Antiherpesvirus Agent Research Articles

4′-Thio-5-Ethyl-2′-Deoxyuridine5′-Triphosphate (TEDUTP): Synthesis and Substrate Properties in DNA-Synthesizing Systems

An efficient synthesis of the 5′-phosphate and 5′-triphosphate of a 4′-thio-2′-deoxynucleoside is described for the first time. The 5′-triphosphate of the antiherpesvirus agent 4′-thio-5-ethyl-2′-deoxyuridine (TEDU) has been shown to be a good substrate for human placental DNA polymerase α, calf thymus terminal deoxynucleotidyl transferase, and the reverse transcriptases of human immunodeficiency virus and avian myeloblastosis virus. As it is known that TEDU is a substrate only for herpesvirus-encoded thymidine kinases and not the cellular kinases, it is likely that the utilization of TEDUTP by DNA-synthesizing enzymes results in the selective toxicity seen in vitro in herpesvirus-infected cells.

Antiviral Activities and Pharmacokinetics of Penciclovir and Famciclovir in Pekin Ducks Chronically Infected with Duck Hepatitis B Virus

Famciclovir (FCV) is the oral form of the potent and selective antiherpesvirus agent penciclovir (PCV). In order to provide more information on the spectrum of activity of PCV, the activities of FCV and PCV against duck hepatitis B virus (DHBV) in chronically infected ducks were examined. As part of this investigation, the oral pharmacokinetics of FCV and PCV were determined in ducks. Oral treatment of DHBV-infected ducks (twice daily for 21 days) with either PCV (20 mg kg−1 or 100 mg kg−1) or FCV (5 mg kg−1 or 25 mg kg−1) suppressed virus replication, as measured by both plasma viral DNA and DNA polymerase levels. Both markers were reduced to undetectable levels within 4 days of the start of treatment, and after the cessation of treatment there was a delay of 2 to 8 days before plasma DHBV DNA and DNA polymerase levels began to increase, indicating that virus replication had resumed. The demonstration of efficacy of PCV and its oral form FCV against DHBV suggested that the two compounds may have clinical benefits. against human hepatitis B virus. Clinical trials are currently ongoing.

A Direct Approach to the Synthesis of Famciclovir and Penciclovir

Abstract Reaction of 2-amino-6-chloropurine with triethyl 3-bromopropane-1,1,1-tricarboxylate followed by decarbethoxylation/transesterification of the unpurified product was the key sequence in synthesising both the anti-herpesvirus agent penciclovir and its oral from famciclovir in three isolated steps.

Acyl carbamate directing groups in nucleoside synthesis: Applications in the synthesis of 2′-deoxy-5-ethyl-4′-thiouridine

The use of the 3- O-( N-acyl)carbamoyl directing groups in the synthesis of the potent anti-Herpes virus agent 2′-deoxy-5-ethyl-4′-thio-D-uridine is described. This includes details of experiments to optimise the carbamate substitution and a multi-gram exemplification of the key steps.

Mode of action of (R)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine against herpesviruses.

The activity, metabolism, and mode of action of (R)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine (H2G) against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) and varicella-zoster virus (VZV) were studied. Compared to acyclovir (ACV), H2G has superior activity against VZV (50% inhibitory concentration of 2.3 microM) and Epstein-Barr virus (50% inhibitory concentration of 0.9 microM), comparable activity against HSV-1, and weaker activity against HSV-2. The antiviral effect on HSV-1 showed persistence after removal of compound. H2G was metabolized to its mono-, di- and triphosphate derivatives in virus-infected cells, with H2G-triphosphate being the predominant product. Only small amounts of H2G-triphosphate were detected in uninfected cells (1 to 10 pmol/10(6) cells), whereas the level in HSV-1-infected cells reached 1,900 pmol/10(6) cells. H2G was a substrate for all three viral thymidine kinases and could also be phosphorylated by mitochondrial deoxyguanosine kinase. The intracellular half-life of H2G-triphosphate varied in uninfected (2.5 h) and infected (HSV-1, 14 h; VZV, 3.7 h) cells but was always longer than the half-life of ACV-triphosphate (1 to 2 h). H2G-triphosphate inhibited HSV-1, HSV-2, and VZV DNA polymerases competitively with dGTP (Ki of 2.8, 2.2, and 0.3 microM, respectively) but could not replace dGTP as a substrate in a polymerase assay. H2G was not an obligate chain terminator but would only support limited DNA chain extension. Only very small amounts of radioactivity, which were too low to be identified by high-performance liquid chromatography analysis of the digested DNA, could be detected in purified DNA from uninfected cells incubated with [3H]H2G. Thus, H2G acts as an anti-herpesvirus agent, particularly potent against VZV, by formation of high concentrations of relatively stable H2G-triphosphate, which is a potent inhibitor of the viral DNA polymerases.

