No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Design, Synthesis, and Biological Evaluation of Unconventional Aminopyrimidine, Aminopurine, and Amino-1,3,5-triazine Methyloxynucleosides
ChemMedChem
Abstract
Herein we describe a class of unconventional nucleosides (methyloxynucleosides) that combine unconventional nucleobases such as substituted aminopyrimidines, aminopurines, or aminotriazines with unusual sugars in their structures. The allitollyl or altritollyl derivatives were pursued as ribonucleoside mimics, whereas the tetrahydrofuran analogues were pursued as their dideoxynucleoside analogues. The compounds showed poor, if any, activity against a broad range of RNA and DNA viruses, including human immunodeficiency virus (HIV). This inactivity may be due to lack of an efficient metabolic conversion into their corresponding 5'-triphosphates and poor affinity for their target enzymes (DNA/RNA polymerases). Several compounds showed cytostatic activity against proliferating human CD4(+) T-lymphocyte CEM cells and against several other tumor cell lines, including murine leukemia L1210 and human prostate PC3, kidney CAKI-1, and cervical carcinoma HeLa cells. A few compounds were inhibitory to Moloney murine sarcoma virus (MSV) in C3H/3T3 cell cultures, with the 2,6-diaminotri-O-benzyl-D-allitolyl- and -D-altritolyl pyrimidine analogues being the most potent among them. This series of unconventional nucleosides may represent a novel family of potential antiproliferative agents.
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
... Numerous other protocols can be found in literature for the syntheses of the derivatized pyrimidines as well [5] . These chemical building block possess valuable biological activities: antibacterial [6] , antiviral [7] , antifungal [8] , anti-inflammatory and analgesic [9] , anti-malarial, and anticancer etc., as illustrated by Fig. 1 . ...
... Both the naphthalene group and 2-amino-6-methylpyrimidin-4-ol group were determined to be planar with respective root mean square (r.m.s) deviations of 0.0071 and 0.0082 Å in the molecule A, 0.0023 and 0.0118 Å in the molecule B, and 0.0041 and 0.0131 Å in the molecule C, respectively. The dihedral angle between the naphthalene group and 2-amino-6-methylpyrimidin-4-ol group was found to be 86.28 (7) °in the molecule A, 88.69(7) °in the molecule B, and 87.28 (6) °in the molecule C. The dihedral angle inspection infers that the naphthalene group plane is almost perpendicular to the 2-amino-6-methylpyrimidin-4-ol group plane in all three independent molecules. The sulfonyl group was shown to be twisted at respective dihedral angles of 49.7(2) °and 56.7(2) °with respect to the naphthalene group and 2-amino-6-methylpyrimidin-4-ol group in the molecule A, 48.9 (2) °and 56.1 (2) °in the molecule B, and 52.1 (2) °and 48.1 (2) °in the molecule C. The selected bond distances and bond angles are listed in Table S1. ...
Recently, syntheses and quantum chemical insights in the structures and properties of crystalline organic compounds have attracted significant attention of the scientific community. In the current work we report the synthesis of two arylsulfonylated 2-amino-6-methylpyrimidin derivatives, A and B. X-ray diffraction technique confirmed the structures of both compounds. The single-crystal analysis showed the presence of various non-covalent interactions that are responsible for their structural stabilities. Theoretical calculations of A and B were performed at the B3LYP/6-311++G(d,p) level. The calculated structures of both compounds were found to be in good agreement with the experimentally reported structural parameters. Frontier molecular orbital (FMO) analysis showed that employing different moieties to bind with the 2-amino-6-methylpyrimidin-4-ol group causes certain changes to the FMOs energies and energy gaps, thus affecting the stability, reactivity, and other properties of the resulting compounds. The Natural Bond Order (NBO) analysis showed high stabilization energies within the molecules of both compounds. The calculated global reactivity parameters (GRP) confirmed noticeable stability of both compounds, showing the compound B to be more stable than the compound A.
... 5 Whatever the origin of pyrimidine occurrence, whether natural or synthesized, it has proved to be privileged for therapeutics as remarkable pharmacophores. Some of the fused heterocyclic ring systems are potential antibacterial (5-amino-thiazolo [4,5d]pyrimidine), 6 antifungal (pyrrolo [2,3-d]pyrimidines), 7 anti-viral (2,4-diaminopyrimidinederivative), 8 anticancer (pyrazolopyrimidine), 9 anti-inflammatory and analgesic (N-(4-hydroxy-6-tosyl-5,6,7,8-tetrahydropyrido [4,3-d]pyrimidin-2-yl)isonicotinamide), 10 and antimalarial (sulfadiazine) agents, as shown in Figure 1. These heterocyclic compounds are highly recognized chemical building blocks with significant medicinal applications. ...
Two heterocyclic compounds named 2,6-diaminopyrimidin-4-ylnaphthalene-2-sulfonate (A) and 2,6-diaminopyrimidin-4-yl4-methylbenzene sulfonate (B) were synthesized. The structures of heterocyclic molecules were established by the X-ray crystallographic technique, which showed several noncovalent interactions as N···H···N, N···H···O, and C–H···O bonding and parallel offset stacking interaction. Hydrogen-bonding interactions were further explored by the Hirshfeld surface (HS) analysis. Nonlinear optical (NLO) and natural bond orbital (NBO) properties were calculated utilizing the B3LYP/6-311G(d,p) level. Frontier molecular orbitals (FMOs) and molecular electrostatic potential (MEP) were calculated utilizing the time-dependent density functional theory (TD-DFT) at the same level. The NBO analysis showed that the molecular stabilities of compounds A and B were attributed to their large stabilization energy values. The second hyperpolarizability (γtot) values for A and B were obtained as 3.7 × 10⁴ and 2.7 × 10⁴ au, respectively. The experimental X-ray crystallographic and theoretical structural parameters of A and B were found to be in close correspondence. Both the molecules reveal substantial NLO responses that can be significant for their utilization in advanced applications.
... 5-iododeoxyuridine is pyrimidine-based heterocyclic antiviral agents that have been used extensively for the treatment of viral infections (Jain et al., 2006). 2-(4-methyl-5-nitro-6-(pyrrolidin-1-yl)-pyrimidin-2-ylamino)-3-phenylpropanoic acid (Fig. 39) exhibited antiviral activity with IC 50 of 73 μg mLG 1 (Danesh et al., 2015) while 2,4diaminopyrimidine derivative (IC 50 = 13 μg mLG 1 ) was the most effective among the series screened by Fernandez-Cureses et al. (2015). Other recently reported pyrimidines with promising antiviral activities in Fig. 39, were 7-(4-methylphenyl)-8,9-diphenyl-7H-pyrrolo[3,2-e] [1,2,4]-triazolo[1,5c]pyrimidine-2-thione (Mohamed et al., 2015a) and 5-(5-(sec-butythio)-1,3,4-thiadiazol-2yl)-2methylpyrimidin-4-amine (Wu et al., 2015) (Fig. 3). ...
The pyrimidine moiety is one of the most widespread heterocycles in biologically occurring compounds, such as nucleic acids components (uracil, thymine and cytosine) and vitamin B1. Due to its prebiotic nature to living cells in biodiversity, it is an highly privileged motif for the development of molecules of biological and pharmaceutical interest. This present work deals with the exploration of chemistry and medicinal diversity of pyrimidine which might pave way to long await discovery in therapeutic medicine for future drug design.
