Ferrocenyl pseudo-dipeptides derived from 1,2-O-isopropylidene-α-D-xylofuranose: Synthesis, electrochemistry and cytotoxicity evaluation

Article abstract of DOI:10.1016/j.jorganchem.2014.10.002

In this article, we describe the synthesis of a new series of ferrocene conjugates of pseudo-dipeptides derived from d-xylose and different L-amino acids. The pseudo-dipeptides (3a-f) were synthesized by the reaction of 5-amino-5-deoxy-1,2-O-isopropyliden

Full text of DOI:10.1016/j.jorganchem.2014.10.002

Journal of Organometallic Chemistry 774 (2014) 26e34
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Ferrocenyl pseudo-dipeptides derived from 1,2-O-isopropylidene-
D-xylofuranose: Synthesis, electrochemistry and cytotoxicity
evaluation
a-
,
Sadanala Bhavya Deepthi a, Rajiv Trivedi a *, Lingamallu Giribabu a, B. Sridhar b,
Pombala Sujitha c, C. Ganesh Kumar c
a Inorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500 007, India
b Laboratory of X-ray Crystallography, CSIR-Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500 007, India
c Medicinal Chemistry and Pharmacology Division, CSIR-Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500 007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
In this article, we describe the synthesis of a new series of ferrocene conjugates of pseudo-dipeptides
derived from -xylose and different -amino acids. The pseudo-dipeptides (3aef) were synthesized by
the reaction of 5-amino-5-deoxy-1,2-O-isopropylidene- -D-xylofuranose (1) with different N-Boc-L-
amino acids (2aef). Subsequently, the pseudo-dipeptides were insitu converted to amino-amides (4aef)
and treated with ferrocenoyl chloride to obtain the ferrocenyl xylofuranose pseudo-dipeptide conjugates
(5aef). The structure of the pseudo-dipeptide 3b was determined by X-ray crystallography. Low elec-
trochemical diffusion coefficient (Df) values were obtained for the ferrocenyl compounds (5aef) in
DMSO-buffer solutions. Promising cytotoxicity was observed for the ferrocenyl pseudo-dipeptides (5aef)
as compared to the parent pseudo-dipeptides (3aef).
Received 25 July 2014
Received in revised form
19 September 2014
Accepted 1 October 2014
Available online 15 October 2014
D
L
a
Keywords:
Ferrocene
Pseudo-dipeptides
Carbohydrates
Electrochemistry
Cytotoxicity
© 2014 Elsevier B.V. All rights reserved.
Introduction
peptide chains [17e26]. These types of ferrocenyl peptide conju-
gates can behave as potential mimic of natural turn (secondary
The past few years have witnessed a myriad of promising bio-
logical applications for organometallic compounds and have
encouraged the scientists to design new metal complexes for such
applications [1e6]. In the domain of bioorganometallic chemistry,
several organometallic drug derivatives have shown promising
anticancer, antimalarial, antibacterial and protein inhibition activ-
ities [7e11]. Metallocenes, particularly ferrocene derivatives, de-
serves special place due to their diverse structural and physical
properties [12]. Some of the ferrocene containing drugs such as
ferrocifen and ferroquine are known for their excellent anticancer
and antimalarial activities respectively [13e15].
The conjugation of ferrocene to a biomolecule is an interesting
area of research [16]. A plethora of ferrocenyl peptide conjugates
have been designed for the conformational and biological studies
[17e30]. The distance between the two cyclopentadienyl rings of
ferrocene (3.3 Ǻ) is ideal to form an appropriate orientation for
efficient intra molecular hydrogen bonding between the podand
structure) inducers in proteins. The secondary structures of pep-
tides ( -helices, -sheets and -turns) are predominantly the most
a
b
b
important conformations that influence the three-dimensional
structure as well as the biological activities. Extensive work has
been carried out in designing and conformational studies of fer-
rocenyl peptide conjugates by the research groups of Hirao
[17e22], Kraatz [23e26], Meltzer-Nolte [27,28] and Heinze [29,30].
Apart from the three-dimensional structural studies, several fer-
rocenyl peptide conjugates have been synthesized and utilized for
the biological applications [31e34].
Biological activities of ferrocene conjugates of oligopeptides
such as [Leu5]-enkephalin, bradykinin, angiostatin II have been
studied [35e41]. b-sheet like conformations often play an impor-
tant structural role in Alzheimer's and Parkinson's diseases. Recent
reports on the ferrocene-peptide conjugates depicting such con-
formations have appeared in the literature [23e26].
Sugar amino acids constitute an important component in syn-
thetic bioorganic chemistry [42]. Rapic and co-workers have re-
ported on the conformational studies and antimicrobial activity of
ferrocene labelled sugar amino acids [43,44]. The utility of ferro-
cenyl glycopeptides as potential biomarkers have been
* Corresponding author. Tel.: þ91 40 27191667; fax: þ91 40 27160921.
E-mail addresses: trivedi@iict.res.in, rtrajiv401@gmail.com (R. Trivedi).
http://dx.doi.org/10.1016/j.jorganchem.2014.10.002
0022-328X/© 2014 Elsevier B.V. All rights reserved.

S.B. Deepthi et al. / Journal of Organometallic Chemistry 774 (2014) 26e34
27
demonstrated by Papini [45]. Although, the carbohydrate derived
pseudo-dipeptides have demonstrated efficient catalytic activity
[46], reports pertaining to their organometallic analogues are
scarce. Moreover, such pseudo-dipeptides and the ferrocene
labelled sugar amino acids have been derived from hexose sugars
(glucose and mannose). Therefore, the design of a new class of
ferrocenyl peptide conjugates derived from a pentose sugar
(xylose) and the study of their electrochemical and biological
properties was undertaken. Herein, we report the synthesis, char-
acterization and cytotoxicity evaluation of ferrocenyl xylofuranosyl
obtained were found to be hygroscopic in nature. Hence, direct
conjugation of ferrocenoyl chloride with the insitu prepared amino-
amides was adopted. The ferrocenyl peptides (5aef) were synthe-
sized from the reaction of amino-amides with ferrocenoyl chloride
in presence of triethylamine in dichloromethane solution.
In the 1H NMR spectra of pseudo-dipeptides (3aef), the protons
of the amino acid side chain were observed in the region
d
1.0e1.2 ppm, while the gem-dimethyl groups of the xylofuranose
ring appeared in the region 1.3e1.5 ppm. The Boc-protons were
observed as singlet at 1.4 ppm and the chiral proton of the amino
acid residue was observed in the region 3.8 ppm. The eNH proton
of the N-Boc protected amino acid was observed around 4.8 ppm.
For all the pseudo-dipeptides (3aef), the anomeric proton (H-1) of
the xylofuranose ring appeared as doublet around 5.9 ppm and
the eNH proton of the sugar residue appeared around 6.7 ppm. In
case of -phenylalanine derived pseudo-dipeptide (3f), the phenyl
d
d
pseudo-dipeptides derived from different
L-amino acids.
d
d
Results and discussion
d
d
Synthesis and characterization
L
ring protons appeared in the (aromatic) region
d 7.1e7.3 ppm.
