1. Polymorphs and solvates of felodipine: analysis of crystal structures and thermodynamic aspects of sublimation and solubility processes
German L. Perlovich,* Svetlana V. Blokhina, Nikolay G. Manin. CrystEngComm, 2012, 14, 8577–8588
Felodipine(Fel) (ethylmethyl-4-(2,3-dichlorophenyl)-1,4-dihy-dro-2,6-dimethyl-3,5-pyridinedicarboxylate) has been chosen as the subject of this study. Being a calcium channel blocker, felodipine is widely used for treating hypertension. The choice of this compound can be explained by the following reasons. Firstly, felodipine has very poor water solubility, so enhancing this property is of great importance. Secondly, the crystal structure information for felodipine polymorphic forms I and II and formamide (FA) crystallosolvate [Fel + FA], described in the literature together with the data of the present investigation, makes it possible to conduct successful comparative analysis of both molecular conformational states in crystals and their packing architectures. The existence of more than two felodipine polymorphic modifications with melting points close to forms I and II has been indicated in several reports including those by Rollinger and Burger and Kercet al.
2. Role of polymer chemistry in inﬂuencing crystal growth rates from amorphous felodipine
Umesh S. Kestur and Lynne S. Taylor*. CrystEngComm, 2010, 12, 2390–2397
Thermal analysis was performed using a TA Q2000 DSC equipped with a refrigerated cooling accessory (TA Instruments, New Castle, DE, USA). Nitrogen, 50mL min-1, served as the purge gas and reference and sample pans were matched for weight to within 0.01mg. 3–7mg of the sample were weighed into an aluminium T zero sample pan with a pin hole (TA instruments, New Castle, DE, USA) and sealed. The glass transition temperature (Tg) was determined by heating the sample at 10 oC min-1 and the onset temperature is reported. The thermal history of the samples was erased by heating the sample beyond Tg followed by cooling and reheating, before the actual Tg measurements were made. Melting point (Tm) depression measurements for felodipine alone and felodipine in the presence of polymers were made by heating the samples at 1 oC min-1 to beyond the melting point. Polymers were intimately mixed with pure crystalline felodipine using a cryogenic mill. The offset of melting was taken as the extrapolated offset of the bulk melting endotherm.
3. Polymorphism of felodipine co-crystals with 4,4’-bipyridine
Artem O. Surov, Katarzyna A. Solanko, German L. Perlovich*. CrystEngComm,2014, 16, 6603–6611
In this paper, we focus on the structures and physico-chemical properties of three co-crystals of the API felodipine (Fel)with 4,4’-bipyridine (BP), namely two polymorphs of the co-crystal with a 1 : 1 molar ratio and a co-crystal having a 2 : 1 molar ratio (Fig. 1). This work is a continuation of our previous studies concerning new crystalline forms of felodipine. Felodipine is one of the well-known calcium-channel blocking drugs, and it is it self tetramorphic: forms I and II have been known for a long time, and we have quite recently reported two new polymorphs, forms III and IV. Several solvates are also known in the literature. A solvate with formamide has been reported by Lou et al., and Rollinger and Burger have also described an unstable solvate with acetone, characterized by thermal, IR spectroscopic and powder X-ray diffraction techniques.