NOVEL ASPARTYL PROTEASE INHIBITORS: SYNTHETIC STUDIES AND PRELIMINARY EVALUATION

Aspartic Proteases are proteolytic enzymes involved in a large number of biological processes, playing an essential role in several important diseases. Their inhibitors have emerged as useful drugs in the treatment of cancer, parasitic, fungal and viral infections as well as inflammatory, immunological, respiratory, cardiovascular and neurodegenerative disorders. Acquired Immunodeficiency Syndrome (AIDS) and Alzheimer Disease (AD) are controlled by aspartic proteases, HIV-Pr and BACE-1 respectively. HIV-Pr plays an essential role in the replication and maturation of the Human Immunodeficiency Virus, while BACE-1 is involved in the production and deposition of amyloid--peptide (A), recognized as a possible cause for AD. Aspartic proteases inhibitors can be classified into the two major categories of peptidomimetic and nonpeptide inhibitors. The former, designed to emulate their natural substrates, are oligopeptides containing a not-hydrolizable dipeptide isostere. Currently, many designed potent and selective protease peptidomimetic inhibitors of the human immunodeficiency virus protease (HIV-1 Pr) are used in the treatment of AIDS as they efficiently slow down or halt disease progression. Even very potent in vitro peptidomimetic BACE-1 inhibitors were developed but their poor pharmacokinetic profile has prevented them from being further developed to oral bioavailable CNS drug. Thus, more recent attempts have been directed towards the discovery of small non peptidic inhibitors, that have higher blood brain barrier penetration and are capable to efficiently bind the active site of the enzyme lowering the production of A protein. This thesis is divided in two parts. In the frame of a research activity aimed at the design and synthesis of peptidomimetic HIV-Pr inhibitors, the first part of this work is focused on the synthesis of chiral optically pure -allylamines as key intermediates for the stereoselective synthesis of dipeptidic isosters. In particular, in chapter 2 the development of a revised version of Julia olefination is described, that allowed the obtainment of a small library of -aminoalkenes derived from Ala, Ileu, Leu, Phe, Pro, Tyr, Val with good yields and exccellent e.e.s. With respect to the original Julia reaction, in this modified version -aminoesters derived from aminoacids are employed as the starting material, this avoiding the use of the aminoaldehydes normally used in the classical olefination methods, whose reproducibility is often affected by the low configurational and chemical stability of -chiral parent aldehydes. The second part of the thesis deals with the synthesis and biological evaluation of functionalized 3,4-dihydropyrimidines (DHPMs) as BACE 1 inhibitors. This heterocyclic scaffold is present in many biologically and pharmacologically active compounds and it possesses the requisite features for an effective inhibitory activity against BACE-1, as shown by our preliminary studies run (Chapter 4) on a group of 3,4-dihydropyrimidinones (X = O) e 3,4-dihydropyrimidinthiones with measured affinities in the micromolar range. With the aim of obtaining inhibitors with improved potency, the study was extended to 2-iminoDHPMs having a guanidine group embedded in the heterocyclic scaffold, due to the structural features of the guanidine moiety, suitable for an optimal interaction with BACE-1 active site. The library of DHPMs was obtained by Biginelli reaction in which a variety of different aliphatic and aromatic aldehydes, were reacted -dicarbonylic compounds and with urea, thiourea and guanidine. Molecular docking experiments (Chapter 5) assisted the choice of the most appropriate substituents to append on the heterocyclic scaffold; inhibitory activity was determined measuring IC50 values (Chapter 5), with fluorimetric assays using the FRET technique. In chapter 5 we describe some preliminary approaches to the obtainment of DHPM as single enantiomers.