Synthesis and Biological Activities of C (5)-N-Spin-Labeled Uridines and Related Derivatives

Direct introduction of a N-atom in one step at C (5) of 5-hydroxyuridine (4a) or 5-hydroxy-2′-deoxyuridine (4b) by certain primary amines led to the synthesis of two novel C(5)-N-spin-labeled nucleoside analogs and to several C(5)-N-aryl adducts. Substitution by 4-amino-2,2,6,6-tetramethylpiperidinooxyl (3) at C(5) of 4a or 4b led to the spin-labeled nucleosides 5-[(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)amino]uridine and -2′-deoxyuridine ( 2a and 2b , respectively). The analogous C(5)-substituted aniline adducts 5-anilino uridine (5a) and 5-anilino-2′-deoxyuridine (5b) and the p-toluidine adducts 5-(p-toluidino)uridine (6a) and 5-(p-toluidino)-2-deoxyuridine (6b) were also prepared. In addition, results of the antiviral and antimetabolic activity of some of these analogs are reported.     

Aziridination of the uracil 5,6-olefinic bond of 3-N-3′,5′-Di-O-tribenzoyl-5-vinyl-2′-deoxyuridine

Oxidation of N-aminophthalimide with lead tetra-acetate at -50° gives N-acetoxyaminophthalimide ( 3 ) which selectively aziridinates the 5,6-double bond present in 3-N-3′,5′-di-O-tribenzoyl-5-vinyl-2′-deoxyuridine ( 1a ) to yield 2-[1′-(2′-deoxy-β-D-ribofuranosyl)]-7-(1-phthalimido)-4-N-3′,5′-di-O-tribenzoyl-6-vinyl-2,4,7-triazabicyclo[4.1.0]heptan-3,5-dione ( 5 ).     

Synthesis of diols containing 5-benzyluracil base and their polymers

Preparation of analogs of acyclic nucleoside, two diols containing 5-benzyluracil base derived from 2-(5-benzyluracil-1-yl)propanoic acid (BUPA), and the corresponding model polymers of polynucleotide with linear polyester backbone and 2-(5-benzyluracil-1-yl)propionamido-type pendant as a side chain are described. N-(1′,3′-Dihydroxy-2′-methyl-2′-propyl)-2-(5-benzyluracil-1-yl)propionamide (HEBUPA) and its isomer N(β,β′-dihydroxyethyl)-2-(5-benzyluracil-1-yl)propionamide (HEBUPA) were prepared through the selective N-acylation of primary aminodiol, 2-methyl-2-amino-1,3-propanediol and secondary aminodiol, diethanolamine with BUPA, respectively, by the active ester-N-hydroxy-5-norbornene-2,3-dicarboximide (HONB) method. The resulting diols were polycondensed with active diamide of benzotriazole (HBT) such as 1,1′-(terephthaloyl)bisbenzotriazole (PBBT), 1,1′-(isophthaloyl)bisbenzotriazole (IPBBT), 1,1′-(sebacocyl)bisbenzotriazole (SeBBT), giving semirigid and flexible polyesters containing 5-benzyluracil derivative as the side group, by the selective O-acylation of active diamide-benzotriazole technique. Diols HMBUPA and HEBUPA were found to be very potent inhibitors of uridine phosphorylase isolated from Sarcoma 180 cells, with K_i values of 0.13 and 0.11 μM, respectively.     

α-Thioureidoalkylation of functionally substituted ureas: II. Synthesis of thio analogs of N-hydroxyalkyl-1,5-diphenylglycolurils

Reactions of N-(hydroxyalkyl)ureas with 4,5-dihydroxy-4,5-diphenylimidazolidine-2-thiones gave previously unknown 4,6-dialkyl-1-hydroxyalkyl-3a,6a-diphenyl-5-thioxooctahydroimidazo[4,5-d]imidazol-2-ones which may be regarded as thio analogs of N-(hydroxyalkyl)glycolurils.     

