Solid-phase synthesis of metal-complex containing peptides

Article abstract of DOI:10.1016/j.tet.2007.03.147

We report the synthesis of Fmoc protected single amino acid chelates (SAAC) and their metal complexes. The modified amino acids are suitable for solid-phase peptide synthesis. The use of 4-hydroxymethylbenzoic acid AM (HMBA-AM) resin allows the nucleophil

Full text of DOI:10.1016/j.tet.2007.03.147

Tetrahedron 63 (2007) 4918–4928
Solid-phase synthesis of metal-complex containing peptides
a
Georg Dirscherl, Robert Knape, Paul Hanson and Burkhard Konig
a
b
a,
*
€
aInstitut fu€r Organische Chemie, Universita€t Regensburg, Universita€tsstrasse 31, D-93040 Regensburg, Germany
bDepartment of Chemistry, Kansas University, Lawrence, KS, USA
Received 2 March 2007; accepted 22 March 2007
Available online 27 March 2007
Abstract—We report the synthesis of Fmoc protected single amino acid chelates (SAAC) and their metal complexes. The modified amino
acids are suitable for solid-phase peptide synthesis. The use of 4-hydroxymethylbenzoic acid AM (HMBA-AM) resin allows the nucleophilic
cleavage of the peptide–metal complexes from the resin without decomplexation.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
2.1. Metal chelates
Peptides with metal complexes in their side chains and
peptide–metal complex conjugates have been used to en-
hance or control binding affinities and peptide conforma-
tions. Banerjee and Stephenson et al. have reported the
solid-phase synthesis of peptides bearing 2,20-dipicolyl-
amine single amino acid chelate (dpa-SAAC) for peptide
based technetium and rhenium radiopharmaceuticals.1 Met-
zler-Nolte and co-workers prepared N-terminally modified
bioconjugates by a series of dpa based copper or zinc com-
plexes for potential applications as artificial metallochaper-
ones.2 Recent reports on dpa-SAAC describe a more flexible
preparation of peptide–Re and peptide–Tc ligand conjugates
with non-terminal SAAC.3 However, the reported synthesis
of peptide–metal complex conjugates on solid phase is either
limited to conjugation of the metal complex to the N-termi-
nus of the resin-bound peptide or focus on the coordination
of Tc(CO)3 and Re(CO)3.4 To extend the scope of solid-
phase synthesis of peptide—metal complex conjugates, we
report here their preparation from modified amino acids
bearing metal complex ligands or metal complexes in their
side chains. The modified amino acids can be incorporated
at any position into the peptide during synthesis and the
use of 4-hydroxymethylbenzoic acid AM (HMBA-AM)
resin allows nucleophilic cleavage of the peptide from the
resin avoiding decomplexation.
We have selected the iminodiacetic acid (IDA) motif as
metal complex binding sites, known for its ability to bind
imidazole residues and N-terminal His, and triazen-bis-
zinc–cyclen, dipyridylmethyl amine (dpa) and bis-diypridyl-
methyl amine (bis-dpa) zinc complexes, which show affinity
to phosphate groups. First we will discuss the synthesis of
the modified amino acids bearing the respective ligand or
complex, and then describe their use in solid-phase peptide
synthesis.
2.2. Synthesis of Fmoc-amino acids with ligand
or metal complex side chain
The synthesis of Fmoc protected IDA amino acid 1 (Fig. 1)
has been described by reductive amination of tert-butyl
2-oxoacetate,5 the starting material for this synthesis is
rather expensive, or the nucleophilic substitution of the ly-
sine side chain as reported by Tampe et al.6 After optimiza-
tion of the reaction conditions of hydrogenolytic cleavage
of the Z-protecting group and Fmoc protection using the
more reactive Fmoc–OSu instead of Fmoc–Cl, 1 was ob-
tained in good yield from the latter method. The ligand
O
O
OH
O
O
O
-
OH
Cu2+
OH
O
O
N
N
O
HO
O-
HO
HN
NHFmoc
Fmoc
Keywords: Solid-phase peptide synthesis; Metal complex; Single amino
acid chelate.
O
2
1
* Corresponding author. Fax: +49 941 943 1717; e-mail: burkhard.koenig@
chemie.uni-regensburg.de
Figure 1. Fmoc protected IDA amino acid 1 and its copper(II) complex 2.
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.03.147

G. Dirscherl et al. / Tetrahedron 63 (2007) 4918–4928
4919
Boc
Boc
Boc
Boc
Boc
N
N
N
N
N
N
Boc
Boc
Boc
Boc
Boc
Boc
N
N
N
N
N
N
N
N
N
N
N
Boc
N
N
N
HN
Z-Lys-OBzl * benzenesulfate
N
N
K2CO3, 1,4-Dioxane
86%
Cl
OR2
O
3
R1
NH
4: R1 = Z, R2 = Bzl
10 bar H2, Pd/C, EtOH
5: R1 = H, R2 = H
Fmoc-OSu, DIPEA, DCM
68 %
6: R1 = Fmoc, R2 = H
H
H
H
H
HN
HN
NH
HN
NH
Zn2+
NH
N+
H
H
H
H
H
N+
N+
N+
Zn2+
N
N
N+
H
N
N+
H
N
N
N
H
N
N
Zn(ClO4)2 * 6 H2O
N
N
HCl / ether
MeOH
2 equiv
NH
HN
Hepes buffer (pH 8)
quant.
quant
6 Cl-
.
H
N
8
7
OH
O
Fmoc
O
OH
Fmoc NH
Scheme 1. Preparation of Fmoc protected amino acid 6 and the bis(ZnII–cyclen) compound 8.
was converted into its copper complex using either 2 equiv
of Cu2(OH)2CO3 or a stoichiometric amount of CuCl2
with 1 equiv of base. In both cases, mass spectrometric
analysis (ESMS) confirmed the complete formation of
complex 2.
The synthesis of amino acids 15 with binuclear Zn(II) dpa
complex starts from Boc-L-tyrosine methyl ester (Scheme 2).
The Mannich reaction with dpa and paraformaldehyde
afforded ligand 11.11 Saponification and subsequent Fmoc-
protection resulted in the desired amino acid 14. The com-
plexation of 14 with 2 equiv of either Zn(NO)3$6H2O or
ZnCl2 gave dpa metal complexes 15.
Amino acid complex 8 was prepared from the previously
reported triazene-bis-cyclen 37 by reaction with a-amino
Z-protected L-Lys-OBn (Scheme 1). The nucleophilic aro-
matic substitution gave compound 4 in 86% yield and Z
and benzyl protecting groups were simultaneously removed
by hydrogenation using 10% palladium on charcoal as cata-
lyst. Fmoc protection gave compound 6. The complexation
of the cyclen ligands with Zn(II) requires careful control of
the reaction conditions. After Boc deprotection with HCl sat-
urated ether the hydrochloride salt 7 must be neutralized by
base for metal ion complexation and the complexation step
typically requires elevated temperatures,8 conditions which
may cleave the Fmoc group. Ion exchange chromatography
for deprotonation of the hydrochloride salt was therefore
not applicable and a buffered solution was used for complex-
ation. A clean twofold Zn(II)-complexation was achieved in
Hepes buffer (pH 8) with Zn(ClO4)2$6H2O yielding the pro-
tected amino acid 8.
