The Experts below are selected from a list of 375 Experts worldwide ranked by ideXlab platform
Hiromitsu Takayama - One of the best experts on this subject based on the ideXlab platform.
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Total Syntheses of Pleiocarpamine, Normavacurine, and C-Mavacurine.
Organic letters, 2019Co-Authors: Keigo Sato, Noriyuki Kogure, Mariko Kitajima, Hiromitsu TakayamaAbstract:The total syntheses of C-mavacurine-type indole alkaloids, (±)-pleiocarpamine, (±)-normavacurine, and (±)-C-mavacurine, were accomplished. The key step in the syntheses was the cyclization between the metal carbenoid at C16 and the N1 position in a Corynanthe-type compound that was equipped with a diazo function. For this cyclization, the N4 modification of the substrate using an amine–borane complex was indispensable to fix the molecular conformation.
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Total Syntheses of Pleiocarpamine, Normavacurine, and C‑Mavacurine
2019Co-Authors: Keigo Sato, Noriyuki Kogure, Mariko Kitajima, Hiromitsu TakayamaAbstract:The total syntheses of C-mavacurine-type indole alkaloids, (±)-pleiocarpamine, (±)-normavacurine, and (±)-C-mavacurine, were accomplished. The key step in the syntheses was the cyclization between the metal carbenoid at C16 and the N1 position in a Corynanthe-type compound that was equipped with a diazo function. For this cyclization, the N4 modification of the substrate using an amine–borane complex was indispensable to fix the molecular conformation
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Two novel indole alkaloids, Kopsiyunnanines A and B, from a Yunnan Kopsia
Tetrahedron Letters, 2008Co-Authors: Mariko Kitajima, Noriyuki Kogure, Rongping Zhang, Hiromitsu TakayamaAbstract:Two novel indole alkaloids having unusual skeletons were isolated from the aerial part of Yunnan Kopsia arborea. Kopsiyunnanine A (1) is a new class of bisindole alkaloid composed of vallesiachotamine (modified Corynanthe-type) and Aspidospermatan-type alkaloids. Kopsiyunnanine B (2) is a new Corynanthe-type oxindole alkaloid rearranged by D ring rotation.
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New Procedure to Mask the 2,3-π Bond of the Indole Nucleus and Its Application to the Preparation of Potent Opioid Receptor Agonists with a Corynanthe Skeleton
Organic letters, 2006Co-Authors: Hiromitsu Takayama, Mariko Kitajima, Sumphan Wongseripipatana, Hayato Ishikawa, Kaori Misawa, Naoki Okada, Yoshio Hatori, Toshihiko Murayama, Kimihito Tashima, Kenjiro MatsumotoAbstract:Treatment of indole alkaloids with hypervalent iodine in the presence of ethylene glycol provides 2,3-ethylene glycol bridged adducts that could be converted into the original indoles under mild reductive conditions. This procedure, which involves masking of the reactivity of the indole nucleus at the beta-position, was utilized for the modification of the benzene ring of the indoline derivative and was applied to the preparation of potent opioid receptor agonists with the Corynanthe skeleton. [reaction: see text]
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m chloroperbenzoic acid oxidation of Corynanthe type indole alkaloid mitragynine afforded unusual dimerization products
Heterocycles, 2004Co-Authors: Hayato Ishikawa, Mariko Kitajima, Hiromitsu TakayamaAbstract:The m-chloroperbenzoic acid oxidation of a Corynanthe-type indole alkaloid, mitragynine (1), in the presence of trifluoroacetic acid produced unusual dimeric compounds (3 and 4), both of which had a linkage between the C-7 and C-12' positions in the indole part of the starting material.
Mariko Kitajima - One of the best experts on this subject based on the ideXlab platform.
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Total Syntheses of Pleiocarpamine, Normavacurine, and C-Mavacurine.
Organic letters, 2019Co-Authors: Keigo Sato, Noriyuki Kogure, Mariko Kitajima, Hiromitsu TakayamaAbstract:The total syntheses of C-mavacurine-type indole alkaloids, (±)-pleiocarpamine, (±)-normavacurine, and (±)-C-mavacurine, were accomplished. The key step in the syntheses was the cyclization between the metal carbenoid at C16 and the N1 position in a Corynanthe-type compound that was equipped with a diazo function. For this cyclization, the N4 modification of the substrate using an amine–borane complex was indispensable to fix the molecular conformation.
