Fullerene unsymmetrical bis-adducts as models for novel peptidomimetics

Article abstract of DOI:10.1002/ejoc.200900791

Two classes of unsymmetrical, orthogonally protected bisfulleropyrrolidine amino acids have been prepared as models for fullerene-based peptidomimetics with the carbon sphere inserted into the peptide backbone. Two successive [3+2] cycloadditions of azome

Full text of DOI:10.1002/ejoc.200900791

FULL PAPER
DOI: 10.1002/ejoc.200900791
Fullerene Unsymmetrical Bis-Adducts as Models for Novel Peptidomimetics
Dragana Milic*[a] and Maurizio Prato[b]
Keywords: Fullerenes / Cycloaddition / Aminoacids / Heterocycles / Peptidomimetics
Two classes of unsymmetrical, orthogonally protected bis-
fulleropyrrolidine amino acids have been prepared as models
for fullerene-based peptidomimetics with the carbon sphere
inserted into the peptide backbone. Two successive [3+2]
cycloadditions of azomethine ylides (thermally generated
from formaldehyde and the corresponding orthogonally pro-
tected glycino-amines and -acids) to C60 afforded NHFmoc/
fering the possibility of selective deprotection under both
acidic and basic conditions. In both classes of unsymmetrical
bis-adducts, the distribution of all the trans (t1–t4) and equa-
torial (eЈ and eЈЈ) isomers was quite similar except for the t3
NHBoc/CO2Me compound, which rapidly decomposed dur-
ing chromatography. All compounds were characterized by
UV/Vis, 1H and 13C NMR spectroscopy, and mass spectrome-
CO2tBu and NHBoc/CO2Me fulleropyrrolidine couples, of- try.
The first covalently modified [6,6]-double bond is labeled
Introduction
as the 1,2-site. For a second attack on a [6,6]-double bond
nine different sites are available: Three from the same side
of the sphere (cis, cn, n = 1–3), four from the opposite side
(trans, tn, n = 1–4), and two orthogonally directed (equatori-
als, eЈ and eЈЈ). With different addends the formation of
nine regioisomeric bis-adducts is possible, whereas with
identical addends eight isomers should be considered be-
cause attack at both eЈ and eЈЈ positions leads to the same
products.
The unique structural and physicochemical features of
C60 have stimulated extensive research with a view to find-
ing applications in biomedical fields.[1] In fact, the fullerene
sphere fits almost perfectly into the hydrophobic pocket of
HIV protease modifying its activity.[2] As a result of the
ability of C60 to accept up to six electrons, fullero deriva-
tives possess excellent radical scavenging ability,[3] acting as
antioxidants,[4] membrane lipid peroxidation suppressors,[5]
and cell oxidative stress defenders. The generation of singlet
oxygen upon photo-oxidation of fullerenes, consequent
DNA cleavage, and pro-oxidative activity make them at-
tractive tools for photodynamic cancer therapy.[6] However,
the bioavailability of C60 is severely limited by extremely
low solubility in water and biological media. Two basic stra-
tegies for overcoming this obstacle include a noncovalent
encapsulation of C60 into polar carriers[7] and, more often,
its covalent modification.[8] Although C60 mono-adducts
generally exhibit much higher solubility in all solvents than
pristine fullerene, the carbon sphere subunit is still too big
to be completely solubilized by the new addends. As a con-
sequence, in polar media C60 derivatives tend to aggregate
and form micelles.[9] Apart from the reduced solubility, this Figure 1. Relative positions of the addends in C60 bis-adducts.
Double bonds have been omitted for clarity.
phenomenon changes the physicochemical properties of ful-
lerene derivatives. Better covering of the carbon sphere and
consequent decreased micellar aggregation can be achieved
The synthesis of fullero-amino acids[10] and their incor-
by introducing two or more addends. The relative positions
poration into peptides[11] has attracted much interest as a
of the addends in C60 bis-adducts are depicted in Figure 1.
result of physicochemical studies as well as their biological
applications. So far the fullero subunit has been incorpo-
rated into peptides as hydrophobic side-chains (Figure 2, a),
with no examples of the replacement of Cα with C60 having
been found. Besides the improvement in solubility, the in-
troduction of a second addend on to C60 leads to the pos-
sible incorporation of the fullerene amino acid into the pep-
[a] Faculty of Chemistry University of Belgrade,
Studentski trg 12–16, POB 51, 11158 Belgrade, Serbia
Fax: +381-11-2636061
E-mail: dmilic@chem.bg.ac.rs
[b] Dipartimento di Scienze Farmaceutiche, Università degli Studi
di Trieste,
Piazzale Europa 1, 34127 Trieste, Italy
476
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Fullerene Bis-Adducts as Models for Novel Peptidomimetics
tide backbone. Up to nine bis-regioisomers with different
and strictly defined geometries (from linear to various V-
shaped forms, Figure 2, b) may allow the influence of a ri-
gid structural subunit on the peptidomimetic conformation,
properties, and biological behavior to be studied.
Figure 3. HPLC chromatograme (right) of the equatorial isomers
(eЈ and eЈЈ) and their UV spectra (left).
Figure 2. Fulleropeptides containing C60 as either a side-chain (a)
or a backbone constituent (b).
Following this conceptual challenge, we present herein
the synthesis of two classes of fulleropyrrolidine (Fp) bis-
adducts containing orthogonally protected amino and car-
boxylic groups serving as models that could be used in the
synthesis of novel fullero-peptidomimetics with the carbon
spheroid inserted into the peptide backbone.