2.3. Solid phase peptide synthesis
2.3.1. Synthesis of dpa containing peptides. As a first pep-
tide compound 16 was prepared (Scheme 3). After complete
characterization by two-dimensional NMR, peptide 16 was
complexed in solution. This approach allowed the use of the
versatile Rink amide MBHA resin, a resin based on MBHA
with a modified Rink amide linker as an ideal tool for Fmoc
N
N
M2+
N
N
N
N
Fmoc
OH
Fmoc
OH
N
H
N
H
Amino acid 9 with a tridentate donor side chain was prepared
according to a literature procedure9 from Fmoc–lysine
hydrochloride pyridine-2-carboxyaldehyde by reductive
amination with NaBH(OAc)3.10 The dpa complexes 10
are obtained quantitatively using stoichiometric amounts of
the appropriate metal salts in a water/methanol solution
(Fig. 2).
O
O
10
9
10a: M = Zn
10b: M = Cu
10c: M = Ni
Figure 2. Dpa amino acid 9 and dpa metal complexes 10 (M¼Zn, Cu and
Ni).

4920
G. Dirscherl et al. / Tetrahedron 63 (2007) 4918–4928
N
N
N
N
Zn2+
N
Zn2+
N
N
N
ZnCl2, Zn(NO3)2 * 6 H2O
N
OH
N
N
O
2,2´-dipicolylamine
(HCOH)n
N
or Zn(ClO4)2
2 equiv
Boc-L-Tyr-OMe
MeOH/H2O
EtOH/H2O
53 %
H
N
H
N
R1
Fmoc
O
OR2
O
OH
LiOH, MeOH/H2O
11: R1 = Boc, R2 = Me
12: R1 = Boc, R2 = H
15
95%
-
HCl/ether
15a: * 3 NO3
15b: * 3 Cl-
quant .
Fmoc-OSu, DIPEA, DCM
78%
13: R1 = H * HCl, R2 = H
14: R1 = Fmoc, R2 = H
Scheme 2. Synthesis of bis-dpa amino acid 14 and bis-dpa metal complexes 15.
SPPS, providing peptide amides in high yields and pu-
rities.12 After Fmoc deprotection, the Fmoc protected ali-
phatic amino acids, glycine and alanine were coupled with
HBTU, HOBt and DIPEA in NMP/DMF using the conven-
tional frit-equipped syringe technique. All coupling steps
were carried out only once. Standard deprotection and wash-
ing cycles as outlined in Scheme 3 were performed after each
coupling step. The SAAC 9 was then coupled using the same
coupling reagents and equivalents of reagents. The reaction
was completed after 3 h indicated by a negative Kaiser test13
and the deprotected N-terminus was subsequently coupled to
Fmoc protected amino acids glycine, leucine and valine. Fi-
nal Fmoc deprotection completes the solid-phase synthesis
and gave peptide 16 after cleavage from the resin with
1. piperidine
2. wash
3. Fmoc-Gly-OH (5 eq.)
4. HOBt, HBTU, DIPEA
Fmoc
O
Rink
Fmoc-Gly
O
Rink
N
N
N
1. Cycle 2: Fmoc-Ala-OH (5 eq.)
O
H
N
O
Rink
Fmoc
2. Cycle 3: SAAC 13 (5 eq.)
N
H
N
H
O
O
N
N
O
N
O
1. Cycle 4: Fmoc-Gly-OH (5 eq.)
2. Cycle 5: Fmoc-Leu-OH (5 eq.)
3. Cycle 6: Fmoc-Val-OH (5 eq.)
4. piperidine
5. wash
6. TFA, TIS, H2O (90:5:5)
O
O
H
N
H
H2N
N
NH2
N
N
H
N
H
H
O
O
16
Zn2+
N
N
N
Zn(NO3)2 * 6 H2O
O
O
O
H
N
H
N
H2O
H2N
NH2
N
H
N
N
H
H
17
O
O
O
Scheme 3. Solid-phase synthesis of peptide conjugate 16 and peptide metal complex 17.

G. Dirscherl et al. / Tetrahedron 63 (2007) 4918–4928
4921
N
1. Cycle 2: Fmoc-Ala-OH
2. Cycle 3: Fmoc-Gly-OH
3. Cycle 4: SAAC 13
N
4. Cycle 5: Fmoc-Val-OH
N
5. Cycle 6: Fmoc-Ala-OH
6. Cycle 7: SAAC 13
7. Cycle 8: Fmoc-Gly-OH
O
1. piperidine
2. wash
O
O
O
H
H
N
H
N
H
N
8. Cycle 9: Fmoc-Val-OH
N
Fmoc
O
Rink
H2N
N
H
N
H
N
H
NH2
9. piperidine
3. Fmoc-Gly-OH (5 eq.)
4. HOBt, HBTU, DIPEA
O
O
O
O
N
10. wash
11. TFA, TIS, H2O (90:5:5)
Cycle 1
18
N
N
N
N
Zn2+
N
Zn(NO3)2 * 6 H2O
H2O
O
O
O
O
H
N
H
N
H
N
H
N
H2N
N
H
N
H
N
H
NH2
O
O
O
O
19
N
Zn2+
N
N
Scheme 4. SPRS of dinuclear peptide metal complex 19.
90% TFA, 5% TIS and 5% H2O. After subsequent precipita-
tion using cold diethyl ether and centrifugation (see Section
4 for details), the peptide conjugate was dissolved in water,
lyophilized and characterized by ESIMS and two-dimen-
sional NMR. Twenty-six milligrams of the target peptide se-
quence 16 were obtained analytically pure. Thus, peptide 16
was treated with Zn(NO3)2$6H2O (1 equiv) to obtain exclu-
sively metal bound peptide conjugate 17 exclusively.
The same approach was used to prepare the dinuclear pep-
tide receptor 19 (Scheme 4). Peptide 18 was first synthesized
on Rink amide MBHA resin. After cleavage from the resin,
1. Fmoc-Ala-OH,
DIC / HOBt
1. piperidine
2. wash
HMBA
Fmoc-Ala
HMBA
O
HO
2. acetic anhydride,
DIPEA
3. Fmoc-Gly-OH
4. HOBt, HBTU, DIPEA
Cycle 1
1. Cycle 2: Fmoc-Leu-OH
2. Cycle 3: Zn(II)-SAAC 14
3. Cycle 6: Fmoc-Ala-OH
O
O
H
N
H
N
HMBA
Fmoc
O
N
N
H
N
H
H
O
O
O
N
Zn2+
N
N
O
O
H
H
N
N
O
H2N
N
H
N
H
1. piperidine
O
N
O
O
2. wash
3. DIPEA / MeOH / DMF (1:5:5)
20
Zn2+
N
N
Scheme 5. Direct SPRS of 20 on HMBA-AM resin.

4922
G. Dirscherl et al. / Tetrahedron 63 (2007) 4918–4928
1. Fmoc-Ala-OH,
DIC / HOBt
from the resin. Otherwise the same procedure as above
was used yielding peptide 20 in >95% purity as verified
via NMR.
HMBA
Fmoc-Ala
O
HMBA
HMBA
HO
O
O
2. acetic anhydride,
DIPEA
2.3.2. Synthesis of peptides containing bis-zinc–cyclen
amino acid 8. First attempt to couple amino acid 8 or 6
in solid-phase protocols to aliphatic amino acids using
HBTU,14 TBTU and DIPEA as coupling reagents failed.
