- Pyrrolizidine Alkaloid Biosynthesis. Synthesis of 3H-Labelled Trachelanthamidine and Isoretronecanol and their Incorporation into Three Pyrrolizidine Bases (Necines)
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(+/-)-Isoretronecanol (22) and (+/-)-trachelanthamidine (24) were prepared by 1,3-dipolar cycloaddition of N-formylproline with ethyl propiolate followed by reduction steps.These 3H-labelled 1-hydroxymethylpyrrolizidines together with putrescine were fed to Senecio isatideus which produces retrorsine (1); S. pleistocephalus which yields rosmarinine (8); and Cynoglossum officinale which affords echinatine (5).The double labelling experiments demonstrated that isoretronecanol is incorporated much more efficiently into rosmarinine than into retrorsine or echinatine, whereas trachelanthamidine is a much more efficient precursor for retrorsine and echinatine.Base hydrolysis of retrorsine and echinatine labelled with trachelanthamidine and of rosmarinine labelled with isoretronecanol established that most of the 3H-label was in the base portions, retronecine (2), heliotridine (6), and rosmarinecine (9), respectively.Further degradation of retronecine and rosmarinecine showed that most of the radioactivity was confined to the β-alanine (4) portion.The biosynthetic pathways to isoretronecanol and trachelanthamidine apparently diverge prior to the formation of these 1-hydroxymethylpyrrolizidines, probably during the cyclisation of an immonium ion (14) to form the 1-formylpyrrolizidines (15) and (17).
- Kunec, Ellen K.,Robins, David J.
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p. 1437 - 1441
(2007/10/02)
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- Necic Acid Synthons. Part 5. Total Synthesis of (+/-)-Retronecic Acid and Related Compounds via Zinc-Mediated Coupling of Halogeno-esters
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Zinc-mediated coupling of suitably substituted halogeno esters affords access to (+/-)-retronecic acid (2) and related intermediates.These approaches lead to racemic retronecic acid on the one hand and to a diastereoisomeric mixture of the acid on the other.
- Ameer, Farouk,Drewes, Siegfried E.,Hoole, Robyn,Kaye, Perry T.,Pitchford, Andrew T.
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p. 2713 - 2718
(2007/10/02)
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- Pyrrolizidine Alkaloid Biosynthesis. Synthesis of 13C-Labelled Putrescines and their Incorporation into Retronecine
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The biosynthesis of the retronecine (3) portion of the pyrrolizidine alkaloid retrorsine (1) has been studied in Senecio isatideus plants using 13C-labelled putrescines.Samples of -(10), -(8), and -putrescine (9) were prepared a
- Khan, Hassan A.,Robins, David J.
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p. 101 - 106
(2007/10/02)
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- Pyrrolizidine Alkaloid Biosynthesis: Stereochemistry of the Formation of Isoleucine in Senecio Species and of its Conversion into Necic Acids
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Incorporation experiments with isoleucine (1) and 2-aminobutanoic acid , stereospecifically labelled with tritium at C-4 and C-3 respectively, have shown that the ethyl migration step during biosynthesis of isoleucine (1) in Senecio species takes place with retention of configuration.It was also shown that coupling of two molecules of isoleucine (1) to give the ten-carbon necic acids of the senecic (2) type takes place with loss of the C-4 pro-S and retention of the C-4 pro-R hydrogen from both components.A new synthesis of βγ-unsaturated amino-asids has been developed which provides for control of the configuration of the olefinic system.
- Cahill, Rosalind,Crout, David H. G.,Gregorio, Maria V. M.,Mitchell, Michael B.,Muller, Urs S.
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p. 173 - 180
(2007/10/02)
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