- Synthesis of Silacyclic Dipeptides: Peptide Elongation at Both N-And C-Termini of Dipeptide
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A new type of peptide bond formation utilizing silacyclic amino acids or peptides is described. This work has the following advantages: (1) imidazolylsilane is a highly fascinating coupling reagent for dipeptide synthesis from N-,C-Terminal unprotected am
- Hattori, Tomohiro,Yamamoto, Hisashi
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supporting information
p. 1758 - 1765
(2022/02/01)
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- Recoverable Dendritic Phase-Transfer Catalysts that Contain (+)-Cinchonine-Derived Ammonium Salts
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Four new phosphorus dendrimeric phase-transfer catalysts are prepared that contain 12 (+)-cinchoninium salts on the surface obtained by the quaternisation of the quinuclidinic N atom. The asymmetric alkylation of a glycinate Schiff base with benzyl bromide is used as a benchmark reaction, and the dendrimeric catalyst that contains an allyl group on the O-9 hydroxy group of the cinchonine units is the most active. The recovery and reuse of the catalyst are possible for five consecutive runs without loss of activity and with only a slight decrease in enantioselectivity. If other electrophiles are used, substituted benzyl bromides give better results than other activated alkyl bromides to afford the corresponding R amino acid derivatives. A comparison of these results with those reported previously for similar cinchoninium salts shows that dendrimers could be a better support than other polymers for this type of organocatalysis.
- Rull, Jordi,Jara, José Juan,Sebastián, Rosa M.,Vallribera, Adelina,Nájera, Carmen,Majoral, Jean-Pierre,Caminade, Anne-Marie
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p. 2049 - 2056
(2016/07/07)
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- Environmentally Benign CO2-Based Copolymers: Degradable Polycarbonates Derived from Dihydroxybutyric Acid and Their Platinum-Polymer Conjugates
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(S)-3,4-Dihydroxybutyric acid ((S)-3,4-DHBA), an endogenous straight chain fatty acid, is a normal human urinary metabolite and can be obtained as a valuable chiral biomass for synthesizing statin-class drugs. Hence, its epoxide derivatives should serve as promising monomers for producing biocompatible polymers via alternating copolymerization with carbon dioxide. In this report, we demonstrate the production of poly(tert-butyl 3,4-dihydroxybutanoate carbonate) from racemic-tert-butyl 3,4-epoxybutanoate (rac-tBu 3,4-EB) and CO2 using bifunctional cobalt(III) salen catalysts. The copolymer exhibited greater than 99% carbonate linkages, 100% head-to-tail regioselectivity, and a glass-transition temperature (Tg) of 37 °C. By way of comparison, the similarly derived polycarbonate from the sterically less congested monomer, methyl 3,4-epoxybutanoate, displayed 91.8% head-to-tail content and a lower Tg of 18 °C. The tert-butyl protecting group of the pendant carboxylate group was removed using trifluoroacetic acid to afford poly(3,4-dihydroxybutyric acid carbonate). Depolymerization of poly(tert-butyl 3,4-dihydroxybutanoate carbonate) in the presence of strong base results in a stepwise unzipping of the polymer chain to yield the corresponding cyclic carbonate. Furthermore, the full degradation of the acetyl-capped poly(potassium 3,4-dihydroxybutyrate carbonate) resulted in formation of the biomasses, β-hydroxy-γ-butyrolacetone and 3,4-dihydroxybutyrate, in water (pH = 8) at 37 °C. In addition, water-soluble platinum-polymer conjugates were synthesized with platinum loading of 21.3-29.5%, suggesting poly(3,4-dihydroxybutyric acid carbonate) and related derivatives may serve as platinum drug delivery carriers.
- Tsai, Fu-Te,Wang, Yanyan,Darensbourg, Donald J.
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supporting information
p. 4626 - 4633
(2016/05/19)
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- Synthesis of models of the BC ring systems of MPC1001 and MPC1001F
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Piperazinedione 13, representing the BC rings of the anti-prostate cancer fungal metabolite MPC1001, was prepared by a route in which a sulfur-stabilized carbanion derived from 22 cyclizes onto the terminal ester of the pendant chain attached to N1. Another model, 14, was synthesized by cyclization of an α-ketoamide nitrogen onto an ester; 14 represents the BC rings of MPC1001F.
- Dong, Shuai,Indukuri, Kiran,Clive, Derrick L. J.,Gao, Jin-Ming
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supporting information
p. 8271 - 8274
(2016/07/06)
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- An efficient synthesis of tert-butyl ethers/esters of alcohols/amino acids using methyl tert-butyl ether
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A facile synthesis of a wide variety of tert-butyl ethers and tert-butyl ester derivatives under mild conditions is described. Alcohols etherified with tert-butyl methyl ether as tert-butyl source and solvent, in the presence of sulfuric acid. Many amino acid tert-butyl esters have been synthesized by this procedure. The reaction is simple, inexpensive, easily scaled up, and proceeds without observable racemization. A green method was developed for the deprotection of this group using Amberlite resin IR 120-H as catalyst.
- Mallesha,Prahlada Rao,Suhas,Channe Gowda
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experimental part
p. 641 - 645
(2012/02/15)
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- Preparation of protected amino acids
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The present invention involves a process for preparing protected amino acids. The process produces a di-tert-butyl amino ester or an N-protected di-tert-butyl amino ester by transesterification of an acidic amino acid or an N-protected acidic amino acid. By-products of the transesterification reaction may be recycled for use as part of the starting material. The N-protected di-tert-butyl amino ester may be hydrogenated to form a di-tert-butyl amino ester, which may subsequently form a di-tert-butyl ester hydrocholride salt.
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- Studies on the enantioselective synthesis of α-amino acids via asymmetric phase-transfer catalysis
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In this paper, we describe investigations into the use of cinchona alkaloid-derived quaternary ammonium phase-transfer catalysts for the asymmetric alkylation of a benzophenone-derived glycine-imine. Utility of this process is demonstrated by the enantioselective synthesis of a range of α-amino acid esters.
- Lygo,Crosby,Lowdon,Peterson,Wainwright
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p. 2403 - 2409
(2007/10/03)
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- A new class of asymmetric phase-transfer catalysts derived from Cinchona alkaloids - Application in the enantioselective synthesis of α-amino acids
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A new class of Cinchona alkaloid-derived quaternary ammonium phase-transfer catalysts bearing a N-anthracenylmethyl function are presented. These catalysts show high stereocontrol in the asymmetric alkylation of a benzophenone-derived glycine-imine, and application of this process to the enantioselective synthesis of a range of α-amino acid esters (e.e. 67-94%) is investigated.
- Lygo, Barry,Wainwright, Philip G.
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p. 8595 - 8598
(2007/10/03)
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