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Total Syntheses of Pleiocarpamine, Normavacurine, and C‑Mavacurine
2019Co-Authors: Keigo Sato, Noriyuki Kogure, Mariko Kitajima, Hiromitsu TakayamaAbstract:The total syntheses of C-mavacurine-type indole alkaloids, (±)-pleiocarpamine, (±)-normavacurine, and (±)-C-mavacurine, were accomplished. The key step in the syntheses was the cyclization between the metal carbenoid at C16 and the N1 position in a Corynanthe-type compound that was equipped with a diazo function. For this cyclization, the N4 modification of the substrate using an amine–borane complex was indispensable to fix the molecular conformation
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Two novel indole alkaloids, Kopsiyunnanines A and B, from a Yunnan Kopsia
Tetrahedron Letters, 2008Co-Authors: Mariko Kitajima, Noriyuki Kogure, Rongping Zhang, Hiromitsu TakayamaAbstract:Two novel indole alkaloids having unusual skeletons were isolated from the aerial part of Yunnan Kopsia arborea. Kopsiyunnanine A (1) is a new class of bisindole alkaloid composed of vallesiachotamine (modified Corynanthe-type) and Aspidospermatan-type alkaloids. Kopsiyunnanine B (2) is a new Corynanthe-type oxindole alkaloid rearranged by D ring rotation.
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New Procedure to Mask the 2,3-π Bond of the Indole Nucleus and Its Application to the Preparation of Potent Opioid Receptor Agonists with a Corynanthe Skeleton
Organic letters, 2006Co-Authors: Hiromitsu Takayama, Mariko Kitajima, Sumphan Wongseripipatana, Hayato Ishikawa, Kaori Misawa, Naoki Okada, Yoshio Hatori, Toshihiko Murayama, Kimihito Tashima, Kenjiro MatsumotoAbstract:Treatment of indole alkaloids with hypervalent iodine in the presence of ethylene glycol provides 2,3-ethylene glycol bridged adducts that could be converted into the original indoles under mild reductive conditions. This procedure, which involves masking of the reactivity of the indole nucleus at the beta-position, was utilized for the modification of the benzene ring of the indoline derivative and was applied to the preparation of potent opioid receptor agonists with the Corynanthe skeleton. [reaction: see text]
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m chloroperbenzoic acid oxidation of Corynanthe type indole alkaloid mitragynine afforded unusual dimerization products
Heterocycles, 2004Co-Authors: Hayato Ishikawa, Mariko Kitajima, Hiromitsu TakayamaAbstract:The m-chloroperbenzoic acid oxidation of a Corynanthe-type indole alkaloid, mitragynine (1), in the presence of trifluoroacetic acid produced unusual dimeric compounds (3 and 4), both of which had a linkage between the C-7 and C-12' positions in the indole part of the starting material.
Norio Aimi - One of the best experts on this subject based on the ideXlab platform.
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A New 9-Methoxyyohimbine-Type Indole Alkaloid from Mitragyna africanus
Chemical & pharmaceutical bulletin, 2004Co-Authors: Hiromitsu Takayama, Mariko Kitajima, Norio Aimi, Hayato Ishikawa, Muhammad AjiAbstract:A new yohimbine-type indole alkaloid (1) was isolated from the stem bark of Mitragyna africanus (WILLD.) collected in Nigeria, along with known seven Corynanthe-type oxindole alkaloids, two secoiridoids, three lignans, and a quinovic acid derivative. Their structures were elucidated by spectroscopic analyses.
