Highlights in the Discovery of Antiviral Drugs: A Personal Retrospective

Structural Studies and Structure Activity Relationships for Novel Computationally Designed Non-nucleoside Inhibitors and Their Interactions With HIV-1 Reverse Transcriptase

Reverse transcriptase (RT) from the human immunodeficiency virus continues to be an attractive drug target for antiretroviral therapy. June 2022 will commemorate the 30th anniversary of the first Human Immunodeficiency Virus (HIV) RT crystal structure complex that was solved with non-nucleoside reverse transcriptase inhibitor nevirapine. The release of this structure opened opportunities for designing many families of non-nucleoside reverse transcriptase inhibitors (NNRTIs). In paying tribute to the first RT-nevirapine structure, we have developed several compound classes targeting the non-nucleoside inhibitor binding pocket of HIV RT. Extensive analysis of crystal structures of RT in complex with the compounds informed iterations of structure-based drug design. Structures of seven additional complexes were determined and analyzed to summarize key interactions with residues in the non-nucleoside inhibitor binding pocket (NNIBP) of RT. Additional insights comparing structures with antiviral data and results from molecular dynamics simulations elucidate key interactions and dynamics between the nucleotide and non-nucleoside binding sites.

Newly Emerging Strategies in Antiviral Drug Discovery: Dedicated to Prof. Dr. Erik De Clercq on Occasion of His 80th Anniversary

Viral infections pose a persistent threat to human health. The relentless epidemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a global health problem, with millions of infections and fatalities so far. Traditional approaches such as random screening and optimization of lead compounds by organic synthesis have become extremely resource- and time-consuming. Various modern innovative methods or integrated paradigms are now being applied to drug discovery for significant resistance in order to simplify the drug process. This review provides an overview of newly emerging antiviral strategies, including proteolysis targeting chimera (PROTAC), ribonuclease targeting chimera (RIBOTAC), targeted covalent inhibitors, topology-matching design and antiviral drug delivery system. This article is dedicated to Prof. Dr. Erik De Clercq, an internationally renowned expert in the antiviral drug research field, on the occasion of his 80th anniversary.

Crystal structure of cis-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N)bis-(thio-cyanato-κN)chromium(III) bromide from synchrotron X-ray diffraction data

The crystal structure of the title complex, cis-[Cr(NCS)2(cyclam)]Br (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-decane, C10H24N4), has been determined from synchrotron X-ray data. The asymmetric unit contains one [Cr(NCS)2(cyclam)]+ cation and one bromide anion. The CrIII ion of the complex cation is coordinated by the four N atoms of the cyclam ligand and by two N-coordinating NCS groups in a cis arrangement, displaying a distorted octa-hedral coordination sphere. The Cr-N(cyclam) bond lengths are in the range 2.075 (3) to 2.081 (3) Å while the average Cr-N(NCS) bond length is 1.996 (16) Å. The macrocyclic cyclam moiety adopts the most stable cis-V conformation. The crystal structure is stabilized by inter-molecular hydrogen bonds involving the cyclam N-H groups as donor groups, and the bromide anion and the S atom of one of the NCS ligands as acceptor groups.

Drug Discovery of Nucleos(t)ide Antiviral Agents: Dedicated to Prof. Dr. Erik De Clercq on Occasion of His 80th Birthday

