1. Efficient Fmoc-Protected Amino Ester Hydrolysis Using Green Calcium(II) Iodide as a Protective Agent
Renaud Binette, Michael Desgagné, Camille Theaud, Pierre-Luc Boudreault Molecules. 2022 Apr 27;27(9):2788. doi: 10.3390/molecules27092788.
In order to modify amino acids, the C-terminus carboxylic acid usually needs to be protected, typically as a methyl ester. However, standard cleavage of methyl esters requires either highly basic or acidic conditions, which are not compatible with Fmoc or acid-labile protecting groups. This highlights the need for orthogonal conditions that permit selective deprotection of esters to create SPPS-ready amino acids. Herein, mild orthogonal ester hydrolysis conditions are systematically explored using calcium(II) iodide as a protective agent for the Fmoc protecting group and optimized for a broad scope of amino esters. Our optimized reaction improved on the already known trimethyltin hydroxide, as it produced better yields with greener, inexpensive chemicals and a less extensive energy expenditure.
2. O-Methylation of carboxylic acids with streptozotocin
Li-Yan Zeng, Yang Liu, Jiakun Han, Jinhong Chen, Shuwen Liu, Baomin Xi Org Biomol Chem. 2022 Jul 6;20(26):5230-5233. doi: 10.1039/d2ob00578f.
The clinically used DNA-alkylating drug streptozotocin (STZ) was investigated using a simple work-up as an O-methylating agent to transform various carboxylic acids, sulfonic acids and phosphorous acids into corresponding methyl esters, and did so with yields of up to 97% in 4 h at room temperature. Good substrate tolerance was observed, and benefited from the mild conditions and compatibility of the reaction with water.
3. Acridinium Ester Chemiluminescence: Methyl Substitution on the Acridine Moiety
Manabu Nakazono, Shinkoh Nanbu, Takeyuki Akita, Kenji Hamase J Oleo Sci. 2021;70(11):1677-1684. doi: 10.5650/jos.ess21186.
Methyl groups were introduced on the acridine moiety in chemiluminescent acridinium esters that have electron-withdrawing groups (trifluoromethyl, cyano, nitro, ethoxycarbonyl) at the 4-position on the phenyl ester. The introduction of methyl groups at the 2-, 2,7-, and 2,3,6,7-positions on the acridine moiety shifted the optimal pH that gave relatively strong chemiluminescence intensity from neutral conditions to alkaline conditions. 4-(Ethoxycarbonyl)phenyl 2,3,6,7,10-pentamethyl-10λ4-acridine-9-carboxylate, trifluoromethanesulfonate salt showed long-lasting chemiluminescence under alkaline conditions. Acridinium esters to determine hydrogen peroxide concentration at pH 7-10 were newly developed.
