1. Leveraging the Knorr Pyrazole Synthesis for the Facile Generation of Thioester Surrogates for use in Native Chemical Ligation
Dillon T Flood, Jordi C J Hintzen, Michael J Bird, Philip A Cistrone, Jason S Chen, Philip E Dawson Angew Chem Int Ed Engl. 2018 Sep 3;57(36):11634-11639. doi: 10.1002/anie.201805191. Epub 2018 Aug 10.
Facile synthesis of C-terminal thioesters is integral to native chemical ligation (NCL) strategies for chemical protein synthesis. We introduce a new method of mild peptide activation, which leverages solid-phase peptide synthesis (SPPS) on an established resin linker and classical heterocyclic chemistry to convert C-terminal peptide hydrazides into their corresponding thioesters via an acyl pyrazole intermediate. Peptide hydrazides, synthesized on established trityl chloride resins, can be activated in solution with stoichiometric acetyl acetone (acac), readily proceed to the peptide acyl pyrazoles. Acyl pyrazoles are mild acylating agents and are efficiently exchanged with an aryl thiol, which can then be directly utilized in NCL. The mild, chemoselective, and stoichiometric activating conditions allow this method to be utilized through multiple sequential ligations without intermediate purification steps.
2. Solid-phase synthesis of reduced selenocysteine tetrapeptides and their oxidized analogs containing selenenylsulfide eight-membered rings
Ludger A Wessjohann, Alex Schneider, Goran N Kaluđerović, Wolfgang Brandt Mol Divers. 2013 Aug;17(3):537-45. doi: 10.1007/s11030-013-9454-x. Epub 2013 Jun 1.
A series of protected and reduced forms of model tetrapeptides that mimic the C-terminus of human thioredoxin reductases were obtained in good yields, using solid-phase peptide synthesis (SPPS). SPPS was performed on the Knorr Amide MBHA resin for Fmoc chemistry using especially protected cystein and selenocystein derivatives. All amino acids have been coupled according to the HBTU/HOBt/DIPEA method. Furthermore, the corresponding oxidized peptides containing eight-membered rings with intramolecular S-S and S-Se bridges were prepared via I[Formula: see text]/MeOH or DMSO/TFA oxidation, respectively.
3. Direct modification of polyketone resin for anion exchange membrane of alkaline fuel cells
Yi-Cun Zhou, Ling Zhou, Chang-Ping Feng, Xiao-Tian Wu, Rui-Ying Bao, Zheng-Ying Liu, Ming-Bo Yang, Wei Yang J Colloid Interface Sci. 2019 Nov 15;556:420-431. doi: 10.1016/j.jcis.2019.08.086. Epub 2019 Aug 24.
A kind of side-chain type anion exchange membranes (AEMs) with high ionic conductivity and good comprehensive stability was prepared via direct modification of commercial engineering plastic polyketone with diamines through Paal-Knorr reaction and quaternization reaction. It was found that the amount of diamine can effectively tune the microphase morphology and properties of the prepared quaternized functionalized-polyketone anion exchange membranes (QAFPK-AEMs). The tensile strength was increased from 18.6 MPa to 38.6 MPa, and the ion exchange capacity (IEC) was increased from 1.11 mmol/g to 2.71 mmol/g depending on the amount of added diamine. The QAFPK-1-6-AEM with the IEC of 1.43 mmol/g showed the highest hydroxide conductivity of 65 mS/cm at 25 °C and 96.8 mS/cm at 80 °C. The high ionic conductivity was achieved through the establishment of effective ionic channels, and it maintained 70% of the initial ionic conductivity after the 192 h treatment in 2 mol/L KOH (aq) at 80 °C. Moreover, a peak power density of 129 mW/cm2 was achieved when the assembled single cell with QAFPK-1-6-AEM was operated at 50 °C. Thus, the prepared QAFPK-AEMs showed great potential applications for the anion exchange membrane fuel cells (AEMFCs).
