 h. c) MCPBA, ClCH2CH2Cl, re-
flux, 20 min. d) TFA, 20 °C, 1 h, then 2  HCl/EtOAc, 20 °C,
2 min. e) 4  HCl/EtOAc, 0 Ǟ 20 °C, 2 h. f) SO2Cl2, CH2Cl2, –40
Ǟ –20 °C, 3 h·g) CH3NO2, tBuOK, THF, –78 Ǟ 0 °C, 2.5 h. h)
0.25  NaOH, THF, 0 °C, 80 min. i) 4  HCl/EtOAc, 20 °C,
20 min. TEBAC = triethylbenzylammonium chloride, MCPBA =
3-chloroperbenzoic acid.
[(NO2)Nva] instead of a (3-Ncp)Ala residue. The latter, ac-
1
cording to its H-NMR spectrum and HPLC-MS analysis
of its total hydrolysate applying the advanced Marfey
method,[18] contained a (NO2)Nva moiety in the peptide
lactone ring of the molecule, corresponding to 2a. The sec-
ond analogue 2b with only one (NO2)Nva was also ob-
served in tiny quantities, but could not be isolated in pure
form. If an external H-(3-Ncp)Ala-OH epimerase really
participates in the biosynthesis of hormaomycin (1) (see
ref.[3a] for the relevant discussion), then an additional sup-
ply of (R)-H-(NO2)Nva-OH should give a mixture of hor-
maomycin (1) and its analogues 2a–c, possibly enriched
with 2b. Therefore, a feeding experiment with (R)-14a was
carried out. However, only hormaomycin (1) itself was iso-
lated in low yields. Apparently, (R)-14a is not accepted by
the hormaomycin synthetase because of its inappropriate
configuration, and the accepted (S)-14a is epimerized in the
peptide lactone ring position to (R)-nitronorvaline [(R)-14a]
during the biosynthesis of analogues 2a,c by an epimerase
Scheme 4. Syntheses of hormaomycin analogue 2b, acyl tripeptides
21a–e as well as O-MOM-protected hormaomycin O-MOM-1 and
its epimer epi-O-MOM-1. Reagents and conditions: a) anisole,
TFA, 20 °C, 2 h. b) Teoc-(S)-(NO2)Nva-OH, HATU, HOAt,
DIEA, TMP, CH2Cl2, 20 °C, 15 h. c) TFA, 20 °C, 1 h. d) 10,
HATU, DIEA, TMP, CH2Cl2, 20 °C, 4–16 h or 10, EDC, HOBt,
DIEA, CH2Cl2, 0 Ǟ 20 °C, 4 h. e) MgBr2·Et2O, EtSH, CH2Cl2,
20 °C, 3–4 h. f) Teoc-AA-OH, EDC, HOAt, DIEA, TMP, CH2Cl2,
0 Ǟ 20 °C, 15 h·g) 5  HCl in Et2O, 20 °C, 1.5 h. h) 20% Et2NH,
MeCN, 40 min. i) HCl·H-Phe-Val-OMe, HATU, DIEA, CH2Cl2,
20 °C, 1.5 h. j) TFA·H-(NO2)Nle-Phe-Val-OMe, HATU, DIEA,
TMP, CH2Cl2, 20 °C, 6 h. k) 26, PyAOP, HOAt, DIEA, TMP,
CH2Cl2, 20 °C, 15 h. EDC = N-(3-dimethylamino)propyl-NЈ-ethyl-
carbodiimide hydrochloride, Chba-OH = 3-chloro-2-hydroxyben-
zoic acid, PyAOP = [(7-azabenzotriazol-1-yl)oxy]tris(pyrrolidino)-
phosphonium hexafluorophosphate.
After removal of the MeZ group, the peptide lactone 9[3b]
in the appropriate module of the hormaomycin syn- was coupled with the N-Teoc-protected 5-nitronorvaline.
thetase.[19] The different yields of 2a and 2b in the experi- After removal of the Teoc group, the resulting intermediate
ment with (S)-14a indicate different affinities of the binding was acylated with Chpca(MOM)-OH (10). Finally, the de-
sites for this amino acid in the multienzyme complex.
sired hormaomycin analogue 2b was obtained after removal
Although analogue 2b could not be prepared in pure of the MOM group in 60% overall yield over 5 steps. The
form by feeding experiments, it ought to be synthesized in HPLC retention time of this substance was the same as that
order to estimate the importance of each nitrocyclopropyl of the presumed 2b, observed in the feeding experiment
moiety in 1 for its biological activity. To evaluate the appli- with H-(NO2)Nva-OH.
cability of 5-nitronorvaline in peptide syntheses, the acyl-
Feeding experiments with both enantiomerically pure
ated tripeptide 21a was prepared (Scheme 4).[15,20] Towards (S)-14b and racemic 6-nitronorleucine rac-14b were success-
that, the known dipeptide 19[21] after removal of the Boc ful in giving, according to HPLC and ESI-MS spectra of
group, was coupled with Teoc-(NO2)Nva-OH to give Teoc- the crude extract, a mixture of hormaomycin (1) and the
(NO2)Nva-Phe-Val-OMe in 59% yield. Subsequent depro- three analogues 3a–c (Table 1). In this case, the isolation of
tection of its N-terminus was followed by acylation with the individual components was complicated because of the
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B. D. Zlatopolskiy, M. Radzom, A. Zeeck, A. de Meijere
FULL PAPER
very similar retention times. Repeated preparative HPLC Table 2. Relative antibacterial activities of hormaomycin (1), alkyl-
ated hormaomycins O-MOM-1 and epi-O-MOM-1 as well as ana-
eventually furnished the analogue 3a in pure form, as well
logue 2b and model compounds 20a and 21d in serial dilution plate
as a mixture of 3b and 3c enriched with the former (ca. 5:1).
diffusion tests against Arthrobacter crystallopoites (strain 20117)
Furthermore, it was impossible to separate the analogue 3c
from hormaomycin (1) itself. On the one side, 6-nitronorle-
ucine is accepted as a substrate that leads to the three pos-
sible hormaomycin analogues 3a–c, yet on the other side
compounds 3a–c were never observed in the culture broth
unless 14b was supplied as a precursor – these facts demon-
strate that this amino acid cannot be an intermediate along
the biosynthetic route to H-(3-Ncp)Ala-OH.[22]
(%) (estimated relative to the activity of hormaomycin at 5·10–2 mg
per 9×0.5 mm plate) at 28 °C.
Compound (mg per
plate)
5·10–2
5·10–3
5·10–4
5·10–5
Hormaomycin (1)
100
19
13
90
39
0
94
0
0
84
23
–
71
–
–
58
2
–
39
–
–
26
0
–
O-MOM-1
epi-O-MOM-1
2b
20a
21d
Table 1. Influence of the configuration and side-chain structure of
selected amino acid precursors on the production of hormaomycin
analogues by Streptomyces griseoflavus (strain W-384).
Table 3. Relative antibacterial activities (%) of hormaomycin (1),
hormaomycin analogues and model peptides compared to that of
penicillin G in serial dilution plate diffusion tests against Arthro-
bacter oxidans (strain 20119) (estimated relative to the activity of
hormaomycin at 1.5·10–2 mg per 6×0.65 mm plate) at 28 °C. Mix-
tures of 3b/3c and 3c/1 were tested.
Substance fed
Incorporation
Analogues produced
(S)-14a
(R)-14a
(S)-14b
rac-14b
(S)-17
+
–
+
+
–
2a–c
–
3a–c
3a–c
–
Compound (mg per
plate)
1.5·10–2
1.5·10–3
1.5·10–4
rac-18
–
–
Hormaomycin (1)
100
78
57
87
97
94
97
9
15
47
0
21
0
72
0
53
83
–
–
–
Ϸ 0
0
27
0
0
44
0
33
57
–
–
–
0
–
13
–
–
Penicillin G
Feeding experiments with 5-nitro-3-thianorvaline (17)
and (2Ј-nitrophenyl)alanine (18) failed to produce any new
hormaomycin analogues.[23] Apparently, these amino acids
are no suitable substrates for the hormaomycin synthetase.
