On the basis of the results obtained in previous series of AMPA potentiators belonging to 3,4-dihydro-2H-benzo- and 3,4-dihydro-2H-pyrido-1,2,4-thiadiazine 1,1-dioxides, the present work focuses on the design of original isosteric 3,4-dihydro-2H-thieno-1,2,4-thiadiazine 1,1-dioxides. Owing to the sulfur position, three series of compounds were developed and their activity as AMPA potentiators was characterized. In each of the developed series, potent compounds were discovered. After screening the selected active compounds on a safety in vivo test, 6-chloro-4-ethyl-3,4-dihydro-2H-thieno[2,3-e]-1,2,4-thiadiazine 1,1-dioxide (24) appeared as the most promising compound and was further evaluated. Its effects on long-term potentiation in vivo and on AMPA-mediated noradrenaline release were measured to predict its potential cognitive enhancing properties. Finally, an object recognition test performed in mice revealed that 24 was able to significantly enhance cognition, after oral administration, at doses as low as 0.3 mg/kg. This study validates the interest of the isosteric replacement of the benzene or pyridine nuclei by the thiophene nucleus in the ring-fused thiadiazine dioxides class of AMPA potentiators.

First described by Alois Alzheimer in 1907, Alzheimer's disease (AD) is the most common dementia type, affecting approximately 20 million people worldwide. As the population is getting older, AD is a growing health problem. AD is currently treated by symptomatic drugs, the acetylcholinesterase inhibitors, based on the cholinergic hypothesis (1976). During the past decade, advances in neurobiology have conducted to the identification of new targets. Although some of these innovative approaches tend to delay onset of AD, others are still symptomatic. In this review, we present an overview of the several strategies and new classes of compounds against AD.

The 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propanoic acid (AMPA) receptors, a subtype of glutamate receptors, are involved in important neuronal functions such as long-term memory. A decrease of the number and activity of these receptors seems to play a role in schizophrenia and in the impairment of cognitive function associated to Alzheimers disease. Therefore, research has been focused on the development of drugs acting on those receptors, in particular of AMPA receptors positive allosteric modulators. Although agonists have an intrinsic activity, allosteric modulators need the release of glutamate to be active. Therefore, these drugs are expected to exhibit a decreasing risk of toxicity compared to pure agonists. In this article, we review the recent advances in the design of positive allosteric modulators of AMPA receptors. Keywords: positive allosteric modulators, ampa receptors, glutamate receptors, long-term memory, ionotropic receptors