Ellagitannins, ellagic acid derivatives, stilbenes and flavonoids in antibacterial stem bark and leaf extracts of African medicinal plants Combretum psidioides and Combretum fragrans

Combretum psidioides and C. fragrans are used as decoctions for diarrhea and wounds in African traditional medicine [1]. In Nigeria, C. fragrans is used for the treatment of Blackleg disease in cattle among Fulani pastoralists. There exists no research on antibacterial compounds of these species but some phytochemical investigations have been performed on C. psidioides; fourteen phenanthrenes and stilbenes are known from the heart wood and pentacyclic triterpenoids have been characterized from the roots [2].
We have found that methanol and butanol extracts of the stem bark of C. psidioides gave good growth inhibitory effects against Mycobacterium smegmatis, S. aureus and P. aeruginosa. Our UHPLC-MS-QTOF results show that the stem bark of C. psidioides contains corilagin and punicalagin along with other ellagitannins as well as ellagic acid rhamnoside. These compounds have not previously been identified in C. psidioides. In addition, combretastatin B-2 along with its dihydrostilbene derivative were for the first time identified in the stem bark of C. psidioides.
A leaf extract of C. fragrans showed promising antibacterial effects, especially against Micrococcus luteus and S. aureus. Our preliminary HPLC-DAD results indicate that this extract contains luteolin and related flavonoids and three unknown ellagitannins. Mass spectrometric data is needed to confirm the identity of the compounds.