Studies on the constituents of the leaves of Pieris japonica D. don. IV. The isolation and the structure of pieristoxin F, pieristoxin G and several toxic components (author's transl)

Abstract

The methanolic extract of the leaves of Pieris japonica D.DON was purified and the final extract was submitted to column chromatography from which pieristoxin-F, pieristoxin-G, deacylpieristoxin-B, pieristoxin-C, asebotoxin-I, grayanotoxin-II, and, as the main poisonous principle, grayanotoxin-III (2.7 g, 0.013% yield) were isolated. Hydrolysis of pieristoxin-F affordea 7-hydroxygrayanotoxin-III. Nuclear magnetic resonance (NMR) spectrum of pieristoxin-F indicated the presence of one O-acetyl and one O-propionyl groups, and partial structures of ≡CCH(OR)CH(OH)C≡and-CHOR. Pieristoxin-F is not oxidized by sodium periodate, and its acetate does not agree with tetraacetyl-asebotoxin-IV. Therefore, the structure of pieristoxin-F was presumed to be 6-acetyl-7-hydroxy-14-propionylgrayanotoxin-III. The composition of pieristoxin-G was found to be C20H32O8·H2O from its elemental analytical values and highresolution mass spectrometry, while its infrared spectrum did not show absorptions for carbonyl and unsaturated bond(s). Pieristoxin-G is reduced by lithium aluminum hydride and consumes sodium periodate. Its NMR spectrum indicated the presence of a partial structure of≡CCH(OH)-CH(OH)C≡ and an epoxide ring. These facts suggested the structure of pieristoxin-G as 7, 9-dihydroxy-2, 3-epoxygranotoxin-III.