Phytochemistry studies on some leguminosae of the Yucatan Peninsula / Rocío de Lourdes Borges Argaez

Tesis (Doctor of Philosophy) .-- Souther Cross University. Centre for Phytochemistry, 2003.

The work described in this thesis deals with fue chemistry of Leguminosae plants belonging to fue genera Lonchocarpus and Pithecellobium. The three plants studied are considered endemic (Lonchocarpus yucatanensis and Pithecellobium albicans) or quasi-endemic (Lonchocarpus xuul) species of the Yucatan Peninsula. Although all three plants are well distributed in the region, little or nothing is known about their chemical constituents. The main objective of ibis project was to identify fue major chemical constituents of fue three plants and to examine these in the context of their bioactivity and as systematic markers. Plant extracts were obtained by successive extraction of powdered plant material using methanol followed by a partition procedure using solvents of increasing polarity. The extracts were fractionated using standard chromatographic methods (column chromatography, VLC, preparative TLC and Sephadex LH-20 column), resulting in the isolation of pure metabolites. Purified products were identified by interpretation of their spectroscopic data and by comparing their data with those published in fue literature, where applicable. The two Lonchocarpus species afforded a unique series of flavonoids while P. albicans produced both common flavonoids and triterpenoid metabolites. The leaf extract of L. xuul yielded a total of eight metabolites that were identified as N-methyl-proline (188), p-coumaric acid methyl ester (181), and six flavonoids. Three of the flavonoids are novel and they were identified as fue chalcone 2´,4-dimethoxylonchocarpin (180), and the flavones, 5,4´-dimethoxy-(6:7)-2,2- dimethylpyranoflavone (182), and 5,4 ´-dihydroxy,3 ´-methoxy-(6:7)-2,2-dimethylpyrano flavone (183). The other three flavonoids are known compounds namely 5,4´- dihydroxy-(6:7)-2,2-dimethylpyranoflavone (184), quercetin-3-0-rutinoside (185) and kaempferol-3-0-rutinoside (186). The stem bark of L. xuul afforded the novel compounds 5-methoxy-(6:7)-2,2- dimethylpyranoflav -3 -ene (189), 413, 5-dimethoxy-( 6: 7)- 2,2-dimethylpyranoflavan (190), 3 13,4 13, 5-trimethoxy-( 6: 7)- 2,2-dimethylpyranoflavan (192), 313,413-dihydroxy-5- methoxy-(6:7)-2,2-dimethylpyranoflavan (195) and 413-5-dimethoxy-313-hydroxy-(6:7)- 2,2-dimethylpyranoflavan (194), together with the known 5,7-dihydroxy-6,8-di-(3- methylbut-2-enyl)flavanone (191) and the probable artefacts 413-ethoxy-5-methoxy- I (6:7)-2,2-dimethylpyranoflavan (193) and 3,4-epoxy-5-methoxy-(6:7)-2,2- dimethylpyranoflavan (200). The root extract of L. xuul produced fue same metabolites present in the stem bark together with the known 2´,4´-dihydroxy-3´-(3-methylbut-2- enyl) chalcone (196). Except for metabolites 191 and 196 isolated only from fue root and stem bark of L. xuul, fue same metabolites were found in the root, stem bark and leaf extracts of L. yucatanensis. A further new flavanone 5-hydroxy(6:7)-2,2-dimethylpyranoflavanone (199) and a new flavan 3B3,4B3,5-trimethoxy-4 ´-hydroxy(6:7)-2,2-dimethylpyranoflavan (197) were also isolated from the root extract of L. yucatanensis. The known compounds isolated from L. xuul and L. yucatanensis were all previously reported in the Leguminosae but not in these species before. The phytochemical study of P. albicans yielded a total of six metabolites: four triterpenes and two flavonoids. The triterpenes were isolated from the stem bark and identified as lupeol (13), B3-amyrin (150), B3-amyrenone (204) and f3-sitosterol (16). The flavonoids were isolated from fue leaf extract and identified as kaempferol-3-0- rhamnoside (202) and quercetin-3-0-rhamnoside (203). Cytotoxicity testing of the isolated flavonoids using the A TP Lite Method, showed that five compounds exhibited cytotoxicity against mouse (P-388) lymphocytic leukaemia cells: 196 (IC50 = 57uM), 194 (IC50 =76uM), 195 (IC50 =51 uM), 197 (IC50 =80 uM) and 182 (IC50 =34 uM). Further evaluation of these metabolites carried out in the cell cycle assay revealed that chalcone 196 caused a G2/M block effect in prostate cancer cells. Finally, data on flavonoid content and substitution pattems from each species, obtained from literature reports, allowed the building of biosynthetic flow-charts of flavonoid type (s) and substitution pattems at intra-generic level. From this analysis it can be concluded that prenylation pattems and flavonoid pattems currently produce no discemable systematic separations in the genus and do not appear to be of great value as chemosystematic markers at this level.