Photochemistry of Bufadienolides. II. Irradiation of Resibufogenin and 14α-Artebufogenin

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Although in the photolysis of 14β-hydroxy compounds, as described in the previous paper, ring formation reaction between C_<21> and 14β-hydroxy group is observed, in the case of resibufogenin (I) and 14α-artebufogenin (IV), which are 14β, 15β-epoxy- and 15-oxocompounds, the photolysis products (A and B, in Fig. 1) were unstable and could not be isolated. However, it should be noted that by treatment with acid the photolysis products were converted into the stable 21-OCH_3 structure, i.e. methyl 3-hydroxy-21-methoxy-15-oxo-5β, 14α-chola-20 (21), 22-dienoate (II) and methyl 14β, 15β-epoxy-3β-hydroxy-21-methoxy-5β-chola-20 (21), 22-dienoate (IV). The fact that the epoxy ring was intact during photolytic conditions was indicated by thin-layer chromatography (Fig. 1) in the irradiation of I by the appearance of spot A which had different Rf value compared with that of spot B, a photolysis product of IV. Furthermore, the progress of the photo-reaction was followed by UV spectra measurement (Fig. 4) and a plausible mechanism for the formation of II and IV is depicted in Chart 2.
公益社団法人日本薬学会の論文
1969-08-25