[A simple method of synthesis of triterpene glycosides similar to glycyrrhizic acid and their hepatoprotective activity in vitro].

A simplified method of synthesis of triterpene l,2-trans-glycosides was developed using the glycosylation of glycyrrhetic acid (GLA) and 18,19-dehydro-GLA by beta-pyranose peracetates in the presence of SnCl(4) and molecular sieves 4 A. The synthesized glycosides exhibited hepatoprotective activity toward the human hepatoma HepG2 cell line on the model of alcohol hepatitis and decreased the level of TNF-alpha protein.

Stiff, and sticky in the right places: the dramatic influence of preorganizing guest binding sites on the hydrogen bond-directed assembly of rotaxanes.

Structural rigidity and the preorganization of thread binding sites are shown to have a major influence on template efficiency in the synthesis of hydrogen bond-assembled rotaxanes. Preorganization is so effective, in fact, that with good hydrogen bond acceptors (amides) a "world record" yield of 97% for a [2]rotaxane is obtained. The truly remarkable feature of this efficient template, however, is that it allows even poor hydrogen bond acceptors (esters) to be used to prepare hydrogen bond-assembled rotaxanes, despite the presence of competing hydrogen bonding groups (anions) which bind the key intermediates at least 10000x more strongly than single, unorganized, ester groups! The structures of the rotaxanes are established unambiguously in solution by (1)H NMR spectroscopy and in the solid state by X-ray crystallography. As a series they provide unique experimental information regarding the nature of amide-ester hydrogen bonding interactions; in particular they suggest that in CDCl(3), amide-ester NH...O=C hydrogen bonds are approximately 1 kcal mol(-)(1) weaker than the corresponding amide-amide interactions.