Operculinic Acid Research Articles

Inhibition of multidrug-resistant MCF-7 breast cancer cells with combinations of clinical drugs and resin glycosides from Operculina hamiltonii

The jalap roots, Operculina hamiltonii D.F. Austin & Staples (Convolvulaceae), are extensively commercialized as a depurative and laxative remedy in traditional medicine of the north and northeast regions of Brazil. The purification by recycling HPLC and structure elucidation of three new acyl sugars or resin glycosides are described here from a commercial product made of powdered roots. Three macrocyclic structures of a tetrasaccharide of (11S)-hydroxyhexadecanoic acid, operculinic acid C (1), the undescribed hamiltonins II and III (3 and 4), in addition to the known batatinoside III (5), presented a diastereoisomeric relationship as one residue of n-dodecanoic acid esterified the oligosaccharide core on a different position in each compound. Furthermore, hamiltonin IV (6) was characterized as an ester-type homodimer of acylated operculinic acid C with the same substitution pattern identified in hamiltonins II (3) and III (4) for each of the dimer subunits. All the isolated resin glycosides did not display any intrinsic cytotoxicity (IC50 > 25 μM). However, a combination of the individual isolated compounds 3–6 (1–50 μM) demonstrated an enhancement of cytotoxic effects with sublethal doses of vinblastine and podophyllotoxin (0.003 μM) in multidrug-resistant breast carcinoma epithelial cells (MCF-7/Vin).

Resin Glycosides from the Roots of Operculina macrocarpa (Brazilian Jalap) with Purgative Activity.

Analysis of the methanol-soluble resin glycosides from the roots of Operculina macrocarpa was assessed by generating NMR profiles of five glycosidic acids obtained through saponification, acetylation, and recycling HPLC purification. Operculinic acid H (1), two novel hexasaccharides, operculinic acids I (2) and J (3), the known purgic acid A (4), and a quinovopyranoside of (-)-(7 R)-hydroxydecanoic acid, operculinic acid K (5), were isolated. Three intact resin glycosides related to 1, the novel macrocarposidic acids A (6) and B (7), in addition to the previously known macrocarposidic acid C (8), were also purified with isovaleroyl, tigloyl, and exogonoyl [(3 S,9 R)-3,6:6,9-diepoxydecanoyl] groups as esterifying residues. A selective intramolecular lactonization was produced to generate a macrocyclic artifact (17) during acetylation of 1, resembling the distinctive structure of the Convolvulaceous resin glycosides.

Four Pentasaccharide Resin Glycosides from Argyreia acuta.

Four pentasaccharide resin glycosides, acutacoside F–I (1–4), were isolated from the aerial parts of Argyreia acuta. These compounds were characterized as a group of macrolactones of operculinic acid A, and their lactonization site of 11S-hydroxyhexadecanoic acid was esterified at the second saccharide moiety (Rhamnose) at C-2. The absolute configuration of the aglycone was S. Their structures were elucidated by established spectroscopic and chemical methods.

Three new resin glycosides compounds from Argyreia acuta and their α-glucosidase inhibitory activity

Three new phenolic compounds, acutacoside C (1), acutacoside D (2) and acutacoside E (3) were isolated from the aerial part of Argyreia acuta. The oligosaccharide chain was composed of two glucoses and three rhamnoses, and the aglycone was (11S)-hydroxyhexadecanoic acid (jalapinolic acid). The core of the three compounds was operculinic acid B, which was rare in resin glycosides. Their structures were established by a combination of spectroscopic and chemical methods. Compounds 1-3 have been evaluated for inhibitory activity against α-glucosidase, which all showed weak inhibitory activities.

Two pentasaccharide resin glycosides from Argyreia acuta

Two new compounds of acutacosides 1 and 2, pentasaccharide resin glycosides were isolated from the aerial parts of Argyreia acuta. The core of the two compounds was operculinic acid A, and they were esterfied at the same position, just one substituent group was linked at C-2 of Rha. The absolute configuration of the aglycone in the two compounds was established by Mosher's method, which was (11S)-hydroxyhexadecanoic acid (jalapinolic acid). Their structures were established by a combination of spectroscopic and chemical methods.