Synthesis of Monofulleropyrrolidines Bearing Protected
Amino and Carboxylic Groups
The synthesis of the protected mono-adducts is outlined
in Scheme 1. Mono-N-alkylation of 1,2-ethanediamine (1)
by tert-butyl bromoacetate (2) and subsequent protection
of the primary amino group gave the hydrochloride salt of
N-alkylated tert-butyl glycinate 4. Liberation of the free
base followed by acidic ester hydrolysis afforded the amino
acid (AA) 6 and subsequent 1,3-dipolar cycloaddition to
C60 provided N-Fmoc-protected Fp 7. The yield of com-
pound 7 was unexpectedly low, 3% under standard reaction
conditions (molar ratio AA/HCHO/C60 = 1:5:1, reflux in
toluene for 1 h). The same yield was achieved by prolonging
Results and Discussion
Synthetic Strategy
Owing to the spatial proximity of the cis-positioned ad- the reaction time to 13 h and no product decomposition
dends and the expected micellar aggregation of these iso- was observed. [To examine the stability of fulleropyrrolidine
mers, we concentrated our efforts on the isolation, charac- 7 under the applied conditions, the compound was heated
terization, and distribution of equatorial and trans unsym- at reflux in toluene and no changes were observed after
metrical bis-adducts that contain terminal amino and car- 6 h (TLC).] No improvement was attained by changing the
boxy groups. For use in peptide synthesis, these functional solvent; in tetrachloroethane the reaction proceeded much
subunits should be orthogonally protected, avoiding at the more slowly than in toluene with the same amount of com-
same time the use of the Cbz or benzyl ester groups due to pound 7 formed. Use of an excess of the amino acid 6
the sensitivity of fullerene to catalytic hydrogenation. Con- (3 molequiv. with respect to C60) resulted in a slightly better
sidering all of these factors, we designed the synthesis of yield (5%). The effect of organic base on Fp formation was
NHFmoc/CO2tBu and NHBoc/CO2Me fulleropyrrolidine also examined. Thus, in the presence of triethylamine (TEA,
couples, allowing for the possibility of selective deprotec- molar ratio AA/:TEA/HCHO/C60 = 1:2:5:1, reflux 1.5 h) a
tion under both acidic and basic conditions. The synthesis complex mixture was formed, whereas with pyridine under
of fulleropyrrolidines (Fp) involves the [3+2] cycloaddition the same reaction conditions a yield of 9% of the Fmoc-
of an azomethine ylide (thermally generated from an alde- protected Fp amine 7 was achieved.
hyde and the corresponding N-substituted glycine) to C60
Fulleropyrrolidines 12 bearing side-chains with protected
(Figure 3). To avoid the formation of a new stereocenter, carboxylic groups were synthesized as outlined in Scheme 1.
formaldehyde was chosen, whereas unsymmetrical bis-ad- N-Alkylation of β-alanine esters 9 with benzyl bromoace-
duct formation was achieved by two successive 1,3-dipolar tate (BBA, 8) followed by hydrogenation of the benzyl es-
cycloaddition reactions using the corresponding orthogo- ters 10 afforded the glycino acids 11. Subsequent azometh-
nally protected glycino-N-alkylamines and glycino-N-alkyl ine ylide formation in the presence of formaldehyde and
acids. As acid-sensitive carboxy and amino protecting [3+2] cycloaddition to C60 proceeded smoothly to afford
groups, tert-butyl ester and Boc were chosen, with methyl the corresponding Fp acids 12a and 12b in yields of 45 and
ester and Fmoc selected as base-sensitive protecting groups. 37%, respectively.
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477

D. Milic, M. Prato
FULL PAPER
Scheme 1. Synthesis of mono-fulleropyrrolidines.
Synthesis of Unsymmetrical Bis-Fulleropyrrolidines
The two possible reactions for the preparation of the
Fmoc/CO2tBu couples 13a–e, which differ in the order of
introduction of the addends, were performed successfully.
Heating of tert-butyl Fp ester 12a, AA 6, Py, and HCHO
(molar ratio 1:1:2:5) at reflux in toluene for 75 min pro-
duced a mixture of bis-adducts 13a–e with no tris-adducts
observed (Scheme 2), whereas twice the amount of amino
acid resulted in a reduction of the reaction time to 30 min.
The same products were obtained by the complementary
reaction of protected Fp amine 7, AA 11a, and HCHO
(Scheme 2) for 30 min at reflux. Owing to the low yield of
Fmoc-protected fulleroamine 7, fullero-amino acids 13a–e
were synthesized by heating a toluene solution of fullero
ester 12a, Fmoc-protected glycino-amine 6, pyridine, and
paraformaldehyde (mol ratio 1:2:2:5) at reflux for 30 min.
Flash chromatography (FC) on fine silica gel afforded pure
products in the following order of elution: unreacted mono-
Fp, trans1, trans2, trans3, trans4, and equatorials.
Both the eЈ and eЈЈ bis-adducts showed the same adsorp-
tion affinity to silica during FC and TLC, whereas HPLC
analysis showed two peaks with identical UV/Vis spectra
(Figure 3).
By analogy, 1,3-dipolar cycloaddition of Boc-protected
glycino-amine 14[12] to Fp-ester 12b led to the second class
of orthogonally protected fullero-amino acids 15a–e, sepa-
rated by FC in the same order of elution as 13a–e. In both
classes of orthogonally protected fullero-amino acids (13
and 15), the product distribution was quite similar (Fig- Scheme 2. Synthesis of unsymmetrical bis-fulleropyrrolidines.
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Fullerene Bis-Adducts as Models for Novel Peptidomimetics
ure 4), except for the t3 isomers, the difference arising here
In class 13, such fine structure partially overlapped with
because compound 15c decomposed rapidly during the multiplet belonging to the Fmoc benzylic hydrogen
chromatography.
atom. The spatial arrangements of the addends were con-
firmed by characteristic substituent-independent UV/Vis
spectra (Figure 6). The results obtained are in agreement
with previous studies.[13]
Figure 4. Distribution of bis-adducts based on the yields of isolated
compounds.
Determination of the Bis-Adduct Structures
The ES-MS spectra of all the isolated regioisomers 13a–
e gave a molecular ion peak of m/z = 1200 corresponding
to the desired bis-adducts. Also, each compound of class 15
gave the molecular ion peak expected for the corresponding
bis-adduct (m/z = 1036). The characteristic structure of the
pyrrolidine signals resulted from the chemical and magnetic
nonequivalence of the corresponding protons and is clearly
1
observed in the H NMR spectra of the NHBoc/CO2Me-
protected fullero-amino acids 15a–e. The two singlets at δ
= 4.77 and 4.73 ppm observed in the spectrum of 15a are
consistent with a D2h symmetry of the trans1 isomer (Fig-
ure 5, a). The diastereotopic methylene hydrogen atoms of
the pyrrolidinic rings in other trans isomers showed pairs of
AB quartets (mainly overlapped, see parts b–d in Figure 5).
Equatorially oriented pyrrolidinic rings in compound 15e
gave pairs of singlets (2ϫCH2) and one AB quartet (two
remaining CH2 groups, Figure 5, e).
Figure 6. Part of the UV/Vis spectra of the bis-adducts 13a–e and
15a–e.
Both classes of compounds showed almost identical ab-
sorption behavior in the visible range (see Exp. Sect.).
