Xylotubercidin against herpes simplex virus type 2 in mice

In memory of an exquisite medicinal chemist, Prof. Morris Robins

Among the most prominent realizations of Morris J. Robins in the antiviral nucleoside chemistry are (i) the synthesis of 8-substituted (methyl-, amino-, bromo-, iodo) derivatives of acyclovir, (ii) xylotubercidin as an inhibitor of herpes simplex virus (HSV) infections, (iii) the anti-HIV activity of the 2',3'-dideoxyriboside of 2,6-diaminopurine (ddDAPR) and the 3'-azido- and 3'-fluoro derivatives thereof (AzddDAPR and FddDAPR, respectively), (iv) the potentiating effect of ribavirin on the anti-HIV activity of 2',3'-dideoxyinosine (ddI) and ddDAPR, (v) S-adenosylhomocysteine hydrolase (SAH) inhibitors principally active against vaccinia virus (VV) and vesicular stomatitis virus (VSV), and (vi) furo[2,3-d]pyrimidinone derivatives active against varicella-zoster virus (VZV).

A Novel Ebola Virus VP40 Matrix Protein-Based Screening for Identification of Novel Candidate Medical Countermeasures

Filoviruses, such as Ebola virus and Marburg virus, are of significant human health concern. From 2013 to 2016, Ebola virus caused 11,323 fatalities in Western Africa. Since 2018, two Ebola virus disease outbreaks in the Democratic Republic of the Congo resulted in 2354 fatalities. Although there is progress in medical countermeasure (MCM) development (in particular, vaccines and antibody-based therapeutics), the need for efficacious small-molecule therapeutics remains unmet. Here we describe a novel high-throughput screening assay to identify inhibitors of Ebola virus VP40 matrix protein association with viral particle assembly sites on the interior of the host cell plasma membrane. Using this assay, we screened nearly 3000 small molecules and identified several molecules with the desired inhibitory properties. In secondary assays, one identified compound, sangivamycin, inhibited not only Ebola viral infectivity but also that of other viruses. This finding indicates that it is possible for this new VP40-based screening method to identify highly potent MCMs against Ebola virus and its relatives.

Sangivamycin and its derivatives inhibit Haspin-Histone H3-survivin signaling and induce pancreatic cancer cell death

Current treatment options for patients with pancreatic cancer are suboptimal, resulting in a five year survival rate of about 9%. Difficulties with treatment are due to an immunosuppressive, fibrotic tumor microenvironment that prevents drugs from reaching tumor cells, but also to the limited efficacy of existing FDA-approved chemotherapeutic compounds. We here show that the nucleoside analog Sangivamycin and its closely-related compound Toyocamycin target PDA cell lines, and are significantly more efficient than Gemcitabine. Using KINOMEscan screening, we identified the kinase Haspin, which is overexpressed in PDA cell lines and human PDA samples, as a main target for both compounds. Inhibition of Haspin leads to a decrease in Histone H3 phosphorylation and prevents Histone H3 binding to survivin, thus providing mechanistic insight of how Sangivamycin targets cell proliferation, mitosis and induces apoptotic cell death. In orthotopically implanted tumors in mice, Sangivamycin was efficient in decreasing the growth of established tumors. In summary, we show that Sangivamycin and derivatives can be an efficient new option for treatment of PDA.

Pyrrolo[2,3-d]pyrimidine (7-deazapurine) as a privileged scaffold in design of antitumor and antiviral nucleosides

7-Deazapurine (pyrrolo[2,3-d]pyrimidine) nucleosides are important analogues of biogenic purine nucleosides with diverse biological activities. Replacement of the N7 atom with a carbon atom makes the five-membered ring more electron rich and brings a possibility of attaching additional substituents at the C7 position. This often leads to derivatives with increased base-pairing in DNA or RNA or better binding to enzymes. Several types of 7-deazapurine nucleosides with potent cytostatic or cytotoxic effects have been identified. The most promising are 7-hetaryl-7-deazaadenosines, which are activated in cancer cells by phosphorylation and get incorporated both to RNA (causing inhibition of proteosynthesis) and to DNA (causing DNA damage). Mechanism of action of other types of cytostatic nucleosides, 6-hetaryl-7-deazapurine and thieno-fused deazapurine ribonucleosides, is not yet known. Many 7-deazaadenosine derivatives are potent inhibitors of adenosine kinases. Many types of sugar-modified derivatives of 7-deazapurine nucleosides are also strong antivirals. Most important are 2'-C-methylribo- or 2'-C-methyl-2'-fluororibonucleosides with anti-HCV activities (several compounds underwent clinical trials). Some underexplored areas of potential interest are also outlined.

