7‐Halogenated 7‐Deazapurine 2′‐Deoxyribonucleosides Related to 2′‐Deoxyadenosine, 2′‐Deoxyxanthosine,and 2′‐Deoxyisoguanosine: Syntheses and Properties

A series of 7‐fluorinated 7‐deazapurine 2′‐deoxyribonucleosides related to 2′‐deoxyadenosine, 2′‐deoxyxanthosine, and 2′‐deoxyisoguanosine as well as intermediates 4b – 7b, 8, 9b, 10b , and 17b were synthesized. The 7‐fluoro substituent was introduced in 2,6‐dichloro‐7‐deaza‐9H‐purine ( 11a ) with Selectfluor (Scheme 1). Apart from 2,6‐dichloro‐7‐fluoro‐7‐deaza‐9H‐purine ( 11b ), the 7‐chloro compound 11c was formed as by‐product. The mixture 11b / 11c was used for the glycosylation reaction; the separation of the 7‐fluoro from the 7‐chloro compound was performed on the level of the unprotected nucleosides. Other halogen substituents were introduced with N‐halogenosuccinimides ( 11a → 11c – 11e ). Nucleobase‐anion glycosylation afforded the nucleoside intermediates 13a – 13e (Scheme 2). The 7‐fluoro‐ and the 7‐chloro‐7‐deaza‐2′‐deoxyxanthosines, 5b and 5c , respectively, were obtained from the corresponding MeO compounds 17b and 17c , or 18 (Scheme 6). The 2′‐deoxyisoguanosine derivative 4b was prepared from 2‐chloro‐7‐fluoro‐7‐deaza‐2′‐deoxyadenosine 6b via a photochemically induced nucleophilic displacement reaction (Scheme 5). The pK_a values of the halogenated nucleosides were determined (Table 3). ¹³C‐NMR Chemical‐shift dependencies of C(7), C(5), and C(8) were related to the electronegativity of the 7‐halogen substituents (Fig. 3). In aqueous solution, 7‐halogenated 2′‐deoxyribonucleosides show an approximately 70% S population (Fig. 2 and Table 1).     

Poly[(μ4‐adamantane‐1,3‐dicarboxylato‐κ5O1:O1′:O3,O3′:O3′)(μ3‐adamantane‐1,3‐dicarboxylato‐κ5O1,O1′:O3,O3′:O3′)dimagnesium]: a layered coordination polymer

The title compound, [Mg₂(C₁₂H₁₄O₄)₂]_n, is the first example of an s‐block metal adamantanedicarboxylate coordination polymer. The asymmetric unit comprises two crystallographically unique Mg^II centers and two adamantane‐1,3‐dicarboxylate ligands. The compound is constructed from a combination of chains of corner‐sharing magnesium‐centered polyhedra, parallel to the a axis, connected by organic linkers to form a layered polymer. The two Mg^II centers are present in distorted tetrahedral and octahedral coordination environments derived from carboxylate O atoms. Tetrahedrally coordinated Mg^II centers have been reported in organometallic compounds, but this is the first time that such coordination has been observed in a magnesium‐based coordination polymer. The bond valance sums of the two Mg^II centers are 2.05 and 2.11 valence units, matching well with the expected value of 2.     

Sulfenylation of heterocyclic 1,3‐dicarbonyl systems: 4‐Hydroxy‐2‐pyrones, 6‐hydroxy‐4‐pyrimidones, 4‐hydroxy‐2‐pyridones, 4‐hydroxy‐6‐pyridazinones,and 5‐hydroxy‐3‐pyrazolones

Anions of enolized heteroaromatic 1,3‐dicarbonyl systems, such as the title compounds 1, 9,14 , and 19 , react in dimethylformamide in the presence of potassium carbonate with diaryl disulfides 2 to yield arylsulfenyl derivatives ( 3, 10, 15, 20 ). The arylthiolate anions 4 formed in this reaction can be oxidized by air to yield the starting disulfides 2 again. Tetraalkylthiuram disulfides 7 react in the same manner to yield dialkylaminothiocarbonylthio derivatives ( 8, 13, 18 ) of the title compounds. Oxidation of the arylsulfenyl derivatives with hydrogen peroxide in sodium hydroxide solution usually leads to sulfoxides ( 5, 11, 16 ), whereas oxidation with peracetic acid affords sulfones ( 6, 12, 17 ).     

