Apparent molar volumes,heat capacities,and molecular excluded volumes of methylated,hydroxy and methoxy derivatives of 1-methylcytosine in aqueous solutions at 25°C

Densities and specific heat capacities of aqueous solutions: 1-methylcytosine; 1-methyl-N⁴-hydroxycytosine; 1,5-dimethylcytosine; I,N⁴-dimethylcytosine; 1,5-dimethyl-N⁴-hydroxycytosine; 1-methyl-N⁴-methoxycytosine; 1,N⁴,N⁴-trimethylcytosine, 1,5-dimethyl-N⁴-methoxycytosine were determined using flow calorimetry and flow densimetry at 25°C. Apparent molar volumes and heat capacities were then determined. Molecular excluded volumes were evaluated. A relationship was found between the values of the increments in partial molar values and the kind of groups substituted. Four types of contributions were distinguished: substitution of hydrogen on C, N, and O (in OH group on N4) atoms by CH₃ group and replacement of hydrogen on N4 atom by OH group. The correlation between the experimental partial molar volumes and calculated molecular excluded volumes was also elaborated.     

Interaction of the mutagenic base analogs O6-methylguanine and N4-hydroxycytosine with potentially complementary bases

Infrared spectroscopy has been employed to study possible base pair interactions, in nonpolar media, between O⁶-methylguanine and uracil, cytosine and adenine; and between derivatives of N⁴-hydroxycytosine and adenine. The association constants of O⁶-methylguanine with uracil, cytosine, and adenine are well below 1M^–1, whereas those for interaction of 1-methyl-N⁴-methoxycytosine and its 5-methyl derivative with adenine are identical, K = 14M^–1. The significance of the latter finding is discussed in relation to the conformation of the exocyclic N⁴-methoxy group. Quantum chemical calculations, with the aid of the perturbation method, were carried out for the interaction of O⁶-methylguanine with uracil, cytosine, and adenine, to establish the most energetically favoured configurations for interactions of the free bases, and of the same base pairs in the B form of DNA. The role of the conformation of the exocyclic —OCH₃ group in O⁶-methylguanine is discussed. The relevance of both the experimental and theoretical results to mutagenesis by O⁶-methylguanine and N⁴-hydroxycytosine is examined.     

Apparent molar heat capacities and volumes,van der Waals volumes and accessible surface areas of alkylated derivatives of cytosine and uracil in aqueous solutions at 25°C.

Densities and specific heat capacities of aqueous solutions: 1,3,5,6-tetramethyluracil, 1,6-dimethyl-3-ethyluracil, 1,6-dimethyl-3-propyluracil, 1,6-dimethyl-3-butyluracil, 1,N⁴-trimethylcytosine, 1,N⁴-dimethyl-5-ethylcytosine, 1,N⁴ dimethyl-5-propylcytosine, 1,N⁴-dimethyl-5-butylcytosine were determined using flow calorimetry and flow densimetry at 25°C. Apparent molar volumes and heat capacities, van der Waals volumes and accessible surface areas were determined. It was stated that for alkylcytosines and alkyluracils partial molar volumes and heat capacities correlate linearly with the number of substituted methylene groups-CH₂-as well as with the van der Waals volumes and accessible surface areas of the compounds studied; for cyclooligouracils the cyclization effect was discussed.     

Studies on the synthesis of heterocyclic compounds. III. Preparation of some pyrazolo[3,4-C] [1,5]benzodiazocin-10(11H)one derivatives

Starting from the readly available N-melhyl-N-(1-phenyl-3-R-pyrazol-5-yl)-2-nitrobenzamides (1a,b), the pyrazoles, 4-aeetyl substituted 2a,b, were prepared in high yield. Reduction of 2a gave the amino derivative 4a, which was eyclized to the desired pyrazolo[3,4-c][1,5]benzodiazo-cin-10(11H)one (5a). Compound 2b afforded 5b directly. Compound 5b was also prepared by the action of phosphorus oxychloride on N-methyl-N-(1,3-diphenylpyrazol-5-yl)-2-acetamido-benzamide (6b).     

