Synthesis of jasplakinolide analogues containing a novel ω-amino acid

Article abstract of DOI:10.1002/chem.200500319

The synthesis of the ω-amino acid 4 is described utilizing a two-dimensional synthesis strategy combined with an enzymatic differentiation of homotopic ester groups. The amino acid 4 features two non-bonded interactions that result in conformational const

Full text of DOI:10.1002/chem.200500319

FULL PAPER
DOI: 10.1002/chem.200500319
Synthesis of Jasplakinolide Analogues Containing a Novel w-Amino Acid
Srinivasa Marimganti,[a] Shazia Yasmeen,[a] Daniela Fischer,[b] and Martin E. Maier*[a]
Dedicated to Prof. R. R. Schmidt for his 70th birthday
Abstract: The synthesis of the w-amino
acid 4 is described utilizing a two-di-
mensional synthesis strategy combined
with an enzymatic differentiation of
homotopic ester groups. The amino
acid 4 features two non-bonded inter-
actions that result in conformational
constraints on a cyclic construct. This
amino acid was incorporated into the
four macrolactams 17, 22, 31, and 37.
The ring in 17 and 22 is 18-membered,
whereas 31 and 37 have a 19-mem-
bered ring. The pairs with the same
ring size differ in a N-methyl group.
For the larger macrolactams (31 and
37) conformational analysis showed
that the macrocyclic rings are some-
what more rigid than in the natural
lead, the depsipeptide jasplakinolide.
Nevertheless, their conformations are
comparable to the natural product.
There are no intramolecular hydrogen
bonds, neither is the cis-rotamer popu-
lated in the N-methyl compound 37.
Due to the increased flexibility of the
smaller macrolactams 17 and 22 and
signal overlap, a distinct solution struc-
ture could not be obtained for these
compounds. The amino acid 4 should
be useful for restricting the conforma-
tion of other small peptides.
Keywords: amino acids · conforma-
tion analysis · natural products ·
peptidomimetic · total synthesis
Introduction
a hydroxy acid. Furthermore, they contain unusual amino
acids, which may be extended, N-methylated, hydroxylated,
or halogenated. Occasionally, they contain fragments from
other biosynthetic pathways, for example polyketides. The
substituents on the polyketide fragment might be used as
conformational control elements. An illustrative example is
the depsipeptide jasplakinolide A (1) (Figure 1). This natu-
ral product, which was isolated from the sponge Jaspis
sp.,[2,3] shows potent antifungal, insecticidal, and antitumor
activity. Related to the latter activity is its use as a tool in
cytoskeletal research, since it stabilizes F-actin.[4] A related
compound is the cyclodepispeptide geodiamolide A,[5,6] (2),
which has somewhat different activity.[7]
Constraining the conformation of a peptide fragment by in-
corporating it in a macrocyclic structure represents an im-
portant strategy for enhancing both binding strength and se-
lectivity. In addition, this maneuver can suppress unwanted
proteolysis. Studying the solution conformation of such a
macrocyclic construct can provide important information on
the peptide surface structure and the area that is presented
to a receptor. The application of this strategy is common in
medicinal chemistry.[1] In a class of natural products, such as
the cyclodepsipeptides, the presence of the macrocyclic ring
most likely also improves binding and stability. Besides a
macrocyclic ring, cyclodepsipeptides are characterized by
the presence of at least one ester bond because they contain
[a] S. Marimganti, S. Yasmeen, Prof. Dr. M. E. Maier
Institut für Organische Chemie, Universität Tübingen
Auf der Morgenstelle 18, 72076 Tübingen (Germany)
Fax : (+49)7071-5137
E-mail: martin.e.maier@uni-tuebingen.de
[b] Dr. D. Fischer
Institut für Organische Chemie, Universität Regensburg
Universitäts-Strasse, 93053 Regensburg (Germany)
Supporting information for this article is available on the WWW
1
under http://www.chemeurj.org/ or from the author: H and 13C NMR
spectra for important compounds.
Figure 1. Structures of the cyclodepsipeptides jasplakinolide (1) and geo-
diamolide (2).
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ꢀ
ꢀ
Besides the tripeptide fragment, the w-hydroxyacid 3 is
part of these depsipeptides (Figure 2). This hydroxy acid
contains four methyl groups in a 1,3-distance giving rise to
two syn-pentane interactions and one 1,3-allylic interac-
tion.[8] As a result of this the carboxyl and hydroxyl groups
at the end of the chain point in one direction, thereby allow-
ing bridging with a peptide fragment. While the synthesis of
the hydroxy acid 3 is feasible,[9] the preparation of a larger
amount is quite costly. We therefore turned to the design of
simpler analogues of this hydroxy acid that also contains
conformation controlling elements.
C H eclipsing the C4 Me, but only the carboxyl group is
pointing out of the plane of the double bond (Figure 3). In
the next lowest conformer 3b (DE=0.93 kJmolꢀ1) 6-H, sur-
ꢀ
ꢀ
prisingly, is anti to the C4 Me. Basically, C4 Me is bisecting
The design of the amino acid 4 followed from looking at
the conformational control elements in the hydroxy acid 3
(Figure 2). Thus, the 1,3-allylic interaction around the cen-
ꢀ
tral trisubstituted double bond should position the allylic C
H in an eclipsed orientation to the double bond.[8] As a con-
sequence, the methyl group at C-6 will point downwards
and orient the 2-hydroxypropyl terminus to the other side,
out of the plane of the double bond. The conformational sit-
uation at the carboxyl terminus seems to be less defined.
Nevertheless, avoidance of syn-pentane interactions between
ꢀ
ꢀ
C2 Me and C4 Me will cause the carboxyl group to point
out of the plane of the central double bond as well. Our
ꢀ
design plan then called for a rigidification of the vinylic C5
C6 bond. Accordingly, the allylic H was replaced with a
two-carbon segment (see dashed lines in Figure 2), resulting
in a meta-disubstituted aryl core. This simplification removes
the stereocenter at C-6.
Figure 3. Calculated low energy conformations of the hydroxy acid 3 and
the amino acid 4 (Chem3D representations).
the angle C6-Me/C-6/C-7. This orients both termini to the
other side of the central p-system. Conformers 3c (DE=
2.00 kJmolꢀ1) and 3d (DE=4.10 kJmolꢀ1) actually match
the expected conformation. Thus, 6-H eclipses the vinylic
methyl and the termini extend nicely to one side. For the
amino acid 4 we found two conformers within 4.184 kJmolꢀ1
of the absolute minimum (E=35.96 kJmolꢀ1) In all cases,
the termini are oriented more or less orthogonal to the
plane of the aryl ring. In the second lowest conformer 4b
(DE=2.45 kJmolꢀ1) the termini point to the opposite side
of the aryl ring. Conformer 4b does have a striking similari-
ty to conformer 3c of the hydroxy acid. Most likely electro-
static interaction and hydrogen bonding cause a substantial
gain in energy if both groups point to the same side. By
looking at several of the calculated minima, it seems that
the conformation of the aryl analogue is more ordered and
less flexible.
Figure 2. Design of the novel w-amino acid 4.
An overlay of conformers 3c and 4b shows a decent over-
lap validating our original design (Figure 4). In another run,
the configuration at the amino bearing carbon was inverted.
In this case we found also several reasonable conformers, in
which both termini extend from the same face of the aryl
ring.
It should be mentioned that alternative strategies for con-
straining the conformation of peptides are known. Frequent-
ly, this involves the use of designed amino acids containing a
In order to probe the design process, conformational
search runs (Macromodel 7.0, MM2* force field, 1000 start-
ing structures) were carried out on hydroxy acid 3 and the
amino acid 4 (without the N-Boc protecting group). The
search for the hydroxy acid 3 found four conformers within
4.184 kJmolꢀ1 (1.0 kcalmolꢀ1) of the minimum (E=
36.14 kJmolꢀ1). The lowest conformer 3a has the allylic
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Jasplakinolide Analogues
FULL PAPER
to the desired acid 4. This route secures this novel amino
acid in gram quantities.
With the acid 4 in hand, the synthesis of various macrocy-
cles was targeted, in which the two ends of acid 4 are bridg-
ed with some tripeptide fragments. Our goal was to prepare
pairs of tripeptide fragments with one of them carrying a N-
methyl group at the middle amino acid. The conformational
analysis of the corresponding macrocycles should provide
some hints on the mutual influence of the parts contained in
the macrocycle. Thus, tripeptide 15 was assembled by a clas-
sical Boc strategy (Scheme 2). That is, DCC-mediated con-
densation of the phenylalanine derivative 12 with N-Boc-d-
Figure 4. Overlay of the calculated conformers 3c and 4b (grey, hydroxy
acid; black, aromatic amino acid).
cyclic backbone.[10] In contrast to our work, a recent paper
describes the synthesis of three jasplakinolide analogues in
which the w-hydroxy acid was replaced with w-amino acids,
for example 6-amino hexanoic acid, lacking conformational
constraints.[11]
The synthesis of the amino acid 4 began with the commer-
cially available 1,3-bis(bromomethyl)benzene (6), which was
subjected to a double alkylation[12,13] with the propionyloxa-
zolidinone[14] 5 (Scheme 1). This way the C-2 symmetric al-
kylation product 7 was obtained in satisfactory yield (58%).
Subsequently, the chiral auxiliary was removed by hydrolysis
Scheme 2. Preparation of the geodiamolide analogue 17. a) DCC, HOBt,
amino acid 13, THF, 0 ! 238C, 12 h (80%); b) TFA, CH2Cl2, 238C; c)
EDCI, HOBt, Boc-l-Ala-OH, Et3N, THF/CH2Cl2 5:1, 0 ! 238C, 16 h
(75%); d) TFA, CH2Cl2, 238C; e) TBTU, HOBt, amino acid 4, iPr2NEt,
DMF, 238C, 3 h (95%, crude); f) NaOH, THF/H2O, 23 8C, 3 h; g) TFA,
CH2Cl2, 238C, 1 h; h) TBTU, HOBt, iPr2NEt, DMF, 238C, 14 h (50%,
three steps).
alanine 13 gave the dipeptide 14. After cleavage of the Boc
protecting group, coupling of the free amine with N-Boc-l-
alanine with the coupling reagent 1-ethyl-3-(3-dimethylami-
nopropyl) carbodiimide hydrochloride (EDCI) provided
compound 15 in 75% yield. Boc cleavage (TFA) and con-
densation of the resulting amine with the amino acid 4 led
to the acyclic tetrapeptide 16. Hydrolysis of the methyl
ester, removal of the Boc group and macrolactam formation
with 2-(1H-benzotriazole-1-yl))-1,1,3,3-tetramethyluronium
tetrafluoroborate (TBTU) in DMF (0.001m) gave rise to the
jasplakinolide (geodiamolide) analogue 17 in 50% yield.
In a similar manner, the tripeptide 20 was assembled
(Scheme 3). Here, N-Boc-N-methyl-d-alanine[16,17] became
the central amino acid of the tripeptide fragment. For the
formation of the peptide bond to the N-methylated amine,
the coupling reagent bromotrispyrrolidinophosphonium hex-
afluorophosphate (PyBroP) came to use. After liberation of
Scheme 1. Preparation of the N-protected w-amino acid 4. a) LDA
(2.4 equiv), THF, ꢀ788C, then add 6 (58%); b) LiOH, H2O2, 238C, 5 h
(95%); c) MeOH, DCC, DMAP, CH2Cl2, 238C (71%); d) PLE, H2O,
pH 7.5, 12 h, 238C (64%); e) (PhO)2P(O)N3, toluene, 238C, 1 h, then
reflux, 3 h, add tBuOH, reflux, 20 h (72%); f) NaOH, THF/H2O, 23 8C,
12 h (80%); PLE=pig liver esterase.
to the diacid 8, which was in turn converted to the dimethyl
ester 9 via DCC-mediated esterification. This maneuver was
necessary in order to allow for a monohydrolysis of the ho-
motopic ester groups. This could be achieved by esterase-in-
duced hydrolysis.[15] Treatment of the monoacid 10 with di-
phenyl-diphosphoryl azide followed by heating of the reac-
tion mixture in the presence of tert-butanol affected a Cur-
tius rearrangement resulting in the N-Boc protected w-
amino acid ester 11. Basic hydrolysis of the ester group led
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M. E. Maier et al.
turn was subjected to a Curtius rearrangement. The result-
ing isocyanate was reacted with 9H-fluoren-9-ylmethanol to
yield the protected b-amino acid 26. Subsequent treatment
of the urethane 26 gave free amine 27.
The carboxyl-protected amino acid 27 was then con-
densed with N-Fmoc-d-tryptophan to yield compound 28
(Scheme 5). Deprotection and another condensation provid-
ed the tripeptide 29. Thereafter, liberation of the terminal
amine and condensation with the w-amino acid 4 gave the
protected seco-compound 30. Both protecting groups could
now be removed in one step by using trifluoroacetic acid.
After concentration of the reaction mixture, macrolactam
formation with TBTU in the presence of HOBt at room
temperature led to compound 31 in very good yield.
Scheme 3. Preparation of the geodiamolide analogue 22. a) DCC, HOBt,
amino acid 18, THF, 0 ! 238C, 12 h (70%); b) TFA, CH2Cl2, 238C; c)
PyBroP, iPr2NEt, N-Boc-l-Ala-OH (13), CH2Cl2, 238C, 1 h (61%); d)
TFA, CH2Cl2, 238C; e) EDCI, HOBt, amino acid 4, CH2Cl2/THF, 0 !
238C, 7 h (52%); f) NaOH, THF/H2O, 23 8C, 3 h (90%); g) TFA,
CH2Cl2, 238C, 1 h; h) TBTU, HOBt, iPr2NEt, DMF, 238C, 14 h (65%).
the terminal amine, EDCI-mediated condensation with the
amino acid 4 provided the seco-compound 21. Ester hydro-
lysis, cleavage of the Boc protecting group and macrolactam
formation delivered the geodiamolide analogue 22 with a N-
methyl amide group.
The difference between jasplakinolide and geodiamolide
is the presence of a b-amino acid in the former one. While
several methods for the synthesis of b-amino acids exist, the
methyl ether derivative 27 was prepared via an asymmetric
alkylation reaction of the oxazolidinone[18] 23 by using tert-
butyl-bromoacetate as electrophile (Scheme 4).[19] The alkyl-
ation product 24 was hydrolyzed to the acid 25, which in
Scheme 5. Synthesis of the tripeptide 29, coupling with amino acid 4, and
formation of macrocycle 31. a) Fmoc-d-Trp-OH, DCC, HOBt, THF, ꢀ10
! 08C, 12 h (91%); b) Et2NH, THF, 0 ! 238C, 80 min (78%); c) Fmoc-
l-Ala-OH, DCC, HOBt, THF, 08C, 12 h (97%); d) Et2NH, THF, 0 !
238C, 80 min (85%); e) DCC, HOBt, THF, amino acid 4, ꢀ20 ! 238C,
8.5 h (92%); f) TFA, CH2Cl2,
0
!
238C, 1.5 h; g) TBTU, HOBt,
iPr2NEt, DMF, 238C, 14 h (92%, two steps).