Shortly after the first identification of hormaomycin (1),
it had been shown that upon removal of both, the chlorine
and the N-hydroxy group from the Chpca unit of 1, at least
the antibiotic and morphogenic activity was completely
lost.[24] In order to find out, whether the free hydroxy func-
tion of Chpca of hormaomycin (1) is crucial for its activity,
the O-MOM-protected peptolide O-MOM-1 and its epimer
2a
2c
3a
3b/3c (ca. 5:1)
3c/1 (1:1)
20b
20c
21a
21b
21c
21e
0
–
at C-2 of (3-Ncp)Ala in the side chain epi-O-MOM-1 were model acyl tripeptide ester 20a exhibited a relatively high
prepared and tested. Towards this, the cyclic precursor 9[3b] activity, noticeably higher than those of O-MOM-1 and epi-
was deprotected and then coupled with the N-acylamino O-MOM-1. This unexpected result triggered the syntheses
acid 25[9] applying the PyAOP reagent.[25] This coupling and tests of several similar compounds 20a–c and 21a–e
step was accompanied by significant racemization at C-2 of (Scheme 4).
the (S)-(3-Ncp)Ala moiety, thus O-MOM-1 (26%) and epi-
The N-acylated tripeptide esters 20b and 20c were pre-
O-MOM-1 (16%) were obtained by separation of the pared in a similar manner as 20a starting from HCl·H-Phe-
obtained mixture of epimers by preparative TLC Val-OMe in 78 and 62% yield over three steps, respectively.
(Scheme 4).[26]
The removal of the O-MOM protecting group with
All of the newly obtained hormaomycin analogues and MgBr2·Et2O and EtSH gave the compounds 21b (75%) and
some model compounds were tested for their antibiotic ac- 21c (97%).
tivity against hormaomycin-hypersensitive Arthrobacter
species (Table 2, Table 3) as well as against other bacteria HCl·H-Phe-Val-OMe with Chpca-Phe-OH obtained after
and Candida albicans.[2c]
O-FM deprotection of 23. The latter was synthesized start-
Compound 21d was prepared in 21% yield by coupling
The hormaomycin analogues 2a–c and 3a–c containing ing from the known Boc-Phe-OFM[27] which, after removal
(NO2)Nva and (NO2)Nle, respectively, exhibited high anti- of the Boc group from its N-terminus, was first acylated
biotic activity against Arthrobacter species, yet none of the with Chpca(MOM)-OH (10) and then O-MOM-depro-
analogues was more active than hormaomycin (1) itself. tected to furnish the acylamino acid 23 in 82% yield over
This indicates that the cyclopropyl groups in 1 are not es- three steps. Finally, the HATU-mediated acylation of H-
sential for its antibacterial activity. Alkylation of the N-hy- (NO2)Nle-Phe-Val-OMe with Chba-OH (3-chloro-2-hy-
droxy group of the Chpca moiety caused almost complete droxybenzoic acid) yielded 21e in 45% yield.[28]
loss of the antibiotic activity (O-MOM-1 and epi-O-MOM-
The corresponding biological assays indicated that all of
1 vs. 1) pointing out that the free hydroxy group of Chpca is the compounds 20b–c and 21b–e at best had rather low hor-
indeed very important. Surprisingly, the O-MOM-protected maomycin-like antibiotic activity. Removal of the O-MOM
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Synthesis and Precursor-Directed Biosynthesis of New Hormaomycin Analogues
FULL PAPER
eronuclear Multiple Quantum Coherence) spectra were also mea-
sured. The signals marked with an asterisk could not be assigned
unambiguously. IR spectra: Bruker IFS 66 (FT-IR) spectrometer,
samples measured as KBr pellets or oils between KBr plates. MS:
EI-MS: Finnigan MAT 95, 70 eV. High resolution EI-MS spectra
with perfluorokerosene as reference substance; pre-selected ion
peak matching at R ϾϾ 10000 to be within 2 ppm of the exact
masses. ESI-MS: Finnigan LCQ. HPLC: pump: Kontron 322 sys-
tem, detector: Kontron DAD 440, mixer: Kontron HPLC 360, data
system: Kontron Kromasystem 200, columns: Knauer Nucleosil-
group from 20a does not improve the antibiotic activity
(20a vs. 21a, compared to O-MOM-1 vs. 1). A possible
reason for the unexpectedly high activity of the acyltripep-
tides 20a and 21a, especially compared to the very low ac-
tivity of (3-Ncp)Ala containing compounds 20b and 21b,
might be a different mode of action compared to that of
hormaomycin (1). The simple tripeptides 21d–e, which
show no biological activity at all, demonstrate the impor-
tance not only of Chpca but also of its combination with
the neighboring amino acids in the model peptides for ac- 100 C18 (analytical, 5 µm, 3 mm×250 mm), preparative: A – Kro-
masil C18 (7 µm, 20 mm×250 mm), B – Knauer Nucleosil-100 C18
(5 µm, 8 mm×250 mm), Kromasil C18 (7 µm,
tivity against the tested strains.
C
–
As an unexpected result, the hormaomycin analogue 2c
showed a remarkable in vitro antibiotic activity against C.
albicans, which, with inhibition zones of 21 and 13 mm
(1.5·10–2 and 1.5·10–3 mg per 6×0.65 mm plate, respec-
tively) in the serial dilution plate diffusion assay, was in the
same range as that for the antimycotic agent nystatine (20
and 14 mm). This is particularly noteworthy, as hormaomy-
cin (1) as well as all of the hormaomycin analogues de-
8 mm×250 mm). Optical rotations: Perkin–Elmer 241 digital po-
larimeter, 1-dm cell; optical rotation values are given in
10–1 degcm2 g–1; concentrations (c) are given in g/100 mL. Circular
dichroism: Jasco J 500A. Molar ellipticities (Θ) are given in de-
greecm2 10–1 mol–1. M.p. Büchi 510 capillary melting point appara-
tus, uncorrected values. TLC: Macherey–Nagel precoated sheets,
0.25 mm Sil G/UV254. The chromatograms were viewed under UV
light and/or by treatment with phosphomolybdic acid (10% in eth-
scribed here and before,[3c,5] were totally inactive against anol), or ninhydrine (0.2% in ethanol), or Ehrlich’s reagent (freshly
prepared solution of 1 g of 4-dimethylaminobenzaldehyde in 25 mL
of 36% HCl and 75 mL of methanol). Column chromatography:
Merck silica gel, grade 60, 230–400 mesh and Baker silica gel, 40–
140 mesh. Preparative TLC: Macherey–Nagel, silica gel Sil G/
UV254, layer thickness 0.25 mm (100×200 mm or 200×200 mm).
Elemental analyses: Mikroanalytisches Laboratorium des Instituts
yeasts.
Conclusion
In summary, these studies show that a replacement of the
cyclopropyl units in the (3-Ncp)Ala moiety by one or two für Organische und Biomolekulare Chemie der Universität
Göttingen. Starting materials: Anhydrous solvents were prepared
according to standard procedures by distillation with drying agents
and were stored under argon. All other solvents were distilled be-
fore use. All reactions were carried out with magnetic stirring if not
stated otherwise and, if air or moisture sensitive, substrates and/
or reagents were handled in flame-dried glassware under argon or
nitrogen. Organic extracts were dried with anhydrous MgSO4.
(2S,1ЈS,2ЈR)-[N-(2-trimethylsilyl)ethyloxycarbonyl]-(2Ј-nitrocyclo-
propyl)alanine (4),[3b] 2-(trimethylsilyl)ethyl N-succinimidyl car-
bonate,[29] 3-nitro-2-pyridinesulfenyl chloride,[30] the cyclic peptide
methylene groups is tolerated by the respective binding do-
mains of the hormaomycin synthetase. Furthermore, 6-ni-
tronorleucine cannot be an intermediate along the biosyn-
thesis route to H-(3-Ncp)Ala-OH. Hormaomycin ana-
logues with nitronorvaline or nitronorleucine instead of (3-
Ncp)Ala residues exhibit a similar biological activity as
hormaomycin (1) itself. However, in the case of an O-alkyl
group on the chloro(hydroxy)pyrrolcarboxylic acid residues
of 1, the antibiotic activity is almost completely lost. The
side chain of hormaomycin (1) alone is not responsible for lactone 9,[3b] HOAt,[31] Chpca(MOM)-OH (10),[9] racemic (2-ni-
trophenyl)alanine (18),[16] Boc-Phe-Val-OMe (19),[21] Boc-Phe-
its biological activity.
