- En Route to a Heterogeneous Catalytic Direct Peptide Bond Formation by Zr-Based Metal-Organic Framework Catalysts
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Peptide bond formation is a challenging, environmentally and economically demanding transformation. Catalysis is key to circumvent current bottlenecks. To date, many homogeneous catalysts able to provide synthetically useful methods have been developed, while heterogeneous catalysts remain largely restricted to the studies addressing the prebiotic formation of peptides. Here, the catalytic activity of Zr6-based metal-organic frameworks (Zr-MOFs) toward peptide bond formation is investigated using dipeptide cyclization as a model reaction. Unlike previous catalysts, Zr-MOFs largely tolerate water, and reactions are carried out under ambient conditions. Notably, the catalyst is recyclable and no additives to activate the COOH group are necessary, which are common limitations of previous methods. In addition, a broad reaction scope tolerates substrates with bulky and Lewis basic groups. The reaction mechanism was assessed by detailed mechanistic and computational studies and features a Lewis acid activation of carboxylate groups by Zr centers toward amine addition in which an alkoxy ligand on adjacent Zr sites assists in lowering the barrier of key proton transfers. The proposed concepts were also used to study the formation of intermolecular peptide bond formation. While intrinsic challenges associated with the catalyst structure and water removal limit a more general intermolecular reaction scope under current conditions, the results suggest that further design of Zr-MOF catalysts could render these materials broadly useful as heterogeneous catalysts for this challenging transformation.
- Conic, Dragan,De Azambuja, Francisco,Harvey, Jeremy N.,Loosen, Alexandra,Parac-Vogt, Tatjana N.,Van Den Besselaar, Maxime
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p. 7647 - 7658
(2021/06/30)
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- The Ugly Duckling Metamorphosis: The Ammonia/Formaldehyde Couple Made Possible in Ugi Reactions.
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Ugi reactions are still a challenge when the concomitant use of ammonia and formaldehyde is required. Herein, we propose a strategy to overcome this challenge using hexamethylenetetramine (HMTA) as a singular key for the employment of these two simple starting materials in the Ugi reaction. Acylaminoacetamide derivatives were prepared in good to excellent yields by this new methodology. The scope and optimization of the reaction conditions were investigated. This novel methodology was successfully applied in the synthesis of two different diketopiperazines (DKPs) using the Ugi/Deprotection+Activation/Cyclization (UDAC) method. A continuous flow approach was also used in this methodology.
- Rosalba, Thaissa Pasquali F.,Kas, Samia Sayegh A.,Sampaio, Ana Beatriz S.,Salvador, Carlos Eduardo M.,Andrade, Carlos Kleber Z.
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p. 2831 - 2842
(2021/05/13)
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- Immobilized Carbodiimide Assisted Flow Combinatorial Protocol to Facilitate Amide Coupling and Lactamization
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Through a screen of over one hundred and 30 permutations of reaction temperatures, solvents, carbodiimide resins, and carbodiimide molar equivalences, in the presence, absence, or combination of diisopropylamine and benzotriazole additives, a convenient and first reported carbodiimide polymer-assisted flow approach to effect amide coupling and lactamization was developed. The protocol entails injecting a single solution (1:9 dimethylformamide: dichloromethane) containing a carboxylic acid and an amine or linear peptide sequence into a continuous stream of dichloromethane. The protocol remained viable in the absence of base, did not require carboxylate preactivation which, and in concert with minimal workup requirements, enabled the isolation of products in high yields. Compared to the utilization of untethered carbodiimide reagents, the flow procedure was also observed to provide a degree of racemization safety.
- Aldrich-Wright, Janice R.,Dankers, Christian,Gordon, Christopher P.,Harman, David G.,Nguyen, Thanh V.,Tadros, Joseph
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supporting information
p. 255 - 267
(2020/06/05)
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- Water-Tolerant and Atom Economical Amide Bond Formation by Metal-Substituted Polyoxometalate Catalysts
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A simple, safe, and inexpensive amide bond formation directly from nonactivated carboxylic acids and free amines is presented in this work. Readily available Zr(IV)- and Hf(IV)-substituted polyoxometalates (POM) are shown to be catalysts for the amide bond formation reaction under mild conditions, low catalyst loading, and without the use of water scavengers, dry solvents, additives for facilitating the amine attack, or specialized experimental setups commonly employed to remove water. Detailed mechanistic investigations revealed the key role of POM scaffolds which act as inorganic ligands to protect Zr(IV) and Hf(IV) Lewis acidic metals against hydrolysis and preserve their catalytic activity in amide bond formation reactions. The catalysts are compatible with a range of functional groups and heterocycles useful for medicinal, agrochemical, and material chemists. The robustness of the Lewis acid-POM complexes is further supported by the catalyst reuse without loss of activity. This prolific combination of Zr(IV)/Hf(IV) and POMs inaugurates a powerful class of catalysts for the amide bond formation, which overcomes key limitations of previously established Zr(IV)/Hf(IV) salts and boron-based catalysts.
- De Azambuja, Francisco,Parac-Vogt, Tatjana N.
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p. 10245 - 10252
(2019/11/03)
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- One-pot preparation of 3-hydroxymethyl 2,5-diketopiperazine for total synthesis of peticinnamin E
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3-Hydroxymethyl 2, 5-diketopiperazine is a structure unit of pepticinnamin E, a natural product and a bi-substrate inhibitor of FPTase. In this paper, a facile synthetic strategy was developed to prepare 3-hydroxymethyl 2, 5-diketopiperazine with high yie
- Sun, Dequn,Sun, Li,Luo, Min,Gou, Zhaopin
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experimental part
p. 5169 - 5170
(2012/06/18)
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- Piperazine compounds
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Compounds are disclosed of formula (I) STR1 wherein R1 represents --COR4, --CO2 R4 or --COCO2 R4 (where R4 represents a hydrogen atom or an unsubstituted or substituted C1-1
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