Discovery and Biomimetic Synthesis of a Polycyclic Polymethylated Phloroglucinol Collection from Rhodomyrtus tomentosa .

Inspired by a previously reported biomimetic synthesis study, four new naturally occurring phloroglucinol trimers 1-4 with unusual 6/5/5/6/6/6-fused hexacyclic ring systems, along with two known analogues ( 5 and 6 ) and two known biogenetically related dimers ( 10 and 11 ), were isolated from Rhodomyrtus tomentosa . Their structures and absolute configurations were unambiguously elucidated by spectroscopic analysis, X-ray diffraction, and electronic circular dichroism calculation. By mimicking two potentially alternative biosynthetic pathways, the first asymmetric syntheses of 1-4 and the racemic syntheses of 5 and 6 were achieved in only five to six steps without the need for protecting groups. Furthermore, phloroglucinol dimers 10 and 11 exhibited significant in vitro antiviral activity against the respiratory syncytial virus.