Acetalization of Grayanotoxin II, III and 1, 2-Cyclohexane-diol Using Some Metal Sulfate as Catalyzer

Abstract

Grayanotoxins are toxic diterpenoids found in Leucothoe grayana MAX., and are unstable in mineral acids. In this paper, the rate of acetalization and dehydration of G-II [1] and GM-III [2] with some metal sulfates were studied by TLC method. Generally, the rate of dehydration of C-10-OH was faster than that of acetalization of C-5-OH and C-6-OH. The rate of dehydration of C-16-OH was slower than that of acetalization. The optimum conditions for conversion of G-III into its acetal was as follows: metal sulfate, NiSO₄; reaction temp., 65.0°C; reaction time, 30 min. The optimum conditions for conversion of G-II into G-II acetal was as follows; metal sulfate, Fe₂(SO₄)₃ or NiSO₄; reaction temp., 65.0°C; reaction time, 70-100 min.