Nucleoside and nucleotide analogues are essential antivirals in the treatment of infectious diseases such as human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), herpes simplex virus (HSV), varicella-zoster virus (VZV), and human cytomegalovirus (HCMV). To celebrate the 80th birthday of Prof. Dr. Erik De Clercq on 28 March 2021, this review provides an overview of his contributions to eight approved nucleos(t)ide drugs: (i) three adenosine nucleotide analogues, namely tenofovir disoproxil fumarate (Viread^®) and tenofovir alafenamide (Vemlidy^®) against HIV and HBV infections and adefovir dipivoxil (Hepsera^®) against HBV infections; (ii) two thymidine nucleoside analogues, namely brivudine (Zostex^®) against HSV-1 and VZV infections and stavudine (Zerit^®) against HIV infections; (iii) two guanosine analogues, namely valacyclovir (Valtrex^®, Zelitrex^®) against HSV and VZV and rabacfosadine (Tanovea^®-CA1) for the treatment of lymphoma in dogs; and (iv) one cytidine nucleotide analogue, namely cidofovir (Vistide^®) for the treatment of HCMV retinitis in AIDS patients. Although adefovir dipivoxil, stavudine, and cidofovir are virtually discontinued for clinical use, tenofovir disoproxil fumarate and tenofovir alafenamide remain the most important antivirals against HIV and HBV infections worldwide. Overall, the broad-spectrum antiviral potential of nucleos(t)ide analogues supports their development to treat or prevent current and emerging infectious diseases worldwide.

Crystal structure of 3,14-diethyl-2,6,13,17-tetra-azoniatri-cyclo-[16.4.0.07,12]docosane tetra-chloride tetra-hydrate from synchrotron X-ray data

The crystal structure of the hydrated title salt, C22H48N4 4+·4Cl-·4H2O (C22H48N4 = H4 L = 3,14-diethyl-2,6,13,17-tetra-azoniatri-cyclo-[16.4.0.07,12]doco-sa-ne), has been determined using synchrotron radiation at 220 K. The structure determination reveals that protonation has occurred at all four amine N atoms. The asymmetric unit comprises one half of the macrocyclic cation (completed by crystallographic inversion symmetry), two chloride anions and two water mol-ecules. The macrocyclic ring of the tetra-cation adopts an exodentate (3,4,3,4)-D conformation. The crystal structure is stabilized by inter-molecular hydrogen bonds involving the macrocycle N-H groups and water O-H groups as donors, and the O atoms of the water mol-ecules and chloride anions as acceptors, giving rise to a three-dimensional network.

A review on recent trends of antiviral nanoparticles and airborne filters: special insight on COVID-19 virus

Novel corona virus (COVID-19) pandemic in the last 4 months stimulates the international scientific community to search for vaccine of antiviral agents suitable for in activating the virus inside and outside the human body. More than 4 million people globally are infected by the virus and about 300,000 dead cases until this moment. The ventilation and airborne filters are also investigated aiming to develop an efficient antiviral filtration technology. Human secretion of the infected person as nasal or saliva droplets goes as airborne and distributes the virus everywhere around the person. N95 and N98 filters are the must use filters for capturing particles of sizes around 300 nm. The average size of the novel corona virus (COVID-19) is 100 nm and there is no standard or special filter suitable for this virus. The nanoparticle-coated airborne filter is a suitable technique in this regard. While the efficiency of this type of filters still needs to be enhanced, new developed nanofiber filters are proposed. Most recently, the charged nanofiber filters of sizes below 100 nm are developed and provide an efficient viral filtration and inactivation. The efficiency of filter must be kept at accepted level without increasing the pressure drop. The present review outlines the most efficient antiviral nanoparticles including the recent functional nanoparticles. The filtration theory, filtration modeling, filter testing, and different types of filter with special concentration on the charged nanofiber filter were discussed. The charged nanofiber filter able to capture novel corona virus (COVID-19) with 94% efficiency and a pressure drop less than 20 MPa.

Fragment-based approach to novel bioactive purine derivatives

Using purine as a scaffold, the methods for preparation of novel 2-aminopurine and purine derivatives substituted at position C 6 by the fragments of natural amino acids, short peptides, and N-heterocycles, including enantiopure ones, have been proposed. The methods for determination of the enantiomeric purity of the obtained chiral compounds have been developed. Conjugates exhibiting high antimycobacterial or anti-herpesvirus activity against both laboratory and multidrug-resistant strains were revealed among the obtained compounds.