Intracellular metabolism of the novel anti-herpesvirus agent 2-amino-7-[1,3-dihydroxy-2-propoxy)methyl]purine compound S2242 in non-infected and herpesvirus-infected cells

Intracellular metabolism of the novel anti-herpesvirus agent 2-amino-7-[1,3-dihydroxy-2-propoxy)methyl]purine compound S2242 in non-infected and herpesvirus-infected cells

Safety of famciclovir in patients with herpes zoster and genital herpes

Safety reporting from individual ongoing and completed clinical studies has demonstrated that famciclovir, the well-absorbed oral form of the antiherpesvirus agent penciclovir, has been well tolerated by more than 3,000 individuals worldwide. An integrated safety evaluation has been performed and includes over 1,600 patients from 11 completed, randomized, double-blind clinical trials and 2 open trials. The famciclovir population consisted of 816 herpes zoster patients (four trials), 409 patients with acute genital herpesvirus infections (seven trials), and 382 patients from two genital herpes suppression studies. Overall, the famciclovir-treated patient population was 57.7% female and ranged in age from 15 to 102 years (mean, 42.6 years), with 31.2% aged 50 years or more and 15.7% aged 65 years or more. The mean duration of exposure to famciclovir was 28.8 days (5.8 days excluding suppression studies). The total daily doses ranged from 125 mg to 2.25 g. The most common adverse experiences reported as related to study medication (famciclovir and placebo) were headache, nausea, and diarrhea. The frequencies of adverse experiences and laboratory abnormalities (hematology, clinical chemistry, and urinalysis parameters) were similar in both famciclovir and placebo recipients. Thus, safety data from the analysis of 13 completed clinical studies demonstrate that famciclovir is tolerated well by patients with either herpes zoster or genital and has a safety profile comparable to that of placebo.

Synthesis, Oral Bioavailability and in vivo Activity of Acetal Derivatives of the Selective Antiherpesvirus Agent 9-(3-hydroxypropoxy) Guanine (BRL 44385)

Acyclic acetal derivatives of the selective antiherpesvirus agent 9-(3-hydroxypropoxy) guanine (BRL44385) and of its 2-aminopurine congener (BRL46720) have been prepared and evaluated in mice for oral delivery of BRL 44385. Guanine derivatives (6 a-c) were prepared via Mitsunobu condensation of an alcohol with a 9-hydroxy-6-methoxypurine (Harnden and Wyatt, 1990). Synthesis of derivatives of 2-aminopurine (10 a-d) was achieved by hydrogenolysis of 9-alkoxy-6-chloropurines, which were obtained either by reaction of an alkoxyamine with 4,6-dichloro-2,5-diformamidopyrimidine and subsequent ring closure or by Mitsunobu condensation of an alcohol with a 6-chloro-9-hydroxypurine. Following oral administration, 2-amino-9-[3-(iso-propoxymethyl)propoxy]-purine (10b, BRL 55792) was very well absorbed and provided high and prolonged concentrations of BRL44385 in the blood. In a cutaneous HSV-1 infection in the ear pinna of mice, orally dosed BRL 55792 was at least 3-fold more potent than both BRL44385 and Acyclovir in reduction of lesion severity.