In order to reach the N-methyl analogue 37 of macrocycle
31, the assembly of the tripeptide part needed to be
changed, since N-methylation was not compatible with the
Fmoc protecting group. Accordingly, the known tryptophan
derivative[3d] 32 was deprotected at the nitrogen and elon-
gated with N-Boc-l-alanine (Scheme 6). At this point, the
methyl ester at the C terminus was cleaved, followed by
amide formation of the resulting acid with the amino acid
27. The selective cleavage of the N-Boc group could be
achieved with TBDMSOTf and 2,6-lutidine.[20] The remain-
der of the synthesis proceeded as before. Thus, DCC-medi-
ated condensation of the resulting amine with the amino
acid 4 gave the tetrapeptide 36. Deprotection and macrolac-
Scheme 4. Synthesis of the b-amino acid 27 via asymmetric alkylation
and Curtius rearrangement. a) NaN(SiMe3)2, THF, ꢀ788C, 2.5 h, then
add BrCH2CO2tBu, ꢀ788C, 3 h (71%); b) H2O2, LiOH, THF, 08C, 5 h
(78%); c) (PhO)2P(O)N3, Et3N, toluene, reflux, add fluorenyl-OH,
reflux, 3 h (45%); d) Et2NH, THF, 0 ! 238C, 12 h (60%).
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Jasplakinolide Analogues
FULL PAPER
Figure 5. Structures for the natural compound jasplakinolide and the 19-
membered ring analogue 31 with the numbering systems used.
3
Table 1. JHH coupling constants in Hz of the methylene protons in 17,
22, 31 and 37. Due to identical chemical shift for H10h/H10t of 17 and
H2h/H2t of 37, the coupling constants could not be determined.
17
22
31
37
2JH1h
13.5
n.d.
3.7
13.1
6.1
14.0
12.7
3.6
13.1
2JH2h
13.6
4.3
10.4
13.0
10.6
3.7
11.0
2.7
13.7
n.d.
n.d.
n.d.
12.9
9.0
4.7
14.0
3.1
,H1t
,H2
,H2t
3JH2h
3JH1h
,H1
3JH2t,H1
3JH1t,H2
2JH6h
2JH6h
,H6t
,H6t
3JH6h
3JH6h
~7 (from COSY)
~5 (from COSY)
12.6
11.3 (via H11)
4.0
,H5
,H5
Scheme 6. Synthesis of the macrocycle 37 with a N-methyl group at the
tryptophan amino acid. a) TFA, CH2Cl2, 238C, 1 h (68%); b) Boc-l-Ala-
OH, DCC, HOBt, THF, 0 ! 238C, 14 h (59%); c) NaOH, THF, 238C,
2 h (74%); d) amino acid 27, DCC, HOBt, ꢀ20 ! 08C, 12 h (96%); e)
TBDMSOTf, 2,6-lutidine, CH2Cl2, 08C, 1 h, then add H2O (56%); f)
amino acid 4, DCC, HOBt, THF, ꢀ20 ! 238C, 18.5 h (60%); g) TFA,
CH2Cl2, 0 ! 238C, 1.5 h; h) TBTU, HOBt, iPr2NEt, 238C, 14 h (45%,
two steps).
3JH6t,H5
4.1
3JH6t,H5
2JH10h
n.d.
n.d.
n.d.
2JH10h
,H10t
,H10t
3JH10h
3JH10h
,H11
,H11
3JH10t,H11
3JH10t,H11
10.3
ferred into proton–proton distances by integration. They are
in very good agreement for compounds 31 and 37 corre-
sponding to a minor influence of the N-methylation in posi-
tion 16 on the overall structure. No intensive cross signals
were found between Ha protons of adjacent amino acids,
thus proving trans conformation for all amide bonds. The
methylated amide in 37 leads to an energy barrier that gives
rise to a separated signal set for the cis-amide. The signal
set for the cis isomer is populated to less than 1%. The sig-
nificant preference for the trans rotamer, to such an extent
unusual for a tertiary amide, was found for the natural com-
pound jasplakinolide as well,[21] thus emphasizing the good
analogy of synthetic analogue and natural product.
The dynamical properties of the whole macrocycles 31
and 37 is consistent including the side-chains having the
same dynamical behavior as the macrocyclic ring. The newly
inserted m-xylyl unit performs an oscillating movement as
ROESY data yield only mean proton–proton distances for
several possible orientations of the phenyl ring in relation to
the macrocyclic ring.
tam formation led to 37. However, in this case the yield for
the macrocyclization was lower.
Conformational Studies
Aside from variations in the side-chains, the major differ-
ence of the four analogues 17, 22, 31, and 37 is the replace-
ment of the polypropionate subunit with a m-xylyl contain-
ing amino acid 4. The 19-membered systems 31 and 37 are
structurally closely related to the natural compound jaspla-
kinolide. Compound 31 possesses a secondary amide in posi-
tion 16 (Figure 5). 1H and 13C resonance assignments via
DQFCOSY, ROESY/NOESY and HMQC spectra were per-
formed in [D6]DMSO and gave a single signal set for 31 and
a doubled signal set for 37 with the trans isomer of the N-
methylated amide populated for > 99%.
3
One large and one small JHH coupling constant (Table 1)
for the methylene groups in positions 2, 6, and 10 of 31 and
in positions 6 and 10 for 37 are typical for a well-defined
gauche–anti orientation with preference for the major ro-
tamer(s) as distinguished by characteristic ROE signals. This
allowed the assignment of the pro-R and pro-S protons of
the methylene groups. Due to signal overlay, a statement on
the methylene protons in position 2 of 37 was not possible.
With ROESY and NOESY measurements, characteristic
proton–proton interactions could be determined and trans-
Via temperature measurements, which gave temperature
coefficients for the amidic NH protons in the range of ꢀ3.7
to ꢀ6.0 ppbKꢀ1, transannular hydrogen bonds could be ex-
cluded, but nevertheless, as coupling constants and ROESY
data show, the 19-membered analogues 31 and 37 are rigid
macrocyclic structures.
Within a MD simulation, calculated structures of 31 and
37 are very well comparable with each other, the only differ-
ence being the orientation of the NH proton respective to
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M. E. Maier et al.
the N-methyl group in position 16 with the proton in 31
pointing into the middle of the macrocyclic ring and the
methyl group in 37 oriented towards the lower side of the
ring (Figure 6).
Figure 7. Structures for the natural compound geodiamolide and the 18-
membered ring analogue 17 with the numbering systems used.
ROESY data again reveal an oscillatory movement for the
m-xylyl unit like in 31 and 37. In case of the geodiamolide
analogues 17 and 22 there are no consistent dynamics for
the whole molecule, but rather an independent dynamical
behavior of the side-chains, that is, benzyl and methyl
groups, as seen in ROESY spectra with cross signals of dif-
ferent sign.
Figure 6. Energy-minimized structures for 31 and 37 after a 100 ps MD
simulation at 300 K. In green, torsion with the largest difference for 31
and 37 with the N-methyl group in 37 oriented onto the lower side of the
ring and the NH proton in position 16 of 31 pointing into the macrocyclic
ring.
The methylene groups in position 1 of 17 and in positions
3
The results presented above are in accordance with NMR
structural investigations of jasplakinolide.[21] Jasplakinolide
does not possess any hydrogen bonds, nor a higher fraction
1 and 10 of 22 exhibit one large and one small JHH coupling
constant (Table 1) defining a preferred gauche–anti orienta-
tion, whereas in position 6 the coupling constants possess
mediated values upon the presence of several rotamers.
Temperature measurements yield low temperature coeffi-
cients for NH4 and NH13 for both structures (NH4: ꢀ1.0,
ꢀ1.1 ppbKꢀ1, respectively; NH13: +0.4, ꢀ1.1 ppbKꢀ1, re-
spectively) with a high probability for those NH protons to
take part in an intramolecular hydrogen bond.
When calculating only a partial structure for 22 with
NOESY/ROESY data a bII’-turn-like structure is obtained
for the macrocyclic part containing the phenylalanine unit.
For this case NH4 is part of a transannular hydrogen bond
with CO(15) as partner, whereas for NH13 there is no geo-
metrically reasonable arrangement for the formation of a
hydrogen bond (Figure 8). At least for this section of the
macrocyclic ring the ROESY data obtained are in accord-
ance with the distances typical for bII’ turns.
3
of cis-amide bonds either. The J coupling constants yield a
more flexible structure for the natural analogue in compari-
son to the compounds 31 and 37, however, the difference is
small. The orientation of the two aromatic side-chains were
not determined in detail in the study presented here. But a
possible “tweezer” structure as stated in literature[21] cannot
be supported by NOEs between side-chain protons.
The 18-membered rings of compounds 17 and 22 show
several structural differences when compared to jasplakino-
lide. They are rather analogues of geodiamolide with a dif-
ference in the position of the aromatic amino acid
(Figure 7).[5]
1H and 13C signal assignment was done by DQFCOSY,
ROESY/NOESY, and HMQC spectra in [D6]DMSO with
results comparable to the 19-membered macrocycles: a
single signal set for 17, the
non-methylated amide and a
doubled signal set for 22 with
the cis isomer of the N-methy-
lated amide populated to less
than 1%.
Investigation
of
the
NOESY/ROESY data results
in mean values of proton–
proton distances being signifi-
cant for the fast exchange of
several conformers. Thus the
18-membered rings 17 and 22
Figure 8. Comparison of the calculated partial structure of 22 with a bII’-turn structure.
are more flexible than the sys-
tems described above and a
preferred structure can not be calculated on the basis of ex-
perimental ROE data. ROESY data confirm a trans config-
uration for all amide bonds in 17 and 22. Additionally the
Nevertheless, the 18-membered rings 17 and 22 are more
flexible compared with 31, 37, or jasplakinolide and an equi-
librium of several fast-exchanging conformers is existent.
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Jasplakinolide Analogues
FULL PAPER
Biological Studies
methyl analogues 22 and 37 only populate the trans-amide
conformer.
The four analogues were tested for cytotoxicity against two
cell lines.[22] Compound 37 turned out to be the most active
one. It inhibits the growth of L929 mouse fibroblasts with an
IC50 of 25 mgmLꢀ1. For the ovary cancer cell line SKOV-3
the IC50 amounts to 20 mgmLꢀ1. Compound 31 did show
weakactivity against the L929 cells. The geodiamolide ana-
logues 17 and 21 were devoid of any activity. While the ac-
tivity of 37 is moderate it does show that the N-Me group
makes a difference. Most remarkably, at a concentration of
40 mgmLꢀ1, the assay with SKOV-3 cells shows many cells
with two nuclei. This is a clear indication that the actin poly-
merization is disturbed. Based on the activity data it can be
said that analogue 37 is the most jasplakinolide-like among
the four compounds.
Experimental Section
General methods: 1H and 13C NMR: Bruker Avance 400, spectra were re-
corded at 295 K either in CDCl3, C6D6, or [D6]acetone; chemical shifts
are calibrated to the residual proton and carbon resonance of the sol-
vent: CDCl3 (dH 7.25, dC 77.0 ppm), C6D6 (dH 7.16, dC 128.0 ppm),
CD3OD (dH 4.78, 3.21, dC 49.0 ppm), or [D6]acetone (dH 2.04, dC 29.8,
206.7 ppm). Conformational NMR analysis: Bruker Avance 600, record-
ed at 600.13 MHz proton resonance frequency at 300 K respectively
320 K (for 22) in [D6]DMSO. Chemical shift calibration to [D6]DMSO
(dH 2.49 ppm, dC 39.5 ppm). Melting points: Büchi Melting Point B-540,
uncorrected. IR: Jasco FT/IR-430. Optical rotation: Jasco polarimeter P-
1020, reported in degree [a]D (c [g per 100 mL], solvent). HRMS (FT-
ICR): Bruker Daltonic APEX 2 with electron spray ionization (ESI).
Flash chromatography: J. T. Baker silica gel 43–60 mm. Thin-layer chro-
matography Machery–Nagel Polygram Sil G/UV254. Analytical HPLC-
MS: HP 1100 Series connected with an ESI MS detector Agilent
G1946C, positive mode with fragmentor voltage of 40 eV, column: Nucle-
osil 100–5, C-18 HD, 5 mm, 70”3 mm Machery Nagel, eluent: NaCl solu-
tion (5 mm)/acetonitrile, gradient: 0/10/15/17/20 min with 20/80/80/99/
99% acetonitrile, flow: 0.6 mLminꢀ1. All solvents used in the reactions
were purified before use. Dry diethyl ether, tetrahydrofuran, and toluene
were distilled from sodium and benzophenone, whereas dry dichlorome-
thane, dimethylformamide, pyridine, and triethylamine were distilled
from CaH2. Petroleum ether with a boiling range of 40–608C was used.
The pH 7 buffer was prepared by dissolving KH2PO4 (85.0 g, 0.625 mol)
and NaOH (14.5 g, 0.3625 mol) in water (1 L). Reactions were generally
run under an argon or nitrogen atmosphere. All commercially available
compounds (Acros, Aldrich, Fluka, Merck) were used as received unless
stated otherwise. l-Phenylalanine methyl ester and Boc-N-methyl-d-ala-
nine (18) were prepared according to the literature reported.[16,17]
Summary
In this paper we describe the synthesis of a novel w-amino
acid 4 that incorporates conformational constraints due to
non-bonded interactions (syn-pentane interactions). The
design was guided by the polypropionate sector of the depsi-
peptide jasplakinolide. This novel amino acid was prepared
by a double alkylation, enzyme-mediated hydrolysis of ho-
motopic ester groups, and a Curtius rearrangement on the
carboxylic acid. The amino acid was incorporated into the
four macrolactams 17, 22, 31, and 37. The former two fea-
ture an 18-membered macrocycle, whereas the latter two
have a 19-membered ring. For the two larger ones, confor-
mational analysis showed that the macrocyclic rings are
more rigid than the jasplakinolide ring, but all in all their
conformations are very well comparable to the natural prod-
uct. Like stated for jasplakinolide in the literature,[21] the 19-
membered analogues exhibit neither intramolecular hydro-
gen bonds, nor is the cis-rotamer populated in case of N-
methylation (37). The conformational features of the 18-
membered (geodiamolide) analogues are quite different.
The macrocyclic ring of compounds 17 and 22 is more flexi-
ble than the other investigated systems. Due to the in-
creased flexibility and signal overlap a distinct solution
structure for 17 and 22 could not be gained. Whether the
ring size or the additional aromatic side-chains in 31 and 37
cause a stabilizing effect on the macrocyclic system could
not be determined. But both features are differing for 17
and 22 and might thus be an explanation for the higher flex-
ibility of these smaller macrocycles. In addition, both N-me-
thylated analogues (22 and 37) populate the trans-amide
conformer to more than 99%.
(2S)-3-(3-{(2S)-2-[(tert-Butoxycarbonyl)amino]propyl}phenyl)-2-methyl-
propanoic acid (4): NaOH (80 mg) in H2O (5 mL) was added to a stirred
solution of methyl ester 11 (0.55 g, 1.64 mmol) in THF (12 mL). The re-
action mixture was stirred for 14 h at room temperature before being
poured into water (25 mL) and extracted with diethyl ether (3”10 mL).
The aqueous layer was acidified to pH 2–3 with 1n HCl and extracted
with ethyl acetate (3”15 mL). The combined organic layers were dried
(Na2SO4), filtered, and concentrated. The crude product was purified by
flash chromatography (ethyl acetate/petroleum ether 1:3) resulting in
acid 4 as a white solid (0.44 g, 85%). M.p. 104–1068C; Rf =0.45 (ethyl
acetate/petroleum ether 1:3); [a]2D3 =+6.0 (c=0.56, CH2Cl2); 1H NMR
(400 MHz, CD3OD): d=0.94 (d, J=6.1 Hz, 3H; CH3NHR), 0.99 (d, J=
6.6 Hz, 3H; CH3CO2H), 1.28 (s, 9H; C(CH3)3), 2.45–2.66 (m, 4H; benzyl-
ic H, CH), 2.86 (dd, J=12.6, 6.1 Hz, 1H; benzylic H), 3.19 (s, 1H; NH),
3.61–3.66 (m, 1H; CHNH), 6.91–6.92 (m, 3H; aryl H), 7.06 ppm (t, J=
7.5 Hz, 1H; Hm, aryl H); 13C NMR (100 MHz, CD3OD): d=17.2
(CH3CHNH), 20.5 (CH3CHCO2H), 28.8 (C(CH3)3), 40.7 (CH2CHCO2H),
42.7 (CHCO2H), 43.8 (CH2CHNH), 49.5 (CHNH), 79.8 (Boc C), 127.9,
128.3, 129.2, 131.2, 140.3, 140.7 (aryl), 157.7 (Boc C=O), 179.9 ppm
(CO2H); IR (film): n˜ =3326, 2974, 2930, 1706, 1653, 1507, 1248,
1169 cmꢀ1; HRMS (ESI): m/z: calcd for C18H27NO4Na: 344.18323; found:
344.18313 [M+Na]+.
