Abstract
We previously developed an HPLC method for determination of lanatoside C, digoxin and α-acetyldigoxin in digitalis glycosides isolated from Digitalis lanata leaves. Here, we present an improved HPLC-UV method to determine those compounds and deslanoside. We used the improved method to examine the effects of various pretreatments on the amounts of the four compounds isolated from the leaves, with the aim of maximizing the yield of digoxin. Leaves were extracted with 50% methanol, followed by clean-up on a Sep-Pak C18 cartridge prior to HPLC analysis. The amounts of lanatoside C, digoxin and α-acetyldigoxin per 100 mg of the leaves without pretreatment were 115.6, 7.45 and 23.8 μg, respectively (deslanoside was not detected). Pretreatment with acetic acid, which activated deglucosylation mediated by digilanidase present in the leaves, increased the amounts of digoxin and α-acetyldigoxin, while lanatoside C and deslanoside were not detected. Pretreatment with sodium methoxide, which hydrolyzed lanatoside C to deslanoside, increased the yields of deslanoside and digoxin, while lanatoside C and α-acetyldigoxin were not detected. The combination of both pretreatments afforded only digoxin in a yield of 115.1 μg/100 mg leaves. Use of the combined pretreatments appears to be effective for maximizing the yield of digoxin from the leaves.
Highlights
Digitalis (D.) lanata is a species of foxglove, and its name comes from the texture of the leaves like fingers of a glove
It is well known that lanatoside C (LC) is transformed into α-acetyldigoxin (ADx) by deglucosylation mediated by digilanidase present in the leaves [1], and ADx is subsequently converted to digoxin by deacetylation
We developed an HPLC method to determine ADx using the same column, and found that the ADx level was increased 10-fold by heating the suspension in 0.05% acetic acid [3]; this pretreatment appeared to promote deglucosylation of LC to ADx by activating digilanidase
Summary
Digitalis (D.) lanata is a species of foxglove, and its name comes from the texture of the leaves like fingers of a glove. Digoxin (Dx) is most commonly used, and is available for per oral administration, while deslanoside (DLC, deacetyl form of lanatoside C) is used for intravenous administration These compounds are obtained by extraction from the leaves of D. lanata. Pekić and Miljković [5] reported conversion of LC to DLC by sodium methoxide Based on these reports, we considered that a suitable pretreatment method or combination of methods would enable us to maximize the yield of Dx from D. lanata. We established Dx immunoassays using highly specific antisera [9]-[12], but since these are specific for Dx, the amounts of other cardiac glycosides co-existing in the leaves cannot be evaluated precisely In those assays, we utilized alkaline hydrolysis and hydrolysis with digilanidase. We used the developed procedure to examine the effectiveness of various pretreatments for maximizing recovery of Dx from the leaves
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