Scopadulcic acid B, a new tetracyclic diterpenoid from Scoparia dulcis L. Its structure, H+, K+-adenosine triphosphatase inhibitory activity and pharmacokinetic behaviour in rats.

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Abstract
The structure of scopadulcic acid B (2, SDB), a major ingredient of the Paraguanyan herb "Typycha kuratu" (Scoparia dulcis L.), was elucidated mainly by comparison of its spectral data with that of scopadulcic acid A (1). SDB inhibited both the K+-dependent adenosine triphosphatase (ATPase) activity of a hog gastric proton pump (H+, K+-ATPase) with a value of 20-30 .mu.M for IC50 and proton transport into grastric vesicles. Pharmacokinetic studies of SDB in rats indicated that plasma SDB concentrations after i.v. injection of the sodium salt of SDB (SDB-Na) were described reasonably well by a two-compartment open model with Michaelis-Menten elimination kinetics. Plasma concentrations after oral administration of SDB-Na or SDB showed a much slower decline than what was expected following the i. v. study. It was suggested that the sustained plasma level of SDB after oral administration of SDB-Na or SDB was accounted for by relatively slow but efficient gastro-intestinal absorption in rats.