Phytochemical studies on some species of the Leguminosae
Five species from four genera of the sub-families Caesalpinioideae and Papilionoideae of the Leguminosae have been investigated. From the root bark of Cassia sieberiana (-)-epiafzelechin lupeol and β-sitosterol were isolated. (-)-Epiafzelechin was identified by spectral analysis with particular use of ¹H NMR in resolving stereochemistry of the C-ring. Lupeol and β-sitosterol were identified by direct comparison with authentic samples. The stem bark of Cynometra hankei yielded four imidazole alkaloids, two of which were novel. The major alkaloids were identified as cynometrine and N₁-demethylcynometrine (novel) by interpretation of ¹H NMR, ¹³C NMR and mass spectral data and by the conversion of N₁-demethylcynometrine to cynometrine. One of the minor alkaloids was identified as cynodine (cynometrine-11-benzoate); this being confirmed by its saponification to cynometrine. The fourth alkaloid, isolated in very small amounts, was also novel. Its identification as N₁-demethylcynodine was confirmed by its conversion to cynodine , The seeds of this species gave the first three mentioned alkaloids. A similar examination of the stem bark of Cynometra manii did not reveal any alkaloids. The seeds of Camoensia brevicalyx yielded five quinolizidine/ indolizidine alkaloids including the known compounds camoensine and camoensidine. ¹³C NMR spectra of these alkaloids were interpreted and proved valuable in assigning H-9-H-11 stereochemistry. The major compound was identified as 12-a-hydroxycamoensine on the basis of detailed interpretation of ¹H NMR, ¹³C NMR and mass spectral data. ¹³C NMR was of particular value in assigning the position of the hydroxyl substituent and ¹H NMR in deciding its stereochemistry. A very minor component was tentatively identified as 12-hydroxycamoensidine. The fifth alkaloid appeared to be 12-hydroxy-16-methoxy-11:12,13:14-tetradehydrocamoensine, a hitherto unrecorded type of quinolizidine/indolizidine alkaloid. The biological significance of these alkaloids was briefly discussed. ·The seeds of Sesbania macrocarpa yielded a single flavonoid glycoside. Hydrolysis of the glycoside gave a flavone and a sugar, identified as kaempferol and rhamnose respectively. On the basis of the UV spectra of the glycoside and the aglycone with a range of different reagents the glycoside was identified as kaempferol-3,7dirhamnoside.