First total synthesis of hormaomycin, a naturally occurring depsipeptide with interesting biological activities

Article abstract of DOI:10.1002/chem.200400249

Some unique features were disclosed during the structure elucidation of the cyclic depsipeptide hormaomycin (1), first isolated in 1989 from a Streptomyces griseoflavus strain and found to have quite an interesting spectrum of biological activities. Besid

Full text of DOI:10.1002/chem.200400249

FULL PAPER
First Total Synthesis of Hormaomycin, a Naturally Occurring Depsipeptide
with Interesting Biological Activities
[a]
Boris D.Zlatopolskiy and Armin de Meijere*
Dedicated to Professor Axel Zeeck on the occasion of his 65th birthday
Abstract: Some unique features were
disclosed during the structure elucida-
tion of the cyclic depsipeptide hormao-
mycin (1), first isolated in 1989 from a
Streptomyces griseoflavus strain and
found to have quite an interesting spec-
trum of biological activities.Besides
one residue of the proteinogenic amino
acid isoleucine [(S)-Ile], it contains two
[a-Thr] as well as two moieties of 3-
(trans-2-nitrocyclopropyl)alanine [(3-
Ncp)Ala] and one of 4-(Z)-propenyl-
proline [(4-PE)Pro].The latter two
have never been found in any natural
product before.The side chain of 1 is
terminated with the residue of 5-
chloro-1-hydroxypyrrole-2-carboxylic
acid [Chpca].This first synthetic access
to hormaomycin 1 will make it possible
to prepare structural analogues of this
interesting natural depsipeptide in
order to elucidate structure–activity re-
lationships and the biologically active
minimal unit.
Keywords:
peptides
natural products
protective groups
·
·
·
units
of
3-methylphenylalanine
synthetic methods · total synthesis
[(bMe)Phe], one of (2R)-allo-threonine
Introduction
The structure elucidation of the cyclic depsipeptide hormao-
mycin (1), first isolated in 1989 from a Streptomyces griseo-
flavus strain[1a] and found to have quite an interesting spec-
trum of biological activities,[1b,c] disclosed some unique fea-
tures.[1a,d] Besides one residue of the proteinogenic amino
acid isoleucine [(S)-Ile], it contains two units of 3-methyl-
phenylalanine [(bMe)Phe], one of (2R)-allo-threonine [a-
Thr] as well as two moieties of 3-(trans-2-nitrocyclopropyl)a-
lanine [(3-Ncp)Ala] and one of 4-(Z)-propenylproline [(4-
PE)Pro].The latter two have never been found in any natu-
ral product before.The side chain of 1 is terminated with
the residue of 5-chloro-1-hydroxypyrrole-2-carboxylic acid
[Chpca].These challenging structural features and the inter-
esting biological properties prompted us to embark on a
total synthesis of 1 (Figure 1).
Figure 1.Structure and absolute configuration of hormaomycin ( 1). I (S)-
Ile; II (2S,3R)-(bMe)Phe; III (R)-a-Thr; IV (1’R,2’R)-(3-Ncp)Ala; V
(2S,4R)-4-(Z)-(4-PE)Pro; VI Chpca.
Results and Discussion
Once the absolute configuration of hormaomycin 1 had
been established[2] and productive syntheses of (2S,1’S,2’R)-
and (2R,1’S,2’R)-3-(trans-2-nitrocyclopropyl)alanine[3] as
well as N-Boc-protected (2S,4R)-4-(Z)-propenylproline[4]
had been developed, the assembly of the hexapeptolide seg-
ment of 1 was initiated.
All four peptide couplings towards the acyclic precursor
16a were performed with the combination of N’-(3-dimethyl-
aminopropyl)-N-ethylcarbodiimide hydrochloride (EDC)
[a] Dr.B.D.Zlatopolskiy, Prof.Dr.A.de Meijere
Institut für Organische und Biomolekulare Chemie
der Georg-August-Universität Göttingen
Tammannstrasse 2, 37077 Göttingen (Germany)
Fax : (+49)551-399-475
E-mail: Armin.deMeijere@chemie.uni-goettingen.de
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DOI: 10.1002/chem.200400249
Chem. Eur. J. 2004, 10, 4718 – 4727

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and 7-aza-1-hydroxybenzotriazole (HOAt).[5] Having in
mind to ring-close an acyclic precursor already containing
the ester bond between the (4-PE)Pro and the a-Thr resi-
dues by forming the peptide bond between the Ile and (4-
PE)Pro moieties, the methoxymethyl or dicyclopropylmeth-
yl ester[6] of Ile, 3a or 3b, were condensed with N-Z-protect-
ed (bMe)Phe-OH 2 (see Scheme 1).The latter was obtained
MeCN (76% over two steps), gave the ester 12 (83%).The
latter, after palladium-promoted removal of the allyl group,
was coupled with the tetrapeptide 11a using the O-(7-aza-
benzotriazole-1-yl)-N,N,N’,N’-tetramethyluronium hexafluor-
ophosphate (HATU)[9] to give the hexadepsipeptide 16a in
79% yield.
4-Methylbenzyloxycarbonyl N-protecting group (MeZ)[10]
had to be applied in the course of this synthesis, since all
other convenient N-protective groups orthogonal to the Boc
group turned out to be incompatible with the restrictions
imposed on the deprotection conditions due to the nitro
group on the (3-Ncp)Ala moiety, the double bond in the (4-
PE)Pro residue as well as the base-sensitive ester bond be-
tween the (4-PE)Pro and a-Thr fragments.[11a,b] The MeZ
group was found to be stable towards 2n HCl/EtOAc at am-
bient temperature for at least 90 min,[11c] whereas under
these conditions the Boc group was cleaved off within
2 min.[11d] On the other hand, the MeZ group can be re-
moved smoothly by treatment with 10% anisole in trifluoro-
acetic acid for 1 h.[11e,f]
The MOM and Boc groups were removed from the termi-
ni of the depsihexapeptide 16a (the ESI-mass spectrum
showed that the MeZ group stayed intact), and the cyclizing
peptide condensation succeeded under high dilution condi-
tions,[12] using the HATU reagent.The cyclodepsipeptide 17
was obtained after HPLC purification in 53% yield over
two steps (Scheme 2).
Scheme 1.Synthesis of the acyclic precursor 16a to the hexapeptolide
fragment of hormaomycin 1.a) EDC, HOAt, DIEA, 2,4,6-collidine,
CH2Cl2, 0!208C, 14 h; b) H2, Pd/C, EtOAc, 208C, 40 min; c) 50%
Et2NH/MeCN, 208C, 1 h; d) EDC, 4-pyrrolidinopyridine, CH2Cl2, 0!
208C, 24 h; e) EDC, HOAt, 2,4,6-collidine, DMF, 0!208C, 14 h;
f) [Pd(PPh3)4], N-methylaniline, DME, 208C, 1 h; g) HATU, HOAt,
DIEA, 2,4,6-collidine, CH2Cl2, 0!208C, 24 h.DCPM =dicyclopropyl-
methyl, All=allyl, Fmoc=9-fluorenylmethyloxycarbonyl, DIEA=N,N-
diisopropylethylamine, EDC=N’-(3-dimethylaminopropyl)-N-ethylcarbo-
diimide hydrochloride, HATU=O-(7-azabenzotriazole-1-yl)-N,N,N’,N’-
tetramethyluronium hexafluorophosphate, HOAt=7-aza-1-hydroxyben-
zotriazole, MeZ=p-methylbenzyloxycarbonyl, MOM=methoxymethyl;
X=MOM (or DCPM).
by acylation of the corresponding amino acid with benzyl N-
succinimidyl carbonate (ZOSu) in 85% yield.The alkylation
of Z-Ile-OH with MOM iodide (generated in situ) gave the
N-protected MOM ester of Ile-OH in 76% yield, which,
after removal of the Z group (100%), was immediately used
in the coupling step.The DCPM ester 3b was obtained just
before the next step by removal of the Fmoc group from the
N-terminus of Fmoc-Ile-ODCPM (100%), which was in
turn prepared by esterification of the intermediate acid
chloride Fmoc-Ile-Cl with dicyclopropylmethanol in the
presence of pyridine in 57% yield.
After removal of the Z group from the N-terminus of the
resulting dipeptides, 4a (66%) and 4b (84%), by catalytic
hydrogenation to give 6a (54%)[7] and 6b (100%), the
latter were coupled with N-Fmoc-protected (2R,1’S,2’R)-(3-
Ncp)Ala-OH 5 to yield tripeptides 7a (80%) and 7b
(79%).The latter, after removal of the Fmoc-group (100%
yield), were coupled with N-Fmoc-protected (bMe)Phe-OH
10 to give tetrapeptides 13a (78%) and 13b (85%).[8]
The 4-pyrrolidinopyridine-catalyzed condensation of the
N-Boc-protected (4-PE)Pro-OH 8 and N,C-protected a-Thr
9, prepared by alkylation of N-MeZ protected d-allo-threo-
nine, which in turn was obtained by reaction between H-a-
Thr-OH and 4-methylbenzyl N-succinimidyl carbonate
(MeZOSu), with allyl bromide in the presence of K2CO3 in
Scheme 2.The final stages in the preparation of hormaomycin 1.a) 2 n
HCl/EtOAc, 208C, 45 min; b) HATU, DIEA, 2,4,6-collidine, CH2Cl2,
0.1 mm, 0!208C, 16 h, 53% after HPLC purification (2 steps); c) anisole,
TFA, 208C, 2 h; d) Teoc-(2S,1’R,2’R)-(3-Ncp)AlaOH, HATU, HOAt,
DIEA, 2,4,6-collidine, CH2Cl2, 208C, 6 h; e) TFA, 208C, 1 h; f) 18,
HATU, HOAt, DIEA, 2,4,6-collidine, CH2Cl2, 208C, 4 h; g) MgBr2·Et2O,
EtSH, CH2Cl2, 208C, 3.5 h, 67% (5 steps). Teoc=(2-trimethylsilylethyl)-
oxycarbonyl.
Chem. Eur. J. 2004, 10, 4718 – 4727
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A.de Meijere and B.D.Zlatopolskiy
FULL PAPER
To complete the assembly of 1, the N-MeZ-protected
cyclic intermediate was deprotected and first coupled with
N-Teoc-protected (2S,1’R,2’R)-(3-Ncp)Ala-OH.After re-
moval of the Teoc group, the intermediate in turn was cou-
pled with the O-MOM-protected 5-chloro-1-hydroxypyrrole-
2-carboxylic acid 18.[4,13]
1H NMR spectrum which did not differ any more from that
of an authentic sample of natural hormaomycin than two
spectra taken of different samples of the natural material
(see Figure 2).
This first synthetic access to hormaomycin (1) will make it
possible to prepare structural analogues of this interesting
natural depsipeptide in order to elucidate structure–activity
relationships and the biologically active minimal unit.
Finally, the MOM group was removed by treatment with
MgBr2·Et2O and EtSH in dichloromethane[14] to give a com-
pound which was expected to be identical with the native
hormaomycin 1.It did indeed disclose the expected [ MꢀH+
+2Na+], [M+Na+] and [MꢀH+] peaks in its positive- and
negative-mode ESI-mass spectra, had the same optical rota-
tion, identical CD trace, at least in the wavelength region
above 210 nm where no impurity interference is expect-
ed,[15a] identical UV spectrum, a very similar 13C NMR spec-
trum and identical HPLC retention time as an authentic
sample of the natural material.The synthetic product also
showed the same capability to inhibit the growth of coryne-
form bacteria as native hormaomycin (1).[15b] However,
there were some differences in their 1H NMR spectra in
CDCl3 (Figure 2).These discrepancies were initially inter-
preted to indicate that a diastereomer of the natural product
had been synthesized.Yet, this possibility was excluded by
the results of LC/MS experiments according to the advanced
Marfey method,[16] which rigorously proved that the MePhe,
Ile, Ncpa and (R)-a-Thr residues were not epimerized in any
of the peptide coupling and deprotection steps.[17] Because
of this inconsistency, the last steps of the synthesis of hor-
maomycin (1), starting from the cyclodepsipeptide 17, were
repeated on a slightly larger scale.This made it possible to
use simple recrystallizations instead of preparative TLC sep-
arations for the purification of intermediates.The thus ob-
tained second sample of synthetic hormaomycin had a
Experimental Section
General aspects: 1H NMR spectra: Bruker AM 250 (250 MHz), Varian
Inova 600 (600 MHz). 1H chemical shifts are reported in ppm relative to
residual peaks of deuterated solvent or tetramethylsilane.Higher order
NMR spectra were approximately interpreted as first-order spectra, if
possible.The observed signal multiplicities are characterized as follows:
s=singlet, d=doublet, t=triplet, q=quartet, quin=quintet, m=multi-
plet, 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 Inova 600
(125.7 MHz) instruments. 13C chemical shifts are reported relative to
peak of solvent or tetramethylsilane.The following abbreviations were
applied: DEPT: +=primary or tertiary (positive signal in DEPT), ꢀ=
secondary (negative signal in DEPT), Cquat =quaternary (no signal in
DEPT); APT: +=primary or tertiary (positive signal in APT), ꢀ=sec-
ondary or quaternary (negative signal in APT); whenever it was necessa-
ry and possible HMBS (Heteronuclear Multiple Bond Connectivity) and/
or HMQS (Heteronuclear Multiple Quantum Coherence) spectra were
also measured.IR spectra: Bruker IFS 66 (FT-IR) spectrometer, samples
measured as KBr pellets or oils between KBr plates.MS: EI-MS: Finni-
gan MAT 95, 70 eV, high resolution EI-MS spectra with perfluorokero-
sene as reference substance; ESI-MS: Finnigan LCQ.HPLC: pump:
Kontron 322 system, detector: Kontron DAD 440, mixer: Kontron HPLC
360, data system: Kontron Kromasystem 200, columns: Knauer Nucleo-
sil-100 C18 (analytical, 5 mm, 3 mm”250 mm), Knauer Nucleosil-100 C18
(preparative, 5 mm, 8 mm”250 mm).Optical rotations: Perkin–Elmer 241
Figure 2.Comparison of 1H NMR spectra (600 MHz, CDCl3) of different samples of synthetic [traces 2 (second run) and 4 (first run)] and natural (traces
1 and 3) hormaomycin 1.All samples were purified by HPLC before measurements.All measurements were carried out at ambient temperature and
with the same spectrometer.
