In a random screening of the anti-Candida activity of more than 500 tree species, the
acetone leaf extract of Ptaeroxylon obliquum (Thunb.) Radlk. (Sneezewood) had very good
antifungal activity against Candida albicans. We isolated the compounds responsible for
the antifungal activity by bio-assay guided fractionation. The acetone leaf extract was
separated into five fractions by solvent-solvent fractionation. The chloroform fraction was
subjected to repeated open column silica gel chromatography. We isolated two antifungal
entities and determined the structures by nuclear magnetic resonance spectroscopy. The
first entity was a mixture of β-amyrin and lupeol found frequently in other plants that
we could not separate. The second entity was a novel compound not isolated before
8,11-Dihydro-5-hydroxy-12-hydroxymethyl-2-methyl-4H-pyrano[2,3-g][1]benzoxepin-4-
one 12-O-acetate given the trivial name of obliquumol. Obliquumol had a higher activity
against some Candida albicans isolates than amphotericin B, the positive control (MIC of
0.04-0.08 compared to 0.11mg/ml) and lower cellular cytotoxicity against mouse fibroblast
cells than amphotericin B. The structure of obliquumol may represent a low toxicity new
scaffold molecule for the development of antifungal compounds.
In ’n voorlopige ondersoek na die aktiwiteit van asetoon blaarekstrakte van meer as
500 boomspesies teen Candida albicans het die ekstrak van Ptaeroxylon obliquum (Thunb.)
Radlk. (Nieshout) baie goeie aktiwiteit gehad. Ons het die aktiewe verbindings deur ’n
bioaktiwiteit-geleide proses geïsoleer. Die asetoon blaarekstrak is in vyf fraksies verdeel
deur oplosmiddel-oplosmiddel fraksionering. Die chloroform fraksie het die hoogste
aktiwiteit gehad en is onderwerp aan herhaalde oop-kolom kolomchromatografie. Ons
het twee antifungus entiteite geïsoleer en die strukture bepaal deur kernmagnetiese
resonansspektroskopie. Die eerste entiteit was ’n mengsel van β-amirien en lupeol,
verbindings wat dikwels in plante aangetref word. Die tweede entiteit was ’n molekuul
wat nog nie tevore gevind is nie, naamlik 8,11-Dihidro-5-hidroksie-12-hidroksiemetiel-2
metiel-4H-pirano[2,3-g]bensoksiepin-4-oon-12-O-asetaat waaraan ons die algemene naam
obliquumol toegeken het. Die verbinding het hoër aktiwiteit as die positiewe kontrole
amfoterisien- B teenoor Candida albicans gehad (MIK 0.04-0.08 teenoor 0.11). Dit het ook
’n laer sitotoksisiteit op muis fibroblastselle as amfoterisien-B gehad. Obliquumol se
buitengewone struktuur mag as ’n raamwerkmolekuul dien vir die ontwikkeling van nuwe
antifungusverbindings.
