Synthesis of Individual Glycosides

Cardenolides Containing Sugars Having a Hydroxyl Group at C-2 

Following this work, Reichstein and coworkers15 effected the first partial synthesis of a naturally occurring cardenolide, convallatoxin. Convalla-toxin [3/3-0-(6-deoxy-a-n-mannopyranosyl) strophanthidin (9)] is considered to be the most potent of all the known, naturally occurring cardenolides, and is obtained from the blossoms of the lily-of-the-valley (Convallaria majalis). The coupling of strophanthidin (2) with 2,3,4-tri-0- acetyl-6-deoxy-a- L-mannosyl bromide was performed using silver car- 

however, solvolysis is carried out in the absence of an acid acceptor (and, therefore, in acid medium), orthoester formation stops, and simple replacement occurs, with net retention of configuration01 as in (11)— (lla). Under the same conditions, 1,2-dfi halides undergo solvolysis with inversion of configuration01 as in (12)— (12a) therefore, irrespective of whether a 1,2-trana or a 1,2-da halide is the starting material, the result 

In Reichstein s synthesis15 of convallatoxin (9), 2,3,4-tri-0-acetyl-6-deoxy-a-L-mannosyl bromide (13) (a 1,2-trans halide) was employed. In contrast to the preparation of simple glycosides, the use of silver carbonate did not lead to orthoester formation instead, glycoside formation took 

Evomonoside (19) is a cardenolide which may be isolated directly from the seeds of Euonymua europaea L., or from the enzymic (strophanthobiase) hydrolysis of evonoside,40 obtained from the same source. The structure of evomonoside W) was elucidated by Tamm and Rosselet, 5 who showed 

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