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The effects of 15 jatrophane diterpene polyesters (1-3 and 5-16) isolated from lipophilic extracts of Euphorbia serrulata, E. esula, E. salicifolia, and E. peplus (Euphorbiaceae) on the reversion of multidrug resistance of mouse lymphoma cells were examined. The structures of five new compounds (1-5) were elucidated by spectroscopic methods, including HRFABMS, ESIMS, (1)H-(1)H homonuclear and (1)H-(13)C heteronuclear correlations, long-range correlation spectra, and NOESY experiments. The stereochemistry and absolute configuration of one compound (3) were determined by X-ray crystallography. The structure-activity relationship is discussed.

The numerical descriptors of isostructurality are critically reviewed and to overcome their limitations a new volumetric measure is proposed. It is de®ned as the percentage ratio of the overlapping volume of molecules in the analyzed structures to the average of the corresponding molecular volumes. For the calculation of this index a numerical approach is presented, which is also capable of treating disordered structures. The use of isostructurality calculations is demonstrated using a series of examples. Homologous 9-alkylthiophenanthrenes are used as simple illustrations of the necessity and applicability of the new descriptor. The structural changes in the inclusion compounds of 5-methoxysulfadiazine with chloroform, dioxane and tetrahydrofuran are analyzed and rationalized with the aid of isostructurality indices. The diverse relationships among a series of helical tubuland diols cocrystallized with simple phenols are also characterized. The modi®cations in molecular and crystal structures are correlated with the calculated degree of isostructurality.

Preparation of P-am ino-3-phosphabicy

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There has been a long time effort to influence or favourably fine tune structural properties by introduction\ud of substituents or guest molecules of different sizes, shapes and chemical composition to consequently\ud alter physico-chemical properties of the respective crystals. These attempts require the recognition,\ud understanding and application of intermolecular interactions, crystallographic and, in case of occurrence,\ud non-crystallographic symmetries. It brings us to the field of crystal engineering, which aims to produce\ud new substances with required properties based on the knowledge of the structural properties of already\ud characterised solids. A series of calixarene crystal structures are presented where the crystal packing is\ud determined by spatial or by electrostatic effects. A series of laterally substituted calixarenes where both\ud steric requirements and electrostatic forces play a role in the crystal architecture shows how the supramolecular\ud synthon can be engineered

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