OFM (22),[27] Chpca(MOM)-(3-Ncp)Ala-OFM (24),[9] PyAOP[31]
were prepared as described previously elsewhere. Feeding experi-
ments and biological assays were carried out as described else-
Experimental Section
General: 1H NMR spectra: Bruker AM 250 (250 MHz), Varian
where.[3a,22,32]
1
Unity 300 (300 MHz), Varian Inova 600 (600 MHz). H chemical
shifts are reported in ppm relative to residual peaks of deuterated
solvents or tetramethylsilane. Higher-order NMR spectra were ap-
proximately interpreted as first-order spectra, if possible. The ob-
served signal multiplicities are characterized as follows: s = singlet,
d = doublet, t = triplet, q = quadruplet, quin = quintuplet, m =
multiplet, as well as br = broad, Ar-H = aryl-H. 13C NMR spectra
[additional DEPT (Distortionless Enhancement by Polarization
Transfer) or APT (Attached Proton Test)]: Bruker AM 250
(62.9 MHz), Varian Unity 300 (75.5 MHz) or Varian Inova 600
(125.7 MHz) instruments. 13C chemical shifts are reported relative
to peaks of solvents or tetramethylsilane. The following abbrevi-
ations are used: DEPT: + = primary or tertiary C (positive signal
Nω-Z-Protected (2S,1ЈS,2ЈR)-3-(2Ј-Aminocyclopropyl)alanine (7):
(2S,1ЈS,2ЈR)-3-(2Ј-Nitrocyclopropyl)alanine (6, 0.150 g, 0.86 mmol)
in anhydrous methanol (20 mL) was hydrogenated at ambient pres-
sure of hydrogen over 10% Pd on charcoal (0.150 g) for 15 h. The
mixture was then filtered through a pad of Celite®, and the filtrate
concentrated under reduced pressure to give the crude diamino acid
as a yellow oil, which was used directly for the next step without
any purification. This material was dissolved in water (4 mL) and
CuSO4 (72 mg, 0.45 mmol) was added. After 1 h NaHCO3 (0.145 g,
1.73 mmol) and then a solution of ZOSu (0.28 g, 1.12 mmol) in
acetone (2 mL) were added to the resulting deep violet solution,
and stirring was continued for an additional 1.5 h. The formed pre-
cipitate was then filtered off, washed with water (100 mL), Et2O
(100 mL) and dried. The resulting copper complex (0.265 g) was
in DEPT), – = secondary C (negative signal in DEPT), Cquat
=
quaternary C (no signal in DEPT); APT: + = primary or tertiary
C (positive signal in APT), – = secondary or quaternary C (nega-
tive signal in APT); whenever it was necessary and possible, HMBC
(Heteronuclear Multiple Bond Connectivity) and/or HMQC (Het-
dissolved in boiling water (5 mL), and Trilon B (0.509 g,
1.367 mmol) was added. The reaction mixture was vigorously
stirred for 10 min and then cooled in an ice bath. After 30 min the
precipitate was filtered off, washed with ice-cold water (50 mL),
Eur. J. Org. Chem. 2006, 1525–1534
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B. D. Zlatopolskiy, M. Radzom, A. Zeeck, A. de Meijere
FULL PAPER
Et2O (100 mL) and dried to give the first crop of 7 (0.112 g) as a
colorless solid. The mother liquor was concentrated under reduced
pressure to ca. 5 mL and cooled in an ice bath. The precipitate was
filtered off and crystallized from methanol to give the second crop
of 7 (12 mg, 52% overall yield over 2 steps). Rf = 0.19 (MeCN/
H2O/AcOH, 10:1:1); m.p. 212–216 °C. [α]2D0 = –14.47 (c = 0.32,
with CH2Cl2, then CH2Cl2/MeOH, 10:1, then CH2Cl2/MeOH, 3:1,
CH2Cl2/MeOH, 1:1 and finally with pure MeOH did not give the
desired product.
Preparation of N,O-Protected ω-Nitroamino Acids 13a,b. General
Procedure (GP 3): To a solution of the Nα-Boc-Nω-Z-protected di-
amino acid (4.09 mmol) in DMA (31 mL) were added tert-butyl
bromide (197 mmol), K2CO3 (106.4 mmol) and benzyltriethylam-
monium chloride (4.09 mmol), and the mixture was vigorously
stirred at 55–60 °C for 24 h. The reaction mixture was then poured
into water (0.7 L), and the resulting emulsion was extracted with
Et2O (2×200 mL). The organic layer was washed with water
(14×50 mL), brine (2×50 mL), dried, filtered and concentrated to
give the respective tert-butyl ester as a colorless oil, which was di-
rectly used for the next step without any further characterization.
1
0.1  HCl). H NMR (250 MHz, CD3OD): δ = 0.56–0.68 (m, 1 H,
3Ј-Ha), 0.78–0.98 (m, 2 H, 3Ј-Hb, 3-Ha), 1.06 (ddd, J = 10.5, 10.5,
10.5 Hz, 1 H, 3-Hb), 2.34 (ddd, J = 7.0, 3.5, 3.5 Hz, 1 H, 1Ј-H),
2.60 (d, J = 14.3 Hz, 1 H, 2Ј-H), 3.74 (d, J = 10.8 Hz, 1 H, 2-H),
5.20 (s, 2 H, Bzl-H), 7.28–7.44 (m, 5 H, Ar-H) ppm. 13C NMR
(62.9 MHz, DCl in D2O): δ = 11.5 (–, C-3Ј), 17.3 (+, C-1Ј), 29.1
(+, C-2Ј), 32.4 (–, C-3), 54.2 (+, C-2), 68.4 (–, Bzl-C), 128.3, 129.1,
129.4 (+, Ar-C), 136.8 (Cquat, Ar-C), 160.6 (Cquat, NCO2), 172.2
(Cquat, C-1). IR (KBr): ν = 3730–2700 cm–1, 3341, 3035, 2949,
˜
1696, 1599, 1529, 1276 ppm. MS (ESI): positive, m/z = 323 (8) [M –
H+ + 2Na+], 301 (80) [M + Na+], 279 (3) [M + H+]; negative,
m/z = 277 (100) [M – H+]. C14H18N2O4 (278.3): calcd. C 60.42, H
6.52, N 10.07; found C 60.26, H 6.32, N 9.89.
The respective tert-butyl ester (3.86 mmol) in EtOAc (15 mL) was
hydrogenated over 10% Pd on charcoal (0.28 g) under ambient
pressure of hydrogen for 2–3 h. The mixture was then filtered and
concentrated under reduced pressure to give the crude monopro-
tected diamino ester which was immediately used without any puri-
fication for the next step. This material was dissolved in 1,2-dichlo-
roethane (50 mL), and the solution added to a vigorously stirred
solution of MCPBA (90% purity, 42.86 mmol) in 1,2-dichloro-
ethane (200 mL) under intensive reflux for 2 min. Stirring under
reflux was continued for an additional 20 min, and the reaction
flask was then placed in an ice-water bath. After 15 min the reac-
tion mixture was concentrated under reduced pressure to ca.
120 mL, the residue diluted with Et2O (400 mL), the solution
washed with saturated aqueous Na2SO3 (2×100 mL), saturated
aqueous NaHCO3 (3×100 mL), water (2×100 mL), brine
(2×50 mL), dried, filtered and concentrated under reduced pres-
sure. The residual brown oil was purified by column chromatog-
raphy to give the desired products as pale yellow oils.
Deprotection of the N-MeZ-Protected Cyclic Peptide Lactone 9: The
N-MeZ-protected cyclic peptide lactone (10.0 mg, 10.1 µmol) was
deprotected by treatment with 10% anisole in TFA (1.1 mL) in the
dark at ambient temperature for 2 h. All volatiles were removed
under reduced pressure (0.05 Torr) at 20 °C. The residues were trit-
urated with hexane (6×5 mL) and dried to give the deprotected
material as a trifluoroacetate, which was directly used in the next
condensation step.
Peptide Condensation Step for the Preparation of Hormaomycin An-
alogues 2b and 11. General Procedure (GP 1): Peptide lactone 9
(10 µmol) was deprotected as described above, taken up with anhy-
drous CH2Cl2 (5 mL), the respective protected amino acid
(19 µmol), HATU (19 µmol) and HOAt (19 µmol) were added, and
the reaction mixture was cooled to 4 °C. After this, a solution of
DIEA (11 µmol) and TMP (57 µmol) in CH2Cl2 (2 mL) were added
at the same temperature within 5 min. The temperature was al-
lowed to reach 20 °C, and stirring was continued for an additional
15 h. Then the reaction mixture was diluted with Et2O (30 mL),
and the mixture washed with 1  KHSO4 (3×5 mL), water
(2×5 mL), saturated aqueous solution of NaHCO3 (3×5 mL),
water (3×5 mL), brine (2×5 mL), dried and concentrated under
reduced pressure. The residue was purified by preparative TLC and/
or recrystallization to give the respective intermediates.
Boc-(S)-(NO2)Nva-OtBu [(S)-13a]: Boc-(S)-Orn(Z)-OH [(S)-12a,
1.50 g, 4.09 mmol] was esterified according to GP 3 to give Boc-
(S)-Orn(Z)-OtBu (1.63 g, 94%, Rf = 0.21, EtOAc/hexane, 1:4),
which was further hydrogenated over 10% Pd on charcoal (0.28 g)
according to GP 3 for 3 h to give the crude monoprotected diamino
ester (Rf = 0.20 CHCl3/MeOH, 10:1) as a colorless oil. The latter
was oxidized according to GP3 using MCPBA (7.40 g, 90% purity,
38.6 mmol). The crude product was purified by column chromatog-
raphy (EtOAc/hexane, 1:6) to give (S)-13a (0.73 g, 55% over three
steps). Rf = 0.36, EtOAc/hexane, 1:6. [α]2D0 = 12.0 (c = 0.73, CHCl3).
