Chemical Investigation Of Two Millettia And Two Erythrina Species (leguminosae) For Bioactive Constituents

Abstract

The family Leguminosae, with some 18,000 species and 650 genera, is the second largest family of dicotyledons. It is divided into three subfamilies; namely Mimosoideae, Caesalpinoideae and Papilionoideae. The family is known for elaborating a wide range of flavonoids including isoflavonoids, the latter being more or less restricted to the subfamily Papilionoideae. Isoflavonoids are known to possess a wide range of biological activities, the most prominent of which being insecticidal and antimicrobial properties. The insecticidal activities are associated with rotenoids which are mainly found in the tribe Tephroseae (including the genus Millettia) , while the antimicrobial activities with pterocarpans and flavanones which are found in the tribe Phaseoleae (including the genus Erythrina). In this study two Millettia and two Erythrina species have been investigated for compounds with potential insecticidal and antimicrobial activities. ..-~'" - Chemical investigation of th& seeds, seed pods and stem bark of two Millettia species (M. dura and M. usaramensis subspecies usaramensis) resulted In the isolation and characterization of isoflavones, rotenoids and chalcones. M. dura produced five novel isoflavones (durallone (1), 6demethyldurallone (2), predurallone (3), isoerythrin-A 4'-(3methylbut-2-enyl) ether (4) and 6-methoxycalopogonium xix isoflavone-A (5)), known isoflavones (formononetin (6), ferrugone (7), jamaicin (8), durmillone (13), calopogonium isoflavone A (14), maximaisoflavone D (15) and maximaisoflavone H (16) ) These isoflavones have lost oxygenation at C-5 and in most cases additional oxygenation occur at C-6, C-8 and/or C-3'. Such oxygenation pattern reflects the taxonomic affinity of M. dura to M. ferruginea. The rotenoids millettone (9), millettosin (10), deguelin (11) and tephrosin (12) have also been isolated from this plant. The second Millettia species investigated, M. usaramensis subsp. usaramensis, produced four new rotenoids wi th trans-B/C ring junction (12a-epimillettosin (17), usararotenoid-A (18), 12-dihydrousararotenoid-A (19), and usararotenoid-B (20)) These compounds represent the first natural rotenoids with 6aR,6aS B/C- ring junction. This plant also elaborated a new QI-hydroxydihydrochalcone (4' -geranyloxY-Ql,4,2'trihydroxydihydrochalcone (21) , a new isoflavone (norisojamaicin (22)) and a new cinnamyl derivative (4-0geranylc innamyl acetate (23)) .::~-T"Woknown chalcones (4'-0geranylisoliquiritigenin (24) and· isoliquiritigenin (25)), four known isoflavones (barbigerone (26), jamaicin (8), maximaisoflavone G (27) and toxicarolisoflavone (29)) and a triterpene (lupeol (28)) were also isolated from this plant. The bark of two Erythrina species (E. burttii and E. sacleuxii) were also investigated resulting in the isolation and characterization of several flavonoids. From the stem bark XlX isoflavone-A (5) ) , known isoflavones (formononetin (6) , ferrugone (7), jamaicin (8), durmillone (13), calopogonium isoflavone A (14) , (16) ) maximaisoflavone D (15) and maximaisoflavone H These isoflavones have lost oxygenation at 'C-5 and in most cases additional oxygenation occur at C-6, C-8 and/or C-3'. Such oxygenation pattern reflects the taxonomic affinity of M. dura to M. ferruginea. The rotenoids millettone (9), millettosin (10), deguelin (11) and tephrosin (12) have also been isol~ted from this plant. The second Millettia species investigated, M. usaramensis subsp. usaramensis, produced four new rotenoids with trans-B/C ring junction (12a-epimillettosin (17), usararotenoid-A (18), 12-dihydrousararotenoid-A (19), and usararotenoid-B (20)) These compounds represent the first natural rotenoids with 6aR,6aS B/C- ring junction. This plant also elaborated a new a-hydroxydihydrochalcone (4' -geranyloxy-a, 4,2'trihydroxydihydrochalcone (21) , a new isoflavone (norisojamaicin (22)) and a new cinnamyl derivative (4-0- .•.--- - geranylcinnamyl acetate (23)) Two known chalcones (4'-0geranylisoliquiritigenin (24) and i·soliquiritigenin (25)), four known isoflavones (barbigerone (26), jamaicin (8), maximaisoflavone G (27) and toxicarolisoflavone (29)) and a triterpene (lupeol (28)) were also isolated from this plant. The bark of two Erythrina species (E. burttii and E. sacleuxii) were also investigated resulting in the isolation and characterization of several flavonoids. From the stem bark xx of Erythrina burttii two new flavanones (abyssinone V-4'methyl ether (30) and burttinone (32)) were characterized. In addition known fl~vanones (abyssinone V (31) and sigmoidin B- 4' -methyl ether (33)), pterocarpans (calopocarpin (34) and neorautenol (35»), an isoflavanone (bidwillon A (36)), a chalcone (isobavachalcone (37) ) and a cinnamyl ester (erythrinasinate (38)) were isolated. In the same way, from the stem bark of E. sacleuxii a new isoflavanone (saclenone-A (39)) and four new isoflavones (7- demethylrobustigenin (40),3'- (3-methylbut-2-enyl)biochanin A (41) , 5'-(3-methylbut-2-enyl)pratensien (42) and 5' - formylpratensein (43)) were isolated and characterized. Some of the isolated compounds and their derivatives were tested for larvicidal, anti-feedant, antibacterial, anti fungal, anti -brine shrimp, cell growth inhibitory and antimalarial activities. Potent larvicidal activities against the larvae of Aedes aegypti were observed for deguelin and tephrosin. Anti -feedant acti vi ties against the 5th instar --- - nymphs of Locus ta migra t.oxi-e were observed for deguelin, tephrosin and calopocarpin ~ . Antibacterial (against Staphylococcus aureus and Bacillus subtilis) and antifungal activities (against Saccharomyces cerevi siae, Candida albicans, Trichophyton mentagrophyte and Microsporum gypsum) were observed with a,4,2'-trihydroxy-4'-O-geranyldihydrochalcone, calopocarpin, neorautenol, sigmoidin B-4'methyl ether and bidwillon A. Cell growth inhibitory