Conclusions
We have described the synthesis and characterization of
two classes of unsymmetrical fulleropyrrolidine bis-adducts
containing orthogonally protected terminal amino and car-
boxy groups. The new compounds represent a model system
for fullerene-based peptidomimetics with the carbon sphere
inserted into the peptide backbone. As a result of the spatial
proximity of the cis addends and consequent possible micel-
lar aggregation, we were mainly interested in the isolation,
characterization, and distribution of equatorial and trans
isomers. Considering the requirements of peptide synthesis
(orthogonally protected amino and carboxylic groups) and
C60 reactivity (sensitivity to catalytic hydrogenation),
NHFmoc/CO2tBu and NHBoc/CO2Me fulleropyrrolidine
couples were designed as model compounds. The two target
classes of compounds were prepared by two successive
[3+2] cycloadditions of azomethyne ylides (thermally gener-
ated from formaldehyde and the corresponding orthogo-
nally protected glycino-amines and -acids) to C60. All com-
1
pounds were characterized by UV/Vis, H and 13C NMR
spectroscopy, and mass spectrometry. Because a low yield
of the Fmoc-protected amino-fulleropyrrolidine (com-
pound 7) was obtained, the formation of a fulleropyrrolid-
Figure 5. Pyrrolidinic signals in the 1H NMR spectra of the bis-
adducts 15a–e (NHBoc/CO2Me).
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479

D. Milic, M. Prato
FULL PAPER
overnight at –20 °C a white precipitate was obtained. Filtering and
washing with DCM until a colorless filtrate was obtained gave the
product 4 (10.36 g, 88%) as a white amorphous solid. 1H NMR
(200 MHz, [D6]DMSO): δ = 9.31 (s, 2 H), 7.89 (d, J = 7.0 Hz, 2
H), 7.67 (d, J = 7.0 Hz, 2 H), 7.52–7.15 (m, 4 H), 5.76 (s, 1 H),
4.40–4.26 (m, 2 H), 4.26–4.17 (m, 1 H), 3.88 (s, 2 H), 3.42–3.22 (m,
2 H), 3.08–2.90 (m, 2 H), 1.25 (s, 9 H) ppm. 13C NMR (50 MHz,
[D6]DMSO): δ = 165.61, 156.20, 143.73, 140.68, 127.59, 127.04,
125.11, 120.12, 83.00, 68.23, 47.25, 46.64, 46.38, 36.61, 27.66 ppm.
ine ester and subsequent introduction of the NHFmoc ad-
dend was found to be a better way to prepare the NHFmoc/
CO2tBu bis-adduct In both classes of bis-adducts, the same
relative polarity (eluting order) was observed by flash
chromatography. The product distribution, based on the
yield of the isolated compounds, was also found to be quite
similar. Different yields of the t3 isomers resulted from ra-
pid decomposition of the NHBoc/CO2Me structure (com-
pound 15c) on a silica column.
IR (DRIFT, KBr): ν = 2970, 2850, 1735, 1640, 1440, 1295,
˜
1162 cm–1. MS (EI): m/z = 397 [M – iBuH]+, 341 [M]+.
tert-Butyl N-(2-{[(9H-Fluoren-9-ylmethoxy)carbonyl]amino}ethyl)-
glycinate (5): A solution of the salt 4 (10.36 g, 24.0 mmol) in chlo-
roform (500 mL) was washed with a satd. solution of NaHCO3
(3ϫ150 mL), dried with anhydrous CaCl2, filtered, and the sol-
vents evaporated to dryness. The product 5 (9.48 g, quantitative)
Experimental Section
Abbreviations: BBA – benzyl bromoacetate, DCM – dichlorometh-
ane, DIPEA – diisopropylethylamine, TBBA – tert-butyl bromo-
acetate, TEA – triethylamine, TFA – trifluoroacetic acid, pyrr –
pyrrolydinic, Fp – fulleropyrrolidine.
1
was obtained as a colorless oil. H NMR (200 MHz, CDCl3): δ =
7.79 (d, J = 7.0 Hz, 2 H), 7.64 (d, J = 7.0 Hz, 2 H), 7.50–7.30 (m,
4 H), 5.48–5.32 (br. s, 1 H), 4.42 (d, J = 6.8 Hz, 2 H), 4.25 (t, J =
6.8 Hz, 1 H), 3.42–3.18 (m, 4 H), 2.79 (t, J = 5.4 Hz, 2 H), 1.50 (s,
9 H) ppm. 13C NMR (50 MHz, CDCl3): δ = 171.65, 156.38, 143.88,
141.15, 127.51, 126.90, 124.98, 119.82, 81.31, 66.54, 51.18, 48.56,
General: FTIR spectra were recorded with a Jasco spectrophotome-
ter FT/IR-200 using NaCl cells (for oils) or KBr powder (DRIFT
system). UV spectra were recorded with a Perkin–Elmer Lambda
20 spectrophotometer. 1H and 13C NMR spectra were recorded
with a Varian Gemini-200 spectrometer at 200 and 50 MHz, respec-
tively, using TMS as the internal standard. Chemical shifts are
given in parts per million (ppm) relative to that of tetramethylsil-
ane. Mass spectra were recorded with a 7070H VG Microsomass
(EI-MS) and PE SCIEX API 1 (ES-MS) spectrometers and com-
pounds were dissolved in methanol unless otherwise noted. Yields
of the azomethine ylide cycloaddition reactions are reported as ab-
solute values without taking into account the recovery of the start-
ing fullerene (30–40%). C60 was purchased from Bucky, USA
(99.5%) and all other reagents and solvents were used as purchased
from Fluka, Aldrich, J. T. Baker, and Cambridge Isotope Laborato-
ries. The silica gel NM Kieselgel 60 (0.063–0.200 mm and 0.015–
0.04 mm) used in column chromatography was obtained from Ma-
cherey–Nagel. The HPLC analysis was conducted with a Waters
instrument with a direct phase Phenomenex Prodigy 5 µ silica
100 Å column.
47.22, 40.67, 28.08 ppm. IR (DRIFT, KBr): ν = 3521, 3443, 2909,
˜
1738, 1640, 1443, 1290, 1158 cm–1. MS (EI): m/z = 397 [MH –
iBuH]+, 341 [MH]+.