Nucleosides and nucleotides. 128. (2′ S)-2′-deoxy-2′- C-methyl-5-iodouridine (SMIU) as a novel potent anti-herpes virus agent

(2′ S)-2′-deoxy-2′- C-methyl-5-halogenopyrimidine nucleosides were designed and synthesized as anti-herpes virus agents. Of these compounds, (2′ S)-2′-deoxy-2′- C-methyl-5-iodouridine (SMIU, 9e) showed the greatest anti-HSV-1 activity in vitro while showing no cytotoxicity. SMIU is a candidate drug for clinical treatment of herpes virus infection disease.

Penciclovir: a review of its spectrum of activity, selectivity, and cross-resistance pattern

The antiherpesvirus agent penciclovir has been evaluated extensively in cell culture. The spectrum of activity of penciclovir against human herpesviruses is similar to that of acyclovir, both compo...

Activity of Famciclovir and Penciclovir in HSV-Infected Animals: A Review

Penciclovir is a potent and highly selective antiherpesvirus agent. Both penciclovir and its oral form, famciclovir, are being evaluated in clinical studies. The activity of penciclovir and famciclovir against herpes simplex virus types 1 and 2 (HSV-1, HSV-2) infections in animals is reviewed. Penciclovir showed potent activity in a variety of cutaneous, genital and systemic HSV infections in mice and guinea-pigs when given either topically or by systemic administration by the subcutaneous, intravenous or oral routes. Comparisons of treatment with famciclovir and penciclovir demonstrated that the improved bioavailability of penciclovir following oral administration of famciclovir resulted in improved efficacy. In addition, there is good evidence to suggest that virus replication within the central nervous system is reduced following treatment with either penciclovir or famciclovir. The relative antiviral potencies in mouse cells and pharmacokinetic properties in mice suggested that acyclovir would be more...

Famciclovir and Penciclovir. The Mode of Action of Famciclovir Including Its Conversion to Penciclovir

Famciclovir is the oral form of penciclovir, a highly selective antiherpesvirus agent. Both famciclovir and penciclovir are being evaluated in clinical studies. This review covers the conversion of famciclovir to penciclovir, the formation and stability of penciclovir-triphosphate, its effect on herpesvirus DNA polymerases and the inhibition of viral DNA synthesis in cell cultures.The conversion of famciclovir into penciclovir is described, emphasising work with human tissues and including the elucidation of the structures of its chiral monoacetylated derivatives. To reflect its metabolism during oral absorption, famciclovir was incubated in duodenal contents, extracts of intestinal wall and liver, and in blood. The major metabolic route was by de-acetylation followed by oxidation of the purine to form penciclovir. This work with human tissues was predictive of the major metabolic pathway in humans.Penciclovir is phosphorylated much more efficiently than acyclovir in herpesvirus-infected cells yet the host cell kinases phosphorylate the two compounds to a small but comparable extent. This highly preferential metabolism in herpesvirus infected cells is a major factor in its selective antiviral activity. The ( S) enantiomer of penciclovir-triphosphate is the major metabolite and it has good stability in HSV-1, HSV-2, and VZV infected cells. At the high concentrations found in infected cells, penciclovir-triphosphate was an effective inhibitor of viral DNA polymerases and of viral DNA synthesis. The efficient entrapment of the active moiety can account for the markedly better antiviral activity of penciclovir than acyclovir when infected cell cultures were treated for a short time. Such assays reflect more closely the clinical situation after oral dosing than do standard assays in which the test compounds are present continuously. The role of these studies in compound selection and development is discussed.

Use of isotopically chiral [4'-13C]penciclovir and 13C NMR to determine the specificity and absolute configuration of penciclovir phosphate esters formed in HSV-1 and HSV-2 infected cells and by HSV-1-encoded thymidine kinase.

Penciclovir is a potent antiherpesvirus agent which is highly selective due to its phosphorylation only in virus infected cells. Phosphorylation of one of the hydroxymethyl groups of penciclovir (PCV) creates a chiral centre leading to the possible formation of (R)- and (S)-enantiomers. The absolute configuration and stereospecificity of the PCV-phosphates produced in cells infected with herpes simplex viruses types 1 and 2 (HSV-1 and HSV-2), as well as by HSV-1-encoded thymidine kinase, were determined using isotopically chiral [4'-13C]PCV precursors and 13C NMR spectroscopy of the isolated metabolites. The absolute configuration of penciclovir-triphosphate (PCV-TP) produced in HSV-1 infected cells was shown to be S with an enantiomeric purity of greater than 95%. However, in contrast fo HSV-1-infected cells in which none of the (R) enantiomer was detected, about 10% of (R)-PCV-TP was produced in HSV-2-infected cells. Phosphorylation of PCV by HSV-1-encoded thymidine kinase was found to give 75% (S)- and 25% (R)-PCV-monophosphate. The proportion of the (S)-isomer appears to be amplified in the subsequent phosphorylations leading to the triphosphate.

