Several series of simple 3-phenylcoumarins have been studied to prevent and treat Alzheimer’s disease and its complications, showing high activity toward AChE and MAO, together with antioxidant activity (
). Among a studied series of polyhydroxy 3-phenylcoumarins, 3-(3′,4′-dihydroxyphenyl)-7,8-dihydroxycoumarin (
. This research group also studied a series of benzamide derivatives at the position 4′, resulting in the compound
Also, from 3-(3′-aminophenyl)coumarin (
Ki = 146 μM), a non-peptidic drug-like β-secretase 1 (BACE-1) inhibitor, the hit fragment containing the
N-acylated ethane-1,2-diamine motif has been identified as a directing probe to pick inhibitory fragments for the S1 pocket of the aspartic protease BACE-1, leading to the most interesting compound (compound
4, with a biphenylmethyl residue) with a
Ki of 3.7 μM
[10]. Separating the amine from the benzene ring at position 3 of the 3-phenylcoumarins by a methylene group proved to be an interesting strategy to obtain more active compounds. When this amine is a bulky amine as a
N,
N-dibenzyl(
N-ethyl)amine fragment, several compounds of a studied series proved to act on three relevant targets in Alzheimer’s disease: σ-1 receptor (σ1R), BACE1 and AChE. These also show potent neurogenic properties, good antioxidant capacity and favorable central nervous system (CNS) permeability. Compound
5 must be highlighted within the series
[11]. Compounds with the same substitution at position 4′, and a 7-aminoalkoxy chain, formed a series of products presenting multitarget interest for the treatment of the middle stage of Alzheimer’s disease. A non-neurotoxic dual AChE/BuChE inhibitor, compound
6, which is also a nanomolar human AChE inhibitor, turned out to be a significant inhibitor of Aβ42 self-aggregation activity, being also a promising neuroprotective agent
[12]. A series of compounds with 7-aminoalkoxy-3-phenylcoumarins, presenting simple substitutions on the phenyl at position 3, were studied, identifying compound
7 as the most potent compound against AChE (IC
50 = 0.27 μM). Kinetic and molecular modelling studies proved that compound
7 works in a mixed-type approach, and interacts concomitantly with the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. In addition, compound
7 blocks β-amyloid (Aβ) self-aggregation with a ratio of 44% at 100 μM, and significantly protects rat pheochromocytoma (PC12) cells from hydrogen peroxide (H
2O
2)-damage in a dose-dependent way
[13]. The 7-substitution of 3-phenylcoumarins has also been used as a building block for a novel series of coumarin-lipoic acid conjugates, resulting in compound
8, the most potent AChE inhibitor, showing a good inhibitory effect on Aβ-aggregation and intracellular ROS formation, as well as the ability of selective bio-metal chelation and neuroprotection against H
2O
2- and Aβ1-42-induced cytotoxicity
[14][15]. Interesting to note is the comparison between two compounds prepared in a study on Alzheimer’s disease, being 6-substituted 3-arylcoumarins. Compounds
9 and
10, with the substituents in the same positions, and small structural differences between them, do not offer great differences in their activities and selectivity against cholinesterases or towards the inhibition of self-induced Aβ42-aggregation; however, they do offer important differences in selectivity against human MAO-A and MAO-B which are worthy of further study
[16].