Abstract
Three new compounds (1–3) with unusual skeletons were isolated from the n-hexane extract of the air-dried aerial parts of Hypericum scabrum. Compound 1 represents the first example of an esterified polycyclic polyprenylated acylphloroglucinol that features a unique tricyclo-[4.3.1.11,4]-undecane skeleton. Compound 2 is a fairly simple MPAP, but with an unexpected cycloheptane ring decorated with prenyl substituents, and compound 3 has an unusual 5,5-spiroketal lactone core. Their structures were determined by extensive spectroscopic and spectrometric techniques (1D and 2D NMR, HRESI-TOFMS). Absolute configurations were established by ECD calculations, and the absolute structure of 2 was confirmed by a single crystal determination. Plausible biogenetic pathways of compounds 1–3 were also proposed. The in vitro antiprotozoal activity of the compounds against Trypanosoma brucei rhodesiense and Plasmodium falciparum and cytotoxicity against rat myoblast (L6) cells were determined. Compound 1 showed a moderate activity against T. brucei and P. falciparum, with IC50 values of 3.07 and 2.25 μM, respectively.
Highlights
Three new compounds (1–3) with unusual skeletons were isolated from the n-hexane extract of the air-dried aerial parts of Hypericum scabrum
The Hypericum genus belonging to the Hypericaceae family with a wide distribution in temperate regions has been utilized in folk medicine of different parts of the globe[1,3,4]
Prior phytochemical and pharmacological investigations into this species have demonstrated that the plant is rich in secondary metabolites, especially polycyclic polyprenylated acylphloroglucinols (PPAPs)[15,16,17,18]
Summary
Three new compounds (1–3) with unusual skeletons were isolated from the n-hexane extract of the air-dried aerial parts of Hypericum scabrum. The 1H NMR spectrum of 1 (Table 1) revealed signals of eight methyl singlets (δH 1.00, 1.05, 1.37, 1.46, 1.50 , 1.54, 1.58, 1.65), two olefinic protons (δH 5.26, 1H, t, J = 7.4 Hz; 4.91, 1H, m), and a phenyl group (δH 7.87, 2H, dd, J = 8.4, 1.2 Hz; 7.51, 1H, t, J = 7.5 Hz; 7.36, 2H, t, J = 7.8 Hz). HMBC correlations from H2-22 and H2-6 to the carbonyl resonances at δC 200.9 and δC 203.3 confirmed the position of the two other ketone groups at C-4 and C-9.
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