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Chem. Eur. J. 2004, 10, 4718 – 4727

Hormaomycin
4718 – 4727
digital polarimeter, 1-dm cell; optical rotation values are given in
Bzl-H), 5.30 (d, J=9 Hz, 0.75H, NH), 6.25 (d, J=8.8 Hz, 0.25H, NH),
7.03–7.35 (m, 10H, Ar-H), 7.30–7.90 (br, 1H, CO2H); 13C NMR
(62.9 MHz, CDCl3): d=14.3, 15.8 (+, C-4), 41.5, 41.8 (+, C-3), 59.1, 59.8
(+, C-2), 67.0, 67.4 (ꢀ, Bzl-C), 127.0 (+, Ar-C), 127.5 (+, Ar-C), 127.6
(+, Ar-C), 127.9 (+, Ar-C), 128.0 (+, Ar-C), 128.3, 128.3 (+, Ar-C),
10ꢀ1 degcm2 gꢀ1; concentrations (c) are given in g per 100 mL.Circular di-
chroism: Jasco J 500A.Molar ellipticities ( V) are given in gradcm2 10ꢀ1
molꢀ1.Mp.:. Büchi 510 capillary melting point apparatus, uncorrected
values.TLC: Macherey-Nagel precoated sheets, 02.5 mm Sil G/UV
-
.
254
The chromatograms were viewed under UV light and/or by treatment
with phosphomolybdic acid (10% in ethanol), or ninhydrin (0.2% in eth-
anol), or Ehrlichꢁs reagent (freshly prepared solution of 1 g of 4-dimethyl-
amino-benzaldehyde in 25 mL of 36% HCl and 75 mL methanol).
Column chromatography: Merck silica gel, grade 60, 230–400 mesh and
Baker silica gel, 40–140 mesh.Preparative TLC: Macherey-Nagel, silica
135.2, 135.9 (Cquat, Ar-C), 140.9, 141.4 (Cquat, Ar-C), 156.0, 157.1 (Cquat,
NCO2), 175.1, 175.4 (Cquat, C-1); IR (KBr): n˜ =3750–2250, 1718, 1518,
1497, 1454, 1416, 1347, 1217 cmꢀ1; MS (EI, 70 eV): m/z (%): 313 (1) [M +],
209 (4) [M +ꢀC8H8], 162 (10), 105 (100) [C8H9+], 91 (48) [C7H7+], 65 (7)
[C5H5+]; HRMS (EI): calcd for C18H19NO4: 313.1314; found 313.1314;
elemental analysis calcd (%) for C18H19NO4 (313.4): C 69.00, H 6.11, N
4.47; found C 69.16, H 6.00, N 4.45.
gel SIL G/UV254
, layer thickness 0.25 mm (100”200 mm or 200”
200 mm).Elemental analyses: Mikroanalytisches Laboratorium des Insti-
tuts für Organische und Biomolekulare Chemie der Universität Göttin-
gen.Starting materials: Anhydrous solvents were prepared according to
standard methods by distillation over drying agents and were stored
under argon.All other solvents were distilled before use.All reactions
were carried out with magnetic stirring and, if air or moisture sensitive,
in flame-dried glassware under argon or nitrogen.Organic extracts were
dried with anhydrous MgSO4. (R)-allo-Threonine,[18] 1-hydroxy-7-aza-
benzotriazol,[19] 2-(trimethylsilyl)ethyl N-succinimidyl carbonate,[20]
(2S,3R)-b-methylphenylalanine,[21] (2R,1’R,2’R)-3-(2’-nitrocyclopropyl)ala-
nine,[3a] (2S,4R)-(N-tert-butyloxycarbonyl)-4-(Z)-propenylproline (8),[4]
(2S,3R)-(N-9-fluorenylmethyloxycarbonyl)-b-methylphenylalanine
(10),[22] 5-chloro-1-methoxymethoxypyrrole-2-carboxylic acid (18),[4] were
prepared as described elsewhere.(2 S,1’R,2’R)-3-(2’-Nitrocyclopropyl)ala-
nine was kindly provided by Oleg V.Larionov (Göttingen).
N-Z-Isoleucine methoxymethyl ester: LiI (0.783 g, 5.85 mmol) was added
to an ice-cold solution of MOM-Cl (0.43 mL, 5.65 mmol) in acetonitrile
(7 mL).The mixture was stirred at the same temperature for 20 min, and
a
solution of Z-Ile-OH (0.75 g, 2.83 mmol), and DIEA (0.731 g,
5.65 mmol) in acetonitrile (5 mL) was then added dropwise within 5 min.
The reaction mixture was allowed to warm to 208C, stirred for an addi-
tional 2 h and then diluted with Et2O (50 mL).After the usual aqueous
work-up (GP 2), the organic layer was dried, and concentrated under re-
duced pressure to give an oily residue which was purified by column
chromatography (2”; Rf =0.21, EtOAc/hexane 1:6) to give the title com-
pound (0.665 g, 76%) as a colorless oil. [a]2D0 =3.9 (c=1.90, CHCl3);
1H NMR (250 MHz, CDCl3): d=0.93 (t, J=6.9 Hz, 3H, 5-H), 0.97 (d, J=
6.8 Hz, 3H, 1’-H), 1.06–1.32 (m, 1H, 4-Ha), 1.35–1.54 (m, 1H, 4-Hb),
1.81–2.03 (m, 1H, 3-H), 3.47 (s, 3H, OMe), 4.38 (dd, J=9, 4.5 Hz, 1H, 2-
H), 5.11 (s, 2H, Bzl-H), 5.22 (d, J=5.8 Hz, 1H, Ha, OCH2O), 5.28 (d, J=
6.0 Hz, 1H, NH), 5.35 (d, J=5.8 Hz, 1H, Hb, OCH2O), 7.28–7.42 (m, 5H,
Ar-H); 13C NMR (62.9 MHz, CDCl3): d=11.2 (+, C-5), 15.1 (+, C-1’),
24.5 (ꢀ, C-4), 37.4 (+, C-3), 57.3 (+, OMe), 58.1 (+, C-2), 66.5 (ꢀ, Bzl-
C), 90.6 (ꢀ, OCH2O), 127.7, 127.7, 128.1 (+, Ar-C), 136.0 (Cquat, Ar-C),
155.9 (Cquat, NCO2), 171.4 (Cquat, C-1); IR (film): n˜ =3390, 3066, 3034,
2965, 2937, 2878, 2832, 1724, 1525, 1455, 1412, 1337, 1220, 1087,
Deprotection of N-Fmoc-protected peptides 7a, 7b, 13a, 13b—General
procedure (GP 1): The protected peptides (1 mmol) were taken up with
acetonitrile or THF (2 mL); diethylamine (2 mL) was added, and the re-
sulting mixture left at ambient temperature for 30 min.All volatiles were
evaporated under reduced pressure, the residue was taken up with tolu-
ene (2”5 mL), which was evaporated under reduced pressure to remove
the last traces of diethylamine.The obtained crude N-deprotected pepti-
des were directly used in the next condensation step.
1041 cmꢀ1
.
N-Fmoc-Isoleucine dicyclopropylmethyl ester: To a stirred ice-cold solu-
tion of N-Fmoc-protected isoleucine (1.0 g, 2.83 mmol) in anhydrous
CH2Cl2 (10 mL) were added oxalyl chloride (0.898 g, 7.07 mmol) and
then DMF (5 drops), and stirring was continued at the same temperature
for 2 h.The mixture was then allowed to warm to 20 8C and stirred for an
additional 1 h.The solvent was blown out with a nitrogen stream and the
crude acyl chloride was dried at 0.01 Torr for 2 h and used without fur-
ther purification.It was dissolved in anhydrous CH 2Cl2 (10 mL) and a
mixture of pyridine/dicyclopropylmethanol 1:1 (1.5 mL) was added. After
40 min, DMAP (0.02 g) was added to the mixture and stirring was contin-
ued for an additional 3 h.The reaction mixture was then diluted with
Et2O (50 mL), washed (according to GP 2), dried, filtered and concen-
trated under reduced pressure.The residue was purified by column chro-
matography [Rf =0.24, EtOAc/hexane 1:10 (0.5% Et3N)].The appropri-
ate fractions were combined, concentrated under reduced pressure, taken
up with Et2O/hexane 1:1 (100 mL), washed with water (3”20 mL), 3%
aqueous NaHCO3 (3”20 mL), water (3”20 mL), brine (2”10 mL),
dried, filtered and concentrated under reduced pressure to give the title
compound (0.72 g, 57%) as a turbid oil. [a]2D0 =ꢀ3.8 (c=0.26, CHCl3);
1H NMR (250 MHz, CDCl3): d=0.16–0.38 (m, 4H, 2’-Ha, DCPM), 0.38–
0.51 (m, 2H, 2’-Hb, DCPM), 0.51–0.64 (m, 2H, 2’-Hc, DCPM), 0.94 (t, J=
7.5 Hz, 3H, 5-H, Ile), 0.96 (d, J=7.5 Hz, 3H, 1’-H, Ile), 1.02–1.16 (m, 2H,
1’-H, DCPM), 1.17–1.34 (m, 1H, 4-Ha, Ile), 1.39–1.47 (m, 1H, 4-Hb, Ile),
1.86–2.09 (m, 1H, 3-H, Ile), 3.90 (t, J=8.8 Hz, 1H, 1-H, DCPM), 4.23
(dd, J=7.3, 7.3 Hz, 1H, 2-H, Ile), 4.34–4.44 (m, 3H, 1-H, 9’-H, Fmoc),
5.36 (d, J=9.8 Hz, 1H, NH), 7.23–7.46 (m, 4H, Ar-H), 7.61 (d, J=
7.5 Hz, 2H, Ar-H), 7.76 (d, J=8.3 Hz, 2H, Ar-H); 13C NMR (62.9 MHz,
CDCl3): d=2.4, 2.6, 2.9 (ꢀ, C-2’, DCPM), 11.6 (+, C-5, Ile), 14.5, 15.3
(+, C-1’, DCPM), 14.6 (+, C-1’, Ile), 24.9 (ꢀ, C-4, Ile), 38.1 (+, C-3, Ile),
47.1 (+, C-9’, Fmoc), 58.3 (+, C-2, Ile), 66.8 (ꢀ, C-1, Fmoc), 83.4 (+, C-
1, DCPM), 119.8, 125.0, 126.9, 127.5 (+, Ar-C), 141.1 (Cquat, Ar-C), 143.7,
143.8 (Cquat, Ar-C), 156.0 (Cquat, NCO2), 171.5 (Cquat, C-1, Ile); IR (film):
n˜ =3400, 3068, 3009, 2964, 2935, 2876, 2832, 1805, 1717, 1508, 1451, 1331,
Peptide condensation step for the preparation of peptides 4a, 4b, 7a, 7b,
13a, 13b—General procedure (GP 2): EDC (1.03 mmol) and HOAt
(1.05 mmol) were added to a cooled (48C) solution of the respective N-
protected amino acid (1 mmol) in anhydrous CH2Cl2 (3 mL).After
10 min, the solution of the appropriate crude N-deprotected peptide
(0.97 mmol) and TMP (3 mmol) in anhydrous CH2Cl2 (1 mL) was added
at the same temperature.The temperature was allowed to reach 20 8C,
and stirring was continued for 15 h.Then the reaction mixture was dilut-
ed with Et2O or EtOAc (30 mL) and washed with 1m KHSO4 (3”5 mL),
water (2”5 mL), 3% aq.solution of NaHCO (3”5 mL), water (3”
3
5 mL), brine (2”5 mL), dried and concentrated under reduced pressure.
The residue was purified by column chromatography or recrystallization.
N-Z-3-(2S,3R)-b-Methylphenylalanine (2): A solution of ZOSu (0.396 g,
1.59 mmol) in acetone (5 mL) was added to a vigorously stirred solution
of 3-(2S,3R)-methylphenylalanine hydrochloride (0.35 g, 1.62 mmol) and
NaHCO3 (0.409 g, 4.87 mmol) in water (5 mL); stirring was continued for
2 h (if an emulsion formed, acetone and/or water were added to obtain a
homogeneous solution).Acetone was then removed under reduced pres-
sure, the residual fraction was diluted with water (25 mL) and washed
with Et2O (3”10 mL).The organic fraction was back-extracted with 5%
aqueous NaHCO3 (3”10 mL), the pH of the combined water fractions
was adjusted to 1 with 1m HCl and the resulting emulsion was extracted
with Et2O (2”50 mL).The organic layer was washed with 1 m HCl (2”
10 mL), water (10”10 mL), brine (2”10 mL), dried, filtered and concen-
trated under reduced pressure.The residual oil was dissolved in Et 2O
(3 mL) and dicyclohexylamine (0.277 g, 1.53 mmol) was added followed
by hexane (20 mL) and the resulting precipitate was filtered and crystal-
lized twice from EtOAc/hexane to give the dicyclohexylammonium salt
of 2 (0.67 g, 85%) as a white solid. To obtain an analytical sample of 2, a
small quantity of the dicyclohexylammonium salt dissolved in EtOAc
and washed twice with 1m HCl, three times with water, twice with brine
to give, after prolonged drying at 0.02 Torr and 608C, 2 as a colorless
solid. M.p. 76.5–798C; [a]D20 =17.3 (c=0.76, CHCl3); 1H NMR (250 MHz,
CDCl3): d=1.31, 1.36 (2”d, J=7.0 Hz, 3H, 4-H), 3.33 (dq, J=7.0,
7.0 Hz, 1H, 3-H), 4.43–4.55 (m, 0.25H, 2-H), 4.60 (dd, J=5.5 Hz, 9 Hz,
0.75H, 2-H), 4.78 (d, J=12.5 Hz, 0.25H, Bzl-H), 4.96–5.20 (m, 1.75H,
1209, 1220, 1091, 1030 cmꢀ1
.
