Despite many years of research, human neutrophil elastase (HNE) still remains an area of interest for many researchers. This multifunctional representative of neutrophil serine proteases is one of the most destructive enzymes found in the human body which can degrade most of the extracellular matrix. Overexpression or dysregulation of HNE may lead to the development of several inflammatory diseases. Previously, we presented the HNE inhibitor with k_inact/K_I value over 2,000,000 [M⁻¹s⁻¹]. In order to optimize its structure, over 100 novel tripeptidyl derivatives of α-aminoalkylphosphonate diaryl esters were synthesized, and their activity toward HNE was checked. To confirm the selectivity of the resultant compounds, several of the most active were additionally checked against the two other neutrophil proteases: proteinase 3 and cathepsin G. The developed modifications allowed us to obtain a compound with significantly increased inhibitory activity against human neutrophil elastase with high selectivity toward cathepsin G, but none toward proteinase 3.

Alphaviruses belong to the worldwide distributed Togaviridae family and Alphavirus genus. They are spherical, enveloped, single-stranded RNA arthropod- borne viruses. Alphaviruses are mostly transmitted by mosquitoes (Aedes spp. and Anopheles spp.) and are geographically distributed in restricted areas where appropriate vectors are present (Fig.1.). The most recognized members of this genus are Sindbis (SINV), Semliki Forest (SFV), Venezuelan equine encephalitis (VEEV), Ross River (RRV), and Chikungunya (CHIKV) viruses. Alphaviruses are infection agents for humans and many animals. Clinically, most human infections with arthritogenic alphaviruses are associated with symptoms such as fever, headache, joint pain, rash, chronic arthritis, and encephalitis. Major events during the alphaviral infection are virus entry, replication, assembly, and budding of new virions. Alphaviral RNA encodes four nonstructural and five structural proteins. Nonstructural proteins are mainly involved in the replication process and virus pathogenesis, while structural proteins form new virions. Both groups of viral proteins are produced as single polyproteins which undergo autoproteolytic maturation. This process is carried out by the two viral proteases, cysteine protease nsP4 and C protein serine protease (CP), and is considered to be critical for virus replication. The capsid protease CP is a chymotrypsin-like serine protease with the catalytic triad including His145, Asp167, and Ser219. What is important, after a suicidal autoproteolytic event the side chain of Trp267 remains bound in a hydrophobic S1 pocket thus inhibiting further trans-proteolytic activity. Alphaviral capsid protein undergoes a single proteolytic reaction before maturation and then, after self- inactivation, it assembles to form a viral capsid shell. Inhibitors of the capsid protease have significant antiviral activity. Compounds belonging to this group can be good candidates for new antiviral drugs.

The O'nyong‐nyong virus (ONNV) is a member of the Alphavirus genus isolated for the first time in 1959 in Gulu (Uganda). The main symptoms of O'nyong‐nyong fever are nonspecific and flu like; a proper diagnosis at the early stage is challenging. Until today, the first ONNV epidemic in 1959–1962 remains one of the largest arbovirus outbreaks ever recorded (over 2 million cases). No specific therapy is available thus far. Capsid protease (CP) is a chymotrypsin‐like serine protease that catalyzes the autoproteolytic maturation of the structural polyprotein and undergoes self‐inactivation upon the release of the mature capsid (C) protein. Despite the discovery of this virus more than 60 years ago, many aspects of CP remain understudied, including substrate specificity. Herein, the structures of the first phosphonic‐type inhibitors and activity‐based probes specific to the ONNV CP are presented.