Synthesis, physicochemical properties and biological evaluation of ester prodrugs of 3-hydroxypyridin-4-ones: Design of orally active chelators with clinical potential

Article abstract of DOI:10.1016/S0223-5234(99)80097-X

The synthesis of a range of hydrophobic ester prodrugs of 3- hydroxypyridin-4-ones with potential for oral administration is described. The distribution coefficient values of a range of these ester prodrugs and the corresponding alcohols in 1-octanol and

Full text of DOI:10.1016/S0223-5234(99)80097-X

Eur. J. Med. Chem. 34 (1999) 475−485
© Elsevier, Paris
475
Original article
Synthesis, physicochemical properties and biological evaluation
of ester prodrugs of 3-hydroxypyridin-4-ones: design of orally active chelators
with clinical potential
Bijaya L. Rai, Zu Dong Liu, Ding Yong Liu, Shu Li Lu, Robert C. Hider*
Department of Pharmacy, King’s College London, Manresa Road, London, SW3 6LX, UK
(Received 4 September 1998; accepted 25 November 1998)
Abstract – The synthesis of a range of hydrophobic ester prodrugs of 3-hydroxypyridin-4-ones with potential for oral administration is
described. The distribution coefficient values of a range of these ester prodrugs and the corresponding alcohols in 1-octanol and MOPS buffer
pH 7.4 are presented together with their rates of hydrolysis at pH 2, pH 7.4, in rat blood and liver homogenate. In vivo iron mobilisation
efficacy of the pivaloyl and benzoyl prodrugs has been compared with their parent drugs using a 59Fe-ferritin loaded rat model. Both classes
of prodrug enhanced the ability of the parent hydroxypyridinone to facilitate the excretion of 59Fe. The influence of the pivaloyl function was
more marked than that of the benzoyl function. The optimal effect was observed with 1-[2≠-(pivaloyloxy)ethyl]-2-methyl-3-hydroxy-4(1H)-
pyridinone 25. However, not all the prodrugs provide increased efficacy which suggests that lipophilicity is not the only factor which
influences the drug efficacy. The metabolism of the compound may have a dominating influence on the overall efficacy. © Elsevier, Paris
hydroxypyridinone / prodrug / iron chelators
1. Introduction
3-Hydroxypyridin-4-ones (HPOs) are selective for
iron (III) under most biological conditions, but unlike
DFO, are efficiently absorbed, when administered
orally [7, 8]. The simple 1,2-dialkyl derivatives, such as
CP20 (Deferiprone, L1) (1), are highly effective at
removing iron from iron overloaded animals [9] includ-
ing man [10, 11] but are associated with two disadvan-
tages; (i) they penetrate cells easily and therefore gain
ready access to the bone marrow and the brain [12] and
(ii) they are rapidly conjugated with glucuronic acid,
thereby loosing their iron binding properties [13]. Pen-
etration of membranes can be effectively decreased by
designing more hydrophilic hydroxypyridinones, for in-
stance hydroxyalkyl hydroxypyridinones [14]. Some of
1-hydroxyalkyl derivatives of HPOs, such as CP102 (2),
CP40 (3) and CP41 (4) (table I), are not rapidly metabo-
lised by Phase II mechanisms and therefore their chelat-
ing action is more prolonged [15]. Not surprisingly the
increased hydrophilicity of such compounds is associated
with a decreased efficiency of absorption from the gas-
trointestinal tract and more seriously, reduced liver ex-
traction. Efficient liver extraction of a chelator leads to
The preferred treatment of â-thalassaemia major is to
maintain high levels of haemoglobin by regular blood
transfusion [1]. Repeated transfusion unfortunately leads
to elevated body iron levels due to the inability of humans
to excrete iron via the kidney [2]. Excess iron is mainly
located within the liver and other highly perfused organs
and this leads to tissue damage, organ failure and even-
tually death [3]. Complications associated with elevated
iron levels can be largely avoided by the use of iron-
specific chelating agents and in particular desferrioxam-
ine (DFO) [4, 5]. The major limiting factor of DFO is that
it is not orally active and has to be administered paren-
tally [6]. This in turn leads to poor patient compliance.
*Correspondence and reprints
Abbreviations: DFO, desferrioxamine; HPO, hydroxypyridinone;
DEAD, diethyl azodicarboxylate; D7.4, distribution coefficient at
pH 7.4; GIT, gastrointestinal tract; HPV, hepatic portal vein;
MOPS, 4-morpholinepropane sulphonic acid; PBS, phosphate
buffer; HPLC, high performance liquid chromatography; EDTA,
ethylenediaminetetraacetic acid; SD, standard deviation.

476
Table I. Chemical structure of CP20 (Deferiprone) and several
1-hydroxyalkyl hydroxypyridinones.
pharmacokinetics for further consideration [17]. In this
work we describe the synthesis, characterisation and
efficacy of a range of such hydrophobic ester prodrugs of
1-hydroxyalkyl hydroxypyridinones.
2. Chemistry
Compound
R1
R2
D7.4
The
1-(hydroxyalkyl)-2-alkyl-3-benzyloxy-4(1H)-
CP20 (1)
CP102 (2)
CP40 (3)
CP41 (4)
CH3
CH3
CH2CH3
CH3
0.17
0.22
0.08
0.13
pyridinones 9–11, were prepared by following the method-
ology as described by Rai and co-workers [14] (figure 2).
The commercially available maltol (5) or ethyl maltol (6)
were benzylated in 90% aqueous methanol to give 7 and
8. Refluxing 7 or 8 with ethanolamine or 3-hydro-
xylpropylamine in aqueous ethanol, in the presence of a
catalytic amount of sodium hydroxide, gave the benzy-
lated alcohols 9–11 which were isolated as the free-bases.
The synthesis of HPO esters, 1-alkanoyloxy- and
1-benzoyloxyalkyl-2-alkyl-3-hydroxy-4(1H)-pyridinones
was accomplished using two methods, either from acid
chlorides (figure 3) or carboxylic acids via an alkyltri-
phenylphosphonium carboxylate intermediate (figure 4).
The reaction of benzyl protected alcohols with acid
chlorides in the presence of catalytic bases, such as
triethylamine [18] or pyridine [19], afforded diesters
CH2CH2OH
CH2CH2OH
(CH2)3OH
CH3
high biliary iron-excretion rates, a highly desirable fea-
ture for the therapy of iron overload [16].