2,2′:3′,2′′‐Terthiophene‐Based all‐Thiophene Dendrons and Dendrimers: Synthesis,Structural Characterization,and Properties

The synthesis of generational dendritic oligothiophenes (DOTs) has been successfully achieved by a divergent/convergent approach that involves halogenation, boronation, and palladium‐catalyzed Suzuki coupling reactions. The key point in the presented synthetic approach is the use of trimethylsilyl (TMS) protecting groups, which allow for the core‐lithiation and subsequent boronation of the dendrons and for the peripheral ipso‐substitution with iodine monochloride or N‐bromosuccimide. In addition, the TMS protecting groups can be completely removed by using tetrabutylammonium fluoride, thus yielding only‐thiophene‐based dendrons and dendrimers. Due to their highly branched structure, all these synthesized DOTs are soluble in organic solvents. Chemical structures were confirmed by NMR spectroscopic, mass spectrometric, and elemental analysis. Concentration‐dependent ¹H NMR spectroscopic investigations revealed that the higher generation compounds tend to aggregate in solution. Such an aggregation behavior was further confirmed by measuring with MALDI‐TOF MS. Both MALDI‐TOF MS and gel‐permeation chromatography (GPC) analyses confirmed the monodispersity of the DOTs. Furthermore, GPC results revealed that these DOT molecules adopt a condensed globular molecular shape. Their optical and electronic properties were also investigated. The results indicated that these DOTs comprise various conjugated α‐oligothiophenes with different chain lengths, which results in the higher generation compounds showing broad and featureless UV/Vis absorption spectra and ill‐defined redox waves.     

Total Syntheses of (+)‐Sarcophytin, (+)‐Chatancin, (−)‐3‐Oxochatancin,and (−)‐Pavidolide B: A Divergent Approach

A concise and divergent approach for the total syntheses of four cembrane diterpenoids, namely (+)‐sarcophytin, (+)‐chatancin, (?)‐3‐oxochatancin, and (?)‐pavidolide B, has been developed, and it also led to the structural revision of (?)‐isosarcophytin. The key steps of the strategy feature a double Mukaiyama Michael addition/elimination, a Helquist annulation, two substrate‐controlled facial‐selective hydrations, and a pinacol rearrangement. The described syntheses not only achieved these natural products in an efficient manner, but also provided insight into the biosynthetic relationship between the two different skeletons.     

Synthesis,Characterization, and Antimicrobial Screening of 4″‐methyl‐2,2″‐diaryl‐4,2′:4′,5″‐terthiazole Derivatives

A series of novel 4″‐methyl‐2,2″‐diaryl‐4,2′:4′,5″‐terthiazole ( 8a‐p ) derivatives has been synthesized and screened for antibacterial activity against four pathogenic bacteria, Escherichia coli, Pseudomonas flurescence, Staphylococcus aureus, and Bacillus subtilis. Among them, compounds 8a and 8j exhibited excellent antibacterial activity with minimum inhibitory concentration range of 1.0 to 5.3 μg/mL and compounds 8m and 8p exhibited moderate to good antibacterial activity with minimum inhibitory concentration range of 16.9 to 29.7 μg/mL against all tested strains. All the synthesized compounds were screened for their in vitro antifungal activity against Cocinida candida. Most of the compounds reported moderate antifungal activity. This study provides valuable directions to our ongoing endeavor of rationally designing more potent antimicrobial agent.     

catena‐Poly[bis(μ‐2,2′‐bipyridin‐6‐olato)‐κ3N,N′:O;O:N,N′‐dicopper(I,II) [[tetrafluoridoniobium(V)]‐μ‐oxido]]

