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SARS CoV-2 a pandemic influenza like infectious disease emerged in December 2019 has spread throughout the world within few months. Scientists are trying their best to find medicine and vaccine. Usnic acid and its derivatives as herbal supplements are widely used as mouth wash, cosmetics, antiviral agents. In this study, usnic acid and its derivative-sodium usnate in comparison with favipiravir are docked with main protease and spike protein RBD 6M0J of SARS Cov-2. Usnic acid and sodium usnate exhibit better binding affinities for main protease and spike RBD. The data has been compared with favipiravir. Favipiravir, usnic acid, sodium usnate shows binding affinity of -4.25, -8.05 and -8.55 kcal/mol respectively with main protease. While favipiravir, usnic acid and sodium usnate exhibit binding affinities of -4.25, -6.02 and -6.53 kcal/mol with spike RBD respectively. One of the interesting features is that the inhibition constant values of usnic acid is 1.27 µM and sodium usnate is 539.86 nM in comparison to favipiravir (764.13 µM) with main protease.

Photodegradation of 2.6 x 10(-5) M aqueous solutions of sodium usnate at various pH was studied. Photodegradation appeared to follow first-order kinetics and was found to be pH dependent. The degradation rate constant was calculated to be 9.20 x 10(-4) min-1, 5.93 x 10(-4) min-1, 9.69 x 10(-4) min-1, and 9.88 x 10(-4) min-1 at pH 6, pH 7, pH 8, and pH 9, respectively.

New, simple, cost effective, accurate and reproducible UV-spectrophotometric methods were developed and validated for the estimation of sodium usnate in pharmaceutical preparations. Sodium usnate was estimated at 290 nm in water and phosphate buffer (pH 3):methanol (11:20 V/V). Beer’s law was obeyed in the concentration range of 0.1–5 μg·cm −3 (r = 0.997) in water and 1–12 μg·cm −3 (r = 0.999) in the phosphate buffer:methanol. The apparent molar absorptivity and Sandell’s sensitivity coefficient were found to be 3.16×10 4 dm 3 ·mol −1 ·cm −1 and 11.58 ng·cm –2 /0.001 A in water and 3.72×104 dm 3 ·mol −1 ·cm −1 and 9.83 ng·cm –2 /0.001 A in phosphate buffer:methanol, respectively, indicating the high sensitivity of the proposed methods. These methods were tested and validated for various parameters according to ICH guidelines. The detection and quantitation limits were found to be 0.0721 and 0.2163 μg·cm –3 in water and 0.163, 0.489 μg·cm −3 in phosphate buffer:methanol, respectively. The proposed methods were successfully applied for the determination of sodium usnate in pharmaceutical preparations. The results demonstrated that the procedure is accurate, precise and reproducible (R.S.D. < 2 %).