Oxovanadium complexes of N-substituted 3-hydroxy-2-methyl-4(1H)-pyridinones: Synthesis, spectroscopic characterization, and the insulin-mimetic activity

Article abstract of DOI:10.3987/COM-03-9719

Five kinds of N-substituted 3-hydroxy-2-methyl-4(1H)-pyridinones, and two kinds of tetradentate ligands, N,N′-[bis(3-hydroxy-1,4-dihydro-2-methyl-4-oxo-1-pyridyl)hexanoyl- and -octanoyl]-1,5-diamino-3-oxapentanes, were synthesized. Treatment of these liga

Full text of DOI:10.3987/COM-03-9719

HETEROCYCLES, Vol. 60, No. 5, 2003
1147
HETEROCYCLES, Vol. 60, No. 5, 2003, pp. 1147 - 1159
Received, 16th January, 2003, Accepted, 19th March, 2003, Published online, 24th March, 2003
OXOVANADIUM COMPLEXES OF N-SUBSTITUTED 3-HYDR-
OXY-2-METHYL-4(1H)-PYRIDINONES:
SYNTHESIS, SPECTRO-
SCOPIC CHARACTERIZATION, AND THE INSULIN-MIMETIC
ACTIVITY
Akira Katoh,*a Kazutoshi Taguchi,a Ryota Saito,a Yae Fujisawa,b
Toshikazu Takino,b and Hiromu Sakuraib
aDepartment of Applied Chemistry, Faculty of Engineering, Seikei University,
b
Musashino-shi, Tokyo 180-8633, Japan and Department of Analytical and
Bioinorganic Chemistry, Kyoto Pharmaceutical University, Yamashina-ku, Kyoto
607-8414, Japan
Abstract ̶ Five kinds of N-substituted 3-hydroxy-2-methyl-4(1H)-pyridinones,
and two kinds of tetradentate ligands, N,N’-[bis(3-hydroxy-1,4-dihydro-2-methyl-
4-oxo-1-pyridyl)hexanoyl- and -octanoyl]-1,5-diamino-3-oxapentanes, were syn-
thesized. Treatment of these ligands with VO(acac)2 in CH3OH exclusively gave
CH3O-coordinated oxovanadium(V) complexes. On the other hand, treatment with
VOSO4 in H2O at around pH 10 afforded oxovanadium(IV) complexes. On the
basis of the inhibitory effect of oxovanadium(IV) complexes on free fatty acid
(FFA) release from rat adipocytes treated with epinephrine in the presence of 0.1%
glucose in vitro, it was revealed that some of oxovanadium(IV) complexes show the
insulin-mimetic activity.
At the present time, patients with diabetes mellitus (DM) are estimated to be over 140 million in the world.
DM results froman absolute or relative deficiency in insulin synthesis on secretion of pancreatic β-cells and
a resistance of target tissues to the action of insulin. Patients with DM suffer from a number of secondary
complications such as retinopathy, nephropathy, and neuropathy. DM is generally classified into type 1
insulin-dependent DM (IDDM), characterized by hyperglycemia due to absolute deficiency of insulin, and
type 2 noninsulin-dependent DM (NIDDM) characterized by hyperglycemia due to resistance of organs to
the action of insulin, according to the definition of WHO in 1985.1 Oral chemotherapeutic agents for type
2 DM have already been developed and are currently available.2 Patients with type 1 DM can be only
treated by daily injections of insulin. However, insulin is a polypeptide with a molecular mass of 5.8 KDa,
and thus easily degradated by proteinases in the ingestive systems. Therefore, novel design and synthesis
of orally active compounds in place of insulin have been paid much attention.3
Historically, vanadate (+5 oxidation state of vanadium) ion was found to be a potent inhibitor of Na+, K+-
ATPase in 1977.4-6 The interaction of vanadium with ATPases and its expression on cellular, organ, and
whole animal levels have been reviewed by Nechay.7 In 1980’s, vanadate ion was demonstrated to show
insulin-mimetic action in intracellular insulin receptor or GLUT4.8,9 Further, it was found that vanadate
ion was reduced to vanadyl (+4 oxidation state or oxovanadium(IV)) in organs and organelles when it was
administered to animals, and when vanadyl sulfate (VOSO4) and its complexes administered orally or

