Unexpected conversion of a polycyclic thiophene to a macrocyclic anhydride

Oxygenation of 2,5,9,12-tetra(tert-butyl)diacenaphtho[1,2-b:1′,2′-d]-thiophene (1, C₄₀H₄₄S) by peracids gave the cyclic sulfonic ester 4 (2,7,10,13-tetra(tert-butyl)diacenaphtho[1,2-c:1′,2′-e]oxathiin 5,5-dioxide, C₄₀H₄₄O₃S) which, when heated in nitrobenzene, is converted into a complex, macrocyclic anhydride 3 (C₈₀H₈₈O₃), which is derived from two molecules of 4. Further investigation found a likely intermediate in this reaction, 4,4′,7,7′-tetra(tert-butyl)-1,1′-biacenaphthylenylidene-2,2′-dione (5, C₄₀H₄₄O₂), apparently formed from 4 by additional oxidation. Anhydride 3 plausibly arises by Diels-Alder reaction of 4 and 5 followed by several ring fragmentations. The structures of 3, 4, and 5 were unambiguously established by X-ray crystallography.     

Efficient bimetallic titanium catalyst for carbonyl-ene reaction

A new family of achiral 3,3′,5,5′-tetrasubstituted-2,2′,6,6′-tetrahydroxy biphenyl ligand 4 was developed. The axial chirality of the ligand could be induced by the chelation of 2,2′,6,6′-tetrahydroxy groups with (R)-BINOL-Ti(OⁱPr)₂ to form an axially chiral bimetallic titanium catalyst 9. Compared with (R)-BINOL-Ti(OⁱPr)₂ catalyst, this novel catalyst 9 exhibited excellent activity and enantioselectivity for the carbonyl-ene reaction of methylstyrene and ethyl glyoxylate. 3,3′,5,5′-Tetrasubstituted groups showed a remarkable effect on both enantioselectivity and yield. With 9d prepared from 3,3′,5,5′-tetramethyl-2,2′,6,6′-tetrahydroxy biphenyl 4d as the catalyst, the best result, up to 97.6% ee and 99% yield, was obtained. Additionally, the bimetallic catalyst 9 also showed better catalytic capability than the corresponding monometallic catalyst.     

Synthesis, variable temperature NMR investigations and solid state characterization of novel octafluorofluorene compounds

The preparation of a number of new 9-substituted octafluorofluorene derivatives, solution NMR studies, and the first examples of solid state structures of octafluorofluorenes [1,2,3,4,5,6,7,8-octafluorofluorene, C₁₃H₂F₈, 1; 1,2,3,4,5,6,7,8-octafluoro-9-(pentafluoro)phenylfluorene, C₁₉HF₁₃, 8; 1,1′,2,2′,3,3′,4,4′,5,5′,6,6′,7,7′,8,8′-hexadecafluoro-9,9′-bifluorenyl, C₂₆H₂F₁₆, 11] are reported. Variable temperature ¹⁹F NMR investigations have been performed on the 9-aryl substituted compounds 1,2,3,4,5,6,7,8-octafluoro-9-(pentafluoro)phenyl-9-hydroxyfluorene, C₁₉HF₁₃O, 4, 1,2,3,4,5,6,7,8-octafluoro-9-(nonafluoro-4′-biphenylyl)-9-hydroxyfluorene, C₂₅HF₁₇O, 5, and 8, and the energetic barriers to rotation of the aryl have been determined. A lower rotational barrier is observed for compound 4 with respect to compound 8, while 5 does not show fluxional behaviour below 338 K. The results of the variable temperature experiments performed on 8 have been rationalized by 2D NMR studies, and compared to the solid state data resulting from the X-ray structural analysis.     

