- Polyneuridine aldehyde: Structure, stability overviews and a plausible origin of flavopereirine
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Polyneuridine aldehyde is a key intermediate in the biosynthetic routes to the family of monoterpene indole alkaloids. The molecule is the first biosynthetic member of the sarpagan-type alkaloids and is an entry to the ajmalan-type and alstophyllan-type alkaloids. To date, no spectral description of the molecule has been reported. We provide herein a full structural description of the molecule. Polyneuridine aldehyde revealed to be highly unstable in solution with decomposition within few hours. Some degradation products were characterized including flavopereirine suggesting an artifactual origin from plant materials.
- Ahamada, Kadiria,Benayad, Sarah,Poupon, Erwan,Evanno, Laurent
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- Enantiospecific total synthesis of the important biogenetic intermediates along the ajmaline pathway, (+)-polyneuridine and (+)-polyneuridine aldehyde, as well as 16-epivellosimine and Macusine A
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The first stereospecific synthesis of polyneuridine aldehyde (6), 16-epivellosimine (7), (+)-polyneuridine (8), and (+)-macusine A (9) has been accomplished from commercially available d-(+)-tryptophan methyl ester. d-(+)-Tryptophan has served here both as the chiral auxiliary and the starting material for the synthesis of the common intermediate, (+)-vellosimine (13). This alkaloid was available in enantiospecific fashion in seven reaction vessels in 27% overall yield from d-(+)-trytophan methyl ester (14) via a combination of the asymmetric Pictet-Spengler reaction, Dieckmann cyclization, and a stereocontrolled intramolecular enolate-driven palladium-mediated cross-coupling reaction. A new process for this stereocontrolled intramolecular cross-coupling has been developed via a copper-mediated process. The initial results of this investigation indicated that an enolate-driven palladium-mediated cross-coupling reaction can be accomplished by a copper-mediated process which is less expensive and much easier to work up. An enantiospecific total synthesis of (+)-polyneuridine aldehyde (6), which has been proposed as an important biogenetic intermediate in the biosynthesis of quebrachidine (2), was then accomplished in an overall yield of 14.1% in 13 reaction vessels from d-(+)-tryptophan methyl ester (14). Aldehyde 13 was protected as the N a-Boc aldehyde 32 and then converted into the prochiral C(16)-quaternary diol 12 via the practical Tollens reaction and deprotection. The DDQ-mediated oxidative cyclization and TFA/Et3SiH reductive cleavage served as protection/deprotection steps to provide a versatile entry into the three alkaloids polyneuridine aldehyde (6), polyneuridine (8), and macusine A (9) from the quarternary diol 12. The oxidation of the 16-hydroxymethyl group present in the axial position was achieved with the Corey-Kim reagent to provide the desired β-axial aldehydes, polyneuridine aldehyde (6), and 16-epivellosimine (7) with 100% diastereoselectivity.
- Yin, Wenyuan,Kabir, M. Shahjahan,Wang, Zhijian,Rallapalli, Sundari K.,Ma, Jun,Cook, James M.
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experimental part
p. 3339 - 3349
(2010/07/13)
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- First enantiospecific total synthesis of the important biogenetic intermediates, (+)-polyneuridme and (+)-polyneuridine aldehyde, as well as 16-epi-vellosimine and macusine A
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(Chemical Equation Presented) The first enantiospecific total synthesis of the alkaloids 16-epi-vellosimine (1), (+)-polyneuridine (2), (+)-polyneuridine aldehyde (3), and macusine A (4) is reported. The key oxidation was accomplished with the Corey-Kim reagent to provide the important biogenetic intermediates, 16-epi-vellosimine (1) and polyneuridine aldehyde (3), the latter of which is required for the conversion of the sarpagan skeleton into the ajmalan system in the biosynthesis of quebrachidine.
- Yin, Wenyuan,Jun, Ma.,Rivas, Felix M.,Cook, James M.
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p. 295 - 298
(2007/10/03)
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- Studies on Apocynaceae: Hemi-Synthesis of Vellosimine from Rhazine - Application of HOMCOR (COSY)-2D NMR Spectroscopy in Structure Eludication of Ajmaline-Sarpagine Skeleton
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The rare indole alkaloid vellosimine (1) has been isolated from Rauwolfia reflexa Teism and Binn.The occurrence of this indolic base has been observed for the first time in R. reflexa.The hemi-synthesis of this compound from rhazine has been achieved.The study of the HOMCOR (COSY)-2D NMR spectroscopy of vellosimine provides important information on structure of the alkaloids having ajmaline-sarpagine skeleton.
- Banerji, J.,Das, B.,Chakrabarti, R.,Shoolery, J. N.
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p. 709 - 711
(2007/10/02)
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