Resin Glycosides from the Yellow-Skinned Variety of Sweet Potato (Ipomoea batatas)

Native to tropical America, Ipomoea batatas has been cultivated for over 5000 years in Mexico. The yellow-skinned tuber crop variety, with an orange flesh, has a higher nutritional value than potato. Raw sweet potato can cause a purge due to its resin glycoside content. Purification of the chloroform-soluble resin glycosides from the roots of this variety was accomplished by preparative-scale HPLC, which allowed for the collection of six oligosaccharides, batatin VII (1) and batatinosides VII-IX (2-4), all of novel structure, together with the known resin glycosides pescaprein I and batatinoside IV. High-field NMR spectroscopy and FAB mass spectrometry were used to characterize each structure, identifying operculinic acid A for compounds 2 and 4, and simonic acid B for 3, as their pentasaccharide glycosidic cores. Batatin VII (1) represents a dimer of the know batatinoside IV, consisting of two units of simonic acid B.

Modulators of antibiotic activity from Ipomoea murucoides

Reinvestigation of the CHCl3-soluble extract from the flowers of Ipomoea murucoides, through preparative-scale recycling HPLC, yielded three pentasaccharides of 11-hydroxyhexadecanoic acid, murucoidins XVII-XIX, in addition to the known murucoidin III and V, all of which were characterized by NMR spectroscopy and mass spectrometry. These compounds were found to be macrolactones of the known pentasaccharides simonic acid B and operculinic acid A. The acylating groups corresponded to acetic, (2S)-methyl-butyric, (E)-cinnamic and octanoic acids. The esterification sites were established at the C-2 of the second rhamnose and C-3 and C-4 of the third rhamnose. The aglycone lactonization was placed at C-2 or C-3 of the first rhamnose. Bioassays for modulation of antibiotic activity were performed against multidrug-resistant strains of Staphylococcus aureus, Escherichia coli Rosetta-gami, and two nosocomial pathogens: Salmonella enterica sv. Typhi and Shigella flexneri. The tested glycolipids did not act as cytotoxic (IC50>4 μg/mL) nor as antimicrobial (MIC>128 μg/mL) agents. However, they exerted a potentiation effect on clinically useful antibiotics against the tested bacteria by increasing their antibiotic susceptibility up to four-fold at concentrations of 25 μg/mL.

Purgin II, a Resin Glycoside Ester-Type Dimer and Inhibitor of Multidrug Efflux Pumps from Ipomoea purga

Reinvestigation of the CHCl(3)-soluble extract from aerial parts of Ipomoea purga was carried out to identify mammalian multidrug-resistance inhibitors. Preparative-scale recycling HPLC was used to purify four new resin glycosides, purgins II (1) and III (2) in addition to purginosides III (3) and IV (4), as well as the known purginosides I (5) and II (6) and purgin I (7). The structures of 1-4 were established through NMR spectroscopy and mass spectrometry. Purgins II (1) and III (2) are the first examples of ester-type dimers of operculinic acid B with three different acylating residues in both monomeric units: (2S)-methylbutyric acid, n-hexanoic, n-decanoic, and trans-cinnamic acids. The macrolactonization site was located at C-2 of the second saccharide unit. The position of the ester linkage for monomeric unit B on the macrocyclic unit A was established as C-4 of the terminal glucose. Purginosides III (3) and IV (4) were found to be pentasaccharides of operculinic acid A with a structure related to that previously described for compounds 5 and 6. Reversal of multidrug resistance by compounds 1-7 was evaluated in vinblastine-resistant human breast carcinoma cells (MCF-7/Vin). Purgin II (1) enhanced vinblastine activity >2140-fold when incorporated at 25 μg/mL. For compounds 2-7, a moderate vinblastine-enhancing activity from 1.4-fold to 6.5-fold was observed.

Resin Glycosides from the Herbal Drug Jalap (Ipomoea purga)

Three new resin glycosides, purginosides I and II (1 and 2) and purgin I (3), were isolated from the aerial parts of Ipomoea purga and purified by preparative-scale recycling HPLC from a chloroform-soluble extract. Their structures were established through NMR spectroscopy and mass spectrometry. Purginosides I and II (1 and 2) are partially acylated branched pentasaccharides derived from operculinic acid A, which is composed of one D-fucose, one D-glucose, and three l-rhamnose units. The site of the aglycon macrolactonization is at C-2 of the second saccharide (rhamnose). In both compounds 1 and 2, three different esterifying residues were located at C-2 of the second rhamnose unit and at C-2 (or C-3) and C-4 on the third rhamnose moiety. The acylating residues were characterized as trans-cinnamic, n-decanoic, and either (+)-(2S)-2-methylbutanoic or n-hexanoic acid. Purgin I (3) was found to be an ester-type dimer of operculinic acid A, acylated by n-dodecanoic, (+)-(2S)-2-methylbutanoic, and trans-cinnamic acids at the same oligosaccharide core positions found in compounds 1 and 2. The site of lactonization by the aglycon in unit A was placed at C-2 of the second saccharide. The position for the ester linkage for the monomeric unit B on the macrocyclic unit A was identified as C-4 of the terminal glucose. This is the first report on the isolation, purification, and structure elucidation of intact individual resin glycoside constituents from the herbal drug jalap.