Therefore the more efficient reagent HOAt was used
instead of HOBt together with the onium salt HATU. DIPEA
was exchanged by collidine,15 a more suitable base for
the HOAt reagent. By using HOAt (2.5 equiv), HATU
(2.5 equiv) and collidine (5 equiv) the coupling of 6
(2ꢀ2.5 equiv) using two coupling cycles gave dipeptide 21
(Scheme 6). A more extended peptide 22 was obtained on
an Fmoc–Ala loaded SASRIN resin using the same coupling
conditions (Scheme 7). In both cases the solely observed
molecular ions in electro-spray mass spectrometry were
only consistent with the mass of the desired compounds.
In the following step, the Boc groups were cleaved with
HCl saturated ether and the neutralized compound 23 was
subsequently treated with Zn(ClO4)2 salt to obtain the pep-
tide complex 24.
1. piperidine
2. wash
H
N
Fmoc
N
H
3. Fmoc-SAAC 10 (2.5 eq.), 3 h
4. wash
5. Fmoc-SAAC 10 (2.5 eq.), 3 h
O
Boc
NH
N
N
N
N
N
N
Boc
N
N
Boc
N
Boc
Boc
N
N
Boc
O
1. piperidine
2. wash
H2N
O
N
H
3. DIPEA / MeOH / DMF (1:5:5)
O
Boc
N
NH
N
N
N
21
N
N
Boc
2.3.3. Synthesis of peptides containing IDA amino acid 2.
To illustrate the incorporation of the IDA amino acid
metal complex 2 into a short peptide sequence by a solid-
phase protocol, peptide 25 was prepared on HMBA-AM
resin using the standard coupling conditions as outlined in
examples of the dpa-chelate (Scheme 8). Electro-spray
mass analysis confirmed the formation of the desired
compound.
N
N
Boc
N
Boc
Boc
N
N
Boc
Scheme 6. Solid-phase synthesis of dipeptide conjugate 21.
16 mg of the target peptide sequence 18 was obtained in
>95% purity as verified by NMR. Two-dimensional NMR
allowed the complete assignment of all resonances. Thus,
peptide 18 was treated with Zn(NO3)2$6H2O (1 equiv) to
obtain metal bound dinuclear peptide receptor 19.
2.3.4. Synthesis of peptides containing bis-dpa-zinc
amino acid 15. Bis(ZnII–nitrate)-SAAC 15a, derived from
complexation of 14 with Zn(NO)3$6H2O, was first tried
for incorporation into a peptide backbone. Due to the poor
solubility of the metal complexes in NMP or DMF, the
coupling was not efficient enough to give pure products.
Fortunately, bis-ZnII–SAAC 15b, having chloride counter
ions, was more soluble in NMP and the synthesis of 26 on
HMBA-AM resin was successful using standard HOBt/
TBTU conditions. Electro-spray mass analysis confirmed
the clean formation of the desired compound.
In the synthesis of peptide 20, the already metal coordi-
nated Fmoc–dpa complex 10a was incorporated into the
peptide chain (Scheme 5). To avoid the loss of metal
ions under acidic conditions, which are necessary to
cleave from Rink amide resin, HMBA-AM was used as
the resin as it allows nucleophilic cleavage of the peptide
1. Fmoc-Leu-OH,
DIC / HOBt
1. piperidine
2. wash
3. Fmoc-Ala-OH
4. HOBt, HBTU, DIPEA
HMBA
Fmoc-Leu
HMBA
O
HO
2. acetic anhydride,
DIPEA
Cycle 1
N
N
N
Zn2+
N
Zn2+
N
O-
N
1. Cycle 2: Fmoc-Val-OH
2. Cycle 3: bis-Zn(II)SAAC 19c,
3. piperidine
O
O
H
N
H
N
4. wash
O
5. DIPEA / MeOH / DMF (1:5:5)
N
H
NH2
O
O
26

G. Dirscherl et al. / Tetrahedron 63 (2007) 4918–4928
4923
1. piperidine
2. wash
1. Cycle 2: Fmoc-Ala-OH
SASRIN
Fmoc-Ala
O
2. Cycle 4: Fmoc-SAAC 10, (2.5 eq.), 3 h,
HOAt, HATU, collidine
3. Fmoc-Ala-OH
4. HOBt, HBTU, DIPEA
3. wash
4. Fmoc-SAAC 10, (2.5 eq.), 3 h,
HOAt, HATU, collidine
5. Cycle 5: Fmoc-Ala-OH
Cycle 1
O
O
H
H
N
SASRIN
Fmoc
N
O
N
N
H
N
H
H
O
O
O
Boc
N
NH
N
N
N
N
N
Boc
N
N
Boc
N
Boc
Boc
N
O
O
N
H
N
H
N
OH
Boc
H2N
N
H
N
H
O
O
O
1. piperidine
2. wash
3. TFA / DCM (1:99), 5 min
Boc
NH
22
N
N
N
N
N
N
Boc
N
N
Boc
Boc
Boc
N
N
N
Boc
O
O
H
N
H
N
OH
H2N
N
H
N
H
O
O
O
HCl / Ether
MeOH
NH
N
23
N
N
H
N
N
NH
H
N
N
HN
NH
H
N
O
O
H
N
H
N
OH
H2N
N
N
H
H
O
O
O
ZnClO4
80 °C, H2O
NH
H
24
N
N
N
N
Zn2+
N
HN
N
N
H
Zn2+ NH
HN
N
H
Scheme 7. Solid-phase synthesis of peptide 22 and peptide complex 24.
3. Conclusion
Peptide–metal complex conjugates were either obtained
by incorporation of the metal coordinated SAAC followed
by mild nucleophilic resin-cleavage or by complexation in
metal salt solution after cleavage from the resin. Our
In conclusion, we have reported the synthesis of Fmoc
protected SAAC and their use in solid-phase synthesis.

4924
G. Dirscherl et al. / Tetrahedron 63 (2007) 4918–4928
1. Fmoc-Ala-OH,
DIC / HOBt
1. piperidine
2. wash
HMBA
Fmoc-Ala
HMBA
HO
O
2. acetic anhydride,
DIPEA
3. Fmoc-Ala-OH
4. HOBt, HBTU, DIPEA
Cycle 1
O-
Cu2+
O
O
N
O
1. Cycle 2: Cu(II)-SAAC 6
2. Cycle 3: Fmoc-Ala-OH
3. Cycle 4: Fmoc-Ala-OH
4. Cycle 5: Fmoc-Phe-OH
O
O
O
H
N
H
N
H
HMBA
N
O
Fmoc
N
N
N
H
H
H
O
O
O
O-
Cu2+
N
O
O
O
1. piperidine
2. wash
O
O
O
H
H
N
3. DIPEA / MeOH / DMF (1:5:5)
H2N
N
O
N
H
N
H
N
H
O
O
O
25
Scheme 8. SPRS of peptide metal complex 25.
reported solid-phase peptide synthesis protocols are suitable
for automation and the position and number of the modified
amino acid within the peptide chain may vary. This allows
the synthesis of libraries of modified peptides with metal
complexes as binding sites in synthetic receptors or as para-
magnetic labels.
as a blue solid in quantitative yield. Mp: decompostition
at 135 ꢁC; IR (KBr disk): ~n [cmꢂ1]¼3414, 2945, 1707,
1622, 1583, 1400, 740; MS (ESI, H2O/MeCN/MeOH+
10 mmol/L NH4Ac): m/z (%)¼544 (100) [MꢂH+]ꢂ, 580
(35) [M+Clꢂ]ꢂ, 1091 (8) [2MꢂH+]ꢂ.
