Homobivalent Lamellarin-Like Schiff Bases: In Vitro Evaluation of Their Cancer Cell Cytotoxicity and Multitargeting Anti-Alzheimer's Disease Potential

Marine alkaloids belonging to the lamellarins family, which incorporate a 5,6-dihydro-1-phenylpyrrolo[2,1-a]isoquinoline (DHPPIQ) moiety, possess various biological activities, spanning from antiviral and antibiotic activities to cytotoxicity against tumor cells and the reversal of multidrug resistance. Expanding a series of previously reported imino adducts of DHPPIQ 2-carbaldehyde, novel aliphatic and aromatic Schiff bases were synthesized and evaluated herein for their cytotoxicity in five diverse tumor cell lines. Most of the newly synthesized compounds were found noncytotoxic in the low micromolar range (<30 μM). Based on a Multi-fingerprint Similarity Search aLgorithm (MuSSeL), mainly conceived for making protein drug target prediction, some DHPPIQ derivatives, especially bis-DHPPIQ Schiff bases linked by a phenylene bridge, were prioritized as potential hits addressing Alzheimer's disease-related target proteins, such as cholinesterases (ChEs) and monoamine oxidases (MAOs). In agreement with MuSSeL predictions, homobivalent para-phenylene DHPPIQ Schiff base 14 exhibited a noncompetitive/mixed inhibition of human acetylcholinesterase (AChE) with Ki in the low micromolar range (4.69 μM). Interestingly, besides a certain inhibition of MAO A (50% inhibition of the cell population growth (IC50) = 12 μM), the bis-DHPPIQ 14 showed a good inhibitory activity on self-induced β-amyloid (Aβ)1-40 aggregation (IC50 = 13 μM), which resulted 3.5-fold stronger than the respective mono-DHPPIQ Schiff base 9

Synthesis and spectroscopic properties of rotamers in the series of 2-(fluoroaryl)-4-substituted pyrroles

A mild, simple and efficient method for the synthesis of ortho, meta and para-fluoroaryl substituted pyrroles was discovered. It was found by NMR spectroscopy, that ortho-fluoroaryl substituted pyrroles exist in the form of inhibited conformational isomers (rotamers). Intramolecular interaction of the hydrogen atom of the pyrrole ring and the fluorine atom in the ortho-position of the aryl substituent leads to the appearance of two sets of signals in the 1H and 13C NMR spectra. Based on the combination of 2D HMBC and HSQC NMR spectroscopy, as well as temperature dependent NMR experiments in DMSO and CDCl3 we conclude that the ratio of obtained rotamers is permanent and does not depend from the temperature