1H NMR (250 MHz, CDCl3): δ = 1.44 [s, 9 H, C(CH3)3], 1.46 [s,
9 H, C(CH3)3], 1.63–1.80 (m, 1 H, 4-Ha), 1.80–1.95 (m, 1 H, 4-Hb),
1.95–2.05 (m, 2 H, 3-H), 4.10–4.28 (m, 1 H, 2-H), 4.43 (t, J =
6.6 Hz, 2 H, 5-H), 5.12 (d, J = 7.5 Hz, 1 H, NH) ppm. 13C NMR
(62.9 MHz, CDCl3): δ = 23.0 (–, C-4), 27.8 [+, C(CH3)3], 28.1 [+,
C(CH3)3], 29.6 (–, C-3), 52.9 (+, C-2), 74.8 (–, C-5), 79.8 [Cquat, C
Deprotection of O-MOM-Protected Hormaomycin Analogues O-
MOM-2b and 11 as Well as Model Acyl Tripeptides 21a–c and Acyl
Amino Ester 23. General Procedure (GP 2): The respective O-
MOM-protected compound (15 µmol) was deprotected by treat-
ment with MgBr2·Et2O (0.30 mmol) and EtSH (0.10 mmol) in
CH2Cl2 or Et2O (10 mL) at ambient temperature for 3 h. The mix-
ture was taken up with Et2O (40 mL) and washed with 1  KHSO4
(3×10 mL), water (4×10 mL), brine (2×5 mL), dried, filtered and
concentrated under reduced pressure. The residue was crystallized
from CH2Cl2/pentane and, if necessary, further purified by column
chromatography or preparative TLC.
(CH3)3], 82.4 [Cquat, C (CH3)3], 155.3 (Cquat, NCO2), 170.9 (Cquat
,
C-1) ppm. IR (film): ν = 3443 cm–1, 3008, 2980, 2868, 1743, 1556,
˜
1499, 1456, 1393, 1369, 1253, 1149, 1055. MS (ESI): positive mode,
m/z = 341 (100) [M + Na+]. C14H26N2O6 (318.4): calcd. C 52.82,
H 8.23, N 8.80; found C 52.56, H 8.57, N 8.84.
Attempted Deprotection of 11: A solution of the protected depsi-
peptide (6.0 mg, 4.62 µmol) in CH2Cl2 (4 mL) was treated with
Boc-(R)-(NO2)Nva-OtBu [(R)-13a]: Boc-(R)-Orn(Z)-OH [(S)-12a,
MgBr2·Et2O (48 mg, 18.6 µmol) and EtSH (11.7 mg, 14 µL, 4.35 g, 11.87 mmol] was esterified according to GP 3 to give Boc-
18.9 µmol) according to GP 2 for 4 h. The crude product after the
usual aqueous work-up (GP, 2) was dried, dissolved in CH2Cl2
(0.5 mL) and treated with 0.1  PPh3 in CH2Cl2 (0.4 mL) and 0.1 
Py·HCl in CH2Cl2 (0.4 mL) for 10 min. The mixture, containing
(according to TLC) two Ehrlich reagent active compounds, was
then placed on the top of a column with Sephadex LH-20. Elution
(R)-Orn(Z)-OtBu (4.70 g, 94%, Rf = 0.35, EtOAc/hexane, 1:3),
which was further hydrogenated in EtOAc (40 mL) over 10% Pd
on charcoal (0.3 g) according to GP 3 for 3 h to give the crude
monoprotected diamino ester as a faint yellow oil. The latter was
oxidized according to GP 3 using MCPBA (21.30 g, 90% purity,
111.1 mmol). The crude product was purified by column
1530
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Eur. J. Org. Chem. 2006, 1525–1534

Synthesis and Precursor-Directed Biosynthesis of New Hormaomycin Analogues
FULL PAPER
chromatography (EtOAc/hexane, 1:6) to give (R)-13a (1.95 g, 52%
over three steps). [α]2D0 = –11.8 (c = 0.68, CHCl3).
bath was removed, and the reaction mixture was allowed to stand
at ambient temperature for an additional 90 min. All volatiles were
then removed under reduced pressure, and the residue was recrys-
tallized from MeOH/EtOAc to give rac-14b·HCl (1.50 g, 94%) as
a colorless solid.
(S)-5-Nitronorvaline Hydrochloride [(S)-14a·HCl]: Compound (S)-
13a (1.20 g, 3.77 mmol) was deprotected with TFA (5 mL) in the
dark at ambient temperature for 1 h. All volatiles were then re-
moved under reduced pressure, and the residue was taken up with
toluene (2×20 mL) which was then distilled off to remove the last
traces of TFA. To transform the resulting trifluoroacetate into hy-
drochloride it was taken up with 2  HCl in EtOAc (3×20 mL)
which was then distilled off. The resulting oil was triturated with
acetone to give a light brown precipitate. Et2O was then added to
complete precipitation. The crude product was filtered off and
washed with acetone/Et2O, 1:1 (200 mL) to give (S)-14a·HCl
(0.420 g, 56%) as an off-white solid. M.p. 132–133 °C (dec.). [α]2D0
= 16.8 (c = 0.22, 0.1  HCl) [lit. (for free base):[14b] [α]2D0 = 22.8 (c
Methyl N-Boc-(S)-5-nitro-4-thianorleucinate (16): SO2Cl2 (0.70 mL,
1.17 g, 8.65 mmol) was added to a solution of Boc-Cys-OMe (15,
2.0 g, 8.50 mmol) in CH2Cl2 (80 mL) at –40 °C within 10 min and
the reaction mixture was stirred at this temperature for an ad-
ditional 3 h. Then the reaction flask was connected to a vacuum
pump, the cooling bath was removed and volatiles were evaporated
until the temperature of the reaction flask reached 0 °C (the ice on
walls of the flask began to thaw) to leave the crude sulfenyl chlo-
ride. The reaction flask was immediately cooled to –78 °C, and the
oily orange residue was dissolved in cold THF (60 mL). Then a
cold (ca. –10 to –20 °C) jelly-like suspension of potassium methyl-
nitronate [prepared from nitromethane (0.92 mL, 1.04 g,
17.04 mmol) and tBuOK (1.34 g, 11.94 mmol)] in THF (50 mL)
was added through a Teflon tube. The transparent orange solution
immediately became turbid. After 2 h the cooling bath was re-
moved, and aqueous AcOH (4 mL in 20 mL H2O) was added to
the reaction mixture when its temperature reached ca. –10–0 °C.
All volatiles were removed under reduced pressure, the residue was
diluted with Et2O (70 mL), the solution washed with H2O
(4×20 mL), 1  KHSO4 (3×20 mL), saturated aqueous NaHCO3
(20 mL), H2O (2×20 mL), brine (2×20 mL), dried, filtered and
concentrated under reduced pressure. The residual orange oil was
purified by column chromatography (EtOAc/hexane, 1:3) to give 16
(1.70 g, 68%) as a faint yellow oil with a distinct odor, which grad-
ually solidified to give a colorless solid. Rf = 0.21, EtOAc/hexane,
1:3; m.p. 59–61 °C. [α]2D0 = –2.2 (c = 0.60, CHCl3). 1H NMR
(250 MHz, CDCl3): δ = 1.451, 1.454 [2×s, 9 H, C(CH3)3], 3.15 (dd,
J = 5.0, 5.0 Hz, 1 H, 3-Ha), 3.50 (dd, J = 5.0, 5.0 Hz, 1 H, 3-Hb),
3.789, 3.793 (2×s, 3 H, OCH3), 4.58–4.66 (m, 1 H, 2-H), 5.21 (d,
J = 13.8 Hz, 1 H, 5-Ha), 5.25–5.40 (br., 1 H, NH), 5.33 (d, J =
13.8 Hz, 1 H, 5-Hb) ppm. 13C NMR (62.9 MHz, CDCl3): δ = 28.1
[+, C(CH3)3], 35.3 (–, C-3), 52.8 (+, C-2), 52.9 (+, OCH3), 76.2
1
= 0.56, diluted. HCl)]. H NMR (300 MHz, D2O): δ = 1.89–2.24
(m, 4 H, 3-H, 4-H), 4.06 (t, J = 5.0 Hz, 1 H, 2-H), 4.56 (t, J =
5.4 Hz, 2 H, 5-H) ppm. 13C NMR (50.3 MHz, D2O): δ = 22.4 (–,
C-4), 26.8 (–, C-3), 52.5 (+, C-2), 74.5 (–, C-5), 171.7 (Cquat, C-1)
ppm. IR (KBr): ν = 3750–1800 cm–1, 2933, 1735, 1552, 1500, 1379,
˜
1349, 1244. MS (ESI): positive mode, m/z = 229 (5) [M – 2H+
+
3Na+], 207 (8) [M – H+ + 2Na+], 185 (12) [M + Na+]; negative
mode, m/z = 345 (100) [2M – 2H+ + Na+]. C5H11ClN2O4 (198.6):
calcd. C 30.24, H 5.58, N 14.10; found C 30.50, H 5.30, N 13.97.