The ferrocenyl xylofuranosyl pseudo-dipeptide conjugates were
synthesized by adopting the synthetic route as depicted in Scheme
1. The pseudo-dipeptides (3aef) were obtained from the coupling
In the 13C NMR spectra of pseudo-dipeptides 3b, 3c, 3d and 3e,
the carbon atoms of the amino acid chain appeared in the region
d
17e19 and
group appeared around
Boc-protecting group were observed around
pseudo-dipeptides (3aef), the signals corresponding to the
d
37 ppm. The carbon atoms of the gem-dimethyl
23 ppm and 26 ppm. The carbons of the
28 ppm. For all the
reaction between 5-amino-5-deoxy-1,2-O-isopropylidene-
a-D-
d
d
xylofuranose (1) and N-Boc protected -amino acids (2aef) in the
L
d
presence of DCC in dichloromethane solution. The N-Boc-depro-
tection of the pseudo-dipeptides (3aef) with TFA was hampered by
the presence of acid sensitive isopropylidene group of xylofuranose
moiety [47,48]. Thus, the amino-amides (4aef) were obtained by
the selective N-Boc deprotection of pseudo-dipeptides (3aef) with
TFA-CH2Cl2 (50% v/v) mixture [48]. The amino-amides (4aef) thus
carbonyl carbons appeared around
pseudo-dipeptide derived from
d
155 ppm and
d 175 ppm. The
L-glycine (3a) appeared as
[M þ Na]þ peak in the ESIþ mass spectrum, while the pseudo-
dipeptides 3bef were characterized by a [M þ H]þ peak in their
Scheme 1. Synthesis of ferrocenyl pseudo-dipeptides 5aef.

28
S.B. Deepthi et al. / Journal of Organometallic Chemistry 774 (2014) 26e34
ESIþ mass spectra. In the IR spectra of the compounds, the char-
acteristic C]O and NeH stretching bands were observed in the
region 1650 and 2928 cmꢀ1 respectively.
2.09(2), 2.8556(19), 157(2), x þ 1/2, ꢀy þ 3/2, ꢀz þ 2], while second
amide NH is connected to hydroxyl group [N1eH1N/O3, 0.90(2),
2.17(2), 3.057(2), 169(2), ꢀx þ 1, yꢀ1/2, ꢀz þ 3/2]. These two NeH
… O hydrogen bonds links the molecules into a hexamer of R66(44)
motif. Thus, the combination of OeH … O and NeH … O hydrogen
In the 1H NMR spectra of the ferrocene derivatives 5aef, the
protons of the gem-dimethyl groups of the xylofuranose moiety
appeared as two singlets around
responding to the protons of the substituted cyclopentadienyl (Cp)
ring appeared around 4.4 and 4.6 ppm, whereas the protons of
the unsubstituted cyclopentadienyl (Cp) ring were characterized by
a singlet at 4.0 ppm. The anomeric proton of the xylofuranose ring
appeared as doublet in the region 5.9 ppm. The eNH protons
appeared in the region 6.4 and 6.8 ppm. For ferrocenyl peptide
5f, the phenyl protons of the phenylalanine residue appeared as
d
1.2e1.4 ppm. The signals cor-
bonds aggregate the molecule into a supramolecular three-
dimensional hydrogen bonding network in the crystal packing
(Fig. 2).
d
d
d
Electrochemical studies
d
d
d
The electrochemical characterization of the compounds 5aef
was performed by means of cyclic voltammetry (CV) in 0.5 mM
methanol solutions. All the ferrocenyl pseudo-peptide conjugates
(5aef) exhibited one electron reversible oxidation wave with
respect to SCE (Fig. 3) in presence of 0.1 M TBAP supporting elec-
trolyte. The compounds exhibited E1/2 values in the range of
564e580 mV with peak separation potentials (Ep) ranging from 86
to 99 mV (vs SCE) and current ratios equal to unity (see
supplementary information).
multiplet in the aromatic region, i.e.
d 7.2e7.4 ppm.
In the 13C NMR spectra of ferrocenyl pseudo-dipeptides 5bed
and 5e, the carbon atoms of the amino acid chain appeared in the
region
dimethyl group appeared around
ferrocenyl pseudo-dipeptides, the signals corresponding to the
d
17e19 and
d
37 ppm. The carbon atoms of the gem-
d
27 ppm and 28 ppm. For all the
d
carbonyl carbons appeared around
d 171 ppm and d 175 ppm. For
compound 5f, [M þ H]þ peak was observed in the ESIþ spectrum,
while the peptides (5aee) were characterized by a [M þ Na]þ peak
in their ESIþ mass spectra. For these compounds, the characteristic
IR spectral bands for C]O and NeH stretching frequencies were
observed in the region 1630 cmꢀ1 and 2940 cmꢀ1 respectively.
The CV experiments were also conducted in DMSO and DMSO-
buffer solutions (phosphate buffer, pH ¼ 7.4). In 0.5 mM DMSO
solution, the compounds exhibited a reversible redox wave with E1/
value ranging from 532 to 550 mV (vs SCE). A solvent induced
2
oxidation of the ferrocene moiety was observed for the ferrocene-
carbohydrate conjugates containing simple amide [52] and amide-
triazole [53] linkers. For the compounds 5aef, the absence of such
oxidation in DMSO solution indicates that the peptide group in-
fluences the stability of the compounds in the solvent. This may be
due to H-bonding interactions; however other soft interactions
cannot be over ruled. When 0.1 M phosphate buffer (pH ¼ 7.4) was
added (in 1:1 ratio) to the 0.5 mM DMSO solution of the com-
pounds, a reversible oxidation wave corresponding to the ferroce-
nium ion was observed with E1/2 (vs SCE) values ranging from 365
to 420 mV. The stabilization of the conjugates in buffer solutions
leads to a slight decrease in the E1/2 value compared to the DMSO
solvent.
Crystal structure of compound 3b
The molecular structure of pseudo-dipeptide 3b was deter-
mined by means of X-ray diffraction studies. Colourless crystal of
the compound 3b was obtained by the slow evaporation of ethyl
acetate solution at room temperature. The compound crystallized
in orthorhombic P212121 space group. The crystallographically
determined configuration and atom numbering scheme are shown
in Fig. 1.
In solid state, the compound is stabilized by both intra and
intermolecular hydrogen bonds. The hydroxyl O3 atom of the furan
ring forms an intra molecular OeH … O bond with the carbonyl O5
atom of amide group [O3eH4O/O5, 0.86(3), 1.91(3), 2.7122(19),
155(2)] and forms a pseudo S(8) ring motif [49e51]. In this com-
pound, two types of NeH … O hydrogen bonds were observed. One
amide NH is connected to amide carbonyl [N2eH2N/O6, 0.81(2),
Determination of diffusion coefficient (Df)
From the literature as well as from our recent studies, it was
observed that the diffusion coefficient (Df) of the ferrocene-
carbohydrate conjugates depends on the stereochemistry and the
protecting groups present on the carbohydrate moiety [53,54].