4.2. 1,4,7-Tri-tert-butyl 10,100-(6-(6-(benzyloxy)-5-
(benzyloxycarbonylamino)-6-oxohexylamino)-1,3,5-
triazine-2,4-diyl)-bis-(1,4,7,10-tetraazacyclododecane-
1,4,7-tricarboxylate) 4
4. Experimental
4.1. Cu–IDA-complex 2
To a solution of Z-Lys–OBzl benzenesulfate (1.96 g,
371 mmol) and K2CO3 (1.03 g, 7.42 mmol) was added bis-
Boc–cyclen triazine 37 (3.73 g, 3.53 mmol) and the reaction
mixture was refluxed for 3 d. The filtrate was concentrated
under reduced pressure and the crude compound was puri-
fied by silica gel column (eluent: CHCl3/MeOH¼95:5;
Rf¼0.73) to give 4 as a white solid (4.19 g, 3.01 mmol,
85%). Mp: 140 ꢁC; [a]D20 ꢂ3.4 (c 0.01 in CHCl3); 1H
NMR (600 MHz, DMSO-d6): d¼1.13–1.55 (m, 58H, Boc–
CH3, Lys–CHCH2CH2, CHCH2CH2CH2), 1.57–1.74 (m,
2H, Lys–CHCH2), 3.06–3.78 (m, 34H, cyclen–CH2,
CHCH2CH2CH2CH2), 4.00–4.08 (m, 1H, CH), 4.98–5.07
(m, 2H, H-Bzl), 5.10 (s, 2H, H-Z), 6.64 (br s, 1H, NH),
7.27–7.38 (m, 10H, H–Aryl), 7.73 (d, 1H, NH); 13C NMR
(150 MHz, DMSO-d6, HSQC, HMBC): d¼22.9 (ꢂ, C-3),
27.9 (+, 12C, Boc), 28.0 (+, 6C, Boc), 28.9 (ꢂ, C-4), 30.5
(ꢂ, C-2), 40.0 (ꢂ, C-5), 49.4 (ꢂ, 16C, cyclen), 54.0 (+,
CH), 65.5 (ꢂ, CH2Bzl), 66.8 (ꢂ, CH2Z), 78.9 (Cquat, Boc),
79.0 (Cquat, Boc), 79.1 (Cquat, 2C, Boc), 79.3 (Cquat, Boc),
79.4 (Cquat, Boc), 127.7 (Cquat, 2C, Aryl), 127.7 (Cquat, 2C,
Compound 1 was first treated with HCl saturated ether to ob-
tain the free iminodiacetic acid functionality: Compound 1
(1.62 g, 2.72 mmol) was dissolved in DCM and cooled to
0 ꢁC using an ice bath. To this mixture 30 mL of HCl satu-
rated ether was added. The mixture was allowed to warm
to room temperature and stirred over night. The reaction
progress was controlled by 1H NMR. The mixture was con-
centrated under reduced pressure and dried under high vac-
uum to obtain product 1a as colourless solid in quantitative
yield and was subsequently used for complexation. Mp:
135 ꢁC; [a]2D0 ꢂ13.9 (c 0.13 in MeOH); IR (KBr disk): ~n
[cmꢂ1]¼3419, 2953, 2619, 1735, 1528, 1250, 740; MS
(ESI, MeOH+10 mmol/L NH4OAc): m/z (%)¼485 (100)
[MH+], 619.4 (7) [MNa+]. EA (C25H28N2O8$3H2O) calcu-
lated (%): C 55.74, H 6.37, N 5.20. Found: C 55.18, H
6.21, N 4.96.
Fmoc–IDA–OH 1a (930 g, 1.79 mmol) and Cu2(OH)2CO3
(395 mg, 1.79 mmol) were suspended in H2O/MeOH solu-
tion (30 mL, 1:1). The mixture was stirred for 3 h at 70 ꢁC
and the resulting blue solution was decanted from the resi-
dual Cu2(OH)2CO3. MeOH was removed under vacuum and
the remaining aqueous solution was lyophilized yielding 2
Aryl), 127.8 (Cquat, Aryl), 127.9 (Cquat, Aryl), 128.3 (Cquat
,
2C, Aryl), 128.3 (Cquat, 2C, Aryl), 155.5 (Cquat, 3C, triazin),
156.1 (Cquat, ester), 172.2 (Cquat, carbamate); IR (KBr disk):
~n [cmꢂ1]¼3441, 2974, 2932, 2360, 2342, 1560, 1542, 1410,

G. Dirscherl et al. / Tetrahedron 63 (2007) 4918–4928
4925
1366, 1250, 1166; MS (ESI, DCM/MeOH+10 mmol/L
NH4OAc): m/z (%)¼1391.2 (100) [MH+], 646.1 (26)
[M+2H+ꢂBoc]2+, 704.7 (7) [MH++NH+4]2+.
in 20 mL H2O and the resulting solution was stirred for
1 h. The MeOH was removed under vacuum and the remain-
ing aqueous solution was lyophilized yielding 10a as a white
solid in quantitative yield. Mp: decomposition at 150 ꢁC;
[a]2D0 ꢂ27.2 (c 0.007 in MeOH); IR (KBr disk): ~n
[cmꢂ1]¼3416, 3066, 2944, 1711, 1609, 1415, 1383, 1312,
1026, 763; MS (ESI, H2O/MeCN): m/z (%)¼613 (100)
[Fmoc–BPA–Zn2+ꢂH+]+, 1229 (10) [2(Fmoc–BPA–
Zn2+)ꢂ3H+]+.
