New and efficient synthesis of 5′-amino-5′-(S)-methyl-2′,5′-dideoxynucleosides

A short, efficient synthesis of 5′-amino-5′-(S)-methyl-2′,5′-dideoxynucleosides 1 has been developed through the diastereoselective addition of methylmagnesium bromide or methyllithium to an intermediate tert-butylsulfinimide.     

Application and details of photoinduced oxidative cyclization of 5-(4′,9′-methanocycloundeca-2′,4′,6′,8′,10′-pentaenylidene)pyrimidine-2,4,6(1,3,5H)-triones and related compounds

As novel methodology for synthesizing the furan ring, a photoinduced oxidative cyclization of 5-(4′,9′-methanocycloundeca-2′,4′,6′,8′,10′-pentaenylidene)pyrimidine-2,4,6(1,3,5H)-triones (7a-c) and related compounds 9a-c was accomplished to give 5,10-methanocycloundeca[4,5]furo[2,3-d]pyrimidine-2,4(1,3H)-dionylium tetrafluoroborates (8a-c⁺·BF₄⁻) and related compounds 2a-c⁺·BF₄⁻, respectively. In the photoinduced oxidative cyclization, the molecular oxygen in air is used as oxidant and the reaction proceeds under mild conditions to give desired products without byproducts, and thus, it is interesting from the viewpoint of the green chemistry. On the reactions of the mono-substituted derivatives 7d,e and 9e,f, the selectivity of the photoinduced cyclizations were reversed as compared with those of the DDQ-promoted oxidative cyclizations. By the NMR monitoring of the reactions of 7a and deuterated compound 7a-D₂ under degassed conditions, the details of the reaction pathway were clarified and rationalized on the basis of the MO calculation by the 6-31G^∗ basis set of the MP2 levels as well.     

Straightforward synthesis of 3′-deoxy-3′,4′-didehydronucleoside-5′-aldehydes via 2′,3′-O-orthoester group elimination: a simple route to 3′,4′-didehydronucleosides

Straightforward, high-yielding syntheses of 3′-deoxy-3′,4′-didehydronucleoside-5′-aldehydes and 3′-deoxy-3′,4′-didehydronucleosides starting from 2′,3′-O-orthoester derivatives of ribonucleosides are described.     

Novel and efficient syntheses of 3′,5′-diamino derivatives of 2′,3′,5′-trideoxycytidine and 2′,3′,5′-trideoxyadenosine. Protonation behavior of 3′,5′-diaminonucleosides

High yielding synthetic routes to 3′,5′-diamino-2′,3′,5′-trideoxycytidine and 3′,5′-diamino-2′,3′,5′-trideoxyadenosine are described. In addition, the protonation behavior of 3′,5′-diamino-2′,3′,5′-trideoxycytidine, 3′,5′-diamino-2′,3′,5′-trideoxyadenosine, 3′,5′-diamino-3′,5′-dideoxythymidine, and 3′,5′-diamino-2′,3′,5′-trideoxyuridine has been studied by means of pH-metric measurements and NMR spectroscopy. The ionization constants and the sequence of protonation sites have been determined.     

An efficient synthesis of new 1-H-4′-methyl-3′,4′-dihydrospiro[piperidine-4,2′(1′H)quinoline] scaffolds

Efficient synthesis of new 3′,4′-dihydrospiro[piperidine-4,2′(1′H)quinolines] by a four step synthetic route based on 1-benzyl-4-piperidone reactivity is reported.     

Practical synthesis of adenosine 3′,5′-cyclic monophosphorodithioate

Adenosine 3′,5′-cyclic monophosphorodithioate (cAMPS₂), which has two exocyclic sulfurs directly attached to phosphorus, was synthesized from adenosine phosphoramidite by intramolecular cyclization employing the phosphotriester method as a key step.     

A concise synthesis of 3′-α-fluoro-2′,3′-dideoxyguanosine (FddG) via 3′-α-selective fluorination of 8,2′-thioanhydronucleoside

The antiviral nucleoside 3′-α-fluoro-2′,3′-dideoxyguanosine (FddG) was synthesized via 3′-α-selective fluorination of 8,2′-thioanhydronucleoside as the key step. Desulfurization of 3′-α-fluoro-3′-deoxy-8,2′-thioanhydronucleoside could be achieved by the treatment with Raney Ni in toluene. This method provides a concise route to 3′-α-fluoro-2′,3′-dideoxynucleosides that avoids the use of explosive and expensive SF₄-related fluorinating reagents.     