Fig. 1. A view of compound 3b, showing the atom-labelling scheme. Displacement
ellipsoids are drawn at the 30% probability level and H atoms are represented by circles
of arbitrary radii.
Fig. 2. Partial packing diagram of compound 3b, showing the hexameric R66(44) motif
formed by intermolecular NeH … O hydrogen bonds (dashed lines). H-atoms not
involved in interactions have been omitted for clarity.

S.B. Deepthi et al. / Journal of Organometallic Chemistry 774 (2014) 26e34
29
weights were expected to exhibit similar Df values. However, a
slightly high Df value was obtained for
dipeptide (5d) as compared to that of
L
-isoleucine derived pseudo-
-leucine derived compound
L
(5e), indicating the steric influence of the amino acid chain on the
Df value of the peptide conjugates. Further, in spite of their low
molecular weight, the
L-alanine and L-valine derived pseudo-
dipeptides (5b and 5c respectively) exhibited high Df values as
compared to the
respectively).
L-leucine and
L-isoleucine derivatives (5d and 5e
In DMSO solutions, except for the peptide derived from
L-valine
(5c), all the compounds have shown slightly low Df values as
compared to those observed in methanol. The low Df value of the
compounds can be attributed to the stabilization of the compounds
in DMSO solutions. In DMSO-buffer solutions, irrespective of the
amino acid side chain, all the compounds (5aef) exhibited the Df
values ranging from 0.061 to 0.067 ꢁ 10ꢀ10 m2 sꢀ1. These low Df
values indicate that the compounds were extensively stabilized in
presence of buffer solution as compared to methanol and DMSO
solutions. These Df values further indicate that, in DMSO-buffer
solutions, the diffusion is independent of the positional isom-
erism of the amino acid side chain.
Fig. 3. Cyclic voltammograms of ferrocenyl peptides 5a, 5b and 5f in 0.5 mM
methanol.
However, in the present study, all the ferrocenyl pseudo-dipeptides
contain the same sugar scaffold, i.e., xylofuranose moiety and
different amino acid residues. Hence, the diffusion coefficient was
determined under different solvent conditions to study the effect of
the amino acid side chain on ferrocenyl carbohydrate conjugates.
The Df value was calculated in methanol, DMSO and DMSO-
buffer solutions. In order to calculate the diffusion coefficient (Df),
the corresponding anodic peak currents (ia) were obtained by
recording the cyclic voltammograms at various scan rates
(20e100 mV). The straight line obtained (see supporting
information) due to the diffusion controlled electrochemical pro-
cess shows that the anodic current (ia) is directly proportional to
Cytotoxic activity (MTT assay)
Considering the vital role of ferrocene and carbohydrate scaf-
folds in biology, the investigation of ferrocene-carbohydrate con-
jugates with cytotoxic [55e59] and antimalarial [60e63] activities
have gained considerable attention. From our recent work, it was
evident that the linker which connects the ferrocene and carbo-
hydrate scaffolds has significant influence on the cytotoxicity of the
compounds [52e55]. It was observed that the ferrocene-
carbohydrate conjugates with biologically compatible (amide, tri-
azole and amide-triazole) linkers exhibited promising cytotoxicity
as compared to those with a hydrophobic (phenoxymethyl triazole)
linker. On the basis of bio-compatibility of the sugar derived
pseudo-dipeptides, it was anticipated that the compounds 3aef
and 5aef should exhibit promising bioactivity. With this anticipa-
tion, the compounds were tested [64] for their cytotoxicity against
five different cell lines: human cervical carcinoma cancer cells
(HeLa), human alveolar adenocarcinoma epithelial cells (A549),
human breast adenocarcinoma cells (MCF-7 and MDA-MB-231)
and human embryonic kidney cells (HEK 293). The IC50 values
(the concentration of the compounds at which 50% of cell growth
was inhibited) obtained are given in Table 2.
the square root of scan rate (y
1/2). The diffusion coefficients (Df) of
ꢀ
ꢀ
5aef were obtained from the RandleseSevcik relationship and are
given in Table 1.
From the calculations, it was observed that, in methanol and
DMSO solutions, the compounds 5aef exhibited variable diffusion
coefficient values with an increase in the molecular weight. In
methanol, among the compounds 5aef, low Df value
(1.946 ꢁ 10ꢀ10 m2 sꢀ1) was obtained for the
L-glycine derived
pseudo-dipeptide (5a), whereas, for the L-phenylalanine derived
pseudo-peptide (5f), a high Df value (3.723 ꢁ 10ꢀ10 m2 sꢀ1) was
obtained. These Df values of the compounds 5a and 5f can be
attributed to the molecular weight of the compounds. However, it
was found that the diffusion coefficient (Df) values for compounds
5bee were dependent on the substituents present on the amino
acid residues. The effect of positional isomerism of the amino acid
chain on the diffusion coefficient can be observed from the Df
The
L
-glycine derived pseudo-dipeptide (3a) and ferrocenyl
pseudo-dipeptide (5a) exhibited specific cytotoxicity against A549
cell line with IC50 values of 9.69
m
L
M and 5.39
-alanine (3b) was toxic towards
M and 5.44
respectively. The corresponding ferrocenyl pseudo-dipeptide (5b)
exhibited toxicity against A549 cell line with an IC50 value 5.75
and was non-toxic toward HeLa cell lines (IC50 value of >100
The compound was also active against the breast cancer cell lines
mM respectively. The
pseudo-dipeptide derived from
A549 and HeLa cell lines with IC50 values 3.49
m
mM
values of the peptides derived from
L-leucine (5d) and L-isoleucine
mM
(5f). The derivatives (5d) and (5f) having identical molecular
mM).
MDA-MB-231 and MCF-7 with IC50 values 7.89
respectively.
mM and 9.85 mM
Table 1
Diffusion coefficient values of ferrocenyl peptides 5aef.
The pseudo-dipeptide with
cytotoxicity towards HeLa and MCF-7 cell lines with IC50 values
>20 M. However, the ferrocenyl pseudo-dipeptide derived from
valine (5c) was found to be non-toxic. The pseudo-dipeptides
containing -leucine and -phenylalanine amino acids (3d and 3f
respectively) were non-toxic towards the tested cell lines. However,
the ferrocenyl pseudo-dipeptide containing -leucine (5d) has
shown toxicity towards MCF-7 cell line with an IC50 value of
8.95 M. The ferrocenyl pseudo-dipeptide derived from -phenyl-
alanine (5f) exhibited promising cytotoxicity towards MDA-MB-
L
-Valine (3c) backbone exhibited
Compound Molecular Amino acid
weighta
Df in
Df in
Df in
CH3OHb DMSOb DMSO-bufferb
m
L-
5a
5b
5c
5d
5e
5f
458
472
500
514
514
640
L
L
L
L
L
L
-Glycine
-Alanine
-Valine
-Leucine
-Isoleucine
1.946
2.977
1.743
2.262
3.457
1.455
0.616
2.124
0.690
0.596
1.005
0.067
0.066
0.061
0.064
0.067
0.064
L
L
L
-Phenylalnine 3.723
a
m
L
Expressed in mg/mmol.
b
Expressed in 10ꢀ10 m2 sꢀ1
.

