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

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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.