- Gold-Catalyzed Amide/Carbamate-Linked N, O-Acetal Formation with Bulky Amides and Alcohols
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A gold-catalyzed N,O-acetal formation was established to construct an amide/carbamate-linked N,O-acetal substructure with bulky alcohols. The acyliminium cation species generated from o-alkynylbenzoic acid ester in the presence of a gold catalyst is highly reactive and underwent nucleophilic attack of various bulky alcohols and phenols at room temperature under neutral conditions, leading to the corresponding N,O-acetals in yields of 34-89% with good functional group tolerance.
- Ohsawa, Kosuke,Ochiai, Shota,Kubota, Junya,Doi, Takayuki
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p. 1281 - 1291
(2021/01/14)
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- Preparation method of N -fluorenylmethoxycarbonyl - L -aspartic -4 -tert-butyl ester
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The invention relates to the technical field of organic synthesis, in particular to a preparation method of a fluorenylmethoxycarbonyl - aspartic -4 - tert-butyl ester, which comprises the following specific steps: L - aspartic acid is used as a starting raw material, L - aspartic acid internal anhydride hydrochloride is obtained through dehydration treatment of phosphorus trichloride. L- Aspartic acid ester hydrochloride and ethanol were subjected to alcoholysis to obtain L -aspartate hydrochloride. The transesterification reaction L-aspartate and tert-butyl ester gives L -butyl-1 -ethyl-4 -butyl acrylate. Further hydrolysis L-butyl-1 - ethyl ester -4 - gives L -butyl-4 -tert-butyl ester. The L-aspartate -4 - tert-butyl ester is reacted with the fluorenylmethoxycarbonyl reagent to obtain the target product fluorenylmethoxycarbonyl - aspartic -4 -tert-butyl ester. The preparation method of the fluorenylmethoxycarbonyl - aspartic -4 - tert-butyl ester provided by the invention is safe and environment-friendly in production process and suitable for industrial large-scale production.
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Paragraph 0013; 0027; 0034-0035; 0036; 0043-0044
(2021/08/25)
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- A mild removal of Fmoc group using sodium azide
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A mild method for effectively removing the fluorenylmethoxycarbonyl (Fmoc) group using sodium azide was developed. Without base, sodium azide completely deprotected Nα-Fmoc-amino acids in hours. The solvent-dependent conditions were carefully studied and then optimized by screening different sodium azide amounts and reaction temperatures. A variety of Fmoc-protected amino acids containing residues masked with different protecting groups were efficiently and selectively deprotected by the optimized reaction. Finally, a biologically significant hexapeptide, angiotensin IV, was successfully synthesized by solid phase peptide synthesis using the developed sodium azide method for all Fmoc removals. The base-free condition provides a complement method for Fmoc deprotection in peptide chemistry and modern organic synthesis. Graphical Abstract: [Figure not available: see fulltext.]
- Chen, Chun-Chi,Rajagopal, Basker,Liu, Xuan Yu,Chen, Kuan Lin,Tyan, Yu-Chang,Lin, Fui,Lin, Po-Chiao
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p. 367 - 374
(2014/03/21)
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- Reliable and safe, gram-scale hydrogenation and hydrogenolysis of O-benzyl ether groups with in situ Pd0/C catalyst
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Hydrogenation of alkenes, alkynes, and hydrogenolysis of O-benzyl ethers with Pd0/C catalyst generated in situ can be readily scaled up under safer conditions than with traditional procedures. The precise control of the palladium loading and the mild conditions developed allow the formation of a very active and reliable Pd0/C catalyst, leading to highly reproducible results. Georg Thieme Verlag Stuttgart - New York.