Batatins III–VI, glycolipid ester-type dimers from Ipomoea batatas

Batatins III–VI ( 1– 4), glycolipid ester-type dimers, were isolated from the tuberous roots of sweet potato ( Ipomoea batatas) using recycle high performance liquid chromatography. Their structures were characterized by means of several high-resolution NMR and mass spectrometry techniques. These compounds are the first examples of ester-type dimers which consist of two units of the heterotetrasaccharide operculinic acid C. Each unit was esterified by a different amount and type of acid residues: (2 S)-methylbutanoic, cinnamic, decanoic (capric) and dodecanoic (lauric) acids. Batatins III–VI ( 1– 4) are an example of the presence of a large number of resin glycoside congeners in each morning glory species caused by partial acylation of their constitutive saccharide cores.

Resin glycosides from the leaves and stems of Ipomoea digitata

Alkaline hydrolysis of the ether-soluble resin glycoside (jalapin) fraction of the leaves and stems of Ipomoea digitata L. (Convolvulaceae) gave six organic acids, isobutyric, (S)-2-methylbutyric, tiglic, n-decanoic, n-dodecanoic, and cinnamic acids, and two glycosidic acids, quamoclinic acid A and operculinic acid A. Further, a new genuine resin glycoside, named digitatajalapin I, was isolated from the jalapin fraction, along with three known resin glycosides. Their structures have been determined on the basis of chemical and spectroscopic data.

Components of Ether-Insoluble Resin Glycoside (Rhamnoconvolvulin) from Rhizoma Jalapae Braziliensis

Alkaline hydrolysis of the ether-insoluble resin glycoside (convolvulin) fraction of the roots of Ipomoea operculata (GOMES) MART. (Convolvulaceae) afforded a glycosidic acid named operculinic acid H along with isovaleric, tiglic, and exogonic (3,6:6,9-diepoxydecanoic) acids. Operculinic acid H was characterized to be 3S,12S-dihydroxyhexadecanoic acid 12-O-beta-D-glucopyranosyl-(1-->3)-O-alpha-L-rhamnopyranosyl-(1-->2)-[O-beta-D-glucopyranosyl-(1-->3)]-O-beta-D-glucopyranosyl-(1-->2)-[O-alpha-L-rhamnopyranosyl-(1-->6)]-O-beta-D-glucopyranoside on the basis of spectroscopic data and chemical evidence. The absolute configuration of exogonic acid determined from the alpha-methoxy-alpha-trifluoromethylphenylacetic acid esters of the hydrogenolysis products revealed that exogonic acid exists as a mixture (ca. 1 : 1) of two epimers, (3S,6S,9R)- and (3S,6R,9R)-diepoxydecanoic acids.

Batatinosides II−VI, Acylated Lipooligosaccharides from the Resin Glycosides of Sweet Potato

Sweet potato ( Ipomoea batatas) belongs to the Convolvulaceae (morning glory family) and is native to Mexico and Central America. Its edible tuberous roots have been much appreciated since pre-Hispanic times in Mesoamerica and now play an important role as a basic diet staple and a medicinal plant worldwide. The hexane-soluble extract from roots, through preparative-scale recycling HPLC, yielded five new lipophilic oligosaccharides of jalapinolic acid, batatinosides II-VI ( 1- 5), as well as the known pescapreins I ( 6) and VII ( 7) and murucoidin I ( 8), which are part of the purgative resin glycoside mixture. NMR spectroscopy and FAB mass spectrometry were used to characterize their structures. Compounds 1 and 2 are tetraglycosidic lactones of operculinic acid C. The pentasaccharide structures for compounds 3 and 4 were confirmed to be macrolactones of simonic acid B, and that characterized for 5 was derived from operculinic acid A. The lactonization site of the aglycone was placed at C-3 of the second saccharide unit in all compounds except 4, where it was placed at C-2. All compounds contain an esterifying residue that is composed of a long-chain fatty acid, n-decanoic acid (capric) or n-dodecanoic acid (lauric). In compound 3, an additional short-chain fatty acid, (2 S)-methylbutyric acid, was also identified.