Synthesis and structure of the grafted layer on silicas chemically modified by aminophosphonic acids

The synthesis and properties of three representatives of a new class of chemically modified silicas containing aminophosphonic acids, namely, (N-methyl-N-propylamino)methylenephosphonic,N-propylaminodi(methylenephosphonic), andN-[2-(propylamino)ethyl]-N,N-di(methylenephosphonic acids), covalently grafted on the silica surface are reported. The modified silicas were obtained by the two-step Kabachnik-Fields reaction in high yields. The concentrations of the grafted groups were determined by elemental analysis and pH-titration. The new materials were characterized by IR and³¹P and¹³C high resolution solid state NMR spectroscopy. The hydration of the modified silicas was found to result in a significant change in the structure of the grafted layer and to increase the mobility of the grafted groups. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2340–2345, December, 1999.     

Synthesis and Irradiation of Vitamin‐B12‐Derived Complexes Incorporating Peripheral G⋅C Base Pairs

The vitamin‐B₁₂ derivative 11 , incorporating a peripheral N⁴‐acetylcytosine moiety, was alkylated under reductive conditions with 2‐(iodomethyl)‐2‐methylmonothiomalonate 8 bearing the complementary guanine moiety. The reaction yielded a mixture of vitamin‐B₁₂‐derived complexes with variations in the cytosine moiety: products 16 – 18 with a cytosine, a N⁴‐acetylated cytosine, and a N⁴‐acetylated reduced cytosine moiety were formed (see Scheme 5). The complexes were photolyzed in CHCl₃/MeCN to yield the dimethylmalonate derivative 22 (Scheme 6) but not the rearranged succinate, in contrast to the results obtained earlier with complexes incorporating the A⋅T base pair (see Scheme 1).     

13C-NMR-Untersuchungen zur Azido-Tetrazol-Valenzisomerie. Tetrazolo[1,5-α]pyrimidine

¹³C NMR has been used to study the azido-tetrazolo valence isomerism of three tetrazolo[1,5-α]pyrimidines. Large chemical shift variations of C-4 carbons were found to be useful to distinguish between azido and tetrazolo isomers. Furthermore, the structure of new heterocycles has been proved and the report of LaNoce and Giuliani concerning 9-methyl-s-triazolo[4,3-c]tetrazolo[1,5-α]pyrimidine is shown to be incorrect.     

Reactions of N-heteroarylformamide oximes and N-heteroarylacetamide oximes with N,N-dimethylformamide dimethyl acetal. Synthesis of 2-methyl-s-triazolo[1,5-x]azines and N-methylcyanoaminoazines

N-Heteroarylformamide oximes 3 (R ? H) were converted with N,N-dimethylformamide dimethyl acetal (DMFDMA) into N-heteroaryl-N-methylcyanoamino compounds 5 , as the main products. In some instances N-heteroarylcyanoamino compounds 4 , cyanoimino compounds 7 , and some other products, such as 9 and 10 were also formed. On the other hand, N-heteroarylacetamide oximes 3 (R ? CH₃) were cyclized under the same reaction conditions into 2-methyl-s-triazolo[1,5-x]azines ( 6 ). N-Heteroarylacetamide O-methyl oximes 11 and 12 were prepared from the corresponding acetamidines 2 (R ? CH₃) and O-methylhydroxylamine.     

Nitrogen bridgehead compounds. Part 50 . Vilsmeier-haack acylation of 6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidin-4-ones,Part 5

6-Methyl-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidin-4-ones 1-5 were subjected to Vilsmeier-Haack acylation with complexes of phosphoryl chloride and different amides. Acylation at position 9 of the pyridopyrim-idines was successful with the iminium salt formed in situ from N-formylpiperidine, N-methylformanilide or N,N-diethylbenzamide, but unsuccessful with the iminium salt formed from N,N-diethylacetamide or N,N-di-ethylisobutyramide, respectively. The iminium salt formed from formanilide, N-methylpyrrolidinone or formamide reacted only with those tetrahydropyridopyrimidinones which contain a strongly electronegative substituent (e.g. CN or CO₂Et) in position 3. With the latter derivatives, the 9-phenylaminomethylene group could be introduced using N,N-diphenylformamide or in a “one-pot” procedure with aniline and triethyl orthoformate. Ethanolysis of 9-N-methyl-N-phenylaminomethylene derivatives 15 and 19 afforded 9-ethoxy-methylene compounds 26 and 27 in the presence of hydrogen chloride. The structures of the 9-substituted 6-methyltetrahydropyridopyrimidin-4-ones 14-25 were elucidated by means of uv, ¹H and ¹³C nmr spectroscopy. 9-Piperidinomethylene 14 , 9-(N-methyl-N-phenylaminomethylene 15-19 and 9-(N-methyl-2-pyrrolidinylidene) 21 derivatives exist as E geometric isomers. 9-Phenylaminomethylene-6-methyl-4-oxo-6,7,8,9-tetra-hydro-4H-pyrido[1,2-a]pyrimidine-3-carbonitrile 20 displays a solvent-dependent E-Z isomerism. The bis-compound 25 contains both E and Z geometric exo C ? CH double bonds. 9-Benzoyl derivatives 23 and 24 exist predominantly as the 1,6,7,8-tetrahydropyridopyrimidin-4-one tautomer.     

