Preparation and characterization of polyester- and poly(ester-carbonate)- paclitaxel conjugates

Article abstract of DOI:10.1016/j.ejmech.2011.04.046

The polyester- and poly(ester-carbonate)-paclitaxel conjugates with low molecular weight were synthesized using dicyclohexylcarbodiimide (DCC) and dimethylaminopyridine (DMAP) as catalysts. Polymeric matrices were obtained by ring-opening polymerization of ε-caprolactone (CL), rac-lactide (rac-LA), l-lactide (LLA) and trimethylene carbonate (TMC). The macromolecular conjugates were characterized by using spectroscopic techniques, such as ¹H, ¹³C NMR and FTIR. The degree of degradation of polyester- and poly(ester-carbonate)-paclitaxel conjugates was tested in vitro under different conditions. The preliminary results of drug release were discussed.

Full text of DOI:10.1016/j.ejmech.2011.04.046

European Journal of Medicinal Chemistry 46 (2011) 3047e3051
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Preparation and characterization of polyester- and poly
(ester-carbonate)-paclitaxel conjugates
*
ꢀ
Marcin Sobczak , Agnieszka Korzeniowska, Piotr Gos, Waclaw L. Kolodziejski
Medical University of Warsaw, Faculty of Pharmacy, Department of Inorganic and Analytical Chemistry, ul. Banacha 1, 02-097 Warsaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The polyester- and poly(ester-carbonate)-paclitaxel conjugates with low molecular weight were
synthesized using dicyclohexylcarbodiimide (DCC) and dimethylaminopyridine (DMAP) as catalysts.
Polymeric matrices were obtained by ring-opening polymerization of 3-caprolactone (CL), rac-lactide
Received 25 February 2011
Received in revised form
13 April 2011
Accepted 14 April 2011
Available online 22 April 2011
(rac-LA), L-lactide (LLA) and trimethylene carbonate (TMC). The macromolecular conjugates were char-
acterized by using spectroscopic techniques, such as 1H, 13C NMR and FTIR. The degree of degradation of
polyester- and poly(ester-carbonate)-paclitaxel conjugates was tested in vitro under different conditions.
The preliminary results of drug release were discussed.
Keywords:
Paclitaxel
Ó 2011 Elsevier Masson SAS. All rights reserved.
Macromolecular conjugates
Polyesters
Control release
1. Introduction
conjugates of paclitaxel, such as poly(ethylene glycol) PEG [4],
poly(L-glutamic acid) (PG) [5], monomethoxy-poly(ethylene
Paclitaxel (PACL) is a natural product with antitumor activity
(Fig. 1). Taxol (paclitaxel) is obtained via a semi-synthetic process
from Taxus baccata. PACL is one of the most common anticancer
drugs used for chemotherapy. It is antimicrotubule agent that
promotes the assembly of microtubules from tubulin dimers and
stabilizes microtubules by preventing depolymerization. This
stability results in the inhibition of the normal dynamic reorgani-
zation of the microtubule network that is essential for vital inter-
phase and mitotic cellular functions.
PACL is usually used to treat patients with lung, ovarian, breast,
head and neck cancer. However some problems such as allergic
reactions, heart and blood vessel effects, infections due to low
white blood cell count, hair loss, joint and muscle pain, irritation at
the injection site, low red blood cell count, mouth or lip sores,
numbness, tingling, or burning in the hands and/or feet, stomach
upset and diarrhea, decrease in urine output and/or swelling of the
hands, face, or feet, have limited its use [1e3]. Therefore, polymeric
conjugates have been extensively studied and proved as promising
delivery systems to augment therapeutic efficacy of chemothera-
peutic agents in the treatment of cancer. Macromolecular
glycol)-b-poly(lactide) (MPEG-PLA) [6], recently attracted more
and more attention.
Poly(lactide) (PLA), poly(D,L-lactide-co-glycolide) (PLGA), and
poly(caprolactone) (PCL) are biodegradable polymers, which are
used most often in the literature of drug delivery [7e15].
