N-ortho-Ferrocenyl benzoyl dipeptide esters: Synthesis, structural characterization and in vitro anti-cancer activity of N-{ortho-(ferrocenyl)benzoyl}-glycine-l-alanine ethyl ester and N-{ortho-(ferrocenyl)benzoyl}-l-alanine-glycine ethyl ester

Article abstract of DOI:10.1016/j.jorganchem.2006.10.018

N-ortho-ferrocenyl benzoyl dipeptide esters 2-6 were prepared by coupling ortho-ferrocenyl benzoic acid 1 to the dipeptide ethyl esters GlyGly(OEt) (2), GlyAla(OEt) (3), GlyPhe(OEt) (4), AlaGly(OEt) (5) and AlaPhe(OEt) (6). The compounds were fully characterized by a range of NMR spectroscopic techniques, mass spectrometry and cyclic voltammetry. The cytotoxicity of 3 and 5 towards lung cancer cells has been determined.

Full text of DOI:10.1016/j.jorganchem.2006.10.018

Journal of Organometallic Chemistry 692 (2007) 1405–1410
www.elsevier.com/locate/jorganchem
Note
N-ortho-Ferrocenyl benzoyl dipeptide esters: Synthesis, structural
characterization and in vitro anti-cancer activity of
N-{ortho-(ferrocenyl)benzoyl}-glycine-L-alanine ethyl ester and
N-{ortho-(ferrocenyl)benzoyl}-L-alanine-glycine ethyl ester
a
b
Alan J. Corry , Alok Goel a,b, Steven R. Alley a,b, Paula N. Kelly a,b, Dermot O’Sullivan ,
a
a,b,
*
David Savage , Peter T.M. Kenny
a
School of Chemical Sciences, Dublin City University, Dublin 9, Ireland
National Institute for Cellular Biotechnology, Dublin City University, Dublin 9, Ireland
b
Received 31 August 2006; received in revised form 11 October 2006; accepted 11 October 2006
Available online 18 October 2006
Abstract
N-ortho-ferrocenyl benzoyl dipeptide esters 2–6 were prepared by coupling ortho-ferrocenyl benzoic acid 1 to the dipeptide ethyl esters
GlyGly(OEt) (2), GlyAla(OEt) (3), GlyPhe(OEt) (4), AlaGly(OEt) (5) and AlaPhe(OEt) (6). The compounds were fully characterized by
a range of NMR spectroscopic techniques, mass spectrometry and cyclic voltammetry. The cytotoxicity of 3 and 5 towards lung cancer
cells has been determined.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Ferrocene; Bioorganometallic chemistry; Dipeptides; Cytotoxicity; Lung cancer
1. Introduction
thesis and structural characterization of N-ferrocenoyl
and N-ferrocenyl amino acid and peptide derivatives have
been previously reported [10–27]. Herein, we report the
synthesis and structural characterization of N-ortho-ferr-
ocenyl benzoyl dipeptide esters and in vitro anti-cancer
activity of N-{ortho-(ferrocenyl)benzoyl}-glycine-L-alanine
ethyl ester and N-{ortho-(ferrocenyl)benzoyl}-L-alanine-
glycine ethyl ester. The N-ortho-ferrocenyl dipeptide esters
2–6 consist of three key components: (i) the electroactive
core; (ii) a conjugated linker that lowers the oxidation
potential and (iii) a peptide derivative that can interact with
other biomolecules via secondary interactions, such as
hydrogen bonding. We have previously reported N-para
and N-meta-ferrocenyl benzoyl dipeptide esters [28–30].
