- The preparation of optically active epineoclausenamide and enantiomeric separation of its racemate
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We synthesized the optically active epineoclausenamide by utilizing chiral reagents, such as R-α-methylbenzylamine and S-α-methylbenzylamine, for the resolution of the intermediate (trans-3-phenyl-oxiranecarboxylic acid 12), followed by amide exchange, cy
- Yan, Yixiao,Zhu, Senmei,Luo, Xuna,Rao, Yu,Su, Jinlong,He, Guantao,Lin, Hansen
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p. 643 - 651
(2021/08/24)
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- Intermolecular Amine Transfer to Enantioenriched trans-3Phenylglycidates by an α/β-Aminomutase to Access Both anti-Phenylserine Isomers
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β-Hydroxy-α-amino acids are noncanonical amino acids with two stereocenters and with useful applications in the pharmaceutical and agrochemical sectors. Here, a 5-methylidene-3,5-dihydro-4H-imidazol-4-one-dependent aminomutase from Taxus canadensis (TcPAM) was repurposed to transfer the amino group irreversibly from (2S)-styryl-α-alanine to exogenously supplied trans-3-phenylglycidate enantiomers, producing anti-phenylserines stereoselectively. TcPAM catalysis inverted the intrinsic regioselective chemistry from amination at Cβ to Cα of enantioenriched trans-3-phenylglycidates to make phenylserine predominantly (97%)phenylisoserine (~3% relative abundance). Gas chromatography?mass spectrometry analysis of the chiral auxiliary derivatives of the biocatalyzed products confirmed that the amine transfer was stereoselective for each glycidate enantiomer. TcPAM converted (2S,3R)-3-phenylglycidate to (2S)-anti-phenylserine predominantly (89%) and (2R,3S)-3-phenylglycidate to (2R)-anti-phenylserine (88%)their antipodes, with inversion of the configuration at Cα in each case. Both glycidate enantiomers formed a small amount (~10%) of syn-phenylserine by retaining the configuration at Cα. The minor syn-isomer likely came from a β-hydroxy oxiranone intermediate formed by intramolecular ring opening of the oxirane ring by the carboxylate before amine transfer. TcPAM had a slight preference toward (2S,3R)-3-phenylglycidate, which was turned(kcat = 0.3 min?1) 1.5 times faster than the (2R,3S)-glycidate (kcat = 0.2 min?1). The catalytic efficiencies (kcatapp/KMapp ≈ 20 M?1s?1) of TcPAM for the antipodes were similar. The kinetic data supported a two-substrate ping-pong mechanism for the amination of the phenylglycidates, with competitive inhibition at higher glycidate substrate concentrations.
- Shee, Prakash K.,Yan, Honggao,Walker, Kevin D.
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p. 15071 - 15082
(2020/12/21)
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- New chiral amino alcohol ligands for catalytic enantioselective addition of diethylzincs to aldehydes
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A study aimed at the synthesis and structure optimization of new, efficient, optically active β-amino alcohol ligands with a structure suitable for immobilization on magnetite nanoparticles has been carried out. The optimized homogeneous amino alcohol catalysts 13a and 13b, the chirality of which arises from the Sharpless epoxidation of suitable allyl alcohols, were tested by employing the well-established enantioselective amino alcohol-promoted addition of diethylzinc to benzaldehyde, giving the corresponding benzyl alcohol with nearly quantitative yield and ee = 95%. Then, their broad applicability as chiral catalysts was evaluated by carrying out the same reaction on a family of aldehydes, including variously substituted aromatic ones as well as an aliphatic analogue. The results have confirmed the validity of the fine-tuning process performed on ligands 13a and 13b. In fact, both exhibited excellent catalytic activity as demonstrated by the chemical yields and ee obtained from all the tested aldehydes, almost independent of the position and type of substitution in the aromatic ring.
- Sappino, Carla,Mari, Alessandra,Mantineo, Agnese,Moliterno, Mauro,Palagri, Matteo,Tatangelo, Chiara,Suber, Lorenza,Bovicelli, Paolo,Ricelli, Alessandra,Righi, Giuliana
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p. 1860 - 1870
(2018/03/23)
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- Reverse turn induced π-facial selectivity during polyaniline-supported cobalt(II) salen catalyzed aerobic epoxidation of N-cinnamoyl L-proline derived peptides
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A novel chemo- and diastereoselective aerobic epoxidation of the N-cinnamoyl peptides catalyzed by polyaniline-supported cobalt(II) salen (PASCOS) is described. The N-cinnamoyl proline derived peptides 1 show a high π-facial selectivity during these epoxidations. The origin of this diastereoselectivity in I has been attributed to (i) the propensity of the N-cinnamoyl proline amide to exist predominantly as trans rotamer in CDCl3, DMSO-d6, and CH3CN medium and (ii) existence of these peptides as organized structures (γ- and β-turns) due to the presence of intramolecular hydrogen bonds. An extensive solution NMR and MD simulation study on 1d and 1f indicates that the origin of the high π-facial selectivity is due to the well-defined γ- and β-turns which result in the hindrance of one face of the cinnamoyl double bond in the transition state of the epoxidation reaction.
