Two series of pentacyclic carbazolones, 22 and 23, have been synthesized utilizing a facile intramolecular Diels-Alder reaction and are allosteric modulators at muscarinic acetylcholine receptors. Their affinities and cooperativities with acetylcholine and the antagonist N- methylscopolamine (NMS) at M1-M4 receptors have been analyzed and compared. All of the synthesized compounds are negatively cooperative with acetylcholine. In contrast, the ...