(R)-5-Nitronorvaline Hydrochloride [(R)-14a·HCl]: Compound (R)-
13a (1.95 g, 6.12 mmol) was dissolved in the ice-cold saturated
solution (ca. 4–5 ) of HCl in EtOAc (50 mL). After 30 min the
cooling bath was removed, and the reaction mixture was allowed
to stand at ambient temperature for an additional 90 min. All vola-
tiles were then removed under reduced pressure, and the residue
was dissolved with MeOH (ca. 5 mL). EtOAc (ca. 60 mL) was then
added and after standing in the refrigerator (4 °C) for 15 h the pre-
cipitate was filtered off to give (R)-14a·HCl (0.73 g, 60%) as a col-
orless solid. The mother liquor was concentrated, and the residue
was recrystallized from MeOH/EtOAc to give a second crop of (R)-
14a·HCl (0.38 g, 91% overall yield). [α]2D0 = –12.1 (c = 0.52, H2O).
(S)-6-Nitronorleucine Hydrochloride [(S)-14b·HCl]: Compound (S)-
13b (2.22 g, 6.68 mmol) was deprotected with TFA (11 mL) in the
dark at ambient temperature for 1 h. All volatiles were then re-
moved under reduced pressure, and the residue was taken up with
toluene (2×15 mL) which was then distilled off to remove the last
traces of TFA. To transform the resulting trifluoroacetate into a
hydrochloride it was taken up with 1  HCl (30 mL) which was
then distilled off. The resulting oil was triturated with acetone to
give a light brown precipitate. The residue was then dissolved in
methanol (15 mL), the resulting solution was filtered through Ce-
lite®, and the filtrate concentrated to ca. 2–3 mL. EtOAc (50 mL)
was added, the precipitate was filtered off and washed with EtOAc
(100 mL) to give (S)-14b·HCl (1.19 g, 84%) as a colorless solid. Rf
(–, C-5), 80.5 [Cquat, C (CH3)3], 155.0 (Cquat, NCO2), 170.7 (Cquat
,
C-1) ppm. IR (KBr): ν = 3750–2850 cm–1, 2400–1850, 1734, 1629,
˜
1558, 1487, 1404. MS (ESI): positive mode, m/z = 317 (30) [M +
Na+], 295 (100) [M + H+]. C10H18N2O6S (294.3): calcd. C 40.81,
H 6.16, N 9.52; found C 40.79, H 5.93, N 9.65.
(S)-5-Nitro-4-thianorleucine Hydrochloride (17·HCl): Degassed
NaOH (0.25 , 43.4 mL, 10.85 mmol) was added to an ice-cold de-
gassed solution of 16 (1.24 g, 4.21 mmol) in THF (10 mL) within
5 min (partial precipitation of the starting material was observed),
and the mixture was stirred at the same temperature. More THF
was then added (2, 3 and 5 mL after 5, 10 and 20 min, respectively).
After 80 min Et2O (50 mL), NaCl (4–5 g) and then dropwise 2 
H2SO4 (5.6 mL, 11.2 mmol) were added to the resulting thick col-
orless suspension. The organic layer was separated, washed with
1  KHSO4 (2×15 mL), brine (2×15 mL), dried, filtered and con-
centrated under reduced pressure. The residual yellow oil was im-
mediately treated with 4  HCl in EtOAc (25 mL) at ambient tem-
perature. After 20 min all volatiles were removed under reduced
pressure and the residual solid was triturated with EtOAc, and the
mixture cooled to 4 °C. After 30 min the precipitate was filtered off
and washed with EtOAc to give 17·HCl (0.74 g, 81% over two
steps) as a colorless solid. This substance has only limited stability
in DMSO and water solution. Because of rapid H/D exchange it
was impossible to observe the signal of C-5 in the 13C NMR spec-
trum of 17·HCl measured in D2O. Rf = 0.85, MeCN/H2O/AcOH,
10:1:1; m.p. 128–129 °C (dec.). [α]2D0 = 9.0 (c = 0.49, H2O). 1H
= 0.09, MeCN/H2O/AcOH, 10:1:1; m.p. 180–181 °C (dec.). [α]2D0
=
10.3 (c = 0.95, H2O). 1H NMR (250 MHz, D2O): δ = 1.40–1.61
(m, 2 H, 4-H), 1.94 (dd, J = 6.8, 6.8 Hz, 1 H, 3-Ha), 1.97–2.12 (m,
3 H, 3-Hb, 5-H), 4.06 (t, J = 6.1 Hz, 1 H, 2-H), 4.57 (t, J = 6.6 Hz,
2 H, 6-H) ppm. 13C NMR (62.9 MHz, D2O): δ = 21.8 (–, C-4),
26.7 (–, C-3), 29.7 (–, C-5), 53.4 (+, C-2), 75.7 (–, C-6), 172.8 (Cquat
,
C-1) ppm. IR (KBr): ν = 3432 cm–1, 3250–2750, 1747, 1556, 1518,
˜
1218, 1120. MS (ESI): positive mode, m/z = 221 (15) [M –H+
+
2Na+], 199 (52) [M + Na+]. C6H13ClN2O4 (212.6): calcd. C 33.89,
H 6.16, N 13.17; found C 34.15, H 5.94, N 13.18.
rac-6-Nitronorleucine Hydrochloride [rac-14b·HCl]: Compound rac-
13b (2.50 g, 7.52 mmol) was dissolved in an ice-cold saturated solu-
tion (ca. 4–5 ) of HCl in EtOAc (50 mL). After 30 min the cooling
Eur. J. Org. Chem. 2006, 1525–1534
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B. D. Zlatopolskiy, M. Radzom, A. Zeeck, A. de Meijere
FULL PAPER
NMR (300 MHz, D2O): δ = 3.38 (dd, J = 6.3, 6.3 Hz, 1 H, 3-Ha),
3.53 (dd, J = 3.8, 3.8 Hz, 1 H, 3-Hb), 4.33 (dd, J = 6.3, 3.8 Hz, 1 H,
2-H), 5.64 (s, 2 H, 5-H) ppm. 13C NMR (62.9 MHz, [D6]DMSO): δ
= 32.0 (–, C-3), 51.8 (+, C-2), 76.7 (–, C-5), 169.1 (Cquat, C-1) ppm.
MS (ESI): positive mode, m/z = 203 (40) [M + Na+], 181 (100) [M
+ H+]; negative mode, m/z = 359 (100) [2M – H+], 217/215 (23/68)
[M + Cl–], 179 (28) [M – H+]. C4H9ClN2O4S (216.6): calcd. C
22.18, H 4.19, N 12.93; found C 22.13, H 4.06, N 13.04.
(2.5 mg, 26%) as a colorless glass and epi-O-MOM-1 (1.5 mg,
16%) as a colorless glass.
