Intramolecular nucleophilic participation by the thiol group during amide hydrolysis. Part 2. The imidazole catalysis dilemma

Catalysis by imidazole and N-methylimidazole buffers of the intramolecular thiolysis of N-n-propyl 2-mercaptomethylbenzamide (forming 2-thiophthalide) has been studied in aqueous solution at 40.0 °C, μ = 1.0. Unlike other buffers previously studied, imidazole and N-methylimidazole are able to catalyze, by a general base route, formation of neutral tetrahedral intermediate; this pathway is rate limiting at pH ≤ 7.5. At higher pH, the previously reported general acid-catalyzed breakdown of this intermediate is rate limiting. The relevance of these observations to the currently accepted pathway for the acylation of papain by amide substrates is discussed. Keywords: amide hydrolysis, intramolecular, thiol participation, imidazole, papain model.

Chemie an starren Grenzflächen, 11. Aerosile mit kovalent beweglich und starr verknüpften Fluoreszenzträgern / Chemistry on Rigid Surfaces, 11. Aerosils with Covalently Movable and Rigid Linked Fluorophors

5-Dimethylamino-1-naphthalene-carbonic acid chloride (1), the analog of dansylchloride, is synthesized. With diazomethane the diazoketone 2 is obtained. The modified aerosil A is formed by the interaction of 1 with amino-aerosil. The density of the coverage is available a) chemically by dissolving the inorganic matrix of A with H2F2 and spectroscopic determination of the formed n-butylamide 9, b) by fluorescence spectroscopy and c) by U V spectroscopy.Silanole groups both in organic substituted compounds and in aerosil react with the fluorescent silanes 6 and 7 using CsF/imidazole-catalysis forming the corresponding siloxanes according to (4 b) and (8). The modified aerosils C, D and E are prepared in this way and characterized. The functionalization of amino-aerosil with 7-chloro-4-nitrobenzeno furazane (10) leading to the modified aerosil B is unsatisfactory.