A new procedure for thioester deprotection using thioglycolic acid in both homogeneous and heterogeneous phase

Classic acetyl thioester protection/deprotection methodologies are widely used in organic synthesis, but deprotection step usually requires harsh conditions not suitable for labile substrates. In this work, a new method for thioester deprotection using a thiotransesterification approach is described. Firstly, thioglycolic acid (TGA) was identified as a good deprotecting reagent in solution. In order to develop a thiol polymer-supported reagent, TGA was anchored to a PEG-based resin through an amide bond (TG-NCO-SH). Both homogeneous and heterogeneous approaches were conveniently carried out at room temperature, in aqueous buffer at pH 8. The mild conditions were suitable for alkyl and phenyl thioesters. Moreover labile thioesters containing thiazolidine and oxazolidine scaffolds, bearing amine, ester and acetal functionalities were also deprotected. The polymer-supported TGA gave better deprotection yields compared to TGA in solution, yields ranging from 61 to 90%. The feasibility of the recovery and reuse of TG-NCO-SH reagent was explored, showing it can be reused at least five times without lossing the activity.

Encryption and authentication of security patterns by ecofriendly multi-color photoluminescent inks containing oxazolidine-functionalized nanoparticles

Counterfeiting of confidential documents has been a costly challenge for banks, companies, and customers. Encryption of invisible security marks, such as barcodes, quick response codes, and logos, in national or international confidential documents by high-security anticounterfeiting inks is the most significant solution for counterfeiting problems. Ecofriendly multi-color photoluminescent anticounterfeiting inks based on highly-fluorescent polymer nanoparticles functionalized with new oxazolidine derivatives were developed for the fast and facile encryption of security labels on cellulosic documents, such as paper currency, passport, and certificate. Depending on the polarity of functionalized polymer nanoparticles, a wide range of colors and fluorescence emissions were observed as a result of polar-polar interactions between the oxazolidine molecules and surface functional groups of the nanoparticles. The fluorescent polymer nanoparticles showed spherical, vesicular, and cauliflower-like morphologies resulted from different surface functional groups. Functional polymer nanoparticles displayed high stability and printability on cellulosic substrates due to hydrogen bonding interactions. The highly-fluorescent polymer nanoparticles were also used to prepare anticounterfeiting inks with different colors and fluorescence emissions. All the ecofriendly polymeric anticounterfeiting inks were loaded to stamps with specific marks, and then applied to different confidential documents. Printed labels displayed highly intense fluorescence emission in different colors (green, orange, pink, and purple depending on the matrix polarity) under UV irradiation (365 nm). These water-based multi-color fluorescent anticounterfeiting inks with highly intense, bright, and sensitive fluorescence emission have potential applications in encryption and authentication of security patterns.

High-resolution structure of intramolecularly proteolyzed human mucin-1 SEA domain

SEA domains are ubiquitous in large proteins associated with highly glycosylated environments. Certain SEA domains undergo intramolecular proteolysis involving a nucleophilic attack of a serine hydroxyl group on the preceding glycine carbonyl. The mucin-1 (MUC1) SEA domain has been extensively investigated as a model of intramolecular proteolysis. Since neither a general base, a general acid, nor an oxyanion hole could be identified in MUC1 SEA, it has been suggested that proteolysis is accelerated by a non-planarity of the scissile peptide bond imposed by protein folding. A reactant distorted peptide bond has been also invoked to explain the autoproteolysis of several unrelated proteins. However, the only evidence of peptide distortion in MUC1 SEA stems from molecular dynamic simulations of the reactant modeled upon a single NMR structure of the cleaved product. We report the first high-resolution X-ray structure of cleaved MUC1 SEA. Structural comparison with uncleaved SEA domains suggests that the number of residues evolutionarily inserted in the cleaved loop of MUC1 SEA precludes the formation of a properly hydrogen-bonded beta turn. By sequence analysis, we show that this conformational frustration is shared by all known cleaved SEA domains. In addition, alternative conformations of the uncleaved precursor could be modeled in which the scissile peptide bond is planar. The implications of these structures for autoproteolysis are discussed in the light of the previous research on autoproteolysis.

Synthesis of unprecedented steroidal spiro heterocycles as potential antiproliferative drugs

Herein we report the straightforward preparation of novel conformationally-restricted steroids from trans-androsterone and estrone, decorated with spiranic oxazolidin-2-one or 2-aminooxazoline motifs at C-17 as potential antiproliferative agents. Such unprecedented pharmacophores were accessed using an aminomethylalcohol derivative at C-17 as the key intermediate; reaction of such functionality with triphosgene, or conversion into N-substituted thioureas, followed by an intramolecular cyclodesulfurization reaction promoted by yellow HgO, furnished such spirocycles in excellent yields. Title compounds were tested in vitro against a panel of six human tumor cell lines, named A549 (non-small cell lung), HBL-100 (breast), HeLa (cervix), SW1573 (non-small cell lung), T-47D (breast) and WiDr (colon), and the results were compared with steroidal chemotherapeutic agents (abiraterone and galeterone); the A-ring of the steroidal backbone, the nature of the heterocycle and the N-substituents proved to be essential motifs for establishing structure-activity relationships concerning not only the potency but also the selectivity against tumor cell lines. Estrone derivatives, particularly those bearing a spiranic 2-aminooxazoline scaffold were found to be the most active compounds, with GI₅₀ values ranging from the low micromolar to the submicromolar level (0.34-1.5 μM). Noteworthy, the lead compounds showed a remarkable increase in activity against the resistant cancer cell lines (T-47D and WiDr) compared to the anticancer reference drugs (up to 120-fold).