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Seven novel triterpenoid acids and lactones with a 9β,19-cyclopropyl-1-en-3-one skeleton have been isolated from the leaves of Combretum erythrophyllum. Spectral analysis has shown these compounds to be either hydrated or dehydrated in ring C and to have unsaturated γ- or δ-lactones in their side-chains. Erythrophyllic acid, the representative compound of this series, has been identified as 3-oxo-cycloart-1,11,24-trien-21-oic acid. The most abundant compound, 3-oxo-cycloart-1,11,24-trien-23,21-olide, yielded two hydrogenolysis products when hydrogenated using Adams catalyst.

The chromonocoumarins frutinones A and B and lignans eudesmin, magnolin, yangambin and kobusin were isolated from lipophilic extract of P. gazensis. This species and two other related Polygala species were subsequently analysed by thermospray liquid chromatography–mass spectrometry and high pressure liquid chromatography coupled with photodiode-array detection. Frutinone A was also found in the roots and aerial parts of P. teretifolia and P. fruticosa, while the presence of frutinone B was limited principally to the roots. Lignans were present in the aerial parts of P. teretifolia. Frutinone A showed antifungal activity against Cladosporium cucumerinum and Candida albicans while eudesmin and kobusin were antifungal against Cladosporium cucumerinum only. © 1997 by John Wiley & Sons, Ltd.

Combretastatin B1, a polyhydroxybibenzyl compound extracted from the fruit of Combretum kraussii, known to contain 'hiccup nut' toxin, reversibly increased the duration, but not the peak or the rate of rise, of the action potential in rat sensory neurones by approximately 300%. This effect was only seen when it was applied to the extracellular side of the membrane. No effects on the resting potential were observed. K+ delayed rectifier currents were inhibited in neurones and in human myotubes with an IC50 of about 300 microM; the HERG-type inward rectifier channels in tumour cells were inhibited to a greater degree. Due to its selective action and the similarity of its blockade to that produced by class III antiarrhythmic drugs, the toxin could be the origin of compounds of potentially significant pharmacological interest.

An acidic damarane arabinofuranoside and its 17-octanor equivalent have been isolated from the leaves of the South American liana, Combretum rotundifolium. Spectral analysis has identified these two compounds as (16R)-16-O-α- l -arabinofuranosyl-3β-hydroxydammara-20,24-dien-29-oic acid and the mansumbinane, (16R)-O-α- l -arabinosyl-3β-hydroxymansumbin-13-en-28-oic acid.

Two alkaloids 1 and 2 were isolated from the seeds of Erythrophleum lasianthum. Their structures were assigned by spectroscopic and chemical means as 3 beta-hydroxynorerythrosuamine (1) and its 3-O-beta-D-glucopyranoside (2). In spontaneously beating atria, both compounds 1 and 2 showed a marked and concentration-dependent positive inotropic activity and a weak negative chronotropic activity. The positive inotropic effect induced by 1 and 2 was not modified by propranolol, prazosin, carbachol, and ranitidine plus pyrilamine. Both 1 and 2 were very active in inhibiting the Na+/K(+)-ATPase isolated from bovine cardiac sarcolemmal vesicles.

New and known combretastatins and their 2′-O-glucosides have been isolated from seeds of Combretum kraussii (Hochst.) (Combreiaceae). They showed in vitro cytoxicity and influenced the tubulin polymerization.

From the root bark of Garcinia livingstonei , three xanthone dimers have been isolated. Structure elucidation was achieved mainly by NMR and mass spectrometry, including extensive NOE difference measurements, and by comparison with monomeric prenylated xanthones previously isolated from the same plant. Garcilivin A–C are structurally related to 1,4,5-trihydroxy-3-(3-methylbut-2-enyl)-9 H -xanthen-9-one and formally derive from the corresponding diene via dimerization by a Diels-Alder-type reaction.

