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Total synthesis of (-)- and ent-(+)-vindoline.

ABSTRACT: [reaction: see text] Two exceptionally concise total syntheses of (-)- and ent-(+)-vindoline are detailed enlisting a diastereoselective tandem [4 + 2]/[3 + 2] cycloaddition of a 1,3,4-oxadiazole. The unique reaction cascade assembles the fully functionalized pentacyclic ring system of vindoline in a single step that forms four C-C bonds and three rings while introducing all requisite functionality and setting all six stereocenters within the central ring including three contiguous and four total quaternary centers.

SUBMITTER: Choi Y

PROVIDER: S-EPMC2587129 | biostudies-literature | 2005 Sep

REPOSITORIES: biostudies-literature

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Total synthesis of (-)- and ent-(+)-vindoline.

Choi Younggi Y Ishikawa Hayato H Velcicky Juraj J Elliott Gregory I GI Miller Michael M MM Boger Dale L DL

Organic letters 20050901 20

[reaction: see text] Two exceptionally concise total syntheses of (-)- and ent-(+)-vindoline are detailed enlisting a diastereoselective tandem [4 + 2]/[3 + 2] cycloaddition of a 1,3,4-oxadiazole. The unique reaction cascade assembles the fully functionalized pentacyclic ring system of vindoline in a single step that forms four C-C bonds and three rings while introducing all requisite functionality and setting all six stereocenters within the central ring including three contiguous and four tota ...[more]

PMID: 16178578

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Total synthesis of (-)- and ent-(+)-vindoline and related alkaloids.

Project description:A concise 11-step total synthesis of (-)- and ent-(+)-vindoline (3) is detailed based on a unique tandem intramolecular [4 + 2]/[3 + 2] cycloaddition cascade of a 1,3,4-oxadiazole inspired by the natural product structure, in which three rings and four C-C bonds are formed central to the characteristic pentacyclic ring system setting all six stereocenters and introducing essentially all the functionality found in the natural product in a single step. As key elements of the scope and stereochemical features of the reaction were defined, a series of related natural products of increasing complexity were prepared by total synthesis including both enantiomers of minovine (4), 4-desacetoxy-6,7-dihydrovindorosine (5), 4-desacetoxyvindorosine (6), and vindorosine (7) as well as N-methylaspidospermidine (11). Subsequent extensions of the approach provided both enantiomers of 6,7-dihydrovindoline (8), 4-desacetoxyvindoline (9), and 4-desacetoxy-6,7-dihydrovindoline (10).

| S-EPMC2531198 | biostudies-literature

Asymmetric total synthesis of vindoline.

Project description:A concise asymmetric total synthesis of (-)-vindoline (1) is detailed based on a tandem intramolecular [4+2]/[3+2] cycloaddition cascade of a 1,3,4-oxadiazole inspired by the natural product structure, in which the tether linking the initiating dienophile and oxadiazole bears a chiral substituent that controls the facial selectivity of the initiating Diels-Alder reaction and sets absolute stereochemistry of the remaining six stereocenters in the cascade cycloadduct. This key reaction introduces three rings and four C-C bonds central to the pentacyclic ring system setting all six stereocenters and introducing essentially all the functionality found in the natural product in a single step. Implementation of the approach also required the development of a unique ring expansion reaction to provide a six-membered ring suitably functionalized for introduction of the Delta (6, 7)-double bond found in the core structure of vindoline and defined our use of a protected hydroxymethyl group as the substituent used to control the stereochemical course of the cycloaddition cascade.

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Total synthesis of (-)-kopsinine and ent-(+)-kopsinine.

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Total synthesis of <i>ent</i>-pavettamine.

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Project description:Concise asymmetric total syntheses of vindoline (1) and vindorosine (2) are detailed based on a unique intramolecular [4 + 2]/[3 + 2] cycloaddition cascade of 1,3,4-oxadiazoles inspired by the natural product structures. A chiral substituent on the tether linking the dienophile and oxadiazole was used to control the facial selectivity of the initiating Diels-Alder reaction and set the absolute stereochemistry of the remaining six stereocenters in the cascade cycloadduct. This key reaction introduced three rings and four C-C bonds central to the pentacyclic ring system setting all six stereocenters and introducing essentially all the functionality found in the natural products in a single step. Implementation of the approach for the synthesis of 1 and 2 required the development of a ring expansion reaction to provide a 6-membered ring suitably functionalized for introduction of the ?(6,7)-double bond found in the core structure of the natural products. Two unique approaches were developed that defined our use of a protected hydroxymethyl group as the substituent that controls the stereochemical course of the cycloaddition cascade. In the course of these studies, several analogues of vindoline were prepared containing deep-seated structural changes presently accessible only by total synthesis. These analogues, bearing key modifications at C6-C8, were incorporated into vinblastine analogues and used to probe the unusual importance (100-fold) and define the potential role of the vinblastine ?(6,7)-double bond.

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Project description:In the first total synthesis of ent-dioxepandehydrothyrsiferol, the signature trans-anti-trans 7,7,6-fused tricyclic polyether framework was constructed in a single bromonium-initiated epoxide-opening cascade that incorporates both endo- and exo-selective epoxide openings, each directed by the substitution pattern of the epoxide (methyl groups). This study thus demonstrates the feasibility of a possible biogenesis.

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Total Synthesis of Decahydroquinoline Poison Frog Alkaloids ent-cis-195A and cis-211A.

Project description:The total synthesis of two decahydroquinoline poison frog alkaloids ent-cis-195A and cis-211A were achieved in 16 steps (38% overall yield) and 19 steps (31% overall yield), respectively, starting from known compound 1. Both alkaloids were synthesized from the common key intermediate 11 in a divergent fashion, and the absolute stereochemistry of natural cis-211A was determined to be 2R, 4aR, 5R, 6S, and 8aS. Interestingly, the absolute configuration of the parent decahydroquinoline nuclei of cis-211A was the mirror image of that of cis-195A, although both alkaloids were isolated from the same poison frog species, Oophaga (Dendrobates) pumilio, from Panama.

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Total Synthesis and Late-Stage C-H Oxidations of ent-Trachylobane Natural Products.

Project description:Herein, we present our studies to construct seven ent-trachylobane diterpenoids by employing a bioinspired two-phase synthetic strategy. The first phase provided enantioselective and scalable access to five ent-trachylobanes, of which methyl ent-trachyloban-19-oate was produced on a 300 mg scale. During the second phase, chemical C-H oxidation methods were employed to enable selective conversion to two naturally occurring higher functionalized ent-trachylobanes. The formation of regioisomeric analogs, which are currently inaccessible via enzymatic methods, reveals the potential as well as limitations of established chemical C-H oxidation protocols for complex molecule synthesis.

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Total Synthesis of (-)-Vindoline and (+)-4-epi-Vindoline Based on a 1,3,4-Oxadiazole Tandem Intramolecular [4 + 2]/[3 + 2] Cycloaddition Cascade Initiated by an Allene Dienophile.

Project description:It is reported that an allene dienophile can initiate a tandem intramolecular [4 + 2]/[3 + 2] cycloaddition cascade of 1,3,4-oxadiazoles, that the intermediate cross-conjugated 1,3-dipole (a carbonyl ylide) can participate in an ensuing [3 + 2] dipolar cycloaddition in a remarkably effective manner, and that the reaction can be implemented to provide the core pentacyclic ring system of vindoline. Its discovery improves a previous total synthesis of (-)-vindoline and was used in a total synthesis of (+)-4-epi-vindoline and (+)-4-epi-vinblastine that additionally enlists an alternative series of late-stage transformations.

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