The organometallic compound ferrocene is a promising
candidate for biological applications due to its stability,
electrochemical properties, and ease of use [1,2]. Ferrocene
can be conjugated to drugs such as antibiotics, aspirin,
anti-malarials and anti-cancer drugs, such as tamoxifen
[3–6]. Ferricenium salts of the form Fc+Xꢀ (X@CCl3CO2)
have demonstrated anti-tumour activity [7]. The relatively
low reduction potential of these compounds is responsible
for generating reactive oxygenated species (ROS) under
physiological conditions and results in anti-cancer activity
[8,9]. Thus, there is increased interest in the synthesis of fer-
rocene derivatives with low oxidation potentials. The syn-
2. Results and discussion
*
Corresponding author. Address: School of Chemical Sciences, Dublin
City University, Dublin 9, Ireland. Tel.: +353 1 7005689; fax: +353 1
7005503.
ortho-Ferrocenyl benzoic acid 1 was prepared as previ-
ously reported [31]. The dipeptide ethyl ester hydrochloride
E-mail address: peter.kenny@dcu.ie (P.T.M. Kenny).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.10.018

1406
A.J. Corry et al. / Journal of Organometallic Chemistry 692 (2007) 1405–1410
salts of GlyGly, GlyAla, GlyPhe, AlaGly and AlaPhe were
coupled to ortho-ferrocenyl benzoic acid using 1,3-dic-
yclohexylcarbodiimide (DCC) and 1-hydroxybenzotriazole
(HOBt) in the presence of excess triethylamine in dichloro-
methane (Scheme 1). Purification by column chromatogra-
phy gave the desired products in yields of between 25% and
47%, and all compounds gave spectroscopic data in accor-
dance to the proposed structures. The yields for this series
of compounds are lower than those reported for the related
meta and para derivatives [28–30]. This could be attributed
to steric hindrance of the ortho substituent with the unsub-
stituted (g5-C5H5) ring. Also in contrast to the related para
and meta derivatives the compounds are not particularly
stable and decompose over a period of time.
unsubstituted (g5-C5H5) ring appears between d 4.06 and
d 4.21.
For example in the 1H NMR spectrum of 5 (obtained in
DMSO-d6) two amide protons were present at d 8.35 and d
8.18. Both of these signals integrate for one proton each
and appear as a doublet and a triplet; the alanine amide
proton as a doublet at d 8.35 and the glycine amide proton
as a triplet at d 8.18. The signals in the aromatic region
confirm the presence of four protons, which appear
between d 7.24 and d 7.80.
In the ferrocenyl region, the typical mono substituted
ferrocene splitting pattern is observed. The peaks of the
ortho protons on the (g5-C5H4) ring appear as the furthest
downfield ferrocenyl signal. In compound 5, this signal
appears at d 4.58 and the meta (g5-C5H4) protons at
d 4.27. The quintet at 4.41 ppm, which integrates for one
proton, represents the a-proton of the alanine amino acid.
There is a multiplet at d 4.01–4.13 that integrates for seven
protons. This corresponds to the unsubstituted (g5-C5H5)
ring of the ferrocene and the methylene group of the ethyl
ester. The CH2 group of the glycyl moiety is seen at d 3.78–
3.93. The methyl group of the alanine moiety and the
methyl group of the ethyl ester of the dipeptide appear as
a doublet at d 1.25 and as a triplet at d 1.17, respectively.
The N-ortho-ferrocenyl benzoyl dipeptide derivatives
2–6 were characterized by a combination of 1H NMR,
1
13C NMR, DEPT-135 and H-13C COSY (HMQC) spec-
troscopy, mass spectrometry and cyclic voltammetry. The
1H and 13C NMR spectra for compounds 2–6 showed
peaks in the ferrocene region that are typical of a ferrocenyl
benzoyl group [32–34]. The aromatic protons appear from
d 7.15 to d 7.8. The protons in the ortho position of the (g5-
C5H4) ring appear between d 4.52 and d 4.76, the meta
peaks appear between d 4.29 and d 4.46, while the
OC2H5
OC2H5
O
O
i
+
H2N
Fe
Fe
O
ii
OC H
2 5
R
2
NH
NH
R1
O
OH
O
iii
Fe
Fe
2-6
1
Scheme 1. Synthesis of N-{ortho-(ferrocenyl)-benzoyl} dipeptide ethyl esters 2–6, (i) NaNO2, HCl, 5 ꢁC; (ii) NaOH/MeOH; (iii) DCC, HOBt,
triethylamine, dipeptide ethyl ester (GlyGly 2, GlyAla 3, GlyPhe 4, AlaGly 5 and 6 AlaPhe 6).

