Preparation and Mechanistic Studies of 2-Substituted Bisthiazolidines by Imine Exchange

Novel enantiopure δ-thiolactones: synthesis, structural characterization, and reactivity studies

A new series of chiral δ-thiolactone derivatives have been prepared. These compounds exemplify the acetalic N-C-S reversibility of fused thiazolidines toward the thermodynamic product. The stereochemistry of the synthesized compounds was elucidated using X-ray crystallography, NOESY spectroscopy, and DFT calculations. The aminolysis reaction of the δ-thiolactone was studied with various alkyl amines, which can open the thioester to yield amido thiols in a single step. This reaction has the potential to be applied in the synthesis of bioactive compounds, polymer chemistry, and dynamic combinatorial chemistry, among others fields.

Rational Design of Benzobisheterocycle Metallo-β-Lactamase Inhibitors: A Tricyclic Scaffold Enhances Potency against Target Enzymes

Antimicrobial resistance is a global public health threat. Metallo-β-lactamases (MBLs) inactivate β-lactam antibiotics, including carbapenems, are disseminating among Gram-negative bacteria, and lack clinically useful inhibitors. The evolving bisthiazolidine (BTZ) scaffold inhibits all three MBL subclasses (B1-B3). We report design, synthesis, and evaluation of BTZ analogues. Structure-activity relationships identified the BTZ thiol as essential, while carboxylate is replaceable, with its removal enhancing potency by facilitating hydrophobic interactions within the MBL active site. While the introduction of a flexible aromatic ring is neutral or detrimental for inhibition, a rigid (fused) ring generated nM benzobisheterocycle (BBH) inhibitors that potentiated carbapenems against MBL-producing strains. Crystallography of BBH:MBL complexes identified hydrophobic interactions as the basis of potency toward B1 MBLs. These data underscore BTZs as versatile, potent broad-spectrum MBL inhibitors (with activity extending to enzymes refractory to other inhibitors) and provide a rational approach to further improve the tricyclic BBH scaffold.

Novel Kinetic Resolution of Thiazolo-Benzimidazolines Using MAO Enzymes

The kinetic resolution of racemic 1H,3H-thiazolo[3,4-a]benzimidazoline (TBIM) heterocycles was achieved using E. coli whole cells expressing the MAO-N D11 enzyme. Several cosolvents were screened using TBIM 2a as the substrate. DMF was the best cosolvent, affording the pure enantiomer (+)-2a in 44% yield, 94% ee. The stereochemistry of TBIM was predicted by means of ab initio calculations of optical rotation and circular dichroism spectra. The reaction scope was investigated for 11 substituted (±) TBIM using an optimized protocol. The best yield and % ee were obtained for the nonsubstituted 2a. Among the substituted compounds, the 5-substituted-TBIM showed better % ee than the 4-substituted one. The small electron donor group (Me) led to better % ee than the electron-withdrawing groups (-NO2 and -CO2Et), and the bulky naphthyl group was detrimental for the kinetic resolution. Docking experiments and molecular dynamics (MD) simulations were employed to further understand the interactions between MAO-N D11 and the thiazolo-benzimidazoline substrates. For 2a, the MD showed favorable positioning and binding energy for both enantiomers, thus suggesting that this kinetic resolution is influenced not only by the active site but also by the entry tunnel. This work constitutes the first report of the enzymatic kinetic resolution applied to TBIM heterocycles.

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.