Administration of ferrocene-modified amino acids induces changes in synaptic transmission in the CA1 area of the hippocampus

Article abstract of DOI:10.1002/aoc.5276

A series of ferrocene-modified amino acid methyl esters with pyrazole linker was prepared in good to quantitative yields starting from easy accessible ferrocene pyrazole carbaldehyde and amino acids in racemic and enantio enriched forms under reductive amination conditions (NaBH (OAc)₃, reflux, 3 hr). The resulting enantiomers were resolved using analytical HPLC on modified cellulose or amylose as chiral selectors. In vivo electrophysiological experiments were performed in the CA1 field of the hippocampus on 3a Fc-Gly, (L)-3b Fc-Ala, and (D)-3b Fc-Ala compounds. An increasing in the amplitudes of responses of local potentials (up to 25%) of the CA1 region in the studied groups was found after intraperitoneal administration of ferrocene compounds 3a and (D)-3b compared with control rats treated with saline.

Full text of DOI:10.1002/aoc.5276

Received: 25 February 2019
DOI: 10.1002/aoc.5276
Revised: 28 August 2019
Accepted: 11 September 2019
F U L L P A P E R
Administration of ferrocene-modified amino acids induces
changes in synaptic transmission in the CA1 area of the
hippocampus
Alexey N. Rodionov1 | Lubov V. Snegur1
| Yulia V. Dobryakova2
|
Mikhail M. Ilyin Jr1 | Vladimir A. Markevich2 | Alexander A. Simenel1,3
1A.N. Nesmeyanov Institute of
A series of ferrocene-modified amino acid methyl esters with pyrazole
linker was prepared in good to quantitative yields starting from easy acces-
sible ferrocene pyrazole carbaldehyde and amino acids in racemic and
enantio enriched forms under reductive amination conditions (NaBH
(OAc)3, reflux, 3 hr). The resulting enantiomers were resolved using analyt-
ical HPLC on modified cellulose or amylose as chiral selectors. In vivo elec-
trophysiological experiments were performed in the CA1 field of the
hippocampus on 3a Fc-Gly, (L)-3b Fc-Ala, and (D)-3b Fc-Ala compounds.
An increasing in the amplitudes of responses of local potentials (up to
25%) of the CA1 region in the studied groups was found after intraperito-
neal administration of ferrocene compounds 3a and (D)-3b compared with
control rats treated with saline.
OrganoElement Compounds, Russian
Academy of Sciences, 28 Vavilov St.,
119991, Moscow, Russian Federation
2Institute for Higher Nervous Activity and
Neurophysiology, Russian Academy of
Sciences, Russian Federation
3Moscow State Mining University, 6
Leninsky Av, 119991, Moscow, Russian
Federation
Correspondence
Lubov V. Snegur, A.N. Nesmeyanov
Institute of OrganoElement Compounds
Russian Academy of Sciences, 28 Vavilov
Street, 119991 Moscow, Russian
Federation.
Email: snegur@ineos.ac.ru
K E Y W O R D S
ferrocene amino acids, hippocampus, HPLC, in vivo electrophysiological experiment, local field
potential
1 | INTRODUCTION
carboxybenzoyl ferrocene), which is the first and only
currently ferrocene-based drug, has been effectively used
Chemistry of metallocenes has been intensively devel-
oped for more than six decades.[1] During the first two
decades of the 21st century, special attention was paid to
the synthesis and bioassay of ferrocene derivatives carry-
ing pharmacophoric groups, namely, nucleic bases, oligo-
nucleotides, various heterocycles, amino acids, peptides,
and sugars.[2–8] In vitro and in vivo studies have demon-
strated that many of such modified ferrocenes display a
wide spectrum of biological activities, including
for a long time for the treatment of iron deficiency pathol-
ogies.[19] However, a potential of ferrocene-substituted
amino acids as drug candidates for the treatment of disor-
ders, especially neurodegenerative ones, is out of view of
scientists. At the same time, according to the projections
of the World Health Organization[20] these are precisely
the disorders which will dominate in the nearest future
and exceed the incidence of cancer and cardiovascular
diseases.
antianemic,[9]
antimicrobial,[10]
antibacterial,[11]
The few literary data[21–25] as well as our own bio-
logical research results,[26] suggest that it is ferrocene-
modified compounds, including those based on amino
antimalarial,[12] tuberculostatic,[13,14] and especially anti-
tumor activities, see recent review articles.[15–18]
Ferroceron (tetrahydrate of sodium salt of ortho-
acids, that can have
a
significant impact on
Appl Organometal Chem. 2019;e5276.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5276

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RODIONOV ET AL.
neurodegenerative processes. In addition, neurodegen-
erative disorders are associated with aberrant iron
deposition in the brain.
It should be emphasized that biological effects of
the chiral ferrocene-based compounds in an enantio-
meric pure (or enantio enriched) forms earlier has vir-
tually been studied only upon planar chiral
ferrocenes.[31–33] Moreover, chemistry of such com-
pounds is presently scarcely investigated. At the same
time, these are precisely enantiomers which optimize
the state of the nervous system, and are involved in the
most important methylation and demethylation pro-
cesses. Furthermore, the so called "thalidomide tragedy"
which has been associated with the use of the drug tha-
lidomide in a racemic form and resulted in severe birth
defects, forced the world community to revise its atti-
tude to the enantiomeric purity of drug formulations
and to make the corresponding supplements to the
State Pharmacopoeias. Therefore, a need in additional
studies of the biological effects of individual stereoiso-
mers is inspired by the requirements of the Pharmaco-
poeias of many countries or regions[34] including
It is known, that iron-containing ferrocene moiety
endows the modified compounds with a number of useful
properties. First, it significantly decreases their toxic-
ity[5,17] and improve their lipid membrane penetrating
ability.[7] Moreover, it allows there compounds to exist
both in salt and neutral forms[27] providing their trans-
port in a blood flow, as well as across the membranes
into cytoplasm (polar medium). An ability of ferrocenyl-
substituted compounds to undergo oxidation and reduc-
tion[28,29] at physiological pH values is their substantial
advantage, that is to say, these compounds present a kind
of mediators, moreover, they can contribute to the trans-
mission of electrical impulses. Therefore, chemical modi-
fication of drugs intended for the treatment of brain
disorders (glycine, gamma-aminobutyric acid (GABA),
beta-phenyl derivatives of GABA (phenibut), other amino
acids, as well as drugs used to treat Alzheimer's disease,
particularly, memantin) enables one to improve the
mediator properties of the existing pharmaceuticals. For
instance, it is known that GABA, being a major mediator
involved in the central inhibition processes activates the
energetic processes in the brain, scarcely penetrates
across the blood-brain barrier (BBB) and only as small as
8% of GABA-containing drug aminalon reaches the brain
targets upon oral administration. A ferrocene moiety
which is generally agreed to be a good vehicle[4,7,17] over-
comes readily the BBB (though this hypothesis did not
find sufficient experimental support[30]) and can facilitate
the targeted drug delivery to the brain. Authors[24] con-
clude that administration of the lipophilic iron-
containing ferrocene compound leads to subtle perturba-
tions of cellular iron within the brain, potentially rep-
resenting a model of iron accumulation similar to that
seen in various neuropathological conditions.
Pharmaceutical
Committee
of
the
Russian
Federation,[35] and by the studies logic.
Herein, based on the commercially available ferro-
cene, we have developed a synthetic procedure and
obtained a series of ferrocenyl-substituted amino acids
with pyrazole linker, namely, glycine, alanine, phenyl
alanine, valine, serine, tyrosine, tryptophan, and proline
ones as methyl esters. This approach to ferrocenyl-
substituted amino acids comprises modification of syn-
thetically available ferrocenyl azoles[6] well-accepted in
terms of biological activity.[36] On the basis of a
ferrocene-pyrazole building block the third amino-acid
moiety was attached. For this purpose, selective
approaches to obtain isomeric ferrocenyl pyrazol carbal-
dehydes were proposed.[37,38] Their subsequent func-
tionalization via the reductive amination with the amino
acid methyl esters of both natural (including both L-, D-
or racemic-forms), and synthetic origin using sodium
SCHEME 1 Synthesis of ferrocene-
modified pyrazole amino acids methyl
esters, R = H (glycine) (a); Me (alanine-
DL, L, D) (b); CH2Ph (phenyl alanine-
DL, L, D) (c); Et (valine-DL, L, D) (d);
CH2OH (serine-DL, L) (e);
4-HOC6H4CH2 (tyrosine-DL, L, D) (f);
CH2-3-indole (tryptophan-DL, L) (g);
proline (DL, L) (h), and Et (α-amino
butyric acid-DL, L, D)) (i)

