Abstract
Chemical investigation on the constituents of Landoltia punctata led to the isolation and identification of 17 compounds, four of which were new and identified as (3β,24S)-9,19-cycloartane-3,22,24,25-tetraol 3-O-[β-d-glucopyranosyl-(1→2)]-[β-d-glucopyranosyl-(1→6)]-β-d-glucopyranoside (1), (3β,24S)-9,19-cycloartane-3,24,25-triol 3-O-[β-d-glucopyranosyl-(1→2)]-[β-d-glucopyranosyl-(1→6)]-β-d-glucopyranoside (2), 3,4'-dihydroxy-7,3'-dimethoxyflavan-5-O-β-d-glucopyranoside (3) and 3,4'-dihydroxy-4,7,3'-trimethoxyflavan-5-O-β-d-glucopyranoside (4). Their structures were elucidated by spectroscopic, chemical, and biochemical methods. Thus, cycloartane triterpenoids were discovered in the Lemnaceae family for the first time. Compound 3 showed antioxidant capacity in the positively charged 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radical (ABTS+•) and superoxide anion radical scavenging assays.
Highlights
The plant of the Lemnaceae, commonly known as duckweed, is a kind of aquatic monocot angiosperm and the smallest with flowers, which is widely distributed on the surface of still, slowly flowing, and polluted waters around the World
We identified 12 flavonoids including two new flavanol glucosides from L. punctata
The result showed that apigenin or luteolin flavonoids are the main constituents of this species, which is in good agreement with the previous reports and our previous study results that the transcripts for key enzymes of flavonoid biosynthesis in L. punctata expressed in high abundance at the transcriptional level [9,10,34]
Summary
The plant of the Lemnaceae, commonly known as duckweed, is a kind of aquatic monocot angiosperm and the smallest with flowers, which is widely distributed on the surface of still, slowly flowing, and polluted waters around the World. Four new compounds: (3β,24S)-9,19-cycloartane-3,22,24,25-tetraol 3-O-[β-D-glucopyranosyl-(1→2)]-[β-Dglucopyranosyl-(1→6)]-β-D-glucopyranoside (1), (3β,24S)-9,19-cycloartane-3,24,25-triol 3-O-[β-Dglucopyranosyl-(1→2)]-[β-D-glucopyranosyl-(1→6)]-β-D-glucopyranoside (2), 3,4'-dihydroxy-7,3'dimethoxyflavan-5-O-β-D-glucopyranoside (3) and 3,4'-dihydroxy-4,7,3'-trimethoxyflavan-5-O-β-Dglucopyranoside (4), (Figure 1), together with 13 known ones apigenin (5), luteolin (6), apigenin-7-Oβ-glucoside (7), luteolin-7-O-β-glucoside (8) [11], vitexin (9), isovitexin (10), orientin (11), isoorientin (12) [12], 6,8-di-C-β-glucosylapigenin (13) [13], 6-C-β-glucosyl-8-C-β-galactosylapigenin (14) [14], β-sitosterol (15), stigmasterol (16) [15], 5,22-diene-3,6-dicarbonyl-stigmasterol (17) [16] were isolated and identified from the 95% ethanol extract of L. punctata This is the first report of cycloartane-type triterpenoids from the Lemnaceae family. The isolation and structural elucidation of these compounds as well as bioactivities of compound 3 were described
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