The Experts below are selected from a list of 8184 Experts worldwide ranked by ideXlab platform
Rinaldo Marini Bettolo - One of the best experts on this subject based on the ideXlab platform.
-
Unexpected Racemization in the Course of the Acetalization of (+)-(S)-5-Methyl-Wieland–Miescher Ketone with 1,2-Ethanediol and TsOH under Classical Experimental Conditions
International journal of molecular sciences, 2019Co-Authors: Francesca Leonelli, Irene Piergentili, Giulio Lucarelli, Luisa Maria Migneco, Rinaldo Marini BettoloAbstract:(+)-(S) and (-)-(R)-5-methyl-Wieland-Miescher ketone (+)-1 and (-)-1, are important synthons in the diastereo and enantioselective syntheses of biological and/or pharmacological interesting compounds. A key step in these syntheses is the chemoselective C(1)O acetalization to (+)-5 and (-)-5, respectively. Various procedures for this transformation have been described in the literature. Among them, the classical procedure based on the use of 1,2-ethanediol and TsOH in refluxing benzene in the presence of a Dean-Stark apparatus. Within our work on bioactive natural products, it occurred to us to observe the partial Racemization of (+)-5 in the course of the acetalization of (+)-1 by means of the latter methodology. Aiming to investigate this drawback, which, to our best knowledge, has no precedents in the literature, we acetalized with 1,2-ethanediol and TsOH in refluxing benzene and in the presence of a Dean-Stark apparatus under various experimental conditions, enantiomerically pure (+)-1. It was found that the extent of Racemization depends on the TsOH/(+)-1 and 1,2-ethanediol/(+)-1 ratios. Mechanism hypotheses for this partial and unexpected Racemization are provided.
-
unexpected Racemization in the course of the acetalization of s 5 methyl wieland miescher ketone with 1 2 ethanediol and tsoh under classical experimental conditions
International Journal of Molecular Sciences, 2019Co-Authors: Francesca Leonelli, Irene Piergentili, Giulio Lucarelli, Luisa Maria Migneco, Rinaldo Marini BettoloAbstract:(+)-(S) and (-)-(R)-5-methyl-Wieland-Miescher ketone (+)-1 and (-)-1, are important synthons in the diastereo and enantioselective syntheses of biological and/or pharmacological interesting compounds. A key step in these syntheses is the chemoselective C(1)O acetalization to (+)-5 and (-)-5, respectively. Various procedures for this transformation have been described in the literature. Among them, the classical procedure based on the use of 1,2-ethanediol and TsOH in refluxing benzene in the presence of a Dean-Stark apparatus. Within our work on bioactive natural products, it occurred to us to observe the partial Racemization of (+)-5 in the course of the acetalization of (+)-1 by means of the latter methodology. Aiming to investigate this drawback, which, to our best knowledge, has no precedents in the literature, we acetalized with 1,2-ethanediol and TsOH in refluxing benzene and in the presence of a Dean-Stark apparatus under various experimental conditions, enantiomerically pure (+)-1. It was found that the extent of Racemization depends on the TsOH/(+)-1 and 1,2-ethanediol/(+)-1 ratios. Mechanism hypotheses for this partial and unexpected Racemization are provided.
Bhubaneswar Mandal - One of the best experts on this subject based on the ideXlab platform.
-
e ethyl 2 cyano 2 2 4 6 trichlorobenzoyl oxy imino acetate a modified yamaguchi reagent for enantioselective esterification thioesterification amidation and peptide synthesis
ACS omega, 2018Co-Authors: Jyoti Chandra, Srinivasa Rao Manne, Sandip Mondal, Bhubaneswar MandalAbstract:Here, the synthesis and applications of (E)-ethyl-2-cyano-2-(((2,4,6-trichlorobenzoyl)oxy)imino)acetate as a Racemization suppressing and easily recyclable version of the Yamaguchi reagent that can be used for amide and peptide synthesis are reported. We demonstrated its application in Racemization-free esterification, thioesterification, amidation, and peptide bond formation. We successfully synthesized oligopeptides on the solid support in dimethylformamide as well as in solution (dichloromethane) by applying this coupling reagent. It is important to note that a mixed-anhydride-based method provides peptide-forming reactions as good as the current methods using built-in coupling reagents. Mechanism investigation, Racemization suppression, and recyclability are also discussed.
