Passibiflorin,epipassibiflorin and passitrifasciatin: cyclopentenoid cyanogenic glycosides from Passiflora

An epimeric mixture of two novel cyclopentenoid cyanogenic glycosides, passibiflorin [1-(6-O-β-D-rhamnopyranosyl-β-D-glucopyranosyloxy)-4-hydroxycyclopent-2-en-1-nitrile] and its C-1 epimer, epipassibiflorin, has been isolated from Passiflora biflora and P. talamancensis. The structures were determined by means of ¹H NMR and ¹³C NMR. Another novel cyclopentenoid cyanogenic glycoside, passitrifasciatin [1-(4-O-β-D-rhamnopyranosyl-β-D-glucopyranosyloxy)-4-hydroxycyclopent-2-en-1-nitrile] is described from Passiflora trifasciata. The structure was determined by means of ¹H NMR. The identification of the sugar moieties was made by HPLC and TLC. The isolation of a β-1 → 4 and a β-1 → 6-rhamnoglucoside of cyclopentenoid cyanogens from three species of subgenus Plectostemma of Passiflora suggests that diglycosides of this type are taxonomically diagnostic for the section.     

Cyanogenic glycosides: a case study for evolution and application of cytochromes P450

Cyanogenic glycosides are ancient biomolecules found in more than 2,650 higher plant species as well as in a few arthropod species. Cyanogenic glycosides are amino acid-derived β-glycosides of α-hydroxynitriles. In analogy to cyanogenic plants, cyanogenic arthropods may use cyanogenic glycosides as defence compounds. Many of these arthropod species have been shown to de novo synthesize cyanogenic glycosides by biochemical pathways that involve identical intermediates to those known from plants, while the ability to sequester cyanogenic glycosides appears to be restricted to Lepidopteran species. In plants, two atypical multifunctional cytochromes P450 and a soluble family 1 glycosyltransferase form a metabolon to facilitate channelling of the otherwise toxic and reactive intermediates to the end product in the pathway, the cyanogenic glycoside. The glucosinolate pathway present in Brassicales and the pathway for cyanoalk(en)yl glucoside synthesis such as rhodiocyanosides A and D in Lotus japonicus exemplify how cytochromes P450 in the course of evolution may be recruited for novel pathways. The use of metabolic engineering using cytochromes P450 involved in biosynthesis of cyanogenic glycosides allows for the generation of acyanogenic cassava plants or cyanogenic Arabidopsis thaliana plants as well as L. japonicus and A. thaliana plants with altered cyanogenic, cyanoalkenyl or glucosinolate profiles.     

New phenolic glycosides isolated from Penthorum chinense Pursh

A phytochemical investigation from 80% ethanol extract of Penthorum chinense Pursh (Saxifragaceae) resulted in the isolation of three new phenolic glycosides (1–3), together with three known phenolic glycosides (4–6). The structures of the new compounds were deduced from their comprehensive spectroscopic analysis including IR, HR-EI-MS, ¹H NMR, ¹³C NMR, DEPT, COSY, HMBC and HMQC. And the structures of known compounds 4–6 were identified by comparison of their spectral data with those reported in the literature.     

Cyanogenic glycosides and menisdaurin from Guazuma ulmifolia, Ostrya virgininana, Tiquilia plicata and Tiquilia canescens

The major cyanogenic glycoside of Guazuma ulmifolia (Sterculiaceae) is (2R)-taxiphyllin (>90%), which co-occurs with (2S)-dhurrin. Few individuals of this species, but occasional other members of the family, have been reported to be cyanogenic. To date, cyanogenic compounds have not been characterized from the Sterculiaceae. The cyanogenic glycosides of Ostrya virginiana (Betulaceae) are (2S)-dhurrin and (2R)-taxiphyllin in an approximate 2:1 ratio. This marks the first report of the identification of cyanogenic compounds from the Betulaceae. Based on NMR spectroscopic and TLC data, the major cyanogenic glucoside of Tiquilia plicata is dhurrin, whereas the major cyanide-releasing compound of Tiquilia canescens is the nitrile glucoside, menisdaurin. NMR and TLC data indicate that both compounds are present in each of these species. The spectrum was examined by CI-MS, ¹H and ¹³C NMR, COSY, 1D selective TOCSY, NOESY, and ¹J/^2,3J HETCOR experiments; all carbons and protons are assigned. The probable absolute configuration of (2R)-dhurrin is established by an X-ray crystal structure. The ¹H NMR spectrum of menisdaurin is more complex than might be anticipated, containing a planar conjugated system in which most elements are coupled to several other atoms in the molecule. The coupling of one vinyl proton to the protons on the opposite side of the ring involves a ⁶J- and a ^5/7J-coupling pathway. A biogenetic pathway for the origin of nitrile glucosides is proposed.     