This difficulty can, in principle, be overcome by the
use of prodrugs, whereby a hydrophobic prodrug is
absorbed from the gastrointestinal tract and then effic-
iently extracted by the liver during the “first pass”. Once
in the hepatocyte, the ester link is cleaved to a much more
hydrophilic chelator (figure 1). Preliminary studies with
hydrophobic ester prodrugs of 1-hydroxyalkyl hydroxy-
pyridinones have demonstrated that they possess suitable
Figure 1. Schematic representation of the use of ester prodrugs of 1-hydroxyalkyl HPOs to enhance both the absorption from the
gastrointestinal tract (GIT) and the liver extraction from the hepatic portal vein (HPV) of the prodrug. Subsequent intracellular
hydrolysis occurs yielding a hydrophilic chelator.

477
Figure 2. Synthetic methodology adopted for the preparation of the benzyl protected alcohols, 1-(hydroxyalkyl)-2-alkyl-3-benzyloxy-
4(1H)-pyridinones 9–11.
12–15 (table II) at elevated temperatures and not the
expected benzyl protected esters, as a result of cleavage
of the benzylic carbon-oxygen bond. Hydrolysis of di-
esters in water generated the desired ester chelators
(table III). At room temperature a mixture of benzyl
protected ester and diester was formed (figure 3). Ex-
amples of ether cleavage by pyridine hydrochloride have
been previously reported [20, 21]. Triethylamine hydro-
chloride probably plays a similar role to that of pyridine
hydrochloride. In contrast, the direct use of the benzyl
protected alcohol and carboxylic acids in the presence of
diethyl azodicarboxylate (DEAD)/triphenylphosphine led
to the formation of the desired benzyl protected esters
16–20 in good yields (figure 4). This reaction is believed
to proceed through the formation of a quaternary phos-
phonium salt, by addition of triphenylphosphine to
DEAD, which reacts in situ with alcohols in the presence
of a carboxylic acid to form an alkoxytriphenylphospho-
nium carboxylate. The phosphonium moiety is then
displaced by the carboxylate anion to give the desired
ester product [22, 23]. Removal of the benzyl group was
achieved by catalytic hydrogenation to yield the bidentate
chelators, which were isolated as free bases or hydrochlo-
ride salts (table III).
3. Physicochemical properties and biological
experiments
3.1. Determination of solution properties
Since one of the critical parameters of ester prodrugs is
the lipophilicity of the compounds, the determination of
distribution coefficients (D values) of prodrugs is impor-
tant. Distribution coefficients of the chelators were mea-
sured using a buffered octanol/aqueous system. A modi-
fied automated continuous flow technique [7, 24] was
Table II. Synthesis of 1-alkanoyloxyalkyl-2-alkyl-3-alkanoyloxy-4(1H)-pyridinones in the presence of triethylamine1 or pyridine2 as catalytic
bases.
Compound
R2
R
n
m.p. (°C)
Yield (%)
Formula
12
13
14
15
C2H5
C2H5
CH3
C(CH3)3
CH(CH3)2
C(CH3)3
C(CH3)3
2
2
2
3
141–142
791
771
742
712
C19H29NO5
C17H25NO5
C18H27NO5
C19H29NO5
133.5–134.5
163–164.5
169–170
CH3

478
essential that prodrug esters are absorbed intact from the
gastrointestinal tract, and are reasonably stable in the
plasma, thereby providing sufficient time for the prodrug
to perfuse the liver. Subsequently, rapid hydrolysis by
hepatic carboxyesterases will generate hydrophilic
metabolites within hepatocytes. In order to identify a lead
prodrug by which specific drug delivery can be achieved,
it is essential to determine the stability of this ester in
different conditions. Preliminary in vitro esterase studies
of the aliphatic ester derivatives of CP102 (2), namely 21,
22 and 23, indicate that the pivaloyl ester analogue 23
may partially fulfil the requirements for relatively effic-
ient liver extraction. This is due to its resistance towards
hydrolysis in pH 2 and 7.4 buffer and a much lower
hydrolysis rate in plasma than the liver, whereas 21 and
22 show much faster hydrolysis rates in plasma [25]. In
this current study, the hydrolysis rates of pivaloyl ester
derivatives 23, 25 and 27 were compared with their
benzoyl analogues 24, 26 and 28 at different pHs (pH 2
and pH 7.4), in rat blood and liver homogenate.
Figure 3. Synthesis of ester prodrugs via acid chlorides,
method (a).
chosen in preference to the traditional shake flask method
owing to a greater accuracy and reproducibility of mea-
surements.
3.2.2. Effıcacy study
In vivo iron mobilisation efficacy of all HPO ligands
has been measured in a non-iron overloaded rat model.
59Fe-ferritin has been used to label the liver iron
pool [26], followed by a challenge with test chelator at a
time when iron released by lysosomal degradation of
ferritin is maximally available. Since the major reason to
3.2. Biological experiments
3.2.1. Stability study
In order to obtain selective delivery of the chelator to
the major chelatable iron pool in the body (the liver), it is
Figure 4. Synthesis of ester prodrug via carboxylic acid, method (b).

479
Table III. Synthesis of 1-alkanoyloxy- and 1-benzoyloxyalkyl-2-alkyl-3-hydroxy-4(1H)-pyridinones and their distribution coefficients
between an aqueous phase buffered at pH 7.4 and octanol.
Compound
R2
R
n
m.p. (°C)
Yield (%)
Formula
D7.4
21
22
23
24
25
26
27
28
C2H5
C2H5
C2H5
C2H5
CH3
CH3
CH3
CH3
CH3
2
2
2
2
2
2
3
3
126–127
106–107
133–134
173–174
139–140
201–203
156–157
168–170
881
C11H15NO4
C13H19NO4
C14H21NO4
C16H17NO4
C13H19NO4
C15H16NO4Cl
C14H21NO4
C16H18NO4Cl
0.58 ± 0.01 (n = 6)
5.06 ± 0.09 (n = 6)
14.5 ± 0.08 (n = 6)
32.8 ± 1.68 (n = 6)
4.70 ± 0.04 (n = 6)
10.9 ± 1.05 (n = 6)
8.78 ± 0.23 (n = 6)
17.6 ± 1.31 (n = 6)
CH(CH3)2
C(CH3)3
C6H5
C(CH3)3
C6H5
962
901; 922
921
922
921
C(CH3)3
C6H5
802
941
2
1Yield obtained from hydrogenolysis reaction of the benzyl protected ester, Yield obtained from hydrolysis of the diester.
develop ester prodrugs of HPOs is to target the liver iron
pool, the 59Fe-ferritin/rat model is considered to be a
suitable system for evaluation of the iron mobilisation
efficacy of such models.
of hydrolytic rates were shown, ranging from 27 600
nmoles/g tissue/h (23) to 481 000 nmoles/g tissue/h (24).
The hydrolytic rates of benzoyl ester derivatives in the
liver are much faster than their pivaloyl ester analogues.
