Preparation and Reactions of 2‐Methyl‐7‐(3‐methyl‐5‐oxo‐1‐phenyl‐2‐pyrazolin‐4‐yl)‐5‐arylthiazolo[3,2‐a]‐pyrimido[4,5‐d]oxazin‐4(5H)‐one

Ethyl 7‐amino‐3‐(3‐methyl‐5‐oxo‐1‐phenyl‐2‐pyrazolin‐4‐yl)‐5‐aryl‐5H‐thiazolo[3,2‐a]pyrimidine‐6‐carboxylate was hydrolyzed with an ethanolic sodium hydroxide and the sodium salt thus formed underwent cyclization with acetic anhydride to afford 2‐methyl‐7‐(3‐methyl‐5‐oxo‐1‐phenyl‐2‐pyrazolin‐4‐yl)‐5‐arylthiazolo[3,2‐a]pyrimido[4,5‐d]oxazin‐4(5H)‐one. This compound was transformed to related heterocyclic systems via its reaction with various reagents. The biological activity of the prepared compounds was tested against Gram positive and Gram negative bacteria as well as yeast‐like and filamentous fungi. They revealed in some cases excellent biocidal properties.     

A Native‐Chemical‐Ligation‐Mechanism‐Based Ratiometric Fluorescent Probe for Aminothiols

Thiol‐containing amino acids (aminothiols) such as cysteine (Cys) and homocysteine (Hcy) play a key role in various biological processes including maintaining the homeostasis of biological thiols. However, abnormal levels of aminothiols are associated with a variety of diseases. The native chemical ligation (NCL) reaction has attracted great attention in the fields of chemistry and biology. NCL of peptide segments involves cascade reactions between a peptide‐α‐thioester and an N‐terminal cysteine peptide. In this work, we employed the NCL reaction mechanism to formulate a Förster resonance energy transfer (FRET) strategy for the design of ratiometric fluorescent probes that were selective toward aminothiols. On the basis of this new strategy, the ratiometric fluorescent probe 1 for aminothiols was judiciously designed. The new probe is highly selective toward aminothiols over other thiols and exhibits a very large variation (up to 160‐fold) in its fluorescence ratio (I₄₅₈/I₆₀₃). The new fluorescent probe is capable of ratiometric detection of aminothiols in newborn calf and human serum samples and is also suitable for ratiometric fluorescent imaging of aminothiols in living cells.