Discovery of a novel class of rosmarinic acid derivatives as antibacterial agents: Synthesis, structure-activity relationship and mechanism of action.

Twenty-seven rosmarinic acid derivatives were synthesized, among which compound RA-N8 exhibited the most potent antibacterial ability. The minimum inhibition concentration of RA-N8 against both S. aureus (ATCC 29213) and MRSA (ATCC BAA41 and ATCC 43300) was found to be 6 µg/mL, and RA-N8 killed E. coli (ATCC 25922) at 3 µg/mL in the presence of polymyxin B nonapeptide (PMBN) which increased the permeability of E. coli. RA-N8 exhibited a weak hemolytic effect at the minimum inhibitory concentration. SYTOX Green assay, SEM, and LIVE/DEAD fluorescence staining assay proved that the mode of action of RA-N8 is targeting bacterial cell membranes. Furthermore, no resistance in wildtype S. aureus developed after incubation with RA-N8 for 20 passages. Cytotoxicity studies further demonstrated that RA-N8 is non-toxic to the human normal cell line (HFF1). RA-N8 also exerted potent inhibitory ability against biofilm formation of S. aureus and even collapsed the shaped biofilm.

New depside and rosmarinic acid derivatives from Perilla frutescens and their anti-inflammatory activity.

Two new depside derivatives 1 and 2 as well as a new pair of rosmarinic acid enantiomers 3a/b were isolated from the leaves of Perilla frutescens (L.) britt. The chemical structures of these compounds were identified based on detailed spectroscopic and physicochemical analyses (HR-ESI-MS, NMR) and comparison of literature data. Compounds 3a/b were obtained by chiral separation, and their absolute configurations were determined by comparison of experimental and calculated ECD spectra. Compounds 3a/b exhibited potential inhibitory activity on nitric oxide (NO) production induced by lipopolysaccharide in RAW264.7 cells with IC50 values of 15.92 ± 3.32 µM and 48.72 ± 4.12 µM.

Synthesis and evaluation of inhibitors of Mycobacterium tuberculosis UGM using bioisosteric replacement.

There is a dearth of tuberculosis (TB) drug development activity as current therapeutic treatments are inadequate due to the appearance of drug-resistant TB. The enzyme UDP-galactopyranose mutase (UGM) is involved in the biosynthesis of galactan which is essential for cell wall integrity and bacterial viability. Its inhibition has thus been featured as profitable strategy for anti-TB drug discovery. In this study, we report on the synthesis of amides derived from rosmarinic acid, their inhibitory effect towards purified UGM using three distinct biochemical assays: FP, HPLC and SPR. The rosmarinic amides generally showed a significantly higher affinity for UGM than the corresponding rosmarinic ester. In particular, compound 5h displayed interesting binding affinity values (Kd = 58 ± 7, 63 ± 9 µM towards KpUGM and MtUGM respectively). Furthermore, a new UGM SPR assay was established and confirmed that 5h binds to UGM with a dissociation constant of 104.8 ± 6.5 µM. Collectively, this study validates the amide bioisosteric strategy which has been successfully implemented to develop UGM inhibitors from rosmarinic acid, providing a substantial basis for further design of novel UGM inhibitors and anti-mycobacterial agents.

Novel Phenolic Constituents of Pulmonaria officinalis L. LC-MS/MS Comparison of Spring and Autumn Metabolite Profiles.

Lungwort (Pulmonaria officinalis L., Boraginaceae) is considered to possess therapeutic properties and it has been traditionally used as a remedy against various lung disorders in many countries. Nevertheless, very few data concerning its phytochemical composition are available. This research aims to provide a detailed description of specialized metabolites from the aerial parts of lungwort. Nine previously undescribed and 36 known phenolic compounds were detected in the 50% methanolic extract. Following multistep preparative procedures, structures of newly discovered compounds were determined using one- and two-dimensional techniques of NMR spectroscopy. Among the identified compounds were caffeic acid esters with aliphatic hydroxycarboxylic acids, conjugates of dicaffeic acid with rosmarinic acid, and previously unknown isomers of isosalvianolic acid A and yunnaneic acid E, as well as other lignans. Concentrations of all identified phenolic derivatives in the investigated herbal material were estimated using a method based on liquid chromatography with high-resolution mass spectrometry detection. Seasonal changes in the concentration of metabolites were also investigated using targeted and untargeted metabolomics techniques.

Lipophilic ester and amide derivatives of rosmarinic acid protect cells against H2O2-induced DNA damage and apoptosis: The potential role of intracellular accumulation and labile iron chelation.

Phenolic acids represent abundant components contained in human diet. However, the negative charge in their carboxylic group limits their capacity to diffuse through biological membranes, thus hindering their access to cell interior. In order to promote the diffusion of rosmarinic acid through biological membranes, we synthesized several lipophilic ester- and amide-derivatives of this compound and evaluated their capacity to prevent H2O2-induced DNA damage and apoptosis in cultured human cells. Esterification of the carboxylic moiety with lipophilic groups strongly enhanced the capacity of rosmarinic acid to protect cells. On the other hand, the amide-derivatives were somewhat less effective but exerted less cytotoxicity at high concentrations. Cell uptake experiments, using ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS), illustrated different levels of intracellular accumulation among the ester- and amide-derivatives, with the first being more effectively accumulated, probably due to their extensive hydrolysis inside the cells. In conclusion, these results highlight the hitherto unrecognized fundamental importance of derivatization of diet-derived phenolic acids to unveil their biological potential.