Propargylated Purine Deoxynucleosides: New Tools for Fluorescence Imaging Strategies

Triazole-Modified Nucleic Acids for the Application in Bioorganic and Medicinal Chemistry

This review covers studies which exploit triazole-modified nucleic acids in the range of chemistry and biology to medicine. The 1,2,3-triazole unit, which is obtained via click chemistry approach, shows valuable and unique properties. For example, it does not occur in nature, constitutes an additional pharmacophore with attractive properties being resistant to hydrolysis and other reactions at physiological pH, exhibits biological activity (i.e., antibacterial, antitumor, and antiviral), and can be considered as a rigid mimetic of amide linkage. Herein, it is presented a whole area of useful artificial compounds, from the clickable monomers and dimers to modified oligonucleotides, in the field of nucleic acids sciences. Such modifications of internucleotide linkages are designed to increase the hybridization binding affinity toward native DNA or RNA, to enhance resistance to nucleases, and to improve ability to penetrate cell membranes. The insertion of an artificial backbone is used for understanding effects of chemically modified oligonucleotides, and their potential usefulness in therapeutic applications. We describe the state-of-the-art knowledge on their implications for synthetic genes and other large modified DNA and RNA constructs including non-coding RNAs.

Drug Discovery of Nucleos(t)ide Antiviral Agents: Dedicated to Prof. Dr. Erik De Clercq on Occasion of His 80th Birthday

Nucleoside and nucleotide analogues are essential antivirals in the treatment of infectious diseases such as human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), herpes simplex virus (HSV), varicella-zoster virus (VZV), and human cytomegalovirus (HCMV). To celebrate the 80th birthday of Prof. Dr. Erik De Clercq on 28 March 2021, this review provides an overview of his contributions to eight approved nucleos(t)ide drugs: (i) three adenosine nucleotide analogues, namely tenofovir disoproxil fumarate (Viread^®) and tenofovir alafenamide (Vemlidy^®) against HIV and HBV infections and adefovir dipivoxil (Hepsera^®) against HBV infections; (ii) two thymidine nucleoside analogues, namely brivudine (Zostex^®) against HSV-1 and VZV infections and stavudine (Zerit^®) against HIV infections; (iii) two guanosine analogues, namely valacyclovir (Valtrex^®, Zelitrex^®) against HSV and VZV and rabacfosadine (Tanovea^®-CA1) for the treatment of lymphoma in dogs; and (iv) one cytidine nucleotide analogue, namely cidofovir (Vistide^®) for the treatment of HCMV retinitis in AIDS patients. Although adefovir dipivoxil, stavudine, and cidofovir are virtually discontinued for clinical use, tenofovir disoproxil fumarate and tenofovir alafenamide remain the most important antivirals against HIV and HBV infections worldwide. Overall, the broad-spectrum antiviral potential of nucleos(t)ide analogues supports their development to treat or prevent current and emerging infectious diseases worldwide.

Synthesis and antibiofilm activity of 1,2,3-triazole-pyridine hybrids against methicillin-resistant Staphylococcus aureus (MRSA)

Antibiotic-resistant bacteria are emerging at an alarming rate, posing a potential threat to human health. A series of 1,2,3-triazole-pyridine hybrids were synthesised as promising antibiofilm agents against planktonic and sessile MRSA.

Design of reverse transcriptase-specific nucleosides to visualize early steps of HIV-1 replication by click labeling

Only a small portion of human immunodeficiency virus type 1 (HIV-1) particles entering the host cell results in productive infection, emphasizing the importance of identifying the functional virus population. Because integration of viral DNA (vDNA) is required for productive infection, efficient vDNA detection is crucial. Here, we use click chemistry to label viruses with integrase coupled to eGFP (HIV_IN-eGFP) and visualize vDNA. Because click labeling with 5-ethynyl-2'-deoxyuridine is hampered by intense background staining of the host nucleus, we opted for developing HIV-1 reverse transcriptase (RT)-specific 2'-deoxynucleoside analogs that contain a clickable triple bond. We synthesized seven propargylated 2'-deoxynucleosides and tested them for lack of cytotoxicity and viral replication inhibition, RT-specific primer extension and incorporation kinetics in vitro, and the capacity to stain HIV-1 DNA. The triphosphate of analog A5 was specifically incorporated by HIV-1 RT, but no vDNA staining was detected during infection. Analog A3 was incorporated in vitro by HIV-1 RT and human DNA polymerase γ and did enable specific HIV-1 DNA labeling. Additionally, A3 supported mitochondria-specific DNA labeling, in line with the in vitro findings. After obtaining proof-of-principle of RT-specific DNA labeling reported here, further chemical refinement is necessary to develop even more efficient HIV-1 DNA labels without background staining of the nucleus or mitochondria.