FERROCENE-BASED AMINO ACIDS AND THE HIPPOCAMPUS
3 of 13
triacetoxyborohydride as a reducing agent affords the
ferrocene-pyrazolyl-amino acids (Scheme 1). As a result,
various ferrocene-substituted amino acids in the form of
methyl esters in good yields were obtained and character-
ized by 1H, 13C NMR, EI-MS, IR and microanalytical
data. It should be noted that all the above reactions are
well scaled up, allowing one to obtain these compounds
in amounts sufficient to perform biological assays. A
series of racemic (L,D)-ferrocene-based pyrazole amino
acids methyl esters (8 pairs of ferrocene-based com-
pounds) was separated, into enantiomers by analytical
HPLC on modified cellulose or amylose as chiral selec-
tors. Based on HPLC results, the enantiomeric purity of
the final ferrocene products derived from L- or D-amino
acids was evaluated. For L- and D-enantiomers the spe-
cific rotation was determined.
obtained via reaction of amino acids with SOCl2 in
methanol.[40]
1H and 13C NMR spectra were recorded on a Bruker
DRX-500 spectrometer at 500.13 and 125.76 MHz, respec-
tively, in CDCl3. Chemical shifts are given in ppm rela-
tive to solvent residual protons (see Supporting
Information). EI mass spectra were recorded on a Fin-
nigan Polaris Q spectrometer (ionizationꢀenergy 70 eV,
the ionization chamber temperature 250 С). IR spectra
were taken on a BrukerTEM37 FTIR spectrometer (KBr
pellets).
2.2 | General procedure
To
a solution of 1-phenyl-3-ferrocenyl-1H-pyrazole-
In the Institute of Higher Nervous Activity and
Neurophysiology of Russian Academy of sciences pri-
mary studies of a biological action of the first repre-
4-carbaldehyde (1.0 mmol) and an amino acid ester
hydrochloride (1.2 mmol) in dried 1,2-dichloroethane
(35 ml) Et3N (0.17 ml, 1.2 mmol) was added followed by
sodium triacetoxy borohydride (0.30 g, 1.4 mmol). The
reaction mixture was heated under reflux for 1–3 hr con-
trolling by TLC. After cooling it for 20 ꢀC, 30 ml of the
saturated aqueous NaHCO3 solution was added. The
product was extracted with dichloromethane (2×30 ml).
Organic fractions were combined and washed with
30 mL of the saturated sodium chloride solution and
dried over the anhydrous Na2SO4. The solvent was
removed under the reduced pressure. The residue was
purified by chromatography on silica gel, eluent CHCl3—
MeOH (9: 1). In some cases, the enantiomers were pre-
cipitated with 0.5 mol HCl in dioxane solution as hydro-
chlorides. Below are given the elemental analysis data,
IR, 1Н and 13С NMR spectroscopy as well as electron ion-
ization mass-spectrometry data for the racemic mixtures,
which are similar to the data for the individual
enantiomers.
sentatives of
a series of ferrocenyl amino acids,
namely, ferrocenyl (phenylpyrazolyl)-glycine methyl
ester (3a), ferrocenyl (phenylpyrazolyl)-(D)-alanine, (D)-
3b, and ferrocenyl (phenylpyrazolyl)-(L)-alanine, (L)-3b,
on the hippocampus which is a part of a temporal
lobe of the brain, have been performed. A significant
(up to 25%) rise of the amplitudes of the hippocampal
local potentials in the CA1 area upon intraperitoneal
administration of ferrocene compounds 3a, and indi-
vidual enantiomer (D)-3b, at a dose of 2.0 mg kg-1 was
established. Other enantiomer (L)-3b
a significant
increase in amplitude after high-frequency stimulation
(up to 85%) is shown.
Thus, primary in vivo electrophysiological studies
were carried out on the brain of animals using newly syn-
thesized ferrocene-amino acids methyl esters in both (L)-
and (D)-enantiomerically enriched forms.
2 | EXPERIMENTAL
2.2.1 | Methyl-2-[(1-phenyl-3-ferrocenyl-
1Н-pyrazole-4-yl)methylamino]acetate or
ferrocenyl (phenylpyrazolyl)glycine methyl
ester (3a)
2.1 | Starting materials and analytical
instrumentations
ꢀ
The
starting
1-phenyl-3-ferrocenyl-1H-pyrazolyl-
Yield 90%. Yellow powder, m.p. 102 С. Found (%): С,
4-carbaldehyde (1) was obtained by two-step procedure
from acetyl ferrocene and phenyl hydrazine in ethanol,
and the following cyclization in Vilsmeier-Haak condi-
tions according to a well-known procedure,[37] yield
85%, m.p. 118 ꢀC, lit. m.p.[39] 118 ꢀC. All solvents were
purified and dried by standards techniques. Sodium
triacetoxyborohydride NaBH (OAc)3 and amino acids
(Acros Organics) were used without preliminary purifi-
cation. Amino acid methyl ester hydrochlorides were
64.25; Н, 5.38; N, 9.80. С23Н23FeN3O2. Calculated (%): С,
64.35; Н, 5.40; N, 9.79. EI-MS, m/z (Irel (%)): 429 [M]+
(100). Н NMR (CDCl3), δ: 1.69 (br.s, 1 Н, NН); 3.64 (s,
2 Н, СН2); 3.77 (s, 3 Н, Me); 4.13 (s, 2 Н, СН2); 4.17 (s,
5 Н, Fc); 4.33, 4.82 (both s, by 2 Н, Fc); 7.28 (t, 1 Н, Рh,
J = 7.5 Hz); 7.45 (m, 2 Н, Рh); 7.75 (d, 2 Н, Рh, J = 8.0
Hz); 8.12 (s, 1 Н, CH). 13С NMR (CDCl3), δ: 42.9, 48.9,
52.1, 67.6, 68.8, 69.4, 77.9, 116.9, 118.6, 125.9, 127.6,
129.3, 139.9, 150.1, 171.4.
1