Inhibitors of Bacterial Multidrug Efflux Pumps from the Resin Glycosides of Ipomoea murucoides

A reinvestigation of the CHCl 3-soluble extract from flowers of the Mexican medicinal arborescent morning glory, Ipomoea murucoides, through preparative-scale recycling HPLC, yielded six new pentasaccharides, murucoidins VI-XI (1- 6), as well as the known pescaprein III (7), stoloniferin I (8), and murucoidins I-V (9- 13). Their structures were characterized through the interpretation of their NMR spectroscopic and FABMS data. Compounds 1-6 were found to be macrolactones of three known glycosidic acids identified as simonic acids A and B, and operculinic acid A, with different fatty acids esterifying the same positions, C-2 on the second rhamnose unit and C-4 on the third rhamnose moiety. The lactonization site of the aglycone was placed at C-2 or C-3 of the second saccharide unit. The esterifying residues were composed of two short-chain fatty acids, 2-methylpropanoic and (2S)-methylbutyric acids, and two long-chain fatty acids, n-dodecanoic (lauric) acid and the new (8R)-(-)-8-hydroxydodecanoic acid. For the latter residue, its absolute configuration was determined by analysis of its Mosher ester derivatives. All members of the murucoidin series exerted a potentiation effect of norfloxacin against the NorA overexpressing Staphylococcus aureus strain SA-1199B by increasing the activity 4-fold (8 microg/mL from 32 microg/mL) at concentrations of 5-25 microg/mL. Stoloniferin I (8) enhanced norfloxacin activity 8-fold when incorporated at a concentration of 5 microg/mL. Therefore, this type of amphipathic oligosaccharide could be developed further to provide more potent inhibitors of this multidrug efflux pump.

Intrapilosins I−VII, Pentasaccharides from the Seeds of Ipomoea intrapilosa

Purification of a CHCl3-soluble extract from seeds of the Mexican medicinal arborescent morning glory, Ipomoea intrapilosa, by means of preparative-scale recycling HPLC, yielded seven new resin glycosides, intrapilosins I-VII (1-7). Their structures were established through the interpretation of their NMR spectroscopic and FABMS data. All pentasaccharides were found to be macrolactones of the known operculinic acid A with different fatty acids esterifying the same positions: C-2 on the second rhamnose unit and C-3 and C-4 on the third rhamnose moiety. The lactonization site of the aglycon could be placed at C-2 of the second saccharide. The fatty acid components of 1-7 were identified as (+)-(2S)-methylbutanoic, octanoic (caprylic), dodecanoic (lauric), and trans-cinnamic. The less common (-)-(2R)-methylbutanoic acid was also isolated as one of the saponification-liberated residues from intrapilosin IV (4). The presence of the (2R)- and (2S)-methylbutanoyl enantiomers bonded to the same oligosaccharide core in intrapilosins IV (4) and V (5) represents an example of diastereoisomerism due to a chiral esterifying moiety in the resin glycoside mixtures of a morning glory species.

Resin Glycosides from Ipomoea pes-caprae

Ipomoea pes-caprae (beach morning-glory; "riñonina" for the herbal drug in Mexico) is prescribed by traditional healers to moderate "heat" in an infected kidney. The hexane-soluble extract from the aerial parts of this medicinal plant, through preparative-scale recycling HPLC, yielded six new lipophilic oligosaccharides of jalapinolic acid: pescaproside B (1) and pescapreins V-IX (2-6). The previously known pescaproside A (7), pescapreins I-IV (8-11), and stoloniferin III (12) were also identified in the analyzed material by means of HPLC comparison with authentic samples. The glycosidic acid structure for all pentasaccharides was confirmed as simonic acid B. Pescaproside B (1), an acylated glycosidic acid methyl ester, is structurally related to pescaprein III (10). Pescapreins V (2) and VI (3) are diasteroisomeric tetraglycosidic lactones of operculinic acid C. Both of these compounds contain (2S)-methylbutyric and n-dodecanoic acids as their esterifying residues. Pescapreins VII (4) and IX (6) are pentasaccharides that contain an n-decanoyl group as their esterifying fatty acid residue instead of the n-dodecanoyl found in pescapreins I (8) and IV (11). Pescaprein VIII (5) represents an isomer of pescaprein II (9) containing an n-dodecanoyl unit as the esterifying residue at position C-4 of the third rhamnose moiety and a 2-methylpropanoyl at C-2 of the second rhamnose. High-field NMR spectroscopy and FAB mass spectrometry were used to characterize all new isolated compounds.

