Crystal structures of the alkaloids vasicinone and peganidine hydrochloride were studied by x-ray structure analysis. The configurations of asymmetric centers C4 and C9 in peganidine were determined. The hydroxyl and acetonyl groups were mutually syn-positioned relative to the tricyclic plane. H-bonds involving the Cl ion, which connected molecular cations transformed by 2 1 screw axes, were formed in the peganidine hydrochloride crystal. H-bonds between the C4 carbonyl and the C9 hydroxyl transformed by a glide plane were formed in the vasicinone crystal. The N1 atom was not involved in forming intermolecular H-bonds.Keywords: quinazolines, vasicinone, peganidine, x-ray structure analysis.Tricyclic quinazoline alkaloids with a C9 hydroxyl such as peganine, vasicinone, and peganidine, are definitely of practical interest. Peganine and peganidine exhibit high anticholinesterase activity whereas vasicinone exhibits bronchodilating activity [1, 2]. Vasicinone was isolated from Peganum harmala as the L-isomer [3,4] or the racemate [5]. The latter form was also obtained by oxidation of (±)-peganine by H 2 O 2 [6]. The alkaloid peganidine is a peganine derivative and contains an acetone substituent in the 4-position. It was also isolated from P. harmala [7] together with deoxypeganidine [8].The structure of (-)-vasicinone hydrobromide was established by an x-ray structure analysis (XSA) and its absolute (S)-configuration at C9 was determined [9]. However, data from the XSA are missing from the CCDC (only the cell constants are given). The crystal structure of the racemate of this base has not been reported.Peganidine has two asymmetric centers at C4 and C9, i.e., its molecule can theoretically exist as four diastereomers. However, the plant alkaloid was isolated only as the racemate [7]. Therefore, the stereochemical question reduces to finding the mutual (cis-or anti-) positioning of the C4 and C9 substituents relative to the plane of the tricyclic system, which has until now been unanswered.Furthermore, an intramolecular H-bond involving the hydroxyl H atom and N1 can theoretically form in vasicinone and peganidine. The formation of such a H-bond was observed for D-hydroxymethylenedeoxyvasicinone [10].
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