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■ Structures of Tetra-O-demethylcolchicine, -isocolchicine, and 10-O-Demethylcolchicine Derivatives.

Yoshiki Kashiwada, Li Sun, Hiroshi Tatematsu, Kenneth F. Bastow, and Kuo-Hsiung Lee*

*Division of Medicinal Chemistry and Natural Products, School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina 27599-7360, U.S.A.

Abstract

During the exhaustive demethylation of both colchicine and isocolchicine analogs, tetra-O-demethyl derivatives with identical structures were produced. Spectral examination (¹H-¹³C long-range COSY nuclear magnetic resonance) of these analogs (5-8) indicated that isocolchicine-type tautomerism is predominant in tetra-O-demethylcolchicine derivatives. Similarly, structures of 10-O-demethylcolchicine derivatives were revised to be an isocolchicine-type shown by formulae (9) and (10).