115491-92-4Relevant academic research and scientific papers
Zn-Catalyzed tert-Butyl Nicotinate-Directed Amide Cleavage as a Biomimic of Metallo-Exopeptidase Activity
Wybon, Clarence C. D.,Mensch, Carl,Hollanders, Charlie,Gadais, Charlène,Herrebout, Wouter A.,Ballet, Steven,Maes, Bert U. W.
, p. 203 - 218 (2018)
A two-step catalytic amide-to-ester transformation of primary amides under mild reaction conditions has been developed. A tert-butyl nicotinate (tBu nic) directing group is easily introduced onto primary amides via Pd-catalyzed amidation with tert-butyl 2-chloronicotinate. A weak base (Cs2CO3 or K2CO3) at 40-50 °C can be used provided that 1,1′-bis(dicyclohexylphosphino)ferrocene is selected as ligand. The tBu nic activated amides subsequently allow Zn(OAc)2-catalyzed nonsolvolytic alcoholysis in tBuOAc at 40-60 °C under neutral reaction conditions. The activation mechanism is biomimetic: the C3-ester substituent of the pyridine in the directing group populates the trans-conformer suitable for Zn-chelation, C=Oamide-Zn-Ndirecting group, and Zn-coordinated alcohol is additionally activated as a nucleophile by hydrogen bonding with the acetate ligand of the catalyst. Additionally, the acetate ligand assists in intramolecular O-to-N proton transfer. The chemoselectivity versus other functional groups and compatibility with challenging reaction partners, such as peptides, sugars, and sterols, illustrates the synthetic applicability of this two-step amide cleavage method. The tBu nic amides do not require purification before cleavage. Preliminary experiments also indicate that other weak nucleophiles can be used such as (hetero)arylamines (transamidation) as exemplified by 8-aminoquinoline.
Functionality-oriented molecular gels: Synthesis and properties of nitrobenzoxadiazole (NBD)-containing low-molecular mass gelators
Yu, Hang,Lü, Yanchao,Chen, Xiangli,Liu, Kaiqiang,Fang, Yu
, p. 9159 - 9166 (2015/02/19)
Two nitrobenzoxadiazole (NBD)-containing cholesteryl (Chol) derivatives were prepared by introducing d/l-phenylalanine into the linkers between the NBD and Chol units. The compounds were denoted as NLC and NDC, respectively. The gelation behaviors of them were tested in 34 liquids. It was found that the chirality of the linkers shows a great effect on the gelation ability and the gel properties of the two compounds. SEM studies demonstrated that the gelator in the gel of NDC/DMSO aggregated into uniform fibrous structures. FTIR, 1H NMR and UV-Vis spectroscopy measurements revealed that intermolecular hydrogen bonding and π-π stacking are two main driving forces to promote the gel formation. Interestingly, the NDC/DMSO gel exhibits rapid and reproducible gel-sol phase transition and fluorescence quenching upon introduction of ammonia. Furthermore, both the gel and the fluorescence emission could be fully recovered upon evaporation of the ammonia gas introduced. Spectroscopy and model system studies revealed the association of ammonia with the nitro group of the NBD unit of the compound, which is recognized as the main reason for the chemical responses of the gel system. On the basis of the discovery, an ammonia sensing film had been fabricated and made into a device. Furthermore, a device-based and conceptual ammonia leaking monitoring instrument was developed. A preliminary test demonstrated that the performance of the system is exceptionally good, a typical and persuasive example to show the important real-life applications of molecular gels. This journal is