N-(2-{[(9H-Fluoren-9-ylmethoxy)carbonyl]amino}ethyl)glycine (6):
TFA (88 mL, 1.14 mol) was added to a stirred, ice-bath cooled
solution of ester 5 (8.94 g, 22.6 mmol) in DCM (55 mL),. After
20 min a solution was warmed to room temperature and stirring
was continued for an additional 5 h. The reaction mixture was
evaporated to dryness and TFA was completely removed by co-
evaporation with toluene. Crystallization from MeOH/Et2O gave
the acid 6 (5.16 g, 67%) as a white solid. M.p. 154–156 °C (MeOH/
1
Et2O). H NMR (200 MHz, [D6]DMSO): δ = 7.89 (d, J = 7.2 Hz,
2 H), 7.69 (d, J = 7.0 Hz, 2 H), 7.61–7.45 (m, 1 H), 7.45–7.20 (m,
3 H), 4.35 (d, J = 6.4 Hz, 2 H), 4.26–4.18 (m, 1 H), 3.89 (s, 2 H),
3.31 (d, J = 5.0 Hz, 2 H), 3.12–2.95 (m, 2 H) ppm. 13C NMR
(50 MHz, [D6]DMSO): δ = 168.10, 156.33, 143.80, 140.76, 127.66,
127.10, 125.12, 120.17, 65.68, 47.22, 46.74, 46.48, 36.76 ppm. IR
Synthetic Procedures
(DRIFT, KBr): ν = 3303, 3004, 2806, 1694, 1540, 1269, 1145 cm–1.
˜
tert-Butyl N-(2-Aminoethyl)glycinate (3): A solution of TBBA (2;
24.80 g, 18.8 mL, 0.13 mol, 0.11 mol-equiv.) in DCM (105 mL) was
added dropwise over 5 h to a vigorously stirred solution of eth-
anediamine (1, 67.28 g, 75.0 mL, 1.12 mol) in DCM (525 mL)
cooled in an ice bath. The reaction mixture was stirred at room
temperature for 24 h, washed with water (3ϫ120 mL), and aque-
ous wash-back-extracted with DCM (120 mL). The combined or-
ganic extracts were dried with anhydrous Na2SO4, filtered, and the
solvents evaporated to dryness to leave the product 3 (15.68 g,
MS (ES; MeOH): m/z = 364 [MH + Na]+, 341 [MH]+.
Fmoc-Protected Fulleroamine 7: A solution of amino acid 6
(283 mg, 0.83 mmol) and pyridine (134 µL, 1.66 mmol, 2 mol-
equiv.) in MeOH (2 mL) was stirred at room temperature for
15 min and then added to a suspension of C60 (600 mg, 0.83 mmol)
and paraformaldehyde (125 mg, 4.15 mmol, 5 mol-equiv.) in tolu-
ene (600 mL). The reaction mixture was heated at reflux over 1.5 h
and the solvents evaporated to dryness. The residue was subjected
to silica column chromatography using toluene and PhMe/EtOAc
(97:3) as eluents (unreacted C60 and the product 7, respectively).
Precipitation with Et2O from a highly concentrated DCM solution
and drying under vacuum afforded Fmoc-protected fulleropyrrol-
idine 7 (998 mg, 9%) as a brown solid. 1H NMR (200 MHz,
1
70%) as a pale-yellow oil. H NMR (200 MHz, CDCl3): δ = 3.21
(s, 2 H), 2.76–2.64 (m, 2 H), 2.64–2.52 (m, 2 H), 1.38 (s, 9 H) ppm.
13C NMR (50 MHz, CDCl3): δ = 171.25, 80.43, 51.72, 51.10, 41.32,
27.63 ppm. IR (DRIFT, NaCl): ν = 3316, 2969, 1734, 1223,
˜
1156 cm–1. MS (EI): m/z = 175 [MH – iBuH]+, 119 [MH]+.
tert-Butyl N-(2-{[(9H-Fluoren-9-ylmethoxy)carbonyl]amino}ethyl)- CDCl3): δ = 7.78 (d, J = 8.0 Hz, 2 H), 7.68 (d, J = 6.0 Hz, 2 H),
glycinate Hydrochloride (4): A solution of Fmoc succinimide
(9.21 g, 27.3 mmol, 0.95 mol-equiv.) in DCM (50 mL) was added
dropwise over 3 h to a stirred solution of amino ester 3 (5.00 g,
28.7 mmol) and DIPEA (3.53 g, 4.7 mL, 27.3 mmol, 0.95 mol-
equiv.) in DCM (200 mL), and stirring was continued at room tem-
perature for 20 h. The reaction mixture was washed with 1  HCl
(5ϫ35 mL) and brine (35 mL), dried with anhydrous Na2SO4, fil-
tered, and concentrated in vacuo to approx. 80 mL. After cooling
7.33–7.29 (m, 4 H), 5.74–5.54 (br. s, 1 H), 4.60–4.43 (m, 2 H), 4.50
(s, 4 H), 4.34 (d, J = 6.0 Hz, 1 H), 3.89–3.71 (m, 2 H), 3.40–3.24
(m, 2 H) ppm. 13C NMR (50 MHz, CDCl3): δ = 154.61, 147.25,
146.19, 146.02, 145.90, 145.59, 145.36, 145.23, 144.48, 143.89,
143.03, 142.58, 142.143, 142.00, 141.83, 141.29, 140.12, 136.09,
127.67, 127.03, 125.03, 119.97, 70.60, 67.60, 66.81, 65.86, 53.62,
47.37 ppm. IR (DRIFT, KBr): ν = 3420, 3004, 2950, 2788, 1720,
˜
1540, 1150 cm–1. MS (ES; MeOH/THF): m/z = 1030 [M – PhH]+,
480
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Fullerene Bis-Adducts as Models for Novel Peptidomimetics
952 [MH]+. UV/Vis (THF): λ = 242 (ε = 82000), 260 (103000), 300
(150 mg, 5 mmol), and C60 (720 mg, 1 mmol) in toluene (500 mL)
was heated at reflux for 45 min, evaporated to dryness and purified
by chromatography a on silica column. Unreacted C60 was eluted
with toluene, whereas elution with PhMe/EtOAc (95:5) gave Fp
esters 12a and 12b, further purified by precipitation with Et2O from
DCM solution.
(35000), 320 (32000), 435 (3500), 704 nm (990 dm3 mol–1 cm–1).
