The structure and absolute configuration of the new 13-membered macrocyclic alkaloids mulgediifoline and oxyretroisosenine were determined on the basis of chemical reactions and conventional spectral studies including differential nOe and 2D NMR techniques, COSY, HETCOR, COLOC, HMBC and NOESY. The absolute stereochemistry of the already known compounds retroisosenine and cis-nemorensic acid was assigned unambiguously.