Flavonoids from the Genus Euphorbia: Isolation, Structure, Pharmacological Activities and Structure–Activity Relationships

Abstract

Plants of the genus Euphorbia are widely distributed across temperate, tropical and subtropical regions of South America, Asia and Africa with established Ayurvedic, Chinese and Malay ethnomedical records. The present review reports the isolation, occurrence, phytochemistry, biological properties, therapeutic potential and structure–activity relationship of Euphorbia flavonoids for the period covering 2000–2020, while identifying potential areas for future studies aimed at development of new therapeutic agents from these plants. The findings suggest that the extracts and isolated flavonoids possess anticancer, antiproliferative, antimalarial, antibacterial, anti-venom, anti-inflammatory, anti-hepatitis and antioxidant properties and have different mechanisms of action against cancer cells. Of the investigated species, over 80 different types of flavonoids have been isolated to date. Most of the isolated flavonoids were flavonols and comprised simple O-substitution patterns, C-methylation and prenylation. Others had a glycoside, glycosidic linkages and a carbohydrate attached at either C-3 or C-7, and were designated as d-glucose, l-rhamnose or glucorhamnose. The structure–activity relationship studies showed that methylation of the hydroxyl groups on C-3 or C-7 reduces the activities while glycosylation loses the activity and that the parent skeletal structure is essential in retaining the activity. These constituents can therefore offer potential alternative scaffolds towards development of new Euphorbia-based therapeutic agents.

Biotransformation of Flavonoids Improves Antimicrobial and Anti-Breast Cancer Activities In Vitro

“…The effect of antimicrobial activities was particularly relevant to the conversion of highly hydrophilic groups and steric hindrance of reactive sites [26]. Magozwi et al revealed that methylation of the hydroxyl groups on C-3 or C-7 reduced the antimicrobial activity of flavonoids [27]. Research on quercetin indicated that the loss of a hydroxyl group at C-3 was associated with low activity [27].…”

New Insights on Euphorbia dendroides L. (Euphorbiaceae): Polyphenol Profile and Biological Properties of Hydroalcoholic Extracts from Aerial Parts

“…Much research has been carried out in order to highlight the phytochemical profile of different Euphorbia spp. This has allowed the identification of numerous classes of secondary metabolites with marked health properties, including multi-drug resistance modulatory activity, antiproliferative, cytotoxic, antiviral, antimicrobial, antioxidant, and anti-inflammatory activity [ 5 , 9 , 13 , 14 , 17 , 19 , 20 ].…”

“…Among these compounds, the most representative are sesquiterpenes, diterpenes, triterpenes, steroids, cerebrosides, phenolic compounds, tannins, and coumarins [ 5 , 20 ].…”

“…Beyond the phenolic acids, the extracts investigated in the present study showed, unlike those investigated previously, a high content of flavonoids as well, with rutin as the most abundant compound ranging from 200 to10,000 times higher with respect to previous results [ 17 ]. This flavonoid was identified also in other Euphorbia species such as E. lathyris and E. geniculate , in which also other quercetin derivatives such as quercetin-3- O -rhamnoside and quercetin-3- O -D-glucopyranoside as well as the aglycon (quercetin) were identified [ 20 ]. On the contrary, rutin is completely absent in the methanol latex extract previously investigated, characterized by the abundant presence of eryodictiol-7- O -glucoside, eriodyctiol, naringenin-7- O -glucoside, naringenin, and quercetin [ 9 ].…”

“…Structure–activity relationship studies showed that methylation of the hydroxyl groups on the C-3 or C-7 position decreases the activities while glycosylation loses the activity. In any case, the parent compound is essential in preserving biological activity [ 20 ]. Indeed, observing the average behaviour of the extracts in terms of antioxidant activity, it can be deduced that FE, the extract richer in rutin and isorhamnetin-3- O -rutinoside (both flavonols), shows the strongest antioxidant activity, followed by FrE, which is the most diversified extract in terms of flavonoid content, followed by LE and BE.…”