Synthesis,structural analysis,and thermal and spectroscopic studies of methylmalonate-containing zinc(II) complexes

The synthesis, crystal structure, thermal analysis and spectroscopic studies of five zinc(II) complexes of formulae [Zn(Memal)(H₂O)]_n (1) and [Zn₂(L)(Memal)₂(H₂O)₂]_n (2-5) [H₂Memal = methylmalonic acid, and L = 4,4′-bipyridine (4,4′-bpy) (2), 1,2-bis(4-pyridyl)ethylene (bpe) (3), 1,2-bis(4-pyridyl)ethane (bpa) (4) and 4,4′-azobispyridine (azpy) (5)] are presented here. The crystal structure of 1 is a three-dimensional arrangement of zinc(II) cations interconnected by methylmalonate groups adopting the μ₃-κ²O:κO’:κO”:κO”’ coordination mode to afford a rare (10,3)-d utp-network. The structures of the compounds 2-5 are also three-dimensional and they consist of corrugated square layers of methylmalonate-bridged zinc(II) ions which are pillared by bis-monodentate 4,4′-bpy (2), bpe (3), bpa (4) and azpy (5) ligands. The Memal ligand in 2-5 adopts the μ₃-κO:κO′:κO′′:κO′′′ coordination mode. Each zinc(II) ion in 1-5 is six-coordinated with five (1)/four (2-5) methylmalonate-oxygen atoms, a water molecule (1-5) and a nitrogen atom from a L ligand (2-5) building distorted octahedral environments. The rod-like L co-ligands in 2-5 appear as useful tools to control the interlayer metal-metal separation, which covers the range 8.4311(5) Å (2) – 9.644(3) Å (5). The influence of the co-ligand on the fluorescence properties of this series of compounds has been analyzed and discussed by steady-state and time resolved spectroscopy on all five compounds in the solid state.     

3-Oxyanthranilic acid derivatives from Actinomadura sp. BCC27169

Eight new compounds including 9′-[2-amino-3-(4″-O-methyl-α-rhamnopyranosyloxy) phenyl]nonanoic acid (1), 9′-[2-amino-3-(4″-O-methyl-α-ribopyranosyloxy)phenyl] nonanoic acid (2), 11′-[2-amino-3-(4″-O-methyl-α-rhamnopyranosyloxy)phenyl]undecanoic acid (3), 11′-[2-amino-3-(4″-O-methyl-α-ribopyranosyloxy)phenyl]undecanoic acid (4), 8-(4′-O-methyl-α-rhamnopyranosyloxy)-3,4-dihydroquinolin-2(1H)-one (5), 8-(4′-O-methyl-α-ribopyranosyloxy)-3,4-dihydroquinolin-2(1H)-one (6), 8-(4′-O-methyl-α-rhamnopyranosyloxy)-2-methyquinoline (7), and 8-(4′-O-methyl-α-ribopyranosyloxy)-2-methylquinoline (8) were isolated from Actinomadura sp. BCC27169. The chemical structures of these compounds were determined based on NMR and high-resolution mass spectroscopy. The absolute configurations of these monosaccharides were revealed by the hydrolysis of compounds 7 and 8. Compounds 3 and 8 exhibited antitubercular activity at MIC 50 μg/mL. Only compound 3 showed cytotoxicity against KB cell at IC₅₀ 18.63 μg/mL, while other isolated compounds were inactive at tested maximum concentration (50 μg/mL).     

Total synthesis of apigenin 7,4′-di-O-β-glucopyranoside, a component of blue flower pigment of Salvia patens, and seven chiral analogues

We have succeeded in the first total synthesis of apigenin 7,4′-di-O-β-d-glucopyranoside (1a), a component of blue pigment, protodelphin, from naringenin (2). Glycosylation of 2 according to Koenigs-Knorr reaction provided a monoglucoside 4a in 80% yield, and this was followed by DDQ oxidation to give apigenin 7-O-glucoside (12a). Further glycosylation of 4′-OH of 12a with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl fluoride (5a) was achieved using a Lewis acid-and-base promotion system (BF₃·Et₂O, 2,6-di-tert-butyl-4-methylpyridine, and 1,1,3,3-tetramethylguanidine) in 70% yield, and subsequent deprotection produced 1a. Synthesis of three other chiral isomers of 1a, with replacement of d-glucose at 7 and/or 4′-OH by l-glucose (1b-d), and four chiral isomers of apigenin 7-O-β-glucosides (6a,b) and 4′-O-β-glucosides (7a,b) also proved possible.     

Isolation of key intermediates during formation of oolongtheanins

Oolongtheanin-3′-O-gallate (2b) was obtained by treatment of (−)-EGCg (1d) with CuCl₂. This transformation was achieved over three steps, with the isolation of two intermediates; their chemical structures were determined through derivatization reactions, MS, and 1D/2D NMR techniques. One intermediate was identified as dehydrotheasinensin A (3); the other was identified as the novel dimer pro-oolongtheanin-3′-O-gallate (6). Compound 3 was converted to 6 by heating in aprotic solvent, and compound 6 was converted to 2b by addition of water.     

