Microwave-assisted multi-step synthesis of novel pyrrolo-[3,2-c]quinoline derivatives

Novel 1H-Pyrrolo[3,2-c]quinoline Based 5-HT6 Receptor Antagonists with Potential Application for the Treatment of Cognitive Disorders Associated with Alzheimer's Disease

Modulators of the serotonin 5-HT6 receptor (5-HT6R) offer a promising strategy for the treatment of the cognitive deficits that are associated with dementia and Alzheimer's disease. Herein, we report the design, synthesis, and characterization of a novel class of 5-HT6R antagonists that is based on the 1H-pyrrolo[3,2-c]quinoline core. The most active compounds exhibited comparable binding affinity to the reference compound, SB-742457, and markedly improved selectivity. Lead optimization led to the identification of (S)-1-[(3-chlorophenyl)sulfonyl]-4-(pyrrolidine-3-yl-amino)-1H-pyrrolo[3,2-c]quinoline (14) (Ki = 3 nM and Kb = 0.41 nM). Pharmacological characterization of the 5-HT6R's constitutive activity at Gs signaling revealed that 14 behaved as a neutral antagonist, while SB-742457 was classified as an inverse agonist. Both compounds 14 and SB-742457 reversed phencyclidine-induced memory deficits and displayed distinct procognitive properties in cognitively unimpaired animals (3 mg/kg) in NOR tasks. Compounds 14 and SB-742457 were also active in the Vogel test, yet the anxiolytic effect of 14 was 2-fold higher (MED = 3 mg/kg). Moreover, 14 produced, in a 3-fold higher dose (MED = 10 mg/kg), antidepressant-like effects that were similar to those produced by SB-742457 (MED = 3 mg/kg). Together, these data suggest that the 4-(pyrrolidine-3-yl-amino)-1H-pyrrolo[3,2-c]quinoline scaffold is an attractive molecular framework for the development of procognitive agents. The results are promising enough to warrant further detailed mechanistic studies on the therapeutic potential of 5-HT6R antagonists and inverse agonists for the treatment of cognitive decline and depression/anxiety symptoms that are comorbidities of Alzheimer's disease.

A convenient approach to an advanced intermediate toward the naturally occurring, bioactive 6-substituted 5-hydroxy-4-aryl-1H-quinolin-2-ones

An advanced intermediate for the total synthesis of the 5-hydroxy-4-aryl-3,4-dihydro-1H-quinolin-2-one natural products and a 3,4-bisdesoxy analog of peniprequinolone were synthesized.

The 3,4-dioxygenated 5-hydroxy-4-aryl-quinolin-2(1H)-one alkaloids. Results of 20 years of research, uncovering a new family of natural products

The title alkaloids are discussed. Emphasis is placed on their isolation, source microorganisms and structure, as well as relevant biological activities and synthetic progress.

Tuneable radical cyclisations: a tin-free approach towards tricyclic and spirocyclic heterocycles via a common precursor

A novel common precursor approach towards both tricyclic and spirocyclic heterocycles is described. Cyclisations are based on thiyl radical/isocyanide methodology and avoid the use of tin.

Palladium-catalyzed cross coupling reaction of N-alkoxyimidoyl bromides and its application to one-pot synthesis of N-arylamines

The synthetic utility of N-alkoxyimidoyl halides is demonstrated using the palladium-catalyzed cross-coupling reaction. The Sonogashira and Suzuki-Miyaura coupling reactions of N-alkoxyimidoyl bromides produced versatile ketoxime ethers in good to excellent yields. A one-pot reaction of the imidoyl bromides with arylboronic acid and allylmagnesium bromide to produce N-arylamines via Suzuki-Miyaura coupling followed by domino reaction involving sequential addition-eliminative rearrangement-addition reactions was developed.

A straightforward route to enantiopure 2-substituted-3,4-dehydro-β-proline via ring closing metathesis

The synthesis of unusual cyclic amino acids, that may be envisaged as proline analogs, is an area of great interest for their potential applications as scaffolds for the design of bioactive peptidomimetics or units for the creation of novel foldamers. We have carried out the preparation of cyclic dehydro-β-amino acids starting from allylic carbonates via a two-step allylic amination/ring closing metathesis (RCM) protocol. The introduction of the allylamino moiety has been carried out either without a catalyst, through an S(N)2' reaction, or in the presence of iridium complexes. The backbone of the allylamino intermediates contains two unsaturations, thus suggesting that RCM could be a valuable tool for the preparation of dihydropyrrole scaffolds. A similar reaction has been already reported in the literature for racemic aromatic-substituted substrates, but no examples of enantiopure derivatives bearing aliphatic chains have been reported. The reaction was optimized by testing different Grubbs' catalysts and carbamate nitrogen protecting groups. Moreover, in view of a future application of these dehydro-β-amino acids as central core of peptidomimetics, the malonate chain was also used to protect nitrogen prior to RCM.

Microwave-Assisted Ruthenium-Catalyzed Reactions

Since the first reports on the use of microwave irradiation to accelerate organic chemical transformations, a plethora of papers has been published in this field. In most examples, microwave heating has been shown to dramatically reduce reaction times, increase product yields, and enhance product purity by reducing unwanted side reactions compared with conventional heating methods. The present contribution aims at illustrating the advantages of this technology in homogeneous catalysis by ruthenium complexes and, when data are available, at comparing microwave-heated and conventionally heated experiments. Selected examples refer to olefin metathesis, isomerization reactions, 1,3-dipolar cycloadditions, atom transfer radical reactions, transfer hydrogenation reactions, and H/D exchange reactions.