Generally the hydrolytic rates of these esters in the liver
were several thousand fold faster than that in the rat
blood. This rapid hydrolysis in the liver will generate the
parent hydrophilic alcohols.
4. Results
4.1. Distribution coeffıcients
Values of distribution coefficients of the ester prodrugs
between an aqueous phase buffered at pH 7.4 and octanol
are presented in table III. The prodrugs are more
lipophilic than the alcohols, as expected. In general, the
expected increase in distribution coefficient was observed
with the increase in the bulk of the ester function. Clearly,
the pivaloyl esters and benzoate esters are more lipophilic
and as a result are predicted to be efficiently absorbed
from the gastrointestinal tract and extracted by the liver.
4.3. Effıcacy study
The iron mobilisation efficacy of pivaloyl (23, 25 and
27) and benzoyl ester prodrugs (24, 26 and 28) were
compared with their parent drugs 2, 3 and 4, and the
1,2-dimethyl derivative 1 (figure 5). Clearly, all the ester
prodrugs were found to be superior to 1. Many prodrugs
provide a clear improvement over their parent com-
pounds in the efficacy model. The pivaloyl ester 23 was
found to increase efficacy from 16.7 to 23%; 25 increased
efficacy from 7.6 to 35.9% and 27 increased efficacy from
29.9 to 39.3%. An enhanced iron excretion was also
produced with the benzoyl ester prodrugs, for instance,
26 provides 16.9% iron excretion, compared with 7.6%
for 3, and 28 increased efficacy from 29.9 to 36.4%. Such
improvement indicates that selective delivery of the drug
to the liver has been achieved. However, not all the
prodrugs provide increased efficacy, thus 24 is less
effective than the parent compound 2, suggesting that
lipophilicity is not the only factor which influences the
drug efficacy.
4.2. Stability study
The preliminary hydrolysis studies of ester prodrugs at
different pH values in rat blood and rat liver homogenate
are presented in table IV. All six ester prodrugs possess
appreciable stability at both pH 7.4 and pH 2. The
hydrolysis rates of these ester derivatives by rat plasma
are more rapid than in PBS, falling in the range
185.6–783.5 nmoles/mL/h. The pivaloyl ester 23 was the
most stable ester, with a plasma esterase activity of 185.6
nmoles/mL/h. The rate of hydrolysis of all esters was
found to be much greater in the liver and a wide variety

480
Table IV. Hydrolysis of ester prodrugs at different pHs, in rat blood and rat homogenate. Values are expressed as means ± SD (n = 3).
Compound
Rate of hydrolysis
pH 2.0
pH 7.4
Rat blood
Rat liver
(nmole/ml/h)
(nmole/ml/h)
(nmole/ml/h)
(nmole/g/h)
23
24
25
26
27
28
5.0 ± 1.1
1.9 ± 0.5
43.7 ± 0.8
0.7 ± 0.4
12.0 ± 4.2
0.6 ± 0.5
0
185.6 ± 27.2
591.2 ± 16.0
285.9 ± 58.9
783.5 ± 115.8
479.2 ± 24
27 600 ± 700
0.8 ± 0.3
3.7 ± 0.2
0.5 ± 0.2
23.3 ± 3.0
0.3 ± 0.1
481 000 ± 15 200
64 800 ± 2 500
325 170 ± 6 300
91 300 ± 5 200
230 131 ± 2 363
364.0 ± 14.4
5. Discussion
Three series of pyridinones were investigated in the
59Fe-ferritin model, the hydroxyalkyl derivatised HPOs,
2, 3 and 4 together with their pivaloyl esters, 23, 25 and
27 and benzoyl esters, 24, 26 and 28. Preliminary analysis
of the results shows that in each case the pivaloyl ester
leads to superior iron excretion via the bile than does the
corresponding benzoyl ester (figure 5). This effect is
particularly marked with the 1-[2≠-(hydroxy)ethyl] de-
rivative 3 where the iron excretion is increased from 7.6%
to 35.9%. This enhancement is almost certainly due to the
increased Dvalue of pivaloyl ester 25, 4.7 as compared to
0.08 for the parent HPO (3). The reason for the more
marginal increase with the benzoyl ester 26 is not clear.
The Dvalue of 26 is higher than that of the pivaloyl ester
25 and therefore absorption from the gastrointestinal tract
might be anticipated to be enhanced. However the ben-
zoyl esters possess lower aqueous solubilities than the
pivaloyl esters and this might adversely influence absorp-
tion; furthermore, based on the stability studies with 24
and 26, the benzoyl esters are found to be hydrolysed
more rapidly in the blood.
The esters investigated for stability in aqueous solution
at pH values 2.0 and 7.4 were found to be relatively stable
(table IV). This is in marked contrast to esters of the
3-hydroxyl function of the pyridinones, which are un-
stable [27]. Thus, esters positioned at the N-alkyl function
appear to be suitable for formulation purposes and are
predicted not to be unduly unstable in the lumen of the
stomach. The stability of the esters in blood was found to
be sufficient to permit delivery to the liver via the portal
stream, the most stable ester being the pivaloyl derivative
23 (table IV). In the liver homogenate, all esters under-
went rapid hydrolysis yielding the more hydrophilic
hydroxypyridinone. Thus in principle the esters described
in this work might be expected to be readily absorbed
from the gastrointestinal tract by virtue of their favour-
able log D values (0–1.5) and be extracted into the
hepatocyte, without undergoing appreciable hydrolysis in
the lumen of the stomach or the blood perfusing the liver.
Although most ester prodrugs provide a clear improve-
ment over the parent hydroxyalkyl compound, some
prodrugs only induce a marginal or even negative effect.
This may result from the different metabolism between
ester prodrug and the parent compound. Although
1-hydroxyalkyl HPOs such as CP102 (2) and CP41 (4) do
not undergo glucuronic conjugation [15], their ester de-
rivatives, which possess different physico-chemical prop-
erties, may be involved in different metabolic pathways.
Normally, esters are predicted to be hydrolysed rapidly in
the liver. However, with some of the ester prodrugs, there
may exist a competition between ester hydrolysis and
phase II metabolism. Metabolic studies need to be under-
taken in order to verify this hypothesis.
Figure 5. Iron mobilisation comparison studies between ester
prodrugs and the parent 1-hydroxyalkyl HPOs in the 59Fe-
ferritin loaded rat model. All chelators were given orally; the
chelator doses were 450 µmol/kg. Values are expressed as
means ± SD (n = 5–9).
In summary, the iron mobilisation efficacy can be
improved by the introduction of a prodrug strategy, but
the selection of ester moieties is critical. The metabolism
of the compound may have a dominating influence on the

481
overall efficacy. Detailed metabolic studies need to be
undertaken in order to identify a lead prodrug for further
development.