1-Benzyl 6-tert-Butyl 3-Azahexanedioate (10a): TEA (11.10 g,
110 mmol, 2 mol-equiv., 15.2 mL) was added to a suspension of
β-alanine tert-butyl ester hydrochloride 9a (10.00 g, 55 mmol) in
dioxane (400 mL) and the reaction mixture was stirred at room
temperature for 15 min. The suspension was then cooled in an ice
bath and a solution of BBA (10.10 g, 44 mmol, 0.8 mol-equiv.,
7.0 mL) in dioxane (100 mL) was added dropwise and the mixture
stirred at room temperature for a further 24 h. After evaporation
to dryness, the residue was diluted with water, extracted with
EtOAc, dried with anhydrous Na2SO4, filtered, evaporated to dry-
ness, and subjected to silica column flash chromatography. Elution
with EtOAc gave the product 10a (9.48 g, 73%) as a colorless oil,
pure enough to be used in the next step. 1H NMR (200 MHz,
CDCl3): δ = 7.36 (s, 5 H), 5.18 (s, 2 H), 3.45 (s, 2 H), 2.86 (t, J =
8.0 Hz, 2 H), 2.43 (t, J = 8.0 Hz, 2 H), 2.04 (br. s, 1 H), 1.46 (s, 9
H) ppm. 13C NMR (50 MHz, CDCl3): δ = 171.97, 171.62, 135.48,
128.49, 128.26, 80.57, 66.50, 50.85, 44.92, 35.93, 28.09 ppm. IR
1
Fp tert-Butyl Ester 12a: Yield 400 mg (45%). H NMR (200 MHz,
CDCl3 + CS2): δ = 4.43 (s, 4 H), 3.39 (t, J = 7.0 Hz, 2 H), 2.86 (t,
J = 7.0 Hz, 2 H), 1.54 (s, 9 H) ppm. 13C NMR (50 MHz, CDCl3
+ CS2): δ = 171.22, 154.68, 147.12, 146.07, 145.85, 145.51, 145.25,
145.10, 144.37, 142.92, 142.45, 142.01, 141.90, 141.71, 139.99,
136.10, 80.65, 70.46, 67.62, 50.25, 35.40, 28.17 ppm. IR (DRIFT,
KBr): ν = 3423, 2791, 1719, 1243, 1116 cm–1. MS (ES; THF): m/z
˜
= 892 [MH/2]+, 446 [MH]+. UV/Vis (THF): λ = 317 (ε = 38000),
433 (4200), 704 nm (890 dm3 mol–1 cm–1).
Fp Methyl Ester 12b: Yield 310 mg (37%). 1H NMR (200 MHz,
CDCl3 + CS2): δ = 4.45 (s, 4 H), 3.83 (s, 3 H), 3.43 (t, J = 7.2 Hz,
2 H), 2.98 (t, J = 7.2 Hz, 2 H) ppm. 13C NMR (50 MHz, CDCl3
+ CS2): δ = 172.52 (CO), 154.77, 146.20, 146.01, 145.38, 144.51,
142.59, 142.17, 141.83, 140.12, 136.16, 70.57, 67.72, 51.05, 49.99,
(DRIFT, NaCl): ν = 3341, 2973, 2929, 1732, 1253, 1155 cm–1. MS
˜
(ES; MeOH): m/z = 317 [MH + Na]+, 294 [MH]+.
34.04 ppm. IR (DRIFT, KBr): ν = 3433, 2790, 1722, 1245,
˜
1115 cm–1. MS (ES; THF): m/z = 850 [MH/2]+, 425 [MH]+. UV/
1-Benzyl 6-Methyl 3-Azahexanedioate (10b): TEA (14.46 g,
144 mmol, 2 mol-equiv., 19.8 mL) was added to a suspension of β-
alanine methyl ester hydrochloride 9b (10.00 g, 72 mmol) in diox-
ane (500 mL) and the reaction mixture was stirred at room tem-
perature for 15 min. A suspension was then cooled in an ice bath,
a solution of BBA (11.48 g, 50 mmol, 0.7 mol-equiv., 7.9 mL) in
dioxane (100 mL) was added dropwise, and the mixture was stirred
at room temperature for a further 24 h. After evaporation to dry-
ness, the residue was diluted with water, extracted with EtOAc,
dried with anhydrous Na2SO4, filtered, evaporated to dryness and
subjected to silica column flash chromatography. Elution with
EtOAc gave the product 10b (7.66 g, 61%) as a colorless oil, pure
Vis (THF):
λ = 320 (ε = 50000), 430 (5000), 704 nm
(1100 dm3 mol–1 cm–1).
NHFmoc-CO2tBu-Protected Bis-Adducts 13a–e: A solution of
Fmoc-protected amino-glycinate (0.76 g, 2.24 mmol, 2 mol-
6
equiv.) in pyridine (2 mL) was added to a suspension of Fp tert-
butyl ester 12a (1.00 g, 1.12 mmol) and paraformaldehyde (0.17 g,
5.60 mmol, 5 mol-equiv.) in toluene (1 L) and the reaction mixture
was heated at reflux for 1 h. After washing with water
(3ϫ300 mL), drying with anhydrous Na2SO4, filtering, and evapo-
ration to dryness, the residue was subjected to column chromatog-
raphy on SiO2 (63–200 µm). Unreacted starting mono-Fp (298 mg,
30%) was recovered by elution with PhMe and PhMe/EtOAc
(100:1), evaporation to dryness, and subsequent precipitation from
a highly concentrated DCM solution with hexane. The bis-adducts
were eluted with PhMe/EtOAc (1:1) and separated by dry column
flash chromatography on fine silica (15–40 µm) using the following
PhMe/EtOAc mixtures as eluents: 100:1.5 (trans1), 100:2 (trans2),
100:3 (trans3), 100:3.5 (trans4), and 100:4 (eЈ + eЈЈ). Precipitation
of the separated bis-adducts from a highly concentrated DCM
solution with hexane gave the products 13a–e as brown solids. The
purity of the compounds was checked by HPLC [SiO2, PhMe/
EtOAc (7:3) 1 mL/min, 320 nm].
13a (trans1): Yield 9.2 mg (0.7%). 1H NMR (200 MHz, CDCl3 +
CS2): δ = 7.87–7.60 (m, 4 H), 7.50–7.20 (m, 4 H), 5.81–5.64 (br. s,
1 H), 4.78 (s, 4 H), 4.75 (s, 4 H), 4.50 (d, J = 7.0 Hz, 2 H), 4.40–
4.23 (m, 1 H), 3.97–3.80 (m, 2 H), 3.55 (t, J = 7.2 Hz, 2 H), 3.50–
3.15 (m, 2 H), 2.98 (t, J = 7.2 Hz, 2 H), 1.62 (s, 9 H) ppm. 13C
NMR (50 MHz, CDCl3 + CS2): δ = 171.13, 153.35, 153.09, 146.03,
145.96, 145.86, 145.63, 145.28, 145.00, 144.42, 144.32, 144.04,
143.77, 142.15, 141.63, 141.41, 141.20, 140.59, 136.39, 136.24,
127.58, 126.96, 124.94, 119.86, 80.51, 68.30, 67.82, 67.75, 66.69,
1
enough to be used in the next step. H NMR (200 MHz, CDCl3):
δ = 7.23 (s, 5 H), 5.04 (s, 2 H), 5.55 (s, 3 H), 3.34 (s, 2 H), 2.78 (t,
J = 6.4 Hz, 2 H), 2.38 (t, J = 6.4 Hz, 2 H), 1.92 (s, 1 H) ppm. 13C
NMR (50 MHz, CDCl3): δ = 172.51, 171.79, 135.30, 128.32,
128.09, 66.32, 51.44, 50.58, 44.51, 34.42 ppm. IR (DRIFT, NaCl):
ν = 3031, 2975, 2930, 1735, 1250, 1155 cm–1. MS (ES; MeOH): m/z
˜
= 252 [MH]+.
