Acyclovir Analogues Research Articles

Valacyclovir and Acyclovir Are Substrates of the Guanine Deaminase Cytosolic PSD-95 Interactor (Cypin).

Valacyclovir, enzymatically hydrolyzed in the body to acyclovir, is a guanine-based nucleoside analog commonly prescribed as an antiviral therapy. Previous reports suggest that guanosine analogs bind to guanine deaminase; however, it is unclear whether they act as inhibitors or substrates. Data from our laboratory suggest that inhibition of guanine deaminase by small molecules attenuates spinal cord injury-induced neuropathic pain. Here, we examine whether the guanosine analogs valacyclovir and acyclovir are deaminated by cypin (cytosolic PSD-95 interactor), the major guanine deaminase in the body, or if they act as cypin inhibitors. Using purified Rattus norvegicus cypin, we use NADH-coupled assay to confirm deamination of valacyclovir and determined Michaelis-Menten constants. Subsequently, we use tryptophan fluorescence quenching assay to calculate dissociation constants for valacyclovir and acyclovir and find that inclusion of the valine motif in valacyclovir increases affinity for cypin compared to acyclovir. To our knowledge, neither Km nor KD values for cypin has been previously reported for either compound. We use Amplex Red assay and demonstrate that both valacyclovir and acyclovir are cypin substrates and that their metabolites are further processed by xanthine oxidase and uricase. Using molecular dynamics simulations, we demonstrate that an alpha helix near the active site is displaced when valacyclovir binds to cypin. Furthermore, we used LC-MS-based assay to directly confirm deamination of valacyclovir by cypin. Taken together, our results demonstrate a novel role for cypin in deamination of valacyclovir and acyclovir and suggest that therapeutics based on purine structures may be inactivated by cypin, decreasing inhibitory efficacy.

Combined Effect of Basic Antiherpetic Drugs with a New Inhibitor of the Terminase Complex of Herpes Simplex Virus Type 1 in Vero Cell Cultures.

Carriers of herpes simplex virus type 1 (HSV-1) account for more than 90% of the global population. Infection manifests itself in the formation of blisters and ulcers on the face or genitals and can cause blindness, encephalitis, and generalized infection. All first- and second-line modern antiherpetic drugs selectively inhibit viral DNA polymerase. The purine-benzoxazine conjugate LAS-131 ((S)-4-[6-(purin-6-yl)aminohexanoyl]-7,8-difluoro-3,4-dihydro-3-methyl-2H-[1,4]benzoxazine), which we have described earlier, uses the large subunit of the HSV-1 terminase complex as a biotarget and selectively inhibits HSV-1 reproduction in vitro. Basically new results were for the first time obtained to characterize the combined effect on human herpesvirus infection for LAS-131 used in combination with practically significant antiviral compounds, including the nucleoside analogs acyclovir (ACV), penciclovir (PCV), ganciclovir (GCV), brivudine (BVdU), iododeoxyuridine (IdU), and adenine arabinoside (Ara-A); the nucleoside phosphonate analog cidofovir (CDV); and the pyrophosphate analog foscarnet (FOS). A cytopathic effect (CPE) inhibition assay showed that the drug concentration that inhibited the virus-induced CPE by 50% decreased by a factor of 2 (an additive effect, FOS) or more (a synergistic effect; ACV, PCV, GCV, IdU, BVdU, Ara-A, and CDV) when the drugs were used in combination with LAS-131. Nonpermissive conditions for HSV-1 reproduction were thus created at lower drug concentrations, opening up new real possibilities to control human herpesvirus infection.

Acid-Promoted Cyclization Reaction of the Guanine Base with 1,1,3,3-Tetramethoxypropane: A Method for the Preparation of M1 dG and its Derivatives.