An overview of functional nanoparticles as novel emerging antiviral therapeutic agents

Research on highly effective antiviral drugs is essential for preventing the spread of infections and reducing losses. Recently, many functional nanoparticles have been shown to possess remarkable antiviral ability, such as quantum dots, gold and silver nanoparticles, nanoclusters, carbon dots, graphene oxide, silicon materials, polymers and dendrimers. Despite their difference in antiviral mechanism and inhibition efficacy, these functional nanoparticles-based structures have unique features as potential antiviral candidates. In this topical review, we highlight the antiviral efficacy and mechanism of these nanoparticles. Specifically, we introduce various methods for analyzing the viricidal activity of functional nanoparticles and the latest advances in antiviral functional nanoparticles. Furthermore, we systematically describe the advantages and disadvantages of these functional nanoparticles in viricidal applications. Finally, we discuss the challenges and prospects of antiviral nanostructures. This topic review covers 132 papers and will enrich our knowledge about the antiviral efficacy and mechanism of various functional nanoparticles.

Crystal structure of trans-di-chlorido-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N)chromium(III) bis-(form-amide-κO)(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N)chromium(III) bis-[tetra-chlorido-zincate(II)]

The structure of the title compound, [CrCl2(C10H24N4)][Cr(HCONH2)2(C10H24N4)][ZnCl4]2 (C10H24N4 = 1,4,8,11-tetra-aza-cyclo-tetra-decane, cyclam; HCONH2 = formamide, fa), has been determined from synchrotron X-ray data. The asymmetric unit contains two independent halves of the [CrCl2(cyclam)]+ and [Cr(fa)(cyclam)]3+ cations, and one tetra-chlorido-zincate anion. In each complex cation, the CrIII ion is coordinated by the four N atoms of the cyclam ligand in the equatorial plane and two Cl ligands or two O-bonded formamide mol-ecules in a trans axial arrangement, displaying a distorted octa-hedral geometry with crystallographic inversion symmetry. The Cr-N(cyclam) bond lengths are in the range 2.061 (2) to 2.074 (2) Å, while the Cr-Cl and Cr-O(fa) bond distances are 2.3194 (7) and 1.9953 (19) Å, respectively. The macrocyclic cyclam moieties adopt the centrosymmetric trans-III conformation with six- and five-membered chelate rings in chair and gauche conformations. The crystal structure is stabilized by inter-molecular hydrogen bonds involving the NH or CH groups of cyclam and the NH2 group of coordinated formamide as donors, and Cl atoms of the ZnCl4 2- anion as acceptors.

The Discovery and Development of Oxalamide and Pyrrole Small Molecule Inhibitors of gp120 and HIV Entry - A Review

Human immunodeficiency virus type-1 (HIV-1) is the causative agent responsible for the acquired immunodeficiency syndrome (AIDS) pandemic. More than 60 million infections and 25 million deaths have occurred since AIDS was first identified in the early 1980s. Advances in available therapeutics, in particular combination antiretroviral therapy, have significantly improved the treatment of HIV infection and have facilitated the shift from high mortality and morbidity to that of a manageable chronic disease. Unfortunately, none of the currently available drugs are curative of HIV. To deal with the rapid emergence of drug resistance, off-target effects, and the overall difficulty of eradicating the virus, an urgent need exists to develop new drugs, especially against targets critically important for the HIV-1 life cycle. Viral entry, which involves the interaction of the surface envelope glycoprotein, gp120, with the cellular receptor, CD4, is the first step of HIV-1 infection. Gp120 has been validated as an attractive target for anti-HIV-1 drug design or novel HIV detection tools. Several small molecule gp120 antagonists are currently under investigation as potential entry inhibitors. Pyrrole, piperazine, triazole, pyrazolinone, oxalamide, and piperidine derivatives, among others, have been investigated as gp120 antagonist candidates. Herein, we discuss the current state of research with respect to the design, synthesis and biological evaluation of oxalamide derivatives and five-membered heterocycles, namely, the pyrrole-containing small molecule as inhibitors of gp120 and HIV entry.

