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.

Structure-Based Bioisosterism Design, Synthesis, Biological Evaluation and In Silico Studies of Benzamide Analogs as Potential Anthelmintics.

A recent screen of 67,012 compounds identified a new family of compounds with excellent nematicidal activity: the ortho-substituted benzamide families Wact-11 and Wact-12. These compounds are active against Caenorhabditis elegans and parasitic nematodes by selectively inhibiting nematode complex II, and they display low toxicity in mammalian cells and vertebrate organisms. Although a big number of benzamides were tested against C. elegans in high-throughput screens, bioisosteres of the amide moiety were not represented in the chemical space examined. We thus identified an opportunity for the design, synthesis and evaluation of novel compounds, using bioisosteric replacements of the amide group present in benzamides. The compound Wact-11 was used as the reference scaffold to prepare a set of bioisosteres to be evaluated against C. elegans. Eight types of amide replacement were selected, including ester, thioamide, selenoamide, sulfonamide, alkyl thio- and oxo-amides, urea and triazole. The results allowed us to perform a structure-activity relationship, highlighting the relevance of the amide group for nematicide activity. Experimental evidence was complemented with in silico structural studies over a C. elegans complex II model as a molecular target of benzamides. Importantly, compound Wact-11 was active against the flatworm Echinococcus granulosus, suggesting a previously unreported pan-anthelmintic potential for benzamides.

A multiscale approach to predict the binding mode of metallo beta-lactamase inhibitors.

Antibiotic resistance is a major threat to global public health. ß-lactamases, which catalyze breakdown of ß-lactam antibiotics, are a principal cause. Metallo ß-lactamases (MBLs) represent a particular challenge because they hydrolyze almost all ß-lactams and to date no MBL inhibitor has been approved for clinical use. Molecular simulations can aid drug discovery, for example, predicting inhibitor complexes, but empirical molecular mechanics (MM) methods often perform poorly for metalloproteins. Here we present a multiscale approach to model thiol inhibitor binding to IMP-1, a clinically important MBL containing two catalytic zinc ions, and predict the binding mode of a 2-mercaptomethyl thiazolidine (MMTZ) inhibitor. Inhibitors were first docked into the IMP-1 active site, testing different docking programs and scoring functions on multiple crystal structures. Complexes were then subjected to molecular dynamics (MD) simulations and subsequently refined through QM/MM optimization with a density functional theory (DFT) method, B3LYP/6-31G(d), increasing the accuracy of the method with successive steps. This workflow was tested on two IMP-1:MMTZ complexes, for which it reproduced crystallographically observed binding, and applied to predict the binding mode of a third MMTZ inhibitor for which a complex structure was crystallographically intractable. We also tested a 12-6-4 nonbonded interaction model in MD simulations and optimization with a SCC-DFTB QM/MM approach. The results show the limitations of empirical models for treating these systems and indicate the need for higher level calculations, for example, DFT/MM, for reliable structural predictions. This study demonstrates a reliable computational pipeline that can be applied to inhibitor design for MBLs and other zinc-metalloenzyme systems.

Increased sensitivity of an infrared motility assay for nematicide discovery.

Parasitic nematodes constitute a health problem for humans, livestock and crops, and cause huge economic losses to developing-country economies. Due to the spread of nematicide resistance, there is an urgent need for new drugs. C. elegans is now recognized as a cost-effective alternative for the screening of compound libraries with potential nematicidal activity, as parasitic organisms are hard to maintain under laboratory conditions. Here we describe an adaptation of a previously reported high throughput (HTP) infrared-based motility assay that leads to increased sensitivity. The modified assay uses L1 instead of L4 stage worms and matches the sensitivity reported by Burns et al. (2015) for the anthelmintic benzamides Wact11 and Wact11p. In addition, this method presents practical advantages over Burns et al. (2015) and other image-based protocols and provides a robust assay with a fast and simple readout ideal for HTP drug discovery.

Synthesis of bicyclic 1,4-thiazepines as novel anti-Trypanosoma brucei brucei agents.

1,4-Thiazepines derivatives are pharmacologically important heterocycles with different applications in medicinal chemistry. In the present work, we describe the preparation of new bicyclic thiazolidinyl-1,4-thiazepines 3 by reaction between azadithiane compounds and Michael acceptors. The reaction scope was explored and the yields were optimized. The activity of the new compounds was evaluated against Nippostrongylus brasiliensis and Caenorhabditis elegans as anthelmintic models and Trypanosoma brucei brucei. The most active compound was 3l, showing an EC50 = 2.8 ± 0.7 µM against T. b. brucei and a selectivity index >71.