Use of isotopically chiral [4′‐13C]famciclovir and 13C NMR to identify the chiral monoacetylated intermediates in the conversion of famciclovir to penciclovir by human intestinal wall extract

Famciclovir is the oral form of the potent antiherpesvirus agent, penciclovir. Hydrolysis of one of the acetyl ester groups of famciclovir creates a chiral centre leading to the possible formation of (R)- and (S)-enantiomers. During its conversion to penciclovir, famciclovir forms two chiral metabolites, namely monoacetyl-6-deoxy-penciclovir and monoacetyl-penciclovir. The absolute configuration and stereospecificity of the monoacetyl metabolites of famciclovir, produced in human intestinal wall extract, were determined using isotopically chiral famciclovir and 13C NMR spectroscopy of the isolated metabolites. 13C NMR showed that the esterase(s), in human intestinal wall extract, hydrolysed the acetyl group preferentially from the pro-(S)-acetoxymethyl group of famciclovir. The specificity of esterase action in forming monoacetyl-6-deoxy-penciclovir and monoacetyl-penciclovir was about 77 and 72%, respectively.

Regiospecific Michael additions with 2-aminopurines

N-9 alkylated materials are the sole products obtained from extended reaction of 2-aminopurines (potential guanine precursors) with Michael acceptors. This was used as the basis for a highly regioselective synthesis of famciclovir, the oral form of the anti-herpesvirus agent penciclovir.

Selection of an oral prodrug (BRL 42810; famciclovir) for the antiherpesvirus agent BRL 39123 [9-(4-hydroxy-3-hydroxymethylbut-l-yl)guanine; penciclovir

The limited oral absorption in rodents of the antiherpesvirus agent 9-(4-hydroxy-3-hydroxymethylbut-l-yl)guanine (BRL 39123 [penciclovir; British approved name]) prompted a search for oral prodrugs. The 6-deoxy derivative of penciclovir (BRL 42359) and the corresponding diacetyl and dipropionyl 6-deoxy derivatives (BRL 42810 [famciclovir; British approved name] and BRL 43599) were tested as oral prodrugs. The in vivo absorption (dose, 0.2 mmol/kg) and the conversion to the active compound, penciclovir, were determined in rats. Compared with the sodium salt of penciclovir given intravenously, the bioavailabilities of penciclovir from orally administered penciclovir, BRL 42359, famciclovir, and BRL 43599 were 1.5, 9, 41, and 27%, respectively. These prodrugs and 6-deoxyacyclovir were tested for stability in rat duodenal contents and for metabolism in rat intestinal wall homogenate, liver homogenate, and blood and in the corresponding human fluids and tissues. Famciclovir was much more stable than BRL 43599 in human duodenal contents (half-lives, greater than 2 h and 7 min, respectively) yet was efficiently converted to penciclovir by the tissue homogenates. The major metabolic pathway was by deacetylation followed by oxidation at the 6 position. The rate of oxidation was comparable to that of 6-deoxyacyclovir, which is known to be converted efficiently to acyclovir in humans. Famciclovir was selected for further evaluation and progression to studies in humans. These subsequent studies confirmed that, after oral dosing with famciclovir, more than half the dose was absorbed and rapidly converted to penciclovir.

Prodrugs of the selective antiherpesvirus agent 9-[4-hydroxy-3-(hydroxymethyl)but-1-yl]guanine (BRL 39123) with improved gastrointestinal absorption properties.