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RODIONOV ET AL.
2.2.2 | (DL)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]
propanoate or (DL)-ferrocenyl
(phenylpyrazolyl)-alanine methyl ester
(3b)
NMR (CDCl3), δ: 18.7, 19.5, 31.7, 42.8, 51.5, 66.7, 67.3,
67.4, 68.5, 69.2, 78.1, 118.4, 119.3, 125.7, 126.9, 129.3,
140.0, 149.9, 175.6.
2.2.6 | (L)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazol-4-yl)methyl-amino]-
3-phenyl propanoate or ferrocenyl
(phenylpyrazolyl)-phenylalanine methyl
ester, (L)-3c
Yield 90%. Yellow powder, m.p. 94 ꢀС. Found (%): С,
64.91; Н, 5.65; N, 9.29. С24Н25FeN3O2. Calculated (%): С,
65.02; Н, 5.45; N, 9.48. EI-MS, m/z (Irel (%)): 443 [M]+
1
(87), 378 [M – Ср]+ (100). IR, ν/cm–1: 1731 (СООМе). Н
NMR (CDCl3), δ: 1.31 (d, 3 Н, Me, J = 6.7 Hz); 2.02 (br.s,
1 Н, NН); 3.43 (q, 1 Н, СН, J = 6.7 Hz); 3.68 (s, 3 Н, Me);
3.70, 3.88 (both d, by 1 Н, СН2, J = 13.1 Hz); 4.02 (s, 5 Н,
Fc); 4.23, 4.75 (both s, by 2 Н, Fc); 7.12 (t, 1 Н, Рh, J = 7.2
Hz); 7.31 (m, 2 Н, Рh); 7.61 (d, 2 Н, Рh, J = 7.9 Hz); 7.80
(s, 1 Н, Pz). 13С NMR (CDCl3), δ: 19.2, 42.3, 51.9, 56.2,
67.2, 67.3, 68.6, 69.3, 78.0, 118.4, 119.1, 125.7, 126.8,
129.3, 140.0, 149.7, 176.0.
25
Yield 90%. Yellow powder, m.p. 130 ꢀС, [α]D –26.0
(c 1.0; CHCl3).
2.2.7 | (D)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazol-4-yl)methyl-amino]-
3-phenyl propanoate or ferrocenyl
(phenylpyrazolyl)-phenylalanine methyl
ester, (D)-3c
25
Yield 91%. Yellow powder, m.p. 130 ꢀС, [α]D +26.0
(c 1.0; CHCl3).
2.2.3 | (L)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]
propanoate, (L)-3b
Yield 90%. Yellow powder, m.p. 75 ꢀС, [α]D25 –27.2 (c 1.0;
МеCN).
2.2.8 | (DL)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
3-methylbutanoate or (DL)-ferrocenyl
(phenylpyrazolyl)-valine methyl
ester (3d)
2.2.4 | (D)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]
propanoate, (D)-3b
ꢀ
Yield 93%. Yellow powder, m.p. 116 С. Found (%): С,
69.40; Н, 5.65; N, 8.15. С26Н29FeN3O2. Calculated (%): С,
69.37; Н, 5.63; N, 8.09. EI-MS, m/z (Irel (%)): 471 [M]+
(70), 406 [M – Ср]+ (100). IR, ν/cm–1: 1726 (СООМе). 1Н
NMR (CDCl3), δ: 1.02 (d, 6 Н, Me, J = 6.8 Hz); 1.96 (br s,
1 Н, NН); 2.00—2.07 (m, 1 Н, СН); 3.21 (d, 1 Н, СН, J =
6.0 Hz); 3.74, 3.97 (both d, by 1 Н, СН2, J = 13.2 Hz); 3.79
(s, 3 Н, Me); 4.12 (s, 5 Н, Fc); 4.32, 4.89 (both s, by 2 Н,
Fc); 7.31 (t, 1 Н, Рh, J = 7.4 Hz); 7.43—7.48 (m, 2 Н, Рh);
7.72 (d, 2 Н, Рh, J = 7.8 Hz); 7.89 (s, 1 Н, Pz). 13С NMR
(CDCl3), δ: 18.7, 19.5, 31.7, 42.8, 51.5, 66.7, 67.3, 67.4,
68.5, 69.2, 78.1, 118.4, 119.3, 125.7, 126.9, 129.3, 140.0,
149.9, 175.6.
Yield 90%. Yellow powder, m.p. 74–75 ꢀС, [α]D25 +26.4 (с
1.0; МеCN).
2.2.5 | (DL)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazol-4-yl)methyl-amino]-
3-phenyl propanoate or ferrocenyl
(phenylpyrazolyl)-phenylalanine methyl
ester (3c)
ꢀ
Yield 90%. Yellow powder, m.p. 131-132 С. Found (%):
С, 69.40; Н, 5.45; N, 8.15. С30Н29FeN3O2. Calculated
(%): С, 69.37; Н, 5.46; N, 8.09. EI-MS, m/z (Irel (%)):
519 [M]+ (72), 454 [M – Ср]+ (100). IR, ν/cm–1: 1744
(СООМе). 1Н NMR (CDCl3), δ: 2.00 (br.s, 1 Н, NН);
3.00 (dd, 1H, CH2, J1 = 8.0, J2 = 13.0 Hz); 3.15 (dd, 1H,
CH2, J1 = 6.0, J2 = 13.0 Hz); 3.76 (t, 1 Н, СН, J = 7.0
Hz); 3.80 (s, 3 Н, Me); 3.86, 4.04 (both d, by 1 Н, СН2,
J = 13.5 Hz); 4.14 (s, 5 Н, Fc); 4.33, 4.79 (both s, by
2 Н, Fc); 7.28-7.42 (m, 5 H +1 Н, Рh); 7.49 (m, 2 Н,
Рh); 7.61 (s, 1 Н, Pz); 7.68 (d, 2 Н, Рh, J = 8.0 Hz);. 13С
2.2.9 | (L)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
3-methylbutanoate (HCl) or (L)-ferrocenyl
(phenylpyrazolyl)-valine methyl ester
hydrochloride, (L)-3d
Yield 90%. Yellow powder, m.p. 136 ꢀС, [α]D25-18.0 (c 1.0;
CHCl3).

FERROCENE-BASED AMINO ACIDS AND THE HIPPOCAMPUS
5 of 13
2.2.10 | (D)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
3-methylbutanoate × HCl or (D)-ferrocenyl
(phenylpyrazolyl)-valine methyl ester
hydrochloride, (D)-3d
13С NMR (CDCl3), δ: 29.8, 38.9, 42.5, 52.1, 62.5, 67.3,
67.6, 68.8, 69.4, 77.8, 115.7, 118.8, 118.9; 126.0, 127.3,
128.5; 129.4, 130.4; 139.8, 150.1, 155.3; 175.3.
2.2.14 | (L)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
3-(4-hydroxyphenyl)propanoate × HCl or
(L)-ferrocenyl (phenylpyrazolyl)-tyrosine
methyl ester hydrochloride, (L)-3f
25
Yield 90%. Yellow powder, m.p. 137 ꢀС, [α]D +17.9
(c 1.0; CHCl3).
2.2.11 | (DL)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
3-hydroxypropanoate or (DL)-ferrocenyl
(phenylpyrazolyl)-serine methyl ester, 3e
25
Yield 90%. Yellow powder, m.p. 182 ꢀС, [α]D –11.2
(c0.81; CHCl3).
2.2.15 | (D)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
3-(4-hydroxyphenyl)propanoate × HCl or
(D)-ferrocenyl (phenylpyrazolyl)-tyrosine
methyl ester hydrochloride, (D)-3f
ꢀ
Yield 87%. Yellow powder, m.p. 170 С. Found (%): С,
62.84; Н, 5.55; N, 9.20. С24Н25FeN3O3. Calculated (%): С,
62.76; Н, 5.49; N, 9.15. EI-MS, m/z (Irel (%)): 459 [M]+
1
(100), 394 [M – Ср]+ (84). IR, ν/cm–1: 1737 (СООМе). Н
NMR (CDCl3), δ: 2.70 (br.s, 2 Н); 3.58-3.72 (m, 2 Н, СН2);
3.78 (s, 3 Н, Me); 3.83, 4.05 (both d, by 1 Н, СН2, J = 13.2
Hz); 3.85 (m, 1H, CH); 4.11 (s, 5 Н, Fc); 4.32 (s, 2 Н, Fc);
4.83 (both s, by 1 Н, Fc); 7.23 (d, 1 Н, Рh, J = 7.3 Hz);
7.42-7.47 (m, 2 Н, Рh); 7.70 (d, 2 Н, Рh, J = 7.8 Hz); 7.90
(s, 1 Н, Pz). 13С NMR (CDCl3), δ: 42.4, 52.2, 62.0, 62.7,
67.2, 67.3, 68.6, 69.3, 77.8, 118.5, 118.7, 125.8, 126.8,
129.3, 139.8, 149.8, 173.3.
25
Yield 89%. Yellow powder, m.p. 182 ꢀС, [α]D +11.1
(c 0.74.; CHCl3).
2.2.16 | (DL)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
3-(1Н-indole-3-yl)propanoate or (DL)-
ferrocenyl (phenylpyrazolyl)-tryptophan
methyl ester (3g)
2.2.12 | (L)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
3-hydroxypropanoate or (L)-ferrocenyl
(phenylpyrazolyl)-serine methyl ester, (L)-
3e
ꢀ
Yield 80%. Orange powder, m.p.(decomp.) 178 С. Found
(%): С, 68.75; Н, 5.45; N, 10.10. С32Н30FeN4O2. Calculated
(%): С, 68.82; Н, 5.41; N, 10.03. EI-MS, m/z (Irel (%)):
558 [M]+ (60), 493 [M – Ср]+ (46). IR, ν/cm–1: 1736
25
1
ꢀ
Yield 87%. Yellow powder, m.p. 165-166 С, [α]D –12.5
(c 1.0; CHCl3).
(СООМе). Н NMR (CDCl3), δ: 2.17 (br s, 1 Н, NН); 3.10
(dd, 1H, CH2, J1 = 8.2, J2 = 14.3 Hz); 3.31 (dd, 1H, CH2, J1
= 4.8, J2 = 14.3 Hz); 3.76 (s, 3 Н, Me); 3.79, 4.01 (both d, by
1 Н, СН2, J = 13.9 Hz); 3.86 (d, 1 Н, СН, J1 = 4.8, J2 = 8.2
Hz); 4.05 (s, 5 Н, Fc); 4.20, 4.26, 4.63, 4.72 (all s, by 1 Н, Fc);
7.03 (s, 1 Н, Ar); 7.14-7.24 (m, 3 Н, Ar); 7.34-7.52 (m, 5 Н,
Рh); 7.70 (d, 1 Н, Pz, J = 7.7 Hz); 8.36 (s, 1 Н, NH-indole);.
13С NMR (CDCl3), δ: 29.5, 42.5, 51.9, 61.1, 67.1, 67.3, 68.6,
69.2, 78.0, 111.0, 111.3, 118.3, 118.7, 119.0, 119.5, 122.1;
123.2, 125.6, 126.6, 127.2, 129.2; 136.2; 139.8, 149.7, 175.3.
2.2.13 | (DL)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
3-(4-hydroxyphenyl)propanoate or (DL)-
ferrocenyl (phenylpyrazolyl)-tyrosine
methyl ester, 3f
ꢀ
Yield 90%. Yellow powder, m.p. 170 С. Found (%): С,
67.40; Н, 5.40; N, 7.85. С30Н29FeN3O3. Calculated (%): С,
67.30; Н, 5.46; N, 7.85. EI-MS, m/z (Irel (%)): 535 [M]+
1
(34), 470 [M – Ср]+ (58). IR, ν/cm–1: 1732 (СООМе). Н
2.2.17 | (L)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
3-(1Н-indole-3-yl)propanoate or (L)-
ferrocenyl (phenylpyrazolyl)-tryptophan
methyl ester, (L)-3g
NMR (CDCl3), δ: 1.95 (br s, 1 Н, NН); 2.83 (dd, 1H, CH2,
J1 = 8.0, J2 = 13.5 Hz); 2.97 (dd, 1H, CH2, J1 = 5.3, J2 =
13.5 Hz); 3.64 (m, 1 Н, CH); 3.73 (s, 3 Н, Me); 3.78, 3.96
(both d, by 1 Н, СН2, J = 13.7 Hz); 4.06 (s, 5 Н, Fc); 4.26,
4.72 (both s, by 2 Н, Fc); 6.69, 7.03 (both d, by 2 Н, Рh,
J = 7.8 Hz); 7.18 (t, 1 Н, Рh, J = 7.2 Hz); 7.37-7.42 (m,
2 Н, Рh); 7.55 (s, 1 Н, Pz); 7.57 (d, 2 Н, Рh, J = 7.0 Hz).
25
ꢀ
Yield 78%. Yellow powder, m.p.(decomp.) 190 С, [α]D
–11.1 (c 1.0; CHCl3).