Cyclopentenylglycine,a precursor of deidaclin in Turnera ulmifolia

When [2-¹⁴C]cyclopentenylglycine was synthesized and fed to seedlings of Turnera ulmifolia, the label was incorporated into the nitrile group of the cyanogenic glycoside deidaclin. The amino acid cyclopentenylglycine was also found to occur naturally in Turnera ulmifolia. These findings indicate that cyclopentenyl cyanogenic glycosides are synthesized from the corresponding amino acids by the same pathway utilized in the biosynthesis of other cyanogenic glycosides.     

Co-occurrence of Valine/Isoleucine-derived and cyclopentenoid cyanogens in a Passiflora species

The valine/isoleucine-derived cyanogenic glycosides linamarin and lotaustralin have been isolated together with the cyclopentenoid cyanogen passibiflorin from Passiflora lutea. This is only the second report of the production of cyanogenic glycosides from more than one biosynthetic pathway in individuals of a single species.     

Antioxidant efficacy of iridoid and phenylethanoid glycosides from the medicinal plant Teucrium chamaedris in cell-free systems

Twelve glycosides, seven iridoids and five phenylethanoids, have been isolated from leaf and root methanolic extracts of Wall Germander (Teucrium chamaedrys), a Mediterranean species historically used as a medicinal plant. Among them, three iridoid and one phenylethanoid glycosides have been isolated and characterized for the first time. All of the structures have been elucidated on the basis of their spectral data, especially 1D and 2D NMR experiments.The antioxidative properties of pure metabolites, as well as of crude organic extracts of the plant, have been analyzed on the basis of their DPPH radical scavenging capability. The antioxidant capacity in cell-free systems of the isolated metabolites was carried out by measuring their capabilities to inhibit the synthesis of thiobarbituric acid reactive species in assay media using as oxidable substrates a vegetable fat and the pentose sugar 2-deoxyribose and to prevent oxidative damage of the hydrosoluble bovine serum albumin (BSA) protein. Phenylethanoid glycosides resulted efficacious DPPH radical, while iridoid glycosides prevent massively the 2-deoxyribose and BSA oxidations in assay media.     

Growth cost and ontogenetic expression patterns of defence in cyanogenic Eucalyptus spp.

Plant defences can incur allocation costs and such costs incurred early in ontogeny may result in opportunity costs with effects evident later in life. A unified understanding of the growth cost of defence requires the identification of plants with varying ontogenetic trajectories of preferably resource demanding defences and an appropriate measurement of the growth cost of these defences. To develop such tools, we first compared nitrogen-based chemical defence (cyanogenic glycosides) in juvenile and adult foliage of three species of Eucalyptus (Myrtaceae). We found marked differences between the species, with two having much lower concentrations of foliar cyanogenic glycosides in seedlings compared to adults. We next used seedlings of two species to measure the resource (nitrogen) and growth cost of deploying cyanogenic glycosides. We found evidence that for every 1.0 nitrogen invested in cyanogenic glycosides, 1.49 additional nitrogens were effectively added to the leaves. We also found that deployment of cyanogenic glycosides was associated with a reduction in net assimilation rate (NAR) at constant leaf nitrogen. We did not, however, detect an overall growth cost associated with cyanogenic glycoside deployment because the rise in leaf nitrogen associated with this deployment apparently counteracted the reduction in NAR.     