Aliphatic polyesters are attractive, because they undergo hydro-
lysis to produce compounds which can be metabolized in vivo
and in the environment [16]. Aliphatic polyesters are commonly
prepared by two different routes: polycondensation and the ring-
opening polymerization (ROP). The ROP of cyclic esters is initi-
ated/catalyzed by metal complexes, organic compounds, or
enzymes, to yield high molecular weight in excellent conversion
and purity [16e21]. The most common catalysts are metal (Sn, Zn
and Al) coordinating compounds, which are useful due to their
selectivity and efficacy. On the other hand, for pharmaceutical
applications metal residues are undesirable considering their
toxicity.
Recently, we found that natural amino acids and creatinine are
satisfactory initiators for ROP of cyclic esters [13,22].
The aim of the present study is to synthesize polyester-
paclitaxel and poly(ester-carbonate)-paclitaxel conjugates of
different molecular weights and to characterize their physico-
chemical properties. We hope that the obtained macromolecular
conjugates are good potential candidates as implant drug delivery
systems.
* Corresponding author. Tel.: þ48 22 572 07 55; fax: þ48 22 572 07 84.
E-mail
addresses:
marcin.sobczak@wp.pl,
marcin.sobczak@wum.edu.pl
(M. Sobczak).
0223-5234/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2011.04.046

3048
M. Sobczak et al. / European Journal of Medicinal Chemistry 46 (2011) 3047e3051
catalyst at 160 ꢀC during 8 h. Then, ethanol and unreacted
substances were evaporated under reduced pressure. TMC was
produce by depolymerization of the polycarbonate. Then the
monomer was crystallized from a mixture of dry benzene/tetra-
hydrofuran (1:4) and dried at 30 ꢀC under vacuum [23].
2.3. Synthesis of polyesters and poly(ester-carbonate)s
Homo-andcopolymerizationofcyclicestersandTMCwerecarried
out in the same way. Monomers (CL, rac-LA, LLA, TMC) and CE were
placed in 10 mL glass ampoules under an argon atmosphere. The
reactionvessels were then left standing at the required temperature in
a thermostated oil bath for the appropriate time (Table 1). After
desired time the ampoule was opened and methylene chloride was
added in order to dissolve the products. Then, the obtained solutions
werewashed with methanol and dilute hydrochloric acid(5%aqueous
solution) under vigorous stirring. The latter operation was repeated
three times. The isolated polymer was dried in vacuum for 3 days.
PCL: 1H NMR (CDCl3,
d
, ppm): 1.38 (2H, m, J ¼ 8.0, 7.2 Hz,
Fig. 1. Structure of paclitaxel.
eOCH2CH2CH2CH2CH2C(O)Oe), 1.63 (4H, m, eOCH2CH2CH2CH2CH2
C(O)Oe), 2.29 (2H, t, J ¼ 7.3 Hz, eOCH2CH2CH2CH2CH2C(O)Oe), 3.73
(2H, t, J ¼ 3.1 Hz, eCH2OH, end group), 4.04 (2H, t, J ¼ 6.7 Hz,
2. Experimental
eOCH2CH2CH2CH2CH2C(O)Oe); 13C NMR (CDCl3,
d, ppm): 24.9
2.1. Chemicals
(eOCH2CH2CH2CH2CH2C(O)Oe), 25.8 (eOCH2CH2CH2CH2CH2C(O)
Oe), 28.4 (eOCH2CH2CH2CH2CH2C(O)Oe), 33.8 (eOCH2CH2CH2
CH2CH2C(O)Oe), 63.9 (eCH2C(O)OH, end group), 64.5 (eOCH2CH2
CH2CH2CH2C(O)Oe), 173.8 (eOCH2CH2CH2CH2CH2C(O)Oe); FTIR
(3S)-cis-3,6-Dimethyl-1,4-dioxane-2,5-dione (L-lactide, 98%, LLA)
was purchased from Aldrich and recrystallized from ethyl acetate for
several times. 3,6-Dimethyl-1,4-dioxane-2,5-dione, (rac-lactide, 98%,
rac-LA) (Aldrich) was crystallized from a mixture of dry toluene with
(KBr, cmꢁ1): 2944 (nasCH2), 2867 (nasCH3),1722 (
PLA: 1H NMR (CDCl3,
eCH(CH3)e), 4.36 (1H, q, J ¼ 7.3, 6.7 Hz, eCH(CH3)OH, end group),
1.58 (3H, d, eCH3); 13C NMR (CDCl3,
, ppm): 169.9 (eC(O)Oe), 69.4
(eCH(CH3)e), 16.9 (eCH3); FTIR (KBr, cmꢁ1): 2999 (nasCH3), 2949
nC]O),1244 (nCeO).