Despite the importance of nucleosides and nucleotides for drug discovery, only a few practical methods to prepare tricyclic nucleosides have been reported. Here, we describe a synthetic strategy for late-stage functionalization of nucleosides and nucleotides via chemo- and site-selective acid-promoted intermolecular cyclization. The nucleoside analogs with an additional ring were obtained in moderate-to-high yields, including some antiviral drugs (acyclovir, ganciclovir, and penciclovir) derivatives, endogenous fused ring nucleoside (M1 dG) and its derivatives, and nucleotide derivatives. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Synthesis of tricyclic acyclovir analogs (3a-3c) Basic Protocol 2: Synthesis of tricyclic nucleosides M1 dG (6) and M1 G (9) Basic Protocol 3: Synthesis of tricyclic nucleotide (12).

Discovery, Chemistry, and Preclinical Development of Pritelivir, a Novel Treatment Option for Acyclovir-Resistant Herpes Simplex Virus Infections.

When the nucleoside analogue acyclovir was introduced in the early 1980s, it presented a game-changing treatment modality for herpes simplex virus infections. Since then, work has been ongoing to improve the weaknesses that have now been identified: a narrow time window for therapeutic success, resistance in immunocompromised patients, little influence on frequency of recurrences, relatively fast elimination, and poor bioavailability. The present Drug Annotation focuses on the helicase-primase inhibitor pritelivir currently in development for the treatment of acyclovir-resistant HSV infections and describes how a change of the molecular target (from viral DNA polymerase to the HSV helicase-primase complex) afforded improvement of the shortcomings of nucleoside analogs. Details are presented for the discovery process leading to the final drug candidate, the pivotal preclinical studies on mechanism of action and efficacy, and on how ongoing clinical research has been able to translate preclinical promises into clinical use.

Screening and application of a broad-spectrum aptamer for acyclic guanosine analogues

Acyclic guanosine analogues, a class of widely used antiviral drugs, can cause chronic toxicity and virus resistance. Therefore, it is essential to establish rapid and accurate methods to detect acyclic guanosine analogues. In this study, five acyclic guanosine analogues (acyclovir, famciclovir, ganciclovir, penciclovir, and valaciclovir) were used as positive targets to obtain broad-spectrum aptamers through Capture-SELEX technology. Real-time quantitative PCR (Q-PCR) was used to monitor the aptamer SELEX process. After the sixteen rounds of selection against mixed targets, sequences were obtained by high-throughput sequencing (HTS). Furthermore, a broad-spectrum aptamer, named CIV6, was found as the higher performance aptamer that was suitable for five acyclic guanosine analogues by graphene oxide (GO) polarization and fluorescence assay. Finally, the aptamer CIV6 was used to construct GO fluorescence assay to detect five acyclic guanosine analogues. The limits of detection (LOD) of acyclovir, famciclovir, ganciclovir, penciclovir, and valaciclovir were 0.48 ng·mL-1, 0.53 ng·mL-1, 0.50 ng·mL-1, 0.56 ng·mL-1, and 0.38 ng·mL-1, respectively.

Acyclovir in the Treatment of Herpes Viruses - A Review.

Herpes Simplex (HSV) viruses are widely spread, highly contagious human pathogens. The statistics indicate that 50-90% of adults worldwide are seropositive for these viruses, mainly HSV-1 and HSV-2. The primary infection results in the appearance of watery blisters (cold sores) on the skin, lips, tongue, buccal mucosa or genitals. The ocular infection is the major cause of corneal blindness in the Western World. Once the HSV virus enters human body, it cannot be completely eradicated because HSV viruses are able to change into their latent form which can survive the treatment. The viron resides in trigeminal ganglia of the host, who becomes vulnerable to the reoccurrence of the disease during the whole lifespan. The neurotropic and neuro-invasive properties of HSV are responsible for neurodegenerative illnesses, such as Alzheimer's disease. Acyclovir and its analogues, being the inhibitors of the viral DNA replication, are the only approved medicines for HSV infection therapies. The current paper presents the up-to-date overview of the important pharmacological features of acyclovir, its analogues and their delivery systems including the mechanism of action, routes of administration, absorption and metabolism, as well as side effects of the therapy. Acyclovir remains the gold standard in the treatment of herpes virus infections, mainly due to the emerging of the new delivery systems improving considerably its bioavailability. The analogues of acyclovir, especially their esters, characterized by significantly higher bioavailability and safety, may gradually replace acyclovir in selected applications.