A.J. Corry et al. / Journal of Organometallic Chemistry 692 (2007) 1405–1410
1407
The 13C spectra of compounds 2–6 show typical mono-
140
o-Fc-Bzl-AlaGly-OEt (5)
o-Fc-Bzl-Gly-OEt
substituted ferrocene peaks between d 68.4 and d 85.6. The
ipso carbon of the (g5-C5H4) ring is present in the narrow
range between d 84.7 and d 85.6. This peak is absent from
the DEPT 135 spectrum. The quaternary carbons and the
methylene carbons of the dipeptide derivatives 2–6 were
identified by the DEPT 135 spectrum.
120
100
80
60
40
20
0
o-Fc-Bzl-GlyAla-OEt (3)
In the 13C NMR spectrum of compound 5, there are
three peaks seen between d 169.7 and d 173.0. These are
due to the three carbonyl groups. Six inequivalent carbons
are present in the aromatic region. This is typical for an
ortho disubstituted benzene group with two different sub-
stituents. The quaternary carbons were identified by
DEPT 135 are seen at d 136.5 and d 136.6 and the four
remaining carbons are at d 125.8, 127.8, 129 and 130.5,
respectively. The peak at d 85 absent from the DEPT
135 spectrum is the ipso ferrocenyl carbon. The carbons
of the unsubstituted (g5-C5H5) ring appear at d 69.8.
The meta carbons of the ferrocenyl group are at d 69.5
and the ortho carbons appear at d 68.4. The methylene
groups can be assigned from the DEPT 135 spectrum.
The methylene of the ester is seen at d 60.8, while the
methylene group of the glycine appears at d 41.1. The
remaining methyl carbons appear at d 18.0 and d 14.4,
respectively.
Both matrix assisted laser desorption ionization
(MALDI) and electrospray ionization (ESI) confirmed
the correct relative molecular mass for all the compounds.
The ESI mass spectra displayed both radical cation and
[M+H]+ species. Sodium and potassium adducts were also
observed 22 Da and 38 Da higher than the protonated
molecular ion species.
In contrast to the corresponding mass spectra of the
meta and para derivatives an important fragment ion at
m/z [M-65]+ is present in all the spectra. This corresponds
to the loss of the unsubstituted (g5-C5H5) ring. The forma-
tion of this ion, which is unique for the N-ortho-ferrocenyl
benzoyl derivatives, is possibly due to steric hindrance
between the ortho substituted benzoyl substituents and
the unsubstituted (g5-C5H5) ring.
The CV curves for compounds 2–6 exhibit quasi-revers-
ible behaviour similar to the Fc/Fc+ redox couple. The Eꢁ
(oxidation potential) values were in 49–52 mV (versus Fc/
Fc+) range. These values are significantly lower than ferr-
ocenoyl dipeptide ester derivatives. For ferrocenoyl-Ala-
Ala-OMe the Eꢁ’ value was reported as 230 mV (versus
Fc/Fc+) [35], while the corresponding value for ferroce-
noyl-Ala-Phe-OMe was reported as 190 mV (versus Fc/
Fc+) [26]. It is explicable in terms of substituent effects.
The benzoyl moiety offers extended conjugation to the pi
electrons of the Cp rings and makes ferrocenyl benzoyl
derivatives 2–6 easier to oxidize.
The cytotoxicity of compounds 3 and 5 were measured
against highly invasive/superinvasive, H1299, lung cancer
cells. Compound 5 showed an IC50 value of 21 lM
(RSD 15%), while compound 3 showed an IC50 value of
5.3 lM (RSD 8%). N-{ortho-(ferrocenyl)-benzoyl}-glycine
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85
Concentration (uM)
Fig. 1. Cytotoxicity of compounds 3 and 5 and the corresponding ortho-
glycine derivative.
ethyl ester was initially tested against the above cell line
and showed an IC50 value of 48 lM (RSD 13%), while
the meta analogue of 5 had an IC50 value of 26 lM
(RSD 20%) [36]. A comparison between the ortho amino
acid and dipeptide compounds 3 and 5 is seen in Fig. 1.
From these results it can be seen that the order of the
amino acids in the dipeptide is crucial for activity. Both
compounds tested have similar structures, however 3 is
much more active against H1299 cancer cells than com-
pound 5. From this is may be assumed that the glycine
moiety of the dipeptide that is attached to the benzoyl
group is important for activity. The benefits of glycine
in treating various diseases have been previously reported
[37].