(4R)-4-Benzyl-3-[(2S)-3-(3-{(2S)-3-[(4R)-4-benzyl-2-oxo-1,3-oxazolidin-3-
yl]-2-methyl-3-oxopropyl}phenyl)-2-methylpropanoyl]-1,3-oxazolidin-2-
one (7): n-Butyllithium (22.5 mL, 56.2 mmol, 2.5m in hexane) was added
at 08C to a solution of diisopropylamine (8.0 mL, 56.2 mmol) in THF
(190 mL). The reaction mixture was stirred at 08C for 30 min, before it
was cooled to ꢀ788C. At this point, propionyl oxazolidinone 5 (12.0 g,
51.5 mmol), dissolved in THF (210 mL), was added. After being stirred
for 1.5 h at ꢀ788C, the solid 1,3-bis(bromomethyl)-benzene (6) (6.17 g,
23.4 mmol) was added in one portion. Stirring was continued for 24 h
with simultaneous warming of the reaction mixture to room temperature.
The amino acid 4 could serve as a novel workbench for
restricting the conformation of small peptides. Furthermore,
the aryl group might serve as a handle for attachment of de-
rived macrocycles to a solid surface. The incorporation of
the m-xylene subunit into the amino acid indicates that
small structural modifications can have subtle effects on a
macrocyclic structure. Finally, it should be noted that the N-
Chem. Eur. J. 2005, 11, 6687 – 6700
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6693

M. E. Maier et al.
The reaction was quenched with NH4Cl (60 mL), and then most of the
organic solvent was removed in vacuo. The residue was extracted with
ethyl acetate (3”50 mL) and the combined organic layers were washed
with brine, dried with Na2SO4, filtered, and concentrated in vacuo. The
residue was purified by flash chromatography (petroleum ether/EtOAc
7:3) to get 7 as a hygroscopic compound (7.72 g, 58%). Rf =0.45 (petro-
leum ether/EtOAc 7:3); [a]2D5 =ꢀ21.9 (c=1.503, CH2Cl2); 1H NMR
(400 MHz, CDCl3): d=1.18 (d, J=6.6 Hz, 6H; CH3), 2.54–2.69 (m, 4H;
benzylic H), 3.11–3.18 (m, 4H; PhCH2), 4.10–4.20 (m, 6H; CHCH3,
OCH2), 4.64–4.70 (m, 2H; NCH), 7.09–7.32 ppm (m, 14H; aryl H);
13C NMR (100 MHz, CDCl3): d=16.2 (CH3), 37.3 (PhCH2), 39.1
(CHCH3), 39.9 (benzylic), 54.7 (NCH), 65.5 (OCH2), 126.8, 127.9, 128.5,
129.0, 130.1, 134.9, 138.9 (aryl), 152.6 (NCO2), 176.1 ppm (CO); IR
(film): n˜ =3028, 2976, 2932, 1770, 1694, 1604, 1588, 1487, 1455, 1393,
1288, 1210, 1103, 1053 cmꢀ1; HRMS (EI): m/z: calcd for C34H36N2O6:
568.257798; found: 568.257289 [M]+.
the formation of diacid in HPLC-MS (maximum 12 h), the reaction mix-
ture was washed with CH2Cl2 (2”500 mL). The aqueous phase was acidi-
fied to pH 2.5 with 25% hydrochloric acid and extracted with ethyl ace-
tate (3”500 mL). The combined organic layers (CH2Cl2 and EtOAc)
were dried with Na2SO4, filtered, and concentrated in vacuo. The crude
product was purified by flash chromatography (ethyl acetate/petroleum
ether 1:4) to provide the monoacid monoester as an oily compound
(1.52 g, 64%). Rf =0.4 (ethyl acetate/petroleum ether 1:4); [a]2D5 =+46.15
(c=1.07, CH2Cl2); 1H NMR (400 MHz, CDCl3): d=1.05 (d, J=6.82 Hz,
3H; CH3CHCO2CH3), 1.08 (d, J=7.1 Hz, 3H; CH3CHCO2H), 2.53–2.58
(m, 2H; benzylic H), 2.62–2.68 (m, 2H; CH), 2.94 (ddd, J=19.4, 13.1,
6.4 Hz, 2H; benzylic H), 3.55 (s, 3H; OCH3), 6.90–6.96 (m, 3H; aryl H),
7.12 (t, J=7.5 Hz, 1H; Hm, aryl H), 10.49 ppm (broad, 1H; CO2H);
13C NMR (100 MHz, CDCl3): d=16.4 (CH3CO2CH3), 16.6 (CH3CO2H),
39.1 (CH2CHCO2CH3), 39.6 (CH2CHCO2H), 41.4 (CHCO2H), 51.5
(OCH3), 126.9, 127.0, 128.4, 129.8, 139.0 (aryl), 176.4 (CO2Me),
182.3 ppm (CO2H); IR (film): n˜ =3025, 2975, 1736, 1707 cmꢀ1; HPLC-
MS: m/z: 264.2, 218.2, 186.2, 171.2, 158.2, 131.2, 91.2; HRMS (EI): m/z:
calcd for C15H20O4: 264.133877; found: 264.136141 [M]+.
(2S)-3-{3-[(2S)-2-Carboxypropyl]phenyl}-2-methylpropanoic acid (8):
H2O2 (11.7 mL of a 30 wt% solution, 102.7 mmol) was added at 08C
through a syringe to a solution of the bisalkylated compound 7 (7.50 g,
13.2 mmol) in THF (250 mL), followed by the addition of LiOH·H2O
(2.20 g, 51.4 mmol), dissolved in water (120 mL). The solution was stirred
at 08C for 5 h. Subsequently, saturated Na2SO3 solution (100 mL) and sa-
turated NaHCO3 solution (100 mL) were added at 08C. The whole mix-
ture was partially concentrated in vacuo and diluted with water
(100 mL). The aqueous layer was extracted with dichloromethane (3”
75 mL) to recover the auxiliary. The aqueous layer was then acidified at
08C to pH 1.5 by using 6m HCl and then extracted with ethyl acetate (4”
100 mL). The combined organic layers were dried (MgSO4), filtered, and
Methyl (2S)-3-(3-{(2S)-2-[(tert-butoxycarbonyl)amino]propyl}phenyl)-2-
methylpropanoate (11):
A solution of the monoester 10 (0.80 g,
3.03 mmol) in toluene (23 mL) was treated with triethylamine (0.5 mL,
3.33 mmol) and DPPA (0.66 mL, 3.03 mmol). After stirring for 30 min,
the mixture was heated under reflux for 3.5 h. The isocyanate formation
was monitored by IR for the appearance of a strong signal in the 2300–
2200 cmꢀ1 region and disappearance of the carboxylic acid carbonyl
peak. The reaction mixture was cooled to 508C, tert-butanol (3 mL,
10 equiv) was added via syringe and the solution heated to reflux for
20 h. The reaction was cooled to room temperature and quenched with
saturated NaHCO3 solution (25 mL). The mixture was extracted with di-
ethyl ether (3”25 mL). The combined organic extracts were dried
(Na2SO4), filtered, and concentrated in vacuo. The crude product was pu-
rified by flash chromatogrophy (ethyl acetate/petroleum ether 1:5), to
provide compound 11 as an oil (0.73 g, 72%). Rf =0.55 (ethyl acetate/pe-
troleum ether 1:5); [a]D23 =+12.3 (c=0.21, CH2Cl2); 1H NMR (400 MHz,
CDCl3): d=0.99 (d, J=6.6 Hz, 3H; CH3CHCO2Me), 1.06 (d, J=6.6 Hz,
3H; CH3CHNR), 1.36 (s, 9H; C(CH3)3), 2.51–2.58 (m, 2H; benzylic H),
2.63–2.68 (m, 1H; CHCO2Me), 2.75 (dd, J=13.1, 5.3 Hz, 1H; benzylic
H), 2.93 (dd, J=13.1, 6.4 Hz, 1H; benzylic H), 3.57 (s, 3H; OCH3), 3.81
(broad, 1H; CHNHR), 4.31 (broad, 1H; NH), 6.90–7.32 ppm (m, 4H;
aryl H); 13C NMR (100 MHz, CDCl3): d=16.3 (CH3CHCO2Me), 19.7
(CH3CHNHR), 28.0 (C(CH3)3)), 39.2 (CH2CHCO2Me), 41.0
(CHCO2Me3), 42.5 (CH2CHNHR), 47.1 (CHNHR), 51.2 (OCH3), 78.8
(Boc quaternary C), 126.6, 127.2, 127.9, 129.9, 137.9, 139.0 (aryl), 154.8
(Boc CO), 176.2 ppm (CO2Me); IR (film): n˜ =3361, 2973, 2930, 2359,
concentrated in vacuo yielding an oily residue (2.95 g, 90%). [a]D25
=
+35.5 (c=0.42, CH2Cl2); 1H NMR (400 MHz, CDCl3): d=1.20 (d, J=
6.8 Hz, 6H; CH3), 2.62–2.72 (m, 2H; benzylic H), 2.75–2.83 (m, 2H;
CH), 3.10 (dd, J=13.1, 6.1 Hz, 2H; benzylic H), 7.07 (d, J=7.1 Hz, aryl
H), 7.10 (s, 1H; Ho, aryl H), 7.26 (t, J=7.6 Hz, 1H; Hm, aryl H),
11.79 ppm (brs, 2H; CO2H); 13C NMR (400 MHz, CDCl3): d=16.3
(CH3), 39.1 (benzylic), 41.3 (CH), 127.1, 128.4, 129.7, 139.0 (aryl),
182.7 ppm (CO2H); IR (film): n˜ =3500–2500 (broad), 1702, 1589, 1463,
1292, 1199, 1044 cmꢀ1; HPLC-MS (ESI): m/z: 250.2, 204.2, 186.2, 177.2,
171.2, 131.2; HRMS (EI): m/z: calcd for C14H18O4: 250.12049; found:
250.118291 [M]+.
Methyl (2S)-3-{3-[(2S)-3-methoxy-2-methyl-3-oxopropyl]phenyl}-2-meth-
ylpropanoate (9): A solution of DCC (8.12 g, 39.4 mmol) in CH2Cl2
(26 mL) was added at 08C to a solution of diacid 8 (3.20 g, 12.8 mmol),
methanol (1.4 mL, 32.8 mmol) and DMAP (96 mg) in dry CH2Cl2
(37 mL). The solution was stirred at 08C for 30 min and then at room
temperature for 6 h. The white precipitate was filtered off, the solvent
evaporated, and the residue redissolved in diethyl ether. The organic so-
lution was washed successively with cold 1n HCl, NaHCO3 solution, and
brine. The dried (Na2SO4) organic layer was filtered, and concentrated.
The crude product was purified by flash chromatography (ethyl acetate/
petroleum ether 1:9) to provide the diester 9 as an oily compound
(2.52 g, 71%). Rf =0.38 (ethyl acetate/petroleum ether 1:9); [a]2D5 =+40.1
(c=0.61, CH2Cl2); 1H NMR (400 MHz, CDCl3): d=1.15 (d, J=6.5 Hz,
6H; CH3), 2.61–2.67 (m, 2H; benzylic H), 2.69–2.77 (m, 2H; CH), 3.00
(dd, J=13.1, 6.7 Hz, 2H; benzylic H), 3.64 (s, 6H; OCH3), 6.97 (s, 1H;
Ho, aryl H), 7.01 (d, J=7.6 Hz, 2H; aryl H), 7.20 ppm (t, J=7.6 Hz, 1H;
Hm, aryl H); 13C NMR (100 MHz, CDCl3): d=16.6 (CH3), 39.6 (benzylic),
41.6 (CH), 51.5 (OCH3), 126.9, 128.3, 129.6, 139.3 (aryl), 176.4 ppm
1735, 1710, 15516, 1364, 1166 cmꢀ1
; HRMS (EI): m/z: calcd for
C19H29NO4: 335.209636; found: 335.207186 [M]+.
Methyl N-(tert-butoxycarbonyl)-d-alanyl-l-phenylalaninate (14): A solu-
tion of DCC (1.5 g, 7.25 mmol) in THF (11 mL) at 08C was added to a
stirred solution of Boc-d-Ala-OH (13) (1.10 g, 5.6 mmol), H-l-Phe-OMe
(12) (1.00 g, 5.6 mmol), hydroxybenzotriazole (0.75 g, 5.6 mmol) in dry
THF (45 mL). Stirring was continued for 12 h at room temperature. The
dicyclohexylurea was filtered off, washed with cold diethyl ether, and the
filtrate was concentrated. Purification was done by flash chromatography
(ethyl acetate/petroleum ether 1:3) yielding a colorless solid (1.55 g,
80%). M.p. 98–998C; Rf =0.35 (ethyl acetate/petroleum ether 1:3);
[a]2D3 =+59.8 (c=0.40, CH2Cl2); 1H NMR (400 MHz, CDCl3): d=1.21 (d,
J=7.1 Hz, 3H; CH3), 1.36 (s, 9H; C(CH3)3), 3.00 (dd, J=13.8, 6.2 Hz,
1H; benzylic H), 3.05–3.10 (m, 1H; benzylic H), 4.04–4.18 (m, 1H;
CHNH), 4.77–4.81 (m, 1H; CHCO2Me), 4.95 (brs, 1H; NHBoc), 6.60
(brs, 1H; NHCHCO2Me), 7.03–7.22 ppm (m, 5H; aryl H); 13C NMR
(100 MHz, CDCl3): d=18.4 (CH3), 28.2 (C(CH3)3), 37.8 (benzylic), 49.9
(CHCO2Me), 52.3 (OCH3), 53.0 (CHNHBoc), 80.0 (Boc C), 127.1, 128.5,
129.2, 135.7 (aryl), 155.3 (Boc C=O), 171.7 (CO2Me), 172.2 ppm
(CO2Me); IR (film): n˜ =2974, 2951, 1736, 1459, 1375, 1361, 1164 cmꢀ1
;
HPLC-MS (ESI): m/z: 278.2, 218.2, 186.2, 171.2, 131.2, 105.2, 91.2;
HRMS (EI): m/z: calcd for C16H22O4: 278.15179; found: 278.152648 [M]+.
(2S)-3-{3-[(2S)-3-Methoxy-2-methyl-3-oxopropyl]phenyl}-2-methylpropa-
noic acid (10): A solution of diester 9 (2.50 g, 9.0 mmol) in MeOH
(5 mL) was emulsified under vigorous stirring in NaCl solution (0.1m,
646.75 mL) to which pH 7 phosphate buffer (3.25 mL) was added,
making the solution 3 mm in phosphate. Then a suspension of PLE
(25 mg, 1000 units, Sigma Aldrich, E-3019) in 3.2m (NH4)2SO4 solution
(1 mL) was added. During the hydrolysis the pH was kept between 7 and
7.5 by the controlled addition of NaOH solution (0.1n). After observing
(CONH); IR (KBr): n˜ =3304, 2987, 2930, 1732, 1664, 1517, 1317 cmꢀ1
;
HRMS (EI): m/z: calcd for C14H18N2O5: 294.119319; found: 294.121541
[MꢀC(CH3)3]+.