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HETEROCYCLES, Vol. 60, No. 5, 2003
intravenously to rats with streptozotocin (STZ)-induced diabetes, they normalized the blood glucose.4,10-13
In addition, the vanadate form exhibited toxicity about 10-15 times higher than the vanadyl one in rats in
terms of LD50 value.14 Therefore, research on oxovanadium(IV) complexes has received much attention.
A number of orally active oxovanadium(IV) complexes have already been reported to exhibit insulin-
mimetic activities in vivo.12,15-21 Recently, it has been reported that the amount of glucose in blood is
mutually related to the amount of FFA in blood.
Therefore, the insulin-mimetic activity of
oxovanadium(IV) complexes has been evaluated by measuring their inhibitory effects on FFA release from
isolated rat adipocytes in vitro.16,18,22-25 However, establishment of a clear correlation between chemical
structures of oxovanadium(IV) complexes and insulin-mimetic activity is yet very difficult due to absolute
lack of available data. Further, only a few papers concerning oxovanadium(IV) complexes including
heterocycles as bidentate ligands have been reported.26
We have intensively studied on synthesis of hydroxyazine-type heterocycles and their application to
chemotherapeutic agents for the iron-overload disease.27 We, therefore, planed to utilize 3-hydroxy-
4(1H)-pyridinone as bidentate and tetradentate ligands in synthesizing oxovanadium(IV) complexes with
VO(O4) coordination mode,12,19,28 because there are some advantages as follows; 1) a facile synthetic
procedure,29-32 2) an easy introduction of various substituents at N-1 position, 3) an effective binding of
oxovanadium ion with a tetradentate ligand by the chelate effect, and 4) an easy adjustment of the
hydrophilicity or lipophilicity of oxovanadium complex. We describe here synthesis of new heterocyclic
1
13
oxovanadium(IV) and (V) complexes and characterization of these complexes on the basis of H-, C-,
51V-NMR, IR, UV-VIS, FAB MS and ESR spectra, cyclic voltammetry (CV), and combustion analysis.
Furthermore, we examined whether synthetic oxovanadium(IV) complexes exhibited insulin-mimetic
activities with regard to the inhibitory effect of the complexes on FFA release from isolated rat adipocytes in
vitro.
O
O
O
OBn
OBn
CH
3
ii
O
V
i
O
O
OCH
O
i
R
N
CH
3
3
N
CH
(CH )
3
2 n
a n=5
b n=7
O
CH
3
O
OH
4a,b
O
N
OH
CH
R
2a,e
iii
CH
O
3
O
O
V
O
O
OCH
3
N
R
OR
RO
3
N
(CH )
O
2 n-3
iii, iv
N
CH
O
CH
3
H C
3
N
3
1a-e
H
CH
3
(CH )
O
(CH )
N
2 n
2 n
O
N
a R = Me
b R = Et
c R = Pr
d R = Bu
R
O
O
O
O
N
O
ii
V
O
N
H
N
H
O
(CH )
H
2 n-3
N
O
R
N
5a,b R=Bn
CH
3
iii
7a,b
e R = (CH ) OCH
O
2 2
3
3a-e
6a,b R=H
Scheme 1 Reagents and conditions: i)
Scheme 2 Reagents and conditions : i) H N(CH ) CO Na,
2 2 n 2
VO(acac) , MeO-H O (1:1), reflux for 2 h; EtOH-H O(1:1), reflux for 48 h; ii) H N(CH ) O(CH ) NH ,
2
2
2 2
2 2
2
2
2
ii) VOSO4, H2O, pH 10, reflux overnight; N,N'-carbonyldiimidazole, dry DMF; iii) H /10%Pd-C, CH OH,
2
3
iii) CH3OH, rt.
2 h; iv) VO(acac) , CH OH-H O (1:1), reflux for 2 h.
2
3
2

HETEROCYCLES, Vol. 60, No. 5, 2003
1149
RESULTS AND DISCUSSION
Synthesis and property of bidentate and tetradentate ligands: Bidentate ligands, N-substituted
3-hydroxy-2-methyl-4(1H)-pyridinones (1a-e), were prepared via three steps from a commercially
available maltol (3-hydroxy-2-methyl-4-pyrone) according to the literature method.29,30 (Scheme 1) The
synthetic procedure for tetradentate ligands is also depicted in Scheme 2. 3-Benzyloxy-2-methyl-4-pyrone
was allowed to react with Na salt of 6-aminohexanoic acid to give compound (4a) in a 88% yield. The
structure was determined by 1H NMR and IR spectra. Two characteristic olefinic protons at C-5 and C-6
positions of the pyridinone ring were observed at δ 6.42 and 7.18 ppm, respectively, and the carboxylic
proton was observed at δ 10.82 ppm. Two absorption bands due to C=O stretching vibrations of 4(1H)-
pyridinone and carboxylic acid were observed at 1627 and 1720 cm-1, respectively. Similarly, reaction of 3-
benzyloxy-2-methyl-4-pyrone with 8-aminooctanoic acid gave compound (4b) in a 90% yield.
Compounds (4a and 4b) were treated with N,N’-carbonyldiimidazole (CDI), and then coupled with 1,5-
diamino-3-oxapentane in dry DMF at room temperature to give compounds (5a and 5b). The absorption
bands owing to C=O stretching vibrations of 4(1H)-pyridinone and amide bond of compound (5a) were
observed at 1628 and 1655 cm-1, respectively. Compounds (5a and 5b) were subjected to the
hydrogenation for 2 h in the presence of 10% Pd-C to give tetradentate ligands (6a and 6b) in high yields.
The pKa value of 3-hydroxy-1-methoxyethyl-2-methyl-4(1H)-pyridinone (1e) was estimated from the pH
titration curve of absorbance at 310 nm at various pH conditions to be 9.8 which is comparable to that31,32
of 3-hydroxy-1,2-dimethyl-4(1H)-pyridinone. The partition coefficient (Coctanol/Cbuffer) of ligands (1a-e)
between KRB (Krebs-Ringer bicarbonate, pH 7.4) buffer,20 which was used in the bioassay, and octanol
was measured by means of UV-VIS spectroscopy,31,32 and the results are summarized in Table 1.
Table 1 Partition coefficients of N-substituted 4(1H)-pyridinones
Ligand
1a
1b
1c
1d
1e
Partition coefficient 0.09
0.27
0.44
1.00
0.16
Among a series of 4(1H)-pyridinones (1a-e), an increase in the methylene chain length at N-1 position
results in an increase of the solubility in octanol, except for compound (1e).
Synthesis of oxovanadium complexes: At first, synthesis of oxovanadium complexes with
bidentate ligands (1a and 1e) was carried out using vanadyl acetylacetonate, VO(acac)2. Compound (1e)
was treated with 0.5 equimolar amount of VO(acac)2 in CH3OH-H2O (1:1) mixture.33 When a solution of
VO(acac)2 (green) was added to a solution of compound (1e) (colorless), a color of the solution turned into
dark purple. After refluxing for 2 h, the solvent was evaporated off, and the crude product was purified
by gel-filtration with Sephadex LH-20 to give oxovanadium complex (compound A) as dark purple
powders. A characteristic absorption band due to V=O stretching vibration was observed at 949 cm-1 in
IR spectrum.34 In general, ε value of absorption band of oxovanadium(IV) complex at the visible region
was very small,35 but this complex showed λmax at 503 nm with ε value of 3450. Measurement of NMR
spectrum of oxovanadium(IV) complex is impossible because of a paramagnetic character. Compound
(A), however, showed a diamagnetic character attributable to oxovanadium(V) complex. A signal based on

