Thiazolium-catalyzed intermolecular Stetter reaction of linear and cyclic alkyl α-diketones

Design, synthesis and evaluation of 1-(1,5-bis(4-substituted phenyl)-2-methyl-1H-pyrrol-3-yl)-N-methylmethanamines as SERT inhibitors with potential antidepressant action

BM212 is a potent anti-TB agent with pharmacophoric features similar to the antidepressant drug sertraline. The shape-based virtual screening of the DrugBank database on BM212 resulted in the identification of several CNS drugs with appreciable Tanimoto scores. The docking simulations also ascertained the selectivity of BM212 towards the serotonin reuptake transporter protein (SERT) with a docking score of -6.51 kcal mol-1. Based on the SAR data available for sertraline and other antidepressant drugs, we designed, synthesized and screened twelve 1-(1,5-bis(4-substituted phenyl)-2-methyl-1H-pyrrol-3-yl)-N-methylmethanamines (SA-1 to SA-12) for in vitro SERT inhibition and in vivo antidepressant activity. The compounds were screened for in vitro 5HT reuptake inhibition using the platelet model. Among the screened compounds, (1-(1,5-bis(4-chlorophenyl)-2-methyl-1H-pyrrol-3-yl)-N-methylmethanamine) showed the same serotonin uptake inhibition (absorbance 0.22) as that of the standard drug sertraline (absorbance 0.22). BM212 had an effect on 5-HT uptake, albeit a weaker one compared to the standard (absorbance 0.671). Further, SA-5 was screened for in vivo antidepressant activity using the unpredictable chronic mild stress (UCMS) protocol to induce depression in mice. The effect of BM212 and SA-5 on the behaviour of the animals was assessed and compared against the standard drug sertraline. SA-5 at 20 mg per kg body weight was found to have a statistically significant impact on the behaviour of depressed animals.

Medicinal chemical optimization of fluorescent pyrrole-based COX-2 probes

Recent studies have demonstrated the ability of human prostaglandin-endoperoxide synthase 2 (COX-2) to guide the formation of fluorescent pyrroles through the Paal-Knorr reaction resulting in the discovery of a central motif. This initial discovery prompted further exploration of this motif for the design of COX-2 inhibitors through the modifications of the substituents on the pyrrole core. This effort led to the discovery of a set of pyrroles whose activity was comparable to Celecoxib, an orally prescribed nonsteroidal anti-inflammatory COX-2 inhibitor. Furthermore, structure-activity relationship (SAR) data, important for the discovery of COX-2 inhibitors, has been obtained.

Palladium-catalyzed directing group assisted and regioselectivity reversed cyclocarbonylation of arylallenes with 2-iodoanilines

A palladium-catalyzed regioselective cyclocarbonylation of N-(2-pyridyl)sulfonyl (N-SO₂Py)-2-iodoanilines with allenes was developed. The regioselectivity of arylallenes was reversed. Control experiments and DFT calculations were performed to understand the reaction details.

N-Heterocyclic Carbene Catalyzed Synthesis of Trisubstituted Epoxides via Tandem Amidation/Epoxidation Sequence

A tandem amidation/epoxidation sequence between various substituted chalcones and N,N-dimethylformamide (DMF) for the synthesis of trisubstituted epoxides employing N-heterocyclic carbene catalysis was developed. This reaction was performed under metal-free conditions in the presence of tert-butyl hydroperoxide (TBHP) as the oxidant. Trisubstituted epoxides bearing a ketone and an amide functionality (N,N-dimethyl formyl group) were synthesized starting from a wide range of chalcones in moderate to good yields with excellent diastereoselectivity.

NHC-catalyzed cleavage of vicinal diketones and triketones followed by insertion of enones and ynones

Thiazolium carbene-catalyzed reactions of 1,2-diketones and 1,2,3-triketones with enones and ynones have been investigated. The diketones gave α,β-double acylation products via unique Breslow intermediates isolable as acid salts, whereas the triketones formed stable adducts with the NHC instead of the coupling products.

A Direct Synthesis of Highly Substituted π-Rich Aromatic Heterocycles from Oxetanes

The ubiquitous use of π-rich five-membered heterocycles has driven the development of new methods for their synthesis for more than a century. Here, we disclose a general and reliable reaction manifold for the construction of highly substituted heterocycles through a facile Lewis-acid-catalyzed oxetane rearrangement. Notably, this methodology employs a keto-oxetane motif as a 1,4-dicarbonyl surrogate, which can be synthesized using robust alkylation or alkenylation reactions, and thus obviates the need to access 1,4-dicarbonyl compounds via umpoled starting materials. We harnessed this reactivity to generate a broad range of substituted furans and pyrroles, and extended this methodology to produce benzo-fused versions thereof.

Recent advances in N-heterocyclic carbene catalyzed achiral synthesis

N-Heterocyclic carbenes (NHCs) have emerged as powerful and elegant organocatalysts in a variety of newly developed and unprecedented enantioselective transformations due to their unique umpolung capacity. As a supplement to conventional enantioselective organocatalysis, NHC-induced non-asymmetric catalysis has gradually attracted much interest in recent years. Herein, this review aims to reveal the recent developments in NHC-promoted non-asymmetric umpolung transformations resulting in the expeditious construction of versatile achiral natural heterocycles, carbocycles and acylated products.

Synthesis of functionalized imidazolidine-2-thiones via NHC/base-promoted aza-benzoin/aza-acetalization domino reactions

Benzylidene thioureas were generated in situ from α-sulfonylamines and used as novel umpolung acceptors in aza-benzoin/aza-acetalization domino reactions giving 5-hydroxy-imidazolidine-2-thiones.

An insight into the mechanism of the aerobic oxidation of aldehydes catalyzed by N-heterocyclic carbenes

N-Heterocyclic carbene catalysis for the aerobic oxidation and esterification of aromatic aldehydes was monitored by ESI-MS (MS/MS) and the key intermediates were intercepted and characterized using the charge-tag strategy.

N-Heterocyclic carbene-catalyzed double acylation of enones with benzils

Thiazolium carbene-catalyzed reaction of aromatic 1,2-diketones with enones in aprotic solvents gave double acylation products in good yields, whereas hydroacylation products were not detected at all.

The unique reactivity of N-phenacyl-derived thiazolium salts toward α-dicarbonyl compounds

Advanced glycation end products (AGEs), a heterogeneous mixture of compounds formed by non-enzymatic chemical reactions between sugars and the nucleophilic residues of proteins, have been implicated in the pathogenesis of a number of diseases. ALT-711 is an N-phenacyl-derived thiazolium carbene developed as a therapeutic agent for cardiovascular diseases that is proposed to function through cleaving preformed AGE-protein crosslinks. However, despite promising results in animal models and clinical trials, its mechanism of action still remains controversial. Herein, we report the first systematic investigations into dicarbonyl cleavage by ALT-711. We demonstrate that it is capable of cleaving α-diketones more efficiently and likely via a distinct mechanism compared with other N-heterocyclic carbene precursors. We also show that ALT-711 reacts rapidly with α-keto aldehydes to form cyclic diol products, and it can efficiently scavenge methylglyoxal under physiological conditions to protect Escherichia coli from lethal concentrations of this reactive α-keto aldehyde. This work suggests ALT-711 may be especially suited for α-dicarbonyl clearance in vivo and supports a mode of action similar to that originally proposed. To this end, our findings may provide insights into the development of next-generation crosslink breakers.