6694
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2005, 11, 6687 – 6700

Jasplakinolide Analogues
FULL PAPER
Methyl N-(tert-Butoxycarbonyl)-l-alanyl-d-alanyl-l-phenylalaninate (15):
A solution of peptide 14 (1.0 g, 2.8 mmol) in CH2Cl2 (22 mL) was treated
with CF3CO2H (2.2 mL) and the mixture stirred at room temperature for
1 h. The solvent was removed in vacuo, and the residue dried by azeo-
tropic removal of H2O with toluene. The crude material was subjected to
the next reaction without further purification. To a cooled (08C) solution
of the crude amine salt (240 mg, 0.96 mmol) and Boc-l-Ala-OH (181 mg,
0.96 mmol) in THF (11 mL) and CH2Cl2 (2.5 mL) were added 1-hydroxy-
benzotriazole (130 mg, 0.96 mmol), Et3N (0.32 mL, 2.3 mmol), and 1-(3-
KHSO4, water, half-saturated NaHCO3, and brine. After being dried
(MgSO4), filtered, and concentrated in vacuo, the residue was purified by
flash chromatography (ethyl acetate) to give the macrocycle 17 as a col-
orless solid (40 mg, 50%, three steps). M.p. 258–2608C; Rf =0.5 (ethyl
acetate); [a]2D8 =ꢀ14.8 (c=0.19, CH2Cl2); 1H NMR (600 MHz,
[D6]DMSO): d=1.01 (d, J=7.3 Hz, 5-CH3), 1.06 (d, J=6.6 Hz, 3H; 11-
CH3), 1.11 (d, J=7.3 Hz, 3H; 5-CH3), 1.12 (d, J=6.6 Hz, 3H; 14-CH3),
2.50 (m, 2H; 6-H, 11-H), 2.59–2.67 (m, 2H; 10-H), 2.86–2.95 (m, 2H; 1-
H, 6-H), 3.33 (dd, J=13.9, 3.7 Hz, 1H; 1-H), 3.74–3.79 (m, 1H; 17-H),
3.94–4.03 (m, 3H; 2-H, 14-H, 5-H), 6.75–6.79 (m, 2H; 4’’-H, 6’’-H), 6.83
(d, J=7.3 Hz, 2H; 4-NH, 13-NH), 6.94 (s, 1H; 2’’-H), 6.98 (dd, J=7.3,
7.3 Hz, 1H; 5’’-H), 7.15–7.19 (m, 3H; 4’-H, aryl H), 7.23–7.27 (m, 2H;
aryl H), 8.17 (d, J=8.1 Hz, 1H; 19-NH), 8.34 ppm (brs, 1H; 16-NH);
13C NMR (150 MHz, [D6]DMSO): d=15.8 (CH3-17), 17.9 (CH3-11), 18.3,
19.1 (CH3-5, CH3-14), 34.6 (C-1), 39.1 (C-6), 39.5 (C-10), 42.0 (C-11),
45.0 (C-5), 47.6 (C-14), 49.6 (C-17), 54.4 ppm (C-2); IR (film): n˜ =3297,
dimethylaminopropyl)-3-ethylcarbodiimide
hydrochloride
(EDCI)
(239 mg, 1.25 mmol). The mixture was then stirred at room temperature
for 16 h. The solvent was removed in vacuo, and the residue purified by
flash chromatography (40% ethyl acetate in petroleum ether) to provide
tripeptide 15 as a colorless solid (0.30 g, 75%). M.p. 149–1518C; Rf =0.33
(40% ethyl acetate in petroleum ether); [a]2D8 =+19.1 (c=0.48, CH2Cl2);
1H NMR (400 MHz, CDCl3): d=1.19 (d, J=7.1 Hz, 3H;
CH3CHNHBoc), 1.24 (d, J=7.0 Hz, 3H; CH3CONH), 1.36 (s, 9H; C-
(CH3)3), 2.96 (dd, J=13.9, 7.1 Hz, 1H; benzylic H), 3.07–3.12 (m, 1H;
benzylic H), 3.62 (s, 3H; OCH3), 4.02–4.17 (m, 1H; CHNHBoc), 4.40–
4.47 (m, 1H; CHNHCO), 4.73–4.78 (m, 1H; CHCO2Me), 5.11 (d, J=
7.3 Hz, 1H; NHBoc), 6.84 (d, J=7.3 Hz, 1H; NHCO2Me), 6.95 (d, J=
6.6 Hz, 1H; NHCO), 7.05–7.22 ppm (m, 5H; aryl H); 13C NMR
(100 MHz, CDCl3): 18.1 (CH3CHNHBoc), 18.4 (CH3CHCONH), 28.3 C-
(CH3)3), 37.8 (benzylic), 48.5 (CHCONH), 50.2 (CHNHBoc), 53.2
(CHCO2Me), 80.1 (Boc C), 127.0, 128.5, 129.2, 135.8 (aryl), 155.3 (Boc
C=O), 171.7 (CO2Me), 171.8 (NHCO), 172.6 ppm (CH2NHCO); IR
(KBr): n˜ =3277, 2979, 2748, 1753, 1707, 1645, 1519, 1456, 1370,
1166 cmꢀ1; HRMS (EI): m/z: calcd for C21H31N3O6: 421.221247; found:
421.225247 [M]+.
2931, 1888, 1640,1526, 1446 cmꢀ1
; HRMS (EI): m/z: calcd for
C28H36N4O4: 492.273621; found: 492.271404 [M]+.
Methyl N-(tert-butoxycarbonyl)-N-methyl-d-alanyl-l-phenylalaninate (19):
A solution of DCC (2.3 g, 11.1 mmol), dissolved in THF (11 mL) was
added at 08C to a stirred solution of Boc-N-Me-d-Ala-OH (18) (1.5 g,
7.4 mmol), H-l-Phe-OMe (12) (1.3 g, 7.4 mmol), hydroxybenzotriazole
(0.99 g, 7.4 mmol) in dry THF (60 mL). Stirring was continued for 7 h at
room temperature. The dicyclohexylurea was filtered off, washed with
cold diethyl ether, and the filtrate concentrated. Purification of the resi-
due by flash chromatography (ethyl acetate/petroleum ether 1:5) gave a
gel-like compound (2.10 g, 75%). Rf =0.33 (ethyl acetate/petroleum ether
1:5); [a]2D5 =+62.8 (c=0.89, CH2Cl2); 1H NMR (400 MHz, CDCl3): d=
1.23 (d, J=6.8 Hz, 3H; CH3), 1.37 (s, 9H; C(CH3)3), 2.64 (s, 3H; NCH3),
2.99–3.07 (m, 2H; benzylic H), 3.63 (s, 3H; OCH3), 4.71–4.77 (m, 2H;
CHCO2Me, CHMe), 6.50 (brs, 1H; NHCHCO2Me), 7.03 (d, J=7.3 Hz,
2H; Ho, aryl H), 7.15–7.23 ppm (m, 3H; aryl H); 13C NMR (100 MHz,
CDCl3): d=13.2 (CH3), 28.3 (C(CH3)3), 29.7 (NCH3), 37.8 (benzylic),
52.2 (OCH3, CHCO2Me), 52.9 (CHNHBoc), 80.5 (Boc C), 127.1, 128.6,
129.1, 135.7, 171.3 (CO2Me), 171.7 ppm (CONH); IR (film): n˜ =3327,
2977, 2934, 2118, 1746, 1688, 1515, 1455, 1390, 1154 cmꢀ1; HRMS (EI):
m/z: calcd for C19H28N2O5: 364.199791, found 364.198514 [M]+.
Methyl N-[(2S)-3-(3-{(2S)-2-[(tert-butoxycarbonyl)amino]propyl}phenyl)-
2-methylpropanoyl]-l-alanyl-d-alanyl-l-phenylalaninate (16): A solution
of peptide 15 (100 mg, 0.24 mmol) in CH2Cl2 (2 mL) was treated with
CF3CO2H (0.18 mL), and the mixture stirred at room temperature for
1 h. The solvent was removed in vacuo, and the residue was dried by
azeotropic removal of H2O with toluene. The crude material was subject-
ed to the next reaction without further purification. To a solution of
crude amine salt and Boc-protected w-amino acid 4 (77 mg, 0.24 mmol)
in DMF (2 mL) were added TBTU (77 mg, 0.24 mmol) HOBt (34 mg,
0.24 mmol), DIEA (0.1 mL, 0.576 mmol) and the mixture was stirred for
3 h at room temperature. The reaction mixture was diluted with water
(3 mL) and extracted with ethyl acetate (3”4 mL). The combined organ-
ic layers were washed with water resulting in almost pure tetrapeptide 16
(133 mg, 90%) as judged by HPLC-MS. This material was used for the
macrolactam formation without any further purification. N-Boc-N-
methyl-d-alanine (18) was prepared according to the literature.[23,24]
Methyl N-(tert-Butoxycarbonyl)-l-alanyl-N-methyl-d-alanyl-l-phenylala-
ninate (20): A solution of peptide 19 (1.0 g, 2.8 mmol) in CH2Cl2 (22 mL)
was treated with CF3CO2H (2.2 mL), and the mixture was stirred at room
temperature for 1 h. The solvent was removed in vacuo, and the residue
dried by azeotropic removal of H2O with toluene. The crude material
was subjected to the next reaction without further purification.
To a stirred solution of the crude amine salt, Boc-l-Ala-OH (0.53 g,
2.8 mmol), PyBroP (1.3 g, 2.8 mmol) in CH2Cl2 (3 mL) was added
DIPEA (1.4 mL, 8.4 mmol) at 08C and the mixture stirred at room tem-
perature for 3 h. The solvent was removed in vacuo and the residue puri-
fied by flash chromatography (ethyl acetate/petroleum ether 1:1) to pro-
vide a gel-like compound (0.69 g, 58%). Rf =0.45 (ethyl acetate/petrole-
um ether 1:1); [a]2D5 =+62.4 (c=1.79, CH2Cl2); 1H NMR (400 MHz,
CDCl3): d=1.21 (d, J=6.8 Hz, 3H; CH3CHNCH3), 1.23 (d, J=7.8 Hz,
3H; CH3CHNHBoc), 1.37 (s, 9H; C(CH3)3), 2.85 (s, 3H; NCH3), 2.97
(dd, J=13.9, 7.1 Hz, 1H; benzylic H), 3.04–3.09 (m, 1H; benzylic H),
3.60 (s, 3H; OCH3), 4.44–4.50 (m, 1H; CHNHBoc), 4.65–4.70 (m, 1H;
CHCO2Me), 5.11 (q, J=6.3 Hz, 1H; CHNCH3), 5.31 (d, J=6.8, 1H;
NHBoc), 6.70 (d, J=7.8 Hz, 1H; NHCHCO2Me), 7.05 (d, J=7.3, 2H;
Ho, aryl H), 7.14–7.24 ppm (m, 3H; aryl H); 13C NMR (100 MHz,
CDCl3): 13.5 (CH3CHCO), 17.9 (CH3CHNHBoc), 28.2 (C(CH3)3), 30.3
(NCH3), 37.4 (benzylic), 46.6 (CHNHBoc), 52.1 (OCH3, CHNMe), 53.0
(CHCO2Me), 79.6 (Boc C), 127.0, 128.4, 129.0, 135.9 (aryl), 155.3 (Boc
C=O), 170.4 (CO2Me), 171.7 (CONMe), 173.7 ppm (CONH); IR (film):
n˜ =3327, 2979, 1742, 1682, 1642, 1520, 1455, 1249, 1169 cmꢀ1; HRMS
(EI): m/z: calcd for C22H33N3O6: 435.236897; found: 435.240391 [M]+.
(3S,6S,9R,12S,15S)-6-Benzyl-3,9,12,15-tetramethyl-4,7,10,13-
tetraazabicyclo[15.3.1]henicosa-1(21),17,19-triene-5,8,11,14-tetrone (17)
(deprotection of the carboxylic and amino groups of compound 16 and
macrocyclization): NaOH (7.7 mg), dissolved in H2O (0.5 mL), was
added to a stirred solution of tetrapeptide 16 (100 mg, 0.160 mmol) in
THF (3 mL). The reaction mixture was stirred for 1 h at room tempera-
ture before being poured into water (5 mL) and extracted with diethyl
ether (3”5 mL). The aqueous layer was acidified to pH 2–3 with 1n HCl
and extracted with ethyl acetate (3”5 mL). The combined organic layers
were dried (Na2SO4), filtered, and evaporated providing the carboxylic
acid in almost quantitative yield. This compound was used directly in the
next step. A solution of above Boc-protected tetrapeptide acid (90 mg,
0.145 mmol) in CH2Cl2 (1.2 mL) was treated with CF3CO2H (0.11 mL,
1.45 mmol), and the mixture stirred at room temperature for 1 h. The sol-
vent was removed in vacuo, and the residue dried by azeotropic removal
of H2O with toluene. The crude material was subjected to the macrolac-
tamization without any further purification. Thus, the residue was dis-
solved in DMF (140 mL) and the stirred solution treated successively
with TBTU (140 mg, 0.435 mmol), HOBt (59 mg, 0.435 mmol), and
iPr2EtN (0.08 mL, 0.44 mmol) at room temperature. The resulting solu-
tion was stirred for 14 h at room temperature and then partitioned be-
tween ethyl acetate and water. After separation of the layers, the aque-
ous layer was extracted with ethyl acetate (2”75 mL), and the combined
organic layers were washed successively with water, 5% aqueous
Methyl N-[(2S)-3-(3-{(2S)-2-[(tert-butoxycarbonyl)amino]propyl}phenyl)-
2-methylpropanoyl]-l-alanyl N-methyl-d-alanyl-l-phenylalaninate (21):
A solution of tripeptide 20 (180 mg, 0.413 mmol) in CH2Cl2 (3.5 mL) was
treated with CF3CO2H (0.32 mL), and the mixture stirred at room tem-
perature for 1 h. The solvent was removed in vacuo, and the residue
Chem. Eur. J. 2005, 11, 6687 – 6700
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6695

M. E. Maier et al.
dried by azeotropic removal of H2O with toluene. The crude material
was subjected to the next reaction without further purification.
1455 cmꢀ1
;
HRMS (ESI): m/z: calcd for C29H38N4O4Na: 529.27853;
found: 529.27827 [M+Na]+.
tert-Butyl (3R)-4-[(4R)-4-Benzyl-2-oxo-1,3-oxazolidin-3-yl]-3-(4-methoxy-
To a cooled (08C) solution of the crude amine salt and amino acid 4
phenyl)-4-oxobutanoate (24):
A solution of compound 23 (5.20 g,
(133 mg, 0.413 mmol) in THF (7 mL) and CH2Cl2 (1.5 mL) were added
0.016 mol) in anhydrous THF (32 mL) was treated at ꢀ788C with
NaHMDS in THF (2m, 8.7 mL, 0.017 mol). After stirring for 2.5 h at the
same temperature, tert-butyl bromoacetate (6.5 mL, 0.048 mol) was
added and the mixture and stirred for additional 3 h at this temperature.
