Prenylated polyphenolic compounds from Glycyrrhiza iconica and their antimicrobial and antioxidant activities

Abstract

A new prenylated isoflavan, iconisoflavan (1), and a new prenylated isoflav-3-ene, iconisoflaven (2) were isolated from the roots of Glycyrrhiza iconica together with four known ones namely (3S)-licoricidin (3), licorisoflavan A (4), topazolin (5) and glycycoumarin (6). The structures were elucidated on the basis of extensive spectroscopic analysis including 1D and 2D NMR as well as HR-MS. Furthermore, the absolute configurations of compounds 1, 3 and 4 were established by electronic circular dichroism (ECD). All the isolated compounds (1-6) were evaluated for their in vitro antimicrobial activities against five pathogenic bacteria and one yeast (Candida albicans) using an in vitro microdilution method. Compounds 1 and 3-5 displayed significant activity against Salmonella typhimurium ATCC 13311 with MIC values ranging from 2 to 8 μg/mL. Additionally, all compounds were screened for their in vitro free radical scavenging activities using an in vitro microdilution DPPH assay spectrofotometrically. The tested compounds exhibited IC50 values in the range of 0.18-0.56 mg/mL, suggesting an activity comparable with that of ascorbic acid (IC50: 0.07 mg/mL). To the best of our knowledge, the present study constitutes the first phytochemical and bioactivity investigation on G. iconica.

Keywords: Antimicrobial and antioxidant activities; Fabaceae; Glycyrrhiza iconica; Isoflavonoids.