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First Asymmetric Total Synthesis of Us-7 and -8, Novel D-seco Corynanthe-Type Oxindole Alkaloids from Uncaria attenuata: Structure Revision of Us-7 and Determination of Absolute Stereochemistry
Organic letters, 2003Co-Authors: Hiromitsu Takayama, Mariko Kitajima, Rika Fujiwara, Yasuko Kasai, Norio AimiAbstract:Starting from (S)-glycidol, the asymmetric total synthesis of novel D-seco Corynanthe-type oxindoles Us-7 and Us-8 was accomplished. The structure of Us-7 was revised from the reported structure 1 with the (3R,7S) form to structure 22 with (3S,7R), and the absolute stereochemistry at C15 of both alkaloids was established.
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studies on the synthesis and opioid agonistic activities of mitragynine related indole alkaloids discovery of opioid agonists structurally different from other opioid ligands
Journal of Medicinal Chemistry, 2002Co-Authors: Hiromitsu Takayama, Mariko Kitajima, Norio Aimi, Dhavadee Ponglux, Hayato Ishikawa, Kenjiro Matsumoto, Mika Kurihara, Fumi Koyama, Tomoyuki Moriyama, Leonard T YamamotoAbstract:Mitragynine (1) is a major alkaloidal component in the Thai traditional medicinal herb, Mitragyna speciosa, and has been proven to exhibit analgesic activity mediated by opioid receptors. By utilizing this natural product as a lead compound, synthesis of some derivatives, evaluations of the structure−activity relationship, and surveys of the intrinsic activities and potencies on opioid receptors were performed with guinea pig ileum. The affinities of some compounds for μ-, δ-, and κ-receptors were determined in a receptor binding assay. The essential structural moieties in the Corynanthe type indole alkaloids for inducing the opioid agonistic activity were also clarified. The oxidative derivatives of mitragynine, i.e., mitragynine pseudoindoxyl (2) and 7-hydroxymitragynine (12), were found as opioid agonists with higher potency than morphine in the experiment with guinea pig ileum. In addition, 2 induced an analgesic activity in the tail flick test in mice.
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Formation of an unusual dimeric compound by lead tetraacetate oxidation of a Corynanthe-type indole alkaloid, mitragynine.
Chemical & pharmaceutical bulletin, 2002Co-Authors: Hiromitsu Takayama, Mariko Kitajima, Hayato Ishikawa, Norio AimiAbstract:Lead tetraacetate oxidation of a Corynanthe-type indole alkaloid, mitragynine, produced mainly 7-acetoxyindolenine derivative (2) together with a dimeric compound (4) as a minor product. The novel structure having a bridge between the C-11' and C-7 positions in the respective indolenine parts and its formation mechanism were studied.
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Structure Elucidation and Chiral-Total Synthesis of a New Indole Alkaloid, (−)-9-Methoxymitralactonine, Isolated from Mitragyna speciosa in Malaysia
Tetrahedron, 2000Co-Authors: Hiromitsu Takayama, Mariko Kitajima, Mika Kurihara, Ikram M. Said, Norio AimiAbstract:Abstract A new Corynanthe-type indole alkaloid, (−)-9-methoxymitralactonine ( 1 ), having a highly conjugated system was isolated from the young leaves of Mitragyna speciosa in Malaysia, and its structure was first deduced by spectroscopic analysis and then confirmed by chiral-total synthesis starting from optically pure epoxy-ketone and 5-methoxy-3,4-dihydro-β-carboline. The chiral HPLC analysis demonstrated that the natural 9-methoxymitralactonine contained predominantly the (−)-enantiomer over the (+)-enantiomer in the ratio of 62:38.
Hayato Ishikawa - One of the best experts on this subject based on the ideXlab platform.