Synthesis and properties of 5-(1,2-dihaloethyl)-2′-deoxyuridines and related analogues

The regiospecific reaction of 5-vinyl-3′,5′-di-O-acetyl-2′-deoxyuridine ( 2 ) with HOX (X = Cl, Br, I) yielded the corresponding 5-(1-hydroxy-2-haloethyl)-3′,5′-di-O-acetyl-2′-deoxyuridines 3a-c . Alternatively, reaction of 2 with iodine monochloride in aqueous acetonitrile also afforded 5-(1-hydroxy-2-iodoethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine ( 3c ). Treatment of 5-(1-hydroxy-2-chloroethyl)- ( 3a ) and 5-(1-hydroxy-2-bromoethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine ( 3b ) with DAST (Et₂NSF₃) in methylene chloride at -40° gave the respective 5-(1-fluoro-2-chloroethyl)- ( 6a , 74%) and 5-(1-fluoro-2-bromoethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine ( 6b , 65%). In contrast, 5-(1-fluoro-2-iodoethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine ( 6e ) could not be isolated due to its facile reaction with methanol, ethanol or water to yield the corresponding 5-(1-methoxy-2-iodoethyl)- ( 6c ), 5-(1-ethoxy-2-iodoethyl)- ( 6d ) and 5-(1-hydroxy-2-iodoethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine ( 3c ). Treatment of 5-(1-hydroxy-2-chloroethyl)- ( 3a ) and 5-(1-hydroxy-2-bromoethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine ( 3b ) with thionyl chloride yielded the respective 5-(1,2-dichloroethyl)- ( 6f , 85%) and 5-(1-chloro-2-bromoethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine ( 6g , 50%), whereas a similar reaction employing the 5-(1-hydroxy-2-iodoethyl)- compound 3c afforded 5-(1-methoxy-2-iodoethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine ( 6c ), possibly via the unstable 5-(1-chloro-2-iodoethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine intermediate 6h . The 5-(1-bromo-2-chloroethyl)- ( 6i ) and 5-(1,2-dibromoethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine ( 6j ) could not be isolated due to their facile conversion to the corresponding 5-(1-ethoxy-2-chloroethyl)- ( 6k ) and 5-(1-ethoxy-2-bromoethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine ( 61 ). Reaction of 5-(1-hydroxy-2-bromoethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine ( 3b ) with methanolic ammonia, to remove the 3′,5′-di-O-acetyl groups, gave 2,3-dihydro-3-hydroxy-5-(2′-deoxy-β-D-ribofuranosyl)-furano[2,3-d]pyrimidine-6(5H)-one ( 8 ). In contrast, a similar reaction of 5-(1-fluoro-2-chloroethyl)-3′,5′-di-O-acetyl-2′-deoxyuridine ( 6a ) yielded (E)-5-(2-chlorovinyl)-2′-deoxyuridine ( 1b , 23%) and 5-(2′-deoxy-β-D-ribofuranosyl)furano[2,3-d]pyrimidin-6(5H)-one ( 9 , 13%). The mechanisms of the substitution and elimination reactions observed for these 5-(1,2-dihaloethyl)-3′,5′-di-O-acetyl-2′-deoxyuridines are described.     

Synthesis of 6-substituted 1-alkoxy-5-alkyluracils

Synthesis of 6-substituted 1-alkoxy-5-alkyluracils 2a-c have been achieved from readily accessible 2-alkyl-3,3-di(methylthio)acryloyl chlorides 4a,b in high overall yields. Treatment of 4a,b with silver cyanate followed by reaction of the resulting isocyanates 5a,b with an appropriate alkoxyamine afforded N-alkoxy-N′-[2-alkyl-3,3-di(methylthio)acryloyl]ureas 6a,b in 85–88% yields. Cyclization of 6a,b in acetic acid containing methanesulfonic acid followed by oxidation with 3-chloroperoxybenzoic acid gave high yields of 1-alkoxy-5-alkyl-6-(methylsulfonyl)uracils 9a,b. Nucleophillic addition-elimination reaction of 9a,b with sodium azide, phenylthiol, or phenylselenol produced 6-azido-1-butoxythymine ( 2a , 98%), 5-ethyl-1-(2-phenoxyethoxy)-6-(phenylthio)uracil ( 2b , 95%), or 5-ethyl-1-(2-phenoxyethoxy)-6-(phenylselenenyl)uracil ( 2c , 91%).     

1H and 13C NMR spectral assignment of N,N′‐disubstituted thiourea and urea derivatives active against nitric oxide synthase

The ¹H and ¹³C NMR resonances of seventeen N‐alkyl and aryl‐N′‐[3‐hydroxy‐3‐(2‐nitro‐5‐substitutedphenyl)propyl]‐thioureas and ureas ( 1–17 ), and seventeen N‐alkyl or aryl‐N′‐[3‐(2‐amino‐5‐substitutedphenyl)‐3‐hydroxypropyl]‐thioureas and ureas ( 18–34 ), designed as NOS inhibitors, were assigned completely using the concerted application of one‐ and two‐dimensional experiments (DEPT, HSQC and HMBC). NOESY studies confirm the preferred conformation of these compounds. Copyright © 2016 John Wiley & Sons, Ltd.     