Thermochemistry of aqueous solutions of alkylated nucleic acid bases. IX. Enthalpies of hydration of 9-methyl-8-alkyladenines and 6,9-dimethyl-8-alkyladenines

Enthalpies of solution in water, H _sol ^o , and enthalpies of sublimation, H _sub ^o , were determined experimentally for a number of crystalline derivatives of adenine: 6,8,9-trimethyladenine; 6,9-dimethyl-8-ethyladenine; 6,9-dimethyl-8-propyladenine; 6,9-dimethyl-8-butyladenine; 8,9-dimethyl-adenine and 9-methyl-8-ethyladenine. Standard enthalpies of hydration, H _hydr ^o , derived from these data were calculated. The latter were discussed together with the values for variously alkylated adenines, determined previously. The data obtained show that the dependence of enthalpy of hydration on the number of methylene groups added upon substitution with 8-n-alkyl groups of 9-methyladenine and 6,9-dimethyladenine is nonlinear.     

Reactions with diazoazoles. Part VI. Unequivocal synthesis of 3-methyl-3h-azolotetrazoles. Correction of the formerly described 3-methylazolotetrazoles in favour of mesoionic 2-methylazolotetrazoles

3-Methyl-3H-pyrazolo[1,5-d]tetrazoles 2 and 3-methyl-6-phenyl-3H-1,2,4-triazolo[1,5-d]tetrazole (4) have been unequivocally synthesized by annulation of the tetrazole moiety to the pyrazole resp. 1,2,4-triazole system. The constitution of some N-methyl substituted azolotetrazoles, formerly described as 3-methyl-3H-pyrazolo[1,5-d]tetrazoles 2, 3-methyl-6-phenyl-3H-1,2,4-triazolo[1,5-d]tetrazole (4) and 1-methyl-6-phenyl-1H-1,2,4-triazolo[4,3-d]tetrazole (5), has to be revised in favour of the corresponding mesoionic 2-methyl derivatives 2′, 4′, 5′. The structures of 3-methyl-3H- as well as of 2-methyl-2H-pyrazolo[1,5-d]tetrazole derivatives 2a, 2c, 2′a have been determined by X-ray analyses. The azapentalenic system is aromatic in all three measured compounds and mesoionic in the case of the 2-methyl-2H- substitution pattern. The phenyl and ester substituents are coplanar with the azapentalene system. 3-, 2-, and 1-Methylpyrazolo[1,5-d]tetrazoles exhibit different behaviour when allowed to react with stannous chloride or sodium ethoxide. Azolotetrazoles with a methyl substituent at N-1, N-2 or N-3 of the tetrazole moiety can be distinguished by a combination of ¹H and ¹³C nmr with respect to the chemical shifts of the N-methyl group and the bridgehead carbon. Results of semiempirical calculations of the pyrazolo[1,5-d]tetrazole anion and of its N-methyl derivatives are discussed.     

Heterocyclic rearrangements. Phenylhydrazones and N-methyl-N-phenylhydrazones of 3-acylisoxazoles

The reaction of 3-benzoyl-5-phenylisoxazole ( 4 ) and 3-acetyl-5-methylisoxazole ( 5 ) with phenylhydrazine and N-methyl-N-phenylhydrazine has been investigated and the reactivity of (E)- and (Z)-phenylhydrazones and N-methyl-N-phenylhydrazones has been studied.     