Traditional cotton water dyeing has a considerable ecological impact because of the use of water, but the available anhydrous cotton dyeing technologies cannot balance low recyclable energy consumption and excellent dyeing effects. In this study, a recyclable anhydrous cotton dyeing technology was designed and implemented by mixing supercritical carbon dioxide, dimethyl sulfoxide, and ethanol for the first time. Compared to the existing anhydrous cotton dyeing technologies, the novel technology could simultaneously obtain low recyclable energy consumption and excellent dyeing effects, such as dye penetration, washing and crocking fastness, levelness, color depth control and color matching. The dye fixations of reactive dyes in the novel technology are 5.1%–26.4% higher than those in traditional water dyeing. Meanwhile, the energy consumption of the novel technology is only 70% of that of traditional water dyeing, and the comprehensive cost of materials and energy of the novel technology is only 56% of that of traditional water dyeing. It is a new green option with low energy consumption for cotton dyeing.
Acyclic nucleoside phosphonates incorporating 2,4-diaminotriazine (DAT) as a 5-aza-analogue of the 2,4-diamino-pyrimidine (DAPym) nucleobase present in PMEO-DAPyms have been synthesized. The lead PMEO-DAT is as inhibitory against HIV, HBV, MSV and VZV replication as the parent PMEO-DAPym and equally inefficient at markedly affecting replication of HSV-1, HSV-2 and HCMV. A rationale for this similar biological profile is proposed on the basis of structural differences in the active site of the viral DNA polymerases. PMEO-DAT is, however, more selective because, unlike PMEO-DAPym, it does not stimulate secretion of β-chemokines in cultured PBMC.
Copyright © 2015. Published by Elsevier B.V.
Nucleoside analogues have been in clinical use for almost 50 years and have become cornerstones of treatment for patients with cancer or viral infections. The approval of several additional drugs over the past decade demonstrates that this family still possesses strong potential. Here, we review new nucleoside analogues and associated compounds that are currently in preclinical or clinical development for the treatment of cancer and viral infections, and that aim to provide increased response rates and reduced side effects. We also highlight the different approaches used in the development of these drugs and the potential of personalized therapy.
Nucleoside triphosphates are moldable entities that can easily be functionalized at various locations. The enzymatic polymerization of these modified triphosphate analogues represents a versatile platform for the facile and mild generation of (highly) functionalized nucleic acids. Numerous modified triphosphates have been utilized in a broad palette of applications spanning from DNA-tagging and -labeling to the generation of catalytic nucleic acids. This review will focus on the recent progress made in the synthesis of modified nucleoside triphosphates as well as on the understanding of the mechanisms underlying their polymerase acceptance. In addition, the usefulness of chemically altered dNTPs in SELEX and related methods of in vitro selection will be highlighted, with a particular emphasis on the generation of modified DNA enzymes (DNAzymes) and DNA-based aptamers.
The acyclic pyrimidine nucleoside phosphonate (ANP) phosphonylmethoxyethoxydiaminopyrimidine (PMEO-DAPym) differs from other ANPs in that the aliphatic alkyloxy linker is bound to the C-6 of the 2,4-diaminopyrimidine base through an ether bond, instead of the traditional alkyl linkage to the N-1 or N-9 of the pyrimidine or purine base. In this study, we have analyzed the molecular interactions between PMEO-DAPym-diphosphate (PMEO-DAPym-pp) and the active sites of wild-type (WT) and drug-resistant HIV-1 reverse transcriptase (RT). Pre-steady-state kinetic analyses revealed that PMEO-DAPym-pp is a good substrate for WT HIV-1 RT: its catalytic efficiency of incorporation (k(pol)/K(d)) is only 2- to 3-fold less than that of the corresponding prototype purine nucleotide analogs PMEA-pp or (R)PMPA-pp. HIV-1 RT recognizes PMEO-DAPym-pp as a purine base instead of a pyrimidine base and incorporates it opposite to thymine (in DNA) or uracil (in RNA). Molecular modeling demonstrates that PMEO-DAPym-pp fits into the active site of HIV-1 RT without significant perturbation of key amino acid residues and mimics an open incomplete purine ring that allows the canonical Watson-Crick base pairing to be maintained. PMEO-DAPym-pp is incorporated more efficiently than (R)PMPA-pp by mutant K65R HIV-1 RT and is not as efficiently excised as (R)PMPA by HIV-1 RT containing thymidine analog mutations. Overall, the data revealed that PMEO- DAPym represents the prototype compound of a novel class of pyrimidine acyclic nucleoside phosphonates that are recognized as a purine nucleotide and should form the rational basis for the design and development of novel purine nucleo(s)(t)ide mimetics as potential antiviral or antimetabolic agents.
Accumulation of antiviral nucleotides in renal proximal tubules is controlled by their basolateral uptake via the human renal
organic anion transporters type 1 (hOAT1) and 3 (hOAT3) and apical efflux via the multidrug resistance protein 4 (MRP4). GS-9148
is a novel ribose-modified nucleotide human immunodeficiency virus (HIV) reverse transcriptase inhibitor, and its oral prodrug
GS-9131 is currently being evaluated in the clinic as an anti-HIV agent. To assess the potential of GS-9148 for nephrotoxicity,
its mechanism of renal transport, cytotoxicity, and renal accumulation were explored in vitro and in vivo. In comparison with
the acyclic nucleotides cidofovir, adefovir, and tenofovir, GS-9148 showed 60- to 100-fold lower efficiency of transport (Vmax/Km) by hOAT1 and was 20- to 300-fold less cytotoxic in cells overexpressing hOAT1, indicating its lower hOAT1-mediated intracellular
accumulation and reduced intrinsic cytotoxicity. GS-9148 was also relatively inefficiently transported by hOAT3. Similar to
acyclic nucleotides, GS-9148 was a substrate for MRP4 as evidenced by its reduced intracellular retention in cells overexpressing
the efflux pump. Consistent with these molecular observations, GS-9148 was inefficiently taken up by fresh human renal cortex
tissue in vitro and showed a limited accumulation in kidneys in vivo following oral administration of [14C]GS-9131 to dogs. Compared to acyclic nucleotide analogs, GS-9148 was also found to have lower net active tubular secretion
in dogs. Collectively, these results suggest that GS-9148 exhibits a low potential for renal accumulation and nephrotoxicity.
Two newly synthesized carbocyclic oxetanocin analogs, (+/-)-9-[(1 beta,2 alpha,3 beta)-2,3-bis(hydroxymethyl)-1-cyclobutyl]adenine (cyclobut-A) and (+/-)-9-[(1 beta,2 alpha,3 beta)-2,3-bis(hydroxymethyl)-1-cyclobutyl]guanine (cyclobut-G) were tested for activity against the infectivity of human immunodeficiency virus (HIV) in vitro. A number of other carbocyclic oxetanocin analogs failed to exert good antiretroviral effects. Both cyclobut-A and cyclobut-G protected CD4+ ATH8 cells against the infectivity and cytopathic effect of HIV type 1 (HIV-1) and suppressed proviral DNA synthesis in ATH8 cells exposed to HIV-1 in vitro at concentrations of 50 to 100 microM. These compounds also inhibited the in vitro infectivity of another human pathogenic retrovirus, HIV-2. Furthermore, both compounds completely suppressed the replication of a monocytotropic strain of HIV-1 in monocytes and macrophages at concentrations as low as 0.5 microM, as assessed by inhibition of HIV-1 p24 gag protein production. We also found that 2'-deoxyguanosine readily reversed the antiretroviral activity of cyclobut-G in our system, whereas the activity of cyclobut-A was hardly reversed by 2'-deoxyadenosine or 2'-deoxycytidine. We noted, however, that these compounds inhibited the proliferation of peripheral blood mononuclear cells at concentrations of greater than or equal to 100 microM in vitro. Although both cyclobut-A and cyclobut-G appear to have a certain level of in vitro toxicity, our observations may have theoretical and clinical implications in understanding the structure-activity relationships of antiretroviral agents active against HIV.