The mixture was allowed to warm to 08C, before saturated NH4Cl solu-
tion (100 mL) was added. Most of the THF was then removed on the
rotary evaporator and the resulting slurry extracted with ethyl acetate
(3”90 mL). The combined organic layers were dried with MgSO4, fil-
tered, and concentrated to give the crude product as a yellow solid. Puri-
fication by flash chromatography (petroleum ether/ethyl acetate 4:1) and
recrystallization from a mixture of hexane/ether gave the pure alkylation
product as white needles (5.1 g, 71%). M.p. 139.5–140.58C; Rf =0.23 (pe-
troleum ether/ethyl acetate 4:1); [a]2D5 =+149.0 (c=1.02, CH2Cl2);
1H NMR (400 MHz, CDCl3): d=1.36 (s, 9H; C(CH3)3), 2.51 (dd, J=17.1,
4.5 Hz, 1H; CH2CO), 2.72 (dd, J=13.3, 9.8 Hz, 1H; PhCH2), 3.19 (dd,
J=16.9, 11.3 Hz, 1H; CH2CO), 3.28 (dd, J=13.3, 2.7 Hz, 1H; PhCH2),
3.69 (s, 3H; OCH3), 3.91 (t, J=8.0 Hz, 1H; CH2O), 3.99–4.02 (m, 1H;
CH2O), 4.47–4.52 (m, 1H; NCH), 5.36 (dd, J=11.3, 4.5 Hz, 1H; CHCO),
6.75 (d, J=8.5 Hz, 2H; aryl H), 7.17–7.28 ppm (m, 7H; aryl H);
13C NMR (100 MHz, CDCl3): d=27.9 (C(CH3)3), 37.4 (PhCH2), 40.4
(CH2CO), 43.8 (CHCO), 55.1 (OCH3), 55.6 (NCH), 65.5 (CH2O), 80.7
(C(CH3)3), 114.0, 127.1, 128.8, 128.9, 129.4, 129.5, 135.5, 152.6 (NCO2),
158.9 (aryl), 170.9 (CHCO), 173.4 ppm (CH2CO2); IR (film): n˜ =2356,
1697, 1646, 1519, 1045 cmꢀ1; MS (EI): m/z (%): 383.1 (6), 206.0 (15),
178.1 (100), 83.9 (20); HRMS (EI): m/z: calcd for C21H21NO6:
383.140500; found: 383.136857 [MꢀC(CH3)3]+.
1-hydroxybenzotriazole
(56.2 mg,
0.413 mmol),
Et3N
(0.15 mL,
1.03 mmol), and EDCI (103 mg, 0.54 mmol), followed by stirring of the
mixture at room temperature for 16 h. The solvent was removed in
vacuo, and the residue purified by flash chromatography (ethyl acetate/
petroleum ether 1:1) to provide a gel-like compound (0.14 g, 55%). Rf =
0.33 (ethyl acetate/petroleum ether 1:1); [a]2D5 =+61.5 (c=0.52, CH2Cl2);
1H NMR (400 MHz, CD3OD): d=1.04 (d, J=6.6, 6H; CH3CHNH,
CH2CH(CH3)), 1.23 (d, J=7.3 Hz, 3H; CH3CHN(CH3)), 1.30 (d, J=
7.1 Hz, 3H; CH3CHNHBoc), 1.36 (s, 9H; C(CH3)3), 2.40–2.72 (m, 4H;
benzylic H), 2.86 (s, 3H; NCH3), 3.09–3.16 (m, 2H; PhCH2), 3.58 (s, 3H;
OCH3), 3.68 (m, 1H; NHBoc), 4.50–4.60 (m, 2H; CH(CH3)NH, CH-
(CH3)NHBoc), 5.03 (q, J=7.1 Hz, 1H; CH(CH3)NCH3), 6.89–7.20 (m,
11H; aryl H, PhCH2CHNH), 7.90 ppm (broad, 1H; COCHNH);
13C NMR (100 MHz, CD3OD): d=14.0 (CH3CHN(CH3)), 16.7 (CH2CH-
(CH3)), 17.4 (CH3CHNH), 20.6 (CH3CHNHBoc), 28.8 (C(CH3)3), 31.4
(NCH3), 38.1 (PhCH2), 38.9 (CH(CH3)CO), 40.7 (CH2CH(CH3)CO), 43.0
(CH2CH(CH3)NH), 47.3 (CH(CH3)NH), 52.7 (CH(CH3)NCH3), 53.8
(OCH3), 55.51 (CHCO2Me), 79.8 (Boc C), 127.8, 128.0, 128.3, 129.2,
129.4, 130.2, 138.4, 140.4, 140.8 (aryl), 157.7 (Boc C=O), 173.1 (N-
(CH3)CO), 173.4 (CO2Me), 175.2 (COCHN(CH3)), 178.7 ppm
(NHCOCH); IR (film): n˜ =3315, 2975, 2932, 1742, 1644, 1526, 1455,
1391, 1247, 1172 cmꢀ1
; HRMS (ESI): m/z: calcd for C35H50N4O7Na:
661.35717; found: 661.34712 [M+Na]+.
(3S,6S,9R,12S,15S)-6-Benzyl-3,9,10,12,1-pentamethyl-4,7,10,13-tetraazabi-
cyclo[15.3.1]henicosa-1,17,19-trien-5,8,11,14-tetrone (22): NaOH (7.5 mg)
in H2O (0.5 mL) was added to a stirred solution of tetrapeptide 21
(100 mg, 0.156 mmol) in THF (3 mL). The reaction mixture was stirred
for 1 h at room temperature before being poured into saturated NaHCO3
solution (5 mL) and extracted with diethyl ether (3”5 mL). The aqueous
layer was acidified to pH 2–3 with 1n HCl and extracted with ethyl ace-
tate (3”5 mL). The combined organic layers were dried (Na2SO4), fil-
tered, and concentrated in vacuo to give the free acid in almost quantita-
tive yield. This acid was used for the next step without further purifica-
tion. To a solution of above N-Boc protected tetrapeptide acid (90 mg,
0.144 mmol) in CH2Cl2 (1.2 mL) was added CF3CO2H (0.11 mL,
1.45 mmol), and the mixture was stirred at room temperature for 1 h.
The solvent was removed in vacuo, and the residue dried by azeotropic
removal of H2O with toluene. The crude material was subjected to the
macrolactamization without any further purification.
(2R)-4-tert-Butoxy-2-(4-methoxyphenyl)-4-oxobutanoic acid (25): A solu-
tion of H2O2 (30% in H2O, 8.3 mL, 0.069 mol) at 08C was added drop-
wise to a solution of compound 24 (5.10 g, 0.0133 mol) in THF (196 mL)
followed by a solution of LiOH in H2O (0.3m in H2O, 66 mL, 0.023 mol).
The reaction mixture was stirred at the same temperature for 5 h, at
which point TLC indicated the complete consumption of the starting ma-
terial. Then saturated aqueous solutions of Na2SO3 and NaHCO3 (40 mL
of each) were added. The mixture was partly concentrated on the rotary
evaporator to remove THF, then diluted with H2O (85 mL), and extract-
ed with CH2Cl2 (3”100 mL). The combined organic layers were dried
with MgSO4, filtered, and concentrated in vacuo to afford recovered
chiral auxiliary (1.5 g, 78% yield). The aqueous layer was acidified to pH
1.5–2.5 with 6m HCl at 08C and extracted with ethyl acetate (3”85 mL).
The combined organic layers were dried over anhydrous MgSO4, filtered,
and concentrated in vacuo to provide the carboxylic acid 25 (2.5 g, 78%).
The residue was dissolved in DMF (140 mL) and the stirred solution was
treated successively with TBTU (140 mg, 0.435 mmol), HOBt (59 mg,
0.435 mmol), and iPr2NEt(0.08 mL, 0.435 mmol) at room temperature.
The solution was stirred at room temperature for 14 h and then parti-
tioned between ethyl acetate and water. After separation of the layers,
the aqueous layer was extracted with ethyl acetate (2”75 mL). The com-
bined organic layers were washed successively with water, 5% aqueous
KHSO4, water, half-saturated NaHCO3 and brine, dried (MgSO4), fil-
tered, and concentrated in vacuo. The residue was purified by flash chro-
matography (ethyl acetate) to provide a colorless sticky solid (50 mg,
62%, three steps). Rf =0.55 (ethyl acetate); [a]2D8 =+18.0 (c=0.30,
CH2Cl2); 1H NMR (600 MHz, [D6]DMSO): d=0.97 (d, J=7.3 Hz, 17-
CH3), 1.07 (d, J=7.3 Hz, 3H; CH3), 1.09 (d, J=5.9 Hz, 3H; 11-CH3),
1.10 (d, J=5.9 Hz, 3H; CH3), 2.36–2.43 (m, 1H; 11-H), 2.48 (m, 1H; 10-
H), 2.49 (m, 1H; 6-H), 2.60–2.70 (m, 2H; 10-H, 1-H), 2.84 (s, 3H;
NCH3), 2.95 (dd, J=13.2, 3.7 Hz, 1H; 6-H), 3.35 (dd, J=13.6, 3.3 Hz,
1H; 1-H), 4.04–4.08 (m, 1H; 5-H), 4.22–4.29 (m, 2H; 17-H, 2-H), 4.39–
4.44 (m, 1H; 14-H), 6.46 (brs, 3H; 13-NH), 6.50 (d, J=8.1 Hz, 4-NH),
6.65, 6.70 (2d, J=7.3 Hz, 2H; 4’’-H, 6’’-H), 6.90 (dd, J=7.3, 7.3 Hz, 1H;
5’’-H), 6.93 (s, 1H; 2’’-H), 7.15–7.19 (m, 1H; 4’-H), 7.21–7.27 (m, 4H; 2’-
H, 4’-H), 8.31 ppm (d, J=8.8 Hz, 1H; 19-NH); 13C NMR (150 MHz,
[D6]DMSO): d=14.3 (CH3-17), 17.5 (CH3-11), 18.4 (CH3-5, CH3-14), 30.5
(NCH3), 35.4 (C-1), 38.6 (C-6), 40.5 (C-10), 43.6 (C-11), 44.3 (C-5), 44.7
(C-14), 53.3 (C-17), 53.4 ppm (C-2); IR (film): n˜ =3302, 2933, 1633, 1520,
1
This acid was used in the next step without further purification. H NMR
(400 MHz, CDCl3): d=1.38 (s, 9H; C(CH3)3), 2.56 (dd, J=16.6, 5.5 Hz,
1H; CH2), 3.03 (dd, J=16.4, 9.8 Hz, 1H; CH2), 3.77 (s, 3H; OCH3), 3.99
(dd, J=10.1, 5.8 Hz, 1H; CH), 6.83 (d, J=8.8 Hz, 2H; aryl H), 7.19 (d,
J=8.5 Hz, 2H; aryl H), 10.53 ppm (s, 1H; CO2H); 13C NMR (100 MHz,
CDCl3): d=27.8 (C(CH3)3), 38.6 (CH2), 46.4 (CH), 55.2 (OCH3), 81.1 (C-
(CH3)3), 114.0, 128.9, 129.1, 159.0, 170.5, 179.2 ppm (CHCO2); IR (film):
n˜ =2977, 1720, 1253, 1160 cmꢀ1
C15H20O5Na: 303.12029; found: 303.11986 [M+Na]+.
tert-Butyl (3R)-3-{[(9H-fluoren-9-ylmethoxy)carbonyl]amino}-3-(4-me-
;
HRMS (ESI): m/z: calcd for
thoxyphenyl)propanoate (26): Et3N (0.5 mL, 3.6 mmol) and DPPA
(0.71 mL, 3.2 mmol) were added to a solution of carboxylic acid 25
(0.92 g, 3.2 mmol) in toluene (18 mL). The reaction mixture was stirred
at room temperature for 30 min and then heated to reflux. Evolution of
N2 was observed between 70–808C. The reaction progress was monitored
by HPLC-MS. After complete conversion of the starting material to the
isocyanate (3.5–4 h), the reaction mixture was cooled to 508C and then
treated carefully with FmocOH (1.93 g, 0.009 mol). The mixture was re-
fluxed for 3 h. After the complete conversion of the isocyanate to the car-
bamate 26, the mixture was cooled to room temperature and diluted with
saturated NaHCO3 solution (32 mL). Most of the toluene was removed
on the rotary evaporator before the mixture was extracted with diethyl
ether (3”30 mL). The combined organic layers were dried over anhy-
6696
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2005, 11, 6687 – 6700

Jasplakinolide Analogues
FULL PAPER
drous MgSO4, filtered, and concentrated in vacuo. Flash chromatography
(petroleum ether/ethyl acetate 85:15) of the residue afforded pure carba-
mate 26 as a colorless oil (0.61 g, 45%). Rf =0.45 (petroleum ether/ethyl
acetate 70:30); [a]2D5 =+51.9 (c=1.02, CH2Cl2); 1H NMR (400 MHz,
CDCl3): d=1.35 (s, 9H; C(CH3)3), 2.71 (dd, J=14.1, 4.8 Hz, 1H;
CH2CO), 2.77–2.85 (m, 1H; CH2CO), 3.78 (s, 3H; OCH3), 4.19 (t, J=
6.8 Hz, 1H; CHCH2O), 4.38 (d, J=3.7 Hz, 2H; CH2O), 5.07 (d, J=
4.5 Hz, 1H; NHCH), 5.73 (d, J=6.3 Hz, 1H; NH), 6.85 (d, J=8.8 Hz,
2H; aryl H), 7.21 (d, J=7.8 Hz, 2H; aryl H), 7.28 (brs, 2H; aryl H), 7.38
(t, J=7.3 Hz, 2H; aryl H), 7.57 (brs, 2H; aryl H), 7.74 ppm (d, J=7.5,
Hz, 2H; aryl H); 13C NMR (100 MHz, CDCl3): d=27.9 (C(CH3)3), 41.8
(CH2CO), 47.1 (CHCH2O), 51.3 (NHCH), 55.2 (OCH3), 66.6 (CH2O),
81.2 (C(CH3)3), 113.9, 119.9, 125.0, 126.9, 127.3, 127.6, 133.0, 141.2, 143.8,
155.5 (NHCO), 158.9, 170.1 ppm (CO2tBu); IR (film): n˜ =3332, 2973,
2256, 1720, 1527 cmꢀ1; HRMS (EI): m/z: calcd for C29H31NO5: 474.22750;
found: 474.22776 [M+H]+.