- Nandy, Jyoti Prokosh,Prabhakaran,Kumar, S. Kiran,Kunwar,Iqbal, Javed
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p. 1679 - 1692
(2007/10/03)
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- Improved enantioselectivity in the epoxidation of cinnamic acid derivatives with dioxiranes from keto bile acids
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The asymmetric epoxidation of substituted cinnamic acids has been obtained in the presence of different keto bile acid derivatives as optically active carbonyl inducers and Oxone as oxygen source. Predominant or almost exclusive formation of both enantiomeric epoxides is obtained (ee up to 95%) depending on the specific substitution at carbons C(7) and C(12) of the bile acid.
- Bortolini, Olga,Fantin, Giancarlo,Fogagnolo, Marco,Forlani, Roberto,Maietti, Silvia,Pedrini, Paola
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p. 5802 - 5806
(2007/10/03)
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- π-Facial selectivity in polyaniline supported cobalt catalysed aerobic epoxidation of N-cinnamoyl proline derivatives
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Polyaniline supported cobalt salen catalyses the facially selective aerobic epoxidation (oxygen/2-methylpropanal) of N-cinnamoyl proline derived peptides. A high diastereoselectivity is observed for peptides which are able to adopt a γ- or β-turn due to intramolecular hydrogen bonding.
- Prabhakaran,Nandy, Jyoti Prokash,Shukla, Shalini,Iqbal, Javed
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p. 333 - 337
(2007/10/03)
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- Synthesis of taxoids 4. Novel and versatile methods for preparation of new taxoids by employing cis- or trans-phenyl glycidic acid
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A novel route to the synthesis of docetaxel using esterification of (2R,3R)-or (2R,3S)-glycidic acid with 7,10-bis-O-(2,2,2- trichloroethoxycarbonyl)-10-deacetylbaccatin III is described. Related novel taxoids which have new side chains were synthesized from these synthetic intermediates.
- Yamaguchi, Tetsuo,Harada, Naoyuki,Ozaki, Kunihiko,Hayashi, Masahito,Arakawa, Hiroaki,Hashiyama, Tomiki
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p. 1005 - 1016
(2007/10/03)
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- A Catalytic Asymmetric Synthesis of N-Boc-β-Methylphenylalanines
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An efficient, stereodivergent, and enantioselective synthesis of the syn and anti diastereomers of N-Boc-β-methylphenylalanine has been developed. Starting from enantiomerically pure (2S,3S)-2,3-epoxy-3-phenyl-1-propanol, a three-step sequence, consisting of the oxidation of the primary alcohol up to the carboxyl stage, ring opening of the epoxy acid with Me2CuCNLi2, and esterification of the resulting hydroxy acid with methyl iodide, leads to the hydroxy ester anti-W, which has been converted in a stereodivergent manner into both the (2S,3R) and the (2R,3R) diastereomers of N-Boc-β-methylphenylalanine, syn-1 and anti-1, respectively. Activation of the secondary hydroxy group in anti-10 as a mesylate, followed by nucleophilic displacement with sodium azide, hydrogenolysis with simultaneous protection of the amino group, and saponification with LiOH, affords syn-1. The same reaction sequence applied to syn-10, obtained in turn by Mitsunobu reaction of anti-10 with p-nitrobenzoic acid followed by the hydrolysis of the resulting p-nitrobenzoate, leads to anti-1. Both products have been obtained with ≥99% enantiomeric excess.
- Pasto, Mireia,Moyano, Albert,Pericas, Miquel A.,Riera, Antoni
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p. 8425 - 8431
(2007/10/03)
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- Asymmetric synthesis of (-)-dehydroclausenamide
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Asymmetric synthesis of (-)-dehydroclausenamide 1 by scheme 2 was reported. Sharpless epoxidation was applied to cinnamyl alcohol for introduction of two desired chiral centers and the potential hydroxyl group. The key intermediate, γ-lactam (-)-5, was obtained by regio-selective intramolecular cyclization of (-)-6. Subsequent stereo-selective reduction was achieved by reducing C3-tetrahydropyranyl ether of (-)-5. The title natural product was then obtained by successive tosylation, hydrolysis and cyclization.
- Huang, Dai-Fei,Huang, Liang
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p. 3135 - 3142
(2007/10/02)
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