Phenolic Constituents of Licorice. VIII. Structures of Glicophenone and Glicoisoflavanone, and Effects of Licorice Phenolics on Methicillin-Resistant Staphylococcus aureus.

Abstract

Two new phenolic compounds, glicophenone (1) and glicoisoflavanone (2), were isolated from commercial licorice, and their structures were elucidated on the basis of spectroscopic data. Antibacterial assays of licorice phenolics for Staphylococcus aureus, including four strains of methicillin-resistant S. aureus (MRSA), and also for Escherichia coli K12 and Pseudomonas aeruginosa PAO1, were then examined. Two compounds among them, 8-(gamma,gamma-dimethylallyl)-wighteone (21) and 3'-(gamma,gamma-dimethylallyl)-kievitone (28), showed remarkable antibacterial effects [minimum inhibitory concentrations (MICs), 8 microg/ml on the MRSA strains and methicillin-sensitive S. aureus. Licochalcone A (14), gancaonin G (20), isoangustone A (24), glyasperins C (30) and D (31), glabridin, (32), licoricidin (33), glycycoumarin (34) and licocoumarone (40) showed antibacterial effects on the MRSA strains with MIC values of 16 microg/ml. Effects on the beta-lactam resistance of the MRSA strains were also examined, and licoricidin (33) noticeably decreased the resistance of the MRSA strains against oxacillin, as shown by the reduction in the MICs of oxacillin (lower than 1/128-1/1000 in the presence of 8 microg/ml of 33, and 1/8-1/32 in the presence of 4 microg/ml of 33). Mechanistic study suggested that 33 does not inhibit the formation of penicillin-binding protein 2' (PBP2'), but affects the enzymatic function of PBP2'.

Constituents of Psoralea corylifolia Fruits and Their Effects on Methicillin-Resistant Staphylococcus aureus

“…Analogous observations have also been reported on the effects of licorice phenolics on MRSA [8] and on vancomycin-resistant Enterococci (VRE) [26][27][28].…”

“…Several prenylated phenolics obtained from licorice have shown noticeable antibacterial effects on MRSA [8]. Since a number of prenylflavonoids and related compounds were isolated from P. corylifolia [5,9,10], this plant species is expected to be a resource of lead compounds for new anti-MRSA drugs.…”

Chemopreventive Effects of Licorice and Its Components

“…Licorice root contains a variety of oils, alkaloids, polysaccharides, polyamines, triterpenes, phenolic acids, flavones, flavans, chalcones, flavonoids, and isoflavonoids [14][15][16]. The major component of licorice is glycyrrhizin or glycyrrhizic acid [10,17] that is hydrolyzed in the intestine to the active glycyrrhetic acid (GA) by β-glucuronidase [18].…”

Antibacterial Compounds from Glycyrrhiza uralensis

“…Some of these flavonoids have shown inhibitory activities against bacterial growth. [10][11][12] Streptococcus mutans (S. mutans) is an oral pathogen responsible for the initiation and progression of dental caries. 14 There is an urgent need for new antimicrobial compounds that can inhibit S. mutans effectively.…”