THF (5 mL) was added Et2NH (15 mL) at 08C and the mixture was stir-
red at 08C for 15 min and then at room temperature for 1 h. Thereafter,
the reaction mixture was concentrated in vacuo and the crude product
purified by flash chromatography (methanol/dichloromethane/diethyl
amine 2:97.9:0.1) to afford the free amine as a colorless solid (0.069 g,
78%). M.p. 138.7–140.58C; Rf =0.2 (methanol/dichloromethane/diethyl-
amine 2:97.9:0.1); [a]D23 =+43.7 (c=0.21, CH2Cl2); 1H NMR (400 MHz,
CDCl3): d=1.32 (s, 9H; C(CH3)3), 1.52 (s, 2H; NH2), 2.59 (dd, J=14.9,
6.5 Hz, 1H; Tyr CH2), 2.76 (dd, J=14.9, 6.5 Hz, 1H; Tyr CH2), 2.91 (dd,
J=14.6, 9.0 Hz, 1H; Trp CH2), 3.38 (dd, J=14.4, 4.0 Hz, 1H; Trp CH2),
3.69 (dd, J=9.1, J=4.3 Hz, 1H; Trp CH), 3.76 (s, 3H; OCH3), 5.33 (dd,
J=14.9, 6.5 Hz, 1H; Tyr CH), 6.81 (d, J=8.5 Hz, 2H; Tyr aryl H), 6.99
(d, J=2.0 Hz, 1H; Ind NHCH), 7.09 (t, J=7.0 Hz, 1H; Trp aryl H), 7.17
(t, J=6.8 Hz, 1H; Trp aryl H), 7.17 (d, J=8.5 Hz, 2H; Tyr aryl H), 7.33
(d, J=8.0 Hz, 1H; Trp aryl H), 7.64 (d, J=7.8 Hz, 1H; Trp aryl H), 8.02
(d, J=8.5 Hz, 1H; Tyr NH CH), 8.50, 8.54 ppm (2s, 1H; Trp NH);
13C NMR (100 MHz, CDCl3): d=27.8 (C(CH3)3), 30.8 (Trp CH2), 41.7
(Tyr CH2), 48.9 (Tyr CH), 55.1 (OCH3), 55.5 (Trp CH), 81.0 (C(CH3)3),
111.2, 111.4, 113.8, 118.8, 119.4, 122.0, 123.1 (Trp NHCH), 127.3, 127.5,
132.9, 136.4 (Trp aryl C), 158.7, 170.0 (Tyr CO), 173.9 ppm (Trp CO); IR
(film): n˜ =3309, 2923, 1720, 1658, 1249 cmꢀ1; HRMS (EI): m/z: calcd for
C25H31N3O4: 438.23873; found: 438.23879 [M+H]+.
tert-Butyl (3R)-3-amino-3-(4-methoxyphenyl)propanoate (27): Et2NH
(15 mL) at 08C was slowly added to a solution of the Fmoc-protected
amino acid ester 26 (0.271 g, 0.57 mmol) in dry THF (15 mL). Stirring
was continued for 10 min at 08C and then at room temperature for 12 h.
The solution was concentrated in vacuo and the resulting oil purified by
flash
chromatography
(methanol/dichloromethane/diethylamine
5:94.9:0.1). The pure amine 27 was obtained as colorless oil (0.086 g,
60%). Rf =0.5 (methanol/dichloromethane/diethylamine 5:94.9:0.1);
[a]2D5 =+12.3 (c=1.00, CH2Cl2); 1H NMR (400 MHz, CDCl3): d=1.42 (s,
9H; C(CH3)3), 1.81 (s, 2H; NH2), 2.54 (s, 1H; CH2), 2.56 (d, J=2.7 Hz,
1H; CH2), 3.79 (s, 3H; OCH3), 4.32 (dd, J=7.5, 6.0 Hz, 1H; CH), 6.86
(d, J=8.5 Hz, 2H; aryl H), 7.27 ppm (d, J=8.5 Hz, 2H; aryl H);
13C NMR (100 MHz, CDCl3): d=28.0 (C(CH3)3), 45.3 (CH2), 52.0 (CH),
55.1 (OCH3), 80.5 (C(CH3)3), 113.7, 127.3, 136.8, 158.7, 171.3 ppm (C=
O); IR (film): n˜ =3378, 2973, 2842, 1724, 1157 cmꢀ1; HRMS (EI): m/z:
calcd for C14H21NO3: 252.15942; found: 252.15923 [M+H]+.
b) Peptide coupling: To a solution of the amine described above (66 mg,
0.151 mmol) in dry THF (2 mL, 0.07m) were added Fmoc-l-Ala-OH
(46 mg, 0.151 mmol), HOBt (20.3 mg, 0.151 mmol), and DCC (46 mg,
0.22 mmol) at 08C and the mixture was stirred at 08C for 12 h. There-
after, the mixture was filtered and concentrated. Flash chromatography
(methanol/dichloromethane 2:98) yielded the desired tripeptide 29
(0.110 g, 97%) as a slightly yellow solid. M.p. 116.2–123.58C; Rf =0.4
(methanol/dichloromethane 4:96); [a]2D5 =+10.17 (c=1.03, CH2Cl2);
1H NMR (400 MHz, CDCl3): d=1.17–1.21 (m, 12H; C(CH3)3, Ala CH3),
2.42 (dd, J=14.9, 6.3 Hz, 1H; Tyr CH2), 2.56 (dd, J=15.1, 6.5 Hz, 1H;
Tyr CH2), 3.08 (dd, J=14.2, 6.9 Hz, 1H; Trp CH2), 3.20 (dd, J=14.6,
5.3 Hz, 1H; Trp CH2), 3.61 (s, 3H; OCH3), 4.03–4.11 (m, 2H; Ala CH,
Fmoc CH), 4.15–4.29 (m, 2H; Fmoc CH2), 4.69 (brd, J=6.5 Hz, 1H; Trp
CH), 5.15 (dd, J=13.9, 6.5 Hz, 1H; Tyr CH), 5.54 (d, J=6.8 Hz, 1H; Trp
NH), 6.62 (d, J=8.5 Hz, 2H; Tyr aryl H), 6.78 (s, 1H; Ind NHCH), 6.82
(d, J=7.5 Hz, 1H; Ala NH), 6.88 (d, J=8.3 Hz, 2H; Tyr aryl H), 6.94 (d,
J=8.0 Hz, 1H; Tyr NH), 6.99 (t, J=7.5 Hz, 1H; Trp aryl H), 7.05 (t, J=
7.3 Hz, 1H; Trp aryl H), 7.16–7.22 (m, 3H; Fmoc aryl H, Trp aryl H),
7.30 (t, J=7.3 Hz, 2H; Fmoc aryl H), 7.45 (d, J=6.1 Hz, 2H; Fmoc aryl
H), 7.53 (d, J=7.3 Hz, 1H; Trp aryl H), 7.67 (d, J=7.3 Hz, 2H; Fmoc
aryl H), 8.04, 8.11 ppm (2s, 1H; Ind NH); 13C NMR (100 MHz, CDCl3):
d=18.3 (Ala CH3), 27.6 (Trp CH2), 27.7 ((CH3)3), 41.4 (Tyr CH2), 46.9
(Fmoc CH), 49.5 (Tyr CH), 50.8 (Ala CH), 53.6 (Trp CH), 55.1 (OCH3),
67.0 (Fmoc CH2), 81.1 (C(CH3)3), 110.1 (Trp aryl C), 111.1 (Trp aryl
CH), 113.7 (Tyr aryl CH), 118.6, (Trp aryl CH), 119.6 (Trp aryl CH),
119.9 (Fmoc aryl CH), 122.1 (Trp aryl CH), 123.2 (Trp NHCH), 125.0
(Fmoc aryl CH), 127.0 (Fmoc aryl CH), 127.3 (Trp aryl C), 127.5 (Fmoc
aryl CH), 127.7 (Tyr aryl CH), 132.5 (Tyr aryl C), 136.0 (Trp aryl C),
141.2 (Fmoc aryl C), 143.6 (Fmoc aryl C), 156.0 (Fmoc CO), 158.7 (aryl
C), 170.0 (Tyr CO), 170.2 (Ala CO), 172.3 ppm (Trp CO); IR (film): n˜ =
3401, 3289, 3062, 2931, 2117, 1697, 1646, 1245 cmꢀ1; HRMS (ESI): m/z:
calcd for C43H46N4O7Na: 753.32587; found: 753.32533 [M+Na]+.
tert-Butyl (3R)-3-({N-[(9H-fluoren-9-ylmethoxy)carbonyl]-d-tryptophyl}-
amino)-3-(4-methoxyphenyl)propanoate (28):
To a solution of amine 27 (0.080 g, 0.31 mmol) and N-Fmoc-d-tryptophan
(0.135 g, 0.31 mmol) in anhydrous THF (2.2 mL) were added HOBt
(0.043 g, 0.31 mmol) and DCC (0.095 g, 0.46 mmol) at ꢀ108C followed
by stirring of the mixture at 08C overnight. The mixture was filtered
through Celite and concentrated. The crude product was purified by flash
chromatography (dichloromethane/methanol 98:2) to yield pure dipep-
tide 28 (0.192 g, 91%). M.p. 88.9–90.88C; Rf =0.18 (methanol/dichloro-
methane 2:98); [a]2D5 =+7.64 (c=1.03, CH2Cl2); 1H NMR (400 MHz,
CDCl3): d=1.22 (s, 9H; C(CH3)3), 2.50 (dd, J=11.6, 5.3 Hz, 1H; Tyr
CH2), 2.65 (dd, J=14.6, 4.3 Hz, 1H; Tyr CH2), 3.14 (dd, J=14.4, 7.8 Hz,
1H; Trp CH2), 3.31 (dd, J=12.1, 0.5 Hz, 1H; Trp CH2), 3.71, 3.75 (2s,
3H; OCH3), 4.18 (brs, 1H; Fmoc CH), 4.31–4.44 (m, 2H; Fmoc CH2),
4.53 (d, J=3.0 Hz, 1H; Trp CH), 5.22 (dd, J=14.4, 6.3 Hz, 1H; Tyr CH),
5.60 (d, J=5.0 Hz, 1H; Trp NH), 6.57 (d, J=7.8 Hz, 1H; Tyr NH), 6.71
(d, J=7.5 Hz, 2H; Tyr aryl H), 6.78 (s, 1H; Ind NHCH), 6.89 (d, J=
8.5 Hz, 2H; Fmoc CH), 7.11 (t, J=7.4 Hz, 1H; Trp aryl H), 7.19 (t, J=
7.5 Hz, 1H; Trp aryl H), 7.26–7.33 (m, 3H; Fmoc aryl H, Trp aryl H),
7.38 (t, J=7.4 Hz, 2H; Fmoc aryl H), 7.53 (d, J=6.8 Hz, 2H; Fmoc aryl
H), 7.68 (d, J=6.5 Hz, 1H; Trp aryl H), 7.75 (d, J=7.5 Hz, 2H; Tyr aryl
H), 8.03, 8.19 ppm (2s, 1H; Trp NH); 13C NMR (100 MHz, CDCl3): d=
27.6 (C(CH3)3), 28.6 (Trp CH2), 41.2 (Tyr CH2), 46.9 (Fmoc CH), 49.2
(Tyr CH), 55.0 (OCH3), 60.3 (Trp CH), 67.0 (Fmoc CH2), 81.0 (C(CH3)3),
109.8 (Trp aryl CH), 111.2 (Trp aryl CH), 113.6 (Tyr aryl CH), 118.5, (Trp
aryl CH), 119.5 (Trp aryl CH), 119.8 (Fmoc aryl CH), 121.9 (Trp aryl
CH), 123.2 (Trp NHCH), 125.0 (Fmoc aryl CH), 126.9 (Fmoc aryl CH),
127.1 (Trp aryl C), 127.3 (Fmoc aryl CH), 127.5 (Tyr aryl CH), 132.2 (Tyr
aryl C), 136.1 (Trp aryl C), 141.1, (Fmoc aryl C), 143.6 (Fmoc aryl C),
155.9 (Fmoc CO), 158.6 (aryl C-OCH3), 169.9 (Tyr CO), 170.4 ppm (Trp
CO); IR (film): n˜ =3313, 2935, 1716, 1515, 1245 cmꢀ1; HRMS (ESI): m/z:
calcd for C40H41N3O6Na: 682.28876; found: 682.28960 [M+Na]+.
N-[(2S)-3-(3-{(2R)-2-[(tert-Butoxycarbonyl)amino]propyl}phenyl)-2-
methylpropanoyl]-l-alanyl-N-[(1R)-3-tert-butoxy-1-(4-methoxyphenyl)-3-
oxopropyl]-d-tryptophanamide (30)
a) l-Alanyl-N-[(1R)-3-tert-butoxy-1-(4-methoxyphenyl)-3-oxopropyl]-d-
tryptophanamide: Et2NH (6.5 mL) was added dropwise at 08C to a solu-
tion of tripeptide 29 (162 mg, 0.222 mmol) in dry THF (6.5 mL, 0.034m).
The mixture was then stirred for 15 min at 08C and then at room temper-
ature for 1 h. Thereafter, the mixture was concentrated and the oily resi-
due purified by flash chromatography (methanol/dichloromethane/diethyl
amine 2:97.9:0.1) yielding the free amine (0.096 g, 85%) as an oil. Rf =
0.11 (methanol/dichloromethane/diethylamine 2:97.9:0.1); [a]2D5 =+23.9
(c=1.05, CH2Cl2); 1H NMR (400 MHz, CDCl3): d=1.24–1.28 (m, 12H;
C(CH3)3, Ala CH3), 1.84 (s, 2H; NH2), 2.48 (dd, J=15.1, 6.5 Hz, 1H; Tyr
CH2), 2.65 (dd, J=15.1, 6.3 Hz, 1H; Tyr CH2), 3.17 (dd, J=14.6, 7.3 Hz,
N-[(9H-Fluoren-9-ylmethoxy)carbonyl]-l-alanyl-N-[(1R)-3-tert-butoxy-1-
(4-methoxyphenyl)-3-oxopropyl]-d-tryptophanamide (29)
a) tert-Butyl
(3R)-3-(4-methoxyphenyl)-3-(d-tryptophylamino)propa-
noate: To a solution of the dipeptide 28 (0.134 g, 0.203 mmol) in dry
Chem. Eur. J. 2005, 11, 6687 – 6700
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6697

M. E. Maier et al.
1H; Trp CH2), 3.25 (dd, J=14.6, 6.3 Hz, 1H; Trp CH2), 3.40 (q, J=
6.9 Hz, 1H; Ala CH), 3.72, 3.75 (2s, 3H; OCH3), 4.72 (q, J=7.2 Hz, 1H;
Trp CH), 5.21 (dd, J=14.4, 6.5 Hz, 1H; Tyr CH), 6.74 (d, J=8.8 Hz, 2H;
Tyr aryl H), 6.83 (s, 1H; Ind NHCH), 6.97 (d, J=8.5 Hz, 3H; Tyr aryl H,
Tyr NH), 7.07 (t, J=7.2 Hz, 1H; Trp aryl H), 7.14 (t, J=7.2 Hz, 1H; Trp
aryl H), 7.29 (d, J=8.08 Hz, 1H; Trp aryl H), 7.64 (d, J=7.8 Hz, 1H; Trp
aryl H), 7.83 (d, J=8.08 Hz, 1H; Trp NH), 8.29, 8.43 ppm (2s, 1H; Ind
NH); 13C NMR (100 MHz, CDCl3): d=21.3 (Ala CH3), 27.7 C(CH3)3),
27.9 (Trp CH2), 41.2 (Tyr CH2), 49.3 (Tyr CH), 50.5 (Ala CH), 53.4 (Trp
CH), 55.1 (OCH3), 81.1 (C(CH3)3), 110.2 (Trp aryl C), 111.2 (Trp aryl
CH), 113.6 (Tyr aryl CH), 118.6 (Trp aryl CH), 119.3 (Trp aryl CH),
121.8 (Trp aryl CH), 123.2 (Trp NHCH), 127.4 (Tyr aryl CH, Trp aryl C),
132.4 (Tyr aryl C), 136.1 (Trp aryl C), 158.6 (aryl C-OCH3), 170.1 (Tyr
CO), 170.3 (Ala CO), 175.9 ppm (Trp CO); IR (film): n˜ =3297, 3054,
2969, 2927, 1720, 1153 cmꢀ1; HRMS (EI): m/z: calcd for C28H36N4O5:
509.27585; found: 509.27563 [M+H]+.