Ribavirin, an antiviral drug discovered in 1972, is interesting and important for three reasons: (a) it exhibits antiviral activity against a broad range of RNA viruses; (b) it is currently used clinically to treat hepatitis C virus infections, respiratory syncytial virus infections, and Lassa fever virus infections; and (c) ribavirin's mechanism of action has remained unclear for many years. Here we recount the history of ribavirin and review recent reports regarding ribavirin's mechanism of action, including our studies demonstrating that ribavirin is an RNA virus mutagen and ribavirin's primary antiviral mechanism of action against a model RNA virus is via lethal mutagenesis of the RNA virus genomes. Implications for the development of improved versions of ribavirin and for the development of novel antiviral drugs are discussed.
A novel class of acyclic nucleoside phosphonates has been discovered in which the base consists of a pyrimidine preferably
containing an amino group at C-2 and C-4 and a 2-(phosphonomethoxy)ethoxy (PMEO) or a 2-(phosphonomethoxy)propoxy (PMPO) group
at C-6. The 6-PMEO 2,4-diaminopyrimidine (compound 1) and 6-PMPO 2,4-diaminopyrimidine (compound 11) derivatives showed potent
activity against human immunodeficiency virus (HIV) in the laboratory (i.e., CEM and MT-4 cells) and in primary (i.e., peripheral
blood lymphocyte and monocyte/macrophage) cell cultures and pronounced activity against Moloney murine sarcoma virus in newborn
NMRI mice. Their in vitro and in vivo antiretroviral activity was comparable to that of reference compounds 9-[(2-phosphonomethoxy)ethyl]adenine
(adefovir) and (R)-9-[(2-phosphonomethoxy)-propyl]adenine (tenofovir), and the enantiospecificity of (R)- and (S)-PMPO pyrimidine derivatives as regards their antiretroviral activity was identical to that of the classical (R)- and (S)-9-(2-phosphonomethoxy)propyl purine derivatives. The prototype PMEO and PMPO pyrimidine analogues were relatively nontoxic
in cell culture and did not markedly interfere with host cell macromolecular (i.e., DNA, RNA, or protein) synthesis. Compounds
1 and 11 should be considered attractive novel pyrimidine nucleotide phosphonate analogues to be further pursued for their
potential as antiretroviral agents in the clinical setting.
Novel acyclic nucleoside phosphonates with a pyrimidine base preferentially containing an amino group at C-2 and C-4 and a
2-(phosphonomethoxy)ethoxy or (R)-2-(phosphonomethoxy)propoxy group at C-6 selectively inhibit the replication of wild-type and lamivudine-resistant hepatitis
B viruses. The activity of the most potent compounds was comparable to that of adefovir.
Due to the worldwide epidemic of acquired immunodeficiency syndrome (AIDS), the past ten years have witnessed a flurry of activity in the chemotherapy of viral diseases. Unprecedented scientific efforts have been made by scientists and clinicians to combat infections of human immunodeficiency virus (HIY), the causative agent. Looking back over the past ten years, we have made remarkable progress toward the treatment of the viral disease: isolation of HIV only two years after the identification of the disease, plus major strides in the areas of the molecular biology and virology of the retrovirus, etc. More remarkably, the discovery of the chemotherapeutic agent AZT (Retrovir) was made within two years after the isolation and identification of the virus, followed by unprecedented drug development efforts to culminate in the FDA approval of AZT in twenty-three months, which was a record-breaking time for approval of any drug for a major disease. The last six to seven years have particularly been an exciting and productive period for nucleoside chemists. Since the activity of AZI' was established in 1985, nucleoside chemists have had golden opportunities to discover additional anti-HIV nucleosipes, which are hoped to be less toxic and more effective than AZT, and the opportunity continues. As we all are aware, AZT possesses extremely potent anti-HIY activity, and no other nucleoside or non nucleoside has surpassed the potency of AZT in vitro.
When the first edition of this book was published in 1950, it set out to present an elementary outline of the state of knowledge of nucleic acid biochemistry at that time and it was the first monograph on the subject to appear since Levene's book on Nucleic Acids in 1931. The fact that a tenth edition is required after thirty five years and that virtually nothing of the original book has been retained is some measure of the speed with which knowledge has advanced in this field. As a result of this vast increase in information it becomes increasingly difficult to fulfil the aims of providing an introduction to nucleic acid biochemistry and satisfying the requirements of advanced undergraduates and postgraduates in biochemistry, genetics and molecular biology. We have attempted to achieve these aims by con centrating on those basic aspects not normally covered in the general biochemistry textbooks and by providing copious references so that details of methodology can readily be retrieved by those requiring further information. The first seven editions emerged from the pen of J. N. Davidson who died in September 1972 shortly after completing the seventh edition. The subsequent editions have been produced by various colleagues who have tried to retain something of the character and structure of the earlier editions while at the same time introducing new ideas and concepts and eliminating some of the more out -dated material."
Edited by one of the main driving forces behind the field's momentous rise in recent years, this one-stop reference is the first comprehensive resource to integrate recent advances. The first part addresses biochemical aspects and applications, the second and third parts are devoted to compounds with therapeutic potential, with the third part focusing on newly introduced anticancer nucleoside drugs. Essential reading for every scientist working in this area.
Nucleosides are fundamental building blocks of biological systems that are widely used as therapeutic agents to treat cancer, fungal, bacterial, and viral infections. The synthetic potential of enzymes related to nucleoside synthesis has been applied profusely, especially since the introduction of organic solvent methodology. This chapter covers the literature relative to nucleosides with selected examples because of special significance. It presents a range of examples that cover nucleoside analogue syntheses through enzymatic procedures and offers an easily accessible visual reference review. In the synthesis of modified nucleosides, esters are currently used to protect ribose hydroxyl groups. As their subsequent removal is carried out by treatment with ammonia or methoxide, reactive groups present in the ribose or the base may interfere. Molecular modeling helps to explain the selectivity shown by several biocatalysts. It aims to predict which catalyst would be best suited for a particular substrate.
Reaction of anionoid reagents with 2-phenoxy-6-methylpyrimidine (IV) and its N-oxide (III) was carried out to examine the reactivity of the phenoxyl in 4-position. It was found that there is no great difference in the reactivity of the phenoxyl group between (III) and (IV) but the phenoxyl in these compounds were substituted more easily than that in 4-phenoxypyridine. During the course of this reaction, 4-phenylthio-(VII), 4-piperi-dino-(VIII), and 4-morpholino-6-methylpyrimidine 1-oxide (IX), which cannot be prepared by the direct N-oxide formation reaction of the corresponding tertiary bases, were obtained.
The synthesis of 6-(2-amino-3,6-dihydro-6-oxo-4-pyrimidinyl)-1,4-naphthalenediones 13 and 14 as well as their o-methylated derivatives at the 6-position of the pyrimidine ring 16 and 17 is described. The pyrimidine ring was generated by condensation of guanidine with an α-ketoketene-S,S-diacetal. The naphthoquinonoid function resulted from oxidation of a naphthalenamine by the potassium nitrosodisulfonate (Fremy's reagent). The latter amine was produced by reduction of the corresponding nitronaphthalene. The synthesized quinones and their analogous naphthalenamines 9 and 10 have been tested in vitro for cytotoxicity against L1210 leukemia cells; the ID50 of the most active compounds is about 1 μM.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
The importance of nucleoside analogues in chemotherapy and in other potential therapeutic approaches as immunomodulation or regulation of gene expression, is reviewed.