d, ppm): 5.17 (1H, q, J ¼ 6.7 Hz,
hexane and dried at room temperature under vacuum. 3-Capro-
lactone (2-Oxepanone, CL, 99%) was purchased from Aldrich. Before
use,itwasdriedanddistilledoverCaH2 atreducedpressure.Paclitaxel
(97%), from semi-synthetic (from Taxus sp., PACL) (Aldrich), creatinine
(anhydrous,99%, CE) (Aldrich), diethylcarbonate(DEC, 98%)(Aldrich),
propane-1,3-diol (PD, 98%)(Aldrich), stannous octoate (SnOct2, tin (II)
2-ethylhexanoate, 95%) (Aldrich), dicyclohexylcarbodiimide (DDC)
(Aldrich 99%), dimethylaminopyridine (DMAP) (Aldrich 99%), ethanol
(99.8%) (Aldrich), dichloromethane (POCh Poland) and methanol
(POCh), were used as received.
d
(
(
(
nsCH3), 2884 (
dsCH3), 1365e1370 (d1CH þ dsCH3), 1315e1300 (d2CH), 1270
CH COC), 1215e1185 nasCOC rasCH3), 1131 (rasCH3),
CeCH3), 960e950 (rCH3 CC),
CeCOO), 760e740 ( C]O), 715e695 ( C]O), 515
CCO), 415 ( CCO), 350 (d2CeCH3 COC), 300e295
COC þ d2CeCH3), 240 ( CC).
nCH), 1761 (nC]O), 1454 (dasCH3), 1346e1389
d
þ
n
(
n
þ
1100e1090 (nsCOC), 1045 (
875e860 (
þ
n
n
d
g
(d1CeCH3
þ
d
d
s
þ
d
(d
2.2. Synthesis of trimethylene carbonate
2.4. Synthesis of macromolecular conjugates of paclitaxel
Trimethylene carbonate (TMC) was synthesized in the reaction
of equimolar quantities of DEC and PD in the presence of SnOct2 as
A 0.1 g quantity of homopolymer or copolymer and 25 mg of
paclitaxel were dissolved in 50 mL anhydrous methylene chloride.
Table 1
Synthesis of polyesters and poly(ester-carbonate)s.
a
e
Code
Monomer I
-CL
LLA
Monomer II
MI/MII/I
Yield (%)
Mn (Da)
PDa
Mnb (Da)
PDb
TMCc (% mol)
hinhd (dL/g)
hinh (dL/g)
PCL
3
e
50:1
50:1
50:1
81
62
57
60
67
72
43
54
58
39
55
61
4400
4000
3900
2900
3200
3700
2400
2900
3600
2300
3200
3400
1.1
1.2
1.2
1.2
1.2
1.2
1.1
1.2
1.2
1.1
1.2
1.2
3200
2800
2700
e
1.1
1.2
1.1
e
e
0.06
0.12
0.15
0.06
0.08
0.09
0.11
0.15
0.18
0.12
0.20
0.22
0.05
0.07
0.09
0.06
0.07
0.07
0.10
0.14
0.16
0.10
0.18
0.19
PLA-1
PLA-2
COP-1
COP-2
COP-3
COP-4
COP-5
COP-6
COP-7
COP-8
COP-9
e
e
rac-LA
e
e
3-CL
3-CL
3-CL
TMC
TMC
TMC
TMC
TMC
TMC
TMC
TMC
TMC
25:25:1
30:20:1
40:10:1
25:25:1
30:20:1
40:10:1
25:25:1
30:20:1
40:10:1
36
26
18
44
38
28
39
31
25
e
e
e
e
LLA
LLA
LLA
rac-LA
rac-LA
rac-LA
e
e
e
e
e
e
e
e
e
e
e
e
I e initiator (CE).
Reaction conditions: time e 72 h, temp. e 140 ꢀC.
a
Determined by GPC.
Determined by MALDI-TOF.
TMC units content in copolymer chain.