20-H), 2.95 (dd, J=13.2, 10.5 Hz, 1H; 10-H), 3.01 (dd, J=14.0, 5.3 Hz,
1H; 20-H), 3.73 (s, 1H; OCH3), 3.74 (m, 1H; 5-H), 4.46–4.51 (m, 1H;
14-H), 4.62–4.66 (m, 1H; 17-H), 5.13–5.17 (m, 1H; 1-H), 6.82–6.86 (m,
2H; 2’’-H, 2’-H), 6.88 (d, J=7.0 Hz, 1H; 6’’-H), 6.91–6.95 (m, 2H; 4’’-H,
7’’’-H), 6.96–6.99 (m, 1H; 2’’’-H), 7.03 (dd, J=7.5, 7.5 Hz, 1H; 8’’’-H),
7.06–7.12 (m, 2H; 5’’’-H, 3’-H), 7.31 (d, J=7.5 Hz, 1H; 9’’’-H), 7.54 (d,
J=7.9 Hz, 2H; 6’’’-H, 4-NH), 7.82 (d, J=7.9 Hz, 1H; 13-NH), 8.21 (d,
J=8.8 Hz, 1H; 16-NH), 8.50 (d, J=8.8 Hz, 1H; 19-NH), 10.77 ppm (s,
1H; 1’’’-NH); 13C NMR (150 MHz, [D6]DMSO): d=18.7 (CH3-5), 18.8
(CH3-14), 19.4 (CH3-11), 28.4 (C-20), 38.7 (C-10), 41.1 (C-11), 42.3 (C-6),
42.7 (C-2), 46.0 (C-5), 47.0 (C-14), 49.3 (C-1), 52.6 (C-17), 54.8 (OCH3),
110.9 (C-9’’’), 117.8 (C-7’’’), 118.0 (C-6’’’), 120.5 (C-8’’’), 123.3 ppm (C-
2’’’); IR (film): n˜ =3286, 3062, 2965, 2927, 1643, 1542 cmꢀ1; HRMS (ESI):
m/z: calcd for C37H43N5O5: 660.31564; found: 660.31495 [M+Na]+.
Methyl N-(tert-butoxycarbonyl)-l-alanyl-N-methyl-d-tryptophanate (33)
a) N-Me-d-Trp-OMe: A solution of N-Boc-protected amino acid ester[3d]
32 (2.042 g, 6.15 mmol) in dry CH2Cl2 (50 mL) was treated dropwise with
TFA (5.00 mL, 0.0615 mol) at 08C and the mixture stirred at room tem-
perature for 1 h. The mixture was concentrated and the residue dissolved
in ethyl acetate, then washed with water. The aqueous layer was basified
with 1n NaOH to pH 8–9 keeping the temperature at 08C. Both layers
were then extracted with ethyl acetate. The organic layer was dried over
anhydrous MgSO4, filtered, and concentrated to yield the free amine
(0.975 g, 68%). It was used in the next step without further purification.
1H NMR (400 MHz, CDCl3): d=2.37 (s, 3H; NCH3), 3.12 (dd, J=14.4,
7.0 Hz, 1H; CH2), 3.21 (dd, J=14.4, 5.8 Hz, 1H; CH2), 3.59 (t, J=6.0 Hz,
1H; CH), 3.66 (s, 3H; OCH3), 6.96 (d, J=2.02 Hz, 1H; Ind NHCH), 7.11
(t, J=7.8 Hz, 1H; aryl H), 7.17 (t, J=7.8 Hz, 1H; aryl H), 7.29 (d, J=
7.8 Hz, 1H; aryl H), 7.60 (d, J=7.8 Hz, 1H; aryl H), 8.70 ppm (s, 1H;
Ind NH); 13C NMR (100 MHz, CDCl3): d=28.9 (CH2), 34.6 (NCH3), 51.6
(OCH3), 63.6 (CH2CH), 110.4 (aryl C), 111.1, 118.4, 119.2, 121.8, 123.0,
(aryl CH), 127.2, 136.1, (aryl C), 174.9 ppm (CO2); IR (film): n˜ =3405–
b) Peptide coupling: DCC (19.2 mg, 0.093 mmol) was added at ꢀ208C to
a solution of amino acid 4 (19.5 mg, 0.061 mmol), the amine prepared
above (31.0 mg, 0.061 mmol), and HOBt (8.2 mg, 0.061 mmol) in dry
THF (0.8 mL). The mixture was stirred at ꢀ208C for 30 min and then at
room temperature for 8 h. Subsequently, the reaction mixture was filtered
through Celite and the filtrate concentrated in vacuo. Purification of the
residue by flash chromatography (methanol/dichloromethane 2:98) gave
the tetrapeptide 30 as a white solid (0.046 g, 92%). M.p. 109.5–116.58C;
Rf =0.10 (methanol/dichloromethane 2:98); [a]2D5 =+33.1 (c=1.00,
CH2Cl2); 1H NMR (400 MHz, CDCl3): d=0.96 (d, J=6.3 Hz, 3H; CH3),
1.03 (d, J=5.8 Hz, 3H; Ala CH3), 1.12 (d, J=7.0 Hz, 3H; CH3), 1.33–
1.36 (2s, 18H; C(CH3)3), 2.39 (dd, J=12.5, 9.2 Hz, 1H; CH2), 2.55–2.57
(m, 2H; CH2, Tyr CH2), 2.67–2.79 (m, 4H; CH2, CHCH3, Tyr CH2, Trp
CH2), 2.85 (dd, J=13.3, 5.8 Hz, 1H; CH2), 3.06 (dd, J=14.4, 8.4 Hz, 1H;
Trp CH2), 3.33–3.34 (2s, 3H; OCH3), 3.72–3.76 (m, 1H; CHCH3), 4.11–
4.17 (m, 1H; Ala CH), 4.57–4.62 (m, 1H; Trp CH), 5.25 (dd, J=15.4,
7.2 Hz, 1H; Tyr CH), 6.74 (d, J=8.5 Hz, 2H; Tyr aryl H), 6.93–7.02 (m,
5H; Ind NHCH, Trp aryl H, xylyl H), 7.06 (t, J=7.4 Hz, 1H; Trp aryl
H), 7.08–7.12 (m, 3H; Tyr aryl H, xylyl H), 7.30 (d, J=8.0 Hz, IH, Trp
aryl H), 7.51 (d, J=7.8 Hz, 1H; Trp aryl H), 7.82 (d, J=7.5 Hz, 1H; Trp
NH), 8.07 (brs, 1H; Ala NH), 8.28 (d, J=8.3 Hz, 1H; Tyr NH),
10.27 ppm (s, 1H; Ind NH); 13C NMR (100 MHz, CDCl3): d=17.4 (CH3,
Ala CH3), 20.6 (CH3), 28.4, 28.6, 28.9 (C(CH3)3, Trp CH2), 40.9 (CH2),
43.1 (CHCH2),43.2 (Tyr CH2), 43.9 (CH2), 51.3 (CHNBoc), 51.4 (Ala
CH), 55.6 (Tyr CH), 55.6 (Trp CH), 55.7 (OCH3), 79.9, 82.1 (C(CH3)3),
111.1 (Trp aryl C), 112.4 (Trp aryl CH), 114.8 (Tyr aryl CH), 119.5, 119.9,
122.5 (Trp aryl CH), 124.7 (Ind NHCH), 128.0, 128.4 (xylyl CH), 128.8
(Trp aryl C), 129.2 (Tyr aryl CH), 129.3, 131.3 (xylyl CH), 134.4 (Tyr aryl
C), 138.2 (Trp aryl C), 140.4, 140.1 (xylyl C), 157.8 (Boc CO), 160.5 (Tyr
aryl C-OMe), 171.7, 172.9, (Ala CO, Tyr CO), 176.0 (Trp CO), 179.0 ppm
(CO); IR (film): n˜ =3293, 2923, 1681, 1531 cmꢀ1; HRMS (ESI): m/z:
calcd for C46H61N5O8Na: 834.44124; found: 834.43921 [M+Na]+.
2803 (broad), 1731, 1446, 1203 cmꢀ1
.
b) Peptide coupling: Boc-l-Ala-OH (0.305 g, 1.61 mmol), HOBt (0.218 g,
1.61 mmol), and DCC (0.50 g, 2.42 mmol) were added at 08C to a solu-
tion of the foregoing amine (0.375 g, 1.61 mmol) in dry THF (14 mL).
The reaction mixture was stirred at 08C overnight and then filtered
through Celite, and concentrated. Purification of the residue by flash
chromatography (dichloromethane/methanol 98:2) gave the dipeptide 33
as a colorless solid (0.384 g, 59%). M.p. 73.5–77.48C; Rf =0.16 (dichloro-
methane/methanol 98:2); [a]2D6 =+54.33 (c=1.05, CH2Cl2); 1H NMR
(400 MHz, CDCl3): d=0.88 (d, J=6.8 Hz, 3H; Ala CH3), 1.41 (s, 9H; C-
(CH3)3), 2.81 (s, 3H; NCH3), 3.28 (dd, J=15.4, 11.1 Hz, 1H; CH2), 3.45
(dd, J=15.4, 4.8 Hz, 1H; CH2), 3.73 (s, 3H; OCH3), 4.44–4.52 (m, 1H;
Ala CH), 5.26 (dd, J=10.9, 4.9 Hz, 1H; Trp CH), 5.50 (d, J=7.8 Hz, 1H;
NH), 6.98 (d, J=1.7 Hz, 1H; Ind NHCH), 7.10 (t, J=7.4 Hz, 1H; aryl
H), 7.16 (t, J=7.0 Hz, 1H; aryl H), 7.31 (d, J=7.8 Hz, 1H; aryl H), 7.56
(d, J=7.8 Hz, 1H; aryl H), 8.34 ppm (s, 1H; IndNH); 13C NMR
(100 MHz, CDCl3): d=18.1 (Ala CH3), 24.4 (CH2), 28.3 (C(CH3)3), 32.8
(NCH3), 46.5 (Ala CH), 52.3 (OCH3), 58.1 (Trp CH), 79.5 (C(CH3)3),
110.6 (aryl C), 111.2, 118.2, 119.4, 122.0 (aryl CH), 122.4 (Ind NHCH),
127.0, 136.0 (aryl C), 155.1 (NHCO2), 171.1 (Ala CO), 173.5 ppm (Trp
CO); IR (film): n˜ =3926, 2973, 1704, 1646, 1488 cmꢀ1; HRMS (EI): m/z:
calcd for C21H29N3O5Na: 426.19994; found: 426.2000 [M+Na]+.
(3S,7R,10R,13S,16S)-10-(1H-Indol-3-ylmethyl)-7-(4-methoxyphenyl)-
3,13,16-trimethyl-4,8,11,14-tetraazabicyclo[16.3.1]docosa-1(22),18,20-
triene-5,9,12,15-tetrone (31): TFA (1.26 mL) was added dropwise at 08C
to a solution of tetrapeptide 30 (0.063 g, 0.0776 mmol) in dry CH2Cl2
(1.26 mL) and the mixture stirred at room temperature. After HPLC-MS
showed the complete deprotection (ca. 3 h), the mixture was concentrat-
ed on the rotary evaporator. The crude amino acid was used in the next
step without further purification. It was dissolved in dry DMF (59 mL,
0.00098m) and treated with TBTU (56.0 mg, 0.17 mmol), HOBt (22.9 mg,
0.17 mmol), and iPr2NEt (0.040 mL, 0.23 mmol) at room temperature fol-
lowed by stirring at this temperature for 14 h. The mixture was parti-
tioned between ethyl acetate and water. The organic layer was washed
with H2O, 5% aqueous KHSO4 solution, H2O, half saturated NaHCO3
solution, brine, dried over MgSO4, filtered, and concentrated in vacuo.
Purification was achieved by flash chromatography (methanol/dichloro-
methane 2:98). The pure compound 31 was obtained as a colorless solid
(0.046 g, 92%). M.p. 274.5–274.88C (decomp); Rf =0.10 (methanol/di-
chloromethane 2:98); [a]D25 =5.5 (c=0.45, DMSO); 1H NMR (600 MHz,
[D6]DMSO): d=0.87 (d, J=6.1 Hz, 3H; 5-CH3), 0.91 (d, J=7.0 Hz, 3H;
14-CH3), 1.04 (d, J=7.0 Hz, 3H; 11-CH3), 2.22 (dd, J=12.7, 11.0 Hz, 1H;
6-H), 2.35–2.49 (m, 4H; 2-H, 10-H, 2-H, 11-H), 2.78–2.85 (m, 2H; 6-H,
N-(tert-Butoxycarbonyl)-l-alanyl-N-methyl-d-tryptophan (34): NaOH so-
lution (0.4m in H2O, 0.024 g, 0.60 mmol) was added to a solution of the
dipeptide 33 (0.201 g, 0.48 mmol) in THF (3 mL). The reaction mixture
was stirred for 2 h at room temperature, and then diluted with saturated
NaHCO3 solution (7.5 mL). The mixture was then extracted with (3”
4 mL) of diethyl ether. The aqueous layer was acidified to pH 1–2 with
0.5n HCl at 08C. The acidified layer was extracted with ethyl acetate
(3”15 mL). The combined organic layers were dried over anhydrous
MgSO4, filtered, and concentrated in vacuo. The crude acid was purified
by flash chromatography (ethyl acetate/petroleum ether/acetic acid
1:1:0.1) yielding 34 as a pale colorless solid (0.141 g, 74%). M.p. 106.7–
107.48C; Rf =0.12 (ethyl acetate/petroleum ether/acetic acid 1:1:0.1);
[a]2D5 =+44.84 (c=1.17, CH2Cl2); 1H NMR (400 MHz, CDCl3): d=0.86
(d, J=6.8 Hz, 3H; Ala CH3), 1.42 (s, 9H; C(CH3)3), 2.80 (s, 3H; NCH3),
6698
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2005, 11, 6687 – 6700

Jasplakinolide Analogues
FULL PAPER
3.32 (dd, J=15.1, 11.3 Hz, 1H; CH2), 3.48 (dd, J=15.6, 4.8 Hz, 1H;
CH2), 4.49–4.56 (m, 1H; Ala CH), 5.23 (dd, J=10.4, 4.4 Hz, 1H; Trp
CH), 5.71 (d, J=8.0 Hz, 1H; NH), 6.99 (brs, 1H; Ind NHCH), 7.10 (t,
J=7.3 Hz, 1H; aryl H), 7.16 (t, J=7.3 Hz, 1H; aryl H), 7.34 (d, J=
7.8 Hz, 1H; aryl H), 7.56 (d, J=7.8 Hz, 1H; aryl H), 8.55, 8.61 (s, 1H;
Ind NH), 10.62 ppm (s, 1H; CO2H); 13C NMR (100 MHz, CDCl3): d=
17.6 (Ala CH3), 24.2 (CH2), 28.3 (C(CH3)3), 33.3 (NCH3), 46.6 (Ala CH),
58.9 (Trp CH), 79.8 (C(CH3)3), 110.4 (aryl C), 111.3, 118.1, 119.3, 121.9
(aryl CH), 122.7 (Ind NHCH), 127.0, 136.0 (aryl C), 155.4 (Boc CO),
173.8 (Ala CO), 174.2 ppm (Trp CO); IR (film): n˜ =3012, 1762, 1700,
aryl C), 111.3 (Trp aryl CH), 113.8 (Tyr aryl CH), 118.1, 119.2, 121.8 (Trp
aryl CH), 122.5 (Ind NHCH), 127.3 (Trp aryl C), 127.8 (Tyr aryl CH),
133.0 (Tyr aryl C), 135.9 (Trp aryl C), 158.8 (Tyr aryl C-OCH3), 169.0
(Tyr CO), 170.7 (Ala CO), 174.2 ppm (Trp CO); IR (film): n˜ =3324,
2965, 1666, 1515 cmꢀ1
; HRMS (EI): m/z: calcd for C29H38N4O5:
523.29150; found: 523.29154 [M+H]+.
