The Discovery and Development of a Potent Antiviral Drug, Entecavir, for the Treatment of Chronic Hepatitis B

Regio- and Stereoselective Synthesis of C-4' Spirocyclobutyl Ribofuranose Scaffolds and Their Use as Biologically Active Nucleoside Analogues

Novel C-4',C-5' cyclobutane-fused spirocyclic ribonucleoside analogues were prepared. Thermal [2 + 2] cycloaddition between dichloroketene and readily derived 4'-exo-methylene furanoses afforded a first entry to the required constrained ribofuranoses, relying on a carbonyl transposition sequence. Alternatively, an unusual stereoselective ionic [2 + 2] cycloaddition using methyl propiolate promoted by methylaluminoxane gave a complementary, more direct approach to such ribofuranoses. Further conversion to the constrained adenosine analogues revealed promising structure-dependent inhibition of the protein methyltransferase PRMT5:MEP50 complex in the (sub)micromolar range.

Synthesis and Reactivity of Spirocarbocycles as Scaffolds for Nucleoside Analogues

A novel class of substituted spiro[3.4]octanes can be accessed via a [2 + 2]-cycloaddition of dichloroketene on a readily prepared exo-methylene cyclopentane building block. This reaction sequence was found to be robust on a multigram scale and afforded a central spirocyclobutanone scaffold for carbocyclic nucleosides. The reactivity of this constrained building block was evaluated and compared to the corresponding 4'-spirocyclic furanose analogues. Density functional theory calculations were performed to support the observed selectivity in the carbonyl reduction of spirocyclobutanone building blocks. Starting from novel spirocyclic intermediates, we exemplified the preparation of an undescribed class of carbocyclic nucleoside analogues and provided a proof of concept for application as inhibitors for the protein methyltransferase target PRMT5.

Hepatitis B vaccination and immunotherapies: an update

World Health Organization (WHO) estimates that 257 million people were living with chronic hepatitis B virus (HBV) infection. Highest HBV prevalence was found in the WHO Western Pacific Region (6.2%) and in the WHO African Region (6.1%). The HBV vaccine is the best protection against chronic HBV infection and its complications. Globally, routine infant immunization against HBV has increased with an estimated coverage of 84% in 2017. Nevertheless, in many countries further efforts are needed to implement this coverage and ensure national immunization programs for people at major risk for HBV infection. Therapeutic vaccination in chronic HBV infected patients can cause anti-HBV immune responses able to remove and/or cure infected hepatocytes. It shows promising results in murine model and human trials, but these results need to be consolidated by further multicenter clinical studies. In particular, the efficacy of therapeutic vaccine seems to improve by combination therapies.

The evolution of nucleoside analogue antivirals: A review for chemists and non-chemists. Part 1: Early structural modifications to the nucleoside scaffold

This is the first of two invited articles reviewing the development of nucleoside-analogue antiviral drugs, written for a target audience of virologists and other non-chemists, as well as chemists who may not be familiar with the field. Rather than providing a simple chronological account, we have examined and attempted to explain the thought processes, advances in synthetic chemistry and lessons learned from antiviral testing that led to a few molecules being moved forward to eventual approval for human therapies, while others were discarded. The present paper focuses on early, relatively simplistic changes made to the nucleoside scaffold, beginning with modifications of the nucleoside sugars of Ara-C and other arabinose-derived nucleoside analogues in the 1960's. A future paper will review more recent developments, focusing especially on more complex modifications, particularly those involving multiple changes to the nucleoside scaffold. We hope that these articles will help virologists and others outside the field of medicinal chemistry to understand why certain drugs were successfully developed, while the majority of candidate compounds encountered barriers due to low-yielding synthetic routes, toxicity or other problems that led to their abandonment.

A different inhibitor is required for overcoming entecavir resistance: a comparison of four rescue therapies in a retrospective study

AIMS

Little clinical data are available regarding re-establishing the effective inhibition of entecavir (ETV)-resistant mutants. In this retrospective study, we aimed to compare the efficacies of four treatment regimens as rescue therapy for those chronic hepatitis B (CHB) patients with ETV resistance.

METHODS

A total of 65 patients with ETV resistance were assigned either with tenofovir disoproxil fumarate (TDF) monotherapy (n = 21), ETV (0.5 mg) plus adefovir (ADV) combination therapy (n = 19), ETV (1.0 mg) monotherapy (n = 11) or ETV (0.5 mg) plus TDF combination therapy (n = 14). The efficacy and safety of four treatment regimens were compared.

RESULTS

There were no significant differences among the four study groups in baseline characteristics, including HBV DNA levels (χ²  = 0.749, P = 0.862) and hepatitis B e antigen-positivity (χ²  = 0.099, P = 0.992). The median reduction in serum HBV DNA level from baseline at week 48 was -2.37 ± 1.07 log₁₀ IU ml^-1 , -2.16 ± 0.81 log₁₀ IU ml^-1 , -1.17 ± 1.23 log₁₀ IU ml^-1 and -2.49 ± 1.10 log₁₀ IU ml^-1 , respectively (F = 4.078, P = 0.011). The TDF group and ETV (0.5 mg) + TDF group have the highest undetectable HBV DNA rate (76.19% vs. 78.57%) compared to the ETV (0.5 mg) + ADV group and the ETV (1.0 mg) group (63.16% vs. 18.18%, respectively). Two patients in the ETV (1.0 mg) group experienced virological breakthrough at week 48 and was attributed to poor drug adherence.

CONCLUSIONS

TDF monotherapy appeared to deliver the highest undetectable HBV DNA rate in patients with ETV resistance, and ADV plus ETV combination therapy could be another choice for patients with financial restraint.