O-MOM-1: Rf = 0.11, acetone/hexane, 1:3. 1H NMR (600 MHz,
CDCl3): δ = –0.26 [ddd, J = 6.0, 6.0, 6.0 Hz, 1 H, 3Ј-Ha, (3-Ncp)
Ala], 0.07–0.17 [m, 1 H, 3-Ha, (3-Ncp)Ala], 0.52–0.61 [m, 1 H, 1Ј-
H, (3-Ncp)Ala], 0.68–0.79 [m, 1 H, 3-Hb, (3-Ncp)Ala], 0.88 (t, J =
7.2 Hz, 3 H, 5-H, Ile), 1.02 (d, J = 6.6 Hz, 3 H, 1Ј-H, Ile), 1.05
[ddd, J = 6.0, 6.0, 6.0 Hz, 1 H, 3Ј-Hb, (3-Ncp)Ala], 1.10–1.14 [m,
1 H, 3Ј-Ha, (3-Ncp)Ala], 1.19–1.27 [m, 2 H, 4-Ha, Ile, 3Ј-Hb, (3-
Ncp)Ala], 1.29 [d, J = 6.6 Hz, 3 H, 4-H, (βMe)Phe], 1.39 [d, J =
6.6 Hz, 3 H, 4-H, (βMe)Phe], 1.50–1.56 (m, 1 H, 4-Hb, Ile), 1.59 (d,
J = 7.2 Hz, 3 H, 4-H, a-Thr), 1.64–1.70 [m, 1 H, 3-Ha, (3-Ncp)Ala],
1.69 [dd, J = 7.2, 1.8 Hz, 3 H, 3Ј-H, (4-Pe)-Pro], 1.75–1.85 [m, 2 H,
3-H, Ile, 3-Ha, (4-Pe)Pro], 1.90–1.95 [m, 1 H, 3-Hb, (3-Ncp)Ala],
1.95–2.00 [m, 1 H, 1Ј-H, (3-Ncp)Ala], 2.40 [ddd, J = 12.0, 6.0,
6.0 Hz, 1 H, 3-Hb, (4-Pe)-Pro], 3.05 [dq, J = 10.8, 6.6 Hz, 1 H, 3-
H, (βMe)Phe], 3.11–3.17 [m, 1 H, 2Ј-H, (3-Ncp)Ala], 3.24–3.32 [m,
2 H, 4-H, 5-Ha, (4-Pe)-Pro], 3.71 [dq, J = 4.2, 7.2 Hz, 1 H, 3-H,
(βMe)Phe], 3.75 (s, 3 H, OMe), 3.90 (dd, J = 6.6, 5.4 Hz, 1 H, 2-
H), 3.93–3.98 [m, 1 H, 5-Hb, (4-Pe)-Pro], 4.09 [ddd, J = 6.6, 3.0,
3.0 Hz, 1 H, 2Ј-H, (3-Ncp)Ala], 4.26 (dd, J = 13.2, 13.2 Hz, 1 H, 2-
H), 4.30 (dd, J = 11.4, 6.0 Hz, 1 H, 2-H), 4.61 (dd, J = 8.4, 4.8 Hz,
1 H, 2-H), 4.64–4.70 (m, 2 H, 2-H), 5.10–5.17 [m, 1 H, 2-H, (3-
Ncp)Ala], 5.24–5.29 [m, 1 H, 1Ј-H, (4-Pe)-Pro], 5.39 (dq, J = 1.8,
7.2 Hz, 1 H, 3-H, a-Thr), 5.47 (d, J = 6.0 Hz, 1 H, Ha, OCH2O),
5.50 (d, J = 6.0 Hz, 1 H, Hb, OCH2O), 5.64 [dq, J = 10.5, 7.2 Hz,
1 H, 2Ј-H, (4-Pe)-Pro], 5.75–5.81 (br., 2 H, NH), 6.17 (d, J =
4.5 Hz, 1 H, 4-H, Chpca), 6.70 (d, J = 9.0 Hz, 1 H, NH), 6.84 (d,
J = 4.5 Hz, 1 H, 3-H, Chpca), 7.06 (dd, J = 7.5, 7.5 Hz, 1 H, Ar-
H), 7.09 (d, J = 7.2 Hz, 2 H, Ar-H), 7.15 (dd, J = 7.5, 7.5 Hz, 3 H,
Ar-H), 7.16 (d, J = 7.2 H, 1 H, NH), 7.22–7.31 (m, 5 H, Ar-H,
NH), 7.38 (d, J = 9.6 Hz, 1 H, NH), 7.75 (d, J = 9.0 Hz, 1 H, NH),
8.79 (d, J = 9.0 Hz, 1 H, NH) ppm. 13C NMR (150.8 MHz,
CDCl3): δ = 10.8 (+, C-5, Ile), 13.2 [+, C-4, (βMe)Phe], 13.3 [+, C-
3Ј, (4-Pe)-Pro], 15.5 (+, C-1Ј, Ile), 17.2 [–, C-3Ј, (3-Ncp)Ala], 17.3
[–, C-3Ј, (3-Ncp)Ala], 17.5 (+, C-4, a-Thr), 18.3 [+, C-4, (βMe)Phe],
20.7 [+, C-1Ј, (3-Ncp)Ala], 21.3 [+, C-1Ј, (3-Ncp)Ala], 24.9 (–, C-4,
Ile), 29.7 [–, C-3, (3-Ncp)Ala], 34.0 [–, C-3, (3-Ncp)Ala], 35.4 [–, C-
3, (4-Pe)-Pro], 36.7 [+, C-4, (4-Pe)-Pro], 38.6 (+, C-3, Ile), 39.4 [+,
C-3, (βMe)Phe], 42.7 [+, C-3, (βMe)Phe], 50.2 [+, C-2Ј, (3-Ncp)
Ala], 51.5 (+, C-2), 52.9 [–, C-5, (4-Pe)-Pro], 54.7 (+, C-2), 54.9 (+,
C-2), 58.5 [+, C-2Ј, (3-Ncp)Ala], 59.4 (+, OMe, C-2), 59.6 (+, C-
2), 60.2 (+, C-2), 61.5 (+, C-2), 69.9 (+, C-3, a-Thr), 104.5 (–,
OCH2O), 106.1 (+, C-4, Chpca), 111.5 (+, C-3, Chpca), 119.8
(Cquat, C-2, Chpca), 121.5 (Cquat, C-5, Chpca), 126.9, 127.1, 127.5,
127.6, 128.5, 128.6 (+, Ar-C), 127.4 [+, C-1Ј, (4-Pe)-Pro], 128.5 [+,
C-2Ј, (4-Pe)-Pro], 142.3 (2×Cquat, Ar-C), 158.6 (Cquat, C-1, Chpca),
168.8, 169.9, 170.1, 170.2, 171.1, 171.3, 171.4 (Cquat, C-1) ppm. UV
(MeOH): neutral: λmax (ε) = 268 (1.8·104), 201 (7.5·105) nm; basic:
341 (1.4·103), 268 (1.5·104), 205 (9.1·104) nm; acidic: 341 (2.7·103),
268 (1.4·104)nm. CD (MeOH): λmax (Θ) = 268.2 (2.71·104), 259.3
(2.40·104), 222.1 (–41.7·104) nm (c = 8.18·10–6 ). MS (ESI): posi-
tive, m/z (%) = 1196 (100) [M + Na+]; negative, m/z (%) = 1171
(100) [M – H+].
Teoc-(S)-(NO2)Nle-OH:
A
solution of TeocOSu (183 mg,
0.71 mmol) in acetone (7 mL) was added to a vigorously stirred
solution of (S)-14b·HCl (150 mg, 0.71 mmol) and NaHCO3
(0.218 g, 2.60 mmol) in water (7 mL) (if an emulsion formed ace-
tone and/or water were added to obtain a homogeneous solution),
and the mixture was stirred for an additional 15 h. Acetone was
removed under reduced pressure, and the pH value of the residual
water solution was adjusted to 2–3 with 1  KHSO4. The resulting
emulsion was extracted with Et2O (50 mL), and the ethereal layer
was washed with 1  KHSO4 (3×10 mL), water (10×10 mL), brine
(2×5 mL), dried, filtered and concentrated under reduced pressure.
The residue was purified by column chromatography [EtOAc/hex-
ane, 1:2 (2% AcOH)]. The resulting colorless oil was taken up with
hexane (3×15 mL) which was then distilled off under reduced pres-
sure to remove the last traces of AcOH. The partially solidified
residue was triturated with hexane and filtered off to give the title
compound (160 mg, 71%) as a colorless solid. Rf = 0.37 EtOAc/
hexane, 1:2 (2% AcOH) (staining with ninhydrin); m.p. 71–72 °C.
[α]2D0 = 23.7 (c = 0.675, CHCl3). H NMR (250 MHz, CDCl3): δ =
1
0.04 [s, 9 H, Si(CH3)3], 1.00 (t, J = 7.5 Hz, 2 H, 2-H, Teoc), 1.43–
1.61 (m, 2 H, 4-H), 1.68–1.85 (m, 1 H, 3-Ha), 1.85–2.18 (m, 3 H,
3-Hb, 5-H), 4.18 (t, J = 8.0 Hz, 2 H, 1-H, Teoc), 4.40 (t, J = 8.8 Hz,
2 H, 6-H), 6.68–6.82 (d, J = 7.8 Hz, br, 1 H, NH) 6.50–7.80 (br.,
1 H, CO2H) ppm; the signal of 1-H of Teoc and 6-H overlapped
the signal of 2-H. 13C NMR (62.9 MHz, CDCl3): δ = –1.6 [+,
Si(CH3)3], 17.6 (–, C-2, Teoc), 21.9 (–, C-4), 26.6 (–, C-3), 31.6 (–,
C-5), 53.05, 53.7 (+, C-2), 63.8, 64.8 (–, C-1, Teoc), 75.1 (–, C-6),
156.5, 157.7 (Cquat, NCO2), 175.8, 176.6 (Cquat, C-1) ppm. IR
(KBr): ν = 3550–2800 ·cm–1, 3427, 2959, 2908, 2880, 1750, 1726,
˜
1664, 1553, 1410, 1252, 1202, 1068. MS (ESI): negative mode,
m/z = 661 (100) [2M + Na+ – 2H+], 319 (10) [M – H+].
