Molecular Pharmacology, Vol 17, 43-51, Copyright © 1980 by the American Society for Pharmacology and Experimental Therapeutics

A Crystallographic, Conformational Energy, and Biological Study of Actodigin (AY-22,241 ) and Its Genin

¹ School of Pharmacy, Oregon State University, Corvallis, Oregon 97331
² Medical Foundation of Buffalo, Inc., Buffalo, New York 14203, Cardiovascular Division, Department of Medicine, University of Minnesota, Minneapolis, Minnesota 55455
³ Cardiovascular Division, Department of Medicine, Veterans Administration Medical Center, Minneapolis, Minnesota 55417
⁴ Toxicology Research Laboratory, Veterans Administration Medical Center, Minneapolis, Minnesota 55417, Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, Minnesota 55455

A multidisciplinary (crystallographic, conformational energy, biological) study of Actodigin and digitoxigenin was completed, and the data analyzed using the NIH PROPHET computer system. These data were compared to Na⁺,K⁺-ATPase inhibition studies on Actodigin genin, digitoxigenin -D-glucoside, digitoxin, and digitoxigenin -D-digitoxide. This work has shown that Actodigin genin’s ability to inhibit Na⁺,K⁺-ATPase can be largely explained by its lactone carbonyl oxygen position (5.22 Å displaced from the carbonyl oxygen of digitoxigenin, both molecules in their crystallographically observed energy minima) and molecular conformation. The ring D of Actodigin, for example, was found to be in a half chair, unlike those of natural digitalis ring D’s, which exist in an envelope. However, the -D-glucose makes an unexpectedly large contribution to Actodigin’s activity—much larger than with digitoxigenin glucoside. Actodigin genin has very low activity (I₅₀ 7 x 10^-5 M), nearly the least active genin we have studied. These findings were not predicted by a recently proposed Actodigin binding model, and they give new insight into the glycoside binding model proposed by Yoda and Yoda.

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ACKNOWLEDGMENTS We thank Gregory Quarfoth and Ms. Renae Roelofs for their excellent technical assistance in the biological studies; Dr. Romano Deghenghi, Director of Research, Ayrest Laboratories, for providing samples of AV-22,241 and its acetate; and Professor A. Schwartz for a prepublication copy of his Actodigin study (2). The organization and analysis of the data base associated with this investigation were carried out in part using the PROPHET system, a unique national resource sponsored by NIH. Information about PROPHET can be obtained from the Director, Chemical/Biological Information Handling Program, Division of Research Resources, NIH, Bethesda, Maryland 20014.