1H-NMR (CDCl3): δ 1.17 [9H, s, -C(CH3)3], 1.19 (3H, t,
CH2CH3, J = 6.0Hz), 1.38 [9H, s, -C(CH3)3], 2.62 (2H,
q, CH2CH3, J = 6.0Hz), 4.0–4.4 (4H, m, NCH2CH2O),
6.34 (1H, d, 5-H, J = 8.0Hz), 7.34 (1H, d, 6-H, J =
8.0Hz); MS (EI): m/z, 352 [(M + H)+.]; Anal. Calcd. for
C19H29NO5: C, 64.93; H, 8.31; N, 3.98 Found C, 65.24;
H, 8.12; N, 3.98%.
6. Experimental protocols
6.1. Chemistry
Analogous procedure using 9 and isobutyryl chloride
yielded 13 in a yield of 77% (table II).
Melting points are uncorrected. IR spectra are recorded
on a Perkin Elmer 298. Proton NMR spectra were
determined with Perkin-Elmer R32 (90 MHz). Mass
spectra (EI) were recorded on a Joel AX505W. Elemental
analyses were performed by Butterworth Laboratories
Limited, Teddington, Middlesex or Micro analytical labo-
ratories, Department of Chemistry, The University of
Manchester, Manchester, M13 9PL.
6.1.2.2. 1-[2≠-(Isobutyryloxy)ethyl]-2-ethyl-3-(isobuty-
ryloxy)-4(1H)-pyridinone 13
M.p. 133.5–134.5 °C; IR (Nujol): 1 735 (ester C=O),
1
1 625 (pyridinone C=O), 1 580 (C=C) cm–1; H-NMR
(CDCl3): δ 1.13 [6H, d, -CH(CH3)2], 1.18 (3H, t,
CH2CH3, J = 6.0Hz) 1.33 [6H, d, -CH(CH3)2], 2.2–3.1
(3H, m, -CH(CH3)2 & CH2CH3), 4.0–4.4 (4H, m,
NCH2CH2O), 6.35 (1H, d, 5–H, J = 8.0Hz), 7.32 (1H, d,
6–H, J = 8.0Hz); MS (EI): m/z, 323 [M+.]; Anal. Calcd.
for C17H25NO5: C, 63.13; H, 7.79; N, 4.33 Found C,
63.54; H, 8.07; N, 4.41%.
6.1.1. General procedure for the synthesis of the 1-
(hydroxyalkyl)-2-alkyl-3-benzyloxy-4(1H)-pyridinones
The benzyl protected alcohols 9–11, 1-(hydroxyalkyl)-
2-alkyl-3-benzyloxy-4(1H)-pyridinones (figure 1) were
prepared by following the methodology as described by
Rai and co-workers [14] from commercially available
maltol (5) or ethyl maltol (6).
6.1.2.3. 1-[2≠-(Pivaloyloxy)ethyl]-2-methyl-3-pivaloyl-
oxy-4(1H)-pyridinone 14
The alcohol 10, 1-[2≠-(hydroxy)ethyl]-2-methyl-3-
benzyloxy-4(1H)-pyridinone, free base (1.85 g, 7 mmol)
was added to a solution of dimethylformamide (100 mL)
containing pyridine (5.6 g, 70 mmol, 10 eq) and cooled to
0 °C under a nitrogen atmosphere. Pivaloyl chloride
(3.8 g, 28 mmol, 4 eq) dissolved in dimethylformamide
(5 mL) was added dropwise via a syringe with stirring,
the reaction mixture was allowed to warm slowly to
20 °C and then heated at 60 °C for 12 h. Pyridine was
removed azeotropically with benzene and dimethylfor-
mamide was removed under high vacuum. The dark
green residue was dissolved in dichloromethane
(150 mL) and washed with aqueous sodium bicarbonate
(5% w/v, 4 × 100 mL) and water (2 × 100 mL). The
organic fraction was dried over anhydrous sodium sul-
phate, filtered and the solvent was removed in vacuo to
give a brown oil which solidified on standing at room
temperature. Recrystallisation from ethyl acetate/
decolourising charcoal afforded colourless crystals
(1.75 g, 74%); m.p. 163–164.5 °C; IR (Nujol): 1 745
(ester C=O), 1 635 (pyridinone C=O), 1 590 (C=C) cm–1;
1H-NMR (CDCl3): δ 1.18 [9H, s, -C(CH3)3], 1.40 [9H, s,
-C(CH3)3], 2.25 (3H, s, 2-CH3), 4.0–4.4 (4H, m,
NCH2CH2O), 6.35 (1H, d, 5-H, J = 7.5Hz), 7.30 (1H, d,
6-H, J = 7.5Hz); MS (EI): m/z, 337 [M+.]; Anal. Calcd.
for C18H27NO5: C, 64.07; H, 8.06; N, 4.15 Found C,
64.29; H, 8.33; N, 4.02%.
6.1.2. Synthesis of ester derivatives of 1-(hydroxyalkyl)-
2-alkyl-3-benzyloxy-4(1H)-pyridinones. Method (a) (via
acid chlorides)
6.1.2.1. 1-[2≠-(Pivaloyloxy)ethyl]-2-ethyl-3-pivaloyloxy-
4(1H)-pyridinone 12
Triethylamine (8.6 g, 85 mmol) was added to a solu-
tion of 9, 1-[2≠-(hydroxy)ethyl]-2-ethyl-3-benzyloxy-
4(1H)-pyridinone free base (4.65 g, 17 mmol) in dimethyl-
formamide (100 mL) under nitrogen atmosphere at room
temperature. Pivaloyl chloride (trimethylacetyl chloride,
8.2 g, 68 mmol) was added dropwise and the mixture was
heated at 75–78 °C for 22 h. The reaction mixture was
cooled to 20 °C, triethylamine hydrochloride was re-
moved by filtration and dimethylformamide was removed
by rotary evaporation under high vacuum to give a
reddish brown oil. The product was taken into dichlo-
romethane (200 mL), washed with aqueous sodium bicar-
bonate (5% w/v; 3 × 100 mL) and water (2 × 100 mL).
The organic fraction was dried over anhydrous sodium
sulphate, filtered and concentrated to dryness under
reduced pressure to give a reddish brown oil which
solidified on standing at room temperature. Recrystalli-
sation from ethyl acetate after treatment with decolouris-
ing charcoal yielded colourless plates (4.7 g, 79%); m.p.
141–142 °C; IR (Nujol): 1 735 (ester C=O), 1 720 (ester
C=O), 1 620 (pyridinone C=O), 1 580 (C=C) cm–1;

482
Analogous reaction using 11 with pivaloyl chloride
afforded 15 in 71% yield (table II).
