Two Crystalline Forms of Sesquiterpene Lactone Helenalin - X-Ray and NMR Study

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Title:Two Crystalline Forms of Sesquiterpene Lactone Helenalin - X-Ray and NMR Study
Creators:
Rychlewska, Urszula
Buděšínský, Miloš
Szczepanska, Beata
Błoszyk, Ełżbieta
Holub, Miroslav
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 60, 2, pp. 276-299

Abstract

<p>Helenalin, a naturally occurring sesquiterpene lactone of the pseudoguaianolide type, has been reported to exist in two polymorphic forms, both crystallizing in the monoclinic space group <i>P2</i><sub>1</sub>. In this paper we report the X-ray structure of the third room temperature polymorph, crystallizing in the orthorhombic space group <i>P2</i><sub>1</sub><i>2</i><sub>1</sub><i>2</i><sub>1</sub>. The isolated molecules in all three polymorphs exhibit nearly the same molecular conformation, so the three crystalline modifications differ mainly in the mode the molecules pack in the solid state. Two main hydrogen bond acceptors, the oxygen atom of the cyclopentenone ring and the oxygen atom of the lactone carbonyl group, are competing in the hydrogen bond formation with the secondary hydroxyl group. Having an access to two polymorphs which differ in the hydrogen bond acceptors, we have performed the solid state <sup>13</sup>C NMR measurements using a cross-polarization magic angle spinning technique. By comparison of the spectra taken in non-polar solvent with the spectra taken in the solid state we were able to demonstrate the shielding effects resulting from the intermolecular hydrogen bonding in crystals. The fast conformational equilibrium between two conformers <i>TC</i>(10) and <i>TC</i>(7) was suggested from NMR study of helenalin in solution.

Title:Two Crystalline Forms of Sesquiterpene Lactone Helenalin - X-Ray and NMR Study
Creators:
Rychlewska, Urszula
Buděšínský, Miloš
Szczepanska, Beata
Błoszyk, Ełżbieta
Holub, Miroslav
Divisions:Life and Chemical Sciences > Institute of Organic Chemistry and Biochemistry > Collection of Czechoslovak Chemical Communications
Journal or Publication Title:Collection of Czechoslovak Chemical Communications
Volume:60
Number:2
Page Range:pp. 276-299
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc19950276UNSPECIFIED
ID Code:716
Item Type:Article
Deposited On:06 Feb 2009 17:03
Last Modified:06 Feb 2009 16:03

Citation

Rychlewska, Urszula; Buděšínský, Miloš; Szczepanska, Beata; Błoszyk, Ełżbieta; Holub, Miroslav (1995) Two Crystalline Forms of Sesquiterpene Lactone Helenalin - X-Ray and NMR Study. Collection of Czechoslovak Chemical Communications, 60 (2). pp. 276-299. ISSN 0010-0765

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