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Thirteen known (1&ndash, 12 and 16) and three previously undescribed Amaryllidaceae alkaloids of belladine structural type, named carltonine A-C (13&ndash, 15), were isolated from bulbs of Narcissus pseudonarcissus cv. Carlton (Amaryllidaceae) by standard chromatographic methods. Compounds isolated in sufficient amounts, and not tested previously, were evaluated for their in vitro acetylcholinesterase (AChE, E.C. 3.1.1.7), butyrylcholinesterase (BuChE, E.C. 3.1.1.8) and prolyl oligopeptidase (POP, E.C. 3.4.21.26) inhibition activities. Significant human BuChE (hBUChE) inhibitory activity was demonstrated by newly described alkaloids carltonine A (13) and carltonine B (14) with IC50 values of 913 &plusmn, 20 nM and 31 &plusmn, 1 nM, respectively. Both compounds displayed a selective inhibition pattern for hBuChE with an outstanding selectivity profile over AChE inhibition, higher than 100. The in vitro data were further supported by in silico studies of the active alkaloids 13 and 14 in the active site of hBuChE.

Tacrine was the first drug to be approved for Alzheimer’s disease (AD) treatment, acting as a cholinesterase inhibitor. The neuropathological hallmarks of AD are amyloid-rich senile plaques, neurofibrillary tangles, and neuronal degeneration. The portfolio of currently approved drugs for AD includes acetylcholinesterase inhibitors (AChEIs) and N-methyl-d-aspartate (NMDA) receptor antagonist. Squaric acid is a versatile structural scaffold capable to be easily transformed into amide-bearing compounds that feature both hydrogen bond donor and acceptor groups with the possibility to create multiple interactions with complementary sites. Considering the relatively simple synthesis approach and other interesting properties (rigidity, aromatic character, H-bond formation) of squaramide motif, we combined this scaffold with different tacrine-based derivatives. In this study, we developed 21 novel dimers amalgamating squaric acid with either tacrine, 6-chlorotacrine or 7-methoxytacrine representing various AChEIs. All new derivatives were evaluated for their anti-cholinesterase activities, cytotoxicity using HepG2 cell line and screened to predict their ability to cross the blood-brain barrier. In this contribution, we also report in silico studies of the most potent AChE and BChE inhibitors in the active site of these enzymes., This project was conceived by JMC (IQOG, CSIC, Madrid, Spain), initially carried out experimentally by EM, in Madrid, thanks to a Short-Term Scientific Mission (from 30 January until the 28 April 2017) granted by EU COST Action (CA15135: “Multi-target paradigm for innovative ligand identification in the drug discovery process (MuTaLig)”), and continued in Hradec Kralove (Czech Republic) by EM in collaboration with BS, under the supervision of JK, who organized and planned all the biological analysis and wrote the manuscript. JMC is very thankful to EM, BS, and JK for their collaboration, and to the COST Action CA15135 for supporting this project. The study was supported by a grant of Ministry of Defence “Long Term Development Plan” Medical Aspects of Weapons of Mass Destruction of the Faculty of Military Health Sciences, University of Defence, by the Ministry of Education, Youth and Sports of Czech Republic (project ERDF no. CZ.02.1.01/0.0/0.0/18_069/0010054) and by MH CZ - DRO (University Hospital Hradec Kralove, No. 00179906). JMC thanks MINECO (Government of Spain) (SAF2015-65586-R) for support.

Alzheimer&rsquo, s disease (AD) is a complex disorder with unknown etiology. Currently, only symptomatic therapy of AD is available, comprising cholinesterase inhibitors and N-methyl-d-aspartate (NMDA) receptor antagonists. Drugs targeting only one pathological condition have generated only limited efficacy. Thus, combining two or more therapeutic interventions into one molecule is believed to provide higher benefit for the treatment of AD. In the presented study, we designed, synthesized, and biologically evaluated 15 novel fluoren-9-amine derivatives. The in silico prediction suggested both the oral availability and permeation through the blood&ndash, brain barrier (BBB). An initial assessment of the biological profile included determination of the cholinesterase inhibition and NMDA receptor antagonism at the GluN1/GluN2A and GluN1/GluN2B subunits, along with a low cytotoxicity profile in the CHO-K1 cell line. Interestingly, compounds revealed a selective butyrylcholinesterase (BChE) inhibition pattern with antagonistic activity on the NMDARs. Their interaction with butyrylcholinesterase was elucidated by studying enzyme kinetics for compound 3c in tandem with the in silico docking simulation. The docking study showed the interaction of the tricyclic core of new derivatives with Trp82 within the anionic site of the enzyme in a similar way as the template drug tacrine. From the kinetic analysis, it is apparent that 3c is a competitive inhibitor of BChE.