- Felpin, Francois-Xavier,Fouquet, Eric
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experimental part
p. 2893 - 2896
(2011/10/13)
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- A useful, reliable and safer protocol for hydrogenation and the hydrogenolysis of o-benzyl groups: The in situ preparation of an active Pd 0/C catalyst with well-defined properties
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A simple, highly reproducible protocol for the hydrogenation of alkenes and alkynes and for the hydrogenolysis of O-benzyl ethers has been developed. The method features the in situ preparation of an active Pd0/C catalyst from Pd(OAc)2 and charcoal, in methanol. The mild reaction conditions (25°C) and low catalyst loading required (0.025 mol%), as well as the absence of contamination of the product by palladium residues (0/C: It's a kind of magic! A sustainable, simple and highly reproducible protocol for the hydrogenation of alkenes and alkynes (see scheme) and for the hydrogenolysis of O-benzyl ethers has been developed with an in situ generated Pd0/C catalyst. The homemade Pd0/C catalyst allows mild reaction conditions (25°C, 1 atm H2) and low catalyst loading (as low as 0.025 mol%), without any contamination of the product by palladium residues (4 ppb).
- Felpin, Francois-Xavier,Fouquet, Eric
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supporting information; experimental part
p. 12440 - 12445
(2011/01/05)
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- Synthesis of ω-tert-butyl esters of aspartic acid and glutamic acid via B,B-difluoroboroxazolidones
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B,B-Difluoroboroxazolidones (DFBONs) were synthesized for the first time from salts of amino acid and BF3·Et2O, and their properties were examined. DFBONs were used in selective preparation of Glu(OBu(t)) and Asp(OBu(t)) in good yields under catalysis with BF3·Et2O and H3PO4. Amberlite XAD-2 resin was successfully employed to purify the above amino acid derivatives.
- Wang, Jidong,Okada, Yoshio,Wang, Zongmu,Wang, Yuhong,Li, Wei
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p. 2189 - 2191
(2007/10/03)
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- Selective Deprotection of the Nα-tert-Butyloxycarbonyl Group in Solid Phase Peptide Synthesis with Chlorotrimethylsilane and Phenol
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The repetitive deprotection of the Nα-tert-butyloxycarbonyl group during solid phase peptide synthesis was found to be efficient and quantitative by use of a mild new reagent containing 1 M chlorotrimethylsiane and 1 M phenol in dichloromethane.Kinetic studies showed that the half-life for the reaction at 22 deg C with Boc-Val-resin was 17.5 min, a 40-fold increase over the rate in the absence of phenol.The reaction is not due to the presence of HCl in the reagent.The selectivity between the removal at the Nα-tert-butyloxycarbonyl group and benzylic esters, ethers, and carbonate side chain protecting groups was >1E5 and relative to the anchoring benzyl ester bond to the resin support it was 6E3.This is a marked improvement over the selectivity of the conventional 50percent trifluoroacetic acid in CH2Cl2 deprotecting agent and significantly reduces the accumulated byproducts resulting from losses of benzylic groups.The cleavage of the tert-butyl urethane was first order in Me3SiCl and second order in C6H5OH.The preferred reagent is 1 M Me3SiCl-3 M C6H5OH-CH2Cl2 and the deprotection time is 20 min (t1/2 = 1.8 min for Boc-Val-OCH2-resin).Evidence for the mechanism of the reaction was deduced.Several peptides, including Leu-enkephalin, -angiotensin II, and glucagon were successfully synthesized in high yields and excellent purity by the stepwise solid phase method using this new reagent.
- Kaiser, Emil Sr.,Picart, Francis,Kubiak, Teresa,Tam, James P.,Merrifield, R. B.
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p. 5167 - 5175
(2007/10/02)
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- ASYMMETRIC ALKYLATIONS OF A SULTAM-DERIVED GLYCINATE EQUIVALENT: PRACTICAL PREPARATION OF ENANTIOMERICALLY PURE α-AMINO ACIDS
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Deprotonation/alkylation of sultam-derived N-glycinate equivalent 3 gave crystalline products 5 which on mild hydrolysis furnished α-amino acids 7 (ca.100percent e.e.) in high overall yield.
- Oppolzer, Wolfgang,Moretti, Robert,Thomi, Silvia
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p. 6009 - 6010
(2007/10/02)
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