The possible mechanism for their anti-cancer activity
originates from the low redox potential of these derivatives
and their ability to catalyze the generation of reactive oxy-
genated species (ROS), under physiological conditions,
that can oxidatively modify cellular components (e.g.,
DNA), disturb the redox balance in the cell, and/or inter-
fere with the redox-related cellular signalling pathways
[38]. Alternatively, cytotoxicity may arise from direct inter-
actions of these derivatives with other cellular components,
such as proteins [39]. Since, preliminary results imply some
structure activity relationship, it is envisaged that the pep-
tide chain of these derivatives may have a secondary mode
of action. These preliminary results are encouraging and
further studies are in progress to elucidate the mechanism
of action and for the selection of a series that has maximum
cytotoxicity against lung cancer cells.
3. Conclusions
In conclusion, the novel N-ortho ferrocenyl benzoyl
dipeptides 2–6 were prepared using standard peptide cou-
pling protocols. The compounds were characterized using
NMR spectroscopic techniques, mass spectrometry and
cyclic voltammetry. Compounds 3 and 5 were tested
in vitro against H1299 lung cancer cells and showed IC50
values of 5.3 lM and 21 lM, respectively, which is higher
than the corresponding amino acid derivatives.

1408
A.J. Corry et al. / Journal of Organometallic Chemistry 692 (2007) 1405–1410
4. Experimental
4.1. General procedures
–OCH2CH3). 13C NMR (100 MHz) d (DMSO): 170.5,
170.1, 169.7, 136.6, 136.4, 130.4, 129.1, 127.8, 125.8, 84.8,
69.8, 69.1, 68.6, 60.9 (ꢀve DEPT), 42.3 (ꢀve DEPT),
41.0 (ꢀve DEPT), 14.4.
All chemicals were purchased from Sigma/Aldrich and
used as received. Commercial grade reagents were used
without further purification, however, solvents were puri-
fied prior to use. Melting points were determined using a
Griffin melting point apparatus and are uncorrected. Infra-
red spectra were recorded on a Nicolet 405 FT-IR spec-
trometer and UV–Vis spectra on a Hewlett–Packard
8452 A diode array UV–Vis spectrophotometer. NMR
spectra were obtained on a Bruker AC 400 NMR spec-
trometer operating at 400 MHz for 1H NMR and
4.2.2. N-{ortho-(ferrocenyl)-benzoyl}-glycine-L-alanine
ethyl ester 3
For the compound 3 glycine-L-alanine ethyl ester hydro-
chloride (0.2 g, 1.0 mmol) was used as a starting material.
The product was purified by column chromatography {elu-
ant 2:3 petroleum ether (40–60 ꢁC): ethyl acetate}. Recrys-
tallization from petroleum ether (40–60 ꢁC): ethyl acetate
furnished the title compound as an orange solid (0.136 g,
29%). m.p. 102–104 ꢁC, Eꢁ0 = 50 mV (versus Fc/Fc+),
20
100 MHz for 13C NMR. The H and 13C NMR chemical
½aꢁD ¼ ꢀ4ꢂ (c 1.9, EtOH). Mass spectrum: found: [M]+
1
shifts (ppm) are relative to TMS and all coupling constants
(J) are in Hz. Matrix assisted laser desorption ionization
mass spectra were obtained on a Bruker Ultraflex TOF/
TOF mass spectrometer employing a nitrogen laser at
337 nm. Electrospray ionization mass spectra were
462.113, C24H26N2O4Fe requires: 462.124. IR mmax(KBr):
3376, 3281, 1720, 1647, 1480, 1370, 1293 cmꢀ1. UV–Vis
kmax MeCN; 224 (e 340), 445 (e 210) nm.