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HETEROCYCLES, Vol. 60, No. 5, 2003
protons at cis-OCH3 appeared at δ 3.34 ppm, and this chemical shift was completely coincided with that
of cis-bis(maltolato)methoxooxovanadium(V), cis-VO(OCH3)(ma)2.36 From these spectral data and
combustion analysis, compound (A) was assigned to be oxovanadium(V) complex (2e). Bidentate (1a) and
tetradentate ligands (6a and 6b) similarly gave oxovanadium(V) complexes (2a, 7a and 7b),
respectively. Consequently, oxovanadium(IV) complex could not be obtained under the employed
conditions.
Synthesis of oxovanadium(IV) complexes was carried out using vanadyl sulfate (VOSO4)12,36,37 in place of
VO(acac)2. Compound (1e) was treated with 0.5 equimolar amount of VOSO4 in H2O. When a solution
of VOSO4 (light blue) was added to a solution of compound (1e) (colorless), a color of the solution turned
into dark purple. The pH of the reaction mixture was adjusted to 10, and then the resulting mixture was
refluxed overnight. On raising pH of the aqueous solution, a color turned into dark green, and a blue
precipitate came out. The precipitate was collected and washed well with H2O to give oxovanadium(IV)
complex (3e) as blue powders. IR spectrum of complex (3e) is very similar to that of free ligand (1e),
except the following points; (i) the absorption band at 1625 cm-1 attributable to C=O stretching vibration of
free ligand (1e) shifted to 1604 cm-1, (ii) the absorption band at 1400 cm-1 due to O-H in-plane deformation
became small in the intensity, and (iii) a new absorption band owing to V=Ostretching vibration appeared at
970 cm-1. The molecular ion peak of complex (3e) was observed at m/z 432 ([M+H]+) in FAB MS spectrum.
Further, oxovanadium(IV) complexes (3a and 3e) were easily converted into the corresponding
oxovanadium(V) ones (2a and 2e) in CH3OH, It is noteworthy that a facile oxidation of oxovanadium(IV)
complexes to oxovanadium(V) ones occurs in CH3OH even at room temperature when N-substituted 3-
hydroxy-4(1H)-pyridinones were used as bidentate and tetradentate ligands.
1
Characterization of oxovanadium(V) complexes: On measuring H NMR spectrum of
complex (2e), the broadening of each signal was observed, and thus the spectra were measured at various
temperatures. The shape of signals due to 2-CH3 and 5-H apparently changed as shown in Figure 1-a.
At –30 °C, two sets of signals were observed for 2-CH3 and 5-H protons at the range from δ 2.4 to 2.6
and from 6.2 to 6.4 ppm, respectively. On raising temperature up to 30 °C, the signals coalesced into broad
1
singlets. The similar behavior was observed on the variable temperature H NMR spectral study of cis-
VO(OCH3)(ma)2.36 This result indicated that the equilibrium between the two isomers may exist in
CD3OD solution as shown in Figure 1-b. The activation free energy (ΔG≠) for the conversion was
calculated from the difference (Δν) in frequency between two signals and coalescence temperature (Tc)
according to the following equation, and estimated to be roughly 65 KJ mol- 1.
ΔG≠ = 19.14 Tc (9.97 + log Tc / Δν)
UV-VIS spectra of complex (2e) were measured in aqueous solution at various pH values (pH 2.1-11.3).
The absorption bands due to the ligand-to-metal charge transfer (LMCT) were observed at 530-600 nm in
the acidic region. An increase of pH caused the blue-shift of absorption maximum, λmax being 536 nm
with ε value of 1380 at pH 4.6. However, in the basic region, the absorption band due to LMCT
disappeared, indicating the decomposition of the complex.
51V NMR spectra of complex (2e)were measured in D2O at apparent pD 8, and VOCl3 was used an external
standard. Three separated signals, in which one is major and the other two are minor, were observed at δ
-480, -503 and -535 ppm, indicating the existence of three oxovanadium(V) species. (Spectrum (i) in
Figure 2-a). When an excess of ligand (1e) was added to the sample solution, two signals at δ -503 and