6 of 13
RODIONOV ET AL.
2.2.18 | (DL)-Methyl-1-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methyl]
pyrrolidine-2-carboxylate or (DL)-
ferrocenyl (phenylpyrazolyl)-proline
methyl ester (3h)
2.2.21 | (L)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
butanoate or (L)-ferrocenyl
(phenylpyrazolyl)-amino butyric methyl
ester, (L)-3i
25
Yield 90%. Yellow powder, m.p. 120 ꢀС, [α]D –41.2
ꢀ
Yield 80%. Yellow powder, m.p. 140 С. Found (%): С,
66.51; Н, 5.85; N, 8.90. С26Н27FeN3O2. Calculated (%):
С, 66.53; Н, 5.80; N, 8.95. EI-MS, m/z (Irel (%)):
469 [M]+ (100). IR, ν/cm–1: 1744 (СООМе). 1Н NMR
(CDCl3), δ: 1.92-2.09 (m, 3 Н); 2.21-2.32 (m, 1 Н);
2.54-2.63 (m, 1 Н); 3.22-3.27 (m, 1 Н); 3.38-3.43 (m,
1 Н); 3.75 (s, 3 Н, Me); 3.81, 4.08 (both d, by 1 Н, СН2,
J = 13.5 Hz); 4.17 (s, 5 Н, Fc); 4.36 (s, 2 Н, Fc);4.95,
4.98 (both s, by 1 Н, Fc); 7.28 (t, 1 Н, Рh, J = 7.5 Hz);
7.48-7.53 (m, 2 Н, Рh); 7.76 (d, 2 Н, Рh, J = 7.8 Hz);
7.92 (s, 1 Н, Pz). 13С NMR (CDCl3), δ: 21.9, 28.3, 47.0,
47.1, 52.8, 64.0, 66.7, 68.5, 69.2, 111.2, 118.4, 126.0,
129.0, 130.2; 139.0, 150.2, 167.0.
(c 0.73; CHCl3).
2.2.22 | (L)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
butanoate or (D)-ferrocenyl
(phenylpyrazolyl)-amino butyric methyl
ester, (D)-3i
25
Yield 90%. Yellow powder, m.p. 120 ꢀС, [α]D +38.7
(c 0.70; CHCl3).
2.3 | HPLC chromatographic separations
of enantiomers
2.2.19 | (L)-Methyl-1-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methyl]
pyrrolidine-2-carboxylate × HCl or (L)-
ferrocenyl (phenylpyrazolyl)-proline
methyl ester hydrochloride,
(L)-3h
Chiralcel OD and Chiralpak AS-H chiral columns (250 ×
4.6 mm, 5 μm) were used. The HPLC system (Advanced
Separation Technologies, Inc., Whippany, NJ, USA),
Bruker LC 31 with a UV 254 detector was operated at a
flow rate of 1.0 ml min−1 and an ambient temperature.
25
Yield 80%. Yellow powder, m.p. 156 ꢀС, [α]D +20.6
(c 1.07; CHCl3).
2.2.20 | (DL)-Methyl-2-[(1-phenyl-3-
ferrocenyl-1Н-pyrazole-4-yl)methylamino]-
butanoate × HCl or (DL)-ferrocenyl
(phenylpyrazolyl)-amino butyric
methyl ester hydrochloride
(3i)
Yield 90%. Yellow powder, m.p. 130-131 ꢀС. Found
(%): С, 65.60; Н, 6.01; N, 9.10. С25Н27FeN3O2. Calcu-
lated (%): С, 65.65; Н, 5.95; N, 9.19. EI-MS, m/z (Irel
(%)): 457 [M]+ (74), 392 [M – Ср]+ (100). IR, ν/cm–1:
1
1730 (СООМе). Н NMR (CDCl3), δ: 1.05 (t, 3 Н, Me,
J = 7.4 Hz); 1.72 (br s, 1 Н, NН); 1.77—1.88 (m, 2 Н,
СН2); 3.44 (t, 1 Н, СН, J = 6.5 Hz); 3.82, 4.05 (both d,
by 1 Н, СН2, J = 13.3 Hz); 3.84 (s, 3 Н, Me); 4.17 (s,
5 Н, Fc); 4.38, 4.91 (both s, by 2 Н, Fc); 7.28 (t, 1 Н,
Рh, J = 7.3 Hz); 7.48—7.52 (m, 2 Н, Рh); 7.77 (d, 2 Н,
Рh, J = 7.8 Hz); 7.95 (s, 1 Н, Pz). 13С NMR (CDCl3),
δ: 10.3, 26.7, 42.4, 51.7, 62.2, 67.2, 67.3, 68.5, 69.2,
78.0, 118.4, 119.2, 125.7, 126.8, 129.2, 139.9, 149.8,
175.7.
FIGURE 1 Effects of 3a and (D)-3b on field excitatory
postsynaptic potential (fEPSP) in the hippocampal CA1 region. The
time course of fEPSP in 3a (blue line, n=5), (D)-3b (green line,
n=4) and saline (black line, n=5) for 60 min after intraperitoneal
injection (i.p. injection) and after high frequency stimulation (HFS)
in anaesthetized rats. Each point represents the mean
S.E.M. percentage of basal fEPSP amplitude at 0 min; (*),
significant differences against the saline group, p<0.05