Regio- and stereoselective synthesis of spiro-pyrrolidine/pyrrolizidine/thiazolidine-grafted macrocycles through intramolecular 1,3-dipolar cycloaddition reaction

Regioselective synthesis of spiropyrrolidine-grafted 11-membered macrocycle was accomplished through an intramolecular [3+2] cycloaddition of azomethine ylides. The key precursor alkenyl diketone (4a–b) was obtained from simple starting materials. The dipole generated from isatin tethered to O-alkyl enone (4a–b) was reacted intramolecularly to yield the spiropyrrolidine-grafted macrocycles (6a–b). The structures of the cycloadducts were assigned by 2D NMR and confirmed by single crystal analysis.     

Coordination chemistry of anticrowns: Complexation of cyclic trimeric perfluoro-o-phenylenemercury with nitro compounds

Cyclic trimeric perfluoro-o-phenylenemercury (o-C₆F₄Hg)₃ (1) is capable of reacting with nitromethane to give complex {[(o-C₆F₄Hg)₃](CH₃NO₂)} (2) containing one molecule of the nitro compound per one macrocycle molecule. In this complex, the nitromethane ligand is bound to 1 by its both oxygen atoms, one of which is simultaneously coordinated to all three Hg centres of the macrocycle while the other interacts with a single Hg centre. The complex of similar composition, {[(o-C₆F₄Hg)₃](C₆H₅NO₂)} (3), is produced in the interaction of 1 with nitrobenzene. In this complex too, the both oxygen atoms of the nitro group are involved in the bonding to the macrocycle. A distinctive feature of 3 is that here one oxygen atom of the coordinated nitro derivative is bound by only two Hg centres of 1 whereas the other interacts again with a single Hg site. The reaction of 1 with 5-nitroacenaphthene affords a 1:1 complex, {[(o-C₆F₄Hg)₃](C₁₂H₉NO₂)} (4), having a polydecker sandwich structure in the crystal. Unlike in 3, the aromatic rings of the nitroarene units in 4 are disposed virtually in parallel to the macrocycles. The nitro compound in 4 behaves again as a bidentate ligand, forming three Hg-O bonds with one of the adjacent macrocycles and a single Hg-O bond with another molecule of 1. The complex is characterized also by shortened Hg-C contacts between the Hg centres of 1 and the carbon atoms of the nitroarene moiety as well as shortened C-C contacts between the carbon atoms of the nitroarene and the macrocycle. In the interaction of 1 with 1-nitropyrene, complexes of two compositions, viz. {[(o-C₆F₄Hg)₃](C₁₆H₉NO₂)} (5) and {[(o-C₆F₄Hg)₃](C₁₆H₉NO₂)₃} (6) are formed. An X-ray diffraction study of 6 has shown that in this adduct two of three coordinated molecules of the nitro compound are located on one side of the metallacycle plane while the third nitroarene molecule is disposed on its other side. The aromatic rings of all three nitropyrene ligands in 6 are practically parallel to the mean plane of the macrocycle. In contrast to 2-4, each molecule of the nitroarene in 6 is bonded to 1 by a single oxygen atom which is coordinated only to one Hg centre. In the case of one of the nitropyrene ligands that forms much longer Hg-O bond with 1 than two others, an additional contribution to the bonding is made by shortened Hg-C contacts between the macrocycle and the carbon atoms of the aromatic pyrene core and also by shortened C-C contacts between the carbon atoms of the coordinated nitroarene and 1. The synthesized adducts are the first examples of complexes of an anticrown with nitro compounds.     

Hydrothermal synthesis, structure and properties of a new arsenotungstate

A new arsenotungstate, Na[{Cu(2,2′-bpy)(imi)}{Cu(2,2′-bpy)}₂AsW₉O₃₃As(OH)]·8H₂O (1) (2,2′-bpy=2,2′-bipyridine, imi=imidazole), has been hydrothermally synthesized and structurally characterized by elemental analysis, IR, TG and single-crystal X-ray diffraction. The compound 1 represents the first example of an unusual trilacunary arsenotungstate substituted simultaneously arsenide fragment and copper complexes. The compound 1 was used as solid bulk modifier to fabricate bulk-modified carbon paste electrodes (1-CPE) by direct mixing. The electrochemical behavior and electrocatalysis of 1-CPE have been studied in detail. Magnetic measurement for 1 shows the presence of antiferromagnetic interactions within the Cu²⁺ cations.     