New HSV-1 Anti-Viral 1'-Homocarbocyclic Nucleoside Analogs with an Optically Active Substituted Bicyclo[2.2.1]Heptane Fragment as a Glycoside Moiety

New 1′-homocarbanucleoside analogs with an optically active substituted bicyclo[2.2.1]heptane skeleton as sugar moiety were synthesized. The pyrimidine analogs with uracil, 5-fluorouracil, thymine and cytosine and key intermediate with 6-chloropurine (5) as nucleobases were synthesized by a selective Mitsunobu reaction on the primary hydroxymethyl group in the presence of 5-endo-hydroxyl group. Adenine and 6-substituted adenine homonucleosides were obtained by the substitution of the 6-chlorine atom of the key intermediate 5 with ammonia and selected amines, and 6-methoxy- and 6-ethoxy substituted purine homonucleosides by reaction with the corresponding alkoxides. No derivatives appeared active against entero, yellow fever, chikungunya, and adeno type 1viruses. Two compounds (6j and 6d) had lower IC₅₀ (15 ± 2 and 21 ± 4 µM) and compound 6f had an identical value of IC₅₀ (28 ± 4 µM) to that of acyclovir, suggesting that the bicyclo[2.2.1]heptane skeleton could be further studied to find a candidate for sugar moiety of the nucleosides.

Synthesis, Crystal Structure, Spectroscopic Properties, and Hirshfeld Surface Analysis of Diaqua [3,14-dimethyl-2,6,13,17 tetraazatricyclo(16.4.0.07,12)docosane]copper(II) Dibromide

A newly prepared Cu(II) complex salt, Cu(L1)(H2O)2Br2, where L1 is 3,14-dimethyl-2,6,13,17-tetraazatricyclo(16.4.0.07,12) docosane, is characterized by elemental and crystallographic analyses. The Cu(II) center is coordinated by four nitrogen atoms of macrocyclic ligand and the axial position by two water molecules. The macrocyclic ligand adopts an optimally stable trans-III conformation with normal Cu–N bond lengths of 2.018 (3) and 2.049 (3) Å and long axial Cu1–O1W length of 2.632 (3) Å due to the Jahn–Teller effect. The complex is stabilized by hydrogen bonds formed between the O atoms of water molecules and bromide anions. The bromide anion is connected to the neighboring complex cations and water molecules through N–H···Br and O–H···Br hydrogen bonds, respectively. The g-factors obtained from the electron spin resonance spectrum show the typical trend of g∥ > g⊥ > 2.0023, which is in a good accordance to the dx2-y2 ground state. It reveals a coordination sphere of tetragonal symmetry for the Cu(II) ion. The infrared and electronic absorption spectral properties of the complex are also discussed. Hirshfeld surface analysis represents that the H···H, H···Br/Br···H and H···O/O···H contacts are the major molecular interactions in the prepared complex.

Acyclic nucleoside phosphonates containing the amide bond: hydroxy derivatives

Abstract

To study the influence of a linker rigidity and changes in donor-acceptor properties, three series of nucleotide analogs containing a P-X-HN-C(O)- residue (X=CH(OH)CH₂, CH(OH)CH₂CH₂, CH₂CH(OH)CH₂) as a replacement for the P-CH₂-O-CHR- fragment in acyclic nucleoside phosphonates, e.g., adefovir, cidofovir, were synthesized. EDC proved to provide good yields of the analogs from the respective ω-amino-1- or -2-hydroxyalkylphosphonates and nucleobase-derived acetic acids. New phosphorus-nucleobase linkers are characterized by two fragments of the restricted rotation within amide bonds and in four-atom units (P-CH(OH)-CH₂-N, P-CH(OH)-CH₂-C and P-CH₂-CH(OH)-C) in which antiperiplanar disposition of P and N/C atoms was deduced from ¹H and ¹³C NMR spectral data. The synthesized analogs P-X-HNC(O)-CH₂B [X=CH(OH)CH₂, CH(OH)CH₂CH₂, CH₂CH(OH)CH₂] appeared inactive in antiviral assays on a wide variety of DNA and RNA viruses at concentrations up to 100 μM, while two phosphonates showed cytostatic activity towards myeloid leukemia (K-562) and multiple myeloma cells (MM.1S) with IC₅₀ of 28.8 and 40.7 μM, respectively.

