- Pre-isoflavonoid Stages in the Biosynthesis of Amorphigenin: Ring-D Formation and Ring-A Migration
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Despite low incorporations of doubly labelled acetate during the biosynthesis of amorphigenin by Amorpha fruticosa seedlings, it has been possible to solve the ring-D folding by an INADEQUATE n.m.r. experiment; new proposals are made for the mechanism of the enzyme catalysed flavanone-isoflavone transformation step.
- Crombi, Leslie,Holden, Ian,Bruggen, Nicholas Van,Whiting, Donald A.
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- Hydroxylated Rotenoids Selectively Inhibit the Proliferation of Prostate Cancer Cells
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Prostate cancer is one of the leading causes of cancer-related death in men. The identification of new therapeutics to selectively target prostate cancer cells is therefore vital. Recently, the rotenoids rotenone (1) and deguelin (2) were reported to selectively kill prostate cancer cells, and the inhibition of mitochondrial complex I was established as essential to their mechanism of action. However, these hydrophobic rotenoids readily cross the blood-brain barrier and induce symptoms characteristic of Parkinson's disease in animals. Since hydroxylated derivatives of 1 and 2 are more hydrophilic and less likely to readily cross the blood-brain barrier, 29 natural and unnatural hydroxylated derivatives of 1 and 2 were synthesized for evaluation. The inhibitory potency (IC50) of each derivative against complex I was measured, and its hydrophobicity (Slog10P) predicted. Amorphigenin (3), dalpanol (4), dihydroamorphigenin (5), and amorphigenol (6) were selected and evaluated in cell-based assays using C4-2 and C4-2B prostate cancer cells alongside control PNT2 prostate cells. These rotenoids inhibit complex I in cells, decrease oxygen consumption, and selectively inhibit the proliferation of prostate cancer cells, leaving control cells unaffected. The greatest selectivity and antiproliferative effects were observed with 3 and 5. The data highlight these molecules as promising therapeutic candidates for further evaluation in prostate cancer models.
- Russell, David A.,Bridges, Hannah R.,Serreli, Riccardo,Kidd, Sarah L.,Mateu, Natalia,Osberger, Thomas J.,Sore, Hannah F.,Hirst, Judy,Spring, David R.
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p. 1829 - 1845
(2020/06/05)
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- Biosynthesis of Rotenone and Amorphigenin. Study of the Origins of Isopropenyl-substituted Dihydrofuran E-Rings using Isotopically Labelled Late Precursors
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Whilst epoxidation of rot-2'-enonic acid is the most likely source of dalpanol in Amorpha fruticosa seedlings, administration of (5'R,6'S)-dalpanol shows that it is not an intermediate on the path to rotenone and amorphigenin.Labelled 4'-hydroxy- or 5'-hydroxy-rot-2'-enonic acid also do not qualify as intermediates in rotenone biosynthesis, but they are each converted into amorphigenin with chemospecific attack on the methyl group.By administration and re-isolation of amorphigenin from A. fruticosa seedlings, our earlier conclusion that hydroxylation ofrotenone to form amorphigenin proceeds with even label scrambling between C-7' and C-8', probably via an allylic radical, is confirmed.Competitive double-labelling experiments are employed to support a scheme in which rotenone derives directly from rot-2'-enonic acid by an enzyme-induced radical-type reaction without the intervention of an hydroxylated intermediate, and the two labelled hydroxyrot-2'-enonic acids are similarly cyclised using their methyl groups.The incorporations into amorphigenin of labelled 4- and 5-hydroxyrot-2'-enonic acids, both of which are shown to occur naturally in A. fruticosa, are similar, but only about one sixth that of rotenone.This, and our related biosynthetic work, rests on an extensive programme of isotopic labelling and reconstructive synthesis.Our earlier method for making -rotenone has been improved, and similar procedures adapted for - and -amorphigenin. 8'-Labelled rotenones are made by a positional interchange using addition of benzeneselenenyl chloride and elimination of the selenoxide, whilst -amorphigenin is made via addition of phenylselenophthalimide.Unlabelled amorphigenin can be isotopically labelled by oxidation to the aldehyde and reduction using sodium borodeuteride or borotritide and a method additional to those we have described earlier is given for tritium labelling of rot-2'-enonic acid. - and -Labelling in the 5'-position of 4'- and 5'-hydroxyrot-2'-enonic acids can be attained through the catalytic hydrogenolysis of amorphigenin though special methods must be used to scrub the samples totally free from the latter.Methods based on the hydrolysis of labelled 4'-bromorot-2'-enonic acid are also described, and 4'-tritium-labelled 4'-hydroxyrot-2'-enonic acid is made from unlabelled material, or from rot-2'-enonic acid, by simple oxidation/reduction methods.
- Bhandari, Prabha,Crombie, Leslie,Kilbee, Geoffrey W.,Pegg, Stephen J.,Proudfoot, Geoffrey,et al.
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p. 851 - 864
(2007/10/02)
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- Biosynthesis of Rotenoids by Amorpha fruticosa: Sequence, Specificity, and Stereochemistry in the Development of the Hemiterpenoid Segment
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By isolation and radiochemical methods rot-2'-enonic acid, dalpanol, rotenone, and amorphigenin have been identified in Amorpha fruticosa seedlings, and ordered in biosynthetic sequence.Its specific activity shows that 12aβ-hydroxyamorphigenin has origins other than direct 12aβ-hydroxylation of amorphigenin: its occurrence and labelling establish it as a true natural product.Except for isopentenyl alcohol, the potential hemiterpene precursors mevalonic acid, 3-hydroxy-3-methylglutaric acid, and dimethylallyl alcohol are poor precursors for amorphigenin.By employing the already prenylated (E)-rot-2'-enonic acid, it is shown that the 4'-C of this compound becomes 7'-C of rotenone.By assuming normal rear-side attack on an intermediate epoxide, and utilising the known absolute configurations at position 5' of dalpanol and rotenone, a stereochemical sequence can be written. (E)-4'-Labelled rot-2'-enonic acid leads to a (2'S,3'S)-epoxide, which on intramolecular attack by phenolate anion would give (5'R,6'S)-dalpanol, dehydration to rotenone then involving the labelled (pro-S)-7'-methyl group of dalpanol.Neither (6'R)- nor (6'S)-amorphigenol is a precursor of amorphigenin.Administration of rotenone to A. fruticosa seedlings has led, in three experiments designed to avoid inadvertent chemical scrambling of the allylic label, to amorphigenin having even label distribution between C-7' and C-8'.Possible interpretations are considered.
- Crombie, Leslie,Holden, Ian,Kilbee, Geoffrey W.,Whiting, Donald A.
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p. 789 - 798
(2007/10/02)
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