Five prenylated xanthones have been isolated from the root bark of Garcinia livingstonei of which four are novel natural products. The xanthone, 12b-hydroxy-des- d -garcigerrin A was previously isolated from G. gerrardii . Structure elucidation was achieved by a combination of one- and two-dimensional NMR spectroscopic techniques, mass spectroscopy and chemical methods. Two compounds are fungicidal against Cladosporium cucumerinum , a plant pathogenic fungus, whereas a third shows growth inhibitory activity against human colon carcinoma cell lines.

Two new phenolics, named typhaphthalide (a benzylphthalide) and typharin (an isocoumarin) plus sitosterol were isolated and identified from the hexane extract of the rhizomes of Typha capensis. The acetone extract yielded afzelechin, epiafzelechin, and catechin.

Isolation of the novel cycloartenoid ester methyl gardenolate A (3a) , together with gardenolic acid A (2a) and the unusual triterpenoid  -glutinol (D:B- friedo olean-5-en-3  -ol) ( 1a ) from the leaves of Combretum woodii support its differentiation from the closely related C . krausii .

Combetrum petrophilum Retief, which occurs as a small tree in isolated areas of Gauteng Province, is one of approximately 99 species of trees and climbers that comprise the subgenus Combretum in Africa (Stace, 1969, Botanical J. Linnean Soc. 62, 131, Carr, 1988). Fresh leaves were collected from the vicinity of the Strydom tunnel in the summer of 1998 and representative voucher specimens (Nos PRE 17 & 22) were deposited at the National Botanical Institute in Pretoria.

Three chromonocoumarins ( =6H, 7H-[1]benzopyrano[4,3-b][1]benzopyran-6,7-diones) 1–3 have been isolated from the leaves and the root bark of polygala fruticosa BERG. (syn. Polygala oppositifoliaL.; Polygalaceae). The structure of frutinone A (1) was established by X-ray diffraction analysis. The structures of the previously undescribed compounds frutinone B (2) and C (3) were deduced by spectroscopic methods (EI-MS, UV, IR, 1H-and 13C-NMR, including NOE and COSY) in comparison with 1. Chromonocoumarins 1–3 are the first representatives of a new type of naturally occurring compounds. Frutinone A shows strong fungicidal activity against Cladosporium cucumerinum.

The characterisation of a further novel 1α-hydroxycycloartane glycoside, mollic acid 3-β-D-xyloside, and of its genuine aglycone mollic acid is reported. Three new hydrolysis artifacts of the aglycone have been prepared and 13C .n.m.r. spectral data for these compounds are tabulated.

Two new triterpenoid rhamnopyranosides have been isolated from the leaves of Combretum imberbe and their structures established as 23-hydroxyimberbic acid 23- O -α- l -rhamnopyranoside and 23-hydroxyimberbic acid 3- O -α- l ]-rhamnopyranoside 1-acetate by spectral analysis and chemical transformations.

Three novel prenylated xanthones, 1–3, have been isolated from the root bark of Garcinia gerrardii HARVEYex T. R. SIM (G. natalensis SCHLECHTER; G. transvaalensis BURTT DAVY; Guttiferae). Structure elucidation was achieved by a combination of one- and two-dimensional NMR spectroscopic techniques, including long-range HETCOR, mass spectroscopy, and chemical methods. Garcigerrin A (1) and B (2) are pyrano derivatives of 3. They all show a rare 1,4,5 oxygenation pattern of the xanthone nucleus. Xanthone 3 is fungicidal against Cladosporium cucumerinum.

A further novel 1α-hydroxycycloartane glycoside, mollic acid α- L -arabinoside, has been identified in the leaves of Combretum molle.

A new 1α-hydroxy pentacyclic triterpenoid acid, imberbic acid, has been isolated from the leaves of Combretum imberbe and its structure established as 1α,3β-dihydroxyolean-12-en-29-oic acid by chemical and spectral analysis.

The 1α-hydroxycycloartenoid glycoside, mollic acid 3- O -α- l -arabinopyranoside has been isolated from the leaves of Combretum edwardsii , revised 13 C NMR assignments for the aglycone mollic acid are given.