4.3. 2-(((9H-Fluoren-9-yl)methoxy)carbonylamino)-6-
(4,6-bis(4,7,10-tris(tert-butoxycarbonyl)-1,4,7,10-tetra-
azacyclododecan-1-yl)-1,3,5-triazin-2-ylamino)hexa-
noic acid 6
Fmoc–OSuc (405 mg, 1.20 mmol) and DIPEA (155 mL,
1.20 mmol) were added in succession to a suspension of 5
(1.54 g, 1.10 mmol) in DCM (100 mL). The reaction mix-
ture was stirred at room temperature for 12 h. It was ex-
tracted with an aqueous solution of NaH2PO4 (100 mM,
3ꢀ40 mL, pH 5.0) and the organic phase was washed with
water, then dried over anhydrous magnesium sulfate and
the solvent was removed under vacuum. The crude product
was purified by silica column chromatography (eluent:
4.6. 2-{[(9H-Fluoren-9-yl)methoxy]carbonylamino}-3-
{3,5-bis[(bis-pyridin-2-ylmethyl-amino)methyl]-4-
hydroxyphenyl}propanoic acid 14
DIPEA (0.68 mL, 4.0 mmol) and Fmoc–OSuc (236 mg,
0.70 mmol) were added successively to a suspension of 13
(520 mg, 0.48 mmol) in DCM (50 mL). The reaction mix-
ture was stirred at room temperature for 12 h. The mixture
was extracted with an aqueous solution of NaH2PO4
(100 mM, 3ꢀ20 mL, pH 5.0) and the organic phase was
washed with water, then dried over anhydrous magnesium
sulfate and the solvent was removed under vacuum. The
crude product was purified by silica column chromatography
(eluent: CHCl3/MeOH¼95:5; Rf¼0.05) to give 14 (309 mg,
0.37 mmol, 78%) as a pale yellow solid. Mp: decomposition
88 ꢁC; [a]D20 +41.5 (c 0.02 in CHCl3); IR (KBr disk): ~n
[cmꢂ1]¼3414, 3252, 3057, 3057, 2924, 2822, 2362, 1714,
1592. 1H NMR (600 MHz, CDCl3, COSY, HSQC,
HMBC): d¼2.97 (dd, 1H, 2J¼13.2 Hz, 3J¼5.0 Hz,
TyrCHCH2), 3.11 (dd, 1H, 2J¼12.7 Hz, 3J¼2.5 Hz,
TyrCHCH2), 3.48–3.50 (m, 2H, TyrCH2N), 3.76–3.86 (m,
10H, Pyr–CH2–N, TyrCH2N), 4.11–4.16 (m, 1H, Fmoc–
CH), 4.17–4.22 (m, 1H, Fmoc–CH2), 4.26–4.31 (m, 1H,
TyrCH), 4.32–4.37 (m, 1H, Fmoc–CH2), 5.95 (d, 1H,
3J¼5.1 Hz, NH), 6.90 (br s, 2H, CH–phenol), 7.10–7.14
(m, 4H, pyr), 7.19–7.27 (m, 6H, pyr, aryl), 7.34–7.39 (m,
2H, aryl), 7.52–7.60 (m, 6H, pyr, aryl), 7.74 (d, 2H,
3J¼7.5 Hz, aryl), 8.61–8.70 (m, 4H, pyr), 10.96 (br s, 1H,
Tyr–OH); 13C NMR (151 MHz, CDCl3, HSQC, HMBC):
d¼37.6 (ꢂ, CH2), 47.4 (+, CH), 54.8 (ꢂ, 2C, CH2), 57.4
(+, CH), 59.6 (ꢂ, 4C, CH2), 66.2 (ꢂ, CH2), 119.8 (+, 2C,
CH), 122.3 (+, 4C, CH), 122.9 (Cquat, 2C), 123.5 (+, 4C,
CH), 125.3 (+, 2C, CH), 127.0 (+, 2C, CH), 127.5 (+,
2C, CH), 129.2 (Cquat, 1C), 131.3 (+, 2C, CH), 136.7
(+, 4C, CH), 141.2 (Cquat, 2C), 144.3 (Cquat, 1C), 149.8 (+,
4C, CH), 154.2 (Cquat, 1C), 155.3 (Cquat, carbamate), 158.3
(Cquat, 4C), 176.6 (Cquat, acid); MS (ESI, DCM/MeCN/
H2O+10 mmol/L TFA): m/z (%)¼413 (100) [M+2H+],
826.4 (30) [MH+]. HRMS calculated for C50H48N7O5
[MH+]: 826.3765; found: 826.3765ꢃ5.8 ppm.
CHCl3/MeOH¼95:5; Rf¼0.38) to give
6 (1052 mg,
0.76 mmol, 68%) as a white solid solid. Mp: 102 ꢁC; [a]D20
+25.0 (c 0.008 in CDCl3); H NMR (400 MHz, CDCl3,
1
COSY, HSQC, HMBC): d¼1.35–1.48 (m, 54H, Boc),
1.49–165 (m, 4H, H-3, H-4), 1.76–1.98 (m, 2H, H-2),
2.99–3.95 (m, 34H, H–cyclen, H-5), 4.13–4.23 (m, 1H, H-
10), 4.26–4.44 (m, 3H, H-1, H-9), 6.07 (br s, 1H, NH),
7.21–7.28 (m, 2H, H-B), 7.31–7.38 (m, 2H, H-C), 7.54–
7.63 (m, 2H, H-A), 7.71 (d, 2H, 3J¼7.3 Hz, H-D); 13C
NMR (100 MHz, CDCl3, HSQC, HMBC): d¼22.0 (ꢂ, C-
3/4), 28.5 (+, 12C, Boc), 28.5 (+, 6C, Boc), 30.9 (ꢂ, C-3/
4), 31.9 (ꢂ, C-2), 40.1 (ꢂ, C-5), 47.2 (+, C-10), 50.2 (ꢂ,
16C, cyclen), 54.3 (+, C-1), 66.9 (ꢂ, C-9), 80.0 (Cquat, 6C,
Boc), 119.9 (Cquat, 2C, C-D), 125.3 (Cquat, 2C, C-A), 127.0
(Cquat, 2C, C-B), 127.6 (Cquat, 2C, C-C), 141.2 (Cquat, 4C,
Fmoc), 143.9 (Cquat, 2C, Fmoc), 144.1 (Cquat, 2C, Fmoc),
156.1 (Cquat, triazin), 156.8 (Cquat, 2C, triazin), 156.8 (Cquat
,
ester), 175.2 (Cquat, acid); IR (KBr disk): ~n [cmꢂ1]¼3433,
2974, 2932, 1693, 1542, 1411, 1366, 1250, 1165; MS
(ESI, DCM/MeOH+10 mmol/L NH4OAc): m/z (%)¼703.7
(100) [MH++NH+4]2+, 1389.1 (33) [MH+], 645.2 (21)
[M+2H+ꢂBoc]2+, 617.1 (21) [MH++2H+ꢂBocꢂDC4H8]2+,
695 (10) [(MH++2H+)]2+. EA (C70H109N13O16$5H2O) cal-
culated (%): C 56.84, H 8.12, N 12.32: Found: C 56.80, H
7.86, N 12.03.
4.4. Bis-Zn–cyclen-complex 8
Hepes buffer (10 mM, pH 8) was prepared and 10 mL was
heated to 80 ꢁC in a round-bottom flask. L-Tyr(tri-Boc-bis-
Cyc)–OH 7 (500 mg, 0.54 mmol) and Zn(ClO4)2 (402 mg,
1.08 mmol) were each dissolved in 10 mL of Hepes buffer
and added dropwise and simultaneously under stirring.
The reaction mixture was stirred for further 3 h at 80 ꢁC
and at room temperature over night. Compound 8 was
obtained as a white solid after lyophilization.
4.7. Bis-bpa–Zn(Cl)-complex 15b
The free ligand 14 (320 mg, 0.39 mmol) was dissolved in
methanol (25 mL). To this solution, ZnCl2 (52.8 mg,
0.39 mmol) in 5 mL H2O was added and the mixture was
stirred at room temperature for 3 h. Methanol was then re-
moved under reduced pressure and the remaining aqueous
solution was lyophilized to give the desired zinc coordinated
complex as a white solid in quantitative yield. Mp: decom-
position >170 ꢁC; [a]D20 +45.0 (c 0.01 in CHCl3); IR
(KBr disk): ~n [cmꢂ1]¼3422, 3055, 2921, 1713, 1606,
1526; MS (ESI, DCM/MeOH+10 mmol/L NH4OAc): m/z
MS (ESI, H2O/MeCN/MeOH+10 mmol/L NH4OAc): m/z
(%)¼456.8 (100) [K4+ꢂ2H+]2+, 476.4 (24) [K4++Clꢂꢂ
H+]2+.
