Sutherlandia frutescens (syn. Lessertia frutescens)has been used as traditional medicine in South Africa for numerous ailments. In this study, plant material was extracted with dichloromethane (DCM), methanol (MeOH) in a Soxhlet apparatus. And then the methanol extract was partitioned into ethyl acetate (EtOAc), 1-butanol (BuOH) and water. The dichloromethane extract, the ethyl acetate extract and the butanol extracts were subjected to further separation; several compounds were isolated by Versaflash normal phase column and reverse phase column, low pressure column chromatography with Sephadex LH20, Toyopearl and MCI CHP20P, and preparative high pressure liquid chromatography (HPLC). 1H- and 13C-NMR-spectroscopy were used to elucidate the structure of these isolated compounds. Antioxidant activity was measured by 1,1- diphenyl-2-picrylhydrazyl radical (DPPH)-radical scavenging, and inhibition of 15-lipoxygenase enzyme (15-LO) from soybeans.
Flavonoids and triterpenoids were suggested to be present by our South African collaborators, some of these substances have been isolated and identified from the EtOAc- and BuOH-extracts. A series of flavonoid glycosides with a hydroxymethylglutaryl moiety and a kaempferol or quercetin aglycone and the known triterpene glucoside sutherlandioside C were isolated. In addition, a substance which appears to be a C-24-epimer or a regioisomer of sutherlandioside C with the glucose moiety bound to C-24 instead of C-25) has been isolated. This is not reported in Sutherlandia frutescens before, and appears to be a new natural product. From preliminary data, the known sutherlandiosides B and D and their 24-epimers / regioiomers appear to be present, as well. In the DCM extract we found 4-hydroxybenzaldehyde. This is not an uncommon natural product, but it has not been reported previously from the genus Lessertia or Sutherlandia. And also in the DCM extract there was found an unknown compound, which might be 6- or 7-methoxylated chromanone, isocoumarin or dihydrobenzofuran. Calculated NMR spectra for these compounds are, however, not in accord with observed data.
The DCM extract and the EtOAc extracts showed higher 15-LO activity than other extracts. In the DPPH-test all extracts had low radical scavenging activity.