Acylphloroglucinol derivatives from the twigs and leaves of Callistemon salignus

Three new acylphloroglucinol derivatives, callisalignones A-C (1-3), six new meroterpenoids, callisalignenes A-F (4-9), along with 18 known analogues (10-27) were isolated from the twigs and leaves of Callistemon salignus. Their structures and absolute configurations were established by comprehensive spectroscopic evidences (NMR, MS, amd electronic circular dichroism calculations). The absolute configurations of callistenones B (13) and H (14) were determined by comparison of their ECD spectra with that of callisalignone B (2). Callisalignones B and C are new adducts of beta-triketone and acylphloroglucinol, whereas callisalignenes A-D are new meroterpenoids of acylphloroglucinol and alpha-phellandrene with different coupling models via hetero-Diels-Alder reaction, respectively. Myrtucommulone D (15) showed significant antibacterial activity against Staphylococcus aureus and three drug resistant S. aureus strains with MIC values of 1.953 and 0.975 mu g/mL, respectively. Isomyrtucommulone B (17) displayed remarkable antibacterial activity against Escherichia coli with an MIC value of 0.122 mu g/mL. Cytotoxic assay revealed that isomyrtucommulone B (17) was the most active against HCT116 with an IC50 value of 2.09 +/- 0.10 mu M. (C) 2017 Elsevier Ltd. All rights reserved.