Synthesis, characterization and antibacterial studies of Schiff bases of acyclovir

There is a crucial medical need for the progress of new antibacterial agents with new and more efficient mechanisms. Schiff bases are stated to have a wide range of pharmacological activities, including antimicrobial, antibacterial, antifungal, antioxidant, and anticancer activities, which are largely due to the distinguishing C=N group. Furthermore, heterocyclic compounds containing acyclic hydroxylated side chains, for example, acyclovir (ACV), are an essential class of antiviral acyclonucleosides. Therefore, this work was to synthesize and evaluate a new series of acyclovir analogues bearing a Schiff base moiety. Some of Schiff's bases synthesis in an ethanolic solution of drug, aldehydes, and glacial acetic acid as a catalyst followed in the synthesis of substituted acyclovir drug compounds. In this work, two new series of acyclovir analogues bearing a Schiff base moiety were Synthesised, characterized, and confirmed by various spectral techniques like FTIR, CHN, and 1HNMR spectra, in addition to melting point and retardation factor (Rf.). The biological activity of synthesized Schiff base compounds measured against a panel of various bacteria. The results revealed that these compounds showed antibacterial activity against Gram-positive bacteria such as bacillus and Gram-negative bacteria such as proteus, E-coli, pseudomonas, and klebsiella. It concluded that synthesized Schiff base compounds showed higher antibacterial activity than acyclovir that they derived from it.

Omeprazole Increases the Efficacy of Acyclovir Against Herpes Simplex Virus Type 1 and 2.

Omeprazole was shown to improve the anti-cancer effects of the nucleoside analogue 5-fluorouracil. Here, we combined omeprazole with the antiviral nucleoside analogues ribavirin and acyclovir. Omeprazole did not affect the antiviral effects of ribavirin in non-toxic concentrations up to 80 μg/mL but increased the acyclovir-mediated effects on herpes simplex virus 1 and 2 (HSV-1 and -2) replication in a dose-dependent manner. Omeprazole alone reduced HSV-1 and -2 titers [but not HSV-induced formation of cytopathogenic effects (CPE)] at concentrations ≥40 μg/mL. However, it exerted substantially stronger effects on acyclovir activity and also increased acyclovir activity at lower concentrations that did not directly interfere with HSV replication. Omeprazole 80 μg/mL caused a 10.8-fold (Vero cells) and 47.7-fold (HaCaT cells) decrease of the acyclovir concentrations that reduced HSV-1-induced CPE formation by 50% (IC50). In HSV-2-infected cells, omeprazole 80 μg/mL reduced the acyclovir IC50 by 7.3- (Vero cells) and 12.9-fold (HaCaT cells). In HaCaT cells, omeprazole 80 μg/mL reduced the HSV-1 titer in the presence of acyclovir 1 μg/mL by 1.6 × 105-fold and the HSV-2 titer in the presence of acyclovir 2 μg/mL by 9.2 × 103-fold. The proton pump inhibitors pantoprazole, rabeprazole, lansoprazole, and dexlansoprazole increased the antiviral effects of acyclovir in a similar fashion as omeprazole, indicating this to be a drug class effect. In conclusion, proton pump inhibitors increase the anti-HSV activity of acyclovir and are candidates for antiviral therapies in combination with acyclovir, in particular for topical preparations for the treatment of immunocompromised individuals who are more likely to suffer from severe complications.

Computer-aided rational design of acyclovir analogs to inhibit purine nucleoside phosphorylase

Purine nucleoside phosphorylase (PNP) is one of the major enzymes in the purine salvage pathway. It is responsible for the elevation of deoxyguanosine, and thus considered as the potent target in T-cell lymphoma. The present study examined acyclovir, reported as a low-affinity PNP inhibitor, for the rational design of new acyclovir derivatives by incorporating halogens, hydroxyl, and bulky amino groups. The molecular actions of designed derivatives were investigated by employing density functional theory, molecular docking, and binding energy calculations. The results revealed that the newly designed compounds were highly stable and showed more affinity to PNP than the parent compound, acyclovir. The quantum mechanics and molecular docking studies suggested that modification of side chains with bulky polar groups provided better binding affinities than substitutions with halogens. The resultant derivatives have strong polar interactions like His257 and Tyr88. Furthermore, the designed derivatives were within the ideal range of ADMET (absorption, distribution, metabolism, elimination, and toxicity) analysis. Considering that, these findings recommend further validation of designed acyclovir derivatives in wet lab confirmatory analysis with the emphasis on the further improvements in the treatment of T-cell-mediated diseases.

