During recent years the chemical structures of a large number of cardiac drugs of both plant and animal origin have been elucidated. The former occur as glycosides and the latter as conjugations of an "aglycone" with suberylarginine. The majority of aglycones of plant origin have been shown to contain the cyclopentanophenanthrene ring system, hydroxylated in varying degrees and carrying a characteristic A^-unsaturated lactone group as the side-chain in position 17. Glycosides of such aglycones, containing one to three sugar residues have been isolated.1It is well known that digitalis preparations lose part of their cardiac activity on storage. While no exact information concerning the cause or nature of this loss of activity is available, various empirical stabilizing measures have been employed, such as buffering of aqueous tinctures or storage of the carefully dried leaves in vacuo.A possible cause for such inactivation may be found in two observations. Jacobs, in a study of the action of enzymes present in Strophanihus kombé seeds on the glycosides of the seeds found that at least three enzymes are present. The first two2 act as glucoside-splitting enzymes and remove one or more of the glucose residues from the original glycoside. The third enzyme3 accomplishes a stereochemical isomerization of the aglycone portion of the glycoside molecule with resultant marked loss of physiological activity. Thus, 4 mg. of isomerized cymarin (allocymarin) failed to kill a 25-g. frog, whereas 0.015 mg. of cymarin is lethal to such an animal. Jacobs clearly showed that isomerization involved the aglycone portion of the cymarin molecule, since the same sugar, cymarose, was obtained from both the active and the inactive glycosides. Further, this change in the aglycone is purely stereochemical, as the same functional groups are present in both aglycones.In a later study on the glycosides of Strophanthus eminii, Jacobs and * This work was carried out during tenure of the Hernheim fellowship by one of us (E. B.).
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