6.1.2.7. 1-[2≠-(Pivaloyloxy)ethyl]-2-methyl]-3-hydroxy-
4(1H)-pyridinone 25
M.p. 139–140 °C; IR (Nujol): 3 150 (OH), 1 720 (ester
C=O), 1 620 (pyridinone C=O), 1 570 (C=C) cm–1;
1H-NMR (DMSO-d6): δ 1.10 [9H, s, -C(CH3)3], 2.33
(3H, s, 2-CH3), 4.29 (4H, s, NCH2CH2O), 6.15 (1H, d,
5-H, J = 7.5Hz), 6.35 (1H, br, s, OH), 7.56 (1H, d, 6-H,
J = 7.5Hz); MS (EI): m/z, 253 [M+.]; Anal. Calcd. for
C13H19NO4: C, 61.64; H, 7.56; N, 5.53 Found C, 61.74;
H, 7.55; N, 5.41%.
6.1.2.4.
loyloxy)-4(1H)-pyridinone 15
1-[3≠-(Pivaloyloxy)propyl]-2-methyl-3-(piva-
M.p. 169–170 °C; IR (Nujol): 1 745 ester (C=O), 1 724
(ester C=O), 1 630 (pyridinone C=O), 1 580 (C=C) cm–1;
1H-NMR (CDCl3): δ 1.22 [9H, s, -C(CH3)3], 1.39 [9H, s,
-C(CH3)3], 1.85–2.18 (2H, m, NCH2CH2CH2O), 2.23
(3H, s, 2-CH3), 3.93 (2H, t, NCH2CH2CH2O), 4.14 (2H,
s, N CH2CH2CH2O), 6.36 (1H, d, 5-H, J = 7.5Hz), 7.25
(1H, d, 6-H, J = 7.5Hz); MS (EI): m/z, 351 [M+.]; Anal.
Calcd. for C19H29NO5: C, 64.93; H, 8.31; N, 3.98 Found
C, 65.07; H, 8.11; N, 3.79%.
6.1.2.8. 1-[2≠-(Pivaloyloxy)ethyl]-2-methyl]-3-hydroxy-
4(1H)-pyridinone hydrochloride 25 HCl salt
M.p. 186.5–188 °C; IR (Nujol): 3 140 (OH), 2 600
1
(OH), 1 725 (ester C=O), 1 630 (C=N) cm–1; H-NMR
(DMSO-d6): δ 1.07 [9H, s, -C(CH3)3], 2.58 (3H, s,
2-CH3), 4.40 (2H, t, +NCH2CH2O), 4.69 (2H t,
+NCH2CH2O), 7.45 (1H, d, 5-H, J = 6.0Hz), 8.26 (1H, d,
6-H, J = 6.0Hz), 9.8 (2H, br, OH).
6.1.2.5.
4(1H)-pyridinone 23
1-[2≠-(Pivaloyloxy)ethyl]-2-ethyl-3-hydroxy-
The pivaloyloxy diester 12 (4.2 g, 12 mmol) was
heated in water (300 mL) at 65–70 °C for 4 h. Water was
removed by rotary evaporation to yield a solid residue.
Recrystallisation from ethyl acetate after treatment with
decolourising charcoal afforded colourless plates (2.95 g,
92%); m.p. 133–134 °C; IR (Nujol): 3 130 (OH), 1 720
(ester C=O), 1 580 (C=C) cm–1; 1H-NMR (DMSO-d6): δ
1.18 [9H, s, -C(CH3)3], 1.27 (3H, t, CH2CH3, J = 6.0Hz),
2.85 (2H, q, CH2CH3, J = 6.0Hz), 4.02–4.45 (4H, m,
NCH2CH2O), 5.25 (1H, br, OH), 6.37 (1H, d, 5-H, J =
8.0Hz), 7.25 (1H, d, 6-H, J = 8.0Hz); MS (EI): m/z, 268
[(M + H)+.]; Anal.Calcd. for C14H21NO4: C, 62.89; H,
7.91; N, 5.23 Found C, 62.72; H, 7.66; N, 5.38%.
Analogous procedure using 13, 14 and 15 yielded 22,
25 and 27 respectively (table III). The hydrochloride salts
were prepared by dissolving the corresponding free bases
in dry chloroform or ethyl acetate or dimethylformamide.
Hydrogen chloride gas was passed until the lightly
coloured solution became colourless. Dry diethylether
was added dropwise until a faint opalescence appeared,
and cooled at 0 °C for 4 h. The corresponding hydrochlo-
ride salts were then separated by filtration and dried.
6.1.2.9. 1-[3≠-(Pivaloyloxy)propyl]-2-methyl-3-hydroxy-
4(1H)-pyridinone 27
M.p. 156–157 °C; IR (Nujol): 3 170 (OH), 1 720 (ester
1
C=O), 1 620 (pyridinone C=O), 1 565 cm–1; H-NMR
(DMSO-d6): δ 1.10 [9H, s, -C(CH3)3], 1.80–2.15 (2H, m,
CH2CH2CH2O), 2.30 (3H, s, 2-CH3), 3.9–4.16 (4H, m,
NCH2CH2CH2O), 6.15 (1H, br, s, OH), 6.15 (1H, d,
5-H, J = 7.5Hz), 7.55 (1H, d, 6-H, J = 7.5Hz); MS (EI):
m/z, 267 [M+.]; Anal. Calcd. for C14H21NO4: C, 62.88; H,
7.92; N, 5.24 Found C, 62.89; H, 8.07; N, 5.20%.
6.1.2.10. 1-[3≠-(Pivaloyloxy)propyl]-2-methyl-3-hydroxy-
4(1H)-pyridinone hydrochloride 27 HCl salt
M.p. 152–153.4 °C; IR (Nujol): 3 100 (OH), 1 725
1
(ester C=O) cm–1; H-NMR (DMSO-d6): δ 1.13 [9H, s,
-C(CH3)3], 1.90–2.30 (2H, m, +NCH2CH2CH2O), 2.56
(3H, s, 2-CH3), 4.10 (1H, t, +NCH2CH2CH2O), 4.45
(2H, t, +NCH2CH2CH2O), 7.46 (1H, d, 5-H, J = 6.0Hz),
8.33 (1H, d, 6-H, J = 6.0Hz), 10.1 (2H, br, OH).