HETEROCYCLES, Vol. 60, No. 5, 2003
1151
–535 ppm completely disappeared. (Specctrum (ii) in Figure 2-a)
2-CH3
5-H
CH
3
30 °C
O
V
R
O
O
OCH
O
3
N
O
CH
3
N
R
10 °C
CH
3
O
V
OCH
O
O
O
R
3
N
O
-30 °C
H C
3
N
R
R = (CH ) OCH3
2 2
2.6
6.2
2.4 ppm
6.4
(b)
(a)
Figure 1 (a) 1H NMR spectra of oxovanadium(V) complex (2e) in CD3OD; : free ligand.
(b) A possible structure in equilibrium
CH
3
-480 ppm
O
V
R
O
O
OCH
O
(i)
3
N
-503 ppm
-535 ppm
O
CH
3
δ=-480 ppm
N
R
+
CH
3
(ii)
O
V
O
O
R
OCH
3
N
δ=-503 ppm
O D
2
O D
2
2+
O
D O
2
OCH
3
δ=-535 ppm
V
-450
-500
-550 ppm
O D
2
D O
2
(a)
O D
2
(b)
Figure 2 (a) 51V NMR spectra of oxovanadium(V) complex (2e) in D2O at pD 8; i) oxovanadium(V)
complex, ii) an additional ligand (1e). (b) The tentative assignment of observed three signals.
From these and reported data,36,37 the two minor signals were tentatively assigned to be the ligand
dissociation products, [VO(L)(D2O)2(OCH3)]+ and [VO(D2O)4(OCH3)]2+ as shown in Figure 2-b.

1152
HETEROCYCLES, Vol. 60, No. 5, 2003
Characterization of oxovanadium(IV) complexes:
UV-VIS spectra of oxovanadium(IV)
complexes were measured both in H2O and DMSO solutions, and the results are summarized in Table 2.
The absorption bands of complexes (3a-e) at about 600 nm were attributable to d-d transitions. On the
other hand, the absorption bands at λmax 535-560 nm apparently increased with time, and these bands
corresponded to LMCT bands of oxovanadium(V) complexes, indicating that oxovanadium(IV) complexes
were gradually oxidized to the corresponding oxovanadium(V) ones even in aqueous solution.
Table 2 UV-VIS spectral data for oxovanadium(IV) complexes (3a-e)
Solventa
Complex
λmax / nm
3a
3b
3c
H2O
599
613
605
607
602
610
598
607
606
607
538
555
536
556
541
561
548
552
541
556
394
403
400
401
401
404
402
401
395
401
DMSO
H2O
DMSO
H2O
DMSO
H2O
3d
3e
DMSO
H2O
DMSO
a in H2O, 1.0 mM; in DMSO, 5.0 mM
Since oxovanadium(IV) ion, which has an unpaired electron, is paramagnetic, ESR spectrum and magnetic
susceptibility
complexes.10,28,34
are useful tools for investigation of electronic structure of oxovanadium(IV)
Table 3 ESR parameters of oxovanadium(IV) complexes (3a-e) in DMSO
g-value
A-value (x10-4 cm-1)
A0b
a
Complex
g0
g/ /
g⊥
A
A⊥
/ /
3ac
3bc
3cd
3dd
3ed
1.979
1.977
1.971
1.983
1.979
1.947
1.953
1.950
1.951
1.950
1.995
1.989
1.982
1.999
1.994
79.43
153.9
153.2
159.9
162.9
162.9
42.12
80.14
80.58
81.12
79.59
43.61
40.91
40.19
37.94
a
g = (g + 2 g⊥)/3; b A = (A + 2A⊥)/3; c c 3.0 mM; d c 5.0 mM.
0
/ /
0
/ /
Complexes (3a-e) showed typical isotopic eight line ESR spectra at room and liquid nitrogen temperature,
suggesting that they exist in a single isomer. The ESR parameters, universal constants (g-values) and
hyperfine coupling constants (A-values) were calculated, and the results are summarized in Table 3. These
values were consistent with those of oxovanadium(IV) complexes with VO(O4) coordination mode.10

