Antimicrobial, Cytotoxic, and α-Glucosidase Inhibitory Activities of Ethanol Extract and Chemical Constituents Isolated from Homotrigona apicalis Propolis-In Vitro and Molecular Docking Studies.

The chemical investigation of Homotrigona apicalis propolis collected in Binh Dinh province, Vietnam, led to the isolation of nine compounds, including four sesquiterpenes: spathulenol (1), 1αH,5ßH-aromandendrane-4ß,10α-diol (2), 1ß,6α-dihydroxy-4(15)-eudesmene (3), and 1ßH,5ßH-aromandendrane-4α,10ß-diol (4); three triterpenes: acetyl oleanolic acid (5), 3α-hydroxytirucalla-8,24-dien-21-oic acid (6), and ursolic acid (7); and two xanthones: cochinchinone A (8) and α-mangostin (9). Sesquiterpens 1-4 and triterpene 6 were isolated for the first time from stingless bee propolis. Plants in the Cratoxylum and Aglaia genus were suggested as resin sources of the propolis sample. In the antibacterial activity evaluation, the EtOH extract only showed moderate activity on S. aureus, while the isolated compounds 7-9 showed good antibacterial activity, with IC50 values of 0.56 to 17.33 µg/mL. The EtOH extract displayed selective cytotoxicity against the A-549 cancer cell line, with IC50 values of 22.82 ± 0.86 µg/mL, and the xanthones 8 and 9 exhibited good activity against the KB, HepG-2, and A-549 cancer cell lines, with IC50 values ranging from 7.55 ± 0.25 µg/mL to 29.27 ± 2.07 µg/mL. The cytotoxic effects of xanthones 8 and 9 were determined by the inhibition of the EGFR and HER2 pathways using a molecular docking study. Compounds 8 and 9 displayed strong binding affinity with EFGR and HER2, with values of -9.3 to -9.9 kcal/mol. Compounds 5, 8, and 9 showed potential α-glucosidase inhibitory activities, which were further confirmed by computational studies. The binding energies of compounds 5, 8, and 9 were lower than that of arcabose.

Synthesis of auronol derivatives and their immunostimulating activity.

The first synthesis of alphitonin-4-O-ß-D-glucopyranoside (1) was described. Since, the nitrile group, a strong hydrogen bond acceptor with a significant solvation shell, is considered to have capacity comparable to sugar for facilitating the cell membrane permeation of the molecules, several alphitonin-4-O-ß-D-glucopyranoside and maesopsin-4-O-ß-D-glucopyranoside analogues were prepared by replacing glucopyranose moieties with acetonitrile groups. Immunostimulating activity evaluation on lymphocyte proliferation indicated that the compound 7 with an acetonitrile group at OH-4 of alphitonin had a strong stimulation effect on lymphocyte proliferation. Interestingly, when tested against the normal cell NIH/3T3, 7 had no inhibition even at the concentration of 100 µg/mL.

Facile, protection-free, one-pot synthesis of aureusidin.

A new, reliable, and convenient protection-free one-pot method for the synthesis of aureusidin (1) is described. The present synthetic approach involves the condensation of 4,6-dihydroxybenzofuranone with 3,4-dihydroxybenzaldehyde in the presence of concentrated HCl to afford aureusidin (1) in good yield with high purity. This procedure offers a short and simple route for the preparation of aureusidin (1), a bioactive natural product from several vegetal species, as well as for synthesis of other aurones.