Alkoxy-derivatives of 1,2,4,6,8-penta-azanaphthalene (pyrimido[5,4-e]-as-triazine) undergo transetherification when treated with boiling alcohols in the presence of silver oxide. Appropriate methoxy-compounds give 5-ethoxy-3-methyl-, 5-propoxy-3-methyl, and (more slowly) 5-isopropoxy-3-methyl-penta-azanaphthalene; also 5,7-diethoxy-, 5,7-dipropoxy-, 5,7-di-isopropoxy-, 5,7-diethoxy-3-methyl-, and 5-ethoxy-3,7-dimethyl-penta-azanaphthalene. Synthetic routes to the methoxy-substrates and to one of the products are reported; other structures are confirmed by u.v. and 1H n.m.r. spectra.
Reactions of 6-chloropurines with 1,4-diazabicyclo[2.2.2]octane
(DABCO) give the corresponding ‘DABCO-purines’ 1a–d,
which undergo facile displacement reactions with alkoxides in dimethyl
sulfoxide to afford 6-oxy-substituted purines.
Stereoselective chain-extension of carbohydrate aldehydes with the hydroxymethylating reagent (dimethylphenylsilyl)methylmagnesium chloride (1) followed by acid-mediated cyclization gives access to 2,5-anhydro-hexitols. The stereoselectivity of the ring closure depends on the nature of the acid, i.e., treatment with excess BF3.Et2O or catalytic H2SO4 leads to tetrahydrofurans with 2,3-cis or 2,3-trans configuration, respectively. Concomitant elimination is effectively suppressed in case of cyclisation of the more sterically hindered isopropyl substituted silanes.
Deoxygenation of thiazolylketose acetates using SmI2–(CH2OH)2 or TMSOTf–Et3SiH affords thiazolyl C-glycosides with opposite α/β ratios. Examination of the thiazolyl α- and β-C-ribofuranoside pair by NOE experiments reveals that the earlier configuration assigned to one of these isomers has to be revised. Having prepared authentic anomeric α- and β-ribofuranose aldehydes from the corresponding thiazolyl C-glycosides by cleavage of the thiazole ring, each aldehyde was transformed into (1→6)-C-disaccharides via Wittig olefination with a galactose 6-phosphorane.
Synthesis of (R)-(−)- and (S)-(+)-synadenol (1a and 2a, 95−96% ee) is described. Racemic synadenol (1a + 2a) was deaminated with adenosine deaminase to give (R)-(−)-synadenol (1a) and (S)-(+)-hypoxanthine derivative 5. Acetylation of the latter compound gave acetate 6. Reaction with N,N-dimethylchloromethyleneammonium chloride led to 6-chloropurine derivative 7. Ammonolysis furnished (S)-(+)-synadenol (2a). Absolute configuration of 1a was established by two methods: (i) synthesis from (R)-methylenecyclopropanecarboxylic acid (8) and (ii) X-ray diffraction of a single crystal of (−)-synadenol hydrochloride. Racemic methylenecyclopropanecarboxylic acid (10) was resolved by a modification of the described procedure. The R-enantiomer 8 was converted to ethyl ester 13 which was brominated to give vicinal dibromides 14. Reduction with diisobutylaluminum hydride then furnished alcohol 15 which was acetylated to the corresponding acetate 16. Alkylation−elimination procedure of adenine with 16 yielded acetates 17 and 18. Deprotection with ammonia afforded a mixture of Z- and E-isomers 1a and 19 of the R-configuration. Comparison with products 1a and 2a by chiral HPLC established the R-configuration of (−)-synadenol (1a). These results were confirmed by X-ray diffraction of a single crystal of (−)-synadenol hydrochloride. The latter forms a pseudosymmetric dimer with adenine−adenine base pairing in the lattice with the nucleobase in an anti-like conformation. Enantiomers 1a and 2a exhibit varied enantioselectivity toward different viruses. Both enantiomers are equipotent against human cytomegalovirus (HCMV) and varicella zoster virus (VZV). The S-enantiomer 2a is somewhat more effective than R-enantiomer 1a in herpes simplex virus 1 and 2 (HSV-1 and HSV-2) assays. By contrast, enantioselectivity of antiviral effect is reversed in Epstein-Barr virus (EBV) and human immunodeficiency virus type 1 (HIV-1) assays where the R-enantiomer 1a is preferred. In these assays, the S-enantiomer 2a is less effective (EBV) or devoid of activity (HIV-1).
New nucleoside analogues 14−17 based on a methylenecyclopropane structure were synthesized and evaluated for antiviral activity. Reaction of 2,3-dibromopropene (19) with adenine (18) led to bromoalkene 20, which was benzoylated to give N6,N6-dibenzoyl derivative 23. Attempts to convert 20 or 23 to bromocyclopropanes 21 and 22 by reaction with ethyl diazoacetate catalyzed by Rh2(OAc)4 were futile. By contrast, 2,3-dibromopropene (19) afforded smoothly (E)- and (Z)-dibromocyclopropane carboxylic esters 24 + 25. Alkylation of adenine (18) with 24 + 25 gave (E)- and (Z)-bromo derivatives 21 + 22. Base-catalyzed elimination of HBr resulted in the formation of (Z)- and (E)-methylenecyclopropanecarboxylic esters 26 + 27. More convenient one-pot alkylation−elimination of adenine (18) or 2-amino-6-chloropurine (30) with 24 + 25 afforded (Z)- and (E)-methylenecyclopropane derivatives 26 + 27 and 31 + 32. The Z-isomers were always predominant in these mixtures (Z/E 2/1). Reduction of 26 + 27 and 31 + 32 with DIBALH afforded (Z)- and (E)-methylenecyclopropane alcohols 14 + 16 and 33 + 34. The latter were resolved directly by chromatography. Compounds 14 + 16 were converted to N6-(dimethylamino)methylene derivatives 28 and 29 which were separated and deprotected to give 14 and 16. Reaction of 33 and 34 with HCO2H led to guanine analogues 15 and 17. The 1H NMR spectra of the Z-analogues 14 and 15 are consistent with an anti-like conformation of the nucleobases. By contrast, 1H NMR and IR spectra of bromo ester 21 are indicative of syn-conformation of adenine. Several Z-(hydroxymethyl)methylenecyclopropanes exhibited in vitro antiviral activity in micromolar or submicromolar range against human and murine cytomegalovirus (HCMV and MCMV), Epstein−Barr virus (EBV), human herpes virus 6 (HHV-6), varicella zoster virus (VZV), and hepatitis B virus (HBV). Analogues 14, 15, and 33 were the most effective agents against HCMV (IC50 1−2.1, 0.04−2.1, and 0.8−5.6 μM), MCMV (IC50 2.1, 0.3, and 0.3 μM) and EBV in H-1 (IC50 0.2, 0.3, and 0.7 μM) and Daudi cells (IC50 3.2, 5.6, and 1.2 μM). Adenine analogue 14 was active against HBV (IC50 2 μM), VZV (IC50 2.5 μM), and HHV-6 (IC50 14 μM). Synadenol (14) and the E-isomer (16) were substrates of moderate efficiency for adenosine deaminase from calf intestine. The E-isomer 16 was more reactive than Z-isomer 14. The deamination of 14 effectively stopped at 50% conversion. Synadenol (14) was also deaminated by AMP deaminase from aspergillus sp.
The additions of the enantiomerically pure organozinc reagents 17 and 33 to the THF-aldehyde 1 in the presence of the monodentate Lewis acid boron trifluoride—ether give the nonchelation-controlled addition products 7 and 36, respectively (stereoselectivity 95:5, 86:14). These results provide a route to oligo(tetrahydrofuran)s with the relative stereochemistry trans-syn-cis. A stereodirecting effect of the chiral center in the organozinc reagent 17 is found, leading to simple diastereoselectivies in the reaction with achiral aldehydes and to a matched-mismatched case in the reaction with the chiral aldehyde 1.