HETEROCYCLES, Vol. 60, No. 5, 2003
1153
Further, oxovanadium(IV) complex with maltol, which is strucurally very close to the present 4(1H)-
pyridinone, has been proven to be the trans isomer by X-Ray crystallographic analysis.36 From these data,
the obtained oxovanadium(IV) complexes probably exist in the trans form. The measurement of magnetic
susceptibility of the oxovanadium(IV) complex (3e) was carried out by using Evans’ method.38 A number
of unpaired electron (n) was calculated to be 1.15, indicating the formation of oxovanadium(IV) complex
with an unpaired electron.
The electrochemical behavior of oxovanadium(IV) complexes in aqueous solution was evaluated by means
of CV with a glassy carbon electrode, and a typical cyclic voltammogram of complex (3a) is shown in
Figure 3. The electron transfer processes of complexes (3a,3b,3e) were quasi-reversible, because ipa/ipc
ratios (0.91 for 3a, 0.88 for 3b, and 0.92 for 3e) were close to unity, although values of the peak-to-peak
separation (ΔEp) (110 mV for 3a, 90 mV for 3b, and 115 mV for 3e) were greater than 60 mV. It is
noteworthy that E1/2 vs Ag/AgCl values (315 mV for 3a, 320 mV for 3b, and 300 mV for 3e) are
approximately 130-150 mV lower than that of bis(maltolato)oxovanadium(IV), VO(ma)2,36 indicating that
these complexes are less stable towards the oxidation. As ΔEp values were larger than 60 mV, cyclic
voltammgrams were measured at various scan rates (ν). A plot of ipc and ν1/2 gave a straight line,
indicating that the electron transfer proceeds at the diffusion control.
50µA
Figure 3 Cyclic voltammogram of oxovanadium(IV)
complex (3a) in H2O: 1.0 mM complex; 0.1 M NaCl;
scan rate 100 mV s-1; a working electrode: glassy
carbon; an auxiliary electrode: Pt wire; a reference
-200
0
200
400
600
mV vs Ag / AgCl
electrode: Ag/AgCl
The inhibitory effect of oxovanadium complexes on FFA release from rat adipocytes: It
is well recognized that the hydrophobicity of oxovanadium(IV) complexes is one of the most important
factors for predicting the insulin-mimetic activity.20
Table 4 Partition coefficients of oxovanadium(IV) complexes
Ligand
3a
3b
3c
3d
3e
Partition coefficient
a)
0.06
0.96 1.85
0.07
a) not measurable due to high water solubility.
Thus, the partition coefficient of oxovanadium(IV) complexes (3a-e) was measured as the same manner
described above, and the results are summarized in Table 4. Among a series of complexes, an increase in
the methylene chain length results in an increase of the solubility in octanol. Complexes (3c and 3d)

1154
HETEROCYCLES, Vol. 60, No. 5, 2003
showed higher solubility in octanol than the corresponding free ligands (1c and 1d).
Previously, we have demonstrated that the FFA release from isolated rat adipocytes is a good in vitro
evaluation system to find a compound which shows an insulin mimetic action.13 Therefore, the insulin-
mimetic activity of oxovanadium(IV) complexes was evaluated by in vitro experiments, in which the
inhibition of release of FFA from isolated rat adipocytes treated with epinephrine, was estimated in the
presence of 0.1% glucose. The obtained IC50 values are summarized in Table 5, when IC50 value of
VOSO4, as a positive control, was calibrated to be 1.0 mM.
Table 5 IC50 values of oxovanadium(IV) complexes (3a-e) in the presence of
0.1% glucose
Complex 3a
IC50 / mM
3b
3c
3d
3e
VOSO4
VO(ma)2
*
*
2.5
2.3
1560
1.0
2.5
* not measurable due to the low activity in the in vitro evaluation system.
Complexes (3a and 3b) did not show measurable activity, while complexes (3c and 3d) with relatively
high partition coefficients (see Table 4) exhibited comparable activities to VO(ma)2, although these values
were lower than VOSO4. As seen in Table 5, VO(ma)2 exhibited higher IC50 value than VOSO4, when the
complexes were tested under the same experimental conditions. However, VO(ma)2 was found to treat
DM in experimental animals when it was given by daily intravenous injections or through drinking
water.12,39-41 Therefore, the present complexes (3c and 3d) might be possible to reduce the high blood
glucose level of experimental diabetic animals.
EXPERIMENTAL
Melting points were measured on a Mel-Temp apparatus in open capillaries and are uncorrected. IR and
UV-VIS spectra were recorded on a JASCO FT/IR-230 infrared and on a JASCO Ubest V-550
spectrophotometers, respectively. 1H NMR spectra were obtained on JEOL GX-270 and JEOL JNM-
LA400D NMR spectrometers, and chemical shifts were expressed in ppm (δ) downfield from internal TMS.
51V NMR spectra were obtained on a JEOL JNM-LA400D spectrometer, and chemical shifts were reported
in ppm (δ) downfield from external VOCl3. FAB MS spectra were taken on a JEOL DX303 with a DA
5000 data system by using a Xe beam and a glycerol matrix. ESR spectra were recorded on a JEOL
RE1X spectrometer (X band) with a 100 KHz modulation. The magnetic field was calibrated by Mn(II)
doped in MgO powder. Measurement were carried out at 298 K in solution and at 77 K in liquid nitrogen
at the frozen state. Thin layer chromatography (TLC) was performed on silica gel 60F-254 with a 0.2 mm
layer thickness. Column chromatography was carried out with Merck Kieselgel 60 (230-400 mesh).
Combustion analysis was performed on a PERKIN ELMER series II CHNS/O analyzer 2400. Cyclic
voltammograms were collected using a HUSO Electro Chemical System (HECS) 315 B Cyclic
Voltammograph. N-Substituted 3-hydroxy-2-methyl-4(1H)-pyridinones (1a-e) were prepared according
to the literature methods.29,30
Bis(1,4-dihydro-1,2-dimethyl-4-oxo-3-pyridinolato)methoxooxovanadium(V)(2a)
To a solution of compound (1a) (122 mg, 0.88 mmol) in CH3OH-H2O (1:1) (8 mL) mixture was added a