Comparative analysis of stability of tricyclic analogues of acyclovir in an acidic environment

In the presented studies, the effect of hydrogen ions on the stability of the tricyclic aciclovir derivative (i.e. 3,9-dihydro-3-[(2-hydroxyethoxy)methyl]-6-(4-methoxyphenyl)-9-oxo-5H-imidazo[1,2-a]purine; 6-(4-MeOPh)-TACV) and its esters (acetyl (Ac-), iso-butyryl (iBut-), pivaloyl (Piv-), ethoxycarbonyl (Etc-) and nicotinoyl (Nic-)) has been assessed. The HPLC chromatographic method (Lichrospher RP-18 column, 5 μm, 250 mm × 4 mm) with UV detection (262 nm) was used to observe changes in the concentration of the tested compounds. The mobile phase consisted of acetonitrile–phosphate buffer (pH 6; 20 mM; 17 mM KH2PO4, 3 mM K2HPO4) (35:65, v/v). The studies were carried out in the pH range 0.42–1.38 in the water-organic environment at constant ionic strength (0.50 M). The observed rate constants of the degradation reactions of the tested compounds were determined, kinetic equations describing the dependence of kpH as a function of pH for the proper acid catalysis were determined and the parameters of the equations describing the reaction of formation the observed product were determined. The dependence of durability on the chemical structure of the tested compounds was indicated and the mechanism of observed reactions was proposed.

ДИНАМІЧНИЙ МАРКЕТИНГОВИЙ АНАЛІЗ ВІТЧИЗНЯНОГО РИНКУ ПРОТИВІРУСНИХ ЛІКАРСЬКИХ ЗАСОБІВ ГРУП J05AB01, J05AХ05, J05AХ10

У статті висвітлені результати маркетингового аналізу груп противірусних препаратів, які рекомендовано для лікування хворих на дитячі вірусні інфекції (вітряну віспу, кір, краснуху). Упродовж 42 місяців - з 01.01.2013 до 01.07.2016 р. - був проведений щомісячний моніторинг їх асортименту, середніх оптово-відпускних цін, коефіцієнтів ліквідності та платоспроможності населення. Встановлено, що противірусні препарати груп ацикловіру У05ДВ01), інозинпранобексу^05ДХ05) та інших противірусних У05ДХ10: амізону, протефлазіду, флавозіду) є достатньо представлені на вітчизняному фармацевтичному ринку, доступність яких зросла наприкінці моніторингу. Найнижчою їх оптово-відпускна ціна була у січні 2013 р., а найвищою - у жовтні - листопаді 2014 та 2015 рр., березні - квітні 2016 р. Не спостерігається прямої залежності між динамікою оптової ціни препаратів і динамікою курсу гривні відносно до долара, оскільки стрибки підйому оптово-відпускних цін випереджували ріст долара на 1-3 місяці для одних ліків, а для інших, навпаки, на тлі загального росту відбулося різке зниження ціни. Тому на даний час цей сегмент оптового фармацевтичного ринку лікарських засобів не можна вважати достатньо прогнозованим.