The „dimeric” and „trimeric” oligo(tetrahydrofurans) (oligo-THFs) 24, 28, 32, and 38 were synthesized stereoselectively according to a linear and a convergent synthetic strategy. The oligo-THFs thus obtained are important intermediates for the synthesis of artificial ion channels. Furthermore, they can be used in the total synthesis of Annonaceae acetogenins, a class of natural occurring oligo-THFs with promising pharmacological properties.
Nucleoside and nucleotide analogues have proven to be an effective approach toward the development of antiviral compounds. This approach has so far yielded a number of clinically useful antiviral drugs, such as BVDU (brivudin), (val)aciclovir, cidofovir, adefovir dipivoxil, and tenofovir disoproxil fumarate, and current perspectives justify the further development of other nucleoside analogues, such as FV-100, and that of the DAPy-based nucleotide analogues, the 5-aza analogue of cidofovir, and prodrug derivatives thereof.
My search for a selective antiviral chemotherapy started more than 40 years ago with interferon inducers, then shifted to nucleoside analogs with the discovery of BVDU (brivudin), a highly selective anti-HSV-1 and anti-VZV agent, and to dideoxynucleoside analogs such as d4T (stavudine), anti-HIV agents. The search culminated in the discovery of acyclic nucleoside phosphonates (ANPs) (in collaboration with Antonin Holý), a key class of compounds active against HIV, hepatitis B virus, and DNA viruses at large; the best known of these compounds is tenofovir. Along the way, the principle of the non-nucleoside reverse transcriptase inhibitors (NNRTIs) was established. This work, initiated in collaboration with the late Paul A.J. Janssen, eventually led to the identification of rilpivirine as perhaps an "ideal" NNRTI.
Within 25 years after zidovudine (3'-azido-2',3'-dideoxythymidine, AZT) was first described as an inhibitor of HIV replication, 25 anti-HIV drugs have been formally approved for clinical use in the treatment of HIV infections: seven nucleoside reverse transcriptase inhibitors (NRTIs): zidovudine, didanosine, zalcitabine, stavudine, lamivudine, abacavir and emtricitabine; one nucleotide reverse transcriptase inhibitor (NtRTI): tenofovir [in its oral prodrug form: tenofovir disoproxil fumarate (TDF)]; four non-nucleoside reverse transcriptase inhibitors (NNRTIs): nevirapine, delavirdine, efavirenz and etravirine; ten protease inhibitors (PIs): saquinavir, ritonavir, indinavir, nelfinavir, amprenavir, lopinavir, atazanavir, fosamprenavir, tipranavir and darunavir; one fusion inhibitor (FI): enfuvirtide; one co-receptor inhibitor (CRI): maraviroc and one integrase inhibitor (INI): raltegravir. These compounds are used in various drug combination (some at fixed dose) regimens so as to achieve the highest possible benefit and tolerability, and to diminish the risk of virus-drug resistance development.
Purine and pyrimidine analogues remain an important class of drugs in the treatment of cancer. Although these agents share many structural and biochemical characteristics, each compound has unique activities that make it a useful drug. The basis of selectivity of these agents is not clearly denned (because the molecular targets exist in both tumor cells and normal host tissues) but is believed to be primarily due to differences in metabolism and proliferative states between tumor cells and normal cells. For instance, the greater expression of deoxycytidine kinase in leukemias and lym-phomas is believed to contribute to the sensitivity of these malignancies to nucleoside analogues that are activated by this enzyme. Furthermore, most normal cells in a patient are quiescent and, therefore, are not sensitive to these agents. However, the selectivity of antimetabolites is still poor and better agents are needed with fewer toxicities. Analysis of the existing agents identifies three primary characteristics of antimetabolites that are important to their ability to kill tumor cells: sufficient metabolism to active metabolite; long retention of active metabolite; and potent and sustained inhibition of DNA replication or function. The analogue should be a reasonable substrate for the activating enzymes, although clearly this aspect of the activity of an analogue can be affected by the potency of the active metabolite against the enzymatic target. For instance, an analogue that produces a very potent active metabolite would not be as dependent on activation. In addition to all the anabolic enzymes involved in the activation of nucleoside analogues, there are numerous catabolic enzymes that interact with these compounds, and these enzymes can also have profound impact on their biological activity and are important in the activity of all of the purine and pyrimidine antimetabolites. The compound should be a good selective inhibitor of DNA replication and have minimal effects on RNA and protein synthesis, as inhibition of these activities leads to toxicity. The primary intracellular targets of the existing purine and pyrimidine antimetabolites are DNA polymerases, thymidylate synthetase, and ribonucleotide reductase. Although some of the currently approved agents (FUra, mercaptopurine, thioguanine, and aza-Cyd) are converted to ribonucleotide metabolites and are extensively incorporated into RNA, the primary activity of these compounds that results in their antitumor activity is their inhibition of DNA synthesis or disruption of DNA function. Unless there is selective activation in tumor cells, nucleoside analogues that target RNA synthesis or function should be extremely cytotoxic, since all cells require RNA for vitality. As with most other classical antitumor agents, the inhibition of DNA replication is the most important action of purine and pyrimidine metabolites responsible for their antitumor activity. Disruption of de novo purine biosynthesis or RNA effects are secondary to activities that disrupt DNA replication or cause DNA damage. However, inhibition of DNA synthesis is not sufficient to kill a tumor cell. For example, an agent such as aphidicolin, which is a potent inhibitor of DNA replication, is a good cell synchronizer, because it only inhibits DNA synthesis and, unlike nucleoside analogues, it does not cause any lasting inhibition. Once it is removed from the cell, DNA synthesis readily resumes without lasting toxicity. Nucleoside analogues have two attributes that result in a lasting inhibition of DNA replication after removal of the drug by natural processes within the body. First, the active metabolites of these agents are nucleotide analogues, which do not readily penetrate cell membranes and, therefore, are retained in the cell after the drug has been removed, which is an attribute that is unique to this class of antitumor agents. The half-life for the removal of the triphosphates from cells can be quite long, which leads to continued use by the polymerases and, thus, continued inhibition of DNA replication. The intracellular retention time of the active metabolites (nucleoside triphosphate) can vary considerably between the various analogues, and this can have an important effect on the activity of an agent against solid tumor cells. The much longer half-life of dFdC-TP than araCTP is believed to be a primary contributing factor to the solid tumor activity of gemcitabine and the lack of solid tumor activity of araC. Second, nucleosides are incorporated into DNA, resulting in a DNA molecule that is not easily extended and must be repaired before synthesis can resume. Therefore, an agent that causes DNA damage that is poorly or slowly repaired will result in prolonged damage to the DNA, which will lead to the induction of apoptosis. In conclusion, purine and pyrimidine antimetabolites are an important class of drugs used in the treatment of cancer and viral diseases. Although the toxicity of these compounds can limit their usefulness, the antimetabolites will continue to play an important role in the treatment of cancer for the foreseeable future. It is likely that some of the new nucleoside analogues that are currently in the pipeline will be approved for use in the coming years. Although drug discovery is being pursued of new anticancer agents that target enzyme activities more closely associated with the cancer phenotype, the unpredicted toxicity of these new agents could still be a major issue of these agents as well. The design, synthesis, and evaluation of new purine and pyrimidine analogues is still a productive area for discovering new drugs for the treatment of cancer, since many years of knowledge with respect to their potential actions and toxicity has accumulated. Novel nucleoside analogues with unique actions are continuously being identified, and the information provided in this review indicates that small structural modifications of nucleoside analogues can have profound effects on their chemical stability and spectrum of biological activity.