HETEROCYCLES, Vol. 60, No. 5, 2003
1155
solution of VO(acac)2 (106 mg, 0.4 mmol) in CH3OH-H2O (1:1) (8 mL) mixture, and then the mixture was
refluxed for 2 h. Removal of the solvent gave the crude product, which was purified by gel-filtration with
Sephadex LH-20 with MeOH as an eluent to give the product (2a) (53 mg, 39%) as deep purple powders:
IR (KBr): 949 cm-1 (νV=O); λmax(CH3OH): 503 nm (ε 3420). Anal. Calcd for C15H19N2O6V: C, 47.00; H,
5.26; N, 7.31. Found: C, 47.01; H, 5.09; N, 7.38.
Bis(1,4-dihydro-1-methoxyethyl-2-methyl-4-oxo-3-pyridinolato)methoxooxovanadium
(V)(2e) 60 mg (23%); IR (KBr): 1606 (νC=O) and 948 cm-1 (νV=O); λmax(CH3OH): 503 nm (ε 3450); H
1
NMR (δ, 400 MHz; CD3OD at 30 °C): 2.49 (6H, br s, 2-CH3), 3.30 (6H, s, -CH2-O-CH3), 3.34 (3H, s, -
OCH3), 3.67 (4H, br s, N-CH2-), 4.30 (4H, br s -O-CH2-), 6.29 (2H, br s, 5-H), 7.59 (2H, d, J =7.3 Hz,
6-H); 51V NMR (δ, 400 MHz; in solvent): -374 (CDCl3), -390 (CD3OD), and -410 ppm (D2O). Anal.
Calcd for C19H27N2O8V: C, 49.36; H, 5.89; N, 6.06. Found: C, 49.64; H, 6.02; N, 6.14.
Bis(1,4-dihydro-1,2-dimethyl-4-oxo-3-pyridinolato)oxovanadium(IV)(3a)
To a solution of compound (1a) (1.0 g, 7.2 mmol) in H2O (10 mL) was added dropwise VOSO4·3.6H2O
(0.82 g, 3.6 mmol) in H2O (5 mL). The pH of the reaction mixture was adjusted to 10 with 10 M KOH,
and then the resulting mixture was refluxed overnight. After cooling to rt, the precipitate was collected by
filtration and washed several times with H2O, and then dried over anhydrous P2O5 to give the product (3a)
(1.04 g, 84%) as blue solids: IR (KBr): 1606 (νC=O) and 967 cm-1 (νV=O). Anal. Calcd for C14H16N2O5V:
C, 48.99; H, 4.70; N, 8.16. Found: C, 48.70; H, 4.53; N, 7.81.
Bis(1,4-dihydro-1-ethyl-2-methyl-4-oxo-3-pyridinolato)oxovanadium(IV)(3b)
yield: 66 %; IR (KBr): 1603 (νC=O) and 964 cm-1 (νV=O). Anal. Calcd for C16H20N2O5V: C, 51.76; H,
5.43; N, 7.54. Found: C, 51.50; H, 5.45; N, 7.63.
Bis(1,4-dihydro-2-methyl-4-oxo-1-propyl-3-pyridinolato)oxovanadium(IV)(3c)
yield: 72%; IR (KBr): 1603 (νC=O) and 979 cm-1 (νV=O). Anal. Calcd for C18H24N2O5V: C, 54.14; H,
6.06; N, 7.01. Found: C, 54.30; H, 6.06; N, 7.17.
Bis(1-butyl-1,4-dihydro-2-methyl-4-oxo-3-pyridinolato)oxovanadium(IV)(3d)
yield: 72%; IR (KBr): 1605 (νC=O) and 976 cm-1 (νV=O). Anal. Calcd for C20H28N2O5V·0.5H2O: C, 55.04;
H, 6.70; N, 6.42. Found: C, 55.02; H, 6.80; N, 6.38.
Bis(1,4-dihydro-2-methyl-1-methoxyethyl-4-oxo-3-pyridinolato)oxovanadium(IV)(3e)
yield: 73%; IR (KBr): 1604 (νC=O) and 979 cm-1 (νV=O); FAB MS: m/z 432 ([M+H]+). Anal. Calcd for
C18H24N2O7V: C, 50.12; H, 5.61; N, 6.49. Found: C, 50.16; H, 5.83; N, 6.49.
3-Benzyloxy-1-carboxypentyl-2-methyl-4(1H)-pyridinone(4a)
To a mixture of 6-aminohexanoic acid (1.31 g, 10 mmol) and 3-benzyloxy-2-methyl-4-pyrone (1.18 g, 5.5
mmol) in EtOH-H2O (1:1) mixture (8 mL) was added 1 M NaOH (10 mL, 10 mmol), and then the reaction
mixture was refluxed for 48 h. The pH of the reaction mixture was adjusted to 8 with 6 M HCl. After
concentration to a half volume, the aqueous layer was washed with CHCl3 (200 mL) to remove 3-

