Molecular Structure of the Pyrrolizidine Alkaloid Trichodesmin from Rindera oblongifolia.

The known pyrrolizidine alkaloids trichodesmine, trichodesmine N-oxide, lindelofine, and trichelanthic acid were isolated from Rindera oblongifolia for the first time. The absolute configurations of the chiral centers of trichodesmine, which contains an 11-membered macrocycle, were established as 7R,8R,11R,12R,13R by an X-ray crystal structure analysis. A study of the conformation of trichodesmine showed that the nature of intra- and intermolecular H-bonds and packing factors were decisive in realizing one conformer or another of the 11-membered macrocycle. [ABSTRACT FROM AUTHOR]