Profiling of the Resin Glycoside Content of Mexican Jalap Roots with Purgative Activity

Mexican Jalap roots, a prehispanic medicinal plant complex still considered to be a useful laxative, can be found as an ingredient in some over-the-counter products sold by herbalists in contemporary Mexico. The drug is prepared from the dried roots of several morning glories, all of which have been identified as members of the genus Ipomoea. Analysis of several commercial samples was assessed by generating HPLC and 13C NMR spectroscopic profiles of the glycosidic acids obtained through saponification of the resin glycoside contents. These profiles distinguish the three Mexican jalaps currently in frequent use and can serve as analytical tools for the authentication and quality control of these purgative herbal drugs. Ipomoea purga, the authentic "jalap root", yielded two new hexasaccharides of convolvulinic and jalapinolic acids, purgic acids A (1) and B (2), respectively. Scammonic acid A (3), a tetrasaccharide, was produced from Ipomoea orizabensis, the Mexican scammony or false jalap. Operculinic acid B (4), a pentasaccharide, was identified in Ipomoea stans. Semipreparative HPLC was performed to obtain pure samples of new compounds 1 and 2 in sufficient quantity to elucidate their structure by high-field NMR spectroscopy. Purgic acid A (1) was identified as (11S)-hydroxytetradecanoic acid 11-O-beta-D-quinovopyranosyl-(1-->2)-O-beta-D-glucopyranosyl-(1-->3)-O-[beta-D-fucopyranosyl-(1-->4)]-O-alpha-L-rhamnopyranosyl-(1-->2)-O-beta-D-glucopyranosyl-(1-->2)-O-beta-D-quinovopyranoside, while purgic acid B (2) was characterized with (11S)-hydroxyhexadecanoic acid as its aglycon but having the same glycosidation sequence in the oligosaccharide core.

Resin Glycosides from the Flowers of Ipomoea murucoides

The CHCl(3)-soluble extract from the flowers of the Mexican medicinal plant Ipomoea murucoides, through preparative-scale recycling HPLC, yielded murucoidins I-V (1-5), which are new pentasaccharides of jalapinolic acid, as well as the known stoloniferin I (6). Saponification of the crude resin glycoside mixture yielded two glycosidic acids, simonic acid B (9) and operculinic acid A (10), and their esterifying residues were composed of the two short-chain fatty acids, 2-methylpropanoic and (2S)-methylbutyric acids. All the isolated compounds (1-6) were characterized through high-field NMR spectroscopy. Compound 4 exhibited marginal cytotoxicity against Hep-2 cells (ED(50) 4 microg/mL).

Characterization of an anti-tuberculosis resin glycoside from the prairie medicinal plant Ipomoea leptophylla.

The organic soluble extract from the leaves of the native North American prairie plant Ipomoea leptophylla (big root morning glory) showed in vitro activity against M. tuberculosis. Bioassay-guided fractionation of this extract resulted in the identification of two new resin glycosides (6, 7). Base-catalyzed hydrolysis of these glycosides gave operculinic acid (1) as the glycosidic acid component as well as trans-cinnamic acid, propanoic acid, and lauric acid. The complete structure elucidation was accomplished through derivatization, 1D and 2D NMR spectroscopy (TOCSY, ROESY, HSQC, HMBC), and MS/MS experiments on 6 and 7 as well as the permethylated derivative 8.

Resin Glycosides. XXV. Multifidins I and II, New Jalapins, from the Seed of Quamoclit x multifida.

Alkaline hydrolysis of the ether-soluble resin glycoside fraction of seeds of Quamoclit (Q.) x multifida, a hybrid between Q. pinnata and Q. coccinea, gave new glycosidic acids, multifidinic acids A and B, along with two known glycosidic acids, quamoclinic acid A and operculinic acid A, and three organic acids, (2S)-2-methylbutyric acid, n-decanoic acid and n-dodecanoic acid. Further, as major ether-soluble resin glycosides, new jalapins named multifidins I and II, were isolated accompanied by quamoclins I-IV, which were previously obtained from seeds of Q. pinnata. The structures of multifidins I and II, and multifidinic acids A and B have been determined on the basis of chemical and spectral data.