A practical synthesis of 28a-homo-28a-selenolupane triterpenes and the corresponding selenosaponins containing d-mannose, l-arabinose, l-rhamnose, and d-idose moieties is described. Selenium containing triterpenes were obtained from the readily available 3-O-allyl-homobetulin mesylate by nucleophilic substitution with the selenocyanate ion which upon reduction of the -SeCN group afforded the free selenol. Glycosylation using classical Schmidt donors gave 1,2-trans selenosaponins as the main product as well as minute amounts of 1,2-cis isomers. This is one of the very few examples of the synthesis of selenoglycosides by direct glycosylation of free selenols. The studied selenol showed high resistance to air oxidation resulting in good stability during the synthesis of selenolupane derivatives. Cytotoxic activities of new homoselenolupane derivatives were also evaluated in vitro and revealed that some triterpenes exhibited an interesting profile against human cancer cell lines.

Department of Chemical Biology and Genetics Centre of the Region Haná for Biotechnological and Agricultural Research Palacký University Šlechtitelů 27 783 71 Olomouc Czech Republic

Institute of Organic Chemistry Polish Academy of Sciences Kasprzaka 44 52 01 224 Warsaw Poland

Institute of Organic Chemistry Polish Academy of Sciences Kasprzaka 44 52 01 224 Warsaw Poland and Pharmaceutical Research Institute Rydygiera 8 01 793 Warsaw Poland

Institute of Physical Chemistry Polish Academy of Sciences Kasprzaka 44 52 01 224 Warsaw Poland

Laboratory of Growth Regulators Centre of the Region Haná for Biotechnological and Agricultural Research Institute of Experimental Botany ASCR and Palacký University Šlechtitelů 27 783 71 Olomouc Czech Republic

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