6.1.3. Synthesis of ester derivatives of 1-(hydroxyalkyl)-
2-alkyl-3-benzyloxy-4(1H)-pyridinones. Method (b) (via
carboxylic acid)
6.1.2.6. 1-[2≠-(Isobutyryloxy)ethyl]-2-ethyl-3-hydroxy-
4(1H)-pyridinone 22
M.p. 106–107 °C; IR (Nujol): 3 140 (OH), 1 738 (ester
C=O), 1 620 (pyridinone C=O), 1 565 (C=C) cm–1;
1H-NMR (DMSO-d6): δ 1.04 [6H, d, -CH(CH3)2, J =
5.5Hz], 1.13 (3H, t, CH2CH3, J = 6.0Hz), 2.3–2.68 [1H,
m, -CH(CH3)2], 2.75 (2H, q, CH2CH3, J = 6.0Hz), 4.27
(4H, br, s, NCH2CH2O), 5.55 (1H, br, s, OH), 6.15 (1H,
d, 5–H, J = 8.0Hz), 7.55 (1H. d, 6–H, J = 8.0Hz); MS
(EI): m/z, 253 [M+.]; Anal. Calcd. for C13H19NO4: C,
61.65; H. 7.56; N, 5.53 Found C, 61.56; H, 7.45; N,
5.64%.
6.1.3.1. 1-[2≠-(Benzoyloxy)ethyl]-2-ethyl-3-benzyloxy-
4(1H)-pyridinone 18
A solution of 9, 1-[2≠-(hydroxy)ethyl]-2-ethyl-3-
benzyloxy-4(1H)-pyridinone, the free base (5.5 g,
20 mmol) and triphenylphosphine (5.8 g, 22 mmol, 1.1
eq) in tetrahydrofuran (200 mL) was added dropwise to a
solution of diethyl azodicarboxylate (DEAD, 3.8 g,
22 mmol, 1.1 eq) and benzoic acid (2.6 g, 21 mmol, 1.05
eq) in distilled tetrahydrofuran (59 mL) at 0 °C with

483
stirring via a pressure equalising funnel under nitrogen
for 45 min before the reaction was allowed to warm
slowly to 20 °C and stirred for 18 h. Tetrahydrofuran was
removed by rotary evaporation to give a yellow oil. The
crude material was purified by column chromatography
on silica gel (eluant, methanol:chloroform; 8:92, Rf =
0.55) to afford a pale yellow oil (7.6 g, > 95%). IR
(nujol): 1 720 (ester C=O), 1 625 (pyridinone C=O),
6.1.3.6.
4(1H)-pyridinone 24
1-[2≠-(Benzoyloxy)ethyl]-2-ethyl-3-hydroxy-
The benzyl protected ester 18 (7 g, 18.6 mmol) was
dissolved in dimethylformamide (150 mL) and Pd/C
catalyst (5%, 0.7 g) was added. The solution was stirred
at 20 °C under a constant stream of hydrogen for 24 h.
The reaction mixture was then filtered and dimethylfor-
mamide was removed under high vacuum. The residue
was treated with activated charcoal in chloroform, filtered
and concentrated in vacuo to dryness. Recrystalisation
from chloroform/diethylether afforded colourless crystals
(4.9 g, 92%); m.p. 173–174 °C; IR (Nujol): 3 240 (OH),
1 720 (ester C=O), 1 620 (pyridinone C=O), 1 560 cm–1;
1H-NMR (CDCl3): δ 1.23 (3H, t, CH2CH3, J = 6.0Hz),
2.85 (2H, q, CH2CH3, J = 6.0Hz), 4.25 (2H, t,
NCH2CH2O), 4.57 (2H, t, NCH2CH2O), 6.40 (1H, d,
5-H, J = 8.0Hz), 6.70 (1H, s, OH), 7.30 (1H, d, 6-H, J =
8.0Hz), 7.4–7.65 (3H, m, benzoyl-m,p-H), 7.85–8.08
(2H, m, benzoyl-o-H); MS (EI):m/z, 287[M+.]; Anal.
Calcd. for C16H17NO4: C, 66.88; H, 5.96; N, 4.87 Found
C, 66.78; H, 6.01; N, 4.92%.
1
1 570 cm–1; H-NMR (CDCl3): δ 1.03 (3H, t, CH2CH3,
J = 6.0Hz), 2.65 (2H, q, CH2CH3, J = 6.0Hz), 4.15 (2H,
t, NCH2CH2O), 4.49 (2H, t, NCH2CH2O), 5.24 (2H, s,
CH2Ph), 6.40 (1H, d, 5-H, J = 8.0Hz), 7.20–7.65 (8H, m,
Ph and benzoyl-m,p-H), 7.32 (1H, d, 6-H, J = 8.0Hz),
7.85–8.05 (2H, m, benzoyl-o-H); MS (EI): m/z, 377
[M+.].
Analogous procedure reacting 9, 10 and 11 with glacial
acetic acid, pivalic acid and benzoic acid yielded the
viscous oils of 16–20 respectively in a yield of > 95%.
6.1.3.2.
1-[2≠-(Acetyloxy)ethyl]-2-ethyl-3-benzyloxy-
4(1H)-pyridinone 16
1H-NMR (CDCl3): δ 1.03 (3H, t, CH2CH3, J = 6.0Hz),
2.0 (3H, s, CH3), 2.62 (2H, q, CH2CH3, J = 6.0Hz),
3.94–4.35 (4H, m, NCH2CH2O), 5.27 (2H, s, CH2Ph),
6.36 (1H, d, 5-H, J = 8.0Hz), 7.17–7.57 (6H, m, ArH &
6-H); MS (EI): m/z, 315 [M+.].
6.1.3.7.
4(1H)-pyridinone hydrochloride 24 HCl salt
1-[(2≠-Benzoyloxy)ethyl]-2-ethyl-3-hydroxy-
M.p. 156–158 °C; IR (Nujol): 1 720, 1 635 cm–1; H-
NMR (DMSO-d6): δ 1.21 (3H, t, CH2CH3, J = 6.0Hz),
3.08 (1H, q, CH2CH3, J = 6.0Hz), 4.55–4.95 (4H, m,
+NCH2CH2O), 7.50 (1H, d, 5-H, J = 6.5Hz), 7.50–7.74
(3H, m, benzoyl-m,p-H), 7.80–8.05 (2H, m, benzoyl-o-
H), 8.44 (1H, d, 6-H, J = 6.5Hz), 9.25 (2H, br, OH).
Analogous hydrogenolysis reaction using 16, 17, 19
and 20 gave 21, 23, 26 and 28 respectively (table III).
1
6.1.3.3. 1-[3≠-(Pivaloyloxy)ethyl]-2-ethyl-3-benzyloxy-
4(1H)-pyridinone 17
1H-NMR (CDCl3): δ 1.00 (3H, t, CH2CH3, J = 6.0Hz),
1.14 [9H, s, -C(CH3)3], 2.63 (2H, q, CH2CH3, J =
6.0Hz), 3.85–4.4 (4H, m, NCH2CH2O), 5.24 (2H, s,
CH2Ph), 6.37 (1H, d, 5-H, J = 8.0Hz), 7.1–7.55 (6H, m,
ArH & 6-H).