A novel copper–niobium oxyfluoride, {[Cu₂(C₁₀H₇N₂O)₂][NbOF₄]}_n, has been synthesized by a hydrothermal method and characterized by elemental analysis, EDS, IR, XPS and single‐crystal X‐ray diffraction. The structural unit consists of one C₂‐symmetric [NbOF₄]⁻ anion and one centrosymmetric coordinated [Cu₂(obpy)₂]⁺ cation (obpy is 2,2′‐bipyridin‐6‐olate). In the [NbOF₄]⁻ anion, each Nb^V metal centre is five‐coordinated by four F atoms and one O atom in the first coordination shell, forming a square‐pyramidal coordination geometry. These square pyramids are then further connected to each other via trans O atoms [Nb—O = 2.187 (3) Å], forming an infinite linear {[NbOF₄]⁻}_n polyanion. In the coordinated [Cu₂(obpy)₂]⁺ cation, the oxidation state of each Cu site is disordered, which is confirmed by the XPS results. The disordered Cu sites are coordinated by two N atoms and one O atom from two different obpy ligands. The [NbOF₄]⁻ and [Cu₂(obpy)₂]⁺ units are assembled via weak C—H...F hydrogen bonds, resulting in the formation of a three‐dimensional supramolecular structure. π–π stacking interactions between the pyridine rings [centroid–centroid distance = 3.610 (2) Å] may further stabilize the crystal structure.     

Total Syntheses of (+)‐Sarcophytin, (+)‐Chatancin, (−)‐3‐Oxochatancin,and (−)‐Pavidolide B: A Divergent Approach

A concise and divergent approach for the total syntheses of four cembrane diterpenoids, namely (+)‐sarcophytin, (+)‐chatancin, (?)‐3‐oxochatancin, and (?)‐pavidolide B, has been developed, and it also led to the structural revision of (?)‐isosarcophytin. The key steps of the strategy feature a double Mukaiyama Michael addition/elimination, a Helquist annulation, two substrate‐controlled facial‐selective hydrations, and a pinacol rearrangement. The described syntheses not only achieved these natural products in an efficient manner, but also provided insight into the biosynthetic relationship between the two different skeletons.     

Two Bulky Conjugated 4′‐(4‐Hydroxyphenyl)‐4,2′:6′,4′′‐terpyridine‐based Layered Complexes: Synthesis,Structure, and Photocatalytic Hydrogen Evolution Activity

Two new layered complexes with the formulas of {[Cu(H₂O)(HL)₂Cl](NO₃)}_n ( 1 ) and {[Cu(H₂O)₂(HL)₂](NO₃)₂}_n ( 2 ) were solvothermally synthesized by the reactions of the bulky conjugated 4′‐(4‐hydroxyphenyl)‐4,2′:6′,4′′‐terpyridine ligand (HL) with different Cu^II salts, which were further used as photocatalysts to achieve hydrogen production from water splitting. Single‐crystal structural analyses reveal that both complexes feature coplanar (4 4) layers with different connection manners between the HL extended Z‐shaped chains. More interestingly, 1 possessing more negative conduction band potential and higher structural stability exhibits a large hydrogen production rate of 2.43 mmol · g^–1 · h^–1, which is four times higher than that of 2 . Thus, the Cu^II‐based coordination polymers modified by the bulky conjugated organic ligand can become potentially promising non‐Pt photocatalysts for hydrogen production from water splitting.     

Two Energetic Salts based on 5,5′‐Bitetrazole‐1,1′‐diolate: Syntheses,Characterization, and Properties

Two salts based on 1H,1′H‐5,5′‐bitetrazole‐1,1′‐diolate (BTO) anion with pyrazole ( 1 ) and imidazole ( 2 ) cations were synthesized with metathesis reactions. Structural characterization was accomplished for them by using the element analysis, Fourier transform infrared spectroscopy (FT‐IR), NMR and mass spectrum, and X‐ray single crystal diffraction. Thermal analysis for the title salts were determined by means of differential scanning calorimetry (DSC) and thermogravimetry‐derivative thermogravimetry (TG‐DTG) as well as the calculation of non‐isothermal kinetic parameters. Consequently, both salts shown acceptable thermal stabilities as the decomposition temperatures were over 200 °C. The enthalpies of formation were calculated for these salts using the measured combustion energies with a result of 70.6 kJ · mol^–1 for 1 and –47.8 kJ · mol^–1 for 2 , respectively. Impact and friction sensitivities were also tested and the results indicated that these salts both have low sensitivities (>40 J, 120 N). The title energetic salts possess acceptable performance, they can therefore be applied in the field of energetic materials.     

