In silico and in vitro studies of isolated constituents from Callistemon citrinus leaves: Anti-microbial potential and inhibition of iNOS activity.

Phytochemical investigation of Callistemon citrinus (Curtis) Skeels (syn. Callistemon lanceolatus (Sm.) Sweet and Melaleuca citrina (Curtis) Dum.Cours.) leaves resulted in the isolation of five undescribed compounds, including one acylphloroglucinol derivative and four monoterpene galloylglucosides, in addition to 29 known diverse secondary metabolites. Interestingly, this study reports chemosystematically significant isolation of the monoterpene galloylglucosides from the genus for the first time. Furthermore, exploration of the isolated compounds as inhibitors of inflammation-related molecular targets, molecular docking studies targeting human adipocyte lipid-binding protein FABP4 (3P6H) and human nitric oxide synthase (3E7G) were carried out in order with the in vitro evaluation of the isolated compounds for their anti-microbial and inhibitory of inducible nitric oxide synthase (iNOS) activities. Molecular docking studies revealed that eighteen compounds showed lower docking scores than ibuprofen, the native ligand in the crystal structure 3P6H, and nine compounds showed lower docking scores than AR-C95791, the native ligand in the binding site of 3E7G. Additionally, in vitro studies revealed that seven compounds showed moderate iNOS inhibitory activity. They also were moderately cytotoxic to HepG2, LLC-PK 1 and Vero cells. Pulverulentone A showed moderate antibacterial activity against MRSA (IC 50 22.2 μM) and antifungal activity against C. neoformans, while corosolic acid showed strong antibacterial activity against VRE (IC 50 15.9 μM).Thus, the in silico and in vitro studies indicated that some isolated compounds hold potentials as inhibitors of iNOS activity and anti-microbial agents. [Display omitted] • Isolation of five undescribed compounds, one acylphloroglucinol and four monoterpenegalloylglucosides from C. citrinus leaves • In addition to the isolation of 29 known compounds. • This is the first report for the occurrence of the monoterpene galloylglucosides in the genus Callistemon. • Molecular docking of the isolated compounds to study their potential as inhibitors for FABP4 protein and iNOS. • Some of the isolated compounds were tested for their antimicrobial and inhibitory of iNOS activities. [ABSTRACT FROM AUTHOR]