6.1.3.8.
4(1H)-pyridinone 21
1-[2≠-(Acetyloxy) ethyl]-2-ethyl-3-hydroxy-
M.p. 126–127 °C; IR (Nujol): 3 200 (OH), 1 740 (ester
C=O), 1 625 (pyridinone C=O), 1 585 (C=C) cm–1;
1H-NMR (DMSO-d6): δ 1.23 (3H, t, CH2CH3, J =
6.0Hz), 2.04 (3H, s, CH3), 2.83 (2H, q, CH2CH3, J =
6.0Hz), 4.02–4.47 (4H, m, NCH2CH2O), 6.37 (1H, d,
5-H, J = 8.0Hz), 6.77 (1H, br, s, OH), 7.28 (1H, d, 6-H,
J = 8.0Hz); MS (EI): m/z, 225 [M+.]; Anal. Calcd. for
C11H15NO4: C, 58.65; H, 6.71; N, 6.21 Found C, 58.49;
H, 6.70; N, 6.21%.
6.1.3.4. 1-[(2≠-Benzoyloxy)ethyl]-2-methyl-3-benzyloxy-
4(1H)-pyridinone 19
1H-NMR (CDCl3): δ 2.08 (3H, s, 2-CH3), 4.10 (2H, t,
NCH2CH2O), 4.40 (2H, t, NCH2CH2O), 5.18 (2H, s,
CH2Ph), 6.45 (1H, d, 5-H, J = 7.5Hz), 7.0–8.1 (11H, m,
ArH, & 6-H).
6.1.3.5. 1-[(3≠-Benzoyloxy)propyl]-2-methyl-3-benzyl-
6.1.3.9.
1-[2≠-(Pivaloyloxy)ethyl]-2-ethyl-3-hydroxy-
oxy-4(1H)-pyridinone 20
4(1H)-pyridinone hydrochloride 23 HCl salt
1H-NMR
(CDCl3):
δ
1.65–2.4
(2H,
m,
M.p. 184.5–186 °C; IR (Nujol): 3 120 (OH), 2 600
(OH), 1 720 (ester C=O), 1 630 (C=N) cm–1; 1H NMR
(DMSO-d6): δ 1.07 [9H, s, -C(CH3)3], 1.18 (3H, t,
CH2CH3, J = 6.0Hz), 3.01 (2H, q, CH2CH3, J = 6.0Hz),
4.41 (2H, t, +NCH2CH2O), 4.72 (2H, t, +NCH2CH2O),
NCH2CH2CH2O), 2.10 (3H, s, 2-CH3), 3.80 (2H, t,
NCH2CH2CH2O), 4.20 (2H, t, NCH2CH2CH2O), 5.06
(2H, s, CH2Ph), 6.28 (1H, d, 5-H, J = 7.5Hz), 6.9–8.1
(11H, m, ArH & 6-H).

484
7.46 (1H, d, 5–H, J = 6.5Hz), 8.26 (2H, d, 6–H, J =
6.5Hz), 8.5 (2H, br, OH).
examined was dissolved in buffer (saturated with octanol)
so as to give an absorbance of between 0.5–1.5 absor-
bance units at the preselected wavelength (≈280 nm). The
flow rate of the aqueous circuit was limited to 1 mL. The
computer program calculates the partition coefficient
(D7.4) for each octanol addition.
6.1.3.10. 1-[(2≠-Benzoyloxy)ethyl]-2-methyl-3-hydroxy-
4(1H)-pyridinone hydrochloride 26 HCl salt
M.p. 201–203 °C; IR (KBr): 3 502, 1 719, 1 630 cm–1;
1H-NMR (DMSO-d6): δ 2.55 (3H, s, 2-CH3), 4.50 (4H,
br, s, +NCH2CH2O), 7.10–7.95 (6H, m, ArH & 5-H),
8.20 (1H, d, 6-H, J = 6.0Hz), 7.9–9.6 (2H, br, OH); Anal.
Calcd. for C15H16NO4Cl: C, 58.16; H, 5.21; N, 4.52; Cl,
11.45 Found C, 58.38; H, 5.27; N, 4.45; Cl, 11.12%.
6.2.2. Ester hydrolysis studies in phosphate buffer (pH 2
and 7.4), rat blood and liver homogenate
Each ester prodrug, 10 µmol in 0.1mL of acetonitrile
solution (50% v/v in water), was added to 0.9 mL of
phosphate buffer (PBS) (100 mM, pH 7.4 or pH 2.0). The
samples were incubated at 37 °C for various time inter-
vals up to 24 h. At the end of the incubation, the samples
were removed from the incubator and immediately sub-
jected to extraction as described below. Fresh heparinised
rat whole blood was used throughout the present study.
The whole blood (0.5 mL) was added in the phosphate
buffer (0.5 mL, 0.139 M, pH 7.4) containing the ester
substrate (2.0 µmol). Subsequently the samples were
incubated at 37 °C for 0, 10, 20, 40 or 60 min. The
hydrolytic reaction was terminated by removing the
samples onto an ice bath and extracting the hydrolytic
product immediately. The rat liver was removed from the
animal and immersed in ice-cold PBS (100 mM, pH 7.4)
in order to remove excess blood. The livers were blotted
dry, weighed and cut into small pieces. Thereafter, the
tissue was homogenised in PBS (100 mM, pH 7.4) in the
ratio of 1 g liver tissue in 4 mL buffer. Similarly, each
ester (2 µmol) was added to 1.0 mL of liver homogenate,
which was diluted before use with PBS (100 mM, pH 7.4)
to a concentration of 1 g liver tissue in 400 mL mixture.
The incubation was carried out at 37 °C for 0, 10, 20, 40
or 60 min and the termination of the reaction was the
same as for the blood samples.
6.1.3.11. 1-[(3 ≠-Benzoyloxy)propyl]-2-methyl-3-hydroxy-
4(1H)-pyridinone hydrochloride 28 HCl salt
M.p. 168–170 °C; IR (KBr): 3 477, 1 710, 1 634 cm–1;
1H-NMR
(DMSO-d6):
δ
2.0–2.5
(2H,
m,
NCH2CH2CH2O), 2.55 (3H, s, 2-CH3), 4.0–4.7 (4H, m,
+NCH2CH2CH2O), 7.10–7.95 (6H, m, ArH & 5-H),
8.15 (1H, d, 6-H, J = 6.0Hz), 8.9–10.1 (2H, br, OH).
Anal. Calcd. for C16H18NO4Cl: C, 59.35; H, 5.60; N,
4.33; Cl, 10.95 Found C, 59.11; H, 5.64; N, 4.31; Cl,
10.68%.