Thiophene‐Based,Radial π‐Conjugation: Synthesis,Structure, and Photophysical Properties of Cyclo‐1,4‐phenylene‐2′,5′‐thienylenes

The synthesis of cyclo‐1,4‐phenylene‐2′,5′‐thienylenes (CPTs) as the first example of a thiophene‐based, radially π‐conjugated system is described. X‐ray crystal structures, UV‐vis absorption and emission spectra, and theoretical studies revealed the unique structural and photophysical properties of CPTs. With all of these unique structural and photophysical properties, the radially π‐conjugated CPTs are expected to open a door for the discovery and development of new functional organic materials.     

Thiophene‐Based,Radial π‐Conjugation: Synthesis,Structure, and Photophysical Properties of Cyclo‐1,4‐phenylene‐2′,5′‐thienylenes

The synthesis of cyclo‐1,4‐phenylene‐2′,5′‐thienylenes (CPTs) as the first example of a thiophene‐based, radially π‐conjugated system is described. X‐ray crystal structures, UV‐vis absorption and emission spectra, and theoretical studies revealed the unique structural and photophysical properties of CPTs. With all of these unique structural and photophysical properties, the radially π‐conjugated CPTs are expected to open a door for the discovery and development of new functional organic materials.     

Nucleotides,Part LXV,Synthesis of 2′‐Deoxyribonucleoside 5′‐Phosphoramidites: New Building Blocks for the Inverse (5′‐3′)‐Oligonucleotide Approach

The syntheses of the 3′‐O‐(4,4′‐dimethoxytrityl)‐protected 5′‐phosphoramidites 25 – 28 and 5′‐(hydrogen succinates) 29 – 32 , which can be used as monomeric building blocks for the inverse (5′‐3′)‐oligodeoxyribonucleotide synthesis are described (Scheme). These activated nucleosides and nucleotides were obtained by two slightly different four‐step syntheses starting with the base‐protected nucleosides 13 – 20 . For the protection of the aglycon residues, the well‐established 2‐(4‐nitrophenyl)ethyl (npe) and [2‐(4‐nitrophenyl)ethoxy]carbonyl (npeoc) groups were used. The assembly of the oligonucleotides required a slightly increased coupling time of 3 min in application of the common protocol (see Table 1). The use of pyridinium hydrochloride as an activator (instead of 1H‐tetrazole) resulted in an extremely shorter activation time of 30 seconds. We established the efficiency of this inverse strategy by the synthesis of the oligonucleotide 3′‐conjugates 33 and 34 which carry lipophilic caps derived from cholesterol and vitamin E, respectively, as well as by the formation of (3′‐3′)‐ and (5′‐5′)‐internucleotide linkages (see Table 2).     

α‐Radical Phosphines: Synthesis,Structure, and Reactivity

A series of phosphines featuring a persistent radical were synthesized in two steps by condensation of dialkyl‐/diarylchlorophosphines with stable cyclic (alkyl)(amino)carbenes (cAACs) followed by one‐electron reduction of the corresponding cationic intermediates. Structural, spectroscopic, and computational data indicate that the spin density in these phosphines is mainly localized on the original carbene carbon from the cAAC fragment; thus, it remains in the α‐position with respect to the central phosphorus atom. The potential of these α‐radical phosphines to serve as spin‐labeled ligands is demonstrated through the preparation of several Au^I derivatives, which were also structurally characterized by single‐crystal X‐ray diffraction.     