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HETEROCYCLES, Vol. 60, No. 5, 2003
benzyloxy-2-methyl-4-pyrone. The aqueous layer was adjusted to pH 4 with 10% citric acid, and the
resulting solid was dissolved in CHCl3 (300 mL). The organic layer was washed with saturated NaCl
solution (100 mL), and then dried over anhydrous Na2SO4. Removal of the solvent afforded the product
(4a) (1.81 g, 88%) as pale brown solids; mp: 106-109 °C; IR (KBr): 3260-2760 (νO-H, br), 1720 (νC=O),
1
1627 (νC=O), 752 and 706 cm-1 (δC-H); H NMR (δ, 270 MHz; CDCl3): 1.31 (2H, m, -CH2-), 1.62 (4H, m,
-CH2-x2), 2.10 (3H, s, -CH3), 2.32 (2H, t, J =7.1 Hz, -CH2-CO-), 3.80 (2H, t, J =7.0 Hz, N-CH2-),
5.14 (2H, s, -O-CH2-), 6.65 (1H, d, J =7.6 Hz, 5-H), 7.28-7.39 (6H, m, 6-H, -Ph), and 10.82 ppm (1H,
br s, -OH). Anal. Calcd for C19H23NO4·0.5H2O: C, 67.43; H, 6.99; N, 4.13. Found: C, 67.38; H, 7.08; N,
4.16.
3-Benzyloxy-1-carboxyheptyl-2-methyl-4(1H)-pyridinone(4b)
2.67 g (93%); mp: 135-137℃; IR (KBr): 1717 (νC=O), 1623 (νC=O), 752 and 706 cm-1 (δC-H); 1H NMR (δ,
270 MHz; CDCl3): 1.31 (6H, m, -CH2-x3), 1.60 (4H, m, -CH2-x2), 2.09 (3H, s, -CH3), 2.35 (2H, t, J
=7.3 Hz, -CH2-CO-), 3.75 (2H, t, J =7.3 Hz, N-CH2-), 5.20 (2H, s, -O-CH2-), 6.63 (1H, d, J =7.6 Hz,
5-H), 7.23 (1H, d, J =7.6 Hz, 6-H), 7.29-7.38 (5H, m, -Ph). Anal. Calcd for C21H27NO4: C, 70.56; H, 7.61;
N, 3.92. Found: C, 70.34; H, 7.74; N, 3.63.
N,N’-[Bis(3-benzyloxy-1,4-dihydro-2-methyl-4-oxo-1-pyridyl)hexanoyl]-1,5-diamino-
3-oxapentane(5a)
N,N’-Carbonyldiimidazole (165 mg, 1 mmol) was added to a solution of compound (4a) (336 mg, 1
mmol) in dry DMF (10 mL), and the mixture was stirred at rt. After 1 h, 1,5-diamino-3-oxapentane (47
mg, 0.45 mmol) was added to the mixture, and then the reaction mixture was stirred for 120 h at 40°C.
After removal of the solvent, the oily residue was dissolved in CHCl3 (80 mL). The organic layer was
successively washed with H2O (40 mL), 5% citric acid (40 mL), 5% NaHCO3 (40 mL), H2O (40 mL),
saturated NaCl solution (40 mL), and then dried over anhydrous Na2SO4. Removal of the solvent gave a
crude product, which was purified by column chromatography on silica gel with CHCl3:CH3OH (5:1)
mixture as an eluent to give the product (5a)(146 mg, 44%) as pale brown amorphous solids: IR (KBr):
3270 (νN-H), 1655 (νC=O), 1628 (νC=O), 752 and 702 cm-1 (δC-H); 1H NMR (δ, 270 MHz; CDCl3): 1.22 (4H,
m, -CH2-x2), 1.58 (8H, m, -CH2-x4), 2.08 (6H, s, -CH3x2), 2.21 (4H, t, J=7.1 Hz, -CH2-CO-x2), 3.38
(4H, m, -CH2-O-x2), 3.47 (4H, m, -CH2-NH-x2), 3.72 (4H, t, J =7.1 Hz, N-CH2-x2), 5.14 (4H, s, -
CH2-Phx2), 6.37 (2H, d, J =7.3 Hz, 5-Hx2), 7.24 (2H, d, J =7.3 Hz, 6-Hx2), 7.28-7.34 (10H, m, -
Phx2). Anal. Calcd for C42H54N4O7 · 0.5H2O: C, 68.54; H, 7.53; N, 7.61. Found: C, 68.20; H, 7.55;
N, 7.44.
N,N’-[Bis(3-benzyloxy-1,4-dihydro-2-methyl-4-oxo-1-pyridyl)octanoyl]-1,5-diamono-
3-oxapentane(5b)
1
yield: 52%; IR (KBr): 3270 (νN-H), 1625 (νc=o), 752 and 702 cm-1 (δC-H); H NMR (δ, 270 MHz; CDCl3):
1.24 (12H, m, -(CH2)2-(CH2)3-(CH2)2-x2), 1.59 (8H, m, N-CH2-CH2-x2, -CH2-CH2-CO-x2), 2.08 (6H, s,
-CH3x2), 2.17 (4H, t, J =7.3 Hz, -CH2-CO-x2), 3.43 (4H, t, J =7.3 Hz, -CH2-O-x2), 3.52 (4H, m, -
CH2-NHx2), 3.72 (4H, t, J =7.3 Hz, N-CH2-x2), 5.19 (4H, s, -CH2-Phx2), 6.40 (2H, d, J =7.7 Hz, 5-
Hx2), 6.75 (2H, t, J =5.2 Hz, -NH-x2), 7.20 (2H, d, J =7.7 Hz, 6-Hx2), 7.35-7.41 (10H, m, -Phx2).
Anal. Calcd for C46H62N4O7 · 0.5H2O: C, 69.96; H, 8.02; N 7.07. Found: C, 69.68; H, 8.08; N, 7.36.

