Due to the rapidly growing bacterial antibiotic-resistance and the scarcity of novel agents in development, bacterial infection is still a global problem. Therefore, new types of antibacterial agents, which are effective both alone and in combination with traditional antibiotics, are urgently needed. In this paper, a series of antibacterial ocotillol-type C-24 epimers modified from natural 20(S)-protopanaxadiol were synthesized and evaluated for their antibacterial activity. According to the screening results of Gram-positive bacteria (B. subtilis 168 and MRSA USA300) and Gram-negative bacteria (P. aer PAO1 and A. baum ATCC19606) in vitro, the derivatives exhibited good antibacterial activity, particularly against Gram-positive bacteria with an minimum inhibitory concentrations (MIC) value of 2–16 µg/mL. The subsequent synergistic antibacterial assay showed that derivatives 5c and 6c enhanced the susceptibility of B. subtilis 168 and MRSA USA300 to chloramphenicol (CHL) and kanamycin (KAN) (FICI < 0.5). Our data showed that ocotillol-type derivatives with long-chain amino acid substituents at C-3 were good leads against antibiotic-resistant pathogens MRSA USA300, which could improve the ability of KAN and CHL to exhibit antibacterial activity at much lower concentrations with reduced toxicity.

The calix [6] arene and 5,11,17,23,29,35-butyl-25,26,27,28,29,30-diethyl phosphates calix [6] arene (EtPO6) were synthesized and their complexation with different metal ions were investigated. The calix [6] arene and EtPO6 were characterized by IR spectrum. The complexation between the host (calix [6] arene and EtPO6) and the guest (metal ions) were investigated by UV-VIS spectrum and extraction experiments. The results show that the complexation of metal ions by calix [6] aren ranked as Na+> Cu2+> Pb2+> UO22+> Fe3+> Cr3+> Ni2+, and the complexation of metal ions by EtPO6 ranked as UO22+> Cu2+> Fe3+> Pb2+> Na+> Cr3+> Ni2+. Compared with calix [6] aren, the extraction capacity of UO22+, Cu2+, Fe3+, Pb2+, Cr3+and Ni2+ions by EtPO6 increased by 37.6%, 10.2%, 10.6%, 9.6%, 2.2%, 4.4%, respectively, while that of Na+ion decreased by 22.3%.