Discovery of structurally diverse polyprenylated acylphloroglucinols with quorum sensing inhibitory activity from Hypericum seniawinii Maxim.

Four previously undescribed polyprenylated acylphloroglucinols, hyperisenins A-D (1-4), along with two known analogues (5 and 6), were obtained from the aerial part of Hypericum seniawinii Maxim. Compounds 1 and 2 were two highly degraded polyprenylated acylphloroglucinols with a cyclohexanone-monocyclic skeleton, while compound 3 was the first example of O-prenylated acylphloroglucinols with a 6/6/6 ring system. Their structures were identified by analyzing NMR, HRESIMS data, and quantum chemical calculations. The biosynthetic pathway of 1 and 2 might originate from bicyclic polyprenylated acylphloroglucinols via a series of complex retro-Claisen, keto - enol tautomerism, and intramolecular cyclization. The bioassay results showed that 4 exhibited quorum sensing inhibitory activity against Pseudomonas aeruginosa, which could decrease the activation of the rhl system, and significantly reduce rhamnolipid levels at a concentration of 100 µM, and the mechanism might be the ability to bind 4 to lasR and pqsR.