Synthesis of multifunctional peptides containing a fluorophore group as fluorescent probe

Abstract

Alzheimer Disease (AD) is the most common cause of dementia in the elderly population. Symptoms of the disease are: difficulty in remembering newly learned information, mood and behaviour changes, memory loss, judgment alteration and difficulties in daily and usual activities. Today Alzheimer disease affects more than 30 million people worldwide and it is estimated that more than 100 million people will be affected by 2050 mainly because of the fast growth of the elderly population. Currently, it is generally accepted that Alzheimer disease originates from a process called amyloid cascade that occurs in the synaptic cleft, wherein A aggregation due to its union with Cu(II), is a key event. In this work, elaborated in collaboration with the group of Bioinorganic Chemistry led by Professor Patrick Gámez, the peptides with sequences Ac-His-Lys(Cm)-His-Lys-NH2 and Ac-His-Lys(4-DMN)-His-NH2 have been synthesized. These peptides encompass two amino acid derivatives containing two fluorescent probes: coumarin and 4-N,N-dimethylamino-1,8-naphthalimido. These peptide sequences will be studied as potential therapeutic agents due to its chelating properties of the Cu (II), as well as copper sensors for AD diagnosis.The amino acid derivatives have been synthesized in aqueous phase while peptides were synthesized in solid phase through the Fmoc strategy, using as polymer support Rink Amide resin. The peptides prepared were functionalized with an acetyl group in the N-terminus and a carboxamide group in the C-terminus. To obtain the desired synthetic sequence, Fmoc amino acids, protected at the N-terminus with the 9-fluorenylmethoxycarbonyl group (Fmoc), which is labile to piperidine, were used. For generating the amide bonds, N,N'-diisopropycarbodiimide (DIC) and Oxyma have been used. The cleavage of the peptide from the resin was performed under acidic conditions using trifluoroacetic acid (TFA) in the presence of triisopropylsilane (TIPS) as carbocation scavenger agent. The characterization of the products was carried out using different techniques such as 1H and 13C NMR, HPLC and HPLC-MS.