4,5-Dihydroxyimidazolidin-2-ones in α-ureidoalkylation of N-carboxyalkyl-, N-hydroxyalkyl-, and N-(aminoalkyl)ureas 4.* α-Ureidoalkylation of N-(2-acetylaminoethyl)ureas

α-Ureidoalkylation of N-(2-acetylammoethyl)ureas with various 4,5-dihydroxyimidazoli-din-2-ones was systematically studied. Novel N-(2-acetylaminoethyl)glycolurils were obtained. Their yields were found to decrease both when moving from l,3-H₂-to l,3-Alk₂-4,5-dihydroxy-imidazolidin-2-ones and when increasing the size of the substituent at the second N atom in the starting acetylaminoethylurea. The higher yields were achieved with 4,5-diphenyl-4,5-dihydroxyimidazolidin-2-one as the starting compound. 2-(2-Acetylaminoethyl)-4-methylgly-coluril exhibits nootropic activity.     

Synthesis of brain-targeted 5-iodo-, 5-vinyl- and (E)-5-(2-iodovinyl)-2′-deoxyuridines coupled to a dihydropyridine ⇌ pyridinium salt redox chemical delivery system

5-Iodo-3′-O-(1-methyl-1,4-dihydropyridyl-3-carbonyl)-2′-deoxyuridine (15a) , 5-vinyl-3′-O-(1-methyl-1,4-di-hydropyridyl-3-carbonyl)-2′-deoxyuridine (15b) and (E)-5-(2-iodovinyl)-3′-O-(1-methyl-1,4-dihydropyridyl-3-carbonyl)-2′-deoxyuridine (15c) were synthesized for future evaluation as lipophilic brain-selective antiviral agents for the treatment of herpes simplex encephalitis. Quaternization of the 3′-O-(3-pyridylcarbonyl) compounds 10–11 using iodomethane afforded the corresponding 1-methylpyridinium salts 12–13 which were reduced with sodium dithionite to yield the corresponding 3′-O-(1-methyl-1,4-dihydropyridyl-3-carbonyl) compounds 14–15.     

Selective acylation of ribonucleotides and ribonucleosides with acylimidazoles

Selective acylation of ribonucleotides and ribonucleosides can be achieved by using N-acylimidazole on a preparative scale with good yields (50–80%). For uridine 3′-phosphate (Up): in the presence of MDCAI, the 2′-O-acyl-derivative is the main product, while in the presence of an excess of TEAH, the 5′-O-acyl-derivative is the main product. For ribonucleosides (U_R or A_R or ψ_R): in the presence of MDCAI, the acylations take place preferably at 2′-OH or 3′-OH of ribonucleosides and only 3′-O-acyl-derivatives can be isolated by crystallization; in the presence of an excess of TEAH. 5′-O-acyl-derivative is obtained as the main product. Arabinonucleoside and deoxyribonucleoside are only slowly acylated to form 5′-O-acyl-derivatives as the main products by acylimidazole in the presence of MDCAI. Possible mechanisms of these acylations have been discussed.     

Nucleosides. Part LVI. Aminolysis of carbamates of adenosine and cytidine

The 2-(4-nitrophenyl)ethoxycarbonyl(npeoc) group, introduced 1984 as protecting group for exocyclic amino functions of nucleic-acid bases, reacts with amines under mild conditions to urea derivatives. Treatment of 2′,5′-di-O-acetyl-N⁶-[2-(4-nitrophenyl) ethoxycarbonyl]cordycepin ( 3 ) with NH₃/MeOH overnight at room temperature affords cordycepin ( 4 ) and N₆-carbamoylcordycepin ( 5 ). Preliminary investigations towards the elucidation of the reaction mechanism indicate that the aminolysis proceeds via an addition-elimination or an isocyanate mechanism, depending on the reaction conditions. The phenoxycarbonyl (phoc) group at N⁶ or N⁴ was chosen to study the mild conversion of carbamates with aromatic amines into ureas of adenosine and cytidine, respectively.     

