Pitsubcosides U−V, two sesquiterpenoid glycosides with multifunctional activities from Pittosporum subulisepalum

Abstract

In our previous study, nineteen previously unreported antibacterial sesquiterpenoid glycosides, designated as pitsubcosides A−S, including twelve eudesmane-scaffold and seven cadinene-scaffold ones, were isolated from Pittosporum subulisepalum. To further explore structurally diverse bio-active metabolites, our research efforts were focused on the sub-fraction (Fr. E), from which two additional sesquiterpenoid glycosides, pitsubcosides U−V (1−2), were isolated alongside eleven known analogs. The structures of these compounds were elucidated through comprehensive spectroscopic analyses, including 1D and 2D NMR, HRESIMS, and calculated electronic circular dichroism (ECD) analysis. Notably, compounds 1 and 2 exhibited potent inhibitory effects against Bacillus cereus (B. cereus) with the minimum inhibitory concentration (MIC) values of 3.13 μM and 6.25 μM, respectively. Scanning electron microscopy (SEM) observations revealed the antibacterial mechanism, which involves either preventing biofilm formation or disrupting existing cell membranes. Furthermore, compound 1 showed anti-fungal activity against Sclerotinia sclerotiorum (S. sclerotiorum), achieving a relative inhibitory rate of 92.3 % at a concentration 100 μM. Additionally, compound 1 showed inhibitory effects on the production of nitric oxide (NO) in the lipopolysaccharide (LPS)-induced BV-2 microglial cells by suppressing the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), with IC₅₀ value of 6.37 μM. Western blot analysis and molecular docking simulation corroborated the anti-inflammatory properties of compound 1. The results indicated that P. subulisepalum can be developed as potential antibacterial and anti-inflammatory resource.