Inclusion crystals of 2,2′,7,7′,9,9′-hexahalo-9,9′-bisfluorenyl derivatives: a new family of polyhalo aryl hosts

The preparation and inclusion properties of the new halo aryl hosts, 2,2′,7,7′,9,9′-hexahalo-9,9′-bisfluorenyl derivatives 5-7, are described. The host compounds 5-7 having four halogen atoms on the aromatic rings form stable inclusion crystals with many guest compounds, whereas the parent compound 4 does not. The X-ray structures of the host 4 and representative inclusion compounds of hosts 5-7 were determined, allowing rationalization of several of the experimental observations.     

Syntheses, crystal structures and photoluminescence properties of three novel organically bonded indium selenates or selenites

Three new organically bonded indium(III) selenates or selenites, namely, In₂(2,2′-bipy)₂(SeO₄)₃(H₂O)₂·2H₂O (1), In₂(2,2′-bipy)₂(SeO₄)(C₂O₄)₂·0.5H₂O (2) and In₂(2,2′-bipy)₂(SeO₃)₂(C₂O₄) (3) (2,2′-bipy=2,2′-bipyridine) have been synthesized by hydro/solvothermal reactions by using the in situ ligand synthesis technique (2 and 3) and structurally characterized. The structure of compound 1 features a dimer composed of two InO₄N₂ octahedra bridged by three SeO₄ tetrahedra via cornering sharing. The structure of compound 2 shows a 2D inorganic-organic hybrid layer in which the indium (III) ions are bridged by both selenate and oxalate anions, whereas the structure of compound 3 possesses a 2D inorganic-organic hybrid layer composed of the indium (III) ions interconnected by both selenite and oxalate anions. The adjacent layers are further interconnected via π…π interactions between the bipy ligands. Compound 1 displays an intra-ligand luminescent emission band at λ_max=360 nm whereas compounds 2 and 3 both exhibit intra-ligand luminescent emission bands at λ_max=389 nm.     

Synthesis of procyanidins by stepwise- and self-condensation using 3,4-cis-4-acetoxy-3-O-acetyl-4-dehydro-5,7,3′,4′-tetra-O-benzyl-(+)-catechin and (−)-epicatechin as a key building monomer

3,4-cis-4-Acetoxy-3-O-acetyl-4-dehydro-5,7,3′,4′-tetra-O-benzyl-(+)-catechin (1a) or (−)-epicatechin (1b) reacted high regio- and stereo-selectively with 1.5 equiv of the 5,7,3′,4′-tetra-O-benzyloxyflavan-3-ol (4a or 4b) in the presence of 1 equiv of TMSOTf to give the corresponding procyanidins. On the other hand, the self-condensation of 1a in the presence of a catalytic amount of B(C₆F₅)₃ afforded wide-range procyanidins from dimer to 15-mer like a biomass.     

N^N^C platinum(II) and palladium(II) cyclometallates of 6,6′-diphenyl-2,2′-bipyridine, L: Crystal and molecular structure of [Pd(L-H)Cl]

Reaction of K₂[PtCl₄] or Na₂[PdCl₄] with 6,6′-diphenyl-2,2′-bipyridine, L, gives the cyclometallated species [Pt(L-H)Cl], 1, and [Pd(L-H)Cl], 2, respectively, where L-H is a terdentate N^N^C anionic ligand originated by direct activation of a C(sp²)-H bond. The crystal structure of 2 has been solved by X-ray diffraction and compared to that of the analogous complex [Pd(L′-H)Cl] L′ = 6-phenyl-2,2′-bipyridine. The second phenyl ring in 2 entails a considerable distortion of the coordination around the metal. A similar distortion is also to be expected in the analogous compound 1, due to the almost equal covalent radii of palladium(II) and platinum(II).From the complexes 1 and 2 the chloride can be displaced with AgBF₄ and substituted by CO or PPh₃ to give the corresponding cationic species. By reaction of 1 with Na[BH₄] substitution of H⁻ for Cl⁻ can be achieved: the rare hydrido complex [Pt(L-H)H], stabilized only by nitrogen ligands, was isolated in the solid state and fully characterized in solution. It is noteworthy that in the case of the 6-phenyl-2,2′-bipyridine the analogous terminal hydride [Pd(L′-H)H] is unstable. In platinum chemistry the reaction of 6-substituted 2,2′-bipyridines is known to give either N^N^C or N′^C(3) rollover cyclometallation, depending on the nature of the metal precursor. In the case of 6,6′-Ph₂-2,2′-bipy cyclometallation was also shown to undergo multiple C-H activation giving the C^N^C pincer complex [Pt(L-2H)(DMSO)]. The latter species can be related to complex 1: indeed its reaction with HCl produces complex 1 and [Pt(L-H)(DMSO)Cl], a rollover species with a pendant phenyl substituent.     

