Novel flavonoids from leaf extracts of Markhamia acuminata and Spathodea campanulata

The medicinal uses of Markhamia acuminata (Klotzsch) Schum. (syn. M. zanzibarica;) and Spathodea campanulata P. Beauvois (Bignoniaceae) in traditional medical systems of Africa and the limited information regarding their chemical constituents prompted the present investigation. This report deals with the flavonoid patterns of the two species with a view of chemotaxonomical significance for Bignoniaceae.

The series of naturally occurring flavonoids is extended by identification of 3',4',5,7-tetrahydroxy-5'-methoxy-flavanone and apigenin 5-O-α-L-rhamnopyranosyl-7-O-ß-D-glucopyranoside from a methanol extract of M. acuminata, while dihydrokaempferol-7-O-(2''-O-formyl)-ß-D-glucopyranoside was obtained from S. campanulata. Formic acid as an acylating acid of a carbohydrate moiety in the flavonoid series is a new discovery. They are accompanied in the leaves of M. acuminata by a series of known flavones (apigenin, luteolin, luteolin-7-rutinosid) and flavanones (naringenin, naringenin-7-rutinosid, eriocitrin), while flavones (apigenin, luteolin, diosmetin) were associated with common flavonols (quercetin-glycosides) in S. campanulata. However, it should be noted that this is the second report [1] on the presence of flavanones within the Bignoniaceae, apparently confined to the tribe Tecomeae. The occurrence of flavones and flavonols meet the known flavonoid patterns encountered in members of the Bignoniaceae. The structures of these compounds were established from spectroscopic studies.

Reference: 1. Mansoor, A., Neeru, J. et al. (1991), J. Chem. Res., Synopses 5: 109.