Intramolecular diels-alder reactions. 4. Additions to naphthalene

N-Methyl-N-2-propynyl-1-naphthalenecarboxamide, N-methyl-N-2-propynyl-1-naphthaleneacetamide, and N-methyl-N-3-butynyl-1-naphthalenecarboxamide undergo intramolecular Diels-Alder reactions at 190°, 250°, and 270° to give lactams 1,6 , and 9 , respectively. The cyclization temperatures are higher by 80-120° as compared to those of the corresponding anthracene derivatives. Elaboration of lactam 6 gave the trans-4a-aryldecahydroisoquinoline derivative 7a which, as the (-) isomer, was shown to have the same absolute stereochemistry as morphine.     

Fluorescence Quenching by Intercalation of a Pyrene Group Tethered to an N4‐modified Cytosine in Duplex DNA

A series of duplex DNA oligomers was prepared that contain a pyrene chromophore linked by a trimethylene chain (‐(CH₂)₃‐) to N⁴ of a cytosine. The pyrene group stabilizes the DNA as evidenced by an increase in melting temperature. The absorption spectrum of the linked pyrene chromophore shows a temperature‐dependent shift and there is also a strong induced circular dichroism spectrum attributed to the pyrene group. The fluorescence of the pyrene chromophore is strongly quenched at room temperature by linkage to the DNA, but it increases above the melting temperature. We attribute these observations to intramolecular intercalation of the pyrene group at a base pair adjacent to its linkage site at cytosine.     

Adducts of phenanthrene 9,10-imine and of benz[a]anthracene 5,6-imine to some nitrogen heterocycles

N-4-Pyridinyl-, N-2-quinolinyl-, and 2-pyrazinylphenanthrene 9,10-imines 4–6 , as well as N-4-pyridinyl- and N-2-pyrazinylbenz[a]anthracene 5,6-imines 12 and 13 were prepared by sodium hydride-mediated interaction of the parent arene imines, 1 and 10 , and the respective chloropyridine, chloroquinoline or chloropyrazine. N-Nicotynoyl-, N-2-pyridinoyl- and N-6-quinolinoylphenanthrene 9,10-imines 7–9 were obtained by interaction of N-trimethylsilylphenanthrene 9,10-imine ( 2 ) and the appropriate pyridine- or quinolinecarbonyl chlorides. Reaction of N-methylsulfonylphenanthrene 9,10-imine with thymine, cytosine, 5-fluorocytosine, purine, 6-chloropurine and adenine afforded, in the presence of either potassium carbonate or 1,5-diazabicyclo[3.4.0]non-5-ene, adducts 16–22 , respectively. The structures of the adducts were conformed by multinuclear nmr and by NOESY and C-H correlation 2D nmr spectrometry.     

Tautomer‐Specific Resonant Photoelectron Imaging of Deprotonated Cytosine Anions

Tautomers of the nucleobases play fundamental roles in spontaneous mutations of DNA. Tautomers of neutral cytosine have been studied in the gas phase, but much less is known about charged species. Here, we report the observation and characterization of three tautomers of deprotonated cytosine anions, [trans‐keto‐amino‐N3H‐H8b] (tKAN3H8b^?), [cis‐keto‐amino‐N3H‐H8a] (cKAN3H8a^?) and [keto‐amino‐H] (KAN1^?), produced by electrospray ionization. Excited dipole‐bound states (DBSs) are uncovered for the three anions by photodetachment spectroscopy. Excitations to selected DBS vibrational levels of cKAN3H8a^? and tKAN3H8b^? yield tautomer‐specific resonant photoelectron spectra. The current study provides further insight into tautomerism of cytosine and suggests a new method to study the tautomers of nucleobases using electrospray ionization and anion spectroscopy.     

Synthesis, structure, and biological evaluation of C-2 sulfonamido pyrimidine nucleosides

The C-2 sulfonamido pyrimidine nucleosides were prepared by opening the 2,2′- or 2,3′-bond in anhydronucleosides under nucleophilic attack of sulfonamide anions. Reaction of the sodium salt of p-toluenesulfonamide or 2-(aminosulfonyl)-N,N-dimethylnicotinamide with 2,2′-anhydro-1-(β-d-arabinofuranosyl)cytosine gave the C-2 sulfonamido derivatives in excellent yields. Ring opening of the less reactive 2,2′-anhydrouridine and 2,3′-anhydrothymidine could be accomplished with DBU/CH₃CN activation of p-toluenesulfonamide, giving moderate yields for C-2 sulfonamido derivatives. The action of acetic acid or ZnBr₂/CH₂Cl₂ on 5-methyl-N²-tosyl-1-(2-deoxy-5-O-trityl-β-d-threo-pentofuranosyl)isocytosine led to the cleavage of both the protection group and the nucleoside bond, yielding 5-methyl-N²-tosylisocytosine as the major product. Structures of the prepared C-2 sulfonamido nucleosides were confirmed by the 1D and 2D NMR experiments, and X-ray structural analysis of 4-imino-N²-tosylamino-1-(β-d-arabinofuranosyl)pyrimidine. Both methods confirmed β-configuration and anti-conformation of the 2-sulfonamido nucleosides. The investigated compounds displayed moderate inhibition of tumor cell growth in vitro, as determined by the MTT assay using six different human tumor cell lines.     