b) Peptide coupling: A solution of acid 4 (0.029 g, 0.056 mmol), the
amine prepared above (0.018 g, 0.056 mmol), and HOBt (0.0075 g,
0.056 mmol) in dry THF (0.7 mL) was treated with DCC (0.017 g,
0.084 mmol) at ꢀ208C. The reaction mixture was first stirred at the same
temperature for 30 min and then at room temperature for 18 h. The pre-
cipitate of urea was then filtered off and the filtrate concentrated on the
rotary evaporator. Purification of the residue by flash chromatography
(dichloromethane/methanol 96:4) gave tetrapeptide 36 as a colorless
solid (0.028 g, 60%). M.p. 78.8–85.28C; Rf =0.12 (dichloromethane/meth-
anol 94:6); [a]2D5 =+30.45 (c=0.57, CH2Cl2); 1H NMR (400 MHz,
CDCl3): d=0.84 (d, J=6.8 Hz, 3H; Ala CH3), 1.00 (d, J=6.8 Hz,3H;
CH3), 1.04 (d, J=6.3 Hz, 3H; CH3), 1.35–1.37 (2s, 18H; C(CH3)3), 2.39
(dd, J=13.3, 8.6 Hz, 1H; CH2), 2.54–2.61 (m, 2H; CH2, Tyr CH2), 2.63–
2.72 (m, 1H; CHCH3), 2.75 (dd, J=15.5, 6.1 Hz, 1H; Tyr CH2), 2.90–3.03
(m, 5H; NCH3, CH2), 3.12 (dd, J=15.5, 11.2 Hz, 1H; Trp CH2), 3.47 (dd,
J=15.4, 5.1 Hz, 1H; Trp CH2), 3.66 (s, 3H; OCH3), 3.70–3.76 (m, 1H;
CHCH3), 4.42–4.49 (m, 1H; Ala CH), 5.30–5.35 (m, 1H; Tyr CH), 5.58
(dd, J=11.1, 5.0 Hz, 1H; Trp CH), 6.75 (d, J=8.6 Hz, 2H; Tyr aryl H),
6.95 (s, 1H; Ind NHCH), 6.97 (s, 1H; xylyl H), 6.99–7.01 (m, 3H; Trp
aryl H, xylyl H), 7.05 (t, J=7.5 Hz, 1H; Trp aryl H), 7.14 (t, J=7.5 Hz,
1H; xylyl H), 7.19 (d, J=8.6 Hz, 2H; Tyr aryl H), 7.29 (d, J=8.1 Hz,
1H; Trp aryl H), 7.53 (d, J=7.8 Hz, 1H; Trp aryl H), 8.06 (d, J=8.3 Hz,
2H; Tyr NH, Ala NH), 10.26 ppm (s, 1H; Ind NH); 13C NMR (100 MHz,
CDCl3): d=16.1 (Ala CH3), 17.8 (CH3), 20.9 (CH3), 24.8 (Trp CH2), 28.4,
28.9 (C(CH3)3), 32.0 (NCH3), 40.9 (CH2), 43.0 (CH2), 43.1 (Tyr CH2),
44.0 (CH2), 47.3(Ala CH), 51.3 (CHNBoc), 51.4 (Tyr CH), 55.8 (OCH3),
58.7 (Trp CH), 79.8, 82.0 (C(CH3)3), 111.3 (Trp aryl C), 112.3 (Trp aryl
CH), 114.9 (Tyr aryl CH), 119.3, 119.8, 122.5 (Trp aryl CH), 124.0 (Trp
NHCH), 128.0, 128.4 (xylyl CH), 128.7 (Trp aryl C), 129.1 (Tyr aryl CH),
129.4, 131.3 (xylyl CH), 134.7 (Tyr aryl C), 138.1 (Trp aryl C), 140.5,
141.3 (xylyl C), 157.8 (Boc CO), 160.5 (Tyr aryl C-OMe), 171.7, 171.8,
(Ala CO, Tyr CO), 176.2 (Trp CO), 179.0 ppm (CO); IR (film): n˜ =3309,
2973, 1650, 1519, 1160 cmꢀ1; HRMS (EI): m/z: calcd for C47H63N5O8:
848.45689; found: 848.45733 [M+Na]+.
1463, 1373, 1245 cmꢀ1
; HRMS (ESI): m/z: calcd for C20H27N3O5Na:
412.18429; found: 412.18462 [M+Na]+.
N-(tert-Butoxycarbonyl)-l-alanyl-N-[(1R)-3-tert-butoxy-1-(4-methoxy-
phenyl)-3-oxopropyl]-N-methyl-d-tryptophanamide (35): HOBt (0.135 g,
0.33 mmol) and DCC (0.101 g, 0.49 mmol) at ꢀ208C were added to a so-
lution of acid 34 (0.128 g, 0.33 mmol) and amine 27 (0.082 g, 0.33 mmol)
in dry THF (1.5 mL). The mixture was stirred at 08C overnight, filtered,
and the filtrate concentrated. The crude tripeptide was purified by flash
chromatography (ethyl acetate/petroleum ether 50:50) providing 35 as a
colorless solid (0.196 g, 96%). M.p. 109.2–112.68C; Rf =0.25 (ethyl ace-
tate/petroleum ether 1:1); [a]2D5 =+21.85 (c=1.02, CH2Cl2); 1H NMR
(400 MHz, CDCl3): d=0.86 (d, J=6.8 Hz, 3H; Ala CH3), 1.33 (s, 9H; C-
(CH3)3), 1.39 (s, 9H; C(CH3)3), 2.65 (dd, J=15.4, 6.0 Hz, 1H; Tyr CH2),
2.78 (dd, J=15.6, 8.0 Hz, 1H; Tyr CH2), 2.91 (s, 3H; NCH3), 3.18 (dd,
J=15.6, 10.6 Hz, 1H; Trp CH2), 3.42 (dd, J=15.1, 5.5 Hz, 1H; Trp CH2),
3.74 (s, 3H; OCH3), 4.33–4.39 (m, 1H; Ala CH), 5.29–5.34 (m, 2H; Tyr
CH, NH), 5.60 (dd, J=10.3, 5.5 Hz, 1H; Trp), 6.77 (d, J=8.5 Hz, 2H;
Tyr aryl H), 6.92 (brs, 1H; NHCH), 7.04 (d, J=8.0 Hz, 1H; NH), 7.08 (t,
J=7.4 Hz, 1H; Trp aryl H), 7.15–7.16 (m, 3H; Tyr aryl H, Trp aryl H),
7.29 (d, J=8.1 Hz, 1H; Trp aryl H), 7.56 (d, J=7.5 Hz, 1H; Trp aryl H),
8.52 ppm (s, 1H; Ind NH); 13C NMR (100 MHz, CDCl3): d=16.9 (Ala
CH3), 23.16 (Trp CH2), 27.8, 28.2 (C(CH3)3), 30.6 (NCH3), 41.5 (Tyr
CH2), 46.5 (Ala CH), 49.5 (Tyr CH), 55.1 (OCH3), 56.5 (Trp CH), 79.6,
80.8 (C(CH3)3), 110.7 (Trp aryl C-8), 111.0 (Trp aryl CH), 113.7 (Tyr aryl
CH), 118.4, 119.1, 121.7 (Trp aryl CH), 122.0 (Ind NHCH), 127.3 (Trp
aryl C), 127.5 (Tyr aryl CH), 132.9 (Tyr aryl C), 136.0, (Trp aryl C), 155.4
(Boc CO), 158.7 (Tyr aryl C-OCH3), 169.1 (Tyr CO), 169.8 (Ala CO),
174.2 ppm (Trp CO); IR (film): n˜ =3332, 2977, 1666, 1515, 1160 cmꢀ1
;
HRMS (ESI): m/z: calcd for C34H46N4O7Na: 645.32587; found: 645.32523
[M+Na]+.
N-[(2S)-3-(3-{(2R)-2-[(tert-Butoxycarbonyl)amino]propyl}phenyl)-2-
methylpropanoyl]-l-alanyl-N-[(1R)-3-tert-butoxy-1-(4-methoxyphenyl)-3-
oxopropyl]-N-methyl-d-tryptophanamide (36)
(3S,7R,10R,13S,16S)-10-(1H-Indol-3-ylmethyl)-7-(4-methoxyphenyl)-
3,11,13,16-tetramethyl-4,8,11,14-tetraazabicyclo[16.3.1]docosa-
1(22),18,20-triene-5,9,12,15-tetrone (37): TFA (0.5 mL, 6.13 mmol) was
added at 08C to a solution of tetrapeptide 36 (0.025 g, 0.0303 mmol) in
dry CH2Cl2 (0.5 mL). The reaction mixture was stirred at room tempera-
ture for 1.5 h, before the solvents were evaporated on the rotary evapora-
tor. The crude amine salt was used in the next step without further purifi-
cation.
a) l-Alanyl-N-[(1R)-3-tert-butoxy-1-(4-methoxyphenyl)-3-oxopropyl]-N-
methyl-d-tryptophanamide:
A
solution of tripeptide 35 (0.120 g,
0.19 mmol) and 2,6-lutidine (0.134 mL, 1.16 mmol) in dry CH2Cl2
(2.8 mL) was treated with TBDMSOTf (0.17 mL, 0.76 mmol) at 08C.
After 1 h of stirring at 08C, HPLC-MS analysis showed that the tert-butyl
residue was replaced by the tert-butyldimethylsilyl group. The reaction
was then quenched by adding H2O (8 mL). The mixture was extracted
with ethyl acetate (3”15 mL). The combined organic layers were dried
over anhydrous MgSO4, filtered, and concentrated. The crude product
was purified by flash chromatography using a stepwise gradient (di-
chloromethane/methanol, 100:0; 98:2; 97:3; 90:10). The free amine was
obtained as yellow oil (0.057 g, 56%). Rf =0.12 (dichloromethane/metha-
nol/diethyl amine 95.9:4:0.1); [a]2D6 =+16.65 (c=0.65, CH2Cl2); 1H NMR
(400 MHz, CDCl3): d=0.68 (d, J=6.8 Hz, 3H; Ala CH3), 1.30–1.36 (m,
11H; C(CH3)3, NH2), 2.67 (dd, J=15.4, 5.5 Hz, 1H; Tyr CH2), 2.78 (dd,
J=15.1, 7.1 Hz, 1H; Tyr CH2), 2.83 (s, 3H; NCH3), 3.19 (dd, J=15.6,
11.1 Hz, 1H; Trp CH2), 3.41 (dd, J=15.5, 5.0 Hz, 1H; Trp CH2), 3.72 (s,
3H; OCH3), 3.88–3.93 (m, 1H; Ala CH), 5.31–5.36 (m, 1H; Tyr CH),
5.55 (dd, J=10.9, 5.4 Hz, 1H; Trp CH), 6.76 (d, J=8.6 Hz, 2H; Tyr aryl
H), 6.90 (brs, 1H; Ind NHCH), 7.05 (d, J=7.4 Hz, 1H; Tyr aryl H), 7.12
(t, J=7.2 Hz, 1H; Trp aryl H), 7.20 (d, J=8.5 Hz, 2H; Tyr aryl H), 7.27
(d, J=7.6 Hz, 1H; Trp aryl H), 7.45 (d, J=8.1 Hz, 1H; NH), 8.52 ppm (s,
1H; Ind NH); 13C NMR (100 MHz, CDCl3): d=17.0 (Ala CH3), 23.4
(Trp CH2), 27.8 (C(CH3)3), 30.5 (NCH3), 41.1 (Tyr CH2), 47.3 (Ala CH),
49.8 (Tyr CH), 55.2 (OCH3), 57.3 (Trp CH), 81.2 (C(CH3)3), 110.0 (Trp
To a solution of the crude amino acid salt (0.0303 mmol) in dry DMF
(30 mL, 0.001m) were added TBTU (0.029 g, 0.090 mmol), HOBt
(0.0122 g, 0.090 mmol), and iPr2NEt (0.020 mL, 0.121 mmol) followed by
stirring of the mixture at room temperature for 14 h. The mixture was
partitioned between ethyl acetate and water. The combined organic
layers were washed with water, 5% aqueous KHSO4 solution, water, half
saturated NaHCO3 solution, water, brine, dried over anhydrous MgSO4,
filtered, and concentrated. Purification of the residue by flash chromatog-
raphy (dichloromethane/methanol 96:4) furnished the desired macrocycle
37 as a white powder (8.9 mg, 45%). M.p. 169.7–1778C (decomp); Rf =
0.41 (dichloromethane/methanol 94:6); [a]2D5 =6.5 (c=0.45, DMSO);
1H NMR (600 MHz, [D6]DMSO): d=0.60 (d, J=7.0 Hz, 3H; Ala CH3),
0.94 (d, J=6.1 Hz, 3H; C-5 CH3), 1.04 (d, J=7.0 Hz, 3H; C-11 CH3),
2.33 (dd, J=12.7, 9.2 Hz, 1H; 6-H), 2.37 (dd, J=14.0, 2.6 Hz, 1H; 10-H),
2.41–2.47 (m, 2H; 2-H), 2.49 (m, 1H; 11-H), 2.76 (dd, J=13.1, 4.4 Hz,
1H; 6-H), 2.92 (s, 3H; NMe), 2.96 (dd, J=14.0, 10.5 Hz, 1H; 10-H), 3.04
(dd, J=14.9, 11.4 Hz, 1H; 20-H), 3.13–3.17 (m, 1H; 20-H), 3.72 (s, 3H;
OCH3), 3.72–3.78 (m, 1H; 5-H), 4.56 (ddd, J=13.8, 6.8, 6.6 Hz, 1H; 14-
H), 5.15–5.19 (m, 1H; 1-H), 5.49 (dd, J=11.0, 4.8 Hz, 1H; 17-H), 6.85–
6.90 (m, 3H; 2’’-H, 2’-H, 6’’-H), 6.91–6.96 (m, 2H; 4’’-H, 7’’’-H), 6.99–7.00
Chem. Eur. J. 2005, 11, 6687 – 6700
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6699

M. E. Maier et al.
(m, 1H; 2’’’-H), 7.02 (dd, J=7.5, 7.5 Hz, 1H; 8’’’-H), 7.08 (dd, J=7.5,
7.5 Hz, 1H; 5’’-H), 7.18 (d, J=8.8 Hz, 1H; 3’-H), 7.29 (d, J=7.9 Hz, 1H;
9’’’-H), 7.56 (d, J=7.9 Hz, 1H; 6’’’-H), 7.63 (d, J=7.0 Hz, 1H; 4-NH),
7.86 (d, J=7.9 Hz, 1H; 13-NH), 8.43 (d, J=7.9 Hz, 1H; 19-NH),
10.77 ppm (brs, 1H; 1’’’-NH); 13C NMR (150 MHz, [D6]DMSO): d=16.5
(Ala CH3), 18.9 (5 CH3), 19.6 (11 CH3), 24.3 (C-20), 30.0 (NCH3), 38.4
(C-10), 41.1 (C-11), 41.7 (C-2), 42.0 (C-6), 44.6 (C-14), 46.2 (C-5), 48.7
(C-1), 54.8 (OCH3), 55.1 (C-17), 110.9 (C-9’’’), 117.8 (C-7’’’), 117.9 (C-
6’’’), 120.5 (C-8’’’), 122.7 ppm (C-8’’’); HRMS (ESI): m/z: calcd for
C38H45N5O5: 674.33129; found: 674.33154 [M+Na]+.
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Acknowledgements
This workwas supported by the Deutsche Forschungsgemeinschaft (Ma
1012/13-1, 13-2) and the Fonds der Chemischen Industrie. S.Y. thanks the
DAAD for a fellowship (sandwich program). Partial support by COST
D28 is also gratefully acknowledged. We also thank Dr. F. Sasse (GBF
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Received: March 22, 2005
Published online: August 24, 2005
6700
www.chemeurj.org
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2005, 11, 6687 – 6700