Graphical abstract

Purine derivatives with antituberculosis activity

The review summarizes the data published over the last 10 – 15 years concerning the key groups of purine derivatives with antituberculosis activity. The structures of purines containing heteroatoms (S, O, N), fragments of heterocycles, amino acids and peptides, in the 6-position, as well as of purine nucleosides are presented. The possible targets for the action of such compounds and structure – activity relationship are discussed. Particular attention is paid to the most active compounds, which are of considerable interest as a basis for the development of efficient antituberculosis drugs.

The bibliography includes 99 references.

Crystal structure of [2,13-bis-(acetamido)-5,16-dimethyl-2,6,13,17-tetra-aza-tri-cyclo-[16.4.0.07,12]docosane-κ4N]silver(II) dinitrate from synchrotron X-ray data

The asymmetric unit of the title compound, [Ag(C24H46N6O2)](NO3)2 [C24H46N6O2 is (5,16-dimethyl-2,6,13,17-tetra-aza-tri-cyclo-[16.4.0.07,12]docosane-2,13-di-yl)diacetamide, L], consists of one independent half of the [Ag(C24H46N6O2)]2+ cation and one nitrate anion. The Ag atom, lying on an inversion centre, has a square-planar geometry and the complex adopts a stable trans-III conformation. Inter-estingly, the two O atoms of the pendant acetamide groups are not coordinated to the AgII ion. The longer distance of 2.227 (2) Å for Ag-N(tertiary) compared to 2.134 (2) Å for Ag-N(secondary) may be due to the effects of the attached acetamide group on the tertiary N atom. Two nitrate anions are very weakly bound to the AgII ion in the axial sites and are further connected to the ligand of the cation by N-H⋯O hydrogen bonds. The crystal packing is stabilized by hydrogen-bonding inter-actions among the N-H donor groups of the macrocycle and its actetamide substituents, and the O atoms of the nitrate anions and of an acetamide group as the acceptor atoms.

Synthesis and Biological Evaluation of Novel Hybrid Molecules Containing Purine, Coumarin and Isoxazoline or Isoxazole Moieties

Introduction:

The 1,3-dipolar cycloaddition reactions of nitrile oxides formed in situ (in the presence of NCS and Et₃N) from the oximes of (purin-9-yl)acetaldehyde or (coumarinyloxy)acetaldehyde with allyloxycoumarins or 9-allylpurines, respectively resulted in 3,5-disubstituted isoxazolines. The similar reactions of propargyloxycoumarins or 9-propargylpurines led to 3,5-disubstituted isoxazoles by treatment with PIDA and catalytic amount of TFA.

Methods:

The new compounds were tested in vitro as antioxidant agents and inhibitors of soybean lipoxygenase LO, AChE and MAO-B.

Results:

The majority of the compounds showed significant hydroxyl radical scavenging activity. Compounds 4k and 4n presented LO inhibitory activity.

Conclusion:

Compound 13e presents an antioxidant significant profile combining anti-LO, anti-AChE and anti-MAO-B activities.

Synthesis of Spironucleosides: Past and Future Perspectives

Spironucleosides are a type of conformationally restricted nucleoside analogs in which the anomeric carbon belongs simultaneously to the sugar moiety and to the base unit. This locks the nucleic base in a specific orientation around the N-glycosidic bond, imposing restrictions on the flexibility of the sugar moiety. Anomeric spiro-functionalized nucleosides have gained considerable importance with the discovery of hydantocidin, a natural spironucleoside isolated from fermentation broths of Streptomyces hygroscopicus which exhibits potent herbicidal activity. The biological activity of hydantocidin has prompted considerable synthetic interest in this nucleoside and also in a variety of analogues, since important pharmaceutical leads can be found among modified nucleoside analogues. We present here an overview of the most important advances in the synthesis of spironucleosides.