Potential oral prodrugs of the antiherpesvirus acyclonucleoside 9-[4-hydroxy-3-(hydroxymethyl)but-1-yl]guanine (1, BRL 39123) have been synthesized and evaluated for bioavailability of 1 in the blood of mice. Reduction of 9-[4-acetoxy-3-(acetoxymethyl)but-1-yl]-2-amino-6-chloropurine (13) using ammonium formate and 10% palladium on carbon afforded the 2-aminopurine 14, which was hydrolyzed to the monoacetate 15 and to 2-amino-9-[4-hydroxy-3-(hydroxymethyl)but-1-yl]purine (5). The 2-aminopurine 5 was subsequently converted to additional monoester (17, 21-23) and diester (16, 24) derivatives and to its di-O-isopropylidene derivative 18. Both 5 and its esters (14-17, 21, 22) and also 18 were well absorbed after oral administration and converted efficiently to 1, the diacetyl (14) and dipropionyl (16) esters providing concentrations of 1 in the blood that were more than 15-fold higher than those observed after dosing either 1 or its esters (25-27). Some 6-alkoxy-9-[4-hydroxy-3-(hydroxymethyl)but-1-yl]purines (8-10), the preparation of which has been reported previously, also showed improved absorption properties, but their conversion to 1 was less efficient than for the 2-aminopurine derivatives. On the basis of these results and subsequent experiments involving determinations of rates of conversion to 1 in the presence of rat and human tissue preparations, 9-[4-acetoxy-3-(acetoxymethyl)but-1-yl]-2-aminopurine (14, BRL 42810) was identified as the preferred prodrug of 1. Oral bioavailability studies in healthy human subjects confirmed 14 as an effective prodrug, and this compound is now being evaluated in clinical trials.

Some biological properties of BRL 42810, a well absorbed oral prodrug of the antiherpesvirus agent BRL 39123 : M.R. Boyd, R. Boon, S.E. Fowles, K. Pagano, D. Sutton, R.A. Vere Hodge and B.D. Zussman. Beecham Pharmaceuticals, Research Division, Great Burgh, Epsom, Surrey, United Kingdom

Some biological properties of BRL 42810, a well absorbed oral prodrug of the antiherpesvirus agent BRL 39123 : M.R. Boyd, R. Boon, S.E. Fowles, K. Pagano, D. Sutton, R.A. Vere Hodge and B.D. Zussman. Beecham Pharmaceuticals, Research Division, Great Burgh, Epsom, Surrey, United Kingdom

Selection of an oral prodrug (BRL 42810) for the anti-herpesvirus agent BRL 39123 : R.A. Vere Hodge, D. Sutton, M.R. Boyd and M. Cole. Beecham Pharmaceuticals Research Division, Great Burgh, Epsom, Surrey, United Kingdom

Selection of an oral prodrug (BRL 42810) for the anti-herpesvirus agent BRL 39123 : R.A. Vere Hodge, D. Sutton, M.R. Boyd and M. Cole. Beecham Pharmaceuticals Research Division, Great Burgh, Epsom, Surrey, United Kingdom

Inhibitory activity of (E)-5-(2-bromovinyl)-2'-deoxyuridine on the salmonid herpesviruses, Oncorhynchus masou virus (OMV) and Herpesvirus salmonis.

The highly potent and selective anti-herpesvirus agent, (E)-5-(2-bromovinyl)-2'deoxyuridine (BVdU), was examined for its inhibitory effect on the salmonid herpesviruses Oncorhynchus masou virus (OMV) and Herpesvirus salmonis (H. salmonis). Minimum inhibitory concentrations (MIC) of BVdU for OMV and H. salmonis were 1.25 and 3.0 micrograms/ml, respectively; these values were equal to or higher than those obtained for acyclovir or cytarabine. OMV DNA polymerase activity was reduced in a dose-dependent fashion by BVdU 5'-triphosphate (BVdUTP) within the concentration range of 3 to 30 microM. However, BVdUTP could also be substituted for the natural substrate, TTP, in the OMV DNA polymerase assay. It is postulated that the inhibitory action of BVdU on the salmonid herpesviruses is more or less similar to that on other herpesviruses and resides with respect to the inhibition of the virus DNA polymerase activity as well as incorporation of BVdU into the viral DNA.