4.5. Fmoc–bpa–Zn(NO3)2 10a
To the SAAC 9 (850 mg, 1.54 mmol) in 80 mL MeOH was
added a solution of Zn(NO3)2$6H2O (458 mg, 1.54 mmol)

4926
G. Dirscherl et al. / Tetrahedron 63 (2007) 4918–4928
(%)¼1070.4 (100) [K3++2CH3COOꢂ]+, 1010.3 (45)
(ꢂ, C-2), 40.1 (ꢂ, C-14), 40.8 (ꢂ, C-22), 41.8 (ꢂ, C-18),
48.3 (+, C-10), 51.1 (+, C-21), 52.6 (+, C-1), 54.9 (ꢂ, C-
5), 56.7 (ꢂ, C-7), 57.4 (+, C-27), 124.2 (+, 2C, C-B),
124.6 (+, 2C, C-D), 140.7 (+, 2C, C-C), 147.8 (+, 2C, C-
[K3+ꢂH++CH3COOꢂ]+, 505.4 (6) [K3+ꢂH+]2+.
4.8. Peptide 16
A), 155.1 (Cquat, 2C, C-E), 165.4 (Cquat, C-8), 168.4 (Cquat
C-20), 171.4 (Cquat, C-17), 171.7 (Cquat, C-26), 171.7 (Cquat
C-12), 172.7 (Cquat, C-15); MS (ESI, H2O/NH4OAc): m/z
(%)¼394.3 (100) [M]2+, 901.4 (14) [M2++TFA]+, 787.4
(8) [M2+ꢂH+]+, 850.4 (3) [M2++NOꢂ3 ]+.
,
,
The synthesis was performed manually in a 5-mL syringe
equipped with porous filter using Fmoc protected Rink
amide resin (100 mg, subst.: 0.7 mmol/g). SPPS of Fmoc
protected aliphatic amino acids and SAAC 9 according to
the specific stated procedure provided peptide 16 as a white
solid. 1H NMR (600 MHz, DMSO-d6, COSY, HSQC,
4.10. Peptide 18
3
HMBC): d¼0.85 (d, 3H, J¼6.7 Hz, H-29a), 0.83 (d, 3H,
3
3J¼6.9 Hz, H-24a), 0.81 (d, 3H, J¼6.7 Hz, H-29b), 0.80
The synthesis was performed manually in a 5-mL syringe
equipped with porous filter using Fmoc protected Rink
amide resin (50 mg, subst.: 0.7 mmol/g). SPPS of Fmoc pro-
tected amino acid monomers and SAAC 9 according to the
specific stated procedure provided compound 18 as a white
solid. 1H NMR (600 MHz, DMSO-d6, COSY, HSQC,
3
3
(d, 3H, J¼6.9 Hz, H-24b), 1.22 (d, 3H, J¼7.06 Hz, H-
11), 1.23–1.32 (m, 2H, H-3), 1.42–1.46 (m, 2H, H-22),
1.47–1.52 (m, 1H, H-2a), 1.54–1.59 (m, 1H, H-23), 1.60–
1.67 (m, 1H, H-2b), 1.69–1.76 (m, 2H, H-4), 1.90–1.96
(m, 1H, H-28), 3.06–3.13 (m, 2H, H-5), 3.52–3.62 (m, 2H,
3
2
3
3
H-14), 3.68 (dd, 1H, J¼5.8 Hz, J¼16.7 Hz, H-18a), 3.74
HMBC): d¼0.75–0.83 (dd, 6H, J1¼6.7 Hz, J2¼6.9 Hz,
3
(dd, 1H, 3J¼5.6 Hz, 2J¼16.7 Hz, H-18a), 4.06 (dd, 1H,
H-21, H-210), 0.94 (d, 6H, J¼6.7 Hz, H-35, H-350), 1.17
3
3
3
3J1¼6.9 Hz, J2¼8.9 Hz, H-27), 4.18–4.22 (m, 1H, H-1),
(d, 3H, J¼7.2 Hz, H-11), 1.20 (d, 3H, J¼7.2 Hz, H-25),
1.20–1.32 (m, 4H, H-3), 1.55–1.42 (m, 2H, H-20a, H-20b),
1.55–1.67 (m, 2H, H-2a, H-20a), 1.69–1.78 (m, 4H, H-4),
1.82 (s, 1H, H-36), 1.85 (s, 1H, H-36), 1.92–1.99 (m, 1H,
H-20), 2.01–2.07 (m, 1H, H-34), 3.04–3.12 (m, 4H, H-5),
3.62–3.66 (m, 1H, H-30b), 3.67–3.76 (m, 2H, H-14b, H-
4.31–4.40 (m, 2H, H-21, H-10), 4.50 (br s, 7H, H-7), 7.00
(s, 1H, H-31a), 7.33 (s, 1H, H-31b), 7.41–7.45 (m, 2H, H-
3
B), 7.51 (d, 2H, J¼7.9 Hz, H-D), 7.67 (d, 1H, NH-30),
3
3
7.87 (dd, 1H, J1¼7.7 Hz, J2¼7.7 Hz, H-Ca), 7.87 (dd,
3
3
1H, J1¼7.7 Hz, J2¼7.7 Hz, H-Cb), 7.96 (d, 1H, NH-25),
8.00–8.08 (m, 2H, NH-13, NH-19), 8.19 (d, 1H,
3J¼7.7 Hz, NH-16), 8.55 (d, 1H, 3J¼7.3 Hz), 8.61–8.63
(m, 2H, H-A); 13C NMR (150 MHz, DMSO-d6, HSQC,
HMBC): d¼18.0 (+, C-29a), 18.4 (+, C-11), 19.2 (+, C-
29b), 21.5 (+, C-24a), 22.4 (ꢂ, C-3), 23.1 (+, C-24b), 23.1
(ꢂ, C-4), 24.1 (+, C-23), 30.4 (+, C-28), 31.2 (ꢂ, C-2),
40.0 (ꢂ, C-14), 40.1 (ꢂ, C-22), 41.8 (ꢂ, C-18), 48.3 (+,
C-10), 51.1 (+, C-21), 52.5 (+, C-1), 53.8 (ꢂ, C-5), 56.9
(ꢂ, 4C, C-7), 57.5 (+, C-27), 123.9 (+, 2C, C-B), 124.7 (+,
2C, C-D), 137.6 (+, 2C, C–C), 149.1 (+, 2C, C-A), 150.1
(Cquat, 2C, C-E), 165.5 (Cquat, C-8), 168.4 (Cquat, C-20),
171.4 (Cquat, C-17), 171.7 (Cquat, C-26), 171.8 (Cquat, C-
12), 172.8 (Cquat, C-15); MS (ESI, DCM/MeOH+NH4OAc):
m/z (%)¼363.2 (100) [M+2H+]2+, 725.6 (71) [MH+].