FERROCENE-BASED AMINO ACIDS AND THE HIPPOCAMPUS
7 of 13
2.4 | Electrophysiological experiments
sets was 30 s). Electrophysiological studies were per-
formed 30 min before the drug treatment, within 1 h after
the injection and within 1 h after the high-frequency
stimulation (Figure 1, 2).
Electrophysiological studies were carried out on the anes-
thetized Wistar rats weighting 350 g. The animals were
anesthetized with ethylcarbamate (1.75 g kg-1; intraperi-
toneally). Electrodes for the electric stimulation were
implanted according to the following stereotaxic coordi-
nates: hippocampal sector CA1 AP 2.7, L is 1.5; ventral
hippocampal commissure (VHC) AP 1.3, L is 1.0 with the
rat´s skull position at the same horizontal level. Bipolar
electrodes made from 80 μm diameter nichrome wire
were used for recording and stimulation. Penetration
depth of the stimulation and recording electrodes was
assessed from the recorded response measurements (opti-
mal ratio of amplitude and stimulating current). To
record the focal potentials of the field CA1 VHС was
stimulated with 50-100 μs rectangular pulses. A series of
ten paired stimulus presentations was applied (inter-
stimulus interval in a pair was 30 ms, pulse pair interval
was 20 s). Optimal parameters for the stimulating current
varied from 100 to 400 μА. Efficiency of the synaptic
transmission was assessed from the change in the ampli-
tude characteristics of the induced responses of the hip-
pocampal field CA1 on the testing stimulation of the
VHC. Long term potentiation presenting an interneuro-
nal synaptic transmission was induced by the high-
frequency stimulation of the ventral hippocampal com-
missure (five stimulus sets each comprising four repeats
of five stimuli with the 100 Hz stimulation frequency and
an interval of 200 μs; an interval between the stimulus
3 | RESULTS AND DISCUSSIONS
In this article, new ferrocene-based amino acids methyl
esters with a pyrazole linker were synthesized in racemic
and enantiomerically enriched forms. It is known that
aberrant iron deposition in the brain is associated with
neurodegenerative disorders. We would like to find out
whether the synthesized ferrocene amino acids affect the
hippocampus, and whether the action of individual enan-
tiomers is different.
First ferrocene derivatives of amino acids such as
ferrocenyl alanine (Fc-Ala) and ferrocenyl phenylalanine
(Fc-Phe) were obtained by Schlögl in several steps as far
back as 1957.[41] Systematic studies started in the end of
1990s and are performed nowadays though less actively
(see reviews[2,4] and a book[7]). Synthetic approaches to
the ferrocene modification of amino acids are rather sim-
ple. They comprise the synthesis of Schiff bases from
acetylferrocene or formylferrocene and an amino acid.[42]
However, such ferrocenyl imines are unstable com-
pounds. They are usually reduced and then isolated as
methyl or ethyl esters of the corresponding acids.[43]
Starting from ferrocene carboxylic acid through
ferrocenoyl benzotriazole ester, Kraatz synthesized ferro-
cene amino acid derivatives.[4,44,45] To obtain ferrocene-
modified amino acids previously reported an approach
developed for ferrocenylalkyl azoles.[46] Starting from
ferrocenyl alcohols FcCH (OH)R and ethyl esters of gly-
cine and β-alanine under acidic catalysis in aqueous
organic medium the corresponding products were
obtained.[46] Recently Ziegler and co-workers elaborated
new synthetic route to ferrocene complexes of such type
using a sulfonamide linking strategy.[47,48] Ferrocene-
based pyrazole-containing amino acids were successfully
ꢀ
ꢀ
prepared by Vukicevic and co-workers, and evaluated as
promising antitumor agents.[49] In a recent review, ferro-
cene conjugates with several natural amino acids were
subjected to the detailed conformational and DFT ana-
lyses in order to determine the turn-inducing potential
of
ferrocene
scaffolds
in
the
corresponding
peptidomimetics.[50]
FIGURE 2 Effects of (L)-3b on field excitatory postsynaptic
potential (fEPSP) in the hippocampal CA1 region. The time course
of fEPSP in (L)-3b (red line, n=9) and saline (black line, n=5) for
60 min after intraperitoneal injection (i.p. injection) and after high
frequency stimulation (HFS) in anaesthetized rats. Each point
represents the mean S.E.M. percentage of basal fEPSP amplitude
at 0 min; (*), significant differences against the saline group, p<0.05
3.1 | Synthesis
In this paper, we propose an approach to ferrocene-
substituted amino acids based on synthetically available

8 of 13
RODIONOV ET AL.
TABLE 1 Enantiomeric resolution of 3 (b-d), 3i, and 3 (e-h) racemic mixtures on columns Chiralcel OD and Chiralpak AS-H,
respectively
HPLC datab
Moleculea and compound number
Retention factor, k'1
Retention factor, k'2
Separation factor, α
2.17
2.83
1.30
3b
1.75
1.16
4.90
2.98
1.72
6.63
1.70
1.48
1.35
3i
3d
3c
Moleculea and compound number
HPLC datac
Retention factor, k'1
5.60
Retention factor, k'2
Separation factor, α
6.37
1.14
3f
4.15
4.80
1.16
3e
(Continues)

FERROCENE-BASED AMINO ACIDS AND THE HIPPOCAMPUS
9 of 13
TABLE 1 (Continued)
4.37
4.90
1.12
3g
0.84
1.29
1.54
3h
a* in the structures means the stereogenic center.
bMobile phase, hexane–isopropanol 90:10 (v/v).
cMobile phase, hexane–isopropanol –TEA 90:10:0.01 (v/v/v).
ferrocenyl pyrazoles[32,33,39] using a reductive amination
strategy. The interaction of ferrocenyl pyrazoles bearing
an aldehyde group in the pyrazole moiety with amino
acid esters, such as glycine, alanine, phenyl alanine,
valine, serine, tryptophan, tyrosine, proline, and
2-aminobutyric acid, using sodium triacetoxyborohydride
in dichloroethane under reflux conditions afforded the
target products in 78-93% yields after chromatographic
purification (Scheme 1). When L- or D-amino acids were
used, the corresponding final products were isolated in
enantiomerically enriched forms (see Experimental).
Their purity is confirmed by the HPLC method. In the
reactions of racemic amino acids, the final products are
isolated as racemic mixtures.
It is known that sodium triacetoxyborohydride NaBH
(OAc)3 is often used in the reductive amination reaction.
Being a milder reductive agent compared to, e.g., sodium
borohydride or lithium aluminium hydride, it is effective
in the carbonyl and aldehyde group reduction, with the
С=С multiple bonds, cyano or nitro groups remaining
intact.[51] We have found that NaBH (OAc)3 effectively
reduced Fc-formylpyrazole in reaction with mono-
aminotetraphenyl porphyrine to form the -СН2-NH- bond
in the corresponding ferrocenyl porphyrine.[52]
2-aminobutiric acid, a number of ferrocenyl-substituted
amino acids methyl esters in racemic forms and in L- and
D-forms were obtained in high yields.
3.2 | HPLC resolution
In addition to enantio enriched Fc-derived amino acids,
racemic mixtures were obtained. The synthesized eight
ferrocene derivatives 3b–i contain one asymmetric car-
bon atom in their structures and give racemic mixtures of
two enantiomers (Table 1). It is logical to suppose that
the two enantiomers may possess different biological
activities. So we separated the racemic mixtures into two
enantiomers using high-performance liquid chromatogra-
phy (HPLC). Earlier, this method of separation was suc-
cessfully used for racemic ferrocene compounds with
different simple substituents,[53] the chiral sorbents based
upon β- and γ-cyclodextrins turned out to be effective in
these cases. To separate mixtures of racemic ferrocene
derivatives having bulky substituents such as azoles[29]
including thiazoles[54] and nitro-imidazoles[55] we used
modified cellulose or amylose as chiral stationary phases.
The enantiomeric resolution analytical data are sum-
marized in Table 1. It should be noted that the
stereogenic centre in these compounds is located on the
periphery of the molecule far from the ferrocene core.
We successfully separated all 8 pairs of investigated
compounds. Enantiomeric purity confirmed for L- and D-
enantiomers. The recognition mechanism on cellulose or
amylose is apparently connected, with formation of
Thus, ferrocenyl pyrazole derivatives of amino acids
methyl esters were synthesized via the reductive ami-
nation using sodium triacetoxyborohydride according to
Scheme 1. As a result, starting from methyl esters of
amino acids such as glycine, alanine, phenylalanine,
valine, serine, tyrosine, tryptophan, proline and