Synthesis of enantiomerically pure helicene like bis-oxazines from atropisomeric 7,7′-dihydroxy BINOL: preliminary measurements of the circularly polarized luminescence

A racemic sample of 2,2′,7,7′-tetrahydroxy-1,1′-binaphthyl was resolved with (S)-proline and the separated enantiomers were independently converted to atropisomeric bis-oxazines by aromatic Mannich reaction. These chirally pure oxazines were then converted to the helicene like cyclic ethers. The circularly polarized luminescence (CPL) profile was consistent with the isolation of the targeted helical-like molecules in optically pure form, prepared from the achiral primary amines. The compounds of interest displayed active and opposite CPL activities for each set of the helicene like isomers (P)-/(M)-3 and (P)-/(M)-5.     

Metal-directed supramolecular assembly of metal(II) benzoates (M = Co,Ni, Cu,Zn, Mn,and Cd) with 4,4′-bipyridine: Effects of metal coordination modes and novel catalytic activities

Six polymeric metal(II)-benzoate complexes of formula [Co₂(O₂CPh)₄(4,4′-bpy)₂]_n (1-Co), [Ni(O₂CPh)₄(H₂O)₂(4,4′-bpy)]_n (2-Ni), [Cu₂(O₂CPh)₄(4,4′-bpy)]_n (3-Cu), [Zn₂(O₂CPh)₂(OH)₂(4,4′-bpy)₂]_n (4-Zn), [Zn₃(O₂CPh)₄(μ-OH)₂(4,4′-bpy)₂]_n (5-Zn), and [Cd₂(O₂CPh)₄(4,4′-bpy)₂]_n (6-Cd) have been synthesized and characterized (4,4′-bpy = 4,4′-bipyridine). 1-Co and 6-Cd show ladder-type double chains, 2-Ni does a helical structure, 3-Cu does a one-dimensional chain containing paddle-wheel units, 4-Zn does a zigzag chain, and 5-Zn does two-dimensional sheets. Since different structures provide different coordination geometry of each metal ion, it is clear that selection of appropriate metal ions can control the coordination geometry of each metal ion to form different crystal structures. Reactivity study of the compounds 1–7 for the transesterification of a variety of esters has shown that 4-Zn and 5-Zn are very efficient and the best among them. The catalyst 6-Cd containing Cd ion, well known as an inert metal ion for the ligand substitution, also catalyzed efficiently the transesterification of a variety of esters, and its reactivity is comparable to 4-Zn and 5-Zn. Moreover, the redox-active metal-containing polymers, 1-Co, 3-Cu, and 7-Mn, have shown efficient catalytic reactivities for the transesterification reactions, while 2-Ni has displayed a very slow conversion. The reactivities of the compounds used in this study are in the order of 5-Zn > 4-Zn > 6-Cd > 7-Mn ∼ 3-Cu > 1-Co > 2-Ni, indicating that the non-redox metal-containing compounds (5-Zn, 4-Zn, and 6-Cd) show better activity than the redox-active metal-containing compounds (7-Mn, 3-Cu, 1-Co, and 2-Ni). These results suggest that it is possible to tune the catalytic activities by changing from Zn to those metals such as Cd, a kinetically inert metal, or Cu, Mn, and Co, the redox-active metals.     