Heterocycles from substituted amides,V.. 1,2,3,5-Oxathiadiazolin-4-one 2-oxides from thionyl chloride and N-hydroxyureas

The reaction of certain N-hydroxy-N-methyl-N′-aryl ureas, 2 , with thionyl chloride are shown to give a new heterocycle, 1,2,3,5-oxathiadiazolin-4-one 2-oxides, 3 , in a synthesis that appears to have more severe structural requirements than the previously reported ring closures from α-hydroxyacylanilides and thionyl chloride. Isolable amounts of 3 are obtained only if the aryl group contains deactivating substituents, and the hydroxy group is attached to the N-alkyl nitrogen; otherwise, resin formation or ring chlorination are found to occur. The assigned structure as 3 was verified by a full three dimensional X-ray analysis of a representative example, 3a , 3-(4-bromophenyl)-5-methyl-1,2,3,5-oxathiadiazolin-4-one.     

An efficient one-pot synthesis of N,N′-disubstituted phenylureas and N-aryl carbamates using hydroxylamine-O-sulfonic acid

We have developed an efficient one-pot method for the microwave-assisted synthesis of ureas and carbamates via a proposed Lossen rearrangement. Herein we report the first examples of the direct conversion of benzoyl chlorides into N,N′-disubstituted ureas and N-aryl carbamates using hydroxylamine-O-sulfonic acid as reagent. Using our general method, we have produced 11 examples of N,N′-disubstituted phenylureas in yields up to 95% using various substituted anilines, and primary and secondary amines. Additionally, we were able to generate a series of N-aryl carbamates in moderate yields using primary, secondary and tertiary alcohols.     

Nucleosides. Part LXI. A Simple Procedure for the Monomethylation of Protected and Unprotected Ribonucleosides in the 2′-O- and 3′-O-Position Using Diazomethane and the Catalyst Stannous Chloride

Intensive studies on the diazomethane methylation of the common ribonucleosides uridine, cytidine, adenosine, and guanosine and its derivatives were performed to obtain preferentially the 2′-O-methyl isomers. Methylation of 5′-O-(monomethoxytrityl)-N²-(4-nitrophenyl)ethoxycarbonyl-O⁶-[2-(4-nitrophenyl)ethyl]-guanosine ( 1 ) with diazomethane resulted in an almost quantitative yield of the 2′- and 3′-O-methyl isomers which could be separated by simple silica-gel flash chromatography (Scheme 1). Adenosine, cytidine, and uridine were methylated with diazomethane with and without protection of the 5′ -O-position by a mono- or dimethoxytrityl group and the aglycone moiety of adenosine and cytidine by the 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) group (Schemes 2–4). Attempts to increase the formation of the 2′-O-methyl isomer as much as possible were based upon various solvents, temperatures, catalysts, and concentration of the catalysts during the methylation reaction.     

Accelerating effects of N‐aryl‐N′,N′‐dialkyl ureas on epoxy‐dicyandiamide curing system

This report focuses on epoxy‐dicyandiamide (DICY) curing system accelerated by N‐aryl‐N′,N′‐dialkyl urea, aiming at clarifying the accelerating mechanism and the relationship between accelerating effect and molecular structure of the accelerators. Nine N‐aryl‐N′,N′‐dialkyl ureas were synthesized and investigated with measurements of differential scanning calorimetry, thermo gravimetric/differential thermal analysis and NMR spectroscopy. The results revealed that the ureas released the corresponding secondary amines by the thermal dissociation in the presence of epoxide, which led to the formation of tertiary amines that catalyze the addition reaction of DICY to epoxide. Moreover, a tendency that the ureas able to release more compact amines exhibited higher acceleration effects was discovered. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis of novel C-2 substituted pyrimidine nucleoside analogs

A series of 2-(2-oxoalkylidene)-4(1H)-pyrimidinone nucleoside analogs were synthesized by the addition of the lithium enolates of methylketones to 2,5′- and 2,2′-anhydrouridines and to 2,5′-anhydrothymidines. Alternatively, 2-thiouridine was alkylated with bromomethyl ketones to yield 2-(2-oxoalkyl)thio-4(1H)-pyrimidinone ribofuranosides in good yields. These intermediates were subsequently transformed into the title compounds via an Eschenmoser sulfur extrusion reaction. The 2-(2-oxoalkylidene)-4-(1H)-pyrimidinone nucleoside analogs exhibit enol proton signals in their ¹H nmr spectra indicative of hydrogen bonding between N-3 and keto oxygen. These structures offer functional groups with potential for Watson-Crick hydrogen bonding.     

