Abstract
During a phytochemical investigation of the unripe fruits of Rubus chingii Hu (i.e., Fructus Rubi, a traditional Chinese medicine named “Fu-Pen-Zi”), a number of highly oxygenated terpenoids were isolated and characterized. These included nine ursane-type (1, 2, and 4–10), five oleanane-type (3, 11–14), and six cucurbitane-type (15–20) triterpenoids, together with five ent-kaurane-type diterpenoids (21–25). Among them, (4R,5R,8R,9R,10R,14S,17S,18S,19R,20R)-2,19α,23-trihydroxy-3-oxo-urs-1,12-dien-28-oic acid (rubusacid A, 1), (2R*,4S*,5R*,8R*,9R*,10R*,14S*,17S*, 18S*,19R*,20R*)-2α,19α,24-trihydroxy-3-oxo-urs-12-en-28-oic acid (rubusacid B, 2), (5R,8R,9R,10R, 14S,17R,18S,19S)-2,19α-dihydroxy-olean-1,12-dien-28-oic acid (rubusacid C, 3), and (3S,5S,8S,9R, 10S,13R,16R)-3α,16α,17-trihydroxy-ent-kaur-2-one (rubusone, 21) were previously undescribed. Their chemical structures and absolute configurations were elucidated on the basis of spectroscopic data and electronic circular dichroism (ECD) analyses. Compounds 1 and 3 are rare naturally occurring pentacyclic triterpenoids featuring a special α,β-unsaturated keto-enol (diosphenol) unit in ring A. Cucurbitacin B (15), cucurbitacin D (16), and 3α,16α,20(R),25-tetrahydroxy-cucurbita-5,23- dien-2,11,22-trione (17) were found to have remarkable inhibitory effects against NF-κB, with IC50 values of 0.08, 0.61, and 1.60 μM, respectively.
Highlights
The Rubus genus is large and diverse, and Flora of China lists 139 species as endemic to China [1]
Semi-preparative HPLC was performed on a Waters e2695 system coupled with a 2998 photodiode array (PDA) detector and a 2424 evaporative light-scattering detector (ELSD) (Waters, Milford, MA, USA)
HEK293 with a stable Nuclear factor-κB (NF-κB) expression cell line was used for the luciferase assay [11,12,47]
Summary
The Rubus genus (family Rosaceae) is large and diverse (with about 700 species distributed worldwide), and Flora of China lists 139 species as endemic to China [1]. PTlhineglacrognestcaonutpolfinJ1gα,2co=n1s2ta.7nHt ozf sJu1αg,2g=es1t2e.d7 tHhze asuxigaglepsotesdititohnefaoxriHal-2p.oMsitoiorenovfoerr,Hth-e2.cMororerelaotvioenr,stohfeHco-2r/reHla3t-i2o5n, sHo-f2/HH-22/-H243,and H2-24/H3-25 in the ROESY NMR experiment (Figure 3) confirmed the β-orientation for both H-2 and the CH2OH group at C-4. 25, H-2/H2-24, and H2-24/H3-25 in the ROESY NMR experiment (Figure 3) confirme5doft1h2e β-orientation for both H-2 and the CH2OH group at C-4. The α-orientation of OH-19 was determined by ROESY NMR experiment, in a similar way to 1 (Figure 3). Detailed comparisons suggested that the 1D NMR data were closely related to those of 3α,16β,17-trihydroxy-ent-kaurane-2-one, which was previously isolated from Homalanthus acuminatus [38]. The only noticeable difference was that the chemical shifts of CH2OH-17 (δH: 3.37 and 3.44, δC: 66.3) in 21 were significantly distinguished when compared with 3α,16β,17-trihydroxy-ent-kaurane-2-one (δH: 3.09 and 3.12; δC: 69.8), indicating that these two compounds are epimeric at C-16. Fluconazole (MIC80: 0.125 μg/mL) was used as the positive control [46]
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