Structures of the novel diterpene glycosides from Stevia rebaudiana

From the commercial extract of the leaves of Stevia rebaudiana, two new diterpenoid glycosides were isolated besides the known steviol glycosides including stevioside, rebaudiosides A–F, rubusoside, and dulcoside A. The structures of the two new compounds were identified as 13-[(2-O-6-deoxy-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid β-d-glucopyranosyl ester (1), and 13-[(2-O-6-deoxy-β-d-glucopyranosyl-3-O-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid β-d-glucopyranosyl ester (2), on the basis of extensive NMR and MS spectral data as well as chemical studies.     

Cyanogenic glycosides and the systematics of the Flacourtiaceae

A survey of 682 accessions including 550 species and most genera of the Flacourtiaceae for cyclopentenoid cyanogenic glycosides showed the presence of only three compounds. These were found only in the tribes Berberidopsideae, Oncobeae, Pangieae and Banaraeae. The family is thus divided into cyanogenic and acyanogenic members. The former group possess compounds of similar structure to those of the Passifloraceae and have been considered primitive morphologically. It seems improbable that the Passifloraceae are derived from the acyanogenic, and putatively evolutionarily more advanced, group of Flacourtiaceae.     

Brevistylumsides A and B,diterpene glycosides from Illicium brevistylum

A phytochemical investigation of 80% ethanol extract of Illicium brevistylum (Illiciaceae) resulted in the isolation of two new diterpene glycosides (1 and 2), together with three known diterpenes (3–5). The structures of the new compounds were deduced on the basis of comprehensive spectroscopic analysis including IR, HR-ESI–MS, ¹H NMR, ¹³C NMR, DEPT, COSY, HMBC and HSQC. The structures of known compounds 3–5 were identified by comparison of their spectral data with those reported in the literature.     

Triterpenoid saponins from the stem bark of Symplocos spicata

From the stem bark of Symplocos spicata a mixture of triterpenoid saponins was obtained. It behaved as a pure compound in TLC and HPLC, but heterogeneity was suspected on the basis of chemical and NMR spectral data. It was separated to give two analogous glycosides, which were identified as 3,28-O-bis-β-d-glucopyranosides of 19α-hydroxyarjunolic and 19α-hydroxyasiatic acids.     

13C核磁共振谱在三萜和三萜甙化学中的应用

本文简略地叙述了三萜和三萜甙的~(13)C NMR谱及其在研究生物合成、立体化学和阐明结构等方面的应用。     

Acylated 5,7,2',6'-oxygenated flavone glycosides from Andrographis alata

Five acylated 5,7,2',6'-oxygenated flavone glycosides along with the known 5,2',6'-trihydroxy-7-methoxyflavone-2'-O-beta-d-glucopyranoside have been isolated from the whole plant of Andrographis alata. The structures of the compounds were established from spectral (mainly 1D and 2D NMR) and chemical studies.     

Identification of cardiac glycosides in fractions from Periploca forrestii by high-performance liquid chromatography/diode-array detection/electrospray ionization multi-stage tandem mass spectrometry and liquid chromatography/nuclear magnetic resonance

Cardiac glycosides are a class of naturally occurring compounds that are characterized by some interesting biological activities and are widely distributed in the plant kingdom and can also be found in some animals. There is an interest in the chemical characterization of these molecules due to their toxicity and their use in medicines. In the study reported here, a combination of electrospray ionization tandem mass spectrometry with high-performance liquid chromatography equipped with diode-array detector (HPLC-DAD/ESI-MSⁿ), and hyphenation to both liquid chromatography and nuclear magnetic resonance spectroscopy (HPLC/NMR) were utilized for the on-line analyses of cardiac glycosides from Periploca forrestii. The fragmentation patterns and ¹H NMR spectra of nine isolated cardiac glycosides were investigated; their fragmentation rules and ¹H NMR spectral characteristics were summarized and applied to the structural identification of similar constituents in fractions from P. forrestii. As a result, a total of nine trace cardiac glycosides were tentatively determined by analyses of accurate molecular masses, representative fragment ions and characteristic ¹H NMR signals provided by HPLC/high-resolution mass spectrometry (HRMS), HPLC-DAD/ESI-MSⁿ and HPLC/¹H NMR experiments, respectively. Of these, eight (2–9) are new compounds and one (1) is reported from P. forrestii for the first time. Results of the present study can benefit the rapid identification and targeted isolation of new cardiac glycosides from crude plant extracts.     