-
(E)‑Ethyl-2-cyano-2-(((2,4,6-trichlorobenzoyl)oxy)imino)acetate: A Modified Yamaguchi Reagent for Enantioselective Esterification, Thioesterification, Amidation, and Peptide Synthesis
2018Co-Authors: Jyoti Chandra, Srinivasa Rao Manne, Sandip Mondal, Bhubaneswar MandalAbstract:Here, the synthesis and applications of (E)-ethyl-2-cyano-2-(((2,4,6-trichlorobenzoyl)oxy)imino)acetate as a Racemization suppressing and easily recyclable version of the Yamaguchi reagent that can be used for amide and peptide synthesis are reported. We demonstrated its application in Racemization-free esterification, thioesterification, amidation, and peptide bond formation. We successfully synthesized oligopeptides on the solid support in dimethylformamide as well as in solution (dichloromethane) by applying this coupling reagent. It is important to note that a mixed-anhydride-based method provides peptide-forming reactions as good as the current methods using built-in coupling reagents. Mechanism investigation, Racemization suppression, and recyclability are also discussed
-
ethyl 2 tert butoxycarbonyloxyimino 2 cyanoacetate boc oxyma an efficient reagent for the Racemization free synthesis of ureas carbamates and thiocarbamates via lossen rearrangement
Advanced Synthesis & Catalysis, 2017Co-Authors: Srinivasa Rao Manne, Kishore Thalluri, Rajat Subhra Giri, Jyoti Chandra, Bhubaneswar MandalAbstract:Boc-Oxyma (Ethyl 2-(tert-butoxycarbonyloxyimino)-2-cyanoacetate) has been reported previously as an efficient coupling reagent for the synthesis of amides, peptides, esters, thioesters and hydroxamic acids. It is known for its excellent Racemization suppression capability, and also as an environment friendly reagent as it generates only Oxyma as solid byproduct that can be recovered easily and recycled for the synthesis of the same reagent. In this update, we report a simple, efficient, environment friendly, chemoselective and Racemization free method for the synthesis of ureas, carbamates and thiocarbamates from hydroxamic acids via Lossen rearrangement by using Boc-Oxyma. We have achieved Racemization free di- and tri-peptidyl ureas with very good yield by using this protocol. A rigorous mechanistic investigation is also incorporated.
Lirong Yang - One of the best experts on this subject based on the ideXlab platform.
-
highly efficient dynamic kinetic resolution of secondary aromatic alcohols using a low cost solid super acid as a Racemization catalyst
Tetrahedron Letters, 2013Co-Authors: Gang Xu, Jianping Wu, Yongjun Chen, Yongmei Cheng, Liang Wang, Lirong YangAbstract:A new, efficient dynamic kinetic resolution (DKR) of secondary aromatic alcohols using self-made solid super acid TiO2/SO42- as a Racemization catalyst was developed. Low-cost and easily produced TiO2/SO42- showed excellent Racemization activity. When coupled with the lipase, Novozym 435, good biocompatibility was observed, and optically pure aromatic acetate (>99%) was obtained with a high yield. It is noteworthy that the system could be reused more than 10 times with little loss of yield or reduction in the enantiomeric excess (ee) value of product.
-
highly efficient dynamic kinetic resolution of secondary aromatic alcohols with low cost and easily available acid resins as Racemization catalysts
Tetrahedron Letters, 2010Co-Authors: Yongmei Cheng, Chensheng Zhang, Jianping Wu, Gang Xu, Lirong YangAbstract:Abstract A new and efficient dynamic kinetic resolution (DKR) process of secondary aromatic alcohols was developed with acid resins as Racemization catalysts. Acid resin CD8604 was shown to have excellent Racemization activity and good biocompatibility. When employing CD8604 and complex acyl donors as Racemization catalyst and acyl donor, respectively, enantiomerically pure aromatic acetate was obtained with excellent yield and ee values through the DKR process. It is noteworthy that the system could be reused more than 10 times with little loss of yield and ee value.
Jan-e. Bäckvall - One of the best experts on this subject based on the ideXlab platform.