10 of 13
RODIONOV ET AL.
specific hydrogen bonds between the strongly basic nitro-
gen atom of the NH-group, on the one hand, and carba-
mate units on the modified cellulose or amylose, on the
other hand. Some interesting conformities should be
marked. First, retention factors k'1 and k'2 for compounds
3b, 3d and 3i with aliphatic substituents R (Table 1)
decrease with a growing or branching chain length of R,
excluding k'2 for 3i. For example, for 3b and 3d from k'1
2.17 and k'2 2.83 (R = methyl) to 1.16 and 1.72 (R = iso-
propyl), respectively; bulky phenyl substituent signifi-
cantly increases both k'1 and k'2 values, for compound 3c
to 4.90 and 6.63, respectively (R = CH2-phenyl). The sep-
aration factors α for these compounds are significant, and
for compound 3i, where R = ethyl, reaches maximum
value α = 1.7, that is, the enantiomers on the sorbent
(column Chiralcel OD) are well separated.
and colleagues, the possible role of D-amino acids (D-
serine and D-asparagine) in stimulating the proliferation
of breast cancer was indicated.[58]
Herein, impact of ferrocene-substituted alanine
amino acid obtained in D- and L-forms, (D)-ferrocenyl
(phenylpyrazolyl)-alanine methyl ester, (D)-3b, and (L)-
ferrocenyl (phenylpyrazolyl)-alanine methyl ester, (L)-3b,
as well as ferrocenyl (phenylpyrazolyl)-glycine, 3a on the
efficiency of interneuronal interactions was studied by
the in vivo (in vivo means on alive, anaesthetized animals)
recording the hippocampal local field potentials (LFP).
The local field potential (LFP) is an electrophysiologi-
cal signal generated by a summed electrical current
flowing from many neighboring neurons in a small
amount of nervous tissue. Introduction of a ferrocene-
containing compound, a good redox mediator, can pro-
duce an increase in the amplitudes of local field poten-
tials. This will mean that such ferrocene-based
compounds are involved in the synaptic plasticity of the
brain area. Hippocampus is a key structure involved in
the learning and memory processes.[57] One of the com-
mon model of processes taking place in the hippocampus
during learning is a development of a long-term potentia-
tion of the synaptic transmission in the hippocampal sec-
tor CA1.[59]
The response amplitudes of the local potentials of the
hippocampal field means that a bipolar nichrome elec-
trode was lowered into the CA1 region of the hippocam-
pus to record field excitatory postsynaptic potentials
(fEPSPs). The fEPSP amplitude in the CA1 field evoked
by stimulation of the ventral hippocampal commissure
(VHC). Thus, fEPSP characteristics can change under dif-
ferent experimental conditions. Here we injected the
ferrocene-based compounds which increased amplitudes
of fEPSP in the CA1 hippocampal area.
During the testing of the ferrocenyl (phe-
nylpyrazolyl)-glycine methyl ester (3a) and (D)-
ferrocenyl (phenylpyrazolyl)-alanine methyl ester, (D)-
3b, at a dose of 2.0 mg kg-1 (in a DMSO—Н2О solu-
tion, intraperitoneally) two groups of animals were
studied and one control group (animals were injected
with saline). It was shown that response amplitudes of
the focal potentials of the hippocampal field CA1 in
the tested animals injected with ferrocene-containing
compounds (number of animals in a first group, n =
5, in a second group, n = 4) raised from 15% to 25%
compared to the saline-treated control animals (n = 5)
(see Figure 1). That is, the effects of the introduction
at the first hour of both substances are almost the
same, only compound (D)-3b is slower goes to the
level of 20% of the control. It can be argued that the
compounds 3a and (D)-3b cause long-term changes in
synaptic plasticity.
3.3 | Biological tests.
Electrophysiological measurements in the
CA1 area of the hippocampus
Antitumor activity of ferrocene compounds is presently
under active investigations,[15–18] and the authors have
also succeeded in this field.[28,29,54,55] However, at the
moment there are only a few publications on the effects
of the ferrocene-substituted compounds on the
brain.[21–25,56,57] This subject is only beginning to attract
the attention of scientists working in the field of organo-
metallic chemistry. In particular, in animal (rats) studies
it was established that oral (e.g. dietary) administration
of (3,5,5-trimethylhexanoyl)ferrocene did not result in
accumulation of iron in the brain tissues.[21] In vivo
experiments have investigated ferrocene-thiazolidinones
as anxiolytics, that is, anxiety-inhibiting substances.[22] It
has been found that the high dose-dependent anxiolytic
activity of the synthesized ferrocene-thiazolidinones may
be associated with their preferred interaction with the
benzodiazepine-binding site of the GABA receptors. In
other experiments, when ferrocene was exposed, in hip-
pocampal slices ex vivo a significant accumulation of iron
was found.[57]
For electrophysiological studies, we used ferrocene
derivatives of glycine, L- and D-alanine. These are the
first representatives of the synthesized series. Moreover,
both glycine and alanine are used in medical practice.
The role of L-amino acids in biological processes is well
known, in contrast to D-amino acids. It seemed to us
important and necessary to study both L-and D-alanine
ferrocene compounds, the more so this necessary require-
ment is indicated in the pharmacopoeias of European
and other countries to investigate the bio-effects of all ste-
reoisomers. Also, in a recent article by Dr. Armstrong