Z-(bMe)Phe-Ile-OMOM (4a): Z-Ile-OMOM (0.415 g, 1.34 mmol) was
hydrogenated over 10% Pd on charcoal (0.150 g) under hydrogen at am-
bient pressure in EtOAc (10 mL) with AcOH (0.080 g, 1.34 mmol) for
Chem. Eur. J. 2004, 10, 4718 – 4727
www.chemeurj.org
ꢀ 2004 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
4721

A.de Meijere and B.D.Zlatopolskiy
FULL PAPER
1 h.The mixture was then filtered, concentrated under reduced pressure,
taken up with Et2O (40 mL), washed with saturated aqueous NaHCO3
(3”10 mL), brine (2”10 mL), dried, filtered and concentrated under re-
duced pressure to give the deprotected ester of isoleucine 3a as a free
base which was directly used for the condensation with N-Z-protected b-
methylphenylalanine (2; 0.400 g, 1.28 mmol) employing EDC (0.257 g,
1.34 mmol), HOAt (0.173 g, 1.28 mmol) and TMP (0.500 mL, 3.78 mmol)
in CH2Cl2 (5 mL) according to GP 2.After 2 h, the reaction mixture was
subjected to the usual aqueous work-up and the resulting crude product
was purified by crystallization from EtOAc/hexane to give the dipeptide
4a (0.40 g, 66%) as a colorless solid. Rf =0.17 (EtOAc/hexane 1:6); Rf =
0.35 (EtOAc/hexane 1:4); m.p. 111–1128C; [a]2D0 =ꢀ8.5 (c=0.30, CHCl3);
1H NMR (250 MHz, CDCl3): d=0.81 (d, J=6.8 Hz, 3H, 1’-H, Ile), 0.87
(t, J=6.8 Hz, 3H, 5-H, Ile), 0.94–1.17 (m, 1H, 4-Ha, Ile), 1.24–1.45 (m,
1H, 4-Hb, Ile), 1.35 [d, J=7.3 Hz, 3H, 4-H, (bMe)Phe], 1.68–1.87 (m,
1H, 3-H, Ile), 3.17 [dq, J=7.3 Hz, 1H, 3-H, (bMe)Phe], 3.42 (s, 3H,
OMe), 4.27–4.41 (m, 2H, 2”2-H), 5.09 (s, 2H, Bzl-H), 5.13 (d, J=6.0 Hz,
1H, Ha, OCH2O), 5.21 (d, J=5.8 Hz, 1H, Hb, OCH2O), 5.43 (d, J=9 Hz,
1H, NH), 5.98 (d, J=7.8 Hz, 1H, NH), 7.15–7.30 (m, 6H, Ar-H), 7.30–
7.42 (m, 4H, Ar-H); 13C NMR (62.9 MHz, CDCl3): d=11.2 (+, C-5, Ile),
14.9 (+, C-1’, Ile), 16.9 [+, C-4, (bMe)Phe], 24.8 (ꢀ, C-4, Ile), 37.5 (+,
C-3, Ile), 42.2 [+, C-3, (bMe)Phe], 56.1 (+, C-2, Ile), 57.5 (+, OMe),
60.2 [+, C-2, (bMe)Phe], 66.5 (ꢀ, Bzl-C), 90.6 (ꢀ, OCH2O), 126.6, 127.5,
127.5, 127.7, 128.17 (”2) (+, Ar-C), 136.2, 141.9 (Cquat, Ar-C), 156.2
(Cquat, NCO2), 170.4, 170.6 (Cquat, C-1); IR (KBr): n˜ =3330, 3275, 3065,
3033, 2965, 2928, 2874, 2832, 1741, 1689, 1654, 1536, 1293, 1275, 1253,
1242, 1155, 1071, 1012 cmꢀ1; MS (EI, 70 eV): m/z (%): 470 (4) [M +], 366
(11) [M +ꢀC8H8], 319 (18) [M +ꢀC8H9NO2], 289 (15), 268 (8), 224 (20),
199 (6), 105 (10) [C8H9+], 91 (100) [C7H7+], 86 (10), 45 (12) [CHO2+];
HRMS (EI): calcd for C26H34N2O6: 470.2417; found 470.2417; elemental
analysis calcd (%) for C26H34N2O6 (470.6): C 66.36, H 7.28, N 5.95; found
C 66.58, H 7.19, N 6.10.
emulsion was extracted with Et2O (30 mL) and the ethereal layer was
back-extracted with 3% aqueous NaHCO3 (5”10 mL, TLC control for
the completeness of extraction was necessary).The combined aqueous
fractions were washed with Et2O (2”10 mL), acidified to pH 2 with 3m
HCl, and the resulting emulsion was extracted with Et2O (40 mL).The
organic phase was washed with 3m HCl (2”10 mL), water (3”10 mL),
brine (2”5 mL), dried, filtered and concentrated under reduced pressure.
The residue was triturated with cold pentane and filtered.The resulting
semisolid was dried at 0.02 Torr for prolonged time to give 5 (0.423 g,
93%) as a colorless foam. Rf =0.08 (EtOAc/hexane 1:1); m.p. (softening)
50–578C; [a]2D0 =ꢀ56.7 (c=0.36, CHCl3); 1H NMR (250 MHz, CDCl3):
d=0.71–0.82 (m, 0.4H, 3’-Ha), 1.11 (ddd J=6.2, 6.2, 6.2 Hz, 0.6H, 3’-Ha),
1.17–1.51 (m, 1H, 3’-Hb), 1.75–2.13 (m, 2H, 3-H), 3.61–3.76, 3.76–3.89
(2”m, 1H, 1’-H), 3.99–4.12 (m, 0.5H, 2-H), 4.12–4.27 (m, 1.5H, 9’’’-H, 2-
H), 4.27–4.56 (m, 2H, 1’’-H), 4.56–4.69, 4.71–4.87 (2”m, 1H, 2’-H), 5.48
(d, J=7.0 Hz, 0.6H, NH), 7.01–7.13 (m, 0.4H, NH), 7.23–7.42 (m, 4H,
Ar-H), 7.42–7.61 (m, 2H, Ar-H), 7.75 (d, J=7.5 Hz, 2H, Ar-H), 7.90–
10.50 (br, 1H, CO2H); 13C NMR (62.9 MHz, CDCl3): d=17.3, 17.6 (ꢀ, C-
3’), 21.4, 22.0 (+, C-1’), 32.8, 33.2 (ꢀ, C-3), 46.8 (+, C-9’’’), 53.0 (+, C-2),
59.0 (+, C-2’), 66.7, 67.0 (ꢀ, C-1’’), 119.8 (+, Ar-C), 124.2, 124.4 (+, Ar-
C), 124.8 (+, Ar-C), 126.9, 127.6 (+, Ar-C), 141.1 (Cquat, Ar-C), 143.0,
143.3 (Cquat, Ar-C), 143.3, 143.5 (Cquat, Ar-C), 155.9, 156.8 (Cquat, NCO2),
173.8, 174.6 (Cquat, C-1); IR (KBr): n˜ =3331, 2965, 2934, 1736, 1689, 1653,
1525, 1455, 1391, 1367, 1251, 1176 cmꢀ1; MS (EI, 70 eV): m/z (%): 396
(1) [M +], 196 (36) [C14H12O+], 178 (51) [C14H10+], 165 (100), 139 (6);
HRMS (EI): calcd for C21H20N2O6: 396.1321; found 396.1321; elemental
analysis calcd (%) for C21H20N2O6 (396.4): C 63.63, H 5.09, N 7.07; found
C 63.56, H 5.21, N 7.00.
Fmoc-(2R)-(3-Ncp)Ala-(bMe)Phe-Ile-OMOM (7a): The compound 4a
(0.370 g, 0.786 mmol) was hydrogenated over 10% Pd on charcoal
(0.100 g) under hydrogen at ambient pressure in EtOAc (10 mL) with
AcOH (0.048 g, 0.800 mmol) for 1 h. The mixture was then filtered, con-
centrated under reduced pressure, taken up with Et2O (40 mL), washed
with saturated aqueous NaHCO3 (3”10 mL), brine (2”10 mL), dried, fil-
tered and concentrated under reduced pressure to give the deprotected
dipeptide 6a as a free base together with cyclo-[(bMe)Phe-Ile].This mix-
ture was directly used for the condensation with the N-Fmoc-protected
Z-(bMe)Phe-Ile-ODCPM (4b): Fmoc-Ile-ODCPM (0.540 g, 1.21 mmol)
was N-deprotected according to GP 1, and the resulting amino ester 3a
was coupled with N-Z-protected (b-methylphenylalanine)
2 (0.36 g,
1.15 mmol) employing EDC (0.227 g, 1.18 mmol), HOAt (0.160 g,
1.18 mmol) and TMP (0.418 g, 3.45 mmol) in CH2Cl2 (5 mL) according to
GP 2.After 6 h, the reaction mixture was subjected to the usual aqueous
work-up, and the resulting crude product was triturated with pentane and
then purified by crystallization from hexane to give the dipeptide 4b
(0.50 g, 84%) as a colorless solid. Rf =0.17 [EtOAc/hexane 1:6 (0.5%
amino acid
5
(0.320 g, 0.807 mmol) employing EDC (0.160 g,
0.835 mmol), HOAt (0.111 g, 0.816 mmol) and TMP (0.430 mL,
3.254 mmol) in CH2Cl2 (5 mL) according to GP 2.After 15 h, the reac-
tion mixture was subjected to the usual aqueous work-up, and the result-
ing crude product was first crystallized from CH2Cl2/hexane and then pu-
rified by column chromatography [Rf =0.28, CHCl3/MeOH 60:1 (1%
EtOH)] to give tripeptide 7a (0.220 g, 39% over two steps) as a colorless
solid.[ a]2D0 =ꢀ15.3 (c=0.40, CHCl3); 1H NMR (250 MHz, CDCl3): d=
0.82 (q, J=7.3 Hz, 6H, 5-H, 1’-H, Ile), 0.93–1.17 [m, 2H, 4-Ha, Ile, 3’-Ha,
(3-Ncp)Ala], 1.26–1.43 (m, 1H, 4-Hb, Ile), 1.32 [d, J=6.5 Hz, 3H, 4-H,
(bMe)Phe], 1.48–1.70 [m, 1H, 3’-Hb, (3-Ncp)Ala], 1.70–1.84 [m, 2H, 3-H,
Ile, 1’-H, (3-Ncp)Ala], 1.84–1.99 [m, 2H, 3-H, (3-Ncp)Ala], 3.22 [dq, J=
7.4 Hz, 1H, 3-H, (bMe)Phe], 3.40 (s, 3H, OMe), 4.00–4.10 (m, 1H, 2-H),
4.20 (dd, J=6.5, 6.5 Hz, 1H, 2-H), 4.26–4.44 [m, 3H, 1-Ha, 9’-Ha, Fmoc,
2’-H, (3-Ncp)Ala], 4.49 (dd, J=10.6, 6.9 Hz, 1H, 1-Hb, Fmoc), 4.62 (dd,
J=8.5, 8.5 Hz, 1H, 2-H), 5.09 (d, J=5.9 Hz, 1H, Ha, OCH2O), 5.20 (d,
J=5.9 Hz, 1H, Hb, OCH2O), 5.63 (d, J=8.0 Hz, 1H, NH), 6.17 (d, J=
8.0 Hz, 1H, NH), 6.95 (d, J=8.5 Hz, 1H, NH), 7.14–7.31 (m, 7H, Ar-H),
7.40 (dd, J=7.5, 7.5 Hz, 2H, Ar-H), 7.58 (dd, J=7.3, 5.0 Hz, 2H, Ar-H),
7.77 (d, J=7 Hz, 2H, Ar-H); 13C NMR (62.9 MHz, CDCl3): d=11.4 (+,
C-5, Ile), 15.0 (+, C-1’, Ile), 17.1 [+, C-4, (bMe)Phe], 17.9 [ꢀ, C-3’, (3-
Ncp)Ala], 22.1 [+, C-1’, (3-Ncp)Ala], 24.9 (ꢀ, C-4, Ile), 34.0 [ꢀ, C-3, (3-
Ncp)Ala], 37.7 (+, C-3, Ile), 41.9 [+, C-3, (bMe)Phe], 46.9 (+, C-9’,
Fmoc), 54.0 [+, C-2, (bMe)Phe], 56.3 [+, C-2, Ile], 57.7 (+, OMe), 58.7
[+, C-2, (3-Ncp)Ala], 59.0 [+, C-2’, (3-Ncp)Ala], 67.1 (ꢀ, C-1, Fmoc),
90.9 (ꢀ, OCH2O), 119.9, 124.9, 126.9, 127.0, 127.6, 127.7, 128.4 (+, Ar-
C), 141.1, 141.2 (Cquat, Ar-C, Fmoc), 141.6 [Cquat, Ar-C, (bMe)Phe], 143.5,
1
Et3N)]; m.p 105–1068C; [a]D20 =9.0 (c=0.31, CHCl3); H NMR (250 MHz,
CDCl3): d=0.23–0.41 (m, 4H, 2’-Ha, DCPM), 0.41–0.53 (m, 2H, 2’-Hb,
DCPM), 0.53–0.64 (m, 2H, 2’-Hc, DCPM), 0.81 (d, J=6.8 Hz, 3H, 1’-H,
Ile), 0.89 (t, J=7.3 Hz, 3H, 5-H, Ile), 0.95–1.21 (m, 3H, 4-Ha, Ile, 1’-H,
DCPM), 1.35 [d, J=7.3 Hz, 3H, (bMe)Phe], 1.37–1.48 (m, 1H, 4-Hb, Ile),
1.71–1.90 (m, 1H, 3-H, Ile), 3.19 [dq, J=7.3 Hz, 1H, (bMe)Phe], 3.90 (t,
J=8.5 Hz, 1H, 1-H, DCPM), 4.26–4.42 (m, 2H, 2”2-H), 5.09 (s, 2H,
Bzl-H), 5.42 (d, J=9.0 Hz, 1H, NH), 6.06 (d, J=7.5 Hz, 1H, NH), 7.15–
7.30 (m, 6H, Ar-H), 7.30–7.40 (m, 4H, Ar-H); 13C NMR (62.9 MHz,
CDCl3): d=2.4, 2.7 (ꢀ, C-2’, DCPM), 11.4 (+, C-5, Ile), 14.3, 14.5 (+, C-
1’, DCPM), 14.8 (+, C-1’, Ile), 16.7 [+, C-4, (bMe)Phe], 24.9 (ꢀ, C-4,
Ile), 37.9 (+, C-3, Ile), 42.2 [+, C-3, (bMe)Phe], 56.1 (+, C-2, Ile), 60.1
[+, C-2, (bMe)Phe], 66.5 (ꢀ, Bzl-C), 82.9 (+, C-1, DCPM), 126.5, 127.4,
127.5, 127.6, 128.1 (”2) (+, Ar-C), 136.2, 141.9 (Cquat, Ar-C), 156.1 (Cquat
,
NCO2), 170.2, 170.5 (Cquat, C-1, Ile); IR (KBr): n˜ =3300, 3270, 3010, 2965,
2875, 1732, 1690, 1655, 1535, 1454, 1379, 1334, 1292, 1275, 1255, 1240,
1196, 1137, 1013 cmꢀ1; MS (EI, 70 eV): m/z (%): 520 (8) [M +], 416 (7)
[M +ꢀC8H8], 381 (8) [M +ꢀC7H9NO2], 296 (20), 268 (11), 224 (20), 176
(6), 105 (7) [C8H9+], 95 (100), 86 (17), 67 (10); HRMS (EI): calcd for
C31H40N2O5: 520.2937; found 520.2937; elemental analysis calcd (%) for
C31H40N2O5 (520.7): C 71.51, H 7.74, N 5.38; found C 71.51, H 7.42, N
5.40.