30
S.B. Deepthi et al. / Journal of Organometallic Chemistry 774 (2014) 26e34
Table 2
IC50 values of compounds 3aef and 5aef.
Compound
IC50
(m
M)a
A549
HeLa
MDA-MB-231
MCF-7
HEK 293
Pseudo-dipeptides
3a
3b
3c
3d
3e
3f
9.69 0.14
3.49 0.01
>100
>100
16.21 0.06
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
29.41 0.09
>100
>100
>100
>100
>100
>100
>100
>100
5.44 0.02
22.69 0.14
>100
26.54 0.05
>100
>100
Ferrocenyl peptides
5a
5b
5c
5.39 0.02
5.75 0.03
>100
>100
>100
>100
>100
7.89 0.02
>100
>100
9.85 0.03
>100
>100
>100
>100
5d
5e
5f
>100
>100
>100
0.46 0.09
0.12 0.05
>100
4.89 0.02
>100
0.51 0.04
0.17 0.09
>100
8.95 0.02
>100
>100
1.07 0.02
0.49 0.04
>100
>100
>100
79.26 0.13
9.42 0.08
5.89 0.03
2.98 0.01
0.91 0.08
0.25 0.01
Doxorubicinb
Cisplatinb
a
Values are the mean of two experiments.
Positive control or standards.
b
231 cell line with an IC50 value of 2.98
m
M.
L
-isoleucine derived
constants (J) were expressed in Hz. Infrared spectra were recorded
on a Thermo Nicolet Nexus 670 spectrometer using KBr discs.
Melting points were determined on a Toshniwal melting point
apparatus and are uncorrected. The cyclic voltammetry (CV) was
pseudo-dipeptide (3e) was active against A549 and HeLa cell lines,
while the ferrocenyl analogue (5e) was active against HeLa and
MDA-MB-231 cell lines. All pseudo-dipeptides (3aef) and ferro-
cenyl pseudo-dipeptides (5aef) were found to be nontoxic
performed with
a conventional three-electrode configuration
(IC50 > 100
m
M) towards HEK 293 normal cell lines.
consisting of glassy carbon working electrode, platinum wire
auxiliary electrode and saturated calomel (SCE) reference electrode.
The cyclic voltammograms were recorded on CHI620 model elec-
trochemical analyser, in the presence of 0.1 M tetrabutylammo-
nium perchlorate (TBAP) supporting electrolyte at a scan rate of
From this study, it was observed that the cytotoxicity of the
compounds depends on the amino acid residue present on the
pseudo-dipeptide. In case of some of the compounds, a significant
toxicity was observed when the N-Boc group was replaced with the
ferrocenoyl moiety. The compounds 5b, 5e and 5f were found to
0.1
V . 5-amino-5-deoxy-1,2-O-isopropylidene-a-D-xylofur-
sꢀ1
exhibit promising cytotoxicity (IC50 < 10
mM) on MDA-MB-231, the
anose was prepared according to the literature procedures [52].
hormone-independent breast cancer cell lines.
General procedure for the synthesis of pseudo-dipeptide ligands
(3aef)
Conclusions
In conclusion, herein we describe the synthesis and electro-
chemical characterization of ferrocenyl xylofuranose conjugates
connected through peptide linker. The ferrocenyl compounds have
shown reversible electrochemical oxidation under different sol-
vents such as methanol, DMSO and DMSO-buffer solution. The
electrochemical calculations indicated that in methanol and DMSO,
the Df value of the compounds depends on the nature of the amino
acid residue. On the other hand, in DMSO-buffer solution, under
physiological pH (7.4), the Df value was independent on the nature
of the amino acid residue present on the compounds. The low Df
values of the compounds in DMSO-buffer solution indicate the
strong stabilizing ability of the peptide linkers in aqueous solutions.
Among all the tested compounds, 5f has shown promising cyto-
toxicity against hormone-independent breast cancer cell lines,
To a solution of N-Boc-L-amino acid (1 equiv.) in anhydrous
CH2Cl2, freshly prepared solution of DCC (1.2 equiv.) in anhydrous
CH2Cl2 was added at 0 ꢂC and the resulting white suspension was
stirred for 30 min. To this suspension, a solution of 1 (1.5 equiv.) in
anhydrous CH2Cl2 was added drop-wise at 0 ꢂC. The reaction
temperature was allowed to rise to room temperature and stirring
was continued for 12 h. The resulting white precipitate was filtered
and washed with CH2Cl2. The combined washings were evaporated
under reduced pressure to give crude mass, which was further
purified by column chromatography using hexane-ethyl acetate
mixture.
5-(N-Boc-L-glycinlyamido)-5-deoxy-1,2-O-isopropylidene-a-D-
MDA-MB-231(IC50 of 2.98 mM). From the results, it was observed
that the cytotoxicity of the compounds (5aef) depends on the
amino acid residue present in the pseudo-dipeptide conjugate.
xylofuranose (3a)
White solid; yield: 0.29 g (85%); mp: 116 ꢂC; [
a]
24: þ35.58
D
(CH3OH, c 0.1); IR (KBr, ymax): 3374, 3334, 2992, 2934 (NeH), 1714,
1635 (C]O), 1523, 1166, 1079, 863, 635 cmꢀ1 1H NMR (CDCl3,
;
Experimental section
300 MHz): d
1.31 (s, 3H, CH3), 1.46 (s. 6H, BocCH3), 1.47 (s, 3H, CH3),
3.26e3.30 (m, 1H, H-5), 3.78e3.85 (m, 3H, H-5 and acidCH2), 4.03
(bs, 1H, OH), 4.05e4.07 (m, 1H, H-3), 4.58 (d, 3JH,H ¼ 3.5 Hz, 1H, H-
Optical rotations were determined on a JASCO J-120 polarim-
eter. 1H spectra were recorded for CDCl3 solutions on 300 MHz
(Avance 300) and 500 MHz (Innova 500) instruments. Chemical
shifts for protons were reported by taking tetramethylsilane (TMS)
as the internal standard. 13C NMR spectra were recorded at
75.5 MHz on an Avance 300 instrument and the carbon shifts were
referenced to the 13C signal of CDCl3 at 77.0 ppm. Coupling
2), 4.69 (bs, 1H, BocNH), 5.21 (dd, JH,H ¼ 5.7 and 5.8 Hz, 1H, H-4),
3
3
5.91 (d, JH,H ¼ 3.5 Hz, 1H, H-1), 6.81e6.84 (m, 1H, NH) ppm; 13C
NMR (CDCl3, 75.5 MHz):
d
26.03 (CH3), 26.71 (CH3), 28.24 (BocCH3),
37.25
(
GlyCH2), 44.14 (C-5), 73.91 (C-2), 79.57 (C-3), 80.61
BocC(CH3)3), 84.84 (C-4), 104.72 (C-1), 111.51 (C(CH3)2), 156.18
BocCO), 171.66 (NHCO) ppm; Anal. calcd. for C15H26N2O7: C, 52.01;
(
(

S.B. Deepthi et al. / Journal of Organometallic Chemistry 774 (2014) 26e34
31
3
H, 7.57; N, 8.09%; found: C, 51.68; H, 7.42; N, 7.84%; MS (ESIþ): (m/
z) ¼ 369 [M þ Na]þ.
