Abstract
To obtain diterpene glycosides from an aqueous extract of the aerial parts of Isodon henryi and further investigate their cytotoxicities, in this study, a total of seven compounds were isolated, including six ent-kaurane diterpene glycosides (1–6) and one diterpene aglycon (7). Among the seven ent-kaurane diterpenes obtained, four were novel compounds, including ent-7,20-epoxy- kaur-16-en-1α,6β,7β,15β-tetrahydroxyl-11-O-β-d-glucopyranoside (1), ent-7,20-epoxy-kaur-16-en- 6β,7β,14β,15β-tetrahydroxyl-1-O-β-d-glucopyranoside (2), ent-7,20-epoxy-kaur-16-en-6β,7β,15β- trihydroxyl-1-O-β-d-glucopyranoside (3), and ent-7,20-epoxy-kaur-16-en-7β,11β,14α,15β-tetrahydr- oxyl-6-O-β-d-glucopyranoside (4), and three were isolated from this plant for the first time (5–7). Their structures were elucidated by utilizing spectroscopic methods and electronic circular dichroism analyses. Furthermore, the cytotoxicities of all seven compounds were investigated in four human cancer cell lines, including A2780, BGC-823, HCT-116, and HepG2. The IC50 values of these diterpenes ranged from 0.18 to 2.44 mM in the tested cell lines. In addition, the structure–cytotoxicity relationship of diterpene glycosides was also evaluated to study the effect of glycosylation on the cytotoxicity of diterpene compounds.
Highlights
Diterpenoids from Isodon plants possess potent cytotoxic activities and are potential candidates for the treatment of cancer [1,2,3,4,5,6,7,8]
Phytochemical investigations on a water extract of the aerial parts of I. henryi resulted in the isolation of four new compounds 1–4, along with three known compounds 5–7
The isolated compounds were identified as ent-7,20-epoxy-kaur-16-en-1α,6β,7β,15β-tetrahydroxyl-11-O-β-dglucopyranoside (1), ent-7,20-epoxy-kaur-16-en-6β,7β,14β,15β-tetrahydroxyl-1-O-β-d-glucopyranoside (2), ent-7,20-epoxy-kaur-16-en-6β,7β,15β-trihydroxyl-1-O-β-d-glucopyranoside (3), and ent-7,20epoxy-kaur-16-en-7β,11β,14α,15β-tetrahydroxyl-6-O-β-d-glucopyranoside (4)
Summary
Diterpenoids from Isodon plants possess potent cytotoxic activities and are potential candidates for the treatment of cancer [1,2,3,4,5,6,7,8]. Since the 1980s, an increasing number of investigations have focused on the cytotoxicities of diterpenoids from Isodon plants [9,10,11,12,13,14]. In the past five years, we have performed continuous studies on the cytotoxicities of phytochemicals, including structure–activity relationship analyses of Isodon plants, in order to discover antitumor dominant compounds. Only a few diterpenoid glycosides have been reported from Isodon plants. There are few studies that have analyzed the structure–activity relationship of diterpenoid glycosides and the corresponding aglycones. To investigate glycoside-caused effects on cytotoxicity, the separation and preparation of diterpene glycosides were firstly performed by TLC tracing. Structure–activity relationship analyses of these two diterpenoid glycosides and their common aglycone were conducted.
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