title: Binary system of (R)- and (S)-nitrendipine--polymorphism and structure.
abstract: Three monotropically related modifications of (RS)-nitrendipine (RS-NTD) were investigated. With the aid of the optical antipodes of NTD, it was possible to construct a binary phase diagram, from which it is obvious that the thermodynamically stable mod. I of RS-NTD (mp 156-158.5 degrees C, heat of fusion 41.1 +/- 0.2 kJ mol-1) is a racemic compound, while mod. II (mp 130-134 degrees C, heat of fusion 29.4 kJ mol-1) and mod. III (mp 124-126 degrees C, heat of fusion 27.2 kJ mol-1) occur as conglomerates of different modifications of R- and S-NTD. The eutectic points (calculated) are at 150 degrees C and at 19% and 81% molar fraction of an enantiomer, respectively. Two modifications of the enantiomers are characterized (En-mod. I, thermodynamically stable form, mp 156-158 degrees C, heat of fusion 34.5 +/- 1.3 kJ mol-1 and En-mod. III, mp 121 degrees C), whereas a third modification (En-mod. II) must be hypothesized pursuant to the phase diagram (mp ca. 152 degrees C). IR spectra, DSC curves, and X-ray powder diffractograms of the different phases are described. The crystal structure of the enantiomer En-mod. I is reported (monoclinic, P2(1), density 1.346 g cm-3) and compared with the X-ray structure of the racemic compound (monoclinic, P2(1)/c, density 1.356 g cm-3). A comparison with similar studies on nimodipine has been made to emphasize the parallels to a substance of this chemical group.
authors.affiliation: Institut für Pharmakognosie der Universität Innsbruck, Austria. artur.burger@nibk.ac.at
authors.forename: A
authors.initials: A
authors.lastname: Burger
authors.forename: J M
authors.initials: JM
authors.lastname: Rollinger
authors.forename: P
authors.initials: P
authors.lastname: Brüggeller
mesh_terms: D002121:Calcium Channel Blockers / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D015394:Molecular Structure; D009568:Nitrendipine / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism; D014961:X-Ray Diffraction
chemical_list: D002121:Calcium Channel Blockers; D009568:Nitrendipine