Proton‐Catalyzed Disulfide Exchange of S‐Alkylthio Cysteine Derivatives
Although N‐unprotected S‐alkylthio cysteine derivatives are relatively stable in acid solutions, N‐acylsubstituted and N‐urethane protected S‐alkylthio cysteines react easily by disulfide exchange. As a rule the frequently used tert.‐butyloxycarbonyl amino protecting group, present in ethylthio cysteine derivatives can′t be removed selectively without disulfide cleavage, whilst the 2‐(p‐biphenylyl)isopropyloxycarbonyl and the 2‐phenyl‐isopropyloxycarbonyl amino protecting groups are removable without any structure change of the alkylthio thiol protecting groups. It is advisable to realize this acid demasking of the amino groups by means of weak deblocking reagents. Comperative experiments in acid solution prove S‐tert.‐butylthio group to be the most stable protecting function, whilst isopropylthio cysteine derivatives are more stable than the corresponding S‐ethylthio compounds. All these results and experiments with addition of different thiols as well as u.v.‐spectroscopic investigations indicate, that the observed acid catalyzed disulfide exchange proceeds via a carbonyl neighbouring group effect and formation of thiazolidinium and thiazolinium intermediates, respectively.
Die durch Acylierung der Aminothiazole (I) mit γ‐Chlorbuttersäurechlorid (II) erhaltenen γ‐Chlorbuttersäureamide (III) cyclisieren unter Basenkatalyse zu den Thiazolylpyrrolidonen (IV).
Die Cyclisierungen von 2-(4-Chlorbutyrylamino)-thiazolen sowie des 2,5-Di-(4-chlorbutyrylamino)-1,3,4-thiadiazols fiihren in Gegenwart von Piperidin oder Ammoniak zu l-[Thiazolyl-(2)]-pyrrolidonen-(2) bzw. dem 2,5-Di-(2-oxo-pyrrolidino)-l ,f,Cthiadiazol in Analogie zur Synthese von l-Arylpyrr0lidonen-(2)'~). Die nach ' ) zu erwartende Bildung heterocyclisch kondensierter 1,3-Diazepinone wurde nicht beobachtet.
Syntheses of Some 2-Pymolidones Carrying N-Heterocycles as SubstituentsCyclisations of 2-(4-~hlorobutyrylamino)thiazoles or 2,5-bis(4-chlorobutyrylamino)-l,3,4-thiadiazole in the presence of piperidine or ammonia lead to 1-[2-thiazolyl]-2-pyrrolidones and 2,5-bis(2-oxopyrrolidino)-l,3,4-thiadiazole, in analogy to the synthesis of l-aryl-2-pyrr01idone'~). The formation of 1,3-diazepinones according to ' ) was not observed.1967 haben Tsatsm und Costakis') durch Reaktion von 2-Aminobenzthiazol (la) mit 4-Chlorbutyrylchlorid (2a) und Cyclisierung des entstandenen 4-Chlorbutyrylaminobenzthiazols (3a) ein Produkt erhalten, dem aufgrund des NMR-Spektrums die Struktur eines Diazepinons zugeordnet
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