The biosynthesis and metabolism of anthraquinones in Rumex obtusifolius

Fairbairn, James; Muhtadi, Farid J.

doi:10.1016/s0031-9422(00)89992-6

Cited by 13 publications

(5 citation statements)

References 13 publications

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“…1.17 alpinus, R. obtusifolius, and Rhamnus frangula) in the early 1970s [90][91][92] simply evidenced its acetogenic nature. Although a biosynthetic origin of 17 from eight acetate units seems obvious, as many as four different folding modes might in principle be imaginable for its biosynthesis, 26 not only the so-called 93 modes F and S, but also the modified modes F 0 and S 0 .…”

Section: Biosynthesismentioning

confidence: 99%

Knipholone and related 4-phenylanthraquinones: structurally, pharmacologically, and biosynthetically remarkable natural products

et al. 2008

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This review gives the first comprehensive overview of the rapidly emerging young class of 4-phenylanthraquinones isolated from the three genera Bulbine, Bulbinella, and Kniphofia, all from the plant family Aphodelaceae: their occurrence, structural elucidation (with particular emphasis on the phenomenon of axial chirality), partial and total synthesis, their pharmacological (i.a., antimalarial and antitumoral) activities, and their biosynthetic origin (from acetate units). Particular emphasis is given to the stereostructure of knipholone, the most abundant of these naturally occurring phenylanthraquinones. The most recent highlight is the discovery of the first dimeric representatives, named joziknipholones, involving interesting phenomena of--partially or fully restricted--rotation at the sp2-sp2 and sp2-sp3 axes.

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Section: Biosynthesismentioning

confidence: 99%

Knipholone and related 4-phenylanthraquinones: structurally, pharmacologically, and biosynthetically remarkable natural products

et al. 2008

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“…Several aspects of the phytochemistry of R. obtusifolius have been reported previously. These include the isolation and characterisation of α-picoline (Wilkinson, 1958), anthraquinones (Fairburn and Muhtadi, 1972) and glucopyranosides in roots (Kasai et al, 1981(Kasai et al, , 1982. However the structure of the proanthocyanidin has not previously been reported.…”

Section: Introductionmentioning

confidence: 99%

Isolation and Characterisation of Procyanidins from Rumex obtusifolius

Spencer

Sivakumaran

Fraser

et al. 2007

Phytochemical Analysis

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An acetone:water (7:3) extract obtained from the leaves of Rumex obtusifolius was fractionated into procyanidin oligomer and polymer fractions using a linear gradient and a simple step method on Sephadex LH-20. The chemical characteristics of the procyanidin fractions were studied by 13C-NMR spectroscopy, acid-catalysed degradation in the presence of benzyl mercaptan, matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) MS and electrospray ionisation (ESI) MS. The 13C-NMR showed that the polymer fraction consisted predominantly of procyanidin polymers, some with galloyl groups attached. The thiolysis reaction products indicated a mean degree of polymerisation (DP) of 4.3 for the step method, and a range of 2.3-8.2 mean DP for the gradient fractionation, with epicatechin as the most abundant flavan-3-ol extension unit, while the terminal units consisted of equal proportions of catechin, epicatechin and epicatechin gallate. Singly charged ions observed in MALDI-TOF/MS showed a range of oligomeric procyanidins and their polygalloyl derivatives. These species (in the range DP 2-7) were also observed by ESI/MS but the spectra were more complex due to overlapping multiply charged ions. Isolation of oligomers from the Sephadex LH-20 fraction by chromatography on polyamide and C18 yielded B1, B2, B3 and B7 dimers, an A-type trimer and a B2 3,3'-O-digallate.

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“…The 13 C signal of this carbon atom was likewise enhanced. From this unambiguously established pattern of intact acetate-derived C 2 units incorporated, without bond cleavage, and, in particular, due to the fact that the first ring (the “western” one) contains two (not three) intact C 2 units, the chrysophanol part of the phenylanthraquinone 2a clearly follows the F -type folding mode 2 2.…”

Section: Resultsmentioning

confidence: 72%

“…From this unambiguously established pattern of intact acetate-derived C 2 units incorporated, without bond cleavage, and, in particular, due to the fact that the first ring (the "western" one) contains two (not three) intact C 2 units, the chrysophanol part of the phenylanthraquinone 2a clearly follows the F-type folding mode. 23 Under these optimized conditions, three of the four C 2 units of the phloroglucinol part of 4a were clearly identified: the coupling between the two exocyclic carbon atoms of the acetyl group (i.e., the assumed starter unit), C-5′/C-4′, and to a smaller extent also C-1′/C-6′ (see Figure 2). The only connectivity not clearly visible was the one expected to join the two quaternary carbon atoms C-2′ and C-3′.…”

Section: Resultsmentioning

confidence: 97%

“…Biosynthetically, both molecular portions of knipholone ( 4a ) are of high interest: The “northern” half, in its free form the long-known anthraquinone chrysophanol ( 5 ), is widely distributed in plants and fungi, but only little work has been reported on its biosynthetic origin. In the early 1970s, feeding experiments with [ 14 C]-acetate proved the acetogenic nature of chrysophanol ( 5 ) in plants, , but since no NMR-active nuclei (like 13 C) were used, no information about the folding type was acquired. Due to the loss of one C-atom in the course of its biosynthesis, the structure of 5 might, in principle, be compatible with different folding modes.…”

Section: Introductionmentioning

confidence: 99%

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Polyketide Folding in Higher Plants: Biosynthesis of the Phenylanthraquinone Knipholone

et al. 2007

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The biosynthesis of knipholone, as an axially chiral phenylanthraquinone, in higher plants was examined by feeding experiments with [13C2]-labeled precursors. [13C2]-Acetate and advanced synthetic intermediates were fed to sterile cultures of Kniphofia pumila (Asphodelaceae), with subsequent NMR analysis on the isolated natural product involving 2D INADEQUATE and SELINQUATE experiments. Due to its uneven number of carbon atoms, and because of its uncertain decarboxylation site, the "northern" part of the molecule (i.e., the chrysophanol portion) might originate from four different cyclization modes. According to the labeling pattern of the product isolated after incorporation, this anthraquinone part of knipholone is formed by the so-called F folding mode (originally established for fungi). The acetophenone part of the molecule, which does not undergo a decarboxylation reaction, originates from four acetate units. The surprising lack of randomization of the intact [13C2] units in this "southern" part reveals the absence of a free symmetric intermediate as initially anticipated. This is in agreement with the intact incorporation of the "authentic" southern molecular portion, 4,6-dihydroxy-2-methoxyacetophenone, while the corresponding symmetrical candidate trihydroxyacetophenone was clearly not incorporated, showing that the O-methylation of the freshly cyclized tetraketide is the step that prevents symmetrization of the acetophenone.

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The biosynthesis and metabolism of anthraquinones in Rumex obtusifolius

Cited by 13 publications

References 13 publications

Knipholone and related 4-phenylanthraquinones: structurally, pharmacologically, and biosynthetically remarkable natural products

Knipholone and related 4-phenylanthraquinones: structurally, pharmacologically, and biosynthetically remarkable natural products

Isolation and Characterisation of Procyanidins from Rumex obtusifolius

Polyketide Folding in Higher Plants: Biosynthesis of the Phenylanthraquinone Knipholone

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