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■ Crude Drugs from Aquatic Plants. VI. On the Alkaloid Constituents of Chinese Nupharis Rhizoma, the Dried Rhizoma of Nuphar pumilum (TIMM.) DC. (Nymphaceae): Structures and Rearrangement Reaction of Thiohemiaminal Type Nuphar Alkaloids

Masayuki Yoshikawa,* Toshiyuki Murakami, Shuji Wakao, Atsushi Ishikado, Nobutoshi Murakami, Johji Yamahara, and Hisashi Matsuda

*Kyoto Pharmaceutical University, Misasagi, Yamashina, Kyoto 607-8414, Japan

Abstract

From chinese Nupharis Rhizoma, the dried rhizoma of Nuphar pumilum (TIMM.) DC. (Nymphaceae), four thiohemiaminal type nuphar alkaloids with potent immunosuppressive activity, 6-hydroxythiobinupharidine, 6,6’-dihydroxythiobinupharidine, 6-hydroxythionuphlutine B, 6’-hydroxythionuphlutine B, have been isolated together with nine inactive nuphar alkaloids. The configurations of the 6- and 6’-hydroxyl groups in those thiohemiaminal type nuphar alkaloids were confirmed on the basis of their 2D-NMR analysis. During the course of chemical elucidation of those thiaspirane type dimeric sesquiterpene alkaloids, new arragement reaction of the thiaspirane ring in thiohemiaminal type alkaloids with 6-hydoxyl group was found and the reaction pathway was discussed. By using this rearrangement reaction, 6-hydroxythionuphlutine B was chemically related with 6-hydroxythiobinupharidine, so that the absolute stereostructures of thionuphlutine B and its related compounds such as 6-hydroxythionuphlutine B, 6’-hydroxythionuphlutine B, and thionuphlutine B β-sulfoxide, were characterized.