Determined by viscosity method (before degradation).
b
c
d
e
Determined by viscosity method (after 8 weeks).

M. Sobczak et al. / European Journal of Medicinal Chemistry 46 (2011) 3047e3051
3049
DCC (10 mg) and DMAP (5 mg) were added at room temperature.
The reaction was continued under stirring for 24 h. The precipitate
was filtered out and the filtrate was washed with hydrochloric acid
(5% aqueous solution) and methanol [6]. The conjugates isolated
from the solution’s organic phase were kept under vacuum at room
temperature for 48 h.
The purpose of our work was to obtain the polyester and
poly(ester-carbonate) conjugates of PACL. Polymers were synthe-
sized by ring-opening polymerization (ROP) of CL, LLA, rac-LA and
TMC using CE as a catalyst (Scheme 1).
The first test of LLA polymerization in the presence of CE was
described by Wang [24]. The results of the ROP of LLA, rac-LA and CL
in the presence of CE and glycols (ethylene glycol, diethylene glycol
or 1,4-butanediol) were already published by us [13]. The paper is
a continuation of our earlier investigations.
PACL: 1H NMR (DMSO,
3.97, 4.54, 4.86, 5.37, 6.24, 7.36, 7.45, 7.47, 7.59, 7.66, 7.84, 7.92, 8.84;
13C NMR (DMSO,
, ppm): 20.3, 26.0, 57.0, 69.2, 73.2, 76.4, 79.9, 83.2,
127.0, 127.9, 128.3, 129.2, 129.6, 133.0, 134.1, 138.9, 165.9, 168.4,
172.3, 202.0; FTIR (KBr, cmꢁ1): 2933 (nsCH3), 1728 (
C]O), 1647
NH), 1371, 1246, 1178, 1071, 709 (finger print);
d, ppm): 0.97, 1.46, 1.74, 2.07, 2.18, 3.57,
d
The polymerization reactions of CL, LLA and rac-LA in the
presence of CE were carried out at 140 ꢀC for 72 h (Table 1). The
chemical structures of the obtained homopolymers were
confirmed by 13C, 1H NMR and IR studies (Experimental part). The
spectroscopic data are in agreement with what was reported in the
literature. The respective reaction yields were in the 81 (PCL), 62
(PLA-1) and 57% (PLA-2) range. For the homopolymers, the
number-average molecular weights (Mn) determined by GPC were
in the range 3900e4400 Da. The polydispersity indexes (PD) were
within 1.1e1.2 limits. The Mn of homopolymers determined using
MALDI-TOF MS were in the 2700e3200 Da ranges.
The copolymers were prepared under similar conditions. Melt
polymerization was performed at 140 ꢀC for 72 h under an argon
atmosphere. The molar ratio of CL (LLA, rac-LA):TMC:CE was 25:25:1,
30:20:1, or 40:10:1. The results of these melt polymerization runs are
summarized in Table 1. The chemical structure of the resulting
precipitated copolymers was characterized by 1H NMR and 13C NMR.
The signals observed in 1H NMR spectra of CL/TMC copolymers
can be attributed to the following units: 4.21 [eCH2CH2CH2OC(O)
Oe], 4.12 [eCH2CH2CH2CH2CH2C(O)Oe], 4.03 [eCH2CH2CH2OC(O)
OeCL], 3.61 [HOCH2e], 2.29 [eCH2CH2CH2CH2CH2C(O)Oe], 2.00
[eCH2CH2CH2OC(O)Oe], 1.63 [eCH2CH2CH2CH2CH2C(O)Oe], 1.38
[eCH2CH2CH2CH2CH2C(O)Oe] ppm. In 13C NMR spectra of CL/TMC
copolymers, the main signals characteristic for repeating and
n
(n
2.5. Characterizations
The polymerization products and macromolecular conjugates of
PACL were characterized by means of 1H and 13C NMR (Varian
300 MHz) at room temperature, with CDCl3 or DMSO as solvent and
TMS as internal reference. The FTIR spectra were recorded from KBr
pellets (Spectrum 1000, PerkineElmer). Relative molecular mass
and molecular mass distributions were determined by MALDI-TOF
MS and GPC techniques. The MALDI-TOF spectra were measured in
the linear mode on a Kompact MALDI 4 Kratos analytical spec-
trometer using a nitrogen gas laser with 2-[(4-hydroxyphenyl)
diazenyl] benzoic acid (HABA) as a matrix. GPC measurements were
made at 25 ꢀC in the tetrahydrofuran solution using Shimadzu C-R4
Chromatopac apparatus. The molecular weights were calibrated
with polystyrene standards. Polymers viscosity were measured in
N,N-dimethylformamide (at 30 ꢀC) using an Ubbelohde viscometer
(on Stabinger Viscometer SVM 3000).