1H NMR (400 MHz)
d (CDCl3): 7.80 (1H, d,
J = 7.6 Hz, ArH), 7.40–7.44 (2H, m, ArH), 7.27 (1H, t,
J = 7.6 Hz, ArH), 6.72 (1H, d, J = 6.8 Hz, –CONH–),
6.15 (1H, br.s, –CONH–), 4.50–4.52 {3H, m, ortho on
(g5-C5H4), –CH(CH3)}, 4.29 {2H, s, meta on (g5-C5H4)},
4.20 (2H, q, J = 6.8 Hz, –OCH2CH3), 4.11 {5H, s, (g5-
C5H5)}, 3.97 (2H, t, J = 4.8 Hz, –CONHCH2–), 1.39
{3H, d, J = 7.2 Hz, –CH(CH3)}, 1.28 (3H, t, J = 6.8 Hz,
–OCH2CH3).
performed on
spectrometer.
a
Bruker Esquire ion trap mass
4.2. General procedure for the synthesis of N-{ortho-
(ferrocenyl)benzoyl} dipeptide esters
4.2.1. N-{ortho-(ferrocenyl)-benzoyl}-glycine-glycine ethyl
ester 2
13C NMR (100 MHz) d (CDCl3):173.0, 171.3, 168.4,
136.9, 135.5, 131.3, 130.0, 128.3, 126.7, 85.6, 70.2, 69.7,
69.6, 69.2, 61.9 (ꢀve DEPT), 48.5, 44.0 (ꢀve DEPT),
18.7, 14.5.
Glycine-glycine ethyl ester hydrochloride (0.2 g,
1.0 mmol) was added to a solution of ortho-ferrocenyl ben-
zoic acid (0.3 g, 1.0 mmol), 1-hydroxybenzatriazole (0.2 g,
1.5 mmol), triethylamine (0.5 ml) and dicyclohexylcarbo-
diimide (0.45 g, 2.1 mmol) in 50 ml of dichloromethane at
0 ꢁC. After 30 min the temperature was raised to room tem-
perature and the reaction was allowed to proceed for 48 h.
The precipitated N-N0-dicyclohexylurea was removed by
filtration and the filtrate was washed with water, 10%
potassium hydrogen carbonate and 5% citric acid. The
dichloromethane was then dried over MgSO4 and the
solvent was removed in vacuo. The product was purified
by column chromatography {eluant 2:3 petroleum ether
(40–60 ꢁC): ethyl acetate}. Recrystallization from petro-
leum ether (40–60 ꢁC)-ethyl acetate furnished the title com-
pound as orange needles (0.198 g, 44%), m.p. 69–71 ꢁC,
Eꢁ0 = 49 Mv (versus Fc/Fc+). Mass spectrum: found:
[M]+Å, 448.106; C23H24N2O4Fe requires, 448.109. IR
4.2.3. N-{ortho-(ferrocenyl)-benzoyl}-glycine-L-
phenylalanine ethyl ester 4
For the compound 4 glycine-L-phenylalanine ethyl ester
hydrochloride (0.2 g, 0.7 mmol) was used as a starting
material. The product was purified by column chromatog-
raphy {eluant 2:3 petroleum ether (40–60 ꢁC): ethyl ace-
tate}. The resultant product was recrystallized from
petroleum ether (40–60 ꢁC): ethyl acetate and furnished
the title compound as orange needles, (0.105 g, 28%),
20
m.p. 51–53 ꢁC, Eꢁ0 = 51 mV (versus Fc/Fc+), ½aꢁD ¼ þ2ꢂ
(c 2.1, EtOH). Mass spectrum: found: [M]+ 538.168,
C30H30N2O4Fe requires: 538.156. IR mmax(KBr): 3331,
2933, 1735, 1654, 1648, 1523, 1376, 1216 cmꢀ1. UV–Vis
kmax EtOH; 323 (e 1570), 440 (e 360) nm.
m
max(KBr): 3397, 2983, 1737, 1657, 1650, 1524, 1379,
1H NMR (400 MHz) d (DMSO): 8.29 (1H, t, J = 6 Hz,
–CONH–), 8.18 (1H, d, J = 7.6 Hz, –CONH–), 7.62 (1H,
d, J = 8 Hz, ArH), 7.32 (1H, t, J = 8 Hz, ArH), 7.03–7.15
(7H, m, ArH), 4.48 {2H, s, ortho on (g5-C5H4)}, 4.30–
4.37 {1H, m, J = 6.4 Hz, –CH(CH2Ph)}, 4.09 {2H, s, meta
on (g5-C5H4)}, 3.86–3.92 {7H, m, (g5-C5H5),
–OCH2CH3}, 3.64 (2H, t, J = 5.2 Hz, –NHCH2CO–),
2.80–2.85 {2H, m, –CH(CH2Ph)}, 0.92 (3H, t,
1202 cmꢀ1. UV–Vis kmax EtOH; 326 (e 1430), 439 (e
290) nm.