FERROCENE-BASED AMINO ACIDS AND THE HIPPOCAMPUS
11 of 13
Within 60 min after the beginning of recordings in
the group of rats injected with the compound 3a (Fc-gly-
cine-based), the response amplitude following the high-
frequency stimulation (HFS) was significantly higher
compared to that for the saline-injected control group
animals (157.7 7.9% и 132.25 9.3%, respectively; p <
0.05 according to the t-test). However, additional stimula-
tion with the introduction of compound (D)-3b (Fc-ala-
nine-based) has a lesser effect, but higher than in control
and at one level about 145%.
4 | CONCLUSION
Using the reductive amination strategy, a series of
ferrocene-containing amino acid esters with pyrazole
linkers were obtained, both in racemic form and in the
form of individual enantiomers in high yields. For the first
time primary electrophysiological studies of ferrocene-
modified amino acids were carried out in vivo. It was found
that after 60 min after intraperitoneal administration of the
studied compounds, effects were registered in the CA1
zone of the hippocampus, i.e. in the brain of animals.
Moreover, these effects are different for the (L)- and (D)-
enantiomers. Biological studies have revealed the involve-
ment of ferrocene-based compounds in the synaptic plas-
ticity of the CA1 hippocampus brain region.
Overall, our results suggest that compounds 3a and
(D)-3b enhanced the amplitudes of basal synaptic trans-
mission and long-term potentiation (LTP) as compared to
control animals.
Figure 2 shows the data for administration from
compound (L)-3b (n = 9). In this group of animals
(Wistar rats), nine animals were tested, the largest
number, and five in the control group (n = 5). It can
be seen that during the first hour after injection, the
effect is at the control level, in contrast to the action
of the D-enantiomer (up to 25% in compare to control).
After high-frequency stimulation (the second hour) a
rather significant increase (up to 180%) is shown.
Although the error bars after high-frequency stimula-
tion are large (the red line) the high level of error bars
is normal after HFS in in vivo electrophysiological
experiments.[60–62]
ACKNOWLEDGMENTS
This work was supported by Ministry of Science and
Higher Education of the Russian Federation using the
equipment of Center for molecular composition studies
of A.N. Nesmeyanov Institute of Organoelement Com-
pounds, Russian Academy of Sciences, Moscow.
L.V.S. wishes to thank Dmitry G. Genzel for the kind
assistance and Dmitry S. Denisenko for preparing the
graphical abstract.
CONFLICTS OF INTEREST
Thus, the effects of ferrocene enantiomers on the CA1
hippocampal region are considerably different. One ste-
reoisomer has a significant effect, while the other has a
minor effect on the CA1 zone of the hippocampus. Over-
all, this result is not surprising. The biological actions of
enantiomers are usually different. That is why it is impor-
tant to study the actions of each enantiomer, which is
required in the research of drug candidates and is fixed
in the pharmacopoeias.
All authors declare no conflict of interest.
ORCID
Lubov V. Snegur https://orcid.org/0000-0001-9227-2326
REFERENCES
[1] C. Elschenbroich, Organometallchemie, B.G. Teubner Verlag/-
GWV Fachverlage GmbH, Wiesbaden 2008.
[2] D. R. van Staveren, N. Metzler-Nolte, Chem. Rev. 2004, 104,
5931.
Thus, pronounced responses of the hippocampal
region of the brain to the ferrocene-containing com-
pounds were detected in vivo. Naturally, there is a
need in further studies with varying the doses and the
ferrocene preparations per se to accumulate the statisti-
cal data and to review the results. However, it should
be noted that the chosen class of the ferrocene-
modified amino acids displays a biological action on
the region of the brain, i.e. hippocampus. The biologi-
cal model was well chosen and a significant change
(an increase of 15–25% compared to the control) in the
amplitude of the local potentials in the hippocampal
region СА1 was detected. The results obtained on
choosing a dose (2.0 mg kg–1) based on a considerable
experience of other biological studies performed by us
suggests that the ferrocene compounds can act in a
low dose range.
[3] E. W. Neuse, J. Inorg. Organomet. Polym. Mater. 2005, 15, 3.
[4] H.-B. Kraatz, J. Inorg. Organomet. Polym. Mater. 2005, 15, 83.
[5] L. V. Snegur, V. N. Babin, A. A. Simenel, Y. S. Nekrasov,
L. A. Ostrovskaya, N. S. Sergeeva, Russ. Chem. Bull. 2010, 59,
2167.
[6] L. V. Snegur, A. A. Simenel, A. N. Rodionov, V. I. Boev, Russ.
Chem. Bull. 2014, 63, 26.
[7] N. Metzler-Nolte, Conjugates of peptides and peptide nucleic
acids with organometal complexes: synthesis and application,
in Bioorganometallics: Biomolecules, Labeling, Medicine, (Ed:
G. Jaouen), Wiley-VCH, Weinheim 2006.
[8] K. Kowalski, Coord. Chem. Rev. 2016, 317, 132. https://doi.org/
10.1016/j.ccr.2016.02.008
[9] A. N. Nesmeyanov, L. G. Bogomolova, I. G. Andrianova,
V. D. Vil´chevskaya, N. S. Kochetkova, Farm. Chem. J. (Engl.
Transl.) 1972, 6, 269.
ꢀ
ꢀ
ꢀ
ꢀ
[10] N. S. Radulovic, M. Z. Mladenovic, Z. Stojanovic-Radic,
ꢀ
ꢀ
ꢀ
ꢀ
G. A. Bogdanovic, D. Stevanovic, R. D. Vukicevic, Mol.