Hydrogenation of Benzyl Esters 10a,b to 11a,b: The catalyst (5%
Pd/C, 10% w/w) was added to a solution of the benzyl ester
(30 mmol) in MeOH (300 mL) and the suspension was hydroge-
nated at atmospheric pressure for 24 h. Filtration and subsequent
evaporation to dryness gave the corresponding acid as a sticky oil
in quantitative yield.
6-tert-Butyl Hydrogen 3-Azahexanedioate (11a): M.p. 199–201 °C
(MeOH/AcOEt). 1H NMR (200 MHz, D2O): δ = 3.44 (s, 2 H), 3.12
(t, J = 6.6 Hz, 2 H), 2.58 (t, J = 6.6 Hz, 2 H), 1.28 (s, 9 H) ppm.
13C NMR (50 MHz, D2O): δ = 173.20, 172.79, 85.56, 51.20, 44.82,
33.32, 29.03 ppm. IR (DRIFT, KBr): ν = 3434, 3069, 2977, 2419,
˜
1729, 1604, 1389, 1160 cm–1. MS (ES; MeOH): m/z = 227 [MH +
Na]+, 204 [MH]+.
53.72, 50.34, 47.39, 35.57, 28.17 ppm. IR (DRIFT, KBr): ν = 3420,
˜
6-Methyl Hydrogen 3-Azahexanedioate (11b): 1H NMR (200 MHz,
D2O): δ = 3.70 (s, 3 H), 3.61 (s, 2 H), 3.32 (t, J = 6.6 Hz, 2 H),
2.83 (t, J = 6.6 Hz, 2 H) ppm. 13C NMR (50 MHz, D2O): δ =
175.96, 174.09, 55.85, 52.57, 46.06, 33.41 ppm. IR (DRIFT, KBr):
2942, 2784, 1720, 1513, 1461, 1347, 1151, 747, 483, 454 cm–1. MS
[ES; THF/MeOH (1:1)]: m/z = 1200 [MH]+. UV/Vis (THF): λ =
244 (ε = 130000), 263 (135000), 301 (45000), 317 (50000), 458 (900),
491 nm (4000 dm3 mol–1 cm–1).
ν = 3430, 2982, 2420, 1730, 1602, 1395, 1157 cm–1. MS (ES;
˜
1
13b (trans2): Yield 58.3 mg (4.3%). H NMR (200 MHz, CDCl3 +
MeOH): m/z = 185 [MH + Na]+, 162 [MH]+.
CS2): δ = 7.82–7.60 (m, 4 H), 7.50–7.20 (m, 4 H), 5.80–5.67 (br. s,
1 H), 4.80–4.20 (m, 11 H), 3.90–3.70 (m, 2 H), 3.44 (t, J = 7.2 Hz,
2 H), 3.38–3.26 (m, 2 H), 2.93 (t, J = 7.2 Hz, 2 H), 1.60 (s, 9
Synthesis of the Fulleropyrrolidines 12: A suspension of amino acid
11 (1 mmol; 200 mg of 11a or 160 mg of 11b), paraformaldehyde
Eur. J. Org. Chem. 2010, 476–483
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
481

D. Milic, M. Prato
FULL PAPER
H) ppm. 13C NMR (50 MHz, CDCl3 + CS2): δ = 171.40, 158.76,
158.53, 156.39, 153.14, 153.00, 152.90, 152.71, 152.36, 152.13,
148.30, 147.60, 146.91, 146.31, 146.11, 145.96, 145.56, 145.06,
144.09, 143.82, 143.69, 143.54, 142.42, 142.28, 141.20, 139.50,
134.44, 133.85, 133.78, 127.61, 127.00, 125.01, 119.91, 80.73, 69.16,
at reflux for 1.5 h, evaporated to dryness, and purified by
chromatography on SiO2 (63–200 µm). Unreacted starting mono-
Fp (243 mg, 28%) was isolated by elution with PhMe/EtOAc
(100:1) and subsequent precipitation with hexane from highly con-
centrated DCM solution. The second fraction containing all the
68.99, 67.71, 67.59, 67.42, 66.75, 53.54, 50.28, 47.32, 35.49, bis-adducts was obtained by elution with PhMe/EtOAc (1:1) and
28.22 ppm. IR (DRIFT, KBr): ν = 3420, 2942, 2784, 1720, 1513,
repurified by chromatography by DC-FC on fine SiO2 (15–40 µm)
using the following PhMe/EtOAc mixtures as eluents: 100:2
(trans1), 100:3 (trans2), 100:4 (trans3), 100:5 (trans4), and 100:6 (eЈ
+ eЈЈ). Precipitation of the separated bis-adducts from a highly con-
centrated DCM solution with hexane gave the products 15a–e as
brown solids. The purity of the compounds was checked by HPLC
(SiO2, PhMe, 320 nm).
˜
1461, 1347, 1151, 747, 483, 454 cm–1. MS [ES; THF/MeOH (1:1]:
m/z = 1200 [MH]+. UV/Vis (THF): λ = 248 (ε = 131000), 263
(118000), 300 (63000), 429 (4900), 476 (4900), 625 (600), 654 (620),
689 (450), 723 nm (1300 dm3 mol–1 cm–1).
1
13c (trans3): Yield 85.2 mg (6.3%). H NMR (200 MHz, CDCl3 +
CS2): δ = 7.77 (d, J = 7.0 Hz, 2 H), 7.64 (d, J = 7.0 Hz, 2 H), 7.47–
7.18 (m, 4 H), 5.65–5.53 (br. s, 1 H), 4.55–4.00 (m, 11 H), 3.80–
3.63 (m, 2 H), 3.34 (t, J = 7.2 Hz, 2 H), 3.28–3.13 (m, 2 H), 2.83
1
15a (trans1): Yield 10.6 mg (1.0%) H NMR (200 MHz, CDCl3 +
CS2): δ = 5.50–5.30 (br. s, 1 H), 4.74 (s, 4 H), 4.73 (s, 4 H), 3.88 (s,
(t, J = 7.2 Hz, 2 H), 1.53 (s, 9 H) ppm. 13C NMR (50 MHz, CDCl3 3 H), 3.79 (br. q, J = 5.8 Hz, 2 H), 3.60 (t, J = 7.2 Hz, 2 H), 3.39
+ CS2): δ = 171.46, 158.13, 157.55, 156.46, 155.52, 155.31, 154.86,
154.60, 149.01, 148.92, 148.65, 148.74, 148.13, 146.58, 146.50,
145.24, 145.11, 144.86, 144.72, 144.53, 143.86, 143.55, 142.48,
141.60, 141.38, 141.24, 141.01, 139.69, 136.39, 136.31, 135.56,
135.37, 134.48, 131.34, 130.51, 128.81, 128.53, 128.38, 128.15,
(t, J = 5.8 Hz, 2 H), 3.08 (t, J = 7.2 Hz, 2 H), 1.54 (s, 9 H) ppm.