C12H24N2O6Si (320.4): calcd. C 44.98, H 7.55, N 8.74; found C
45.16, H 7.29, N 8.66.
O-MOM-Protected Hormaomycin O-MOM-1 and its Epimer epi-
O-MOM-1: The ester 25 (5.4 mg, 10.0 µmol) was deprotected with
20% Et2N in MeCN (1 mL) for 40 min. The mixture was then con-
centrated under reduced pressure, the residue was washed with hex-
ane, taken up with Et2O (30 mL), washed with 1  NaHSO4
(3×5 mL), water (3×5 mL), brine (2×5 mL). The organic layer
was dried, filtered and concentrated under reduced pressure. The
resulting crude N-acyl amino acid 26 [Rf = 0.42, EtOAc/hexane,
1:2 (2% AcOH)] was dried at 0.01 Torr for 1 h and then introduced
in the coupling reaction with the deprotected depsipeptide obtained
after treatment of the N-MeZ-protected cyclodepsipeptide
9
(8.0 mg, 8.18 µmol) with 10% anisole in TFA (1 mL) as described
before using PyAOP (8.4 mg, 16.1 µmol), HOAt (2.2 mg,
16.2 µmol), DIEA (1.3 mg, 10.1 µmol) and TMP (3.8 mg,
31.4 µmol) in CH2Cl2 (1 mL) according to GP 1 for 15 h. The mix-
ture was then diluted with Et2O and subjected to the usual aqueous
work-up (GP, 1). TLC analysis showed the presence of the two
main reaction products which were separated by preparative TLC
(100×200 mm, acetone/hexane, 1:3, threefold development). Each
fraction was additionally purified by preparative TLC (40×80 mm,
acetone/hexane, 1:3, threefold development) to give O-MOM-1
epi-O-MOM-1: Rf
=
0.09, acetone/hexane, 1:3. 1H NMR
(600 MHz, CDCl3): δ = 0.68 [ddd, J = 6.6, 6.6, 6.6 Hz, 1 H, 3Ј-Ha,
(3-Ncp)Ala], 0.79–0.92 [m, 2 H, 1Ј-H, 3-Ha, (3-Ncp)Ala], 0.98 (t, J
= 7.2 Hz, 3 H, 5-H, Ile), 1.01 (d, J = 6.6 Hz, 3 H, 1Ј-H, Ile), 1.15
[ddd, J = 6.6, 6.6, 6.6 Hz, 1 H, 3Ј-Hb, (3-Ncp)Ala], 1.19–1.32 [m,
6 H, 3Ј-H, (3-Ncp)Ala, 4-H, (βMe)Phe, 4-Ha, Ile], 1.34 [d, J =
7.2 Hz, 3 H, 4-H, (βMe)Phe], 1.46–1.62 [m, 3 H, 4-Hb, Ile, 3-H, (3-
Ncp)Ala], 1.64–1.70 [m, 1 H, 3-Ha, (3-Ncp)Ala], 1.69 [dd, J = 7.2,
1.8 Hz, 3 H, 3Ј-H, (4-Pe)-Pro], 1.76 [ddd, J = 11.4, 11.4, 11.4 Hz,
1532
www.eurjoc.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 1525–1534

Synthesis and Precursor-Directed Biosynthesis of New Hormaomycin Analogues
FULL PAPER
Kozhushkov, S. V. Nikolaev, A. Zeeck, A. de Meijere, Chem.
Eur. J. 2004, 10, 4708–4717; for the total synthesis of 1 see: b)
B. D. Zlatopolskiy, A. de Meijere, Chem. Eur. J. 2004, 10,
4718–4727; c) For an investigation of its structure in solution
and the synthesis of some new analogues see: U. M.
Reinscheid, B. D. Zlatopolskiy, C. Griesinger, A. Zeeck, A.
de Meijere, Chem. Eur. J. 2005, 11, 2929–2945.
K. Otoguro, H. Ui, A. Ishiyama, N. Arai, M. Kobayashi, Y.
Takahashi, R. Masuma, K. Shiomi, H. Yamada, S. Omura, J.
Antibiot. 2003, 56, 322–324.
S. I. Kozhushkov, B. D. Zlatopolskiy, M. Brandl, P. Alver-
mann, M. Radzom, B. Geers, A. de Meijere, A. Zeeck, Eur. J.
Org. Chem. 2005, 854–863.
O. V. Larionov, S. I. Kozhushkov, M. Brandl, A. de Meijere,
Mendeleev Commun. 2003, 199–200.
3-Ha, (4-Pe)Pro], 1.90–1.99 (m, 1 H, 3-H, Ile), 2.05–2.13 [m, 1 H,
1Ј-H, (3-Ncp)Ala], 2.40 [ddd, J = 11.4, 6.0, 6.0 Hz, 1 H, 3-Hb, (4-
Pe)-Pro], 3.13–3.23 [m, 1 H, 3-H, (βMe)Phe], 3.23–3.32 [m, 2 H, 4-
H, 5-Ha, (4-Pe)-Pro], 3.62 (s, 3 H, OMe), 3.67–3.75 [m, 1 H, 3-H,
(βMe)Phe], 3.85 [ddd, J = 6.6, 3.0, 3.0 Hz, 1 H, 2Ј-H, (3-Ncp)Ala],
3.96–4.01 (m, 1 H, 2-H), 4.05–4.09 [m, 1 H, 5-Hb, (4-Pe)-Pro], 4.13
[ddd, J = 6.6, 3.0, 3.0 Hz, 1 H, 2Ј-H, (3-Ncp)Ala], 4.13–4.21 (m,
1 H, 2-H), 4.56–4.72 (m, 3 H, 2-H), 4.61 (dd, J = 9.0, 4.5 Hz, 1 H,
2-H), 4.84 (dd, J = 9.0, 2.4 Hz, 1 H, 2-H), 5.20–5.35 [m, 2 H, 1Ј-
H, (4-Pe)Pro, 3-H, a-Thr], 5.22 (d, J = 6.0 Hz, 1 H, Ha, OCH2O),
5.28 (d, J = 6.0 Hz, 1 H, Hb, OCH2O), 5.61 [dq, J = 10.5, 7.2 Hz,
1 H, 2Ј-H, (4-Pe)-Pro], 6.03 (d, J = 4.8 Hz, 1 H, 4-H, Chpca), 6.33–
6.46 (br., 1 H, NH), 6.57–6.69 (br., 1 H, NH), 6.70 (d, J = 4.8 Hz,
1 H, 3-H, Chpca), 7.13–7.34 (m, 14 H, Ar-H, NH), 7.57–7.71 (br.,
1 H, NH) ppm; the absorption of water masked the signal of 4-H
of a-Thr residue. 13C NMR (150.8 MHz, CDCl3): δ = 10.2 (+, C-
5, Ile), 13.4 [+, C-4, (βMe)Phe, C-3Ј, (4-Pe)-Pro], 14.7 (+, C-1Ј, Ile),
17.4 [–, C-3Ј, (3-Ncp)Ala], 17.9 [–, C-3Ј, (3-Ncp)Ala], 18.6 (+, C-4,
a-Thr), 21.5 [+, C-4, (βMe)Phe], 24.4 [+, C-1Ј, (3-Ncp)Ala], 24.9
(–, C-4, Ile), 29.3 [+, C-1Ј, (3-Ncp)Ala], 29.7 [–, C-3, (3-Ncp)Ala],
30.9 [–, C-3, (3-Ncp)Ala], 35.6 [–, C-3, (4-Pe)-Pro], 36.6 [+, C-4, (4-
Pe)-Pro], 37.5 (+,C-3, Ile), 39.0 [+, C-3, (βMe)Phe], 40.2 [+, C-3,
(βMe)Phe], 52.3 (+, C-2), 52.9 [–, C-5, (4-Pe)-Pro], 53.2 (+, C-2),
54.4 (+, C-2), 55.8 (+, C-2), 59.0 [+, C-2Ј, (3-Ncp)Ala], 59.3 [+, C-
2Ј, (3-Ncp)Ala], 59.49 (+, OMe, C-2), 59.53 (+, C-2), 60.7 (+, C-
2), 72.2 (+, C-3, a-Thr), 104.2 (–, OCH2O), 104.9 (+, C-4, Chpca),
110.9 (+, C-3, Chpca), 118.7 (Cquat, C-2, Chpca), 122.1 (Cquat, C-
5, Chpca), 126.8, 127.1, 127.3, 128.6, 128.7, 128.8 (+, Ar-C), 127.7
[4]
[5]
[6]
[7]
[8]
R. Matsueda, R. Walter, Int. J. Peptide Protein Res. 1980, 16,
392–401.
a) See ref.[3b] for an appropriate discussion; b) Moreover, the
side chain of hormaomycin (1) showed only limited stability
to conditions [20% piperidine or diethylamine in MeCN, 10%
tris(aminomethyl)amine in CH2Cl2, etc] routinely used for the
Fmoc deprotection (cf. ref.[9]).