12 of 13
RODIONOV ET AL.
Divers. 2014, 18, 497. https://doi.org/10.1007/s11030-014-
9511-0
I. K. Sviridova, N. S. Sergeeva, Russ. Chem. Bull. Int. Ed. 2013,
62, 2056.
[11] D. Scutaru, L. Tataru, I. Mazilu, E. Diaconu, T. Lixandru,
C. Simionescu, J. Organomet. Chem. 1991, 401, 81.
[12] C. Biot, G. Glorian, L. A. Maciejewski, J. S. Brocard, J. Med.
Chem. 1997, 40, 3715.
[13] G. M. Maguene, J. Jakhlal, M. Ladyman, A. Vallin,
D. A. Ralambomanana, T. Bousquet, J. Maugein, J. Lebibi,
L. Pélinski, Eur. J. Med. Chem. 2011, 46, 31.
[14] V. N. Kulikov, R. S. Nikulin, A. N. Rodionov, E. S. Babusenko,
V. N. Babin, L. V. Kovalenko, Y. A. Belousov, Russ Chem Bull
2017, 66, 1122. https://doi.org/10.1007/s11172-017-1864-y
[15] C. Ornelas, New J. Chem. 2011, 35, 1973.
[30] A. Pinto, U. Hoffmans, V. Ott, G. Fricker, N. Metzler-Nolte,
ChemBioChem 2009, 10, 1852.
[31] L. Delhaes, C. Biot, L. Berry, P. Delcourt, L. A. Maciejewski,
D. Camus, J. S. Brocard, D. Dive, ChemBioChem 2002, 3, 418.
[32] B. Ferber, S. Top, A. Vessières, R. Welter, G. Jaouen, Organo-
metallics 2006, 25, 5730.
[33] J. L. Kedge, H. V. Nguyen, Z. Khan, L. Male, M. K. Ismaile,
H. V. Roberts, N. J. Hodges, S. L. Horswell, Y. Mehellou,
J. H. R. Tucker, Eur. J. Inorg. Chem. 2017, 2, 466.
[34] European Pharmacopoeia. http://www.edqm.eu/en/ph-eur-
reference-standards-627.htm
[16] G. Gasser, I. Ott, N. Metzler-Nolte, J. Med. Chem. 2011, 54, 3.
[17] V. N. Babin, Y. A. Belousov, V. I. Borisov, V. V. Gumenyuk,
Y. S. Nekrasov, L. A. Ostrovskaya, I. K. Sviridova,
N. S. Sergeeva, A. A. Simenel, L. V. Snegur, Russ. Chem. Bull.
2014, 63, 2405.
[35] Russia State Pharmacopoeia (XIII Edition), Moscow. 2016.
http://pharmacopoeia.ru/en/gosudarstvennaya-farmakopeya-
xiii-online-gf-13-online/(in English)
[36] L. V. Snegur, Y. S. Nekrasov, N. S. Sergeeva, Z. V. Zhilina,
V. V. Gumenyuk, Z. A. Starikova, A. A. Simenel,
N. B. Morozova, I. K. Sviridova, V. N. Babin, Appl. Organomet.
Chem. 2008, 22, 139.
[18] G. Jaouen, A. Vessières, S. Top, Chem. Soc. Rev. 2015, 44,
8802.
[19] A. N. Nesmeyanov, L. G. Bogomolova, N. S. Kochetkova,
V. D. Vilchevskaya, N. P. Palitsyn, I. G. Andrianova,
O. P. Belozerova, Drug for Anemia and Ozena. USSR Patent
263807, 29 December 1966.
[20] http://www.euro.who.int/ru/publications/abstracts/health-
2020.-a-european-policy-framework-and-strategy-for-the-21st-
century-2013.
[37] A. N. Rodionov, A. A. Simenel, Y. S. Nekrasov, V. V. Kachala,
E. Y. Osipova, K. Y. Zherebker, Russ. Chem. Bull. Int. Ed. 2010,
59, 405.
[38] E. Y. Osipova, A. N. Rodionov, D. E. Arhipov, M. M. Ilyin,
A. A. Simenel, Russ. Chem. Bull. Int. Ed. 2014, 63, 2285.
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
[39] M. Joksovic, Z. Ratkovic, M. Vukicevic, R. D. Vukicevic,
Synlett 2006, 16, 2581. https://doi.org/10.1055/s-2006-950436
[40] L. F. Tietze, T. Eicher, Reaktionen and Synthesen im organisch-
chemischen. Praktikum und Forschungslaboratorium, Georg
Thieme Verlag, Stuttgart–New York 1991.
[21] J. Lykkesfeldt, E. Morgan, S. Christen, L. T. Skovgaard,
T. Moos, J. Biochem. Mol. Toxicol. 2007, 21, 145.
ꢀ
[22] A. Pejovic, M. S. Denic, D. Stevanovic, I. Damljanovic,
ꢀ
ꢀ
M. Vukicevic, K. Kostova, M. Tavlinova-Kirilova,
[41] K. Schlögl, Monatsh. Chem. 1957, 88, 601.
ꢀ
ꢀ
ꢀ
P. Randjelovic, N. M. Stojanovic, G. A. Bogdanovic,
[42] A. M. Osman, M. A. El-Magharaby, K. M. Hassan, Bull. Chem.
Soc. Jpn. 1975, 48, 2226.
[43] A. Hess, J. Sehnert, T. Weyhermu1ller, N. Metzler-Nolte,
Inorg. Chem. 2000, 39, 5437.
ꢀ
ꢀ
ꢀ
ꢀ
P. Blagojevic, M. D'hooghe, N. S. Radulovic, R. D. Vukicevic,
Eur. J. Med. Chem. 2014, 83, 57. https://doi.org/10.1016/j.
ejmech.2014.05.062
[23] F. F. Zhang, Q. Wan, X. L. Wang, F. -F. Zhang, Q. Wan, X. -
L. Wang, Z. -D. Sun, Z. -Q. Zhu, Y. -Z. Xian, L. -T. Jin,
K. Yamamoto, J. Electroanal. Chem. 2004, 571, 133. https://
doi.org/10.1016/j.jelechem.2004.04.019
[44] H. S. Mandal, H.-B. Kraatz, J. Organomet. Chem. 2003, 674, 32.
https://doi.org/10.1016/S0022-328X(03)00182-7
[45] H.-B. Kraatz, J. Lusztyk, G. D. Enright, Inorg. Chem. 1997, 36,
2400. https://doi.org/10.1021/ic961454t
[24] E. A. Malecki, E. E. Cable, H. C. Isom, G. R. Connor, Biol.
Trace Elem. Res. 2002, 86, 73. https://doi.org/10.1385/BTER:
86:1:73
[25] R. J. Ward, D. Dexter, A. Florence, F. Aouad, R. Hider,
P. Jenner, R. R. Crichton, Biochem. Pharmacol. 1995, 49, 1821.
https://doi.org/10.1016/0006-2952(94)00521-M
[26] A. N. Rodionov, L. V. Snegur, A. A. Simenel,
Y. V. Dobryakova, V. A. Markevich, Russ. Chem. Bull. Int. Ed.
2017, 66, 136.
[46] V. I. Boev, P. M. Betankourt, L. V. Popova, V. N. Babin, Zh.
Obshch. Khim. 1991, 61, 1651.
[47] K. Chanawanno, T. S. Blesener, B. R. Schrage, V. N. Nemykin,
R. S. Herrick, C. J. Ziegler, J. Organomet. Chem. 2018, 870,
121. https://doi.org/10.1016/j.jorganchem.2018.06.018
[48] K. Chanawanno, C. Holstrom, L. A. Crandall, H. Dodge,
V. N. Nemykin, R. S. Herrick, C. J. Ziegler, Dalton Trans.
2016, 45, 14320. https://doi.org/10.1039/C6DT02669A
ꢀ
ꢀ
ꢀ
ꢀ
[49] M. Joksovic, V. Markovic, Z. D. Juranic, T. Stanojkovic,
ꢀ ꢀ
L. S. Jovanovic, I. S. Damljanovic, K. M. Szécsényi,
[27] L. V. Popova, V. N. Babin, Y. A. Belousov, Y. S. Nekrasov,
A. E. Snegireva, N. P. Borodina, G. M. Shaposhnikova,
O. B. Bychenko, P. M. Raevskii, N. M. Morozova, A. I. Ilyina,
K. G. Shitkov, Appl. Organomet. Chem. 1993, 7, 85.
ꢀ
ꢀ
ꢀ
ꢀ
N. Todorovic, S. Trifunovic, R. D. Vukicevic, J. Organomet.
Chem. 2009, 694, 3935. https://doi.org/10.1016/j.jorganchem.
2009.08.013
ꢀ
ꢀ
ꢀ
[28] L. V. Snegur, A. A. Simenel, Y. S. Nekrasov, E. A. Morozova,
Z. A. Starikova, S. M. Peregudova, Y. V. Kuzmenko,
V. N. Babin, L. A. Ostrovskaya, N. V. Bluchterova,
M. M. Fomina, J. Organomet. Chem. 2004, 689, 2473.
[29] L. V. Snegur, S. I. Zykova, A. A. Simenel, Y. S. Nekrasov, Z.
A. Starikova, S. M. Peregudova, M. M. Il´in, V. V. Kachala,
[50] M. Čakic Semencˇic, L. Barišic, Croat. Chem. Acta 2017, 90,
537. https://doi.org/10.5562/cca3246
[51] A. F. Abdel-Magid, K. G. Carson, B. D. Harris,
C. A. Maryanoff, R. D. Shah, J. Org. Chem. 1996, 61, 3849.
[52] E. Y. Osipova, A. N. Rodionov, A. A. Simenel, Y. A. Belousov,
O. M. Nikitin, V. V. Kachala, J. Porphyr. Phthalocyanids. 2012,
16, 1225.

FERROCENE-BASED AMINO ACIDS AND THE HIPPOCAMPUS
13 of 13
[53] D. W. Armstrong, W. DeMond, B. P. Czech, Anal. Chem. 1985,
57, 481.
Nat. Commun. 2014, 5, 3374. https://doi.org/10.1038/
ncomms4374
[54] A. N. Rodionov, K. Y. Zherebker, L. V. Snegur,
A. A. Korlyukov, D. E. Arhipov, A. S. Peregudov, M. M. Ilyin,
M. M. Ilyin Jr., O. M. Nikitin, N. B. Morozova, A. A. Simenel,
J. Organomet. Chem. 2015, 783, 83.
[55] L. V. Snegur, M. V. Lyapunova, D. D. Verina, V. V. Kachala,
A. A. Korlyukov, M. M. Ilyin Jr., V. A. Davankov,
L. A. Ostrovskaya, N. V. Bluchterova, M. M. Fomina,
V. S. Malkov, K. V. Nevskaya, A. G. Pershina, A. A. Simenel,
J. Organomet. Chem. 2018, 871, 10. https://doi.org/10.1016/j.
jorganchem.2018.06.019
[61] I. Klyubin, T. Ondrejcak, J. Hayes, W. K. Cullen, A. J. Mably,
D. M. Walsh, M. J. Rowan, Philos. Trans. R. Soc. B. Biol. Sci.
2013, 369, 20130147. https://doi.org/10.1098/rstb.2013.0147
[62] R. L. Lethbridge, S. G. Walling, C. W. Harley, Brain Behav.
2014, 4, 95. https://doi.org/10.1002/brb3.199
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in the Supporting Information section at the end of this
article.
[56] N. Mejri, N. Malek Said, S. Guizani, I. Essouissi, M. Saidi,
Nucl. Med. Biol. 2013, 40, 561.
[57] B. I. Milner, L. R. Squire, E. R. Kandel, Neuron 1998, 20, 445.
[58] S. Du, Y. Wang, N. Alatrash, C. A. Weatherly, D. Roy,
F. M. MacDonnell, D. W. Armstrong, J. Pharm.
Biomed. Anal. 2019, 164, 421. https://doi.org/10.1016/j.jpba.
2018.10.047
[59] T. V. Bliss, G. L. Collingridge, Nature 1993, 361, 31.
[60] N. W. Hu, A. J. Nicoll, D. Zhang, A. J. Mably, T. O'Malley,
S. A. Purro, C. Terry, J. Collinge, D. M. Walsh, M. J. Rowan,
How to cite this article: Rodionov AN,
Snegur LV, Dobryakova YV, Ilyin Jr MM,
Markevich VA, Simenel AA. Administration of
ferrocene-modified amino acids induces changes in
synaptic transmission in the CA1 area of the
hippocampus. Appl Organometal Chem. 2019;
e5276. https://doi.org/10.1002/aoc.5276