3
2
30a), 3.94 (dd, 1H, J¼16.6 Hz, J¼6.1 Hz, H-14a), 4.11–
4.23 (m, 3H, H-33, H-10, H-19), 4.28–4.34 (m, 2H, H-24,
H-1), 4.49 (m, 8H, H-7), 7.00 (s, 1H, H-8), 7.29–7.33 (m,
1H, H-8), 7.42–7.45 (m, 4H, H-B), 7.53 (d, 4H,
3
4
3J¼7.9 Hz, H-D), 7.67 (dd, 1H, J¼27.7 Hz, J¼8.7 Hz,
3
H-22), 7.86–7.90 (m, 4H, H-C), 7.91 (d, 1H, J¼7.4 Hz,
H-12), 8.08–8.21 (m, 4H, H-15, H-26, H-28, H-31), 8.61–
8.66 (m, 4H, H-A); 13C NMR (150 MHz, DMSO-d6,
i
HSQC, HMBC): d¼17.7 (+, Pr), 17.7 (+, C-11), 18.2 (+,
iPr), 18.2 (+, C-25), 19.1 (+, Pr), 22.3 (ꢂ, 2C, C-3), 23.1
i
(ꢂ, C-4), 29.7 (+, C-34), 30.5 (+, C-20), 31.3 (ꢂ, C-2),
31.7 (ꢂ, C-20), 41.6 (ꢂ, C-14), 41.9 (ꢂ, C-30), 48.0 (+, C-
10), 48.2 (+, C-24), 52.0 (+, C-1), 52.5 (+, C-33), 53.7 (ꢂ,
C-5), 56.9 (ꢂ, C-7), 57.3 (+, C-19), 123.9 (+, C-B), 124.7
(+, C-D), 137.6 (+, C-C), 149.1 (+, C-A), 151.4 (Cquat, C-
E), 174.1 (Cquat, C-9), 167.9 (Cquat, C-16), 168.1 (Cquat, C-
4.9. Peptide complex 17
13), 168.1 (Cquat, C-29), 170.8 (Cquat, C-18), 171.0 (Cquat
C-27), 171.5 (Cquat, C-32), 171.7 (Cquat, C-23), 174.1 (Cquat
,
,
To a solution of peptide 16 (20 mg, 0.03 mmol) in 10 mL
H2O was added Zn(NO3)2$6H2O (8.4 mg, 0.03 mmol). Af-
ter the mixture was stirred over night a white solid was ob-
tained after lyophilization. 1H NMR (600 MHz, DMSO-d6,
COSY, HSQC, HMBC): d¼0.80–0.86 (m, 12H, H-29, H-
C-9); MS (ESI, H2O/NH4OAc): m/z (%)¼365 (100)
[M+3H+]3+, 547 (24) [M+2H+]2+, 1092.7 (0.3) [MH+].
4.11. Peptide complex 19
3
24), 1.08–1.19 (m, 2H, H-4), 1.12 (d, J¼7.0 Hz, 3H, H-
11), 1.42–1.48 (m, 5H, H-22, H-2a, H-3), 1.53–1.61 (m,
2H, H-2b, H-23), 1.91–1.97 (m, 1H, H-28), 2.56–2.62 (m,
2H, H-5), 3.53–3.75 (m, 4H, H-14, H-18), 4.00 (d, 2H,
To a solution of peptide 18 (10 mg, 0.01 mmol) in 10 mL
H2O was added Zn(NO3)2$6H2O (5.6 mg, 0.02 mmol).
After the mixture was stirred over night a white solid was
obtained after lyophilization. MS (ESI, H2O/MeOH+
NH4OAc): m/z (%)¼407.3 (100) [M4+ꢂH+]3+, 608.9 (74)
[M4+ꢂ2H+]2+, 365.8 (40) [(M4+ꢂ2Zn2++3H+)]3+.
3
3
2J¼16.0 Hz, H-7a), 4.07 (dd, J¼9.0 Hz, J¼6.8 Hz, 1H,
H-27), 4.17 (m, 1H, H-1), 4.24 (dd, 2J¼16.0 Hz,
4J¼2.3 Hz, 2H, H-7b), 4.30–4.40 (m, 2H, H-10, H-21),
7.02 (s, 1H, N-H), 7.34 (s, 1H, N-H), 7.59–7.66 (m, 2H,
3
H-B, H-D), 7.93–7.99 (m, 1H, N-H), 8.05 (t, J¼5.5 Hz,
4.12. Peptide complex 20
1H, N-H), 8.08–8.12 (m, 2H, H-C), 8.15 (d, 1H,
3
3J¼7.7 Hz, N-H), 8.50 (d, J¼7.2 Hz, 1H, NH), 8.71 (d,
The synthesis was performed manually in a 5-mL syringe
equipped with porous filter using HMBA-AM resin
(100 mg, subst.: 0.83 mmol/g). SPPS of Fmoc protected
amino acids and SAAR 10a according to the specific stated
procedure provided compound 20 as a white solid. 1H NMR
3J¼4.8 Hz, 2H, H-A); 13C NMR (150 MHz, DMSO-d6,
HSQC, HMBC): d¼18.0 (+, C-29a), 18.5 (+, C-11), 19.2
(+, C-29b), 21.5 (+, C-24a), 22.8 (ꢂ, C-3), 23.1 (+, C-
24b), 23.1 (ꢂ, C-4), 24.1 (+, C-23), 30.4 (+, C-28), 31.5

G. Dirscherl et al. / Tetrahedron 63 (2007) 4918–4928
4927
(600 MHz, DMSO-d6, COSY, HSQC, HMBC): d¼0.80 (d,
amino acids and SAAR 15b according to the specific
stated procedure provided compound 26 as a white solid.
MS (ESI, H2O/MeOH+NH4OAc): m/z (%)¼543.4 (100)
[K3++CH3COOꢂ]2+, 1145.6 (50) [K3++2CH3COOꢂ]+.
3
3H, J¼6.7 Hz, H-180), 0.85 (d, 3H, 3J¼6.5 Hz, H-18),
3
1.08 (d, 3H, J¼6.9 Hz, H-11), 1.15–1.28 (m, 2H, H-3),
3
1.25 (d, 3H, J¼7.3 Hz, H-25), 1.38–1.50 (m, 5H, H-2a,
H-4, H-21), 1.52–1.62 (m, 2H, H-2b, H-17), 2.39 (t, 2H,
3J¼7.2 Hz, H-5), 3.21–3.40 (m, 1H, H-10), 3.60 (s, 3H,
OMe), 3.66–3.71 (m, 4H, H-7, H-16), 4.18–4.29 (m, 3H,
H-24, H-15, H-1), 7.20–7.23 (m, 2H, H-B), 7.50 (d, 2H,
Acknowledgements
We thank the Fonds der Chemischen Industrie and the Uni-
€
3
3
3J¼7.7 Hz, H-D), 7.74 (dd, 1H, J1¼6.7 Hz, J2¼7.7 Hz,
versitat Regensburg for support. R.K. thanks the German
Academic Exchange Service (DAAD) for a fellowship
within the ISAP programme.
