Mannich base approach to 5-methoxyisatin 3-(4-isopropylphenyl)hydrazone: A water-soluble prodrug for a multitarget inhibition of cholinesterases, beta-amyloid fibrillization and oligomer-induced cytotoxicity

Targeting protein aggregation for the therapy of neurodegenerative diseases remains elusive for medicinal chemists, despite a number of small molecules known to interfere in amyloidogenesis, particularly of amyloid beta (A?) protein. Starting from previous findings in the antiaggregating activity of a class of indolin-2-ones inhibiting A? fibrillization, 5-methoxyisatin 3-(4-isopropylphenyl)hydrazone 1 was identified as a multitarget inhibitor of A? aggregation and cholinesterases with IC50s in the low ?M range. With the aim of increasing aqueous solubility, a Mannich-base functionalization led to the synthesis of N-methylpiperazine derivative 2. At acidic pH, an outstanding solubility increase of 2 over the parent compound 1 was proved through a turbidimetric method. HPLC analysis revealed an improved stability of the Mannich base 2 at pH2 along with a rapid release of1 in humanserum as wellas anoutstanding hydrolytic stability of the parent hydrazone. Coincubation of A?1-42 with 2resulted inthe accumulation oflow MW oligomers, asdetected with PICUPassay. Cell assays on SH-SY5Y cells revealed that 2 exerts strong cytoprotective effects in both cell viability and radical quenching assays, mainly related to its active metabolite 1. These findings show that 2 drives the formation of non-toxic, off-pathway A? oligomers unable to trigger the amyloid cascade and toxicity.