4.75 (bs, 1H, BocNH), 4.95 (dd, JH,H ¼ 1.9 Hz and 5.9 Hz, 1H, H-4),
5.84 (d, 3JH,H ¼ 2.9 Hz, 1H, H-1), 6.71 (bs, 1H, CONH) ppm; 13C NMR
(CDCl3, 300 MHz):
d
11.28 (isoleuCH3), 15.61 (isoleuCH3), 24.78 (iso-
5-(N-Boc-L-alaninlyamido)-5-deoxy-1,2-O-isopropylidene-
a
-D-
leuCH2), 26.12 (CH3), 26.82 (CH3), 28.30 (BocCH3), 37.14 (isoleuCH),
49.22 (isoleuCH), 59.43 (C-5), 73.77 (C-2), 79.62 (BocC(CH3)3), 79.85
(C-3), 84.80 (C-4), 104.78 (C-1), 111.45 (C(CH3)2), 155.86 (BocCO),
175.04 (NHCO) ppm; Anal. calcd. for C19H34N2O7: C, 56.70; H, 8.51;
N, 6.96%; found C, 56.50; H, 8.26; N, 6.65%; MS (ESIþ): m/z ¼ 403
[M þ H]þ.
xylofuranose (3b)
24
White solid; yield: 0.31 g (87%); mp: 155e160 ꢂC; [
a]
¼ ꢀ11.45
D
(CHCl3, c 0.1); IR (KBr, ymax): 3301, 2987, 2933 (NeH), 1665 (C]O),
1531, 1166, 1078, 862, 645 cmꢀ1; 1H NMR (CDCl3, 300 MHz):
d
1.28
(s, 3H, CH3), 1.36 (d, 3H, 3JH,H ¼ 6.8 Hz, alaCH3), 1.43 (s, 3H, CH3), 1.44
(s, 9H, BocCH3), 3.15e3.23 (m, 1H, H-5), 3.46 (s, 1H, OH), 3.75e3.81
(m, 2H, H-3 and H-5), 3.91e3.97 (m, 1H, BocNHCH), 4.49 (d,
3JH,H ¼ 3.8 Hz, 1H, H-2), 4.63 (d, 3JH,H ¼ 3.0 Hz, 1H, BocNH), 4.84 (dd,
3JH,H ¼ 7.6 Hz and 1.6 Hz, 1H, H-4), 5.82 (d, 3JH,H ¼ 3.8 Hz, 1H, H-1),
5-(N-Boc-L-phenylalaninlyamido)-5-deoxy-1,2-O-isopropylidene-
a
-D-xylofuranose (3f)
24
White solid; yield: 0.38 g (86%); mp: 135e140 ꢂC; [
a]
¼ þ35.8
6.75 (m, 1H, NH) ppm; 13C NMR (CDCl3, 75.5 MHz): 17.96 (alaCH3),
d
D
26.20 (CH3), 26.91 (CH3), 28.41 (BocCH3), 37.21 (alaCH), 50.10 (C-5),
73.78 (C-2), 79.95 (C-3), 80.56 (BocC(CH3)3), 84.86 (C-4), 104.86 (C-
1), 111.40 (C(CH3)2), 155.59 (BocCO), 174.78 (NHCO) ppm; Anal. calcd.
for C16H28N2O7: C, 53.32; H, 7.83; N, 7.77%; found: C, 53.19; H, 7.51;
N, 7.58%; MS (ESIþ): m/z ¼ 361 [M þ H]þ.
(CHCl3, c 0.1); IR (KBr, ymax): 3429, 3351, 2983, 2932 (NeH), 1665
(C]O), 1523, 1168, 1007, 858, 592 cmꢀ1; 1H NMR (CDCl3, 300 MHz):
d
1.28 (s, 3H, CH3), 1.41 (s, 9H, BocCH3), 1.49 (s, 3H, CH3), 3.02e3.10
(m, 3H, H-5 and ArCH2), 3.63e3.74 (m, 1H, H-5), 3.85e3.90 (m, 2H,
3
H-3 and OH), 4.21e4.28 (m, 1H, BocNHCH), 4.48 (d, JH,H ¼ 3.4 Hz,
1H, H-2), 4.67 (d, 3JH,H ¼ 2.0 Hz, 1H, BocNH), 4.97 (m, 1H, H-4), 5.79
3
(d, JH,H ¼ 3.4 Hz, 1H, H-1), 6.39 (bs, 1H, BocNH), 7.15 (m, 2H, Ar),
5-(N-Boc-L-valinlyamido)-5-deoxy-1,2-O-isopropylidene-a-D-
7.25e7.31 (m, 3H, Ar) ppm; 13C NMR (CDCl3, 75.5 MHz):
d 26.17
xylofuranose (3c)
24
(CH3), 26.84 (CH3), 28.33 (BocCH3), 37.21 (phealaCH2), 38.45 (phea-
laCH), 55.97 (C-5), 73.74 (C-2), 79.67 (C-3), 80.39 (BocC(CH3)3), 84.85
(C-4), 104.77 (C-1), 111.35 (C(CH3)2), 127.11 (Ar), 128.71 (Ar), 129.24
(Ar), 136.32 (Ar), 155.40 (BocCO), 173.34 (NHCO), ppm; Anal. calcd.
for C22H32N2O7: C, 60.54; H, 7.39; N, 6.42%; found C, 60.19; H, 7.05;
N, 6.14%; MS (ESIþ): m/z ¼ 437 [M þ H]þ.