H-Ca), 7.74 (dd, 1H, 3J1¼7.7 Hz, 3J2¼7.7 Hz, H-Cb),
3
7.81–7.96 (m, 1H, C-14), 8.05 (d, 1H, J¼7.1 Hz, NH-8),
3
3
8.11 (d, 1H, J1¼6.9 Hz, H-23), 8.16 (t, 1H, J¼5.9 Hz,
H-20), 8.43–8.47 (m, 2H, H-A); 13C NMR (150 MHz,
DMSO-d6, HSQC, HMBC): d 17.0 (+, C-25), 21.5 (+, H-
11), 21.6 (+, C-180), 22.9 (+, C-18), 24.1 (ꢂ, C-17), 26.3
(ꢂ, C-4), 32.3 (ꢂ, C-2), 40.4 (ꢂ, C-21), 41.6 (ꢂ, C-16),
47.5 (+, C-24), 50.1 (+, C-10), 51.3 (+, C-1), 51.8 (+, C-
15), 51.8 (+, OMe), 53.5 (ꢂ, 4C, C-7), 122.0 (+, 2C, C-B),
122.4 (+, 2C, C-D), 136.4 (+, 2C, C-C), 148.7 (+, 2C, C-
Supplementary data
Supplementary data associated with this article can be found
in the online version, at doi:10.1016/j.tet.2007.03.147.
References and notes
A), 159.5 (Cquat, 2C, C-E), 168.5 (Cquat, C-22), 171.8 (Cquat
C-13), 172.1 (Cquat, C-19), 172.9 (Cquat, C-26), 175.5 (Cquat
,
,
C-9); MS (ESI, H2O/MeOH+NH4OAc): m/z (%)¼359.1
(100) [M]2+, 717.3 (14) [M2+ꢂH+]+, 352.1 (30)
[MꢂOMe+OH]2+, 703.3 (20) [(MꢂOMe+OH)ꢂH+]+.
1. Banerjee, S. R.; Maresca, K. P.; Francesconi, L.; Valliant, J.;
Babich, J. W.; Zubieta, J. Nucl. Med. Biol. 2005, 32, 1–20;
Stephenson, K. A.; Banerjee, S. R.; Sogbein, O. O.;
Levadala, M. K.; McFarlane, N.; Boreham, D. R.; Maresca,
K. P.; Babich, J. W.; Zubieta, J.; Valliant, J. F. Bioconjugate
Chem. 2005, 16, 1189–1195; Banerjee, S. R.; Maresca, K. P.;
Stephenson, K. A.; Valliant, J. F.; Babich, J. W.; Graham,
W. A.; Barzana, M.; Dong, Q.; Fischman, A. J.; Zubieta, J.
Bioconjugate Chem. 2005, 16, 885–902; Stephenson, K. A.;
Banerjee, S. R.; McFarlane, N.; Boreham, D. R.; Maresca,
K. P.; Babich, J. W.; Zubieta, J.; Valliant, J. F. Can. J. Chem.
2005, 83, 2060–2066; Stephenson, K. A.; Zubieta, J.;
Banerjee, S. R.; Levadala, M. K.; Taggart, L.; Ryan, L.;
McFarlane, N.; Boreham, D. R.; Maresca, K. P.; Babich,
J. W.; Valliant, J. F. Bioconjugate Chem. 2004, 15, 128–136;
Stephenson, K. A.; Banerjee, S. R.; Besanger, T.; Sogbein,
O. O.; Levadala, M. K.; McFarlane, N.; Lemon, J. A.;
Boreham, D. R.; Maresca, K. P.; Brennan, J. D.; Babich,
J. W.; Zubieta, J.; Valliant, J. F. J. Am. Chem. Soc. 2004, 126,
8598–8599.
4.13. Dipeptide 21
The synthesis was performed manually in a 5-mL syringe
equipped with porous filter using HMBA-AM resin
(100 mg, subst.: 1.1 mmol/g). SPPS of Fmoc protected
amino acids and SAAC 6 along with HOAt and HATU
as coupling reagents according to the specific stated
procedure provided compound 21 as a white solid. MS
(ESI, DCM/MeOH+10 mmol/L NH4OAc): m/z (%)¼626.6
(100) [M+2H+]2+, 1252.1 (29) [MH+], 1220.1 (4) [MH+ꢂ
CH3OH].
4.14. Peptide 22
The synthesis was performed manually in a 5-mL syringe
equipped with porous filter using SASRIN resin (100 mg).
SPPS of Fmoc protected amino acids and SAAC 6 along
with HOAt and HATU as coupling reagents according to
the specific stated procedure provided compound 22 as
2. Kirin, S. I.; Duebon, P.; Weyhermueller, T.; Bill, E.; Metzler-
Nolte, N. Inorg. Chem. 2005, 44, 5405–5415.
3. Stephenson, K. A.; Zubieta, J.; Banerjee, S. R.; Levadala,
M. K.; Taggart, L.; Ryan, L.; McFarlane, N.; Boreham,
D. R.; Maresca, K. P.; Babich, J. W.; Valliant, J. F.
Bioconjugate Chem. 2004, 15, 128–136.
a
white solid. MS (ESI, DCM/MeOH+10 mmol/L
NH4OAc): m/z (%)¼726.1 (100) [M+2H+]2+, 1451.4 (20)
[MH+], 1463.2 (4) [M+Na+].
4. See Ref. 5 and: Banerjee, S. R.; Levadala, M. K.; Lazarova, N.;
Wei, L.; Valliant, J. F.; Stephenson, K. A.; Babich, J. W.;
Maresca, K. P.; Zubieta, J. Inorg. Chem. 2002, 41, 6417–
6425; Levadala, M. K.; Banerjee, S. R.; Maresca, K. P.;
Babich, J. W.; Zubieta, J. Synthesis 2004, 1759–1766;
Stephenson, K. A.; Banerjee, S. R.; Besanger, T.; Sogbein,
O. O.; Levadala, M. K.; McFarlane, N.; Lemon, J. A.;
Boreham, D. R.; Maresca, K. P.; Brennan, J. D.; Babich,
J. W.; Zubieta, J.; Valliant, J. F. J. Am. Chem. Soc. 2004, 126,
8598–8599; Wei, L.; Babich, J.; Eckelman, W. C.; Zubieta, J.
Inorg. Chem. 2005, 44, 2198–2209; Banerjee, S. R.; Babich
John, W.; Zubieta, J. Chem. Commun. 2005, 1784–1786.
5. Levadala, M. K.; Banerjee, S. R.; Maresca, K. P.; Babich, J. W.;
Zubieta, J. Synthesis 2004, 1759–1766.
4.15. Peptide complex 25
The synthesis was performed manually in a 5-mL syringe
equipped with porous filter using HMBA-AM resin
(100 mg, subst.: 0.83 mmol/g). SPPS of Fmoc protected
amino acids and SAAR 2 according to the specific stated
procedure provided compound 25 as a white solid. MS
(ESI, H2O/MeOH+NH4OAc): m/z (%)¼441 (8)
[(M+2H+)]2+, 882 (8) [MH+], 904 (6) [M+Na+].
4.16. Peptide complex 26
The synthesis was performed manually in a 5-mL syringe
equipped with porous filter using HMBA-AM resin
(100 mg, subst.: 1.1 mmol/g). SPPS of Fmoc protected
6. Hutschenreiter, S.; Neumann, L.; Raedler, U.; Schmitt, L.;
Tampe, R. ChemBioChem 2003, 4, 1340–1344.

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8. Kruppa, M. Ph.D. Thesis, University of Regensburg, 2006.
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unpublished, procedure of Dr. Kate Jolliffe, University of
Sydney, Australia. See also Ref. 5.
Hammarstroem, L.; Styring, S.; Aakermark, B. J. Am. Chem.
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