A guanine derivative with an acyclic side chain, 2-hydroxyethoxymethyl, at position 9 has potent antiviral activity [dose for 50% inhibition (ED50) = 0.1 μM] against herpes simplex virus type 1. This acyclic nucleoside analog, termed acycloguanosine, is converted to a monophosphate by a virus-specified pyrimidine deoxynucleoside (thymidine) kinase and is subsequently converted to acycloguanosine di- and triphosphates. In the uninfected host cell (Vero) these phosphorylations of acycloguanosine occur to a very limited extent. Acycloguanosine triphosphate inhibits herpes simplex virus DNA polymerase (DNA nucleotidyltransferase) 10-30 times more effectively than cellular (HeLa S3) DNA polymerase. These factors contribute to the drug's selectivity; inhibition of growth of the host cell requires a 3000-fold greater concentration of drug than does the inhibition of viral multiplication. There is, moreover, the strong possibility of chain termination of the viral DNA by incorporation of acycloguanosine.
The identity of the kinase that phosphorylates acycloguanosine was determined after separation of the cellular and virus-specified thymidine kinase activities by affinity chromatography, by reversal studies with thymidine, and by the lack of monophosphate formation in a temperature-sensitive, thymidine kinase-deficient mutant of the KOS strain of herpes simplex virus type 1 (tsA1).
Of a series of nucleoside analogues synthesised, 9-(2-hydroxyethoxymethyl) guanine was found to have marked antiviral activity in animal models of herpes virus infections, associated with very low toxicity.
Of a series of five newly synthesized 2'-deoxyuridine derivatives, including 5-vinyl-dUrd, 5-ethynyl-dUrd, 5-(1-chlorovinyl)-dUrd, (E)-5-(2-bromovinyl)-dUrd, and (E)-5-(2-iodovinyl)-dUrd, the last two compounds were found to exert a marked inhibitory effect on the replication of herpes simplex virus type 1 [ID50 (mean inhibitory dose), 0.004-0.02 microgram/ml]. Both (E)-5-(2-bromovinyl)-dUrd and (E)-5-(2-iodovinyl)-dUrd were highly selective in their anti-herpes activity in that they did not affect the growth or metabolism of the host (primary rabbit kidney) cells unless drug concentrations were used that were 5,000- to 10,000-fold greater than those required to inhibit virus multiplication. In this sense (E)-5-(2-bromovinyl)-dUrd and (E)-5-(2-iodovinyl)-dUrd proved more selective in their activity against herpes simplex virus type 1 than all other anti-herpes compounds that have been described so far. In animal model systems (namely, cutaneous herpes infections of athymic nude mice), (E)-5-(2-bromovinyl)-dUrd suppressed the development of herpetic skin lesions and mortality therewith associated, whether the compound was administered topically or systemically. Under the same conditions, the standard anti-herpes drug 5-iodo-dUrd (Idoxuridine) offered little, if any, protection. Although the precise mechanism of action of (E)-5-(2-bromovinyl)-dUrd and (E)-5-(2-iodovinyl)-dUrd remains to be established, preliminary findings indicate that they do not specifically act at the thymidylate synthetase step.
Solution structure of anti-AIDS drug, 2',3'-dideoxyinosine (ddI) has been assessed by NMR spectroscopy and pseudorotational analysis in conjunction with its analogues: 2',3'-dideoxyadenosine (ddA), 2',3'-dideoxyguanosine (ddG) and 2',3'-dideoxycytidine (ddC). The absence of 3'-hydroxyl groups in these compounds has prompted us to establish the relationship between proton-proton and corresponding endocyclic torsion angles in the 2',3'-dideoxyribofuranose moiety on the basis of five available crystal structures of 2',3'-dideoxynucleosides. A subsequent pseudorotational analysis on ddI (1), ddA (2), ddG (3) and ddC (4) shows that the twist C2'exo-C3'-endo forms of sugar are overwhelmingly preferred (75-80%) over the C2'-endo envelope forms. The phase angles (P) for North and South conformers with the corresponding puckering amplitude (psi m) for ddI (1), ddA (2) and ddG (3) are as follows: PN = 0.1 degrees, PS = 161 degrees and psi m = 34.1 degrees for ddI (1); PN = 1.4 degrees, PS = 160 degrees and psi m = 34.2 degrees for ddA (2) and PN = 2.4 degrees, PS = 163 degrees and psi m = 33.6 degrees for ddG (3). The predominant North conformer of ddC (4) is intermediate between twist C2'-exo-C3'-endo and C3'-endo envelope (P = 10.9 degrees) with a psi m of 34.7 degrees. Note that these preponderant North-sugar structures (approx. 75-80%) found in the solution studies of ddI (1), ddA (2), dG (3) and ddC (4) are not reflected in the X-ray crystal structures of 2',3'-dideoxyadenosine and 2',3'-dideoxycytidine. The constituent sugar residues in both of these crystal structures denosine and 2',3'-dideoxycytidine. The constituent sugar residues in both of these crystal structures are found to be in the South-type geometry (ddA crystalizes in C3'-exo envelope form, while ddC adopts the form intermediate between the C3'-exo envelope and C3'-endo-C4'-exo twist form). This means that X-ray structures of ddA (2) and ddC (4) only represent the minor conformer of the overall pseudorotamer population in solution. An assumption that the structure of the pentofuranose sugar (i.e. P and psi m) participating in conformational equilibrium described by the two-state model remains unchanged at different temperatures has been experimentally validated by assessing five unknown pseudorotational parameters with eight unique observables (3J1'2', 3J1'2", 3J2'3', 3J2'3", 3J2"3', 3J2"3", 3J3'4' and 3J3"4') for 2',3'-dideoxynucleosides.(ABSTRACT TRUNCATED AT 400 WORDS)
Various 3-hydroxy-2-phosphonylmethoxypropyl (HPMP) and 2-phosphonylmethoxyethyl (PME) derivatives of purine [adenine (A), guanine (G), 2,6-diaminopurine (DAP), 2-monoaminopurine (MAP), hypoxanthine (HX)] and pyrimidine [cytosine (C), uracil (U), thymine (T)] have been evaluated for their antiviral properties. PMEDAP, (S)-HPMPA [and the cyclic phosphonate thereof, (S)-cHPMPA)], (S)-HPMPC, PMEG, PMEA, HPMPG and HPMPDAP proved to be effective inhibitors of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2). (S)-HPMPA and (S)-cHPMPA were the most effective inhibitors of varicella-zoster virus (VZV), and (S)-HPMPC was the most effective inhibitor of cytomegalovirus (CMV). Against adenovirus (types 2, 3 and 4) and vaccinia virus again (S)-HPMPA and (S)-cHPMPA showed the greatest inhibitory activity. As a rule, the PME derivates were much less inhibitory to VZV, CMV, vaccinia and adenovirus than the HPMP derivatives. However, PMEA, PMEDAP and PMEMAP showed marked and selective activity against the human immunodeficiency virus (HIV). (S)-HPMPA was selected for further evaluation in animal model infections. It proved efficacious in the topical treatment of HSV-1 keratitis in rabbits and cutaneous HSV-1 infection in hairless mice, and in the systemic treatment of both HSV-1 and vaccinia virus infections in mice.
Virazole is a synthetic nucleoside active in tissue culture against at least 16 DNA and RNA viruses. Applied topically, it inhibits herpetic keratitis in rabbits and tail lesions induced by herpes, vaccinia, and vesicular stomatitis viruses in mice. Injected intraperitoneally into mice, it inhibits splenomegaly and hepatomegaly induced by Friend leukemia virus and respiratory infections caused by influenza A0, A2, and B viruses and parainfluenza 1 virus. Oral or aerosol treatment of parainfluenza virus infections is also effective.
