A click chemistry approach to pleuromutilin derivatives, evaluation of anti-MRSA activity and elucidation of binding mode by surface plasmon resonance and molecular docking

Design, Synthesis, Biological Evaluation, and Molecular Docking Studies of Pleuromutilin Derivatives Containing Thiazole

In this study, we designed and synthesized a series of pleuromutilin derivatives containing thiazole. The in vitro antimicrobial efficacy of these synthesized compounds was examined by using four strains. Compared with tiamulin (MIC = 0.25 μg/mL), compound 14 exhibited potency in inhibiting MRSA growth (MIC = 0.0625 μg/mL) in these derivatives. Meanwhile, the time-killing kinetics further demonstrated that compound 14 could efficiently inhibit the MRSA growth. After exposure at 4 × MIC, the postantibiotic effect (PAE) of compound 14 was 1.29 h. Additionally, in thigh-infected mice, compound 14 exhibited a more potent antibacterial efficacy (-1.78 ± 0.28 log10 CFU/g) in reducing MRSA load compared to tiamulin (-1.21 ± 0.23 log10 CFU/g). Moreover, the MTT assay on RAW 264.7 cells demonstrated that compound 14 (8 μg/mL) had no significant cytotoxicity. Docking studies indicated the strong affinity of compound 14 toward the 50S ribosomal subunit, with a binding free energy of -9.63 kcal/mol. Taken together, it could be deduced that compound 14 was a promising candidate for treating MRSA infections.

Design and Synthesis of Pleuromutilin Derivatives as Antibacterial Agents Using Quantitative Structure-Activity Relationship Model

The quantitative structure-activity relationship (QSAR) is one of the most popular methods for the virtual screening of new drug leads and optimization. Herein, we collected a dataset of 955 MIC values of pleuromutilin derivatives to construct a 2D-QSAR model with an accuracy of 80% and a 3D-QSAR model with a non-cross-validated correlation coefficient (r2) of 0.9836 and a cross-validated correlation coefficient (q2) of 0.7986. Based on the obtained QSAR models, we designed and synthesized pleuromutilin compounds 1 and 2 with thiol-functionalized side chains. Compound 1 displayed the highest antimicrobial activity against both Staphylococcus aureus ATCC 29213 (S. aureus) and Methicillin-resistant Staphylococcus aureus (MRSA), with minimum inhibitory concentrations (MICs) < 0.0625 μg/mL. These experimental results confirmed that the 2D and 3D-QSAR models displayed a high accuracy of the prediction function for the discovery of lead compounds from pleuromutilin derivatives.

Proline-Hinged α-Helical Peptides Sensitize Gram-Positive Antibiotics, Expanding Their Physicochemical Properties to Be Used as Gram-Negative Antibiotics

The outer membrane (OM) of Gram-negative bacteria is the most difficult obstacle for small-molecule antibiotics to reach their targets in the cytosol. The molecular features of Gram-negative antibiotics required for passing through the OM are that they should be positively charged rather than neutral, flat rather than globular, less flexible, or more increased amphiphilic moment. Because of these specific molecular characteristics, developing Gram-negative antibiotics is difficult. We focused on sensitizer peptides to facilitate the passage of hydrophobic Gram-positive antibiotics through the OM. We explored ways of improving the sensitizing ability of proline-hinged α-helical peptides by adjusting their length, hydrophobicity, and N-terminal groups. A novel peptide, 1403, improves the potentiation of rifampicin in vitro and in vivo and potentiates most Gram-positive antibiotics. The "sensitizer" approach is more plausible than those that rely on conventional drug discovery methods concerning drug development costs and the development of drug resistance.

Synthesis and Biological Activities of Oxazolidinone Pleuromutilin Derivatives as a Potent Anti-MRSA Agent

A series of pleuromutilin derivatives containing an oxazolidinone skeleton were synthesized and evaluated in vitro and in vivo as antibacterial agents. Most of the synthesized derivatives exhibited potent antibacterial activities against three strains of Staphylococcus aureus (including MRSA ATCC 33591, MRSA ATCC 43300, and MSSA ATCC 29213) and two strains of Staphylococcus epidermidis (including MRSE ATCC 51625 and MSSE ATCC 12228). Compound 28 was the most active antibacterial agent in vitro (MIC = 0.008-0.125 μg·mL-1) and exhibited a significant bactericidal effect, low cytotoxicity, and weak inhibition (IC50 = 20.66 μmol·L-1) for CYP3A4, as well as exhibited less possibility to cause bacterial resistance. Furthermore, in vivo activities indicated that the compound was effective in reducing MRSA load in a murine thigh infection model. Moreover, it clearly facilitated the healing of MRSA skin infection and inhibited the secretion of the TNF-α, IL-6, and MCP-1 inflammatory factors in serum. These results suggest that oxazolidinone pleuromutilin is a promising therapeutic candidate for drug-resistant bacterial infections.

Design, synthesis and antibacterial evaluation of pleuromutilin derivatives

We report herein the design, synthesis, and structure-activity relationship studies of pleuromutilin derivatives containing urea/thiourea functionalities. The antibacterial activities of these new pleuromutilin derivatives were evaluated in vitro against Gram-positive pathogens (GPPs) (Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecium) and Mycoplasma pneumoniae by the broth dilution method. Most of the targeted compounds exhibit good potency in inhibiting the growth of pathogens including Methicillin-susceptible S. aureus (MSSA, ATCC29213, MIC: 0.0625-16 μg/mL), Methicillin-resistant S. aureus (MRSA, ATCC43300, MIC: 0.125-16 μg/mL) and M. pneumoniae (ATCC15531 MIC: 0.125-1 μg/mL, ATCC29342 MIC: 0.0625-0.25 μg/mL and drug resistant strain MIC: 0.5-2 μg/mL). In particular, the compounds 6m and 6n containing phenyl-urea group showed excellent activity with the MIC value less than 0.0625 μg/mL against S. aureus ATCC29213. The compound 6h exhibited better activity than tiamulin against Methicillin-resistant S. aureus ATCC43300.