13C NMR (50 MHz, CDCl3 + CS2): δ = 172.67, 153.43, 153.43,
147.60, 146.08, 145.39, 144.16, 142.26, 140.69, 136.41, 79.44, 68.48,
67.96, 67.89, 54.26, 51.98, 50.08, 34.20, 28.57 ppm. IR (DRIFT,
KBr): ν = 3433, 3333, 2967, 1722, 1692, 1520, 1255, 1170,
˜
127.95, 127.83, 127.64, 127.01, 125.03, 119.94, 80.84, 70.31, 70.22, 1115 cm–1. MS [ES; THF/MeOH (1:1)]: m/z = 1036 [MH]+. UV/
69.84, 69.59, 67.61, 66.78, 53.51, 50.24, 47.32, 35.90, 28.24 ppm.
Vis (THF): λ = 285 (ε = 95000), 308 (50000), 320 (56000), 458
IR (DRIFT, KBr): ν = 3420, 2942, 2784, 1720, 1513, 1461, 1347,
(1100), 492 nm (4200 dm3 mol–1 cm–1).
˜
1151, 747, 483, 454 cm–1. MS [ES; THF/MeOH (1:1)]: m/z = 1200
[MH]+. UV/Vis (THF): λ = 285 (ε = 63000), 413 (5000), 465 (2700),
702 (270), 743 nm (140 dm3 mol–1 cm–1).
1
15b (trans2): Yield 34.1 mg (3.2%). H NMR (200 MHz, CDCl3 +
CS2): δ = 5.50–5.25 (br. s, 1 H), 4.70, 4.41 (ABq, J = 9 Hz, 4 H),
4.52, 4.37 (ABq, J = 9 Hz, 4 H), 3.87 (s, 3 H), 3.74 (br. q, J =
6.0 Hz, 2 H), 3.52 (t, J = 7.2 Hz, 2 H), 3.31 (t, J = 6.0 Hz, 2 H),
1
13d (trans4): Yield 23.5 mg (1.7%). H NMR (200 MHz, CDCl3 +
CS2): δ = 7.78 (d, J = 7.0 Hz, 2 H), 7.64 (d, J = 7.0 Hz, 2 H), 7.50– 3.04 (t, J = 7.2 Hz, 2 H), 1.55 (s, 9 H) ppm. 13C NMR (50 MHz,
7.25 (m, 4 H), 5.60–5.50 (br. s, 1 H, NH), 4.55–3.95 (m, 11 H), CDCl3 + CS2): δ = 172.62, 158.74, 156.02, 153.12, 153.05, 152.94,
3.75–3.60 (m, 2 H), 3.28 (t, J = 7.2 Hz, 2 H), 3.22–3.07 (m, 2 H),
2.79 (t, J = 7.2 Hz, 2 H), 1.55 (s, 9 H) ppm. 13C NMR (50 MHz,
CDCl3 + CS2): δ = 171.46, 154.52, 152.53, 151.33, 150.38, 148.21,
147.53, 146.02, 145.44, 144.90, 144.53, 143.83, 142.55, 142.02,
152.84, 152.34, 152.24, 148.33, 148.30, 147.63, 147.60, 147.02,
146.97, 146.36, 146.19, 146.17, 146.01, 145.59, 145.53, 145.26,
145.10, 144.14, 143.74, 143.61, 143.59, 142.51, 142.48, 142.41,
142.33, 141.47, 141.40, 139.53, 134.45, 133.70, 79.55, 69.27, 69.09,
141.66, 141.22, 127.64, 127.02, 125.06, 119.94, 80.70, 69.31, 69.06, 67.75, 67.72, 67.59, 54.21, 51.99, 50.02, 34.05, 28.55 ppm. IR
67.96, 67.08, 66.88, 66.77, 53.70, 50.22, 47.31, 35.39, 28.24 ppm.
(DRIFT, KBr): ν = 3433, 3333, 2967, 1722, 1692, 1520, 1255, 1170,
˜
IR (DRIFT, KBr): ν = 3420, 2942, 2784, 1720, 1513, 1461, 1347,
1115 cm–1. MS [ES; THF/MeOH (1:1)]: m/z = 1036 [MH]+. UV/
Vis (THF): λ = 272 (ε = 50000), 285 (120000), 311 (58000), 431
(5200), 476 (5400), 624 (800), 660 (930), 689 (750), 721 nm
(1000 dm3 mol–1 cm–1).
˜
1151, 747, 483, 454 cm–1. MS [ES; THF/MeOH (1:1)]: m/z = 1200
[MH]+. UV/Vis (THF): λ = 242 (ε = 130000), 266 (116000), 300
(62000), 411 (1100), 449 (700), 642 (180), 709 nm
(130 dm3 mol–1 cm–1).