White solid; yield: 0.36 g (92%); mp: 130e135 ꢂC; [
a
]
¼ þ16.93
D
(CHCl3, c 0.1); IR (KBr, ymax): 3397, 3341, 2984, 2929 (NeH), 1657
(C]O), 1528, 1166, 1015, 861, 638 cmꢀ1; 1H NMR (CDCl3, 400 MHz):
3
d
0.95 (dd, JH,H ¼ 6.4 Hz and 8.9 Hz, 6H, valCH3), 1.29 (s, 3H, CH3),
1.44 (s, 3H, CH3), 1.45 (s, 9H, BocCH3), 1.51e1.53 (m, 1H, valCH),
3.19e3.23 (m, 1H, H-5), 3.75e3.82 (m, 2H, H-5 and H-3), 3.88 (s, 1H,
OH), 3.96e3.98 (m,1H, BocNHCH), 4.51 (d, JH,H ¼ 3.9 Hz, 1H, H-2),
3
4.72 (bs, 1H, BocNH), 4.97 (dd, JH,H ¼ 7.9 Hz and 1.0 Hz, 1H, H-4),
3
General procedure for the synthesis of ferrocenyl pseudo-dipeptides
(5aef)
5.84 (d, JH,H ¼ 3.9 Hz, 1H, H-1), 6.71 (m, 1H, NH) ppm; 13C NMR
3
(CDCl3, 75.5 MHz): d
17.86 (valCH3),19.31 (valCH3), 26.09 (CH3), 26.82
(CH3), 28.27 (BocCH3), 30.22 (valCH), 37.11 (valCH), 60.3 (C-5), 73.77
(C-2), 79.85 (C-3), 80.55 (BocC(CH3)3), 84.80 (C-4), 104.81 (C-1),
111.53 (C(CH3)2), 161.11 (BocCO), 174.16 (NHCO) ppm; Anal. calcd. for
The selective N-Boc deprotection of the pseudo-dipeptides
(3aef) (1 mmol) was carried out by reacting them with a TFA-
CH2Cl2 mixture (50% v/v, 4 mL). The stirring was continued till the
disappearance of the starting material (approximately 4 h) and the
solvent was evaporated to dryness. The resulting residue was dis-
solved in CH2Cl2 and cooled in an ice bath. To this solution, Et3N
(1 mmol) was added drop wise and the resulting solution was
stirred at 0 ꢂC for 30 min. At this temperature, a solution of ferro-
cenoyl chloride (approx. 1 mmol) in CH2Cl2 and Et3N (1.5 mmol)
were added. The reaction mixture was allowed to attain room
temperature and the stirring was continued for 12 h. The reaction
mixture was quenched with saturated NaHCO3 solution and
extracted with CH2Cl2. After drying over anhydrous NaSO4, the
combined organic layers were evaporated to dryness and the crude
compound was purified by silica gel column chromatography using
hexane and ethyl acetate mixture.
C
18H32N2O7: C, 55.65; H, 8.30; N, 7.21%; found: C, 55.49; H, 8.19; N,
7.15%; MS (ESIþ): m/z ¼ 389 [M þ H]þ.
5-(N-Boc-L-leucinlyamido)-5-deoxy-1,2-O-isopropylidene-a-D-
xylofuranose (3d)
24
White solid; yield: 0.35 g (87%); mp: 120e125 ꢂC; [
a]
¼ ꢀ12.97
D
(CHCl3, c 0.1); IR (KBr, ymax): 3363, 2979, 2927 (NeH), 1661 (C]O),
1522, 1169, 1011, 860, 650 cmꢀ1; 1H NMR (CDCl3, 300 MHz):
d
0.94
(dd, 6H, 3JH,H ¼ 3.8 Hz and 2.3 Hz, leuCH3), 1.28 (s, 3H, CH3), 1.40 (s,
12H, BocCH3 and CH3),1.61e1.68 (m, 3H, leuCH2 and leuCH), 3.15e3.22
(m, 1H, H-5), 3.46 (s, 1H, OH), 3.70e3.80 (m, 1H, H-5), 3.81e3.84 (d,
3JH,H ¼ 2.3 Hz, 1H, BocNHCH), 3.91e4.01 (m, 1H, H-3), 4.49 (d, 1H,
3JH,H ¼ 3.0 Hz, H-2), 4.68 (bs, 1H, BocNH), 4.77 (m, 1H, H-4), 5.82 (d,
1H, 3JH,H ¼ 3.0 Hz, H-1), 6.71 (bs, 1H, CONH) ppm; 13C NMR (CDCl3,
75.5 MHz):
d
21.86 (leuCH3), 22.86 (leuCH3), 24.72 (leuCH2), 26.07
(CH3), 26.77 (CH3), 28.25 (BocCH3), 37.03 (leuCH), 40.57 (leuCH3),
53.17 (C-5), 73.66 (C-2), 79.89 (C-3), 80.65 ((BocC(CH3)3), 84.71 (C-
4), 104.80 (C-1), 111.47 (C(CH3)2), 155.83 (BocCO), 175.04 (NHCO)
ppm; Anal. calcd. for C19H34N2O7: C, 56.70; H, 8.51; N, 6.96%; found:
C, 56.58; H, 8.27; N, 6.38%; MS (ESIþ): m/z ¼ 403 [M þ H]þ.
5-(N-ferrocenoyl-L-glycinylamido)-5-deoxy-1,2-O-isopropylidene-
a
-D-xylofuranose (5a)
Orange solid; yield: 0.29 g (63%); m. p.: 75 ꢂC; [
a
]
D
24: þ30.12
(CH3OH, c 0.1); IR (KBr, ymax): 3423, 2932 (NeH), 1634 (C]O), 1544,
1379, 1163, 1074, 822, 627 cmꢀ1; 1H NMR (CDCl3, 300 MHz):
d 1.30
(s, 3H, CH3), 1.47 (s, 3H, CH3), 3.30e3.40 (m, 2H, H-5), 3.76e3.80 (m,
1H, H-3), 4.06e4.08 (m, 3H, GlyCH2, OH), 4.11e4.17 (m,1H, H-4), 4.22
(s, 5H, C5H5), 4.34 (dd, J ¼ 1.6 and 1.4 Hz, 2H, C5H4), 4.57 (d,
J ¼ 3.1 Hz, H-2), 4.71 (dd, J ¼ 1.6 Hz and 1.4 Hz, 2H, C5H4), 5.91 (d,
J ¼ 3.1 Hz, H-1), 6.64 (m, 1H, NH), 7.10e7.13 (m, 1H, NH) ppm; 13C
5-(N-Boc-L-isoleucinlyamido)-5-deoxy-1,2-O-isopropylidene-
a-D-
xylofuranose (3e)
24
White solid; yield: 0.34 g (84%); mp: 135e140 ꢂC; [
a]
¼ þ22.13
D
(CHCl3, c 0.1); IR (KBr, ymax): 3356, 2978, 2930 (NeH), 1663 (C]O),
1522, 1169, 1016, 856, 650 cmꢀ1 1H NMR (CDCl3, 400 MHz):
;
NMR (CDCl3, 75.5 MHz): d 26.09 (CH3), 26.80 (CH3), 37.42 (CH2),
d
0.92e0.95 (m, 6H, isoleuCH3), 1.08e1.17 (m, 2H, isolueCH2), 1.29 (s,
43.52 (C-5), 68.25, 68.31, 69.88, 71.03 (Cp), 73.94 (C-2), 79.50 (C-3),
84.81 (C-4), 104.80 (C-1), 111.59 (C(CH3)2), 171.36 (CO), 171.97 (CO),
ppm; Anal. calcd for C21H26FeN2O6: C, 55.04; H, 5.72; N, 6.11%;
found C, 54. 79; H, 5.43; N 5.81%; MS (ESIþ): m/z ¼ 481 [M þ Na]þ.
