Spirocyclic iridoid alkaloids from Plumeria rubra
Plumerianoids A-D (1-4) with a new intact spirocyclic iridoid alkaloid skeleton, along with a new degraded alkaloid 8-epi-plumerianine (5), and a known one (6), were isolated and characterized from Plumeria rubra. The structure of 6 was revised as (8R,13S)-plumerianine. These alkaloids consist of three epimeric pairs (1/2, 3/4, and 5/6), exhibiting virtually identical NMR spectra within each pair. Furthermore, the electronic circular dichroism (ECD) curves of each epimeric pair are roughly mirror-like, reminiscent of enantiomers. This study calls for attention on the structural elucidation of special compound classes when the associated chiral centers are far away from the chromophores and/or at the terminal of the molecules. In addition, compound 3 exhibited moderate antiplasmodial activity.
Xin-Hua Gao, Bin Zhou, Flavia M Zimbres, Zai-Yong Zhang, Maria B Cassera, Jin-Xin Zhao, Jian-Min Yue. Org Biomol Chem. 2024 Dec 13. doi: 10.1039/d4ob01870b.