complexation between doxycycline hyclate and β

COMPLEXATION BETWEEN DOXYCYCLINE HYCLATE AND ΒCYCLODEXTRIN. EXPERIMENTAL AND THEORETICAL STUDIES
KOGAWA, A.C.1*, ZOPPI, A.2*, QUEVEDO, M.A.2, NUNES SALGADO, H.R.1, LONGHI, M. R.2
1
Departamento de Fármacos e Medicamentos - Controle de Qualidade, Faculdade de Ciências
Farmacêuticas, Universidade Estadual Paulista-UNESP, Araraquara, São Paulo, Brasil.
2
Departamento de Farmacia. Facultad de Ciencias Químicas. Universidad Nacional de Córdoba. Córdoba.
Argentina.
*e- mail: [email protected]; [email protected]
Keywords: doxycycline, β-cyclodextrin, NMR spectroscopy, molecular modeling.
1. Introduction
Doxycycline (DOX) is a drug effective against a
large variety of bacteria. In addition, it has
antiprotozoal actions and may be administered
in conjunction with quinine in the management
of falciparum malaria. Unfortunately DOX is
quite susceptible to light, thus diverse strategies
towards increasing its photostability are
envisioned. A commonly applied approach to
increase the stability of drugs is the formation of
complexes with macromolecules, of which
molecular encapsulation with β-cyclodextrin
(βCD) constitutes an alternative for the
development of new pharmaceutical dosage
forms. The objective of this work was to
investigate the possibility of obtaining an
inclusion complex between DOX and βCD in
order to enhance this drug stability, by
combining both experimental and theoretical
approaches.
2. Methods
For experimental studies, nuclear magnetic
resonance techniques (1H NMR and 2D
ROESY) were determined in solution (D2O,
pD=2.3). All experiments were performed on a
Bruker® Avance II High Resolution
Spectrometer.
Theoretical
studies
were
performed applying molecular modeling and
docking techniques using Gaussian03 and
Autodock3 packages. Molecular dynamics
simulations and energetic analyses were applied
using the Amber9 software suite.
3. Results
The minimum energy conformation of DOX
was obtained by simulated annealing analyses,
which was afterwards employed for the
molecular docking calculations. Docking results
suggested the formation of an inclusion
complex between DOX and βCD, with a unique
cluster being predicted. In this model, the
aromatic ring of DOX (ring D, Fig. 1) was
inserted into βCD hydrophobic cavity, with a
mean docked energy of -11.03 Kcal/mol.
Molecular dynamics simulations in explicit
solvent conditions showed that the inclusion
complexed is maintained throughout the
simulation (5 ns), with ring D deeply buried into
the βCD cavity and ring A oriented toward the
wide ring of βCD. Energetic component
analyses demonstrated that the complex is
mainly stabilized by hydrophobic contacts, with
a
minor
contribution
of
electrostatic
interactions.
The 1H NMR studies evidenced a marked
shielding effect on internal βCD protons, which
confirms the inclusion complex formation. 2D
ROESY assays showed correlation between the
internal protons of βCD and aromatic protons of
DOX, suggesting that ring D is inserted into
βCD cavity.
CH3
H3C
OH
N
CH3
OH
D
C
B
A
O
OH
OH
O
OH
O
NH2
Figure 1. Molecular structure of DOX.
4. Conclusion
We were able to successfully combine
molecular modeling studies with experimental
spectroscopic assays, in order to elucidate the
molecular basis of DOX-βCD interaction. The
work performed allows us to study the
complexation between DOX and βCD at a
molecular level.
Acknowledgments
CAPES; CNPq; PADC-FCFAR-UNESP; União
Química Indústria Farmacêutica and Consejo
Nacional de Investigaciones Científicas y
Tecnológicas de la Nación (CONICET),
Argentina.