3H, CH3), 1.45 (s, 12H, BocCH3 and CH3), 1.87e1.97 (m, 1H, isoleuCH),
3.18e3.23 (m, 1H, H-5), 3.71e3.85 (m, 2H, H-5 and H-3), 3.87 (s, 1H,
OH), 3.96e3.99 (m, 1H, BocNHCH), 4.51 (d, JH,H ¼ 2.9 Hz, 1H, H-2),
3

32
S.B. Deepthi et al. / Journal of Organometallic Chemistry 774 (2014) 26e34
5-(N-ferrocenoyl-L-alaninylamido)-5-deoxy-1,2-O-isopropylidene-
(s,1H, C5H4), 5.90 (d,1H, 3JH,H ¼ 3.5 Hz, H-1), 6.35e6.38 (m,1H, NH),
a
-D-xylofuranose (5b)
7.47e7.33 (m, 1H, NH) ppm; 13C NMR (CDCl3, 75.5 MHz):
d 11.17
Orange solid; yield: 0.27 g (57%); mp: 74 ꢂC; [
a]
24: þ44.69
(
isoleuCH3), 15.56
(
isoleuCH3), 25.10
(
isoleuCH2), 26.08 (CH3),
D
(CH3OH, c 0.1); IR (KBr, ymax): 3446, 2929 (NeH), 1635 (C]O), 1540,
26.82(CH3), 37.32 (isoleuCH), 43.41 (isoleuCH), 57.88 (C-5), 67.93,
68.50, 69.79, 70.88 (Cp), 73.84 (C-2), 79.53 (C-3), 84.81 (C-4),104.78
(C-1),111.56 (C(CH3)2),171.96 (CO),173.79 (CO) ppm; Anal. calcd. for
1379,1163,1075, 625 cmꢀ1; 1H NMR (CDCl3, 300 MHz):
d 1.28 (s, 3H,
CH3), 1.43 (s, 3H, CH3), 1.47 (bs, 3H, alaCH3), 3.31e3.33 (m, 1H, H-5),
3.76e3.81 (m, 1H, H-5), 4.04 (s, 1H, OH), 4.09e4.12 (m, 1H, H-3),
4.21 (s, 5H, C5H5), 4.40 (bs, 2H, C4H4), 4.57 (d, 1H, 3JH,H ¼ 3.0 Hz, H-
2), 4.64e4.65 (m, 1H, alaNHCH), 4.67 (bs, 1H, C4H4), 4.70 (bs, 1H,
C4H4), 4.74e4.76 (m, 1H, H-4), 5.91 (d, 3JH,H ¼ 3.0 Hz, 1H, H-1), 6.34
(d, J ¼ 6.7 Hz, NH), 6.80e6.83 (m, 1H, NH), ppm; 13C NMR (CDCl3,
C
25H34FeN2O6: C, 58.37; H, 6.66; N, 5.45%; found: C, 57.94; H, 6.56;
N, 5.27%; MS (ESIþ): (m/z) ¼ 537 [M þ H]þ.
5-(N-ferrocenoyl-L-phenylalaninylamido)-5-deoxy-1,2-O-
isopropylidene-
a-D-xylofuranose (5f)
75.5 MHz):
d
17.73 (alaCH3), 25.06 (CH3), 25.80 (CH3), 36.36 (alaCH),
Orange solid; yield: 0.42 g (73%); mp: 108 ꢂC; [
a]
24: þ41.62
D
47.97 (C-5), 60.99, 67.13, 67.25, 68.87 (Cp), 72.78 (C-2), 78.58 (C-3),
83.78 (C-4), 103.80 (C-1), 110.56 (C(CH3)3), 170.16 (CO), 173.60 (CO)
ppm; Anal. calcd for C22H28FeN2O6: C, 55.95; H, 5.98; N, 5.93%;
found C, 55.73; H, 5.79; N 5.68%; MS (ESIþ): m/z ¼ 495 [M þ Na]þ.
(CH3OH, c 0.1); IR (KBr, ymax): 3321, 3089, 2985, 2930 (NeH), 1625
(C]O), 1536, 1164,1075, 860, 699 cmꢀ1; 1H NMR (CDCl3, 300 MHz):
d
1.28 (s, 3H, CH3), 1.44 (s, 3H, CH3), 3.14e3.28 (m, 3H, ArCH2 and H-
5), 3.68e3.76 (m, 1H, H-5), 3.92e3.95 (m, 1H, phealaNHCH), 4.06 (s,
5H, C5H5), 4.25 (s, 1H, OH), 4.32e4.36 (m, 2H, C5H4), 4.52e4.54 (m,
2H, C5H4), 4.72e4.86 (m, 2H, H-4 and H-2), 5.88 (d, 1H,
5-(N-ferrocenoyl-L-valinylamido)-5-deoxy-1,2-O-isopropylidene-a-
3
D-xylofuranose (5c)
3JH,H ¼ 3.8 Hz, H-1), 6.27 (d, 1H, JH,H ¼ 7.4 Hz, NH), 7.28e7.38 (m,
Orange solid; yield: 0.29 g (60%); mp: 74 ꢂC; [
a]
24: ¼ ꢀ1.71
5H, Ar), 6.96 (m, 1H, NH) ppm; 13C NMR (CDCl3, 75.5 MHz):
D
(CH3OH, c 0.1); IR (KBr, ymax): 3317, 3095, 2963, 2932 (NeH), 1631
d
26.09(CH3), 26.82(CH3), 38.18 (PheCH), 37.32 (PheCH2), 54.59 (C-5),
(C]O), 1533,1163, 1075, 823, 635 cmꢀ1; 1H NMR (CDCl3, 300 MHz):
67.64, 68.70, 69.81, 70.91 (Cp), 73.77 (C-2), 79.37 (C-3), 84.85 (C-4),
104.76 (C-1), 111.52 (C(CH3)3), 127.36, 128.90, 129.10, 136.27 (Ar),
171.38 (CO), 173.25 (CO) ppm; Anal. calcd. for C28H32FeN2O6: C,
61.32, H, 5.88, N, 5.11%; found: C, 61.04; H, 5.72; N, 5.07%; MS (ESIþ):
m/z ¼ 571 [M þ H]þ.
