Metabolites with Antioxidant and Photo-Protective Properties from Usnea roccellina Motyka, a Lichen from Colombian Andes

The antioxidant and photo-protective efficacy of the extract and isolated compounds from the lichen Usnea rocellina Motyka were evaluated. The antioxidant activity was determined by scavenging the DPPH radicals and ferric reducing power. The photo-protective property of extracts and isolated compound against ultraviolet A (UVA) and B (UVB) radiations was measured in vitro by calculation of their sun protection factor (SPF), critical wavelength and UVA ratio comparing to commercialised sunscreens (avobenzone and benzophenone-3). 3-methoxycarbonyl-2-hydroxy-6-methoxy-4-methylbenzoic acid (1), reported here for the first time, along with (+)-(9b-R)-usnic acid (2) and decarboxythamnolic acid (3) were isolated. The structure of the isolated compounds was characterized by interpreting their spectroscopic (NMR, IR, UV), and spectrometric data. The findings of this study demonstrated that the compound 3 is a better antioxidant compared to other isolated compound and extract, and was similar to standard (BHT and ascorbic acid) ascorbic acid. On the other hand, 1 showed to be an UVB absorbing with a moderate in vitro SPF whereas 2 and 3 showed broad UVB and UVA absorbing properties. The possible skin penetration, determined by calculating octanol/water partition coefficients allowed to confirm this property in 2 and 3. These results suggest 3 as a dual agent with antioxidant and broad spectrum absorbing properties therefore it is able to prevent oxidative skin damage caused by solar radiation.