-
chemoenzymatic dynamic kinetic resolution of secondary alcohols using an air and moisture stable iron Racemization catalyst
Chemistry: A European Journal, 2017Co-Authors: Karl P J Gustafson, Arnar Guðmundsson, Kayla Lewis, Jan-e. BäckvallAbstract:Herein, we report on a metalloenzymatic dynamic kinetic resolution of sec-alcohols employing an iron-based Racemization catalyst together with a lipase. The iron catalyst was evaluated in Racemization and then used in dynamic kinetic resolution of a number of sec-alcohols to give enantiomerically pure products in good to high yields. The iron catalyst is air and moisture stable and is readily accessible.
-
combined ruthenium ii and lipase catalysis for efficient dynamic kinetic resolution of secondary alcohols insight into the Racemization mechanism
Journal of the American Chemical Society, 2005Co-Authors: Belen Martinmatute, Michaela Edin, Krisztian Bogar, Betul F Kaynak, Jan-e. BäckvallAbstract:Combined Ruthenium(II) and Lipase Catalysis for Efficient Dynamic Kinetic Resolution of Secondary Alcohols. Insight into the Racemization Mechanism
Francesca Leonelli - One of the best experts on this subject based on the ideXlab platform.
-
Unexpected Racemization in the Course of the Acetalization of (+)-(S)-5-Methyl-Wieland–Miescher Ketone with 1,2-Ethanediol and TsOH under Classical Experimental Conditions
International journal of molecular sciences, 2019Co-Authors: Francesca Leonelli, Irene Piergentili, Giulio Lucarelli, Luisa Maria Migneco, Rinaldo Marini BettoloAbstract:(+)-(S) and (-)-(R)-5-methyl-Wieland-Miescher ketone (+)-1 and (-)-1, are important synthons in the diastereo and enantioselective syntheses of biological and/or pharmacological interesting compounds. A key step in these syntheses is the chemoselective C(1)O acetalization to (+)-5 and (-)-5, respectively. Various procedures for this transformation have been described in the literature. Among them, the classical procedure based on the use of 1,2-ethanediol and TsOH in refluxing benzene in the presence of a Dean-Stark apparatus. Within our work on bioactive natural products, it occurred to us to observe the partial Racemization of (+)-5 in the course of the acetalization of (+)-1 by means of the latter methodology. Aiming to investigate this drawback, which, to our best knowledge, has no precedents in the literature, we acetalized with 1,2-ethanediol and TsOH in refluxing benzene and in the presence of a Dean-Stark apparatus under various experimental conditions, enantiomerically pure (+)-1. It was found that the extent of Racemization depends on the TsOH/(+)-1 and 1,2-ethanediol/(+)-1 ratios. Mechanism hypotheses for this partial and unexpected Racemization are provided.
-
unexpected Racemization in the course of the acetalization of s 5 methyl wieland miescher ketone with 1 2 ethanediol and tsoh under classical experimental conditions
International Journal of Molecular Sciences, 2019Co-Authors: Francesca Leonelli, Irene Piergentili, Giulio Lucarelli, Luisa Maria Migneco, Rinaldo Marini BettoloAbstract:(+)-(S) and (-)-(R)-5-methyl-Wieland-Miescher ketone (+)-1 and (-)-1, are important synthons in the diastereo and enantioselective syntheses of biological and/or pharmacological interesting compounds. A key step in these syntheses is the chemoselective C(1)O acetalization to (+)-5 and (-)-5, respectively. Various procedures for this transformation have been described in the literature. Among them, the classical procedure based on the use of 1,2-ethanediol and TsOH in refluxing benzene in the presence of a Dean-Stark apparatus. Within our work on bioactive natural products, it occurred to us to observe the partial Racemization of (+)-5 in the course of the acetalization of (+)-1 by means of the latter methodology. Aiming to investigate this drawback, which, to our best knowledge, has no precedents in the literature, we acetalized with 1,2-ethanediol and TsOH in refluxing benzene and in the presence of a Dean-Stark apparatus under various experimental conditions, enantiomerically pure (+)-1. It was found that the extent of Racemization depends on the TsOH/(+)-1 and 1,2-ethanediol/(+)-1 ratios. Mechanism hypotheses for this partial and unexpected Racemization are provided.