Synthesis of purine and 7-deazapurine nucleoside analogues of 6-N-(4-Nitrobenzyl)adenosine; inhibition of nucleoside transport and proliferation of cancer cells

Human equilibrative nucleoside transporter 1 (hENT1) is a prototypical nucleoside transporter protein ubiquitously expressed on the cell surface of almost all human tissue. Given the role of hENT1 in the transport of nucleoside drugs, an important class of therapeutics in the treatment of various cancers and viral infections, efforts have been made to better understand the mechanisms by which hENT1 modulates nucleoside transport. To that end, we report here the design and synthesis of novel tool compounds for the further study of hENT1. The 7-deazapurine nucleoside antibiotic tubercidin was converted into its 4-N-benzyl and 4-N-(4-nitrobenzyl) derivatives by alkylation at N3 followed by a Dimroth rearrangement to the 4-N-isomer or by fluoro-diazotization followed by SN Ar displacement of the 4-fluoro group by a benzylamine. The 4-N-(4-nitrobenzyl) derivatives of sangivamycin and toyocamycin antibiotics were prepared by the alkylation approach. Cross-membrane transport of labeled uridine by hENT1 was inhibited to a weaker extent by the 4-nitrobenzylated tubercidin and sangivamycin analogues than was observed with 6-N-(4-nitrobenzyl)adenosine. Type-specific inhibition of cancer cell proliferation was observed at micromolar concentrations with the 4-N-(4-nitrobenzyl) derivatives of sangivamycin and toyocamycin, and also with 4-N-benzyltubercidin. Treatment of 2',3',5'-O-acetyladenosine with aryl isocyanates gave the 6-ureido derivatives but none of them exhibited inhibitory activity against cancer cell proliferation or hENT1.

The unabated synthesis of new nucleoside analogues with antiviral potential: a tribute to Morris J. Robins

The furo[2,3-d]pyrimidin-2(3H)-one is the key structural determinant in the exquisitely potent activity of its derivatives (R = 2-deoxyribosyl; R' = p-pentylphenyl) against VZV (varicella-zoster virus) replication. [structure: see text].

Synthesis and biological activity of 5-fluorotubercidin

The electrophilic fluorination of 4-chloropyrrolo[2,3-d]pyrimidine (1) was studied culminating a 59% conversion of compound 1 to 4-chloro-5-fluoropyrrolo[2,3-d]pyrimidine (2) using Selectfluor. This transformation proceeded via the 4-chloro-5,6-dihydro-5-fluoro-6-hydroxypyrrolo[2,3-d]pyrimidine (3) in a 9:1 trans:cis ratio. The trans isomer of compound 3 was studied by 1H NMR and 19F NMR, and the 5-H tautomer (4) was observed as another intermediate. A modified Vorbruggen procedure of compound 2 and tetra-O-acetylribose gave 4-chloro-5-fluoro-7-(2,3,5,-tri-O-benzoyl-beta-D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine (6) in a 65% yield. Treatment of compound 6 with ammonia (l) in dioxane gave 5-fluorotubercidin (7). No antibacterial activity was observed. An MTT assay (Promega) against Huh-7 liver cells, normal mouse spleen cells stimulated with Con A (a T-cell mitogen), and normal mouse spleen stimulated with LPS (a B-cell mitogen) showed no significant toxicity. Increased activity of 7 over tubercidin was observed against L-1210 cells and toxicity in fibroblast cells was reduced.

Synthesis and antiproliferative and antiviral activity of carbohydrate-modified pyrrolo[2,3-d]pyridazin-7-one nucleosides

Sugar-modified analogs of 4-amino-1-(beta-D-ribofuranosyl)pyrrolo[2,3-d]pyridazin-7-one (1) and 4-amino-3-bromo-1-(beta-D-ribofuranosyl)pyrrolo[2,3-d]pyridazin-7- one (3) were prepared in an effort to obtain selective antiviral agents. Treatment of ethyl 3-cyano-1-(2,3,5-tri-O-benzyl-1-beta-D-arabinofuranosyl)pyrrole-2- carboxylate (6) with hydrazine afforded 4-amino-1-(2,3,5-tri-O-benzyl-1-beta-D- arabinofuranosyl)pyrrolo[2,3-d]pyridazin-7-one (7). Treatment of 7 with bromine afforded 4-amino-3-bromo-1-(2,3,5-tri-O-benzyl-beta-D-arabinofuranosyl) pyrrolo[2,3-d]pyridazin-7-one hydrobromide (9). The benzyl ether functions of 7 and 9 were removed with boron trichloride to afford 4-amino-1-(beta-D-arabinofuranosyl)pyrrolo[2,3-d]pyridazin-7-one (8) and its 3-bromo analog 10. 4-Amino-1-(2-deoxy-beta-D-erythro-pentofuranosyl)pyrrolo[2,3-d]pyrida zin-7- one (13) was prepared by the sodium salt condensation of ethyl 3-cyanopyrrole-2-carboxylate (5) with 2-deoxy-3,5-di-O-p-toluoyl-alpha-D-erythro-pentofuranosyl chloride (11) followed by ring annulation with hydrazine. Deprotection of ethyl 3-cyano-1-(2-deoxy-3,5-di-O-p-toluoyl-beta-D-erythro-pentofuranosyl)pyrr ole- 2-carboxylate (12) using sodium ethoxide furnished ethyl 1-(2-deoxy-beta-D-erythro-pentofuranosyl)-3-cyanopyrrole-2-carboxy late (14) which served as the starting material for the preparation of 4-amino-1-(2,3-dideoxy-beta-D-glycero-pentofuranosyl)pyrrolo[2,3-d] pyridazin-7-one (20). Selective protection of the 5'-hydroxyl group of 14 with tert-butyldimethylsilyl chloride followed by a Barton type deoxygenation sequence of the 3'-hydroxyl groups afforded ethyl 3-cyano-1-[2,3-dideoxy-5-O-tert-butyldimethylsilyl)-beta-D-glycero- pentofuranosyl]pyrrole-2-carboxylate (18). Deprotection of 18 with tetra-n-butylammonium fluoride and ring annulation with hydrazine afforded 20. The acyclic analog 4-amino-1-[(1,3-dihydroxy-2-propoxy)methyl]pyrrolo[2,3-d]pyridazin -7-one (24) was prepared via the sodium salt glycosylation of 5 with (1,3-dihydroxy-2-propoxy)methyl bromide (22) followed by a ring annulation with hydrazine. N-Bromosuccinimide treatment of 13, 20, and 25 afforded the 3-bromo derivatives 15, 21, and 25. Evaluation of these compounds in L1210, HFF, and KB cells showed that the sugar-modified analogs all were less cytotoxic than their corresponding ribonucleoside analogs. The compounds also were less active against human cytomegalovirus (HCMV) and herpes simplex virus type 1 (HSV-1). The 3-bromo derivatives were much more active than the 3-unsubstituted analogs in both the cytotoxicity, and antiviral assays. However, there was only modest separation between activity against HCMV and cytotoxicity and there was virtually no selectivity for activity against HSV-1.