TiCl3‐Mediated Synthesis of 2,3,3‐Trisubstituted Indolenines: Total Synthesis of (+)‐1,2‐Dehydroaspidospermidine, (+)‐Condyfoline,and (−)‐Tubifoline

2,3,3‐Trisubstituted indolenine constitutes an integral part of many biologically important monoterpene indole alkaloids. We report herein an unprecedented access to this skeleton by a TiCl₃‐mediated reductive cyclization of tetrasubstituted alkenes bearing a 2‐nitrophenyl substituent. The proof of concept is demonstrated firstly by accomplishing a concise total synthesis of (+)‐1,2‐dehydroaspidospermidine featuring a late‐stage application of this key transformation. A sequence of reduction of nitroarene to nitrosoarene followed by 6π‐electron‐5‐atom electrocyclization and a 1,2‐alkyl shift of the resulting nitrone intermediate was proposed to account for the reaction outcome. A subsequent total synthesis of (+)‐condyfoline not only illustrates the generality of the reaction, but also provides a mechanistic insight into the nature of the 1,2‐alkyl shift. The exclusive formation of (+)‐condyfoline indicates that the 1,2‐alkyl migration follows a concerted Wagner–Meerwein pathway, rather than a stepwise retro‐Mannich/Mannich reaction sequence. Conditions for almost quantitative conversion of (+)‐condyfoline to (?)‐tubifoline by way of a retro‐Mannich/1,3‐prototropy/transannular cyclization cascade are also documented.     

Chemical Etiology of Nucleic Acid Structure: The Pentulofuranosyl Oligonucleotide Systems: The (1′→3′)‐β‐L‐Ribulo, (4′→3′)‐α‐L‐Xylulo,and (1′→3′)‐α‐L‐Xylulo Nucleic Acids

Under potentially prebiotic scenarios, ribose (pentose), the component of RNA is formed in meager amounts, as opposed to ribulose and xylulose (pentuloses). Consequently, replacement of ribose in RNA, with pentulose sugars, gives rise to prospective oligonucleotide candidates that are potentially prebiotic structural variants of RNA that could be formed by the same type of chemical pathways that gave rise to RNA from ribose. The potentially natural alternative (1′→3′)‐ribulo oligonucleotides and (4′→3′)‐ and (1′→3′)‐xylulo oligonucleotides consisting of adenine and thymine were synthesized and found to exhibit no self‐pairing or cross‐pairing with RNA. This signifies that even though pentulose sugars may have been abundant in a prebiotic scenario, the pentulose nucleic acids (NAs), if and when formed, would not have been competitors of RNA, or interfered with the emergence of RNA as a functional informational system. The reason for the lack of base pairing in pentulose NA highlights the contrasting and central role played by the furanosyl ring in RNA and pentulose NA, enabling and optimizing the base pairing in RNA, while impeding it in pentulose NA.     

Poly­[[[(1,10‐phenanthroline‐κ2N,N′)­zinc(II)]‐μ3‐5‐hydroxy­isophthalato‐κ4O,O′:O′′:O′′′] monohydrate]

In the title compound, {[Zn(C₈H₄O₅)(C₁₂H₈N₂)]·H₂O}_n or {[Zn(OH‐BDC)(phen)]·H₂O}_n (where OH‐H₂BDC is 5‐hydroxy­isophthalic acid and phen is 1,10‐phenanthroline), the Zn atoms are coordinated by two N atoms from the phen ligands and by four O atoms from hydroxy­isophthalate ligands in a highly distorted octahedral geometry, with Zn—O distances in the range 2.042 (4)–2.085 (5) Å and Zn—N distances of 2.133 (5) and 2.137 (5) Å. The {[Zn(OH‐BDC)(phen)]·H₂O}_n infinite zigzag polymer forms a helical chain of [Zn₂(OH‐BDC)₂]_n units. Face‐to‐face π–π interactions (3.60–3.75 Å) occur between two phen rings belonging to the same helical chain. Consolidation of the packing structure is achieved by O—H⋯O hydrogen‐bonding interactions between the carboxyl­ate O atoms, the hydroxyl group and the water mol­ecule, forming two‐dimensional sheets.