N-Fmoc-3-(2R,1’R,2’R)-(trans-2’-Nitrocyclopropyl)alanine (5):
A solu-
tion of Fmoc-OSu (0.416 g, 1.36 mmol) in acetone (7 mL) was added to a
vigorously stirred solution of 3-(2R,1’R,2’R)-(trans-2’-nitrocyclopropyl)-
alanine (0.20 g, 1.15 mmol) and NaHCO3 (0.202 g, 2.40 mmol) in water
(5 mL) (if a precipitate formed, acetone and/or water was added to
obtain a homogeneous solution) and stirring continued for an additional
3 h.Acetone was then removed under reduced pressure, and the pH of
the residual water solution was adjusted to 1 with 3m HCl.The resulting
143.7 (Cquat, Ar-C, Fmoc), 156.0 (Cquat, NCO2), 170.2, 170.6, 171.2 (Cquat
,
C-1); IR (KBr): n˜ =3330, 3275, 3067, 2966, 1718, 1643, 1542, 1451, 1368,
1227, 1163, 1139, 1091 cmꢀ1; MS (EI, 70 eV): m/z (%): 715 (0.04) [M +],
518 (3), 429 (13), 321 (5), 196 (20), 178 (100), 165 (54), 134 (16), 86 (23),
45 (20) [CHO2+]; MS (ESI): positive mode: m/z (%): 737 (30) [M+Na+];
negative mode: m/z (%): 749 (40) [M+Clꢀ].
4722
ꢀ 2004 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 4718 – 4727

Hormaomycin
4718 – 4727
Fmoc-(2R)-(3-Ncp)Ala-(bMe)Phe-Ile-ODCPM (7b): The dipeptide 4b
(0.35 g, 0.67 mmol) was taken up with EtOAc (10 mL) and hydrogenated
over 10% Pd/C (0.15 g) under hydrogen at ambient pressure for 2 h. The
reaction mixture was filtered through a pad of Celite and concentrated
under reduced pressure to give the deprotected dipeptide 6b, which was
directly used for the coupling with 5 (274 mg, 0.69 mmol), using EDC
(137 mg, 0.72 mmol), HOAt (96 mg, 0.71 mmol) and TMP (0.25 mL,
2.02 mmol) according to GP 2 to give compound 7b (405 mg, 79%) as a
colorless solid after two recrystallizations from THF/hexane 1:1. Rf =0.52
(EtOAc/hexane 2:3); m.p 151–1558C; [a]2D0 =ꢀ3.8 (c=0.26, CHCl3);
1H NMR (250 MHz, CDCl3): d=0.20–0.38 (m, 4H, 2’-H, DCPM), 0.37–
0.49 (m, 2H, 2’-H, DCPM), 0.49–0.62 (m, 2H, 2’-H, DCPM), 0.80 (d, J=
7.0 Hz, 3H, 1’-H, Ile), 0.86 (t, J=7.5 Hz, 3H, 5-H, Ile), 0.94–1.20 [m, 4H,
4-Ha, Ile, 3’-Ha, 3-(Ncp)Ala, 1’-H, DCPM], 1.33–1.49 [m, 1H, 3’-Hb, 3-
(Ncp)Ala], 1.34 [d, J=7.0 Hz, 3H, 4-H, (b-Me)Phe], 1.50–1.68 (m, 1H, 4-
Hb, Ile), 1.71–1.85 [m, 2H, 3-H, Ile, 1’-H, 3-(Ncp)Ala], 1.85–2.05 [m, 2H,
3-H, 3-(Ncp)Ala], 3.22 [dq, J=7.0 Hz, 1H, 3-H, (b-Me)Phe], 3.79 (t, J=
8.6 Hz, 1H, 1-H, DCPM), 4.01–4.09 (m, 1H, 2-H), 4.21 (dd, J=6.5 Hz,
1H, 2-H), 4.26–4.43 [m, 3H, 2’-H, 3-(Ncp)Ala, 1-Ha, 9’-Ha, Fmoc], 4.49
(dd, J=10.3, 7.0 Hz, 1H, 1-Hb, Fmoc), 4.61 (dd, J=5.5 Hz, 1H, 2-H),
5.58 (d, J=8.3 Hz, 1H, NH), 6.14 (d, J=7.8 Hz, 1H, NH), 6.84 (d, J=
8.0 Hz, 1H, NH), 7.12–7.31 (m, 5H, Ar-H), 7.33 (d, J=7.8 Hz, 2H, Ar-
H), 7.40 (dd, J=7.3, 7.3 Hz, 2H, Ar-H), 7.58 (d, J=7.0 Hz, 2H, Ar-H),
7.77 (d, J=7.3 Hz, 2H, Ar-H); 13C NMR (62.9 MHz, CDCl3): d=2.4, 2.7
(ꢀ, C-2’, DCPM), 11.4 (+, C-5, Ile), 14.1, 14.4 (+, C-1’, DCPM), 14.8 (+,
C-1’, Ile), 16.7 [+, C-4, (b-Me)Phe], 17.7 [ꢀ, C-3’, 3-(Ncp)Ala], 21.97 [+,
C-1’, 3-(Ncp)Ala], 24.9 (ꢀ, C-4, Ile), 33.9 [ꢀ, C-3, 3-(Ncp)Ala], 38.1 (+,
C-3, Ile), 41.7 [+, C-3, (b-Me)Phe], 46.8 (+, C-9’, Fmoc), 53.8 (+, C-2),
56.2 (+, C-2), 58.5 (+, C-2), 58.8 [+, C-2’, 3-(Ncp)Ala], 67.0 (ꢀ, C-1,
Fmoc), 83.1 (+, C-1, DCPM), 119.7, 124.8, 126.6, 127.4 (” 2) (+, Ar-C),
The mixture was then allowed to cool to 608C, and stirring was continued
for an additional 16 h.The reaction mixture was cooled to 20 8C, Et2O
(50 mL) and water (20 mL) were then added.The organic layer was
washed with water (4”10 mL), saturated aqueous NaHCO3 (2”10 mL),
brine (2”5 mL), dried, filtered and concentrated under reduced pressure.
The residual oil was triturated with Et2O/pentane 1:2 to give a colorless
solid.Then more pentane was added to complete the precipitation, 9 was
filtered off and dried under reduced pressure (0.116 g, 84%). Rf =0.16
(EtOAc/hexane 1:3); m.p. 47–488C; [a]2D0 =ꢀ20.4 (c=0.30, CHCl3);
1H NMR (250 MHz, CDCl3): d=1.20 (d, J=6.5 Hz, 3H, 4-H), 2.35 (s,
3H, 1’-H), 2.74 (d, J=6.3 Hz, 1H, OH), 4.09–4.26 (m, 1H, 3-H), 4.47
(dd, J=7.5, 3.8 Hz, 1H, 2-H), 4.67 (d, J=5.3 Hz, 2H, 1-H, All), 5.08 (s,
2H, Bzl-H), 5.27 (ddt, J=10.3, 1.0, 1.0 Hz, 1H, trans-3-H, All), 5.34 (ddt,
J=17.3, 1.0, 1.0 Hz, 1H, cis-3-H, All), 5.66 (d, J=7.3 Hz, 1H, NH), 5.90
(ddt, J=17.3, 10.3, 5.8 Hz, 1H, 2-H, All), 7.17 (d, J=8.0 Hz, 2H, Ar-H),
7.26 (d, J=8.0 Hz, 2H, Ar-H); 13C NMR (62.9 MHz, CDCl3): d=18.7 (+,
C-4), 20.9 (+, C-1’), 59.3 (+, C-2), 65.9 (ꢀ, C-1, All), 67.4 (ꢀ, Bzl-C),
68.4 (+, C-3), 118.7 (ꢀ, C-3, All), 128.0, 128.9 (+, Ar-C), 132.8 (+, C-2,
All), 132.8, 137.7 (Cquat, Ar-C), 156.4 (Cquat, NCO2), 169.9 (Cquat, C-1); IR
(KBr): n˜ =3409, 3327, 3056, 2972, 2941, 2889, 1744, 1690, 1536, 1463,
1382, 1338, 1284, 1233, 1183 cmꢀ1; MS (EI, 70 eV): m/z (%): 307 (2)
[M +], 263 (4) [M +ꢀC2H4O], 202 (8) [M +ꢀC8H9], 105 (100) [C8H9+], 77
(5) [C6H5+], 41 (5) [C3H5+]; HRMS (EI): calcd for C16H21NO5: 307.1420;
found 307.1420; elemental analysis calcd (%) for C16H21NO5 (307.5):
C 62.53, H 6.89, N 4.56; found C 62.80, H 6.84, N 4.41.
MeZ-a-Thr[(4-PE)Pro]-OAll (12): EDC (0.324 g, 1.69 mmol) was added
to a cooled (48C) solution of the N-Boc-protected (2S,4R)-4-(Z)-prope-
nylproline (8; 0.340 g, 1.33 mmol), the N,C-protected amino acid
9
(0.400 g, 1.30 mmol) and 4-pyrrolidinopyridine (0.250 g, 1.69 mmol) in an-
hydrous CH2Cl2 (3 mL).The temperature was allowed to reach 20 8C,
and stirring was continued for 15 h.Then the reaction mixture was dilut-
ed with Et2O (30 mL) and washed with 1m KHSO4 (3”5 mL), water (2”
5 mL), 3% 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 column chromatography (EtOAc/hexane 1:6) to
give 12 (0.588 g, 83%) as a turbid oil. Rf =0.43 (EtOAc/hexane 1:3);
[a]2D0 =ꢀ35.4 (c=0.28, CHCl3); 1H NMR (250 MHz, CDCl3): d=1.32,
1.34 (2”d, J=6.5 Hz, 3H, 4-H, a-Thr), 1.36, 1.39 [2”s, 9H, C(CH3)3],
1.64, 1.65 [2”dd, J=1.5, 7.0 Hz, 3H, 3’-H, (4-PE)Pro], 1.63–1.81 [m, 1H,
3-Ha, (4-PE)Pro], 2.21–2.46 [m, 1H, 3-Hb, (4-PE)Pro], 2.33, 2.35 (2”s,
3H, 1’-H, MeZ), 2.93–3.19 [m, 2H, 4-H, 5-Ha, (4-PE)Pro], 3.51–3.67,
3.69–3.83 [2”m, 1H, 5-Hb, (4-PE)Pro], 4.10–4.27 [m, 1H, 2-H, (4-
PE)Pro], 4.48–4.65 (m, 1H, 2-H, a-Thr), 4.68 (d, J=5.2 Hz, 2H, 1-H,
All), 4.97–5.13 (m, 2H, Bzl-H, MeZ), 5.17–5.43 [m, 4H, 3-H, All, 3-H, a-
Thr, 1’-H, (4-PE)Pro], 5.54 [dq, J=10.2, 7.0 Hz, 1H, 2’-H, (4-PE)Pro],
5.80–6.01 (m, 1H, 2-H, All), 6.42 (d, J=9.2 Hz, 1H, NH), 7.13, 7.17 (2”
d, J=7.9 Hz, 2H, Ar-H), 7.23, 7.25 (d, J=7.9 Hz, 2H, Ar-H); 13C NMR
(62.9 MHz, CDCl3): d=12.8 [+, C-3’, (4-PE)Pro], 15.8, 16.3 (+, C-4, a-
Thr), 20.8 (+, C-1’, MeZ), 27.9 [+, C(CH3)3], 35.3, 36.1 [+, C-4, (4-
PE)Pro], 35.8, 36.9 [ꢀ, C-3, (4-PE)Pro], 51.1, 51.3 [ꢀ, C-5, (4-PE)Pro],
57.0, 57.4 [+, C-2, (4-PE)Pro], 59.0, 59.1 (+, C-2, a-Thr), 65.5, 66.0 (ꢀ,
128.2 (” 2) (+, Ar-C), 140.96, 141.49 (Cquat, Ar-C, Fmoc), 141.5 [Cquat
,
Ar-C, (b-Me)Phe], 143.5, 143.6 (Cquat, Ar-C, Fmoc), 155.9 (Cquat, NCO2),
169.8, 170.5, 171.0 (Cquat, C-1); IR (KBr): n˜ =3490, 2966, 1717, 1645, 1543,
1451, 1368, 1147 cmꢀ1; MS (ESI): positive mode: m/z (%): 787 (70)
[M+Na+]; negative mode: m/z (%): 799 (38) [M+Clꢀ]; elemental analy-
sis calcd (%) for C44H52N4O8 (764.9): C 69.09, H 6.85, N 7.32; found C
69.06, H 6.79, N 7.19.
