PEPPSI complexes as potential prodrugs: enzyme inhibition, antioxidant activity, electrochemical characterization, molecular docking analysis

In this study, enzyme inhibition and antioxidant activity analyzes of previously characterized pyridine-enhanced precatalyst preparation stabilization and initiation (PEPPSI)-type Palladium(II) complexes with benzimidazole-type ligands {dichloro[L]pyridine palladium(II), L1: 1-(2-methyl-2-propenyl)-3-[benzylbenzimidazole]-2-ylidene, L2: 1-(2-methyl-2-propenyl)-3-[4-chloro benzylbenzimidazole]-2-ylidene, L3: 1-(2-methyl-2-propenyl)-3-[3-methylbenzylbenzimidazole]-2-ylidene, L4: 1-(2-methyl-2-propenyl)-3-[3,4,5-thrimethoxybenzylbenzimidazole]-2-ylidene, L5: 1-(2-methyl-2-propenyl)-3-[3-naphthylbenzylbenzimidazole]-2-ylidene, L6: 1-(2-methyl-2-propenyl)-3-[anthracen-9-ylmethylbenzimidazole]-2-ylidene} were performed and evaluated as potential drugs for neurodegenerative disorders such as Alzheimer disease and Parkinson disease. Inhibition of tyrosinase enzyme of N-heterocyclic carbenes (NHC) complexes was determined for the first time in literature. Chelating activities of the complexes were determined and compared with EDTA. Electrochemical characterization was performed using cyclic voltammetry method. Moreover, global reactivity descriptors and electronic transitions were evaluated by DFT/TDDFT methods and molecular docking interactions with human acetylcholine esterase, human butyrylcholine esterase and oxidoreductase were studied.

Synthesis of the First Resorcin[4]arene-Functionalized Triazolium Salts and Their Use in Suzuki–Miyaura Cross-Coupling Reactions

Two bulky triazolium salts, namely 1-{4(24),6(10),12(16),18(22)-tetramethylenedioxy- 2,8,14,20-tetrapentylresorcin[4]arene-5-yl}-4-phenyl-3-methyl-1H-1,2,3-triazolium tetrafluoro borate (1) and 1,4-bis{4(24),6(10),12(16),18(22)-tetramethylenedioxy-2,8,14,20-tetrapentyl resorcin[4]arene-5-yl}-3-methyl-1H-1,2,3-triazolium iodide (2), have been synthesized and assessed in the palladium-catalyzed Suzuki–Miyaura cross-coupling of aryl chlorides, with aryl boronic acids. As a general trend, the reaction rates obtained with 1 were significantly higher (up to 5 times) than those observed for 2, this mainly reflected a sterically more accessible metal center in the catalytic intermediates formed with 1. The presence of flexible pentyl chains in these intermediates, which might sterically interact with the metal center, when the latter adopts an exo-orientation with respect to the cavity, were likely responsible for the observed good performance.

Metal Confinement through N-(9-Alkyl)fluorenyl-Substituted N-Heterocyclic Carbenes and Its Consequences in Gold-Catalysed Reactions Involving Enynes

A series of gold(I) and gold(III) complexes containing bulky bis-N,N'-(9-alkylfluorenyl) heterocyclic carbene (^R F-NHC) ligands have been prepared in high yields from appropriate imidazolinium, imidazolium and benzimidazolium salts. In all complexes, the carbene ligand provides high steric protection of the Au-X bond trans to the carbenic C atom. Irrespective of the metal oxidation state, the complexes showed high efficiency in a tandem 3,3-rearrangement/Nazarov reaction of an enynyl acetate. One of the Au^III complexes, [AuCl₃ (^R F-NHC)], was further found to be suitable for the efficient cyclisation of a propargylcarboxamide. Furthermore, unlike related NHC-gold(I) complexes based on conventional bulky N-heterocyclic carbenes (notably, 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr), 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and 1,3-(bis-tert-butyl)imidazol-2-ylidene (ItBu)), the studied [Au^I Cl(^R F-NHC)] complexes catalysed the conversion of a 1,6-enyne in the presence of indole into a single product; this arises from the embracing character of the ligand, which prevents indole addition on one of the catalytic intermediates. A structure/selectivity relationship was established for all carbenes tested that took into account percent buried volumes and topographic steric maps. The results illustrate the high potential of confining NHCs in organic synthesis.

Pd-PEPPSI-IPentCl: a new highly efficient ligand-free and recyclable catalyst system for the synthesis of 2-substituted indoles via domino copper-free Sonogashira coupling/cyclization

One pot synthesis of 2-substituted indolesviaSonogashira coupling (without a copper catalyst) followed by intermolecular cyclization using Pd-PEPPSI-IPent^Cl.

PEPPSI-SONO-SP2: a new highly efficient ligand-free catalyst system for the synthesis of tri-substituted triazine derivatives via Suzuki–Miyaura and Sonogashira coupling reactions under a green approach

Consecutive Suzuki–Miyaura and Sonogashira cross coupling reactions catalyzed by a new competent palladium catalyst PEPPSI-SONO-SP² under mild and green reaction conditions.

N-Alkylfluorenyl-substituted N-heterocyclic carbenes as bimodal pincers

Two N-heterocyclic carbene precursors having their nitrogen atoms substituted by the expanded 9-ethyl-9-fluorenyl group, namely imidazolinium chloride 6 and imidazolium chloride 7, have been synthesized in high yields from fluorenone (1).

Molecular recognition of upper rim functionalized cavitand and its unique dimeric capsule in the solid state

Calix[4]resorcinarene-based cavitand recognized the methyl group of the guests to form 1 : 1 host–guest complexes. In the solid state, the cavitand formed a dimeric capsule in which two molecules of nitromethane were entrapped by weak noncovalent interactions.

Directional properties of fluorenylidene moieties in unsymmetrically substituted N-heterocyclic carbenes. Unexpected CH activation of a methylfluorenyl group with palladium. Use in palladium catalysed Suzuki–Miyaura cross coupling of aryl chlorides

The confining properties of N-heterocyclic carbenes with alkylfluorenyl substituents have been investigated.