Thermal decomposition of allantoin as probed by matrix isolation FTIR spectroscopy

The optimized geometries, energies of the possible conformers of allantoin (2,5-dioxo-4-imidazolidinyl urea, the diureide of glyoxylic acid) as well as the barriers for conformational interconversion have been calculated using the density functional theory [DFT(B3LYP)/6-311++G(d,p)] method. The calculations predicted the existence of four conformers (gC, tT, g′C, and g′T; where the first and second symbols in the name of the conformers designate the conformation around the exocyclic NHC-NHCO and CNH-CO axes, respectively), with the gC form contributing to more than 98% of the population in gas phase at room temperature. This conformer is different from that corresponding to the monomeric unit found in crystalline RS-allantoin (g′C; Mootz, D. Acta Crystallogr.1965, 19, 726), stressing the importance of intermolecular H-bonding in determining the structure of the crystal. Upon sublimation under vacuum (10⁻⁶ mbar), the compound was found to undergo extensive decomposition to urea, isocyanic acid, NH₃, and carbon. The identification of the decomposition products was made by using matrix isolation infrared spectroscopy. In consonance with the theoretical predictions, the allantoin molecules surviving thermal decomposition were found to undergo conformational isomerization and be present in the cryogenic argon matrix in both the gC and g′C conformations. The solid state room temperature infrared spectrum of allantoin was also investigated and assigned.     

Conformational isomerism of 1,2-bis(imidazol-1′-yl)ethane in five-coordination polymers: Influence of metal ions and m-isophthalate ligands bearing different substituents

Four novel coordination polymers, {[Zn(gauche-bime)(bdc)] · 0.5H₂O}_n (1), {[Zn(anti-bime)(HO-bdc)] · 2.5H₂O}_n (2), [Cu(gauche-bime)_0.5(anti-bime)_0.5(O₂N-bdc)]_n (4) and [Ni₂(gauche-bime)(anti-bime)(O₂N-bdc)₂(H₂O)₂]_n (5) were successfully prepared by the solvothermal reactions of 1,2-bis(imidazol-1′-yl)ethane (bime), m-isophthalic acid (H₂bdc) or its two derivatives (HO-H₂bdc = 5-hydroxyisophthalic acid, O₂N-H₂bdc = 5-nitroisophthalic acid) with different metal ions. Interestingly, bime in the four complexes exhibit different conformations owing to the synergetic influence of coexistent neutral (–H), electron-donating (–OH) or electron-withdrawing (–NO₂) groups of the dicarboxylate ligands and different metal ions. In 1 and 2, only one conformation of bime (gauche in 1 and anti in 2) is displayed, while the mixed conformations of bime (gauche:anti = 1:1) are observed in 4 and 5. At the same time, one previously reported compound {[Zn(anti-bime)(O₂N-bdc)] · H₂O}_n (3) as a comparable substance in the research system was also mentioned, in which the anti-conformation of bime was observed.     

A facile synthesis of fused spiroketal skeleton: 2,2′-spirobi(4-aryl-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydrochroman)

A one-pot synthesis of fused spiroketal skeleton, 2,2′-spirobi(4-aryl-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydrochroman) 4a-c, has been achieved for the first time by an application of Michael reaction between dimedone (5,5-dimethylcyclohexan-1,3-dione) 1 and trans,trans-diarylideneacetone (1,5-diaryl-1,4-pentadien-3-one) 2 using anhydrous ZnCl₂ as catalyst. The spiroketalization was achieved efficiently via intramolecular cyclization of the Michael 1:2 adduct.     

Synthesis and crystal structure of 2′-deoxy-2′-fluoro-4′-thioribonucleosides: substrates for the synthesis of novel modified RNAs

We report herein the synthesis of appropriately protected 2′-deoxy-2′-fluoro-4′-thiouridine (5), -thiocytidine (7), and -thioadenosine (35) derivatives, substrates for the synthesis of novel modified RNAs. The synthesis of 5 and 7 was achieved via the reaction of 2,2′-O-anhydro-4′-thiouridine (3) with HF/pyridine in a manner similar to that of its 4′-O-congener whereas the synthesis of 35 from 4′-thioadenosine derivatives was unsuccessful. Accordingly, 35 was synthesized via the glycosylation of the fluorinated 4-thiosugar 25 with 6-chloropurine. The X-ray crystal structural analysis revealed that 2′-deoxy-2′-fluoro-4′-thiocytidine (8) adopted predominately the same C3′-endo conformation as 2′-deoxy-2′-fluorocytidine.