Pyrazolo[1,5-d]triazines-1,2,4. II étude des pyrazolo[1,5-d]triazinones,des pyrazolo[1,5-d]triazinediones et des pyrazolo[1,5-d]triazinethiones

The synthesis of 1,2-dihydro-l-oxopyrazolo[1,5-d]-1,2,4-triaxine was achieved by rerrangment of 2-(5-pyrazolyl)-1,3,4-oxadiazole under alkaline condition. The cyclization of the N-carbethoxyhydrazone of the pyrazole-5-carboxaldehyde gave the 3,4-dihydro-4-oxopyrazolo[1,5-d]1,2,4-triazine. Electrophilic substitutions of the l-pyrazolotriazinome were made either on the lactam nitrogen with methylsulfate, benzylchloride and monochloracetic axid or on the pyrazole ring with bromine. The synthesis of pyrazolo[1,5-d]-1,2,4-triazine was made from teh l-pyrazolotrizinone via the l-pyrazolotrizinone. The methylation of l-pyrazolotrizinone and 8-bromo-l-pyrazolotrizinone afforded N-and S-methyl derivatives. The sysnthesis of 1,2,3,4-tetrahydropyrazolo[1,5-d]-1,2,4-triazine-1,4-diones was axhived by cyclising N-carbethoxyhydrazides of pyrrole-5-carboxylic acid. The structures of the derivatives were determined by ¹H-nmr.     

Synthesis and antimalarial effects of 2-(3,4-dichloroanilino)-7-[[[(dialkylamino)alkyl]amino]]-5-methyl-s-triazolo[1,5-a]pyrimidines

3,4-Dichlorophenylisothioeyanate ( 10 ) was allowed to react with 2-methy1-2-thiopseudourea to give methyl 4-(3,4-dichlorophenyl)(dithioaltophanimidate ( 11 ) (41%), which upon treatment with hydrazine afforded 3-amino-5-(3,4-dichloroanilino)-s-triazole ( 12 ) (54-91%). Ring-closure with ethyl acetoacetale in acetic acid afforded 2-(3,4-dichloroanilino)-5-methyl-s-triazolo[ 1,5-α ]-pyrimidin-7-ol ( 13 ) (81%). Chlorination with phosphorus oxychloride gave 7-chloro-2-(3,4-dichloroanilino)-5-methyl-s-triazolo[1,5-α ]pyrimidine ( 14 ) (98%), which was condensed with various amines to yield the desired 2-(3,4-diehloroanilino)-7-¶[(dialkylamino)alkyl]arnino¶-5-methyl-s-triazolo[ 1,5-α]pyrimidines ( 6 a-d). The structures of the s-triazolo[ 1,5-α ]pyrimidines were based on nmr spectroscopy and ring stability considerations. Several of the amino-s-triazolo[ 1,5-α ]pyrimidines possessed antimalarial activity against P. berghei in mice.     

Facile synthesis of novel 3-quinoxalinyl-1,5-benzodiazepines via ring transformation. Stable tautomers in the 1,5-benzodiazepin-2-one ring system

Novel 3-quinoxalinyl-1,5-benzodiazepines 4, 5, 6, 9, 10 were synthesized via the ring transformation of 3-(N,N-dimethylcarbamoyl)furo[2,3-b]quinoxaline hydrochloride ( 1 ). The 3-quinoxalinyl- 1 ,5-benzodiazepine hydrochlorides 4 and 6 are the tautomers of the N^1′-H (or N⁵-H) form and the C³-H form, respectively, which are stable in solid and solution. However, 4 (NH form) was found to be converted into 6 (C³-H form) by refluxing in acetic acid. The individual spectral evidences and different reactivity of these tautomers are described.