ALKYLATION OF [1,2,4]TRIAZOLO[1,5- a ][1,3,5]TRIAZIN-7(3 H )-ONES

The results of pioneering research on the alkylation of fused [1,2,4]triazolo[1,5- a ][1,3,5]triazine system are presented, including computational studies of the reaction between 5-dimethylamino[1,2,4]triazolo[1,5- a ][1,3,5]triazin-7(3H)-one and bromoethane. The reaction of 5-amino-substituted [1,2,4]triazolo[1,5- a ][1,3,5]triazin-7(3 H )-ones with allyl bromide, bromoethane, or 2acetoxyethoxymethyl bromide occurred selectively with the formation of products due to alkylation at the N-3 nitrogen atom of the heterocyclic system. The removal of acetyl protecting group from 5-amino-substituted {2-[(7-oxo[1,2,4]triazolo[1,5- a ][1,3,5]triazin-3(7 Н )-yl)methoxy]ethyl}acetates gave 5-aza analogs of acyclovir, containing a substituted amino group at position 5 of the heterocyclic 3-[(2-hydroxyethoxy)methyl][1,2,4]triazolo[1,5- a ][1,3,5]triazin-7(3 H )-one system. Authors: Irina V. Ul'yankina, Anna V. Zavodskaya, Victor E. Parfenov, Alexander A. Gidaspov, Andrey K. Shiryaev, Eugenia V. Selezneva, Vladimir V. Bakharev*

Alkylation of [1,2,4]triazolo[1,5-a][1,3,5]triazin-7(3H)-ones

The results of pioneering research on the alkylation of fused [1,2,4]triazolo[1,5-a][1,3,5]triazine system are presented, including computational studies of the reaction between 5-dimethylamino[1,2,4]triazolo[1,5-a][1,3,5]triazin-7(3H)-one and bromoethane. The reaction of 5-amino-substituted [1,2,4]triazolo[1,5-a][1,3,5]triazin-7(3H)-ones with allyl bromide, bromoethane, or (2-acetoxyethoxy)methyl bromide occurred selectively with the formation of products due to alkylation at the N-3 nitrogen atom of the heterocyclic system. The removal of acetyl protecting group from 5-amino-substituted {2-[(7-oxo[1,2,4]triazolo[1,5-a][1,3,5]triazin-3(7H)-yl)methoxy]ethyl}acetates gave 5-aza analogs of acyclovir, containing a substituted amino group at position 5 of the heterocyclic 3-[(2-hydroxyethoxy)methyl][1,2,4]-triazolo[1,5-a][1,3,5]triazin-7(3H)-one system.

Hybrid MC/QC simulations of water-assisted proton transfer in nucleosides. Guanosine and its analog acyclovir

To provide an in-depth insight into the molecular basis of spontaneous tautomerism in DNA and RNA base pairs, a hybrid Monte Carlo (MC)–quantum chemical (QC) methodology is implemented to map two-dimensional potential energy surfaces along the reaction coordinates of solvent-assisted proton transfer processes in guanosine and its analog acyclovir in aqueous solution. The solvent effects were simulated by explicit inclusion of water molecules that model the relevant part of the first hydration shell around the solute. The position of these water molecules was estimated by carrying out a classical Metropolis Monte Carlo simulation of dilute water solutions of the guanosine (Gs) and acyclovir (ACV) and subsequently analyzing solute–solvent intermolecular interactions in the statistically-independent MC-generated configurations. The solvent-assisted proton transfer processes were further investigated using two different ab initio MP2 quantum chemical approaches. In the first one, potential energy surfaces of the ‘bare’ finite solute–solvent clusters containing Gs/ACV and four water molecules (MP2/6-31+G(d,p) level) were explored, while within the second approach, these clusters were embedded in ‘bulk’ solvent treated as polarizable continuum (C-PCM/MP2/6-31+G(d,p) level of theory). It was found that in the gas phase and in water solution, the most stable tautomer for guanosine and acyclovir is the 1H-2-amino-6-oxo form followed by the 2-amino-6-(sZ)-hydroxy form. The energy barriers of the water-assisted proton transfer reaction in guanosine and in acyclovir are found to be very similar – 11.74 kcal mol−1 for guanosine and 11.16 kcal mol−1 for acyclovir, and the respective rate constants (k = 1.5 × 101 s−1, guanosine and k = 4.09 × 101 s−1, acyclovir), are sufficiently large to generate the 2-amino-6-(sZ)-hydroxy tautomer. The analysis of the reaction profiles in both compounds shows that the proton transfer processes occur through the asynchronous concerted mechanism.

