Anthelmintic flavonoids and other compounds from Combretum glutinosum Perr. ex DC (Combretaceae) leaves

Nine known com­pounds have been isolated from Combretum glutinosum leaves, including flavonoids and triterpenes. The crystal structures of umuhengerin and (20S,24R)-ocotillone are reported for the first time; the latter structure confirms the absolute configuration. The crude extracts and the isolated com­pounds were tested for their anthelmintic activity on the larvae and adult worms of Haemonchus contortus. The best activity on both stages of the parasite was obtained with the flavonoids.
A chemical study of the hydro-ethanol extract of the leaves of Combretum glutinosum resulted in the isolation of nine com­pounds, including 5-de­methyl­sin­en­se­tin (1), umuhengerin (2), (20S,24R)-ocotillone (3), lupeol (4), β-sitosterol (5), oleanolic acid (6), betulinic acid (7), corymbosin (8) and β-sito­sterol glucoside (9). Four com­pounds have been isolated for the first time from the genus Combretum [viz. (1), (2), (3) and (8)]. The crystal structures of flavonoid (2), C20H20O8, Z′ = 2, and triterpene (3), C30H50O3, Z′ = 1, have been determined for the first time; the latter confirmed the absolute configuration of native (20S,24R)-ocotillone previously derived from the crystal structures of related derivatives. The mol­ecules of (3) are linked into supra­molecular chains by inter­molecular O—H⋯O hydrogen bonds. The crude extracts obtained by aqueous decoction and hydro-ethano­lic maceration, as well as the nine isolated com­pounds, were tested for their anthelmintic activity on the larvae and adult worms of Haemonchus contortus, a hematophage that causes parasitic disorders in small ruminants. The evaluated anthelmintic activity showed that the extracts at different doses, as well as all the com­pounds tested at 150 µg ml−1, inhibited the migration of the larvae and the motility of the adult worms of the parasite com­pared with the phosphate buffer solution negative reference control. The best activity was obtained with flavonoids (1), (2) and (8) on both stages of the parasite. The flavones that showed good activity can be used for the further development of other derivatives, which could increase the anthelmintic efficacy.