Microtropiosides A–F: ent-Labdane diterpenoid glucosides from the leaves of Microtropis japonica (Celastraceae)

Abstract

From a 1-BuOH-soluble fraction of a MeOH extract of the leaves of Microtropis japonica, collected in the Okinawa islands, six ent-labdane glucosides, named microtropiosides A-F, were isolated together with one known acyclic sesquiterpene glucoside. Their structures were elucidated by a combination of spectroscopic analyses, and their absolute configurations determined by application of the beta-D-glucopyranosylation-induced shift-trend rule in (13)C NMR spectroscopy and the modified Mosher's method.

Microtropins Q–W, <i>ent</i>-Labdane Glucosides: Microtropiosides G–I, Ursane-Type Triterpene Diglucoside and Flavonol Glycoside from the Leaves of <i>Microtropis japonica</i>

“…and the structures were elucidated mainly by spectroscopic evidence. The structures of known compounds, microtropin D (14), 5) microtropiosides A and F (15, 16), 4) lilyn (17) , were assignable to hydroxy groups, triple bond and ester functional groups, respectively. The 13 C-NMR spectrum exhibited five signals for an aglycone together with six signals for a 2-ethyl-2,3-dihydroxybutyrate moiety and six for 6-substituted glucopyranoside, which were seen in microtropins A-P. 5,6) The absolute structure of glucose was determined to be D by HPLC analysis of its hydrolyzate using a chiral detector, and thus the mode of sugar linkage was β from the coupling constant of the anomeric proton.…”

“…10) Therefore, the structure of 4 was elucidated to be 2S,6ξ-heptanediol 2-O-β-D-glucopyranoside 6′-O-(2″S,3″R)-2″-ethyl-2,″3″-dihydroxybutyric acid ester, as shown in Fig. 1 4 were those of α-and β-anomers, respectively. The ester linkage was expected on C-6′ from its 13 C-NMR signals at 65.4 (α) and 65.6 (β) and therefore its structure was elucidated to be D-glucose 6′-O-(2″S,3″R)-2″-ethyl-2,″3″-dihydroxybutyric acid ester.…”

“…Microtropis japonica HALLIER f. (Celastraceae) is an evergreen tree of about 5 m in height, and has a distinct distribution in restricted southern parts of Kanto, Kyushu, Okinawa islands and Taiwan. 3) In previous papers, we have reported the isolation of six new ent-labdane diterpenoid glucosides, named microtropiosides A -F, from the 1-BuOH-soluble fraction of a MeOH extract of the leaves of Microtropis japonica 4) and microtropins A-P from the branches of the title plant. 5,6) Further extensive isolation work on the leaf extract afforded seven esters of (2″S,3″R)-2″-ethyl-2″,3″-dihydroxybutyric acid, named microtropins Q-W (1-7) and the acid itself (8) (Fig.…”

“…1), three new ent-labdane glucosides, named microtropiosides G-I (9-11), a triterpene glucoside (12), and a flavonol glycoside (13) (Fig. 2) along with microtropin D (14), 5) microtropiosides A and F (15, 16), 4) a flavonol glycoside, kaempferol 3-O-β-D-(2″-O-β-D-glucopyranosyl) galactopyranoside (lilyn) (17) 7,8) and 2-ethyl-3-methylmaleimide N-β-D-glucopyranoside (18). 9) This paper deals with the structural elucidation of these new compounds.…”

Microtropins J-P: 6’-O-(2”&lt;i&gt;S&lt;/i&gt;,3”&lt;i&gt;R&lt;/i&gt;)-2”-Ethyl-2”,3”-Dihydroxybutyrates of Phenolic Alcohol &lt;i&gt;&amp;#223&lt;/i&gt;-D-Glucopyranosides from the Branches of &lt;i&gt;Microtropis japonica&lt;/i&gt;

“…In continuous research on subtropical resource plants, a Celestraceous plant, Microtropis japonica, collected in Okinawa attracted our attention and its constituents were investigated. In previous papers, the isolation of ent-labdane diterpene glucosides, microtroipiosides A-F [3,4], from the leaves of M. japonica, and the 2-ethyl-2,3-dihydroxybutyrate of nine aliphatic glucosides, microtropins A-I [4], from its branches has already been reported. Further extensive isolation work on a MeOH extract of the branches of M. japonica resulted in the isolation of seven new aromatic glucoside (2S,3R)-2-ethyl-2,3-dihydroxybutyrates (1-7), named microtropins J-P, along with two known compounds, vanillic (8) [5] and salicylic (9) acids (Figure 1).…”