2.6. Paclitaxel released from macromolecular conjugates
Dried macromolecular conjugate (0.05 g) was poured into
aqueous buffered solution (25 mL, pH 1 or 7) at 37 ꢀC for 3 or 8
weeks. The mixture was stirred. When the process time was
completed, water was removed under reduced pressure. Then,
25 mL of ethanol was added to the flask and the mixture was stirred
for 2 h. Next, the sample was removed and filtered. The amount of
paclitaxel released was analyzed using a UV spectrophotometer
(UV-1202 Shimadzu) at the lmax value of 229 nm. The quantity of
released drug was determined from the calibration curve obtained
previously under the same conditions.
terminal units appear at
d
¼ 173.5 [eC(O)e, CLCLCL],173.3 [eC(O)e,
CLCLTM] 155.2 [eC(O)e, CLTMCCL], 155.0 [eC(O)e, TMCTMCCL],
154.9 [eC(O)e, TMCTMCTM] 67.8 [TMCeCH2CH2CH2CH2CH2C(O)
Oe], 64.1 [eCH2CH2CH2CH2CH2C(O)Oe, eCH2CH2CH2OC(O)Oe],
61.2 [eOCH2CH2CH2Oe], 60.5 [eCH2CH2CH2OC(O)OeCL], 34.0
[eCH2CH2CH2CH2CH2C(O)Oe], 28.3 [eCH2CH2CH2CH2CH2C(O)Oe],
28.0 [eCH2CH2CH2OC(O)OeCL], 25.2 [eCH2CH2CH2CH2CH2C(O)
Oe], 24.4 [eCH2CH2CH2CH2CH2C(O)Oe] ppm (the Supplementary
material).
The chemical structure of the LA/TMC copolymers obtained was
Degradation was evaluated by the hinh of polymers decrease.
characterized by 1H NMR. For all products, peaks appeared at 5.14
[eCH(CH3)COOe],
4.26
[HOCH(CH3)COOe],
4.21
[eCH2CH2CH2OC(O)Oe], 3.61 [HOCH2e], 1.98 [eCH2CH2CH2OC(O)
Oe], 1.46 [eCH(CH3)COOe] ppm. In 13C NMR spectra of LA/TMC
copolymers, the signals characteristic appear at 169.7 [eCOOe,
TMCeLAeTMC and LAeLAeLA], 154.6 [eCOOe, TMCeTMCeLA],
154.0 [eC(O)e, TMCTMCTM] 71.4 [eCH(CH3)COOeTMC], 69.0
3. Results and discussions
Recently, a progressive interest has arisen for preparation of
paclitaxel prodrugs. It iscommonly known that the 20- and 7-hydroxyl
groups of paclitaxel are suitable for its structure modification [6].
O
C
O
C
O
C
O
C
O
CE
CE
x
y
+
CH
O
CH
O
O CH2CH2CH2 O
O
O
O
O
C
O
CH3
CH3
C
O
x
y
O
C
O
C
+
x
y
CH2CH2CH2CH2CH2
O
O CH2CH2CH2 O
O
O
x
y
C
O
O
Scheme 1. Synthesis of poly(ester-carbonate)s.

3050
M. Sobczak et al. / European Journal of Medicinal Chemistry 46 (2011) 3047e3051
Table 2
Synthesis of macromolecular conjugates of PACL.