5′-Epimeric 3′-deoxy-3′,4′-didehydronucleoside-5′-C-phosphonates: synthesis and structural assignment by NMR and X-ray analyses

Epimeric 5′-(RS) dialkyl 3′-deoxy-3′,4′-didehydro-5′-C-phosphonates were prepared by nucleophilic addition of various dialkyl phosphites to 3′-deoxy-3′,4′-didehydronucleoside-5′-aldehydes. Whereas direct NMR configuration assignment for the C5′ atom bearing the phosphoryl and hydroxy groups using the J (P,H4′) and J (H5′,H4′) coupling constants is impossible due to the absence of the H4′ atom, successful separation, crystallisation and X-ray crystallographic analysis of a pair of epimeric 5′-C-phosphonates, followed by correlation with a series of NMR parameters, led to efficacious configuration assignment of individual epimers in the mixtures.     

Synthesis of new fluorescent 2-(2′,2″-bithienyl)-1,3-benzothiazoles

Bithienyl-1,3-benzothiazole derivatives were synthesised by reacting various 5-formyl-5′-alkoxy- or 5-formyl-5′-N,N-dialkylamino-2,2′-bithiophenes with ortho-aminobenzenethiol in good to excellent yields. Evaluation of the fluorescence properties of these compounds was carried out. They show strong fluorescence in the 450-600 nm region, as well as high quantum yields and large Stokes’ shifts.     

Regioselective monobromination of (E)-1-(2′-hydroxy-4′,6′-dimethoxyphenyl)-3-aryl-2-propen-1-ones using bromodimethylsulfonium bromide and synthesis of 8-bromoflavones and 7-bromoaurones

A wide variety of monobrominated compounds 2a-l have been prepared in good yields from (E)-1-(2′-hydroxy-4′,6′-dimethoxyphenyl)-3-aryl-2-propen-1-ones (1a-l) through regioselective ring bromination using 1.5 equiv of bromodimethylsulfonium bromide (BDMS) at room temperature. Similarly, some of the 2′-hydroxychalcones can be converted directly into tribromides 3 or dibromides 4 by employing 4.0 equiv of BDMS under different reaction conditions which in turn can be transformed into 8-bromoflavones and 7-bromoaurones on treatment with 0.2 M ethanolic KOH solution. Mild reaction conditions, good yields and no chromatographic separation are some of the salient features of the present protocol.     

A simple route for the synthesis of 3,3,3′,3′-tetramethyl-2,3,3′,4′-tetrahydro-1H,1′H-[4,9′-bixanthene]-1,1′(2′H,9′H)-dione and its derivatives catalyzed by Mn and other transition metal cations

A simple and efficient unusual coupling reaction of 9-(2-hydroxy-4,4-dimethyl-6-oxocyclohex-1-en-1-yl)-3,3-dimethyl-2,3,4,9-tetrahydro-1H-xanthen-1-one and its derivatives was accomplished in the presence of Mn²⁺, Cu²⁺, Cd²⁺, Hg²⁺, Fe³, or La³⁺. The structure elucidation was accomplished by IR, ¹H NMR, ¹³C NMR, X-ray crystallography, UV-Visible and elemental analysis. A reaction mechanism is proposed.     

A novel one-pot and efficient procedure for the synthesis of 3H-spiro[isobenzofuran-1,6′-pyrrolo[2,3-d]pyrimidine]-2′,3,4′,5′-tetraones

A novel and practical one-pot procedure is described for the preparation of several new of 3H-spiro[isobenzofuran-1,6′-pyrrolo[2,3-d]pyrimidine]-2′,3,4′,5′-tetraones based on the addition reaction of ninhydrin and 6-aminouracils followed by oxidative cleavage of their corresponding dihydroxyindenopyrrolopyrimidines.     

Synthesis of (3′R,5′S)-3′-hydroxycotinine using 1,3-dipolar cycloaddition of a nitrone

To synthesize (3′R,5′S)-3′-hydroxycotinine [(+)-1], the main metabolite of nicotine (2), cycloaddition of C-(3-pyridyl)nitrones 3a, 3c, and 15 with (2R)- and (2S)-N-(acryloyl)bornane-10,2-sultam [(2R)- and (2S)-8] was examined. Among them, l-gulose-derived nitrone 15 underwent stereoselective cycloaddition with (2S)-8 to afford cycloadduct 16, which was elaborated to (+)-1.     