6.2. Physicochemical and biological evaluation
6.2.1. Determination of distribution coeffıcients using the
filter probe method. Free ligands
Distribution coefficients were determined using an
automated continuous flow technique similar to that
described by Tomlinson [24] by following the methodol-
ogy as described by Rai and co-workers [14]. The system
comprised an IBM compatible PC running the “TOP-
CAT” program [28, 29], which controlled both a
Metrohm 665 Dosimat autoburette and a Pye-Unicam
Lambda 5 UV/vis spectrophotometer, as well as perform-
ing all calculations of distribution coefficients. All distri-
bution coefficient determinations were performed using
AnalaR grade reagents under a nitrogen atmosphere using
a flat-based glass vessel equipped with a sealable lid at
25 °C. The aqueous and octanol phases were presaturated
with respect to each other before use. The filter probe
consisted of a polytetrafluoroethylene (PTFE) plunger
associated with a gel-filtration column. The aqueous
phase (50 mM MOPS buffer, pH 7.4, prepared using
Milli-Q water) was separated from the two phase system
(1-octanol/MOPS buffer, pH 7.4) by means of a hydro-
philic cellulose filter 5 µm diameter, 589/3 Blauband
filter paper, Schleicher and Schuell) mounted in the
gel-filtration column adjuster (SR 25/50, Pharmacia). A
known volume (normally 25–50 mL) of MOPS buffer
(saturated with octanol) is taken in the flat base mixing
chamber. After a base line was obtained, the solution was
used for reference absorbance. The compound to be
6.2.2.1. Extraction and HPLC procedures for analysis of
hydrolytic product
All of the incubated samples, in the PBS buffers, whole
blood and liver homogenate, were added with organic
solvent (acetonitrile:isopropanol = 80/20 v/v), solid NaCl
and HCl solution (2 M, except the samples incubated in
PBS with pH 2.0). The samples were then mixed and
centrifuged. The upper organic layer was separated,
evaporated and analysed by an established HPLC
method. A Hewlett Packard Model 1090M Series-II
HPLC system, complete with an auto injector, auto
sampler and diode array detector, linked to a HP 900-300
data station was used in the present study. A polymer
PLRP-S column (15 cm × 0.46 cm) and a gradient mobile
phase system, utilising PBS (10 mM, pH 2.90, containing

485
[6] Propper R.D., Cooper B., Rufo R.R., Nienhuis A.W., Anderson W.F.,
Bunn H.F., Rosenthal H.R., Nathan D.G., N. Engl. J. Med. 297
(1977) 418–423.
2 mM EDTA) and acetonitrile, were used for the separa-
tion of the analytes. The eluents were monitored at
285 nm.
[7] Dobbin P.S., Hider R.C., Hall A.D., Taylor P.D., Sarpong P., Porter
J.B., Xiao G., Van der Helm D., J. Med. Chem. 36 (1993)
2448–2458.
6.2.3. Method of iron mobilisation effıcacy study in
rat [25]
[8] Gyparaki M., Porter J.B., Hirani S., Streater M., Hider R.C., Huehns
E.R., Acta Haematol. 78 (1987) 217–221.
Hepatocytes of normal fasted rats (190–230 g) were
labelled with 59Fe by administration of 59Fe-ferritin from
tail vein. One hour later, each rat was administered orally
with chelator (450 µmol/kg). Due to the poor water
solubility associated with several hydrophobic prodrug
molecules, 70% 1,2-propanediol in water (v/v) has been
used as the solvent. The efficacy of 1 in the presence of
70% 1,2-propanediol has been compared. No detectable
difference in iron excretion was induced in the presence
of the solvent. Control rats were administered with an
equivalent volume of 70% 1,2-propanediol. The rats were
placed in individual metabolic cages and urine and faeces
collected. Rats were allowed access to food 1 h after oral
administration of chelator. There was no restriction of
water throughout the study period. The investigation was
terminated 24 h after the 59Fe-ferritin administration, rats
were sacrificed and the liver and gastrointestinal tract
(including its content and faeces) were removed for
gamma counting.
[9] Porter J.B., Morgan J., Hoyes K.P., Burke L.C., Huehns E.R., Hider
R.C., Blood 76 (1990) 2389–2396.
[10] Olivieri N.F., Koren G., St Louis P., Freedman M.H., McClelland
R.A., Templeton D.M., Semin. Hematol. 27 (1990) 101–104.
[11] Porter J.B., Singh S., Hoyes K.P., Epemolu O., Abeysinghe R.D.,
Hider R.C., Adv. Exp. Med. Biol. 356 (1994) 361–370.
[12] Liu Z.D., Habgood M., Abbot J., Hider R.C., J. Pharm. Pharmacol.
49 (1997) 106.
[13] Singh S., Epemolu R.O., Dobbin P.S., Tilbrook G.S., Ellis B.L.,
Damani L.A., Hider R.C., Drug Met. Disp. 20 (1992) 256–261.
[14] Rai B.L., Dekhordi L.S., Khodr H., Jin Y., Liu Z., Hider R.C., J.
Med. Chem. 41 (1998) 3347–3359.
[15] Singh S., Choudhury R., Epemolu R.O., Hider R.C., Eur. J. Drug
Metab. Pharmacokinet. 21 (1996) 33–41.
[16] Hider R.C., Choudhury R., Rai B.L., Dehkordi L.S., Singh S., Acta
Haematol. 95 (1996) 6–12.
[17] Choudhury R., Epemolu R.O., Rai B.L., Hider R.C., Singh S., Drug
Met. Disp. 25 (1997) 332–339.
[18] Moerker T., Peter H., United States Patent No. 4, 908, 371, (1990).
[19] Casagrande C., Santangelo F., Saini C., Doggi F., Gerli F., Cerri O.,
Arzneim-Forsch Drug Res. 36 (1986) 291–303.
[20] Gates M., Tschudi G., J. Am. Chem. Soc. 78 (1956) 1380–1393.
[21] Filler R., Khan B.T., McMullen C.W., J. Org. Chem. 27 (1962)
4660–4662.
Acknowledgements
[22] Mitsunobu O., Yamada Y., Bull. Chem. Soc. Jpn. 40 (1967)
2380–2382.
The authors would like to thank Apotex Research Inc.
Canada and Biomed EC grant BMH4-CT97-2149 for
supporting this research project.
[23] Mitsunobu O., Synthesis 1 (1981) 1–28.
[24] Tomlinson E., J. Pharm. Sci. 71 (1982) 602–604.
[25] Choudhury R., Ph. D. Thesis. Metabolism and pharmacokinetics of
1-hydroxyalkyl-3-hydroxypyridin-4-one chelating agents. King’s
College London, University of London, (1996).
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