Bioassay guided isolation of naphthoquinones from Onosma aksoyii, investigation of their cytotoxic properties

The genus Onosma L. (Boraginaceae) includes about 230 species, distributed mainly in the Mediterranean region and Central Asia. Major constituents of Onosma species are alkaloids, naphthoquinones, polyphenols, phytosterols, terpenoids and fatty acids [1], [2].

Naphthoquinones are naturally widespread secondary metabolites deriving from some higher plants, fungi and bacteria. They exhibit significant biological activities such as cytotoxicity, antimalarial, antibacterial, antifungal and wound healing [2], [3]. Recently naphthoquinone derivatives have also been recognized as potent topoisomerase inhibitors [4].

As part of our ongoing studies performed on Turkish Onosma species, we carried out cytotoxicity guided isolation studies to identify and characterize new naphthoquinone-type constituents from Onosma aksoyii, Aytaç&Türkmen a recently determined endemic species.

As a result, four compounds, one of which was new (1), were isolated from O. aksoyii, and their structures were elucidated by spectral methods (NMR and MS). According to the cytotoxicity screening results, IC₅₀ values of these compounds were ranging between 6.485 μM and 32 μM. Further studies are in progress to determine DNA topoisomerase inhibitory effects of the isolated compounds.

Fig. 1 Structure of compound 1

• References

• 1 Al-Shehbaz IA. The genera of boraginaceae in the southeastern United States. J Arnold Arbor Suppl Ser 2018; 1 (05) : 1-169.
• 2 Kumar N, Kumar R, Kishore K. Onosma L.: a review of phytochemistry and ethnopharmacology. Pharmacogn Rev 2013; 7 (14) : 140.
• 3 Binzet RA. New species of Onosma L. (Boraginaceae) from Anotolia. Turk J Botany 2016; 40 (02) : 194-200.
• 4 Liu LF. DNA topoisomerase poisons as antitumor drugs. Annu Rev Biochem 1989; 58 (01) : 351-375.