MeZ-a-Thr-OH: NaHCO3 (0.360 g, 4.29 mmol) and then a solution of
MeZOSu (0.486 g, 1.85 mmol) in dioxane (7 mL) were added to a vigo-
rously stirred solution of allo-d-threonine (0.200 g, 1.68 mmol) in water
(7 mL), and stirring was continued for 3 h (if a precipitate formed, diox-
ane and/or water was added to obtain a homogeneous solution).The mix-
ture was then concentrated under reduced pressure, diluted with water
(40 mL) and washed with CH2Cl2 (4”10 mL).The pH of the water frac-
tion was adjusted to ca.1–2 with solid NaHSO 4, and the resulting emul-
sion was extracted with EtOAc (2”40 mL).The organic layer was
washed with water (4”20 mL), brine 2”10 mL), dried and concentrated
under reduced pressure.The residue was recrystallized from Et O/hexane
2
and then from CH2Cl2/hexane to give the title compound (0.175 g, 39%)
as a colorless solid.The mother liquor from the second crystallization
was concentrated, and the residue was recrystallized again from Et2O/
hexane to give a second crop of the title compound (0.23 g, 90% overall
yield). Rf =0.13 (EtOAc/hexane 1:3 (2% AcOH); threefold development
was applied); m.p. 78–808C; [a]2D0 =ꢀ24.6 (c=0.32, CHCl3); 1H NMR
(250 MHz, CDCl3): d=1.27 (d, J=6.5 Hz, 3H, 4-H), 2.34 (s, 3H, 1’-H),
3.70–4.40 (br, 2H, OH, CO2H), 4.05–4.27 (m, 1H, 3-H), 4.33–4.44 (m,
1H, 2-H), 5.07 (s, 2H, Bzl-H), 5.77 (d, J=7.5 Hz, 1H, NH), 7.15 (d, J=
8.0 Hz, 2H, Ar-H), 7.24 (d, J=8.0 Hz, 2H, Ar-H); 13C NMR (62.9 MHz,
CDCl3): d=18.7 (+, C-4), 21.1 (+, C-1’), 59.3 (+, C-2), 67.4 (ꢀ, Bzl-C),
69.0 (+, C-3), 128.3, 129.2 (+, Ar-C), 132.7, 138.1 (Cquat, Ar-C), 156.9
(Cquat, NCO2), 173.3 (Cquat, C-1); IR (KBr): n˜ =3400, 3213, 2988, 2931,
2889, 1723, 1678, 1537, 1422, 1275, 1225, 1210 cmꢀ1; MS (EI, 70 eV): m/z
(%): 267 (3) [M +], 223 (5) [M +ꢀCO2], 162 (8) [M +ꢀC8H9], 105 (100)
[C8H9+], 77 (6) [C6H5+], 45 (5) [CHO2+]; HRMS (EI): calcd for
C13H17NO5: 267.1107; found 267.1107; elemental analysis calcd (%) for
C13H17NO5 (267.3): calcd. C 58.42, H 6.41, N 5.24; found C 58.59, H 6.13,
N 5.08.
C-1, All), 66.4, 67.0 (ꢀ, Bzl-C), 70.8, 70.8 (+, C-3), 79.6, 79.7 [Cquat
,
C(CH3)3], 118.2, 118.9 (ꢀ, C-3, All), 126.3, 126.3 (+, Ar-C), 127.9 (+,
Ar-C), 128.7, 128.8 [+, C-2’, (4-PE)Pro], 129.0, 129.1 [+, C-1’, (4-
PE)Pro], 130.9, 131.2 (+, C-2, All), 132.7, 133.1 (Cquat, Ar-C), 137.2,
137.6 (Cquat, Ar-C), 153.0, 153.5 (Cquat, NCO2, Boc), 155.4, 155.9 (Cquat
,
NCO2, MeZ), 168.4, 168.4 (Cquat, C-1, a-Thr), 171.6, 171.9 [Cquat, C-1, (4-
PE)Pro]; IR (KBr): n˜ =3330, 3009, 2977, 2932, 2871, 1747, 1703, 1520,
1478, 1453, 1399, 1367, 1253, 1161 cmꢀ1; MS (EI, 70 eV): m/z (%): 544
(2) [M +], 488 (6) [M +ꢀC4H8], 444 (5) [M +ꢀC5H8O2], 339 (26), 210
(11), 154 (100) [C8H12NO2+], 110 (83) [C7H12N+], 105 (100) [C8H9+], 57
(49) [C4H9+], 41 (15) [C3H5+]; HRMS (EI): calcd for C29H40N2O8:
544.2785; found 544.2785; elemental analysis calcd (%) for C29H40N2O8
(544.7): C 63.95, H 7.40, N 5.14; found C 63.99, H 7.32, N 4.99.
Fmoc-(bMe)Phe-(2R)-(3-Ncp)Ala-(bMe)Phe-Ile-OMOM (13a): The tri-
peptide 7a (205 mg, 0.29 mmol) was deprotected according to GP 1 and
then directly coupled with the N-Fmoc-protected b-methylphenylalanine
(10)[21] (126 mg, 0.31 mmol) according to GP 2 using EDC (60 mg,
0.31 mmol), HOAt (42 mg, 0.31 mmol) and TMP (106 mg, 0.88 mmol) in
CH2Cl2/MeCN 2:1 (3 mL) to give 13a (195 mg, 78%) as a colorless solid
after recrystallization from CHCl3/hexane. Rf =0.27 [CHCl3/MeOH 70:1
MeZ-a-Thr-OAll (9): A suspension of dried K2CO3 (0.034 g, 0.247 mmol)
in
a
solution of the N-MeZ-protected allo-d-threonine (0.12 g,
0.449 mmol) and allyl bromide (0.08 mL, 0.946 mmol) in anhydrous
MeCN (4 mL) was vigorously stirred in a sealed tube at 858C for 2 h.
Chem. Eur. J. 2004, 10, 4718 – 4727
www.chemeurj.org
ꢀ 2004 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
4723

A.de Meijere and B.D.Zlatopolskiy
FULL PAPER
(1% EtOH)]; m.p. 209–2128C (decomp.); [a]2D0 =ꢀ40.2 (c=0.3, THF);
1H NMR (250 MHz, [D8]THF): d=0.78 (d, J=7.0 Hz, 3H, 1’-H, Ile), 0.80
(t, J=7.0 Hz, 3H, 5-H, Ile), 0.94–1.17 [m, 2H, 4-Ha, Ile, 3’-Ha, (3-
Ncp)Ala], 1.20 [d, J=6.8 Hz, 3H, 4-H, (b-Me)Phe], 1.33 [d, J=7.0 Hz,
3H, 4-H, (b-Me)Phe], 1.34–1.54 [m, 4H, 3-H, 4-Hb, Ile, 1’-H, 3’-Hb, (3-
Ncp)Ala], 1.59–1.87 [m, 2H, 3-H, (3-Ncp)Ala], 3.10 [dq, J=10.3, 7.1 Hz,
1H, 3-H, (b-Me)Phe], 3.21 [dq, J=7.5, 7.5 Hz, 1H, 3-H, (b-Me)Phe], 3.31
(s, 3H, OMe), 3.95 [ddd, J=6.8, 3.3, 3.3 Hz, 1H, 2’-H, (3-Ncp)Ala], 4.13–
4.40 (m, 5H, 2”2-H, 1-H, 9’-H, Fmoc), 4.46 [ddd, J=3.3, 3.3, 3.3 Hz, 1H,
2-H, (3-Ncp)Ala], 4.55 (dd, J=8.6, 8.6 Hz, 1H, 2-H), 5.03 (d, J=5.6 Hz,
1H, Ha, OCH2O), 5.11 (d, J=5.6 Hz, 1H, Hb, OCH2O), 6.97–7.46 (m,
16H, 4”NH, 12”Ar-H), 7.54 (dd, J=10.9, 8.9 Hz, 2H, Ar-H), 7.66 (dd,
J=9.9, 7.6 Hz, 2H, Ar-H), 7.77 (d, J=7.5 Hz, 2H, Ar-H); 13C NMR
(62.9 MHz, [D8]THF): d=11.9 (+, C-5, Ile), 15.9 (+, C-1’, Ile), 17.9 [+,
C-4, (b-Me)Phe], 18.6 [+, C-4, (b-Me)Phe], 18.8 [ꢀ, C-3’, (3-Ncp)Ala],
23.1 [+, C-1’, (3-Ncp)Ala], 26.0 (ꢀ, C-4, Ile), 34.7 [ꢀ, C-3, (3-Ncp)Ala],
38.6 (+, C-3, Ile), 42.7 [+, C-3, (b-Me)Phe], 44.0 [+, C-3, (b-Me)Phe],
48.4 (+, C-9’, Fmoc), 52.7 (+, C-2), 57.3 (+, C-2), 57.9 (+, OMe), 59.6
(+, C-2), 60.1 [+, C-2’, (3-Ncp)Ala], 62.1 (+, C-2), 67.6 (ꢀ, C-1, Fmoc),
91.4 (ꢀ, OCH2O), 126.3, 126.3, 127.4, 127.7, 128.0, 128.5, 128.9, 129.1,
129.2, 129.3 (+, Ar-C), 142.4, 142.4 (Cquat, Ar-C, Fmoc), 143.9 [Cquat, Ar-
C, (b-Me)Phe], 144.2 [Cquat, Ar-C, (b-Me)Phe], 145.3, 145.5 (Cquat, Ar-C,
Fmoc), 157.7 (Cquat, NCO2), 171.3, 171.4, 171.6, 172.1 (Cquat, C-1); IR
(KBr): n˜ =3300, 2967, 1708, 1668, 1637, 1543, 1370, 1247 cmꢀ1; MS (ESI):
positive mode: m/z (%): 898 (100) [M+Na+]; elemental analysis calcd
(%) for C49H57N5O10 (876.0): C 67.18, H 6.56, N 7.99; found C 67.15, H
6.46, N 8.06.
208C for 45 min, was then again carefully heated with heat-gun until the
catalyst had dissolved and stirred for another 15 min.The reaction mix-
ture was then diluted with Et2O (40 mL), washed with 1m NaHSO4 (3”
10 mL), water (10”10 mL), brine (2”10 mL), dried, filtered and concen-
trated under reduced pressure.The residue was taken up with Et 2O/
hexane 1:2, filtered, concentrated and purified by column chromatogra-
phy [Rf =0.34 (EtOAc/hexane 1:2 (1.5% AcOH)] to give 14 (0.121 g,
1
90%) as a yellow oil.[ a]2D0 =ꢀ71.7 (c=0.32, CHCl3); H NMR (250 MHz,
CDCl3): d=1.35, 1.40 [2”s, 9H, C(CH3)3], 1.41, 1.43 (2”d, J=5.7 Hz,
3H, 4-H, a-Thr), 1.63, 1.65 [2”dd, J=1.5, 6.7 Hz, 3H, 3’-H, (4-PE)Pro],
1.67–1.86 [m, 1H, 3-Ha, (4-PE)Pro], 2.24–2.49 [m, 1H, 3-Hb, (4-PE)Pro],
2.33, 2.34 (2”s, 3H, 1’-H, MeZ), 2.91–3.20 [m, 2H, 4-H, 5-Ha, (4-
PE)Pro], 3.40–4.30 (br, 1H, CO2H), 3.61, 3.73 [2”ddd, J=2.7 Hz, 1H, 5-
Hb, (4-PE)Pro], 4.11–4.29 [m, 1H, 2-H, (4-PE)Pro], 4.51 (dd, J=8.6,
3.5 Hz, 1H, 2-H, a-Thr), 5.05 (s, 2H, Bzl-H, MeZ), 5.15–5.31 [m, 1H, 1’-
H, (4-PE)Pro], 5.31–5.44 (m, 1H, 3-H, a-Thr), 5.45–5.60 [m, 1H, 2’-H,
(4-PE)Pro], 5.63 (d, J=7.6 Hz, 0.4H, NH), 6.46 (d, J=9.2 Hz, 0.6H,
NH), 7.13, 7.17 (2”d, J=7.9 Hz, 2H, Ar-H), 7.21, 7.22 (d, J=7.9 Hz, 2H,
Ar-H); 13C NMR (62.9 MHz, CDCl3): d=13.0 [+, C-3’, (4-PE)Pro], 15.8,
16.3 (+, C-4, a-Thr), 21.0 (+, C-1’, MeZ), 28.1 [+, C(CH3)3], 35.5, 36.2
[+, C-4, (4-PE)Pro], 36.0, 37.0 [ꢀ, C-3, (4-PE)Pro], 51.3, 51.6 [ꢀ, C-5,
(4-PE)Pro], 57.0, 57.5 [+, C-2, (4-PE)Pro], 59.1, 59.3 (+, C-2, a-Thr),
66.8, 67.0 (ꢀ, Bzl-C), 71.2, 71.4 (+, C-3, a-Thr), 80.5, 80.6 [Cquat
,
C(CH3)3], 126.5, 126.6 (+, Ar-C), 128.1, 128.2 [+, C-2’, (4-PE)Pro],
128.9, 129.0 [+, C-1’, (4-PE)Pro], 129.10, 129.13 (+, Ar-C), 132.8, 133.0
(Cquat, Ar-C), 137.6, 137.9 (Cquat, Ar-C), 153.7, 154.2 (Cquat, NCO2, Boc),
155.8, 156.4 (Cquat, NCO2, MeZ), 171.2, 171.7 (Cquat, C-1), 172.0, 172.2
(Cquat, C-1); IR (KBr): n˜ =3700–2750, 2979, 1729, 1520, 1404, 1369, 1257,
1162, 1061 cmꢀ1; MS (EI, 70 eV): m/z (%): 504 (2) [M +], 448 (7) [M +
ꢀC4H8], 404 (27) [M +ꢀC5H8O2], 299 (21), 210 (14), 154 (100)
[C8H12NO2+], 110 (92) [C7H12N+], 105 (100) [C8H9+], 57 (50) [C4H9+],
41 (16) [C3H5+]; HRMS (EI): calcd for C26H36N2O8: 504.2472; found
504.2472.