Code
Composition
Drug contenta
pH 7
pH 7
pH 1
pH 1
% Released after 3 weeks
% Released after 8 weeks
% Released after 3 weeks
% Released after 8 weeks
CON-1
CON-2
CON-3
CON-4
CON-5
CON-6
PCLePACL
2.6
3.6
3.7
2.9
3.4
3.6
18
24
27
8
15
14
43
65
72
17
29
26
e
e
PLA-1ePACL
PLA-2ePACL
COP-3ePACL
COP-6ePACL
COP-9ePACL
e
e
e
e
11
18
9
23
41
38
Reaction conditions: room temperature, time e 24 h, argon atmosphere.
a
PACL units content in macromolecular conjugates (%mol), determined by 1H NMR.
[eCH(CH3)COOe], 61.5 [eCH2CH2CH2OC(O)Oe], 58.4 [LAeCH2CH2
CH2OC(O)Oe, eHOCH2CH2CH2Oe], 31.4 [eCH2CH2CH2OC(O)Oe],
16.5 [eCH(CH3)COOe] ppm (the Supplementary material).
The Mn of the synthesized copolymers were relatively low in the
range of 2900e3700, 2400e3600 and 2300e3400 g/mol, for CL/
TMC, LLA/TMC and rac-LA/TMC copolymers respectively.
ring of paclitaxel (7.92 ppm) and the signal intensity of the CH2COO
(for PCL and CL/TMC copolymers) or CH(CH3)COO (for PLA and LA/
TMC copolymers) has been compared. The drug content in the
macromolecular conjugates amounts to 2.6e3.7 mol%.
The kinetic rates of PACL release from macromolecular conju-
gates at pH 7 or 1 are shown in Table 2.
-
The co-monomers composition had influenced on the molecular
weight of the copolymer: the higher CL content in the co-monomer
feed results in a higher molecular weight of the copolymer formed
(Table 1). Copolymer compositions were determined from the 1H
NMR spectra by taking the ratio of the peak areas corresponding to
It was found that the rate of PACL release from obtained
macromolecular conjugates depends on the structure of the poly-
mer. The CON-2 (PLA) and CON-3 (PLA) conjugates released PACL
faster compared to the CON-1 (PCL) conjugates. The percentage of
released PACL after 8 weeks incubation was about 43% from CON-1,
65% from CON-2 and 72% from CON-3 at pH 7.
We have found that macromolecular conjugates containing TMC
units slowly released PACL compared to the PCL or PLA conjugates.
The percentage of released PACL after 3 weeks incubation was
about 18% from CON-1, 24% from CON-2, 27% from CON-3, 8% from
CON-4, 15% from CON-5 and 14% from CON-6 at pH 7, for respec-
tively. The result seems logical, because it is known that poly-
carbonate is relatively resistant on the hydrolysis.
The results suggest a higher stability of obtained macromolec-
ular conjugates of PACL to chemical hydrolysis at pH 7 than 1. The
amount of released drug within 8 weeks was about 23% from CON-
4, 41% from CON-5 and 38% from CON-6 at pH 1. However, 17%
PACL was released from CON-4, 29% from CON-5 and 26% from
CON-6 at pH 7.
the TMC (eCH2CH2CH2OC(O)Oe) protons at
CL (eCH2CH2CH2CH2CH2C(O)Oe) protons at
d
¼ 2.00 ppm and the
d
¼ 2.30 ppm. The CL
content in the copolymer of CL and TMC exceeded the CL feed ratio
for copolymers (amounts to 64e82 mol%). As it is common
knowledge, carbon dioxide is sometimes eliminated during ROP of
TMC and, hence, that some ether linkages are formed in the poly-
carbonate. It was found that no elimination of carbon dioxide was
detected in our experiments, because no peak at 3.4 ppm, which
can be assigned to eCH2OCH2e, is present.
The hinh of CL/TMC copolymers increase only from 0.06 to
0.09 dL/g with an increase CL content in the copolymer chain.
Similar to the results obtained from the copolymerization of LLA
or rac-LA with TMC, increasing the LA content in the co-monomer
feed from 25:25:1 to 40:10:1 increased Mn of the copolymer
formed. For example, When the LLA/TMC/CE ratio was 25:25:1, the
Mn (from GPC) was 2400 g/mol. However, when the LLA/TMC/CE
ratio was 40:10:1, the Mn (from GPC) was 3600 g/mol. Similarly, the
Mn of COP-7 is smaller about 30% than Mn of COP-9.
