Synthesis and Antibacterial Evaluation of Novel 3-Substituted Ocotillol-Type Derivatives as Leads.

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.

Synthesis and biological evaluation of novel H6 analogues as drug resistance reversal agents.

Hederagenin is a naturally occurring pentacyclic triterpenoids compound with multiple pharmacological activities. We recently showed that H6, a synthetic derivative of hederagenin, could enhance the anticancer activity of paclitaxel in drug-resistant cells in vitro and in vivo, but showed poor solubility. With the aim of improving the drug resistant reversal activity of H6, here we designed and synthesized a series of novel H6 analogues. Our results showed that compound 10 at the concentration of 5 µM significantly enhanced the cytotoxicity of paclitaxel to drug-resistant KBV cells and sensitized cells to paclitaxel in arresting cells in G2/M phase and inducing apoptosis. We found that compound 10 might block the drug efflux of P-gp via stimulating P-gp ATPase activity. Importantly, compound 10 enhanced the efficacy of paclitaxel against KBV cancer cell-derived xenograft tumors. Finally, we summarized a preliminary structure-activity relationship of hederagenin by the drug resistant reversal activity of H6 analogues in vitro and compound 10 and H6in vivo. This study highlights the importance of nitrogen-containing derivatives of hederagenin C-28 in the development of novel drug resistance reversal agents.

Design and synthesis of 28-hydroxy protopanaxadiol as a novel probe template.

To explore the antitumour mechanism of 20(S)-protopanaxadiol (PPD) while maintaining its uncovered pharmacological active site 3-hydroxyl, 28-hydroxy protopanaxadiol (17), a small molecular probe template of PPD was first designed and synthesised based on the Baldwin's reaction. Thus, 28-hydroxyl of 17 was built successfully as a derivatized site of molecular probe's functional and report groups. The important intermediates and final product were confirmed by ESI-MS and nuclear magnetic resonance spectra with good yield. These studies provided a valuable basis for probe research of PPD.

Design, synthesis and biological evaluation of novel α-hederagenin derivatives with anticancer activity.

In an attempt to arrive at a more potent cytotoxic agent than the parent compound α-hederagenin (H), 24 α-hederagenin derivatives (5-8, 11-24, 27-28, 31-32, and 35-36) were synthesized in a concise and efficient strategy and screened for in vitro cytotoxicity against the human cancer cell lines MKN45 and KB. Among these compounds, the polyamine derivative 15 exhibited more potency than the parent compound with IC50 values in the range of 4.22 µM-8.05 µM. Compound 15 increased Bax/bcl-2 ratio that disrupted the mitochondrial potential and induced apoptosis. Therefore, the present studies highlight the importance of polyamine derivatives of α-hederagenin in the discovery and development of novel anticancer agents.