Crystal structure of bis-[(oxalato-κ2O1,O2)(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4N)chromium(III)] dichromate octa-hydrate from synchrotron X-ray data

The asymmetric unit of the title compound, [Cr(C2O4)(C10H24N4)]2[Cr2O7]·8H2O (C10H24N4 = 1,4,8,11-tetra-aza-cyclo-tetra-decane, cyclam; C2O4 = oxalate, ox) contains one [Cr(ox)(cyclam)]+ cation, one half of a dichromate anion that lies about an inversion centre so that the bridging O atom is equally disordered over two positions, and four water mol-ecules. The terminal O atoms of the dichromate anion are also disordered over two positions with a refined occupancy ratio 0.586 (6):0.414 (6). The CrIII ion is coordinated by the four N atoms of the cyclam ligand and one bidentate oxalato ligand in a cis arrangement, resulting in a distorted octa-hedral geometry. The Cr-N(cyclam) bond lengths are in the range 2.069 (2)-2.086 (2) Å, while the average Cr-O(ox) bond length is 1.936 Å. The macrocyclic cyclam moiety adopts the cis-V conformation. The dichromate anion has a staggered conformation. The crystal structure is stabilized by inter-molecular hydrogen bonds involving the cyclam N-H groups and water O-H groups as donors, and the O atoms of oxalate ligand, water mol-ecules and the Cr2O72- anion as acceptors, giving rise to a three-dimensional network.

Ni-Pd Catalyzed Cyclization of Sulfanyl 1,6-Diynes: Synthesis of 1'-Homonucleoside Analogues

The Ni-Pd catalyzed addition-cyclization of sulfanyl 1,6-diynes 2-9 with nucleobases is described. The reactions of N-tethered 1,6-diynes with N³-benzoylthymine, N⁴,N⁴-bis(Boc)cytosine, N³-benzoyluracil and N⁶,N⁶-bis(Boc)adenine exclusively afforded the pyrrolylmethyl and furylmethyl nucleotides in good yields. Deprotection of nucleobases was completed by treatment with acids or bases. Furthermore, the reactions of pyrroles and furans with nucleophiles such as alkoxides and amines underwent detosylation and conversion to the alkoxymethyl- and arylaminomethyl-pyrroles and furans in good yields.

Crystal structure of bis-[cis-(1,4,8,11-tetra-aza-cyclo-tetra-deca-ne-κ4N)bis(thio-cyanato-κN)chrom-ium(III)] dichromate monohydrate from synchrotron X-ray diffraction data

The structure of the complex salt, cis-[Cr(NCS)2(cyclam)]2[Cr2O7]·H2O (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-decane, C10H24N4), has been determined from synchrotron data. The asymmetric unit comprises of one [Cr(NCS)2(cyclam)]+ cation, one half of a Cr2O72- anion (completed by inversion symmetry) and one half of a water mol-ecule (completed by twofold rotation symmetry). The CrIII ion is coordinated by the four cyclam N atoms and by two N atoms of cis-arranged thio-cyanate anions, displaying a distorted octa-hedral coordination sphere. The Cr-N(cyclam) bond lengths are in the range 2.080 (2) to 2.097 (2) Å while the average Cr-N(NCS) bond length is 1.985 (4) Å. The macrocyclic cyclam moiety adopts the cis-V conformation. The bridging O atom of the dichromate anion is disordered around an inversion centre, leading to a bending of the Cr-O-Cr bridging angle [157.7 (3)°]; the anion has a staggered conformation. The crystal structure is stabilized by inter-molecular hydrogen bonds involving the cyclam N-H groups and water O-H groups as donor groups, and the O atoms of the Cr2O72- anion and water mol-ecules as acceptor groups, giving rise to a three-dimensional network.