Cardenolides and a lignan from asclepias subulata

Four new glycosides (three cardenolides and a lignan), nine previously reported cardenolide glycosides and a known triterpenoid were isolated from the ethyl acetate extract of the aerial parts of Asclepias subulata. The elucidation of the structures and stereochemistry of the new glycosides has been accomplished using mainly ¹H and ¹³C NMR and mass (EI and FAB) spectral data of their acetyl derivatives and comparison of these data with those of known glycosides from the same plant as well as from other plants. The new compounds were identified as 16α-hydroxycalactin, 3β-(β-D-glucopyranosyloxy)-19-car coroglaucigenin 3β-D-glucoside and 4-(β-D-glucopyranosyloxy)-larciresinol.     

Cyanogenic allosides and glucosides from Passiflora edulis and Carica papaya

Leaf and stem material of Passiflora edulis (Passifloraceae) contains the new cyanogenic glycosides (2R)-beta-D-allopyranosyloxy-2-phenylacetonitrile (1a) and (2S)-beta-D-allopyranosyloxy-2-phenylacetonitrile (1b), along with smaller amounts of (2R)-prunasin (2a), sambunigrin (2b), and the alloside of benzyl alcohol (4); the major cyanogens of the fruits are (2R)-prunasin (2a) and (2S)-sambunigrin (2b). The major cyanogenic glycoside of Carica papaya (Caricaceae) is 2a; only small amounts of 2b also are present. We were not able to confirm the presence of a cyclopentenoid cyanogenic glycoside, tetraphyllin B, in Carica papaya leaf and stem materials. In detailed 1H NMR studies of 1a/b and 2a/b, differences in higher order effects in glucosides and allosides proved to be valuable for assignment of structures in this series. The diagnostic chemical shifts of cyanogenic methine and anomeric protons in 1a/b are sensitive to anisotropic environmental effects. The assignment of C-2 stereochemistry of 1a/b was made in analogy to previous assignments in the glucoside series and was supported by GLC analysis of the TMS ethers.     

Flavonoid glycosides and their p-coumaroyl esters from Campylospermum calanthum leaves

Six new compounds, comprising three flavonoid glycosides and their respective coumaroyl esters, have been isolated and characterized from the methanol extract of the leaves of Campylospermum calanthum, along with three known flavonoid aglycones, 7-O-methyl apigenin (1), 7-O-methyl luteolin (2), and 7-O-methyl quercetin (3). Their structures were elucidated based on chemical evidence as well as spectroscopic analysis including 1D and 2D NMR (1H-1H COSY, HSQC, HMBC, and NOESY) spectroscopy and by comparing their spectral data with those reported for related compounds.     

Structures of the novel α-glucosyl linked diterpene glycosides from Stevia rebaudiana

From the commercial extract of the leaves of Stevia rebaudiana, two new minor diterpene glycosides having α-glucosyl linkage were isolated besides the known steviol glycosides including stevioside, steviolbioside, rebaudiosides A–F, rubusoside and dulcoside A. The structures of the two compounds were identified as 13-[(2-O-(3-α-O-d-glucopyranosyl)-β-d-glucopyranosyl-3-O-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid β-d-glucopyranosyl ester (1), and 13-[(2-O-β-d-glucopyranosyl-3-O-(4-O-α-d-glucopyranosyl)-β-d-glucopyranosyl-β-d-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid β-d-glucopyranosyl ester (2), on the basis of extensive NMR and MS spectral data as well as chemical studies.     

New glycosides of the campesterol derivative from the rhizomes of Tacca chantrieri

Seven new glycosides of the campesterol derivative (24R,25S)-ergost-5-ene-3beta,26-diol (1-7) were isolated from the rhizomes of Tacca chantrieri (Taccaceae). Their structures were determined by extensive spectroscopic analysis, including 2D NMR data, and a few chemical transformations.