Alkaloids of Catha edulis. Part 3. Structures of cathedulins K1, K2, K6, and K15; new Macrolide-bridged polyesters of euonyminol

Abstract

It is shown by mass spectral and ¹H and ¹³C n.m.r. methods, together with ethanolysis, that the structure of the polyester alkaloid cathedulin K2 (C₄₀H₅₁NO₁₉) is compiled from euonyminol (1), one evoninic acid residue (cf. 2), five acetic acid residues, and one 2-hydroxyisobutyric acid residue. Some of the ester residues can be positioned on the basis of spectral information. The remainder are assigned as a result of a study of the products formed when cathedulin K2 is treated under controlled conditions with methanolic diethylamine. Four compounds were isolated, C₂₈H₃₇NO₁₃(5), C₃₄H₄₅NO₁₆(6), C₃₆N₄₇NO₁₇(7), and C₃₈H₄₉NO₁₈(8), the structures being assigned spectrally. This leads to the formulation of cathedulin K2 as (4). Using this information, together with further spectral data and information from models, cathedulin K1 (C₄₂H₅₃NO₂₀), K6 (C₃₈H₄₉NO₁₈), and K15 (C₃₆H₄₇NO₁₇) are allocated structures (9), (10), and (11) respectively.