Acylated Glycosidic Acid Methyl Esters Generated from the Convolvulin Fraction of Rhizoma Jalapae Braziliensis by Treatment with Indium(III) Chloride in Methanol

Abstract

Four hexaglycosides of methyl 3S,12S-dihydroxyhexadecanoate (1-4) were provided after treatment of the crude convolvulin fraction from Rhizoma Jalapae Braziliensis (the root of Ipomoea operculata (GOMES) MART., Convolvulaceae) with indium(III) chloride in methanol. The structures of 1-4 were elucidated on the basis of spectroscopic and chemical methods. Their sugar moieties were partially acylated with organic acids including (3S,9R)-3,6:6,9-diepoxydecanoic (exogonic) acid, (E)-2-methylbut-2-enoic (tiglic) acid, and isovaleric acid.Key words resin glycoside; convolvulin; Ipomoea operculata; Rhizoma Jalapae Braziliensis; acylated glycosidic acid methyl ester; indium(III) chloride Rhizoma Jalapae Braziliensis, the root of Ipomoea operculata (GOMES) MART. (Convolvulaceae), is used as a crude laxative drug. Its active ingredients are known to be ether-soluble resin glycoside called jalapin and ether-insoluble resin glycoside called convolvulin. 1,2) In preceding papers, we reported seven glycosidic acids, operculinic acids A-G, and two organic acids, n-decanoic acid and n-dodecanoic acid, as the alkaline hydrolysis products of the crude jalapin fraction of the crude drug, and isolation and structural elucidation of 18 new genuine jalapins, operculins I-XVIII, from the fraction.3-8) We also reported a glycosidic acid, operculinic acid H, along with three organic acids such as isovaleric acid, (E)-2-methylbut-2-enoic (tiglic) acid, and (3S,9R)-3,6:6,9-diepoxydecanoic (exogonic) acid, which exists as an equilibrium mixture (ca. 1 : 1) at the C-6 spiro center, formed by the alkaline hydrolysis of the crude convolvulin fraction. 9) As part of our studies on the resin glycosides from this crude drug, herein we report the isolation and structural elucidation of four acylated glycosidic acid methyl esters. We could afford these methyl esters by effectively treating the crude convolvulin fraction with indium(III) chloride in methanol (MeOH), a catalyst reagent for the mild methyl esterification of carboxylic acids, as previously reported. 10) Results and DiscussionPowdered roots of I. operculata, which was purchased from Paul Müggenburg Gmbh & Co., a botanical raw materials company in Hannover, Germany, were extracted with MeOH. This extract was suspended in H 2 O, and then successively extracted with ether and n-butanol (BuOH). The n-BuOHsoluble fraction was subjected to MCI gel CHP20 column chromatography to yield a crude convolvulin fraction.3) Despite numerous trials, our attempt for the isolation of pure resin glycosides from the crude convolvulin fraction has never become successful. This fraction was therefore treated with indium(III) chloride in MeOH, as in the cases of the crude convolvulin fractions from Pharbitis Semen 11) and seeds of Quamolit pennata.12) The treated fraction was successively separated over Sephadex LH-20 and silica gel column chromatography and HPLC on octadecyl silica (ODS), affording four compounds, referred to as IOM-1-IOM-4.IOM-1 (1) was obtained as an amorphous powder and its molecular form...

Resin glycosides from Convolvulaceae plants

“…Hence, the fraction was treated with indium(III) chloride in MeOH, which was reported to be a catalyst for mild methyl esterification of carboxylic acids by Mineno and Kansui [32]. The treated fraction exhibited a number of separate spots by TLC on silica gel and was successively separated by Sephadex LH-20 and silica gel column chromatography and HPLC using an ODS column, affording four compounds, referred to as IOM-1 ( 70 )−IOM-4 ( 73 ) [33].…”

“…The structures of 70 – 73 were determined as shown in Fig. 5 using their NMR spectra, including HMBC and 1 H- 1 H TOCSY spectra, negative-ion FAB-MS, and the structural analyses of their hydrolysates produced by alkaline hydrolysis and partial deacylation [33].…”

“…In addition, no distinct peak was detected in the region of m/z 1700–4000 in the negative-ion FAB-MS of the crude convolvulin fraction. Therefore, a part of the crude convolvulin fraction might be a mixture of monomers composed of free carboxylic acid forms corresponding to 72 and 73 [33].…”

“…The structures of 77 – 83 were determined as indicated in Fig. 6 using similar methods as those used for 70 – 73 [33]. Compounds 77 – 83 were all monomers of methyl esters of glycosidic acids esterified with several organic acids at the sugar moiety.…”

Acylated Aminooligosaccharides with Inhibitory Effects against α-Amylase from Streptomyces sp. HO1518

“…There is a chiral carbon at the β position of the carbonyl function. To determine its absolute chemistry, the alkaline hydrolysis method followed by methyl esterification reaction [ 23 , 24 ] was applied to 2 and 5 . Unfortunately, the efforts for obtaining its corresponding methyl 3-hydroxybutyrate failed, mainly due to the limit amount of 2 and 5 obtained.…”