ALKALOIDS OF CATHA-EDULIS .4. STRUCTURES OF CATHEDULINS E3, E4, E5, E6, AND K12 - NOVEL SESQUITERPENE ALKALOIDS WITH MONO-MACROLIDE AND BIS-MACROLIDE BRIDGES

Alcoholysis and reduction shows that cathedulin E3, C54H60N2O23, is made up of a euonyminol core (3) (octaacetate), together with 4 acetates, a hydroxyisobutyrate and evoninate (1) and cathate residues. The latter, a novel residue, is shown to be (4). By study of 1H and 13C NMR data for the intact alkaloid and its hydrogenolysis and partial methanolysis products, E3 is formulated as (12). Cathedulin E4, converted into E3 by acetylation, is (13). Corresponding to both alkaloids is a minor series in which one acetate is replaced by a benzoate residue. Cathedulin E6, C57H62N2O22, formulated as (17), is also based on a euonyminol core but gives, on methoylsis, dimethyl evoninate, methyl benzoate, methyl nicotinate and trimethyl gallate; a 2-acetoxyisobutyrate and a further acetate residue are also present. Alkaloid E6 bears to E5 (16) the same relationship as does E4 to E3. The minor alkaloid cathedulin K12, C54H62N2O23, has the structure (18), similar to E3 but with the cathate span reductively cleaved; this suggests a biosynthetic connection.