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New Procedure to Mask the 2,3-π Bond of the Indole Nucleus and Its Application to the Preparation of Potent Opioid Receptor Agonists with a Corynanthe Skeleton
Organic letters, 2006Co-Authors: Hiromitsu Takayama, Mariko Kitajima, Sumphan Wongseripipatana, Hayato Ishikawa, Kaori Misawa, Naoki Okada, Yoshio Hatori, Toshihiko Murayama, Kimihito Tashima, Kenjiro MatsumotoAbstract:Treatment of indole alkaloids with hypervalent iodine in the presence of ethylene glycol provides 2,3-ethylene glycol bridged adducts that could be converted into the original indoles under mild reductive conditions. This procedure, which involves masking of the reactivity of the indole nucleus at the beta-position, was utilized for the modification of the benzene ring of the indoline derivative and was applied to the preparation of potent opioid receptor agonists with the Corynanthe skeleton. [reaction: see text]
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m chloroperbenzoic acid oxidation of Corynanthe type indole alkaloid mitragynine afforded unusual dimerization products
Heterocycles, 2004Co-Authors: Hayato Ishikawa, Mariko Kitajima, Hiromitsu TakayamaAbstract:The m-chloroperbenzoic acid oxidation of a Corynanthe-type indole alkaloid, mitragynine (1), in the presence of trifluoroacetic acid produced unusual dimeric compounds (3 and 4), both of which had a linkage between the C-7 and C-12' positions in the indole part of the starting material.
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A New 9-Methoxyyohimbine-Type Indole Alkaloid from Mitragyna africanus
Chemical & pharmaceutical bulletin, 2004Co-Authors: Hiromitsu Takayama, Mariko Kitajima, Norio Aimi, Hayato Ishikawa, Muhammad AjiAbstract:A new yohimbine-type indole alkaloid (1) was isolated from the stem bark of Mitragyna africanus (WILLD.) collected in Nigeria, along with known seven Corynanthe-type oxindole alkaloids, two secoiridoids, three lignans, and a quinovic acid derivative. Their structures were elucidated by spectroscopic analyses.
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studies on the synthesis and opioid agonistic activities of mitragynine related indole alkaloids discovery of opioid agonists structurally different from other opioid ligands
Journal of Medicinal Chemistry, 2002Co-Authors: Hiromitsu Takayama, Mariko Kitajima, Norio Aimi, Dhavadee Ponglux, Hayato Ishikawa, Kenjiro Matsumoto, Mika Kurihara, Fumi Koyama, Tomoyuki Moriyama, Leonard T YamamotoAbstract:Mitragynine (1) is a major alkaloidal component in the Thai traditional medicinal herb, Mitragyna speciosa, and has been proven to exhibit analgesic activity mediated by opioid receptors. By utilizing this natural product as a lead compound, synthesis of some derivatives, evaluations of the structure−activity relationship, and surveys of the intrinsic activities and potencies on opioid receptors were performed with guinea pig ileum. The affinities of some compounds for μ-, δ-, and κ-receptors were determined in a receptor binding assay. The essential structural moieties in the Corynanthe type indole alkaloids for inducing the opioid agonistic activity were also clarified. The oxidative derivatives of mitragynine, i.e., mitragynine pseudoindoxyl (2) and 7-hydroxymitragynine (12), were found as opioid agonists with higher potency than morphine in the experiment with guinea pig ileum. In addition, 2 induced an analgesic activity in the tail flick test in mice.
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Formation of an unusual dimeric compound by lead tetraacetate oxidation of a Corynanthe-type indole alkaloid, mitragynine.
Chemical & pharmaceutical bulletin, 2002Co-Authors: Hiromitsu Takayama, Mariko Kitajima, Hayato Ishikawa, Norio AimiAbstract:Lead tetraacetate oxidation of a Corynanthe-type indole alkaloid, mitragynine, produced mainly 7-acetoxyindolenine derivative (2) together with a dimeric compound (4) as a minor product. The novel structure having a bridge between the C-11' and C-7 positions in the respective indolenine parts and its formation mechanism were studied.
Stephen F. Martin - One of the best experts on this subject based on the ideXlab platform.
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Design, Synthesis, and Evaluation of Novel Anti-Trypanosomal Compounds.
