Synthesis, chemistry, and biological activity of 5-thiocyanatopyrimidine nucleosides as potential masked thiols

Visible light induced regioselective C-3 thiocyanation of imidazoheterocycles through naphthalimide dye based photoredox catalysis

A visible light induced C-3 thiocyanation of imidazo[1,2-a]pyridines by using a naphthalimide based photoredox catalyst has been reported. Tolerance of electron withdrawing and donating groups at different positions of the imidazo[1,2-a]pyridine ring led to a wide substrate accessibility of this method. This methodology is further reproducible with other heterocycles like benzo[d]imidazo[2,1-b]thiazoles, indoles, azaindoles, and anilines.

Discovery and Mechanism Study of SARS-CoV-2 3C-like Protease Inhibitors with a New Reactive Group

3CLpro is an attractive target for the treatment of COVID-19. Using the scaffold hopping strategy, we identified a potent inhibitor of 3CLpro (3a) that contains a thiocyanate moiety as a novel warhead that can form a covalent bond with Cys145 of the protein. Tandem mass spectrometry (MS/MS) and X-ray crystallography confirmed the mechanism of covalent formation between 3a and the protein in its catalytic pocket. Moreover, several analogues of compound 3a were designed and synthesized. Among them, compound 3h shows the best inhibition of 3CLpro with an IC50 of 0.322 μM and a kinact/Ki value of 1669.34 M-1 s-1, and it exhibits good target selectivity for 3CLpro against host proteases. Compound 3c inhibits SARS-CoV-2 in Vero E6 cells (EC50 = 2.499 μM) with low cytotoxicity (CC50 > 200 μM). These studies provide ideas and insights to explore and develop new 3CLpro inhibitors in the future.

A general approach to the synthesis of 5-S-functionalized pyrimidine nucleosides and their analogues

A palladium-catalyzed C–S coupling reaction has been used as a key step for the introduction of S-functionality at the C-5 position of the cytosine and uracil nucleosides and their analogues.

Novel process for generating useful electrophiles from common anions using Selectfluor fluorination agent

In the present work, the electrophile equivalents Cl+, Br+, SCN+, and NO2+ are generated from their respective sodium, potassium, and in some cases ammonium salts (M+X-) by reaction with Selectfluor electrophilic fluorination agent in acetonitrile solution at room temperature. These generated electrophilic species subsequently react in situ with a variety of aromatic substrates containing one or more substituent groups including H, F, Cl, CH3, COOH, C(O)CH3, NO2, and OR' and NR'R' ' where R' and R' ' are H or CH3. The resulting substitution products are, in most cases, isolable as pure compounds in high yield. Variations in the process include the use of other anions, electrophilic fluorination agents, and solvents.

Synthesis and characterization of a new 5-thiol-protected deoxyuridine phosphoramidite for site-specific modification of DNA

A new nucleotide analogue was developed for site-specific incorporation of a reactive thiol group into DNA. This creates a unique site for the post-synthetic modification of that nucleotide with a variety of molecular tags, such as photo-cross-linkers and fluorescent or spin-label moieties. 5'-O-(4,4'-Dimethoxytrityl)-5-[S-(2,4-dinitrophenyl)thio]-2'-deoxyuridin e 3'-O-(2-cyanoethyl N,N'-diisopropylphosphoramidite) was synthesized and incorporated at internal positions in several oligonucleotides using automated DNA synthesis and standard phosphoramidite chemistry. The coupling yield of the analogue was comparable to the coupling yield for a standard phosphoramidite, and no significant differences were observed in the overall yields of the dinitrophenyl-labeled oligonucleotides compared to the corresponding unmodified oligonucleotides. Characterization of the dinitrophenyl-modified oligonucleotides included enzymatic degradation, HPLC chromatography, and gel electrophoresis. Deprotection of the mercaptan group with beta-mercaptoethanol yielded an oligonucleotide containing 5-mercaptodeoxyuridine which was then selectively modified, without purification, by reaction with 5-(iodoacetamido)fluorescein. Incorporation of the dinitrophenyl-modified oligonucleotide into double-stranded DNA was achieved using the polymerase chain reaction. CHaracterization of the dinitrophenyl-labeled product by immunodetection with anti-dinitrophenyl antibodies confirmed the stability of the protecting group to the thermocycling and thus established the use of this thiol-protected mercaptodeoxyuridine phosphoramidite for preparation of site-specifically modified DNA.

Phosphorolysis of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) and other 5-substituted-2'-deoxyuridines by purified human thymidine phosphorylase and intact blood platelets

Various 5-substituted-2'-deoxyuridines (dUrd), including 5-ethyl,5-propyl-, 5-trifluoromethyl-, 5-hydroxymethyl-, 5-formyl-, 5-vinyl-, (E)-5-(2-chlorovinyl)-, (E)-5-(2-bromovinyl)-, 5-fluoro-, 5-chloro-, 5-bromo-, 5-iodo-, 5-cyano-, 5-thiocyano-, 5-nitro- and 5-amino-dUrd, were shown to be effective substrates for the thymidine (dThd) phosphorylase isolated from human blood platelets. Some of dUrd analogs, i.e. the highly potent and selective antiherpes agent (E)-5-(2-bromovinyl)-dUrd, were degraded more rapidly than the natural substrates, dUrd and dThd. All dUrd analogs were also readily catabolised by intact human blood platelets. The potent inhibitors of thymidine phosphorylase, 6-amino-thymine and 6-amino-5-bromo-uracil, strongly inhibited the phosphorolysis of (E)-5-(2-bromovinyl)-dUrd by both purified enzyme and intact platelets.

Role of thymidine kinase in the inhibitory activity of 5-substituted-2'-deoxyuridines on the growth of human and murine tumor cell lines

Twenty-four 5-substituted 2'-deoxyuridines have been evaluated for their inhibitory effects on the growth of three human lymphoblast cell lines (Namalva, RAji and TK- (thymidine kinase deficient) Raji) and these inhibitory effects were compared to those for two murine leukemia cell lines (L1210/0 and L1210/BdUrd). The latter was selected from the parental L1210/0 cell line by its ability to grow at high concentrations of 5-bromo-dUrd and could also be considered as TK-. There was a close correlation between the inhibitory effects of the deoxyuridine analogs on Namalva, Raji and L1210 cells: the correlation coefficient (r) for log ID50 (median inhibitory dose) for L1210 cell growth, on the one hand, and log ID50 for Namalva or Raji cell growth, on the other hand, was 0.902 and 0.929, respectively. There was also a strong correlation (r = 0.936) between the log ID50 values for the two human lymphoblast cell lines. However, there was no significant correlation (r less than 0.40) either between the log ID50 for the TK- Raji cells and the parental TK+ Raji cells, or between the log ID50 for the TK- L1210/BdUrd cells and the parental TK+ L1210/0 cells. We may conclude therefore, that (i) the murine leukemia L1210 cell system is predictive for the growth-inhibitory effects of 5-substituted 2'-deoxyuridines on human lymphoblast cell lines, and (ii) the antitumor cell activity of the 5-substituted 2'-deoxyuridines is, to a large extent, dependent on the thymidine kinase activity of the tumor cells.