- Synthesis of trans-B/C-Rotenoids: X-Ray and NMR Data for cis- and trans-Forms of Isorotenone
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Reduction of 6a,12a-didehydrorotenoids with diisobutylaluminium hydride gives clean 1,4-reduction leading to unstable trans-B/C-fusions, not previously known for enolisable rotenoids: they are epimerised to stable cis-forms under acid conditions.Applied initially to isorotenone, the method is extended to trans-B/C-deguelin, α-toxicarol, the 'core' rotenoid structure and the 6aS,12aR,5'R- and 6aR,12aS,5'R-rotenone stereoisomers. 1H and 13C NMR data are compared for the cis- and trans-forms and the geometry and conformations of the isorotenones are compared by X-ray analysis, providing insight into the reasons for the instability of the trans-forms.Reduction of the ridge-tile-like cis-isorotenone by sodium borohydride occurs from one face to give a cis-12α-hydroxy product, whilst the flatter trans-structure is attacked from both faces to give trans-12α- and 12β-hydroxy products.
- Begley, Michael J.,Crombie, Leslie,Hadi, Hamid bin A.,Josephs, Jonathan L.
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p. 2605 - 2614
(2007/10/02)
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- DEGUELIN CYCLASE, A PRENYL TO CHROMEN TRANSFORMING ENZYME FROM TEPHROSIA VOGELLII
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Seeds and plant parts of Tephrosia vogellii were investigated in order to provide systems for the study of prenyl to chromen transformation in rotenoids, as exemplified by the conversion of rot-2-enonic acid into deguelin.No hydroxylated intermediate was found.A cell free preparation has been obtained from T. vogellii seedlings or seeds and shown to catalyse the reaction.The water soluble enzyme has been partially purified using ammonium sulphate precipitation, gel chromatography and ion exchange procedures.Data for the enzyme named degueline cyclase, are reported - optima for pH and temperature and Km (which indicates strong binding between enzyme and substrate).Results relevant to Mr determination are discussed.The enzyme has a requirement for oxygen, but not for cofactors.It is inhibited by chloride ion and chelating agents, particularly 1,10-phenanthroline.Deguelin cyclase can convert the 11-hydroxyrotenoid sumatrolic acid into α-toxicarol and lapachol into dehydro-α-lapachone, though the prenyl to chromen conversion is not general.It does not convert rot-2'-enonic acid into rotenone under the conditions studied.Deguelin cyclase seems not to belong to the P450 group and resembles more closely the non-heme iron protein isopenicillin N synthase. Key words: Tephrosia vogellii; Leguminosae; rotenoids; biosynthesis; deguelin; rot-2'-enonic acid; deguelin cyclase; enzyme isolation; enzyme properties.
- Crombie, Leslie,Rossiter, John T.,Bruggen, Nicholas van,Whiting, Donald A.
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p. 451 - 462
(2007/10/02)
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- Synthesis of Novel Labile Rotenoids with Unnatural trans-B/C Ring Systems
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6a,12a-Dehydrorotenoids are cleanly reduced in 1,4-fashion by DIBAL to give rotenoids having the unstable, unnatural, trans-B/C fusion, readily epimerised by acid to the cis-forms: an X-ray structure for (+/-)-trans-isorotenone confirms the nature of the ring fusion.
- Begley, Michael J.,Crombie, Leslie,Hadi, A. Hamid bin A.,Josephs, Jonathan L.
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p. 204 - 205
(2007/10/02)
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