Fmoc-(bMe)Phe-(2R)-(3-Ncp)Ala-(bMe)Phe-Ile-ODCPM (13b): The
tripeptide 7b (0.420 g, 0.549 mmol) was deprotected according to GP 1,
and the resulting product 11b was then directly coupled with 10 (0.242 g,
0.603 mmol) according to GP 2 using EDC (0.114 g, 0.595 mmol), HOAt
(0.080 g, 0.588 mmol) and TMP (0.200 g, 1.650 mmol) in CH2Cl2 (3 mL).
After 1 h, a precipitate formed in the reaction mixture, and anhydrous
DMF (2 mL) was added to obtain a homogeneous solution.After 15 h,
the reaction mixture was concentrated under reduced pressure.The re-
sulting solid was washed with water (100 mL), 3% aqueous NaHCO3
(100 mL), water (100 mL), Et2O (100 mL), pentane (50 mL), dried at
0.5 Torr and then crystallized twice from THF/hexane to give 13b
(0.430 g, 85%) as an off-white solid. Rf =0.29 (CHCl3/MeOH 70:1); m.p
210–2158C (decomp.); [a]2D0 =ꢀ26.3 (c=0.32, THF); 1H NMR (250 MHz,
[D8]THF): d=0.22–0.57 (m, 7H, 2’-H, DCPM), 0.67–0.90 (m, 2H, 1’-H,
2’-H, DCPM), 0.78–0.86 (m, 1H, 1’-H, DCPM), 0.81 (d, J=6.5 Hz, 3H,
1’-H, Ile), 0.83 (t, J=7.3 Hz, 3H, 5-H, Ile), 0.92–1.19 [m, 4H, 4-H, Ile, 3’-
H, (3-Ncp)Ala], 1.20 [d, J=7.3 Hz, 3H, 4-H, (bMe)Phe], 1.32 [d, J=
7.0 Hz, 3H, 4-H, (bMe)Phe], 1.30–1.50 [m, 4H, 3-H, Ile, 1’-H, 3-H, (3-
Ncp)Ala], 3.11 [dq, J=9.6, 7.2 Hz, 1H, 3-H, (bMe)Phe], 3.24 [dq, J=7.4,
7.4 Hz, 1H, 3-H, (bMe)Phe], 3.81 (t, J=8.5 Hz, 1H, 1-H, DCPM), 3.94
[ddd, J=6.8, 3.3, 3.3 Hz, 1H, 2’-H, (3-Ncp)Ala], 4.13–4.41 (m, 5H, 2”2-
H, 1-H, 9’-H, Fmoc), 4.41–4.51 (m, 1H, 2-H), 4.61 (dd, J=8.5, 7.8 Hz,
1H, 2-H), 6.97–7.40 (m, 16H, 2”NH, 14”Ar-H), 7.48 (d, J=8.5 Hz, 1H,
NH), 7.58 (d, J=8.3 Hz, 1H, NH), 7.66 (dd, J=8.1 Hz, 2H, Ar-H), 7.77
(d, J=7.8 Hz, 2H, Ar-H); 13C NMR (62.9 MHz, [D8]THF): d=3.3, 3.5,
3.6, 3.7 (ꢀ, C-2’, DCPM), 12.2 (+, C-5, Ile), 15.6, 15.9 (+, C-1’, DCPM),
16.1 (+, C-1’, Ile), 17.7 [+, C-4, (bMe)Phe], 18.7 [+, C-4, (bMe)Phe],
18.9 [ꢀ, C-3’, (3-Ncp)Ala], 23.2 [+, C-1’, (3-Ncp)Ala], 26.2 (ꢀ, C-4, Ile),
35.0 [ꢀ, C-3, (3-Ncp)Ala], 39.1 (+, C-3, Ile), 42.8 [+, C-3, (bMe)Phe],
44.1 [+, C-3, (bMe)Phe], 48.5 (+, C-9’, Fmoc), 52.8 (+, C-2), 57.4 (+,
C-2), 59.3 (+, C-2), 60.2 [+, C-2’, (3-Ncp)Ala], 62.1 (+, C-2), 67.8 (ꢀ, C-
1, Fmoc), 83.4 (+, C-1, DCPM), 126.4 (” 2), 127.5, 127.7, 128.1, 128.6,
129.1, 129.1, 129.3, 129.4 (+, Ar-C), 142.5 (Cquat, Ar-C, Fmoc), 144.1
MeZ-a-Thr[Boc-(4-PE)Pro]-(bMe)Phe-(2R)-(3-Ncp)Ala-(bMe)Phe-Ile-
OMOM (16a): The tetrapeptide 13a (180 mg, 0.21 mmol) was deprotect-
ed according to GP 1 in MeCN (2 mL), taken up with anhydrous CH2Cl2
(5 mL), the dipeptide acid 14 (0.114 g, 0.23 mmol), HATU (96 mg,
0.25 mmol) and HOAt (31 mg, 0.23 mmol) were added, and the reaction
mixture was cooled to 48C.After this, a solution of DIEA (29 mg,
0.22 mmol) and TMP (75 mg, 0.62 mmol) in CH2Cl2 (2 mL) was added at
the same temperature within 5 min.The temperature was allowed to
reach 208C, and stirring was continued for an additional 15 h.After
aqueous work-up according to GP 2 and two recrystallizations from
EtOAc/hexane 1:2, the depsipeptide 16a (185 mg, 79%) was obtained as
a
colorless powder. Rf =0.46 (EtOAc/hexane 1:1); m.p. 125–1278C;
[a]D20 =0 (c=0.21, CHCl3); [a]2D0 =ꢀ29.0 (c=0.2, THF); 1H NMR
(250 MHz, CDCl3): d=0.76 (d, J=6.8 Hz, 3H, 1’-H, Ile), 0.89 (t, J=
7.3 Hz, 3H, 5-H, Ile), 0.95–1.11 [m, 2H, 4-Ha, Ile, 3’-Ha, (3-Ncp)Ala],
1.11–1.60 [m, 5H, 3-H, 4-Hb, Ile, 3-Ha, 1’-H, 3’-Hb, (3-Ncp)Ala], 1.24 [d,
J=7.5 Hz, 3H, 4-H, (b-Me)Phe], 1.27 [d, J=7.5 Hz, 3H, 4-H, (b-
Me)Phe], 1.36 [s, 9H, C(CH3)3], 1.43 (d, J=6.5 Hz, 3H, 4-H, a-Thr), 1.68
[dd, J=6.6, 1.6 Hz, 3H, 3’-H, (4-PE)Pro], 1.76 [dd, J=11.6, 11.6 Hz, 1H,
3-Ha, (4-PE)Pro], 1.87–2.02 [m, 1H, 3-Hb, (3-Ncp)Ala], 2.32 (s, 3H, 1’-H,
MeZ), 2.43 [ddd, J=12.3, 6.5, 6.5 Hz, 1H, 3-Hb, (4-PE)Pro], 2.99–3.20
[m, 1H, 4-H, (4-PE)Pro], 3.11 [dd, J=9.8, 9.8 Hz, 1H, 5-Ha, (4-PE)Pro],
3.21–3.38 [m, 2H, 3-H, (b-Me)Phe, 5-Hb, (4-PE)Pro], 3.49 (s, 3H, OMe),
3.70 (dd, J=9.8, 7.0 Hz, 1H, 2-H), 3.86 [dq, J=3.9, 6.5 Hz, 1H, 3-H, (b-
Me)Phe], 4.14 (dd, J=11.1, 6.3 Hz, 1H, 2-H), 4.34–4.55 [m, 3H, 2-H, 2’-
H, (3-Ncp)Ala], 4.59 (dd, J=9.9, 5.1 Hz, 1H, 2-H), 4.67 (dd, J=10.4,
10.4 Hz, 1H, 2-H), 5.03 (dd, J=2.9, 2.9 Hz, 2H, Bzl-H), 5.27 [ddq, J=
10.5, 10.5, 1.6 Hz, 1H, 1’-H, (4-PE)Pro], 5.46–5.60 [m, 2H, 3-H, a-Thr, 2’-
H, (4-PE)Pro], 5.61 (d, J=6.3 Hz, 1H, Hb, OCH2O), 6.57 (d, J=8.3 Hz,
1H, NH), 6.99 (d, J=6.0 Hz, 1H, NH), 7.02 (d, J=6.0 Hz, 1H, NH),
7.07–7.38 (m, 14H, Ar-H), 7.57 (d, J=10.0 Hz, 1H, NH), 7.95 (d, J=
5.8 Hz, 1H, NH); The peak of Bzl-H masked absorption for Ha of
OCH2O; 13C NMR (62.9 MHz, CDCl3): d=11.5 (+, C-5, Ile), 13.0 [+, C-
3’, (4-PE)Pro], 15.6 (+, C-1’, Ile), 17.5 [+, C-4, (b-Me)Phe], 18.2 [ꢀ, C-
3’, (3-Ncp)Ala], 18.4 [+, C-4, (b-Me)Phe], 19.2 (+, C-4, a-Thr), 20.9 (+,
C-1’, MeZ), 21.7 [+, C-1’, (3-Ncp)Ala], 24.9 (ꢀ, C-4, Ile), 28.1 [+,
C(CH3)3], 31.5 [ꢀ, C-3, (3-Ncp)Ala], 36.1 [ꢀ, C-3, (4-PE)Pro], 36.1 [+,
C-4, (4-PE)Pro], 36.9 (+, C-3, Ile), 40.4 [+, C-3, (b-Me)Phe], 41.8 [+,
[Cquat
, Ar-C, (bMe)Phe], 144.4 [Cquat, Ar-C, (bMe)Phe], 145.4, 145.6
(Cquat, Ar-C, Fmoc), 157.8 (Cquat, NCO2), 171.1, 171.5, 171.9, 172.1 (Cquat
,
C-1); IR (KBr): n˜ =3250, 3065, 2967, 2933, 1709, 1665, 1636, 1542, 1451,
1369, 1246 cmꢀ1; MS (ESI): positive mode: m/z (%): 948 (100) [M+Na+];
elemental analysis calcd (%) for C54H63N5O9 (926.1): C 70.03, H 6.86, N
7.56; found C 69.94, H 6.68, N 7.32.
MeZ-a-Thr[(4-PE)Pro]-OH (14): [Pd(PPh3)4] (0.034 g, 29.4 mmol) was
added to
a vigorously stirred solution of the ester 12 (0.145 g,
0.266 mmol) and N-methylaniline (0.1 mL, 0.923 mmol) in DME
(4.0 mL) and the resulting suspension was carefully heated with a heat-
gun to obtain a homogeneous solution.The mixture was left to stir at
4724
ꢀ 2004 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2004, 10, 4718 – 4727

Hormaomycin
4718 – 4727
C-3, (b-Me)Phe], 50.8 (+, C-2), 51.9 [ꢀ, C-5, (4-PE)Pro], 56.1 (+, C-2),
57.5 (+, OMe), 59.1 (+, C-2), 59.3 (+, C-2), 60.7 (+, C-2), 61.2 (+, C-
2), 61.6 [+, C-2’, (3-Ncp)Ala], 66.7 (ꢀ, Bzl-C), 70.4 (+, C-3, a-Thr), 80.7
[Cquat, C(CH3)3], 90.9 (ꢀ, OCH2O), 126.3, 126.7, 127.5, 127.7, 128.2, 128.3,
128.4, 128.5, 128.7, 128.8 [+, Ar-C and C-1’, C-2’, (4-PE)Pro], 133.0,
133.2, 137.9, 140.9, 142.6 (Cquat, Ar-C), 156.3 (Cquat, NCO2), 169.0, 170.3,
170.6, 171.1, 171.4, 173.1 (Cquat, C-1); IR (KBr): n˜ =3340, 2969, 2936,
2878, 1730, 1637, 1541, 1515, 1452, 1370, 1179 cmꢀ1; MS (ESI): positive
mode: m/z (%): 1001 (100) [M+Na+]; negative mode: m/z (%): 977
(100) [MꢀH+]; HRMS (ESI): calcd for [C53H67N7O11Na+]: 1000.4792;
found 1000.4792.
137.6, 141.6, 141.8 (Cquat, Ar-C), 154.5, 154.6 (Cquat, NCO2), 170.31,
170.33, 170.8, 171.1, 173.0, 173.8 (Cquat, C-1); IR (KBr): n˜ =3308, 3062,
2972, 2934, 1729, 1648, 1543, 1454, 1368, 1254, 1162, 1091 cmꢀ1; MS
(ESI): positive mode: m/z (%): 1163 (100) [M+Na+]; negative mode: m/
z (%): 1138 (50) [MꢀH+], 1175 (50) [M+Clꢀ]; elemental analysis calcd
(%) for C60H81N7O15 (1140.4): C 63.20, H 7.16, N 8.60; found C 63.09, H
7.27, N 8.46.
N-Teoc-3-(2S,1’S,2’R)-(trans-2’-Nitrocyclopropyl)alanine:
A solution of
TeocOSu (0.358 g, 1.38 mmol) in acetone (5 mL) was added to a vigo-
rously stirred solution of 3-(2S,1’R,2’R)-(trans-2’-nitrocyclopropyl)alanine
(0.200 g, 1.15 mmol) and NaHCO3 (0.202 g, 2.40 mmol) in water (7 mL)
(if an emulsion formed, acetone and/or water was added to obtain a ho-
mogeneous solution), and stirring was continued for another 2 h. N,N-Di-
methylaminopropylamine (0.055 mL, 0.44 mmol) was then added. After
an additional 10 min acetone was removed under reduced pressure and
the pH of the residual water solution was adjusted to 2–3 with 1m
NaHSO4.The resulting emulsion was extracted with Et 2O (50 mL), and
the ethereal layer was washed with 1m NaHSO4 (2”10 mL), water (10”
10 mL), brine (2”5 mL), dried, filtered and concentrated under reduced
pressure.The residual oil (03. 00 g) was dissolved in Et 2O (5 mL), and cy-
clohexylamine (0.094 g, 0.95 mmol) was added. The mixture was concen-
trated under reduced pressure and treated with boiling hexane.The re-
sulting precipitate was filtered off and washed with Et2O/pentane 1:4 to
give the cyclohexylammonium salt of the title compound (0.386 g, 81%)
N-MeZ-protected cyclohexadepsipeptide (17): 2m HCl in EtOAc (2 mL)
was added to the hexadepsipeptide 16a (0.188 g, 0.165 mmol). The reac-
tion mixture was stirred at 208C for 45 min in a dark place and was then
concentrated under reduced pressure at 208C.The residue was triturated
with anhydrous Et2O to give the hydrochloride of the deprotected mate-
rial as a colorless solid (0.160 g, 0.157 mmol). MS (ESI): positive mode:
m/z (%): 1019 (5) [M+Na+], 997 (100) [M+H+]; negative mode: m/z
(%): 995 (50) [MꢀH+].It was taken up with anhydrous CH 2Cl2 (1.5 L).