Broad-spectrum antiviral activities of neplanocin A, 3-deazaneplanocin A, and their 5'-nor derivatives

The neplanocin A analogs, 3-deazaneplanocin A, 9-(trans-2',trans-3'-dihydroxycyclopent-4'-enyl)adenine (DHCA), and 9-(trans-2',trans-3'-dihydroxycyclopent-4'-enyl)-3-deazaadenine (DHCDA), all potent inhibitors of S-adenosylhomocysteine (AdoHcy) hydrolase, were studied for their broad-spectrum antiviral potential. 3-Deazaneplanocin A, DHCA, and DHCDA proved specifically effective against vesicular stomatitis virus, vaccinia virus, parainfluenza virus, reovirus, and rotavirus. Their selectivity was greater than that of neplanocin A, particularly against vesicular stomatitis virus and rotavirus. As could be expected from adenosine analogs that are directly targeted at AdoHcy hydrolase, 3-deazaneplanocin A, DHCA, and DHCDA were fully active in adenosine kinase-deficient cells, implying that their activity did not depend on phosphorylation by adenosine kinase. None of the AdoHcy hydrolase inhibitors showed selective activity against human immunodeficiency virus (type 1). 3-Deazaneplanocin A at a dose of 0.5 mg/kg per day conferred marked protection against a lethal infection of newborn mice with vesicular stomatitis virus.

Antiviral activities of 2'-deoxyribofuranosyl and arabinofuranosyl analogs of sangivamycin against retro- and DNA viruses

Eight sugar-modified pyrrolopyrimidine nucleoside analogs related to the antibiotic sangivamycin were evaluated in cell culture against herpes simplex types 1 (HSV-1) and 2 (HSV-2), cytomegalovirus (CMV), adenovirus, and visna virus. Five of the compounds were highly active against most of the viruses with 50% inhibition (ED50) values of 1-10 microM. The selectivity of the agents was low, with inhibition of uninfected cell proliferation occurring within 5-fold that of the virus ED50 for most of the viruses. The compounds did not possess RNA virus-inhibitory activity when evaluated against certain myxo-, paramyxo-, picorna-, reo-, rhabdo-, and togaviruses. Two of the nucleosides were tested further in a cell line persistently infected with Friend leukemia virus where they were inhibitory to both virus yield and cell proliferation at 4-5 microM. Several of the sangivamycin analogs were tested in animal models using a twice-a-day treatment regimen. They proved to be inactive against HSV-1, murine CMV and/or Friend leukemia virus infections in mice.

Inhibition of herpes simplex virus DNA replication by ara-tubercidin

Preliminary studies of the biochemical basis for the antiviral activity of the pyrrolo[2,3-d]pyrimidine nucleoside ara-tubercidin were conducted. Herpes simplex virus DNA synthesis was 3-fold more sensitive to inhibition by ara-tubercidin than was cellular DNA synthesis. Partially purified herpes DNA polymerases were more sensitive to inhibition by ara-tubercidin 5'-triphosphate than were cellular polymerases alpha and beta. Inhibition of viral DNA polymerase was competitive with dATP and noncompetitive with dTTP. The results suggest that the viral DNA polymerase plays a significant role in the antiviral activity of ara-tubercidin.