Tetrahedron, 2020Co-Authors: Lance T. Lepovitz, Alan R. Meis, Sarah M. Thomas, Justin Wiedeman, Alexandra Pham, Kojo Mensa-wilmot, Stephen F. MartinAbstract:Abstract Human African trypanosomiasis (HAT) is a deadly neglected tropical disease caused by the protozoan parasite Trypanosoma brucei. During the course of screening a collection of diverse nitrogenous heterocycles, we discovered two novel compounds that contain the tetracyclic core of the Yohimbine and Corynanthe alkaloids, were potent inhibitors of T. brucei proliferation and T. brucei methionyl-tRNA synthetase (TbMetRS) activity. Inspired by these key findings, we prepared several novel series of hydroxyalkyl δ-lactam, δ-lactam, and piperidine analogs and tested their anti-trypanosomal activity. A number of inhibitors were more potent against T. brucei than these initial hits with one hydroxyalkyl δ-lactam derivative being 25-fold more effective in our assay. Surprisingly, most of these active compounds failed to inhibit TbMetRS. This work underscores the importance of verifying, irrespective of close structural similarities, that new compounds designed from a lead with a known biological target engage the putative binding site.
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multicomponent assembly processes for the synthesis of diverse yohimbine and Corynanthe alkaloid analogues
ACS Combinatorial Science, 2013Co-Authors: Brett A Granger, Kyosuke Kaneda, Zhiqian Wang, Zhenglai Fang, Stephen F. MartinAbstract:A strategy involving a Mannich-type multicomponent assembly process followed by a 1,3-dipolar cycloaddition has been developed for the rapid and efficient construction of parent heterocyclic scaffolds bearing indole and isoxazolidine rings. These key intermediates were then readily elaborated using well-established protocols for refunctionalization and cross-coupling to access a diverse 180-member library of novel pentacyclic and tetracyclic compounds related to the Yohimbine and Corynanthe alkaloids. Several other new multicomponent assembly processes were developed to access dihydro-β-carboline-fused benzodiazepines, pyrimidinediones, and rutaecarpine derivatives.
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Multicomponent Assembly Processes for the Synthesis of Diverse Yohimbine and Corynanthe Alkaloid Analogues
2013Co-Authors: Brett A Granger, Kyosuke Kaneda, Zhiqian Wang, Zhenglai Fang, Stephen F. MartinAbstract:A strategy involving a Mannich-type multicomponent assembly process followed by a 1,3-dipolar cycloaddition has been developed for the rapid and efficient construction of parent heterocyclic scaffolds bearing indole and isoxazolidine rings. These key intermediates were then readily elaborated using well-established protocols for refunctionalization and cross-coupling to access a diverse 180-member library of novel pentacyclic and tetracyclic compounds related to the Yohimbine and Corynanthe alkaloids. Several other new multicomponent assembly processes were developed to access dihydro-β-carboline-fused benzodiazepines, pyrimidinediones, and rutaecarpine derivatives
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diversity oriented synthesis concise entry to novel derivatives of yohimbine and Corynanthe alkaloids
Tetrahedron Letters, 2012Co-Authors: Zhiqian Wang, Kyosuke Kaneda, Zhenglai Fang, Stephen F. MartinAbstract:A novel MCAP-cycloaddition sequence has been applied to the facile synthesis of β-carboline intermediates to gain rapid access to novel derivatives of yohimbine-like and Corynanthe-like compounds that may be easily diversified by cross-coupling reactions and N-derivatizations to generate small compound libraries.
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General strategy for the syntheses of Corynanthe, tacaman, and oxindole alkaloids.
The Journal of organic chemistry, 2006Co-Authors: Alexander Deiters, Martin Pettersson, Stephen F. MartinAbstract:We report herein the total synthesis of the Corynanthe alkaloid dihydroCorynantheol and the formal syntheses of the indole alkaloids tacamonine, rhynchophylline, and hirsutine. The strategies for assembling the Corynanthe and tacaman skeletal frameworks comprised of both the classical ABD → ABCD and ABC → ABCD approaches wherein the variously substituted piperidinone D-rings were formed via ring-closing metathesis (RCM) followed by a 1,4-addition to introduce the requisite side chain at C(15). Since 1,4-additions to α,β-unsaturated lactams represent an underdeveloped field, we conducted a series of studies with two unsaturated lactams employing organocuprates and metal enolates as the nucleophiles. These studies revealed that organocuprates derived from Grignard reagents and either stoichiometric amounts of CuCN or catalytic amounts of CuBr·DMS complex are excellent nucleophiles for such additions; TMSCl was a crucial additive for optimizing these reactions. The anion derived from ethyl 1,3-dithiolane-2-c...