The solution was cooled to 48C (internal temperature), HATU (73 mg,
0.192 mmol) and HOAt (22 mg, 0.163 mmol) were added, and then a sol-
ution of DIEA (62 mg, 0.480 mmol) in CH2Cl2 (50 mL) was added over
30 min.The cooling bath was removed and stirring continued for an addi-
tional 2 h at ambient temperature.Then the reaction mixture was cooled
again to 48C, and a second portion of each, HATU (73 mg, 0.192 mmol)
and HOAt (22 mg, 0.163 mmol), was added, and then a solution of
DIEA (62 mg, 0.480 mmol) in CH2Cl2 (50 mL) was added within 30 min.
The temperature was allowed to reach 208C and stirring was continued
for 15 h.After this, the solvent was removed under reduced pressure, the
residue was taken up with Et2O, and after the usual aqueous work-up
(GP 2) and concentration under reduced pressure, the crude product was
purified first by column chromatography (Rf =0.17, acetone/hexane 1:3)
and then by recrystallization (Et2O/pentane) to give a crude product
(120 mg), which was finally purified by preparative HPLC to give cyclo-
depsipeptide 17 (86 mg, 53% over two steps) as a colorless solid.Prepa-
rative HPLC: isocratic, 75% MeCN in H2O (0.1% TFA); analytical
HPLC: isocratic, 50% MeCN in H2O (0.1% TFA) for 20 min, then gradi-
ent 50% ! 99% MeCN (0.1% TFA) for 15 min, then isocratic, 99%
MeCN in H2O (0.1% TFA) for 10 min, flow rate=0.5 mLminꢀ1, tR =
34.93 min, purity >98%; [a]2D0 =ꢀ15.5 (c=0.20, CHCl3); 1H NMR
(600 MHz, CDCl3): d=0.64 [ddd, J=14.4, 7.2, 7.2 Hz, 1H, 3-Ha, (3-
Ncp)Ala], 0.72 (d, J=6.6 Hz, 3H, 1’-H, Ile), 0.74 [ddd, J=6.6, 6.6, 6.6 Hz,
1H, 3’-Ha, (3-Ncp)Ala], 0.79 (t, J=7.2 Hz, 3H, 5-H, Ile), 1.04–1.12 (m,
1H, 4-Ha, Ile), 1.23 [d, J=6.6 Hz, 3H, 4-H, (b-Me)Phe], 1.27–1.34 [m,
1H, 1’-H, (3-Ncp)Ala], 1.37 [d, J=6.6 Hz, 3H, 4-H, (b-Me)Phe], 1.37–
1.43 [m, 1H, 3-Hb, (3-Ncp)Ala], 1.45–1.54 (m, 1H, 4-Hb, Ile), 1.54–1.57
[m, 1H, 3’-Hb, (3-Ncp)Ala], 1.57 (d, J=6.6 Hz, 3H, 4-H, a-Thr), 1.65 [dd,
J=6.6, 1.5 Hz, 3H, 3’-H, (4-PE)-Pro], 1.66–1.76 [m, 2H, 3-H, Ile, 3-Ha,
(4-PE)Pro], 2.23 [ddd, J=12.0, 5.4, 5.4 Hz, 1H, 3-Hb, (4-PE)-Pro], 2.35
(s, 3H, 1’-H, MeZ), 3.05 [dq, J=6.6, 6.6 Hz, 1H, 3-H, (b-Me)Phe], 3.15–
3.28 [m, 2H, 4-H, 5-Ha, (4-PE)-Pro], 3.54 [dq, J=7.2, 6.6 Hz, 1H, 3-H,
(b-Me)Phe], 3.71 (dd, J=6.0, 5.4 Hz, 1H, 2-H), 3.76 [ddd, J=6.6, 3.3,
3.3 Hz, 1H, 2’-H, (3-Ncp)Ala], 3.98 (dd, J=10.5, 6.3 Hz, 1H, 2-H), 4.01–
4.08 [m, 1H, 5-Hb, (4-PE)-Pro], 4.46–4.54 (m, 2H, 2-H), 4.54 (dd, J=9.6,
9.6 Hz, 1H, 2-H), 4.69 (dd, J=8.4 Hz, 1H, 2-H), 5.03 (d, J=12.0 Hz, 1H,
Bzl-Ha), 5.15 (d, J=12.0 Hz, 1H, Bzl-Hb), 5.19–5.25 [m, 1H, 1’-H, (4-
PE)-Pro], 5.39 (dq, J=1.8, 6.6 Hz, 1H, 3-H, a-Thr), 5.56 [dq, J=10.8,
6.6 Hz, 1H, 2’-H, (4-PE)-Pro], 6.21–6.37 (br, 2H, NH), 6.44 (d, J=
8.4 Hz, 1H, NH), 6.48 (d, J=9.6 Hz, 1H, NH), 7.06–7.18 (m, 4H, Ar-H),
7.19–7.27 (m, 8H, Ar-H), 7.26–7.34 (m, 2H, Ar-H), 7.48 (d, J=8.4 Hz,
1H, NH); 13C NMR (150.8 MHz, CDCl3): d=10.3 (+, C-5, Ile), 13.3 [+,
C-3’, (4-PE)-Pro], 14.6 [+, C-1’, Ile, C-4, (b-Me)Phe], 17.3 [ꢀ, C-3’, (3-
Ncp)Ala], 17.7 [+, C-4, (b-Me)Phe], 18.4 (+, C-4, a-Thr), 21.2 (+, C-1’,
MeZ), 21.3 [+, C-1’, (3-Ncp)Ala], 24.7 (ꢀ, C-4, Ile), 32.0 [ꢀ, C-3, (3-
Ncp)Ala], 35.4 [ꢀ, C-3, (4-PE)-Pro], 36.6 [+, C-3, Ile, C-4, (4-PE)-Pro],
39.4 [+, C-3, (b-Me)Phe], 44.5 [+, C-3, (b-Me)Phe], 52.5 [ꢀ, C-5, (4-
PE)-Pro], 53.3 (+, C-2), 54.6 (+, C-2), 58.6 (+, C-2), 59.0 [+, C-2’, (3-
Ncp)Ala], 59.4 (+, C-2), 60.1 (+, C-2), 60.7 (+, C-2), 67.2 (ꢀ, Bzl-C),
72.6 (+, C-3, a-Thr), 127.1, 127.2, 127.5, 127.6, 128.3, 128.6, 128.8, 129.2
(+, Ar-C), 127.8 [+, C-1’, (4-PE)-Pro], 128.0 [+, C-2’, (4-PE)-Pro],
as a colorless solid. Rf =0.24 [EtOAc/hexane 1:3 (2% AcOH)]; [a]D20
=
22.80 (c=0.46, CHCl3) for CHA salt; 1H NMR (250 MHz, CDCl3): d=
0.04 [s, 9H, Si(CH3)3], 1.00 (dd, J=9.5, 7.3 Hz, 2H, 2-H, Teoc), 1.14
(ddd, J=6.0, 6.0, 6.0 Hz, 1H, 3’-Ha), 1.60–1.95 (m, 2H, 1’-H, 3’-Hb), 1.98–
2.19 (m, 2H, 3-H), 4.18 (dd, J=8.4, 8.4 Hz, 2H, 1-H, Teoc), 4.33–4.46,
4.46–4.59 (2”m, 1H, 2-H), 5.33–5.46 (m, 1H, NH), 7.08–7.25 (br, 1H,
CO2H); the signal of 2’-H is masked by the absorption of 1-H, Teoc;
13C NMR (62.9 MHz, CDCl3): d=ꢀ1.9 [+, Si(CH3)3], 17.3 (ꢀ, C-3’ and
C-2, Teoc), 22.0 (+, C-1’), 33.1, 33.3 (ꢀ, C-3), 52.7, 53.2 (+, C-2), 59.0 (+,
C-2’), 63.7, 64.8 (ꢀ, C-1, Teoc), 156.4, 157.4 (Cquat, NCO2), 174.5, 174.8
(Cquat, C-1); IR (KBr; for CHA salt): n˜ =3419, 3250–2600, 2952, 2863,
1722, 1632, 1541, 1492, 1406, 1368, 1248, 1206, 1163, 1053 cmꢀ1; MS
(ESI): positive mode: m/z (%): 363 (28) [MꢀH++2Na+], 341 (26)
[M+Na+]; negative mode (%): m/z: 657 (100) [2Mꢀ2H++Na+], 317
(28) [MꢀH+].
Hormaomycin 1: An ethereal solution (50 mL) of the CHA salt of N-
Teoc-protected
(2S,1’R,2’R)-(3-nitrocyclopropyl)alanine
(23.2 mg,
55.61 mmol) was washed with 1m H2SO4 (3”5 mL), 1m KHSO4 (2”
5 mL), water (3”5 mL), brine (2”5 mL), dried, filtered and concentrated
under reduced pressure.The resulting N-protected amino acid was dried
at 0.02 Torr for 2 h and then coupled with the depsipeptide, obtained
after deprotection of the N-MeZ-protected cyclodepsipeptide 17
(17.0 mg, 17.4 mmol) with 10% anisole in TFA (1.1 mL) in the dark at
ambient temperature for 2 h, using HATU (19.8 mg, 52.1 mmol), HOAt
(7.1 mg, 52.2 mmol), DIEA (2.3 mg, 17.8 mmol) and TMP (19.0 mg,
156.8 mmol) in CH2Cl2 (1.5 mL) at ambient temperature for 15 h. The re-
action mixture was then diluted with Et2O (30 mL) and the crude prod-
uct obtained after the usual aqueous work-up (GP 2) was purified by
crystallization from CH2Cl2/pentane to give Teoc-(S)-(3-Ncp)Ala-cyclo-
hexadepsipeptide (19.7 mg, 100%; Rf =0.43, acetone/hexane 1:2) as a col-
orless solid, which was used for the next step without any characteriza-
tion.The Teoc group was cleaved off from this substance (197. mg, max.
17.4 mmol) with TFA (1.0 mL) for 1 h. The mixture was concentrated
under reduced pressure at 208C and then taken up with toluene (3”
15 mL) which was distilled off to remove the last traces of TFA.The re-
sulting deprotected depsipeptide was coupled with 18 (10.0 mg,
48.7 mmol) using HATU (17.8 mg, 46.7 mmol), DIEA (2.6 mg, 20.1 mmol)
and TMP (17.7 mg, 146.1 mmol) in CH2Cl2 (1.5 mL) at ambient tempera-
ture for 2.5 h. The mixture was then taken up with Et2O (30 mL), and
the crude product obtained after the usual aqueous work-up (GP 2) was
purified by recrystallization from CH2Cl2/pentane to give the O-MOM
protected 1 (20.5 mg, 100%; Rf =0.36 acetone/hexane 1:2) as a colorless
solid which was used for the next step without any characterization.The
O-MOM protected hormaomycin (20.5 mg, max. 17.4 mmol) was depro-
tected using MgBr2·Et2O (120 mg, 0.464 mmol) and EtSH (30 mL,
0.405 mmol) in CH2Cl2 (10 mL) at ambient temperature for 3 h.The mix-
ture was taken up with Et2O (40 mL) and washed with 1n KHSO4 (3”
10 mL), water (4”10 mL), brine (2”5 mL), dried, filtered and concen-
Chem. Eur. J. 2004, 10, 4718 – 4727
www.chemeurj.org
ꢀ 2004 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
4725

A.de Meijere and B.D.Zlatopolskiy
FULL PAPER
trated under reduced pressure.The residue was crystallized from CH Cl2/
Ncp)Ala-OH and to Dr.B.Knieriem (Göttingen) for his careful proof-
reading of the final manuscript.
2
pentane to give the crude hormaomycin 1 (17.5 mg, 90% purity accord-
ing to HPLC), which was further purified by preparative HPLC.The
fraction containing the desired product was collected, and its pH value
was carefully adjusted to 6.9 (pH meter) with diluted aqueous ammonia,
and then it was lyophilized.The residue was dissolved in EtOAc and fil-
tered through cotton wool to give, after removal of the solvent under re-
duced pressure, the pure synthetic hormaomycin 1 (13.2 mg, 67% over fi-
ve steps from 17) as a colorless glass. Rf =0.24 (acetone/hexane 3:7);
preparative HPLC: column: JASCO Nucleosil C18 (250”8 mm); isocrat-
ic, 62% MeCN in 0.07% aqueous TFA; flow rate=2.5 mLminꢀ1; analyti-
cal HPLC: the same column; the same conditions; the same flow rate;
[1] a) N.Andres, H.Wolf, H.Zähner, E.Rössner, A.Zeeck, WA. .
König, V.Sinnwell, Helv. Chim. Acta 1989, 72, 426–437; b) H.
Zähner, N.Andres, A.Zeeck, E.Rössner, H.Wolf, W.A.König, V.
Sinnwell, A.Fredenhagen, Eur. Pat. Appl. 1990 EP 385936 AI
19900905; c) H.Wolf, N.Andres, DECHEMA Monogr. 1993, 129,
53–61; d) E.Rössner, A.Zeeck, W.A.König,
Angew. Chem. 1990,
102, 84–85; Angew. Chem. Int. Ed. Engl. 1990, 29, 64–65.
[2] The previously unknown absolute configurations of the two nitrocy-
clopropylalanine residues as well as the 4-propenylproline moiety in
1 were established by a series of feeding experiments with the ap-
propriate enantiomerically pure deuterium-labeled amino acids.It
was additionally confirmed (in the case of 4-propenylproline) by a
series of HPLC and HPLC/MS experiments.