Unexpected formation of 2′-deoxy-N3-(3,3,3-trifluoro-1-propenyl)uridine via a Michael-type addition to 3,3,3-trifluoropropyne

Reaction of 3,3,3-trifluoropropyne with 2′-deoxy-5-iodouridine under conditions that have previously been used to prepare 5-alkynyl-2′-deoxyuridine derivatives gave 2′-deoxy-N3-(3,3,3-trifluoro-1-propenyl)uridine. This unexpected alkylation is a result of a Michael-type addition of N3 on the pyrimidine base to the electron deficient trifluoropropyne.     

Synthesis and conformational properties of 2′-deoxy-2′-methylthio-pyrimidine and -purine nucleosides: Potential antisense applications

A convenient and shorter synthesis of 2′-deoxy-2′-methylthiouridine analogs 5 , ?5-methyluridine 6 , -cyti-dine 15 , ?5-methylcytidine 16 , -adenosine 27 and -guanosine 34 was accomplished. Successful conversion of ribonucleosides (5-methyl U, U, A, G) into the corresponding 2′-substituted nucleosides involves nucleophilic displacement (S_N2) of an appropriate leaving group at the 2′-position by methanethiol, a soft nucleophile. Reaction between 2,2′-anhydrouridine and methanethiol in the presence of N¹,N¹,N³,N³-tetramethylguani-dine in N,N-dimethylformamide gave 5 , in 75% yield. Preparation of 6 by a similar route was described. Acylated 5 and 6 were transformed into their triazole derivatives, which on ammonolysis furnished 15 and 16 , respectively in good yield. Similarly, tetraisopropyldisiloxanyl (TIPS) protected 2′-O-aratriflates- of-adenosine and -guanosine reacted with methanethiol in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene at - 25°, followed by deblocking of the TIPS protecting group furnished 27 and 34 , respectively. The confor-mational flexibility (N/S equilibrium) of the sugar moiety in nucleosides 5 , 15 , 27 and 34 was studied utilizing nmr spectroscopy, suggesting that the 2′-methylthio group influenced the sugar conformation to adopt a rigid S-pucker in all cases. The extra stiffness of the sugar moiety in these analogs is believed to be due to the electronegativity of the substituent and the steric bulk. The usefulness of these nucleosides to prepare uniformly modified 2′-deoxy-2′-methylthio oligonucleotides for antisense therapeutics is proposed.     

Syntheses of polymerizable viologens bearing a terminal vinyl group

Viologens that bore a terminal vinyl group were synthesized by four sequences of reactions: (1) N-vinylbenzyl-N′-n-propyl-4,4′-bipyridinium bromide chloride (V) was synthesized by the reaction of 4-(4′-pyrodyl)-N-n-propyl pyridinium bromide (III) with vinylbenzyl chloride; (2) N-β-acrylamidoethyl-N′-n-propyl-4,4′-bipyridinium dibromide (IX) was synthesized by the Menschutkin reaction of III with 2-aminoethyl bromide hydrobromide and subsequent reaction with acryloyl chloride; (3) N-β-methacryloyloxyethyl-N′-n-propyl-4,4′-bipyridinium dibromide and its analogs (XI) were synthesized by the reactions of III with the corresponding acyloxyalkyl bromides; and (4) N-vinyloxycarbonylmethyl-N′-n-propyl-4,4′-bipyridinium bromide chloride (XIII) was synthesized by the reaction of III with vinyl chloroacetate. With the exception of monomer XIII in which hydrolysis in large extent was observed during attempted polymerization, the synthesized monomers polymerized smoothly in aqueous solutions by a conventional radical procedure. Comparisons of the absorption peaks of the radical cations produced by reductions in aqueous solutions with those produced in films by ultraviolet (UV) irradiation indicate that the radical cations of polymers are associated intramolecularly in aqueous solutions.     

Synthesis of novel N-(1,2,3,7,8,9,9a,9b-octahydro-3-(phenylmethyl)-5H-dipyrrolo [1,2-c,3,2-e]pyrimidine-5-ylidene)benzenamine derivatives

N-(1,2,3,7,8,9,9a,9b-Octahydro-3-(phenylmethyl)-5H-dipyrrolo [1,2-c,3,2-e]pyrimidine-5-ylidene)benzenamine were prepared in moderate yields from the novel intermediate 1′-(phenylmethyl)-(2,3′-bipyrrolidin)-2-one 4 .