A novel corneal explant model system to evaluate antiviral drugs against feline herpesvirus type 1 (FHV-1).

Feline herpesvirus type-1 (FHV-1) is the most common viral cause of ocular surface disease in cats. Many antiviral drugs are used to treat FHV-1, but require frequent topical application and most lack well-controlled in vivo studies to justify their clinical use. Therefore, better validation of current and novel treatment options are urgently needed. Here, we report on the development of a feline whole corneal explant model that supports FHV-1 replication and thus can be used as a novel model system to evaluate the efficacy of antiviral drugs. The anti-herpes nucleoside analogues cidofovir and acyclovir, which are used clinically to treat ocular herpesvirus infection in cats and have previously been evaluated in traditional two-dimensional feline cell cultures in vitro, were evaluated in this explant model. Both drugs suppressed FHV-1 replication when given every 12 h, with cidofovir showing greater efficacy. In addition, the potential efficacy of the retroviral integrase inhibitor raltegravir against FHV-1 was evaluated in cell culture as well as in the explant model. Raltegravir was not toxic to feline cells or corneas, and most significantly, inhibited FHV-1 replication at 500 µM in both systems. Importantly, this drug was effective when given only once every 24 h. Taken together, our data indicate that the feline whole corneal explant model is a useful tool for the evaluation of antiviral drugs and, furthermore, that raltegravir appears a promising novel antiviral drug to treat ocular herpesvirus infection in cats.

Molecular clefts of Rebek revisited: potential application as drug carriers for the antiviral acyclovir

Complexation studies between two artificial receptors (molecular clefts of Rebek) naphthalene imide 5 and 5-azacytosine-β-naphthylethyl ester 9 and the antiviral nucleoside analog acyclovir 10 were performed and evaluated by determination of the equilibrium constants of 1:1 complexes using 1H and 13C NMR titrations as well as solubility titrations with reversed phase HPLC. The results showed an association between 9 and 10 but not between 5 and 10 through hydrogen bonding and π-stacking interactions and pointed out a complementarity between acyclovir 10 and the molecular cleft 9 similar to that observed with DNA guanine-cytosine base pairing. Docking simulations provide structural models of such interactions. The results so far obtained prompt us to propose 9 as a potential carrier for acyclovir 10.

Синтез ациклических аналогов нуклеозидов гликозилиированием 1,2,4-триазоло[1,5-а]пиримидин-7-онов по одностадийному методу Форбрюггена

New analogues of acyclovir have been prepared by reacting 1,2,4-triazolo[1,5-a]pyrimidin-7-ones 1а-i and (2-acetoxyethoxy)methyl acetate 2 in the presence of trimethylsilyl trifluoromethanesulfonate as a catalyst. Thei nteraction between the compounds 1а-е and 2 has led to a mixture of N3 and N4 isomers. In contrast, the reaction of compounds 1g-i and 2 proceeded selectively to form N3 isomers. In the case of compounds 1a-c the predominant product is the one with the acyclic moiety in azine ring (N4 isomer). Interaction between 1d-f and 2 has led to mixtures comprising mainly N3 isomer. It has been found that the ratio of glycosylation products 1 and 2 are thermodynamically controlled. The structure of the obtained compounds has been proved by 1Н, 13С, two-dimensional 1Н-13С NMR spectroscopy and X-ray analysis.

Transporter-mediated uptake of UDP-glucuronic acid by human liver microsomes: assay conditions, kinetics, and inhibition.