A simple and stereodivergent strategy for the synthesis of 3′-C-branched 2′,3′-dideoxynucleosides exploiting (Z)-but-2-en-1,4-diol and (R)-2,3-cyclohexylideneglyceraldehyde

Barbier type additions of allylic bromide 4, derived from (Z)-but-2-en-1,4-diol 2 to (R)-2,3-cyclohexylideneglyceraldehyde 1 were performed through mediation with Zn employing Luche’s procedure and also with low valent Cu, Co, and Fe which were produced via bimetal redox strategy in THF to afford 5c,d as the major products. From these, 5a,b were prepared following an oxidation-reduction protocol. Compound 5c was exploited as a representative starting material to develop a simple and inexpensive strategy toward the synthesis of 3′-C-branched 2′,3′-dideoxynucleosides having stereodiversity at 3′- and 4′-positions.     

Synthesis of (±)-4′-ethynyl-5′,5′-difluoro-2′,3′-dehydro-3′-deoxy- carbocyclic thymidine: a difluoromethylidene analogue of promising anti-HIV agent Ed4T

Synthesis of (±)-4′-ethynyl-5′,5′-difluoro-2′,3′-dehydro-3′-deoxy-carbocyclic-thymidine (8) was carried out. The difluoromethylylidene group of 8 was constructed by the electrophilic fluorination to the cyclopentenone 11 by using Selectfluor^®. Introduction of thymine base was investigated based on the Mitsunobu reaction by employing cyclopentenyl allyl alcohols variously substituted at the 4-position. It was found the 4-methoxycarbonyl derivative 14 gave the highest selectivity both in terms of regio- and stereochemistry.     

Clean and efficient microwave-solvent-free synthesis of 1-(2′,4′-dichlorophenacyl) azoles

Microwave induced N-alkylation of several azoles with 2,2′,4′-trichloroacetophenone (TCA) under solvent-free conditions allowed to obtain the corresponding 1-(2′,4′-dichlorophenacyl) azoles with satisfactory to good selectivities and yields. TGA and DSC measurements were achieved for the synthesized compounds and showed a close relationship between the thermal behavior and the reaction temperature under microwave heating. Non-purely thermal microwave effects were evidenced during the alkylation of pyrazole and 1H-indazole under the selected conditions.     

Highly diastereoselective chemoenzymatic synthesis of (2′R)- and (2′S)-2′-deoxy[2′-H]guanosines

In an effort to develop an efficient synthetic method of highly diastereoselective (2′R)- and (2′S)-2′-deoxy[2′-²H]guanosines, chemoenzymatic conversion was investigated. The synthesis of (2′R > 98% de)-2′-deoxy[2′-²H]guanosine was achieved by biological transdeoxyribosylation using (2′R > 98% de)-2′-deoxy[2′-²H]uridine, 2,6-diaminopurine, and Enterobacter aerogenes AJ-11125, followed by treatment with adenosine deaminase. (2′S > 98% de)-2′-Deoxy[2′-²H]guanosine was synthesized from (2′S > 98% de)-2′-deoxy[2′-²H]uridine and 2,6-diaminopurine using thymidine phosphorylase and purine nucleoside phosphorylase instead of E. aerogenes AJ-11125.     

Diastereoselective synthesis of trisubstituted piperidines: a versatile synthon for elaboration of uncommon poly(aza)heterocyclic structures

Hetero Michael addition on chiral β′-amino-α,β-unsaturated ketone furnished, after some structural modifications, β,β′-diaminoketals. Mannich type reaction of these diamines with an aldehyde led, with a high diastereoselectivity, to trisubstituted piperidines. Starting from a functionalized aldehyde and after subsequent deprotection of the amino group, an intramolecular Michael addition provided octahydro-2H-pyrrolo-[3,4-b]-pyridine, an uncommon framework found in compounds exhibiting biological activity.     

Synthesis and properties of novel 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol⁻¹ by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄⁻ and 12a-c·BF₄⁻) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄⁻) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄⁻ and 12a,c·BF₄⁻ in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄⁻ and 12a-c·BF₄⁻ observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄⁻ and 12a-c·BF₄⁻ were studied, and structural characterization of 11c·BF₄⁻ based on the X-ray crystal analysis and MO calculation was also performed.