Protocetraric acid: an excellent broad spectrum compound from the lichen Usnea albopunctata against medically important microbes.

The aim of this study was to investigate the antimicrobial property of the compounds present in the lichen Usnea albopunctata. Ethyl acetate extract of the lichen was purified by column chromatography to yield a major compound which was characterised by spectroscopic methods as protocetraric acid. In this study, protocetraric acid recorded significant broad spectrum antimicrobial property against medically important human pathogenic microbes. The prominent antibacterial activity was recorded against Salmonella typhi (0.5 µg/mL). Significant antifungal activity was recorded against Trichophyton rubrum (1 µg/mL), which is significantly better that the standard antifungal agent. Protocetraric acid is reported here for the first time from U. albopunctata. Thus the results of this study suggest that protocetraric acid has significant antimicrobial activities and has a strong potential to be developed as an antimicrobial drug against pathogenic microbes.

Cyclo(L-Pro-D-Arg): a new antibacterial and antitumour diketopiperazine from Bacillus cereus associated with a rhabditid entomopathogenic.

In continuation of our search for new antimicrobial secondary metabolites from Bacillus cereus associated with rhabditid entomopathogenic nematode, a new microbial diketopiperazine, cyclo(L-Pro-D-Arg), was isolated from the ethyl acetate extract of fermented modified nutrient broth. The chemical structures of the isolated compounds were identified based on their 1D, 2D NMR and high-resolution electrospray ionisation-mass spectroscopy data. Antibacterial activity of the compound was determined by minimum inhibitory concentration and disc diffusion method against medically important bacteria, and the compound was recorded to have significant antibacterial activity against test bacteria. The highest activity was recorded against Klebsiella pneumoniae (1 µg/mL). Cyclo(L-Pro-D-Arg) was recorded to have significant antitumor activity against HeLa cells (IC50 value 50 µg/mL), and this compound was recorded to have no cytotoxicity against normal monkey kidney cells (VERO) up to 100 µg/mL). To the best of our knowledge, this is the first time that cyclo(L-Pro-D-Arg) has been isolated from a microbial natural source.