1
15c (trans3): Yield 38.3 mg (3.6%). H NMR (200 MHz, CDCl3 +
13e (equatorials): Yield 31.1 mg (2.3%). 1H NMR (200 MHz, CS2): δ = 5.40–5.15 (br. s, 1 H), 4.47, 4.38 (ABq, J = 9 Hz, 4 H),
CDCl3 + CS2): δ = 7.87–7.52 (m, 8 H), 7.50–7.18 (m, 8 H), 5.61– 4.22, 4.12 (ABq, J = 9 Hz, 4 H), 3.82 (s, 3 H), 3.67 (br. q, J =
5.40 (br. s, 2 H), 4.60–4.37 (m, 4 H), 4.17–3.83 (m, 18 H), 3.72–
3.55 (m, 4 H), 3.20 (t, J = 7.2 Hz, 4 H), 3.17–3.00 (m, 4 H), 2.73
(t, J = 7.2 Hz, 4 H), 1.53 (s, 9 H), 1.50 (s, 9 H) ppm. 13C NMR
(50 MHz, CDCl3 + CS2): δ = 171.30, 158.89, 158.64, 156.32,
153.40, 152.86, 152.66, 149.65, 148.77, 147.93, 147.63, 147.10,
146.59, 146.52, 145.63, 145.07, 144.88, 144.53, 144.26, 143.79,
143.61, 143.05, 142.15, 141.77, 141.62, 141.51, 141.34, 141.24,
140.55, 139.04, 136.64, 135.51, 135.48, 127.67, 127.59, 127.02,
5.0 Hz, 2 H), 3.39 (t, J = 7.0 Hz, 2 H), 3.18 (br. t, J = 5.0 Hz, 2
H), 2.94 (t, J = 7.0 Hz, 2 H), 1.51 (s, 9 H) ppm. 13C NMR
(50 MHz, CDCl3 + CS2): δ = 172.47, 158.01, 155.87, 155.43,
155.37, 155.30, 154.71, 154.63, 148.98, 148.90, 148.78, 148.67,
148.14, 148.10, 146.52, 146.48, 145.20, 145.06, 144.77, 144.72,
144.50, 143.85, 143.51, 142.44, 141.51, 141.35, 141.16, 140.93,
139.68, 139.65, 137.50, 136.32, 135.46, 135.44, 128.47, 126.88,
79.42, 69.81, 69.57, 67.73, 67.66, 66.84, 54.13, 51.87, 49.92, 33.92,
126.97, 124.96, 119.97, 119.88, 80.65, 69.65, 69.43, 69.29, 67.52, 28.48 ppm. IR (DRIFT, KBr): ν = 3433, 3333, 2967, 1722, 1692,
˜
67.23, 66.97, 66.72, 66.49, 53.70, 53.29, 50.21, 50.06, 47.28, 39.44,
1520, 1255, 1170, 1115 cm–1. MS [ES; THF/MeOH (1:1)]: m/z =
1036 [MH]+. UV/Vis (THF): λ = 260 (ε = 52000), 274 (75000), 285
(110000), 320 (70000), 417 (6000), 467 (3500), 702 (450), 742 nm
(220 dm3 mol–1 cm–1).
35.29, 28.18 ppm. IR (DRIFT, KBr): ν = 3420, 2942, 2784, 1720,
˜
1513, 1461, 1347, 1151, 747, 483, 454 cm–1. MS [ES; THF/MeOH
(1:1)]: m/z = 1200 [MH]+. UV/Vis (THF): λ = 242 (ε = 102000),
253 (96000), 301 (44000), 316 (44000), 395 (7400), 423 nm
(6800 dm3 mol–1 cm–1).
1
15d (trans4): Yield 17.0 mg (1.6%). H NMR (200 MHz, CDCl3 +
CS2): δ = 5.35–5.10 (br. s, 1 H), 4.50–4.00 (m, 8 H), 3.82 (s, 3 H),
3.62 (q, J = 7.5 Hz, 2 H), 3.36 (t, J = 8.0 Hz, 2 H), 3.14 (t, J =
7.5 Hz, 2 H), 2.90 (t, J = 8.0 Hz, 2 H), 1.56 (s, 9 H) ppm. 13C
NMR (50 MHz, CDCl3 + CS2): δ = 172.60, 158.50, 152.64, 151.40,
150.72, 148.25, 147.50, 146.05, 145.44, 144.88, 144.61, 142.57,
NHBoc-CO2Me-Protected Bis-Adducts 15a–e: A suspension of the
Fp methyl ester 12b (874 mg, 1.03 mmol), paraformaldehyde
(155 mg, 5.15 mmol, 5 mol-equiv.), and Boc-protected amino-gly-
cinate 14[12] (225 mg, 1.03 mmol) in toluene (500 mL) was heated
482
www.eurjoc.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 476–483

Fullerene Bis-Adducts as Models for Novel Peptidomimetics
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142.17, 141.75, 141.40, 141.22, 138.58, 136.10, 135.40, 131.32,
79.48, 69.75, 69.48, 67.70, 67.58, 67.20, 54.18, 51.95, 50.04, 34.09,
28.54 ppm. IR (DRIFT, KBr): ν = 3433, 3333, 2967, 1722, 1692,
˜
1520, 1255, 1170, 1115 cm–1. MS [ES; THF/MeOH (1:1)]: m/z =
1036 [MH]+. UV/Vis (THF): λ = 220 (ε = 60000), 267 (87000), 286
(120000), 308 (94000), 414 (2000), 453 (1100), 640 (270), 705 nm
(550 dm3 mol–1 cm–1).
15e (equatorials): Yield 27.7 mg (2.6%). 1H NMR (200 MHz,
CDCl3 + CS2): δ = 5.30–5.10 (br. s, 1 H, NH), 4.13, 3.95 (ABq, J
= 9 Hz, 4 H, pyrr), 4.10 (s, 2 H), 3.96 (s, 2 H), 3.79 (s, 3 H), 3.78
(s, 3 H), 3.56 (br. q, J = 7.0 Hz, 4 H), 3.26 (t, J = 8.0 Hz, 4 H),
3.07 (br. t, J = 7.5 Hz, 4 H), 2.85 (t, J = 8.0 Hz, 4 H), 1.52 (s, 9
H), 1.48 (s, 9 H) ppm. 13C NMR (50 MHz, CDCl3 + CS2): δ =
172.50, 158.80, 158.55, 156.55, 153.30, 152.82, 149.77, 148.82,
147.90, 147.50, 147.26, 146.65, 146.50, 145.67, 145.11, 144.92,
144.57, 144.30, 143.62, 143.10, 142.15, 141.72, 141.59, 141.47,
141.20, 139.12, 136.68, 135.52, 80.65, 69.65, 69.62, 69.43, 69.29,
67.52, 67.23, 66.97, 66.72, 66.49, 54.10, 53.89, 51.99, 51.75, 50.25,
50.11, 34.10, 33.90, 28.18 ppm. IR (DRIFT, KBr): ν = 3433, 3333,
˜
2967, 1722, 1692, 1520, 1255, 1170, 1115 cm–1. MS [ES; THF/
MeOH (1:1)]: m/z = 1036 [MH]+. UV/Vis (THF): λ = 231 (ε =
50000), 257 (62000), 285 (123000), 318 (63000), 423 nm
(4800 dm3 mol–1 cm–1).
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Acknowledgments
This work was supported by the University of Trieste, the Italian
Ministry of Education (MIUR) and the Serbian Ministry of Sci-
ence (grant no. 142049).
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Received: July 15, 2009
Published Online: December 3, 2009
Eur. J. Org. Chem. 2010, 476–483
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