Photochemistry of Bufadienolides. I. Irradiation of Bufalin, Bufotalin and Gamabufotalin

概要

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The results of photolysis of bufadienolides, which have an α-pyrone ring on a C_<17> position of the steroidal moiety, particularly those of 14β-hydroxy compounds such as bufalin (I), bufotalin (X), gamabufotalin (XVI) and their acetates (II, XI and XVII), are described. Photolysis of I or II in ethanol gave the photoproduct (III), or (IV). The spectral data suggested III and IV had a partial structure either A or B (Chart 1). Then the structure of III and IV were finally proved to be identical with the authentic samples which were prepared from I. Photolysis of I or II in methanol gave V or VI. By hydrolysis III and V were easily converted into the corresponding carboxylic acid (VII), from which methyl ester (V) was prepared by the treatment with diazomethane (Chart 2). Photolysis of X or XI, having 16-β-acetoxyl groups besides 14β-hydroxyl group, in methanol, afforded XII or XIII, respectively (Chart 3). When XVI or XVII, 11α-hydroxy and 11α-acetoxy compounds, were irradiated in methanol, XVIII or XIX were obtained, respectively (Chart 4). These results indicate that photolysis of the other 14β-hydroxy compounds in bufadienolides might be considered to afford the photoproducts having the same moiety as above. A plausible mechanism for the formation of III, V, XII, XVIII, and etc. via the photopyrone (c), the formyl ketene (d) and enol from (f) is depicted in Chart 5.
公益社団法人日本薬学会の論文
1969-08-25