Crystal structure of cis-di-chlorido-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4N)chromium(III) (oxalato-κ2O1,O2)(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4N)chromium(III) bis(perchlorate) from synchrotron data

In the asymmetric unit of the title compound, [CrCl2(C10H24N4)][Cr(C2O4)(C10H24N4)](ClO4)2 (C10H24N4 = 1,4,8,11-tetra-aza-cyclo-tetra-decane, cyclam; C2O4 = oxalate, ox), there are two independent halves of the [CrCl2(cyclam)]+ and [Cr(ox)(cyclam)]+ cations, and one perchlorate anion. In the complex cations, which are completed by application of twofold rotation symmetry, the CrIII ions are coordinated by the four N atoms of a cyclam ligand, and by two chloride ions or one oxalate bidentate ligand in a cis arrangement, displaying an overall distorted octa-hedral coordination environment. The Cr-N(cyclam) bond lengths are in the range of 2.075 (5) to 2.096 (4) Å while the Cr-Cl and Cr-O(ox) bond lengths are 2.3358 (14) and 1.956 (4) Å, respectively. Both cyclam moieties adopt the cis-V conformation. The slightly distorted tetra-hedral ClO4- anion remains outside the coordination sphere. The supra-molecular architecture includes N-H⋯O and N-H⋯Cl hydrogen bonding between cyclam NH donor groups, O atoms of the oxalate ligand or ClO4- anions and one Cl ligand as acceptors, leading to a three-dimensional network structure.

Spectroscopic characterization and molecular structure of 3,14-dimethyl-2,6,13,17-tetraazapentacyclo[16.4.0.1(2,17).1(6,13).0(7,12)]tetracosane

Constrained cyclam derivatives have been found to exhibit anti-HIV effects. The strength of binding to the CXCR4 receptor correlates with anti-HIV activity. The conformation of the macrocyclic compound is very important for co-receptor recognition. Therefore, knowledge of the conformation and crystal packing of macrocycles has become important in developing new highly effective anti-HIV drugs. Structural modifications of N-functionalized polyaza macrocyclic compounds have been achieved using various methods. A new synthesis affording single crystals of the title tetraazapentacyclo[16.4.0.1(2,17).1(6,13).0(7,12)]tetracosane macrocycle, C22H40N4, is reported. Formaldehyde reacts readily at room temperature with the tetraazatricyclo[16.4.0.0(2,17)]docosane precursor to yield a macropolycycle containing two five-membered rings. Characterization by elemental, spectroscopic and single-crystal X-ray diffraction analyses shows that the asymmetric unit contains half of a centrosymmetric molecule. The molecular structure shows a trans conformation for the two methylene bridges owing to molecular symmetry. The crystal structure is stabilized by intramolecular C-H...N hydrogen bonds. NMR and IR spectroscopic properties support the methylene-bridged macrocyclic structure.

Crystal structure of trans-diammine(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ(4) N)chromium(III) tetra-chlorido-zincate chloride monohydrate from synchrotron data

The asymmetric unit of the title complex salt, [Cr(C10H24N4)(NH3)2][ZnCl4]Cl·H2O, is comprised of four halves of the Cr(III) complex cations (the counterparts being generated by application of inversion symmetry), two tetra-chlorido-zincate anions, two chloride anions and two water mol-ecules. Each Cr(III) ion is coordinated by the four N atoms of the cyclam (1,4,8,11-tetra-aza-cyclo-tetra-deca-ne) ligand in the equatorial plane and by two N atoms of ammine ligands in axial positions, displaying an overall distorted octa-hedral coordination environment. The Cr-N(cyclam) bond lengths range from 2.0501 (15) to 2.0615 (15) Å, while the Cr-(NH3) bond lengths range from 2.0976 (13) to 2.1062 (13) Å. The macrocyclic cyclam moieties adopt the trans-III conformation with six- and five-membered chelate rings in chair and gauche conformations. The [ZnCl4](2-) anions have a slightly distorted tetra-hedral shape. In the crystal, the Cl(-) anions link the complex cations, as well as the solvent water mol-ecules, through N-H⋯Cl and O-H⋯Cl hydrogen-bonding inter-actions. The supra-molecular set-up also includes N-H⋯Cl, C-H⋯Cl, N-H⋯O and O-H⋯Cl hydrogen bonding between N-H or C-H groups of cyclam, ammine N-H and water O-H donor groups, and O atoms of the water mol-ecules, Cl(-) anions or Cl atoms of the [ZnCl4](2-) anions as acceptors, leading to a three-dimensional network structure.

