Synthesis of Fmoc-protected amino ketones bearing tert-butyl based side-chain protecting groups

Covalent-reversible peptide-based protease inhibitors. Design, synthesis, and clinical success stories

Dysregulated human peptidases are implicated in a large variety of diseases such as cancer, hypertension, and neurodegeneration. Viral proteases for their part are crucial for the pathogens' maturation and assembly. Several decades of research were devoted to exploring these precious therapeutic targets, often addressing them with synthetic substrate-based inhibitors to elucidate their biological roles and develop medications. The rational design of peptide-based inhibitors offered a rapid pathway to obtain a variety of research tools and drug candidates. Non-covalent modifiers were historically the first choice for protease inhibition due to their reversible enzyme binding mode and thus presumably safer profile. However, in recent years, covalent-irreversible inhibitors are having a resurgence with dramatic increase of their related publications, preclinical and clinical trials, and FDA-approved drugs. Depending on the context, covalent modifiers could provide more effective and selective drug candidates, hence requiring lower doses, thereby limiting off-target effects. Additionally, such molecules seem more suitable to tackle the crucial issue of cancer and viral drug resistances. At the frontier of reversible and irreversible based inhibitors, a new drug class, the covalent-reversible peptide-based inhibitors, has emerged with the FDA approval of Bortezomib in 2003, shortly followed by 4 other listings to date. The highlight in the field is the breathtakingly fast development of the first oral COVID-19 medication, Nirmatrelvir. Covalent-reversible inhibitors can hipothetically provide the safety of the reversible modifiers combined with the high potency and specificity of their irreversible counterparts. Herein, we will present the main groups of covalent-reversible peptide-based inhibitors, focusing on their design, synthesis, and successful drug development programs.

A copper-catalyzed, pH-neutral construction of high-enantiopurity peptidyl ketones from peptidic s-acylthiosalicylamides in air at room temperature

A copper-catalyzed transformation of peptidic thiol esters and boronic acids gives peptidyl ketones and takes place in DMF or DMF/H(2)O at room temperature in air (see scheme). This aerobic reaction only occurs at a thiol ester group capable of coordinating to Cu through its appendage on the sulfur center and is not hampered by racemization of the reactants or products.

Synthesis of high enantiopurity N-protected alpha-amino ketones by thiol ester-organostannane cross-coupling using pH-neutral conditions

An efficient synthesis of high enantiopurity N-protected alpha-amino ketones is described. Complementing other studies using boronic acids and thiol esters, this Cu(I) diphenylphosphinate (CuDPP)-mediated, palladium-catalyzed coupling of alpha-amino thiol esters with aryl, heteroaryl, allyl, and alkenyl organostannanes gives N-protected alpha-amino ketones in high yields with high enantiopurity (in almost all cases) under mild and pH-neutral reaction conditions. The viability of pi-deficient heteroarylstannanes is an advantage of this reaction compared to the related boronic acid system.

Evaluation of Solution and Solid-Phase Approaches to the Synthesis of Libraries of α,α-Disubstituted-α-acylaminoketones

Solid phase, solution, and hybrid approaches to the synthesis of small focused libraries of alpha,alpha-disubstituted-alpha-acylaminoketones have been explored. Solution and hybrid approaches that used support-bound reagents and scavenger resins were the most productive.

Solid-phase synthesis of C-terminal modified peptides

Solid-phase synthesis of biomolecules, of which peptides are the principal example, is well established. However, synthetic peptides containing modifications at the carboxy termini are often desired because of their potential therapeutic properties. As a result, there is a necessity for effective solid-phase strategies for the preparation of peptides with C-terminal end groups other than the usual carboxylic acid and carboxamide functionalities. The present article primarily reviews literature reports on methods for solid-phase synthesis of C-terminal modified peptides. In addition, general information about biological activities and/or synthetic applications of each individual class of peptide is also provided.