1H NMR (400 MHz) d (DMSO): 8.50 (1 H, t, J = 6 Hz,
–CONH–), 8.70 (1H, t, J = 6 Hz, –CONH–), 7.79 (1H, d,
J = 7.6 Hz, ArH), 7.40 (1H, t, J = 7.6 Hz, ArH), 7.24–
7.29 (2H, m, ArH), 4.64 {2H, t, J = 2 Hz, ortho on (g5-
C5H4)}, 4.27 (2H, t, J = 2 Hz), meta on (g5-C5H4), 4.22
(2H, q, J = 7.2 Hz, –OCH2CH3), 4.06 (5H, s, g5-C5H5),
3.87 (2H, d, J = 5.6 Hz, –NHCH2CO–), 3.83 (2H, d,
J = 5.6 Hz, –NHCH2CO–), 1.28 (3H, t, J = 7.2 Hz,
J = 7.2 Hz, –OCH2CH3). 13C NMR (100 MHz)
d
(DMSO): 171.7, 170.3, 169.2, 137.3, 136.6, 136.4, 130.7,
129.5, 129.1, 128.6, 127.7, 127.0, 125.7, 84.7, 69.8, 69.1,

A.J. Corry et al. / Journal of Organometallic Chemistry 692 (2007) 1405–1410
1409
69.1, 68.6, 60.9 (ꢀve DEPT), 54.1, 42.2 (ꢀve DEPT), 37.3
4.3. General procedure for in vitro cytotoxicity assays
(ꢀve DEPT), 14.3.
Lung cancer cells (H1299, highly invasive/superinvasive;
H1299 carboplatin resistant variant) were harvested by
trypsinisation and a cell suspension of 1 · 104 cells/ml
was prepared in a cell culture medium. The cell suspension
(100 ll) was added to a flat bottom 96-well plate (Costar,
3599), plates were agitated gently in order to ensure even
dispersion of cells over the surface of the wells, and then
cells were incubated for an initial 24 h in a 37 ꢁC, 5%
CO2 incubator, to allow cell attachment to the wells. A
stock solution of a test sample was prepared in dimethyl
sulfoxide; dilute solutions of the test sample were prepared
by spiking the cell culture medium with a calculated
amount of the stock solution. 100 ll aliquot of the each
dilute solution was added to each well of the plate, plate
was gently agitated, and then incubated at 37 ꢁC, 5%
CO2 for 6–7 days, until cell confluency reached 80–90%.
Assessment of cell survival in the presence of the ferrocenyl
derivatives (2–6) was determined by the acid phosphatase
assay. The concentration of drug that kills 50% of the cells
(the IC50 value) was determined by plotting % survival of
cells (relative to the control cells) against concentration
of the ferrocenyl derivative.
4.2.4. N-{ortho-(ferrocenyl)-benzoyl}-L-alanine-glycine
ethyl ester 5
For compound 5 L-alanine-glycine ethyl ester hydro-
chloride (0.2 g, 1.0 mmol) was used as a starting material.
The product was purified by column chromatography {elu-
ant 2:3 petroleum ether (40–60 ꢁC): ethyl acetate}. Recrys-
tallization from petroleum ether (40–60 ꢁC): ethyl acetate
furnished the title compound as orange needles (0.181 g,
39%). m.p 55–57 ꢁC, Eꢁ0 = 51 mV (versus Fc/Fc+),
20
½aꢁD ¼ þ0:3ꢂ (c 2.05, EtOH). Mass spectrum: found:
[M]+ 462.09, C24H26N2O4Fe requires: 462.12. IR
m
max(KBr): 3326, 2933, 1752, 1655, 1638, 1509,
1200 cmꢀ1. UV–Vis kmax EtOH; 321 (e 1050), 441 (e
240) nm.
