Aims: Actinobacteria, the Gram positive bacteria are known to produce about 10,000 bioactive secondary metabolites. Among them, 80% of the metabolites are produced by Streptomyces like antibiotics, anticancer, antimicrobial, antioxidant, enzymes, etc. But most of the Streptomyces species are still to be explored for the different bioactivities. Hence, the present work is designed to evaluate the antioxidant activities of the secondary metabolites produced by the strains of Streptomyces designated as OS-6 and TES-25 on the free radicals generated in the different in vitro assays. Methodology and results: The antioxidant activity of ethyl acetate and chloroform extracts of OS-6 and TES-25 was analyzed by performing different antioxidant assays viz. molybdate ion reduction assay, DPPH radical scavenging assay, ABTS radical cation decolourization assay, reducing power assay, deoxyribose degradation assay, lipid peroxidation assay, superoxide anion scavenging assay and DNA nicking assay. The total phenolic content was also determined. The findings showed that maximum hydrogen or electron donating and hydroxyl radical scavenging activities were exhibited by OS-6 ethyl acetate extract in all the assays. Conclusion, significance and impact of study: The potent antioxidant activity may be due to the presence of different polyphenolic compounds as depicted from the total phenolic content of the extracts. Further study includes the isolation of compounds responsible for the antioxidant activity.

Alkannin/shikonin (A/S) and their derivatives are naturally occurring naphthoquinones majorly found in Boraginaceae family plants. They are integral constituents of traditional Chinese medicine Zicao (roots of Lithospermum erythrorhizon). In last two decades significant increase in pharmacological investigations on alkannin/shikonin and their derivatives has been reported that resulted in discovery of their novel mechanisms in various diseases and disorders. This review throws light on recently conducted pharmacological investigations on alkannin/shikonin and their derivatives and their outputs. Various analytical aspects are also discussed and brief summary of patent applications on inventions containing alkannin/shikonin and its derivatives is also provided.