This study characterized the kinetics, variability, and factors that affect UDP-glucuronic acid (UDP-GlcUA) uptake by human liver microsomes (HLM). Biphasic kinetics were observed for UDP-GlcUA uptake by HLM. Uptake affinities (assessed as Kd) of the high- and low-affinity components differed by more than an order of magnitude (13 ± 6 vs. 374 ± 175 µM), but were comparable in terms of the maximal rate of uptake, with mean Vmax values differing less than 2.3-fold (56 ± 26 vs. 131 ± 35 pmol/min per mg). Variability in total intrinsic transporter activity (Uint) for microsomal UDP-GlcUA uptake across 12 livers was less than 4-fold. Experiments performed to optimize the conditions for microsomal UDP-GlcUA uptake demonstrated that both components were trans-stimulated by preloading (luminal addition) with an alternate UDP-sugar, and essentially abolished by the thiol-alkylating agent N-ethylmaleimide. Furthermore, interaction studies undertaken with a panel of drugs, alternate UDP-sugars, and glucuronide conjugates, at low (2.5 μM) and high (1000 μM) UDP-GlcUA concentrations, demonstrated that both components were inhibited to varying extents. Notably, the nucleoside analogs zidovudine, stavudine, lamivudine, and acyclovir inhibited both the high- and low- affinity components of microsomal UDP-GlcUA uptake by >45% at an inhibitor concentration of 100 μM. Taken together, these data demonstrate that human liver microsomal UDP-GlcUA uptake involves multiple protein-mediated components, and raises the possibility of impaired in vivo glucuronidation activity resulting from inhibition of UDP-GlcUA uptake into the endoplasmic reticulum membrane by drugs and other compounds.

Synthesis of acyclic nucleoside analogues based on 1,2,4-triazolo[1,5-a]pyrimidin-7-ones by one-step Vorbrüggen glycosylation

New acyclovir analogues were obtained by reaction of 1,2,4-triazolo[1,5-a]pyrimidin-7-ones 4a–i with (2-acetoxyethoxy)methyl acetate 5 in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) as catalyst (Vorbrüggen procedure). Coupling between compounds 4a–f and 5 led to a mixture of N3- and N4-isomers 6 and 7, respectively. On the contrary, the reaction of compounds 4g–i with 5 proceeded selectively with formation of N3-isomers only. It was found that the ratio of 6a–f and 7a–f depends on the presence or the absence of N,O-bis(trimethylsilyl)acetamide (BSA). Glycosylated products 6a–f and 7a–f underwent reversible isomerization under TMSOTf treatment. The ratio of glycosylated products of the coupling reaction between 4 and 5 was thermodynamically controlled. A similar reaction occurred if ZnCl2 was chosen as a catalyst, although lower yields of the acyclic analogues of nucleosides were observed. The glycosylation of other purines (adenine and guanine) can be achieved via the non-BSA modification of the Vorbrüggen procedure.

Rapid Viral Expansion and Short Drug Half-Life Explain the Incomplete Effectiveness of Current Herpes Simplex Virus 2-Directed Antiviral Agents

The nucleoside analogues acyclovir (ACV) and famciclovir (FCV) reduce the frequency and severity of herpes simplex virus 2 (HSV-2) genital shedding, yet despite their high potency in vitro and a lack of induced drug resistance, frequent episodes of breakthrough mucosal shedding occur. We tested a published stochastic, spatial mathematical model of HSV-2 replication and spread, in concert with pharmacokinetic and pharmacodynamic equations, against virologic data from clinical trials of twice-daily acyclovir and famciclovir suppression. The model reproduced the key features of clinical trial data, including genital shedding episode rate, expansion and decay dynamics, and heterogeneous peak viral production and duration. In simulations, these agents shortened episode duration by limiting the extent of viral production by 1 to 2 log units and limiting the formation of secondary ulcers by ∼50%. However, drug concentrations were noninhibitory during 42% of the dosing cycle. Even if drug concentrations were high at episode initiation, prolonged episodes often ensued due to drug decay over ensuing hours and subsequent rebound of rapidly replicating HSV-2. The local CD8(+) T-cell density was more predictive of episode viral production (R(2) = 0.42) and duration (R(2) = 0.21) than the drug concentration at episode onset (R(2) = 0.14 and 0.05, respectively), though the model projected that an agent with an equivalent potency but a two times longer half-life would decrease shedding by 80% compared to that of standard twice-daily regimens. Therefore, long half-life is a key characteristic of any agent that might fully suppress HSV-2 reactivations.