The composition of the LA/TMC copolymers was determined
from the integrations of the bands at 4.2 ppm for TMC and at
4.9e5.2 ppm for LLA (or rac-LA). It should be noted that each LA
molecule contains two lactyl units. As indicated in Table 1, the LA
content in the copolymer of LA and TMC exceeded the LA feed ratio
for copolymers (amounts to 56e75 mol%). The intrinsic viscosities
of LA/TMC copolymers lie between 0.11 and 0.22 dL/g.
The macromolecular conjugates were obtained from the reac-
tions of homopolymers (PCL, PLA-1, PLA-2) and copolymers (COP-3,
COP-6, COP-9) with PACL (Table 2) (Scheme 2).
The chemical structures of the prepared macromolecular
conjugates of PACL were confirmed by 1H and 13C NMR studies.
Typical proton NMR spectrum of the reaction product of PCL with
PACL is shown in Fig. 2. All the conjugate spectra have revealed
characteristic peaks of PACL, indicating successful preparation of
the macromolecular conjugates of PACL.
The PACL content in macromolecular conjugates was calculated
by 1H NMR. The signal intensity of the two hydrogen on the phenyl
DMAP
+
HO
R
COOH
HO PACL
HO
R COO PACL
DDC
Scheme 2. Synthesis of macromolecular conjugates of PACL.
Fig. 2. The 1H NMR spectrum of the PCLePACL conjugate (in DMSO-d6).

M. Sobczak et al. / European Journal of Medicinal Chemistry 46 (2011) 3047e3051
3051
Summing up, PACL release depends upon the kind of the
References
polymer matrix (ability to biodegradation) as well as pH for the
media. To prove our hypothesis additional experiments were
carried out. Tests of the degradation of homo- and copolymers
were conducted in the buffer of pH 7 at 37 ꢀC. The results of
intrinsic viscosity of original and hydrolytic degraded polymers
are shown in Table 1. The degradation process is rather slow, if it
is compared with the rate of PACL release. This fact is due to the
hydrophobic character of the obtained polyesters and poly
(carbonate-ester)s, which determines that they are not soluble
in water solutions, and also because the low area of the polymer
exposed to the hydrolysis solution. The results suggested that the
hydrolytic degradation rate of the homo- and copolymers
depended upon the CL, LA or TMC content in polymer chain. The
hinh of homopolymers changed from 17 to 42% within 8 weeks.
However, the hinh of copolymers changed from 0 to 14% after 8
weeks incubation. This showed that the LA units were earlier
degraded before TMC and CL units due to its higher hydrophi-
licity and faster degradation.
[1] C.M. Spencer, D. Faulds, Paclitaxel e a review of its pharmacodynamic and
pharmacokinetic properties and therapeutic potential in the treatment of
cancer, Drugs 48 (1994) 794e847.
[2] R. Panchagnula, Review: pharmaceutical aspects of paclitaxel, Int. J. Pharm.
172 (1998) 1e15.
[3] A.K. Singla, A. Garg, D. Aggarwal, Paclitaxel and its formulations, Int. J. Pharm.
235 (2002) 179e192.
[4] R.B. Greenwald, C.W. Gibert, A. Pendri, C.D. Conover, J. Xia, A. Martinez, Drug
delivery systems: water soluble taxol 20-poly(ethylene glycol) ester prodrugs-
design and in vivo effectiveness, J. Med. Chem. 39 (1996) 424e431.
[5] C. Li, D.F. Yu, R.A. Newman, F. Cabral, L.C. Stephen, N. Hunter, L. Milas,
S. Wallace, Complete regression of well-established tumors using a novel
water-soluble poly
(L-glutamic acid)-paclitaxel conjugate, Cancer Res. 58
(1998) 2404e2409.
[6] X. Zhang, Y. Lib, X. Chen, X. Wang, X. Xu, Q. Liang, J. Hu, X. Jing, Synthesis and
characterization of the paclitaxel/MPEG-PLA block copolymer conjugate,
Biomaterials 26 (2005) 2121e2128.
[7] K.E. Uhrich, S.M. Cannizzaro, R.S. Langer, K.M. Shakesheff, Polymeric systems
for controlled drug release, Chem. Rev. 99 (1999) 3181e3198.
[8] K. Hoste, K. De Winne, K. Schacht, Polymeric prodrugs, Int. J. Pharm. 277
(2004) 119e131.
