Cardiac glycosides. 1. A systematic study of digitoxigenin D-glycosides

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Abstract
A series of digitoxigenin glycosides was studied: 5 with .beta.-D-sugars varying stepwise in sugar structure from .beta.-D-digitoxose to .beta.-D-galactose, including 1 .beta.-D/.alpha.-D pair. I50 [50% inhibition] values for these glycosides and digitoxigenin were determined with hog kidney Na+,K+-ATPase. A major and unexpected role for 4''-OH conformation in the sugar is suggested. All the glycosides with an equatorial 4''-OH were more active than the 2 with the 4''-OH axial [digitoxigenin .beta.-D-galactoside (6) I50 = 6.45 .times. 10-8 M; digitoxigenin 2''-deoxy-.alpha.-D-ribo-hexopyranoside (.alpha.-3a) I50 = 9.33 .times. 10-8 M; digitoxigenin I50 = 1.17 .times. 10-7 M]. Stereochemistry of the 3''-OH had much less of an activity role than that of the 4''-OH, in contrast to extisting models of sugar-site binding.