30-norfriedelanes and other compounds from the stem bark and fruits of Caloncoba glauca (Achariaceae), their antiplasmodial activity, structure-activity relationship and computational validation

Abstract

Two new 30-norfriedelane triterpenoids namely glaucalactone C (1) and glaucanoic acid (2) along with sixteen known compounds (3-18) have been isolated from the methanolic extracts of the stem bark and fruits of Caloncoba glauca (P.Beauv.) Gilg (Achariaceae). The structures of all the isolated compounds have been established with the aid of their extensive spectroscopic analyses (1D and 2D-NMR) as well as mass spectrometry. Six compounds (1-5, 9) were screened for antiplasmodial activity against two strains P. falciparum Dd2 and P. falciparum 3D7. The results showed that glaucanoic acid (2) was the most active one with IC₅₀ values of (3.5 ± 0.1 μg/mL) and (4.6 ± 0.7 μg/mL) against PfDd2 and Pf3D7, respectively, while glaucalactone C (1) moderately inhibited PfDd2 (9.4 ± 0.1 μg/mL) and weakly Pf3D7 (15.9 ± 2.3 μg/mL). The molecular docking analyses of the isolated compounds showed that compounds 1-4 and 9-11 are potential drug targets and were further supported by their ADMET studies that revealed welwitschiilactones B and C (4 and 5) as well as β-sitosterol (10) as the most qualified compounds to be safe as drugs. The results indicate that C. glauca is an important source of good candidates in new antiplasmodial drug development.

Keywords: 30-norfriedelane triterpenes; Achariaceae; Caloncoba glauca; Molecular docking; Plasmodium falciparum.