d
1.03 (s, 3H, valCH3), 1.04 (s, 3H, valCH3), 1.28 (s, 3H, CH3), 1.43 (s, 3H,
CH3), 2.18e2.24 (m, 1H, valCH), 3.36e3.41 (m, 1H, H-5), 3.76e3.82
(m, 1H, H-5), 4.01e4.10 (m, 1H, H-3), 4.02 (s, 1H, OH), 4.22 (s, 1H,
C5H5), 4.24e4.25 (m,1H, valNHCH), 4.37e4.40 (m, 3H, C5H4 and H-2),
4.55 (dd, 1H, J ¼ 5.3 and 3.4 Hz, H-4), 4.69 (s, 1H, C5H4), 4.73 (s, 1H,
C5H4), 5.89 (d, J ¼ 3.5 Hz, H-1), 6.42 (d, J ¼ 8.5 Hz, NH), 6.81e6.82
X-crystallography
(m, 1H, NH) ppm; 13C NMR (CDCl3, 75.5 MHz):
d 173.74 (CO), 171.32
(CO), 111.57 (C(CH3)2), 104.73 (C-1), 84.80 (C-4), 79.55 (C-3), 73.81
X-ray data for the compound 3b was collected at room tem-
perature using a Bruker Smart Apex CCD diffractometer with
(C-2), 70.90, 69.81, 68.56, 67.92 (Cp), 58.74 (C-5), 37.31 (valCH), 31.04
(
valCH), 26.84 (CH3), 26.09 (CH3), 19.44 (alaCH3), 18.54 (valCH3) ppm;
graphite monochromated MoK
a
radiation (
l
¼ 0.71073 Å) using
u-
Anal. calcd. for C24H32FeN2O6: C, 57.61; H, 6.45; N, 5.60%; found: C,
scan method. Preliminary lattice parameters and orientation
matrices were obtained from four sets of frames. Unit cell di-
mensions were determined using 6163 reflections in the range of
57.49; H, 6.12; N, 5.47%; MS (ESIþ): m/z ¼ 523 [M þ Na]þ.
5-(N-ferrocenoyl-L-leucinylamdio)-5-deoxy-1,2-O-isopropylidene-
2.45 < q
< 27.90ꢂ. Integration and scaling of intensity data was
a
-D-xylofuranose (5d)
accomplished using SAINT program [65]. The structure was solved
by direct methods using SHELXS97 and refinement was carried out
by full-matrix least-squares technique using SHELXL97 [66].
Anisotropic displacement parameters were included for all non-
hydrogen atoms. The hydrogen atoms attached to nitrogen and
oxygen atoms were located in a difference density map and refined
isotropically. All other H atoms were positioned geometrically and
treated as riding on their parent C atoms [CeH ¼ 0.93e0.97 Å and
24
Orange solid; yield: 0.32 g (62%); mp: 160 ꢂC; [
a]
¼ ꢀ4.42
D
(CH3OH, c 0.1); IR (KBr, ymax): 3327, 2931, 2851, 1661 (C]O), 1533,
1163, 1012, 859, 656 cmꢀ1; 1H NMR (CDCl3, 300 MHz):
d
0.96e1.01
(m, 6H, leuCH3), 1.07e1.16 (m, 2H, leuCH2), 1.28 (s, 3H, CH3), 1.44 (s,
3H, CH3), 1.91e1.94 (m, 1H, leuCH), 3.32e3.34 (m, 1H, H-5),
3.43e3.47 (m, 1H, H-5), 3.77e3.84 (m, 1H, H-3), 3.99 (s, 1H, OH),
4.07e4.09 (m, 2H, leuNHCH and H-2), 4.21 (s, 5H, C5H4), 4.39 (dd,
2H, 3JH,H ¼ 1.6 Hz and 1.5 Hz, C5H4), 4.56 (dd, 1H, 3JH,H ¼ 4.4 Hz and
3.2 Hz, H-4), 4.74 (dd, 2H, 3JH,H ¼ 1.6 Hz and 1.5 Hz, C5H4), 5.89 (d,
3JH,H ¼ 3.5 Hz, 1H, H-1), 6.05e6.07 (m, 1H, NH), 6.98e7.01 (m, 1H,
U
iso(H) ¼ 1.5Ueq(C) for methyl H or 1.2Ueq(c) for other H atoms]. The
methyl groups were allowed to rotate but not to tip. In the absence
of significant anomalous scattering effects, Friedel pairs were
merged. The absolute configuration of the procured material was
known in advance.
NH) ppm; 13C NMR (CDCl3, 75.5 MHz):
d
22.01 (leuCH3), 22.96
(
leuCH3), 24.88 (leuCH2), 26.06 (CH3), 26.81 (CH3), 33.86 (leuCH),
40.94 (leuCH), 51.80 (C-5), 68.17, 68.27, 69.81, 70.91 (Cp), 73.80 (C-2),
79.62 (C-3), 84.79 (C-4), 104.77 (C-1), 111.56 (C(CH3)3), 171.25 (CO),
174.63 (CO) ppm; Anal. calcd for C25H34FeN2O6: C, 58.37; H, 6.66; N,
5.45%; found: C, 58.14; H, 6.41; N, 5.11%; MS (ESIþ): m/z ¼ 537
[M þ Na]þ.
Crystal data for 3b: C16H28N2O7, M ¼ 360.40, colourless block,
0.21 ꢁ 0.18 ꢁ 0.08 mm3, orthorhombic, space group P212121 (No.
19),
a
¼
9.4265(6),
b
¼
12.4214(8),
c
¼
16.6600(11) Å,
V ¼ 1950.7(2) Å3, Z ¼ 4, Dc ¼ 1.227 g/cm3, F000 ¼ 776, CCD Area
Detector, MoK
a
radiation,
l
¼ 0.71073 Å, T ¼ 294(2)K, 2qmax ¼ 50.0ꢂ,
18772 reflections collected, 1973 unique (Rint ¼ 0.0177). Final
5-(N-ferrocenoyl-L-isoleucinylamido)-5-deoxy-1,2-O-
GooF ¼ 1.050, R1 ¼ 0.0286, wR2 ¼ 0.0731, R indices based on 1901
isopropylidene-
a
-D-xylofuranose (5e)
reflections with I > 2s
(I) (refinement on F2), 245 parameters, 0 re-
Orange solid; yield: 0.36 g (69%); mp: 88 ꢂC; [
a]
24: ꢀ27.69
straint,
m
¼ 0.096 mmꢀ1
.
D
(CH3OH, c 0.1); IR (KBr, ymax): 3320, 2965, 2934 (NeH), 1632 (C]O),
1532, 1163, 1075, 860, 636 cmꢀ1
;
1H NMR (CDCl3, 300 MHz):
In vitro cytotoxicity assay
d
0.93e1.01 (m, 8H, isoleuCH2 and isoleuCH3), 1.28 (s, 3H, CH3), 1.44 (s,
3H, CH3), 1.60e1.64 (m, 1H, isoleuCH), 3.32e3.37 (m, 1H, H-5),
The cell lines used for testing the in vitro cytotoxicity included
A549 derived from human alveolar adenocarcinoma epithelial cells
(ATCC No. CCL-185), HeLa derived from human cervical cancer cells
(ATCC No. CCL-2), MDA-MB-231 derived from human breast
iso-
3.76e3.82 (m, 1H, H-5), 4.01 (s, 1H, OH), 4.09e4.12 (m, 2H,
leuNHCH and H-3), 4.21 (s, 1H, C5H5), 4.38e4.41 (m, 3H, C5H4 and H-
2), 4.56 (dd, 3JH,H ¼ 6.7 Hz and 3.5 Hz, H-4), 4.68 (s, 1H, C5H4), 4.71

S.B. Deepthi et al. / Journal of Organometallic Chemistry 774 (2014) 26e34
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33
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