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Valenti S, Barrio M, Negrier P, Romanini M, Macovez R, Tamarit JL. Comparative Physical Study of Three Pharmaceutically Active Benzodiazepine Derivatives: Crystalline versus Amorphous State and Crystallization Tendency. Mol Pharm 2021; 18:1819-1832. [PMID: 33689364 PMCID: PMC8594866 DOI: 10.1021/acs.molpharmaceut.1c00081] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
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Chemical derivatization and amorphization
are two possible strategies
to improve the solubility and bioavailability of drugs, which is a
key issue for the pharmaceutical industry. In this contribution, we
explore whether both strategies can be combined by studying how small
differences in the molecular structure of three related pharmaceutical
compounds affect their crystalline structure and melting point (Tm), the relaxation dynamics in the amorphous
phase, and the glass transition temperature (Tg), as well as the tendency toward recrystallization. Three
benzodiazepine derivatives of almost same molecular mass and structure
(Diazepam, Nordazepam and Tetrazepam) were chosen as model compounds.
Nordazepam is the only one that displays N–H···O
hydrogen bonds both in crystalline and amorphous phases, which leads
to a significantly higher Tm (by 70–80
K) and Tg (by 30–40 K) compared
to those of Tetrazepam and Diazepam (which display similar values
of characteristic temperatures). The relaxation dynamics in the amorphous
phase, as determined experimentally using broadband dielectric spectroscopy,
is dominated by a structural relaxation and a Johari–Goldstein
secondary relaxation, both of which scale with the reduced temperature T/Tg. The kinetic fragility
index is very low and virtually the same (mp ≈ 32) in all three compounds. Two more secondary relaxations
are observed in the glass state: the slower of the two has virtually
the same relaxation time and activation energy in all three compounds,
and is assigned to the inter-enantiomer conversion dynamics of the
flexible diazepine heterocycle between isoenergetic P and M conformations.
We tentatively assign the fastest secondary relaxation, present only
in Diazepam and Tetrazepam, to the rigid rotation of the fused diazepine–benzene
double ring relative to the six-membered carbon ring. Such motion
appears to be largely hindered in glassy Nordazepam, possibly due
to the presence of the hydrogen bonds. Supercooled liquid Tetrazepam
and Nordazepam are observed to crystallize into their stable crystalline
form with an Avrami exponent close to unity indicating unidimensional
growth with only sporadic nucleation, which allows a direct assessment
of the crystal growth rate. Despite the very similar growth mode,
the two derivatives exhibit very different kinetics for a fixed value
of the reduced temperature and thus of the structural relaxation time,
with Nordazepam displaying slower growth kinetics. Diazepam does not
instead display any tendency toward recrystallization over short periods
of time (even close to Tm). Both these
observations in three very similar diazepine derivatives provide direct
evidence that the kinetics of recrystallization of amorphous pharmaceuticals
is not a universal function, at least in the supercooled liquid phase,
of the structural or the conformational relaxation dynamics, and it
is not simply correlated with related parameters such as the kinetic
fragility or activation barrier of the structural relaxation. Only
the crystal growth rate, and not the nucleation rate, shows a correlation
with the presence or absence of hydrogen bonding.
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Affiliation(s)
- Sofia Valenti
- Grup de Caracterització de Materials, Departament de Física and Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, EEBE, Campus Diagonal-Besòs, Av. Eduard Maristany 10-14, Barcelona, Catalonia 08019, Spain
| | - Maria Barrio
- Grup de Caracterització de Materials, Departament de Física and Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, EEBE, Campus Diagonal-Besòs, Av. Eduard Maristany 10-14, Barcelona, Catalonia 08019, Spain
| | - Philippe Negrier
- Université Bordeaux, Laboratoire Ondes et Matière d'Aquitaine, UMR 5798, 351 Cours de la Libération, Talence F-33400, France
| | - Michela Romanini
- Grup de Caracterització de Materials, Departament de Física and Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, EEBE, Campus Diagonal-Besòs, Av. Eduard Maristany 10-14, Barcelona, Catalonia 08019, Spain
| | - Roberto Macovez
- Grup de Caracterització de Materials, Departament de Física and Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, EEBE, Campus Diagonal-Besòs, Av. Eduard Maristany 10-14, Barcelona, Catalonia 08019, Spain
| | - Josep-Lluis Tamarit
- Grup de Caracterització de Materials, Departament de Física and Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, EEBE, Campus Diagonal-Besòs, Av. Eduard Maristany 10-14, Barcelona, Catalonia 08019, Spain
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