HETEROCYCLES, Vol. 60, No. 5, 2003
1157
N,N’-[Bis(3-hydroxy-1,4-dihydro-2-methyl-4-oxo-1-pyridyl)hexanoyl]-1,5-diamino-
3-oxapentane(6a)
A suspension of 10% Pd-C (10 mg) in CH3OH (10 mL) was prehydrogenated with H2 for 30 min. To this
suspension was added a solution of compound (5a)(90 mg, 0.12 mmol) in CH3OH (5 mL). The mixture
was stirred for 2 h under hydrogen atmosphere. After removal of the catalyst by filtration, the filtrate was
evaporated off to give the product (6a)(59 mg, 88%) as colorless amorphous solids: IR (neat): 1660 (νC=O
)
and 1627 cm-1 (νC=O); H NMR (δ, 270 MHz; CD3OD): 1.35 (4H, m, -CH2-CH2-CH2-x2), 1.64 (4H, m,
N-CH2-CH2-x2), 1.76 (4H, m, -CH2-CH2-CO-x2), 2.22 (4H, t, J =7.1 Hz, -CH2-CO-x2), 2.44 (6H, s, -
CH3x2), 3.33 (4H, m, -NH-CH2-x2), 3.50 (4H, t, J =6.5 Hz, -CH2-O-x2), 3.92 (4H, t, J =6.8 Hz, N-CH2-
1
x2), 6.47 (2H, d, J =6.6 Hz, 5-Hx2), 7.18 (2H, d, J =6.6 Hz, 6-Hx2). Anal. Calcd
for C28H42N4O7 ·
4H2O: C, 54.32; H, 8.14; N, 9.04. Found: C, 54.40; H, 8.19; N, 8.88.
ꢀ
N,N’-[Bis(3-hydroxy-1,4-dihydro-2-methyl-4-oxo-1-pyridyl)octanoyl]-1,5-diamino-
3-oxapentane(6b)
yield: 83%; IR (neat): 1660 (νC=O) and 1627 cm-1 (νc=o); 1H NMR (δ, 270 MHz; CD3OD): 1.36 (12H, m, -
(CH2)2-(CH2)3-(CH2)2-x2), 1.59 (4H, m, N-CH2-CH2-x2), 1.75 (4H, m, -CH2-CH2-CO-x2), 2.18 (4H, t,
J =7.3 Hz, -CH2-CO-x2), 2.46 (6H, s, -CH3x2), 3.31 (4H, m, -NH-CH2-x2), 3.51 (4H, t, J =6.6 Hz, - CH2-
O-x2), 4.09 (4H, t, J =7.7 Hz, N-CH2-x2), 6.50 (2H, d, J=7.0 Hz, 5-Hx2), 7.70 (2H, d, J =7.0 Hz, 6-Hx2).
Anal. Calcd for C32H50N4O7 · 2.5H2O: C, 59.31; H, 8.55; N, 8.64. Found: C, 59.51; H, 8.62; N, 8.29.
N,N’-[Bis(3-hydroxy-1,4-dihydro-2-methyl-4-oxo-1-pyridyl)hexanoyl]-1,5-diamino-
3-oxapentanomethoxooxovanadium(V)(7a)
To a solution of compound (6a)(186 mg, 0.33 mmol) in CH3OH-H2O (1:1) mixture (5 mL) was added a
solution of VO(acac)2 (80 mg, 0.30 mmol) in CH3OH-H2O (1:1) mixture (10 mL), and then the mixture
was refluxed for 2 h. Removal of the solvent and subsequent gel-filtration with Sephadex LH-20 with
distilled CH3OH as an eluent afforded the product (7a)(42 mg, 22%) as deep purple powders: IR (KBr):
949 cm-1 (νV=O); λmax(10% aqueous CH3OH): 527 nm (ε 2840). Anal. Calcd for C29H43N4O9V·2H2O: C,
51.31; H, 6.98; N, 7.86. Found: C, 51.61; H, 7.03; N, 8.08.
N,N’-[Bis(3-hydroxy-1,4-dihydro-2-methyl-4-oxo-1-pyridyl)octanoyl]-1,5-diamino-
3-oxapentanomethoxooxovanadium(V)(7b)
30 mg (23%); IR (KBr): 953 cm-1 (νV=O); λmax(30% aqueous CH3OH): 527 nm (ε 1870). Anal. Calcd
for C33H51N4O9V·0.8H2O: C, 55.57; H, 7.43; N, 7.86. Found: C, 55.65; H, 7.64; N, 7.74.
Measurement of the partition coefficient
To a solution of sample (5 mL) in KRB buffer solution (120 mM NaCl, 1.27 mM CaCl2, 1.2 mM MgSO4,
4.75 mM KCl, 1.2 mM KH2PO4, and 24 mM NaHCO3: pH 7.4) (ligand : 1.0x10-4 M ; complex: 1.0x10-5
M) was added octanol (5 mL). The mixture was stirred at 600 rpm for 4 h with a magnetic stirrer, and
then centrifuged at 4000 rpm for 20 min with a centrifugal separator. The concentrations of a ligand and its
complex in each phase were measured from absorbance. The partition coefficient was calculated from the
following equation ; P =Coctanol/Cbuffer
.
Measurement of cyclic voltammetry

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To a solution of each oxovanadium(IV) complex (1 mM) in H2O was added NaCl (0.1 M) as a supporting
electrolyte. Cyclic voltammetry was carried out by generating triangular waves at an ambient temperature.
A carbon electrode was used together with an Ag/AgCl electrode as a reference and a platinum wire as an
auxiliary electrode. Current-voltage curves were recorded on an X-Y recorder.
ACKNOWLEDGEMENT
This work was partially supported by the Japan Private School Promotion Fundations.
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