Alkaloids of catha edulis. Part 2. Constitution of cathedulins E2 and E8, polyesters of a new sesquiterpene pentaol

Abstract

Cathedulin E2 yields on ethanolysis a new 1-eq, 2-ax, 8-ax, 9-ax, 15-pentahydroxylated agarofuran, as deduced from ¹H, ¹³C, and nuclear Overhauser n.m.r. Data, together with cyclic carbonate formation. Ethyl acetate, benzoate, and nicotinate in the molar ratio 2 : 1 : 2 are also produced. Graded alcoholysis (methanolic triethylamine, 5°C) gives an 8-denicotinoyl derivative identical with cathedulin E8 from Catha edulis, whilst at 25 °C the 8,15-bis(denicotinyl) derivative is produced. Aqueous-methanolic sodium hydrogencarbonate further strips the 1- and 2-acetate residues leaving only the 9-benzoate ester. The placing of these ester residues is deduced from a study of the spectral changes caused by graded hydrolysis, thus leading to complete structural proposals for cathedulin E2 and E8.