[9] T. Ouchi, Y. Ohya, Macromolecular prodrugs, Prog. Polym. Sci. 20 (1995)
211e257.
In conclusion we can state that the rates of PACL release and the
biodegradation of macromolecular conjugates depends on the
chemical composition. Our preliminary studies showed that the
PACL could be released from the prepared macromolecular conju-
gates, but detail kinetic studies still remain to be done.
[10] J. Khandare, T. Minko, Polymer-drug conjugates: progress in polymeric pro-
drugs, Prog. Polym. Sci. 31 (2006) 359e397.
[11] M. Sobczak, E. Ole˛dzka, W. Kolodziejski, R. Kuzmicz, Pharmaceutical appli-
ꢀ
cation of polymers, Polimery 52 (2007) 411e420.
[12] M. Sobczak, E. Witkowska, E. Ole˛dzka, W. Kolodziejski, Synthesis and struc-
tural analysis of polyester prodrugs of norfloxacin, Molecules 13 (2008)
96e106.
ꢀ
[13] M. Sobczak, K. Nurzynska, W. Ko1odziejski, Seeking polymeric prodrugs of
4. Conclusions
norfloxacin. Part 2. Synthesis and structural analysis of polyurethane conju-
gates, Molecules 15 (2010) 842e856.
[14] M. Sobczak, Synthesis and characterization of polyester conjugates of cipro-
floxacin, Eur. J. Med. Chem. 45 (9) (2010) 3844e3849.
[15] M. Sobczak, G. Na1ecz-Jawecki, W.L. Ko1odziejski, P. Gos, K. Zó1towska,
Synthesis and study of controlled release of ofloxacin from polyester conju-
gates, Int. J. Pharm. 402 (2010) 37e43.
[16] R.H. Platel, L.M. Hodgson, Ch.K. Williams, Biocompatible initiators for lactide
polymerization, Polym. Rev. 48 (2008) 11e63.
[17] A.C. Albertsson, I.K. Varma, Recent developments in ring opening polymeri-
zation of lactones for biomedical applications, Biomacromolecules 4 (2003)
1466e1486.
[18] O. Dechy-Cabaret, B. Martin-Vaca, D. Bourissou, Controlled ring-opening
polymerization of lactide and glycolide, Chem. Rev. 104 (2004) 6147e6176.
[19] J.C. Wu, T.L. Yu, C.T. Chen, C.C. Lin, Recent developments in main group
complexes catalyzed/initiated polymerization of lactides and related cyclic
esters, Coord. Chem. Rev. 250 (2006) 602e626.
In this work the production of macromolecular conjugates
made from PCL, PLA or copolymers of CL, LA and TMC was eval-
uated. The release rates of the PACL were shown to be directly
dependent on the nature of polymers. The obtained results
demonstrate that the homo- and copolymers of CL, LA, rac-LA and
TMC are interesting materials for the controlled release of PACL.
They are good potential candidates to be applied as implantation
drug delivery carriers.
ꢀ
Acknowledgments
[20] R.A. Gross, A. Kumar, B. Kalra, Polymer synthesis by in vitro enzyme catalysis,
Chem. Rev. 101 (2001) 2097e2124.
[21] M. Labet, W. Thielemans, Synthesis of polycaprolactone: a review, Chem. Soc.
Rev. 38 (2009) 3484e3504.
[22] M. Sobczak, E. Ole˛dzka, W.L. Ko1odziejski, Polymerization of cyclic esters using
aminoacid initiators, J. Macromol. Sci. A 45 (2008) 872e877.
The work was supported by the research program (Project
MNiSW-0451/B/H03/2010/39, N N209 045139) of the Committee of
Scientific Research in Poland.
ꢀ
ꢀ
[23] W. Kuran, M. Sobczak, T. Listos, C. De˛bek, Z. Florjanczyk, New route to oli-
gocarbonate diols suitable for the synthesis of polyurethane elastomers,
Polymer 41 (2000) 8531e8541.
Appendix. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ejmech.2011.04.046.
[24] Ch Wang, H. Li, X. Zhao, Ring opening polymerization of L-lactide initiated by
creatinine, Biomaterials 25 (2004) 5797e5801.