Activity-guided fractionation of the MeOH extract of the fruits of Tetrapleura tetraptera TAUB. (Mimosaceae) afforded 4 saponins 1 4 , which exhibited strong molluscicidal properties against the schistosomiasis-transmitting snails Biomphalaria glabrata. Chemical, enzymatic, and spectral methods (DCI-MS, 'H-NMR, 'k-NMR) showed that they were N-acetylglycosides of oleanolic acid and of echinocystic acid. Apart from saponin 1 (aridanin), previously isolated from this plant, glycosides 2 4 are new naturally occurring compounds Introduction. ~ There is still an urgent need for highly potent plant molluscicides in order to avoid the transmission of the parasitic disease schistosomiasis [ 11. Tetrapleura tetraptera TAUB. (Mimosaceae), locally known as Aridan, is a large tree growing throughout the rain forest belt of West Africa. The plant has many traditional uses, mainly in the management of convulsions, leprosy, inflammation, and rheumatic pains [2]. Molluscicidal activity of this plant was reported by Adewunmi and Marquis [3]. The activity seemed to be linked to triterpenoid saponins and coumarinic compounds. Because of the strong molluscicidal properties of the fruits of Tetrapleura tetraptera, field trials have been carried out, and this tree is now considered to be a promising plant in the local control of schistosomiasis [4]. Only one active compound, a mono-N-acetylglycoside of oleanolic acid ( = 3p-hydroxyolean-12-en-28-oic acid), aridanin (l), has been isolated and identified from this species [5]. Thus, further phytochemical investigation is required. The present paper deals with the identification of additional saponins from the fruits of Tetrapleura tetraptera.
Results. -Dried fruit pulp of Tetrapleura tetraptera (200 g) collected in Nigeria was extracted successively with CH,Cl,, MeOH, and H,O. The MeOH extract (80 g) which is molluscicidal at 25 ppm was then partitioned between H,O and BuOH. Fractionation of 20 g of the BuOH extract by column chromatography on silica gel was monitored by TLC. Several of the 17 fractions collected presented a strong molluscicidal activity (< 20 ppm), namely Fractions 7, 9, 10, 11, and 12 (1150, 500, 450, 500, and 1100 mg, resp.). These fractions were further separated by reversed-phase chromatography on RP-8 or liquid-liquid chromatography [6] (see Exper. Part) to afford four saponins 1-4. Compound 1 (995 mg) was obtained from Fraction 7, 2 (60 mg) from Fraction 9, 3 (220 mg) from Fractions 11 and 12, and 4 (90 mg) from Fraction 12.
Acidic hydrolysis with 4~ HCI of saponins 1, 3, and 4 afforded oleanolic acid, identified by comparison with an authentic sample (TLC, HPLC). The aglycone of