Isolation of chemical compounds and their biological activity analysis from Nepalese medicinal plants

Abstract

Medicinal plants are one of the major sources of drugs all over the world. People have been using medicinal plants as traditional medicine, rationale herbal drug or as a source of therapeutically pure compounds. The various forms include extract, paste, decoction, fumes, burnt form etc. with notable bioactivities. The bio-inactive compounds serve as lead compounds for the synthesis or partial synthesis of very important drugs. The Nepalese biosphere has developed high biodiversity of medicinal plants between 60 m and 8848 m (Mt. Everest). Results obtained from our ongoing studies on Nepalese medicinal plants have been discussed in this thesis. On the basis of traditional uses, availability, ethnomedicinal uses and chemical and biological virginity, six Nepalese medicinal plants: Aconogonon molle, Bombax ceiba, Pterocarpus marsupium, Swertia angustifolia, Begonia picta and Leea aspera have been selected and studied. Chemical isolation and biological activity analysis of these plants has been performed. From these plants total 100 compounds were isolated with 6 new compounds with different classes like; flavonoids, xanthones, coumarins, iridoids, lignans, chalcones, phenolic acids, terpenoids, etc. Three new glycosides: thotneoside A, thotneoside B and thotneoside C together with 16 known compounds were isolated from the leaves of Aconogonon molle. Similarly, 16 known compounds from the flowers and 11 known compounds from the stem were also isolated. Two new aromatic compounds: simalin A and simalin B along with 5 known compounds were isolated from the stem bark of Bombax ceiba and 24 known compounds were also isolated from the flowers. A new chalcone: bijayasaline and 6 known compounds were isolated from the heartwood of Pterocarpus marsupium. Four known compounds were isolated from the whole plant of Swertia angustifolia. Five known compounds were isolated from the whole plant of Begonia picta. Seven known compounds were isolated from the aerial parts of Leea aspera. The structures of these compounds were elucidated on the basis of UV, IR, NMR, MS and CD spectral data, chemical methods and comparison with literatures data. The antioxidant activities of the isolated phenolic compounds were analyzed by DPPH scavenging activity analysis. The IC50 values of potent compounds were compared with Trolox as positive control. Compounds like: thotneoside (1), thotneoside B (2) quercetin (4), quercetin 3-O--D-galactopyranoside (5), quercetin 3-O-(6’’-O-galloyl)--D-galactopyranoside (6), quercetin 3-O--D-galacturonopyranoside (7), quercetin 3-O--D-glucuronopyranoside (8), quercetin 3-O--L-rhamnopyranoside (9), rutin (10), quercetin 3-O--L-arabinopyranoside (11), epicatechin-3-O-gallate (14), 1,3,6-tri-O-galloyl glucopyranoside (15), gallic acid (16), quercetin-3-O-(6’’-O-caffeoyl)--D-galactopyranoside (20), quercetin-3-O--D-glucopyranoside (21), quercetin-3-O--L-arabinofuranoside (22), isomangiferin (44), mangiferin (45), bijayasaline (61), pterostilbene (62), orientin (63) and isoorientin (64) have shown potent antioxidant activity. The extract of B. ceiba flowers, A. molle flowers and L. aspera aerial parts showed the potent anti-inflammatory activity towards inhibition of TNF-α secretion in the presence of LPS in a murine RAW264.7 macrophage cell line and -hexosaminidase activity (%) inhibition in a RBL-2H3 cell line.