Torsion angles C-H between the sugar C-H bonds were deduced from X-ray data on 60 nucleosides and nucleoside phosphates with the aid of the pseudorotation model for five-membered rings. Two pseudorotation ranges were considered classified as type N [C(2′)-exo, C(3′)-endo] and type S [C(2′)-endo, C(3′)-exo] conformers, each characterized by a narrow range of the phase angle of pseudorotation P. The various values of φHH along the ring bonds, and hence the corresponding coupling constants, must obey certain interrelationships. It was shown that the coupling J2′3′ as well as the sum J1′2′ + J3′4′ should be practically independent of the position of the N ⇄ S conformational equilibrium; values taken from the literature were then used to extract a set of Karplus parameters valid for the system in question. The effect of pseudorotation (within each of the two ranges of P) on the coupling constants is explored. For all practical purposes, the percentage of S-type conformer in aqueous solution of the common nucleosides and nucleoside phosphates can be calculated by taking 10J1′2′. The purine ribosides show a small conformational preference for the S type conformer (ΔG°av = -0.12 kcal mol-1), whereas the pyrimidine derivatives slightly favor the N-type ribose conformer (ΔG°av = +0.16 kcal mol-1). Published coupling constants of two compounds in which a keto group must lie over the sugar ring, orotidine and β-cyanuric acid ribonucleoside, were reinterpreted as follows: (i) the ribose ring in these compounds is "flatter" than in the normal series, (ii) the N type conformer is favored over the S type by 0.4-0.5 kcal mol-1, and (iii) the N type rings are characterized by a higher P value than normally occurs. On the basis of known coupling cosstants of dinucleoside phosphates at various temperatures, we proposed a three-state dynamic conformational equilibrium model for the common dimers: (i) unstacked S type, (ii) unstacked N type, and (iii) fully stacked N type. The 2′,5′ dimers, A2′p5′A and A2′p5′C, behave in another manner; two stacked forms seem to be present, differing in the conformation of the 2′-ribose residue. The deoxyribose ring in all common deoxyribonucleosides and their 5′-phosphates show equilibrium compositions that are substantially biased toward the S type conformer over a wide temperature range. This preference may be due to an entropy, rather than to an enthalpy, difference.
The amplitude (τm) and phase angle of pseudorotation (P) of the sugar ring in several β-purine and β-pyrimidine nucleosides and nucleotides were calculated from the known endocyclic torsion angles. A statistical classification of the number of compounds for which P falls in a given range shows that only two relatively narrow pseudorotational ranges are preferred by β sugars in the solid, each occupying less than 10% of the total pathway.
Bromovinyldeoxyuridine (BVdUrd) is a potent antiherpesvirus compound with low cytotoxicity. To gain an insight into its selectivity and mechanism of inhibition, we chemically synthesized the 5'-triphosphate of BVdUrd, BVdUTP, and tested its effect on the activities of DNA polymerases [DNA nucleotidyltransferase (DNA directed), EC 2.7.7.7] of two herpesviruses--i.e., herpes simplex virus type 1 (HSV-1) and Epstein-Barr virus (EBV)--as well as cellular DNA polymerases alpha, beta, and gamma. The effects on the DNA polymerases were determined under assay conditions optimal for the individual polymerases. We found that the BVdUTP was considerably more inhibityory to the utilization of dTTP by the HSV-1 DNA polymerase then by the cellular DNA polymerases. For instance, as little as 1 microM BVdUTP inhibited the utilization of dTTP by HSV-1 DNA polymerase 50%, whereas the same concentration inhibited the DNA polymerase alpha and the DNA polymerase beta activities only 9% and 3%, respectively. The BVdUTP inhibited DNA synthesis by competing with the natural substrate, dTTP. The Km for dTTP and the Ki for the BVdUTP of the HSV-1 DNA polymerase were 0.66 and 0.25 microM, respectively. Kinetic analyses with the DNA polymerases alpha and beta and the EBV DNA polymerase also reflected a similar difference in sensitivity between the HSV-1 enzyme and other enzymes. Increasing the concentration of either the DNA template or the enzyme in the reaction mixture did not bring about a significant change in the extent of inhibition. Preincubation of the inhibitor with the enzyme was not necessary for inhibition. Studies on time course of inhibition revealed that the compound is inhibitory even after the initiation of DNA synthesis. These studies indicate that the ability of BVdUTP to preferentially inhibit the HSV-1 DNA polymerase may contribute towards its selective inhibition of the viral DNA replication in infected cells.
Several water-soluble ester derivatives of acyclovir [9-[(2-hydroxyethoxy)methyl]guanine], i.e., the 2'-O-glycyl-, 2'-O-alpha-alanyl-, 2'-O-beta-alanyl- and 2'-O-3-carboxypropionyl esters, were synthesized and evaluated for their antiviral activity in cell culture. The compounds were all prepared directly from acyclovir by application of the usual esterification methods with the appropriate acyl precursors and isolated as their hydrochloride or sodium salts. When assayed in primary rabbit kidney cell cultures against various herpes simplex virus type 1 and type 2 strains, the four acyclovir esters proved almost as active as acyclovir itself, suggesting that they were readily hydrolyzed to release the parent compound.
A rational approach to the design of antiherpetic nucleoside analogues is based in part on the broad specificity of virus-coded thymidine kinases. Herpes virus thymidine kinase 'activates' many 5-substituted 2'-deoxyuridines, analogues of thymidine (e.g., idoxuridine, trifluridine, edoxudine, brivudine), 5-substituted arabinofuranosyluracil derivatives (e.g., 5-Et-Ara-U, BV-Ara-U, Cl-Ara-U), acyclonucleosides of guanine (e.g., aciclovir, ganciclovir, penciclovir), and purine nucleosides with the pentafuranosyl ring replaced by a cyclobutane ring (e.g., cyclobut-G, cyclobut-A). Activation involves selective, and frequently regiospecific, phosphorylation of these analogues to the 5'-monophosphates. These are further phosphorylated by cellular enzymes to the 5'-triphosphates, which are usually competitive inhibitors of the viral-coded DNA polymerases. Some analogues are also incorporated into viral, and to a lesser extent cellular, DNA. A recent, unusual, exception is human cytomegalovirus, which does not code for a thymidine kinase, but for a protein with the sequence characteristics of protein kinase and which phosphorylates ganciclovir to its 5'-monophosphate. The interaction of the analogues with cellular catabolic enzymes such as uridine and thymidine nucleoside phosphorylases is also discussed, as is the relationship between physicochemical properties (configuration, conformation, electronic and hydrophobic parameters) and antiviral activities, with particular reference to those drugs that are licensed, or under consideration, for clinical use.
The need for antiviral drugs is growing rapidly as more viral diseases are recognized. The methods used to discover antiviral drugs have evolved considerably over the past 40 years and the overall process of discovery can be broken down into subprocesses which include lead generation, lead optimization and lead development. Various methods are now employed to ensure these processes are carried out efficiently. For lead generation, screening methodologies have developed to the extent where hundreds of thousands of compounds can be screened against a particular target. An alternative approach is to use the structures of enzyme substrates as a starting point for drug discovery. Much use is now made of X-ray crystallographic data of target-inhibitor complexes for the optimization of lead structures, and methods for preparing libraries of compounds to assist both generation and optimization of leads are well-developed. The methods used to predict and improve the pharmacokinetic properties of compounds are also changing rapidly. Finally, novel approaches to antiviral therapy using oligonucleotide-based compounds or by modulating the host immune response are also being explored. This review discusses these approaches, provides examples of where their application has been successful and sets them against a historical background.
This review provides a summary of the most useful approaches that have been used to prepare nucleoside triphosphates. The goal is to illustrate the most practical methods for obtaining nucleoside triphosphates and, more importantly, to hint at areas wherein further research might lead to superior approaches. Syntheses of some nucleoside triphosphate analogues are discussed to illustrate how synthetic methods for obtaining nucleoside triphosphates have been applied in different ways.