[3] For the synthesis of all four stereoisomers of 3-(trans-2-nitrocyclo-
propyl)alanine see: a) O.V.Larionov, T.F.Savelieva, K.A.Kochet-
kov, N.S.Ikonnikov, S.I.Kozhushkov, D.S.Yufit, J.A.K.Howard,
tR =14.54 min, purity >99%; [a]D20
=
20.0 (c=0.1, MeOH); 1H NMR
(600 MHz, CDCl3): d=ꢀ0.68 [ddd, J=6.7, 6.7, 6.7 Hz, 1H, 3’-Ha, (3-
Ncp)Ala], ꢀ0.15 [dddd, J=14.2, 9.8, 3.5, 3.5 Hz, 1H, 3-Ha, (3-Ncp)Ala],
0.23–0.33 [m, 1H, 1’-H, (3-Ncp)Ala], 0.58 [ddd, J=14.2, 4.3, 4.3 Hz, 1H,
3-Hb, (3-Ncp)Ala], 0.90 (t, J=7.2 Hz, 3H, 5-H, Ile), 0.98–1.04 [m, 1H, 3’-
Hb, (3-Ncp)Ala], 1.02 [ddd, J=6.4, 6.4, 6.4 Hz, 1H, 3’-Ha, (3-Ncp)Ala],
1.04 (d, J=6.8 Hz, 3H, 1’-H, Ile), 1.27–1.35 (m, 1H, 4-Ha, Ile), 1.33 [d,
J=7.2 Hz, 3H, 4-H, (b-Me)Phe], 1.41 [d, J=7.2 Hz, 3H, 4-H, (b-
Me)Phe], 1.54 (d, J=6.7 Hz, 3H, 4-H, a-Thr), 1.54–1.63 [m, 2H, 3-Ha, (3-
Ncp)Ala, 4-Hb, Ile], 1.69 [dd, J=6.6, 1.8 Hz, 3H, 3’-H, (4-PE)Pro], 1.75–
1.99 [m, 4H, 3-Hb, 1’-H, 3’-Hb, (3-Ncp)Ala, 3-H, Ile], 1.82 [ddd, J=11.4,
11.4, 11.4 Hz, 1H, 3-Ha, (4-PE)Pro], 2.39 [ddd, J=11.4, 6.0, 5.4 Hz, 1H,
3-Hb, (4-PE)Pro], 2.90 [ddd, J=6.7, 3.5 Hz, 1H, 2’-H, (3-Ncp)Ala], 3.03
[dq, J=11.1, 7.2 Hz, 1H, 3-H, (b-Me)Phe], 3.22–3.34 [m, 2H, 4-H, 5-Ha,
(4-PE)Pro], 3.43–3.52 [m, 1H, 2-H, (3-Ncp)Ala], 3.68 [dq, J=4.5, 7.2 Hz,
1H, 3-H, (b-Me)Phe], 3.94–4.02 [m, 1H, 5-Hb, (4-PE)Pro], 4.05 [ddd, J=
6.5, 3.8, 3.8 Hz, 1H, 2’-H, (3-Ncp)Ala], 4.28 [dd, J=11.8, 6.2 Hz, 1H, 2-
H, (4-PE)Pro], 4.38 [dd, J=10.2, 10.2 Hz, 1H, 2-H, (b-Me)Phe], 4.47
[dd, J=9.5, 4.5 Hz, 1H, 2-H, (b-Me)Phe], 4.59 (dd, J=9.8, 2.5 Hz, 1H, 2-
H, a-Thr), 4.67 (dd, J=9.0, 9.0 Hz, 1H, 2-H, Ile), 5.13 [ddd, J=7.5, 7.5,
7.5 Hz, 1H, 2-H, (3-Ncp)Ala], 5.24–5.31 [m, 1H, 1’-H, (4-PE)Pro], 5.41
(dq, J=6.6, 2.5 Hz, 1H, 3-H, a-Thr), 5.64 [dq, J=10.2, 6.6 Hz, 1H, 2’-H,
(4-PE)Pro], 6.15 (d, J=4.9 Hz, 1H, 4-H, Chpca), 6.47 (d, J=6.0 Hz, 1H,
NH), 6.80 (d, J=8.4 Hz, 1H, NH), 6.82 (d, J=9.6 Hz, 1H, NH), 6.84 (d,
J=4.9 Hz, 1H, 3-H, Chpca), 7.00–7.06 (m, 1H, Ar-H), 7.11–7.16 (m, 4H,
Ar-H), 7.15–7.19 (m, 1H, Ar-H), 7.21–7.25 (m, 4H, Ar-H), 7.27 (d, J=
9.5 Hz, 1H, NH), 8.06 (d, J=9.4 Hz, 1H, NH), 9.08 (d, J=9.8 Hz, 1H,
NH), 10.60–11.25 (br, 1H, OH, Chpca); 13C NMR (150.8 MHz, CDCl3):
d=10.6 (+, C-5, Ile), 13.3 [+, C-3’, (4-PE)Pro], 13.3 [+, C-4, (b-
Me)Phe], 15.0 (+, C-1’, Ile), 17.0 (+, C-4, a-Thr), 17.4 [ꢀ, 2”C-3’, (3-
Ncp)Ala], 18.0 [+, C-4, (b-Me)Phe], 20.5 [+, C-1’, (3-Ncp)Ala], 21.8 [+,
C-1’, (3-Ncp)Ala], 24.9 (ꢀ, C-4, Ile), 33.4 [ꢀ, C-3, (3-Ncp)Ala], 35.3 [ꢀ,
C-3, (3-Ncp)Ala], 35.6 [ꢀ, C-3, (4-PE)Pro], 36.7 [+, C-4, (4-PE)Pro],
38.1 (+, C-3, Ile), 39.3 [+, C-3, (b-Me)Phe], 41.9 [+, C-3, (b-Me)Phe],
50.7 [+, C-2, (3-Ncp)Ala], 52.0 [+, C-2, (3-Ncp)Ala], 52.8 [ꢀ, C-5, (4-
PE)Pro], 54.7 (+, C-2, Ile), 55.2 (+, C-2, a-Thr), 58.2 [+, C-2’, (3-
Ncp)Ala], 59.3 [+, C-2’, (3-Ncp)Ala], 59.9 [+, C-2, (b-Me)Phe], 60.2 [+,
C-2, (b-Me)Phe], 61.4 [+, C-2, (4-PE)Pro], 69.2 (+, C-3, a-Thr), 103.2
(+, C-4, Chpca), 109.3 (+, C-3, Chpca), 119.5 (Cquat, C-2, Chpca), 121.4
(Cquat, C-5, Chpca), 126.9, 127.2, 127.5, 127.6, 128.5, 128.7 (+, Ar-C),
127.5 [+, C-1’, (4-PE)Pro], 128.4 [+, C-2’, (4-PE)Pro], 141.6, 142.2
(Cquat, Ar-C), 159.6 (Cquat, C-1, Chpca), 168.7, 168.9, 169.8, 170.9, 171.3,
171.5, 172.1 (Cquat, C-1); UV (MeOH): lmax (e)=204 (5”104), 275 nm
(9.6”103); CD (MeOH): lmax [V]=279 (6.01”104), 224.2 nm (ꢀ6.500”
103) (c=1.754”10ꢀ4 m); MS (ESI): positive mode: m/z (%): 1174 (100)
[MꢀH++2Na+], 1151 (80) [M+Na+]; negative mode: m/z (%): 1127
(100) [MꢀH+].
V.N.Khrustalev, Yu.N.Belokon, A.de Meijere,
Eur. J. Org. Chem.
2003, 869–877; for a partial elucidation of the relative and absolute
configurations of the two 3-(trans-2-nitrocyclopropyl)alanine moiet-
ies in hormaomycin 1, and the synthesis of enantiomerically pure
mixtures of epimers of 3-(trans-2-nitrocyclopropyl)alanine, see also:
b) J.Zindel, A.de Meijere, J. Org. Chem. 1995, 60, 2968–2973; c) J.
Zindel, A.Zeeck, WA. .König, A.de Meijere,
Tetrahedron Lett.
1993, 34, 1917–1920.
[4] B.Zlatopolskiy, E.Melotto, A.de Meijere, unpublished results.
[5] L.A.Carpino, A.El-Faham, Tetrahedron 1999, 55, 6813–6830.
[6] L.A.Carpino, H.G.Chao, S.Ghassemi, E.M.Mansour, C.Riemer,
R.Warrass, D.Sadat-Aalaee, GA. .Truran, H.Imazumi, A.El-
Faham, D.Ionescu, M.Ismail, T.L.Kowaleski, C.H.Han, H.Wen-
schuh, M.Beyermann, M.Bienert, H.Shroff, F.Albericio, SA. .
Triolo, N.A. Sole, S.A. Kates, J. Org. Chem. 1995, 60, 7718–7719.
[7] The relatively low yield must be attributed to the noticeable sus-
ceptibility of the MOM ester to nucleophilic attack by the free
amino group, especially when formation of a diketopiperazine ring
is possible.
[8] The tetrapeptide 13b can also be used towards the synthesis of vari-
ous analogues of 1.
[9] L.A.Carpino, J. Am. Chem. Soc. 1993, 115, 4397–4398.
[10] Although several N-MeZ-acylated glycines were prepared as early
as in 1951 (cf.: D.M. Channing, P.B. Turner, G.T. Young,
Nature
1951, 167, 487–488), the authors considered that “these compounds
appear to offer little advantage over the corresponding carbobenzyl-
oxy compounds”; to the best of our knowledge, the application of p-
methylbenzyloxycarbonyl group for peptide synthesis has never
been considered again.
[11] a) The N-Alloc-protected cyclic fragment of 1 was successfully pre-
pared, but all attempts to obtain the appropriate deprotected cyclic
hexadepsipeptide failed, presumably due to an O!N acyl shift; an
attempted transprotection with Boc2O (cf:. E.C.Roos, P.Bernabe,
H.Hiemstra, W.N.Speckamp, B.Kaptein, W.H.J.Bösten,
J. Org.
Chem. 1995, 60, 1733–1740) gave an inseparable mixture of unreact-
ed and transprotected peptides in 34% yield, although with model
peptides this technique worked pretty well (90–100% yield of the
desirable product).b) The ester bond between the (4-PE)Pro and a-
Thr fragments may also be cleaved under strongly acidic (TFMSA
in TFA, TMSOTf) conditions.c) For the model dipeptide MeZ-Phe-
Val-OMe.d) From the secondary amino group of the (4-PE)Pro res-
idue of the C-TMSE-protected acyclic precursor of the cyclic part of
1.e) The rate of cleavage of the conventional Z-protective group
was unacceptably slow even in the case of the model ester Z-
Thr(OFmocPro)-OMe (incomplete deprotection with 20% thio-
anisole in TFA in 12 h at ambient temperature).f) The 3-methylben-
zyloxycarbonyl and 3,5-dimethylbenzyloxycarbonyl groups were also
tested, but turned out to be somewhat less suitable for application
in this synthesis.
Acknowledgements
This work was supported by the Deutsche Forschungsgemeinschaft (SFB-
416, Project A3) and the Fonds der Chemischen Industrie.The authors
are indebted to Prof.Dr.A.Zeeck, Mr.H-.P.Kroll and Ms.M.Klinge-
biel (Göttingen) for their advice and indispensable help in establishing
the identity of synthetic and natural hormaomycin, to Prof.Dr.W.A.
König (Hamburg) for performing the GC control experiments, to Mr.O.
V.Larionov (Göttingen) for his generous gift of (2 S,1’R,2’R)-H-(3-
[12] A.Ehrlich, HU. .Heyne, R.Winter, M.Beyermann, H.Haber,
L.A.Carpino, M.Bienert, J. Org. Chem. 1996, 61, 8831–8838.
4726
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Hormaomycin
4718 – 4727
[13] a) Chpca-(3-Ncp)Ala-OH was also synthesized, but turned out to be
too unstable to be used for condensation with the deprotected 17.
b) The condensation between Chpca(MOM)-(3-Ncp)Ala-OH and 17
(after its deprotection) using the PyAOP[9] reagent unexpectedly
caused significant epimerization at the a-carbon of the (3-Ncp)Ala
residue in the side chain and gave a separable mixture of epimers
(MOM-1 and epi-MOM-1) in moderate yield.
methylphenylalanine, provided by us, as one of the reference com-
pounds (previously[1d] a mixture of all stereoisomers of 3-methylphe-
nylalanine had been used as a reference).These latest results were
in accordance with those obtained before.
[18] a) D.F.Elliot, J. Chem. Soc. 1950, 62; b) P.G.Anderson, D.Guijaro,
D.Tanner, J. Org. Chem. 1997, 62, 7364–7375.
[19] L.A.Carpino, Patent US 5580981, 1996.
[14] S.Kim, I.S.Kee, Y.H.Park, J.H.Park,
Synlett 1991, 183–184.
[20] R.E.Shute, D.H.Rich, Synthesis 1987, 346–349.
[15] a) The CD spectra were measured in methanol.b) It is noteworthy
that both MOM-1 and epi-MOM-1 were equally active in this test
and their activity was about 3.5 times lower than the activity of 1.
[16] Compare: K.Fujii, Y.Ikai, T.Mayumi, H.Oka, M.Suzuki, K.
Harada, Anal. Chem. 1997, 69, 3346–3352.
[21] a) G.Li, D.Patel, V.J.Hruby,
J. Chem. Soc. Perkin Trans. 1 1994,
3057–3059; b) E.Nicolas, K.C.Russel, V.J.Hruby,
1993, 58, 766–770.
[22] D.M.Birney, D.C.Cole, C.E.Crosson, B.F.Kahl, B.W.Neff, T.W.
J. Org. Chem.
Reid, K.Ren, R.D.Walkup, J. Med. Chem. 1995, 38, 2478–2482.
[17] We are grateful to Prof.W.A.König (Hamburg) for repeating some
GC separations[1d] to determine the absolute configuration of the 3-
methylalanine residue in hormaomycin 1, using pure (2S,3R)-3-
Received: March 15, 2004
Published online: July 28, 2004
Chem. Eur. J. 2004, 10, 4718 – 4727
www.chemeurj.org
ꢀ 2004 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
4727