1H NMR (400 MHz) d (DMSO): 8.35 (1H, d, J =
7.2 Hz, –CONH–), 8.18 (1H, t, J = 7.2 Hz, –CONH–),
7.80 (1H, d, J = 8 Hz, ArH), 7.41 (1H, t, J = 8 Hz, ArH),
7.24–7.38 (2H, m, ArH), 4.57–4.59 {2H, m, ortho on (g5-
C5H4)}, 4.41 {1H, quint, J = 7.6 Hz, –CH(CH3)}, 4.25–
4.29 {2H, m, meta on (g5-C5H4)}, 4.01–4.13 {7H, m,
–OCH2CH3, (g5-C5H5)}, 3.78–3.93 (2H, m, –CONH-
CH2–), 1.25 {3H, d, J = 7.6 Hz, –CH(CH3)}, 1.17 (3H, t,
J = 7.2 Hz, –OCH2CH3). 13C NMR (100 MHz)
d
Acknowledgements
(DMSO): 173.0, 170.1, 169.7, 136.6, 136.5, 130.5, 129.0,
127.8, 125.8, 85.0, 69.8, 69.5, 68.8, 68.5, 68.4, 60.8 (ꢀve
DEPT), 48.7, 41.1 (ꢀve DEPT), 18.0, 14.4.
DS thank the Irish American Partnership and Dublin
City University for the funding of a studentship award
1999–2002. This research was partly supported by the Na-
tional Institute for Cellular Biotechnology under the Pro-
gramme for Research in Third Level Institutions (PRTLI,
round 3, 2001–2006). AJC thank the Embark Initiative
and IRCSET for all their support.
4.2.5. N-{ortho-(ferrocenyl)benzoyl}-L-alanine-L-
phenylalanine ethyl ester 6
For the compound 6 L-alanine-L-phenylalanine ethyl
ester hydrochloride (0.2 g, 0.7 mmol) was used as starting
material. The product was purified by column chromatog-
raphy {eluant 2:3 petroleum ether (40–60 ꢁC): ethyl ace-
tate}. Recrystallization from petroleum ether (40–60 ꢁC):
ethyl acetate furnished the title compound as an orange
solid (0.102 g, 25%), m.p. 137–139 ꢁC, Eꢁ0 = 52 mV (versus
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20
Fc/Fc+), ½aꢁD ¼ þ2ꢂ (c 2.05, EtOH). Mass spectrum:
found: [M]+ 552.158, C31H32N2O4Fe requires: 552.171.
IR mmax(KBr): 3397, 3309, 2932, 1742, 1645, 1509, 1496,
1210 cmꢀ1. UV–Vis kmax EtOH; 323 (e 1570), 440 (e
340) nm.
1H NMR (400 MHz) d(DMSO): 8.37–8.46 (2H, m,
–CONH-), 7.80 (1H, d, J = 7.2 Hz, ArH), 7.60 (1H, t,
J = 7.2 Hz, ArH), 7.38–7.47 (7H, m, ArH), 4.76 {2H, t,
J = 1.2 Hz, ortho on (g5-C5H4)}, 4.60–4.76 {2H, m,
–CH(CH3), –CH(CH2Ph)}, 4.42–4.46 {2H, m, meta on
(g5-C5H4)}, 4.21–4.26 {7H, m, (g5-C5H5), –OCH2CH3},
3.19–3.23 {2H, m, –CH(CH2Ph)}, 1.35 {3H, d,
J = 7.2 Hz, –CH(CH3)}, 1.27 (3H, t, J = 7.6 Hz,
OCH2CH3).
–
13C NMR (100 MHz) d (DMSO): 172.6, 171.7, 169.5,
137.3, 136.5, 130.5, 129.5, 129.1, 128.6, 128.5, 127.8,
126.9, 125.8, 85.0, 69.8, 69.5, 68.7, 68.5, 60.9 (ꢀve DEPT),
53.9, 48.6, 33.7 (ꢀve DEPT), 18.1, 14.4.

1410
A.J. Corry et al. / Journal of Organometallic Chemistry 692 (2007) 1405–1410
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