Antiviral Drugs

Viruses are major pathogenic agents causing a variety of serious diseases in humans, other animals, and plants.

Drugs that combat viral infections are called antiviral drugs. There are no effective antiviral drugs for many viral infections. However, there are several drugs for influenza, a couple of drugs for herpesviruses, and some new antiviral drugs for treatment of HIV and hepatitis C infections.

The arsenal of antivirals is complex. As of March 2014, it consists of approximately 50 drugs approved by the FDA, approximately half of which are directed against HIV. Antiviral drug creation strategies are focused on two different approaches: targeting the viruses themselves or targeting host cell factors.

Direct virus-targeting antiviral drugs include attachment inhibitors, entry inhibitors, uncoating inhibitors, protease inhibitors, polymerase inhibitors, nucleoside and nucleotide reverse transcriptase inhibitors, nonnucleoside reverse-transcriptase inhibitors, and integrase inhibitors.

Protease inhibitors (darunavir, atazanavir, and ritonavir), viral DNA polymerase inhibitors (acyclovir, valacyclovir, valganciclovir, and tenofovir), and an integrase inhibitor (raltegravir) are included in the list of Top 200 Drugs by sales for the 2010s.

Phosphonylated Acyclic Guanosine Analogues with the 1,2,3-Triazole Linker

A novel series of {4-[(2-amino-6-chloro-9H-purin-9-yl)methyl]-1H-1,2,3-triazol-1-yl}alkylphosphonates and {4-[(2-amino-6-oxo-1,6-dihydro-9H-purin-9-yl)methyl]-1H-1,2,3-triazol-1-yl}alkylphosphonates as acyclic analogues of guanosine were synthesized and assessed for antiviral activity against a broad range of DNA and RNA viruses and for their cytostatic activity toward three cancerous cell lines (HeLa, L1210 and CEM). They were devoid of antiviral activity; however, several phosphonates were found slightly cytostatic against HeLa cells at an IC₅₀ in the 80–210 µM range. Compounds (1R,2S)-17k and (1S,2S)-17k showed the highest inhibitory effects (IC₅₀ = 15–30 µM) against the proliferation of murine leukemia (L1210) and human T-lymphocyte (CEM) cell lines.

Crystal structure of bis-[trans-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ(4) N)bis-(thio-cyanato-κN)chromium(III)] tetra-chlorido-zincate from synchrotron data

The structure of the title compound, [Cr(NCS)2(cyclam)]2[ZnCl4] (cyclam = 1,4,8,11-tetra-aza-cyclo-tetra-decane, C10H24N4), has been determined from synchrotron data. The asymmetric unit contains two independent halves of the Cr(III) complex cations and half of a tetra-chlorido-zincate anion. In each complex cation, the Cr(III) atom is coordinated by the four N atoms of the cyclam ligand in the equatorial plane and by two N-bound NCS(-) anions in a trans axial arrangement, displaying a distorted octa-hedral geometry with crystallographic inversion symmetry. The mean Cr-N(cyclam) and Cr-N(NCS) bond lengths are 2.065 (4) and 1.995 (6) Å, respectively. The macrocyclic cyclam moieties adopt centrosymmetric trans-III configurations with six- and five-membered chelate rings in chair and gauche configurations, respectively. The [ZnCl4](2-) anion, which lies about a twofold rotation axis, has a slightly distorted tetra-hedral geometry. The crystal packing is stabilized by hydrogen-bonding inter-actions between the N-H groups of the cyclam ligands, the S atoms of the NCS(-) groups and the Cl(-) ligands of the anion.