[9]
B. D. Zlatopolskiy, H.-P. Kroll, E. Melotto, A. de Meijere, Eur.
J. Org. Chem. 2004, 4492–4502.
[10]
These deprotection conditions worked quite satisfactorily for
Z-Orn(Npys)-( S)-1-phenethylamide to completely cleave off
the Npys group within 2 min and give the appropriate amino
amide, in: 75% yield. For this model compound the Npys
group was only partially cleaved off with MgBr2·Et2O/EtSH in
CH2Cl2, and it was rather insensitive to 2-pyridinethiol N-ox-
ide to give only traces of deprotected material after 5 h. Cf.
B. D. Zlatopolskiy, Dissertation, University of Göttingen, 2003.
[+, C-1Ј, (4-Pe)-Pro], 128.1 [+, C-2Ј, (4-Pe)-Pro], 141.6 (2×Cquat
,
Ar-C), 157.9 (Cquat, C-1, Chpca), 169.8, 170.0, 170.2, 170.9 (× 2),
171.2, 171.3 (Cquat, C-1) ppm. UV (MeOH): neutral: λmax (ε) = 261
(1.7·104), 201 (6.6·105) nm; basic: 341 (1.4·103), 267 (1.4·104), 226
(2.1·104), 204 (7.6·104) nm; acidic: 341 (2.7·103), 269 (2.0·104) nm.
CD (MeOH): λmax (Θ) = 274 (2.08·104), 221.6 (–4.99·104) nm (c =
6.48·10–6 ). MS (ESI): positive, m/z (%) = 1196 (100) [M + Na+];
negative, m/z (%) = 1207 (40) [M + Cl–], 1171 (100) [M – H+].
[11]
[12]
[13]
F. Yokokawa, H. Sugiyama, T. Shioiri, N. Katagiri, O. Oda, H.
Ogawa, Tetrahedron 2001, 57, 4759–4766.
P. Chevallet, P. Garrouste, B. Malawska, J. Martinez, Tetrahe-
dron Lett. 1993, 34, 7409–7412.
a) K. E. Gilbert, W. T. Borden, J. Org. Chem. 1979, 44, 659–
661; b) P. Peterli-Roth, M. P. Maguire, E. Leon, H. Rapoport,
J. Org. Chem. 1994, 59, 4186–4193.
[14]
a) Previously, the amino acids 14a and 14b were obtained in
enantiomerically pure form by separation of racemates. The
nucleophilic substitution of iodine on a suitably protected 4-
iodohomoserine with AgNO2 in benzene gave the correspond-
ing derivative of racemic 5-nitronorvaline in low yield, which
could be deprotected.[14b] Racemic 6-nitronorleucine was ob-
tained by hydrolysis of the corresponding N,N,O-tris(trimethyl-
silyl)derivative, which in turn was prepared by alkylation of
trimethylsilyl N,N-bis(trimethylsilyl)glycinate with 1-nitro-4-
bromobutane (41%);[14c] b) B. Mauer, W. Keller-Schierlein,
Helv. Chim. Acta 1969, 52, 388–396; c) E. Bayer, K. Schmidt,
Tetrahedron Lett. 1973, 14, 2051–2054.
Deprotection with HCl always gave better yields of these amino
acids, with TFA significant amounts of unidentified side prod-
ucts were formed.
a) N. A. Meanwell, H. R. Roth, E. C. R. Smith, D. L. Wedding,
J. J. K. Wright, J. S. Fleming, E. Gillespie, J. Med. Chem. 1991,
34, 2906–2916; b) Y. Endo, M. Ohno, M. Hirano, A. Itai, K.
Shudo, J. Am. Chem. Soc. 1996, 118, 1841–1855.
Supporting Information (for details see the footnote on the first
page of this article): Full experimental procedures and spectro-
scopic data for 2a–c, 3a–c, Teoc-(2S)-(3-Acp)Ala(Z)-OH, 8, 11, (S)-
13b, rac-13b, Teoc-(S)-(NO2)Nva-OH, 20a–c, 21a–e, Chpca-
(MOM)-Phe-OFm, 23, Chpca-Phe-OH, and description of the
feeding experiments with 14a,b.
Acknowledgments
This work was supported by the Deutsche Forschungsgemeinschaft
(SFB 416, Projects A3 and B5) and the Fonds der Chemischen
Industrie. The authors are indebted to Mrs. M. Klingebiel and Mr.
H.-P. Kroll (Göttingen) for excellent technical assistance and to Dr.
B. Knieriem (Göttingen) for his careful proofreading of the final
manuscript.
[15]
[16]
[17]
[18]
The same hormaomycin analogues, albeit only in trace quanti-
ties precluding their isolation and characterization, were ob-
served after feeding of 2-(2Ј-nitrocyclopropyl)glycine (cf. ref.[5]).
[1] For the isolation of a cyclosporine analogue which lacks immu-
nosuppressive, but has potential anti-HIV1-activity see: A.
Billich, F. Hammerschmid, P. Reichl, R. Wender, G. Zenke, V.
Quesniaux, B. Rosenwirth, J. Virol. 1995, 69, 2451–2461.
[2] a) N. Andres, H. Wolf, H. Zähner, E. Rössner, A. Zeeck, W. A.
König, V. Sinnwell, Helv. Chim. Acta 1989, 72, 426–437; b) E.
Rössner, A. Zeeck, W. A. König, Angew. Chem. 1990, 102, 84–
85; Angew. Chem. Int. Ed. Engl. 1990, 29, 64–65; c) N. Andres,
H. Wolf, H. Zähner, Z. Naturforsch., Teil C 1990, 45, 851–855.
[3] For the final elucidation of the structure of hormaomycin (1)
see: a) B. D. Zlatopolskiy, K. Loscha, P. Alvermann, S. I.
a) K. Fujii, Y. Ikai, T. Mayumi, H. Oka, M. Suzuki, K. Har-
ada, Anal. Chem. 1997, 69, 3346–3352; b) Y. Suzuki, M. Ojika,
Y. Sakagami, K. Kaida, R. Fudou, T. Kameyama, J. Antibiot.
2001, 54, 22–28; c) Unfortunately, (NO2)Nva totally decom-
posed under the relatively harsh conditions of total hydrolysis
(6  HCl/AcOH = 1:1, 105 °C, 24 h). The fact that only the
(S)-epimer of (3-Ncp)Ala was observed in this case indicates
that analogue 2a had been formed; d) See Supporting Infor-
Eur. J. Org. Chem. 2006, 1525–1534
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1533

B. D. Zlatopolskiy, M. Radzom, A. Zeeck, A. de Meijere
FULL PAPER
mation (for details see the footnote on the first page of this
[25] L. A. Carpino, J. Am. Chem. Soc. 1993, 115, 4397–4398.
[26] More efficiently O-MOM-1 was obtained by stepwise attach-
ment of the side chain. In this case no epimerization at C-2 of
article) to ref.[3a] for experimental details.
[19] J. Piel, University of Bonn, personal communication.
[20] The only described peptide coupling with (NO2)Nva (via a
mixed anhydride) gave the desired dipeptide Boc-(NO2)Nva-
(NO2)Nva-OMe only in low (ca. 40%) yield (cf. B. Mauer, W.
Keller-Schierlein, Helv. Chim. Acta 1969, 52, 603–610).
[21] T. Kitagawa, H. Kuroda, H. Sasaki, K. Kawasaki, Chem.
Pharm. Bull. 1987, 35, 4294–4301.
[22] For an appropriate discussion on the biosynthetic pathway to
the (3-Ncp)Ala units in hormaomycin (1) see: M. Brandl, S. I.
Kozhushkov, B. D. Zlatopolskiy, P. Alvermann, B. Geers, A.
Zeeck, A. de Meijere, Eur. J. Org. Chem. 2005, 123–135.
[23] In the case of 18 this may be associated with its limited stability
under the conditions of the feeding experiment.
(S)-(3-Ncp)Ala was observed.[3b]
.
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Received: November 2, 2005
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Published Online: January 19, 2006
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Eur. J. Org. Chem. 2006, 1525–1534