6-Hydroxypyrimidines substituted at positions 2 and 4 by hydrogen, methyl, amino, cyclopropylamino, dimethylamino, methylsulfanyl, or hydroxyl group afford by the reaction with diisopropyl 2-(chloroethoxy)methylphosphonate in the presence of NaH, Cs(2)CO(3), or DBU a mixture of N(1)- and O(6)-[2-(diisopropylphosphorylmethoxy)ethyl] isomers which were converted to the free phosphonic acids by treatment with bromotrimethylsilane followed by hydrolysis. Analogously, 2,4-diamino-6-hydroxypyrimidine gave on reaction with [(R)- and (S)-2-(diisopropylphosphorylmethoxy)propyl] tosylate, followed by deprotection, the enantiomeric 6-[2-(phosphonomethoxy)propoxy]pyrimidines. 2,4-Diamino-6-sulfanylpyrimidine gave, on treatment with diisopropyl 2-(chloroethoxy)methylphosphonate in the presence of NaH and subsequent deprotection, 2,4-diamino-6-[[2-(phosphonomethoxy)ethyl]sulfanyl]pyrimidine. 2-Amino-4-hydroxy-6-[2-(phosphonomethoxy)ethyl]pyrimidine was obtained from the appropriate 2-amino-4-chloropyrimidine derivative by alkaline hydrolysis and ester cleavage. Direct alkylation of 2-amino-4,6-dihydroxypyrimidine afforded a mixture of 2-amino-4,6-bis[2-(phosphonomethoxy)ethyl]- and 2-amino-1,4-bis[2-(phosphonomethoxy)ethyl]pyrimidine. None of the N(1)-[2-(phosphonomethoxy)ethyl] isomers exhibited any antiviral activity against DNA viruses or RNA viruses tested in vitro. On the contrary, the O(6)-isomers, namely the compounds derived from 2,4-diamino-, 2-amino-4-hydroxy-, or 2-amino-4-[2-(phosphonomethoxy)ethoxy]-6-hydroxypyrimidine, inhibited the replication of herpes viruses [herpes simplex type 1 (HSV-1) and type 2 (HSV-2), varicella-zoster virus (VZV), and cytomegalovirus (CMV)] and retroviruses [Moloney sarcoma virus (MSV) and human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2)], their activity being most pronounced against the latter. The antiviral activity was lower if the oxygen at the position 6 was replaced by a sulfur atom, as in 2,4-diamino-6-[2-(phosphonomethoxy)ethylsulfanyl]pyrimidine. In analogy to N(9)-[2-(phosphonomethoxy)propyl]-2,6-diaminopurine (PMPDAP), solely the (R)-2,4-diamino-6-[2-(phosphonomethoxy)propoxy]pyrimidine exerted antiviral activity, whereas its (S)-enantiomer was essentially inactive.
2,4-Diamino-6-hydroxypyrimidines substituted in position 5 by an allyl, benzyl, cyanomethyl, ethoxycarbonylmethyl, phenyl, cyclopropyl, or methyl group were prepared either by C5-alkylation or by formation of the pyrimidine ring by cyclization. Their alkylation with 2-[(diisopropoxyphosphoryl)methoxy]ethyl tosylate afforded N1- and O6-regioisomers that were separated and converted to the free phosphonic acids by treatment with bromotrimethylsilane followed by hydrolysis. Reaction of 2,4-diamino-6-[[(diisopropoxyphosphoryl)methoxy]ethoxy]pyrimidine with elemental bromine, N-chloro-, or N-iodosuccinimide gave the corresponding phosphorus-protected 5-bromo-, 5-chloro-, and 5-iodo derivatives, respectively. Their deprotection afforded 2,4-diamino-5-bromo- and -5-chloro-6-[2-(phosphonomethoxy)ethoxy]pyrimidines. 2,4-Diamino-5-methyl-6-[2-(phosphonomethoxy)ethoxy]pyrimidine was synthesized also by cross-coupling of the 5-bromo compound with AlMe(3), followed by deprotection. The compounds showed poor, if any, inhibitory activity against DNA viruses such as herpes simplex virus type 1 and type 2, cytomegalovirus, varicella-zoster virus, and vaccinia virus. In contrast, several 5-substituted 2,4-diaminopyrimidine derivatives markedly inhibited retrovirus replication in cell culture. The 5-methyl derivative was exquisitely inhibitory to human immunodeficiency virus and Moloney murine sarcoma virus-induced cytopathicity in cell culture (EC(50) approximately 0.00018 mumol/mL) but also cytostatic to CEM cell cultures. In contrast, the 5-halogen-substituted derivatives showed pronounced antiretroviral activity (EC(50) = 0.0023-0.0110 mumol/mL), comparable to that of the reference drugs adefovir and tenofovir, but were devoid of measurable toxicity at 0.3 mumol/mL.
(E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU, Brivudin, Zostex, Zerpex, Zonavir), now more than 20 years after its discovery, still stands out as a highly potent and selective inhibitor of herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV) infections. It has been used in the topical treatment of herpetic keratitis and recurrent herpes labialis and the systemic (oral) treatment of herpes zoster (zona, shingles). The high selectivity of BVDU towards HSV-1 and VZV depends primarily on a specific phosphorylation of BVDU to its 5'-diphosphate (DP) by the virus-encoded thymidine kinase (TK). After further phosphorylation (by cellular enzymes), to the 5'-triphosphate (TP), the compound interferes as a competitive inhibitor/alternate substrate with the viral DNA polymerase. The specific phosphorylation by the HSV- and VZV-induced TK also explains the marked cytostatic activity of BVDU against tumor cells that have been transduced by the viral TK genes. This finding offers considerable potential in a combined gene therapy/chemotherapy approach for cancer. To the extent that BVDU or its analogues (i.e., BVaraU) are degraded (by thymidine phosphorylase) to (E)-5-(2-bromovinyl)uracil (BVU), they may potentiate the anticancer potency, as well as toxicity, of 5-fluorouracil. This ensues from the direct inactivating effect of BVU on dihydropyrimidine dehydrogenase, the enzyme that initiates the degradative pathway of 5-fluorouracil. The prime determinant in the unique behavior of BVDU is its (E)-5-(2-bromovinyl) substituent. Numerous BVDU analogues have been described that, when equipped with this particular pharmacophore, demonstrate an activity spectrum characteristic of BVDU, including selective anti-VZV activity.
Almost 20 years after the broad antiviral activity spectrum of the first acyclic nucleoside phosphonates was described, several of these compounds have become important therapies for DNA virus and retrovirus infections. Here, we review the discovery and development of acyclic nucleoside phosphonates, focusing on cidofovir and its potential in the treatment of various herpes-, papilloma-, polyoma-, adeno- and pox-virus infections, adefovir for the treatment of hepatitis B and tenofovir for the treatment of AIDS and the prevention of HIV infections.
Following the discovery of the first effective antiviral compound (idoxuridine) in 1959, nucleoside analogues, especially acyclovir (ACV) for the treatment of herpesvirus infections, have dominated antiviral therapy for several decades. However, ACV and similar acyclic nucleosides suffer from low aqueous solubility and low bioavailability following oral administration. Derivatives of acyclic nucleosides, typically esters, were developed to overcome this problem and valaciclovir, the valine ester of ACV, was among the first of a new series of compounds that were readily metabolized upon oral administration to produce the antiviral nucleoside in vivo, thus increasing the bioavailility by several fold. Concurrently, famciclovir was developed as an oral formulation of penciclovir. These antiviral ‘prodrugs’ thus established a principle that has led to many successful drugs including both nucleoside and nucleotide analogues for the control of several virus infections, notably those caused by herpes-, retro- and hepatitisviruses. This review will chart the origins and development of the most important of the antiviral prodrugs to date.
British Journal of Pharmacology (2006) 147, 1–11. doi:10.1038/sj.bjp.0706446